Cascade Cycles Research Articles

Investigation on cascading cogeneration system of ORC (Organic Rankine Cycle) and CaCl2/BaCl2 two-stage adsorption freezer

It is important to improve the heat utilization efficiency for the waste heat as well as the geothermal heat because both of them will exhaust to the environment or flow back to the ground directly after the energy was recovered. In order to achieve that, a novel cascading cycle driven by the low temperature heat source was developed. This cycle featured for the high exergy efficiency for the heat utilization because the energy was utilized two steps by ORC (Organic Rankine Cycle) and CaCl2/BaCl2 two-stage adsorption refrigeration system sequentially with the heat source of higher temperature and lower temperature. For ORC system, a test unit with the fluid of compressed air was established for investigating the internal efficiency of the scroll expander, and the performance of R245fa working fluid was analyzed. For the freezer a CaCl2/BaCl2 two-stage adsorption refrigeration system was set up and tested. Results showed that for the cascading cycle 390–560 W electricity and 1.92–2.7 kW refrigeration can be gotten under the condition of about 22.85–25.1 kW heating power, and correspondingly the total energy and exergy efficiency was 10.1%–13.1% and 18.5%–20.3%, respectively. The cascading cycle improved the exergy efficiency for the heat utilization to 20.4%–29.1%.

Solar Powered Cascading Cogeneration Cycle with ORC and Adsorption Technology for Electricity and Refrigeration

As a renewable source, solar energy has received more and more attention in recent years. Solar energy can readily provide heat efficiently within the temperature range of 70–100°C. For the utilization of this energy source, a cascading cycle was designed and was discussed. An organic Rankine cycle (ORC) and an adsorption refrigeration cycle were combined to provide the first- and second-stage energy conversion cycle, respectively. In the analysis, R600 was used as the working fluid for the ORC and a silica gel–water working pair was analyzed for the adsorption refrigeration cycle. The energy efficiency for electrical generation and refrigeration, as well as the exergy efficiency of the cascading cycle, was assessed. For an environmental temperature of 30°C and a refrigeration temperature of 12°C, the results showed that typically 1 kW of electricity and 6.3 kW of refrigeration could be generated from approximately 15 kW heating power. The electricity generation efficiency was between 0.1 and 0.15, while the refrigeration coefficient of performance was approximately 0.8. The exergy efficiency was found to be between 0.84 and 0.89 and between 0.32 and 0.46 for the single ORC and adsorption refrigeration cycle, respectively. The overall exergy efficiency was between 0.56 and 0.74.

CO2LD: An innovation educational project for High Degree Professional Training in Refrigeration

Refrigeration is one of the technology sectors that has sufered the most changes in the last twenty years, because of the negative impact of the fuids used in the refrigeration cycles, i.e., refrigerants, due to their impact on the ozone layer and their contribution to global warming. As a result of their negative efects, the European Union has established several directives to restrict the use of refrigerant fuids, and the sector therefore needs to adapt to the new regulations. This process of adaptation of the refrigeration sector to the new regulations must be carried out by all the agents involved, including those engaged in the training and education of the future refrigeration technicians. To allow this to be accomplished, a project called CO2LD was developed to introduce the future technology in High Degree Professional Training in Refrigeration. The objective of the project consisted in introducing more efcient and more sustainable refrigeration systems, namely R134a/CO 2 cascade cycles, into the Advanced Vocational Training in Refrigeration studies, and in creating a collaborative framework among students, secondary schools, refrigeration technicians, refrigeration companies, and the University in order to facilitate the transfer of know-how. This paper presents the objectives of the project, describes its development, and analyzes its main conclusions.

Efficiency of Cascade Refrigeration Cycle Using C3H8, N2O, and N2

This article presents a new natural gas liquefaction cycle that utilizes propane (C3H8), nitrogen monoxide (N2O), and nitrogen gas (N2) cycles. A liquefaction cycle with staged compression was designed and simulated using HYSYS software for improving cycle efficiency. This included a cascade cycle with a three-stage compression consisting of a C3H8, an N2O, and an N2 cycle. The new C3H8, N2O, and N2 liquefaction cycle is compared to the optimized cascade cycle using propane, ethylene, and methane. The compressor work, specific energy, and coefficient of performance (COP) of the cascade cycles were compared and analyzed. The COP of the new cascade cycle that utilizes three-stage compression process 3 is 25% higher than that of basic single-stage process 1. Also, the new liquefaction cycle requires less specific power for the same amount of liquefied natural gas (LNG) produced by optimized cascade cycle. For example, the specific power and COP of the new cascade cycle are respectively up to 16% less and 14% higher than those of the optimized cascade cycle under the same conditions of feed gas composition and liquefaction rate.

