Change search
ReferencesLink to record
Permanent link

Direct link
Efficiency loss analysis for oxy-combustion CO2 capture process: Energy and Exergy analysis
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Energy and Process Engineering.
2011 (English)MasteroppgaveStudent thesis
Abstract [en]

Natural gas combined cycles with oxy-fuel combustion is expected to be an important component of the future carbon constrained energy scenario. An oxy-combustion power cycle enables the fuel to burn in a nitrogen free environment and thereby helps separate the CO2 stream for storage. Depending on the oxygen source and purity, the CO2 stream may need further purification via a purification unit (CPU) before compressing it to a high pressure for storage. The major energy penalty in this type of power cycle is the production of oxygen and the downstream purification to remove volatiles. It is this energy penalty which results in the cost of avoiding the CO2 emissions to the atmosphere. Cryogenic Air Separation Units (ASU) for oxygen production con- tribute to approximately 20% of the total energy penalty of such power plants. Oxygen Transport Membranes (OTM) for oxygen production offers a potential solution to reduce the energy penalty of oxy-combustion natural gas cycles. The energy penalties associated with OTMs are that membranes operate at high temperatures and require a sweep gas to establish an oxygen partial pressure difference between the feed and permeate streams. Further, while the Cryogenic ASU has minimum integration with the power process, oxy-combustion cycles with OTMs are tightly integrated with the power plant. Thus the contributions to efficiency penalty in an OTM-based cycles are distributed and not easily identified. The objective of the thesis is to answer the question: "Where does the plant efficiency loss originate in oxy-combustion CO2 capture process using Oxygen Transport Membrane as compared to one with cryogenic ASU?" The contribution of the work will be to highlight the losses at the sub-process and at the equipment level. This work studies three different cases of oxy-combustion natural gas combined cycles (NGCC) with CO2 capture. The baseline scenario, modified/improved scenario and the advanced scenario. The baseline scenario is a simple oxy-combustion NGCC power plant with ASU as the oxygen source. Various losses associated with this system are studied in detail. The modified/improved scenario involves analysis of possible modifications to the baseline case and applying the results in-order to improve the baseline case. The modified scenario is expected to have a better overall plant performance. The advanced scenario involves usage of OTM for oxygen production. The power plants are simulated in Aspen HYSYS and plant mass and heat balances are calculated. Using the stream enthalpy, entropy and composition, we can calculate the stream exergy values. Control volumes help us analyze the component and sub-system exergy losses and arrive at the overall power plant exergetic efficiency. The base- line power plant scheme is found to have an exergetic efficiency of 47 percentage points with a thermal efficiency of 49.6 percentage, with capture. The modified power plant scheme is obtained by increasing the gas turbine pressure ratio and this has a significant impact on the over- all system design and hence the performance. The modified system has exergetic and thermal efficiency of 49 and 51 percentage points respectively. The advanced power plant with OTM, also called as the Advanced Zero Emissions Powerplant (AZEP) has an exergetic efficiency of 51 and a thermal efficiency of 53.4 percentage. In all the cases, the combustor where most of the fuel is burnt is responsible for majority of the exergy destruction. There is potential for improving the ASU and thereby achieving a lesser specific oxygen production power and also due to system integration and other improvements, the overall oxy-combustion NGCC power plant is expected to play an important role in 5 - 10 years. Also as the working fluid is different from that of a normal air based power plant, significant work needs to be done in the gas turbine and compressor part. Also detailed cost estimations, reliability and flexibility studies, operability and safety related studies need to be carried out in-order to boost the confidence in oxy-fuel NGCC power plants and take it to the next phase.

Place, publisher, year, edition, pages
Institutt for energi- og prosessteknikk , 2011. , 115 p.
Keyword [no]
ntnudaim:6354, MSISEE Innovative Sustainable Energy Engineering, Carbon Dioxide Capture
URN: urn:nbn:no:ntnu:diva-14177Local ID: ntnudaim:6354OAI: diva2:448155
Available from: 2011-10-14 Created: 2011-10-14

Open Access in DiVA

fulltext(10985 kB)1598 downloads
File information
File name FULLTEXT01.pdfFile size 10985 kBChecksum SHA-512
Type fulltextMimetype application/pdf
cover(77 kB)45 downloads
File information
File name COVER01.pdfFile size 77 kBChecksum SHA-512
Type coverMimetype application/pdf
attachment(4406 kB)95 downloads
File information
File name ATTACHMENT01.zipFile size 4406 kBChecksum SHA-512
Type attachmentMimetype application/zip

By organisation
Department of Energy and Process Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 1598 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 369 hits
ReferencesLink to record
Permanent link

Direct link