Yukitaka Kato

Kinetic study of the hydration of magnesium oxide for a chemical heat pump

Abstract A kinetic study of the hydration of magnesium oxide was performed to test the possibility of developing a magnesium oxide/water chemical heat pump. The hydration rate of magnesium oxide was measured by a gravimetric analysis with a sample of average particle size 10 μm for the reaction temperature 373–423 K and the reaction vapor pressure 12.3–47.4 kPa. It was a reasonable hypothesis that the reactant magnesium oxide had four reaction regimes. An empirical rate equation based on this hypothesis was proposed with parameters determined from experimentally measured values. The performance of the heat pump was estimated numerically using the rate equation. The heat output rate was large enough in comparison with other common heat pumps. It was shown that the reaction system would be applicable to a chemical heat pump system.

Kinetic feasibility of a chemical heat pump for heat utilization of high-temperature processes

To utilize heat generated from high-temperature processes, the kinetic feasibility of a calcium oxide/lead oxide/carbon dioxide chemical heat pump was examined experimentally by kinetic studies of CaO/CO2 and PbO/CO2 reaction systems, which constitute the heat pump’s reaction. In order to determine the optimal reaction conditions that still allow practical operation of the heat pump, both reaction systems were examined with respect to thermal drivability and reaction material durability. The heat pump was able to store heat of about 860°C and transform it to a heat of above 880°C under sub-atmospheric pressure without mechanical work. An applied system that combined the heat pump with a high-temperature process was proposed for high-efficiency heat utilization. The scale of the heat pump in the combined system was estimated from the experimental results.

Thermal analysis of a magnesium oxide/water chemical heat pump for cogeneration

A chemical heat pump is examined experimentally as a chemical heat storage system in order to evaluate the contribution of the chemical heat pump to decentralised cogeneration. A new system that combines cogeneration with a chemical heat pump that uses a magnesium oxide/water reaction is proposed, and the feasibility of the combined system is discussed. A packed bed reactor of a magnesium oxide/water chemical heat pump was examined experimentally under various operation conditions. Thermal performance of the heat pump was analysed using the experimental results. The heat pump containing the reactor is expected to enhance the energy utilisation efficiency of the cogeneration system by storing and utilising surplus exhaust heat generated by the cogeneration system.

Durability to repetitive reaction of magnesium oxide/water reaction system for a heat pump

Abstract The feasibility of using a magnesium oxide/water system in a heat pump was examined experimentally from the viewpoint of enhancing the durability of the repetitive reaction cycle and increasing the heat output performance. Three kinds of magnesium oxide materials tested in this study were formed using the following precursors: ultra fine magnesium oxide powder, common magnesium hydroxide and magnesium ethoxide. The reaction cycles for both hydration and dehydration of the magnesium oxide materials were examined in each experiment. A new magnesium oxide material using ultra fine magnesium oxide powder as the precursor was the most appropriate material for the heat pump, because it exhibited high durability and high heat output performance compared to the other oxides. Although reactivity of the new material decreased during the initial five reaction cycles, the reactivity remained relatively constant over the next 19 cycles. Based on the experimental results, the thermal performance of a heat pump using the new material was simulated numerically. The new material produces an outputting of 180 W/kg after 24 repetitions over a 15-min period. It was concluded that the high durability of the new material was due to the high purity of the starting materials.

Durability characteristics of the hydration of magnesium oxide under repetitive reaction

The durability of the magnesium oxide/water reaction system under repetitive reaction conditions was examined experimentally to demonstrate the operability of a magnesium oxide/water chemical heat pump. Changes in the reactivity in the hydration of magnesium oxide, which was the most sensitive process in the repetitive reaction, were measured at hydration temperatures from 90–170°C and pressures from 31.2–70.1 kPa. A lower temperature and a higher pressure for the hydration reaction were effective in maintaining reactivity. The effect of different reaction conditions experienced during repetitive cycles to the standard repetitive cycle was discussed. From microscopic observations, nucleation in primary particles of the material induced by the structure change during repetitive reaction was an important factor in the enhancement of durability.

