Operational Guidelines Plonninge Biogas Plant

8/19/2019 Operational Guidelines Plonninge Biogas Plant

http://slidepdf.com/reader/full/operational-guidelines-plonninge-biogas-plant 1/148

Operational guidelines for Plönningebiogas plant



Release History

Version 1.0, June 2011

Any question about this document should be addressed to:

Bioprocess Control Sweden ABScheelevägen 22SE-223 63 LundSweden

Tel: +46 (0)46 163950Fax: +46 (0)46 163959E-mail: [email protected] Web: www.bioprocesscontrol.com

mailto:[email protected]


http://www.bioprocesscontrol.com/








3.3.1 Logger 1 ............................................................................................................. 61

3.3.2 Logger 2 ............................................................................................................. 62

3.3.3 Logger 3 ............................................................................................................. 63

3.4 Energy measuring (Energimätningar) ....................................................................... 64

3.4.1 Alarm list (Larm) ............................................................................................... 65

4 ANALYSIS AND MONITORING ............................................................................... 66

4.1 Determination of feedstock characteristics ................................................................ 66

4.1.1 pH ....................................................................................................................... 66

4.1.2 Moisture content ................................................................................................. 67

4.1.3 Total (TS) and volatile solids (VS) .................................................................... 68

4.1.4 Biochemical methane potential (BMP) test ....................................................... 69

4.2

Monitoring of process parameters in anaerobic digestion process ............................ 70

4.2.1 Temperature ....................................................................................................... 71

4.2.2 pH ....................................................................................................................... 71

4.2.3 Alkalinity ............................................................................................................ 71

4.2.4 Nutrients and toxins ........................................................................................... 72

4.2.5 Biogas flow and composition ............................................................................. 73

4.2.6 Volatile fatty acids (VFA) and dissolved hydrogen (DH) ................................. 74

4.3 Sampling and analysis ............................................................................................... 74

4.3.1

Sampling points .................................................................................................. 74

4.3.2 Analysis of liquid samples ................................................................................. 80

4.4 Analysis of gaseous samples ..................................................................................... 89

4.5 Online monitoring and data logging .......................................................................... 93

5 EVALUATION OF THE OPERATION AND PROCESS PERFORMANCES ...... 94

5.1 Process operation ....................................................................................................... 94

5.1.1 Organic loading rate (OLR) ............................................................................... 94

5.1.2 Hydraulic retention time (HRT) ......................................................................... 94

5.2 Process performances ................................................................................................ 95

5.2.1 Gas normalization .............................................................................................. 95

5.2.2 Gas productivity ................................................................................................. 95

5.2.3 Gas yield ............................................................................................................. 96

5.2.4 VS reduction ....................................................................................................... 96

5.3 Process stability ......................................................................................................... 97

6 DOCUMENTATION ..................................................................................................... 99

6.1

Navigation ............................................................................................................... 100

6.2 Sorting of raw data (Rådatasortering) ..................................................................... 101



6.3 Raw data (Rådata) ................................................................................................... 102

6.4 “Manual” data (Manuell data) ................................................................................. 103

6.5 Daily data (Dagsvärden) .......................................................................................... 105

6.6 Weekly data (Veckovärden) .................................................................................... 107

6.7 Monthly data (Månadsvärden) ................................................................................. 109

6.8 Printable document (Utskriftsformulär) .................................................................. 112

6.9 How to insert data from the data logger .................................................................. 113

6.9.1 Download data from Datalogger ...................................................................... 113

6.9.2 Insert data into Process_data.xlsm ................................................................... 116

7 METHODOLOGY FOR PROCESS IMPROVEMENTS ....................................... 120

7.1 Meetings .................................................................................................................. 121

8 OPERATIONAL ROUTINES .................................................................................... 122 8.1 Daily operational routines ....................................................................................... 122

8.2 Weekly operational routines .................................................................................... 133

9 PROCESS EVALUATION ......................................................................................... 136

9.1 Weekly evaluation ................................................................................................... 136

9.1.1 Saving the data for weekly evaluation ............................................................. 138

9.2 Monthly evaluation .................................................................................................. 142

9.3 Yearly evaluation ..................................................................................................... 143



1

1 INTRODUCTION

The Plönninge biogas plant serves as a demonstration and research site and was built to promote small scale biogas production. It is situated at Plönninge Agricultural High School

and is operated in collaboration with Region of Halland.

Region of Halland has, together with Bioenergicentrum Halland, an ambition to promoteregional development related to renewable energy sources. The focus is on agriculturalenterprises and most of the work is carried out by Plönninge Agricultural High School. Toensure that this facility can serve as a demonstration plant for future farm-based biogas plantsin the region and around the world, it is important that the plant can be run as efficiently as possible and that the produced biogas can be fully utilized.

The purpose of this document is to serve as a support and a guide for operators at thePlönninge biogas plant.

1.1 Description of the plant

GeneralThe biogas plant in Plönninge is a small farm scale plant that has been in operation since2004. It was constructed by Läckeby Water AB with the original objective of decomposingremnant silage and cow manure from farms and other available waste products in the area.

The volume of the digester is 300 m3 with an expected gas production of 250-300 Nm3/day.The average retention time of the digester is around 30 days, depending on the availability ofmanure.

OperationManure from around 80 cows is collected in a manure tank, which is then pumped into alarger mixing tank. Furthermore, this is mixed, in the same tank, with more solid substrates(e.g. silage or potatoes). Iron chloride (FeCl3) is also added to reduce the amount of hydrogensuphide (H2S) in the produced biogas, by precipitation of FeS from sulphur-containing

compounds. The mixed material is then pumped further into a buffer tank where it spendsaround one day before it is fed into the digester. The digester is top mixed with two sets ofimpellers and it is kept at an average temperature of 37 ºC. As the material is fed into thedigester, digested slurry or digestate is removed into two serial connected storage units, whereit is stored for around half a year before it is used as a fertilizer to cultivate crops at the farm.

The produced gas is consumed in three different ways using the following systems: i) in a gas burner for producing heat; ii) in a Stirling engine for producing electricity and heat; and iii) inan upgrading unit for producing biomethane as a vehicle fuel.



2

Originally, only the gas burner was installed at the plant but, in order to promote the production of higher value products, the Stirling engine and the biogas upgrading unit wereinstalled in 2008; the Stirling engine started operations in 2011.



3

2 DESCRIPTION OF THE OPERATIONAL UNITS

The most important operational units at the Plönninge biogas plant are presented in thissection. They have been divided into four categories:

1)

Operational units for liquid and solid materials2) Operational units for gas flows3) Operational units in the control room4) Heating / cooling system

An overview picture of the Plönninge biogas site, where some of the larger operational unitshave been marked, can be seen in Figure 2-1.

Figure 2-1 Satellite photo (Google maps) of Plönnige biogas site.

A simplified process drawing of Plönninge biogas plant can be seen in Figure 2-2.



4

PS

LC

FI

LC

LC

LC

LS

TC

LC

TC

Pi FI

GFL1

DigesterRK1, 300 m 3

Digestate storage 1ERK1, 1600 m 3

FI Flow indicator

LC Level control

PS Tryckutlösare

LS Level switch

TC Temperature control

PI Pressure indicator

LC

Manure storageLT1, 1200 m 3

TITI

Gas alarmTorch

Condensation trapSF1

Condensed water

Raw gasstorage

GL1,

Ironchloride

Buffer tankBT1, 12 m 3

Mixing tankPB1, 50 m 3

Manure tank 1PB2, 12 m 3

Manure tank 2PB3, 50 m 3

PotatoesFruit &

Vegetables

Horsemanure

Silage

Manual loading

Gas burnerGP1, 60 kW

FI

GF1Condensation trap

SF2

Condensed water

Digestate storage 2ERK2, 1500 m 3

LC

P1

P2

P3

P4

P6

Stirling engine

SM1, 8kW (36 kW)

Electricproduction

Water scrubberWS1

High pressure gasstorage

Gas pump

X-ripper

P7

Figure 2-2 Simplified process drawing of the Plönnige biogas plant.



5

2.1 Operational units for solid and liquid materials

In this section all the operational units that handle the liquid and solid material in thePlönninge biogas plant are listed and described. A summary of their properties can be seen inTable 2-1.

Table 2-1 Summary of operational units handling liquid and solid material.

Abbreviation

Volume(m 3)

Mixing Heating Sensors Connectionsin

Connectionsout

Manuretank 1

PB2 12 Recirculation No Level Stable (cow) PB1

Manuretank 2

PB3 50 Recirculation No Level Stable (calf) LT1

Mixing tank PB1 50 Submersiblemixer,recirculation

No Level PB2, Manualloading

BT1

Buffer tank BT1 12 Recirculation No Level PB1 RK1, ERK1

Digester RK1 300 Mixer Yes Level, levelswitch,temperature (2)

BT1 ERK1

Digestatestorage 1

ERK1 1600 Submersiblemixer (2)

No Level RK1 ERK2

Digestate

storage 2

ERK2 1500 Mobile mixer No No ERK1 -

Manurestorage

LT1 1200 Mobile mixer No No PB2, PB3,RK1

-

In total, there are eight operational units handling the solid and liquid material in Plönninge.



6

2.1.1 Manure tanks 1 & 2

Figure 2-3 Photos of manure tank 1.

A Housing covering the manure tankB Tap for manure samplingC Container used for loading the 1.7 m pilot plant (described in a separated document)

with manureD Pipe for recirculationE Motor for recirculation pumpF Manure tank (lid)

RoleThe role of the manure tanks is to collect and store manure from the cow stables.

DimensionsThe manure from the cow stable is collected in two tanks (PB2 and PB3) that are situated below ground. Both tanks have a rectangular shape with PB2 having a volume of 12 m3 andPB3 having a volume of 50 m3.

MixingThe tanks are mixed by recirculation of the content. The same pump is used for bothrecirculating and removing content. This is controlled by an actuator that regulates a 3 wayvalve.

ConnectionsManure tank 1 (PB2) is connected to the main cow stable on the incoming side and the mixingtank on the outgoing side.



7

Manure tank 2 (PB3) is connected to the calf stable on the incoming side and the manurestorage tank (LT1) on the outgoing side. The content can also be pumped to the buffer tank(BT1) by manually regulating several valves.

SensorsBoth manure tanks have level sensors to monitor the occupancy of the tank and to make surethat no flooding will occur or the pumps will go dry.

Regulation/AutomationThe outgoing pump is regulated by the level in the manure tank and in the mixing tank. Amaximum and minimum level is specified by the user in the control panel. The minimumlevel is important in order to avoid that the pump goes dry and the maximum level isimportant in order to avoid flooding of the tank. If the level reaches the minimum level theoutgoing pump will be inactivated, whereas if it reaches the maximum level the outgoing pump will be activated in order to reach an acceptable level in the mixing tank.

OperationAt the moment, only manure tank 1 (PB1) is in operation. The manure is pumped from themanure tank into the mixing tank.

2.1.2 Mixing tank

Figure 2-4 Photo of mixing tank.



8

A Waste containers for fruit and vegetablesB Feeder band connecting the funnel and the mixing tankC Loading funnel for wasteD Disintegration unit with cutting knifesE Mechanical lid for covering mixing tankF Mixing tankG Container for FeCl3 solution

RoleThe role of the mixing tank is to mix the solid substrates with the manure.

DimensionsThe mixing tank is situated below ground and has a cylindrical shape with a total volume of50 m3. The tank is covered with a lid to minimize the odors and keep away the rain water.

MixingThe mixing is carried out with a submersible mixer and recirculation of the content. As for themanure tank, the same pump is used for recirculating and pumping away the content,controlled with an actuator that regulates a T-valve. The submersible mixer is manuallyoperated using an on/off button placed next to the control panel.

Figure 2-5 Photo of the buttons for controlling the submersible mixer.



9

ConnectionsThe mixing tank is connected to the manure tank 1 (PB2) on the incoming side and the buffertank on the outgoing side.

SensorsThe mixing tank has a level sensor to monitor the occupancy of the tank and to make sure thatit will not flood or that the pump goes dry.

Regulation/AutomationThe outgoing pump is regulated by the level of the mixing tank and the buffer tank. Amaximum and minimum level is specified by the user in the control panel. The minimumlevel is important in order to avoid that the pump goes dry and the maximum level isimportant in order to avoid flooding of the tank. If the level reaches the minimum level theoutgoing pump becomes inactive, whereas if it reaches the maximum level the outgoing pumpwill be activated in order to reach an acceptable level in the buffer tank.

OperationIn the mixing tank, the manure from manure tank 1 is mixed with all the solid substrates. Thesubstrates are manually added with the help of a front loader, or a lift system for certaincontainers. When the lift system is used, the substrate is also passed through a disintegrationunit equipped with knives for reducing the size of the solid material.

To load substrate through the front loader, the cover has to be opened from an open/close

panel located next to the tank.

MiscellaneousIn the mixing tank, FeCl3 solution is added manually from a container placed next to the tank.

X-ripper (to be installed)

Figure 2-6 Pictures of the X-ripper (Vogelsang).



10

RoleThe role of the X-ripper is to reduce the particle size of the added solid substrate. Its robustdesign, using the proven double-shaft system, allows for economical shredding of largeamounts of solids in liquid media.

ConnectionsThe X-ripper is connected to the mixing tank.

OperationThe solid material is loaded into the receiving funnel and shredded by the X-ripper beforefalling into the mixing tank. More detail description needs to be added once the X-ripper isinstalled on the site.

