CEREAL STRAW TORREFACTION: RESULTS ON PILOT PLANT TEST
June 2013
í n d i c e
1. Overview of CENER experience in torrefaction2. Torrefaction process concept and reactor technology3. Straw torrefaction4. Torrefaction reactor modeling and up-scalling studies5. Conclusions
1. Overview of CENER experience in torrefaction
• 2006-2007: Feasibility study biomass torrefaction for cofiring applications
• 2007-2008: Evaluation and selection of technologies. Laboratory and bench scaletesting.
• 2008-2009: Design and construction of pilot plant. Pilot plant commissioning.
• 2010: Modifications in the pilot plant. Transfer of the pilot plant from Noain to thenew CB2G in Aoiz.
MILESTONES
1. Overview of CENER experience in torrefaction
new CB2G in Aoiz.
• 2011: Beech woodchips torrefaction. First pelletization tests. Torrefactionreactor model development.
• 2012: Torrefaction and pelltization of beech and pine woodchips.
• 2013: Straw torrefaction and pelletisation.
• New materials for testing: 2013-2014 in the frame of SECTOR project(www.sector-project.eu):
• Extensive testing of straw, woody energy crops (poplar, eucaliptus andpaulonia), pruning from olive trees and bagasse
Beech woodchips Pine woodchips Chopped straw
MATERIALS PROCESED IN THE PILOT PLANT
1. Overview of CENER experience in torrefaction
1 OptimizationOptimization isis neededneededand tests are ongoing withdifferent die design toimprove pellet density anddurability.
TORREFIED PELLETS PROPERTIES
Parameter Units Beech Pine Straw 1
Torrefaction degree % 14-22 14-19 13
Hardgrove grindability index
NA 22-26 N.D. N.D.
Bulk Densitykg/m3
(ar)620-680 580-610 590
Pellet durability % 96.2-97.2 92.5-95.4 84
1. Overview of CENER experience in torrefaction
Moisture Content % (ar) 3.7-5.6 3.5-5.5 3.8-5.6
Higher Heating ValueGJ/t (daf)
20.9-21.9 21.4-21.8 20.5
Lower Heating ValueGJ/t (daf)
19.6-20.7 20.1-20.5 19.3
C % (daf) 52.0-54.3 53.1-54.0 50.5
H % (daf) ~6.0 ~6.0 6.2
N % (daf) 0.12-0.18 0.12-0.18 0.77
Ash Content % (db) 1.6-1.8 0.4-0.7 6.0
Volatile matter content % (db) 75.6-80.5 76.0-80.0 74.8
N.D.: Not detremined
EFECT OF TORREFACTION DEGREE ON PRODUCT CHARACTERISTICS
1. Overview of CENER experience in torrefaction
LH
V t
orr
efie
d b
iom
ass
/ in
itia
l LH
V
Straw (Laboratory test)
Pine (Laboratory test)
Pine (Small pilot plant)
Beech (CB2G pilot test)
Pine (CB2G pilot plant)
0% 5% 10% 15% 20% 25% 30% 35% 40%LH
V t
orr
efie
d b
iom
ass
/ in
itia
l LH
V
(d.a
.f.)
Torrefaction degree
Pine (CB2G pilot plant)
Straw (CB2G pilot plant)
2. Torrefaction process concept and reactor technology
CENER TORREFACTION PROCESS CONCEPT
2. Torrefaction process concept and reactor technology
WET BIOMASS DRY BIOMASS
Indirectly heated reactor using thermal fluid at temperatures between 250 and 300ºC
The combustible vapors are burned to heat up the thermal fluid.
Previous biomass drying down to 5-15% moisture content No drying is required
Flue gases from the boiler are used in the drier. Flue gases from the boiler are used air preheater.
