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Economic analysis of Organic Rankine Cycle (ORC) and Organic Rankine Cycle with internal heat exchanger (IORC) based on industrial waste heat source constraint
Available online at www.sciencedirect.com Available online at www.sciencedirect.com
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Energyonline Procedia 00 (2018) 000–000 Available onlineatat www.sciencedirect.com Available www.sciencedirect.com Energy Procedia 00 (2018) 000–000
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www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy Procedia 158 Energy Procedia 00(2019) (2017)2403–2408 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Economic analysis of Organic Rankine Cycle (ORC) and Organic EconomicThe analysis of Organic Rankine Cycle (ORC) and Organic 15th International Symposium on District Heating and Cooling Rankine Cycle with internal heat exchanger (IORC) based on Rankine Cycle with internal heat exchanger (IORC) based on wasteofheat source constraint Assessingindustrial the feasibility using the heat demand-outdoor industrial waste heat source constraint temperature function for a long-term district heat demand forecast Fan Wei*, Guo Senchuang, Han Zhonghe Fan Wei*, Guo Senchuang, Han Zhonghe c a,b,c a b of energy power mechanical China Electric.,Power University, Baoding 071003, I.School Andrić *, A.andPina , P.engineering, Ferrãoa,North J. Fournier B. Lacarrière , O. Le China Correc
School of energy power and mechanical engineering, North China Electric Power University, Baoding 071003, China IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Abstract c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract a
In order to compare the economics of ORC and IORC systems based on industrial flue gas waste heat. 5 working fluids were In order to compare economics of of ORC and IORC based on industrial flue gaswere wastecompared, heat. 5 working were selected establish the economic model systems. The systems thermal performance and economy and thefluids constraint selected to establish economic of systems.and Thethethermal performance and economy wereanalyzed. compared, the constraint relationship between the exhaustmodel gas temperature performance of different systems was Theand results show that Abstract relationship exhaust gasdry temperature and is thehigher performance different systems was analyzed. show the net powerbetween of ORCthe system using working fluid than the of system using wet working fluid, andThe theresults economic ofthat the the net power of ORC system using dry working fluid isand higher the system wet working fluid,fluid and the economic of the system using wet working fluid is better. The IORC ORCthan systems using using the same dry working have an equivalent District heating are commonly addressed in theORC literature as using one ofthe thesame mostdry effective solutions for an decreasing the system wet networks working is better. The IORC working fluid equivalent exhaust using temperature with a fluid net power difference of 0. and When the systems exhaust gas temperature is higher than the have equivalent exhaust greenhouse gas emissions from the building sector. These systems requiregas high investments which are returned throughexhaust the heat exhaust temperature with a net power difference of 0. When the exhaust temperature is higher than the equivalent temperature, the net power of the IORC system is higher than the ORC system; If the exhaust gas temperature is lower than the sales. Due the to the changed conditions building renovation policies, heat demand in the futureis could decrease, temperature, nettemperature, power of climate thetheIORC systemofisand higher than the ORC system; If the exhaust gas temperature lower than the equivalent exhaust economics the IORC system deteriorates; the economics of the IORC system is inferior to prolonging the investment return period. equivalent exhaust temperature, the economics of the IORC system deteriorates; the economics of the IORC system is inferior to the ORC system using the same dry working fluid. The main scopeusing of thisthepaper to assess thefluid. feasibility of using the heat demand – outdoor temperature function for heat demand the ORC system sameisdry working forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 Copyright © 2018 Elsevier Ltd. All rights reserved. ©buildings 2019 The Authors. Published by Elsevier Ltd. and typology. Three weather scenarios vary in both construction period (low, medium, high) and three district Copyright ©that 2018 Elsevier Ltd. Allresponsibility rights reserved. Selection and peer-review under of the scientific committee of the 10th International Conference on Applied This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) th renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand on values were Conference Applied Selection and peer-review under responsibility of the scientific committee of the 10 International Energy (ICAE2018). Peer-review under responsibility of the scientific committee ofpreviously ICAE2018developed – The 10th International Conference on Applied Energy. compared with results from a dynamic heat demand model, and validated by the authors. Energy (ICAE2018). The results showed that Cycle; when waste only weather change is considered, marginperformance; of error could be acceptable for some applications Keywords: Organic Rankine heat; thermodynamic performance;the economic internal heat exchanger. (the errorOrganic in annual demand lower 20% for all weather scenarios considered).internal However, introducing renovation Keywords: Rankine Cycle;was waste heat; than thermodynamic performance; economic performance; heat after exchanger. scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the 1.The Introduction in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and 1.decrease Introduction renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the Low-temperature waste heat power could generation canfunction recycleparameters low-grade energy considered, in industrial coupled scenarios). The values suggested be usedtechnology to modify the for heat the scenarios and Low-temperature waste heat powerand generation technology candegradation. recycle low-grade heat energy intechnology industrial production, improve energy efficiency mitigate environmental Organic Rankine cycle improve the accuracy of heat demand estimations.
