Chemical Heat Pump Research Articles

An Unified Approach to Limits on Power Generation and Power Consumption in Thermo-Electro-Chemical Systems

This research presents a unified approach to power limits in power producing and power consuming systems, in particular those using renewable resources. As a benchmark system which generates or consumes power, a well-known standardized arrangement is considered, in which two different reservoirs are separated by an engine or a heat pump. Either of these units is located between a resource fluid (‘upper’ fluid 1) and the environmental fluid (‘lower’ fluid, 2). Power yield or power consumption is determined in terms of conductivities, reservoir temperatures and internal irreversibility coefficient, F. While bulk temperatures Ti of reservoirs’ are the only necessary state coordinates describing purely thermal units, in chemical (electrochemical) engines, heat pumps or separators it is necessary to use both temperatures and chemical potentials mk. Methods of mathematical programming and dynamic optimization are applied to determine limits on power yield or power consumption in various energy systems, such as thermal engines, heat pumps, solar dryers, electrolysers, fuel cells, etc. Methodological similarities when treating power limits in engines, separators, and heat pumps are shown. Numerical approaches to multistage systems are based on methods of dynamic programming (DP) or on Pontryagin’s maximum principle. The first method searches for properties of optimal work and is limited to systems with low dimensionality of state vector, whereas the second investigates properties of differential (canonical) equations derived from the process Hamiltonian. A relatively unknown symmetry in behaviour of power producers (engines) and power consumers is enunciated in this paper. An approximate evaluation shows that, at least ¼ of power dissipated in the natural transfer process must be added to a separator or a heat pump in order to assure a required process rate. Applications focus on drying systems which, by nature, require a large amount of thermal or solar energy. We search for minimum power consumed in one-stage and multi-stage operation of fluidized drying. This multi-stage system is supported by heat pumps. We outline the related dynamic programming procedure, and also point out a link between the present irreversible approach and the classical problem of minimum reversible work driving the system.

Simulation of gas exothermic chemical reaction in porous media reactor with lattice Boltzmann method

Exothermic reactor is the main part in a chemical heat pump. It involves complex multi-component exothermal chemical reaction in catalyst-filled porous media. The lattice Boltzmann method (LBM) is developed to simulate the characteristics of fluid flow, heat and mass transfer coupling chemical reaction in the exothermic reactor of the isopropanol/acetone/hydrogen chemical heat pump system. Fractal theory is used to structure a porous medium model in the reactor. The simulation results show that LBM is suitable for the simulation and the conversion has an optimal value with different inlet velocities.

Experimental Studies on Energy Efficiencies of CaSO<sub>4</sub> Chemical Heat Pump for Waste Heat Recovery & Cold/Hot Heat Production

From the viewpoints of energy saving and environmental impacts, we have been studying Chemical heat pumps (CHP) especially focusing on using calcium systems. The CaSO4/ CaSO4·1/2H2O gas-solid reversible reaction is used to store around 393K and release hot/cold heat. In this paper, we studied the energy efficiencies of CaSO4 CHP in heat enhancement mode for commercial use with various cases. As a result, it is found that the stored heat is converted/released at 353K /278K level hot/cold heat. The CaSO4 CHPs could be commercially used for wider operating temperature ranges in appropriate heat source conditions. Furthermore, the thermal efficiency was obtained to be more than 1.3, and the coefficient of performance (COP) was obtained to be about 18. It means the CaSO4 CHPs could be more efficiently than other types of heat pumps

Chemical Energy Transportation of Waste Heat for Heating/Drying and Cooling/Dehumidifying

From the viewpoints of energy and environmental problems, an effective energy utilization system for thermal energy management using chemical heat pump container (CHPC) is proposed. In this system, waste heat etc. is stored as chemical energy in CHPC. The stored heat is transported with almost no heat loss by CHPC transportation using truck, train, ship etc. At heat supply area, the stored heat is upgraded to higher temperature heat for heating/drying or lower temperature heat for cooling/refrigerating/dehumidifying without adding extra energy by the chemical heat pump function. In this study, the simulation on local recycling energy system using CHPC for heating/drying and cooling/dehumidifying was performed. The heat storing/releasing characteristics, the energy efficiencies and the CO2 emissions were shown. As a result, the system using CHPC was found to be much more effective than domestic boiler system and even more effective than similar transportation systems using latent heat storage container etc. Especially, the system using CHPC can supply hot-heat and cold-heat effectively without adding extra energy at heat supply area.