Additional fuel could be necessary, mainly for drying, depending on biomass moisture content and target torrefaction degree
No additional fuel is necesaryon biomass moisture content and target torrefaction degree
Particle size reduction below 8-40 mm depending on the feedstock
• The core of the process equipment is thetorrefaction reactor of special design manufacturedby LIST AG (www.list.ch):
• It is a cylindrical horizontal reactor with an agitatorshaft and attached elements of special designprocuring axial transport characteristic for all kindof biomass, radial product homogenisation insidethe reactor and excellent heat transfer conditions.
• Reactor heating is carried out indirectly through
TORREFACTION REACTOR
2. Torrefaction process concept and reactor technology
• Reactor heating is carried out indirectly throughthe hot reactor walls, the actively heated shafttube and the actively heated internal shaftelements using thermal oil as heat transfer fluid.
• Main advantages of this kind of Torrefaction reactor are:• The technology is very flexible being able to process a very wide range of very different biomasses
(particle size distributions, bulk densities and compositions, products requiring different transportmechanisms)
• It can process biomass with high fines content• Good ratio of heat transfer surface to volume of reactor allowing shorter residence times and
procuring high performance. Reactor walls, shaft tube and internal shaft elements are activelyheated.
• Continuous and very effective product renewal / product mixing from the internal heating surface,
ADVANTAGES2. Torrefaction process concept and reactor technology
• Continuous and very effective product renewal / product mixing from the internal heating surface,generating higher heat transfer rates and avoiding radial temperature profiles inside the reactor
• The design of the shaft elements provide an axial conveying quite close to plug flow, assuring a goodproduct residence time control (narrow residence time distribution), and at the same time an excellentmixing of the product in each section of the reactor, assuring a good product temperature controlover the whole length of the reactor (avoiding temperatures differences in the product and minimizingthe risk of smouldering)
• Large free gas and vapour space allows the flow of the torrefaction gas with minimal pressure dropkeeping biomass feeding and product discharge at low pressure reducing inert gas consumption
• Large vapour dome cross section minimize dust entrainment with the gas• Using thermal oil as heat transfer medium facilitate energy integration and process control. At the
same time plant operation is more flexible and safer.
• Torrefaction reactor accept a wide range of valuesof feedstock properties: density and fines content
FEEDSTOCK FLEXIBILITY
2. Torrefaction process concept and reactor technology
Parameter Reactor
Dimension /nominal size, mm < 40 mm
Bulk density, kg/m 3 >50 (1)
Moisture, % 5-15%
Amount of fines, % (≤ 3,15 mm) < 89% (1)
Dust content (<250 microns) <62%(1)
Exampleof feedstock: Sample code: 2012-122
• Feedstock with up to 89% fines (<3.15mm) and up to 62% dust (<250 microns)have been tested
05
1015202530354045
< 3,15 3,15 - 8 8 - 16 16 - 31,531,5 - 45 45 - 63
% w
/w
dp (mm)
Dust content (<250 microns) <62%(1) Tested feedstock. Limits could depend case by case
on other feedstock characteristics and process
conditions
Exampleof feedstock: Sample code: 2012-122Chipped < 30 mm ; Average particle size 8,0 mm
• Wood mixing, homogeneous temperature and residence time control : to warranty producthomogeneity for all size fractions
PRODUCT HOMOGENEITY2. Torrefaction process concept and reactor technology
Heating value Elemental analysis
Sample codeSample origin
Moisture AshHHV
(MJ/kg)LHV
(MJ/kg)%C %H %N
% w/w-"ar" % d.b. d.a.f. d.a.f.
