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Frontiers of Chemical Science and Engineering

ISSN 2095-0179

ISSN 2095-0187(Online)

CN 11-5981/TQ

Postal Subscription Code 80-969

2018 Impact Factor: 2.809

Front. Chem. Sci. Eng.    2019, Vol. 13 Issue (2) : 415-426    https://doi.org/10.1007/s11705-018-1725-8
RESEARCH ARTICLE
Intrinsic kinetics and external diffusion of catalytic steam gasification of fine coal char particles under pressurized and fluidized conditions
Xuantao Wu, Jie Wang()
Department of Chemical Engineering for Energy, Key Laboratory of Coal Gasification and Energy Chemical Engineering of Ministry of Education, East China University of Science and Technology, Shanghai 200237, China
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Abstract

Catalytic steam gasification of fine coal char particles was carried out using a self-made laboratory reactor to determine the intrinsic kinetics and external diffusion under varying pressures (0.1–0.5 MPa) and superficial gas flow velocities (GFVs) of 13.8– 68.8 cm∙s−1. In order to estimate the in-situ gas release rate at a low GFV, the transported effect of effluent gas on the temporal gasification rate pattern was simulated by the Fluent computation and verified experimentally. The external mass transfer coefficients (kmam) and the effectiveness factors were determined at lower GFVs, based on the intrinsic gasification rate obtained at a high GFV of 55.0 cm∙s–1. The kmam was found to be almost invariable in a wider carbon conversion of 0.2–0.7. The variations of kmam at a median carbon conversion with GFV, temperature and pressure were found to follow a modified Chilton-Colburn correlation: Sh=0.311Re2.83Sc13(PP0)2.07 (0.04<Re<0.19), where P is total pressure and P0 is atmospheric pressure. An intrinsic kinetics/external diffusion integrating model could well describe the gasification rate as a function of GFV, temperature and pressure over a whole gasification process.

