A Model for Combustion Losses in a Pulverized Fuel Fired Power Plant Boiler

Abstract

A model for the estimation of combustion losses in a pulverized fuel power plant boiler is presented. The model is based on the formulation of a probability density function which relates the probability of a fuel particle remaining unburnt to the combustion and resident times. An empirical model is also presented which relates the unburnt carbon loss to average particle size and excess air. The two models are shown to be in close agreement with each other. The models are validated from the experiments on a power plant boiler. The dependence of boiler efficiency on particle size and excess air is also examined and an empirical correlation between optimum excess air and particle size is derived. The mechanism of two-way coupling between boiler and turbine side parameters is also illustrated. It has been shown that the optimum excess air levels for maxima in plant heat rate and boiler efficiency are not the same, since the two-way coupling influences both the turbine heat rate and boiler efficiency. The effect of two-way coupling has been found to be more predominant for particle sizes of the order of 200 μm.