production, improve energy efficiency and mitigate environmental degradation. Organic Rankine cycle technology © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +86 13102911666; fax: +86 0312-7522100 * Corresponding author. Tel.: +86 13102911666; fax: +86 0312-7522100 E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected]
1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility the scientific Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.291
Fan Wei et al. / Energy Procedia 158 (2019) 2403–2408 Fan Wei/ Energy Procedia 00 (2018) 000–000
2404 2
can effectively absorb low-grade heat energy to achieve thermal power conversion, and has the advantages of simple structure, high system efficiency and environmental friendliness. In order to promote the application of ORC technology as soon as possible, many researchers have conducted research on ORC system structure and system performance [1-3]. Zhang et al. [4] optimized the system parameters for the geothermal source ORC, the results show that the different objective functions and the optimal parameters are different. DAI et al. [5] compared the thermal performance of the ORC system with internal heat exchanger and ORC system without internal heat exchanger under the same conditions of net power, the results show that the thermal efficiency of the ORC system with internal heat exchanger is relatively high. In practice, a series of work such as selection of working fluid, system structure and parameter determination should be carried out based on specific heat source conditions. Both the initial temperature of the heat source fluid and the temperature after the heat release constrain the thermal performance of the system. Therefore, the analysis of the heat source conditions on the thermodynamic characteristics and economic constraints of different structural types of systems, which contribute to the application of ORC technology. In this paper, the thermal performance and economics of ORC and IORC systems are studied, and the thermal characteristics and economical differences of different systems under the same heat source conditions are analysed. 2. Modeling 2.1. Thermodynamic model The schematic diagram of Organic Rankine Cycle (ORC) system is shown in Fig.1. Due to the thermal properties of the dry working fluid, the working fluid is superheated at the expander outlet. To efficiently utilize the superheated exhaust heat, an internal heat exchanger (IHE) is equipped, which is shown in Fig.2.
Fig.1. Schematic diagram of ORC system
Fig.2. Schematic diagram ORC system with internal heat exchanger
Absorbed heat of working fluid in evaporator is,
Q1 mg c ta tb m f h1 h4
(1)
where ta is flue gas temperature at the inlet of evaporator; tb is exhaust gas temperature; mg is mass flow rate of flue gas; c is specific heat capacity of flue gas; h1 is specific enthalpy at expander inlet r; h4 is specific enthalpy at evaporator inlet. Power output of expander is,
Pi m f h1 h2 m f h1 h2 s i
(2)
where ηi is relative internal efficiency of expander; h2 is specific enthalpy at expander outlet; h2s is specific enthalpy of expander outlet after working fluid experiences an isentropic process. Released heat of working fluid in condenser is calculated,
Fan Wei et al. / Energy Procedia 158 (2019) 2403–2408 Fan Wei / Energy Procedia 00 (2018) 000–000
2405 3
Q2 mf (h3 h3 )
(3)
Pp m f h4 h3 m f h4 s h3 / p
(4)
where h3 is specific enthalpy at condenser outlet. Consumption power of feed pump is,
where ηp is feed pump efficiency; h4s is specific enthalpy at feed pump outlet after working fluid experiences an isentropic process. Net power output of system is,
Pnet Pi Pp
(5)
QIHE m f h6 h5 m f h2 h3
(6)
Energy balance equation in the IHE is,
where h6 is specific enthalpy at evaporator inlet.
