A Comparative Study on Performance of Shell-and-Tube and Coil-Tube Economizer for Once-Through Boilers

Abstract

The research was to design and develop shell-and-tube and coil-tube economizers for once-through boiler generating steam with 250 kg/h steam producing rate at 408 kPa pressures. The measured temperature of exhaust gas boiler was 453 K entering the cross-flow economizer used to preheat the feeding water with the heating surface area and tube length of 3.55 m² and 34 m. The research found that the economizer shell and tube exhaust with gas at 7.65 m/s produced the heat transfer coefficients of the tube outer and inner area at 33.42 and 5.71 W/m²K, respectively while the pressure drops for shell and tube were 25.69 and 2.27 Pa. The effectiveness of the economizers was 0.40 and the energy saving cost was 78,600 Baht/year. The payback period is around 2.66 years. When compared the coil tube economizer exhaust gas at 5.33 m/s, the heat transfer coefficient of the tube outer and inner area were 54.42 and 0.89 W/m²K, respectively while the pressure drops for shell and tube were 87.42 and 0.65 Pa. The effectiveness of the economizers was 0.36 and the energy saving cost was 75,300 Baht/year. The payback period is around 2.52 years. The compared shell-and-tube economizer and coil-tube economizer were suitable for once-through boilers generating steam of 500 kg/h rate at pressure steam test of 102-408 kPa.