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Alternative cooling systems for CO2 capture technology

Singu, Yeshwanth (2015). Alternative cooling systems for CO<sub>2</sub> capture technology. Master of Engineering Thesis, Charles Darwin University.

Document type: Thesis
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Author Singu, Yeshwanth
Title Alternative cooling systems for CO2 capture technology
Institution Charles Darwin University
Publication Date 2015
Thesis Type Master of Engineering
0913 - Mechanical Engineering
Abstract A new CO2 capture technology for the IGCC power plant of 500MW capacity was proposed by Surovtseva, Amin and Barifcani in the year 2011. This technology required a cooling system to cool the flue gas from 35°C to -55°C for effective carbon dioxide capture. The initial work estimated that the energy required for cooling will be in the order of 13 MW through basic thermodynamic analysis, but the detailed analysis of the refrigeration system was not covered. The cooling system for this technology was further analysed and improved by Qi Tian (CDU Student-2014-2015). But it required energy in the order of 50MW after heat recovery for operation. This made the capture technology an energy intensive one as it consumed 10% of the plant capacity when compared to 5-7% for the existing technologies. The objective of this thesis is to research for multiple alternatives for the cooling system and to design an effective cooling system whose energy requirement is in the order of 13 MW as estimated by the initial works.

The first alternative involved integration of a conventional JT based cooling cycle with a multistage heat exchanger system. For this case the energy required for achieving the cooling was found to be in the order of 130MW. This approach did not perform as expected because of the high influence of negative JT coefficient of Hydrogen in the flue gas.

The second alternative researched was redesigning the cooler, used after the heat recovery system, with optimum refrigerant combinations at the operating conditions and with different refrigeration cycles. This also did not lead to the expected result as the energy consumption by the system was in the order of 60 MW to 80MW.

The third alternative researched was the sub-cooling of the separated CO2, which exits the heat recovery system, in a JT valve and using it as a cold source to further reduce the feed gas temperature. This further reduced the cooling load on the final stage chiller substantially and brought down the power consumption to 11.7MW which is even lesser when compared to initial prediction of 13MW thus arriving the thesis objective. The additional heat transfer units were designed as another outcome of this thesis.

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