Thermodynamic and kinetic investigation of a chemical reaction-based miniature heat pump

Representative reversible endothermic chemical reactions (paraldehyde depolymerization and 2-proponal dehydrogenation) are theoretically assessed for their use in a chemical heat pump design for compact thermal management applications. Equilibrium and dynamic simulations are undertaken to explore the operation of the heat pump which upgrades waste heat from near room temperature by approximately 20° in a minimized system volume. A model is developed based on system mass and energy balances coupled with kinetic equations to ascertain mixture conditions at each state point in the loop, as well as mass flow rate, minimum work input, and minimum endothermic reactor volume according to defined reservoir temperatures and desired heat load. Assuming that a pervaporation process is employed in both reaction systems to achieve the requisite mixture compositions for sustained operation, the simulations show that the chemical heat pump can pump 5W of power with endothermic reactor volumes of as little as 60–93cm3, depending on the selected chemical reaction. Low exergy efficiencies remain a significant design consequence, but the system performance in terms of environmental impact and COP are comparable with, and in some cases better than, the performance of alternative technologies under the same conditions.

Modeling and computational simulation of adsorption based chemical heat pumps

In this study a methodology is developed for the design of a packed bed reactor to be used in a Chemical Heat Pump (CHP). Adsorption and desorption of ethanol on active carbon packing in the reactor are investigated. Depending on the cycle, i.e. adsorption or desorption, cooling or heating of the reactor material is modeled through transient energy equation. The parameters associated with the vapor-carbon adsorption kinetics are experimentally determined. Then spatial distribution of temperature and adsorbed vapor amount are obtained with respect to time in adsorption–desorption cycles. These profiles are used to predict heating or cooling powers and COP for different adsorbent bed geometries and adsorption/desorption cycle times. Strong effect of heat transfer resistance of the packing, hence reactor size, on the system performance is observed.

Optimization of magnesium hydroxide composite material mixed with expanded graphite and calcium chloride for chemical heat pumps

A composite chemical heat storage material (EMC) comprising a mixture of expanded graphite (EG), magnesium hydroxide (Mg(OH)2), and calcium chloride (CaCl2) was developed as a magnesium oxide/water chemical heat pump reactant. The optimization of a mixing weight ratio between the Mg(OH)2 content of EMC and EMC itself was discussed from the viewpoints of both heat storage capacity and reactivity by considering the reaction rate constants from a kinetic analysis. It was confirmed that the dehydration reactivity of EMC increased as the mixing weight ratio decreased; however, the heat capacity of the EMC unit mass decreased. A multiplied factor consisting of the multiplied value dehydration rate constant and mixing weight ratio was introduced. It was suggested that a weight ratio of approximately 0.80 was the optimized value when the mixing molar ratio between CaCl2 and Mg(OH)2 was 0.10. Dehydration of EMC with an optimized mixing weight ratio and dehydration of pure Mg(OH)2 were conducted under various temperatures to compare the reaction rate constants of each material. From this study, it was demonstrated that EMC performed better on dehydration than pure Mg(OH)2.

Reaction characteristics of various gypsum as chemical heat pump materials

From the viewpoints of energy savings and environmental impacts, the authors have been studying on Chemical Heat Pump (CHP) systems such as a calcium sulfate/water reaction system for effective waste energy utilization. The CHP system using hydration of CaSO4/dehydration of CaSO4·1/2H2O reaction can use low-temperature level thermal energy effectively in many processes. The reaction material CaSO4 is prepared from original material: gypsum (CaSO4·2H2O). Although the natural gypsum is used in many fields; an enormous amount of resources has become waste. We are trying to solve the problems of the energy consumption, environmental pollution and waste material at the same time by the CHPs using CaSO4·1/2H2O hydration/dehydration reaction.More studies on the reaction characteristics of various CaSO4 materials are necessary for the CHP reaction system in different conditions. We examined the hydration/dehydration conversions, reaction rates etc. of several CHP materials. We prepared two types of original particles. The one (A) is a just crushed natural gypsum (710–1000 μm), and the other (B) is a granulated same size particles by fine particles (<10 μm).As a result, the changes of conversion and reaction rate showed some differences. It was probably caused by impurities in the gypsum to some extent. The impurities may have affected the stability of the data and the final conversions etc. The hydration conversions of CaSO4 from the natural gypsum which contains some of impurities such as Thailand one were lower than 85%, and the conversions of the natural gypsum which contains fewer impurities such as Australia or Morocco one were higher than 90%. The granulated particle (B) has some effect of adsorption because of the wider specific surface area. We need to design the reaction materials from the viewpoints of the purity and the heat/mass transfer characteristics in order to meet the chemical heat pump performance.

