The Experts below are selected from a list of 2085 Experts worldwide ranked by ideXlab platform
Petter Neksa - One of the best experts on this subject based on the ideXlab platform.
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reducing the exergy destruction in the cryogenic heat exchangers of Hydrogen Liquefaction processes
International Journal of Hydrogen Energy, 2018Co-Authors: Petter Neksa, Oivind Wilhelmsen, David Berstad, Ailo Aasen, Geir SkaugenAbstract:Abstract A present key barrier for implementing large-scale Hydrogen Liquefaction plants is their high power consumption. The cryogenic heat exchangers are responsible for a significant part of the exergy destruction in these plants and we evaluate in this work strategies to increase their efficiency. A detailed model of a plate-fin heat exchanger is presented that incorporates the geometry of the heat exchanger, nonequilibrium ortho-para conversion and correlations to account for the pressure drop and heat transfer coefficients due to possible boiling/condensation of the refrigerant at the lowest temperatures. Based on available experimental data, a correlation for the ortho-para conversion kinetics is developed, which reproduces available experimental data with an average deviation of 2.2%. In a plate-fin heat exchanger that is used to cool the Hydrogen from 47.8 K to 29.3 K with Hydrogen as refrigerant, we find that the two main sources of exergy destruction are thermal gradients and ortho-para Hydrogen conversion, being responsible for 69% and 29% of the exergy destruction respectively. A route to reduce the exergy destruction from the ortho-para Hydrogen conversion is to use a more efficient catalyst, where we find that a doubling of the catalytic activity in comparison to ferric-oxide, as demonstrated by nickel oxide-silica catalyst, reduces the exergy destruction by 9%. A possible route to reduce the exergy destruction from thermal gradients is to employ an evaporating mixture of helium and neon at the cold-side of the heat exchanger, which reduces the exergy destruction by 7%. We find that a combination of Hydrogen and helium-neon as refrigerants at high and low temperatures respectively, enables a reduction of the exergy destruction by 35%. A combination of both improved catalyst and the use of Hydrogen and helium-neon as refrigerants gives the possibility to reduce the exergy destruction in the cryogenic heat exchangers by 43%. The limited efficiency of the ortho-para catalyst represents a barrier for further improvement of the efficiency.
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simulation and experiment of a Hydrogen Liquefaction test rig using a multi component refrigerant refrigeration system
International Journal of Hydrogen Energy, 2011Co-Authors: Songwut Krasaein, Jacob H Stang, Arne M Bredesen, Petter NeksaAbstract:Abstract A small-scale laboratory Hydrogen Liquefaction plant that contains a new innovative MR (multi-component refrigerant) refrigeration system is proposed. A test rig was constructed to verify the simulation of this system. Initial experiments indicated that the rig were able to adequately cool normal Hydrogen gas from 25 °C to −158 °C at a flow rate of 0.6 kg/h using a simplified five-component MR mixture refrigeration system. The power consumption of pre-cooling from the MR compressor was 1.76 kW h per kilogram of feed Hydrogen gas. After two weeks, the lowest temperature was about −180 °C when a few additional grams of nitrogen gas were charged into the rig. The simulation and experimental data were in good agreement, and the primary conclusion was that pre-cooling Hydrogen gas with the MR refrigeration system resulted in a lower energy consumption per kilogram of feed Hydrogen gas compared to conventional refrigeration systems.
