Task capture of C02 out of a mixture of C02 H20 N2

Combustion in the power plant

Figure 11.2 Tasks of carbon capture.

of numerous components, mainly C02, H20 and, above all, N2, which enters via the combustion air. Hence, the main task, to start with, is to develop concepts for separating the C02 from this mixture of three main elements. Besides these, however, other constituents, too, are encountered, like oxygen and argon as well as traces of S02, NOx and others. Although taking account of these ancillary components does not affect the basic concept for capturing carbon, it greatly influences the concrete design and performance of the separation process.

To separate the C02 from the gas mixture of C02, H20 and N2, three basic technological routes are being pursued:

• post-combustion C02 scrubbing;

• the oxyfuel process; and

• IGCC with carbon capture (pre-combustion C02 separation).

It is expected that these three technologies will be implemented in the first generation of coal-fired power plants with carbon capture. Each has its specific properties and merits, so that parallel development of all three technologies is a sensible policy. In addition, building on these basic technologies, solutions are being investigated for the more distant future with a view to reducing the energy and cost outlays associated with carbon capture.

These three technologies for carbon capture are presented in the following sections. Proceeding from the basic idea of carbon capture, that is, splitting up the gas mixture of C02, H20 and N2, the discussion looks into specific properties, advantages and disadvantages, special development tasks and the deployment options in the chemical industry.

Post-Combustion C02 Scrubbing The Basic Idea of Carbon Capture

In its basic concept, post-combustion C02 scrubbing is the simplest and most obvious technology for capturing the carbon from the power-plant process (see Figure 11.3). The idea is to target the flue-gas stream directly. Here, the C02 is selectively extracted from the waste-gas stream using a special scrubbing solution downstream of the power station. This is done in an absorber. The waste gas freed from the C02 is released into the atmosphere, while the scrubbing solution loaded with the C02 is further processed. It is conducted to a desorber where the C02 is driven out of the scrubbing liquid by the addition of heat. The C02 is now available

C02 scrubbing

Figure 11.3 Basic idea of post-combustion C02 capture by means of scrubbing.

C02 scrubbing

Figure 11.3 Basic idea of post-combustion C02 capture by means of scrubbing.

in a captured, pure form. The scrubbing solution regenerated in this way is returned to the absorber where it again absorbs CO2.

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