Dehydration and Hydration Behavior of Rare-earth Hydroxides for Chemical Heat Pumps

Abstract Pure and mixed rare-earth hydroxides are expected to be new materials for chemical heat pumps. In this study, the dehydration and hydration behavior of these materials was investigated by thermogravimetry. The dehydration temperature could be lowered by increasing the Nd or Gd ion content in the hydroxides. La0.50Gd0.50(OH)3 is an ideal candidate material for chemical heat pumps that can store thermal energy at 300 °C; further, heat output can be generated from the heat source at 40 °C.

The application of entransy theory in optimization design of Isopropanol–Acetone–Hydrogen chemical heat pump

In the present work, a multi-parameter optimization approach of Isopropanol–Acetone–Hydrogen (IAH) chemical heat pump is developed based on the entransy theory. In the optimization process, the total low-temperature heat consumed by the heat pump system generally decreases while the high-temperature heat recovered by the heat pump increases remarkably. When the temperatures of the reboiler and endothermic reaction are fixed, the temperature of exothermic reaction in the optimal design scheme is larger than that in the initial design scheme, and the high-temperature heat released from the exothermic reactor increases significantly in the optimal design scheme. The enthalpy efficiency (COP) and exergy efficiency monotonously increase as the entransy efficiency increases in the optimization process. The entransy efficiency has a definite physical meaning and pays more attention to the quality of the high-temperature heat recovered by the heat pump than enthalpy efficiency; it does not introduce an additional parameter and has more succinct expression than exergy efficiency. The multi-parameter optimization approach taking entransy efficiency as the objective function is very effective in the optimization design of IAH chemical heat pump.

Exergetic efficiency of high-temperature-lift chemical heat pump (CHP) based on CaO/CO2and CaO/H2O working pairs

The use of reversible chemical reactions in recuperation of heat has gained significant interest due to higher magnitude of reaction heat compared to that of the latent or sensible heat. To implement chemical reactions for upgrading heat, a chemical heat pump (CHP) may be used. A CHP uses a reversible chemical reaction where the forward and the reverse reactions take place at two different temperatures, thus allowing heat to be upgraded or degraded depending on the mode of operation. In this work, an exergetic efficiency model for a CHP operating in the temperature-level amplification mode has been developed. The first law and the exergetic efficiencies are compared for two working pairs, namely, CaO/CO2 and CaO/H2O for high-temperature high-lift CHPs. The exergetic efficiency increases for both working pairs with increase in task, TH, decrease in heat source, TM, and increase in condenser, TL, temperatures. It is also observed that the difference in reaction enthalpies and specific heats of the involving reactants affects the extent of increase or decrease in the exergetic efficiency of the CHP operating for temperature-level amplification.

Thermal energy storage using thermo-chemical heat pump

A theoretical study was performed to investigate the potential of storing thermal energy using a heat pump which is a thermo-chemical storage system consisting of water as sorbet, and sodium chloride as the sorbent. The effect of different parameters namely; the amount of vaporized water from the evaporator, the system initial temperature and the type of salt on the increase in temperature of the salt was investigated and hence on the performance of the thermo chemical heat pump. It was found that the performance of the heat pump improves with the initial system temperature, with the amount of water vaporized and with the water remaining in the system. Finally it was also found that lithium chloride salt has higher effect on the performance of the heat pump that of sodium chloride.

Optimization design of recuperator in a chemical heat pump system based on entransy dissipation theory

Based on the entransy dissipation theory, the multi-parameter optimization design of recuperator is conducted in an Isopropanol–Acetone–Hydrogen (IAH) chemical heat pump system. The performance of the heat pump system can be improved significantly through the multi-parameter optimization, when the main operation parameters of chemical heat pump remain unchanged. When the main operation parameters of chemical heat pump and the heat transfer area of recuperator remain unchanged, the heat transfer rate of recuperator, the high-temperature heat released from the exothermic reactor, and the coefficient of performance (COP) and exergy efficiency of IAH heat pump system greatly increase while the compressor power decreases remarkably as entransy dissipation number decreases. This is done only by optimizing the combination of design parameters of recuperator taking entransy dissipation number as the objective function under certain constraint conditions, and the cost is no more than the low-temperature waste heat having no practical value.

Thermochemical energy storage technologies for building applications: a state-of-the-art review

This paper presents a comprehensive and state-of-the-art review on thermochemical energy storage (ES) technologies using thermochemical materials (TCMs) for building applications. Thermochemical storage devices (materials, open and closed sorption as well as chemical heat pump) enhance the energy efficiency of systems and sustainability of buildings by reducing the mismatch between supply and demand. Thermal ES (TES) systems using TCMs are particularly attractive and provide a high ES density at a constant temperature. Technical and economical questions will need to be answered for all possibilities, which warrant more development and large-scale demonstration of TES in future. Copyright , Oxford University Press.

