Manufacture 1

7/30/2019 Manufacture 1

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MANUFACTURE

OFPRODUCER GAS


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PREFACE

This report provides the information

pertaining to the construction, operation and

maintenance of a 500kg per hour biomass

gasifier system .

The first part of the report provides detailed

information regarding the construction and the

working of the gasifier system. The second

part provides information regarding operation

and maintenance of the gasifier system.

This also includes operating the thermal

equipment with the producer gas.


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PART 1

SOLID BIO-RESIDUE GASIFIER SYSTEM


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INTRODUCTON:

Biomass has been a major energy source prior

to the discovery of fossil fuels like coal and

petroleum. Even though its rule is presently

diminished to developed countries. It is widely

used in rural communities of the developing

countries, further it is used for limitedindustrial uses. Biomass besides being in solid

form can be converted into gaseous form

through gasification.

1.0CONCEPT AND PRINCIPLEBiomass is a natural substance, which

stores solar energy by the process of

photosynthesis in the presence of sunlight.

It chiefly includes cellulose, lignin with anaverage composition of C8H10O3 with

slight variation depending on the nature of

the biomass. The producer gas thus

generated during the gasification process is

combustive. This process is thus possible


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in a device called gasifier in a limited

supply of air. The clean combustible gas is

combusted in a burner to generate heat. Inthe reactor the biomass process after

undergoing drying in the upper zones

leaving behind char. The volatilities

undergoes oxidation in the combustion

zone with air being partially supplied in

the surrounding nozzles and the remaining

drawn from the open top. The product

gases of oxidation further gets reduced by

a bed of charcoal and yield a combustiblegases having a calorific value of 4.5-5

MJ/KG with an average composition of

CO-20%, CH4-4%, H2-20%,CO2-12%

and rest N2.


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2.0USAGE OF PRODUCER GASThermal energy of the usage the order4.55.0 MJ is released by forming 1ml of

producer gas in the burner. Flame

temperature of as high as 1680K by

optimal premixing of air with gas . For

applications which require thermal energy

gasifiers can be a good option as a gas

generator.

Typically the heat generated by 1 litre offuel oil is generated by 3.5-4 kg of

biomass . The exact composition depends

upon the energy content of the producer

gas , which in turn depends upon the

moisture content of the biomass used .Gasifier is an ideal solution for the above

situation, where hot gas after combustion

can be directly let into the end used

equipment.


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3.0SYSTEM DESCRIPTION ANDWORKING

The overall schematic of the gasifier

system is depicted in the figure.

The reactor is basically a downdraft

system where both gas and feed stock

move downward as reaction proceeds. Airrequired for gasification is partly drawn

from the top and the remaining air from

the air nozzle surrounding the combustion

zone . The required suction for this process

is obtained by using the venture effect of

spray nozzles (scrubber) and blower.

Biomass after drying and pyrolysing in the

upper zone of the reactor , undergoes

volatile combustion leading fixed carbonor char by the time it reaches the oxidation

zone , in the oxidation zone volatiles

undergo oxidation with the release of CO2

and H2O. This process undergoes

reduction, in the presence of hotbed of


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charcoal and yield a combustible gas

mixture.

The hot gas is led to cyclone and further to

cooling in cleaning train, where the raw

gas which cools to ambient temperature by

a water spray arrangement in cooling

section. The gas then flows to the burnernear the drier.


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3.1REACTORThe reactor is basically mild steel

fabricated shell with insulated liningand has an inner lining of ceramic ,

compose largely of alumina . There are

2 sets of nozzles (provided around

combustion zone) which are kept open

during the operation of the system. The

individual air nozzles are provided

with a water seal which are kept open

during the operation and closed to shut

down respectively .There are ignition ports provided

below the air nozzles for torching the

reactor ( to start the reactor ) , water

seals are provided with pneumatic

valves which drain out water duringinitial starter and fills water into the

seals during emergency situations. This

arrangement is separate for 2 sets of air

nozzles in corporated.


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A water seals forms the top of the

reactor with a removable cover.

This cover is kept open during theentire operation of the system to

facilitate loading of chips and the air

being drawn from the top, there is a

motorized screw at the bottom to

extract the char . The char outlet is into

a stainless steel fabricated container.

The container has a capacity to hold

approximately 1 shift discharge from

the system.The screw system is decided by the set

of timers both for frequency of

operation and duration. The container

provided has pneumatic valves.

