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Illustration of the hot and cold layers in the plate-fin-heat exchanger and their governing variables. Fins are used in both layers to enhance the heat transfer coefficient and area, The hot layers are filled with catalyst and the cold layers are open.
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Liquefaction of hydrogen is a promising technology for transporting large quantities of hydrogen across long distances. A key challenge is the high power consumption. In this work, we discuss refrigeration strategies that give minimum entropy production/exergy destruction in a plate-fin heat exchanger that cools the hydrogen from 47.8 K to 29.3 K....
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... heat that is generated when liquefied orthohydrogen converts to para-hydrogen in e.g. storage tanks will lead to full evaporation, since the enthalpy difference of orthopara conversion exceeds the latent heat of evaporation at low temperatures. In the plate-fin heat exchanger, cold and hot layers are placed in a repeating unit as illustrated in Figs. 1 and 2. If boundary effects are neglected, the behavior of the complete heat exchanger can be represented by considering only a repeating unit of hot and cold streams as shown in Fig. 1, which sequentially make up the full plate-fin heat exchanger that has n = 2N number of layers in total, where N is the number of times the unit is repeated. ...
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... exceeds the latent heat of evaporation at low temperatures. In the plate-fin heat exchanger, cold and hot layers are placed in a repeating unit as illustrated in Figs. 1 and 2. If boundary effects are neglected, the behavior of the complete heat exchanger can be represented by considering only a repeating unit of hot and cold streams as shown in Fig. 1, which sequentially make up the full plate-fin heat exchanger that has n = 2N number of layers in total, where N is the number of times the unit is repeated. Fins are included to increase the available heat transfer area as well as to induce turbulence to enhance the heat transfer. Two configurations will be studied in this work: A ...
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... L is the total length of the heat exchanger (see Fig. 1) and the overall heat transfer coefficient of the complete model depended on the state variables both in the hot (T, P, η) and cold layers (T a ...
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... the unit can be derived by use of nonequilibrium thermodynamics [40]. The framework of nonequilibrium thermodynamics has successfully giving insight into a variety of examples ranging from thermoelectric generators [41] to ion-exchange membranes [42] and gas-liquid interfaces [43]. The local entropy production of the repeating unit illustrated in Fig. 1 ...
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... heat exchanger studied in this work is one of several heat exchangers in a Claude refrigeration cycle with a production capacity of 50 tons of liquid hydrogen per day. A sketch of the layout of such a process is presented in Fig. 1 in Ref. [16]. The purpose of the heat exchanger is to cool the reacting hydrogen where catalyst is present from 47.8 K to a target temperature for the reacting hydrogen of 29.3 K. The cold-side refrigerant inlet temperature is 28.9 K. Before final expansion, the reacting hydrogen stream is very close to the Joule-Thomson inversion ...
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Citations
... Trial & Error 5.910 Cardella et al. [9] 2017 Not Mentioned (NM) 6.000 45.00 Cardella et al. [10] 2017 Sequential Quadratic Programming (SQP) 5.900 43.00 Cardella et al. [11] 2017 SQP 5.910 Hå nde and Wilhelmse [12] 2019 NM Yin and Ju [13] 2020 GA 7.133 Qyyum et al. [1] 2021 MCD 6.450 47.20 Jackson and Brodal [14] 2021 i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( x x x x ) x x x at times, is one of the reasons earlier studies do not change the cycle temperatures. The temperature at the exit of PMR is À155 C with the corresponding para-H 2 concentration of 35%. ...
Hydrogen (H2) liquefaction process is one of the complex processes because of the highly non-linear interaction between design variables and objective function. Finding a feasible
design for such a complex process is challenging. Knowledge of refrigerant selection, composition, cycle temperatures, and compression ratio is essential in finding this feasible design. This study presents a simple, yet efficient approach inspired by process knowledge, known as knowledge-based optimization (KBO), to selecting an optimal mixed refrigerant (MR) composition and studying the effect of each refrigerant on the performance of the H2 liquefaction process. The infeasible design shows approach temperature (i.e., MITA) values as -33.5 C, -4.0 C, and -11.65 C. The design variables' values are adjusted based on the
KBO approach to keep the MITA value in the range of 1-2 C. The share of each MR component in optimal case is 17% C1, 5% C2, 70% C3, 8% N2 in precooling, 9% C1, 80% N2, 11% H2 in cooling and 85% H2, 15% He in liquefaction cycle. Further, the KBO approach guides in selecting the lower and upper limit of each refrigerant based on their impact inside heat exchangers. Additionally, the heat flow behavior of H2 streams is analyzed for adiabatic and isothermal ortho-to-para reactors. This study will help process engineers and engineering practitioners to develop an energy-efficient and cost-effective initial design for the H2 liquefaction process.
