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Conceptual design and thermodynamic optimization of a novel composition tunable zeotropic organic Rankine cycle
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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
design and thermodynamic optimization of novel 10thConceptual International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Kong, Conceptual design and thermodynamic optimization of aa Hong novel The 15th International Symposium on District Heating and Cooling China composition tunable zeotropic organic Rankine cycle composition tunable zeotropic organic Rankine cycle Assessing the feasibility of using the optimization heat demand-outdoor a Conceptual design and aathermodynamic of Yang a novel Chaonan Chenaa, Renlong Huang , Xianglong Luoa,a,*, Jianyong Chenaa, Zhi a, Ying Chaonan Chen , Renlong Huang ,aXianglong *, Jianyong Chen , Zhi Yang , Ying temperature function for long-term heat demand forecast aLuo district Chen composition tunable zeotropic organic Rankine cycle a Chen I. Andrić *, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre Chaonan Chen , Renlong Huang , Xianglong Luo *, Jianyong Chen , Zhi Yang , Ying Chen
a,b,c a a b of Material and Energy, c Guangdong University c of Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter, School a a Key Laboratory of Functional aTechnology, a, a Guangdong University a Guangdong Provincial Soft Condensed Matter, School of No. 100 Waihuan Xi of Material and Energy, Technology, No. 100aPanyu Waihuan Xi Guangzhou 510006, China a Road, Guangzhou Higher Education Mega Center, District, IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Road, bGuangzhou Higher Education Mega Center, Panyu District, Guangzhou 510006, China Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c a Systèmes Énergétiques et Environnement - IMT Atlantique, rue Alfred Kastler, 44300 Nantes, France GuangdongDépartement Provincial Key Laboratory of Functional Soft Condensed Matter, School4of Material and Energy, Guangdong University of Abstract Technology, No. 100 Waihuan Xi Abstract Road, Guangzhou Higher Education Mega Center, Panyu District, Guangzhou 510006, China a
Organic Rankine cycle (ORC) is recently receiving increasing attention and regarded one of the most promising Organic heat-to-power Rankine cycletechnology. (ORC) is recently receiving increasing attention and regarded one of power the most promising Abstract low-grade Compared to the conventional high-grade fossil energy-to technologies, low-grade heat-to-power technology. Compared to the conventional high-grade fossil energy-to power technologies, Abstract ORC is much more sensible to the environmental temperature variation due to the low temperature of heat sources. A ORC is much more sensible the environmental temperature variation to most the low temperature of for heatdecreasing sources. A District heating networks are to commonly addressed the literature as and one due of the effective solutions the conventional ORC is typically designed under ain given condition mostly operate under off-design conditions, conventional ORC is typically designed under a given condition and mostly operate under off-design conditions, greenhouse gas from the building sector. Thesestudy systems require high investments which areof returned through the heat OrganicinRankine cycleaverage (ORC) is recently receiving increasing attention andzeotropic regarded one the most promising resulting lowemissions annual performance. This proposes a novel ORC in which the mixture resulting inheat-to-power average performance. This proposes a novel heat zeotropic ORC inpower whichcould mixture sales. Due tolow theannual changed climate conditions renovation policies, demand in the future decrease, low-grade technology. Compared tobuilding thestudy conventional high-grade fossil energy-to technologies, composition can be tuned in response to and the environmental temperature variation using liquid -the separation composition can be tuned in response to the environmental temperature variation using liquid separation prolonging the investment return period. ORC is much more sensible to the environmental temperature variation due to the low temperature of heat sources. A condensation. A thermodynamic optimization model is formulated to optimized the mixture composition according condensation. A thermodynamic optimization model is formulated to optimized the mixture composition according The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand conventional ORC is typically designed under a given condition and mostly operate under off-design conditions, to the environmental temperature. A concept design of liquid-separation condensation -based composition tuning Thelow district of Alvalade, located inthe Lisbon wassignificantly used as acondensation case study. the The district is consisted of 665 toforecast. the environmental temperature. A that concept design ofORC liquid-separation -based tuning resulting in annual average performance. This(Portugal), study proposes a novel zeotropic ORC in composition which the mixture system is conducted. The results show proposed can improve overall efficiency without buildings thatcan varybe inThe both construction period and scenarios (low, the medium, three district system is conducted. results show that the proposed ORC canweather significantly improve overall efficiency without oand composition tuned in be response toby the environmental temperature variation using liquid -heat separation C source. extra cost increment, which can improved uptypology. to 9.15 %Three compare to the conventional ORC forhigh) 100 o renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were C heat source. extra cost increment, which can be improved by up to 9.15 % compare to the conventional ORC for 100 condensation. thermodynamic optimization model adjustment, is formulated to optimized the mixture composition according Keywords: organicARankine cycle, zeotropic mixture, composition liquid-separation condenser compared with results from a dynamic heat demand model, previously developed and validated by the authors. © 2019 The Authors. Published by Elsevier Ltd. Keywords: organic Rankine cycle, zeotropic mixture, composition adjustment, liquid-separation condenser to the environmental temperature. A concept design of liquid-separation condensation -based composition tuning This an open accessthat article under CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/) Theisresults showed when onlythe weather is license considered, the margin of error could be acceptable for some applications system is conducted. The results show thatchange the proposed ORC can significantly improve the overall efficiency without Peer-review responsibility of lower the scientific committee of ICAE2018 – Theconsidered). 10th International Conference on Appliedrenovation Energy. (the error inunder annual demand was than 20% for all weather scenarios However, after introducing 1. Introduction extra cost increment, which can be improved by up to 9.15 % compare to the conventional ORC for 100 oC heat source. scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). 1. Introduction Keywords: organic Rankine cycle, zeotropic mixture, composition adjustment, liquid-separation condenser
The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the The world abundant low-grade energy such as solar energy, geothermal energy, waste heat. Effective decrease in thehas number of heating hours of 22-139h during the heating season (depending on theand combination of weather and The world has abundant low-grade energy such solar energy, geothermal energy, and waste heat. Effective utilizing these low-grade energies is significant in asalleviating shortage and environmental deterioration. renovation scenarios considered). On the other hand, function interceptenergy increased for 7.8-12.7% per decade (depending on the utilizing these low-grade energies is significant in energylow-grade shortageheat-to-power and environmental deterioration. 1. Introduction Organic cycle is considered thealleviating promising technology. coupled Rankine scenarios). The (ORC) values suggested couldone be of used tomost modify the function parameters for the scenarios considered, and Organic Rankine cycle (ORC) is considered one of the most promising low-grade heat-to-power technology. improve the accuracy of heat demand estimations.
The world has abundant low-grade energy such as solar energy, geothermal energy, and waste heat. Effective utilizing these low-grade energies is significant in alleviating energy shortage and environmental deterioration. © 2017 The Authors. Published by Elsevier Ltd. Organic Rankine (ORC) is of the most promising low-grade heat-to-power technology. Peer-review undercycle responsibility of considered the Scientificone Committee of The 15th International Symposium on District Heating and Cooling.
* Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . * E-mail Corresponding Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . address:author. [email protected] Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected]
1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102and Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection peer-review responsibility the scientific * Corresponding author. under Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). E-mail address: [email protected] 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of theLtd. Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2018 Elsevier All by rights reserved. 1876-6102 Copyright © 2019 The Authors. Published Elsevier Ltd. Selection peer-review under under responsibility the scientificlicense committee of the 10th International Conference on Applied Energy (ICAE2018). This is anand open access article the CCofBY-NC-ND (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.2019.01.467
2020 2
Chaonan Chen et al. / Energy Procedia 158 (2019) 2019–2024 Author name / Energy Procedia 00 (2018) 000–000
The recent research on the ORC mostly aimed to improve the thermodynamic, economic, environmental, and safety performance under fixed operation condition. Actually, the heat source and heat sink parameters may remarkedly change with system working condition, time, and season. Take a 100 oC industrial waste heat driven ORC in Beijing of China as an example, the environment temperature varies from -10 oC in winter to 30 oC in summer with about 50 o C difference which is almost half of the system operation temperature limit. Thus, the operation performance of ORC is significantly affected by the variation in environment temperature. A traditional ORC is typically designed under a fixed operation condition and operates mostly at off-design condition, leading to low annual average efficiency. Thus, many studies have investigated the off-design performance and control strategy by steady-state simulation, dynamic simulation, and experimental validation. Traditional passive controlling strategies such as pressure sliding and/or flow rate adjustment are used for dynamic control. Although these passive control strategies are effective in success to transfer one state to another, the performance cannot be guaranteed given the ORC is constrained by the equipment capacity and non-adjustable working fluid