NO Emission and Burnout Characteristic in Combustion of Coal Gasification Fine Slag with Preheating Technology

Abstract

ABSTRACT Medium-temperature (850 ~ 1000°C) preheating technology has proven to burn coal gasification fine slag (CGFS) steadily. However, the potential of further de-NO x and improving burnout at high preheating temperature (>1000°C) has not been reported. Likewise, the feasibility of preheating treatment at low temperature (<800°C) has also not been verified. Aiming to better understand the influence of preheating treatment on disposing CGFS, the preheating technology with a wider range of preheating temperature (600 ~ 1400°C) was tested on a two-stage drop-tube furnace system in this study. The effects of preheating temperature (Tp), O2 concentration at the outlet of system (O2outlet) and the excess air ratio in preheating zone (λ1) on NO emission and burnout were investigated. Our results showed that by increasing Tp above 1000°C and maintaining O2outlet concentration above 4%, the combustion of CGFS could achieve both low NO emission and high combustion efficiency. A critical preheating temperature of CGFS was obtained to be 600°C. Under this condition, the conversion ratios of C and N were extremely low in the preheating process, and the final NO emission hardly changed with λ1. Under pyrolysis condition (λ1 = 0), Tp should increase to 1400°C for achieving satisfying reduction of NO emission. λ1 had a positive effect on the reduction of NO emission as Tp was above 800°C. By controlling Tp to 1200°C and λ1 to 0.6, 39.2% of fuel nitrogen could be converted to gaseous nitrogen, in which the portion of N2 was 56.1%. Compared with coal, N-containing species in syngas of CGFS were mainly composed of NO, NO2 and N2. Finally, application prospect in the combustion of CGFS using a burner based on the idea of preheating is provided.