Under normal operation top valve iskept open and bottom is closed .The

switch provided will result in top valve

closing and the bottom opening to

unload the char collected in container.

The system also has a provision to


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keep both the valves open for

maintenance and during system

shutdown both valves are closed. Thesystem has necessary safety intelocks

and alarms for improper usage . The

screw is cooled both internally and

externally for which cooling tower is

employed.


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3.2COOLING AND CLEANINGTOWER

CYCLONE: The hot dust laden gas

that exits the reactor is passed through

a hot cyclone . Cyclone does the

function of removal of certain quantity

of solid particles . The dust that gets

separated falls into a collection bin

below and thus needs to be emptied

periodically.

COOLING SYSTEM: Twin H2O

spray stations are employed with spray

from top. The spray is developed from

a jet which mixes with the gas and

cools the gas to the ambienttemperature and in process removes

dust and tar. There is a small dump

provided at the bottom which form exit

for the cooler for separating gas and

H2O gets collected in the H20 seal and


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overflows by gravity to a

sump,moisture trap is provided at exit

of the scrubber to remove the H2Oparticles in gas .

FLARE

This is provided to check the initial

quality of the combustible gas. Gas is

flared in the burner for few minutes

prior to changeover to drier .It is an

automatic operational system.


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LOADING OF CHARCOAL

The reactor is loaded with drycharcoal, preferably till the top or 1m

above the air nozzle level. The size of

charcoal to be loaded is around

40mm*40mm*50mm. Care is taken to

allow only charcoal which is free of

metal pieces, plastic etc.

FEED STOCK REQUIREMENT

The range of biomass that can be usedin the reactor as feed stock are coconut

shells without fibre, different species

of wood whose density is above 300-

350kg/m^3. The maximum moisture

content should be around 12-15 %.


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START UP PROCEDURE

Gasifier start up

1.Switch on the instrumentation andcontrol panel.

2.Push the switch to start-up mode,

which will automatically open the

gas nozzle towards the flare.

Manually close fully the main gas

valve near the gasifier. Manually

open the flare line bypass valve.

3.Keep the main gas feed valve closed

near the drier.4.Switch on the cooling tower pump

and fan.

5.Open the reactor top cover.

6.Top the reactor with properly sized

biomass.7.Open all the ignition ports.

8.Hold a flame in the form of a bio-

stack till the char gets red hot.

Combustible gas gets compressed

within few minutes after the ignition.


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9.After successfully torching the

reactor close the ignition ports. Open

the air nozzle plugs to allow air entrythrough the air nozzle in the reactor.

10.Light the gas in the flare once theoxygen level falls below 2% the gas.

Start-up diffusion mode typically

within the reactor.

11.Top the biomass chips in thereactor as they undergo mixing

thoroughly at regular intervals of

time depending upon theconsumption of feed time has to be

set manually. Normally the

consumption or time period is 10-20

minutes.

12.System has to operate on flaremode for more than half an hour for

stabilization and to ensure gas of

good quality.


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RUN MODE

1.Manually push the button and

energize the run mode.

2.At-least one of the drier local pumps

switch needs to be on.

3.All the drier panels should not beunder flame condition

simultaneously.

4.Open main gas feed valve.

5.Close the flame line valve.

STOP MODE

Manually switch is in the stop mode

energizing. This system is already in

emergency mode.

1.Switch off the cooling tower.

2.Close the flare line valve.


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SCREW OPERATION MODE

Though the manual switch

energizes the cyclic timer this cantake place when main gas valve is

open in auto mode or manual inch

mode to operate the screw

interlocks and the top valve should

be open, ash discharged bottom

valve should be closed and screw

choking pump should be on. A

separate switch for unload is

provided which can be operated byauthorised personnel. In closed

mode screw motor can be switched

on with interlock of ash discharge

top valve and ash discharge bottom

valve both being open.


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INSTRUMENTATION

The system is provided with H2O tube

manometer at strategic locations formonitoring the health of gasifier.

Pressure switches are provided for

pumping the cooled H20 is provided

with thermostat and O2 level sensor or

controller is provided to indicate O2

percent in producer gas line. These

lines are connected to audio visual

annunciators. In the event of O2 level

exceeding 2%, the operator has tocheck for air leakage into system. The

operation of the screw is automatic

with both on/off timers. The controller

is set at 400 -440 *C. Poor quality of

gas as well as flame failure willgenerate alarm at pre-set temperature.