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simulation on a proposed large scale liquid Hydrogen plant using a multi component refrigerant refrigeration system
International Journal of Hydrogen Energy, 2010Co-Authors: Songwut Krasaein, Jacob H Stang, Petter NeksaAbstract:The problem is that today every H2 Liquefaction plant has low exergy efficiency of just between 20–30%. It is based on the pre-cooled Claude system, which is still the same as 50 years ago with littleimprovement. Method to resolve the challenges of the future plants is finding a completely newconfiguration with more efficient system. For this dissertation, a multi-component refrigerant (MR)refrigeration cycle is proposed to solve the problem. The work is divided into four parts: a literaturereview, a design and simulation of a small-scale laboratory plant, an experiment with the smallplant, and a design and simulation of a proposed large-scale plant. First, this study investigated thesimulation of a newly proposed small-scale laboratory liquid Hydrogen plant with the new,innovative MR refrigeration system. The simulated test rig was capable of liquefying a feed of 2kg/h of normal Hydrogen gas at 21 bar and 25 oC to normal liquid Hydrogen at 2 bar and −250 oC.The simulated power consumption for pre-cooling the Hydrogen from 25 oC to −198 oC with thisnew MR compressor was 2.07 kWh/kgGH2. This was the lowest power consumption available whencompared to today’s conventional Hydrogen Liquefaction cycles, which are approximately 4.00kWh/kgGH2. Exergy analysis of the test rig’s cycle, which is required to find the losses and optimize the proposed MR system, was evaluated for each component using the simulation data. It was foundthat the majority of the losses were from the compressors, heat exchangers, and expansion valves.Then, a small-scale laboratory Hydrogen Liquefaction plant that contains the new innovative MRrefrigeration system was constructed to verify the simulation of this system. Initial experimentsindicated that the rig was able to adequately cool normal Hydrogen gas from 25 oC to −158 oC at aflow rate of 0.6 kg/h using a simplified 5-component MR composition refrigeration system. Thepower consumption of pre-cooling from the MR compressor was 1.76 kWh per kilogram of feedHydrogen gas. After two weeks, the lowest attained temperature was about −180 oC when a fewadditional grams of nitrogen gas were charged into the rig. There were some differences, but mostof all, the simulation and experimental data were in good agreement. The primary conclusion wasthat pre-cooling Hydrogen gas with the MR refrigeration system resulted in a lower energyconsumption per kilogram of feed Hydrogen gas compared to conventional refrigeration systems.Finally, a liquid Hydrogen plant based on the MR refrigeration system is proposed. A cycle that iscapable of producing 100 tons of liquid Hydrogen per day is simulated. The MR system can be usedto cool feed normal Hydrogen gas from 25 oC to the equilibrium temperature of −193 oC with a highefficiency. In addition, for the transition from the equilibrium temperature of the Hydrogen gas from−193 oC to −253 oC, a new proposed four H2 Joule-Brayton cycle refrigeration system withoptimization is recommended. The overall power consumption of the proposed plant for the basedcase is 6.35 kWh/kgLH2. The current plant in Ingolstadt is used as a reference, which has an energyconsumption of 13.58 kWh/kgLH2 and an efficiency of 21.28%. The efficiency of the proposedsystem is around 45% or more, where this depends on the assumed efficiency values for thecompressors and expanders, together with effectiveness of heat exchangers. Importantly, thevariables and constraints are preliminary studied together with how to adjust these to achieveoptimal steady-state operation. The optimization problem has 23 variables and 26 constraints. Asimplified 5-component composition of refrigerant suggested for the plant is found. The plantoptimization was also conducted with two more pinch temperatures (1 and 3 oC). Power saving isincreased with a pinch temperature of 1 oC as compared to 3 oC. This figure can have a significantimpact on plants selection. In addition, pressure drops in heat exchangers are also employed in thesimulation for the study, however it is shown that they don’t have much significant impact on theoverall plant total power consumption. The proposed system has smaller compressor motors andsmaller crankcase compressors; thus, it could represent a plant with the lowest construction costwith respect to the amount of liquid Hydrogen produced in comparison to today’s plants, e.g., in Ingolstadt and Leuna. Therefore, the proposed system has many improvements that serves as anexample for future Hydrogen Liquefaction plants.
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exergy analysis on the simulation of a small scale Hydrogen Liquefaction test rig with a multi component refrigerant refrigeration system
International Journal of Hydrogen Energy, 2010Co-Authors: Songwut Krasaein, Jacob H Stang, Petter NeksaAbstract:Abstract This study investigates the simulation of a proposed small-scale laboratory liquid Hydrogen plant with a new, innovative multi-component refrigerant (MR) refrigeration system. The simulated test rig was capable of liquefying a feed of 2 kg/h of normal Hydrogen gas at 21 bar and 25 °C to normal liquid Hydrogen at 2 bar and −250 °C. The simulated power consumption for pre-cooling the Hydrogen from 25 °C to −198 °C with this new MR cycle was 2.07 kWh/kgGH2 from the ideal minimum of 0.7755 kWh per kilogram of feed Hydrogen gas. This was the lowest power consumption available when compared to today’s conventional Hydrogen Liquefaction cycles, which are approximately 4.00 kWh/kgGH2. Hence, the MR cycle’s exergy efficiency was 38.3%. Exergy analysis of the test rig’s cycle, which is required to find the losses and optimize the proposed MR system, was evaluated for each component using the simulation data. It was found that the majority of the losses were from the compressors, heat exchangers, and expansion valves. Suggestions are provided for how to reduce exergy in each component in order to reduce the exergy loss. Finally, further improvements for better efficiency of the test rig are explained to assist in the design of a future large-scale Hydrogen Liquefaction plant.
