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Title: Integrated process and solvent design for CO₂ removal from natural gas
Author: Keskes, Emmanuel
ISNI:       0000 0001 3597 7936
Awarding Body: Imperial College London (University of London)
Current Institution: Imperial College London
Date of Award: 2007
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Carbon dioxide (C02) capture is of crucial importance for the environment. A large number of countries agreed on the fact that greenhouse gases, especially C02 can have harmful effects leading to major climate changes; in particular, since the ratification of the Kyoto Protocol in 1997 it is apparent that action should be taken. In this context, new solutions are necessary to reduce carbon dioxide emissions. In this work, we present the new challenge that the Kyoto Protocol represents for the petroleum industry, especially considering that large amount of C02, which would be captured from large C02 emissions sources, could be reinjected in oil and gas reservoirs. Re-injection will lead to increased productions of oil and gas, which can compensate the cost of C02 capture. Unfortunately, the oil and gas produced will be increasingly richer in C02 and specific absorption processes must be designed to address this problem. Such processes should show flexibility with respect to the feed C02 content. Physical absorption processes are currently the most promising option, as they are more economical for removing large quantities of C02. A cryogenic absorption process (Ryan-Holmes) using n-butane as a solvent demonstrated the advantages of using alkanebased solvents. The adaptation of the Ryan-Holmes process to high temperatures offers real potential. This requires the identification of the optimal alkane solvent. Integrated process and solvent design using state of the art thermodynamics, process modelling and optimisation can bring significant new benefits. Advanced thermodynamic models such as SAFT-VR can be used advantageously in this study as they have proven successful for predicting the phase behaviour (VLE) of a large range of n-alkane/C02 mixtures [A. Galindo and F.J. Bias, J. Phys. Chern. B, .2002, 106, 4503], and for a large range of pressure and temperature. The SAFT-VR equation of state has been used to study mixtures of C02 and methane in detail, and it is found that it describes accurately both supercritical and coexistence states. This equation of state has been implemented within gPROMS software, allowing its use for process modelling. The units used in a separation have been modelled with mass and energy balance equations. The dimensioning of the units has also been performed as the sizes of the units are required to estimate their cost. A complete cost estimation has been carried out in order to estimate the capital and operating expenses of the plant. We have applied this new integrated approach to process and solvent design to identify the most appropriate flowsheet to perform profitable capture of C02 for feed C02 contents from 10% to 70%. We have also carried out a sensitivity study which shows that changes in the thermodynamic model parameters has a limited impact on the optimal process. The effect of the presence of small quantities of ethane in the feed has also been evaluated on the optimal flowsheet, and we find that ethane is co-absorbed with C02. Finally, we show that it is possible to design a process that covers the full range of feed C02 contents [10%, 70%], and we give the values of the control variables and the economics performance as a function of the feed C02 content.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available