Thermal calculations of a natural circulation power boiler operating under a wide range of loads

The article presents the development of a comprehensive methodology for thermal-flow computations of a natural circulation power boiler. For this purpose, calculation methods available in the literature were used, and in several cases in-house methods were developed. These in-house methods are one of the main outputs of the work. They include a new approach to computing the heat transfer occurring in the wall superheaters and hanger tubes situated in parallel in a single combustion gas duct. A new method of calculating the heat transfer in the rotary air heater was also proposed. Based on this, an in-house computer program was created. The computations performed cover all heated surfaces of the boiler with the nominal output of 350 x 10(3) kg/h of superheated steam and concern several characteristic points of its steady-state operation. Additional CFD computations were performed for the boiler furnace chamber. All the obtained results were compared with the data made available by the boiler manufacturer. Small differences observed only slightly affect the heat distribution in the heated surfaces of the boiler. This confirms the correctness of the proposed calculation methodology and the in-house developed mathematical models. The models can support the power boiler design process.