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development of large scale Hydrogen Liquefaction processes from 1898 to 2009
International Journal of Hydrogen Energy, 2010Co-Authors: Songwut Krasaein, Jacob H Stang, Petter NeksaAbstract:Abstract This paper presents a review of the development of large-scale Hydrogen Liquefaction processes throughout the world from 1898 to 2009. First, there is a concise literature review including numerous past, present, and future designs given such as the first Hydrogen Liquefaction device, long time ago simple theoretical processes, today's actual plants with efficiencies 20–30%, a list of the capacity and location of every Hydrogen Liquefaction plant in the world, and some modern more efficient proposed conceptual plants with efficiencies 40–50%. After that, further information about the development and improvement potential of future large-scale liquid Hydrogen Liquefaction plants is given. It is found that every current plant is based on the pre-cooled Claude system, which is still the same as was 50 years ago with little improvement. Methods to resolve the challenges of the future plants include proposing completely new configurations and efficient systems coupled with improved efficiencies of the main system components such as compressors, expanders, and heat exchangers. Finally, a summary and comparison of the process efficiencies are described, including a newly proposed Multi-component Refrigerant (MR) system being developed by NTNU and SINTEF Energy Research AS.
Oivind Wilhelmsen - One of the best experts on this subject based on the ideXlab platform.
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comparing exergy losses and evaluating the potential of catalyst filled plate fin and spiral wound heat exchangers in a large scale claude Hydrogen Liquefaction process
International Journal of Hydrogen Energy, 2020Co-Authors: Geir Skaugen, David Olsson Berstad, Oivind WilhelmsenAbstract:Abstract Detailed heat exchanger designs are determined by matching intermediate temperatures in a large-scale Claude refrigeration process for Liquefaction of Hydrogen with a capacity of 125 tons/day. A comparison is made of catalyst filled plate-fin and spiral-wound heat exchangers by use of a flexible and robust modeling framework for multi-stream heat exchangers that incorporates conversion of ortho-to para-Hydrogen in the Hydrogen feed stream, accurate thermophysical models and a distributed resolution of all streams and wall temperatures. Maps of the local exergy destruction in the heat exchangers are presented, which enable the identification of several avenues to improve their performances. The heat exchanger duties vary between 1 and 31 MW and their second law energy efficiencies vary between 72.3% and 96.6%. Due to geometrical constraints imposed by the heat exchanger manufacturers, it is necessary to employ between one to four parallel plate-fin heat exchanger modules, while it is possible to use single modules in series for the spiral-wound heat exchangers. Due to the lower surface density and heat transfer coefficients in the spiral-wound heat exchangers, their weights are 2–14 times higher than those of the plate-fin heat exchangers. In the first heat exchanger, Hydrogen feed gas is cooled from ambient temperature to about 120 K by use of a single mixed refrigerant cycle. Here, most of the exergy destruction occurs when the high-pressure mixed refrigerant enters the single-phase regime. A dual mixed refrigerant or a cascade process holds the potential to remove a large part of this exergy destruction and improve the efficiency. In many of the heat exchangers, uneven local exergy destruction reveals a potential for further optimization of geometrical parameters, in combination with process parameters and constraints. The framework presented makes it possible to compare different sources of exergy destruction on equal terms and enables a qualified specification on the maximum allowed pressure drops in the streams. The mole fraction of para-Hydrogen is significantly closer to the equilibrium composition through the entire process for the spiral-wound heat exchangers due to the longer residence time. This reduces the exergy destruction from the conversion of ortho-Hydrogen and results in a higher outlet mole fraction of para-Hydrogen from the process. Because of the higher surface densities of the plate-fin heat exchangers, they are the preferred technology for Hydrogen Liquefaction, unless a higher conversion to heat exchange ratio is desired.
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reducing the exergy destruction in the cryogenic heat exchangers of Hydrogen Liquefaction processes
International Journal of Hydrogen Energy, 2018Co-Authors: Petter Neksa, Oivind Wilhelmsen, David Berstad, Ailo Aasen, Geir SkaugenAbstract:Abstract A present key barrier for implementing large-scale Hydrogen Liquefaction plants is their high power consumption. The cryogenic heat exchangers are responsible for a significant part of the exergy destruction in these plants and we evaluate in this work strategies to increase their efficiency. A detailed model of a plate-fin heat exchanger is presented that incorporates the geometry of the heat exchanger, nonequilibrium ortho-para conversion and correlations to account for the pressure drop and heat transfer coefficients due to possible boiling/condensation of the refrigerant at the lowest temperatures. Based on available experimental data, a correlation for the ortho-para conversion kinetics is developed, which reproduces available experimental data with an average deviation of 2.2%. In a plate-fin heat exchanger that is used to cool the Hydrogen from 47.8 K to 29.3 K with Hydrogen as refrigerant, we find that the two main sources of exergy destruction are thermal gradients and ortho-para Hydrogen conversion, being responsible for 69% and 29% of the exergy destruction respectively. A route to reduce the exergy destruction from the ortho-para Hydrogen conversion is to use a more efficient catalyst, where we find that a doubling of the catalytic activity in comparison to ferric-oxide, as demonstrated by nickel oxide-silica catalyst, reduces the exergy destruction by 9%. A possible route to reduce the exergy destruction from thermal gradients is to employ an evaporating mixture of helium and neon at the cold-side of the heat exchanger, which reduces the exergy destruction by 7%. We find that a combination of Hydrogen and helium-neon as refrigerants at high and low temperatures respectively, enables a reduction of the exergy destruction by 35%. A combination of both improved catalyst and the use of Hydrogen and helium-neon as refrigerants gives the possibility to reduce the exergy destruction in the cryogenic heat exchangers by 43%. The limited efficiency of the ortho-para catalyst represents a barrier for further improvement of the efficiency.
