Analysis of the thermodynamic performance of a waste-heat-recovery boiler with additional water spray onto combustion air stream

This study presents a preliminary thermodynamic research on the development of a new boiler (called a WSWHR boiler), which aims to recover waste heat from an exhaust-gas stream by spraying additional water onto the incoming air stream. In this boiler, the water condensed at the main boiler and the waste-heat-recovery system is reserved in one tank and then recirculated by spraying onto the incoming air during heat recovering process. This new boiler shows no limitation in operation because all the water condensed at the main boiler and the waste-heat exchanger is sprayed onto the incoming-air stream and reacting zone in the combustion chamber. The WSWHR boiler is expected to have an efficiency as high as 92-98% when the boiler outlet temperature is controlled near 50-70 °C. The maximum difference in efficiency occurs near 60 °C in TG-Bo, and its values are about 8% and 6% greater than those of the basic and WHR boilers, respectively. Furthermore, as more water is added onto the incoming air, the NOx emission predicted by simple Chemkin model decreases significantly.