2.2. Economic model Investment cost of ORC system is composed of equipment cost, system operation cost and management cost. Equipment mainly includes evaporator, condenser, feed pump and expander, and also contains IHE for IORC system. The total equipment cost of the system is calculated as,
Cost 0 C BM , E C BM , C C BM ,T C BM , P C BM , IHE
(7)
According to purchase power of US dollar in 1996, investment cost of every equipment can be calculated [6],
CBM CP0 FBM
(8)
where FBM is comprehensive factor of material and pressure; Cp0 is basic cost of equipment, and calculated by
lg C p0 K1 K 2 lg X K 3 (lg X ) 2
(9)
where X is the technical parameter of the equipment, the heat exchange area for the heat exchanger, the output power Pi for the expander, and the consumption power Pp for the feed pump [6-8]. Comprehensively considering investment cost and generation income, electrical generation cost is defined to evaluate system economy. It reflects the cost per kW·h electricity and specific calculation relation is [6, 7], CRF
LEC
i (1 i )TS (1 i )TS 1
CRF Cost2016 COM s Wnet OPs
(10) (11)
Fan Wei et al. / Energy Procedia 158 (2019) 2403–2408 Fan Wei/ Energy Procedia 00 (2018) 000–000
2406 4
where COMsis the cost of system operation and maintenance, is 1.5% of Cost2017; OPs is annual operation time of system and is set as 7500 hours; Ts is the overall operation time of system and set as 20 years; i is bank interest rate and is set as 6%. 3. Results and discussions R600a, R245fa, R365MFC, R152a and R161 are selected. For industrial flue gas waste heat, heat source temperature is 150℃, temperature range of exhaust gas is 70-100℃, and mass flow rate of flue gas is 10 kg·s-1. Condensing temperature is 35℃, cooling water temperature is 25℃, and pinch point temperature differences of evaporator and condenser are 15℃ and 5℃, respectively. Isentropic efficiency of expander is 85%, feed pump efficiency is 80%. Pressure loss and heat loss from equipment and piping and valves are neglected.
3.1. Thermodynamic analysis Because the relationship between expander enthalpy drop and mass flow is different, the trend of the net power output of the ORC system using different working fluids is firstly increased and then decreased, as shown in Fig. 3(a). The net power output of the ORC system using dry working fluid is significantly higher than the system using wet working fluid. In addition, the maximum net power output does not occur when the heat absorption is maximum. The IORC and ORC systems using the same dry working fluid have an equivalent exhaust temperature with a net power difference of 0, as shown in Fig. 3(b). When systems absorb the same amount of heat from the heat source, The IORC system's expander exhaust enthalpy is slightly lower than the ORC system, however its flow is greater, and thus the exhaust heat of IORC is higher. When the exhaust gas temperature is lower than the equivalent exhaust temperature, the heat recovery from IHE is less, and the heat release of the IORC system is higher than ORC system, and thus the IORC system has lower thermal performance. The IORC system has better thermal performance when the exhaust temperature is higher than the equivalent exhaust temperature.
(a) Net power of ORC systems with different working fluids
(b) Net power difference between IORC and ORC systems
Fig.3 Net power output of different systems
3.2. Economic analysis and comparison of different systems The investment cost of systems using different working fluids decreases with increasing exhaust temperature, as shown in Fig.4. When the system absorbs the same amount of heat from the heat source, the investment cost of the IORC system is higher than the ORC system using the same dry working fluid. There are two reasons for this. First, the cost of IHE; secondly, the parameters of equipment of IORC system are different from those of the ORC system, resulting in changes in equipment costs. Therefore, if the exhaust gas temperature is lower than the equivalent exhaust temperature, the economics of the IORC system is inferior to the ORC system using the same dry working fluid. The investment cost of the ORC system using wet working is lower, and the ORC system using R152a has the lowest investment cost.
