Studies on coal devolatilization and char reactivity under PFBC conditions. Final report.

摘要

A fundamental combustion study was performed at Babcock and Wilcox's Alliance Research Center to characterize the combustion properties of Pittsburgh No. 8 and Texas lignite coals under conditions simulating pressurized fluidized-bed combustion (PFBC) using a bench-scale reactor. Over 400 combustion tests were performed at temperatures ranging from 1425(degree) to 1,725(degree)F, a maximum pressure of 280 psig, maximum superficial gas velocities of approximately 5 ft/sec to 20 ft/sec, and several oxygen concentrations using six coal particle sizes. A database of combustion profiles at PFBC conditions was obtained. A fundamental model of the chemical kinetics of the coal combustion at elevated pressures was developed based on this database. The kinetic models were used to derive the rate constants and activation energies of coal combustion for the two coals. For coal devolatilization, the effects of each test variable on the rate of reaction, the volatile yield, and the reaction order were evaluated. The apparent orders of coal devolatilization for Pittsburgh No. 8 and Texas lignite coals were determined to be less than one and vary with coal properties and test conditions. For char oxidation, the rates were reported as apparent kinetic rates and were derived based on the information which was obtained at the early stage of char oxidation. The kinetic rate constant of Pittsburgh No. 8 coal was found to be insensitive to the tested particle sizes. Increasing temperature, pressure, and superficial gas velocity increased the kinetic rate constant. The kinetic rate constant of Texas lignite coal was found to be approximately 2.5 times that of Pittsburgh No. 8 coal. The kinetic data obtained from this study in the low-temperature range was comparable to those reported by others in the literature. 40 refs., 37 figs., 15 tabs.