SupplierCompany: Vogelsang Sverige AB

Adress: Duvesjön 450SE – 442 92 Romelanda

Contact person

Klas-Göran Brevik

Tel: +46 (0) 31 7512 70 0 E-mail: [email protected]








12

Substrate handling units

Figure 2-8 Photos of substrate handling units.

A Bunker silosB Lifting device for 200 L barrelsC 200 L barrelsD 140 L waste containersE Loading of glucose from a 200 L barrel

Many different types of substrates are added to the mixing tank. The substrates are eitheradded directly to the mixing tank with a front loader, or via the old macerator unit or the X-ripper. Examples of how several substrates are processed and handled can be seen in Table2-2.



13

Table 2-2 Example of several processed substrates.

Storage Pretreatment Front loader Maximumstorage time

Silage Bunker silo No Yes Several monthsPotatoes 140 L waste

container, bunkersilo

X-ripper, oldmacerator

Yes/No (with oldmacerator)

1 month

Fruit and Vegetables 140 L wastecontainer

Old macerator No 1 week

Jam 200 L barrel No Yes 1 monthGlucose 200 L barrel Heated (winter) Yes Several monthsHorse manure Bunker silo No Yes Several months

FeCl 3 solution container

Biogas from anaerobic digestion of animal waste (i.e. manure) typically contains 500 to 3000 ppm of H2S, depending on the composition of solid substrates. Removal of H2S is needed toreduce air pollution, protecting at the same time the power generation equipment, andincreasing the safety of the operations.

Figure 2-9 Photo of FeCl3 solution container .

Role

The role of the FeCl3 solution is to reduce the levels of H2S in the produced gas. The iron precipitates out the sulfur and prevents the production of H2S in the digester.



14

ConnectionsThe FeCl3 solution container is connected to the mixing tank.

Regulation/AutomationThe FeCl3 solution container is operated with a manually switched tap.

OperationEvery day, a certain amount of FeCl3 solution is added into the mixing tank by the operator.The addition of the solution is regulated by opening and closing a tap.

Front loader

Figure 2-10 Photo of the front loader .

RoleThe role of the front loader is to transport some of the solid material from its storage unit andto load it into the mixing tank.

Operation

The front loader is shared by the whole farm and should only be operated by personnel with proper training. It has a few different lifting devices for different types of material. A deviceformed like a scoop is normally used to handle loose material, like silage and horse manure,while a specially designed device with attachment points is used to handle liquid or semisolidmaterials in barrels, such as jam and glucose.

Miscellaneous The lifting device for loading loose material has weighting cells for controlling the loadedamount of material.

Since the front loader is shared by the whole farm, it is important to be handled with care.



15

2.1.3 Buffer tank

Figure 2-11 Photo of the buffer tank.

A Buffer tankB Motor for pumpC Actuator for T-valveD T-valveE Recirculation pipeF Pipe to digester

RoleThe role of the buffer tank is to provide an additional place for the substrate to mix and be

further disintegrated before pumped into the digester.

DimensionsThe buffer tank is situated below the ground and has a rectangular shape with a total volumeof 12 m3. The tank is covered with a lid to minimize the odors and keep away the rain water.

MixingThe buffer tank is mixed by recirculation of the content. The same pump is used forrecirculating and pumping away the content. This is controlled by an actuator that regulates avalve in a T-connection.





17

2.1.4 Digester

Figure 2-12 Photos of the digester and digestate pump.

A Ladder for climbing to digester roofB Biogas outlet pipeC Top cover and motor for mixerD DigesterE Manhole coverF Digestate feeding pump

RoleIn the digester, the anaerobic degradation of the organic material in to biogas is taking place.

Dimensions The digester has a cylindrical shape with a total volume of 300 m3.

MixingThe content of the digester is mixed by a top mixer with impellers at two different levels. Thespeed of the mixer can be controlled.At the top of the mixer there are two specially designed rotor blades which prevent formationof floating hard layers inside the digester. More detail description needs to be added oncerotor blades are installed on the site.



18

ConnectionsThe digester is connected to the buffer tank on the incoming side and digestate storage 1 onthe outgoing side. There is also an outgoing biogas pipe from the top of the digester.

SensorsThe digester has three sensors

Bottom temperature sensor Top temperature sensor Level sensor

Regulation/AutomationThe operation of the digester is controlled mainly in three ways:

1) The level in the digester is maintained by controlling the pump for the outgoingsludge. The sought level is entered in the control panel and is maintained by activatingor deactivating the outgoing pump.

2) The temperature in the digester is maintained by controlling a shunt valve thatregulates the flow of heating water. A PID controller regulates the shunt valve basedon the difference between the setpoint temperature and the actual temperature. Thesetpoint temperature, along with the P (Proportional), I (Integral) and D (derivative)constants can be entered in the control panel.

3) The top mixer is controlled by an on/off timer as well as a direction setting in thecontrol panel.

Operation Normally, feeding from the buffer tank is set to give a retention time in the digester of around30 days. The temperature is normally set to be around 37 ºC and the slurry volume isnormally set to be around 270 m3 (i.e. the height of the slurry level is about 760 cm).

MiscellaneousThe digester has a manhole cover at the bottom, where it is possible to enter in the digesterwhen it is empty. There is also a smaller manhole cover on the top. There is a ladder on theside of the digester, allowing the possibility to climb onto the digester roof.

Supplier

Company: Svenska Neuero Adress: Sätuna Storegården

521 98 Broddetorp

Contact person

Stefan Persson

Tel: 046-249630 E-mail: [email protected]



19

2.1.5 Digestate storage containers 1 & 2

Figure 2-13 Photos of digestate storage container 1 (upper) and digestate storage container 2 (bottom).

A Cover of digestate storage 1B Digestate storage container 1C Digestate storage container 2

RoleIn the digestate storage container 1 & 2, the digestate is stored when coming from the digesteruntil used as a fertilizer.

DimensionsDigestate storage container 1 has a total volume of 1600 m3 and digestate storage container 2a total volume of 1500 m3.

MixingDigestate storage container 1 has two submersible mixers that are regulated via the control panel. Digestate storage container 2 has no mixing.



20

ConnectionsThe digestate storage container 1 is connected to the digester on the incoming side and thedigestate storage container 2 on the outgoing side. The digestate storage container 1 can also be connected to the manure storage tank and the buffer tank.

The digestate storage container 2 is connected to the digestate storage container 1 on theincoming side. The digestate storage container 2 is emptied by pumping its content into thefertilizer tanks.

SensorsThere is a level sensor in the digester storage container 1.

Regulation/AutomationThe digestate storage container 1 is filled with digestate from the digester using a pump. Thecontent of the digestate storage unit 1 is then flown by gravity force into the digestate storagecontainer 2.

OperationThe digestate storage container 1 is filled first when the digestate is pumped out from thedigester.

Miscellaneous No gas from any of the digester storage units is collected. The digester storage container 1 has

an open cover only for preventing the rain water and digester storage container 2 has no coverat all. The digester storage container 2 is mainly emptied during spring and fall, when thefertilizer is needed for cultivating crops.



21

2.2 Operational units for storage, purification, analysis and distribution of biogas

2.2.1 Raw gas storage

Figure 2-14 Photos of raw gas storage.

A Raw gas storage containerB Gas pipe from pilot plantC Valve for connection to pilot plantD Water block

RoleThe role of the raw gas storage unit is to store the produced raw gas in order to maintain astable flow to the gas utilization units (upgrading, burner and Stirling engine).

ConnectionsThe raw gas storage unit is connected to the gas system of the plant. The pressure in the rawgas storage unit and the gas fan in the gas room determine if the gas flows out from thestorage unit or not.



22

SensorsThe raw gas storage unit has two sensors:

A Level sensor (%), which can measure how full the storage unit is. A Pressure sensor (mbar), which measures the pressure in the raw gas storage unit.

OperationThe gas storage unit is filled as the biogas produced from the reactor. The emptying isdependent on the gas level in the storage unit as well as the status of the gas utilization units.

Normally, the upgrading unit is prioritized and activated when the level in the gasstorage is above 60 % and deactivated at a level below 20 %.

The Stirling engine is normally activated when the upgrading unit cannot take anymore gas (i.e. high pressure storage is full) and is also normally activated at levelsabove 60 % and deactivated at a level below 20 %.

The gas burner is the third in line and is normally activated when the level of the gasstorage is above 80 % and deactivated at a level below 20%.

The torch is ignited if the pressure in the gas storage gets too high.

MiscellaneousThe raw gas storage has a water block controlling the release in the atmosphere of the excessgas (i.e. when the pressure in the storage unit exceeds 13-14 mbar).





24

A Gas filterB Incoming gas pipeC Outgoing gas pipe to upgrading unitD Outlet for gas samplingE Condensation trapF Outgoing gas pipe to Stirling engineG Flow meter for measuring the flow to gas burnerH Flow meter for measuring total gas flowI Gas fanJ Outgoing gas pipe for torchK Outgoing gas pipe for gas burner

RoleThe gas room is the core of the gas system at the biogas site and contains most of the sensors,valves and fans. The unit for removing condensation is also located in the gas room, wherethe gas sampling also takes place.

ConnectionsThe gas room is connected to the gas storage/digester on the incoming side and the upgrading,Stirling engine, gas burner and torch on the outgoing side.

SensorsFour sensors are placed in the gas room:

two pressure sensors two flow meters

MiscellaneousThe gas room contains a gas filter to make sure no particles are coming into any of the gasutilization units.



25

2.2.3 Upgrading unit

Figure 2-16 Photo of upgrading unit (water scrubber).

A Upgrading unitB Scrubber columnC Gas compressor

RoleThe role of the upgrading unit is to upgrade the biogas to biomethane by removing the carbondioxide (CO2). The technique used is water scrubbing, i.e. dissolving the carbon dioxide intowater at high pressure.

CapacityThe upgrading unit can handle raw gas flows up to 18 m3/hour.

ConnectionsThe upgrading unit is connected to the raw gas storage unit on the incoming side and the high pressure storage on the outgoing side.

Regulation/AutomationThe upgrading unit is activated when the sought level in the raw gas storage is obtained and

the high pressure storage is not full (below 170 bar). This is carried out by opening a valveand activating the fan in the gas room.

SupplierCompany: Biorega AB

Adress: L RyaSE - 314 92, Långaryd

Homepage: www.biorega.se

Contact person: Peter Karlsson

Tel: +46 (0)371 430 11 Email: [email protected]



26

2.2.4 High pressure gas storage

Figure 2-17 Photo of high pressure gas storage unit.

A High pressure gas storage for biomethaneB Pressure sensor

RoleThe role of the high pressure gas storage unit is to store the upgraded biomethane at a high pressure (230 bar) so it can be filled into vehicles using the standard gas filling system.

ConnectionsThe high pressure gas storage unit is connected to the upgrading unit on the incoming sideand the gas pump on the outgoing side.

SensorsA pressure sensor is used.

OperationThe high pressure storage unit is filled up when the upgrading unit is active. It is emptiedwhen the gas pump from the filling station is used.



27

2.2.5 Filling station

Figure 2-18 Photo of the filling station.

A Filling pumpB Payment system for gas filling

RoleThe filling station allows the filling of the upgraded biomethane in corresponding vehicles.

ConnectionsThe filling station is connected to the high pressure gas storage unit on the incoming side.

Sensors

The filling station has a flow meter that measures the amount of gas that is filled into a car.

OperationA valve on the filling device opening connects the high pressure storage unit to the gas tank inthe car. The pressure difference between the two systems makes the gas flow from the high pressure storage unit into the car reservoir until an equal pressure is achieved.



28

2.2.6 Stirling engine

Figure 2-19 Photo of the Stirling engine.

RoleThe role of the Stirling engine is to produce electricity by utilizing the compression andexpansion of gas given from the heat produced from the combustion of biogas.

CapacityThe production capacity of the Stirling engine is 8 kW electricity, whereas the total capacity(including heat) is 36 kW.

ConnectionsThe Stirling engine is connected to the raw gas storage unit on the incoming side. The heatingsystem is lead through the Stirling engine, where it absorbs some of the produced heat. Beforethe heating water reaches stirling engine, it is lead through a cooler (see heating/coolingsystem below) to make sure the incoming water is at a low enough temperature. The leftover products from the combustion are released into the atmosphere through a chimney.



29

Regulation/AutomationThe Stirling engine is activated when the sought level in the raw gas storage is obtained andthe prioritized gas utilization units (upgrading unit) cannot consume more gas. This is carriedout by opening a valve and activating the fan in the gas room.

2.2.7 Gas burner

Figure 2-20 Photo of the gas burner.

RoleThe role of the gas burners is to combust the incoming biogas and produce heat in the heatingsystem.

CapacityAccording to the specification, the capacity of the gas burner is supposed to be 60 kW.However, normally a lower capacity, close to 50 kW, is obtained.

ConnectionsThe gas burner is connected to the raw gas storage unit on the incoming side. The heatingsystem is lead through the gas burner were it absorbs the produced heat. The leftover productsfrom the combustion are released into the atmosphere through a chimney in the roof.



30

SensorsThe gas burner is equipped with temperature sensors.

Regulation/AutomationThe gas burner is activated when the sought level in the raw gas storage is obtained and the prioritized gas utilization units cannot consume more gas. This is carried out by opening avalve and activating the fan in the gas room.

2.2.8 Torch

Figure 2-21 Photo of the torch.

A Torch for excess biogas

RoleThe role of the torch is to burn of any excess gas the other gas utilization units cannot

consume. This is carried out to avoid the release of the gas into the atmosphere.

CapacityThe torch is designed to handle gas flows up to 10 m3/h.

