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

2

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

3

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

4

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

5

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]

6

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

7

(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

8

(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

9

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

10

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

11

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

12

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

13

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

14

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

17

Thanks to: German Federal Ministry of Education and Research

RWE AG, Vattenfall Europe AG, MIBRAG mbH and Romonta AG

Contact: M. Eng. Lingmei Zhou lingmei.Zhou@der.tu-freiberg.de lingmeizhou@hotmail.com

Thank you for your attention – Questions?