Development of the scheme of stepwise combustion of coal in the inverter firebox of a power unit of 1000 MW power

The desire to increase the efficiency of using the heat of burned solid fuel leads to the significant growth of the initial steam parameter at steam-turbine plants. At the maximum temperatures of fresh and secondary steam of 700–720°С, the price of connecting of steam pipelines between the boiler and turbine is up to 20% of the price of a power plant unit, which dictates the necessity to decrease their length. One of the methods to achieve this is the application of an inverter firebox. An M-shaped profile of boiler, allowing one to decrease the length of heat-resistant steam pipelines, was developed at NRU MPEI. A distinctive feature of the profile is two inclined connecting gas flues between the firebox and convective shaft, starting from the gas windows located in the lower third of the firebox height. The boiler was designed for the steam production of 2493 t/h with the parameters of fresh steam of 35 MPa and 710°C. Thermal and aerodynamic calculations made it possible to get the sizes of boiler and dimensions of heating surfaces, and they also allow one to get the values of temperatures in the characteristic points along the gas path. On the basis of the results of calculations, the coefficient of efficiency of the boiler was 93.07% and the fuel consumption was 91.13 kg/s. For this boiler, the technology of effective stepwise burning of coal in a direct-flow-vortex torch (DFVT) in a system of vertical and horizontal tangential torches in the mode of solid slag removal, previously successively used in boilers with a traditional profile and upgraded to an inverter firebox, is proposed. The layouts of the direct-flow burners and nozzles for even and odd vertical sections of the firebox and also in a horizontal section were proposed. Organization of staged air supply in the vertical direction with a high fraction of in-firebox recycle of hot gases leads to low concentration of nitrogen oxides.