In the medium term, CO₂ scrubbing technology is the only retrofit option available for capturing CO₂

Over the long term, coal will be the cornerstone of a sustainability-focussed energy supply both on a global and on a national scale. For this reason RWE is pressing ahead with the development of technologies that will provide us with a foundation for sustainable coal-based power generation. The focus of our work lies on lignite, one of our domestic resources.
If you want to achieve the CO₂ reduction targets set by policy-makers, over the long term you will need to implement carbon capture and storage (CCS). This holds especially true when taking account of the planned nuclear phase-out.
Solely due to the long investment cycles in the power plant sector – typically 40 years – it will take several decades before the new power plants equipped with fully integrated CO₂ capture technology will be widely realized. Thus, at an early stage RWE Power made a decision to develop advanced CO₂ scrubbing technology in parallel to our IGCC/CCS project; from today’s point of view, CO₂ scrubbing is the only carbon capture technique that allows retrofitting into existing power plants in the medium term.

How does CO₂ scrubbing work?

In principle, the basic CO₂-scrubbing process is very simple. In an absorber about 90% of the CO₂ contained in the flue gas can be bound to a CO₂ solvent at a relatively low temperature and, hence, removed. By raising the temperature, the solvent  “loaded” with CO₂ is rid of it in a desorber and subsequently transported as a lean solvent back to the absorber, where the scrubbing cycle starts again. The captured CO₂ has a high degree of purity and after being compressed is available for transport and underground storage.

Cooperation with BASF and Linde to further develop CO₂ scrubbing technology

CO₂ scrubbing has been used successfully in the chemical, petroleum, and gas industries for a long time, though under process conditions that – in some instances – differ considerably from those that are relevant for use in power plants. Hence, what could be more logical than pooling the relevant expertise of strong partners, adapting the technology to our needs, and improving energy and economic efficiency of carbon scrubbing to such an extent that it meets our requirements? In BASF and Linde we have found two partners for this purpose that are global leaders in their respective fields and complement each other perfectly.

A new CO₂ solvent developed by BASF and optimized capture plant technology developed by Linde form the basis of the optimized CO₂ scrubbing technology. The use of the CO₂ scrubbing technology to be developed will permit 90% of CO₂ of the flue gas in the new power plants to be captured and either utilized to make other products or stored underground.

Erection of a pilot CO₂ scrubbing plant at RWE’s Niederaussem power plant site

As part of our cooperation we are currently erecting a pilot plant at the existing Niederaußem power plant location, due to be commissioned in the middle of 2009. The pilot CO₂ scrubbing plant is being built by Linde at the 1,000-MW BoA 1 lignite-fired unit, which, with a net efficiency of over 43%, is the most modern and most efficient lignite-fired unit worldwide. It is equipped with optimized plant technology and is the forerunner to the two power plant units BoA 2&3 being built at the Neurath site. In Niederaussem, the carbon capture technology to be developed can thus be adapted to this type of power plant in an ideal manner.

An extensive investigation programme conducted under real operating conditions to test the new CO₂ solvents developed by BASF will be completed at the end of 2010. The height of the pilot CO₂ scrubbing plant (40 m) corresponds to that of the future commercial plant. The plant also comprises all individual components of large plants, but on a smaller scale. The diameter of the absorber column was limited to the size required to obtain representative results. Depending on the set test parameters, up to 300 kg CO₂ per hour can be separated from a flue gas bypass (corresponds to a capture rate of 90 %). Provided that the pilot phase is completed successfully, it is planned to have a demonstration phase immediately afterwards, during which an industrial-scale plant is to be built. Our goal is to make carbon capture technology utilizable for the retrofit of existing modern plants or new power plants by 2015. 

CO₂ scrubbing for the next generation of lignite fired power plants

The BoA 1 site at Niederaussem is ideally suited for the project for an additional reason. Preparations for commissioning of the prototype lignite-drying plant started in May 2008. Demonstration operation is set to start at the end of 2008/the beginning of 2009. Hence, it is possible to test the pilot CO₂ scrubbing plant at BoA 1 using dry lignite. The coal predrying technique developed by RWE is a key technology for the next generation of lignite-based power plants, allowing the net efficiency of a power plant to be increased by a further 4%-points to more than 47%. By pooling the world’s leading power plant technologies, the Niederaussem site permits the testing of both a CO₂ scrubbing process optimized for retrofits and a capture technique adapted to the demands of the next generation of dry lignite-fired power plants. 
As shown in the animated graphics, it will, over the long term, be possible to equip advanced coal-based power plants with fully integrated CO₂ scrubbing plants, permitting an ideal arrangement of processes.

CO2 scrubbing process overview

You want to know more? Please find more information on this topic in our infotheque.