Comparison of VSA To PSA
The simplicity of the VSA process may allow for greater efficiency and cost savings, and less maintenance than PSA systems. The VSA process operates on the steepest part of the isotherm curves and thus has the potential to extract maximum sieve and power efficiencies. The integrated rotary lobe blower, which also serves as a vacuum regenerator, results in low feed pressure. The dramatically lower pressure swings in the VSA system eliminate the need for a feed air compressor, which translates into lower power consumption for VSA systems. As a result, power savings of as much as 50% can be achieved, when compared to the most simple PSA systems. However, VPSA systems typically have comparable or better power efficiencies.
The low pressure air input into the adsorber vessel in combination with the high efficiency of the vacuum applied during the desorption stage means that a single absorption vessel may be used. In contrast to traditional PSA systems, which require feed air compressors as well as process valves and associated dryers and feed air filtering systems, this single-vessel VSA system eliminates many of the design problems associated with two-bed PSA.
Maintenance issues typically associated with two-bed PSA systems are greatly reduced with VSA technology. VSA systems are less susceptible to sieve dusting because the pressure swings are of a lower order of magnitude. These lower operating pressures also eliminate any water condensate. Overall, VSAs are not as susceptible to humid environments as PSA systems, while PSA feed compressors require water removal hardware, and oil-removal hardware if an oil-lubricated compressor is used. Oil-less compressors are available, but are typically higher priced than oil-lubricated compressors. The above-mentioned rotary lobe blower is a rotary device that does not require the high level of routine maintenance typical of air compression systems. The use of a vacuum step provides a superior regeneration of the molecular sieve, thus extending sieve life. Overall, the VSA adsorber vessel has much longer service life than two-bed PSA vessels, which commonly need re-packing of sieve material every 3–5 years.
Read more about this topic: Vacuum Swing Adsorption
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