Utilization of high temperature heat from nuclear reactor using inorganic chemical heat pump

A new chemical heat pump designed to utilize high-temperature heat generated from high-temperature gas reactor (HTGR) is discussed. The calcium oxide / lead oxide / carbon dioxide reaction system was found to be a suitable reaction system for the desired heat pump from experimental survey of inorganic oxide / carbon dioxide reaction systems. The proposed heat pump using the reaction system was expected to be heat storage and heat transform system for HTGR. To demonstrate the validity of the heat pump, equilibrium relationship and kinetics of the reaction system was studied experimentally. The practical operation conditions of the heat pump were revealed from the experiment. This system was available to store heat above 800°C and transform it to higher temperature under a thermal driving condition. The heat output of the heat pump was valued enough compared to a common system. The applied system of the heat pump combined with HTGR was proposed to show the way of effective utilization of HTGR.

Thermal performance of a packed bed reactor of a chemical heat pump for cogeneration

A magnesium oxide/water chemical heat pump was examined experimentally as a heat storage system. A packed bed reactor of a magnesium oxide/water chemical heat pump was operated under various conditions. The heat storage and output performances of the heat pump were discussed. The heat pump is capable of being an alternative system of common water sensible heat storage because of the high-energy storage density of the heat pump. The heat pump containing the reactor is expected to enhance the energy utilization efficiency of a cogeneration system.

Application of inorganic oxide/carbon dioxide reaction system to a chemical heat pump

A new chemical heat pump designed to utilize waste heat generated from high-temperature processes carried out at temperatures above 570 K is discussed. Inorganic oxide/carbon dioxide reaction systems were surveyed experimentally, and the lead oxide/carbon dioxide reaction system was found to be a suitable reaction system for the heat pump. A mechanical driving type and a thermal driving type of heat pump using the reaction are proposed. This system proved feasible at operating temperatures above 570 K and was durable enough to withstand numerous reaction cycles. An empirical reaction rate equation for the carbonation of lead oxide, which is an important process in the operation of the heat pump, is proposed. Using the rate equation, feasibility of the mechanical driving type heat pump using this reaction system was demonstrated numerically.

Interferometric measurements of gas diffusivity in supercritical water

Abstract This study constitutes a part of attempt to develop a clean and high efficiency combustion system utilizing reactions in supercritical water. This study is aimed at establishing the measuring techniques of transport properties and observing techniques of reaction zone in supercritical water. First, the refractive index of water was measured because previous values were not available in supercritical region. The measurements were made at the temperatures from ambient temperature to 420°C and pressures from atmospheric pressure to 27MPa. The results show that the refractive index is constant in the experimental conditions within experimental errors. Next, the mass diffusivity of gas in supercritical water was measured. Nitrogen was used in this experiment to avoid the effects of reaction. The mass diffusivity of nitrogen in supercritical water was calculated from the fringe shift. The value of the coefficient was intermediate between gas and liquids one.

Kinetic measurement on the isobutene/water/tert‐butanol chemical heat pump; dehydration of tert‐butanol

For this heat pump kinetic study, the dehydration rate of tert-butanol (an endothermic reaction) was measured under conditions suitable for operating a chemical heat pump. The proposed Langmuir-Hinshelwood rate equation agreed well with the experimental rate data. The heat pump kinetic study was examined in a batchwise operation by using both the endothermic reaction rate equation and a previously proposed rate equation for the exothermic reaction. Although the endothermic reaction rate was suitable for a heat pump, an improvement of the endothermic reaction rate was desired since it was found to be too slow. The endothermic reaction was about 5 to 20 times slower than the exothermic reaction. The absorbed and released heat rates per batch cycle were almost the same as for conventional heat pumps.