Fan Wei et al. / Energy Procedia 158 (2019) 2403–2408 Fan Wei / Energy Procedia 00 (2018) 000–000
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Fig.4 Investment cost of ORC systems with different working fluids
Due to the different relationship between investment cost and net power output, the LEC of different systems showed a trend of decreasing first and then slightly improving, as shown in Fig.5. If the exhaust gas temperature is not constrained, the ORC system using R152a has the lowest LEC and is the most economical. The R245fa ORC system is the most economical if the exhaust gas temperature is limited to no more than 90 °C.
Fig.5 LEC of different systems
The LEC difference maintains a positive value as the exhaust gas temperature changes, as shown in Fig.6. When the exhaust gas temperature is greater than the equivalent exhaust temperature, the more obvious the net power output increment of the IORC system, the smaller the LEC difference between the two systems. The LEC difference for the two systems using R600a is the smallest, 0.0069-0.0108$/(kW•h), R245fa is 0.0081-0.0136$/(kW•h), and the LEC difference for R365mfc is the highest, 0.0073-0.0213$/ (kW•h). Therefore, the investment cost of the IORC system increases significantly, and the net power output increment is relatively low, which leads to the economics of the IORC system being inferior to the ORC system.
Fig.6 LEC difference between IORC and ORC systems using the same dry working fluid
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Fan Wei et al. / Energy Procedia 158 (2019) 2403–2408 Fan Wei/ Energy Procedia 00 (2018) 000–000
4. Conclusions The thermal performance of an IORC system is not necessarily better than an ORC system using the same working fluid. The IORC system has a thermal performance advantage only if the exhaust gas temperature is higher than the equivalent exhaust temperature. The ORC system using the wet working fluid has lower net power output and investment cost. If the exhaust gas temperature is not constrained, the ORC system using R152a is the most economical, and R245fa is the most economical if the exhaust gas temperature is limited to no more than 90 °C. The investment cost of the IORC system increases significantly, and the net power output increment is relatively low, which leads to the economics of the IORC system being inferior to the ORC system. Acknowledgements This paper acknowledges the support by the National Natural Science Foundation of China (No.51306059) and the Fundamental Business Special Funds for the Central Universities (2014MS151). References [1] Al-SULAIMAN F A, DINCER I, HAMDULLAHPUR F. Exergy modeling of a new solar driven trigeneration system[J]. Solar Energy, 2011, 85(9):2228-2243. [2] SCHUSTER A, KARELLAS S, KAKARAS E,et al. Energetic and economic investigation of Organic Rankine Cycle applications[J]. Applied Thermal Engineering, 2009, 29(8–9):1809-1817. [3] STOPPATO A. Energetic and economic investigation of the operation management of an Organic Rankine Cycle cogeneration plant[J]. Energy, 2012, 41(1):3-9. [4] Shengjun Z, Huaixin W, Tao G. Performance comparison and parametric optimization of subcritical Organic Rankine Cycle (ORC) and transcritical power cycle system for low-temperature geothermal power generation[J]. Applied Energy, 2011, 88(8): 2740-2754 [5] Dai Y, Wang J, Gao L. Parametric optimization and comparative study of organic Rankine cycle (ORC) for low grade waste heat recovery[J]. Energy Conversion and Management, 2009, 50(3): 576-582 [6] TURTON R, BAILIE R C, WHITING W B, et al .Analysis, Synthesis and Design of Chemical Processes[M]. New Jersey: Prentice Hall PTR, 1998 [7] Yongqiang Feng , Yaning Zhang , Bingxi Li, et al . Comparison between regenerative organic Rankine cycle (RORC) and basic organic Rankine cycle (BORC) based on thermoeconomic multi-objective optimization considering exergy efficiency and levelized energy cost (LEC)[J]. Energy Conversion and Management, 2015,(96): 58-71 [8] TCHANCHE B, QUOILIN S, DECLAYE S,et al. Economic feasibility study of a small scale organic rankine cycle system in waste heat recovery application[C]. 10th ASME Biennial Conference on Engineering Systems Design and Analysis, Istanbul, TURKEY, 2010.
