- Email: [email protected]
Dual Reutilization of LNG Cryogenic Energy and Thermal Waste Energy with Organic Rankine Cycle in Marine Applications
Available online at www.sciencedirect.com
ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy Procedia 142 Energy Procedia 00(2017) (2017)1401–1406 000–000 www.elsevier.com/locate/procedia
9th International Conference on Applied Energy, ICAE2017, 21-24 August 2017, Cardiff, UK
Dual Reutilization of LNG Cryogenic Energy and Thermal Waste 15th International Symposium on District Heating and Cooling Energy The with Organic Rankine Cycle in Marine Applications Assessing the feasibility ofTsougranis using the heat Wu demand-outdoor a a Emmanouil-Loizos , Dawei * temperature function for a long-term district heat demand forecast School of Marine Science and Technology, Newcastle University, Armstrong Biulding, Newcastle upon Tyne, NE1 7RU, United Kingdom a
Abstract a
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b
Veoliafuel Recherche & Innovation, 291 Avenue Dreyfous France by 50% between 2017 LNG is a promising alternative at competitive price [1]. The LNG Daniel, market78520 is setLimay, to increase c Département Systèmes Énergétiques et Environnement IMT Atlantique, 4 rue Alfred Kastler, Nantes, number France of LNG and 2020. The worldwide fleet of LNG powered vessels is now expanding rapidly and the44300 increasing terminals are planned and constructed at major ports around the world. This study proposes a new Organic Rankine Cycle (ORC) with LNG Direct Expansion (DE) for the reutilization of the cryogenic energy within LNG storage tanks and potential waste thermal energy from various sources in the marine context. The proposed ORC system is designed Abstract in terms of the field testing data from a real marine application and analysed through dynamic simulation using Siemens LMS Imagine.Lab AMESim.addressed Three optimal workingasfluids on high vacuum and above District heating networks are commonly in the literature one ofare theexamined most effective solutions for decreasing the atmospheric condensing pressures in the temperature range of -110˚C and 300˚C. The proposed ORC system is greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat characterized significant improvement thermal efficiency and policies, power production in comparison the existing sales. Due to by thea changed climate conditionsinand building renovation heat demand in the futureofcould decrease, ORC systems by waste prolonging thedriven investment returnthermal period. energy.
The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand ©forecast. 2017 TheThe Authors. by Elsevier districtPublished of Alvalade, locatedLtd. in Lisbon (Portugal), was used as a case study. The district is consisted of 665 Peer-review under responsibility of the scientific of theThree 9th International Conference Appliedhigh) Energy. buildings that vary in both construction periodcommittee and typology. weather scenarios (low,onmedium, and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were Keywords: energy; ORC; waste thermal energy; marine applications comparedLNG withcryogenic results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation 1.scenarios, Introduction the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the investigates number of heating hours of 22-139h during the heating (depending on the of weather and This study and proposes an Organic Rankine Cycleseason (ORC) that utilizes thecombination LNG cryogenic energy renovation scenarios considered). On the of other increased 7.8-12.7% decade (depending and the exhaust waste thermal energy the hand, mainfunction enginesintercept of an LNG ferry.for The vessel’sper power plant consistson of the 4 coupled The values suggested could usedLNG to modify the function parameters for the scenarios considered, and Dual Fuelscenarios). (DF) Engines running on natural gas.beThe cryogenic energy that is released during the vaporization of improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +44 (0) 191 208 8113; Cooling. E-mail address: [email protected]
Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy.