S081011 排熱利用高温ヒートポンプサイクル適用評価([S081]高効率ヒートポンプの要素技術とその応用)

To reduce energy consumption utilizing heat recovery systems is increasingly important in industrial applications. The screening of refrigerants is discussed with a case study for high-temperature heat pumps in this study. The overall coefficients of performance of four different cycle configurations to increase water temperature up to 160℃ using waste heat of 80℃ are thermodynamically compared for three refrigerants. This case study suggests that the multiple stage cycle reduces throttling loss and exergy loss in condensers and achieves the highest overall COP with a refrigerant having the critical temperature about the target outlet water temperature. Cascade cycles bring relatively high COP and also advantages in practical situations.

Exergy Assessment of Recovery Solutions from Dry and Moist Gas Available at Medium Temperature

The Agence Nationale de la Recherche (ANR-EESI) ENERGY ReCOvery from Low Temperature heat sources (ENERCO_LT) project is a waste heat recovery project that aims to reduce energy consumption in industrial gas production sites, by producing electrical power from exothermic processes discharges at low and medium temperature. Two promising thermal sources, consisting of: (i) almost dry gas flow at 165 °C and (ii) moist gas flow at 150 °C with a dew point at 60 °C, were then investigated. In this paper, the challenge was to discern suitable recovery solutions facing resource specificities and their thermodynamic constraints, in order to minimize the overall exergy destruction, i.e., to move up the exergy efficiency of the entire system. In this spirit, different designs, including Organic Rankine Cycles (ORCs) and CO2 transcritical cycles, operating as simple and cascade cycles, were investigated. Combined exergy analysis and pinch optimization was performed to identify the potential of various working fluids, by their properties, to overcome the global irreversibility according to the studied resource. Supercritical parameters of various working fluids are investigated too, and seem to bring promising results regarding system performances.

Performance of cascade cycles working with blends of CO 2 + natural refrigerants

In this paper, an analysis on the performance of a cascade refrigeration cycle operated with blends of carbon dioxide (or R744) plus hydrocarbons (ethane or R170, propane or R290, ethylene or R1150, propylene or R1270) and dimethyl ether (or RE170) as the low-temperature working fluid was carried out. The properties of the investigated blends were used to simulate the behaviour of a cascade cycle using ammonia (or R717) as the high-temperature-circuit working fluid. The aim of this work was to study the possibility of using carbon dioxide mixtures in those applications where temperatures below its triple point (216.59 K) are needed. The analysis was carried out by developing a software based on the Carnahan–Starling–DeSantis (CSD) Equation of State (EoS) using binary interaction parameters derived from the experimental data in the literature. Results show that adding R744 to HCs and dimethyl ether reduces the cycle performance, even if acceptable values are always achieved for the COP. Main attractive of the R744 + natural refrigerant blends is connected with their GWP, ODP and flammability properties lower than those of pure fluids.

