The high-performance scrubber REAplus
Ever since the 1980s, flue-gas desulphurization (FGD, or its German equivalent REA) plants have been filtering sulphur dioxide (SO2) out of the flue gas from lignite-fired power stations. The scrubbing method, in which the SO2 is washed out using limestone slurry, has long since proved its worth. Today, more than 95% of the desulphurization plants in power stations and industrial facilities worldwide are being reliably and successfully operated on the basis of this technology.
However, the high efficacy of today's flue-gas scrubbing is no reason for RWE to rest on its laurels. Its success is the spur that drives us on to develop new processes designed to make coal-based power generation even more environmentally compatible. This is where the REAplus concept comes in. This has been implemented in a pilot plant at the Coal Innovation Centre in collaboration with Andritz Energy & Environment (AE&E), a plant builder.
What counts in this concept is that we optimize even further the chemical processes in the desulphurization to achieve the highest possible degree of SO2 capture. The progress here, compared with the previous method, lies in the staggered sequence of the scrubbing process and in improved contact between lime slurry and flue-gas SO2. The pilot scrubs 50,000 cubic metres of flue gas an hour from the BoA power plant. Trialling is focusing on the capture targets to be achieved and the suitability for continuous operations.
REAplus' highly efficient desulphurization renders superfluous any pre-treatment of flue gases in the pilot CO2 scrubbing plant that is likewise linked to BoA 1. The combination of REAplus and post-combustion capture creates conditions at Niederaussem that are unique worldwide for trialling modern, trail-blazing power-plant engineering.
At the end of 2011, another component was added to the REAplus plant: a wet precipitator, which is to allow for even better separation of sulphur and particulate matter from the power-plant flue gas. Following the initial test stage in 2012, a long-term test will be carried out until the end of 2013.
The special precipitator was manufactured by the plant-construction company Steuler-KCH GmbH from Siershahn/Westerwald County, and has a unique feature: instead of steel-pipe electrodes, which are normally incorporated into wet precipitators, Steuler-KCH GmbH has used plastic pipes. This allows flue-gas components that have been separated electrostatically to be flushed out, avoiding the formation of corrosion during operations.
In July 2014, the REAplus technology was implemented on an industrial scale for the first time at the Niederaußem power plant's G1 FGD absorber. The design used here is 50 times larger than the pilot plant. Apart from the REAplus module, a second, conventional FGD absorber is installed at power plant unit G. As a result, the new technology can be compared directly with a conventional system.
The new absorber scheme permits the auxiliary power requirements to be lowered compared with conventional flue gas desulphurisation plants. Thus, this innovative technology boosts the efficiency of flue gas desulphurisation. Since the newly developed REAplus technology has so far been used successfully in unit G, the two FGD absorbers installed in Niederaussem's unit H were also equipped with this technology in May 2015.
REAplus' highly efficient desulphurisation renders superfluous any pre-treatment of flue gases in the pilot CO2 scrubbing plant that is likewise linked to BoA 1. The combination of REAplus and post-combustion capture creates conditions at Niederaußem that are unique worldwide for trialling modern, trail-blazing power-plant engineering.