Gasification characteristics of different coal chars in 1t/d continuous pressurized fluidized-bed gasifier.

Gasification experiments of four different kinds of coal chars by air-steam or air-oxygen-steam mixture gases were carried out in a 1t/d continuous pressurized fluidized-bed gasifier in a range of temperature of 1150 to 1320K and total pressure of 0.6 to 1.9MPa. From observed exit gas composition, gasification characteristics were evaluated in terms of the carbon conversion, carbon and cold gasification efficiencies and the steam conversion as well as the char conversion. The surface area and the demineralized carbon structure of particles discharged through the overflow pipe and collected by the cyclone were analyzed at different char conversion levels and were compared with those reported in our previous paper of batch experiments.Though all above gasification characteristics depended on the char reactivity, a certain relationship was found between the gasification efficiency, HC, and the carbon conversion, CC. The former increased in proportion to CC and reached about 0.75 at complete carbon gasification, i.e. CC=1, and this result was affected neither by the nature of char nor the gasification temperature. For all chars, gasification was fairly rapid during the initial stage of gasification, giving a rate greater than that of batch steam gasification due to contribution of the char combustion in the former. The rate decreased with the mean residence time of char particles for the char conversions higher than 0.8 to 0.9.For each char, the surface area depended on the char conversion and its variation was shown to be identical to those observed in our previous batch steam gasification. The (002) peak due to graphite structure was observed to grow in the X-ray diffraction spectra of overflow particles, corresponding well to the decrease of the gasification rate towards completion of gasification.