... Donaubauer et al. [28] discussed the reliability of the two kinetic models of the ortho-para hydrogen conversion, and established a onedimensional mathematical model to analyze the operation and performance of the CFPFHE. On the basis of Wilhelmsen et al. [25], Hande et al. [29] further discussed the optimization strategy of cooling hydrogen from 47.8 K to 29.3 K in the CFPFHE with minimum entropy production/exergy loss. Park et al. [30] carried out an experiment of hydrogen flowing through the pipe filled with the ortho-para hydrogen conversion catalyst, and obtained a corresponding pressure drop correlation to improve the mathematical model of the [19,20]. ...
In order to develop the correlations of the fin performances of the catalyst filled plate fin heat exchanger (CFPFHE) for hydrogen liquefaction, a numerical model of the plain fin filled with catalyst at 30–80 K is established. The effects of temperature, the structural parameters of the fin and catalyst layer and the operating condition on the fin performances of the fin channel are analyzed and discussed. The results show that the temperature distribution patterns and fin performances at 30–40 K and above 40 K have obvious differences. The results above 40 K can be characterized by that at 70–80 K. The sensitivity analysis shows that the distributions of sensitivity at 70–80 K and 30–40 K are similar. The heat transfer and ortho-para hydrogen conversion performances are mainly affected by the structural parameters of the fin and the operating condition, while the flow performance is mainly affected by the structural parameters of the catalyst layer. The correlations of the flow and heat transfer performances at 70–80 K and 30–40 K are obtained by fitting the data points on the response surface with more than 97% of the fitting degrees and within ±15% of the deviations. Meanwhile, the correlations of the ortho-para hydrogen conversion performance show that the mass space velocities at 70–80 K and 30–40 K should be lower than 1.25 and 7.50 kg m⁻³ s⁻¹ respectively to reach the standard of the ortho-para hydrogen conversion. The correlations of the fin performances can be used as the basis of optimization design of the CFPFHE.
... Thus, alternatives such as ammonia have been identified to overcome the inherent difficulties of handling H 2 , since the former has a boiling point of around − 33.4 • C and can be stored cheaply at ambient pressure in large quantities (Bartels et al. [8]), with a well-developed pre-existing infrastructure for transportation (Elishav et al. [9]). In contrast, H 2 liquifies at − 252.8 • C, undergoing an ortho-para exothermic conversion in the cooling process (Hande et al. [10]), which requires very large energy inputs and expensive and complex equipment (Hammad et al. [11]), making this energy storage route less feasible at a large scale. On the other hand, although ammonia is actually used primarily for nitrogen-based fertilizer production (Jeonghoon et al. [12]), it shows good potential for applications as fuel in thermal power generation (Ezzat et al. [13]) and transport (Hansson et al. [14]) sectors, and it can be reconverted to H 2 through thermolysis at the point of use (Cechetto et al. [15]). ...
Ammonia is an industrial chemical and the basic building block for the fertilizer industry. Lately, attention has shifted towards using ammonia as a carbon-free energy vector, due to the ease of transportation and storage in liquid state at −33 °C and atmospheric pressure. This study evaluates the prospects of blue and green ammonia as future energy carriers; specifically, the gas switching reforming (GSR) concept for H2 and N2 co-production from natural gas with inherent CO2 capture (blue), and H2 generation through an optimized value chain of wind and solar power, electrolysers, cryogenic N2 supply, and various options for energy storage (green). These longer-term concepts are benchmarked against conventional technologies integrating CO2 capture: the Kellogg Braun & Root (KBR) Purifier process and the Linde Ammonia Concept (LAC). All modelled plants utilize the same ammonia synthesis loop for a consistent comparison. A cash flow analysis showed that the GSR concept achieved an attractive levelized cost of ammonia (LCOA) of 332.1 €/ton relative to 385.1–385.9 €/ton for the conventional plants at European energy prices (6.5 €/GJ natural gas and 60 €/MWh electricity). Optimal technology integration for green ammonia using technology costs representative of 2050 was considerably more expensive: 484.7–772.1 €/ton when varying the location from Saudi Arabia to Germany. Furthermore, the LCOA of the GSR technology drops to 192.7 €/ton when benefitting from low Saudi Arabian energy costs (2 €/GJ natural gas and 40 €/MWh electricity). This cost difference between green and blue ammonia remained robust in sensitivity analyses, where input energy cost (natural gas or wind/solar power) was the most influential parameter. Given its low production costs and the techno-economic feasibility of international ammonia trade, advanced blue ammonia production from GSR offers an attractive pathway for natural gas exporting regions to contribute to global decarbonization.
