1998 Volume 77 Issue 8 Pages 785-792
The reactivity of entrained coal char is an important issue for improving total efficiency of the entrained bed gasifier by recycling cyclone captured char. This study aims to elucidate the differences of reactivities among chars that have different heating history. Four kinds of coals were used for the experiments. Char samples were collected by cyclone in the 3 ton/day bench scale entrained bed gasifier. In addition, carbonized char samples were prepared in the batch reactor to compare with reactivities of entrained chars.
The differences of reactivities among char samples - were successfully correlated with the difference of numbers of active site. The effects of pressure and temperature were also investigated. The dependency of reaction rate constants on pressure was proportional to 1/4 power of total pressure at 1270 K. The pressure dependence on reactivities was not observed under the conditions of pressure over 1.6 MPa at the higher temperature as 1570 K. This may be caused by the reaction limiting step change from reaction control to diffusion control.
The experimental results show that the entrained chars have the higher reactivities than carbonized char. This suggests that the entrained char recycle to the gasifier is beneficial to improve total efficiency of gasifier.