Heat transfer characteristics of a heat-recovery boiler built based on a modular mini boiler

The objective of this study is to design a heat-recovery boiler for a 1 MW-class gas engine-based cogeneration system intended to recover heat from engine exhaust gas. To accommodate high-pressure applications, a water tube-type boiler is selected. For ensuring effective water circulation within the boiler, an innovative modular-type boiler based on the mini-boiler concept is developed. This boiler comprises finned tube-type risers, and their heat-transfer characteristics are measured and compared with the conventional correlation used in the design process. Additionally, an inlet guide vane is developed to address the temperature nonuniformity resulting from the shape mismatch between the gas engine outlet and heat-recovery boiler inlet. The performance of the proposed boiler was evaluated by integrating it into an experimental rig. The diamond-shaped inlet guide vane, which was designed by computational fluid dynamics, facilitated a uniform temperature distribution. However, the temperature became nonuniform downstream owing to the influence of a downcomer. Although the modular heat-recovery boiler effectively produced steam from gas engine exhaust gasses, its heat-transfer performance in the downstream section was lower than expected, necessitating additional heat-transfer area.