Heat transfer studies at different speeds and loads of regenerative air preheater in thermal power plant

Abstract

Regenerative air preheater is one of the largest heat recovery systems in thermal power plants. There are various factors, which determine the heat transfer rate in regenerative air preheaters (RAPH) such as, material of heating elements, temperature difference between air and flue gas, quantity of flue gas, amount of air passing through the RAPH and its rotational speed. In all power plants, RAPH is designed to operate at constant speed where the maximum heat transfer is achieved in full load operation. The rate of heat transferred to the air is compared at different loads and speeds of the RAPH and the optimum speed at which maximum heat transfer rate occurs is found in this experimental study. Speed is varied using a Variable Frequency Drive (VFD) power supply to the RAPH motors. Based on the study, it is inferred that the optimum speed varies with load of the power plant. A cost benefit analysis is also carried out, which clearly indicates that more amount of energy could be conserved by operating the RAPH at various speeds rather than at constant speed.