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Institute of Energy Process Engineering and Chemical Engineering
Chair EVT
Kinetic study on gasification of chars from co-pyrolysis of German brown coal and wheat straw
Zhou, L., Schurz, M., Reichel, D., Zhang, G.
6th International Freiberg Conference on IGCC & XtL Technologies – IFC2014
19th – 22nd May 2014 – Dresden/Radebeul, Germany
Session 12-3 –Gasification kinetics
1 Introduction
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Advantage of thermal co-processing
For kinetics study § Better understand the process and design coal gasifiers
§ The gasification of char with CO↓2 Fundamentally to study the char reactivity Easily adopted in the laboratory scale
Economics Efficiency
Environment Flexibility
Thermal co-processing of coal
and biomass
2 Materials and methods 2.1 Sample list
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Experiment plan and conditions § Samples: Wheat straw (WS), Rhenish brown coal (WS), co-pyrolysis chars (Mix) § WS ratios: 10, 50 and 90 wt.% based on raw WS § Pyrolysis temperatures (P): 750 and 1000 ̊C § Gasification temperatures (G): 750, 800, 850, 900 and 1000 ̊C
Example for experiments list § WS/P750/G750, HKN/P750/G750 § MIX10%/P750/G750, MIX50%/P750/G750
2 Materials and methods 2.2 Sample characteristics
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Proximate analysis of wheat straw and Rhenish brown coal Ultimate analysis of wheat straw and Rhenish brown coal Index of basicity [1] of Rhenish brown coal and wheat straw The value are 0.03 for wheat straw and 0.28 for Rhenish brown coal.
Index of basicity =w(A)∗Fe↓2 O↓3 +CaO+MgO+ Na↓2 O+ K↓2 O/SiO↓2 + Al↓2 O↓3 (2.1)
Sample
Moisture (Accept)
Ash
Volatile matter
Fixed carbon
Sum
wt.% (d) Wheat straw 10.93 6.88 75.85 17.27 100
Rhenish brown coal 51.12 5.47 50.7 43.83 100
Sample C H N Stotal Cl O Sum wt.% (d)
Wheat straw 49.26 5.98 0.67 0.3 0.2 43.59 100 Rhenish brown coal 69.04 5.01 0.79 0.64 0.04 24.48 100
2 Materials and methods 2.4 Vertical flow through fixed bed reactor
Schematic of quartz glass reactor
Experimental conditions of gasification in quartz glass reactor
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Experimental conditions Values
Flow of CO2 4.6 L/h in STP (100 vol.%)
Temperature 750-1000 °C
Char samples WS, HKN, blend chars (<2 mm, 1 gram)
CO2 flow goes through the char particles
Carbon consumed is calculated by data from on-line GC
CO↓2 +C⇆2CO +172KJ/mol [2]
2 Materials and methods 2.5 Equations Ø Carbon conversion X of char
W↓0 : initial char mass, W↓t : char mass at time t
W↓a : ash mass of the initial char Ø Co-processing
Biomass ratio(%)= Dry biomass weight/Dry Total feed weight ∗100
Biomass char ratio(%)= biomass ratio∗biomass char yield∗100 Ø Additive model
(Y)↓blend = x↓1 (Y)↓coal + x↓2 (Y)↓biomass Y: different parameters during the reaction
x↓n : biomass or coal amount ratio Ø Kinetics
§ Arrhenius equation [3] § Gasification models Volume reaction model (VRM) [4]
Shrinking core model (SCM) [5] Random pore model (RPM) [6,7]
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X (%)= W↓0 − W↓t /W↓0 − W↓a ∗100
E1CP just contains about 5.8 wt.% WS char instead of 10 wt.%
3 Results and discussion 3.1 Gasification of co-pyrolysis char samples
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(a) (b)
Gasification of single and co-pyrolysis chars at (a) 750, (b) 1000 ̊C (a) (b)
