Furnaces of the Unified-Family Drum-Type Gas-Fired Boilers

The article deals with supporting calculations of the furnace dimensions and the method for combustion of natural gas for two types of unified-family drum-type boilers with steam capacities of 75–150 and 200–320 t/h at superheat steam pressures of 3.9, 6.9, 9.8, and 13.8 MPa and temperatures of 440, 510, 540, and 560°C. An approach to unification and the requirements of environmental sustainability, economic efficiency, and flexibility and the basic engineering solutions for each boiler type are set forth. A method was proposed and implemented that allows, using the Boiler Designer software, finding the temperatures of the flue gases, hot air, and recycle gases that are necessary for conducting the thermal analysis of the boiler furnace with a single-stage tubular air preheater and determining the most rational unified design of the latter. The basic concepts and criteria are set forth that underlie the calculations of the furnace size in its plan, the furnace height, and the number and arrangement of swirl burners. With the furnace software for expanded thermal analysis of the furnace, the effect of the superheated steam pressure and the furnace height on the enthalpy increment of 1 kg of the working medium in the evaporating heating surfaces was determined for all boilers of the series in question at the nominal load under conventional fuel combustion conditions without recirculation. For the furnace outlet screen, the increment was calculated using the Boiler Designer software. The correspondence between the obtained enthalpy increments and the recommended values was evaluated. For the case of a significant divergence between the above figures, additional engineering solutions were proposed that facilitate the unification of the boilers. Based on the results of the analysis of the boiler furnaces and the expert estimations of the required convection pass height, a furnace height value was selected for each boiler group. The possibility of reducing the nitrogen oxide concentrations in the combustion products of the unified boilers was studied. The calculation investigations show that it is possible to achieve the required nitrogen oxide concentrations in all boilers at the selected furnace heights by stepwise and staged combustion or by injecting the recycle gasses into the burner box. Specific recommendations for the implementation of the above measures are provided.