Cost based optimization of excess air for fuel oil/gas-fired steam boilers

Computational method of determining an optimal value of excess air needed for firing fuel oil (or gaseous fuel) in a steam boiler is presented. The method is based on a cost approach aimed at minimizing the total expenses which include both (a) "internal costs" associated with incomplete combustion, unburned carbon, and heat loss with waste flue gas, and (b) "external costs" caused by emission of NOx and SOx and other gaseous and particulate effluents from the boiler into the environment. Mathematical models for predicting the relevant heat losses, and also for estimation of NOx and SOx emission in a fuel-oil-fired / gas-fired furnace are presented. Some case studies concerned firing fuel oil in a steam boiler under various operating conditions have been considered.