WO1981000904A1

WO1981000904A1 - Refrigeration process and device

Info

Publication number: WO1981000904A1
Application number: PCT/FR1980/000139
Authority: WO
Inventors: J Merigoux; F Meunier
Original assignee: Tech Ind Therm Cetiat Centre; J Merigoux; F Meunier
Priority date: 1979-09-20
Filing date: 1980-09-19
Publication date: 1981-04-02
Also published as: FR2465970A1; FR2465970B1; JPS56501330A

Abstract

Refrigeration process wherein: an adsorbing compound is heated until evaporation and on which a refrigerating fluid has been adsorbed; the vapours so produced from the refrigerating fluid are condensed and the liquid so produced is stored; then, this refrigerating liquid is again vaporized and the vapours thus expanded are again adsorbed on the adsorbing body, so that said expansion produces cold; and wherein this is effected by means of two tanks (3, 4) containing an adsorbing compound (7), these two tanks (3, 4) working respectively and alternatively in desorption and adsorption, so as to allow for a continuous production of cold, characterized in that the tank working in the adsorption mode is cooled. There is also disclosed such a plant. Application: air conditioning.

Description

METHOD AND DEVICE FOR REFRIGERATION

The invention relates to a new process for producing cold from a heat source; it also relates to an installation for the implementation of this process. The invention relates more particularly to a new refrigeration process produced from solar energy.

There are already several methods of using solar energy to produce cold. For example, it has been suggested to use absorption groups: ammonia or lithium bromide, in which the coolant is absorbed with the release of heat by a liquid phase, to desorb at higher pressure under the action. of solar energy. After condensation at a temperature compatible with an available cold source, the refrigerant is expanded during the absorption phase which takes place at lower pressure. This relaxation causes vaporization and is accompanied by a production of cold.

These installations generally use pumps and other devices which, on the one hand, increase the price and, on the other hand, limit their use in distant countries or by non-specialized personnel. Lithium bromide groups have a relatively good coefficient of performance (COP), but they have the significant drawback of being difficult to regulate, because outside a fairly limited temperature range, lithium bromide crystallizes and thus no longer circulates.

Recently, it has been proposed to replace the fluid. refrigerant for systems absorbed by a solid adsorbent such as a zeolite. Thus, during the day, the energy supplied by the sun allows the desorption of the zeolite and the released refrigerant is stored in liquid form in a tank after condensation in an exchanger. On the other hand, during the night, the zeolite can again re-adsorb the gaseous refrigerant previously vaporized in the e-vaporizer, with simultaneous production of cold. The advantages of such a solid adsorption system compared to those with liquid absorption are multiple.

However, as a general rule, it is much more interesting to produce cold during the day, that is to say at the time when it is most needed. This is true both in air conditioning and conservation, although to a lesser degree. Unfortunately, to date refrigeration systems operating on this principle of solid adsorption have an intermittent cycle: day and night, which limits its practical scope, except to use bulky storage organs, which then considerably increases the cost of these facilities.

In US patent 3, 270, 512 of NASA, a refrigeration system has been described, in particular for spacecraft, comprising two tanks each containing an adsorbent compound, such as a silica gel, and working alternately in adsorption and in desorption . This device, which can only operate in direct sunlight, has a fairly long cycle and therefore a fairly low efficiency. When it is desired to use this installation on the ground, the cycle lasts one day, which is practically incompatible with industrial exploitation. The invention overcomes these drawbacks. It relates more particularly to an improvement to the refrigeration process by solid adsorbents which is continuous and which requires only reduced maintenance and results in low auxiliary consumption. In this process, where two tanks are used each containing a solid adsorbent (zeolite or other), said tanks operate alternately in adsorption, then in desorption. However, during the desorption phase, the heat is supplied by any source such as a hot water exchanger supplied by any means such as a solar collector, while during the adsorption phase, the heat is removed by an exchanger connected to a cold source, such as an air or water exchanger as the case may be. In one embodiment, the heat from the solar collectors can optionally pass through storage so as to regularize the production.

The evaporator is placed in a buffer tank to allow the storage of the frigories produced.

The invention relates essentially to an appropriate installation. This refrigerating installation of the type comprising: - a heat source intended to heat a heating fluid,

- a solid adsorbent compound having a high adsorption capacity, but a low adsorption energy, - a refrigerant adsorbed on said solid adsorbent component,

- a condenser intended to liquefy the refrigerant vapors produced under the effect of the action of the heating fluid from the heat source on the adsorbent compound saturated with refrigerant,

- an evaporator intended to vaporize the refrigerant produced,

- And two tanks intended to receive the adsorbent compound, these two tanks working respectively one in desorption, the other in adsorption is characterized in that said tanks are connected, on the one hand to one another and on the other hand, by a set of valves and pipes to the condenser and to the evaporator .

