Design optimization of a large municipal solid waste incinerator

Abstract

This paper discusses a number of design modifications and changes in operational conditions which have a major influence on the overall performance of the large Sheffield municipal solid waste incinerator plant (30 MW) which incorporates a heat recovery system for district heating. The effect of installing four different baffle configurations inside the radiation shaft and various primary and secondary air distribution patterns have been investigated using mathematical modelling, in attempt to eliminate the existing recirculation zone inside the shaft and at the same time obtain optimum combustion conditions which would minimize the emission of pollutants and reduce maintenance costs at the plant. A mathematical model of the finite difference type was employed to predict the three dimensional reacting flows within these modified incinerator designs. The κ - ε submodel has been employed for turbulence, together with a combustion model of the Magnussen type. A Lagrangian model was used to estimate the residence times for different cases. The results obtained from the modelling work demonstrate that the suggested modified design produces longer residence times in the incinerator, improves the temperature profile at the exit, reduces the concentration of products of incomplete combustion and increases the overall boiler efficiency by nearly 8%. Using these modelling results a preliminary economic assessment of the potential benefits of the suggested modified incinerator design compared to the original design has been made assuming the energy recovered is sold as steam. The calculation indicated that because of significant savings in running and maintenance costs, an 18% reduction in net waste disposal cost may be achieved.