Energy & Fuels, Vol.19, No.5, 2006-2013, 2005
Performance of Chinese coals under conditions simulating entrained-flow gasification
A novel, two-stage entrained-flow gasifier is being developed by the Thermal Power Research Institute in China. In the present work, the factors that affect the pyrolysis and gasification reactivity of 14 potential coals for this plant have been studied, under conditions that simulate the temperature, pressure, and particle heating rates in the proposed gasifier. The work was performed using a high-temperature, high-pressure, variable-heating-rate wire-mesh apparatus (2000 degrees C, 3.0 MPa). The trends in reactivity, measured for three of the coals at laboratory scale, and a 20-kg/h (small) pilot plant in China were similar. The use of the wire mesh reactor (WMR), coupled with a residual char reactivity measurement, using a thermogravimetric analyzer, has proved useful in characterizing coals selected for entrained-flow gasification. The data have allowed the comparison of reactivities within the suite of coals. The results showed a general trend of declining reactivity with increasing rank. However, the scatter in the data, as in most such cases, does not allow the construction of simple correlations to help predict the performance of individual coals; therefore, the reactivities of individual coals must be evaluated experimentally, The pilot gasifier that is under construction is intended to achieve almost-complete conversion of the coal injected into both stages. The results suggest that overall conversions in the high-temperature first stage of the reactor will be only marginally sensitive to sample reactivity, However, the second stage of the pilot reactor is expected to give an exit gas temperature of similar to 900 degrees C. It is likely that the reactivity of the coals injected into the second stage will have a greater effect on achieving the desired high conversions, The ash melting temperature and slag Viscosity for the same suite of coals have been assessed using existing mathematical models, which were primarily developed for combustion-based applications. This has shown that the ash,and slag properties will vary widely, depending on the composition of the ash. Unsuccessful attempts were made to measure the viscosity of a slag sample from a pilot-scale gasifier in China under the appropriate conditions. However, the work has highlighted the difficulties involved in making valid measurements for gasifier slags, which should help to guide future work.