FR2607143A1 - Nonazeotropic mixtures of at least three compounds which can be employed in thermodynamic compression cycles - Google Patents

Abstract

Nonazeotropic mixtures of fluids which can be employed in thermodynamic compression cycles, for example in heat pumps comprising R23, R11 and at least one fluid c chosen from the group made up of the halogenated compounds of methane and ethane which have a boiling point of -85 to +60 DEG C, excluding R23, R11 and R142b in molar proportions such that the molar ratio R23/R11 is from 0.1:1 to 1.2:1 and the molar ratio R23 + R11 / R23 + R11 + C is from 0.20:1 to 0.5:1. Mixtures of the invention can be employed as working fluid for heat pumps in which the fluid circulates in an evaporator E1, a compressor K1, a condenser E2 and an expansion valve D1. The heat exchanges take place with the external fluids 5, 6 and 7, 8 respectively. The mixtures of the invention make it possible to supply heat to the condenser at a temperature of +50 to +100 DEG C while having an internal pressure limited to 0.3 MPa.

Description

The use of mixtures of non-azeotropic fluids in a thermodynamic compression cycle, and for example in a heat pump, with a view to improving the coefficient of performance of said heat pump, has been the subject of French patents FR-A-2,337,855, FR-A-2,474,151, FR-A-2,474,666 and FR-A-2,497,931.

In particular, the published patent application FR-A-2 474 151 describes non-azeotropic mixtures of two constituents for increasing the performance of a heat pump and thus reducing the operating costs of said heat pump. . The two-component mixtures thus described do not, however, make it possible to increase the thermal power for a given compressor.

The object of the present invention is to show that specific mixtures of fluids make it possible to increase the thermal power delivered by a heat pump and simultaneously its coefficient of performance with respect to the case where the same heat pump operates with a pure fluid. By employing in a heat pump the fluid mixtures proposed by the invention, it is thus possible to reduce the investment time and the operating cost. Indeed, the mixed working fluids according to the invention allow an increase in the heat capacity of a given heat pump, without modifying the components of said heat pump, in particular without modifying the compressor and also allow an increase in the coefficient performance.

There are two conventional ways of increasing the thermal power delivered by a heat pump; a first way is to equip it with a compressor of greater capacity, which allows to suck a larger volume flow, but this solution leads to over-investment. The other way to increase the heat capacity of a heat pump is to use a working fluid whose boiling point is lower than that of the usual fluid. In any case, such a substitution leads to a degradation of the coefficient of performance and also to a more restricted range of applications of the machine, since the critical temperature of the lower boiling fluid is generally lower.

The principle of the invention consists in selecting a nonazeotropic mixture specific for fluids, said mixture being characterized by the fact that it comprises alpha) of trifluoromethane (R23) fluid (a), beta) of trichlorofluoromethane (R11) fluid (b) , gamma) at least one fluid (c) selected from the group consisting of halogenated compounds of methane and ethane having a boiling point of -85 to +60 C and preferably -60 to +50 OC, excluding R23, R11 and chloro-1-difluoro-1,1-ethane (R142b), the molar proportion of fluids (a), (b) and (c) in the non-azeotropic mixture of fluids being such that the molar ratio a / b of the number of moles of fluid (a) to the number of moles of fluid (b) in the mixture is from about 0.1: 1 to about 1.2: 1 and preferably from about 0.2: 1 to about 1.05: 1 and the molar ratio (a + b) / (a + b + c) of the sum of the number of moles of the fluid (a) and the number of moles of the fluid (b) contained in the mixture at total moles of fluids (a), (b) and (c) forming the mixture of from about 0.2 to about 0.5: 1 and preferably from about 0.25: 1 to about 0.4 1.

For the purposes of the present invention, the term "nonazeotropic mixture" refers to a mixture of fluids, comprising at least three distinct fluids, whose constant fluid change temperature at constant pressure is not constant.

The fluid (c) that is employed can form an azeotrope with the fluid (a) or with the fluid (b) provided that the mixture (a) + (b) + (c) obtained is a non-aqueous mixture. azeotropic. A fluid (c) is generally used which does not form azeotrope with either the fluid (a) or the fluid (b). When several fluids (c) are used, fluids which do not form azeotropes with each other, or fluids forming azeotropes with each other and behaving like a single fluid, can be used; these fluids (c) must be chosen so that the final mixture of fluids (a), (b) and (c) is a non-azeotropic mixture.

For the purposes of the present invention, the term "halogenated compound of methane and ethane" refers to all the derivatives of one or other of these hydrocarbons comprising at least one halogen atom, such as fluorine, chlorine or bromine. or iodine in their molecule. It is generally preferred to use halogenated compounds comprising at least one fluorine atom, possibly at least one chlorine atom, and not comprising a bromine atom or a diode atom in their molecule.

