Design optimization of Coventry municipal solid waste incinerator

This paper discusses a number of design modifications and changes in operational conditions that have a major influence on the overall performance of the large Coventry municipal incinerator plant (65 MW), which incorporates a heat recovery system for district heating. Four different secondary air-injection systems and various primary air-distribution patterns along the grate were investigated using a computational fluid dynamic model, in an attempt to obtain optimum combustion conditions that would minimize potential emissions of toxic pollutants and reduce maintenance costs at the plant. The modeling work showed that the use of four large high-speed secondary air jets firing toward a common center, together with optimizing the primary air distribution along the grate, produces substantially longer residence times and improves temperature profile at the exit. The novel feature of the proposed secondary air-injection system is the formation of a large and significantly strong recirculation zone, located above the burning refuse bed, in the middle of the furnace shaft. This strong recirculation zone improves the overall performance of the incinerator due to intensive mixing of hot gaseous products evolving from the refuse bed with the combustion air supplied as the secondary air, and greatly improves the gas phase combustion and helps to reduce emissions of chlorinated organic compounds. Results obtained clearly demonstrate that the proposed secondary air-injection system has an excellent potential to satisfy most requirements for emissions levels and gas resident times specified by the European Directives (EEC) for municipal incinerators with a vertical radiation shaft.