forebiom, busan, feb. 2014 · 2016-11-23 · air blown biomass gasifier had been operated with gas...
TRANSCRIPT
Byungho Song
Kunsan National University
The product yield of pyrolysis of biomass and a kinetic study of gasification of biomass char
FOREBIOM, Busan, Feb. 2014
‐ Biomass gasification process
‐ Gas yield from pyrolysis of coal, and biomass
‐ Prediction of gas yields at pyrolysis stage
‐ Kinetic study of gasification of biomass char
‐ Gas‐solids reaction models
‐ Experimental
‐ Results
‐ Concluding remarks
‐ References
Contents
Air blown biomass gasifier had been operated with gas turbine over 4,000 hrs.
Gasifier pressure is 18 atm and temperature of 950‐1000’C
100 ton/day biomass is fed to gasifier though a lock hopper.
Produced syngas is cooled at 350‐400’C and sent to 4.2 MW gas turbine.
The used gas from the turbine is used to operate a steam turbine producing 1.8 MW more.
18 MW IGCC Combined Heat and Power demonstration plant at Varnamo, Sweden
4
Extension of the Värnamo plant for fuel production
Pyrolysis and gasification
Process simulation is essential to develop biomass conversion processes!
Processes in a biomass gasifier
Main reactions in biomass gasification processes
Kinetic information is needed!
Fig. 1. Typical yields of various product from fast pyrolysis of wood.
Fig. 2. Product yields from wood, and agricultural residues [Blasi et al., 1999]
Product yields from pyrolysis
Gas yields from devolatilization of a coal
Pyrolysis
Gas yields at pyrolysis and gasification atmosphere. [Hwang et al., 2013] – Woody biomass chip
Steam gasification
Prediction of Gas yields at pyrolysis stage
Biomass pyrolysis products could be predicted through elemental balances, energy balance and empirical relationships.
Neves et al. (2011) drived some empirical relationships from the collected data over the wide temperature range for biomass pyrolysis.
, , , 2 ,j F ch F tar F H O G Fj
Y Y Y Y Y
, 4, , 2, 2,G F CH F CO F CO F H FY Y Y Y Y
, :j FY
, :i FY
, :ash FY
2, 0.106 2.43 exp( 0.66 10 )ch FY T
Mass balance at pyrolysis unit, Input = output
mass fraction of j th element in fuel, daf basis (kg j/kg daf fuel)
yield of I th product, daf basis (kg i/kg daf fuel)
ash content in fuel, daf basis (kg ash/kg daf fuel)
The relationship for char yield is given as;
The elemental carbon balance at pyrolysis stage;
, , , , , , ,C F C ch ch F C L L F C G G FY Y Y Y Y Y Y
, , , , , , 4 4, , , , 2 2,C F C ch ch F C tar tar F C CH CH F C CO CO F C CO CO FY Y Y Y Y Y Y Y Y Y Y This can be rearragnged as;
(1)
2, 0.93 0.92exp( 0.42 10 )C chY T
2, 0.07 0.85exp( 0.48 10 )O chY T
2 2, 0.41 10 0.10exp( 0.24 10 )H chY T
The elemental composition of char;
, ,/ 1.14C tar C FY Y
, ,/ 1.13H tar H FY Y
, ,/ 0.8O tar O FY Y
The CHO composition of tar seems relatively close to that of parent fuel:
, , , , , , , , 2 2, , 2 2 ,O F O ch ch F O tar tar F O CO CO F O CO CO F O H O H O FY Y Y Y Y Y Y Y Y Y Y
, , , , , , 4 4, , 2 2, , 2 2 ,H F H ch ch F H tar tar F H CH CH F H H H F H H O H O FY Y Y Y Y Y Y Y Y Y Y
9.38422, 1.145 1 exp 0.11 10H FY T
42, ,7.23
0.04293 101 ( / 632)H F CO FY Y
T
44, ,0.146 2.18 10CH F CO FY Y
The oxygen balance;
Hydrogen balance;
(3)
(4)
(5)
(6)
(2)
The above set of six simultaneous equations could be solved as a linear system A*X=B (‘linsolve’ at matlab).
Neves et al. [2011] fitted the collected data on the lower heating value of total pyrolysisgas by Eq. (7)
2GLHV 6.23 2.47 10 T (7)
daf daf daf daf dafC H O N S
Anthracite-Korea, Moonkyung 1 84.27 1.99 11.91 0.96 0.87Bituminous-Minto 2 81.83 5.57 3.60 1.08 7.92Bituminous-Australian 3 81.35 4.84 13.17 0.41 0.24Bituminous-Senwha 4 73.16 4.11 21.51 0.73 0.49SubB-Highvale 5 77.84 4.09 16.75 1.01 0.31Lignite-Pittsburg 6 83.24 5.85 6.41 1.69 2.81Lignite-Costello 7 68.43 5.48 23.94 1.19 0.96Flax [Reed & Williams, 2004] 8 43.30 6.50 50.20 0.00 0.00Flax [Guiying, 2010] 9 46.71 5.77 46.50 0.82 0.20Biomass [Neves, 2011] 10 49.00 5.90 44.00 0.00 0.00wheat straw [Blasi et al, 1999] 11 43.60 6.20 49.82 0.30 0.08wood [Blasi et al., 1999] 12 46.40 5.90 47.61 0.09 0.00Switch Grass [Mohammad] 13 47.94 6.17 44.98 0.79 0.12Coal [Mohammad] 14 73.11 4.33 21.16 0.98 0.42
Table 1. Elemental analysis of coal and biomass.