properties. Recently, zeotropic mixture is used in ORC due to its better heat match with heat sources and heat sinks. The researchers showed that in the zeotropic ORC, mixture composition is one of the key optimization variables affecting the ORC performance. Collings et al. [1] proposed a dynamic zeotropic fluid organic Rankine cycle where the mixture composition is dynamically adjusted during operation in response to changing heat sink conditions. Their case study results showed that the annual average thermal efficiency can be improved by up to 23% over a conventional ORC. The researches indicated that composition-adjustable ORC system can achieve significantly higher thermal efficiency than conventional ORC system as the ambient temperature decreases. Liquid-vapor separation condensation is a novel heat transfer intensification concept where liquid is separated from the fluid during condensation to maintain high quality, and condensation flow pass is optimized to meet the velocity requirement. The thermo-economic superiority of liquid-separation condenser (LSC) over traditional condenser has been theoretically and experimentally testified in refrigeration system and ORC. In addition to the thermo-economic performance improvement in LSC-based ORC, the LSC is also possible in adjusting the composition. Luo et al. [2] proposed a novel zeotropic ORC coupling LSC and multi-pressure evaporation and investigated the contribution of composition adjustment using LSC. Their results showed that the composition tuning using LSC is possible in ORC in addition to the thermo-economic performance improvement. In this paper, a novel ORC with LSC-based composition tuning system is proposed and conceptually designed. A thermodynamic analysis considering environmental temperature variation is formulated to achieve the dynamic composition requirement for maximizing the full condition net power output. A case study is elaborated to testify the proposed novel ORC by comparing with the traditional ORC for different zeotropic mixture. 2.Problem description Fig.1a shows a representation of a basic zeotropic ORC cycle system (BZORC) whereas Fig.2 shows a representation of the proposed novel zeotropic ORC with LSC-based composition tuning system (LZORC). As shown in Fig.1, the BZORC system is composed of an evaporator, an expander, a pump, and a condenser. Liquid zeotropic mixture working fluid is pumped into the evaporator by the pump and heated into superheat vapor in the evaporator. Next, the vapor expands in the in expander and, condensed into saturate liquid in the condenser and a cycle is finished. As environmental air temperature gradually varies with time and season, the available temperature difference almost keeps constant due to fixed its composition and pressure constraints for those ORC condensing pressure close to atmospheric pressure. Thus, such ORC leads to low annual average efficiency due to temperature mismatch between working fluid and heat sink. Fortunately, LZORC can improve the temperature match between working fluid and heat sink due to the dynamic composition tuning. As shown in Fig.2, considering heat sink temperature varying from summer to winter (as showed in Fig.2 (b)), the mixture composition can to be adjusted to match the ambient temperature, and available temperature difference of ORC is increased, resulting in the increment of power output or thermal efficiency.
Chaonan Chen et al. / Energy Procedia 158 (2019) 2019–2024 Author name / Energy Procedia 00 (2018) 000–000
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(a) (b) Fig.1. BZORC: (a) schematic diagram; (b) available temperature difference.
(a) (b) Fig.2. LZORC: (a) schematic diagram; (b) available temperature difference. Fig.3a shows the temperature-composition characteristic of the zeotropic mixtures with liquid-vapor separation during condensation. Line abde indicates the liquid-separation condensation process whereas line abg represents conventional condensation process. Obviously, at any given temperature or vapor quality, the original stream can be divided into two streams with different composition. The composition of the vapor with more volatile component and liquid phase with less volatile component can be achieved. Thus, the LZORC can obtain different composition streams by controlling the vapor quality or condensation pressure. Suppose the condensation start from point a with composition w(a), line ab indicates the condensation of the first part. Liquid-vapor separation is performed at point b and the liquid composition becomes w(c) while the vapor composition becomes w(d). Thus, two liquid streams with composition w(c) and w(d) are achieved. Moreover, the composition can be controlled by liquid-vapor separation at different vapor quality by reasonably structure arrangement of the LSC. A conceptual composition adjustment implementation in LZORC is shown in Fig. 3b. It consists of storage tanks, mixers, and valves. The outlet of separator is connected to valve V1 whereas the outlet of second condenser is connected to valve V2. The outlet of composition adjustment system is connected to the inlet of pump. First of all, storage a and b are empty whereas storage e reserve original design composition of zeotropic mixture. The zeotropic mixture is separated into two streams in the separator. The volatile component (i.e., R245fa) of liquid is less than vapor during liquid-vapor separation. Thus, volatile component of streams stored in storage a is always more than the original design composition streams whereas volatile component of streams stored in storage b is always less than the original design composition streams.