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 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy. 10.1016/j.egypro.2017.12.526
Emmanouil-Loizos Tsougranis et al. / Energy Procedia 142 (2017) 1401–1406 E.L. Tsougranis/ Energy Procedia 00 (2017) 000–000
1402 2
the LNG into natural gas is significant. The LNG latent heat is the major part of the cryogenic energy that needs to be recovered before it gets dissipated to the surroundings. Moreover, the waste thermal energy due to exhaust gasses is currently utilized through exhaust economizers that producing steam for the main gas boiler. The dynamic modelling of the proposed ORC system is based on the real-time data from the case vessel and is analysed when three engines operate at 86% load. The thermodynamic cycles are designed with a maximum pressure of 15 bar in terms of practical engineering constrains on the ferry. The defining element of the ORC technology is the working fluid which determines the operating cycle temperature and pressure ranges, resulting to improved thermal efficiency and power production. The dominant working fluid selection criteria are the low freezing point (below -90oC) and the high thermal stability temperature (above 250oC). 2. The Regenerative ORC system with Direct Expansion of LNG For utilizing the LNG cold energy and the thermal waste energy on board a ship, a new ORC system is proposed. The ORC system consists of an ORC cycle with a regenerator and a direct expansion cycle for LNG. Specifically, the ORC cycle is used for the expansion and condensation of the working fluid that drives the Expander A in Figure 1. The expansion of the working fluid is succeeded through the regenerator and the condensation through the LNG cold energy which acts as heat sink. The direct expansion cycle utilizes the expansion of the LNG into natural gas which is pressurised at 15bars and runs the Expander B. The ORC system is characterized by two pumps; the ORC pump which is operated in vacuum and the cryogenic pump that increase the LNG pressure from 5 bars into 15bars. The phase change of the working fluid from vapour into liquid and the phase change of LNG from liquid into vapour takes place in the condenser at the same time.
Fig. 1. Regenerative ORC system with Direct Expansion schematic diagram.
The ORC system is dynamically modelled and analysed with Siemens LMS Imagine.Lab AMESim. Initially, the ORC system model is examined with the working fluid Isobutane R600a. In the simulation modal, LNG is assumed to be pure Methane (CH4). The model is tested in two different pressure limits (vacuum and above atmospheric pressure at the low-pressure side). The overall ORC system thermal efficiency is given by:
Thermal
W5,6 + W14,15 - W1,2 - W10,11 Q 5,2'
(1)
Figure 2 depicts the dynamic model of the ORC system which consists of the Regenerative ORC and of the LNG Direct Expansion cycle with R600a working fluid.
Emmanouil-Loizos Tsougranis et al. / Energy Procedia 142 (2017) 1401–1406 E.L.Tsougranis/ Energy Procedia 00 (2017) 000–000
1403 3
Fig. 2. The ORC system dynamic model in Siemens LMS Imagine.Lab AMESim.
The thermodynamic cycle of the ORC system using R600a is depicted in Figure 3. In high vacuum Figure 3(a) the temperature range utilization is from -110 ˚C up to 300 ˚C; in zero vacuum Figure 3(b) the temperature range is reduced between -10˚C and 300˚C. Therefore, the low condensing pressures of the cycle which is correlated with the cryogenic temperatures, which increases dramatically the pressure ratio of the expander resulting to high work output and improved thermal efficiency; however, the complexity and cost of the ORC system is increased [2]. Moreover, the regenerator transfers specific enthalpy up to 200kJ/kg from the hot expanded vapour working fluid (8-8’) to the cold liquid working fluid (2-2’). On the hot side of the regenerator the working fluid remains in vapour phase while on the cold side the working fluid is in liquid phase. The thermodynamic cycle of CH 4 remains unchanged since the LNG must be vaporized to natural gas at a constant temperature of 2˚C (point 15) before to be injected in to the Dual Fuel engines. The limitation of the ORC system cycle is the temperature of the regenerator (point 8’) must be above 70˚C, to allow the superheating of natural gas (point 14) at 69˚C.
Emmanouil-Loizos Tsougranis et al. / Energy Procedia 142 (2017) 1401–1406 E.L. Tsougranis/ Energy Procedia 00 (2017) 000–000
1404 4
Fig. 3. (a) The ORC system thermodynamic cycle between 0.01 to 14.85bar; (b) The ORC system thermodynamic cycle between 1 to 14.85bar.
