Experience of implementation of in-furnace methods of decreasing NO_x in E-320-13.8-560GM boilers: Problems and ways for their solution

During natural gas combustion, the content of nitrogen oxides in combustion products is approximately 450 mg/m³ in many E-320-13.8-560GM boilers in service, which is more than 3.5 times higher than the established maximum NO_x concentrations in flue gases for such boilers. Estimates according to the existing techniques have shown that gas combustion on the basis of in-furnace techniques (the feeding of combustion products to burners together with air in the volume of 15% and two-stage combustion with 20% air feeding through the nozzles upstream of the burners) enables one to decrease NO_x emissions to the level of concentrations of less than 100 mg/m³, which is lower than the maximum allowable values. However, the application of any of the proposed measures with respect to a boiler makes its operation under normal load significantly difficult, since the thermal capacity of the superheater is higher in both cases, which leads to an increase in the temperature of superheated steam above the maximum allowable temperature. On the basis of the developed adapted boiler model, which was created using the Boiler Designer software, we performed numerical studies to determine the required boiler reconstruction volume; the implementation of this reconstruction will provide reliable boiler operation at all working loads and ensure the normative values of NO_x emissions. According to the results of thermal calculations, it was proposed to reduce the surface of the cold stage of the superheater circuit and increase the size of the economizer. It is noted that the implementation of environmental protection measures usually decreases the boiler efficiency. At the same time, it has been established that the technical and economic performance of the E-320-13.8-560GM boiler does not decrease owing to an increase in the economizer surface and a decrease in air inflows and overflows in regenerative air heaters and remains at the same level if the air inflow volume decreases from the available 30 to 20%. The fundamental solutions that were used for the E-320-13.8-560GM boiler to decrease NO_x emissions can also be used for other BKZ gas-and-oil-fired boilers.