JP2006241221A - Coolant composition for car air conditioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coolant which has excellent features, is not ozone-depleting, has an extremely low global warming potential, is safe and non-toxic by mixing a coolant, dimethyl ether and carbon dioxide. <P>SOLUTION: The coolant composition for car air conditioners contains 5-40 wt% of dimethyl ether and 95-60 wt% of carbon dioxide. Preferably, the coolant composition contains 8-12 wt% of dimethyl ether and 92-88 wt% of carbon dioxide. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a refrigerant composition containing dimethyl ether and carbon dioxide, which is mainly used in car air conditioners.

  Until now, chlorofluorocarbon (CFC chlorofluorocarbon, HCFC hydrochlorofluorocarbon) has an excellent refrigerant capacity and thus has been widely used worldwide as a refrigerant for car air conditioners and the like. However, since CFCs contain chlorine and destroy the ozone layer, the production of CFCs out of specific CFCs was abolished in 1996 in Japan and Europe and America. The production of HCFC (hydrochlorofluorocarbon), which is the same specific chlorofluorocarbon, will be regulated after 2004, and will be completely abolished by 2010 in Europe and by 2020 in other developed countries.

  In addition, alternative chlorofluorocarbon (HFC hydrofluorocarbon, PFC perfluorocarbon, SP6), which replaces the above-mentioned specific chlorofluorocarbon, has zero ozone depletion coefficient, low toxicity, nonflammability, satisfactory characteristics and performance, but is incompatible with mineral oil, lubrication There is a problem of deterioration of the property. In particular, this alternative chlorofluorocarbon does not destroy the ozone layer but has a very high global warming potential.Therefore, although there is no specific regulation and it is left to the voluntary action of the industry, its use will be abolished in the near future. It will be greatly regulated.

  Recently developed natural refrigerants such as carbon dioxide, ammonia, water, and air also have features of zero ozone depletion coefficient and almost zero global warming coefficient, but safety, performance, convenience, etc. There are difficulties. Ammonia is as efficient as HFC, but has toxicity, irritating odor, and incompatibility with copper. Water and air are non-combustible and non-toxic, but very low efficiency.

On the other hand, carbon dioxide is nonflammable and has low toxicity, and has a large sensible heat effect. Therefore, carbon dioxide has recently been used for EHP refrigerants such as Ecocute for heating and supplying hot water. However, since carbon dioxide has a small latent heat effect, it is extremely inefficient to use for cooling. Furthermore, when carbon dioxide is used as a refrigerant for a car air conditioner, the operating pressure on the condenser side of the car air conditioner becomes supercritical (CO ₂ critical pressure: 7.4 MPa, critical temperature: 31 ° C.) at a high pressure of 8 MPa or more. In order to liquefy the refrigerant in the condenser with this high-pressure gas-phase refrigerant, it is necessary to keep the refrigerant at 31 ° C. or lower, as can be seen from the Mollier diagram of CO ₂ . For this reason, it circulates around the condenser of a car air conditioner with water, turns it with a special refrigerator gas, cools the condenser, or lowers the temperature of the outside air taken in with a gas cooler to a temperature at which it can sufficiently exchange heat. Ingenuity is required.

  On the other hand, dimethyl ether (DME) has a very high latent heat effect and is known to be convenient for use in cooling. However, since it is flammable, it is not practically used from the viewpoint of safety.

  An object of the present invention is to provide a refrigerant composition for a car air conditioner that has no risk of ozone layer destruction, has a small adverse effect on global warming, has no toxicity, and has an excellent cooling capacity.

  The present inventors have found that carbon dioxide dissolves well in dimethyl ether. Furthermore, since the critical temperature of dimethyl ether (DME) is 127 ° C., which is much higher than that of carbon dioxide, dimethyl ether (DME) is converted into carbon dioxide. As a result of various studies on the possibility of obtaining a flame retardant or non-flammable refrigerant with high thermal efficiency, the present invention has been reached. Is.