... To reduce energy consumption, a refrigeration strategy that gives minimum entropy production/exergy destruction in a plate-fin heat exchanger that cools the hydrogen from 47.8 K to 29.3 K has been discussed in 2019 by Hande et al. [27]. Two reference cases have been studied; one where the feed stream enters at 20bar, and one where it enters at 80 bar. ...
The present work aims at performing a comparative study between precooled Claude cycle and an Active Magnetic Regeneration Cycle (AMR cycle) applied to hydrogen liquefaction. It deals with a comparison between performances and energy consumption evaluated for the two systems at similar operating conditions. For Claude system, energy and material balances have been performed by using Aspen Hysys simulator. Thus, liquefaction power, energy consumption and coefficient of performance (COP) have been calculated. While, the AMR system considered is constituted of 6 stages operating in cascade. Each stage contains two regenerator beds, composed of a typical magnetic material, through which a carrier fluid is forced to follow alternatively between two heat reservoirs. Thermal analysis and evaluation of performances have been performed at once by a numerical model, developed on the basis of energy equations for fluid and solid within the regenerator bed, and Aspen Hysys simulator. Using the following magnetic materials (Gd, Dy, Tb and Ho), the COP found for the AMR system is 0.096. This value is higher than Claude cycle efficiency for which a COP of 0.094 was found. In terms of energy consumption, the value found for the AMR cycle is 0.053 kW which can be neglected compared to the Claude cycle consumption (14.5 kW).
... They found that the thermal gradient and ortho-para hydrogen conversion are the two main sources of exergy loss of the CFPFHX, accounting for 69% and 29% of the total exergy loss respectively. Hande et al. [24] investigated the thermodynamic performance of the CFPFHX in the temperature range of 47.8 Ke29.3 K under the operating pressure of 20 bar and 80 bar. ...
... Meanwhile, the para-hydrogen ratio of equilibrium hydrogen is a function of temperature, which is expressed by temperature dependent equation [24]: ...
... In order to compare and verify the correctness of the existing kinetic models of ortho-para hydrogen conversion, the Elovich model [22,24], the Langmuir Hinshelwood model Fig. 3 e Results of regional discretization. ...
A mathematical model of the plate-fin heat exchanger filled with catalyst (CFPFHX) is established to investigate the continuous cooling process coupled with ortho-para hydrogen conversion at 42–70 K. The flow and heat transfer performance and the efficiency of ortho-para hydrogen conversion in the CFPFHX are quantitatively evaluated, and the effects of the structural parameters on the flow and heat transfer coupled with ortho-para hydrogen conversion are analyzed. The results show that the Elovich model is the best existing kinetic models of ortho-para hydrogen conversion with an average relative deviation of 1.8%. The Colburn heat transfer factor (j factor) of the hot side of the CFPFHX is 4.3 times that of the plate-fin heat exchanger (PFHX), and the thermal enhancement factor (TEF) of the hot side is 37.7% of that of the PFHX. Meanwhile, for the CFPFHX, the j factor and the TEF of the hot side under different structural parameters are always about 8–10 times and 68%–93% of that of the cold side respectively. Therefore, the CFPFHX can ensure the flow and heat transfer performance and realize the ortho-para hydrogen continuous conversion. And a fin with the larger flow area (high fin height, wide fin spacing and small fin thickness) has a better flow and heat transfer performance and ortho-para hydrogen conversion. The outlet para-hydrogen ratio youtp-H2 and the mass space velocity vm in the CFPFHX have an approximate linear trend. When mass space velocity vm ≤ 0.6589 kg/(m³·s), the outlet para-hydrogen ratio youtp-H2 can meet the requirement at 42–70 K. Above all, the mechanism of flow and heat transfer coupled with ortho-para hydrogen conversion is revealed for the first time in this study, which can provide a theoretical guidance for the application of the integrated technology in large scale hydrogen liquefaction process.
... Despite that "equilibrium hydrogen" has received some critique in recent literature [34], this clearly demonstrates the usefulness of the concept in an effective treatment of the heat exchangers of a hydrogen liquefaction process. In Ref. [29,35], it was shown that there is significant potential to reduce the irreversibilities in heat exchangers by improved design and operation. We refer to these works for further details on how to improve the performance of the heat exchangers and will in the following outline additional measures to improve the efficiency. ...