ScienceDirect ScienceDirect
Energyonline Procedia 00 (2018) 000–000 Available onlineatat www.sciencedirect.com Available www.sciencedirect.com Energy Procedia 00 (2018) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy Procedia 158 Energy Procedia 00(2019) (2017)2403–2408 000–000 www.elsevier.com/locate/procedia
10th International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Hong Kong, 10th International Conference on Applied Energy China(ICAE2018), 22-25 August 2018, Hong Kong, China
Economic analysis of Organic Rankine Cycle (ORC) and Organic EconomicThe analysis of Organic Rankine Cycle (ORC) and Organic 15th International Symposium on District Heating and Cooling Rankine Cycle with internal heat exchanger (IORC) based on Rankine Cycle with internal heat exchanger (IORC) based on wasteofheat source constraint Assessingindustrial the feasibility using the heat demand-outdoor industrial waste heat source constraint temperature function for a long-term district heat demand forecast Fan Wei*, Guo Senchuang, Han Zhonghe Fan Wei*, Guo Senchuang, Han Zhonghe c a,b,c a b of energy power mechanical China Electric.,Power University, Baoding 071003, I.School Andrić *, A.andPina , P.engineering, Ferrãoa,North J. Fournier B. Lacarrière , O. Le China Correc
School of energy power and mechanical engineering, North China Electric Power University, Baoding 071003, China IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France Abstract c Département Systèmes Énergétiques et Environnement - IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France Abstract a
In order to compare the economics of ORC and IORC systems based on industrial flue gas waste heat. 5 working fluids were In order to compare economics of of ORC and IORC based on industrial flue gaswere wastecompared, heat. 5 working were selected establish the economic model systems. The systems thermal performance and economy and thefluids constraint selected to establish economic of systems.and Thethethermal performance and economy wereanalyzed. compared, the constraint relationship between the exhaustmodel gas temperature performance of different systems was Theand results show that Abstract relationship exhaust gasdry temperature and is thehigher performance different systems was analyzed. show the net powerbetween of ORCthe system using working fluid than the of system using wet working fluid, andThe theresults economic ofthat the the net power of ORC system using dry working fluid isand higher the system wet working fluid,fluid and the economic of the system using wet working fluid is better. The IORC ORCthan systems using using the same dry working have an equivalent District heating are commonly addressed in theORC literature as using one ofthe thesame mostdry effective solutions for an decreasing the system wet networks working is better. The IORC working fluid equivalent exhaust using temperature with a fluid net power difference of 0. and When the systems exhaust gas temperature is higher than the have equivalent exhaust greenhouse gas emissions from the building sector. These systems requiregas high investments which are returned throughexhaust the heat exhaust temperature with a net power difference of 0. When the exhaust temperature is higher than the equivalent temperature, the net power of the IORC system is higher than the ORC system; If the exhaust gas temperature is lower than the sales. Due the to the changed conditions building renovation policies, heat demand in the futureis could decrease, temperature, nettemperature, power of climate thetheIORC systemofisand higher than the ORC system; If the exhaust gas temperature lower than the equivalent exhaust economics the IORC system deteriorates; the economics of the IORC system is inferior to prolonging the investment return period. equivalent exhaust temperature, the economics of the IORC system deteriorates; the economics of the IORC system is inferior to the ORC system using the same dry working fluid. The main scopeusing of thisthepaper to assess thefluid. feasibility of using the heat demand – outdoor temperature function for heat demand the ORC system sameisdry working forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 Copyright © 2018 Elsevier Ltd. All rights reserved. ©buildings 2019 The Authors. Published by Elsevier Ltd. and typology. Three weather scenarios vary in both construction period (low, medium, high) and three district Copyright ©that 2018 Elsevier Ltd. Allresponsibility rights reserved. Selection and peer-review under of the scientific committee of the 10th International Conference on Applied This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) th renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand on values were Conference Applied Selection and peer-review under responsibility of the scientific committee of the 10 International Energy (ICAE2018). Peer-review under responsibility of the scientific committee ofpreviously ICAE2018developed – The 10th International Conference on Applied Energy. compared with results from a dynamic heat demand model, and validated by the authors. Energy (ICAE2018). The results showed that Cycle; when waste only weather change is considered, marginperformance; of error could be acceptable for some applications Keywords: Organic Rankine heat; thermodynamic performance;the economic internal heat exchanger. (the errorOrganic in annual demand lower 20% for all weather scenarios considered).internal However, introducing renovation Keywords: Rankine Cycle;was waste heat; than thermodynamic performance; economic performance; heat after exchanger. scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the 1.The Introduction in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and 1.decrease Introduction renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the Low-temperature waste heat power could generation canfunction recycleparameters low-grade energy considered, in industrial coupled scenarios). The values suggested be usedtechnology to modify the for heat the scenarios and Low-temperature waste heat powerand generation technology candegradation. recycle low-grade heat energy intechnology industrial production, improve energy efficiency mitigate environmental Organic Rankine cycle improve the accuracy of heat demand estimations.