Performance analysis of Isopropanol–Acetone–Hydrogen chemical heat pump

The performance of an Isopropanol–Acetone–Hydrogen (IAH) chemical heat pump system is investigated in terms of enthalpy efficiency (COP) and exergy efficiency, in which the exothermic and endothermic reactions take place in the gas phase. The increase of reflux ratio, temperature of endothermic reaction and temperature of exothermic reaction reduces the performance of the heat pump when the other operating parameters remain unchanged. However, the performance of the IAH chemical heat pump improves with the increase of the ratio of molar quantity of hydrogen to that of acetone in the entry of exothermic reactor and the number of heat transfer units of regenerator. Generally, a better performance of the chemical heat pump corresponds to a larger number of trays in the distillation column. The performance of the system can be improved significantly after multi-parameter optimization design. The coefficient of performance (COP) pays more attention to the heat released from the exothermic reactor, while the exergy efficiency takes into consideration of both heat released from the exothermic reactor and temperature of exothermic reaction.

Fundamental Experiment and Analysis of Direct Energy Conversion Using Proton-Conducting Ceramic Fuel Cells Supplied with High-Temperature Nuclear Heat and Natural Gas

A system to utilize high-temperature nuclear heat effectively is proposed here. The system comprises a High-Temperature Gas-cooled nuclear Reactor (HTGR), reaction vessels to produce H2 using the steam-reforming reaction of CH4 or the Iodine-Sulfur (I-S) process, chemical heat pumps and He gas turbines. The chemical heat pumps are operated between the two decomposition temperatures of SO3 (~900°C) and HI (~500°C) of the I-S process. The pump system transfers heat from lower temperature to higher one with repeated H2 absorption-desorption cycles, and the overall thermal conversion ratio from H2O to H2 can be enhanced. The material candidate for H2 absorption in heat pump is considered TiH2 and ZrCoH3 (or UH3) according to the two reaction temperatures. The decomposition of the metal hydrides proceeds at their respective plateau pressures that are a function of temperature regardless of the H content in metals. Variations of the temperature and the equilibrium H2 pressure with repetitions of the heat-pump cycle are shown in the present paper comparatively. In addition, proton-conducting fuel cell system supplied with CH4 is incorporated in the high-temperature utilization system.

A221 硫酸カルシウム系ケミカルヒートポンプにおける増熱モードでの各種条件下エネルギー効率の実験的評価(OS-7: 次世代ヒートポンプ・冷凍システム(6))

From the view point of energy saving and environmental impacts, we have been studying Chemical heat pump (CHP) especially focusing on using calcium systems. The CaSO_4/Caso_4 1/2H_2O gas-solid reversible reaction is used to store at around 393K and release hot/cold heat. In this paper, we studied the energy efficiencies of CaSO_4 CHPs could be used for commercial for wider operating temperature ranges in appropriate heat source conditions.

Parameters to take into account when developing a new thermochemical energy storage system

Thermal energy storage by chemical reactions is one of the most suitable energy storage systems for buildings and industrial applications due to the wide range of working temperatures as well as the high energy storage density provided. Developing and characterizing chemical reactions is now one of the most promising areas of research. Chemical heat pumps are one of the systems used when chemical reactions are utilized as thermochemical energy storage technology. Nevertheless, the main problem to implement this technology is found in the material behaviour within the reactors used. Therefore, material and reaction characterization have been identified as key issues to design a proper system. The main goal of this paper is to highlight the parameters to take into account previous to the design.

Output characteristics evaluation of heat upgrading operation in CaBr2/H2O chemical heat pump

Output characteristics evaluation of heat upgrading operation in CaBr₂/H₂O chemical heat pump

Energy Recycling System Using Chemical Heat Pump Container

From the viewpoints of energy and resource problems, an effective energy utilization system for wide area energy management using chemical heat pump container (CHPC) is proposed. In this system, waste heat at factory area is stored as chemical energy in the CHPC. The stored heat is transported with no heat loss by the CHPC transportation using truck, train, ship etc. At heat supply area, the stored heat is upgraded to higher temperature heat for heating or lower temperature heat for cooling/ refrigerating without adding extra energy by the chemical heat pump function. In this study, the simulation on local recycling energy system using CHPC for wide Tokyo area was performed and the efficiencies on energy, cost and CO2 emission were shown. As a result, the system using CHPC was found to be more effective than similar transportation systems using latent heat storage container etc. Especially, the system using CHPC can supply hot-heat and cold-heat without adding extra energy at heat supply area effectively.