ConnectionsThe torch is connected to the raw gas storage on the incoming side. The leftover productsfrom the combustion are released into the atmosphere.





32

Figure 2-22 Photos of the control room.

A Pipe and valve controlling the substrate entering the digester

B Pipe and valve controlling the substrate leaving the digesterC Moisture analyzerD Gas composition analyzerE Digestate sampling hoseF Digestate pumpG Stirling engineH Shunt valve regulating the heating of the digesterI Control panelJ Gas burnerK Control cabinetL Computers and printerM Work station

The control room is the place where the operation of the biogas plant is controlled via thecontrol panel. This is also the location of the Stirling engine, gas burner, large parts of theheating/cooling system, as well as for simple substrate analysis. The control room alsocontains a work station with a computer, where all data can be entered and accessed. In thecontrol room a number of tools (e.g., moisture analyzer, pH meter, portable gas analyzer) arealso available.



33

2.3.1 Control cabinet

Figure 2-23 Photos of the control cabinet.

A Control cabinetB Control panel

The control cabinet is the place for the electronic communication interface. Here all theoperational units are centrally controlled. A short description of some of the units in thecontrol cabinet is presented below.

PLCThe PLC (Programmable Logical Controller) is a local computer that controls all processes inthe plant. It receives incoming signals from sensors and sends out outgoing signals to control pumps, valves, etc.

RelaysThe relays determine if certain processes or units are active or not (e.g. motors, valves, etc).This is performed with the help of electromagnets that open or close certain high voltageelectrical circuits using low voltage or low current circuits.



34

Digester top mixer frequency converterIt regulates the speed of the top mixer in the digester by regulating the frequency of its powerinput. It operates within a 0-60 Hz interval.

2.3.2 Work station

Figure 2-24 Photo of the work station.

The work station is the place where all information regarding the process is gathered and processed. The process data from the datalogger in the control panel can also be downloadedonto a computer at the work station.



35

2.4 Heating/cooling system

Figure 2-25 Photo of the heating/cooling system.

A Shunt valveB WM1C Cooler

The heating/cooling system at the site is connected to the same system that PlönningeAgricultural High School also uses. This makes it possible to easily utilize the extra heat produced from the gas burner. A measuring device (WM1) measures the heat energy produced and consumed by the plant by monitoring the incoming and outgoing heating water.

The only operational unit that is heated by the heating/cooling system is the digester. This process is controlled by a shunt valve (A) that acts on signal from a PID controller in the PLC.The heat energy that is consumed in the digester is monitored by the device WM1 (B).

The heating/cooling system is also used to cool the upgrading unit and the Stirling engine. Tomake sure the Stirling engine can operate properly, a cooler (C) is connected to theheating/cooling system just ahead of the engine. This is necessary since the Stirling enginerequires cold incoming water to be able to handle the excess heat produced in thecompression/expansion process.



36

3 CONTROL PANEL

Figure 3-1 Photo of control cabinet with control panel.

Many parts of the process can be monitored and controlled from the control panel. A touchscreen is used to navigate between the different menus. It is developed by Apptronic in 2004and has been continuously updated over the years.

The control panel can be found on one of the control cabinet doors in the control room(Figure3-1).





38

3.2 Process overview (Huvud)

Figure 3-3 Screenshot of process overview (översikt) menu.

From the process overview menu(Figure 3-3) the different menus available in the control panel including the operational panels, alarm list, data logger and energy measuring can beaccessed. In Table 3-2 a list of all functionalities in the process overview can be seen.

Table 3-2 Functionalities of process overview menu.

Name Action Information displayed

A Blandningstank Go tomixing tank menu Mixing tank pumpon (green) oroff (white)B Pumpbrunn 2 Go tomanure tank 1 menu Manure tank 1 pumpon (green) oroff (white)C Prumpbrunn3 Go tomanure tank 2 menu Manure tank 2 pumpon (green) oroff (white)D Bufferttank Go tobuffer tank menu Buffer tank pumpon (green) oroff (white)E Rötkammare Go todigester menu F Efterrötkammare Go todigestate storage menu G Gasmätning Go togas measuring menu Raw gas storage pressure (mbar)H Gasanvändning Go togas utilization menu I Huvud Go tostart menu J Larm Go toalarm list K Energimätning Go toenergy measuring menu L Loggning Go todata logger

Separate information displayed1 “pump symbol” Pump to digestate storageon (green) oroff (white)2 Producerad energi Produced energy for the current day (kWh)3 Förbrukad energi Consumed energy for the current day (kWh)



39

3.2.1 Mixing tank menu (Blandningstank)

Figure 3-4 Screenshot of the mixing tank menu.

From the Mixing tank(Figure 3-4) menu, the operation of the mixing tank can be controlled.You can choose to have it in automatic mode (the pumping and mixing are automaticallycontrolled) or manual mode. A list of the functionalities in the mixing tank menu can be seenin Table 3-3.

Table 3-3 Functionalities of mixing tank menu.

Name Action Information displayedA Inställningar Mixing tank settings menuB Driftsläge Change betweenautomatic and manual

operation of the pumpIf pump operation is inautomatic or manual mode

C Ventil AV1 Change betweencirculation and feedingmode for the pump

If pump direction is incirculation or feedingmode

D Pump P1 Turn pumpon or off in manual mode If pump ison (0) or off (1)E Översikt Process overview menuF Larm Alarm listG Energimätning Energy measuring menuH GP 1 Buffer tank menuI PB2 Manure tank 1 menu

Separate information displayed1 “Level indicator” Liquid level in mixing tank as well as lower and upper boundaries2 Nivå i PB1 Liquid level and corresponding volume in mixing tank

3 “Valve symbol ”AV1 If pump direction is incirculation or feeding mode4 “Pump symbol” P1 If pump ison or off



40

Mixing tank settings menu

Figure 3-5 Screenshot of the mixing tank settings menu.

FunctionalitiesFrom the mixing tank settings menu, instructions on how the mixing tank should be operatedcan be set. Parameters such as circulation time for each feeding of material as well as theupper and lower level boundary of the mixing tank can be controlled. A list of thefunctionalities in the mixing tank menu can be seen in Table 3-4.

Table 3-4 Functionalities of mixing tank settings menu.

Name Action Information displayedA Cirkulationstid Set time for circulation ahead of

feedingCurrent time for circulation ahead of feeding

B Övre nivå i tank Upper boundary for liquid level Current upper boundary for liquid levelC Undre nivå i tank Lower boundary for liquid level Current lower boundary for liquid levelD Tillbaka Go back to the Mixing tank menu



41

3.2.2 Manure tank 1 (Pumpbrunn 2)

Figure 3-6 Screenshot of manure tank 1 menu.Functionalities

From the manure tank 1 menu(Figure 3-6) the operation of the manure tank 1 can becontrolled. It can be operated in automatic mode (the pumping and mixing is automaticallycontrolled) or manual mode. A list of the functionalities in the manure tank menu can be seenin Table 3-5.

Table 3-5 Functionalities of manure tank 1 menu.

Name Action Information displayedA Inställningar Manure tank 1 settings menuB Driftsläge Change between automatic and

manual operation of the pumpIf pump operation is inautomatic or manual mode

C Ventil AV2/3 Change between circulation andfeeding mode for the pump


D Pump P2 Turn pumpon or off in manualmode

If pump ison (0) oroff (1)

E Översikt Process overview menuF Larm Alarm listG Energimätning Energy measuring menuH PB1 Mixing tank menuI PB3 Manure tank 2 menu

Separate information displayed1 “Level indicator” Liquid level in manure tank 1 as well as lower and upper boundaries2 Nivå i PB2 Liquid level and corresponding volume in manure tank 13 “Valve symbol ”

AV2If pump direction is incirculation or feeding mode

4 “Pump symbol” P2 If pump ison or off



42

Manure tank 1 settings menu

Figure 3-7 Screenshot of manure tank 1 settings menu.

FunctionalitiesFrom the manure tank 1 settings(Figure 3-7) menu, the instructions on how the manure tank 1should be operated can be set. Parameters such as circulation time before each feeding ofmaterial as well as the upper and lower level boundary of the manure tank 1 can be controlled.A list of the functionalities in the manure tank 1 menu can be seen in Table 3-6.

Table 3-6 Functionalities of manure tank settings menu.

Name Action Information displayedA Cirkulationstid Set time for circulation (mixing)

before feedingCurrent time for circulation (mixing) beforefeeding

B Övre nivå i tank Upper boundary for liquid level Current upper boundary for liquid levelC Undre nivå i tank Lower boundary for liquid level Current lower boundary for liquid levelD Tillbaka Manure tank 1 menu



43

3.2.3 Manure tank 2 (Pumpbrunn 3)

Figure 3-8 Screenshot of manure tank 2 menu.

FunctionalitiesFrom the manure tank 2 menu(Figure 3-8), the operation of the manure tank 2 can becontrolled. It can be operated in automatic mode (the pumping and mixing is automaticallycontrolled) or manual mode. A list of the functionalities in the manure tank 2 menu can beseen in Table 3-7.

Table 3-7 Functionalities of manure tank 2 menu.

Name Action Information displayedA Inställningar Manure tank 2 settings menuB Driftsläge Change between automatic and


C Ventil AV5 Change between circulation andfeeding mode for the pump


D Pump P3 Turn pumpon or off in manual mode If pump ison (0) or off (1)E Översikt Process overview menuF Larm Alarm listG Energimätning Energy measuring menuH PB1 Mixing tank menuI PB3 Manure tank 1 menu

Separate information displayed1 “Level indicator” Liquid level in manure tank 2 as well as lower and upper boundaries2 Nivå i PB3 Liquid level and corresponding volume in manure tank 23 “Valve symbol ” AV 5 If pump direction is incirculation or feeding mode4 “Pump symbol” P3 If pump ison or off



44

Manure tank 2 settings menu

Figure 3-9 Screenshot of the manure tank 2 settings menu.

FunctionalitiesFrom the manure tank 2 settings(Figure 3-9) menu, the instructions on how the manure tank 2should be operated can be set. Among the parameters which can be set are the circulation timefor each feeding of material as well as the upper and lower level boundary of the manure tank2. The functionalities presented in the manure tank 2 settings menu are listed in Table 3-8.

Table 3-8 Functionalities of the manure tank 2 settings menu.

Name Action Information displayedA Cirkulationstid Set time for circulation ahead of

feedingCurrent time for circulation ahead of feeding

B Övre nivå i tank Upper boundary for liquid level Current upper boundary for liquid levelC Undre nivå i tank Lower boundary for liquid level Current lower boundary for liquid levelD Tillbaka Manure tank 2 menu



45

3.2.4 Buffer tank menu (Bufferttank)

Figure 3-10 Screenshot of the buffer tank menu.

FunctionalitiesFrom the buffer tank menu(Figure 3-10), the operation of the buffer tank can be controlled.The operation can be set in automatic mode (the pumping and mixing is automaticallycontrolled) or manual mode. A list of the functionalities in the buffer tank menu can be seenin Table 3-9.

Table 3-9 Functionalities of the buffer tank menu.

Name Action Information displayedA Inställningar Buffer tank settings menu

B Driftsläge Change between automatic andmanual operation of the pump If pump operation is inautomatic or manual modeC Ventil AV11 Change between circulation and

feeding mode for the pumpIf pump direction is incirculation or feedingmode

D Pump P4 Turn pumpon or off in manual mode If pump ison (0) or off (1)E Flödesmätning Go to Flödesmätning menuF Översikt Process overview menuG Larm Alarm listH Energimätning Energy measuring menuI PB3 Manure tank 2 menuJ RK1 Digester menu

Separate information displayed1 “Level indicator” Liquid level in buffer tank as well as lower and upper boundaries

2 Nivå i PB3 Liquid level and corresponding volume in buffer tank3 “Valve symbol ” AV11 If pump direction is incirculation or feeding mode4 “Pump symbol” P4 If pump ison or off





47

Buffer tank flow measuring menu

Figure 3-12 Screenshot of the buffer tank flow measuring menu.FunctionalitiesFrom the buffer tank flow measuring menu(Figure 3-12), the feeding of the digester can befollowed. A list of the functionalities listed in the buffer tank flow measuring menu can beseen in Table 3-11.

Table 3-11 Functionalities buffer tank flow measuring menu.

Name Action Information displayedA Tillbaka Back to buffer tank menu

Separate information displayed1 Momentant flöde Current flow rate to digester2 Beskickad mängd Volume counter for each individual feeding cycle3 Dygnsmängd Volume fed to digester current day (starts at 00:00)4 Total mängd Total amount fed to digester since flow meter was installed



48

3.2.5 Digester menu (Rötkammare)

Figure 3-13 Screenshot of the digester menu.

FunctionalitiesFrom the digester menu(Figure 3-13) the operation of the digester can be controlled. Theoperation can be set to automatic mode (the pumping to the digestate storage is automaticallycontrolled) or manual mode. Changing the settings for the temperature control and the mixercan also be performed in this menu. A list of the functionalities in the digester menu is presented in Table 3-12.

Table 3-12 Functionalities of the digester menu.

Name Action Information displayedA Inställningar Digester settings menuB Driftsläge Change betweenautomatic and


C Ventil AV11 Change betweencirculation andfeeding mode for the pump


D Pump P4 Turn pumpon or off in manualmode

If pump ison (0) oroff (1)

E Temp I RK1 Digester temperature controlmenu

Current temperature in digester

F “ Mixer symbol ” OM5 Mixer settings menu If mixer ison or off G Översikt Process overview menuH Larm Alarm listI Energimätning Energy measuring menu



49

J BT1 Buffer tank storageK ERK1 Digestate storage menu

Separate information displayed1 “Level indicator” Liquid level in digester as well as lower and upper boundaries2 Nivå i RK1 Liquid level and corresponding volume in digester

3 “Pump symbol” P6 If digestate pump ison or off

Digester settings menu

Figure 3-14 Screenshot of the digester settings menu.

