THERMAL ASPECTS OF HEATING BOILER PLANTS OPERATION WITH HEAT-RECOVERY AND EXHAUST GAS RECIRCULATION

Abstract

The feature analysis of application for heating boiler plants of relatively small heating capacity, which are not equipped with air heaters, of the method of reducing the emission of nitrogen oxides due to decrease the temperature in the boiler furnace by recirculating exhaust gases into the blown air are presented. At the same time, heating gas-consuming boiler plants with traditional heat recovery systems of exhaust gases and implementation of this method with the selection of recycled gases after the boiler and heat-recovery exchanger are considered. The study results for a water-heating boiler with a heating capacity of 2 MW of the change regularities of the combustion temperature in the boiler furnace, the its exhaust gases temperature and water heated in the boiler as well as the boiler efficiency, depending on its relative heat load changed (from 30 to 100%) and with different parts of recirculated gases (from 10 to 20%) in the mixture with the blown air are presented. The studies were performed with and without them recirculation and heat recovery of flue gases. The research results show that the use of waste gas recirculation causes a noticeable decrease (by 150 – 250°C) in the combustion adiabatic temperature and a slight (by 0.5 – 4.7°C) decrease in the boiler waste gases temperature. Recirculation also leads to a decrease in boiler efficiency by 1.3 – 3.1% during the heating period, and the use of the considered heat recovery system of boiler waste gases with heating of return heat-network water by cooling them provides an increase in boiler efficiency by 2.5 – 8.1%. The resulting increase in boiler efficiency with a heat recovery and recirculation system is 0.1–4.8%.