CCS consists of three main process steps.
• Carbon capture: In a first step, the CO2 is captured from the process concerned (power plant, chemical plant, steel mill, ...) using special separation methods. It is then treated, so that it is available in a very pure form.
• Transport: If the captured CO2 is to be sequestered below ground, it will in most cases have to be transported to a suitable storage site. This makes CO 2 transportation, too, an essential CCS component. Depending on circumstances, the CO2 can be transported by pipeline, ship, railway or truck.
• Carbon storage: The third step is the permanent storage of the C02 in subterranean, geological formations that will prevent the C02 from escaping thanks to impermeable cap rock, but also using other mechanisms.
The capture methods developed today are able to remove approx. 90% of the C02 from the process, leaving 10% residual emissions. For each of the three main process steps, additional investment is necessary beyond that for a conventional power plant. Also, CCS technology requires considerable amounts of energy, for two reasons. First, carbon capture in the power-plant process needs energy in the form of heat and electricity. Second, storage of the captured C02 requires that it is available in a highly compressed form at supercritical pressures of more than 100 bar. Transportation, too, usually needs C02 compression. C02 compression is the second significant factor in the energy requirements of CCS technology. Overall, the technologies that are being developed for first-generation commercial CCS power stations must put up with an efficiency loss of over 10 percentage points.
The following sections discuss the three process steps in CCS technology. 11.3
For the capture of C02 from industrial processes, various concepts have been developed. Since, as was noted earlier, electricity generation and, hence, power-plant engineering were the initial focus of developments in CCS technology, present concepts are mainly geared toward deployment in power stations. All the same, some concepts use technologies that are already being implemented in other industries, though not for the purpose of avoiding C02, but rather on economic grounds to obtain valuable materials able to earn a price high enough to cover outlays. Moreover, these applications involve completely different, that is, much smaller, dimensions. Also, some of the solutions designed for power generation can also be transferred to C02 management in the chemical industry.
The tasks involved in capturing C02 from a power plant process can be described in greater detail and are summarized in Figure 11.2. Coal is burned in a power station, yielding a gas mixture (the flue gas) as combustion product that consists
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