Effect of pressure on gasification reactivity of three Chinese coals with different ranks

Abstract

The gasification reactivities of three kinds of different coal ranks (Huolinhe lignite, Shenmu bituminous coal, and Jincheng anthracite) with CO₂ and H₂O was carried out on a self-made pressurized fixed-bed reactor at increased pressures (up to 1.0 MPa). The physicochemical characteristics of the chars at various levels of carbon conversion were studied via scanning electron microscopy (SEM), X-ray diffraction (XRD), and BET surface area. Results show that the char gasification reactivity increases with increasing partial pressure. The gasification reaction is controlled by pore diffusion, the rate decreases with increasing total system pressure, and under chemical kinetic control there is no pressure dependence. In general, gasification rates decrease for coals of progressively higher rank. The experimental results could be well described by the shrinking core model for three chars during steam and CO₂ gasification. The values of reaction order n with steam were 0.49, 0.46, 0.43, respectively. Meanwhile, the values of reaction order n with CO₂ were 0.31, 0.28, 0.26, respectively. With the coal rank increasing, the pressure order m is higher, the activation energies increase slightly with steam, and the activation energy with CO₂ increases noticeably. As the carbon conversion increases, the degree of graphitization is enhanced. The surface area of the gasified char increases rapidly with the progress of gasification and peaks at about 40% of char gasification.

Keywords

coal / gasification / pressure / reaction order / shrinking core model

References

[1] Kajitani S, Suzuki N, Ashizawa M, Hara S. CO₂ gasification rate analysis of coal char in entrained flow coal gasifier. Fuel, 2006, 85(2): 163-169

[2] Huang J J, Fang Y T, Chen H S, Wang Y. Coal gasification characteristic in a pressurized fluidized bed. Energy & Fuels, 2003, 17(6): 1474-1479

[3] Liu G, Tate A G, Bryant G W, Wall T F. Mathematical modeling of coal char reactivity with CO₂ at high pressures and temperatures. Fuel, 2000, 79(10): 1145-1154

[4] Kajitani S, Hara S, Matsuda H. Gasification rate analysis of coal char with a pressurized drop tube furnace. Fuel, 2002, 81(5): 539-546

[5] Muhlen H J, van Heek K H, Juntgen H. Influence of pretreatment temperature and pressure on the char reactivity during hydrogasification. Fuel, 1986, 65(4): 591-593

[6] Li S, Xiao X. Influence of pretreatment temperature and pressure on the char reactivity during hydrogasification. Fuel, 1993, 72: 1351-1353

[7] Li S, Sun R. Kinetic studies of a lignite char pressurized gasification with CO₂, H₂ and steam. Fuel, 1994, 73(3): 413-416

[8] Bhatia K S, Perlmutter S D. A random pore model for fluid-solid reactions. I. Isothermal kinetic control. American Institute of Chemical Engineers, 1980, 26(3): 379-386

[9] Liu G S, Niksa S. Coal conversion submodels for design applications at elevated pressures. Part II. Char gasification. Progress in Energy and Combustion Science, 2004, 30(6): 679-717

[10] Li C Y, Zhao J T, Fang Y T, Wang Y. Pressurized fast-pyrolysis characteristics of typical Chinese coals with different ranks. Energy & Fuels, 2009, 23(10): 5099-5105

[11] Zhang L X, Huang J J, Fang Y T, Wang Y. Gasification reactivity and kinetics of typical Chinese anthracite chars with steam and CO₂. Energy & Fuels, 2006, 20(3): 1201-1210

[12] Ahn D H, Gibbs B M, Ko K H, Kim J J. Gasification kinetics of an Indonesian subbituminous coal char with CO₂ at elevated pressure. Fuel, 2001, 80(11): 1651-1658

[13] Linares-Solano A, Mahajan O P, Walker P Jr. Reactivity of heat-treated coals in steam. Fuel, 1979, 58(5): 327-332

[14] Liu T F, Fang Y T, Wang Y. An experimental investigation into the gasification reactivity of chars prepared at high temperatures. Fuel, 2008, 87(4-5): 460-466

[15] JÜntgen H. Reactivities of carbon to steam and hydrogen and applications to technical gasification processes—A review. Carbon, 1981, 19(3): 167-173

[16] Goyal A, Zabransky R F, Rehmat A. Gasification kinetics of Western Kentucky bituminous coal char. Industrial & Engineering Chemistry Research, 1989, 28(12): 1767-1778

[17] Jones R B, Mccourt C B, Morley C, King K. Maceral and rank influences on the morphology of coal char. Fuel, 1985, 64(10): 1460-1467

[18] Hurt R H, Davis K A, Yang N Y C, Headley T J, Mitchell G D. Residual carbon from pulverized-coal-fired boilers. 2. Morphology and physicochemical properties. Fuel, 1995, 74(9): 1297-1306

[19] Sadhukhan A K, Gupta P, Saha R K. Characterization of porous structure of coal char from a single devolatilized coal particle: Coal combustion in a fluidized bed. Fuel Processing Technology, 2009, 90(5): 692-700

Acknowledgments

This work was supported by the Major State Basic Research Development Program of China (973 Program, Grant No. 2006JQJ11131) , the National High-Tech R&D program of China (863 program, No.2008AA050302).

RIGHTS & PERMISSIONS

2014 Higher Education Press and Springer-Verlag Berlin Heidelberg