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With CO2 scrubbing, the spray scrubber takes on the task of the absorber.
© IFK der Universität Stuttgart
CO2 capturing

The CASPAR test plant is a three-stage spray scrubber, whereby each stage has a five-metre spray zone.
© IFK der Universität Stuttgart

Efficiently capturing carbon dioxide with spray scrubbers

Spray scrubbers have been successfully used in power plants for years for desulphurising flue gas. Now it is intended that they should scrub another material – namely climate-harming carbon dioxide (CO2). Until now a hurdle preventing large-scale CO2 capturing has been the high investment costs for the plant technology and the considerable amount of energy required for the operation. The University of Stuttgart is therefore working with partners to improve this process.

The amine scrubbing medium pours down in the spray scrubber like a large rainforest shower. The flue gas flows towards the droplets from below. The amine scrubbing medium binds the CO2 in the flue gas enabling it to be scrubbed from it. The cleaned flue gas can then be released to the environment without the climate-harming carbon dioxide. The technique is already used for desulphurising flue gas and is now being transferred to CO2 capturing.

The best available technology in industry is a scrubbing process using packed column absorbers, whose deployment, however, entails considerable investment and energy. The aim of the research project, entitled “UPSCALE – Effiziente Abtrennung von CO2 aus Kraftwerksrauchgasen mit Hilfe eines Sprühwäschers” (Efficient capturing of CO2 from power plant flue gases using a spray scrubber), is to try and reduce these. The project is being funded by the German Federal Ministry of Economic Affairs and Energy as part of its COORETEC initiative. For this purpose the Institute of Combustion and Power Plant Technology (IFK) at the University of Stuttgart is working together with the plant constructor Babcock Noell and the power plant operators EnBW, Eon and Vattenfall.

Spray scrubbers support flexible mode of operation

The idea of the project partners is to integrate an additional spray scrubber in the flue gas cleaning system used in power plants. In comparison with packed column absorbers, spray scrubbers have numerous advantages: first of all they are substantially cheaper to realise since expensive and heavy internal components are no longer required. This reduces the structural requirements for the steel assembly and thus the investment costs. In addition, spray scrubbers cause substantially lower pressure drops than column absorbers with internal components. The work for overcoming this pressure loss is achieved using blowers whose energy requirement lowers the efficiency of the overall process. The lower pressure drop therefore has a direct impact on the efficiency and operating costs of the power plant.

A further advantage of the spray scrubber process results from the future requirements for fossil fuel-fired power plants as a consequence of the energy turnaround. The high proportion of fluctuating renewable fuels in the grid requires frequent load changes and the increasing partial load operation of conventional power plants. The spray scrubbing process can help to meet these increased demands on the power plant flexibility, since it covers a wider output range than packed column absorbers.

In the spray scrubbing process, there is also greater flexibility in terms of the various scrubbing materials that can be used than with column absorbers. This also provides potential for further improving the process.
In the project the consortium built the CASPAR spray scrubber plant and gathered operating experience. The plant is designed to accept 120 cubic metres of flue gas per hour and has a three-stage spray scrubber, whereby each step has a five-metre spray zone. CASPAR’s modular structure and considerable flexibility enables various scrubbing heights to be tested by means of cascade tests, i.e. several consecutive sequences. The researchers achieved their goal of attaining 90% CO2 capturing rates for realistic construction heights for the spray scrubber. The project, which came to a conclusion at the end of 2013, confirmed the feasibility of the process. The scientists are now planning a follow-up project to further optimise the spray scrubber and transfer it to large-scale plants.



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Project management
Universität Stuttgart