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ASH DISCHARGE VALVES

Switches are turns on manually for ash

discharge.

Interlocks are provided to ensure weather

emergency switches are not energized. This

allows discharge to take place even in

emergency mode. Under normal operation ashtop valve is open and bottom valve is closed.

During discharge top valve is closed and

bottom valve is open. In stop mode both the

valves are in closed position.


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SAFETY VALVES / INTERLOCKS

1.Push button to switch on flare ignition in

start up mode.

2.Flare igniton button works automatically

in emergency mode.

3.Main gas blowers are ON when scrubber

pumps are ON and not in emergencymode.

4.Alarms are installed to warn if discharge

valves are opened for more than 10

minutes.

5.Ash discharge valve is open only if screwvalve is OFF.


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OPERATION

AND

MAINTAINANCE


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DRIER OPERATION

1.Start the drier with fuel oil combustion.2.Once it is ensured that the gasifier operation is

satisfactory and gas generated is combustible,

feed the gas only when oxygen level drops

below 2%.

3.To start the gas feed into dries, close the flareline valve manually and push the switch intorun mode by which flare line valves closes and

main gas line opens.

4.Use the valve near the burner and blower tocontrol the quantity of gas flow. Reduce the oil

flow while increasing gas flow. Airflow has tobe controlled by using BUTTERFLY valve.

5.Always divert gas into the drier when oilflame is on.

6.Once the gas flow starts manometer indicatespositive pressure.

7.Do not switch off the combustion blower incase of flame failure. This is the only way to

remove the gas inside the drier.

8.Set the PID controller at desired temperature.


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9.Flame failure is indicated with the help ofthermocouple and controller within 15 seconds

of flame failure.10. Gas feed to drier will cut off and flare line

will open in the following cases.

1.Power failure

2.Flame failure


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MONITORING THE SYSTEM

The normal and proper working of gasifier is

ensured by visual inspecton of air nozzle.Continuos flow of biomass is a good sign of

normal gasification process with the

generation of good quality of air. For a given

flow rate sudden or abnormal increase in

pressure indicates the buildup of ash. Thissituation is temporary and can be eliminated

by installing screw conveyors for few seconds

until pressure comes back to normal.

ASH EXTRACTIONThe screw provided needed to be operated

periodically to remove ash formed in the

reactor during gasification process.. this is

required to keep pressure drop within limits

therby allowing trouble free operation.


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SHUT DOWN OF OPERATION

During shut down following process must be

followed.1.Switch off the blower if in operation and

close the main gas valve and open flare

bypass valve.

2.Immediately ignite the gas.3.

Top the biomass chips in the reator.

4.Close air nozzle valves, this closes air entryinto reactor.

5.Allow the fumes to come out of the reactortop.

6.Switch off the pump if in operation.7.Switch off the instrumentation and panel.


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MALFUNCTIONING AND TROUBLE

SHOOTING

It is important to know the reasons formalfunctioning of reactor. These may be the

following reasons.

1.There could be air leakages into gasifier,resulting in dilution of producer gas .this

leakage can occur at reactor or coolingtower.

2.There can be blockages in the reactor or inthe cooling and cleaning section, causing

resistance to gas flow.

Total pressure drop should not exceed

300-350mm at full load operation.


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MAINTAINANCE OF SYSTEM

GASIFIER SECTION

REACTOR

1.Rotate ash conveying screw one turn beforestart up for ash removal.

2.Unload the reactor once the pressure dropsexceed the limit or else unload the ash every

1200hrs.

3.The collection of bin below the cyclone has avolume of 25lts and needs to be emptied every

8hrs.this operation is performed withoutshutting down the gasifier.

4.Extract solid residue from the screw exit waterafter each screw operation.

5.Tighten the bolts and nuts after the first 25minutes of run.


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COOLING AND CLEANING SYSTEM

COOLER

1.Clean the cooler sprays and check the spraypattern once every 150 hours of run.

2.Clean the water dump seal-off the solidresidues once every 150 hours of run orduring any schedule weekly shutdowns.

3.Tighten all the bolts and nuts after the first25 hours of run.

VALVES AND BLOWERS1. Clean the control valves pipelines and

blower every 150hours run.

2. Lubricate the bearings of the blower and

change the gland once every 600hours of

operation, use lithium soap based grease.