production, improve energy efficiency and mitigate environmental degradation. Organic Rankine cycle technology © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. * Corresponding author. Tel.: +86 13102911666; fax: +86 0312-7522100 * Corresponding author. Tel.: +86 13102911666; fax: +86 0312-7522100 E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected]
1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102 Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection and peer-review under responsibility the scientific Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of ICAE2018 – The 10th International Conference on Applied Energy. 10.1016/j.egypro.2019.01.291
Fan Wei et al. / Energy Procedia 158 (2019) 2403–2408 Fan Wei/ Energy Procedia 00 (2018) 000–000
2404 2
can effectively absorb low-grade heat energy to achieve thermal power conversion, and has the advantages of simple structure, high system efficiency and environmental friendliness. In order to promote the application of ORC technology as soon as possible, many researchers have conducted research on ORC system structure and system performance [1-3]. Zhang et al. [4] optimized the system parameters for the geothermal source ORC, the results show that the different objective functions and the optimal parameters are different. DAI et al. [5] compared the thermal performance of the ORC system with internal heat exchanger and ORC system without internal heat exchanger under the same conditions of net power, the results show that the thermal efficiency of the ORC system with internal heat exchanger is relatively high. In practice, a series of work such as selection of working fluid, system structure and parameter determination should be carried out based on specific heat source conditions. Both the initial temperature of the heat source fluid and the temperature after the heat release constrain the thermal performance of the system. Therefore, the analysis of the heat source conditions on the thermodynamic characteristics and economic constraints of different structural types of systems, which contribute to the application of ORC technology. In this paper, the thermal performance and economics of ORC and IORC systems are studied, and the thermal characteristics and economical differences of different systems under the same heat source conditions are analysed. 2. Modeling 2.1. Thermodynamic model The schematic diagram of Organic Rankine Cycle (ORC) system is shown in Fig.1. Due to the thermal properties of the dry working fluid, the working fluid is superheated at the expander outlet. To efficiently utilize the superheated exhaust heat, an internal heat exchanger (IHE) is equipped, which is shown in Fig.2.
Fig.1. Schematic diagram of ORC system
Fig.2. Schematic diagram ORC system with internal heat exchanger
Absorbed heat of working fluid in evaporator is,
Q1 mg c ta tb m f h1 h4
(1)
where ta is flue gas temperature at the inlet of evaporator; tb is exhaust gas temperature; mg is mass flow rate of flue gas; c is specific heat capacity of flue gas; h1 is specific enthalpy at expander inlet r; h4 is specific enthalpy at evaporator inlet. Power output of expander is,
Pi m f h1 h2 m f h1 h2 s i
(2)
where ηi is relative internal efficiency of expander; h2 is specific enthalpy at expander outlet; h2s is specific enthalpy of expander outlet after working fluid experiences an isentropic process. Released heat of working fluid in condenser is calculated,
Fan Wei et al. / Energy Procedia 158 (2019) 2403–2408 Fan Wei / Energy Procedia 00 (2018) 000–000
2405 3
Q2 mf (h3 h3 )
(3)
Pp m f h4 h3 m f h4 s h3 / p
(4)
where h3 is specific enthalpy at condenser outlet. Consumption power of feed pump is,
where ηp is feed pump efficiency; h4s is specific enthalpy at feed pump outlet after working fluid experiences an isentropic process. Net power output of system is,
Pnet Pi Pp
(5)
QIHE m f h6 h5 m f h2 h3
(6)
Energy balance equation in the IHE is,
where h6 is specific enthalpy at evaporator inlet.