Keywords coal char      catalytic steam gasification      pressure      kinetics      diffusion     
Corresponding Author(s): Jie Wang   
Just Accepted Date: 19 March 2018   Online First Date: 26 June 2018    Issue Date: 22 May 2019
 Cite this article:   
Xuantao Wu,Jie Wang. Intrinsic kinetics and external diffusion of catalytic steam gasification of fine coal char particles under pressurized and fluidized conditions[J]. Front. Chem. Sci. Eng., 2019, 13(2): 415-426.
 URL:  
https://academic.hep.com.cn/fcse/EN/10.1007/s11705-018-1725-8
https://academic.hep.com.cn/fcse/EN/Y2019/V13/I2/415
Fig.1  Schematic diagram of pressurized reactor and apparatus system used for steam gasification. MFC: mass flow controller; PMP: piston micro pump; P: pressure transducer; T: thermocouple; BP: back pressure valve; MF: mass flow meter
Fig.2  Some simulated results of fluid dynamics in the steam condenser. (a) Grid division; (b) CO2 concentration distributions with gasification time; (c) water strip distributions with gasification time. Operated at atmospheric pressure: temperature, 750 °C; catalyst loading, 10 wt-% K2CO3; GFV, 13.8 cm?s–1
Fig.3  CO2 release rate and carbon conversion during thermal decomposition of CuCO3 determined experimentally and by simulation. Experimental condition: total pressure, 2.0 MPa; GFV, 13.8 cm?s–1; heating rate, 10 °C?min−1. (a) Determined experimentally without condenser (case I, marks red ■ and blue ■) and with condenser (case II, marks red ○ and blue ○); (b) determined experimentally without condenser (case I, marks red ■ and blue ■) and with an additional reactor (case III, marks red △ and blue △). Dash lines, simulated results
Fig.4  Temporal profiles of CO2 and CO release rates and total carbon conversion obtained from the steam gasification experiments at different GFVs in comparison to the in-situ profiles simulated. (a) 13.8 cm?s–1; (b) 55.0 cm?s–1. Marks denote the experimental data (■, total carbon conversion; □, CO2 release rate; ○, CO release rate); Dash lines, simulated results. Gasification conditions: 0.1 MPa; 750 °C; 10 wt-% K2CO3
Exp. no. Total pressure /MPa Flow rate /(cm?s–1) Δr0.2/r 0.2/% Δr0.5/r 0.5/% Δr0.8/r 0.8/% Δ r¯/r¯/%
1a) 0.5 55.0 0.65 1.17 5.62 0.35
2 0.1 68.8 3.75 0.59 2.06 0.32
3 0.1 55.0 4.56 0.10 1.13 0.92
4 0.1 41.3 5.86 1.94 4.88 2.80
5 0.1 27.5 5.46 2.11 5.60 2.82
6 0.1 13.8 4.02 5.65 10.06 7.34
7 0.5 13.8 4.97 9.69 34.15 14.50
8 1.0 13.8 3.21 12.68 54.08 19.76
9 1.5 13.8 6.02 11.60 44.65 21.36
10 2.0 13.8 9.81 11.97 56.65 25.88
Tab.1  Relative errors of the gasification rate caused by fluid dynamic of gasification system obtained at 750 °C and with varying total pressure and flow rate
Fig.5  (a) Temporal profiles of carbon conversion and (b) mean gasification rates obtained experimentally with different particle sizes. Gasification condition: 0.1 MPa; 750 °C; 55.0 cm?s–1; 10 wt-% K2CO3. Particle diameter range (average diameter) in subset a: □, 0.016–0.070 (0.022) mm; ○, 0.023–0.092 (0.032) mm; △, 0.025–0.111 (0.038) mm; ▿, 0.040–0.134 (0.051) mm
Fig.6  (a) Temporal profiles of carbon conversion and (b) mean gasification rates obtained experimentally with different GFVs. Gasification condition: 0.11 MPa, 750 °C, catalyst loading of 10% K2CO3. Marks in subset (a) □, 13.8 cm?s–1; ○, 19.3 cm?s–1; △, 27.5 cm?s–1; ▿, 55.0 cm?s–1; ◇, 68.8 cm?s–1
Fig.7  The change of η with the carbon conversions (marks) and the mean η (dash lines) obtained experimentally at different GFVs. Gasification condition: 0.1 MPa; 750 °C; 10 wt-% catalyst. Black (mark and line), 13.8 cm?s–1; red, 16.5 cm?s–1; green, 27.5 cm?s–1; blue, 41.3 cm?s–1
Fig.8  The kinetically derived kmam (○) and the η (●) of external diffusion at the carbon conversion of 0.5 and the calculated results from the Sherwood correlation (dash lines). Gasification condition in subset (a) 0.1 MPa, 750 °C; in subset (b) 0.1 MPa, 13.8 cm?s–1; in subset (c) 750 °C, 13.8 cm?s–1
Physical variable Total pressure /MPa
0.1 0.2 0.4 0.5
v/(10–3 m2?s–1) 0.1341 0.0671 0.0335 0.0268
Dlam/(10–3 m2?s–1) 0.2128 0.1064 0.0532 0.0426
Dtur/(10–3 m2?s–1) 0.0214 0.0215 0.0237 0.0254
Deff/(10–3 m2?s–1) 0.2343 0.1279 0.0769 0.0680
Cs,b/(mol?m–3) 4.7020 9.4040 18.8081 23.5101
dp/(10–3 m) 0.0254 0.0254 0.0254 0.0254
at/(m2?mol–1) 1.8289 1.8289 1.8289 1.8289
ε 0.6962 0.6962 0.6962 0.6962
Tab.2  Physical variables used in Eq. (4) for the gasification at different pressures (gasification temperature, 750 °C; carbon conversion, 0.5)
Fig.9  The fitting result of the dimensionless number correlation to the experimental data obtained with various GFVs (■ marks), temperatures (● marks) and pressures (▲ marks)
Fig.10  The profiles of r(x) r0.5 as a function of carbon conversion obtained with different temperatures (670, 690, 710, 730 and 750 °C), total pressures (0.1, 0.15, 0.2, 0.4 and 0.5 MPa) and GFVs (13.8, 16.5, 19.3, 27.5, 41.3 and 55.0 cm?s–1). Symbols, experiment data; Dash line: fitted result. Note: it could be seen that the relative rate profile overlapped irrespective of these different parameters
Fig.11  The profiles of gasification rate vs. carbon conversion obtained experimentally (marks) and simulated (dash lines) in the presence of mass transfer. (a) With different GFVs (□, 13.8 cm?s–1; ○, 16.5 cm?s–1; △, 19.3 cm?s–1; ▿, 41.3 cm?s–1) at 0.1 MPa and 750 °C; (b) with different temperatures (□, 690 °C; ○, 710 °C; △, 730 °C; ▿, 750 °C) at 0.1 MPa and 13.8 cm?s–1 ; (c) with different pressures (□, 0.1 MPa; ○, 0.2 MPa; △, 0.4 MPa; ▿, 0.5 MPa) at 750 °C and 13.8 cm?s–1
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