The working fluid in cryogenic cycles is characterized by low freezing point (below -50˚C) and in high temperature cycles is defined by its high thermal stability (above 250˚C) [3]. Table 1 presents the candidate working fluids with its properties. In this study, the ORC thermodynamic cycle is placed between -110˚C and 300˚C maximum temperature range. Specifically, three working fluids are examined through the dynamic model of the ORC system in vacuum and above atmospheric condensing pressures. The working fluids have also been selected regarding the acceptable flammability level, toxicity and environmental impact. Table 1. Working fluids properties. Freezing Point (˚C)
Max Temperature Stability (˚C)
Classification
Critical Temperature (˚C)
Critical Pressure (bar)
Molar mass (g/mol)
Isobutane R600a
-160
327
Hydrocarbons
134.7
36.4
58.12
Cyclopentane C5H10
-93.9
277
Hydrocarbons
238.57
45.71
70.13
Ehtylene C2H4
-169
327
Hydrocarbons
9.2
50.42
28.05
3. Simulation results and discussion Table 2 presents the performance characteristics of the ORC system operating in 0.01 and 1 bar condensation pressures. When the ORC system operates in vacuum (0.01 to 14.85bar) the thermal efficiency is increased up to 48%. The respective power output of the system is increased by 52% to 577KW. Therefore, the operating pressure range between 0.01 and 1bar for the working fluid R600a defines the performance of the ORC system. Without the regenerator, the ORC system thermal efficiency is reduced by 1.1% and 2.9% for high vacuum and zero vacuum of the condensation pressure respectively. Table 3 indicates the model design characteristics for both cases.
E.L.Tsougranis/ Energy Procedia 00 (2017) 000–000 Emmanouil-Loizos Tsougranis et al. / Energy Procedia 142 (2017) 1401–1406
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Table 2. ORC system performance characteristics using R600a. Pressure range (bar)
Thermal Efficiency (%)
Pout (KW)
Qin (KW)
QLNG (KW)
h_Regenerator (KJ/Kg)
With the regenerator
0.01-14.85
48
577
1201.57
716.6
40
1-14.85
31.2
276.3
885.17
716.6
200
Without the regenerator
0.01-14.85
46.9
552.5
1175.9
716.6
0
1-14.85
28.3
240
846.7
716.6
0
Table 3. The ORC system design characteristics using R600a. ORC Design Characteristics Turbine A
Condenser
Evaporator-Heater
0.01-14.85bar
1-14.85bar
Displacement (cm3)
920
1210
Speed (rev/min)
4187
2363
Shaft Torque (Nm)
1256
709
Pressure Ratio
1400:1
14:1
Hydraulic diameter (mm)
200
135
Equivalent Length (m)
5.2
5
Heat exchanged Volume (m3)
0.238
0.0063
Hydraulic diameter (mm)
100
100
Equivalent Length (m)
8
8
Heat exchanged Volume (m )
0.023
0.023
Displacement (cm )
588
281
Speed (rev/min)
400
800
Torque (Nm)
129
69
Hydraulic diameter (mm)
160
160
Equivalent Length (m)
2
2
Heat exchanged Volume (m3)
0.6
0.6
Displacement (cm )
590
590
Speed (rev/min)
462
462
Torque (Nm)
103
103
Displacement (cm3)
2192
2192
Speed (rev/min)
1951
1951
Shaft Torque (Nm)
585
585
Pressure Ratio
3
3
3
Vacuum Pump
Regenerator
LNG Pump
Turbine B
3
3
Figure 4 shows the thermodynamic response of the ORC operating with Cyclopentane and Ethylene working fluids. It is observed that Ethylene in Figure 4(b) has almost the same condensing temperatures -110˚C and -100˚C for high vacuum and 1 bar condenser pressure, respectively. Consequently, the thermal efficiency and the Power Output is slightly affected compared to R600a and C5H10 (Table 2). Low pressure working fluid C5H10 operating between 0.01bar and 11.7bar pressure range can utilize only the temperature range between -50˚C and 250˚C. However, it is characterized by a thermal efficiency of 42.18% running in vacuum as is shown on Table 2. C 5H10 operating at 1 bar pressure, Figure 2(a), presents a 27.97% thermal efficiency and a 47.7% reduce in power production. Also, C 5H10 cannot utilize the Regenerator, thus the complexity and cost of the ORC system are decreased. Compare the results from Table 2 and 4, Isobutane (R600a) demonstrates the highest thermal efficiency 48% and Power Output 577KW in vacuum condensing pressure utilizing the temperature range between -110˚C and 300˚C. Therefore, for ORC thermodynamic cycles operating in vacuum condensing pressures which can utilize a large temperature range, R600a
Emmanouil-Loizos Tsougranis et al. / Energy Procedia 142 (2017) 1401–1406 E.L. Tsougranis/ Energy Procedia 00 (2017) 000–000
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is the most preferable working fluid. For ORC thermodynamic cycles that operate above atmospheric pressure and can also employ large temperature difference (-100˚C to 300˚C) avoiding the complexity and extra cost of the vacuum condenser, Ethylene is the most suitable working fluid. Furthermore, Cyclopentane demonstrates high thermal efficiency in low pressure for small temperature range cycles. Thus, for applications where the temperature range is about 100˚C to 150˚C, C5H10 is a potential high performance working fluid without the need of a regenerator [4].
