E.ON AG
09/09/2010  07:18 h
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Picture: Pre-Combustion Capture

Turning Coal into Clean Hydrogen:

Pre-Combustion Capture

As the name suggests, pre-combustion capture involves capturing CO2 before a fuel is burned. The first step of this process is to separate air into nitrogen and oxygen. The second step is to combust coal at high temperatures using insufficient oxygen and steam. This step, called coal gasification, creates syngas, which consists mainly of CO2, carbon monoxide (CO), and hydrogen (H2).

Next, a catalytic converter uses steam to transform CO into a mixture of CO2 and H2. The CO2 is then washed out of this gas mixture and pressurized for transport to a storage facility. The hydrogen that remains can be used to generate electricity in a combined-cycle gas turbine (CCGT), which operates at a high level of thermal efficiency.
Gasification of solid fuels is already used to produce various chemical compounds and synthetic fuels.

Before pre-combustion capture can be used on a utility scale, it must first be tested in demonstration plants. The focus of R&D is currently on hydrogen-fueled CCGTs and on optimizing the integration of gasification equipment, gas-purification equipment, and the CCGT itself.
Picture: Overview of pre-combustion capture
The individual steps of pre-combustion capture (coal gasification, CO2 scrubbing, gas turbine operation) have all been tested on an industrial scale but haven't been integrated into a large power plant to test their efficiency, their impact on the plant's availability, and their commercial viability.

Although pre-combustion capture is suitable for a new, purpose-built generating unit, it can only be retrofitted onto integrated gasification combined cycle (IGCC) units. Currently, there are only four coal-fired IGCC units in operation worldwide. Their technical and operational complexity remains a challenge. They capture CO2 during the coal-gasification process, which yields a hydrogen-rich gas that fuels a gas turbine to generate electricity.

Perfecting pre-combustion capture rests on the development of highly efficient combustion technologies for hydrogen turbines, which are currently at the pilot stage. Significant advances are needed before they're ready for commercial operation.

E.ON is meeting these technical challenges by working systematically to refine the pre-combustion process. We're involved, along with a number of other German energy utilities, in a government-sponsored project called COORIVA. Its purpose is develop a plan for building, starting in 2015, a carbon-capture IGCC that gasifies both lignite and hard coal. The project, which is coordinated by Freiberg Technical University, will also evaluate studies on IGCC processes and develop a simulation model for various gasifier technologies and IGCC connections.

E.ON is also a member of the FutureGen Alliance in the United States. Its purpose is to build a nearly zero-emission IGCC unit with a capacity of 275 MWel. The unit is expected to enter service in 2012. In addition, E.ON has conducted a feasibility study for a 450 MW IGCC to be sited at Killingholme power station in the United Kingdom.

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