JPH0128868B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Fields of Industrial Application The present invention is applicable to fields of relatively low temperature applications, such as refrigeration, refrigeration, or air conditioning, and fields of relatively high temperature applications, such as hot water supply, space heating, or industrial applications.
This article relates to a method of operating a chemical heat pump that can be applied to various household heat utilization fields.

Conventional configurations and their problems The most widely used conventional refrigerators (freezers) are electric compression refrigerators that use fluorocarbons or ammonia as refrigerants. It has high efficiency, and combined with mass production, it has become quite inexpensive. However, depending on the application, there are problems such as the operation noise is loud, the absorption temperature is limited to about 50°C when using an atmospheric heat source, and it consumes a considerable amount of electricity.

On the other hand, absorption heat pumps have come into practical use as large-scale devices for a wide range of cooling and heating applications. Unlike electric compression heat pumps, this system uses solar heat, waste heat, or combustion heat as its main energy source, so it can be said to be advantageous in terms of energy. However, since the system uses an aqueous lithium bromide solution as the absorbent material and water as the heat medium, and these liquids are circulated to operate the system, the absorbent material and heat medium must always be either liquid or gas. Therefore, due to the solubility of lithium bromide, there is a limit to the concentration of this solution, approximately
Up to 70% concentration. In addition, considering the efficiency of the system, the concentration range typically used is approximately 50% or less, and for these reasons it is a heat pump with a low temperature difference. In other words, the low temperature is about 5℃ and the high temperature is about 60℃, and in order to obtain lower temperatures or higher temperatures, special considerations such as dual effect are required, resulting in an expensive system. There were flaws.

In contrast, chemical heat pumps, which can be called intermittent absorption type heat pumps in which the absorbent material can be solid, have recently attracted attention. As already mentioned, the absorbing material can be solid, which has the advantage of widening the selection range, as well as being able to use heat storage or cold storage heat for a long period of time, producing little operating noise, and requiring no or very little auxiliary power. There are things that less is better.

Chemical heat pumps that use water as a refrigerant have been researched and developed more than ever before. In particular, many types of absorbent materials (hereinafter "absorbent materials" shall be interpreted as including adsorbents) have been developed.
Representative examples include sodium sulfide (5←→0 hydrate) and zeolite. All of these have advantages and disadvantages.

Sodium sulfide is strongly alkaline and is highly alkaline.
Since it corrodes glass and the like, it is necessary to use expensive materials for the device, and it is also toxic to the human body, making it difficult to use. Zeolite has a high ability to absorb water vapor, making it advantageous when used for air conditioning. On the other hand, when regenerating zeolite that has once absorbed water vapor, high-temperature heat is required due to its large absorption capacity.For example, when regenerating using solar energy, an expensive high-efficiency collector must be used, or else If this happens, regeneration will be performed with extremely low efficiency.
Moreover, since zeolite does not have selectivity in absorbing gas, it is easily deactivated by impurity gas. In addition, zeolite itself is expensive, and since it is a porous solid, it has poor thermal conductivity and requires internal fins to compensate for heat transfer inside the zeolite tank. system is difficult. Regarding calcium chloride, chemical heat pumps that utilize absorption equilibrium between dihydrogen and monohydrogen have been reported. The advantages of this system are many. First, calcium chloride is a commonly used desiccant, and is inexpensive and easily available. It is also non-toxic and corrosive, easy to handle, and does not require expensive installation. Furthermore, it selectively absorbs water vapor and does not require consideration for small amounts of impurity gas.

However, even in this system, the temperature difference with water at the same vapor pressure is about 40°C, making it impossible to obtain extremely low temperatures or extremely high temperatures. In other words, if the atmospheric temperature is 5℃ in winter, the theoretical maximum temperature is
The temperature reaches 45℃, which is often insufficient. Also, if the outside temperature in summer is 30℃, theoretically -10
C., but since a temperature difference of 10 to 15.degree. C. occurs due to heat exchange, the temperature is actually within the range of 0 to 5.degree. C., which is insufficient for freezing.

Purpose of the Invention The present invention makes it possible to supply high-temperature hot water of 70°C or higher in the winter, or -
The aim is to create a chemical heat pump with a high temperature difference, such as 10°C, which is sufficient for freezing.