Fig. 4. (a)The ORC Thermodynamic cycles with Cyclopentane (C5H10); (b) The ORC Thermodynamic cycles with Ethylene (C2H4). Table 4. ORC working fluids performance comparison.
Working Fluid C5H10 Working Fluid C2H4
Thermal Efficiency (%)
Pout (KW)
Qin (KW)
QLNG (KW)
h_Regenerator (KJ/Kg)
Pressure range: 0.01-11.7bar
42.18
450.9
1068.9
716.6
0
Pressure range: 1-11.7bar
29.97
235.6
842.33
716.6
0
Pressure range: 0.69-14.95bar
41.3
435
1052.2
716.6
120
Pressure range: 1.26-14.95bar
38.3
381.8
996.27
716.6
150
4. Conclusion This study proposes dual utilization of the cryogenic and waste thermal energy of a powered LNG vessel with a regenerative ORC with LNG direct expansion. Isobutane demonstrates the highest thermal efficiency of 48% operating at high vacuum condensing pressure with the thermodynamic cycle between -110˚C and 300˚C. Ethylene is suitable as working fluid for cycles with condensing pressure above atmospheric pressure. Cyclopentane presents relatively high thermal efficiency of 42% in high vacuum while operating between -50˚C and 250˚C. References [1] Palmer‐Huggins D, Michot Foss M. LNG MARINE FUEL APPLICATIONS. 1st ed. Texas: BEG CEE; 2017. [2] Macchi E, Astolfi M. Organic rankine cycle (ORC) power systems. 1st ed. Elsevier; 2017. [3] Lee H, Kim K. Energy and Exergy Analyses of a Combined Power Cycle Using the Organic Rankine Cycle and the Cold Energy of Liquefied Natural Gas. Entropy 2015;17:6412-6432. [4] Post Guillen D, Zia J. Modifications and Optimization of the Organic Rankine Cycle to Improve the Recovery of Waste Heat. Oak Ridge: U.S. Department of Energy; 2013.
ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia
Energy Procedia 142 Energy Procedia 00(2017) (2017)1401–1406 000–000 www.elsevier.com/locate/procedia
9th International Conference on Applied Energy, ICAE2017, 21-24 August 2017, Cardiff, UK
Dual Reutilization of LNG Cryogenic Energy and Thermal Waste 15th International Symposium on District Heating and Cooling Energy The with Organic Rankine Cycle in Marine Applications Assessing the feasibility ofTsougranis using the heat Wu demand-outdoor a a Emmanouil-Loizos , Dawei * temperature function for a long-term district heat demand forecast School of Marine Science and Technology, Newcastle University, Armstrong Biulding, Newcastle upon Tyne, NE1 7RU, United Kingdom a
Abstract a
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal b
Veoliafuel Recherche & Innovation, 291 Avenue Dreyfous France by 50% between 2017 LNG is a promising alternative at competitive price [1]. The LNG Daniel, market78520 is setLimay, to increase c Département Systèmes Énergétiques et Environnement IMT Atlantique, 4 rue Alfred Kastler, Nantes, number France of LNG and 2020. The worldwide fleet of LNG powered vessels is now expanding rapidly and the44300 increasing terminals are planned and constructed at major ports around the world. This study proposes a new Organic Rankine Cycle (ORC) with LNG Direct Expansion (DE) for the reutilization of the cryogenic energy within LNG storage tanks and potential waste thermal energy from various sources in the marine context. The proposed ORC system is designed Abstract in terms of the field testing data from a real marine application and analysed through dynamic simulation using Siemens LMS Imagine.Lab AMESim.addressed Three optimal workingasfluids on high vacuum and above District heating networks are commonly in the literature one ofare theexamined most effective solutions for decreasing the atmospheric condensing pressures in the temperature range of -110˚C and 300˚C. The proposed ORC system is greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat characterized significant improvement thermal efficiency and policies, power production in comparison the existing sales. Due to by thea changed climate conditionsinand building renovation heat demand in the futureofcould decrease, ORC systems by waste prolonging thedriven investment returnthermal period. energy.