Among the fluids (c) which are preferably used in the mixtures according to the present invention, the following compounds may be mentioned as non-limiting examples: monochlorodifluoromethane (R22) - dichlorodifluoromethane (R12) - the azeotropic mixture R500 constituted by weight of 73.8% of R12 and 26.2% of 1,1-difluoroethane (R152a) and the azeotropic mixture R502 consisting of 118.8% R22 and 51.2% chloropentafluoroethane ( R115).

The non-azeotropic mixtures that are particularly preferred according to the present invention are the following:
R23-R11-R22; R23-R11-R12; R23-R11-R500 and R23-R11-R502.

The non-azeotropic mixtures according to the present invention can be used in heat pump installations for heating and / or thermal conditioning of premises. In the method of heating and / or thermal conditioning of a room by means of a heat pump using the nonazeotropic mixtures according to the present invention, said heat pump operates with a condensation step, an expansion step, a step of evaporation and a step of compressing the nonazeotropic mixture used as a working fluid.

In the cycle of a given heat pump, for identical operating conditions, the evaporation pressure of a mixture of the above type is greater, all things being equal, than the evaporation pressure of the fluid or fluids. which would be used without the fluid (a).

As a result, the molar volume of the vapors sucked into the compressor is lower, which for a given displacement compressor increases the molar flow rate of the fluid and therefore the thermal capacity of the heat pump. Moreover, the use of a mixed working fluid comprising R 23, R 11 and at least one fluid (c) generally leads to an increase in the volumetric efficiency in the case of reciprocating piston compressors and is therefore also favorable to an increase in thermal capacity. The increase in volumetric efficiency is even higher than the molar concentration of the fluid (a) is important. The mole fraction of the fluid (a) should be within the limits defined above; In fact, the compressors have a range of application limited by certain operating parameters (maximum discharge temperature and pressure difference) and, in particular, by the maximum pressure of the compressor. discharge. The condensation pressure of a mixture according to the invention will preferably be less than 0.3 MPa (30 bar).

The fluid mixtures proposed by the invention are more particularly usable when the outlet temperature of the external fluid circulating in the condenser is preferably between +50 C and +100 C.

Heat pumps, in which the mixtures defined above are usable, can be of any type.

The compressor may be, for example, a piston compressor with lubricated or dry pistons, a screw compressor or a centrifugal compressor. The exchangers can be between, for example, double-tube heat exchangers, tube and shell heat exchangers, plate heat exchangers or plate heat exchangers or conventional finned heat exchangers for heat transfer with air. An exchange mode is generally countercurrent; this is well done in the case of coaxial exchangers used for water / refrigerant exchanges in low power heat pumps. It can be made approximately in the air / refrigerant exchangers according to an arrangement described in the French patent application FR-A-2 474 666. The thermal power delivered can vary, for example, between a few kilowatts for heat pumps used in domestic heating and several megawatts for heat pumps for collective heating.

A preferred procedure is that described in the French patent application FR-A-2,497,931.

This procedure comprises the following steps: (a) the mixed vapor phase working fluid is compressed, (b) the compressed mixed fluid from step (a) is brought into thermal exchange contact with a relatively external fluid. cold and that it is desired to heat up, and this contact is maintained until substantially complete condensation of said mixed fluid, (c) the substantially completely condensed mixed fluid coming from step (b) with a cooling fluid defined in step (f), so as to further cool said mixed fluid, (d) expanding the cooled mixed fluid from step (c), (e) expanding the mixed fluid, from step (d), in heat exchange contact with an external fluid which constitutes a source of heat, the contact conditions allowing the partial vaporization of said expanded mixed fluid, (f) placing the partially vaporized mixed fluid, from the step (e), in heat exchange contact with the substantially completely liquefied mixed fluid sent to step (c), said partially vaporized mixed fluid constituting the cooling fluid of said step (c), the contact conditions allowing continuing the vaporization started in step (e), and g) returning the mixed vaporized fluid, from step (f) to step (a).

Figure 1 schematically illustrates a conventional arrangement of a water / water heat pump in which the blends of the present invention may be employed. This heat pump comprises an evaporator El in which the mixture is introduced through the conduit 1 and from which it is vaporized by the conduit 2, a compressor K1 in which the mixture in vapor form is compressed and from which it emerges from the conduit 3 for beech sent into the condenser E2, where it spring condensed through the conduit 4 and is expanded in the expansion valve D1 and is recycled to the evaporator. The cold source is water that enters the evaporator E1 through the duct 5 and leaves it cooled by the duct 6. The hot source is water that enters through the duct 7 in the condenser
E2 and in the spring heated by the conduit 8.

Figure 2 shows another heat pump arrangement, including an internal exchanger, in which the mixtures according to the invention can be used.