The invention also relates to a refrigeration process, in particular for the implementation of this installation. This refrigeration process in which:

- a refrigerant is vaporized by heating, previously fixed on an adsorbent compound,

- the vapors thus produced are condensed and the refrigerant produced is stored,

- Then this refrigerant is vaporized and adsorbed again on the body adsorbing the vapors thus relaxed, so that by this expansion, cold is produced, and in which, one operates with two tanks each containing an adsorbent compound, these two tanks working respectively and alternately in desorption and in adsorption. This process is characterized in that during the treatment, the tank working in adsorption is cooled by the passage of a coolant over the condenser. In practice: - the operating cycle is reversed when each tank is close to its equilibrium point, that is to say when the adsorption and desorption phases have reached in each of the tanks the vicinity of the point of balance, - before reversing the cycle, we aim to equalize the temperatures between the two tanks.

As adsorbent solid material, known compounds are used which have, on the one hand, a high adsorption capacity and, on the other hand, a low energy-absorbing value. We can mention activated carbon, silica gels, activated aluminas. In practice, zeolites are successfully used which gives excellent results. As is known, these zeolites, natural or synthetic, are crystalline aluminosilicates whose silica content varies from one type to another. Preferably 13 X type zeolites are used.

As heating fluid, water or a heat transfer fluid, also sometimes called thermal fluid, is advantageously used, such as mixtures of di-phenyl and qiphelynl oxide known under the name of "diphyl" and marketed under the names from Gtilliotherm, Dowtherms, etc ...

As refrigerant under vacuum, known fluids such as water, methanol, ammonia, etc. are used. Water vapor is preferably used because, for a given mass of zeolite, it is thus treated more water vapor than methanol. Thus for a given quantity of frigories to be produced, less zeolite will be needed with water vapor than with methanol, which advantageously reduces the dimensions of the tanks. In addition, as is known, this liquid is kept under vacuum to allow the cycle which takes place between the evaporation pressure and that of condensation. Consequently, the pressure of this fluid is determined by the temperatures desired for these two phases of condensation and evaporation.

The manner in which the invention can be implemented and the advantages which ensue therefrom will emerge more clearly from the exemplary embodiments which follow, given by way of indication and without limitation in support of the appended figures. FIG. 1 schematically represents an installation for implementing the invention.

Figure 2 shows such an installation operating in its first phase. Figure 3 shows the same installation in the next phase. FIG. 4 illustrates the intermediate phase of operation, one of the characteristics of the invention.

Figure 5 shows a tubular condenser evaporator capable of being implemented in the invention. Referring to the figures:

- 1 denotes a heat source of any known type, in which in practice the temperature of the heating fluid is between 80 ° C and 150 ° C (in some cases, this temperature can even reach -20 ° C) ; this source 1 can either be recovery heat, or a solar collector such as for example a collector of the flat thermal type, under vacuum or not, with or without selective surface, or at concentration, for example of the parabolic or spherical type. rique or cylindro-parabolic:

- 2 denotes a duct where the heating fluid circulates;

- 3 and 4 designate two tanks made of stainless steel or other material, resistant to vacuum and corrosion, each containing / a heat exchanger 5 and 6 where the heating or cooling fluid circulates; this exchanger is advantageously a coil of air conditioning fins, the interstices of which are filled with zeolite 7a or 7b; the zeolite 7 which is in the form of small sticks or better of balls, surrounds the tubes of the battery where circulates the heating fluid from 2 or cooling and the fins promote a rapid and uniform heat transfer between this fluid and the zeolite; - 8 designates a refrigerant circuit under vacuum, for example water vapor, connecting each tank, respectively 3 or 4 in order: firstly, to a first heat exchanger 9 serving as a condenser, for example of the tubular type shown in FIG. 5, cooled either by water, either by air, which passes through a chimney 10 where this condenser is placed, and is sucked in by a fan 11 in order to accelerate the heat exchanges, then in series, to a second exchanger 12 placed in a buffer tank 13 allowing store cold water or ice produced; this exchanger 12 serving as an evaporator and this tank 13 being connected by a set of valves and pumps suitable for the plant to be cooled or for air conditioning; it is taken from this storage tank 13, known per se, as and when required;

- 14, 15, 16 and 17 designate multi-way valves, in particular three ways.