  That is, the present invention is based on the total weight of dimethyl ether and carbon dioxide, 5-40 wt% dimethyl ether, 95-60 wt% carbon dioxide, preferably 5-12 wt% dimethyl ether, 95-88 carbon dioxide. The present invention relates to a refrigerant composition for car air conditioners containing wt%. Thereby, the ozone layer is not destroyed, the global warming potential is extremely small (GWP is about 3), there is no toxicity, and the refrigerant | coolant which has the outstanding cooling capability can be provided. Furthermore, by using the refrigerant composition of the present invention for a car air conditioner, the temperature of the refrigerant in the condenser can be operated at a higher temperature. An advantageous effect is obtained that a special device such as a cooler is not required.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

  The dimethyl ether used in the refrigerant composition of the present invention includes, for example, coal gasification gas, LNG tank BOG (Boil of Gas), natural gas, ironworks by-product gas, petroleum residue, waste, and biogas as raw materials. As described above, dimethyl ether is directly synthesized from hydrogen and carbon monoxide, or indirectly from methanol and carbon monoxide via methanol synthesis.

  The carbon dioxide used in the refrigerant composition of the present invention can be obtained, for example, by compression, liquefaction and purification using by-product gas generated from ammonia synthesis gas or hydrogen production plant for heavy oil desulfurization as a raw material.

  The mixing ratio of dimethyl ether and carbon dioxide in the refrigerant composition of the present invention is appropriately determined according to the type of refrigerator such as a car air conditioner or commercial / home air conditioner in which the refrigerant is used, but the refrigerant composition of the present invention. Is preferably 5 to 40% by weight of dimethyl ether, 95 to 60% by weight of carbon dioxide, more preferably 8 to 12% by weight of dimethyl ether and 92 to 92% of carbon dioxide, based on the total weight of dimethyl ether and carbon dioxide. Contains 88% by weight. When the dimethyl ether is less than 5% by weight, a sufficient coefficient of performance described later cannot be obtained, and the characteristics as a refrigerant are inferior. On the other hand, when dimethyl ether is larger than 40% by weight, the refrigerant composition is out of the flame-retardant region, which is not preferable for safety.

  In the refrigerant composition of the present invention, for example, an appropriate amount container such as a service can is filled with a predetermined amount of liquefied dimethyl ether from a liquefied dimethyl ether filling tank according to the capacity of a car air conditioner, and then a predetermined amount from a liquefied carbon dioxide filling tank. By filling liquefied carbon dioxide, a refrigerant composition having the above-mentioned mixing ratio can be obtained. In addition, the refrigerant composition of the present invention is filled with liquefied dimethyl ether in an appropriate amount container such as a service can according to the capacity of a car air conditioner, and then filled with carbon dioxide gas in the gas phase portion of the container, and dissolved under pressure in dimethyl ether. It can also be prepared by mixing.

  The refrigerant composition of the present invention may be composed only of dimethyl ether and carbon dioxide, or may contain other components in addition to the mixed medium. Other components that can be added to the refrigerant composition of the present invention include alcohols such as ethanol.

  The principle of the cooling system is based on the continuous heat exchange between the surrounding medium and the latent heat that takes heat energy from the surrounding medium when the substance (refrigerant) is vaporized. Further, since the evaporation temperature of the refrigerant depends on the pressure, if the pressure is lowered, the evaporation temperature also decreases, so that a lower temperature can be obtained.

  On the other hand, the principle of the heating / hot water supply system is achieved by continuous heat exchange with water, air, or the like because it takes heat from the surroundings by evaporation of the refrigerant and becomes a compressed high-temperature gas.

  The system for car air conditioners is also based on the principle of such a cooling / heating system, and is a refrigerant cycle system including a compressor, a condenser, an expansion valve, and an evaporator. A non-limiting example of a refrigerant cycle system for a car air conditioner is shown in FIG. Here, in the cooling air-conditioning, the high-pressure and high-temperature refrigerant in the compressor is cooled by the outside air in the condenser and becomes a liquid phase. This liquid-phase refrigerant evaporates by heat absorption exchange with the interior air in the evaporator, and cools the interior air.

The role of each device in FIG. 1 is as follows.
-EQ1 compressor: The cold refrigerant turned into a gas in the evaporator is sucked and compressed into a high-temperature and high-pressure gas.
-EQ2 condenser: The high-temperature high-pressure gaseous medium discharged from the compressor is cooled and condensed with water or air (outside air) to form a liquid (for heating / hot water supply).
-EQ3 expansion valve: A high-temperature and high-pressure liquid refrigerant is expanded into a low-temperature and low-pressure refrigerant.
-EQ4 evaporator: A low-temperature and low-pressure refrigerant is brought into contact with the surrounding gas at the outlet of the expansion valve, and the heat is removed to evaporate and vaporize the gas (for cooling).