Jacob H Stang - One of the best experts on this subject based on the ideXlab platform.
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simulation and experiment of a Hydrogen Liquefaction test rig using a multi component refrigerant refrigeration system
International Journal of Hydrogen Energy, 2011Co-Authors: Songwut Krasaein, Jacob H Stang, Arne M Bredesen, Petter NeksaAbstract:Abstract A small-scale laboratory Hydrogen Liquefaction plant that contains a new innovative MR (multi-component refrigerant) refrigeration system is proposed. A test rig was constructed to verify the simulation of this system. Initial experiments indicated that the rig were able to adequately cool normal Hydrogen gas from 25 °C to −158 °C at a flow rate of 0.6 kg/h using a simplified five-component MR mixture refrigeration system. The power consumption of pre-cooling from the MR compressor was 1.76 kW h per kilogram of feed Hydrogen gas. After two weeks, the lowest temperature was about −180 °C when a few additional grams of nitrogen gas were charged into the rig. The simulation and experimental data were in good agreement, and the primary conclusion was that pre-cooling Hydrogen gas with the MR refrigeration system resulted in a lower energy consumption per kilogram of feed Hydrogen gas compared to conventional refrigeration systems.
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simulation on a proposed large scale liquid Hydrogen plant using a multi component refrigerant refrigeration system
International Journal of Hydrogen Energy, 2010Co-Authors: Songwut Krasaein, Jacob H Stang, Petter NeksaAbstract:The problem is that today every H2 Liquefaction plant has low exergy efficiency of just between 20–30%. It is based on the pre-cooled Claude system, which is still the same as 50 years ago with littleimprovement. Method to resolve the challenges of the future plants is finding a completely newconfiguration with more efficient system. For this dissertation, a multi-component refrigerant (MR)refrigeration cycle is proposed to solve the problem. The work is divided into four parts: a literaturereview, a design and simulation of a small-scale laboratory plant, an experiment with the smallplant, and a design and simulation of a proposed large-scale plant. First, this study investigated thesimulation of a newly proposed small-scale laboratory liquid Hydrogen plant with the new,innovative MR refrigeration system. The simulated test rig was capable of liquefying a feed of 2kg/h of normal Hydrogen gas at 21 bar and 25 oC to normal liquid Hydrogen at 2 bar and −250 oC.The simulated power consumption for pre-cooling the Hydrogen from 25 oC to −198 oC with thisnew MR compressor was 2.07 kWh/kgGH2. This was the lowest power consumption available whencompared to today’s conventional Hydrogen Liquefaction cycles, which are approximately 4.00kWh/kgGH2. Exergy analysis of the test rig’s cycle, which is required to find the losses and optimize the proposed MR system, was evaluated for each component using the simulation data. It was foundthat the majority of the losses were from the compressors, heat exchangers, and expansion valves.Then, a small-scale laboratory Hydrogen Liquefaction plant that contains the new innovative MRrefrigeration system was constructed to verify the simulation of this system. Initial experimentsindicated that the rig was able to adequately cool normal Hydrogen gas from 25 oC to −158 oC at aflow rate of 0.6 kg/h using a simplified 5-component MR composition refrigeration system. Thepower consumption of pre-cooling from the MR compressor was 1.76 kWh per kilogram of feedHydrogen gas. After two weeks, the lowest attained temperature was about −180 oC when a fewadditional grams of nitrogen gas were charged into the rig. There were some differences, but mostof all, the simulation and experimental data were in good agreement. The primary conclusion wasthat pre-cooling Hydrogen gas with the MR refrigeration system resulted in a lower energyconsumption per kilogram of feed Hydrogen gas compared to conventional refrigeration systems.Finally, a liquid Hydrogen plant based on the MR refrigeration system is proposed. A cycle that iscapable of producing 100 tons of liquid Hydrogen per day is simulated. The MR system can be usedto cool feed normal Hydrogen gas from 25 oC to the equilibrium temperature of −193 oC with a highefficiency. In addition, for the transition from the equilibrium temperature of the Hydrogen gas from−193 oC to −253 oC, a new proposed four H2 Joule-Brayton cycle refrigeration system withoptimization is recommended. The overall power consumption of the proposed plant for the basedcase is 6.35 kWh/kgLH2. The current plant in Ingolstadt is used as a reference, which has an energyconsumption of 13.58 kWh/kgLH2 and an efficiency of 21.28%. The efficiency of the proposedsystem is around 45% or more, where this depends on the assumed efficiency values for thecompressors and expanders, together with effectiveness of heat exchangers. Importantly, thevariables and constraints are preliminary studied together with how to adjust these to achieveoptimal steady-state operation. The optimization problem has 23 