Experimental Study on Combustion Characteristics of Pulverized Coal Based on Partial Gasification of Circulating Fluidized Bed

Abstract

How to reduce nitrogen oxides in coal combustion process has always been a hot and difficult topic in the research process. In this paper, under the condition of circulating fluidized bed air equivalence ratio of 0.61 and gasification temperature of 970 °C, the partial gasification and combustion method is used to study the influence of the secondary air distribution modes on the gasification and combustion characteristics. Three aspects are discussed in this test: partial gasification characteristics, combustion characteristics, and coal-nitrogen migration and transformation characteristics. The experimental results show that under partial gasification conditions of the circulating fluidized bed, nearly 87% of the fuel nitrogen at the outlet of the circulating fluidized bed is converted into nitrogen in the coal gas, and the ratio of fuel nitrogen to N₂ is about 64.11%, the conversion rate of HCN is about twice that of NH₃, and the combustion reactivity of partial gasification fuels increased at the outlet of circulated fluidized bed. Different secondary air distribution modes will affect the combustion process and the temperature distribution of the combustion chamber. When the secondary air is mixed with the high-temperature coal-based fuel in advance, the entire combustion reaction and the maximum temperature point in the combustion chamber will be moved up. When secondary air is injected simultaneously with high-temperature coal-based fuels, NOₓ emissions are approximately 90 mg/m³ (@6% O₂), the conversion rate of fuel nitrogen to NOₓ is 2.09%, and when nearly half or all of the secondary air is directly premixed into the high-temperature coal-based fuel, the NOₓ emissions are about 70 mg/m³ (@6% O₂), the conversion ratio of fuel nitrogen to NOₓ is reduced to about 1.63%.