Fig. 2. The result of test run with a biomass of flax (C=46.71, H=5.77, O=46.5)
Fig. 3. The result of test run with a biomass of flax (C=46.71, H=5.77, O=46.5)
Fig. 4. The result of test run with a Switch grass (C=47.94, H=6.17, O=44.98)
200 300 400 500 600 700 800 900 10000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8Yields of daf char=line, tar=+, gas=dot, H2O=line
T, C
Yiel
d (k
g/kg
daf
fuel
)
0 500 10000
0.5Y-CO2,F
T, CYiel
d (k
g/kg
daf
fuel
)
0 500 10000
0.5Y-H2O,F
T, CYiel
d (k
g/kg
daf
fuel
)
0 500 10000
0.5
Y-CO,F
T, CYiel
d (k
g/kg
daf
fuel
)
0 500 10000
0.05
0.1Y-CH4,F
T, CYiel
d (k
g/kg
daf
fuel
)
0 500 1000-0.02
0
0.02Y-H2,F
T, CYiel
d (k
g/kg
daf
fuel
)
The gasification of wood chip and palm pellet have been performed in TGA and thermobalance to get kinetic parameters.
Kinetic parameters of biomass gasification can be evaluated through the use of gas‐solids reaction model.
Kinetic study of gasification of biomass char
Carbon conversionashWW
WWX
0
0
1
0)( dXXkk s
Shrinking core model,Chem. reaction controlledWen (1968)
Volumetric modelIshida and Wen(1978)
Modified volumetric modelKasaoka et al. (1985)
Conversion with time
Specific reactionrate
)1ln( Xt 3/1)1(1 Xt
3/1]1[3X
1/1 )]1ln([
XdtdX
XXks
1
1)(
Average reaction rate
)1ln( Xt
Gas‐solids reaction models
Reaction rate
Experimental ‐ Analysis of wood chip and palm pellet
Proximate analysis(wt%) Wood chip Wood pellet Palm pellet
Moisture 5.7 8.1
Fixed Carbon 14.4 13.9
Volatile Matter 76.4 76.6
Ash 3.5 1.4
Elemental analysis
C 51.2 60.68
H 6.36 7.21
O* 39.74 31.24
N 0 0.19
S 0.29 -
Ash 2.41 0.66
Cl 0.01
HHV**, kcal/kg 5,144 6,039
* by difference**calculated by Dulong’s equation
Fig 1. Schematic diagram of thermobalance reactor.1: Water, 2: micro pump, 3: steam generator, 4: gas preheater, 5: sample basket, 6: electrical heater, 7: hatch, 8: electrical balance, 9: motor and winch assembly, 10: cold trap, 11: vacuum pump, 12: gas regulator, 13: flow meter
1
2
3
6
5
10
11
nitrogen
8
9
ventcoolingwater
air
12
13
Personalcomputer
7
4
inert purgeExperimental apparatus
Fig. Photo of TGA (Setaram TG92)T= 600 – 900’CPCO2 = 50%Sample mass= 10 ‐ 30 mg
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
Car
bon
conv
ersi
on, X
(-)
Dimensionless gasification time, t/t30 min (-)
900C 800C 750C 700C
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
Car
bon
conv
ersi
on, X
(-)
Dimensionless gasification time, t/t30 min (-)
900C 800C 700C 600C
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
Car
bon
conv
ersi
on, X
(-)
Dimensionless gasification time, t/t30 min (-)
900C 800C 700C 600C
(a) Palm - CO2 (b) Wood Chip - CO2 (c) Wood Chip – H2O
Results ‐ Conversion behavior
• The rate of H2O gasification was found to be a bit higher compared to CO2gasification.
• About 8 times increase in CO2 gasification rate was observed with 100C increase in temperature.
• About 5 times increase in H2O gasification rate with 100C increase.
Thermobalance
(a) Conversion data based on the shrinking core model
(c) Modified volumetric reaction model
Conversion behavior with the models [woodchip]
(b) Volumetric reaction model
(5.0)
(4.0)
(3.0)
(2.0)
(1.0)
0.0
1.0
2.0
3.0
0.8 0.9 1.0 1.1 1.2
ln k
(h-1
)
1000/T, K-1
Kinetic parameters
Sample (Gasifying Agent)
Activation Energy
(kJ mol–1)
Frequency Factor(108 h–1)
Palm (CO2)
176.5 3.8
Woodchip (CO2)
171.4 4.6
Woodchip (H2O)
168.0 5.2
• Lower activation energy for wood chip may be due to its higher amount of ash that may contain catalytic alkali species.
XPRTdt
dXOH
1025,168exp1055.140 51.06
2
XPRTdt
dX nCO
1506,176exp1064.381
2
6
XPRTdt
dX nCO
1434,171exp1091.456
2
6
Palm (CO2)
Wood Chip (CO2)
Wood Chip (H2O)
• Apparent reaction rates could be obtained as:
• The data with various pressure of CO2 will be needed further to get the exponent in the rate equation.
Kinetic rate expressions
Concluding remarks • The product yield and gas composition in pyrolysis step could be successfully
predicted by a combination of mass balances and empirical relationship among the their components.
• Tar conversion scheme should be needed further.
• Gasification behavior of biomass could be well described by modified volumetric reaction model.
• Activation energy for wood chip and palm pellet were similar and found to be 168‐176 kJ/mol. Lower activation energy of wood chip might be due to its higher ash component with catalytic effect.
• Apparent reaction rates are provided.
‐ End ‐
Blasi et al., Ind. Eng. Chem. Res., 38, 2216‐2224 (1999)
Hwang et al., Waste Management, (2013)
Neves et al., Progress in Energy and Combustion Science, 37, 611‐630 (2011)
Song and Watkinson, J. Ind. Eng. Chem., 10(3), 460‐467 (2004)
References