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Gasification of a char has so far been mainly studied at low temperatures and low heating rates with a TGA (thermogravimetric analyzer). Studies on gasification of a char in CO 2 at elevated temperatures and high heating rates are necessary to develop IGCC technology. With a unique fluidized bed, the effect of pyrolysis time on char reactivity was investigated. It was found that a longer pyrolysis time led to lower reactivity of a char, while this effect leveled off as pyrolysis time increased. The pyrolysis time also had an influence on the temperature dependence of gasification reactivity. Initial char gasification rate decreased as pyrolysis time increased. The pyrolysis time had effect on the entire process of char gasification. The effect of pyrolysis time was more remarkable for a coal with high volatile matter content among the three coals tested. The gasification rate of a char was very different from that of a raw coal (gasification without pyrolysis in advance), which suggested an influence of pyrolysis time and atmosphere on char reactivity. Accordingly, those results obtained from a TGA are necessary to be corrected when applied to a practical entrained flow gasifier.

Studies of the gasification of char in CO 2 at elevated temperatures are necessary for the development of IGCC technology. Experiments at high heating rates and elevated temperatures revealed that the temperature dependence of gasification reactivity was very different for low compared with high temperature ranges. To elucidate these mechanisms, the reaction of mineral matter and the change in morphology during gasification of a char at elevated temperatures were examined by char characterisation. CO 2 gasification experiments showed a large difference in gasification rate for chars prepared at higher temperatures compared to those prepared at lower temperatures. Changes in char particle morphology and mineral matter during gasification are also quite different. At higher carbonisation temperatures, mineral reactions during pyrolysis, which occurs in addition to ash fusion, appear to be one of the factors accounting for these differences. Certainly, a change of mechanism is involved. Graphite enrichment may also contribute to the decrease in char reactivity.

Gasification kinetics of char is thought as a key factor in designing and operating gasifiers. The widely used present technique, TGA method, is limited in temperature and heating rate ranges. A fluidized bed reactor (FBR) method is described which is suitable for measuring char reactivity at elevated temperatures up to 1873 K by using CO 2 as the gasifying agent. It is capable of carbonizing coal samples under various conditions including rapid heating as well as slow heating, and in-situ measuring char gasification rate directly after carbonization. Char reactivity is evaluated from the time variation of CO concentration in the exit gas. The heterogeneous global model, incorporated with the two-phase model, is used to describe the reaction of chars. On the basis of the model, the film mass transfer resistance and the bubble-emulsion mass transfer resistance are calculated and their influence on the measured results is assessed. Proper selection of operating parameters for assuring reasonable measurement is discussed. Data processing methods have been developed to give fundamental, quantitative measurements of char reactivity, allowing direct comparison of reactivity between chars.

A numerical simulation study was conducted for a jetting fluidized bed coal gasifier with a conical distributor. It was based on a steady-state model which took account of hydrodynamics, mass heat transfer and reactions in the grid zone, bubble zone and freeboard zone of the gasifier. Temperature of the particles and gas in the jet, compositions in the dilute phase and the dense phase, and some hydrodynamic characteristics were calculated. Effects of some operating conditions such as oxygen and steam flow rates, bed temperature and bed pressure on the temperatures in the jet and gas compositions in the gasifier were numerically investigated.