PDF Publication Title:
Text from PDF Page: 034
The operating conditions are always subcrit- ical which guarantees good efficiency lev- els. In the most favourable application range (approx. -10 to -50°C), pressures are still on a level where already available com- ponents, e.g. for R410A, can be matched with acceptable effort. Resulting design criteria For the high temperature side of such a cascade system, a compact cooling unit can be used, whose evaporator serves on the secondary side as the condenser for CO2. Chlorine-free refrigerants are suitable, e.g. NH3, HCs or HFCs, HFO and HFO/HFC blends. With NH3, the cascade heat exchanger should be designed in a way that the dread- ed build-up of ammonium carbonate in the case of leakage is prevented. This technol- ogy has been applied in breweries for a long time. A secondary circuit for larger plants with CO2 could be constructed utilising, to a wide extent, the same principles for a low pressure pump circulating system, as is often used with NH3 plants. The essential difference is the condensing of CO2 in the cascade cooler, while the receiver tank (accumulator) only serves as a supply ves- sel. The extremely high volumetric refrigerating capacity of CO2 (latent heat through the changing of phases) leads to very low mass flow rates, allows for small cross sectional pipe and minimal energy needs for the circu- lating pumps. There are different solutions for the combi- nation with a further compression stage, e.g. for low temperatures. Fig. 30 shows a variation with an additional receiver, which one or more booster com- pressors will bring down to the necessary evaporation pressure. Likewise, the dis- charge gas is fed into the cascade cooler, condenses and is carried over to the receiv- er. The feeding of the low pressure receiver (LT) is achieved by a level control device. Instead of conventional pump circulation the booster stage can also be built as a so- called LPR system.The circulation pump is thus not necessary, but the number of evap- orators is then limited with view to an even distribution of the injected CO2. In the case of a system breakdown where a high rise in pressure could occur, safety valves can vent the CO2 to the atmosphere with the necessary precautions. As an alter- native, additional cooling units for CO2 con- densation are also used where longer shut- off periods can be bridged without a critical pressure increase. For systems in commercial applications, a direct expansion version is possible as well. Supermarket plants with their usually widely branched pipe work offer an especially good potential in this regard: The medium tem- perature system is carried out in a conven- tional design or with a secondary circuit, for low temperature application combined with a CO2 cascade system (for subcritical oper- ation). A system example is shown in Fig. 31. For a general application, however, not all requirements can be met at the moment. It is worth considering that system technology changes in many respects and specially ad- justed components are necessary to meet the demands. Halogen free (natural) refrigerants Simplified sketch Simplified sketch Fig. 30 Casacde system with CO2 for industrial applications Fig. 31 Conventional refrigeration system combined with CO2 low temperature cascade 34PDF Image | REFRIGERANT REPORT 21
PDF Search Title:
REFRIGERANT REPORT 21Original File Name Searched:
A-501-21_EN.pdfDIY PDF Search: Google It | Yahoo | Bing
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
Heat Pumps CO2 ORC Heat Pump System Platform More Info
CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com (Standard Web Page)