Closed-loop refrigerators

Fhe mechanical contact seal is a very positive seal. The seal is normally oil-buffered. The mechanical seal, which is the most complex and expensive, is used where gas leakage to the atmosphere cannot be tolerated. This may be due to the cost of the gas, as in closed-loop refrigeration, or where the process gas is toxic or flammable. The mechanical contact seal requires more power than the other seals, which is a deterrent to its use on lower power compressors. 

A closed-loop refrigerant condenser ought to be one of the cleanest services in a process plant. Even seal- or lube-oil leaks affect the evaporator efficiency, rather than the condenser. I have measured rather high [e.g., 140 Btu/[(h)(ft2)(°F)] heat-transfer coefficients in such condensers, even after that condenser has been in service for several years since its last cleaning. 

The closed loop refrigeration circuit compresses and cools the high-pressure refrigerant, which is partly gas and liquid. The liquid is pressurised by pumping and mixed with the vapour at the inlet of the main heat exchanger. This two-phase mixture passes the heat exchanger and leaves the exchanger in liquid phase at essentially the same temperature as the LNG. 

Note Composition of the vapor leaving the evaporator and the liquid leaving the condenser is identical in a closed-loop refrigerant system.)... 

Where cooling is required as well as heating, a closed loop refrigeration circuit, servoed in a similar manner, can be used. A more sophisticated temperature controller, which can both heat and cool, can be made from a Peltier thermoelectric device. In this device a voltage across a series of thermocouple junctions sets up a temperature... 

A closed-loop refrigerant condenser ought to be one of the cleanest services in a process plant. Even seal- or lube-oil leaks affect the evaporator efficiency, rather than the condenser. I have measured... 

The contact seal can be used under 1,000 psig. It is more complex, but has the advantage of not leaking while shut down. The contact seal is used extensively in refrigeration service where the compressor is part of a closed loop, and the shutdown feature is desirable. As mentioned, the seals must have a source of cooling and buffer fluid. In many cases, this fluid is lubricating oil. If contamination is not a problem, a combined lube and seal system can be used. 

Special Conditions in Closed Circuit - Where heating or cooling is used in a closed loop circuit (e.g., hot oil and refrigeration system), consideration must be given to overpressure conditions that might occur on loss of fluid flow, loss of heat input or loss of heat removal. 

Fig. 2. Block diagram for the complete closed-loop behavior. Here, the block corresponding to the refrigeration system is neglected.

Closed-loop systems. In closed-loop systems, groundwater abstraction is not required. Such systems can be used in poorly permeable formations, such as hard rocks or clays. Closed-loop systems may be direct circulation where the heat pump refrigerant is pumped through a closed loop installed in the ground. More frequently they utilize indirect circulation. Here, water, usually with added anti-freeze (e.g., ethylene glycol or ethanol), is circulated through a closed polyethene hose system (the collector... 

Hot water heat exchanger. In this H/Ex., heat contained in some of the refrigerant vapor from the first stage generator is transferred to a two pipe, closed loop, hot water heating circuit. 

Shukri, T. (2004), LNG Technology Selection, Hydrocarbon Engineering, 9(2), pp. 71-76. Swenson, L. K. (1977), Single Mixed Refrigerant Closed Loop Process for liquefying Natural Gas, US Patent, 4,033,73. 

Similar to the liquid-nitrogen loops, this apparatus is based on the double-circuit principle. The refrigerating circuit uses hydrogen, includes a liquefier, and is entirely closed. The refrigerated circuit is a liquid-neon bath in which the samples are immersed. 

Closed-Loop Subsystem Earth connection subsystem in which a fluid, typically water or a refrigerant, is circulated continuously through a system and not released. 

Krikke, H., Bloemhof-Ruwaardz, J., and Wassenhove, L. V. N. Concurrent product and closed-loop supply chain design with an application to refrigerators. International Journal of Production Research 41, no. 16 (2003) 3689-3719. 

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