Transporting CO2 by pipeline is the most efficient method. This is because, unlike the other three options, CO2 is prepared for pipeline transport in the state that is also required for storage. This means that no further conversion of the aggregation state is necessary with the associated large energy consumption. Downstream of capture, the CO - is brought to supercritical pressure at the entry point to the pipeline. Also, pipeline transport is a continuous process. Immediately after capture and compression, the CO2 is pipelined to the CO2 depository for storage. In the other variants, ship, railway and truck, by contrast, transportation is discontinuous. This necessitates interim storage of the CO -- both at the start and at the end of the transport chain. Depending on specific circumstances and the accessibility of the plant in which the carbon is captured, and on the CO2 storage site, it might even be necessary to re-load the CO2, entailing further interim storage.
Once the carbon [dioxide] is captured from the process, it is available in a virtually pure form under atmospheric pressure or slight overpressure. For transportation by pipeline, the CO - is compressed to a supercritical pressure in a range between about 100 and 200 bar. The lower threshold ensures that the pressure remains above the critical pressure of 74 bar along the entire transport route, even taking account of pressure losses. This rules out any phase change during transport. On long routes, however, it will become necessary to deal with pressure loss by having booster stations at certain intervals. An economic alternative is to choose such a high pressure at the entry point into the pipeline, that the pressure remains sufficiently high along the entire transport route even without further compression.
For the first CCS projects executed in the power plant sector and used to demonstrate CCS technology on a commercial scale with all the steps in the process chain, it is necessary to implement individual, low-capacity pipelines. For a typical plant size, the captured CO2 to be transported here amounts to some 1 to 3 million tons per year. Compared with the CO2 amounts that can occur and possibly be separated in processes in the chemical industry, however, these quantities are already very large. Such individual, small pipelines have very high specific costs, together with enormous planning and approval outlays. This being so, in any future commercial implementation and expansion of CCS technology, the aim must be to aggregate carbon dioxide transportation from regions with high total CO2 and to channel the carbon by shared pipeline to the CO2 storage sites. Such pipelines require far-sighted planning in sufficient capacities. Ideally, a comprehensive pipeline infrastructure will emerge which will connect all potential carbon-capture installations and the CO2 depositories in a region or a country. In many cases, this would be the most efficient, flexible and least-cost concept for transporting CO2.
For the chemical industry, with its relatively low amounts of CO2 compared with the power plant sector, a link-up to other pipeline projects is of special significance, so that future CCS projects should aim at early inclusion in pipeline planning and, specifically, the planning of a pipeline infrastructure. For a specific location, there is also the job of connecting to a shared long-distance pipeline, that is, the planning and building of a spur line.
Pipelines for transporting CO2 have been in operation since the 1970s. The USA runs a pipeline network with a total length of over 3000 km to provide CO2 for enhanced oil recovery (EOR). Every year, approx. 35 million tons of CO2 are transported in this way. Pipelines for transporting CO2 are largely identical with those for natural gas transport, specifically as regards monitoring measures and security installations.
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