Refrigeration circuits

If no satisfactory process drawings exist you can identify major sections of the process (e.g., heat exchanger trains, refrigeration circuits, distillation equipment, reactor systems) that probably represent equipment that can be isolated from the rest of the process. 

A block diagram of the DX system is shown in Figure 29.1. It has two main circuits - the air circuit and the refrigerant circuit. In the chilled-water system, there are additional circuits ... 

The behaviour of lubricating oil in a refrigerant circuit and its physical interaction with the refrigerant itself is a dominant factor in the design of circuits in general and evaporators in particular. 

The four main components of a vapour compression refrigeration circuit - the evaporator, the compressor, the condenser and the expansion valve - must be selected to give a balanced system. 

Two condensers, or a condenser assembly having two separate refrigerant circuits and permitting rapair to one circuit while the other is working. If there is one assembly with forced convection, there are at least two fans. 

The heat reclaim packaged unit system comprises water-cooled room units with reverse cycle valves in the refrigeration circuits. The water circuit is maintained at 21-26°C, and may be used as a heat source or sink, depending on whether the individual unit is heating or cooling. (See Figure 28.11.)... 

Hot discharge gas from a refrigeration circuit can be used to heat water (see Figure 6.5). 

Many systems are shut down for periods of the year, either for process closure or if not required in winter. The advice of the supplier should be sought as to the correct procedure. In the case of refrigerant circuits, it is advisable to pump down into the receiver or condenser to minimize leakage losses. Water towers should be drained in winter in this climate, if not in use, and the tank heater disconnected. 

Figure 3.17. Distillation column with heat pump (a) Separate refrigerant circuit (b) Using column fluid as the...

For several months before the accident, conditions at the plant had been deteriorating. Procedures were not carefully followed and several mechanical features were either shutdown or compromised. Examples include the refrigeration circuit that was depleted of coolant and the vent gas scrubber that was out of service. The temperature indicator on one tank was defective. The temperature in one of the tanks had been allowed to exceed the maximum limit by as much as 15°C with no corrective action. 

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. 

DESICCANT - Any absorbent or adsorbent, liquid or solid, that will remove water or water vapor from a material. In a refrigeration circuit, the desiccant should be insoluble in the refrigerant. 

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. 

The selection of an appropriate enhancement technique must take into account the nature of the fluid stream(s) involved. For example, some enhancanent methods, particularly those involving fine surface features, are susceptible to contanfinants which could reduce the effectiveness. Heavily fouled streams, or those containing oil, such as a refrigerant circuit using an ineffective oil separator, would not be ideal candidates. Some incur a pressure drop penalty, and, as highlighted earlier, active methods invariably involve an extra power input. 

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... 

Other fluids than ammonia have been used in the refrigeration circuit (see [636]), and absorption refrigeration (normally based on ammonia/water) [637, 638] has been used instead of mechanical refrigeration. It has been proposed to remove the ammonia from the partly cooled reactor effluent by absorption in water. This procedure makes it necessary to dry the recycle gas before it reenters the converter. The drying may be done with molecular sieves or by injection of liquid ammonia into the gas stream and separation of the resulting ammonia -water mixture [32, 639]. 

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