The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand ©forecast. 2017 TheThe Authors. by Elsevier districtPublished of Alvalade, locatedLtd. in Lisbon (Portugal), was used as a case study. The district is consisted of 665 Peer-review under responsibility of the scientific of theThree 9th International Conference Appliedhigh) Energy. buildings that vary in both construction periodcommittee and typology. weather scenarios (low,onmedium, and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were Keywords: energy; ORC; waste thermal energy; marine applications comparedLNG withcryogenic results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation 1.scenarios, Introduction the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the investigates number of heating hours of 22-139h during the heating (depending on the of weather and This study and proposes an Organic Rankine Cycleseason (ORC) that utilizes thecombination LNG cryogenic energy renovation scenarios considered). On the of other increased 7.8-12.7% decade (depending and the exhaust waste thermal energy the hand, mainfunction enginesintercept of an LNG ferry.for The vessel’sper power plant consistson of the 4 coupled The values suggested could usedLNG to modify the function parameters for the scenarios considered, and Dual Fuelscenarios). (DF) Engines running on natural gas.beThe cryogenic energy that is released during the vaporization of improve the accuracy of heat demand estimations. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +44 (0) 191 208 8113; Cooling. E-mail address: [email protected]
Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy.
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 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 9th International Conference on Applied Energy. 10.1016/j.egypro.2017.12.526
Emmanouil-Loizos Tsougranis et al. / Energy Procedia 142 (2017) 1401–1406 E.L. Tsougranis/ Energy Procedia 00 (2017) 000–000
1402 2
the LNG into natural gas is significant. The LNG latent heat is the major part of the cryogenic energy that needs to be recovered before it gets dissipated to the surroundings. Moreover, the waste thermal energy due to exhaust gasses is currently utilized through exhaust economizers that producing steam for the main gas boiler. The dynamic modelling of the proposed ORC system is based on the real-time data from the case vessel and is analysed when three engines operate at 86% load. The thermodynamic cycles are designed with a maximum pressure of 15 bar in terms of practical engineering constrains on the ferry. The defining element of the ORC technology is the working fluid which determines the operating cycle temperature and pressure ranges, resulting to improved thermal efficiency and power production. The dominant working fluid selection criteria are the low freezing point (below -90oC) and the high thermal stability temperature (above 250oC). 2. The Regenerative ORC system with Direct Expansion of LNG For utilizing the LNG cold energy and the thermal waste energy on board a ship, a new ORC system is proposed. The ORC system consists of an ORC cycle with a regenerator and a direct expansion cycle for LNG. Specifically, the ORC cycle is used for the expansion and condensation of the working fluid that drives the Expander A in Figure 1. The expansion of the working fluid is succeeded through the regenerator and the condensation through the LNG cold energy which acts as heat sink. The direct expansion cycle utilizes the expansion of the LNG into natural gas which is pressurised at 15bars and runs the Expander B. The ORC system is characterized by two pumps; the ORC pump which is operated in vacuum and the cryogenic pump that increase the LNG pressure from 5 bars into 15bars. The phase change of the working fluid from vapour into liquid and the phase change of LNG from liquid into vapour takes place in the condenser at the same time.
Fig. 1. Regenerative ORC system with Direct Expansion schematic diagram.
The ORC system is dynamically modelled and analysed with Siemens LMS Imagine.Lab AMESim. Initially, the ORC system model is examined with the working fluid Isobutane R600a. In the simulation modal, LNG is assumed to be pure Methane (CH4). The model is tested in two different pressure limits (vacuum and above atmospheric pressure at the low-pressure side). The overall ORC system thermal efficiency is given by:
Thermal
W5,6 + W14,15 - W1,2 - W10,11 Q 5,2'
(1)
Figure 2 depicts the dynamic model of the ORC system which consists of the Regenerative ORC and of the LNG Direct Expansion cycle with R600a working fluid.
Emmanouil-Loizos Tsougranis et al. / Energy Procedia 142 (2017) 1401–1406 E.L.Tsougranis/ Energy Procedia 00 (2017) 000–000
1403 3
Fig. 2. The ORC system dynamic model in Siemens LMS Imagine.Lab AMESim.