2.2. Economic model Investment cost of ORC system is composed of equipment cost, system operation cost and management cost. Equipment mainly includes evaporator, condenser, feed pump and expander, and also contains IHE for IORC system. The total equipment cost of the system is calculated as,
Cost 0 C BM , E C BM , C C BM ,T C BM , P C BM , IHE
(7)
According to purchase power of US dollar in 1996, investment cost of every equipment can be calculated [6],
CBM CP0 FBM
(8)
where FBM is comprehensive factor of material and pressure; Cp0 is basic cost of equipment, and calculated by
lg C p0 K1 K 2 lg X K 3 (lg X ) 2
(9)
where X is the technical parameter of the equipment, the heat exchange area for the heat exchanger, the output power Pi for the expander, and the consumption power Pp for the feed pump [6-8]. Comprehensively considering investment cost and generation income, electrical generation cost is defined to evaluate system economy. It reflects the cost per kW·h electricity and specific calculation relation is [6, 7], CRF
LEC
i (1 i )TS (1 i )TS 1
CRF Cost2016 COM s Wnet OPs
(10) (11)
Fan Wei et al. / Energy Procedia 158 (2019) 2403–2408 Fan Wei/ Energy Procedia 00 (2018) 000–000
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where COMsis the cost of system operation and maintenance, is 1.5% of Cost2017; OPs is annual operation time of system and is set as 7500 hours; Ts is the overall operation time of system and set as 20 years; i is bank interest rate and is set as 6%. 3. Results and discussions R600a, R245fa, R365MFC, R152a and R161 are selected. For industrial flue gas waste heat, heat source temperature is 150℃, temperature range of exhaust gas is 70-100℃, and mass flow rate of flue gas is 10 kg·s-1. Condensing temperature is 35℃, cooling water temperature is 25℃, and pinch point temperature differences of evaporator and condenser are 15℃ and 5℃, respectively. Isentropic efficiency of expander is 85%, feed pump efficiency is 80%. Pressure loss and heat loss from equipment and piping and valves are neglected.
3.1. Thermodynamic analysis Because the relationship between expander enthalpy drop and mass flow is different, the trend of the net power output of the ORC system using different working fluids is firstly increased and then decreased, as shown in Fig. 3(a). The net power output of the ORC system using dry working fluid is significantly higher than the system using wet working fluid. In addition, the maximum net power output does not occur when the heat absorption is maximum. The IORC and ORC systems using the same dry working fluid have an equivalent exhaust temperature with a net power difference of 0, as shown in Fig. 3(b). When systems absorb the same amount of heat from the heat source, The IORC system's expander exhaust enthalpy is slightly lower than the ORC system, however its flow is greater, and thus the exhaust heat of IORC is higher. When the exhaust gas temperature is lower than the equivalent exhaust temperature, the heat recovery from IHE is less, and the heat release of the IORC system is higher than ORC system, and thus the IORC system has lower thermal performance. The IORC system has better thermal performance when the exhaust temperature is higher than the equivalent exhaust temperature.
(a) Net power of ORC systems with different working fluids
(b) Net power difference between IORC and ORC systems
Fig.3 Net power output of different systems
3.2. Economic analysis and comparison of different systems The investment cost of systems using different working fluids decreases with increasing exhaust temperature, as shown in Fig.4. When the system absorbs the same amount of heat from the heat source, the investment cost of the IORC system is higher than the ORC system using the same dry working fluid. There are two reasons for this. First, the cost of IHE; secondly, the parameters of equipment of IORC system are different from those of the ORC system, resulting in changes in equipment costs. Therefore, if the exhaust gas temperature is lower than the equivalent exhaust temperature, the economics of the IORC system is inferior to the ORC system using the same dry working fluid. The investment cost of the ORC system using wet working is lower, and the ORC system using R152a has the lowest investment cost.
