THE ECONOMICS OF CO_2 AND MIXED GAS GEOSEQUESTRATION FROM STATIONARY GREENHOUSE GAS EMITTERS

摘要

Greenhouse gas emission sources generally produce mixed gases. Previous studies of geosequestration have typically examined the sequestration of pure CO_2. This paper analyses the cost of separating a gas mixture from a power station flue gas stream followed by offshore sub-surface storage. We analyse the costs of separating and storing varying gas mixtures with increasing concentrations of CO_2 - from one extreme - in which we store the entire flue gas stream containing both CO_2 and N_2 - to the other extreme - in which we separate as much CO_2 as is technically possible. We examine the use of gas membrane separation as well as chemical absorption to achieve varying concentrations of CO_2, in the gas mixtures sequestered. The results indicate that, using a gas membrane separation system, the lowest sequestration cost per tonne of CO_2 avoided occurs when a mixed gas with a CO_2 content of about 60% is sequestered. Lower costs and higher tonnages of CO_2 avoided can be achieved using an amine based absorption separation system. The results also confirm that at the lowest cost point, and over most of the range of cases studied, the cost of separation is significantly greater than the cost of storage. However, this would depend on the source of the CO_2, the distance between the source and the injection site, and, the reservoir into which CO_2 is injected.