The thermodynamic cycle of the ORC system using R600a is depicted in Figure 3. In high vacuum Figure 3(a) the temperature range utilization is from -110 ˚C up to 300 ˚C; in zero vacuum Figure 3(b) the temperature range is reduced between -10˚C and 300˚C. Therefore, the low condensing pressures of the cycle which is correlated with the cryogenic temperatures, which increases dramatically the pressure ratio of the expander resulting to high work output and improved thermal efficiency; however, the complexity and cost of the ORC system is increased [2]. Moreover, the regenerator transfers specific enthalpy up to 200kJ/kg from the hot expanded vapour working fluid (8-8’) to the cold liquid working fluid (2-2’). On the hot side of the regenerator the working fluid remains in vapour phase while on the cold side the working fluid is in liquid phase. The thermodynamic cycle of CH 4 remains unchanged since the LNG must be vaporized to natural gas at a constant temperature of 2˚C (point 15) before to be injected in to the Dual Fuel engines. The limitation of the ORC system cycle is the temperature of the regenerator (point 8’) must be above 70˚C, to allow the superheating of natural gas (point 14) at 69˚C.
Emmanouil-Loizos Tsougranis et al. / Energy Procedia 142 (2017) 1401–1406 E.L. Tsougranis/ Energy Procedia 00 (2017) 000–000
1404 4
Fig. 3. (a) The ORC system thermodynamic cycle between 0.01 to 14.85bar; (b) The ORC system thermodynamic cycle between 1 to 14.85bar.
The working fluid in cryogenic cycles is characterized by low freezing point (below -50˚C) and in high temperature cycles is defined by its high thermal stability (above 250˚C) [3]. Table 1 presents the candidate working fluids with its properties. In this study, the ORC thermodynamic cycle is placed between -110˚C and 300˚C maximum temperature range. Specifically, three working fluids are examined through the dynamic model of the ORC system in vacuum and above atmospheric condensing pressures. The working fluids have also been selected regarding the acceptable flammability level, toxicity and environmental impact. Table 1. Working fluids properties. Freezing Point (˚C)
Max Temperature Stability (˚C)
Classification
Critical Temperature (˚C)
Critical Pressure (bar)
Molar mass (g/mol)
Isobutane R600a
-160
327
Hydrocarbons
134.7
36.4
58.12
Cyclopentane C5H10
-93.9
277
Hydrocarbons
238.57
45.71
70.13
Ehtylene C2H4
-169
327
Hydrocarbons
9.2
50.42
28.05
3. Simulation results and discussion Table 2 presents the performance characteristics of the ORC system operating in 0.01 and 1 bar condensation pressures. When the ORC system operates in vacuum (0.01 to 14.85bar) the thermal efficiency is increased up to 48%. The respective power output of the system is increased by 52% to 577KW. Therefore, the operating pressure range between 0.01 and 1bar for the working fluid R600a defines the performance of the ORC system. Without the regenerator, the ORC system thermal efficiency is reduced by 1.1% and 2.9% for high vacuum and zero vacuum of the condensation pressure respectively. Table 3 indicates the model design characteristics for both cases.