For liquid hydrogen (LH2) to become an energy carrier in energy commodity markets at scales comparable to for instance LNG, liquefier capacities must be scaled up several orders of magnitude. While state-of-the-art liquefiers can provide specific power requirements down to 10 kWh/kg, a long-term target for scaled-up liquefier trains is 6 kWh/kg. High capacity will shift the cost weighting more towards operational expenditures, which motivates for measures to improve the efficiency. Detailed exergy analysis is the best means for gaining a clear understanding of all losses occurring in the liquefaction process. This work analyses in detail a hydrogen liquefier that is likely to be realisable without intermediate demonstration phases, and all irreversibilities are decomposed to the component level. The overall aim is to identify the most promising routes for improving the process. The overall power requirement is found to be 7.09 kWh/kg, with stand-alone exergy efficiencies of the mixed-refrigerant pre-cooling cycle and the cryogenic hydrogen Claude cycle of 42.5% and 38.4%, respectively. About 90% of the irreversibilities are attributed to the Claude cycle while the remainder is caused by pre-cooling to 114 K. For a component group subdivision, the main contributions to irreversibilities are hydrogen compression and intercooling (39%), cryogenic heat exchangers (21%), hydrogen turbine brakes (15%) and hydrogen turbines (13%). Efficiency improvement measures become increasingly attractive with scale in general, and several options exist. An effective modification is to recover shaft power from the cryogenic turbines. 80% shaft-to-shaft power recovery will reduce the power requirement to 6.57 kWh/kg. Another potent modification is to replace the single mixed refrigerant pre-cooling cycle with a more advanced mixed-refrigerant cascade cycle. For substantial scaling-up in the long term, promising solutions can be cryogenic refrigeration cycles with refrigerant mixtures of helium/neon/hydrogen, enabling the use of efficient and well scalable centrifugal compressors.
... The second law of thermodynamics is utilized as a basis for assessing the irreversibility (entropy generation) associated with simple heat transfer processes [48]. It can help designers identify major source(s) of irreversibility and then improve the performance of the device by making decisions such as modifying the operating conditions of the device, optimizing the device geometry or changing the working fluid [49][50][51][52][53][54][55]. ...
The impetus of this numerical investigation is to explore the performance aspects of laminar forced convection flow of biologically synthesized water–silver nanofluid inside an internally spiral-ribbed heat exchanger tube from both the first and second laws of thermodynamics perspectives. The two-phase mixture model is used to perform the required simulations. The impacts of the volume concentration of nanoadditives (φ), Reynolds number (Re) as well as the width (W), height (H) and pitch (P) of the ribs on the hydrothermal aspects and irreversibility behavior of the nanofluid are assessed, and the results are compared with the findings of smooth tube. It was found that the use of nanofluid and the use of rifled tube instead of water and smooth tube, respectively, are suitable ways to improve system performance from both the first and second laws of thermodynamics perspectives. Moreover, it was reported that the best hydrothermal performance of the nanofluid through the rifled tube occurs at φ = 1%, Re = 2000, W = 3 mm, H = 1 mm, P = 4 mm, while the minimum total irreversibility in the flow of water–silver nanofluid inside a rifled tube occurs at φ = 1%, Re = 2000, W = 3 mm, H = 0.5 mm, P = 4 mm.
... Johannessen and Kjelstrup, 2004 reported similar findings for chemical reactors and Magnanelli et al. (2018), for membrane separation of gases. Another concept that has been recently discussed in the literature is energy efficient highways in state-space (Hånde and Wilhelmsen, 2019;Johannessen and Kjelstrup, 2004;Wilhelmsen et al., 2011). Whether such highways also exists for continuous, rate-based distillation columns remains to be investigated. ...
In this work, we apply the rate-based model of Taylor and Krishna to describe the separation of air in a low-pressure, packed distillation column. By use of numerical optimization, we identify the temperature profile for heat exchange with the column and its surroundings that minimizes the total entropy production. Optimal operation of the column reduces the entropy production by nearly 50%, and the total heating- and cooling duties by 30% and 50%, respectively. We find that the local entropy production is more uniform for the optimal solution than in the adiabatic column, a property that may be helpful for new designs. Using the equilibrium stage model, the state of minimum entropy production has higher cooling/heating duties than in the rate-based model case. This shows that more sophisticated models can be beneficial for the development of reliable strategies to improve the energy efficiency of distillation columns.
... In Ref. [48], we showed that a good strategy to lower the entropy production/exergy destruction in a heat exchanger in the hydrogen liquefaction process is to modify the design and operation such that the local exergy destruction is equally distributed in space. An inspection of the local exergy destruction of HX-2 displayed in Fig. 6c shows that this is far from the case. ...
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.
... The second-law of thermodynamics is utilized as a basis for assessing the irreversibility (entropy generation) associated with simple heat transfer processes [31]. It can help designers identify major source(s) of irreversibility and then, improve the performance of the device by making decisions such as modifying the operating conditions of the device, optimizing the device geometry or changing the working fluid [32][33][34][35][36][37][38]. ...
