Waste heat recovery mechanism for coal-fired flue gas in a counter-flow direct contact scrubber

Scrubbers are more and more used to recover waste heat from coal-fired exhaust flue gas (EFG). But the heat and mass transfer mechanism in the counter flow direct contact scrubber is not clear enough, and the heat recovery rate (E) needs to be improved cost effectively. This paper proposes to use a simulation model to study the heat and mass transfer mechanism and thus to improve the scrubber design without intensive experiments. A mathematical model based on the two-film theory was established, and the finite difference method was used to solve it. The model was validated using experimental data and heat recovery equation is obtained with relation to the main influencing factors. The results show that the most sensitive factors on E are the liquid-to-gas ratio r(wf) and the equivalent diameter of water droplets r(d). In addition, height to diameter ratio (H/D) is more important than flue gas velocity. E can be increased by 25% and 36% when r(wf) increases from 4 to 6 and r(d) decreases from 0.002 m to 0.0015 m, respectively. Intensive simulations help determine the scope of the influencing factors to improve scrubber design. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This paper proposes the use of a simulation model to study the heat and mass transfer mechanism in a scrubber, aiming to improve design without intensive experiments. The most sensitive factors affecting the heat recovery rate were identified as the liquid-to-gas ratio and the equivalent diameter of water droplets. Intensive simulations proved to be effective in determining the influencing factors to enhance scrubber design.