Chaonan Chen et al. / Energy Procedia 158 (2019) 2019–2024 Author name / Energy Procedia 00 (2018) 000–000
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Fig.3. (a) Principle of the composition adjustment; (b) Concept design of the composition adjustment system using liquid-separation condenser 3. Thermodynamic model of LZORC Following assumptions are given before the modelling in order to optimize the BZORC and LZORC. (1) The BZORC and LZORC are all operated under steady state. (2) The influence of composition shift and fractionating is not considered during the operation process. (3) No superheating in the evaporator and no sub-cooling in the condenser are considered. (4) The vapor quality remains constant at different ambient temperature to simplify the condenser performance since the aim of the current study is to investigate the effectiveness and performance of composition tuning. Eq. (1) gives the thermodynamic optimization model of BZORC to achieve the optimal composition by maximizing the annual average output power. Then, the composition is adjusted using the liquid-separation condenser-based composition tuning systems. max 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 = ∑𝑓𝑓(𝑇𝑇𝑇𝑇, 𝑇𝑇𝑇𝑇, 𝑚𝑚𝑚𝑚, 𝑤𝑤) /𝑛𝑛 (1)
4. Result and discussion
Since the mixture R245fa/R365mfc has zero ozone depletion, low toxicity, cost, and liquid at room temperature, R245fa/R365mfc is selected as working fluid in this paper. In this section, the optimization of LZORC driven by low temperature waste heat is analysed using the developed numerical model. The reference design parameters are shown in Table 1. The inlet temperature of the waste heat is 150 ℃ and the inlet temperature of cooling water is taken from Beijing 2017 ambient conditions [3], which is shown in Fig. 4a. Table 1. Optimization conditions for ORC cycle Parameter item Work fluids The inlet temperature of the waste heat water (℃) The mass flow rate of the waste heat water (kg/s）
Value R245fa-R365mfc
Resource [1]
100
[2]
20
[2]
-1~30
[3]
Pinch temperature of evaporator (℃)
5
[2]
Pinch temperature of condenser (℃)
5
[2]
Isentropic efficiency of pump (%)
80
[2]
Isentropic efficiency of expander (%)
80
[2]
Air temperature range (℃)
Traditional zeotropic ORCs are designed based on specific condition that is determined by the properties of working fluid and the maximum ambient temperature in the summer. Zeotropic ORC can significantly improve the thermal efficiency than pure ORC for recovery waste heat. Meanwhile, such ORC may have significant potential to
Chaonan Chen et al. / Energy Procedia 158 (2019) 2019–2024 Author name / Energy Procedia 00 (2018) 000–000
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improve system thermodynamic performance when regulating the zeotropic mixture composition in corresponding to the ambient conditions change from winter to summer. As shown in Fig.4b, the mole fraction of volatile component firstly decreases and increases then as requirement as the ambient temperature changes from winter to summer and from summer to winter. The composition requirement variation ranges from 0.61 to 0.90. It can be seen that in the colder months, the optimal ORC (LZORC) is significantly more efficient than the BZORC. The annual output power of LZORC is 3074.94kWwhereas that of BZORC is 2817.10kW, and the former is 4.48% higher than that of the latter.
(a)
(b)
(c)
Fig. 4. (a) Ambient temperature of Beijing [1]; (b) Composition variation at different months; (c) Comparison between LZORC and BZORC
In addition, R245fa/R113and R245ca/R113 are also studied.Fig.5a shows the comparison among the three working fluids. As the result shows, when R245fa/R113 is selected as working fluid, the composition requirement varies from 0.55 to 0.85, and the annual output power of LZORC is 3547.06kW whereas that of the BZORC is 3445.48kW, and the former is 2.95% higher than that of the latter; when R245ca/R113 is selected as working fluid, the composition requirement varies from 0.33to 0.99, and the annual output power of LZORC is 3074.94kW whereas that of BZORC is 2817.10kW, and the former is 9.15% higher than that of the latter. Obviously, LZORC can efficiently improve the output power compare with BZORC because LZORC can adjust the composition according to the ambient temperature conditions, which can improve the temperature match between working fluids and heat/sink sources. Furthermore, the difference between LZORC and BZORC is small in hot months.
(a)
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Chaonan Chen et al. / Energy Procedia 158 (2019) 2019–2024 Author name / Energy Procedia 00 (2018) 000–000
(b) Fig. 5. Comparison between R245fa/R365mfc, R245fa/R113, and R245ca/R113: (a) Composition variation at different months; (b) Comparison between LZORC and BZORC
5. Conclusions This paper proposed a novel zeotropic organic Rankine cycle with composition tuning using liquid -separation condensation. Binary zeotropic mixture (R245fa/R365mfc, R245fa/R113, and R245ca/R113) are used as the working fluids. The thermodynamic optimization of BZORC and LZORC are conducted and compared. Optimization results showed that LZORC can significantly improve the output power compared to the conventional ORC in terms of 100℃ heat source. Using R245fa/R365mfc, R245fa/R113, and R245ca/R113, the annual output power of LZORC are 4.48%, 9.15% and 2.95% higher than those of BZORC. Acknowledgements The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51476037), Guangdong Special Funding for Applied Technology Research & Development (Grant No. 2016B020243010) References [1] Collings P, Yu Z, Wang E. A dynamic organic Rankine cycle using a zeotropic mixture as the working fluid with composition tuning to match changing ambient conditions. APPL ENERG. 2016; 171:581-591. [2] Luo X, Huang R, Yang Z, Chen J, Chen Y. Performance investigation of a novel zeotropic organic Rankine cycle coupling liquid separation condensation and multi-pressure evaporation. ENERG CONVERS MANAGE. 2018; 161:112-127. [3] Climate Beijing 2017.
