cereal straw torrefaction: results on … torrefaction 4. torrefaction reactor modeling and...

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


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 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


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


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


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


• 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


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


-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


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.


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

cereal straw torrefaction: results on … torrefaction 4. torrefaction reactor modeling and...

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