Boiler Bypass Flue to Adjust Denitration Inlet Flue Temperature Automatic Control System Design and Analysis

Abstract

Under low-load boiler operating conditions, the flue gas temperature at the inlet of the denitration system is lower than the normal working temperature of the catalyst. In order to ensure the reliable input of the denitration system, a bypass flue and an adjustment damper are added to the boiler economizer. Configure control logic and actual debugging to realize automatic control of the inlet temperature of the denitration system, and ensure that the denitration system can be continuously operating when the boiler is running in the 30% -100% load range. At present, environmental protection requirements are getting stricter, almost all the boiler equipment of thermal power plant units have completed the desulfurization, denitration and electrostatic precipitator transformation to meet the pollutant emission standards. The desulfurization and electrostatic precipitator can be used during all load range, however, due to the chemical reaction principle, the denitration system cannot running in low load conditions. In recent years, the flue gas denitration technology widely used in coal-fired power plant boilers is selective catalytic reduction (SCR). Economizer is the last heated surface of the boiler before the air heater, and the purpose is to reduce inlet flue gas temperature of the air preheater and save fuel. The denitration system is arranged between the economizer and the air heater. Generally, the operating temperature of the catalyst used in the selective catalytic reduction reaction is between 300-400°C. The catalyst will not play its due role beyond the temperature range. In the design of conventional boilers, there will be the following problems: when the boiler is operating under high load conditions, the flue gas temperature at the inlet of the denitration system is just within the normal operating range of the catalyst; however, the normal operating temperature of the catalyst cannot be met when the boiler load is low. If the design is changed to increase the flue gas temperature at the inlet of the denitration system to meet the catalyst requirements under low load conditions, the overall flue gas temperature of the boiler will be further increased during high-load operation, resulting in high flue gas temperature, low boiler efficiency and large coal consumption. Therefore, according to the traditional design, the denitration system cannot be put into operation when the boiler is running under low load condition, but this has not been able to meet the requirements of the latest nitrogen oxide emission index. In order to solve the contradiction that the flue gas temperature at the inlet of the denitration system at low load does not meet the working conditions of the catalyst, the