In FIG. 2, the mixed working fluid resulting from the expander via the duct 9 is partially vaporized in the evaporator E3 by the cooling of the cold source water which circulates in the countercurrent of the working fluid and which enters the evaporator
E3 through the conduit 11 and out through the conduit 12. From the evaporator E3 through the conduit 10, the working mixture is fully vaporized and possibly superheated in the exchanger
E4, by countercurrent exchange with the subcooled condensate which enters E4 through the pipe 18 and which is discharged through the pipe 19.

The mixed working fluid in the gaseous state is sucked into the compressor K1 through the pipe 13 and is discharged at high pressure by the pipe 14. Next, it is subcooled and totally condensed in the condenser E5 into which it enters by the duct 14 and from which it emerges in the saturated liquid state by the duct 15. During the condensation in E5, the mixture gives the useful thermal power to the water of the external circuit which, between the pipe of 16 and the outlet pipe 17 flows countercurrently with the working fluid. The mixture, once condensed in E5, enters via line 15 into the recipe flask B1 and exits via line 18; it is then subcooled in the exchanger E4 and accesses the regulator V1 through the pipe 19.

In terms of capacity, this scheme provides an improvement when the working fluid is a mixture of non-azeotropic fluids, because the exchanger E4 where the end of the vaporization is achieved allows to reach for the mixture a temperature at the end of higher boiling, so a stronger suction pressure. This process allows both a reduction of the molar volume at the suction and a reduction of the compression ratio.

The following examples illustrate the use of specific mixtures of fluids according to the invention.

EXAMPLE 1
The operating diagram of the heat pump is shown in Figure 1.

Example 1 refers to three use cases defined below and for which it is possible to use either R22 or
R500, a non-azeotropic mixture according to the present invention.

The temperatures on the external circuits are fixed for each case according to conditions called El, E2 and E3 listed below.

WATER TEMPERATURES C
CONDENSER EVAPORATOR

<tb> I <SEP> I <SEP> I <SEP> I <SEP> I <SEP> I <SEP> I
<tb> Cases <SEP> Tee <SEP> C <SEP> Tse <SEP> C <SEP> Tec <SEP> C <SEP> Tsc <SEP> C <SEP>#T<SEP><SEP> C <SEP >#T'<SEP><SEP> C
<tb> E1 <SEP> 40 <SEP> 1 <SEP> 15 <SEP> 1 <SEP> 30 <SEP> 1 <SEP> 55 <SEP> 1 <SEP> 15 <SEP> 1 <SEP> 25 <SEP > l <SEP>
<tb> E2 <SEP> 40 <SEP> 15 <SEP> 1 <SEP> 40 <SEP> 1 <SEP> 65 <SEP> 1 <SEP> 25 <SEP> 1 <SEP> 25 <SEP> 1
<tb> E3 <SEP> 45 <SEP> 10 <SEP> 20 <SEP> 55 <SEP> 10 <SEP> 35
<Tb>
Tec is the water inlet temperature in the condenser,
Tsc is the outlet temperature of condenser water,
Tee is the inlet temperature of the water in the evaporator, Tse is the evaporator water outlet temperature.

AT and AT 'are defined as follows
AT = Tec-Tse = Tsc-Tee and AT '= Tee ~ Tse = Tsc ~ Tec
Table 1 below indicates the results compared for the following cases - the operation of the heat pump using either R12 or R500, or a non-azeotropic mixture R23-R11-R22 according to the invention.

The COP represents the ratio of the thermal power in watt delivered to the condenser (Qcond) to the compression power in watt transmitted to the working fluid (W). Qévap. is the thermal power in watts taken at the evaporator.

From the results obtained, given in Table 1, it appears that the ternary mixtures such as those recommended according to the present invention, allow a gain in heat recovery recoverable to the condenser compared to the case of a single fluid or azeotropic mixture is comprising as a single fluid (R12 and R500) in the three envisaged cases E1, E2 and E3. This gain in thermal power is simultaneously accompanied by a gain in COP compared to the case where the R12 or the R500 is used.

The preceding examples show that the non-azeotropic mixtures according to the invention simultaneously make it possible to increase the coefficient of performance and the heat capacity of a heat pump.