Experimental and calculated gasification of co-pyrolysis chars at 750 ̊C
3 Results and discussion 3.1 Gasification of co-pyrolysis char samples
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(a) (b)
Experimental and calculated gasification of co-pyrolysis chars at 1000 ̊C (a) (b)
Residual ash of char samples, (a) B5CG, 800 ̊C, (b) E5CG, 1000 ̊C
3 Results and discussion 3.1 Gasification of co-pyrolysis char samples
(a) (b) (c)
Comparison with experimental and calculated gasification of MIX/P1000 chars at 800 °C
Comparison with experimental and calculated co-pyrolysis of WS and HKN
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200 400 600 800 10000.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
200 400 600 800 10000.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Temperature (°C)
Mas
s lo
ss (T
G)
Cal, 10 wt% Cal, 50 wt% Cal, 90 wt%
Exp, 10 wt% Exp, 50 wt% Exp, 90 wt%
3 Results and discussion 3.1 Gasification of co-pyrolysis char samples Ø Characteristics of blend chars and comparison with calculated values Ultimate analysis of MIX/P1000 chars pyrolyzed at 1000 °C Index of basicity (B) of MIX/P1000 chars pyrolyzed at 1000 °C
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Samples Ash C H N S O Sum wt.% (d)
Co-pyrolysis in 1000 °C
Cal 9.96 87.14 0.32 0.63 0.67 1.28 100.00 MIX10%/P1000 9.85 88.56 0.26 0.62 0.71 0.00 100.00
Cal 14.07 83.56 0.29 0.71 0.60 0.77 100.00 MIX50%/P1000 14.59 83.48 0.27 0.64 1.01 0.01 100.00
Co-pyrolysis in 1000 °C Cal MIX10%/P1000 Cal MIX50%/P1000 B (Index of basicity) 0.39 0.33 0.14 0.16
𝐎↓𝐄𝐱𝐩. < 𝐎↓𝐂𝐚𝐥.
𝐁↓𝐄𝐱𝐩. < 𝐁↓𝐂𝐚𝐥. 𝐇↓𝐄𝐱𝐩. < 𝐇↓𝐂𝐚𝐥. Diffusion:
Put particles with different diameters together leading to smaller space between them. Ash sintering (Figure 3.7)
MIX10%/P1000
Low gasification reactivity
Ash of mixed char samples gasified at 800 °C, E7CG
MIX50%/P1000
3 Results and discussion 3.2 Kinetics of co-pyrolysis char samples
Ø 𝐌𝐨𝐝𝐞𝐥 𝐬𝐞𝐥𝐞𝐜𝐭𝐢𝐨𝐧 (a) (b)
Linear fit by VRM for gasification of MIX/P1000 chars at (a) 800 and (b) 1000 °C
(a) (b)
Linear fit by SCM for gasification of MIX/P1000 chars at (a) 800 and (b) 1000 °C
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3 Results and discussion 3.2 Kinetics of gasification of co-pyrolysis chars
(a) (b)
Linear fit by RPM for gasification of MIX/P1000 chars at (a) 800 and (b) 1000 °C
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Kinetic parameters by linear fitting RPM for Mix10%/P1000 from 800 to 1000 °C
Parameters 800 850 900 1000
k(RPM) 0.2213 0.5384 0.9390 1.6982
ψ 2.2879 2.6240 3.3392 4.1701 R2(PRM) 0.9995 0.9994 0.9998 0.9991
Parameters 800 850 900 1000
k(RPM) 0.2127 0.5035 0.8842 1.7864
ψ 2.7442 2.6821 3.0935 4.9905 R2(PRM) 0.9987 0.9998 0.9999 0.9996
Kinetic parameters by linear fitting RPM for Mix50%/P1000 from 800 to 1000 °C
3 Results and discussion 3.2 Kinetics of gasification of co-pyrolysis chars
Ø 𝐊𝐢𝐧𝐞𝐭𝐢𝐜 𝐩𝐚𝐫𝐚𝐦𝐞𝐭𝐞𝐫𝐬 (a) (b)
Arrhenius plots of MIX/P1000 chars with parameters from RPM
Kinetic parameters for gasification of MIX10%/P1000
Kinetic parameters for gasification of MIX50%/P1000
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MIX10%/P1000 Intercept Slope E (kJ/mol) A (1/h) R2
800-875 °C 17.35 -20226.13 168.16 3.44*107 0.99441 875-1000 °C 7.91 -9388.48 78.06 2.73* 103 0.99181
MIX50%/P1000 Intercept Slope E (kJ/mol) A (1/h) R2
800-870°C 19.39 -22483.97 188.24 2.64*108 0.98864 870-1000 °C 8.01 -9478.07 79.35 3.02*103 0.97512
