The current practice is most often to separate the CO2 and simply vent any unused portion to the atmosphere. Therefore, the concept of CO2 separation using industrial processes is not new, unlike the concept of capturing those emissions for environmental reasons.
For industries like upstream natural gas processing, and hydrogen and fertilizers manufacturing, flue gas streams often contain greater than 90% CO2. Consequently, many of these opportunities only require compression technology to pressurize the flue gas for transportation. This advantage makes these capture opportunities some of the most economic today. As noted previously, fertilizer manufacturing (of products such as ammonia and urea) is considered one of the best early opportunities for commercial CO2 capture today, and approximately 13 MtCO2/yr could be captured from this industry now (IPCC, 2005).
CO2 concentrations in natural gas vary by region, with almost no CO2 in Siberian gas and up to 70% in some Indonesian fields; the global average for natural gas is 1 - 2% CO2 (IEA, 2004). Natural gas in Canada can contain anywhere from zero to up to 36% CO2. Therefore, the opportunity of capturing CO2 from natural gas processing facilities varies by location.
Other opportunities in the fuel supply industries include oil refineries, hydrogen production and gasification facilities. However, because of the variety of oil refining processes used worldwide, it is impossible to characterize the industry and to indicate the total potential for CCS. That being said, oil refining is one of the largest emitting industries worldwide, thus opportunities do exist. Hydrogen is considered by many to be the transportation fuel of the future, and hydrogen production (using other fossil fuels as the feedstock) offers the potential to capture CO2 emissions from the transportation industry by capturing it where the fuel is produced. As already discussed, gasification is another option for producing hydrogen in a synfuel mix which also contains CO which could be converted to CO2 for transport to a suitable storage site.
Other high quality industrial sources of CO2 include cement, steel and pulp and paper, where average CO2 concentrations of the flue gases generally exceed 20%. CO2 concentrations from cement production are higher than those from conventional furnaces because more than half of the CO2 comes from an essential chemical reaction used in cement production (IEA, 2004). Substantial amounts of CO2 could be captured during direct iron production (DIP), a process used in regions with a lot of stranded gas (such as the Middle East). Paper mills and ethanol plants both recover "black liquor" (the remaining lignin fraction) from industrial processes and use it to generate energy. These facilities are a source of CO2 emissions that, if captured and stored, may result in the neg-emissions noted earlier, depending on the sustainability of the fuel source.
Some new technologies are needed for applications in existing facilities, to better enable the capture of high concentration streams in the existing capital stock. As well, better process integration is needed for CO2 capture technologies which in many cases could make a big difference in the capture economics. A lack of information on the application of solvent scrubbing or oxy-fuel combustion in industries like cement, glass and metals is a critical gap. If implemented appropriately, industrial processes could be some of the first areas to produce low-cost and very pure CO2 streams for CCS.