E.L.Tsougranis/ Energy Procedia 00 (2017) 000–000 Emmanouil-Loizos Tsougranis et al. / Energy Procedia 142 (2017) 1401–1406
5 1405
Table 2. ORC system performance characteristics using R600a. Pressure range (bar)
Thermal Efficiency (%)
Pout (KW)
Qin (KW)
QLNG (KW)
h_Regenerator (KJ/Kg)
With the regenerator
0.01-14.85
48
577
1201.57
716.6
40
1-14.85
31.2
276.3
885.17
716.6
200
Without the regenerator
0.01-14.85
46.9
552.5
1175.9
716.6
0
1-14.85
28.3
240
846.7
716.6
0
Table 3. The ORC system design characteristics using R600a. ORC Design Characteristics Turbine A
Condenser
Evaporator-Heater
0.01-14.85bar
1-14.85bar
Displacement (cm3)
920
1210
Speed (rev/min)
4187
2363
Shaft Torque (Nm)
1256
709
Pressure Ratio
1400:1
14:1
Hydraulic diameter (mm)
200
135
Equivalent Length (m)
5.2
5
Heat exchanged Volume (m3)
0.238
0.0063
Hydraulic diameter (mm)
100
100
Equivalent Length (m)
8
8
Heat exchanged Volume (m )
0.023
0.023
Displacement (cm )
588
281
Speed (rev/min)
400
800
Torque (Nm)
129
69
Hydraulic diameter (mm)
160
160
Equivalent Length (m)
2
2
Heat exchanged Volume (m3)
0.6
0.6
Displacement (cm )
590
590
Speed (rev/min)
462
462
Torque (Nm)
103
103
Displacement (cm3)
2192
2192
Speed (rev/min)
1951
1951
Shaft Torque (Nm)
585
585
Pressure Ratio
3
3
3
Vacuum Pump
Regenerator
LNG Pump
Turbine B
3
3
Figure 4 shows the thermodynamic response of the ORC operating with Cyclopentane and Ethylene working fluids. It is observed that Ethylene in Figure 4(b) has almost the same condensing temperatures -110˚C and -100˚C for high vacuum and 1 bar condenser pressure, respectively. Consequently, the thermal efficiency and the Power Output is slightly affected compared to R600a and C5H10 (Table 2). Low pressure working fluid C5H10 operating between 0.01bar and 11.7bar pressure range can utilize only the temperature range between -50˚C and 250˚C. However, it is characterized by a thermal efficiency of 42.18% running in vacuum as is shown on Table 2. C 5H10 operating at 1 bar pressure, Figure 2(a), presents a 27.97% thermal efficiency and a 47.7% reduce in power production. Also, C 5H10 cannot utilize the Regenerator, thus the complexity and cost of the ORC system are decreased. Compare the results from Table 2 and 4, Isobutane (R600a) demonstrates the highest thermal efficiency 48% and Power Output 577KW in vacuum condensing pressure utilizing the temperature range between -110˚C and 300˚C. Therefore, for ORC thermodynamic cycles operating in vacuum condensing pressures which can utilize a large temperature range, R600a
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is the most preferable working fluid. For ORC thermodynamic cycles that operate above atmospheric pressure and can also employ large temperature difference (-100˚C to 300˚C) avoiding the complexity and extra cost of the vacuum condenser, Ethylene is the most suitable working fluid. Furthermore, Cyclopentane demonstrates high thermal efficiency in low pressure for small temperature range cycles. Thus, for applications where the temperature range is about 100˚C to 150˚C, C5H10 is a potential high performance working fluid without the need of a regenerator [4].
Fig. 4. (a)The ORC Thermodynamic cycles with Cyclopentane (C5H10); (b) The ORC Thermodynamic cycles with Ethylene (C2H4). Table 4. ORC working fluids performance comparison.
Working Fluid C5H10 Working Fluid C2H4
Thermal Efficiency (%)
Pout (KW)
Qin (KW)
QLNG (KW)
h_Regenerator (KJ/Kg)
Pressure range: 0.01-11.7bar
42.18
450.9
1068.9
716.6
0
Pressure range: 1-11.7bar
29.97
235.6
842.33
716.6
0
Pressure range: 0.69-14.95bar
41.3
435
1052.2
716.6
120
Pressure range: 1.26-14.95bar
38.3
381.8
996.27
716.6
150
4. Conclusion This study proposes dual utilization of the cryogenic and waste thermal energy of a powered LNG vessel with a regenerative ORC with LNG direct expansion. Isobutane demonstrates the highest thermal efficiency of 48% operating at high vacuum condensing pressure with the thermodynamic cycle between -110˚C and 300˚C. Ethylene is suitable as working fluid for cycles with condensing pressure above atmospheric pressure. Cyclopentane presents relatively high thermal efficiency of 42% in high vacuum while operating between -50˚C and 250˚C. References [1] Palmer‐Huggins D, Michot Foss M. LNG MARINE FUEL APPLICATIONS. 1st ed. Texas: BEG CEE; 2017. [2] Macchi E, Astolfi M. Organic rankine cycle (ORC) power systems. 1st ed. Elsevier; 2017. [3] Lee H, Kim K. Energy and Exergy Analyses of a Combined Power Cycle Using the Organic Rankine Cycle and the Cold Energy of Liquefied Natural Gas. Entropy 2015;17:6412-6432. [4] Post Guillen D, Zia J. Modifications and Optimization of the Organic Rankine Cycle to Improve the Recovery of Waste Heat. Oak Ridge: U.S. Department of Energy; 2013.