Theoretical Method for Evaluating the Heat of Combustion of Sewage Sludge in the Lack of Air

Abstract

A procedure based on the modification of the Mendeleev formula and the calculation of chemical equilibrium in an initial mixture is proposed for estimating the heat of combustion of sewage sludge (SWS) under conditions of lack of air. The equilibrium composition of a mixture is proposed to be calculated on the basis of applied programs or chemical equilibrium equations. For the second method, the initial equations and methods for their solution are given. Thus, two cases are considered. The first case is the absence of carbon from the equilibrium mixture and the second is the presence of carbon in the equilibrium mixture. A procedure is proposed for calculating an air deficiency coefficient at which carbon begins to appear in an equilibrium mixture. Test calculations were carried out for dry and wet SWS at a combustion temperature of 700°C using the NASA program and based on chemical equilibrium equations. A comparison between the calculation results obtained by both methods showed satisfactory agreement. For illustration, the calorific value of SWS was calculated at 700°C and an air deficiency coefficient of 0.5–1. The procedure can be used for fuels in which the contribution of sulfur to the heat of combustion of the fuel can be neglected.