TABLE 1

<tb> Cases <SEP> Fluids <SEP> (fraction <SEP> molar) <SEP> Qcond <SEP> Qevap <SEP> W <SEP> COP <SEP> COP / COP <SEP>
<tb> (R12) <SEP>
<tb> E1 <SEP> R12 <SEP> 7005 <SEP> 5520 <SEQ> 1675 <SEQ> 4,18 <SEP> 1
<tb> E1 <SEP><SEP> R500 <SEP> 1 <SEP> 880216908 <SEP> 2000 <SEQ> 4.40 <SEP> 1,052 <SEP> | <September>
<tb> E1 <SEP> R23 (0.10) R11 (0.18) R22 (0.72) <SEP> 11559 <SEP> 9278 <SEP> 2475 <SEP> 4.67 <SEP> 1.117
<tb> E2 <SEP><SEP> R12 <SEP> 1 <SEP> 690915088 <SEP> 1950 <SEP> 3.54 <SEP> 1 <SEP> I
<tb> I <SEP> I <SEP><SEP> I <SEP> I <SEP> I <SEP> I <SEP> I <SEP> -j <SEP>
<tb> E2 <SEP><SEP> R500 <SEP> 1 <SEP> 784715766 <SEP> 1221213,551 <SEP> 1,002 <SEP> 1
<tb> E2 <SEP> I <SEP> R23 (0.10) R11 (0.18) R22 (0.72) <SEP> 11085618234 <SEP> 1282513.841 <SEP> 1.085 <SEP> I <SEP>
<tb> E3 <SEQ> R12 <SEP> 6511 <SEQ> 5072 <SEQ> 1575 <SEQ> 4,13 <SEP> 1
<tb> E3 <SEP><SEP> R500 <SEP> 1 <SEP> 777115910 <SEP> 1188914,111 <SEP> 0.995 <SEP> 1 <SEP>
<tb> E3 <SEP> R23 (0.10) R11 (0.18) R22 (0.72) <SEP> 11401 <SEP> 9159 <SEP> 2300 <SEP> 4.96 <SEP> 1.201
<Tb>
A particular interest of the non-azeotropic mixtures according to the invention is that they allow operation of the heat pumps with an internal pressure limited to 0.3 MPa (30 bar), even in the case of the supply of heat to the condenser. a temperature close to 100 C, by adjusting the molar compositions of the constituents. Indeed, if the temperature pressure relationship is not modifiable for a pure body, it is quite possible in the case of mixing to lower the condensing pressure for a given temperature.

Claims (10)

1) non-azeotropic mixture of fluids that can be used in thermodynamic compression cycles, characterized in that it comprises alpha) of the fluid R23 (a), beta) of the fluid R11 (b) and gamma) at least one fluid (c) selected from the group consisting of the halogenated compounds of methane and ethane having a boiling point of -85 OC to +60 OC excluding R23, R11, and R142b, the molar proportion of the fluids ( a), (b) and (c) in the mixture being such that the molar ratio a / b is from about 0.1: 1 to about 1.2: 1 and the molar ratio (a + b) / (a + b + c) from about 0.2: 1 to about 0.5: 1. 2) Non-azeotropic mixture according to claim 1, wherein the molar proportions of the fluids (a), (b) and (c) in the mixture are such that the molar ratio a / b is about 0.2: 1 at about 1.05: 1 and the molar ratio (a + b) / (a + b + c) is from about 0.25: 1 to about 0.4: 1. 3) A blend according to claim 1 or 2, wherein the fluid (c) is selected from the group consisting of R12, R22, R500 and R502. 4) A mixture according to claim 3, wherein the fluid (c) is R22. 5) A mixture according to claim 3, wherein the fluid (c) is R502. 6) A method of heating and / or thermal conditioning of a room by means of a compression heat pump using as a working fluid a non-azeotropic mixture of fluids according to one of claims 1 to 5, said heat pump operating with a condensation step, an expansion step, an evaporation step and a compression step of said working fluid. 7) The method of claim 6, wherein the external fluid to be heated circulating in the condenser has a condenser outlet temperature of about +50 to about +100 C. 8) Process according to claim 6 or 7, wherein the heat pump operates under conditions such that (a) the working fluid is compressed in the vapor phase, (b) the working fluid is brought into contact with heat exchange. compressed from step (a) with an external cooling fluid and maintaining this contact until substantially complete condensation of said working fluid, (c) heat exchange is brought into contact with the working fluid substantially completely condensed from step (b) with a cooling fluid defined in step (f), thereby further cooling said working fluid, (d) expanding the cooled working fluid from step (c) ), (e) the expanded working fluid from step (d) is brought into heat exchange contact with an external fluid which constitutes a source of heat, the contact conditions allowing the partial vaporization of said working fluid. relaxed, (f) we put the partially vaporized working fluid from step (e) in heat exchange contact with the substantially completely liquefied working fluid fed to step (c), said partially vaporized working fluid constituting the cooling fluid said step (c), the contact conditions for continuing the vaporization initiated in step (e), and (g) returning the vaporized working fluid from step (f) to step (at). 9) Method according to one of claims 6 to 8, wherein the heat exchange with the external fluid or fluids are carried out in heat exchange exchangers in a generally countercurrent exchange mode. 10) Method according to one of claims 6 to 9, wherein the composition of the non-azeotropic mixture used is chosen so that the condensation pressure of said mixture is less than 0.3 MPa.