Coal-fired power plant boiler combustion is a highly complex process, and improving the combustion process requires multiobjective optimization. A combustion process with two objectives is shown in Figure 5.1, where Q 1 is the total heat absorbed by the tubes of heat-transfer equipment inside a boiler such as a water wall, superheater, reheater, and economizer, and maximum Q 1 is expected. Normally, if the temperature of the flue gas is higher than Tmelting , which is the ash-melting temperature shown in Figure 5.1, the ash starts to melt and slagging increases. Therefore, an efficient boiler- combustion process should have maximum Q 1 with flue-gas temperature in the areas close to the sides of the furnace under Tmelting .