Description of the Interaction of Liquid Layer and Flue Gas Flow on the Walls and Inserts of Flue Gas Desulphurisation Plant Scrubbers

Project Number 304

Often, power plant technology relies on wet scrubbers for exhaust gas cleaning, which absorb SO₂ in aqueous solution. To this end, the scrubbing liquid in the flue gas desulphurisation plant is atomised by means of numerous nozzles. In view of the ever more ambitious legal limit values of sulphur dioxide emissions and growing co-firing in power plants, flue gas desulphurisation plant scrubbers are reaching their capacity limits. A potential optimisation source is the absorption room with its nozzles and inserts.

Knowledge of the two-phase flow behaviour in a flue gas desulphurisation plant scrubber facilitates purposeful arrangement of nozzles and the installation of ring-shaped guiding elements on the scrubber wall (so-called wall rings) to control the flow in the flue gas desulphurisation plant scrubbers. Simulations using CFD (computational fluid dynamics) programs considerably improve the understanding of flow processes.

The previous research projects "Fluid Dynamics within FGD Plants" (202), "Optimization of Spray Nozzles in Flue Gas Scrubbers“ (230) and "Flow Correlated Positioning of Spray Nozzles in Flue Gas Scrubbers" (263) have yielded basic findings regarding the two-phase flow behaviour and the applicability of different nozzle arrangements, which were implemented in a commercial CFD program.

A considerable portion of up to 30 % of the sprayed scrubbing suspension forms a liquid layer along the scrubber wall, which has not been included in the considerations to date. Hence, the research project as applied is aimed at determining the influence of the liquid layer in SO₂ flue gas desulphurisation plant scrubbers of fossil-fuelled power plants and implement them in a simulation environment.

On this basis the occurring flow can be described in more detail. The liquid layer has a considerable influence also with regard to the evaluation of scrubber inserts (e.g. wall rings). These wall rings do not only serve to deflect the gas flow from the scrubber wall but also to disperse the film flowing down the wall. This can be of relevance for evaluating the wall ring in terms of its operation and the resulting pressure loss. This project is aimed at identifying the opportunities for presenting the liquid film on the scrubber wall and subsequently incorporating them into the commercial CFD program CFX of Ansys Inc.

The project will be carried out from August 2007 till July 2008 under the guidance of Claudia Bautsch of the Department of Environmental Engineering at the Dortmund University. The Working Group "Flue Gas Cleaning Technology" will support the investigations.