R723: dimethyl ether & ammonia promise further potential

By Sabine Lobnig, Apr 19, 2009, 15:13 2 minute reading

The natural refrigerant blend R723 combines 60% of ammonia’s energy advantages and 40% of dimethyl ether’s oil miscibility. The substance is not only environmentally friendly and energy-efficient, but also available in high quantities. A new article explains benefits and safety issues of dimethyl ether.

When searching for a solubility agent that would enhance the miscibility of lubricating oils with the refrigerant ammonia, compressor manufacturers observed that the use of simplest ether – dimethyl ether – would not only deliver trouble-free operation but would also result in an advantageous refrigerant, whose azeotropic properties allow it to be used like a single-substance refrigerant. The refrigerant R723, a mixture of 40 mass percent dimethyl ether (DME) and 60 mass percent ammonia, also led to reduced pressure-gas temperatures, opening up additional fields of application for natural refrigerants, such as in plants with refrigeration outputs below 100 kilowatts or for portable refrigeration units.

In addition, with a large volumetric refrigeration output, R723 results in correspondingly high Coefficient of Performance (COP) values. Thanks to the low compressor discharge temperature systems can frequently do without cylinder cooling, which allows for the use of air-cooled condensers instead of water-cooled units. Overall, the blend promises high potential in flooded plants for the food industry and high temperature heat pumps.

The refrigerant was developed over several years of research at the ILK Institut fur Luft- and Kaltetechnik (Institute for Refrigeration and Air Conditioning) in Dresden, Germany. Although leading refrigeration system manufacturers have reported good experiences with R723, the industry has remained sceptical about its applicability and remaining safety issues resulting from the combination of a toxic and flammable substance. The German company Schick producing and distributing the natural blend decided to explain the special characteristics and safety requirements of R723 in the latest edition of “Kälte Klima Aktuell” (KKA).

Flammability of DME

DME is indeed flammable, however, the lower explosive limit of 3,4 Vol-% is still higher than that of special gases used in industrial applications, such as acetylene (2,3 Vol-%), n-butane (1,4 Vol-%) or propane (1,7 Vol-%). R723 being an ammonia blend that is only flammable at very high concentrations, the lower explosive limit is 6,0 Vol-%. It hence requires the same safety guidelines as ammonia regarding this parameter. However, a higher specific combustion heat leads to differences in safety technology regarding the system construction. As a result, R723 blend has to be assigned to safety group L3 (like e.g. propane) according to DIN EN378.

DME is physiological harmless

Schick contradicts the argument that DME has narcotic attributes. The natural gas is physiological harmless and has no anaesthetic impact on humans. The still existing misconception may come from the mix-up with di-ethyl ether (C2H5-O-C2H5) that was used as a narcotic substance in the past. The natural gas used for R723 is di-methyl ether (CH3-O-CH3).


By Sabine Lobnig

Apr 19, 2009, 15:13

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