Predicting the Conversion Efficiencies of Any Coal Type in CFBCs

Abstract

This study uses simulations with detailed chemistry to characterize the conversion of the various fuel components—noncondensable gas mixtures, soot, char fines, and coarse char—and to identify the factors that determine unburned carbon emissions (a.k.a. LOI) from CFBCs. It covers virtually the entire operating domain for commercial CFBCs with 20 test cases in 11 full-scale CFBCs for a range of coal quality from brown coals through anthracite. Soot burnout was complete for all cases except one. LOI was entirely determined by incomplete burnout of coarse char particles, except that an anthracite produced fines that burned slower than coarse char. Simulations for a Chinese CFBC accurately depicted how hotter furnace temperatures and load variations affect LOI. The intrinsic char oxidation reactivity determines whether or not char fines and coarse char can effectively compete with noncondensable fuel mixtures for the available O2 at lower elevations, and thereby influence NO production. More reactive chars co...