Structure of the Invention The present invention involves putting water as a heating medium in one container and lithium bromide, which is fixed at room temperature as an absorbent, in the other container, and connecting both containers with a stop valve. is used as an anhydrous salt, and when completely absorbed as a monohydrate salt, the container containing water is operated as a condenser or evaporator, and the container containing lithium bromide is operated alternately as a regenerator or absorber.

DESCRIPTION OF EMBODIMENTS FIG. 1 shows a basic device of a chemical heat pump that is common to both the conventional example and the present invention. The device consists of two tanks A and B connected by a stop valve, with tank A containing 2 water and tank B containing 3 absorbents. A heat exchanger 4 is installed inside both tanks A and B, so that thermal energy can be easily input and output. Furthermore, the device remains airtight after degassing, and there is no gas other than water vapor inside. The maximum amount of water contained in lithium bromide during absorption and desorption is initially A.
It is determined by the sum of the amount of water put into the tank and the amount of water initially contained in lithium bromide in tank B.

The operating method of the device is a so-called batch type, and one cycle consists of two steps: a heat storage step and a heat radiation step.
The heat storage process is a process in which tank B is heated by obtaining heat from a heat source, hot steam comes out from tank B, is condensed in tank A, and heat is output from tank A. At this time, tank A is a condenser, Tank B acts as a regenerator. After this stroke, the absorbent material in tank B is in a high energy state, and if the valve is closed at this time, the energy is conserved. The heat dissipation process is a process in which the regenerated absorbent absorbs the water stored in tank A as water vapor and takes away the latent heat of vaporization from tank A. At this time, tank A is the evaporator, tank B
The tank acts as an absorber. The heat dissipation process can be used in two ways: for cooling and for heating. When used for air conditioning, if tank B is cooled to around room temperature, tank A will emit steam at a lower temperature than room temperature, so cooling can be performed. When used for heating, if tank A is heated near room temperature, tank B will emit absorbed heat at a higher temperature than room temperature, resulting in a heating effect.

By using lithium bromide (solid) as the absorbing material and water as the heating medium in the chemical heat pump described above, it can be easily used as a cold source for freezers, or for hot water supply at relatively high temperatures of 70°C or higher, with a simple device. It turned out that a heat source could be obtained.

A chemical heat pump was formed with the configuration shown in FIG. That is, 180 g of water was placed in tank A, and 870 g of anhydrous lithium bromide crystal was placed in tank B. Then, the entire structure was evacuated using an exhaust pump and an operational test was performed.

First, we kept the temperature of tank B at 30°C and determined how far the temperature of tank A would drop. The second result is
This is shown in curve C in the figure. That is, for about 8 hours -
We were able to obtain temperatures as low as 20℃. Naturally, water freezes and sublimates directly from ice to water vapor. On the other hand, as a conventional example, a heat pump that is completely the same as the above heat pump except that lithium chloride anhydrous salt is used instead of lithium bromide is assembled, and the evaporator temperature change at that time is shown by curve C' in FIG. From both of these, the lithium bromide monoaqueous system according to the present invention was able to maintain a lower temperature for a longer period of time.

In addition, the evaporation temperature of tank A was kept constant at 10°C, and the change in absorption temperature of tank B was determined. Curve D in FIG.
and shown in D′. From this curve, the absorption temperature according to the present invention was about 80°C, which was about 30°C higher than that of the conventional product. This results in approximately 80℃
It is now possible to supply high-temperature hot water nearby, making the heat storage tank more compact,
It has many advantages, such as being able to be adapted to underfloor heating.

Effects of the Invention As described above, when a relatively low cold heat source or a relatively high high temperature heat source is required, solid lithium bromide is used as an absorbent and water is used as a heat medium.
Practical effects can be obtained by using lithium bromide in the operating range between anhydrous and monohydrate salts.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the basic configuration of a chemical heat pump that is an embodiment of the present invention, and FIG. 2 is a diagram showing the performance of a solid lithium bromide monoaqueous chemical heat pump. 1...stop valve, 2...water, 3...absorbent material, 4
…Heat exchanger.

Claims (1)

[Claims] 1. Water is used as a heating medium, and lithium bromide, which is solid at room temperature, is used as an absorbing material. In order to dehydrate and regenerate the lithium bromide that has absorbed water, the lithium bromide is heated until it becomes an anhydrous salt. A method for operating a chemical heat pump, characterized in that when the regenerated anhydrous lithium bromide absorbs water to operate the chemical heat pump, the process is stopped when the lithium bromide becomes monohydrate, and the process is regenerated again.