A Study on the Secondary Air Injection Method of the Combustor Considering Characteristics of Solid Refuse Fuels

This study used a numerical simulation method to design a grate-type combustion boiler for solid refuse fuel (SRF). First, proximate analysis, ultimate analysis, calorific value measurement, and combustion characteristic tests such as thermogravimetric analysis (TGA) and differential thermogravimetric analysis (DTG) were carried out to investigate the combustion characteristics of SRFs and municipal solid waste. To design an optimal SRF combustion steam boiler, the flow field, temperature distribution, chemical species concentration with varying secondary air injection angles and air ratios of the combustor need to be predicted. The secondary air injection angle affects fly ash generation on the grate, and the Cl compound in fly ash promotes high temperature corrosion in the superheater and heat exchanger of the boiler. The low heating values of two types of domestic waste are 13,062 kJ/kg and 14,402 kJ/kg, respectively, and that of fluff and densified SRFs are 19,552 kJ/kg and 29,014 kJ/kg, respectively. The concentration of Cl in densified SRF is 1.80 wt% and that of domestic waste and fluff SRF is 0.50 wt% or lower. The results of the TGA and DTG analyses reveal that the SRFs and domestic wastes complete their reactions at 500 °C or lower and at 540 °C, respectively. According to the numerical calculation results, it is optimal to inject the secondary air normally from the walls to suppress fly ash at the grate in the SRF combustor. Furthermore, an air ratio of 1.87 is recommended for stable combustion and prevention of high temperature corrosion on the walls of the heat exchanger tube. Graphic Abstract Contours of temperature in combustor for SRF-B (°K)