Application of absorption heat pump and direct-contact total heat exchanger to advanced-recovery flue-gas waste heat for gas boiler

Abstract

This paper presents a new technology based on a direct-fired absorption heat pump and a direct-contact total heat exchanger. An analysis of existing techniques for heat recovery shows that the limiting factors of condensing heat recovery are return-water temperature and the ability of air to recover heat. In addition, severe corrosion usually exists in indirect-contact heat exchangers where the flue gas and cool water flow. This new technology solves these problems. A 29-MW gas boiler was transformed by the new technology, having been tested throughout an entire heating season. As a result, the exhaust gas of the direct-contact total heat exchanger decreased to 27.4 °C, with an average COPh and COPove,h of approximately 1.69 and 1.57, respectively. The mean heat recovered was 2.67 MW, yielding a heating efficiency increase of 11.54% and a saving in natural gas consumption of 8.75 × 105 Nm3 per year. Testing showed that the NOx reduction rate was 10.48% and the condensation water flow was 3.11 t/h. Hence, this technology achieved excellent results for both energy conservation and emission reduction, thereby proving the feasibility of its large-scale application.