Types and Applications
Liquid ring systems can be single or multi-stage. Typically a multi-stage pump will have up to two compression stages on a common shaft. In vacuum service, the attainable pressure reduction is limited by the vapour pressure of the ring-liquid. As the vacuum generated approaches the vapour pressure of the ring-liquid, the increasing volume of vapor released from the ring-liquid diminishes the remaining vacuum capacity. The efficiency of the system declines as a result.
Single stage vacuum pumps typically produce vacuum to 35 torr (mm Hg) or 0.047 bar, and two-stage pumps can produce vacuum to 25 torr (mmHgA), assuming air is being pumped and the ring-liquid is water at 15°C (60F) or less. Dry air and 15°C sealant water temperature is the standard performance basis which most manufacturers use for their performance curves.
These simple, but highly reliable pumps have a variety of industrial applications. They are used on paper machines to dewater the pulp slurry and to extract water from press felts. Another application is the vacuum forming of molded paper pulp products (egg cartons and other packaging). Other applications include soil remediation, where contaminated ground water is drawn from wells by vacuum. In petroleum refining, vacuum distillation also makes use of liquid ring vacuum pumps to provide the process vacuum. Liquid ring compressors are often used in vapor recovery systems.
Liquid Ring Vacuum Pumps can use any liquid compatible with the process, provided it has the appropriate vapor pressure properties, as the sealant liquid. Although the most common sealant is water, almost any liquid can be used. The second most common is oil. Since oil has a very low vapor pressure, oil-sealed liquid ring vacuum pumps are typically air-cooled.
The ability to use any liquid allows the liquid ring vacuum pump to be ideally suited for solvent(vapor) recovery. If a process, such as distillation, or a vacuum dryer is generating toluene vapors, for example, then it is possible to use toluene as the sealant, provided the cooling water is cold enough to keep the vapor pressure of the sealant liquid low enough to pull the desired vacuum.
Ionic liquids in liquid ring vacuum pumps can lower the vacuum pressure from about 70 mbar to below 1 mbar.
Read more about this topic: Liquid Ring Pump
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