Field Evaluation of Low-Emission Coal Burner Technology on Utility Boilers. Volume 4. Alternative Concepts for SOx, NOx, and Particulate Emissions Control from a Fuel-Rich Precombustor

摘要

The report gives results of a study of the use of precombustors for the simultaneous control of SO2, NOx, and ash emissions from coal combustion. In Phase 1, exploratory testing was conducted on a small pilot scale--293 kW (million Btu/hr)--pulverized-coal-fired precombustor to identify critical operating parameters. The results from this testing raised several questions regarding the viability of controlling SO2 emissions by injecting calcium-based sorbent materials, under conditions simultaneously conducive to NOx control, and to the rejection of coal ash as a molten slag. In Phase 2, key elements of the sulfur capture process, under the fuel-rich precombustor conditions necessary to control NOx formation, were investigated. Detailed experimental studies were conducted at bench and laboratory scales to investigate the formation of stable sulfides in the entrained flow region of a precombustor, using calcium-based sorbents; study the evolution of sulfur from coal under entrained flow combustion conditions; and investigate the stability of sulfur species in molten slag layers. Study results indicated that the sulfidation reactions between CaO and H2S or COS are fast and, under optimum conditions, can remove a high fraction of the gas-phase sulfur species in a fuel-rich precombustor.