The effects of different airflows on the formation of pollutants during waste incineration

Abstract

An experimental study has been conducted with a fixed bed reactor to simulate, in a laboratory scale, industrial municipal waste incineration using moving grates. Carbon monoxide, nitrogen oxide and temperature measurements have been used to establish the importance of the operating parameters of a municipal waste incinerator in the characteristics of the combustion process. The observation of the different combustion regimes established has served to show the potential impact of the operating conditions on the yields of carbon monoxide and nitrogen oxide. Two different regimes have been identified and that are controlled by the airflow through the fuel (primary airflow). For primary airflows below the stoichiometric requirement an oxygen deficient combustion regime is established within the porous matrix. This regime is characterized by low reaction temperatures, favors endothermic pyrolysis and greatly enhances the production of CO. Within this regime, an increase in primary airflow will result in a decrease in CO yield. For airflows above the stoichiometric requirement the reaction establishes above the fuel, the temperature increases and the CO yield increases weakly with the total airflow rate. The introduction of a secondary airflow downstream of the fuel degradation region results in better mixing and an increase in the reaction temperature. As the secondary air increases the enhancement of mixing becomes less important and fuel dilution leads to a reduction of the temperature. The present experimental results show that the production of NO seems to be controlled only by the oxygen concentration in the secondary zone of combustion. An increase in total airflow, thus, results in an increase in the yield of NO.