The Optimisation of Excess Air and Stack Temperature for the Improvement of Thermal Efficiency and Environmental Performance of Steam Boilers

摘要

The study is aimed at assessing the thermal efficiency of a steam boiler by evaluating the stack temperature of the flue gas and excess air quantities in the burner with a view to improving its performance. For this performance determination, characterised fuel gas and fuel oil were used for heat generation. The characterisation of fuel oil and fuel gas was carried out in the laboratory and it helped in the determination of their calorific values. Fuel gas was characterised by gas chromatographic analysis from which its molecular mass was determined. Fuel oil was characterised by determining its sulphur content by x-ray fluorescence while its density was determined by the hydrometer standard method. The performance of the boiler was closely tied to the excess air and stack temperature. A relationship showing efficiency as a function of stack temperature and excess air was established and used to measure the thermal efficiency of the boiler. Results obtained showed that an increase in either excess air or stack temperature lead to a decrease in thermal efficiency.