Identification of combustion losses and air flow control in power plants burning inhomogeneous fuels

Abstract

Combustion air flow control has a strong effect on the efficiency of a power plant. When using homogeneous fuels such as oil and natural gas the control can be based on an assumption that certain volumetric or mass flow of the fuel needs always a certain air flow for complete combustion. But with inhomogeneous fuels and in multi-fuel boilers this assumption is not relevant. For example composition, density and moisture of peat vary considerably and the combustion air flow cannot be fixed on the basis of fuel flow only. A common strategy is to use measurements of steam flow or pressure and of flue gas oxygen content as feedback information for air flow control. In this paper we will discuss new possibilities to solve the problem. Using a sensitive CO-measurement we can identify CO-loss curve and when we know both CO- and heat losses as functions of O2-content we can determine optimum combustion air flow on-line. The losses and the optimum depend on the boiler load, the fuel proportions, the burner conditions, etc.