FunctionalitiesFrom the digester settings(Figure 3-14) menu, the instructions on how the digester should beoperated can be set. The setpoint for the digester temperature and the lower level boundarycan be specified in this menu. A list of the functionalities in the digester settings menu can beseen in Table 3-12.

Table 3-13 Functionalities of the digester settings menu.

Name Action Information displayedA Undre nivå I tank Set lower boundary for liquid level Current lower boundary for liquid level (cm)B Temp. börvärde Set temperature setpoint Current upper boundary for liquid level (ºC)H Tillbaka Digester menu



50

Digester temperature menu

Figure 3-15 Screenshot of the digester temperature menu.

FunctionalitiesFrom the digester temperature menu(Figure 3-15), the set point for the digester temperaturecan be set and the latest temperature trends can be followed. A list of the functionalities in thedigester temperature control menu can be seen in Table 3-14.

Table 3-14 Functionalities of the digester temperature control menu.


A Börvärde Set the digestate temperature setpoint Current digester temperature setpoint (°C)B REGULATOR Go to digester temperature control menuC Tillbaka Back to digester menu

Separate information displayed1 Temp TC50 Current temperature in from lower sensor in digester2 Temp TC51 Current temperature in upper sensor in digester3 “Gra ph ” Temperature trends for the upper and lower senso r for the last 4 days



51

3.2.5.1.1 Digester temperature control menu

Figure 3-16 Screenshot of the digester temperature control menu.

FunctionalitiesIn the digester temperature control menu(Figure 3-16), the control parameters for the PIDcontroller that regulates the digester temperature can be modified. A list of the functionalitiesin the digester temperature control menu can be seen in Table 3-15.

Table 3-15 Functionalities of the digester temperature control menu.


A K-värde Set the K constant (proportional coefficient) Current value for K constantB I-värde Set the I constant (integral coefficient) Current value for I constantC D-värde Set the D constant (derivative coefficient) Current value for D constantD Samplingsperiod Set the sampling frequency (0=continuous) Current sampling frequencyE Min. Set the minimum controller output Current minimum outputF Max. Set the maximum controller output Current maximum output

Separate information displayed1 Utstyrt värde Current controller output (signal to shunt valve)2 Är Current digester temperature3 Bör Digester temperature setpoint

4 Ut Current controller output (signal to shunt valve)



52

3.2.6 Digestate storage unit (Efterrötkammare)

Figure 3-17 Screenshot of the digestate storage unit menu.

FunctionalitiesFrom the digestate storage unit menu(Figure 3-17), the operation of the digestate storage unit1 and the manually control of the mixers in the digestate storage unit 1 can be controlled. Alist of the functionalities listed in the digestate storage unit menu can be seen in Table 3-16.

Table 3-16 Functionalities of the digestate storage unit menu.

Name Action Information displayedA Inställningar Digestate storage unit 1 settings

menuB ERK1 till LT1 Pumping from digestate storage

unit to manure storage unit menuC Omrörare OM60/61 Set digestate storage unit 1 mixers

on or offIf mixers ison (0) oroff (1)

D Översikt Process overview menuE Larm Alarm listF Energimätning Energy measuring menuG RK1 Digester menuH GAS M Gas measuring menu

Separate information displayed1 “Level indicator” Liquid level in digestate storage 1

2 Nivå i ERK1 Liquid level and corresponding volume in digestate storage 13 “Mixer symbol” OM60 If mixer OM60 ison or off4 “Mixer symbol” OM61 If mixer OM61 ison or off



53

Settings menu of the digester storage unit

Figure 3-18 Screenshot of the digestate storage unit settings menu.

FunctionalitiesFrom the settings menu of the digestate storage unit(Figure 3-18), the instructions for theoperation of the digestate storage unit can be controlled by setting an upper level boundary.When the upper level is reached, an alarm is activated. A list of the functionalities in thedigestate storage unit 1 settings menu can be seen in Table 3-17.

Table 3-17 Functionalities of the digestate storage settings menu.

Name Action Information displayedA Övre nivå I tank Set upper boundary for liquid level Current upper boundary for liquid level (cm)B Tillbaka Back to digestate storage menu





55

3.2.7 Gas measuring menu (Gasmätning)

Figure 3-20 Screenshot of the gas measuring menu.

FunctionalitiesFrom the gas measuring menu(Figure 3-20), the current gas flows, raw gas storage pressureas well as operation of the torch can be followed. A list of the functionalities in the gasmeasuring menu can be seen in Table 3-19.

Table 3-19 Functionalities of the gas measuring menu.


A GM1 Go to gas flow meter menu Current flow rate in flow meter 1B GM3 Go to gas flow meter menu Current flow rate in flow meter 2 (gas burner)

C Inställningar Go to gas measuring settingsmenu

D Översikt Process overview menuE Larm Alarm listF Energimätning Energy measuring menuG ERK1 Digestate storage menuH GAS Gas utilization menu

Separate information displayed1 PC1 Current pressure in raw gas storage

2 GFA1 If torch ison (green) oroff (white) and current days online time of torch3 GF1 If gas pump inon ( green) oroff (white)



56

Gas measuring settings menu

Figure 3-21 Screenshot of the gas measuring settings menu.

FunctionalitiesFrom the gas measuring settings menu(Figure 3-21), the raw gas storage pressure limit foractivating the torch can be set. A list of the functionalities in the gas measuring settings menucan be seen in Table 3-20.

Table 3-20 Functionalities of the gas measuring settings menu.


A Tändning av gasfackla Set minimum raw gas storage pressure for activation of torch Current minimum raw gas storage pressure for activation of torch (mbar)B Tillbaka Go to back to gas measuring

menu



57

Gas flow meters menu

Figure 3-22 Screenshot of the gas flow meters menu.

FunctionalitiesFrom the gas flow meters menu(Figure 3-22), the process parameters of the two gas flowmeters in the system can be followed. A list of the functionalities in the gas flow meters menucan be seen in Table 3-21.

Table 3-21 Functionalities of the gas flow meters menu.

Name Action Information displayedA Tillbaka Back to gas measuring meter

Separate information displayed1 Momentat (GM1) Current value for gas flow meter (total gas flow) (m3/h)2 Dygnsvärde (GM1) Gas produced the current day (total gas flow) (m3/d)3 Totalt (GM1) Total gas production of the plant (total gas flow) m3 4 Momentat (GM3) Current value for gas flow meter (gas burner) (m3/h)5 Dygnsvärde (GM3) Gas produced the current day (gas burner) (m3/d)6 Totalt (GM3) Total gas production of the plant (gas burner) (m3)



58

3.2.8 Gas consumption menu (Gasanvändning)

Figure 3-23 Screenshot of the gas consumption menu.

FunctionalitiesFrom the gas consumption menu(Figure 3-23), the gas consumption units can be monitored.The status of several gas alarm systems can also be followed in this menu. A list of thefunctionalities in the gas consumption menu can be seen in Table 3-22.

Table 3-22 Functionalities of gas consumption menu.


A Inställningar Go to gas utilization settings menuB Översikt Process overview menuC Larm Alarm listD Energimätning Energy measuring menuE GAS M Gas measuring menuF PB1 Mixer tank menu

Separate information displayed1 GASLAGER Level in raw gas layer (%)2 GASVARNARE Level of gas alarm (not functioning)3 GASPANNA If gas burner ison (green) oroff (white) andon time the current day so far

4 STIRLING If stirling engine ison (green) oroff (white) and on time the current day so far5 FORDONSGAS If upgrading unit ison (green) oroff (white) andon time the current day so far



59

Gas consumption settings menu

Figure 3-24 Screenshot of the gas consumption settings menu.

FunctionalitiesFrom the gas consumption settings menu(Figure 3-24), the settings controlling the levels forthe upgrading unit, Stirling engine and the gas burner can be set. This is carried out byspecifying a filling level of the raw gas storage unit at which the gas consumption should beactivated, as well as a corresponding level when it should be deactivated. A list of thefunctionalities in the gas consumption settings menu can be seen in Table 3-23.

Table 3-23 Functionalities of gas flow meter menu.


A Start (Fordonsgasanl.) Set raw gas storage level to activateupgrading unit Current raw gas storage level to activateupgrading unitB Stopp (Fordonsgasanl.) Set raw gas storage level to deactivate

upgrading unitCurrent raw gas storage level todeactivate upgrading unit

C Start (Sterlingmotor Set raw gas storage level to activateStirling unit

Current raw gas storage level to activateStirling unit

D Stopp (Sterlingmotor Set raw gas storage level to deactivateStirling unit

Current raw gas storage level todeactivate Stirling unit

E Max (Gaspanna) Set the maximum raw gas storage levelfor the gas burner

Current the maximum raw gas storagelevel for the gas burner

F Start (Gaspanna) Set raw gas storage level to activate gas burner unit

Current raw gas storage level to activategas burner unit

G Stopp (Gaspanna Set raw gas storage level to deactivate gas burner unit

Current raw gas storage level todeactivate gas burner unit

H Gaslarm Set gas alarm level to give gas alarm Current gas alarm level to give gas alarmI Tillbaka Back to gas utilization menu



60

3.3 Data logger (Logging)

Figure 3-25 Screenshot of the data logger menu.

Functionalities

From the data logger menu(Figure 3-25) the three different loggers in the control panel can be accessed. A list of the functionalities in the data logger menu can be seen in Table 3-24.

Table 3-24 Functionalities of data logger menu.

Name Action Information displayedA Loggning 1 Go toLogger 1 menu B Loggning 2 Go toLogger 2 menu C Loggning 3 Go toLogger 3 menu D Läs av nu View the latest collected data pointsE Nollställ Erase the loggers

F Huvud Back tostart menu G Översikt Go toprocess overview menu H Larm Go toalarm list



61

3.3.1 Logger 1

Figure 3-26 Screenshot of the Logger 1 menu.

Functionalities

From the logger 1 menu(Figure 3-26), the parameters stored in the logger can be seen andtheir trends for the four last days can be monitored. A list of the functionalities in the logger 1menu can be seen in Table 3-25.

Table 3-25 Functionalities of logger 1 menu.

Name Action Information displayedA Tillbaka Back todata logger menu B Loggning 2 Go tologger 2 menu C Loggning 3 Go tologger 3 menu

Separate information displayed1 LOGGER 1 Parameters stored in logger 12 “Graph” Four day trend lines for parameters stored in logger 1



62

3.3.2 Logger 2

Figure 3-27 Screenshot of the Logger 2 menu.

Functionalities

From the logger 2 menu(Figure 3-27), the parameters stored in the logger can be seen andtheir trends for the four last days can be monitored. A list of the functionalities in the logger 2menu can be seen in Table 3-26.

Table 3-26 Functionalities of logger 2 menu.





63

3.3.3 Logger 3

Figure 3-28 Screenshot of Logger 3 menu.

Functionalities

From the logger 3 menu(Figure 3-28), the parameters stored in the logger can be seen andtheir trends for the four last days be monitored. A list of the functionalities in the logger 3menu can be seen in Table 3-27.

Table 3-27 Functionalities of the logger 3 menu.





64

3.4 Energy measuring (Energimätningar)

Figure 3-29 Screenshot of the energy measuring menu.

FunctionalitiesFrom the energy measuring menu (Figure 3-29), the amount of energy that has beenconsumed and produced can be monitored. A list of the functionalities in the energymeasuring menu can be seen in Table 3-28.

Table 3-28 Functionalities of energy measuring menu.


A Huvud Back tostart menu B Översikt Got toprocess overview menu C Larm Go toalarm list

Separate information displayed1 Totalvärden Readings of totallyproduced (blue) andconsumed (red) energy2 Dygnsvärden Readings ofproduced (blue) andconsumed (red) energy for the current day3 “Graph” Trend lines of theproduced (blue) andconsumed (red) energy



65

3.4.1 Alarm list (Larm)

Figure 3-30 Screenshot of the alarm list.

FunctionalitiesFrom the gas alarm list(Figure 3-30) the gas consumption units can be monitored. The statusof several gas alarm systems can also be followed in this menu. A list of the functionalities inthe gas consumption menu can be seen in Table 3-29.

Table 3-29 Functionalities of alarm list.

Name Action Information displayedA ESC Go back to previous menuB “ Arrow up” Go up in listC “Checkmark” Acknowledge alarmD “Magnifying glass” Zoom inE “Wristwatch” Display the time for the alarmsF “Arrow down” Go down in list

Separate information displayed1 “Alarm list” Current alarms in list and if they are active (red) or acknowledged (grey)



66

4 ANALYSIS AND MONITORING

There is an increasing need to analyze the liquid or solid raw materials before their use asfeedstock (substrates) in anaerobic digestion processes and also to monitor suitable process

parameters which can give early indications of imbalances in the microbial system and earlywarnings of external disturbances.

4.1 Determination of feedstock characteristics

Biogas can be produced from a broad range of substrates that are suitable for anaerobicdigestion, e.g. manure, residual sludge, energy crops, municipal solid waste and industrialwaste. Operation of a pilot and/or full-scale anaerobic digester working on a single substrateor in a co-digestion mode requires analysis of each substrate. The substrate should becharacterised with regard to pH, moisture content, total (TS) and volatile solids (VS) and alsoto its potential to produce bio-methane.

