TED-AJ03-143 A UNIQUE MEASUREMENT METHOD FOR GASIFICATION REACTIVITY OF SINGLE CHAR PARTICLES UNDER CONDITION OF ENTRAINED FLOW GASIFIERS

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Integrated coal gasification combined-cycle (IGCC) technology is proposed as one of the promising technologies available to save energy resources and to prevent global warming. As one of the key components included in this process, an entrained flow gasifier has been highlighted in recent years because of its high gasification efficiency and smooth discharge of molten ash. However, the high temperature in an entrained and mechanisms of char gasification from those at a low temperature. Previous research results may not be appropriate for directly application to entrained flow gasification because they were derived at a much lower temperature than in an entrained flow gasifier. Accordingly, the clarification of characteristics and mechanisms of char gasification under conditions close to those in an IGCC system is highly imperative and significant. These factors mean more research is necessary on char gasification at a high heating rate and an elevated temperature. In this work, under conditions close to that in an entrained flow gasifier, we examined the gasification reactivity of a char directly from the change in CO concentration in a uniquely made fluidized bed, which could be operated at a temperature up to 1873 k, in different atmospheres, and within various reaction times. It was able to separate pyrolysis and gasification processes and set pyrolysis time exactly. Moreover, it had the advantages of uniform temperature distribution, stable temperature, changeable pyrolysis time, very high particle-heating rate, in-situ and direct measurement of reaction rate. It was demonstrated that in situ measurement of gasification rate of chars produced under the high heating rate was possible even at elevated temperatures up to 1873K by the bed. It was revealed that even at an elevated temperature, heating rate also had significant influence on char reactivity of gasification. The gasification reactivity of a char at high temperatures was very different from that at low temperatures. To clarify the mechanism of char gasification, investigations through SEM examination, N_2 adsorption analysis, etc. were also conducted. It was clarified that the specific surface area and pore volume of mesopore for chars derived from rapid heating were greater than chars derived from slow heating. The surface of a char pyrolyzed at a low heating rate was smooth, but rough and porous for a char pyrolyzed at a high heating rate, which was pronounced as temperature increased. Moreover, char reactivity was closely related to its specific surface area. These results revealed that it is necessary to derive the gasification kinetics of a char at a high heating rate to obtain valid kinetics for an entrained flow gasifier in an IGCC system. Accordingly, those results obtained from a TGA are necessary to be corrected when applied to a practical entrained flow gasifier in an IGCC system.
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TED-AJ03-143 A UNIQUE MEASUREMENT METHOD FOR GASIFICATION REACTIVITY OF SINGLE CHAR PARTICLES UNDER CONDITION OF ENTRAINED FLOW GASIFIERS

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