CFD Modeling of the Acceptability of Using Pellets Common on the Ukrainian Market as Fuel for a Pellet Boiler with Retort-Type Burner

SET boilers are designed for heat supply of residential buildings, municipal and industrial buildings, equipped with heating systems with natural or forced circulation of water as a coolant. Sketch drawings and some thermal hydraulic characteristics of these boilers are presented in the open access. The developer website states that the boilers operate with automated loading of pellets from wood waste. The developers emphasize that it is possible to use other types of solid fuel with a change in the technical characteristics and service life of the boiler. In order not to conduct a costly experiment with existing equipment, the authors developed a CFD (Computation Fluid Dynamics) model of the processes taking place in a SET water-heating boiler with a capacity of 25 kW when burning various types of pellets using modern ANSYS-Fluent software package. The calculations were performed using the academic license of the ANSYS Student software package. This license is completely free (since 2015) and is intended for solving introductory and educational tasks in an academic environment. When modeling the processes that occur during the combustion of pellets as a fuel, the authors conducted a simulation of the thermal hydraulic characteristics of the flow of a continuous gas phase during its interaction with a discrete phase in the form of pellet granules. The results of CFD modeling were verified according to the passport data presented by the developer of the SET-25 boiler for the case of burning wood pellets. It was shown that the discrepancy of the results does not exceed 2%, therefore the developed model can be used to simulate the combustion of other common types of pellets - from coniferous wood, rapeseed, from bird droppings and straw, as well as from bottom sludge. The results obtained can be useful when designing new designs of water heating boilers and verifying the calculation of the existing ones.