  In order to actually evaluate the cooling capacity of the refrigerant, the above-described refrigerant cycle is numerically modeled, and a general-purpose numerical chemical process simulator is used to perform a known method (for example, Miyara et al. The effect can be analyzed and evaluated according to “Effect of heat transfer characteristics of heat exchanger on performance” (see Japan Refrigeration Association, Vol. 7, No. 1, pages 65-73, 1990, etc.). A general-purpose numerical chemical process simulator has a built-in database of thermodynamic properties of various components, and performs equilibrium thermodynamic calculations between chemical components corresponding to the mechanical engineering functions of various systems.

  In the numerical simulation, each of the systems constituting the compressor, the circulator, the expansion valve, and the evaporator in which the refrigerant circulates is digitized, and the compressor outlet pressure (hereinafter abbreviated as “compression pressure”) (P1), the condenser outlet The temperature (T2), the evaporator temperature (T3) and the concentration of the refrigerant composition components are used as parameters, and the cooling / heating / hot water supply capacity is evaluated as a coefficient of performance (COP).

Coefficient of performance of cooling = total absorbed heat in the evaporator of the cooling ÷ compressor power factor Coefficient of performance of heating / hot water = total amount of exhaust heat in the condenser of the refrigerant ÷ compressor power

  Further, in the present invention, it is preferable to apply a regular dissolution model for melting and an SPK (Soave-Redrich-Kwon) equation for the state equation as a thermodynamic property value estimation equation of the refrigerant, respectively. Can be evaluated.

  In consideration of the physical properties of the refrigerant composition of the present invention, it is necessary to improve and design the mechanical surfaces such as the condenser and the piston so as to match the refrigerant composition of the present invention.

[Example]
Hereinafter, the content of the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

Dimethyl ether / To examine carbon dioxide solubility test dimethylether (DME) The degree of dissolution of carbon dioxide (CO ₂₎ mixed system, and to determine the coefficient of performance of the mixed refrigerant in later-described hot water supply system, the DME / CO ₂ A solubility test was performed. The test method is as follows.
(1) 300 g of dimethyl ether is sealed in a pressure vessel (500 mL), and the weight after sealing is measured with an electronic balance.
(2) Put a pressure vessel in a constant temperature bath and make it constant temperature.
(3) Carbon dioxide is injected to a certain pressure with a booster pump.
(4) The filled carbon dioxide is calculated from the weight before and after filling (d = 0.1 g).

At the time of filling, the pressure vessel was shaken up and down so that DME / CO ₂ was sufficiently mixed, and the test was carried out by standing vertically.

The obtained results are shown in Table 1. As shown in Table 1, the K-volume values of CO ₂ and DME are in the range of 0.66 <KDME <0.80 and 2.59 <KCO ₂ <3.42, respectively, under the measurement conditions. It can be seen that carbon dioxide dissolves well.

(First embodiment)
The coefficient of performance (COP) of the mixed refrigerant of dimethyl ether and carbon dioxide in the refrigerant cycle system shown in FIG. 1 is obtained. The simulation was performed by the following procedure using a numerical chemical process simulator.

Simulation Procedure State quantities (volume, enthalpy, entropy, etc.) of streams (1) to (4) in the refrigerant cycle system of FIG. 1 are determined by simulation, and a coefficient of performance COP of the following equation is obtained.

COP = H1 / H2
H1: Total exhaust heat amount in refrigerant condenser H2: Compressor power amount from (4) to (1) At this time, the following conditions were set.