4.1.1 pH

pH is a measure of the acidity/alkalinity of a solution. A neutral solution (H2O) has a pH of 7.Alkaline or basic solutions have a pH higher than 7 and acidic solutions less than 7. pH isdefined as negative decimal logarithm of the hydrogen concentration in a solution; a low pHindicates a high concentration of hydrogen ions [H+], while a high pH indicates a lowconcentration.

pH = − log[H + ] (1)

pH can be measured experimentally using a pH sensor, which consists of an ion-selectiveelectrode covered with a glass membrane and a reference electrode (e.g. calomel or silverchloride electrode).The pH sensor measure a potential difference between the ion-selectiveand the reference electrodes, and this potential difference is dependent of hydrogenconcentration according to the Nernst equation:

E = E 0 +RT

nF ln[H+

] (2)



67

Figure 4-1 Photo and schematic representation of a pH sensor.

The pH value of the substrate influences the growth of microorganisms; most methanogensand acetogens grow best near neutral pH conditions, whereas acidogens prefer to live in weakacidic conditions.

4.1.2 Moisture content

Moisture content (MC) is the quantity of water contained in a sample. The gravimetricmethod is a widely used method for determination of trace amounts of water in a sample. Thiscan be done by drying a known amount of sample in an oven.

The moisture analyzer is based on the principle of thermogravimetric analysis: the sample isweighted both before and after drying (using a 400 W halogen lamp as a heating source); thewater content is calculated as the ratio between the difference in amounts of the sample before

(mWet ) and after drying (m Dried ) and the initial amount of sample, and the moisture content isusually expressed as weight %.

% = −

× 100 (3)



68

Figure 4-2 Photo of the moisture analyzer used for the determination of the total solids of a target sample.

The total content of solids is a measure of the amount of material remaining after all the waterhas been evaporated.

% =

× 100 = 100 − (%) (4)

4.1.3 Total (TS) and volatile solids (VS)

The dry matter, i.e. all inorganic and organic compounds, is often expressed as TS and can be

measured according to a standard protocol. For a given biomass sample, it is necessary to heatthe sample up to 105 °C in order to remove all water content.

VS is represented by the organic compounds in the sample. After finishing the TSmeasurement, heating the sample up to 550 °C for two hours should be continued for burningup the organic matter. The weight difference between the sample after heating at 105 and 550°C reflects the VS content of the biomass.The next three steps are usually followed to determine the TS and VS of a target sample:

1). Preparationa) Heat a dish to 550 °C for 1 h. b) Place the dish in a desiccator for cooling.

2). TS determinationa) Weigh the dish and record this value. b) Add 2-3 ml of a representative sample into the dish.c) Place the dish with the sample in an oven preheated to 105 °C and allow the volatiles

to evaporate for 20 h.



69

Figure 4-3 The main steps performed for TS determination.

3). VS determinationa) Take the dish out of the oven and allow it to cool to room temperature in a desiccator. b) Weigh the dish and record the value.c) Transfer this dish into a furnace pre-heated to 550 °C (ignition).d) After 2 h, take the dish out of the furnace and cool it to RT in a desiccator.e) Weigh the dish and record the value.

Figure 4-4 The main steps performed for VS determination.

TS is calculated as the ratio between the amount of dried sample (m Dried ) and the initialamount of wet sample (mWet ), whereas VS is calculated as the ratio between the difference inthe amount of sample after drying and burning (m Burned ) and the initial amount of sample.

% =

× 100 (5)

% = −

× 100 (6)

4.1.4 Biochemical methane potential (BMP) test

A laboratory-scale procedure in which substrates are characterized and then evaluated usingthe biochemical methane potential (BMP) analysis is usually carried out in the first step. Thistest provides a preliminary indication of the biodegradability of a substrate and of its potentialto produce methane via anaerobic digestion.

The conventional BMP assay involves incubating a substrate inoculated with anaerobic bacteria for a period of 30 to 60 days, commonly at 37 ºC, and monitoring the biogas production and its composition throughout the test. Most such tests require a relatively high



70

workload for manual sampling of the produced gas at different time points, followed byanalysis, data recording and processing.

The Automatic Methane Potential Test System (AMPTS) II follows the same analysing principles as conventional biochemical methane potential tests, which make the results fullycomparable with common methods. However, in an AMPTS, the sampling, analysis andrecording are fully integrated and automated, the bio-methane production being recordedcontinuously 24 h per day, 7 days per week with minimal workload. The system is able toanalyse substrates with or without pre-treatment in order to allow biogas producers todetermine the methane production potential and degradation profile of any substrate, providing the optimum co-digestion possibilities, retention times and plant utilisation.

Figure 4-5 Photo of AMPTS and a screenshot with the graph page.

The AMPTS provides the following advantages over conventional BMP tests: (i) automatedanalytical procedure, reducing workload and time, (ii) on-line and real-time data logging oftotal biogas or bio-methane production and flow rate, (iii) user friendly interface for real-timedata display and analysis overview, (iv) high quality data allowing extracting process kineticinformation, (v) easy and low maintenance, (vi) cost effectiveness, (vii) possibility ofmultiplexing, allowing simultaneous evaluation of co-digestion and substrate pre-treatment.

4.2 Monitoring of process parameters in anaerobic digestion process

Anaerobic digesters require monitoring of critical parameters (e.g. temperature, pH and buffering capacity, the concentration of nutrients and inhibitors, gas composition) in order toobtain an optimal production efficiency and biogas yield. However, due to the expensiveand/or time-consuming character of most analysis methods for anaerobic digestion, industrialdigesters are usually not extensively monitored and only few parameters may be continuouslymeasured, such as pH and gas flow. Therefore the loading rate of a digester has to be keptrelatively low for safety reasons.



71

4.2.1 Temperature

Anaerobic treatment is normally carried out within two distinct temperature ranges: i)thermophilic range, where the optimal temperature is about 55 ºC, and ii) mesophilic range,where the optimal digestion occurs at about 37 ºC.

The advantages of thermophilic digestion over the mesophilic one include a high CH4 production rate and the support of a higher organic load. However, thermophilic digestionappears unstable in comparison to degradation under mesophilic conditions due todenaturation of enzymes at high temperature.

Besides the two temperature ranges mentioned before, methanogenesis is also possible attemperatures below 20 ºC, under psycrophilic conditions, but occurs at lower rates. At thislow temperature, the enzymatic hydrolysis of organic matter rich in carbohydrates is alsoslow. In conclusion, the mesophilic conditions are the most used for the anaerobic digestionof organic materials.

4.2.2 pH

For the successful operation and control of the anaerobic fermentation it is essential tomeasure the reactor pH since a change in pH is a good indicator of process stress for thesystems with low buffer capacity or alkalinity.

The pH of the reactor should be maintained close to neutrality in anaerobic processes

(between 6.8 and 7.4) to ensure stable operation. Each of the microbial groups involved in the process has a specific pH region for optimal growth. For the acidogens the optimal pH isaround 6, whereas for the acetogens and methanogens the optimal pH is around 7. Forexample, process overloaded results in excessive production of fatty acids and this will bereflected in decreased pH if the buffering capacity of the fermentation liquid is low.

4.2.3 AlkalinityAnother important parameter in anaerobic digestion systems is alkalinity, which is a measureof the capacity of a sample to resist a change in pH. For maintaining a neutral pH and a stableoperation of the reactor, the fermentation mixture should provide enough buffering capacity toneutralize any possible volatile fatty acids (VFA). Carbonic acid (bicarbonate form),dihydrogen phosphate, hydrogen sulphide and ammonia are the compounds that provide asignificant buffering capacity around pH 7.

Even if alkalinity represents the total concentration of bases in solution, it is expressed as ppmor mg/L CaCO3. Alkalinity is determined by a titration method using a buret/digital titratorand a pH meter. Titration is the addition of small quantities of the reagent (H2SO4 or HCl) tothe sample until the sample reaches a certain pH known as an endpoint (pH of 4.3).







74

Even though measuring parameters such as biogas production and composition is common at biogas plants, they have been shown not to be sensitive enough for process monitoring andcontrol. Due to limitations in mass transfer between liquid and gas phases, the gas-phaseconcentration does not always reflect the actual concentration in the liquid.

4.2.6 Volatile fatty acids (VFA) and dissolved hydrogen (DH)

Propionate, butyrate and valerate are intermediate compounds from the acidogenic step andcan be converted further into CH4 and CO2 through the acetogenesis step. Accumulation ofthese acids results in a decreased pH, leading to an increased amount of protonated VFAwhich causes inhibition of degradation of the feedstock. Since accumulation of thesecompounds reflects an imbalance between the microbial groups involved in the degradation,monitoring of these intermediates is therefore a method of tracking the status of the process.

The concentration of dissolved hydrogen has also been shown to be a key factor in thefermenter since its concentration affects thermodynamics and the degradation pathway of theanaerobic process. Hydrogen works as both an intermediate and electron carrier in thedegradation process. High hydrogen concentrations can inhibit volatile acid degradation,resulting in VFA accumulation. Thus, hydrogen accumulation can be suggested as an earlystage indicator of process imbalance and toxic inhibition.

Figure 4-8 Photo of a hydrogen sensor.

Selection of parameters for process monitoring and control depends on the reactorconfiguration, the characteristics of the feedstock, and available sensors, as well as theimplemented control strategy, and may not be generally applicable. However, it is quitecommon that several parameters are monitored at the same time, as they can providecomplementary information about process dynamics.

4.3 Sampling and analysis

4.3.1 Sampling points

At the Plönninge biogas site, the liquid samples can be collected mainly from four places (i.e.

manure tank, mixer tank, buffer tank and digester) whereas the gas sampling is carried outfrom the condensation trap in the gas room.



75

Sampling from the manure tank For sampling from the manure tank a sampling stick and a bucket are required; a descriptionof the operational steps to be followed is presented below.

Figure 4-9 Photo of the sampling port from the manure tank.

1) In the control panel, access the manure tank menu and do the following tasks:

Figure 4-10 Screenshots of manure tank 2 menu with instructions on how to turn on the mixing.



76

a) Make sure the level is high enough for using the pump. The level should be above 50cm.

b) Turn the pump on manual mode.c) Turn the pump on recirculation mode.d) Start the pump and run it for at least five minutes.

2) Remove the cover of the manure tank.

3) Take a sample using the sampling stick. Immerse the stick a bit below the upper liquidlevel and mix in order to get a more representative sample.

4) Empty the content of the sample stick in the bucket.

5) Place the cover back on the manure tank.

6) Take the bucket with the sample back into the control room for analysis.

7) In the control panel, perform the following steps:

a) Turn off the pump. b) Turn the pump on automatic mode again.

Sampling from the mixing tank For taking a sample from the mixing tank, a sampling stick and a bucket are required.1) In the control panel, access the mixing tank menu and do the follwing tasks (same as formanure tank):

a) Make sure the level is high enough for using the pump. The level should be above thelower boundary. b) Turn the pump on to manual mode.c) Turn the pump on to recirculation mode.d) Start the pump and run it for at least five minutes.

2) Turn on the submersible mixer.

3) Remove the cover of the mixing tank.

4) Take a sample using the sampling stick. Immerse the stick a bit below the liquid level andmix in order to get a more representative sample.


6) Put the cover back on the mixing tank.

7) Take the bucket with the sample back into the control room for analysis.

8) Turn off the submersible mixer.

9) In the control panel, perform the following steps:

a) Turn off the pump.



77

b) Turn the pump on automatic mode again.

Sampling from the buffer tank

For taking a sample from the buffer tank, a sampling stick and a bucket is required.

1) In the control panel, access the buffer tank menu and do the follwing tasks (same as formanure tank):

a) Make sure the level is high enough for using the pump. The level should be above thelower mark.

b) Turn the pump on to manual mode.c) Turn the pump on to recirculation mode.d) Start the pump and run it for at least five minutes.

2) Remove the cover of the buffer tank.

3) Take a sample using the sampling stick. Immerse the stick a bit below the liquid level andmix in order to get a more representative sample.

Figure 4-11 Photo of the sampling stick immersed in the buffer tank.






79

Figure 4-13 Photo of the valve of the digestate hose in “closed” position.

2) Go back inside and open (in the same direction as the hose) the valve and hold it open forthree seconds.

Figure 4-14 Photo of the pump from the control room.

3) Go outside, carefully open the valve (the tap should be in same direction as the hose) whileholding the hose outlet firmly into the collecting bucket. The digestate will now flow into the bucket.

Figure 4-15 Photo of the valve of the digestate hose in “open” position and the bucket full witha sample collected from the digester.

4) When no more digestate is flowing from the hose outlet, close the valve again.



80

Figure 4-16 Photo of the valve of thedigestate hose in “closed” position.

Sampling from the condensation trap (in the gas room)For taking and analyzing a gas sample from the condensation trap, an MSA Altair 5IR sensoris required.

Figure 4-17 Photo of the MSA Altair sensor for measuring CH4 and H2S concentrations in a gas sample.

4.3.2 Analysis of liquid samples

The only tests currently performed for raw materials, at the Plönninge biogas plant, are themeasurement of moisture content (which is indirectly a measure of the total solids) and the pH. These measurements are performed using amoisture analyser (Kern MLB_N, version2.1, Germany) and a pH sensor (Impo electronic, type 1510, Denmark), respectively.



81

Figure 4-18 Photo of Kern MLB_N moisture analyser situated in the control room.

Determination of moisture content

1) Turn on the analyzer by pressing the On/Off button until digits appears on the display.2) The analyser needs a pre-heating process before measurement. For that, place a sample trayon the tray support and press the Start/Stop key to initiate the heating.