Fan Wei et al. / Energy Procedia 158 (2019) 2403–2408 Fan Wei / Energy Procedia 00 (2018) 000–000
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Fig.4 Investment cost of ORC systems with different working fluids
Due to the different relationship between investment cost and net power output, the LEC of different systems showed a trend of decreasing first and then slightly improving, as shown in Fig.5. If the exhaust gas temperature is not constrained, the ORC system using R152a has the lowest LEC and is the most economical. The R245fa ORC system is the most economical if the exhaust gas temperature is limited to no more than 90 °C.
Fig.5 LEC of different systems
The LEC difference maintains a positive value as the exhaust gas temperature changes, as shown in Fig.6. When the exhaust gas temperature is greater than the equivalent exhaust temperature, the more obvious the net power output increment of the IORC system, the smaller the LEC difference between the two systems. The LEC difference for the two systems using R600a is the smallest, 0.0069-0.0108$/(kW•h), R245fa is 0.0081-0.0136$/(kW•h), and the LEC difference for R365mfc is the highest, 0.0073-0.0213$/ (kW•h). Therefore, the investment cost of the IORC system increases significantly, and the net power output increment is relatively low, which leads to the economics of the IORC system being inferior to the ORC system.
Fig.6 LEC difference between IORC and ORC systems using the same dry working fluid
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Fan Wei et al. / Energy Procedia 158 (2019) 2403–2408 Fan Wei/ Energy Procedia 00 (2018) 000–000
4. Conclusions The thermal performance of an IORC system is not necessarily better than an ORC system using the same working fluid. The IORC system has a thermal performance advantage only if the exhaust gas temperature is higher than the equivalent exhaust temperature. The ORC system using the wet working fluid has lower net power output and investment cost. If the exhaust gas temperature is not constrained, the ORC system using R152a is the most economical, and R245fa is the most economical if the exhaust gas temperature is limited to no more than 90 °C. The investment cost of the IORC system increases significantly, and the net power output increment is relatively low, which leads to the economics of the IORC system being inferior to the ORC system. Acknowledgements This paper acknowledges the support by the National Natural Science Foundation of China (No.51306059) and the Fundamental Business Special Funds for the Central Universities (2014MS151). References [1] Al-SULAIMAN F A, DINCER I, HAMDULLAHPUR F. Exergy modeling of a new solar driven trigeneration system[J]. Solar Energy, 2011, 85(9):2228-2243. [2] SCHUSTER A, KARELLAS S, KAKARAS E,et al. Energetic and economic investigation of Organic Rankine Cycle applications[J]. Applied Thermal Engineering, 2009, 29(8–9):1809-1817. [3] STOPPATO A. Energetic and economic investigation of the operation management of an Organic Rankine Cycle cogeneration plant[J]. Energy, 2012, 41(1):3-9. [4] Shengjun Z, Huaixin W, Tao G. Performance comparison and parametric optimization of subcritical Organic Rankine Cycle (ORC) and transcritical power cycle system for low-temperature geothermal power generation[J]. Applied Energy, 2011, 88(8): 2740-2754 [5] Dai Y, Wang J, Gao L. Parametric optimization and comparative study of organic Rankine cycle (ORC) for low grade waste heat recovery[J]. Energy Conversion and Management, 2009, 50(3): 576-582 [6] TURTON R, BAILIE R C, WHITING W B, et al .Analysis, Synthesis and Design of Chemical Processes[M]. New Jersey: Prentice Hall PTR, 1998 [7] Yongqiang Feng , Yaning Zhang , Bingxi Li, et al . Comparison between regenerative organic Rankine cycle (RORC) and basic organic Rankine cycle (BORC) based on thermoeconomic multi-objective optimization considering exergy efficiency and levelized energy cost (LEC)[J]. Energy Conversion and Management, 2015,(96): 58-71 [8] TCHANCHE B, QUOILIN S, DECLAYE S,et al. Economic feasibility study of a small scale organic rankine cycle system in waste heat recovery application[C]. 10th ASME Biennial Conference on Engineering Systems Design and Analysis, Istanbul, TURKEY, 2010.