(1) CO ₂ / DME Mixed Refrigerant In order to evaluate the hot water supply capability of the CO ₂ / DME mixed refrigerant, calculation is performed using the discharge pressure of the compressor, the steam pressure, and the CO ₂ / DME mixed ratio as fluctuation parameters.
P1 = 3.7 to 7.5 MPa
P3 = 1.05 to 3.1 MPa
Refrigerant evaporation temperature: around 8 ° C DME / CO ₂ mixing ratio (5/95, 8/92, 10/90, 12/88, 15/85, 20/80, 30/70: weight ratio)
Refrigerant evaporation temperature

(2) CO ₂ single refrigerant For carbon dioxide alone, in this cooling cycle, it is necessary to lower the condenser outlet temperature T2 to 31 ° C. or lower, and it is the outside air of the car air conditioner condenser heat source. This simulation was not performed because the cooling cycle was not established.

In the simulation study of the vapor-liquid equilibrium physical property value of the DME + CO ₂ mixed system, the accuracy of the physical property estimation model to be adopted is an important factor, and the examination was performed as follows.

  In general, the vapor-liquid equilibrium relationship is expressed by the following equation.

Here, the following three points should be examined.
(1) γ _i for DME ⁽⁰⁾ model (2) degree of relative volatility of DME and CO ₂ (3) enthalpy and entropy model

DME is an oxygen-containing low molecular weight compound, but ethanol, which is a representative example, has a boiling point of 78 ° C., whereas DME has a boiling point of −25 ° C., so it has a strong polarity such as alcohol, aldehyde, and ketone groups. It turns out that it does not have. Therefore, a regular dissolution model can be applied to γ _i ^{(0) of} DME.

From the solubility test data of DME / CO ₂ obtained above (Table 1), the K-volume values of CO ₂ and DME were 0.66 <KDME <0.80 and 2.59 <KCO, respectively, under the measurement conditions. ₂ <3.42, and it can be seen that there is no significant difference in volatility between DME and CO ₂ . Thus, a vapor pressure model can be applied to f _i ⁽⁰⁾ .

For enthalpy and entropy, it is appropriate to adopt the SPK (Soave-Redrich-Kwon) state equation because the assumed maximum working pressure of the DME + CO ₂ system is about 10 MPa.

  In addition, since the pouring factor cannot be ignored when the pressure of the system becomes high to some extent (several MPa), this point is also taken into consideration.

Programs The following two types of programs A and B were used.
(1) DME CO ₂ A
Flash calculation under a given composition, T (temperature), P (pressure).

  Bubble points were calculated under the given composition and P1 (compressor pressure).

Accordingly, it is possible to confirm the accuracy of the vapor-liquid equilibrium physical property value estimation model and to determine whether or not total condensation in the condenser is possible.
(2) DME CO ₂ B
Using the simulator described above, COP was obtained for the mixed refrigerant composition containing dimethyl ether and carbon dioxide as follows. still,

In order to evaluate the cooling capacity of a dimethyl ether / carbon dioxide mixed refrigerant, a simulation was performed using the compression pressure (P1), condenser outlet temperature (T2), evaporator temperature (P3), and the mixing ratio of DME / CO ₂ as fluctuating parameters. It was. At this time, the condenser outlet temperature T2 was set to 35 ° C., and the evaporator temperature was set to an average of 4 to 5 ° C. Table 2 shows the simulated DME / CO ₂ weight mixing ratio, and Table 3 shows the simulation results for the cooling characteristics of the refrigerant composition at the mixing ratio.

As is clear from Table 3, with the DME / CO ₂ mixed refrigerant, a cooling cycle can be constructed at a critical pressure of CO ₂ or less. Furthermore, when the DME / CO ₂ mixing ratio is incombustible (the weight ratio of DME is 8 to 12%), the compressor pressure can be operated at about 6.8 MPa even when the evaporation temperature is 35 ° C., and the COP is 2.0. is there. Moreover, since the compressor operating pressure rapidly decreases as the concentration of DME increases with the DME / CO ₂ mixing ratio, it may become an excellent solvent if the flame retardant conditions are relaxed.

Refrigerant cycle system for car air conditioners. DME CO ₂ B program flow

Claims (3)

  A refrigerant composition for a car air conditioner containing 5 to 40% by weight of dimethyl ether and 95 to 60% by weight of carbon dioxide based on the total weight of dimethyl ether and carbon dioxide.   The refrigerant composition according to claim 1, comprising 8 to 12% by weight of dimethyl ether and 92 to 88% by weight of carbon dioxide.   A method of using the refrigerant composition according to claim 1 or 2 for a car air conditioner.

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