Liquid-ring vacuum pumps (LRVPs) and liquid-ring compressors (LRCs) are rotary positive displacement machines used in the process industries to create vacuum and to compress a variety of wet and dry gases and vapors. From production through distribution, the proven technology of the liquid-ring process, proven durability of the pumps in the field and proven low maintenance requirements make the LRVP/LRC one of the most trusted components in oil, gas, chemical and petrochemical operations.
The two major designs of LRVPs are conical-ported and flat-ported. API Standard 681, which covers design requirements for LRVPs, compressors and systems, refers to the conical-ported machine as a radial flow design and the flat-ported machine as an axial flow design. Both radial and axial flow describe how the gas/vapor enters the impeller before it's compressed.
The configurations of these pumps are as unique as each application they are applied to. Because of its broad versatility, many of the most vital and demanding applications are able to use the liquid-ring technology, including vacuum distillation and stripping columns, evaporators, deaerators, reactors, solvent recovery systems, vacuum filters, vinyl chloride monomer and butadiene monomer recovery, waste gas compression, coal-bed methane gas recovery, enhanced oil recovery and vapor recovery systems.
The wide performance range of liquid- ring pumps contributes significantly to their applicability. Typical ranges for compression applications span from 250 cubic feet per meter (cfm) to 1,750 cfm (up to 110 pounds per square inch gauge). Performance for vacuum applications range from 5 cfm to 39,000 cfm (down to 25 Torr).
All LRVPs, when applied to wet gas applications, act as a condenser. The vapor portion of the gas stream is condensed in the ring liquid, so discharge port size becomes a critical component in sizing these machines. In general, conical discharge ports are larger compared to flat ports, allowing additional ring liquid to be recirculated, resulting in a cooler ring temperature and therefore increasing the partial gas pressure. An advantage of the liquid-ring design is the ability to handle large amounts of condensable vapors. The condensing effect enhances the actual pump capacity dramatically when handling saturated gas mixtures.
The compression process is considered nearly isothermal, because the majority of heat is absorbed by and discharged with the service liquid.
Compression ratios are fixed by the distance the impeller travels from the inlet to the discharge. Some single-stage liquid-ring designs can compress the gas to 1 inch of mercury absolute (HgA), while others with a shorter compression stroke blank off at 5 inches of HgA. Single-stage LRVPs with variable discharge ports are available for compression optimization across the entire vacuum range. Two-stage LRVPs use two impellers in sequence to achieve 1 inch HgA performance with the additional advantage of a lower cavitation point.
LRVPs are widely employed in the industry because of their high tolerance of liquid and solid carryover without compromising the pumps' mechanical integrity or efficiency. Whether gas streams are dirty, wet, corrosive, erosive or even potentially explosive -- situations that can cause catastrophic failure in other pumps -- the liquid ring handles the severest challenges.
Liquid-ring pumps are steady performers year in and year out. Unlike other types of vacuum pumps and compressors, liquid-ring machines don't need to be rebuilt or replaced on a regular basis. The ingenious design certainly contributes to this, since the pump has only one moving part, and there is no metal-to-metal contact between the impeller and the casing, making the pump wear-free. No internal lubrication is needed (grease-lubricated bearings are mounted external to the pumping chamber), and the pump runs at low operating temperature and speed.
Low maintenance is another significant advantage of pump design and manufacture. In general, borescope and capacity tests can be applied every five years of operation or as necessary.
The LRVP results in optimal reliability, productivity and return on investment in each application.
For more information, visit www. dekkervacuum.com or call (888) 925-5444.