The Timing of the Cognitive Cycle

We propose that human cognition consists of cascading cycles of recurring brain events. Each cognitive cycle senses the current situation, interprets it with reference to ongoing goals, and then selects an internal or external action in response. While most aspects of the cognitive cycle are unconscious, each cycle also yields a momentary “ignition” of conscious broadcasting. Neuroscientists have independently proposed ideas similar to the cognitive cycle, the fundamental hypothesis of the LIDA model of cognition. High-level cognition, such as deliberation, planning, etc., is typically enabled by multiple cognitive cycles. In this paper we describe a timing model LIDA's cognitive cycle. Based on empirical and simulation data we propose that an initial phase of perception (stimulus recognition) occurs 80–100 ms from stimulus onset under optimal conditions. It is followed by a conscious episode (broadcast) 200–280 ms after stimulus onset, and an action selection phase 60–110 ms from the start of the conscious phase. One cognitive cycle would therefore take 260–390 ms. The LIDA timing model is consistent with brain evidence indicating a fundamental role for a theta-gamma wave, spreading forward from sensory cortices to rostral corticothalamic regions. This posteriofrontal theta-gamma wave may be experienced as a conscious perceptual event starting at 200–280 ms post stimulus. The action selection component of the cycle is proposed to involve frontal, striatal and cerebellar regions. Thus the cycle is inherently recurrent, as the anatomy of the thalamocortical system suggests. The LIDA model fits a large body of cognitive and neuroscientific evidence. Finally, we describe two LIDA-based software agents: the LIDA Reaction Time agent that simulates human performance in a simple reaction time task, and the LIDA Allport agent which models phenomenal simultaneity within timeframes comparable to human subjects. While there are many models of reaction time performance, these results fall naturally out of a biologically and computationally plausible cognitive architecture.

Cognitive Cycle in Mind Model CAM

Cognitive cycle is a basic procedure of mental activities in cognitive level. Human cognition consists of cascading cycles of recurring brain events. This paper presents a cognitive cycle for the mind model CAM (Consciousness And Memory). Each cognitive cycle perceives the current situation, through motivation phase with reference to ongoing goals, and then composes internal or external action streams to reach the goals in response. We use dynamic description logic which is an extended description logic with action to formalize descriptions and algorithms of cognitive cycle. Two important algorithms, including hierarchical goal and action composition, is proposed in the paper.

Analysis of Cryogenic Refrigeration Cycle Using Two Stage Intercooler

This paper presents the comparison of performance characteristics for the several natural gas liquefaction cycles. The liquefaction cycle with the staged compression was designed and simulated for improving the cycle efficiency using HYSYS software. This includes a cascade cycle with a two-stage intercooler which is consisted of a Propane, Ethylene and Methane cycle. In addition, these cycles are compared with a modified staged compression process. The key parameters of the above cascade cycles were compared and analyzed. The COP (Coefficient of Performance) of the cascade cycle with a two-stage intercooler and a modified staged compression process is 13.7% and 29.7% higher than that of basic cycle. Also, the yield efficiency of LNG (Liquefied Natural Gas) improved compared with the basic cycle by 28.5%.

High Performance Cascading Adsorption Refrigeration Cycle with Internal Heat Recovery Driven by a Low Grade Heat Source Temperature

This paper presents the performance of an advanced cascading adsorption cycle that utilizes a driven heat source temperature between 90–130 ºC. The cycle consists of four beds that contain silica gel as an adsorber fill. Two of the beds work in a single stage cycle that is driven by an external heat source, while the other two beds work in a mass recovery cycle that is driven by waste heat of sensible and adsorption heat of the high temperature cycle. The performances, in terms of the coefficient of performance (COP) and the specific cooling power (SCP), are compared with conventional cascading-without-mass-recovery and single-stage cycles. The paper also presents the effect of the adsorbent mass on performance. The results show that the proposed cycle with mass recovery produces as high of a COP as the COP that is produced by the conventional cascading cycle. However, it produces a lower SCP than that of the single-stage cycle.

Dephlegmator Design in Low Temperature Gas Separation

Dephlegmators can be used to reduce power consumption in low temperature gas separation processes. Most existing models have focused on separation process simulation, while the heat exchange characteristics and the refrigeration design were either ignored or based on highly simplified assumptions. This paper presents a new framework for the design of dephlegmators that addresses simulation of multicomponent partial condensation, design of plate-fin heat exchangers (PFHEs) and design of the refrigeration processes that service the dephlegmator. For simulation, a film model is applied to estimate local mass and heat transfer and integration across the separation area. In the design of PFHEs, the key issue is to determine the controlling stream according to the flow pattern in the separation passages. Design of refrigeration focuses on the optimization of the composition when mixed refrigerants are used, and on partition temperature when cascade cycles are used. A systematic methodology is proposed to include all these aspects. Various cases are studied to provide guidelines in the design of dephlegmators used for multicomponent gas mixtures with different refrigeration systems.

