Current state and perspectives of using alternative refrigerants

Measures performed by the government of many countries on fulfillment of resolutions of the Vienna Convention (1985), Montreal protocol (1987) and following amendments to them allowed to considerably reduce production and consumption of chlorofluorocarbons (СFC). Thus, if in 1986 total production of freons in the world constituted 1,123 million tons, in 1994 production and consumption of CFC more than 50 % decreased. However, in the countries of European Union there is still used up to 110 thousand tons of CFC in the operating refrigeration equipment.

In Russia the sector of refrigeration industry includes 15 factories manufacturing domestic refrigeration appliances and their components, 3 factories manufacturing commercial-refrigeration equipment, and 6 factories manufacturing industrial refrigeration machines and compressors.

Single CFC charging of the whole park of refrigeration equipment, according to estimation of the Russian scientific centre "Applied chemistry" constitutes 30...35 thousand tons (1996). Considering the problem of substitution of traditional refrigerants of CFC group (only in the countries of the European Union there is required about 30 thousand tons), it is worthy to note that companies-manufacturers have recently developed considerable amount of alternative refrigerants being effective in relatively narrow range of working temperatures.

There exist so many refrigerants that sometimes it is difficult for a customer to choose the required refrigerant for separate operating conditions.

For substitution of R12, main world producers of chemical products recommend R134a and alternative blends С1 and СМ1, including transitional ones containing in their composition R22, - R401A, R401B, R401C, R409A, and also natural refrigerants R600a, R290, propane - butane blends and R717.

R134a is widely used all over the world as a basic substitute for R12 for the refrigeration equipment operating in the average temperature range. R134a is used in automobile air-conditioners, domestic refrigerators, commercial average temperature equipment, industrial facilities, air-conditioning systems of buildings and production areas, as well on the refrigeration transport. Energy data of R134a are lower that those of R12; for operation with R134a there are required expensive synthetic oils characteristic for their high hygroscopicity; the refrigerant has high GWP parameter.

Recently production and consumption of R134a in the industrially developed countries goes slower that it has been predicted in prognosis; at that one of the reasons for such slow growth is considered to be illegal export of CFC. In the USA and the countries of Western Europe it constitutes 10...15 thousand tons per year. Production capacities after R134a output in the industrially developed countries was estimated as 170 thousand tons in 1997 with the world demand equal to 85 thousand tons. Service blends R401A, R401B, R401C, R409A of HCFC group are recommended to use for retrofit in the operating high-, average-, low-temperature refrigeration systems. They are not mixed with mineral oils (except R409A) and intended for operation with synthetic oils.

С1 refrigerant is recommended for using in domestic refrigeration equipment, it is compatible with mineral oils, as to thermodynamic properties it is equivalent to R12; however, due to fire-risk of the refrigerant there is required introduction of structural alterations into refriegation machines. СМ1 refrigerant is supposed to be used in domestic, commercial and industrial refrigeration equipment. Its use is not connected with the necessity to change the structure of refrigeration machines, СМ1 is compatible with mineral oils, as to its thermodynamic properties it is close to R12, incombustible.

In domestic refrigeration appliances and commercial refrigeration equipment of the countries of Western Europe, the so-called "natural" refrigerants R290, R600a and the blends on their base are more widely used. At present time, consumption of hydrocarbons constitutes about 0,07 kg per 1 кWt of cold-productivity and there is observed the tendency to its further decrease. These are ecologically pure refrigerants resolvable with mineral oils and as to their energy data they are comparable with R12. At the same time there should be inserted some alterations into the compressor structure. Refrigerants are fire risky and explosive; therefore, safety rules should be strictly observed.

For retrofit of R502 in the operating refrigeration systems it is recommended to use refrigeration blends R402B, R402A, R404A, R507 and R408A. Thermodynamic properties of R402A and R402B are similar to properties of R502. Refrigerants are resolvable with synthetic oils. Selection of the type of refrigeration blend is dictated by concrete using and characteristic conditions of the refrigeration equipment being used.

R404A refrigerant is supposed to be used for retrofit of the operating average- and low-temperature equipment operating on R502 and R22, аs well as for charging of the new refrigeration equipment. It is compatible with synthetic oils, is related to HFC group. It is perspective for using in the sphere of low temperatures on the vessel refrigeration transport.

R507 refrigerant has been developed for retrofit of the low-temperature refrigeration systems operating on R502, as to its characteristics it is close to R502, resolvable in synthetic oils, is related to HFC group.

Using of R22 refrigerant, which has properly shown itself in the air-conditioning systems, commercial and transport refrigeration facilities, as well as in air-cooling systems and heat pumps, does not comply with long-term perspectives of development of the refrigeration equipment in connection with the resolution of the Montreal protocol. Moreover, as to its energy data R22 is inferior to R12 in average-temperature refrigeration facilities, and therefore does not meet the world tendencies of increasing of energy effectiveness of the equipment and statements of the Convention (Kyoto, 1997) on restriction of emission of hotbed gases.

At present time production of R22 is n the state of considerable excess of offer over demand. In particular, capacities on R22 production in the Western Europe is estimated as 150 thousand per year, and consumption - 100 thousand per year. In future there will be traced the tendency to reduction of its production. For substitution of R22 there are recommended such refrigerants as R404A, R407C, R410A, R407A, R290 and R717.

R410A refrigerant serves for substitution of R22 in the new high pressure air-conditioning systems; at that there are required structural alterations in the compressor and heat-exchangers. It is compatible in synthetic oils. In future R410A can serve as an alternative refrigerant for substitution of R22, because it has high specific volumetric cold-productivity and low critical temperature.

R407C refrigerant according to its energy effectiveness is close to R22 and is considered as optimal alternative to R22. At present it is widely used in the air-conditioning systems. There's not necessity to insert considerable changes into the refrigeration system.

During operation of zeotrope blends there appeared a number of problems. It is "temperature glide", changing of the blend composition in case of leakage of one of the components, immiscibility of a number of refrigerants with mineral oils, vapor-liquid separation of zeotrope blends in each of the system elements: compressor, heat-exchangers, condenser and evaporator; different resolvability of the blend components in the refrigeration oil.

At present time, 70 % of refrigeration facilities for vegetable- and fruit-storehouses operate on R717, 60% - in the meat industry, 50 % - in the confectionery production; 80 % - in the production of beer and beverages.

There is observed return to using of R717 in the ship refrigerating transport, one of the most important links in the refrigeration chain. Volume of marine transportation by 2005 should make 64 million tons. There is increased volume of cargo transportation in refrigerated containers operating on R134a and R404A, whose portion is 42 % of the total mass of the used containers.

Using of liquid and gaseous nitrogen in one-through coolant systems is perspective.

The level of energy consumption by the refrigeration system is one of the most important parameters determining its effect on the level of global warming. At present time, there is observed the tendency of balancing between energy effectiveness of the refrigeration equipment and total equivalent of global warming - TEWI, suggested by the International institute of cold.

At present time, in creation of refrigeration systems due to danger of climate fluctuation there begin to dominate the following tendencies:

• Preferable using of refrigerants with low global warming potential. To them there are related hydrocarbons, ammonia, nitrogen and carbon dioxide;
• Advancing of technological procedures of servicing of the refrigeration systems;
• Reduction of refrigerant emission out of the refrigeration systems;
• Decreasing of the amount of the refrigerant charged into the system;
• Increasing of requirements to the quality of assembling of refrigeration machines and facilities;
• Improvement of the operating refrigeration machines with the aim of increasing of their energy effectiveness and development of new refrigeration machines.