variables and 26 constraints. Asimplified 5-component composition of refrigerant suggested for the plant is found. The plantoptimization was also conducted with two more pinch temperatures (1 and 3 oC). Power saving isincreased with a pinch temperature of 1 oC as compared to 3 oC. This figure can have a significantimpact on plants selection. In addition, pressure drops in heat exchangers are also employed in thesimulation for the study, however it is shown that they don’t have much significant impact on theoverall plant total power consumption. The proposed system has smaller compressor motors andsmaller crankcase compressors; thus, it could represent a plant with the lowest construction costwith respect to the amount of liquid Hydrogen produced in comparison to today’s plants, e.g., in Ingolstadt and Leuna. Therefore, the proposed system has many improvements that serves as anexample for future Hydrogen Liquefaction plants.
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exergy analysis on the simulation of a small scale Hydrogen Liquefaction test rig with a multi component refrigerant refrigeration system
International Journal of Hydrogen Energy, 2010Co-Authors: Songwut Krasaein, Jacob H Stang, Petter NeksaAbstract:Abstract This study investigates the simulation of a proposed small-scale laboratory liquid Hydrogen plant with a new, innovative multi-component refrigerant (MR) refrigeration system. The simulated test rig was capable of liquefying a feed of 2 kg/h of normal Hydrogen gas at 21 bar and 25 °C to normal liquid Hydrogen at 2 bar and −250 °C. The simulated power consumption for pre-cooling the Hydrogen from 25 °C to −198 °C with this new MR cycle was 2.07 kWh/kgGH2 from the ideal minimum of 0.7755 kWh per kilogram of feed Hydrogen gas. This was the lowest power consumption available when compared to today’s conventional Hydrogen Liquefaction cycles, which are approximately 4.00 kWh/kgGH2. Hence, the MR cycle’s exergy efficiency was 38.3%. Exergy analysis of the test rig’s cycle, which is required to find the losses and optimize the proposed MR system, was evaluated for each component using the simulation data. It was found that the majority of the losses were from the compressors, heat exchangers, and expansion valves. Suggestions are provided for how to reduce exergy in each component in order to reduce the exergy loss. Finally, further improvements for better efficiency of the test rig are explained to assist in the design of a future large-scale Hydrogen Liquefaction plant.
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development of large scale Hydrogen Liquefaction processes from 1898 to 2009
International Journal of Hydrogen Energy, 2010Co-Authors: Songwut Krasaein, Jacob H Stang, Petter NeksaAbstract:Abstract This paper presents a review of the development of large-scale Hydrogen Liquefaction processes throughout the world from 1898 to 2009. First, there is a concise literature review including numerous past, present, and future designs given such as the first Hydrogen Liquefaction device, long time ago simple theoretical processes, today's actual plants with efficiencies 20–30%, a list of the capacity and location of every Hydrogen Liquefaction plant in the world, and some modern more efficient proposed conceptual plants with efficiencies 40–50%. After that, further information about the development and improvement potential of future large-scale liquid Hydrogen Liquefaction plants is given. It is found that every current plant is based on the pre-cooled Claude system, which is still the same as was 50 years ago with little improvement. Methods to resolve the challenges of the future plants include proposing completely new configurations and efficient systems coupled with improved efficiencies of the main system components such as compressors, expanders, and heat exchangers. Finally, a summary and comparison of the process efficiencies are described, including a newly proposed Multi-component Refrigerant (MR) system being developed by NTNU and SINTEF Energy Research AS.
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comparison criteria for large scale Hydrogen Liquefaction processes
International Journal of Hydrogen Energy, 2009Co-Authors: David Olsson Berstad, Jacob H Stang, Petter NeksaAbstract:In a Hydrogen liquefier the pre-compression of feed gas has generally higher stand-alone exergy efficiency than the cooling and Liquefaction sub-process. Direct comparison of liquefiers based on overall exergy efficiency and specific power consumption will favour those with a higher portion of pre-compression. A methodology for comparing Hydrogen Liquefaction processes that compensates for non-uniformity in feed specifications has been developed and applied to three different Hydrogen liquefiers. The processes in consideration have been modified to have equal Hydrogen feed pressure, resulting in a more consistent comparison. Decreased feed pressure results in generally higher power consumption but also higher exergy efficiency, and vice versa. This approach can be adapted to the boundary conditions that the Liquefaction process will be subject to in a real energy system.
