Numerical analysis of the heat recovery efficiency for the post-combustion flue gas treatment in a coffee roaster plant

The heat recovery system for the post-combustion flue gas treatment in a coffee roaster plant is investigated using both a lumped and distributed parameter numerical modelling and a transient CFD approach. The combined analysis of the two numerical approaches enables to estimate the thermo-pneumatic behaviour of the entire plant as well as the optimal design of the heat exchanger. The effects of the heat recovery are evaluated in terms of improved energy efficiency and reduction of the fuel consumption. The counter-flow shell and tube and cross-flow plate fin heat exchangers are designed in order to have similar performance in terms of recovered heat and their performance on the real plant is predicted under actual plant operations. The overall volume of the plate fin device results to be approximately one tenth of the shell and tube architecture's volume, while the pressure drop of the two systems is comparable. Finally, the heat recovery from the flue gas enables to save up to 27% of the fuel necessary to power the post-combustor adopted for the exhausts’ treatment and up to 13% of the total fuel consumption of the plant.