Assessment of thermodynamic irreversibility in different zones of a heavy fuel oil fired high pressure boiler

Abstract

This paper presents a comprehensive second law-based thermodynamic analysis of a heavy oil-fired high-pressure boiler used in a steam power plant. The entire boiler region is divided into four zones to determine the magnitudes of energy loss and irreversibility taking place in these zones so that measures may be taken to reduce them. The energy analysis reveals that the maxi- mum loss of combustion energy of the fuel takes place in the last zone where the exhaust gasses leave the chimney and taken away by these gases, whereas the exergy analysis reveals that the irreversibility rate in the first zone, i.e., furnace region, is the highest as compared to that in other zones. In this zone, 29.26 % of the fuel exergy is destroyed, while the energy loss is zero. In the chimney zone, where the energy loss is the maximum, the exergy destruction is just 4.64 %. Therefore, the real loss is actually taking place in the boiler furnace due to the gen- eration of entropy. The chemical reactions between the fuel and air are the main cause of irreversibility. Decreasing either the percentage of excess combustion air or the exhaust gas temperature or both will cause the irre- versibility rate in the furnace to decrease.