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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
design and thermodynamic optimization of novel 10thConceptual International Conference on Applied Energy (ICAE2018), 22-25 August 2018, Kong, Conceptual design and thermodynamic optimization of aa Hong novel The 15th International Symposium on District Heating and Cooling China composition tunable zeotropic organic Rankine cycle composition tunable zeotropic organic Rankine cycle Assessing the feasibility of using the optimization heat demand-outdoor a Conceptual design and aathermodynamic of Yang a novel Chaonan Chenaa, Renlong Huang , Xianglong Luoa,a,*, Jianyong Chenaa, Zhi a, Ying Chaonan Chen , Renlong Huang ,aXianglong *, Jianyong Chen , Zhi Yang , Ying temperature function for long-term heat demand forecast aLuo district Chen composition tunable zeotropic organic Rankine cycle a Chen I. Andrić *, A. Pina , P. Ferrão , J. Fournier ., B. Lacarrière , O. Le Corre Chaonan Chen , Renlong Huang , Xianglong Luo *, Jianyong Chen , Zhi Yang , Ying Chen
a,b,c a a b of Material and Energy, c Guangdong University c of Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter, School a a Key Laboratory of Functional aTechnology, a, a Guangdong University a Guangdong Provincial Soft Condensed Matter, School of No. 100 Waihuan Xi of Material and Energy, Technology, No. 100aPanyu Waihuan Xi Guangzhou 510006, China a Road, Guangzhou Higher Education Mega Center, District, IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Road, bGuangzhou Higher Education Mega Center, Panyu District, Guangzhou 510006, China Veolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France c a Systèmes Énergétiques et Environnement - IMT Atlantique, rue Alfred Kastler, 44300 Nantes, France GuangdongDépartement Provincial Key Laboratory of Functional Soft Condensed Matter, School4of Material and Energy, Guangdong University of Abstract Technology, No. 100 Waihuan Xi Abstract Road, Guangzhou Higher Education Mega Center, Panyu District, Guangzhou 510006, China a
Organic Rankine cycle (ORC) is recently receiving increasing attention and regarded one of the most promising Organic heat-to-power Rankine cycletechnology. (ORC) is recently receiving increasing attention and regarded one of power the most promising Abstract low-grade Compared to the conventional high-grade fossil energy-to technologies, low-grade heat-to-power technology. Compared to the conventional high-grade fossil energy-to power technologies, Abstract ORC is much more sensible to the environmental temperature variation due to the low temperature of heat sources. A ORC is much more sensible the environmental temperature variation to most the low temperature of for heatdecreasing sources. A District heating networks are to commonly addressed the literature as and one due of the effective solutions the conventional ORC is typically designed under ain given condition mostly operate under off-design conditions, conventional ORC is typically designed under a given condition and mostly operate under off-design conditions, greenhouse gas from the building sector. Thesestudy systems require high investments which areof returned through the heat OrganicinRankine cycleaverage (ORC) is recently receiving increasing attention andzeotropic regarded one the most promising resulting lowemissions annual performance. This proposes a novel ORC in which the mixture resulting inheat-to-power average performance. This proposes a novel heat zeotropic ORC inpower whichcould mixture sales. Due tolow theannual changed climate conditions renovation policies, demand in the future decrease, low-grade technology. Compared tobuilding thestudy conventional high-grade fossil energy-to technologies, composition can be tuned in response to and the environmental temperature variation using liquid -the separation composition can be tuned in response to the environmental temperature variation using liquid separation prolonging the investment return period. ORC is much more sensible to the environmental temperature variation due to the low temperature of heat sources. A condensation. A thermodynamic optimization model is formulated to optimized the mixture composition according condensation. A thermodynamic optimization model is formulated to optimized the mixture composition according The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand conventional ORC is typically designed under a given condition and mostly operate under off-design conditions, to the environmental temperature. A concept design of liquid-separation condensation -based composition tuning Thelow district of Alvalade, located inthe Lisbon wassignificantly used as acondensation case study. the The district is consisted of 665 toforecast. the environmental temperature. A that concept design ofORC liquid-separation -based tuning resulting in annual average performance. This(Portugal), study proposes a novel zeotropic ORC in composition which the mixture system is conducted. The results show proposed can improve overall efficiency without buildings thatcan varybe inThe both construction period and scenarios (low, the medium, three district system is conducted. results show that the proposed ORC canweather significantly improve overall efficiency without oand composition tuned in be response toby the environmental temperature variation using liquid -heat separation C source. extra cost increment, which can improved uptypology. to 9.15 %Three compare to the conventional ORC forhigh) 100 o renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were C heat source. extra cost increment, which can be improved by up to 9.15 % compare to the conventional ORC for 100 condensation. thermodynamic