Figure 4-19 Photo of the moisture analyzerwhen the “Start” key is pressed for initiating the heating.

3) When the temperature of the analyser reaches equilibrium, a downward arrow is displayedon the top right corner. Open the lid and place a sample tray previously kept at room

temperature in the tray support.



82

Figure 4-20 Photo of the sample tray placed on the tray support of the moisture analyzer.



83

4) Press the Tare button and wait the value on the display to stabilize.

Figure 4-21 Photo of the “Tare” key from the moisture analyzer.

5) When a downward arrow appears on the top right corner of the display, the sample may be placed in the sample tray. Make sure that the sample is properly mixed before sampling. Use a

proper sample quantity, e.g. 5-10 g.



84

Figure 4-22 Photo of the previously mixed sample added to the sample try of the moisture analyser.

6) When the display shows a stable value, close the heating cover to start the analysis. A blinking bright light should appear inside the moisture analyser.

Figure 4-23 Photo of the sample before staring the moisture analyser.

7) When the change of moisture content per minute (drying rate) is below 0.1%, themeasurement is completed. Open the heating cover and remove the sample using the trayhandle. Turn off the analyzer by pressing the On/Off button.

8) Calculate the TS value by subtracting the displayed value of moisture content from 100.



85

Figure 4-24 Screenshot of the Excel file process_data.xlsm.

8) Enter the aquired TS value for the sample in the excel file process_data.xlsm.



86

Determination of pH

Figure 4-25 Photo of the pH sensor situated in the control room.

1) Turn on the pH sensor by pressing the On button until numbers appears on the display.

Figure 4-26 Photo of the pH electrode.



87

2) Remove the protection cap of the electrode. Place the sensor in the buffer standardsolution(s) and calibrate it (single- or two-point(s) calibration).

Figure 4-27 Photo of the protection cap of the pH electrode.

3) Place the electrode in the sample. Be sure that the membrane of the electrode is wellimmersed in the liquid.

Figure 4-28 Photo of a pH electrode immersed in a liquid.





89

4.4 Analysis of gaseous samples

The analysis of the biogas samples are performed using an MSA Altair sensor.

Figure 4-31 Photo of MSA Altair sensor for measuring biogas composition.

1) Turn on the MSA Altair sensor by pushing down on the button in the middle and holding itfor a few seconds until a sound is generated and the screen lights up.

Figure 4-32 Photo of MSA Altair sensor in “On” position.



90

2) Perform a pump test by blocking the tubeuntil the screen displays “Pump test OK”.

Figure 4-33 Photo of MSA Altair sensorin its “test” stage.

3) When the calibration is finished, the “FRISKLUFT SETUP” will appear on the display and

at that moment press the right button.

Figure 4-34 Photo of the gas outlet on the condensation trap.



91

4) Open the valve for the gas outlet on the codensation trap.

Figure 4-35 The connection of the gas sensor with the gas outlet on the condensation trap.

5) Connect the sample unit to the gas outlet by placing the plastic tube of the sampling unit

inside the plastic tube of the gas outlet.

Figure 4-36 Photo of the display of the gas sensor.



92

6) Wait for the values on the display to stabilize (this usually takes 1-2 minutes) and then notethe values for CH4 and H2S concentration.

Figure 4-37 Photo of the gas sensor placed in its holder for charging.

7) Place the sampling unit back in its holder for charging. Make sure that the green light is on.

Figure 4-38 Screenshot of the Excel file containing the registered values for CH4 and H2S

concentrations.



93

8) Enter the registred values for CH4 and H2S concentrations in the Excel file process_data.xlsm.

4.5 Online monitoring and data logging

Several process parameters are measured online to give information about the operation of the plant. A number of these parameters are also locally saved in the computer of the control panel.

Totally, there are three data loggers that save and store daily the measured values of 14 parameters (Table 4-1). There is a memory limit in the data logger which causes it tooverwrite older values after a certain time (after about 2-3 months). Therefore, it is importantto download the data on a regular basis.

Table 4-1 Parameters that are logged in the data logger.

Name in control panel Name in Excel file a DescriptionLogger 1 1 TC50 Temp1 Temperature digester bottom

2 TC51 Temp2 Temperature digester top3 LC5 Nivå RK Level in digester4 LC6 Nivå ERK Level in digestate storage unit 15 GM1 DYGN Gasflöde Daily gas production6 GM3 DYGN Gasflöde panna Daily gas flow in gas burner

Logger 2 1 EM1 DYGN EM1 Consumed electricity by operationalunits2 WMM1 DYGN WMM1 Consumed heat energy by digester3 WMM2 DYGN WMM2 Produced heat from plant4 GP1 TID DYGN Tid gaspanna Gas boiler on time5 FI5 DYGN Beskickning Amount fed to digester

Logger 3 1 STERLING TID DYGN Tid stirling Stirling engine on time2 FORDON TID DYGN Tid uppgradering Upgrading on time3 FACKLA TID DYGN Tid fackla Torch on time

a) Excel file for data handling in Plönninge. More information is given in section“6. Documentation”.

The data from the logger can be downloaded as a csv (comma separated values)-file that can be open in Excel. A guide of how this conversion is carried out is presented in chapter 6.





95

5.2 Process performances

There is a number of parameters used to evaluate the performances of a biogas plant. These parameters are often standardized, making it possible to compare different plants with eachother and get a good understanding of what performances should be expected. The normalized

accumulated volume of gas, gas productivity and the reduction in VS are the mostrepresentative parameters which are reviewed and evaluated in a daily, weekly and/ormonthly basis.

5.2.1 Gas normalization

Gas normalization is a way to get a standardized measurement of the gas volume or flow rate by compensating for the effects of temperature and pressure. The pressure deviation is oftenso small that it can be excluded. Since raw biogas contains small amounts of water vapor, thiseffect should be also removed.There are several standards for carrying out such compensation; below is the one accepted byIUPAC (International Union of Pure and Applied Chemistry).

= , ·273.15

273.15 +· (10)

= 1 −10

8.19625 − 1730.630+233,426

1013

(11)

5.2.2 Gas productivity

The gas productivity is a standardized parameter to measure and compare how productive a biogas digester is. It is a measurement that describes the amount of gas produced per reactorvolume and day with the unit 3 / 3 / . Since the parameter considers thevolume of the digester, it may be used for comparison of performances of different biogas plants. The parameter can be calculated from either the total volume of biogas and/ormethane. For standardization, the gas is usually normalized by compensating for the effect oftemperature, pressure and water content; the normalized values are around 9% lower than theones for the raw biogas.

A well performing plant has a biogas productivity (P biogas) of around 2-3 3 / 3 /

and a methane productivity of 1-2 3 / 3 / . However, these valuesdepend greatly of what type of substrate is used and the configuration of the plant. The gas productivity (P) can be calculated by dividing the average normalized gas flow (F) with thetotal volume of the digester (Vdigester ) (Equations 12 and 13):

= (12)



96

ℎ = · ℎ (13)

5.2.3 Gas yield

The gas yield is a standardized parameter to measure and compare how efficient a biogasdigester is. It is a measurement that describes the amount of gas produced per amount oforganic material and is expressed as 3 / . Since the parameter considers how muchgas is produced per amount of organic material, it may be used as a comparison between biogas plants digesting the same or similar substrates. Similarly to the gas productivity, this parameter can be calculated with both total biogas and/or methane. For standardization, thegas is usually normalized by compensating the effect of temperature, pressure and watercontent; the normalized values are around 9% lower than the ones for the raw biogas.

A well performing plant usually has a biogas yield of 0.6-0.8 3 / and a methane productivity of 0.4-0.5 3 / 3 / . As mentioned above, these values dependgreatly on what type of substrate is digested. For a farm scale plant where manure andcarbohydrate rich substrates normally are digested, these values are normally somewhatlower. A good way to find out what level to be expected is to perform a BMP analysis (seesection 4.1.4). A rule of thumb is that the process should have a similar or higher gas yieldcompared to the gas potential from the BMP analysis to be considered as a well performing process.

The gas yield can be calculated by dividing the average normalized gas flow with the organicloading rate (OLR) (Equations 14 and 15):

= (14)

ℎ = · ℎ

(15)

5.2.4 VS reduction

The VS reduction is another measurement that indicates the efficiency of the anaerobic process. It corresponds to the amount of the organic material that was digested duringfermentation. This is an especially interesting parameter if the focus is on waste reductioninstead of gas production.

The expected VS reductions depend greatly on the type of substrate digested.

The VS reduction can be calculated by dividing the difference between the incoming andoutgoing VS to the incoming VS (Equation 16). If the volumetric inflow and outflow can be



97

assumed to be the same (if the volume in the digester is constant) this can be calculated by thesame equation but with concentration of VS instead of the mass.

= −

≈ , − ,

,

(16)

Table 5-2 Process performance parameters.

Recommended value Comment

Gas productivity >1 Nm3/m3/dMethane productivity >0.6 Nm3/m3/dTotal gas yield >0.5 Nm3/kgVS Depends greatly on type of substrateMethane yield >0.3 Nm3/kgVS Depends greatly on type of substrateVS reduction >60 % Depends greatly on type of substrate

5.3 Process stability

One of the most important aspects of having a well performing process is to have a stable process. The losses in gas production can be substantial if the process gets disturbed. Asidefrom that, a constant environment usually makes the microorganisms in the digestate performoptimally.

pH is a well-known parameter to measure the stability of the anaerobic digestion process. Thisis due to the fact that many of the bacterial groups (especially the methane producing bacteria)

are sensitive to pH levels outside the optimal intervals. For a stable process, the pH valueshould be stable around 7-7.5. Normally, an instable process is suffering from decreasing pHdue to production of more intermediate products (i.e. VFA) than the methane producing bacteria can consume. When the pH becomes low enough, the methane producing bacteriagets inhibited, leading to more accumulation of VFA.

Measuring pH is a relatively simple and cheap method, giving a rather good indication of the process’ status. How ever, in order to truly know the condition of a process, the concentrationsof VFA and total alkalinity (TA) (see section 4.2) also need to be measured.

The alkalinity is a measurement of the buffer capacity and therefore gives an indication ofhow much VFA the process can absorb before the pH starts to drop. Normally, the alkalinityis rather high in processes that are fed with cow manure since the manure often is rich in basicions.

The procedure demands a lab with titration equipments and is therefore not performed onroutine basis. However it is recommended to perform the test on the digestate at least three tofour times per year, preferably combined with the VFA analysis. It is however moreinteresting to record the ratio between VFA and total alkalinity (see, VFA/TA) than justalkalinity, since this relationship actually determines the effect on the pH value.



98

The gas composition partly provides information on how the intermediate steps are performing. Normally, the composition is rather constant as long as a similar substrate is fedto the process. However, if the methane concentration starts to decrease, it is a sign that the process is not working under optimal conditions. A lower concentration of methane oftenmeans that there is an inhibition of a methane producing step. A normal methaneconcentration for the Plönninge biogas plant is 60-65 %.

Ammonium nitrogen (N-NH4) gives an indication of how much inorganic nitrogen is presentin the process. The concentration of ammonia is in direct correlation with the concentration of N-NH4, depending especially on pH and temperature. Ammonia can be very toxic for the biomass at higher concentrations. The values for N-NH4 should be lower than 2-3 g/L.

The temperature is an important parameter for the process to perform optimally. In a

mesophilic process, the temperature should be around 35 – 39 ºC. It is important to haveconstant temperature even within this interval (in the interval of starting temperature ±0.5 ºC).A constant temperature will allow the bacteria to perform optimally since they do not have toadapt to temperature changes.

Table 5-3 Process stability parameters.

Recommended value Comment

Temperature 37 ⁰ C Should be stable, max ± 1 ºCVFA <4 g/l Depends on degree of adaption and alkalinityVFA/TA <0.3 >0.3 indicates possible process instabilityN-NH 4 <2-3 g/l High values in combination with high pH is dangerouspH 7.2-8.5 Should be stableMethaneconcentration

60-65 % Depends much on substrate, decreasing concentration givesindication of problem



99

6 DOCUMENTATION

In order to have a good understanding and follow up of the process operation, it is importantto keep a detailed logging of the recorded data. This will help to make a good review of

historical performance and learn lesson from the past on how the plant should be operated better in future. For this purpose an Excel file template has been created in which all the process data can be entered and saved for process evaluation(Table 6-1). The Excel file isnamed Process_data.xlsm in this document.

Table 6-1 Different sheets in the Excel file template.

Sheet Comment Input Manual/Automatic Rådatasortering Sort and remove duplicates in data from data

loggerManual input

Rådata Place to paste the managed data from“ Rådatasortering”

Manual input

Manuell data Input analysis results and amounts of loadedsolid substrate

Manual input

Dagsdata Presentation of daily values from data logger Automatic

Veckodata Presentation of weekly process data Partly manual input

Månadsdata Presentation of monthly process data Automatic (VS/TS required)

Urskriftsformulär Printing form for manual data input -

Beräkningar Used for monthly data calculations -

This Excel file should be updated on daily basis with new results from the different analyses.The data should then be reviewed on a weekly basis to get a good overview of the process performances.



100

6.1 Navigation

To navigate among the different sheets in the Excel file template, click the name of the sheet.

Figure 6-1 Screenshot of the Excel-file, also displaying where to navigate between different sheets.



101

6.2 Sorting of raw data (Rådatasortering)

In this sheet the raw data from the data logger is first pasted(Figure 6-2). A macro function isused automatically to remove all duplicates from the raw data and sort it based on the dates.