As is known, the pressure of the refrigerant is imposed by the choice of the desired condensation and evaporation temperatures.

This installation works as follows:

PHASE I; Tank 3 in desorption - tank 4 in adsorption (figure 2)

The heating fluid 2 from: the heat source 1, for example a solar collector, arrives at the valve 14 - then from there enters the exchanger 5 of the tank 3. The zeolite 7b, contained in this tank 3 s e-heating in contact with the tubing of this exchanger 5 and therefore dries up. At the outlet of the exchanger 5, the heating fluid arrives at the valve 15, then returns to the heat source 1; then the cycle begins again.

The water vapor desorbed from the zeolite 7b leaves the tank 3 by passing through the conduit 8, then passes through the valve 17, and from there on the condenser 9. For example, the pressure of this water vapor at entry into 9 is around 75 millibars. The refrigerant then continues its course in the conduit 18 to the exchanger-evaporator 12 where it vaporizes. This causes the water contained in the storage tank 13 to cool. Finally, this refrigerant continues in the circuit 18 to the valve 16 which then brings it to the top of the tank 4. This water vapor is then adsorbed by the zeolite 7a contained in the tank 4. As adsorption is an exothermic reaction, it is therefore necessary to cool this tank 4. To do this, the conduit 19 which passes through this tank 4 is connected by the valve 1 4 to the exchanger 20, then by the valve 15 returns on the tank 4. The calories produced in 4 are thus removed during the adsorption phase of the zeolite.

In Figures 2 and 3, there is shown:

- in full solid lines, the heating circuit by means of the heating fluid coming from the heat source 1,

- in regular dashes, the refrigerant circuit,

- in dotted lines, the cooling circuit. During the desorption phase of the tank 3, the heating circuit goes from the heat source 1 to the valve 1 4, from there enters the tank 3, goes to the valve 15 and returns to the source 1.

During this time, the refrigerant circuit starts from the tank 4, arrives at the valve 17, passes through the condenser 9, from there also passes through the evaporator 12, arrives at the valve 16 and enters the tank 4.

On the other hand, the cooling circuit of the tank 4 leaves this tank, arrives at the valve 14 and passes through the exchanger 20 and returns to this tank 4.

When the zeolite 7b contained in the tank 3 is almost dry, that is to say when the zeolite is almost completely desorbed, and when the zeolite 7a contained in the tank 4 is saturated with water, then the valves 1 4 are switched on, 15, 16 and 17 and we reverse the circuit to work according to the second phase.

PHASE II; Tank 3 in adsorption - tank 4 in desorption

(figure 3)

When, in the tank during desorption, the content of the desorbed gas drops below a certain value which can be detected for example by an increase in the temperature of the zeolite, the valves 14, 15 are automatically switched as already said , 16 and 17 so as to reverse the cycle in order to avoid or stop the desorption phase at low efficiency (equilibrium point).

In practice, this inversion takes place every fifteen minutes approximately, so that for a given cooling power, it will be possible to considerably reduce the amount of zeolite necessary. It is therefore beneficial to have reasonably short cycles.

This result is fundamental and constitutes considerable and totally unexpected progress compared to the prior techniques, in particular that described in American patent 3, 270, 512 cited in the preamble. Indeed, if we adopted this NASA system on the ground, we would have only one cycle per day, whereas on the other hand the device of the invention allows us to have up to at least a hundred or so. This progress in a ratio of 1 to 100 is unexpected and considerable. In addition, for equal performance, the volume of the installation is considerably reduced.

However, reversing the cycle is an abrupt operation and the vessel which was desorbed is hot as it becomes adsorbent and should be cold and vice versa. The compensation of these temperatures causes heat losses, which decreases the coefficient of performance (COP).

To overcome this drawback, we go through an intermediate phase of short duration (Figure 4) during which the cooling water of the circuit 19 of the tank 4 also passes into the tank 3. To do this, the valves 14 and 15 are modified to have a direct passage (for example by four-way valves), so that the coolant (water) passes through the pipes of the two exchangers 5 and 6 respectively of the two tanks 3 and 4 as indicated by the circuit shown in dotted lines in Figure 4. Thus, the transfer of part of the sensible heat from one tank to the other reduces the delay for cooling or heating the tank, as the case may be. This increases the coefficient of performance of the installation.

During the second phase, the heating water circuit goes from the heat source 1 to the van; - ne 14 which returns it to the exchanger 6 of the tank 4, from there arrives at the second valve 15 and returns to heat source 1.

