Qualitative and Quantitative Comparison of Two Promising Oxy-Fuel Power Cycles for CO2 Capture

Wolfgang Sanz,Herbert Jericha,Emil Göttlich,Bernhard Bauer

doi:10.1115/1.2800350

Wolfgang Sanz, Herbert Jericha + Show 2 more

https://doi.org/10.1115/1.2800350

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Since the Kyoto conference, there is a broad consensus that the human emission of greenhouse gases, mainly CO2, has to be reduced. In the power generation sector, there are three main alternatives that are currently studied worldwide. Among them oxy-fuel cycles with internal combustion with pure oxygen are a very promising technology. Within the European project ENCAP (enhanced CO2 capture) the benchmarking of a number of novel power cycles with CO2 capture was carried out. Within the category oxy-fuel cycles, the Graz Cycle and the semiclosed oxy-fuel combustion combined cycle (SCOC-CC) both achieved a net efficiency of nearly 50%. In a second step, a qualitative comparison of the critical components was performed according to their technical maturity. In contrast to the Graz Cycle, the study authors claimed that no major technical barriers would exist for the SCOC-CC. In this work, the ENCAP study is repeated for the SCOC-CC and for a modified Graz Cycle variant as presented at the ASME IGTI Conference 2006. Both oxy-fuel cycles are thermodynamically investigated based on common assumptions agreed upon with the industry in previous work. The calculations showed that the high-temperature turbine of the SCOC-CC plant needs a much higher cooling flow supply due to the less favorable properties of the working fluid. A layout of the main components of both cycles is further presented, which shows that both cycles rely on the new designs of the high-temperature turbine and the compressors. The SCOC-CC compressor needs more stages due to a lower rotational speed but has a more favorable operating temperature. In general, all turbomachines of both cycles show similar technical challenges and are regarded as feasible.

Highlights

In the last two years global warming, environmental change and destruction of natural resources like water and forest reserves have reached exasperating speed
Other events have followed and today the Kyoto Goal of reducing the global greenhouse gas emissions by a substantial amount compared to the 1990 emissions is acknowledged by the majority of governments around the world
The Graz Cycle plant as presented in [5] and investigated in the ENCAP study suffers from the disadvantages of the working fluid expansion into vacuum

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In the last two years global warming, environmental change and destruction of natural resources like water and forest reserves have reached exasperating speed. A comparative calculation of one high-temperature stage using the same parameters showed that the favorable heat capacities of the Graz Cycle working and cooling fluid lead to a 20 % lower demand of cooling mass flow. The Graz Cycle plant as presented in [5] and investigated in the ENCAP study suffers from the disadvantages of the working fluid expansion into vacuum (very large and expensive condenser, corrosion risk for low pressure turbine with exit below dew point temperature).

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