Indian Journal of Science and Technology

Abstract

Objectives: This paper deals with the theoretical and numerical analysis of a convective recuperator used to recover waste heat from the stack flue gases and use it to pre heat the air before it is fed into the combustion chamber of an oil fired water tube boiler. Methods/Statistical Analysis: Three different tube diameters are considered in the present study. Theoretical analysis is carried out to determine the efficiency and other parameters of the boiler with and without recuperator. To support the theoretically obtained results on improved boiler performance by pre heating the air using recuperator, numerical simulation studies is carried out. Findings: The study showed that 10” inch (0.254 m) pipe diameter arranged in a 3 x 3 array gave a flow velocity of air at around 15 to 25 m/s. The stack flue gas exit temperature decreased from 200o C to 135.50o C whereas the inlet air temperature after pre heating through the recuperator is found to be 85o C with a rise in temperature of around 50o C. After pre heating the air, the efficiency of the boiler improved from 71.90% to 74.60%. The quantity of furnace oil saved per day is 3.76% with respect to its present consumption level. CFD simulations are carried out using ANSYS CFX. A good agreement is found between the data obtained from simulation and theoretical analysis. Payback period by incorporating the recuperator to the existing boiler is estimated to be 60 working days. Application/ Improvements: Optimized performance improvement of existing boiler used in industries is possible without extensive redesign by recovering waste heat leading to energy conservation.

Keywords: Air, Boiler, Convective Recuperator, Flue Gas, Performance, Pre Heat