Meanwhile, the refrigerant circuit goes from the tank 4, arrives at the valve 17 which sends it to the condenser 9, enters the evaporator 12, from there returns to the valve 16 which returns it to the top of the tank 3.

On the other hand, the cooling circuit is then established in the tank 3, therefore passes through the piping of the exchanger 5 of this tank, arrives at the valve 15 "passes through the exchanger 20 and through the valve 14 is returned to the head of the tank.

During the cycle, the mass of zeolite is therefore used several times in the same day and therefore for a given cooling capacity, the mass of zeolite is much lower than in an intermittent system.

As already said, FIG. 5 represents an exchanger of a known tubular type capable of being used at 9 and 12. This condenser consists of an inlet for refrigerant in the form of vapor 31 in a cylindrical enclosure 32 from which a multitude of pipes 33 arranged on either side of the underside of this cylinder 32 leave, said pipes 33 opening into a second cylinder 34 where the condensates of the vapors supplied at 31 are recovered. A pipe 35 takes the liquid formed and brings it to an intermediate storage member 36 before returning it to the normal circuit. The vertical pipes 33 are offset so as to facilitate the passage of water or cooling air.

Such an installation has many advantages over the solutions marketed to date. We can cite :

- possibility of producing cold on demand,

- possibility of producing cold from a solar collector, even during the day, that is to say during the hours when it is most needed, _ thanks to the intermediate phase of heat recovery and optimum use zeolite, better COP than the intermittent system,

- relatively static system, therefore reduced investment and maintenance and better reliability. In addition to the considerable advantages already mentioned compared to the device described in American patent 3,270,512 of NASA, cited in the preamble, one can also add:

- cold production improved by half due to the intermediate phase,

- at equal power, significant reduction in the amount of adsorbent compound required.

- use on the ground, without exposure to direct radiation from the sun. In this way, this type of installation can be used tion with success wherever you want to economically produce cold, especially for storage and especially for air conditioning.

Claims

1. A refrigeration process in which:

an adsorberant compound, present in divided form, on which a refrigerant has been adsorbed, is heated until evaporation,

- the vapors thus produced of refrigerant are condensed and the liquid thus produced is stored,

- then, this refrigerant is vaporized again and adsorbed again on the body adsorbing the vapors thus relaxed, so that this expansion produces cold,

- And in which one operates, by means of two tanks containing the adsorbent compound, these two tanks working respectively and alternately in desorption and in adsorption, characterized in that during the treatment, the tank working in adsorption is cooled by passing a coolant both on the condenser and on said tank.

2. Method according to claim 1, characterized in that the adsorption-desorption cycle is reversed when the essential part of the adsorbent compound of the desorbed tank is desorbed, that is to say when each tank is close to its point d 'balanced.

3. Method according to one of claims 1 and 2, characterized in that before the inversion of the cycle, the temperatures between the two tanks are equalized.

4. Refrigerating installation of the type comprising: - a heat source intended for heating a heating fluid,

- a solid adsorbent compound having a large adsorption capacity and a low adsorption energy, - a refrigerant adsorbed on said solid adsorbent compound;

- a condenser intended to liquefy the refrigerant vapors produced under the effect of the action of the heating fluid from the heat source and passing through the adsorbent compound charged with refrigerant,

- An evaporator intended to vaporize the fried liquid produced, - and two tanks intended to receive the adsorbent compound, said tanks working respectively one in desorption, the other in adsorption, characterized in that said tanks are connected by a part between them and on the other hand, by a set of valves and pipes at the same time, to the condenser and to the evaporator.

5. Installation according to claim 4, characterized in that it has a means capable of automatically switching the valves connecting the tanks to each other and to the condenser and to the evaporator.

6. Installation according to one of claims 4 and 5 characterized in that the heat exchange between the adsorbent compound containing the adsorbed refrigerant and the heating fluid is effected by passage of the latter in a battery of pipes provided with fins, said battery being placed in the tank and the adsorbent compound being placed against the tube and between the fins so as to ensure thermal contact.

7. Refrigerating installation according to one of claims 4 to 6, characterized in that it comprises:

- a heat source intended to heat a heating fluid, - two tanks connected by a set of pipes and valves to the heat source each containing:

. a temperature exchanger through which said heating fluid circulates,

. and an adsorbent compound intended to adsorb a refrigerant,

- a vacuum refrigerant circuit connecting each tank:. first of all to a first heat exchanger serving as a condenser for the refrigerant,. then, in series, to a second exchanger placed in a buffer tank intended to store the produced frigories.