Recently, in coal power plant, air pollution is a serious problem. Especially, the toxic gas is composed of sulfur oxide so that induces human cancer. To reduce the sulfur oxide, a flue gas de-sulfurization unit is equipped before a stack in the plant. In flue gas de-sulfurization unit, sulfur oxide is removed by chemical reaction. The reaction accompanies temperature change of gas due to water injection from the wall of unit. Then the cooled gas is passing through a duct and finally emitted without any sulfur matter. The gas makes a low temperature corrosion of the stack. Therefore, gas reheater is needed after the unit and rotary type of reheater is used well due to thermal efficiency. The rotary heat exchanger exists between flue gas de-sulfurization unit and stack. In the rotary heat exchanger, temperature of gas increases because of hot gas from a boiler. Warm side of rotary heat exchanger makes de-sulfurized gas with water to evaporate so that induces fouling and plugging phenomena. In this study, under a plugging phenomenon, thermal design of the rotary heat exchanger is performed by using CFD. We use operational data of coal power plant to verification of simulation. After that, thermal design of heating element which is a component of rotary heat exchanger is conducted.