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Optimization of cryogenic CO2 purification for oxy-coal combustion
Mälardalen University, School of Sustainable Development of Society and Technology, Västerås, Sweden.
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
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2013 (English)In: Energy Procedia, Elsevier, 2013, 1341-1347 p.Conference paper (Refereed)
Abstract [en]

Oxyfuel combustion is a leading potential CO2 capture technology for power plants. As the flue gas (FG) consists of mainly H2O and CO2, a simpler and more energy-efficient CO2 purification method can be used instead of the standard amine-based chemical absorption approach. For the system of oxyfuel combustion with cryogenic CO2 purification, decreasing the oxygen purity reduces the energy consumption of the Air Separation Unit (ASU) but increases the energy consumption for the downstream cryogenic purification. Thus there exists a trade-off between the energy consumption of the ASU and that for cryogenic purification. This paper investigates the potential efficiency improvement by optimizing this trade-off. The simulated results show that there exists an optimum flue gas condensing pressure for the cryogenic purification, which is affected by the flue gas composition. In addition, decreasing the oxygen purity reduces the combined energy consumption of the ASU and the cryogenic purification, and therefore can improve the electrical efficiency. In summary, prior oxyfuel combustion analyses have assumed a high oxygen purity level of 95 mol% or 99 mol% for the combustion air, which achieves a high CO2 concentration in the flue gases. In this Paper, we demonstrate that a lower level of oxygen purity, such as 80 mol%, in conjunction with a more extensive cryogenic purification of the flue gases can lower the total energy consumption, thereby yielding a significant benefit. However, for oxygen purity levels lower than 75 mol%, it may not be possible to still use the two-stage flash system shown here to achieve a CO2 purity of 95 mol% and a CO2 recovery rate of 90% simultaneously.

Place, publisher, year, edition, pages
Elsevier, 2013. 1341-1347 p.
, Energy Procedia, ISSN 1876-6102 ; 37
Keyword [en]
CO2 capture and storage (CCS), CO2 purity, CO2 recovery rate, Cryogenicpurification, Energy consumption, Oxy-coal combustion, Oxygen purity
National Category
Energy Engineering
URN: urn:nbn:se:kth:diva-116576DOI: 10.1016/j.egypro.2013.06.009ISI: 000345500501065ScopusID: 2-s2.0-84898754949OAI: diva2:596207
11th International Conference on Greenhouse Gas Control Technologies, GHGT 2012; Kyoto; Japan; 18 November 2012 through 22 November 2012

QC 20140627. Updated from submitted to published.

Available from: 2013-01-22 Created: 2013-01-21 Last updated: 2015-10-06Bibliographically approved
In thesis
1. Oxy-coal combustion and its integration with power systems for CO2 capture
Open this publication in new window or tab >>Oxy-coal combustion and its integration with power systems for CO2 capture
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oxy-fuel combustion is one of the technologies for carbon dioxide (CO2) capture and storage (CCS) in fossil fuel based power systems to mitigate global greenhouse gases (GHGs) emissions. When introducing oxy-fuel combustion into the power systems, energy penalty for CCS has significant impacts on the system performance. The heat and mass balance of the oxy-fuel combustion power system need to be investigated due to the change of combustion environment.


This study investigated oxy-fuel combustion with coal as the fuel, so called oxy-coal combustion, and its integration with power systems for CO2 capture. First, mass balance was formulated for the oxy-coal combustion considering flue gas recycle (FGR). Then, computational fluid dynamic (CFD) modelling was conducted on the oxy-coal combustion to identify its characteristics in terms of flame profile and radiation heat transfer. Finally, process simulation was performed on the oxy-coal combustion power system to evaluate its technical and economic performance including the subsystems of air separation unit (ASU), furnace/boiler, and cryogenic CO2 purification. In addition, a new peak and off-peak (POP) operation mode of ASU to shift the energy penalty for CCS and improve the performance of the whole system was addressed and analysed by net present value method.


The results show that oxy-coal combustion can match well to conventional (air-coal) combustion under specific operating conditions, and results in a minimal change of existing boilers under conventional technology. The increase of moisture content in the flue gas has little impact on the flame temperature, but results in a higher surface incident radiation on boiler side walls. Compared with air-coal combustion power systems, oxy-coal combustion power systems have much lower flow rate of flue gas, lower NO and SO2 emissions, higher boiler efficiency, but a higher flue gas dew point. Furthermore, various FGR options in the oxy-coal combustion power system have no clear effect on recycle ratio, flow rate of flue gas, and electrical efficiency of the whole system, but cause much different flue gas compositions at the exit of the boiler. Energy penalty for ASU in the oxy-coal combustion power system accounts for about 7% based on low heating value. Comparatively, ASU has a larger effect than cryogenic CO2 purification on energy consumption in the oxy-coal combustion power system. The new POP operation mode of ASU is technically and economically feasible for shifting the energy use of ASU in the peak and off-peak periods, and more electricity could be generated at a higher price.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xiv, 60 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2013:4
oxy-coal combustion; flue gas recycle; radiation; peak and off-peak operations; cryogenic CO2 purification
National Category
Chemical Engineering
urn:nbn:se:kth:diva-116575 (URN)987-91-7501-612-2 (ISBN)
Public defence
2013-02-08, K1, Teknikringen 56, KTH, Stockholm, 13:00 (English)

QC 20130122

Available from: 2013-01-22 Created: 2013-01-21 Last updated: 2013-01-22Bibliographically approved

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