Shohei Takeda

PERFORMANCE OF A PRESSURIZED TWO-STAGE FLUIDIZED GASIFICATION PROCESS FOR PRODUCTION OF LOW-BTU GAS FROM COAL CHAR

A two-stage pressurized fluidized-bed gasification process has been developed to produce low-heating value gases from coal char. The reactor was 0.075 m id. and 1.4 m long, and gasification experiments were conducted under pressures up to 790 kPa and at temperatures up to 1323 K. A partition disc was used to divide the fluidized bed into two stages, using the first stage as a partial combuster and gasifier and the second stage as a gasifier. The disc was designed to control compositions of coal char particles in both stages so that the heat required for the endothermic gasification reaction in the second stage can be provided by the heat of combustion in the first For conditions examined here, the disc with an opening ratio of 40° was found to give optimum distribution of the char particles in both stages without ash agglomeration. It was also shown that all oxygen gas was completely consumed within the first stage The heating value of the product gas increased with the char feed rale. However, there may ...

Thermal behavior of coal-derived asphaltenes

Abstract Thermal behaviour of coal-derived asphaltenes was investigated under atmospheric pressure by thermogravimetry (TG). The weight loss is rapid from 300 to 500°C and is slow above 500°C. The asphaltene comparatively low in molecular weight shows the greater weight loss. The temperature at which the differential thermogravimetry peak appears, T m , correlates to the asphaltene aromaticity: the asphaltene comparatively high in aromaticity shows higher T m . Of the residual asphaltene after heating up to 600°C, the obtained crystallite thickness through the c -axis direction ( Lc 002 ) has a correlation with the molecular weight of the parent asphaltene: the parent asphaltene comparatively low in molecular weight produces residual asphaltene of larger Lc 002 .

Gasification of hybrid particles of gasification and liquefaction residue of coal.

Hybrid particles of coal ash from gasifier and higher viscous residue and solid pitch from coal liquefaction were successfully produced by two new methods. They were then gasified by steam and oxygen in a fluidized bed under atmospheric pressure. Gasification characteristics of these particles, such as the distribution and yield of gas produced and the carbon conversion, were evaluated as a function of operating variables.

Tar yield in fluidized bed coal gasifier.

Tar yielded in a fluidized bed coal gasifier was analyzed. Taiheiyo coal of size 0.64 and 1.00mm was fed continuously to a 0.083 m diameter fluidized bed and gasified using mixtures of steam and air.Tar Quantity in produced gas decreased rapidly as the bed temperature became higher. Molecular weight of tar became smaller and ratio of methane and ethane in produced gas increased at higher temperature. Tar yield decreased as the tempera-ture of freeboard region just above the bed became higher. But the gas residence time in freeboard region had no effects upon tar yield.

Reactivity of Coal Char with Steam and Carbon Dioxide

To develop a simulation-model of the Hokkaishi-coal gasification pilot plant, a kinetic analysis of coal-char gasification was investigated. Experiments were conducted on the elementary reaction of C-CO2 and C-H2O.Taiheiyo char pre-treated at 600°C same as fed-char into the pilot plant was used as the test samples. Samples were gasified in a 28 mmφ small batch type fluidized bed reactor made of quartz.Reaction rate of the carbon was determined from the observed data of the produced gas.Both reaction processes of C-H2O and C-CO2 were predicted considerably well by a modified mathematical model of unreacted core, namely the rate constant of intraparticle diffusion was corrected dividing by square of unreacted carbon conversion.The activation energy of the C-H2O reaction was 31.2 kcal/mole and 38.5 kcal/mole for the intraparticle diffusion and interfacial reaction respectively. And also, the activa-tion energy of the C-CO2 reaction were 94.5 kcal/mole, and 44.1 kcal/mole respectively.From the results of measured values dx/dt, it was confirmed that the C-H2O reaction processed superiorly as compared with the C-CO2 reaction.