Figure 6-2 Screenshots of “Rådatasortering” sheet where (A) is empty and (B) is pasted and treated data.



102

6.3 Raw data (Rådata)In this sheet the data managed in “Rådatasortering” are inserted. The data from the 3 dif ferentloggers (i.e. loggers 1-3) are here combined.

Figure 6-3 Screenshot of “Rådata” -sheet where data from two data loggers (i.e. loggers 1-2) have been inserted.





104

Figure 6-5 Screenshot of all the “Manuell data” -sheet when one month is expanded to show all daily inputs.



105

6.5 Daily data (Dagsvärden)

In this sheet the data from the data logger is displayed. The form uses the data read from“Rådata” and recalculates it to more manageable units. The data is displayed as daily values,then grouped into months.

An average value for each month is calculated for the various parameters (displayed in therows “Medel”). When possible, the parameters are also added together to give monthly sums(displayed in the row“Total”).

Figure 6-6 Screenshot of “Dagsvärden” -sheet when the display is minimized to show only the monthly values.

The daily values for each month(Figure 6-7) can then easily be displayed by clicking on thecorresponding “+” sign on the left side of the sheet.



106

Figure 6-7 Screenshot of all the “Dagsvärden” -sheet when one month is expanded to show all daily inputs.

As mentioned above, the raw data is modified in the form to give more proper units. To avoid

using decimals the posts in the data logger are stored as larger numbers (e.g. 37o

Ccorresponds to 3700 in the data logger). All the different actions performed to modify the rawdata are presented in Table 6-2.

Table 6-2 List of how the raw data is modified in “Dagsvärden” -sheet.

Parameter Action Raw data Treated dataTemp1 Divide by 100 to give ºC 3710 37.10Temp2 Divide by 100 to give ºC 3710 37.10 Nivå RK Divide by 100 to give meter 721 7.21 Nivå ERK Divide by 100 to give meter 292 2.92

Gasflöde - - -Gasflöde Panna - - -EM1 - - -WMM1 - - -WMM2 - - -Tid gaspanna - - -Beskickning Divide by 10 to give m3/d 98 9.8





108

Table 6-3 . Parameters listed in the “Veckovärden” -sheet.

Parameter Unit Time period Comment

Added amounts

Total kg Day and week Sum of all substratesSubstrate 1 kg Day and week SumSubstrate 2 kg Day and week SumSubstrate 3 kg Day and week SumSubstrate 4 kg Day and week SumSubstrate 5 kg Day and week SumSubstrate 6 kg Day and week SumSubstrate 7 kg Day and week Sum

TS content

Manure tank %ww Day and week AverageMixing tank %ww Day and week AverageBuffer tank %ww Day and week AverageDigester %ww Day and week Average

pH

Manure tank -log[H+] Day and week AverageMixing tank -log[H+] Day and week AverageBuffer tank -log[H+] Day and week AverageDigester -log[H+] Day and week Average

Gas compositionMethane content %Vol Day and week AverageCarbon dioxide content %Vol Day and week AverageHydrogen Sulphide ppmVol Day and week Average

Data logger

Temperature lower °C Day and week AverageTemperature upper °C Day and week AverageLevel digester m Day and week AverageLevel digestate storage m Day and week AverageDaily total gas production m /d Day and week AverageDaily gas consumption burner m3/d Day and week AverageEM1 kWh/d Day and week AverageWMM1 kWh/d Day and week AverageWMM2 kWh/d Day and week Average

Daily On time gas burner min/d Day and week AverageDaily load to digester m /d Day and week AverageDaily On time Stirling engine min/d Day and week AverageDaily On time upgrading min/d Day and week AverageDaily On time torch min/d Day and week Average

Weekly total gas production m /week Day and week SumWeekly gas consumption burner m /week Day and week SumEM1 kWh/week Week SumWMM1 kWh/week Week SumWMM2 kWh/week Week SumWeekly On time gas burner min/week Week SumWeekly load to digester m3/week Week SumWeekly On time Stirling engine min/week Week SumWeekly On time upgrading min/week Day and week SumWeekly On time torch min/week Day and week Sum

Processparameters

VS/TS %TS Day and week Given by userHRT days Day and week AverageOLR kgVS/m /d Day and week AverageTotal gas productivity m /m /d Day and week AverageMethane productivity m3/m3/d Day and week AverageVS reduction %VS Day and week AverageTotal gas yield m /kgVS Day and week AverageMethane yield m3/kgVS Day and week Average



109

6.7 Monthly data (Månadsvärden)

In this sheet all data for every month is summarized and displayed(Figure 6-10). Both theaverage and total values are given.

The only input required is the average VS/TS ratio. All the other parameters are automaticallygenerated from the data recorded in“Rådata” and “Manuell Input” sheets. In this sheet the average values for all parameters are given for each month and the wholeyear ( Medel ). A monthly and a yearly total (Total ) are also given for certain parameters.

Figure 6-10 Screenshot of “Månadsvärden” -sheet.

In Table 6-4 all the parameters displayed in the“Månadsvärden” sheet are listed.



110

Table 6-4 Parameters listed in the“Månadsvärden” -sheet.

Parameter Unit Time period Comment

A Added amounts

Total kg/month Month and year Sum of allsubstrates

Substrate 1 kg/month Month and year SumSubstrate 2 Kg/month Month and year SumSubstrate 3 Kg/month Month and year SumSubstrate 4 kg/month Month and year SumSubstrate 5 kg/month Month and year SumSubstrate 6 kg/month Month and year SumSubstrate 7 kg/month Month and year Sum

B TS content

Manure tank %ww Month and year AverageMixing tank %ww Month and year AverageBuffer tank %ww Month and year AverageDigester %ww Month and year Average

C pH

Manure tank -log[H+] Month and year AverageMixing tank -log[H+] Month and year AverageBuffer tank -log[H+] Month and year AverageDigester -log[H+] Month and year Average

D Gas compositionMethane content %Vol Month and year AverageCarbon dioxide content %Vol Month and year AverageHydrogen Sulphide ppmVol Month and year Average

E Data logger

Temperature lower °C Month and year Average

Temperature upper °C Month and year AverageLevel digester m Month and year AverageLevel digestate storage m Month and year AverageAve daily total gas production

m /d Month and year Average

Ave daily gas consumption burner

m3/d Month and year Average

EM1 kWh/d Month and year AverageWMM1 kWh/d Month and year AverageWMM2 kWh/d Month and year AverageAve daily On time gas burner

min/d Month and year Average

Ave daily load to digester m3/d Month and year AverageAve daily On time Stirlingengine


Ave daily On timeupgrading


Ave daily On time torch min/d Month and year Average

F Data logger

Monthly total gas production

m3/month Month and year Sum

Monthly gas consumption burner

m3/month Month and year Sum

EM1 kWh/month

Month and year Sum



111

WMM1 kWh/month

Month and year Sum

WMM2 kWh/month

Month and year Sum

Monthly On time gas

burner

min/month Month and year Sum

Monthly load to digester m3/month Month and year SumMonthly On time Stirlingengine


Monthly On timeupgrading


Monthly On time torch min/month Month and year Sum

GProcessparameters

VS/TS %TS Month and year Given by the userHRT days Month and year AverageOLR kgVS/m3/d Month and year AverageTotal gas productivity m3/m3/d Month and year AverageMethane productivity m3/m3/d Month and year AverageVS reduction %VS Month and year AverageTotal gas yield m3/kgVS Month and year AverageMethane yield m3/kgVS Month and year Average



112

6.8 Printable document (Utskriftsformulär)This sheet (Figure 6-11) is a printer friendly version of the “Manuell data” -sheet. It can beused if the operator prefers to write down the data on paper before entering it into the Excel-sheet.

Figure 6-11 Screenshot of “Utskriftformat” -sheet.



113

6.9 How to insert data from the data logger

The input of data from the data logger can be divided into two steps:1. Download data from data logger.2. Insert data into the Process_data.xlsm file.

Both these steps are presented below.

6.9.1 Download data from Datalogger

1. The data from the Datalogger need to be first downloaded from the local computer.Use the shortcut called “Gasverk (logggiler )” located on the desktop(Figure 6-12).

Figure 6-12 Screenshot of desktop where “Gasverk (loggfiler)” shortcut is marked out .

2. A list of different files should appear (TEMP, ENERGI, LOGGER1, LOGGER2LOGGER3)(Figure 6-13). Start to download a file by clicking on its name.





115

4. Use the windows explorer to choose where you want to save the log file(Figure 6-15).Preferably a folder for log files needs to be created first. Name the file with the loggername and date. Click “Spara” for saving the data file.

Figure 6-15 Screenshot of “save as” -window that appears when “save” is chosen .



116

6.9.2 Insert data into Process_data.xlsm

1. Open the downloaded log file(Figure 6-16).

Figure 6-16 Screenshot of log file in Excel.

2. Copy all the data and open the Process_data.xlsm and paste it in the top left cell (A1)in the sheet “Rådatasortering” (Figure 6-17).

Figure 6-17 Screenshot of how to paste log file data in Excel.



117

3. All the data should now be pasted into the sheet. To remove the duplicates access the“view” menu (top menu board) and click on the “Macro” -symbol on the right side. Inthe scroll menu that appears choose“View Macro” (Figure 6-18).

Figure 6-18 Screenshot of how to access Macros in Excel.

4. A new window containing a list of macros should now appear(Figure 6-19). Mark thefunctioncalled “Remove Duplicates” and then click on “Run”.

Figure 6-19 Screenshot of how to run the Macro“RemoveDuplicates” in Excel .



118

5. The list without duplicates should now be displayed(Figure 6-20).

Figure 6-20 Screenshot of results after running Macro “RemoveDuplicates” .

1. To insert the data into the data handling algorithms of the Process_data.xlsm, copy allthe data besides the dates and go to the sheet called “Rådata”. There paste the data inits correct position. Remember to paste the data at the location corresponding to the

correct date.a. Logger1 starts with Temp 1 and should therefore be pasted there(Figure 6-21).

Figure 6-21 Screenshot of where to paste data from Logger1.



119

b. Logger 2 starts with EM1 and should therefore be pasted there(Figure 6-22).

Figure 6-22 Screenshot of where to paste data from Logger2



120

7 METHODOLOGY FOR PROCESS IMPROVEMENTS

In order to optimize the process it is important to first define a clear goal of the plantoperation, i.e. whether the purpose of plant operation is for energy production, waste handling

or combination of both. Plönninge biogas plant is defined as a demonstration plant at farm-scale. There is a need not only to show the feasibility of producing vehicle fuel, electricity andheat production, but also a need to use manure wastes as a part of the feedstock and todemonstrate that the digested residues can be used as fertilizers for crops cultivation. In orderto achieve these goals, it is essential to maximize the biogas production at Plönninge biogas plant.

Once the goal of plant operation is defined, it is important to apply a good methodology onhow to constantly improve the plant operation. There are several important aspects to be keptin mind before defining the most suitable strategy for the operation of Plönninge biogas plant.In general, the following aspects can give a big impact on plant operation and biogas production:

i. Quality and quantity of the feedstockii. Whether there is suitable process/plant configuration and instrumentation to ensure

reasonable flexibility for plant optimizationiii. Right operational routine and follow up to ensure that plant operation can be

continuously improvedPlönninge biogas plant has a rather simple process and plant configuration based on selectedfeedstock. The available instruments (i.e. sensors and actuators) can support the basic

requirement of plant operation. Although it is always possible to further improve the plantconfiguration and instrumentation, it is assumed that the process optimization can be based onthe current process/plant configuration and instrumentation. The process optimization strategyshould therefore be focused on feedstock selection and right operation routine and follow up.

FeedstockIn order to achieve as high biogas production as possible, it is important to select feedstockwith high methane potential. In general, liquid cow manure has relative low methane potential. It is therefore important to use more energetic and easy degradable feedstock,

depending of course on their availability at the Plönninge plant.Operational routine and follow up A higher biogas production can also be achieved by implementation of better loading regimeswith a constant pushing of the process, so the biomass throughput and energy throughput ofthe plant can be increased whereas a stable operation can still be retained. Every week ormonth should be seen as new test were the loading regimes is changed a little bit from the last period and the effect of this change is continuously monitored. Depending on the performances obtained, these changes should be considered permanent or be rejected. Thisdynamics of the process parameter changes – continuous evaluation should be implementedas a part of operational routine, so operational lesson in the past can be well recorded,evaluated and follow up in order to improve future operation.



121

7.1 Meetings

In order to have a good follow up of the plant operation, meetings should be held on a regular basis among operators and all personnel should be involved. In these meetings the performance of the plant and any potential problems should be reviewed and discussed.

Objectives and aims for the plant operation should also be set, and any deviation should beevaluated.

Such meetings should at least be held once per month.

Topics that are recommended to be discussed during these meetings include:Performance of plant on weekly and monthly baseAny deviation from the feedstock supply in terms of both quality and quantity?Is there any problem with the operation in terms of technical, logistic and personnel aspects?Any progress and lesson learn since the previous meeting?Any improvement that can be foreseen?Was the set goals reached?Is the economic plan reached/on schedule?Decide on new or keep old goals.



122

8 OPERATIONAL ROUTINESThese operational routines list and describe all the tasks that should be carried out on a dailyand weekly basis at the Plönninge biogas plant.

8.1 Daily operational routines

In this section operational tasks that should be carried out each day are listed and described.Preferably, these tasks are carried out at the beginning of the working day. It is important to build up routines where all these tasks are carried out every day.

1. Perform a quick check of the biogas plant to make sure nothing went wrong during thenight. Look especially for flooding in any of the operational units.

