The simulation and analysis of wood fuel low-grade heat

Modern wood fuel plants use freshly felled and chipped wood, so the flue gas contains a significant amount of vapour. Even after the condensing economizer, the flue gas carries out a considerable amount of heat ejected into the surroundings. It is impossible to use this heat for heating directly because it is too low grade. Additional energy and investment are needed for its utilization, e.g., using mechanical heat pump technology. The utilization effectiveness depends on the heat capacity that the flue gas carries out of the condensing economizer as well as on the temperature to which the gas is cooled down. These two parameters are interdependent and have to be calculated before designing the heat pump. The calculations and simulation of the wood fuel low-grade heat is quite sophisticated due to the fact that the composition of flue gas changes during its cooling process. This article presents a mathematic model of the calculations of flue gases. This model presents simulation and some results which could facilitate the evaluation of the effectiveness of the low-grade heat utilization using heat pump technology. The verification of results, presented in the article, shows correctness of the model and calculations’ accuracy. •Calculation of additional heat exchanger is needed for heat pump application.•Model for calculation of the low-grade wood fuel combustion heat is presented.•Final flue gas temperature influences efficiency of heat pump.•Verification shows the correctness of the mathematical model.