Dave Elliott: Carbon Capture and Storage involves the capture of the CO2 produced from fossil fuel combustion via chemical absorption and then release, with the gas being compressed and pumped along pipes for storage in empty undersea oil and natural gas wells or other geological strata. It is sometimes claimed that CCS can reduce emissions from the use of fossil fuel by 80-89%, although in practice its overall efficiency may be more like 60-70%, since the various CCS processes use energy and supplying that adds more emissions. Coal CCS is usually harder and more expensive than fossil gas CCS, partly because, to get high efficiency, the coal has to be gasified as a first stage. Permanent storage is obviously the ideal, but some doubt whether it can be achieved reliably over very long periods, depending on the location and its geology. Oil and natural gas were trapped underground in strata safely for eons, so it is argued that replacing them with compressed CO2 should not involve extra risks. However, accidental rupture and rapid release of large volumes of gas could be very dangerous, although some of the gas may, in time, combine with rocks to form new solid calcium carbonate deposits. Some experience with geological injection and storage has been gained from Enhanced Oil Recovery using injected gas, although very long term storage would involve new challenges. Progress on the various carbon capture option discussed above is clearly limited, with some greens welcoming that: they see carbon capture as deflecting support from renewables. Some also similarly see the current focus on fossil-derived hydrogen as in the H21 project proposed for Leeds, as a diversion from a switch to genuinely ‘green hydrogen’ produced using renewables sources (with no need for CCS). Others however see this developments as a possible step on the way to the adoption of renewable hydrogen, and as way to establish greener gas in the heating market, ready for later replacement by fully green bio gas and P2G syngas gas, when that becomes available on a wide scale.
Renew Extra 1st Oct 2018 read more »