2. Check the control panel of the SCADA system:i. Check the alarm list If there is any alarm indication for a particular process

unit, please check whether it is possible to make any suitable tuning andadjustment so the process unit can go back to the normal operational mode. Ifthere is no alarm indication, move on to the next point(Figure 8-1).

Figure 8-1 Screenshot of alarm list.



123

ii. Check the conditions of the operational units

1. Digester level and temperature . Make sure the values are within the specifiedlevels (e.g., the same as or close to setpoints). If the values are not within thedefault range, try to identify the reason and check whether it is possible to makeany suitable tuning and adjustment so that the digester level and temperature cancome back into the operational range(Figure 8-2).

Figure 8-2 Screenshot of digester menu.



124

2. Check the filling level; if this is too high or too low, try to identify the reasonand evaluate whether it is possible to make any suitable tuning and adjustmentso that the slurry level of the buffer tank level can be brought back within theoptimal range (Figure 8-3).

Figure 8-3 Screenshot of buffer tank.



125

3. Check the filling level; if this is too high or too low, try to identify the reason andevaluate whether it is possible to make any suitable tuning and adjustment so that theslurry level of the mixing tank level can be brought back within the optimal range(Figure 8-4).

Figure 8-4 Screenshot of mixing tank.



126

4. Manure tank level . Check the filling level; if this is too high or too low, try toidentify the reason and evaluate whether it is possible to make any suitable tuning andadjustment so that the slurry level of the manure tank level can be brought back withinthe optimal range (Figure 8-5).

Figure 8-5 Screenshot of manure tank 2 menu.



127

i. Fill up the mixing tank by manually pumping sufficient amount of the contentfrom manure tank 1 as possible. Make sure that level in the mixing tank doesnot get too high(Figure 8-6).

Figure 8-6 Screenshot of manure tank 1 and mixing tank menus with instruction on how to pump from manuretank 1 to mixing tank.



128

ii. Check the gas utilization. Make sure that the gas storage level is at areasonable level. If it is not, please check the reason and see whether it is possible to make any suitable tuning and adjustment so that the gas storagelevel is brought within the right range(Figure 8-7).

Figure 8-7 Screenshots of gas consumption and gas measuring menu.



129

5. Turn on the submersible mixer(Figure 8-8).

Figure 8-8 Photo of showing how to turn on submersible mixer in mixing tank.

6. Go outside to the gas room and perform a gas composition test(Figure 8-9). Enter theregistered data in the file Process_data.xlsm in the computer.

Figure 8-9 Photos of the equipment used for the analysis of gas composition.



130

7. Go outside to the mixing tank andadd FeCl 3 into the tank (Figure 8-10). This iscarried out by opening the tap and waiting for 5 seconds before closing the tap. Enterthe date and amount in the form placed in the mail box next to the FeCl3 container.

8.

Figure 8-10 Photos of FeCl3 solution adding.

9. Go outside to the front loader andload the X-Ripper withpotatoes (the amountdecided at the operational meeting). Enter the loaded amount in the file



131

Process_data.xlsm in the computer. More detail instruction needs to be added after theinstallation of X-Ripper has been implemented.

10. Take a sample from the buffer tank and perform a quick-TS (using the moisture analyzer) anda pH analysis, and enter the result in the file Process_data.xlsm in the computer(Figure 8-11).

Figure 8-11 Photos of buffer tank sampling and quick TS analysis with moisture analyser.

11. Fill up the buffer tank as much as possible by manually pumping feedstock from themixing tank(Figure 8-12). Make sure that the level in the buffer tank does not get toohigh (e.g., not above 250 cm).



132

Figure 8-12 Screenshots with instructions of how to pump from the mixing tank to the buffer tank.



133

12. Turn off the submersible mixer in the mixing tank(Figure 8-13).

Figure 8-13 Photo of showing how to turn off submersible mixer in mixing tank.

8.2 Weekly operational routines

In this section operational tasks that should be carried out once or several times per week arelisted and described. Suggestions of which week days these tasks should be performed arealso given.

Monday

1. Look at the data from the previous week and decide on whether to keep the sameloading regime or make any adjustment if necessary.

2. Load the silage (if this is specified in the operational plan).

Tuesday1. Take a slurry sample from the manure tank 1 and perform a quick TS (using the

moisture analyzer) and a pH analysis. Enter the data in the Excel fileProcess_data.xlsm.



134

Figure 8-14 Photo of quick TS test with moisture analyser.

3. Load any other substrate available (if this is specified in the operational plan).

Wednesday4. Load the silage (if this is specified in the operational plan).

Thursday1. Collect the waste containers with fruit and vegetables from the local ICA Maxi.

2. Add the fruit and vegetables to the mixing tank via the x-ripper.

Friday1. Load the ensilage (if this is specified in the operational plan).

Task to perform before the weekend

1. Turn on the submersible mixer (from the switch located next to the control panel,(Figure 8-8)); allow it to run for about 60 minutes in order to homogenize thefeedstock in the mixing tank.



135

2. Fill up the buffer tank as much as possible. Make sure the level does not get too high.

3. Fill up the mixing tank as much as possible. Make sure the level in the manure tankdoes not get to low and that the level in the mixing tank does not get to high.

4. Go outside the mixing tank and add a double dosage of iron chloride into the tank.This is performed by opening the tap for 10 seconds. Enter the date and the amount ofiron chloride added in the form placed in the mailbox next to the iron chloridecontainer.

5. Add a double load of potatoes into the mixing tank via the x-ripper.

6. Do not forget turning off the submersible mixer in the mixing tank.



136

9 PROCESS EVALUATION

9.1 Weekly evaluationEvaluation of the plant performance should be carried out weekly. This should be performedindependently by the operator mainly or by a larger working group where other internal andexternal process engineers might be involved. For weekly operational evaluation, the process performance should be studied by comparing the plant performances of the latest week vs. previous weeks. The purpose of the meeting should be to set an operational plan for thecoming week. The time for the meeting should be the same every week (preferably onMonday morning in order to get a fresh start of the week and also maximize the number ofworking days close to the operational changes).

Manipulating parameters, parameters that should be used for tuning the operation.Response parameters, parameters that should be used to evaluate the performance of the plant based on settings of manipulating parameters.

Other important parameters , parameters whose effect on the process should beconsidered when the response from changes in operation can be observed.

The parameters that should be considered in the evaluation are listed below. The parametersare dived into 3 different categories:

Manipulating parameters, parameters that should be used for tuning the operation. Response parameters, parameters that should be used to evaluate the performance of

the plant based on settings of manipulating parameters. Other important parameters, parameters whose effect on the process should be

considered when the response from changes in operation can be observed.

Table 9-1 Parameters considered in process evaluation (for description of parameters, please see section 5.1).

Manipulating parameters Response parameters Other important parametersFeeding interval Methane productivity TS concentration in buffer tankSize of each load Methane yield pH in digesterAmount of added solidsubstrate

Total gas productivity Temperature in digester

Type of solid feedstock Total gas yield H2S concentrationHRT VS reductionOLR Methane concentration

Manipulating parametersThe parameters that should be adjusted to alter the operation are thefeeding rate and addedamount of solid substrate . These parameters will then have an indirect effect on theHRT and the OLR which are important to consider in the evaluation. Especially theHRT should be monitored to make sure it does not get too low (e.g., above 20 days) to avoid washout ofthe bacteria.OLR is a more general parameter to know how hard the process is loaded and itcan be used to compare the operation with other plants.

The focus should be placed on adding as muchsolid substrate as possible to maximize theOLR and still keep a longHRT . However, with this strategy it is important to control theTS



137

concentration in the buffer and mixing tank since too high values could cause problemswith the pumps.

Response parametersThe most important response parameter to consider is themethane productivity . If it hasincreased compared to the previous operational period it could be considered as a positiveresult. However, the reason for the increase in methane production should also beinvestigated. Another important parameter to consider is themethane yield since this givesinformation of how efficient the process is.

Strategy for optimizing the operation

1. Increase the load:

a.

Focus on adding as much as possible of energy rich substrate that is regionalabundant and can be accessible and easier to load into the digester. b. Make sure that the TS content in the buffer tank does not get too high (not over

10%).c. Closely monitor and follow up the operation in order to maximize the performances

of all process units.



138

9.1.1 Saving the data for weekly evaluation

1. Open the Excel data file and in the sheet “Manuell data” copy the data from each dayof the previous week(Figure 9-1).

Figure 9-1 Screenshot of “Manuell data” -sheet where the values for 1 weeks are marked.

2. Go to the sheet “Veckodata” and open the week of interest by clicking on the”+” -signon the left of the week number(Figure 9-2).

Figure 9-2 Screenshot of Veckovärden” -sheet in compressed form (click “+” -signs on right side to show dailyvalues for a week).



139

3. In the top left cell (e.g., Silage for Monday)right click and choose “Paste Special”(“Klistra in special”) (Figure 9-3).

Figure 9-3 Screenshot of how to paste the data from “Manuell data” -sheet into “Veckovärden” -sheet using“Paste Special” .

4. Choose “Values” in the menu that opens(Figure 9-4).

Figure 9-4 Screenshot of “Paste Special” window that appears .



140

5. Now the values should be pasted into the formula; an example is presented below(Figure 9-5):

Figure 9-5 Screenshot of “Veckovärden” -sheet wherethe data from “Manuell data” -sheet has been pasted.

6. Next step is to paste the data from the DataLogger. This is carried out in the same wayas the manual data. Open the sheet “Dagsvärden” and copy the values for the specified

dates (Figure 9-6).

Figure 9-6 Screenshot of “dagsvärden” -sheet where the values for 1 weeks are marked.

7. Go back to the sheet “Veckodata” and right click on top left cell after the manualinputs (e.g., Temp1 for Monday). Choose “Paste Special” and choose values again (Figure 9-7).

Figure 9-7 Screenshot of how to paste the data from “Dagsvärder” -sheet into “Veckovärden” -sheet using “PasteSpecial” .



141

8. The values should now be inserted in the form; an example is presented below(Figure9-8).

Figure 9-8 Screenshot of “Veckovärden” -sheet where the data from “Dagsvärden” -sheet has been pasted.

9. In order to calculate the process parameters a value for VS/TS (% of VS per TS) needsto be entered. This is inserted in the top row under the column “VS/TS” (Figure 9-9).

Figure 9-9 Screenshot of to enter VS/TS value in “Veckovärden” sheet .

10. After this, given that all other necessary data is in place, the process parameters shouldautomatically be calculated(Figure 9-10).

Figure 9-10 Screenshot of “Veckovärden” -sheet showing the calculated process paramteters.

11. All the data for that specific week is in place and the performances can be evaluated.



142

9.2 Monthly evaluation

A review of the plant operation should be carried out on monthly basis by the operator or process engineers. This monthly evaluation should be performed from more plant-wide andsystematic aspects and give a good overview on total mass and energy outputs, as well as

operational economic over a one-month period. The data can then be compared with historicaldata from the previous months in order to set up a strategy to maintain a good operationand/or get further improvement (if possible). It is recommended to present and discuss themonthly evaluation during the first weekly meeting of next month.

In Manipulating parameters, parameters that should be used for tuning the operation. Response parameters, parameters that should be used to evaluate the performance of



The parameters that should be considered in the evaluation are listed. The parameters aredived into 3 different categories:

Mass throughput, in this category parameters that reflect the amount of feedstockentering and of digestate exiting the reactor, type of feedstock and theircharacteristics(VS, TS, pH, BMP), feedstockload regime, etc should be summarized.

Energy throughput, parameters reflecting the totally produced biogas volume,specific biogas production rate, utilization of biogas (heat, vehicle fuel, electricity),electricity consumption, heat consumption, etc should be summarized.

Economical aspects, in this category parameters reflecting the operational costs(material, electricity, manpower, logistic, equipment depreciation, etc.) and potentialincome sources (electricity, vehicle fuel, heat, digestate as fertilizer) should besummarized.

Table 9-2 Examples of parameters that should be considered in process evaluation.

Mass throughput Energy throughput Economic aspectFeedstock volume Biogas volume Operational costFeedstock type Specific biogas production rate Saving from electricity generationSolid content of feedstock Heat production Saving from heat production

Digestate volume Electricity production Potential income from vehicle fuelOLR Biomethane production Potential income from digestateElectricity consumptionHeat consumption



9.3 Yearly evaluation

A yearly review of plant operation should also be carried out by operators or processengineers. This should be very similar to monthly evaluation; however the time scale is over12 months and should give a good overview on the total mass and energy throughputs, as well

as on operational economic parameters. The data can be compared with historical data fromthe previous years in order to set up a yearly strategy to maintain a good operation and/or getfurther improvement (if possible).

In Manipulating parameters, parameters that should be used for tuning the operation. Response parameters, parameters that should be used to evaluate the performance of



The parameters that should be considered in the evaluation are listed below. The parametersare dived into 3 different categories:

Mass throughput, in this category parameters reflecting the amount of feedstockentering and digestate exiting the reactor, type of feedstock used and theircharacteristics (VS, TS, pH, BMP), feedstock loading regime, etc should besummarized.

Energy throughput, parameters reflecting the total produced biogas volume, specific biogas production rate, utilization of biogas (heat, vehicle fuel, electricity), electricityconsumption, heat consumption, etc should be summarized.

Economical aspects, in this category parameters reflecting the operational cost

Date post:	08-Jul-2018
Category:	Documents
Upload:	kvramanan
View:	219 times
Download:	0 times

Operational Guidelines Plonninge Biogas Plant

Documents