Refrigerants composition

A very large percentage of refrigeration systems are not limited by either the compressor driver horsepower, the condenser, or the evaporator. Many refrigeration systems are limited by either  

If the compressor is suction-volume-limited, we say that it is speed-limited. If the compressor is driven by an AC motor, its speed is determined by the motor speed and any connecting gears. If the compressor is driven by a turbine, then the rated speed of the turbine limits the compressor speed. 

For example, adding lighter propane to heavier isobutane in a refinery alkylation unit is a common practice to increase refrigerant circulation. But this will work only when the compressor driver has spare 

The simplest way to lower the compressor discharge pressure is to reduce the cooling-water temperature to the condenser. One neat trick I have used is to use the cooling-tower makeup water on a once-through basis, to the refrigerant condensers. This supply of water is almost always 10 to 20°F cooler than the cooling-water supply. 

Another way to reduce the compressor discharge pressure is to render the refrigerant heavier, or less volatile. Adding isobutane to a propane refrigerant is one common example. Naturally, this will lower the suction pressure to the refrigerant compressor shown in Fig. 22.1, and increase the actual volume of vapor flow. If the compressor is speed-limited, this will not be practical. 

1 used this trick at the Amoco Texas City Refinery in 1975 to increase the refrigeration capacity of my sulfuric acid alkylation unit When 1 was put in charge of this alky unit in 1974,1 foimd that capacity was limited to 18,000 BSD by the refrigerant circulation rate. 1 had plenty of compressor capacity, but as 1 increased the turbine speed to run my compressor faster and circulate more isobutane refrigerant, the compressor suction pressure declined to 1 psig. 

Running the compressor suction below atmospheric pressure is possible, but dangerous. Oxygen can be drawn into the refrigerant loop due to minor air leaks in the suction piping. To avoid this 

---

Refrigerant composition for heavy Inadequate Refrigerant Check ... 

It is a good practice to slowly change the refrigerant composition and observe the effect on the unit. This is a more precise method than calculation. 

When adjusting refrigerant composition by spiking in a light hydrocarbon, remember that the spike component must be dry. A truckload of propane or butane meeting commercial liquefied petroleum gas (LPG) specs is a safe bet. To make propane more volatile, using propylene as a spike is fine. However, propylene will form hydrates (an ice-type solid) in the presence of moisture at temperatures as high as SS F. 

Refrigerant composition (refrigeration systems), 231-234, 241 speed-limited, 232-233 horsepower-limited, 233 accumulator relief valve, 233-234 minimum suction pressure, 234 Refrigerant condenser problems (evaporating problems), 240 Refrigeration systems, 227-241 efficiency, 227-229 diagnosing compressor problems, 229—231 refrigerant composition, 231—234 ... 

Changing refrigerant composition can be a simple, cost-effective method... 

---