Geir Skaugen - One of the best experts on this subject based on the ideXlab platform.
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comparing exergy losses and evaluating the potential of catalyst filled plate fin and spiral wound heat exchangers in a large scale claude Hydrogen Liquefaction process
International Journal of Hydrogen Energy, 2020Co-Authors: Geir Skaugen, David Olsson Berstad, Oivind WilhelmsenAbstract:Abstract Detailed heat exchanger designs are determined by matching intermediate temperatures in a large-scale Claude refrigeration process for Liquefaction of Hydrogen with a capacity of 125 tons/day. A comparison is made of catalyst filled plate-fin and spiral-wound heat exchangers by use of a flexible and robust modeling framework for multi-stream heat exchangers that incorporates conversion of ortho-to para-Hydrogen in the Hydrogen feed stream, accurate thermophysical models and a distributed resolution of all streams and wall temperatures. Maps of the local exergy destruction in the heat exchangers are presented, which enable the identification of several avenues to improve their performances. The heat exchanger duties vary between 1 and 31 MW and their second law energy efficiencies vary between 72.3% and 96.6%. Due to geometrical constraints imposed by the heat exchanger manufacturers, it is necessary to employ between one to four parallel plate-fin heat exchanger modules, while it is possible to use single modules in series for the spiral-wound heat exchangers. Due to the lower surface density and heat transfer coefficients in the spiral-wound heat exchangers, their weights are 2–14 times higher than those of the plate-fin heat exchangers. In the first heat exchanger, Hydrogen feed gas is cooled from ambient temperature to about 120 K by use of a single mixed refrigerant cycle. Here, most of the exergy destruction occurs when the high-pressure mixed refrigerant enters the single-phase regime. A dual mixed refrigerant or a cascade process holds the potential to remove a large part of this exergy destruction and improve the efficiency. In many of the heat exchangers, uneven local exergy destruction reveals a potential for further optimization of geometrical parameters, in combination with process parameters and constraints. The framework presented makes it possible to compare different sources of exergy destruction on equal terms and enables a qualified specification on the maximum allowed pressure drops in the streams. The mole fraction of para-Hydrogen is significantly closer to the equilibrium composition through the entire process for the spiral-wound heat exchangers due to the longer residence time. This reduces the exergy destruction from the conversion of ortho-Hydrogen and results in a higher outlet mole fraction of para-Hydrogen from the process. Because of the higher surface densities of the plate-fin heat exchangers, they are the preferred technology for Hydrogen Liquefaction, unless a higher conversion to heat exchange ratio is desired.
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reducing the exergy destruction in the cryogenic heat exchangers of Hydrogen Liquefaction processes
International Journal of Hydrogen Energy, 2018Co-Authors: Petter Neksa, Oivind Wilhelmsen, David Berstad, Ailo Aasen, Geir SkaugenAbstract:Abstract A present key barrier for implementing large-scale Hydrogen Liquefaction plants is their high power consumption. The cryogenic heat exchangers are responsible for a significant part of the exergy destruction in these plants and we evaluate in this work strategies to increase their efficiency. A detailed model of a plate-fin heat exchanger is presented that incorporates the geometry of the heat exchanger, nonequilibrium ortho-para conversion and correlations to account for the pressure drop and heat transfer coefficients due to possible boiling/condensation of the refrigerant at the lowest temperatures. Based on available experimental data, a correlation for the ortho-para conversion kinetics is developed, which reproduces available experimental data with an average deviation of 2.2%. In a plate-fin heat exchanger that is used to cool the Hydrogen from 47.8 K to 29.3 K with Hydrogen as refrigerant, we find that the two main sources of exergy destruction are thermal gradients and ortho-para Hydrogen conversion, being responsible for 69% and 29% of the exergy destruction respectively. A route to reduce the exergy destruction from the ortho-para Hydrogen conversion is to use a more efficient catalyst, where we find that a doubling of the catalytic activity in comparison to ferric-oxide, as demonstrated by nickel oxide-silica catalyst, reduces the exergy destruction by 9%. A possible route to reduce the exergy destruction from thermal gradients is to employ an evaporating mixture of helium and neon at the cold-side of the heat exchanger, which reduces the exergy destruction by 7%. We find that a combination of Hydrogen and helium-neon as refrigerants at high and low temperatures respectively, enables a reduction of the exergy destruction by 35%. A combination of both improved catalyst and the use of Hydrogen and helium-neon as refrigerants gives the possibility to reduce the exergy destruction in the cryogenic heat exchangers by 43%. The limited efficiency of the ortho-para catalyst represents a barrier for further improvement of the efficiency.