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WATER PUMP

1.Check the foot valve strainer every 150 hoursof operation. Clear off any dust collected on it.

WATER UNDER CIRCULATION

1.Every week slowly add 40 grams of polyelectrolyte in both the tanks and using the

valves keep the water under circulation.

2.Add 500grams of ALUM in both the tanksand using valves kee the water under

circulation.

3.Keep the circulation ON for 30 minutes.4.Allow the water to settle for 1 hour.5.Repeat the above procedures several times

depending on usage and biomass used

during the week.

6.Drain the water slowly through sand andactivated carbon.


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LEAK TEST AFTER ASSEMBLY

The entire gasifier has to qualify a leak test,

which is one of the most important event inthe erection of system. Critical sub-

assemblies like the reactor and ash

extraction system, cooler, cyclone have to

qualify the leak test. However an entire

system must undergo a leak test at all theflange joints after the erection at site.

This has to be done in order to ensure that

air doesnt leak into the system and dilute

the producer gas. To conduct this testconnect a pressure link which supplies air at

a pressure of 100-150mm H2O to the exit

duct-in from the blower ,that is prior to the

duct-in connected to the flare. Fill the water

seals of reactor, cooler , water dump and

cyclone with adequate water upto overflow

level. Further cover the top cover of reactor

and fill the top cover water seal with water.

Next, open the pressure line and apply soap

water at all possible flange joints.


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Incase there is leak, bubbles will form at all

those points. Ensure all the possible leaks

are pluged properly. In a similar mannerconduct leakage test at all the duct-ins that

leads to the burner.

The leak test, is to be conducted every time

whenever the system is dismantled for anyform of maintainance.

CHECK FOR AIR LEAKAGEGASIFIER

IN COLD CONDITION-PRESSURISED

MODE

1.Light a wick . Blow off the flame and holdthe extinguished wick near to all possible

points for leakage, like the flanged joints

and pipe joints. Incase there is a leak, there

will be tendency for the flame to be drawn

inwards or sucked, indicating the leaking

point.

2.Mend all leaks found.3.The leakage of air could also be due to

insufficient water in the water fills under


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the reactor, cyclone and cleaning system.

Ensure that adequate water is retained till

the overflow level.

DOS AND DONTS

DOS

ENSURE THAT1.The Charcoal or biomass does not have

any extraneous materials like, stones,

metal etc.

2.Adequate water level is maintained in allthe water seals.3.Water is being sprayed continuously inthe coolers, water jacket of the screw

conveyor prior during the run.

4.Coolant water temperature does notexceed 5*C above ambient during the

run.

5.Correctly sized dry biomass is beingloaded into the reactor and level

maintained.

6.There is water in the top cover waterseal when it is shut.


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7.Reactor is loaded with biomass duringthe operation at regular time intervals

depending upon the consumption.8.There are no voids or gaps in the reactor

by absorbing through the air nozzle.

DONTS

DO NOT1.Pour water into the reactor under any

circumstance to shut down the reactor.

2.Use larger sized and wet biomassother than specified.

3.Expose the bottom of reactor toatmosphere when the reactor is hot.

4.Operate the gasifier at higherload/flow rate immediately after fresh

start, if done there is a possibility of

biomass not totally converting into

char by the time it reaches the air

nozzle. Hence follow start up

procedure meticulously.

5.Extract more charcoal.


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UNLOADING THE REACTOR AND

PROCEDURE FOR REACTOR

REPAIR

The reactor has to be unloaded once

the pressure drop across the reactor

shoots beyond 350mm H2O or else as

mentioned in the maintainanceschedule. It is better to leave the

system unoperated for sufficiently

long time, say a day so that the reactor

bed cools down and makes the process

of unloading easier. Firstly the ashextraction system supports bolts has to

be lowered till it touches the ground

and then should be secured tightly.

The support bolts has to loosened until

the wheels touch the ground. Use

water to cool the unloaded hot

charcoal pieces, if this is not done then

there might be chances of fire hazard.

The screw once removed needs to be

closely examined for any erosion or

damages. Check the metallic braded


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graphite gland rope before refitting , if

it is too compressed then it has to be

changed.

DAILY CHECK

1.Level in all water seals.2.Drain blower bottom valve.3.

Clean cyclone bottom ash bin.

4.Clean ash extraction system outletduct .

5.Ensure all valves are closed and noair gets into system during

operation.

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