optimization model adjustment, is formulated to optimized the mixture composition according Keywords: organicARankine cycle, zeotropic mixture, composition liquid-separation condenser compared with results from a dynamic heat demand model, previously developed and validated by the authors. © 2019 The Authors. Published by Elsevier Ltd. Keywords: organic Rankine cycle, zeotropic mixture, composition adjustment, liquid-separation condenser to the environmental temperature. A concept design of liquid-separation condensation -based composition tuning This an open accessthat article under CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/) Theisresults showed when onlythe weather is license considered, the margin of error could be acceptable for some applications system is conducted. The results show thatchange the proposed ORC can significantly improve the overall efficiency without Peer-review responsibility of lower the scientific committee of ICAE2018 – Theconsidered). 10th International Conference on Appliedrenovation Energy. (the error inunder annual demand was than 20% for all weather scenarios However, after introducing 1. Introduction extra cost increment, which can be improved by up to 9.15 % compare to the conventional ORC for 100 oC heat source. scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). 1. Introduction Keywords: organic Rankine cycle, zeotropic mixture, composition adjustment, liquid-separation condenser
The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the The world abundant low-grade energy such as solar energy, geothermal energy, waste heat. Effective decrease in thehas number of heating hours of 22-139h during the heating season (depending on theand combination of weather and The world has abundant low-grade energy such solar energy, geothermal energy, and waste heat. Effective utilizing these low-grade energies is significant in asalleviating shortage and environmental deterioration. renovation scenarios considered). On the other hand, function interceptenergy increased for 7.8-12.7% per decade (depending on the utilizing these low-grade energies is significant in energylow-grade shortageheat-to-power and environmental deterioration. 1. Introduction Organic cycle is considered thealleviating promising technology. coupled Rankine scenarios). The (ORC) values suggested couldone be of used tomost modify the function parameters for the scenarios considered, and Organic Rankine cycle (ORC) is considered one of the most promising low-grade heat-to-power technology. improve the accuracy of heat demand estimations.
The world has abundant low-grade energy such as solar energy, geothermal energy, and waste heat. Effective utilizing these low-grade energies is significant in alleviating energy shortage and environmental deterioration. © 2017 The Authors. Published by Elsevier Ltd. Organic Rankine (ORC) is of the most promising low-grade heat-to-power technology. Peer-review undercycle responsibility of considered the Scientificone Committee of The 15th International Symposium on District Heating and Cooling.
* Corresponding author. Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . * E-mail Corresponding Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . address:author. [email protected] Keywords: Heat demand; Forecast; Climate change E-mail address: [email protected]
1876-6102 Copyright © 2018 Elsevier Ltd. All rights reserved. 1876-6102and Copyright © 2018 Elsevier Ltd. All of rights reserved. committee of the 10th International Conference on Applied Energy (ICAE2018). Selection peer-review responsibility the scientific * Corresponding author. under Tel.: +0-000-000-0000 ; fax: +0-000-000-0000 . Selection and peer-review under responsibility of the scientific committee of the 10th International Conference on Applied Energy (ICAE2018). E-mail address: [email protected] 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of theLtd. Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2018 Elsevier All by rights reserved. 1876-6102 Copyright © 2019 The Authors. Published Elsevier Ltd. Selection peer-review under under responsibility the scientificlicense committee of the 10th International Conference on Applied Energy (ICAE2018). This is anand open access article the CCofBY-NC-ND (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.2019.01.467
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Chaonan Chen et al. / Energy Procedia 158 (2019) 2019–2024 Author name / Energy Procedia 00 (2018) 000–000
The recent research on the ORC mostly aimed to improve the thermodynamic, economic, environmental, and safety performance under fixed operation condition. Actually, the heat source and heat sink parameters may remarkedly change with system working condition, time, and season. Take a 100 oC industrial waste heat driven ORC in Beijing of China as an example, the environment temperature varies from -10 oC in winter to 30 oC in summer with about 50 o C difference which is almost half of the system operation temperature limit. Thus, the operation performance of ORC is significantly affected by the variation in environment temperature. A traditional ORC is typically designed under a fixed operation condition and operates mostly at off-design condition, leading to low annual average efficiency. Thus, many studies have investigated the off-design performance and control strategy by steady-state simulation, dynamic simulation, and experimental validation. Traditional passive controlling strategies such as pressure sliding and/or flow rate adjustment are used for dynamic control. Although these passive control strategies are effective in success to transfer one state to another, the performance cannot be guaranteed given the ORC is