3 Results and discussion 3.2 Synergy effect on kinetics parameters Apparent activation energy E for single and MIX/P1000 chars, comparison of experimental and calculated values High T: § E(Exp) < E(Cal) High reactivity Not agree with experimental behavior § E(High T) < 1/2 E(Low T), Film diffusion at around 975 °C (E(975−1000)≈0) Ash sintering can not be reflected More diffusion compared to single char
Pre-exponential factors A for single and MIX/P1000 chars, comparison of experimental and calculated values
A(Exp) < A(Cal) Low reactivity Agree with experimental behavior § Low A values are caused by pore blocking and ash sintering
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E (kJ/mol) WS HKN Cal, 10wt.% E1CP
Cal, 50wt.% E5CP
Low T 217.29 171.22 173.90 168.16 187.66 188.24 High T 125.07 90.73 92.73 78.06 102.99 79.35
≈ ≈ > >
A (1/h) WS HKN Cal, 10wt.% E1CP
Cal, 50wt.% E5CP
Low T 9.31*109 6.40*107 6.01*108 3.44*107 3.36*109 2.64*108 High T 2.89*105 1.12*104 2.70*104 2.73*103 1.10*105 3.02*103
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4 Conclusions
Experimental behavior Lower reactivity for E1CP and E5CP § Synergy effects in co-pyrolysis process(The loss of Oxygen, Hydrogen and catalytic
material) § Pore blocking and ash sintering
Kinetic study
§ Chemical reaction zone: E↓Exp ≈E↓Cal , A↓Exp < A↓Cal Low reactivity
Diffusion controlled zone: E↓Exp < E↓Cal , A↓Exp < A↓Cal Low reactivity § Pre-exponential factor A: Agree with experimental behavior in both zones Low A values are caused by pore blocking and ash sintering
15 TU Bergakademie Freiberg · Institute of Energy Process Engineering and Chemical Engineering · Chair of Energy Process Engineering and Thermal Waste Treatment · Reiche Zeche · Fuchsmuehlenweg 9 · 09599 Freiberg, Germany · Phone: +49 3731 39-4511 · Fax: +49 3731 39-4555 · www.iec.tu-freiberg.de
Reference
[1] M. Sakawa, Y. Sakurai. Influence of coal characteristics on CO2 gasification. Fuel, 61(8) (1982), 717-720. [2] Higman, Chris. Gasification / Chris Higman and Maarten van der Burgt.—2nd ed. [3] G.Q. Lu, D.D. Do. Comparison of structural models for high-ash char gasification. Carbon, 32 (1994), 247-263. [4] M. Ishida, C.Y. Wen. Comparison of zone-reaction model and unreacted-core shrinking model in solid-gas reactions. I. Isothermal analysis, Chem. Eng. Sci., 26 (1971), 1031-1041. [5] J. Szekely, J.W. Evans, A structural model for gas-solid reactions with a moving boundary, Chem. Eng. Sci., 25 (1970), 1091-1107. [6] Bhatia S. K., Perlmutter D. D. A Random Pore Model for Fluid-Solid Reactions: I. Isothermal, Kinetic Control. AIChE J., 26 (1980), 379. [7] Dong Kyun Seo, Sun Ki Lee, Min Woong Kang. Gasification reactivity of biomass chars with CO2. Biomass and bioenergy, 34(2010), 1946-1953.
16 TU Bergakademie Freiberg · Institute of Energy Process Engineering and Chemical Engineering · Chair of Energy Process Engineering and Thermal Waste Treatment · Reiche Zeche · Fuchsmuehlenweg 9 · 09599 Freiberg, Germany · Phone: +49 3731 39-4511 · Fax: +49 3731 39-4555 · www.iec.tu-freiberg.de
IEC – TU Bergakademie Freiberg
Acknowledgement
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Thanks to: German Federal Ministry of Education and Research
RWE AG, Vattenfall Europe AG, MIBRAG mbH and Romonta AG
Contact: M. Eng. Lingmei Zhou [email protected] [email protected]
Thank you for your attention – Questions?