Mehdi Mehrpooya - One of the best experts on this subject based on the ideXlab platform.
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Hydrogen Liquefaction process using solar energy and organic rankine cycle power system
Journal of Cleaner Production, 2019Co-Authors: Bahram Ghorbani, Mehdi Mehrpooya, Majid Aasadnia, Malek Shariati NiasarAbstract:Abstract A novel structure for Hydrogen Liquefaction is developed and thermodynamically analyzed. The modified structure, which produces approximately 290 tons of liquid Hydrogen ( L H 2 ) per day, consists of a basic Hydrogen liquefier system, an organic Rankine cycle, an absorption refrigeration system, and solar parabolic dishes. The new approach of simultaneous considering of exergy destruction rate and exergy efficiency is used to analyze the system, which results in lower energy consumption and higher exergy efficiency. Accordingly, the COP of the plant is calculated as 0.2002 and it consumes 4.02 k W h / k g L H 2 that is 8.93 percent less than the basic liquefier. Moreover, the overall exergy efficiency of it is 73.57% is 24.60% more than the basic system one. As well as, results indicate that the cryogenic sector of the process consumes 73% of the total consumed energy. Furthermore, exergy analysis shows that the most exergy destruction occurs in the solar collectors (43.59%) and heat exchangers (40.23%), and when the exergy efficiency varies 1.9% during a typical day, the exergy destruction change will be 9.5%. As well as, sensitive analysis shows that when solar energy increases by 204% due to adding more solar collectors, boilers energy decreases by 59%. Moreover, when the number of the collectors doubles, the production rates and the energy consumption of the process are also doubled. However, more power will be needed that will increase the operating cost of the liquefier. Therefore, an exergy-economy analysis may be used to address the optimum solutions.
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an exergy based investigation on Hydrogen Liquefaction plant exergy exergoeconomic and exergoenvironmental analyses
Journal of Cleaner Production, 2019Co-Authors: Hojat Ansarinasab, Mehdi Mehrpooya, Milad SadeghzadehAbstract:Abstract In this study, a conventional Hydrogen Liquefaction process is comprehensively analyzed. The studied Hydrogen Liquefaction process is consisted of two independent MR (Mixed Refrigerants) refrigeration cycles. In order to evaluate the Liquefaction process and obtain valuable and noteworthy results, the process is examined through a comprehensive exergy based analyses. The exergy based analyses includes conventional exergy analysis to examine the performance of the Liquefaction process, exergoeconomic analysis to obtain the effect of cost and economy on the performance, and exergoenvironmental analysis to provide beneficial information about the mutual effect of system's performance and environmental conditions. In addition, a sensitivity analysis is provided to assess and determine the mutual interaction among costs, environmental effects of each component, and the amount of exergy destruction. From the results, it is shown that the first refrigeration cycle exergy efficiency is obtained about 67.53% and the second refrigeration stage exergy efficiency is calculated about 52.24%. The whole Hydrogen Liquefaction process is exergy efficiency is 55.47%. The specific energy consumption (SEC) of this process is equal to 1.102 kWh/kgLH2. The total performance coefficient of the total process is 0.1797 which is higher than other reported articles. It is recommended from the Exergoeconomic and Exergoenvironmental analyses that the employed turbo-expanders and compressors are in priority for possible modification of the total process in the future.