constrained by the equipment capacity and non-adjustable working fluid properties. Recently, zeotropic mixture is used in ORC due to its better heat match with heat sources and heat sinks. The researchers showed that in the zeotropic ORC, mixture composition is one of the key optimization variables affecting the ORC performance. Collings et al. [1] proposed a dynamic zeotropic fluid organic Rankine cycle where the mixture composition is dynamically adjusted during operation in response to changing heat sink conditions. Their case study results showed that the annual average thermal efficiency can be improved by up to 23% over a conventional ORC. The researches indicated that composition-adjustable ORC system can achieve significantly higher thermal efficiency than conventional ORC system as the ambient temperature decreases. Liquid-vapor separation condensation is a novel heat transfer intensification concept where liquid is separated from the fluid during condensation to maintain high quality, and condensation flow pass is optimized to meet the velocity requirement. The thermo-economic superiority of liquid-separation condenser (LSC) over traditional condenser has been theoretically and experimentally testified in refrigeration system and ORC. In addition to the thermo-economic performance improvement in LSC-based ORC, the LSC is also possible in adjusting the composition. Luo et al. [2] proposed a novel zeotropic ORC coupling LSC and multi-pressure evaporation and investigated the contribution of composition adjustment using LSC. Their results showed that the composition tuning using LSC is possible in ORC in addition to the thermo-economic performance improvement. In this paper, a novel ORC with LSC-based composition tuning system is proposed and conceptually designed. A thermodynamic analysis considering environmental temperature variation is formulated to achieve the dynamic composition requirement for maximizing the full condition net power output. A case study is elaborated to testify the proposed novel ORC by comparing with the traditional ORC for different zeotropic mixture. 2.Problem description Fig.1a shows a representation of a basic zeotropic ORC cycle system (BZORC) whereas Fig.2 shows a representation of the proposed novel zeotropic ORC with LSC-based composition tuning system (LZORC). As shown in Fig.1, the BZORC system is composed of an evaporator, an expander, a pump, and a condenser. Liquid zeotropic mixture working fluid is pumped into the evaporator by the pump and heated into superheat vapor in the evaporator. Next, the vapor expands in the in expander and, condensed into saturate liquid in the condenser and a cycle is finished. As environmental air temperature gradually varies with time and season, the available temperature difference almost keeps constant due to fixed its composition and pressure constraints for those ORC condensing pressure close to atmospheric pressure. Thus, such ORC leads to low annual average efficiency due to temperature mismatch between working fluid and heat sink. Fortunately, LZORC can improve the temperature match between working fluid and heat sink due to the dynamic composition tuning. As shown in Fig.2, considering heat sink temperature varying from summer to winter (as showed in Fig.2 (b)), the mixture composition can to be adjusted to match the ambient temperature, and available temperature difference of ORC is increased, resulting in the increment of power output or thermal efficiency.
Chaonan Chen et al. / Energy Procedia 158 (2019) 2019–2024 Author name / Energy Procedia 00 (2018) 000–000
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(a) (b) Fig.1. BZORC: (a) schematic diagram; (b) available temperature difference.
(a) (b) Fig.2. LZORC: (a) schematic diagram; (b) available temperature difference. Fig.3a shows the temperature-composition characteristic of the zeotropic mixtures with liquid-vapor separation during condensation. Line abde indicates the liquid-separation condensation process whereas line abg represents conventional condensation process. Obviously, at any given temperature or vapor quality, the original stream can be divided into two streams with different composition. The composition of the vapor with more volatile component and liquid phase with less volatile component can be achieved. Thus, the LZORC can obtain different composition streams by controlling the vapor quality or condensation pressure. Suppose the condensation start from point a with composition w(a), line ab indicates the condensation of the first part. Liquid-vapor separation is performed at point b and the liquid composition becomes w(c) while the vapor composition becomes w(d). Thus, two liquid streams with composition w(c) and w(d) are achieved. Moreover, the composition can be controlled by liquid-vapor separation at different vapor quality by reasonably structure arrangement of the LSC. A conceptual composition adjustment implementation in LZORC is shown in Fig. 3b. It consists of storage tanks, mixers, and valves. The outlet of separator is connected to valve V1 whereas the outlet of second condenser is connected to valve V2. The outlet of composition adjustment system is connected to the inlet of pump. First of all, storage a and b are empty whereas storage e reserve original design composition of zeotropic mixture. The zeotropic mixture is separated into two streams in the separator. The volatile component (i.e., R245fa) of liquid is less than vapor during liquid-vapor separation. Thus, volatile component of streams stored in storage a is always more than the original design composition streams whereas volatile component of streams stored in storage b is always less than the original design composition streams.
