Study On Combustion And NO_x Formation Characteristics Of Chain Boiler In The Condition Of Flue Gas Recirculation

Coal-fired industrial boilers account for 80% of the total amount in China; chain boiler is the main form of industrial boilers, which is characterized by a wide range of utilization and difficulties in tackling with emitted pollutant. Therefore, cost-effective reduction of NO_x from chain boilers is important. Flue gas recirculation is an effective low-NO_x combustion technology.However, the literature does not contain any specific parameters about the chain boiler using flue gas recirculation. So the research of flue gas recirculation impacting on the in-furnace combustion process of chain boiler is necessary.This article use standard gas to simulates cycle gas. The chain boiler combustion process is divided into volatilization zone, main combustion zone, coke combustion zone and burn-out zone. In the unit-boiler experimental bench, we research the impact of flue gas recirculation on the coal combustion features and NO_x emission features in these zones, and then figure out the best operating parameters of flue gas recirculation in this experimental condition.At first, this article research the coal combustion process in the condition of taking the procedure of flue gas recirculation in all zones. We focus on the impact of flue gas recirculation on coal surface temperature, concentration of each gas component(especially NO), coal consumption and NO emission to per gram of consumed coal. The results show that if the flue gas was sent in volatilization zone, the curve of coal surface temperature will move backward; coal fire was delayed; the turning point of fire disappeared. When the flue gas recirculation rate is 20%, NO emission to per gram of consumed coal is facilitated, with a proportion of 41.8% decreased.Then, still in the unit-boiler experimental bench, we research the influence of local flue gas recirculation on the coal combustion process. By comparing the coal consumption and NO emission to per gram of consumed coal, we believe that 20% flue gas recirculation rate is the optimal operating parameters in this experimental condition. It can not only effectively reduce loss of incomplete combustion of solid, but also achieve the purpose of NO reduction.This work provides the theoretical and experiment foundation for exploring a real effective method of low NO_x combustion for industrial boilers. The optimized operational paramters could offer valuable consultant for technological implementation.