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conceptual design and analysis of a novel process for Hydrogen Liquefaction assisted by absorption precooling system
Journal of Cleaner Production, 2018Co-Authors: Majid Aasadnia, Mehdi MehrpooyaAbstract:Abstract Hydrogen Liquefaction processes have effective function in the Hydrogen supply chain. However low efficiency and high Liquefaction costs are still the most important concerns about the Liquefaction plants. In this study a new configuration for a Hydrogen liquefier process is proposed and energy-exergy analyzed. The production rate of the liquid Hydrogen ( L H 2 ) is 90 tons per day that can supply the required L H 2 of at least 90 k-180 k Hydrogen vehicles in an urban area that results in the reduction of pollutions caused by carbon dioxide emission. The process is simulated in Aspen HYSYS simulator. In addition, it is optimized thorough a trial and error approach that is a functional and simple method of complicated systems analysis. The process includes a mixed refrigerant (MR) refrigeration cycle that precools feed gas Hydrogen from 25 °C temperature to − 199.9 °C temperature. A new MR is used in a cascade Joule-Brayton cycle that deep-cools the low-temperature gaseous Hydrogen from − 199.9 °C temperature to − 252.2 °C temperature in the cryogenic section of the plant. The novel process involves also an absorption refrigeration system (ARS) that cools some Hydrogen streams in the precooling and cryogenic sections of the process. The consumed energy per kilogram of produced L H 2 is achieved as 6.47 k W h . This quantity is 2.89 k W h in the ideal conditions. The exergy efficiency of the plant is evaluated to be 45.5% that is significantly more than the exergy efficiency of the in operating Hydrogen liquefiers in the world. The energy analysis reveals that the coefficient of performance (COP) of the overall system is 0.2034. The achieved COP is a higher amount in compare to the other similar processes. A sensitivity analysis is done to show the effect of the various operation conditions of the process on the features of the plant. Accordingly, the optimum mass flow of the ARS is determined as 207 k g / s for the proposed configuration. As well as, the effect of the change in the temperature approach of the heat exchangers and the changes in the adiabatic efficiency of the compressors and expanders on the SEC, COP, and the exergy efficiency of the overall plant is discussed. Furthermore, financial analysis of the plant estimates the capital expenditures (CAPEX), energy expenditures (EEX), and operational and maintenance expenditures (OMEX) as 25413 € 2000 , 7370 € 2000 , and 2033 € 2000 respectively. These can be specially improved be improving of the exergy efficiency of the plant. The results implicates that the proposed configuration has better performance indicators than the in-service liquefiers. Therefore, LHL plant manufacturer can be considered it in the design and development of new plants. As well as, researchers may utilize its operating conditions to improve the proposed processes.
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process development and exergy cost sensitivity analysis of a novel Hydrogen Liquefaction process
International Journal of Hydrogen Energy, 2017Co-Authors: Mirhadi S Sadaghiani, Mehdi Mehrpooya, Hojat AnsarinasabAbstract:Abstract A novel Hydrogen Liquefaction process including a single mixed refrigerant cycle is proposed and investigated by energy, conventional and advanced exergy and exergoeconomic analyses methods. The proposed Liquefaction process can produce 130 tons liquid Hydrogen per day. Results of energy analysis reveals that 7.646 kWh/kg LH 2 power is consumed to liquefy the Hydrogen from 21 bar to 25 °C. Exergy analysis indicates that exergy efficiency of the proposed Hydrogen Liquefaction process is almost 32%, which is higher than Ingolstadt operating Hydrogen Liquefaction plant with exergy efficiency of 21.28%. Also, the power consumption of proposed Hydrogen Liquefaction plant is less than its kind between other similar conceptual processes. Based on the advanced exergy analysis, most part of the exergy destruction rates of the compressors, heat exchangers and air cooler are endogenous, while the dominant part of irreversibilities of the turbo expanders is exogenous. Effect of mole fraction of the mixed refrigerant components on performance of the process is investigated. Also, sensitivity of exergy destruction cost rate and exergoeconomic factor to operating variables of the proposed Hydrogen Liquefaction process is investigated and discussed. Results of the analyses show that maximum exergy destruction cost rate of the process components is 2265.26 $/h, which most of it is endogenous and unavoidable.
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a novel Hydrogen Liquefaction process configuration with combined mixed refrigerant systems
International Journal of Hydrogen Energy, 2017Co-Authors: Majid Asadnia, Mehdi MehrpooyaAbstract:Abstract A novel large-scale plant for Hydrogen liquefying is proposed and analyzed. The liquid Hydrogen production rate of the proposed plant is 100 tons per day to provide the required LH2 for a large urban area with 100,000–200,000 Hydrogen vehicles supply. In the pre-cooling section of the process, a new mixed refrigerant (MR) refrigeration cycle, combined with a Joule–Brayton refrigeration cycle, precool gaseous Hydrogen feed from 25 °C to the temperature −198.2 °C. A new refrigeration system with six simple Linde–Hampson cascade cycles cools low-temperature gaseous Hydrogen from −198.2 °C to temperature −252.2 °C. The process specific energy consumption (SEC) is 7.69 kWh/kg L H 2 which minimum value is 2.89 kWh/kg L H 2 in ideal conditions. The exergy efficiency of the system is 39.5%, which is considerably higher than the existing Hydrogen liquefier plants around the world. However, assuming more efficiency values for the equipment can improve it. The energy analysis specifies that coefficient of performance (COP) of the process is 0.1710 which is a high quantity of its kind between other similar processes. Effect of various refrigerant components concentration, discharge pressure of the high pressure compressors of the pre-cooling section, and Hydrogen feed pressure on the process COP, exergy efficiency, and SEC are investigated. After that, a new MR will be offered for the cryogenic section of the plant. The system improvements are considerable comparing to current Hydrogen liquefying plants, therefore, the proposed conceptual system can be used for future Hydrogen Liquefaction plants design.