Chaonan Chen et al. / Energy Procedia 158 (2019) 2019–2024 Author name / Energy Procedia 00 (2018) 000–000
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Fig.3. (a) Principle of the composition adjustment; (b) Concept design of the composition adjustment system using liquid-separation condenser 3. Thermodynamic model of LZORC Following assumptions are given before the modelling in order to optimize the BZORC and LZORC. (1) The BZORC and LZORC are all operated under steady state. (2) The influence of composition shift and fractionating is not considered during the operation process. (3) No superheating in the evaporator and no sub-cooling in the condenser are considered. (4) The vapor quality remains constant at different ambient temperature to simplify the condenser performance since the aim of the current study is to investigate the effectiveness and performance of composition tuning. Eq. (1) gives the thermodynamic optimization model of BZORC to achieve the optimal composition by maximizing the annual average output power. Then, the composition is adjusted using the liquid-separation condenser-based composition tuning systems. max 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊 = ∑𝑓𝑓(𝑇𝑇𝑇𝑇, 𝑇𝑇𝑇𝑇, 𝑚𝑚𝑚𝑚, 𝑤𝑤) /𝑛𝑛 (1)
4. Result and discussion
Since the mixture R245fa/R365mfc has zero ozone depletion, low toxicity, cost, and liquid at room temperature, R245fa/R365mfc is selected as working fluid in this paper. In this section, the optimization of LZORC driven by low temperature waste heat is analysed using the developed numerical model. The reference design parameters are shown in Table 1. The inlet temperature of the waste heat is 150 ℃ and the inlet temperature of cooling water is taken from Beijing 2017 ambient conditions [3], which is shown in Fig. 4a. Table 1. Optimization conditions for ORC cycle Parameter item Work fluids The inlet temperature of the waste heat water (℃) The mass flow rate of the waste heat water (kg/s）
Value R245fa-R365mfc
Resource [1]
100
[2]
20
[2]
-1~30
[3]
Pinch temperature of evaporator (℃)
5
[2]
Pinch temperature of condenser (℃)
5
[2]
Isentropic efficiency of pump (%)
80
[2]
Isentropic efficiency of expander (%)
80
[2]
Air temperature range (℃)
Traditional zeotropic ORCs are designed based on specific condition that is determined by the properties of working fluid and the maximum ambient temperature in the summer. Zeotropic ORC can significantly improve the thermal efficiency than pure ORC for recovery waste heat. Meanwhile, such ORC may have significant potential to
Chaonan Chen et al. / Energy Procedia 158 (2019) 2019–2024 Author name / Energy Procedia 00 (2018) 000–000
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improve system thermodynamic performance when regulating the zeotropic mixture composition in corresponding to the ambient conditions change from winter to summer. As shown in Fig.4b, the mole fraction of volatile component firstly decreases and increases then as requirement as the ambient temperature changes from winter to summer and from summer to winter. The composition requirement variation ranges from 0.61 to 0.90. It can be seen that in the colder months, the optimal ORC (LZORC) is significantly more efficient than the BZORC. The annual output power of LZORC is 3074.94kWwhereas that of BZORC is 2817.10kW, and the former is 4.48% higher than that of the latter.
(a)
(b)
(c)
Fig. 4. (a) Ambient temperature of Beijing [1]; (b) Composition variation at different months; (c) Comparison between LZORC and BZORC
In addition, R245fa/R113and R245ca/R113 are also studied.Fig.5a shows the comparison among the three working fluids. As the result shows, when R245fa/R113 is selected as working fluid, the composition requirement varies from 0.55 to 0.85, and the annual output power of LZORC is 3547.06kW whereas that of the BZORC is 3445.48kW, and the former is 2.95% higher than that of the latter; when R245ca/R113 is selected as working fluid, the composition requirement varies from 0.33to 0.99, and the annual output power of LZORC is 3074.94kW whereas that of BZORC is 2817.10kW, and the former is 9.15% higher than that of the latter. Obviously, LZORC can efficiently improve the output power compare with BZORC because LZORC can adjust the composition according to the ambient temperature conditions, which can improve the temperature match between working fluids and heat/sink sources. Furthermore, the difference between LZORC and BZORC is small in hot months.
(a)
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Chaonan Chen et al. / Energy Procedia 158 (2019) 2019–2024 Author name / Energy Procedia 00 (2018) 000–000
(b) Fig. 5. Comparison between R245fa/R365mfc, R245fa/R113, and R245ca/R113: (a) Composition variation at different months; (b) Comparison between LZORC and BZORC
5. Conclusions This paper proposed a novel zeotropic organic Rankine cycle with composition tuning using liquid -separation condensation. Binary zeotropic mixture (R245fa/R365mfc, R245fa/R113, and R245ca/R113) are used as the working fluids. The thermodynamic optimization of BZORC and LZORC are conducted and compared. Optimization results showed that LZORC can significantly improve the output power compared to the conventional ORC in terms of 100℃ heat source. Using R245fa/R365mfc, R245fa/R113, and R245ca/R113, the annual output power of LZORC are 4.48%, 9.15% and 2.95% higher than those of BZORC. Acknowledgements The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51476037), Guangdong Special Funding for Applied Technology Research & Development (Grant No. 2016B020243010) References [1] Collings P, Yu Z, Wang E. A dynamic organic Rankine cycle using a zeotropic mixture as the working fluid with composition tuning to match changing ambient conditions. APPL ENERG. 2016; 171:581-591. [2] Luo X, Huang R, Yang Z, Chen J, Chen Y. Performance investigation of a novel zeotropic organic Rankine cycle coupling liquid separation condensation and multi-pressure evaporation. ENERG CONVERS MANAGE. 2018; 161:112-127. [3] Climate Beijing 2017.