2011-257 1,5 1,4 22,2 21,0 55,5 5,9 0,172011-257
10.006/T04;
1,5 1,4 22,2 21,0 55,5 5,9 0,17257 (<8mm) 1,5 1,4 22,3 21,1 55,6 5,9 0,17
257 (16-8mm) 1,5 1,4 22,3 21,1 55,5 5,9 0,16
257 (>16mm) 1,5 1,4 22,2 21,0 55,5 5,9 0,16Difference 0% 0% <0.1 MJ <0.1 MJ <0.1% 0% <0.01%
2011- 260
10.006/T05;
1,0 1,3 20,7 19,4 52,0 6,1 0,16260 (<8mm) 1,0 1,3 20,8 19,5 51,9 6,1 0,16
260 (16-8mm) 1,0 1,3 20.7 19.5 51,7 6,1 0,13
260 (>16mm) 1,0 1,3 20,7 19,5 51,6 6,1 0,13Difference 0% 0% <0.1 MJ <0.1 MJ <0.4% 0% <0.03%
Analysis acceptance repeatability criteria
<0.2% <0.3% <0,12 MJ <0.39% <0.2% <0.03%
• Differences between thedifferent particle sizefractions in a sample aresimilar to analysisacceptance repeatabilitycriteria
• Easy temperature and residence time control : to warranty product homogeneity vs time on stream
PRODUCT HOMOGENEITY2. Torrefaction process concept and reactor technology
• Differencesare similar toanalysisacceptancerepeatabilitycriteria
• Milling equipment• Feeding hopper• Harmer mill – 2-12 mm
• Pelletization equipment
PELLETIZATION PILOT PLANT2. Torrefaction process concept and reactor technology
• Pelletization equipment• Feeding hopper• Mixer – 2 m3
• Continuous addition of water and/oradditives
• Pellet mill (MABRIK) - 40 HP• Cooler and cleaner
• Regulation• Biomass type• Torrefaction degree• Particle size• Moisture content:• Die characteristics
• Compression relation from 6 x16 to 6x46
PELLETIZATION PILOT PLANT2. Torrefaction process concept and reactor technology
• Compression relation from 6 x16 to 6x46• Configuration: diameter and number of
channels, etc
• Measurement• Production rate and efficiency: kg/h per HP• Pellet temperature• Pellet moisture content• Roller temperature• Pellet durability and fines content• Pellet bulk density
PILOT PLANT IN OPERATION2. Torrefaction process concept and reactor technology
• VIDEO OF THE PILOT PLANT IN OPERATION
3. Straw torrefaction
PILOT PLANT TEST RESULT – MASS AND ENERGY BALANCE2. Straw torrefaction
Material Parameter Unit Value
Flow rate kg/h 314
Mass and heat balance of straw torrefaction pilot test at 250ºC (heat transfer fluid)
Balance Heat concept Value (kW)
InputSupplied by heat
transfer fluid (measured)
63,5
Feedstock Moisture % wb 12
Nitrogen kg/h 12
Torrefied productFlow rate kg/h 240
Weight loss % db 13,1
Torrefied gasFlow rate kg/h 86
Temperature ºC 197
(measured)
Output
Transferred heat by reactor (calculated by
simulation)69,0
Losses (measured) 24,0
Heat of reaction (calculated by heat
balance)-29,5
Balance 0,0
PILOT PLANT TEST RESULT – HEAT CONSUMPTION2. Straw torrefaction
Measured heat consumption per kg of product in torrefaction pilot test
1.230
1.430
1.630
1.830
Rea
ctor
hea
t con
sum
ptio
n (k
J/kg
)
Beech
Straw
Pine Straw torrefaction process has lower energy consumption(≈
30
230
430
630
830
1.030
230 240 250 260 270 280 290 300 310
Rea
ctor
hea
t con
sum
ptio
n (k
J/kg
)
Heat transfer fluid temperature (ºC)
lower energy consumption(≈ 950 kJ/kg) than woody biomass (> 1.100 kJ/kg) torrefaction with similar weight loss
PILOT PLANT TEST RESULT – PELLETIZATION TEST2. Straw torrefaction
Energy efficiency of different torrefied biomasses pelletisation
• Pelletisation of torrefiedstraw was possible.
• Optimization of pelletization conditions is
Parameter UnitsTorrefied biomass source
Straw Beech Pine
Pellet production kg/h 380 309 266necessary to improve pellet quality.
