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A comparative study of the carbon dioxide transcritical power cycle compared with an organic rankine cycle with R123 as working fluid in waste heat recovery
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
2006 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 26, no 17-18, 2142-2147 p.Article in journal (Refereed) Published
Abstract [en]

The organic rankine cycle (ORC) as a bottoming cycle1The expression "bottoming cycle" refers to the power cycle that uses waste industrial heat for power generation by supplementing heat from any fossil fuel.1 to convert low-grade waste heat into useful work has been widely investigated for many years. The CO2 transcritical power cycle, on the other hand, is scarcely treated in the open literature. A CO2 transcritical power cycle (CO2 TPC) shows a higher potential than an ORC when taking the behavior of the heat source and the heat transfer between heat source and working fluid in the main heat exchanger into account. This is mainly due to better temperature glide matching between heat source and working fluid. The CO2 cycle also shows no pinch limitation in the heat exchanger. This study treats the performance of the CO2 transcritical power cycle utilizing energy from low-grade waste heat to produce useful work in comparison to an ORC using R123 as working fluid. Due to the temperature gradients for the heat source and heat sink the thermodynamic mean temperature has been used as a reference temperature when comparing both cycles. The thermodynamic models have been developed in EES2EES - Engineering equation solver. The thermodynamic properties for carbon dioxide in EES are calculated by the fundamental equation of state developed by R. Span and W. Wagner, A new equation of state for carbon dioxide covering the fluid region form the triple-point temperature to 1100 K at pressures up to 800 MPa, J. Phys. Chem. Ref. Data, Vol. 25, No. 6, 1996. http://www.fchart.com/ees/ees.shtml.2 The relative efficiencies have been calculated for both cycles. The results obtained show that when utilizing the low-grade waste heat with the same thermodynamic mean heat rejection temperature, a transcritical carbon dioxide power system gives a slightly higher power output than the organic rankine cycle.

Place, publisher, year, edition, pages
2006. Vol. 26, no 17-18, 2142-2147 p.
Keyword [en]
CO2; Efficiency; ORC; Transcritical power cycle
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-6008DOI: 10.1016/j.applthermaleng.2006.04.009ISI: 000239984400012Scopus ID: 2-s2.0-33745233798OAI: oai:DiVA.org:kth-6008DiVA: diva2:10575
Note
QC 20100819Available from: 2006-06-16 Created: 2006-06-16 Last updated: 2012-03-20Bibliographically approved
In thesis
1. Novel cycles using carbon dioxide as working fluid: new ways to utilize energy from low-grade heat sources
Open this publication in new window or tab >>Novel cycles using carbon dioxide as working fluid: new ways to utilize energy from low-grade heat sources
2006 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

This licentiate thesis proposes and analyzes three carbon dioxide novel cycles, namely: the carbon dioxide transcritical power cycle, the carbon dioxide Brayton cycle and the carbon dioxide cooling and power combined cycle. Due to the different characteristics of each cycle, the three cycles are suitable for different applications. The CO2 transcritical power cycle is suitable for harvesting energy from low-grade heat sources, near which a low temperature heat sink is accessible. The CO2 Brayton cycle is suitable for harvesting the energy from relatively high-grade heat sources when there is no low temperature heat sink available. The CO2 cooling and power combined cycle is suitable for applications, where both power and cooling are needed (e.g. automobile applications, in which the cycle can utilize the energy in the engine exhaust gasses to produce power and provide cooling/heating to the mobile compartment room at the same time).

Several models have been developed using the software known as Engineering Equation Solver (EES)1 for both cycle analysis and computer aided heat exchanger design. Different cycle working conditions have been simulated and different working parameters’ influence on the cycle performance has been explained. In addition, Refprop 7.02 is used for calculating the working fluid properties and the CFD tool Femlab has been employed to investigate the particular phenomena influencing the heat exchanger performance.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. viii, 87 p.
Series
Trita-REFR, ISSN 1102-0245 ; 06:50
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-4055 (URN)91-7178-410-1 (ISBN)
Presentation
2006-06-15, Sal MWL74, KTH, Brinellvägen 68, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101124Available from: 2006-06-16 Created: 2006-06-16 Last updated: 2010-11-24Bibliographically approved
2. Thermodynamic Cycles using Carbon Dioxide as Working Fluid: CO2 transcritical power cycle study
Open this publication in new window or tab >>Thermodynamic Cycles using Carbon Dioxide as Working Fluid: CO2 transcritical power cycle study
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interest in utilizing the energy in low‐grade heat sources and waste heat is increasing. There is an abundance of such heat sources, but their utilization today is insufficient, mainly due to the limitations of the conventional power cycles in such applications, such as low efficiency, bulky size or moisture at the expansion outlet (e.g. problems for turbine blades).

Carbon dioxide (CO2) has been widely investigated for use as a working fluid in refrigeration cycles, because it has no ozonedepleting potential (ODP) and low global warming potential (GWP). It is also inexpensive, non‐explosive, non‐flammable and abundant in nature. At the same time, CO2 has advantages in use as a working fluid in low‐grade heat resource recovery and energy conversion from waste heat, mainly because it can create a better matching to the heat source temperature profile in the supercritical region to reduce the irreversibility during the heating process. Nevertheless, the research in such applications is very limited.

This study investigates the potential of using carbon dioxide as a working fluid in power cycles for low‐grade heat source/waste heat recovery.

At the beginning of this study, basic CO2 power cycles, namely carbon dioxide transcritical power cycle, carbon dioxide Brayton cycle and carbon dioxide cooling and power combined cycle were simulated and studied to see their potential in different applications (e.g. low‐grade heat source applications, automobile applications and heat and power cogeneration applications). For the applications in automobile industries, low pressure drop on the engine’s exhaust gas side is crucial to not reducing the engine’s performance. Therefore, a heat exchanger with low‐pressure drop on the secondary side (i.e. the gas side) was also designed, simulated and tested with water and engine exhaust gases at the early stage of the study (Appendix 2).

The study subsequently focused mainly on carbon dioxide transcritical power cycle, which has a wide range of applications. The performance of the carbon dioxide transcritical power cycle has been simulated and compared with the other most commonly employed power cycles in lowgrade heat source utilizations, i.e. the Organic Rankin Cycle (ORC). Furthermore, the annual performance of the carbon dioxide transcritical power cycle in utilizing the low‐grade heat source (i.e. solar) has also been simulated and analyzed with dynamic simulation in this work.

Last but not least, the matching of the temperature profiles in the heat exchangers for CO2 and its influence on the cycle performance have also been discussed. Second law thermodynamic analyses of the carbon dioxide transcritical power systems have been completed.

The simulation models have been mainly developed in the software known as Engineering Equation Solver (EES)1 for both cycle analyses and computer‐aided heat exchanger designs. The model has also been connected to TRNSYS for dynamic system annual performance simulations. In addition, Refprop 7.02 is used for calculating the working fluid properties, and the CFD tool (COMSOL) 3 has been employed to investigate the particular phenomena influencing the heat exchanger performance.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology(KTH), 2011. xxii, 128 p.
Series
Trita-REFR, ISSN 1102-0245 ; 11:03
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-50261 (URN)978-91-7501-187-5 (ISBN)
Public defence
2011-12-09, M2, Brinellvägen 64, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20111205Available from: 2011-12-05 Created: 2011-12-04 Last updated: 2011-12-09Bibliographically approved

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