Performance research and application of the vapor pump boiler equipped with flue gas recirculation system

To improve the boiler thermal efficiency and reduce oxynitride emissions, a novel flue gas waste heat recovery system is proposed. The vapor pump boiler equipped with a flue gas recirculation system is first applied for practical engineering. The oxidizing air is preheated and humidified before the combustion process, which causes the dewpoint temperature of the flue gas to increase. Thus, more waste heat in the flue gas can be recovered by the boiler feedback water. Heat recovery efficiency of the system can reach 82.6%, resulting in a 7-8% increase in the boiler efficiency. In addition, the increases in oxidizing air humidity and flue gas recirculation both reduce oxynitride production. As a result, oxynitride emission decreases from 129 mg/m(3) to 23 mg/m(3), resulting in a reduction of 82.3%. The gas-fired boiler realizes ultra-low oxynitride emission. For a 1.8 MW boiler, annual natural gas consumption can be saved by 7-8%. Given current energy prices in Beijing, the proposed system is economical with a static payback period of 1.2 years. An overall system performance is provided as evidence of the potential benefits. The proposed system is proved to have advantages in energy savings, pollutant reduction, and economic benefits.