Carbon capture and storage (CCS) is a technology for separating the CO2 produced in technical processes and for its permanent leak-tight sequestration in depositories located well below the Earth ' s surface, thus ensuring that the CO2 no longer reaches the atmosphere. This technology can give major CO2-producing processes a climate-compatible shape.
Carbon dioxide is produced in industrial processes primarily when fossil fuels are burned in heat and electricity generation. The three fossil energy sources: coal, oil and natural gas, differ crucially in their applications and properties, and it is these differences that ultimately determine the focus of development work and the future deployment of CCS technology.
In energy terms, coal has a much higher carbon content, so that particularly large quantities of CO2 are generated. Also, the main use of coal is in power generation, so that CO2 emerges here in large amounts at central locations. These two facts mean that the conversion of coal into electricity is an ideal candidate for CCS. This being so, CCS is mainly being developed today for use in the generation of electricity from coal. Besides the technical considerations, the statutory environment, too, plays a role, and it is this aspect that explains why CCS is to be used, first of all, in the conversion of coal into electricity. Trade in CO2 certificates currently extends to power generation, but leaves other industrial sectors still largely exempt. So, for power generation, the emitted CO2 is already a cost factor, that is, the pioneering development of CCS for coal-based electricity generation also has an economic background.
The need to develop CCS for coal-based power generation becomes clear if we take a look at the expansion of coal-fired power plants especially in newly industrialized countries, above all China and India. Coal inputs have been growing dramatically since the start of the new millennium, and there is no end in sight for this development. Here, several specific differences between coal and the other two fossil energy carriers, oil and gas, become apparent. Coal is a very low-cost energy source. It is well distributed around the globe, so that its use makes a
Managing CO2 Emissions in the Chemical Industry. Edited by Leimkuhler © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN: 978-3-527-32659-4
Gasification, gas processing
SNG (synthetic natural gas)
Figure 11.1 Products obtainable from coal gasification.
contribution to security of supply. In addition, the reserves are huge, so that the finite nature of coal, unlike that of oil in particular, is not a big issue as yet, nor will it be a vital question in the foreseeable future. On the contrary, numerous concepts and projects exist that envisage the use of coal as a substitute for oil and gas in the production of, for example, basic materials like naphtha, methanol, etc.-via coal gasification and synthesis-for the chemical industry. Figure 11.1 gives an overview of chemicals and products that can be obtained from coal gasification.
The dramatic rise in the use of coal is also associated with a serious increase in global C02 emissions. To deal with this problem, we need a technical solution that avoids C02 emissions, especially from coal-fired power stations, but also from other coal applications. The basic route involves raising the efficiency of power plants, which will then reduce coal inputs and, hence, C02 emissions while producing the same amount of power. With current developments, like an increase in the steam parameters from the present 270 bar/600°C to 350 bar/700 °C in future or fiuidized-bed lignite drying with internal waste heat utilization (WTA), the efficiency of coal-based power stations is expected to cross the 50% threshold (in terms of net calorific value). Compared with today's global average of approx. 31%, this means a reduction of nearly 40% in specific C02 emissions. Still, although an increase in efficiency has great potential for avoiding C02, it is not enough by itself. Much of the potential is swallowed up by the increase in the quantity of coal used in power generation, and even with efficiencies of over 50%, a considerable residual amount of C02 emissions remains, most of which must be eliminated if climate targets are to be reached. The only technology recognized today that can deliver this is CCS. This makes CCS an essential module in the strategies for lowering global C02 emissions.
What is more, CCS offers a special and unique feature for C02 mitigation: when CCS technology is used in biomass firing systems, we obtain negative C02 emissions, that is, in the overall balance, C02 is actually removed from the atmosphere. Power stations operated using biomass initially emit no C02 since, in a first step, the plants employed absorb C02 for their own growth, which they release again during combustion in power stations. Hence, this cycle is carbon-neutral. So, if the C02 is not emitted into the atmosphere thanks to CCS technology, but is permanently stored below ground, a biomass-based power plant is not only carbon-
11.2 General Description of the Technology with its Components | 393
neutral, but is actually withdrawing CO2 from the atmosphere. CCS is the only technology known today that will enable atmospheric CO2 to be reduced tomorrow.
Even if CCS developments for the conversion of coal into power are very much to the fore today, other applications, too, will follow and gain in importance. CO2 is already being separated from natural gas, for example, in order to treat the gas for further use. The captured CO2 is stored in subterranean strata.
Besides power generation, other CO 2-2ntensive industrial sectors are increasingly thinking about opportunities for carbon capture and storage. Here, steel, cement, refineries, paper and the chemical industry in particular should be mentioned. In many technical processes, carbon capture is the only way to reduce CO2 emissions to a minimum. Also, carbon capture opens up one more option: since the CO2 is extracted in a virtually pure form, it can be used as resource or feedstock, for example, as a carbon source in chemical processes. This offers the opportunity of developing new chemical processes with a CO2 basis.
So, CCS technology offers the chemical industry four interesting perspectives for managing CO2:
• lowering CO2 emissions in chemical processes;
• via coal gasification and synthesis, including capture and storage ofexcess CO2, provision of an alternative to oil and natural gas as basic raw material;
• provision of CO2 as feedstock for chemical processes;
• lowering of CO2 emissions in power generation and process-steam generation.
Furthermore, developments and experience in the power-plant industry can yield important findings that can be transferred to the chemical industry. This is also and especially true of the two essential CCS modules: carbon storage and transportation. Here, it will be possible in future to build on the work of the powerplant industry, all the more so since it seems sensible to include the relatively low CO2 amounts from the chemical industry in the transport and storage infrastructure of power-station projects.
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