Numerical study of a novel cascading adsorption cycle

A novel cascading adsorption cooling cycle for refrigeration purposes is proposed in this paper. This cycle consists of two zeolite adsorbent beds and a silica gel adsorbent bed. The working refrigerant for the three adsorbers is water. The zeolite adsorbent bed is configured as the high temperature stage while the silica gel adsorbent bed acts as the low temperature stage. Both heat and mass recovery are carried out between the two zeolite adsorbent beds. In addition, heat is also exchanged between the zeolite adsorbent and the silica gel adsorbent beds. A lumped model is assumed for this cascading cycle. The COP for the base case is found to be 1.35, which is much higher than the COP of an intermittent cycle (about 0.5) and a two-bed combined heat and mass recovery cycle (about 0.8). However, its specific cooling power (SCP) of 42.7 W/kg is much lower than that of the intermittent cycle. The numerical results indicate that an optimal middle temperature exists for a prescribed driven temperature. The optimal COP increases with an increase in the driven temperature. However, when the driven temperature increases beyond 503 K, there is negligible change in the COP.

Gas Core Reactor with Magnetohydrodynamic Power System and Cascading Power Cycle

The U.S. Department of Energy initiative Generation IV aim is to produce an entire nuclear energy production system with next-generation features for certification before 2030. A Generation IV-capable system must have superior sustainability, safety and reliability, and economic cost advantages in comparison with third generation light water reactors (LWRs). A gas core reactor (GCR) with magnetohydrodynamic (MHD) power converter and cascading power cycle forms the basis for a Generation IV concept that is expected to set the upper performance limits in sustainability and power conversion efficiency among all existing and proposed fission powered systems. A gaseous core reactor delivering thousands of megawatt fission power acts as the heat source for a high-temperature MHD power converter. A uranium tetrafluoride fuel mix, with ~95% mol fraction helium gas, provides a stable working fluid for the primary MHD Brayton cycle. The hot working fluid exiting a topping cycle MHD generator has sufficient heat to drive a conventional helium Brayton cycle with 35% thermal efficiency as well as a superheated steam Rankine cycle, with up to 40% efficiency, which recovers the waste heat from the intermediate Brayton cycle. A combined cycle efficiency of close to 70% can be achieved with only a modest MHD topping cycle efficiency. The high-temperature direct-energy conversion capability of an MHD dynamo combined with an already sophisticated steam-powered turbine industry knowledge base allows the cascading cycle design to achieve breakthrough first-law energy efficiencies previously unheard of in the nuclear power industry. Although simple in concept, the gas core reactor design has not achieved the state of technological maturity that established high-temperature gas-cooled reactors and high-temperature molten salt core reactors have pioneered. However, the GCR-MHD concept has considerable promise; for example, like molten salt reactors the fuel is continuously cycled, allowing high burnup, continuous burning of actinides, and hence greatly improved fuel utilization. The fuel inventory is two orders of magnitude lower than LWRs of comparable power output, and fissile plutonium production is likewise lower than in spent LWR fuel. Besides these features, specific GCR-MHD design challenges such as fission enhanced gas conductivity of the MHD partially ionized gas, GCR safety issues and related engineering problems are discussed.

Synthesis of Mixed Refrigerant Cascade Cycles

This paper considers the synthesis of refrigeration systems with refrigerant mixtures as working fluids. The employed refrigeration topology encompasses features from industrial liquefaction of natural gas (LNG) systems. This configuration consists of a combination of horizontal and vertical cascades generalizing the vertical cascade of pure refrigerant systems. The key features of mixtures exploited here are their ability to evaporate/condense over a temperature range and their potential to generate streams with different compositions through partial condensation. The synthesis problem is formulated and solved as a nonlinear program. The proposed methodology is illustrated using an example of cooling a methane-rich stream.

