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(2006)Journal ArticleGreenhouse gas emission sources generally produce mixed gases. Previous studies of CCh capture and storage have typically examined only sequestration of pure CO2. This paper analyzes the cost of separating a gas mixture from a power station flue gas stream and injecting it into an offshore subsurface reservoir. The costs of separating and storing various gas mixtures were analyzed at two extremes. One extreme in which the entire flue gas stream containing both CO2 and N2 is stored. The other extreme in which as much CO2 is separated as is technically possible using gas membrane capture coupled with chemical absorption. The results indicate that for the gases investigated, using a gas membrane capture system, the lowest sequestration cost per tonne of CO2 avoided occurs when a mixed gas with a CO2 content of about 60% is sequestered. Lower costs and higher tonnages of CO2 avoided can be achieved using an amine based absorption capture system. At the lowest cost point, and for most of the range of cases studied, the cost of capture is significantly greater than the cost of storage. However, this depends on the source of the CO 2, the distance between the source and the injection site, and the reservoir into which CO2 is injected.
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(2006)Journal ArticleThe sequestration of CO2 as a greenhouse mitigation option is becoming an increasingly important priority for industry. Theoretically membrane based CO2 removal systems have the potential to provide a cost effective, low maintenance approach for removing CO2 from gas streams. This study examines the effect of membrane characteristics, operating parameters and system design on sequestration costs for any source-sink combination. The total sequestration cost per tonne of CO2 avoided for separation, transport and storage are compared for the separation of CO2 from a black coalfired power plant in Australia. The results show that the membranes currently available have a total sequestration cost of US$55-61/tonne CO2 avoided. Lower costs for CO2 avoided can be achieved using an MEA amine based absorption separation system. Gas separation membranes would require significant improvements in CO2 permeability and selectivity, together with reductions in the cost of membranes and changes to the process configurations and operating pressures to be competitive against MEA systems for the purposes of geo-sequestration.
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(2006)Journal Article
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(2006)Journal ArticleMembrane technology is being increasingly used in the treatment of waters and wastewaters. The two main costs associated with the adoption of membrane filtration are the membrane module cost and the energy cost. Tradeoffs between selection of membrane capital cost and energy cost are usually identified for process optimisation; however, environmental tradeoffs associated with different operating conditions have received less attention. In order to ensure the sustainable use of membrane filtration, environmental considerations should also influence the choice of operating conditions. Here, we report on application of the method of life cycle assessment (LCA) to assess the environmental performance of different operating conditions of a microfiltration membrane (MF) process. Different membrane chemical cleaning options are compared in the sensitivity analysis component of the study. The results show that operating the MF process at a low flux with a high maximum transmembrane pressure (TMPmax) offers the most environmentally favourable outcome. The sensitivity analysis results show that in the low flux range, the choice of chemical cleaning frequency can affect the overall environmental performance of the process. © 2006 Elsevier B.V. All rights reserved.
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(2006)Journal ArticleAxial vibration of submerged hollow fibre membranes is found to be an effective means of preventing membrane fouling with critical fluxes of 60-80 L h-1 m-2 found to be achievable at vibrational frequencies as low as 10 Hz. Addition of transverse vibrations to the test unit (by means of addition of horizontal vanes) resulted in an approximate doubling of critical flux (to 130 L h-1 m-2 at 10 Hz). Fibre integrity is maintained at the combined longitudinal and transverse vibrations used (equivalent to a pulsating peak shock acceleration of 8.7g at a vibrational frequency of 10 Hz). Performance of the vibrating unit is highly sensitive to coagulation with coagulant addition markedly enhancing the critical flux, particularly at low vibrational frequencies. At a frequency of only 1.7 Hz (100 oscillations per minute (OPM)), critical flux increased from 17 to 46 L h-1 m-2 on addition of 34 mg/L aluminium chlorhydrate (ACH). In the presence of combined axial and transverse vibrations, a five-fold enhancement in critical flux to 86 L h-1 m-2 was achieved at 1.7 Hz in the presence of 34 mg/L ACH. Lower proportional increases in critical flux on addition of coagulant were obtained at higher frequencies presumably as a result of floc breakup under the increasingly turbulent conditions. The results obtained suggest that industrially relevant critical fluxes in submerged membrane units could be achieved by low frequency vibration of the submerged membranes coupled with addition of a suitable coagulant. © 2006 Elsevier B.V. All rights reserved.