• Energy consumption for torrefied straw pelletization seems to be lower than for torrefiedwood.
Pellet production kg/h 380 309 266
Energy efficiency kg/kWh 12,7 10,3 9,0
Pellet temperature ºC 85 88 85
Torrefaction degree % (db) 13,1 14,7 14,1
4. Torrefaction reactor modeling and upscallingstudies
CONSIDERATIONS OF THE MODEL4. Torrefaction reactor modeling and up-scalling studies
• A number of perfectly mixed reactors in series. Theproducts output from one stage will be the input ofthe next.
• The torrefaction process is according the kineticmodel from Di Blasi Lanzetta
• Kinetic parameters are obtained bythermogravimetric analysis of studied biomasses.
• Biomass particles are considered as isothermal.• Biomass particles are considered as isothermal.Intra-particle temperature profiles are neglected.
• Heat of reaction is considered as function of reactiontemperature (correlations developed from pilot testenergy balance)
• Gas-solid heat transfer is neglected (correlationunder developmenet)
• For each stage mass balance and energy balanceequations are solved
• Model calculates:conversion,conversion, temperaturetemperature profile,profile, gasgas temperaturetemperatureandand heatheat demanddemand ofof thethe reactorreactor
Model is used for reactorupscaling and for techno-economic case studies
CONSIDERATIONS OF THE MODEL
• Kinetic constants are obtained by thermogravimetric analysis of studied biomasses
4. Torrefaction reactor modeling and up-scalling studies
EXAMPLE OF MODEL OUTPUT
• Example of conversion and product temperature profiles in reactor by simulation.
20
25
30
20
25
30
T (ºC)/10
4. Torrefaction reactor modeling and up-scalling studies
-5
0
5
10
15
-5
0
5
10
15
- - - - - - -
Length of reactor
Torrefaction
degree (d.a.f)
MODEL VALIDATION
• Biomass conversion in good agreement with experimental results in terms of product conversion
Material Parameter Units
Test result
SimulationPilot plant
Feedstock Flow rate kg/h 300 314
4. Torrefaction reactor modeling and up-scalling studies
Feedstock Flow rate kg/h 300 314
ProductFlow rate kg/h 230 240
Weight loss % db 13,0 13,1
GasFlow rate kg/h 82 86
Temperature ºC 147 197
HEAT OF REACTION CORRELATIONS4. Torrefaction reactor modelling
• Heat of reaction vs. averaged reaction temperature calculated from pilot test heat balance
MASS AND ENERGY BALANCE – INDUSTRIAL PLANT CASE
In order to close the energy balance, required torrefaction degree and thermal efficiency depends on straw moisture content. Efficiency is higher than the case of wet woody biomass.
4. Torrefaction reactor modeling and up-scalling studies
5. Conclusions
5. Conclusions
• Torrefaction of straw was carried out successfully. Axial transport of the biomass inside of thereactor allowed proper torrefaction process without clogging, thereby obtaining ahomogeneous product.
• Thermal efficiency for straw torrefaction is higher than for wood due to the lower moisturecontent and higher reactivity. In the other hand process concept has to be adapted due to thespecial characteristic of straw.
• Subsequent peletisation of torrefied straw was posible. Optimization of pelletization conditionsis necessary to improve pellet quality.
• Energy consumption for torrefied straw pelletization was lower than for torrefied wood in similarconditions.
• Torrefaction process model developed by CENER fits well with the experimental results and isan effective tool for optimization and uspscalling studies to analyze the techno-economicfeasibility and for plant design .
ACKNOWLEDGEMENTS
Thank so much for your attentionContacts: Javier Gil: [email protected]
Ines Echeverría: [email protected]
This infrastructure has been co-funded through the ERDF Funds, the Ministry of Economy andCompetitiveness and the Government of Navarra.
www.cener.com