On the recovery of LNG physical exergy by means of a simple cycle or a complex system

The maximum and minimum temperatures available limit the usable fraction (or Carnot efficiency) of a power cycle. The construction of LNG terminals and the need to vaporize LNG offers a thermal sink at a very much lower temperature than seawater. By using this thermal sink in a combined plant, it is possible to recover power from the vaporization of LNG.To this purpose, in this paper combined systems using LNG vaporization as low-temperature thermal sink are considered and their pros and cons are presented. A system utilizing waste energy as heat source and with a single working fluid is analyzed in detail. However, the use of a single fluid is not the best solution from a thermodynamic point of view. Thus, a series of cascading cycles is also outlined. In these systems, both the thermal source and the thermal sink are exploited as exergy sources.

Development and comparison of advanced cascading cycles coupling a solid/gas thermochemical process and a liquid/gas absorption process

Currently marketed double-effect absorption machines attain coefficients of performance (COP) of the order of 1.2 and, therefore, do not enable standard vapour compression air-conditioning systems to compete. The improvement of the COP requires increasing the high driving temperature level of the system in order to make possible additional stages and further refrigeration effects. But at high temperatures, working couples currently used in absorption systems (H 2O/LiBr, NH 3/H 2O) pose corrosion problems for exchangers or decomposition of the working fluid. The implementation at these high temperatures of a solid/gas thermochemical reaction system enables bypassing these restrictions. The coupling of a chemical reaction process thermally cascaded with a liquid/gas absorption process enables leading to triple-effect machines, indeed quadruple effect, the COP of which are from 30% to 60% higher than commercialised double-effect absorption chillers. Numerous coupling configurations are presented in this paper. A method of evaluation of the COP of the global machine is also developed. A comparison of these different configurations is carried out through value criteria characterising the quality of the obtained coupling. In this way, a first selection of combinations of interest can be performed. As part of a Franco–German cooperation, a triple-effect machine based on this approach is currently being realised. This new concept of coupling must lead to a new generation of thermal machines which will be capable in the near future of competing with vapor compression machines by the complementary use of the potentialities appropriate to each of the sorption processes.

Experimental study of cascading adsorption cycles

A lot of speculation exists on the possibilities of cascading cycles while very few experimental data are available. Herein, experiments on a cascading adsorptive heat pump are reported. The cascading cycle consits of a two adsorber zeolite—water high temperature stage and an intermittent active carbon—methanol low temperature stage. Driving heat is supplied by a boiler to zeolite adsorbers while active carbon adsorber is heated by heat recovered from zeolite adsorber under adsorption. Evaporators from both basic cycles operate at the same temperature and contibute to the evaporating load. Experimental cooling COP is found to be 1.06, much more than the COP of an intermittent cycle (≈0.5) and more than the COP of a two adsorber zeolite water cycle (≈0.75). Despite of the discontinuous operation of the cycle, evaporating rate is nearly constant (≈2.35 kW or 37W per kg of adsorbent). An analysis of the results shows that the components which limit the power of the unit are the evaporators and basically water evaporator. The COP of this cascading cycle is very sensitive to the evaporating temperature lift. If the temperature lift is higher than 45°C, a two adsorber zeolite water cycle has to be preffered. This cycle seems to be well adapted to air conditioning as long as the evaporation temperature lift is less than 45°C.

Theoretical performances of solid adsorbent cascading cycles using the zeolite-water and active carbon-methanol pairs: four case studies

Four cases of cascading solid adsorbent cycles operating at a high regenerating temperature (275°C) are presented. One of these cycles is a double effect zeolite-water cycle, the three other cycles consists in a low temperature active carbon-methanol cycle boosted by a high temperature double effect zeolite-water cycle. The predicted performances as well as the components needed to operate the cycle and the heat management are presented. Cogeneration of chilled water (2°C) and either hot water (70°C) or steam (120°C); cogeneration of refrigeration (−10°C) and hot water (70°C) are very attractive. Production of refrigeration (−10°C) with a COP as high as 0.85 is also possible.

Second law analysis of a solid adsorption heat pump operating on reversible cascade cycles: Application to the Zeolite-water pair

The theoretical efficiencies of a solid adsorption heat pump (using fixed bed heat exchangers are discussed as a function of the number of cascades. A systematic analysis of the heat and entropy flows in and out the heat pump are presented (Tables 1 and 2) in a case study. The impact of the number of cascades and of the temperature differences associated to the heat transfer are discussed using the usual efficiency concepts but also using the entropy generation number as introduced by Bejan [1].