PCI (www.pcigases.com), a Californiabased on-site industrial gas manufacturer, was founded in 1984 to manufacture cryogenic air separation devices for operation in extreme and remote environments. Since then, PCI has continually expanded its technology platforms to include nitrogen membrane systems and Vacuum Swing Adsorption (VSA) oxygen systems. 

This article presents PCI’s VSA oxygen technology and compares it to other forms of oxygen supply in its size class.

Oxygen Technology Comparison 

Within the oxygen requirements of 0.3 to 40 short tons/day (tpd), or 200 K to 25 MM cf/mo in merchant LOX terms, and oxygen purities less than 95 percent, the traditional form of onsite oxygen generation has been the Pressure Swing Adsorption (PSA) system below 20 tpd and double-bed Vacuum Pressure Swing Adsorption (VPSA) systems above 20 tpd. PSA and VPSA systems require a complicated set of valves and twice as much power as VSA systems. Therefore, their total cost of ownership is typically equivalent to or higher than liquid oxygen (LOX) deliveries. Hence, many customers who are presented with the option of PSA systems or LOX supply will choose the latter for reliability purposes. PCI’s Deployable Oxygen Concentrator Systems (DOCS) are designed with a much simpler approach to on-site oxygen supply as they conserve half the power used by PSA systems and significantly reduce maintenance costs. Compared to traditional double-bed VSAs, the single- bed DOCS VSAs reduce capital costs and complexity at a slight trade-off in power efficiency. For customers with requirements typically supplied by LOX, PSAs, or double-bed VSAs between 0.3 and 40 tpd, a DOCS VSA on-site plant in many instances can offer the lowest equivalent cost of oxygen.

While LOX supply costs for a typical customer consuming greater than 2 MM cf/mo may range from $0.30/ccf up to $0.85/ccf depending on distance from an air separation plant (ASU), a VSA on-site plant can be competitive even with LOX users in close proximity. For instance, a customer located close to an ASU with a requirement for 2 MM cf/mo may pay $0.40/ccf and a tank rental charge of $1200/mo. A 10-year discounted cash flow (DCF) model indicates that a customer will typically achieve less than a threeyear payback with a VSA on-site plant. This model assumed a discount rate of 12 percent, standard escalations for energy prices, maintenance costs, and LOX, as well as a 95 percent utilization of the VSA.

In many cases customers have oxygen demands that are variable. Peak oxygen demand can be greater than average demand and the resulting utilization of an on-site plant may be only 60 percent. In this scenario, the economics of LOX typically are more favorable than an on-site system. Deployable Oxygen Concentrator Systems, however, have variable frequency drives that allow linear power turndown of LOX to as low as 25 percent of capacity. Using the same DCF model assumptions in the above example, with the exception that the VSA utilization is 60 percent rather than 95 percent, the payback for a DOCS VSA versus LOX is only slightly longer [than the higher 95 percent utilization case] at less than four years.

Peak oxygen demand can be greater than average demand and the resulting utilization of an on-site plant may be only 60 percent.

Based on the analysis above, LOX customers may be able to achieve a significant savings by considering an on-site VSA solution versus their current LOX supply. Further, customers with variable consumption patterns still may be able to achieve a reasonable payback with significant savings due to the unique turndown capabilities offered by PCI’s DOCS. The Oxygen Supply Map shows where PCI’s DOCS solutions may offer a competitive on-site alternative to typical LOX supplied customers.

VSA Applications 

VSA oxygen production can be used in a range of applications — from producing medical oxygen in hospitals to combustion processes at manufacturing plants.

Government entities and hospitals in the US are becoming more aware of the need to upgrade their disaster preparedness programs, which require that they be self-sufficient for a 72-hour period. This trend is pushing hospitals to take a closer look at onsite oxygen generation for either back-up or as supplemental supply for their medical oxygen. Oxygen for breathing is also used in high altitude environments, like resorts, to supplement low oxygen partial pressures. VSA technology is ideal for this application since PSAs are detrimentally affected by low feed air density at high altitudes.

Drinking water requires the precise application of the oxygen molecule in several parts of a treatment train. VSA on-site generation of oxygen can be used for odor control and to generate ozone for disinfection or remedia- tion. Oxygen also plays an important role in wastewater treatment for aerobic digestion and in aquaculture where the demand for dissolved oxygen in a farm’s body of water rises as the number of aquatic species increases.

High levels of dissolved oxygen are essential to the gold/silver mining industry’s leaching process. Increasing the dissolved oxygen level in gold/silver-bearing slurry enhances the cyanidation process, as well as reduces cyanide and waste treatment costs. VSAs are excellent for this application.

Last but not least, most combustion processes use air as the oxidant. Replacing air with pure oxygen in oxyfuel and oxygenenhanced combustion processes increases thermal efficiency in furnaces and reduces CO2 and NOx emissions. VSA technology can efficiently produce oxygen for these applications.