Development of Computer Program for Combustion Analysis in Pulverized Coal-fired Boilers

OVERVIEW: The requirements in the design of a pulverized coal-fired boiler, (1) the complete combustion of the fuel, (2) the minimal release of environmental pollutants, and (3) the uniformity of steam temperature at the water wall outlet. To attain a design that can both satisfy these requirements over the range from partial load to full load and achieve economical operation, techniques for analyzing flow, combustion and heat transfer inside the furnace are required. To meet that need, we have developed a computer program for analyzing the combustion of pulverized coal, radiation heat transfer, and changes in flow rate distribution and temperature within the water wall tubes by simulation. Concerning the combustion of pulverized coal, we formulated a devolatilization model, a char combustion model, and an NOx and CO reaction model on the basis of fundamental experiments on the combustion of coal particles. Concerning radiant heat transfer between the flame and the water wall tubes, a radiative property model of the gas-particle mixture is incorporated and the heat transport rate is calculated by the discrete transfer (DT) method, which is highly accurate but requires a small computational load. In addition, to analyze the two-phase flow in the water wall tubes, we developed an algorithm that can be applied to an arbitrary flow path network. Comparison of the results calculated by this program with data on furnace operation under various coal and load conditions confirmed that the furnace exit gas temperature can be predicted to within ± 30°C. This technology can be used in the redesigning of existing plants as well as in the design of new 1,000-MW class boilers. Kenji Yamamoto Takeru Fukuchi, D. Eng. Masao Chaki, D. Eng. Yoshio Shimogori Jun’ichirô Matsuda