Up until 40 years ago oxygen was only produced commercially by the cryogenic distillation of air. Product was either delivered as gas or a cryogenic liquid (LOX). This cryogenic process is very energy intensive, results in a high operating cost and, by virtue of the very low operating temperatures, uses many special components that are both expensive and costly to maintain. 

Oxygen produced by the cryogenic process is typically produced at greater than 99 percent purity so that it can be used for essentially all applications.

For very small applications oxygen is delivered in cylinders. As the demand increases it is more economical to use vaporized LOX delivered in cryogenic transports to onsite cryogenic storage vessels. For large industrial applications gaseous oxygen is generated onsite.

To optimize the delivered oxygen cost, it is necessary to balance the capital required to build the oxygen generation and delivery equipment (CAPEX) and the operational costs of production and transportation to the use site (OPEX).

Non-cryogenic Pressure Swing Adsorption (PSA) systems, developed in the 1970s, produce oxygen onsite and greatly reduce the CAPEX. However, PSA power consumption is very high resulting in a high OPEX. Further, conventional PSA produces oxygen at a purity of 93 +/-3 percent. As a result, regulatory requirements limited the penetration of PSA systems in the medical market to homecare oxygen therapy.

In 2001, PCI developed the Expeditionary Deployable Oxygen Concentration System (EDOCS) to meet the oxygen needs of the US Military in the Gulf War. For this project PCI developed a system that retained the CAPEX advantages of a PSA with the OPEX advantages of a vacuum swing adsorption (VSA) process. Today, the EDOCS has been in service by the US military for over ten years.

In 2007, PCI recognized that there was a market need for a line of commercial oxygen generators. Maintaining the concept of the EDOCS simple design, the Deployable Oxygen Concentration System (DOCS) evolved. The DOCS 200 produces 200 lpm of 93 +/- 3 percent oxygen at a delivery pressure of up to 100 psig.

The DOCS has several key advantages over the conventional PSA. With a compact single package design and a low pressure, oil free process, the DOCS is simpler and cheaper to install, is more reliable, and has less than half the power consumption and maintenance cost of a PSA. The result is a lower delivered oxygen cost. A detailed comparison between VSA and PSA is provided on the PCI website pcigases.com.

By utilizing Variable Frequency Drives on both the air blower and the oxygen compressor, the DOCS efficiently adjusts production to match end user process needs resulting in additional power savings when the oxygen consumption is less than the capacity of the generator. This is very important for hospital supply systems as the oxygen requirement varies greatly through any 24-hour period.

Additional features of the DOCS include the ability to remotely monitor and control all functions via an internet connection—no special software is required, just a unique IP address. Both of these features reduce the need for plant visits, which reduces costs and improves on-stream performance.

PCI’s initial focus for the DOCS was on the supply of oxygen to hospitals. The company has designed and now manufactures three DOCS sizes for medical applications that produce 4.8, 12, and 30 m3/hr of oxygen. Oxygen is one of the most important drugs in acute hospital care. Unfortunately, over 60 percent of the world’s population does not have a reliable cost effective oxygen supply (from traditional cryogenic sources).

The company has designed and now manufactures three DOCS sizes for medical applications that produce 4.8, 12, and 30 m3/hr of oxygen.

The specification for oxygen allowed to be delivered to hospitals is defined by monographs in Pharmacopeias—USP in the US. Because oxygen had traditionally been delivered from cryogenic sources, the original USP monograph for medical grade oxygen specified that the gas had to have a purity greater than 99 percent.

However, extensive clinical tests performed in Canada and other countries have led to the conclusion that 93 +/- 3 percent oxygen presented no physiological effect on patients. USP 93 oxygen is now acceptable for use in hospitals as a back-up emergency oxygen supply in the US. The US Food and Drug Administration also cleared the DOCS units for use as a back-up supply for disaster relief, crisis response, and for ambulatory patient use in the United States.

In 2010, the European Community issued an Oxygen 93 monograph allowing noncryogenic generated oxygen to be used in hospitals. To ensure that the patient’s safety and well being cannot be compromised, it added limits to the allowable concentrations for sulfur dioxide and oil.

With these two major health bodies accepting the use of oxygen in the range of 90–96 percent in hospitals, it is only a matter of time before other Ministry of Health (MoH) organizations around the world follow suit.

The International Organization for Standardization (ISO) has published a standard that recommends the required system for an onsite oxygen supply for hospitals—ISO 10083 (oxygen concentrators for use with medical gas pipeline systems). Many countries around the world have started using this standard as the blueprint for their own onsite medical oxygen supply system standard.

Oxygen requirements at hospitals vary greatly depending on the needs of operating rooms and intensive care units. As it is imperative that the hospitals always get the oxygen they need, the design of an onsite oxygen system must address varying needs. In many cases the peak requirement may be two to three times the minimum rate. While the DOCS has the capability to adjust its production rate, clearly it cannot meet the requirement when the machine has to be taken down for maintenance or for periods of loss of power. To cover all these eventualities, ISO 10083 recommends two additional redundancies besides a primary generator.

PCI’s DOCS also can provide a cylinder filling compressor that can refill cylinder banks with surplus oxygen production typically at night when the operating rooms are not functioning. With this type of system, the hospital can be made essentially independent of the costs and logistical issues of outside supplies. Figure 1 illustrates such a system.

No two hospitals are the same so it is very important to analyze the oxygen needs before designing the appropriate system. PCI has designed systems for many hospitals. Figure 2 shows system details for a hospital in SE Asia that uses 35,300 m3/month of oxygen. PCI would choose to use two DOCS 500 units and an oxygen booster for filling cylinders to meet this hospital’s oxygen requirements.

Figure 3 shows the projected cumulative costs for the hospital example given in Figure 2 when comparing delivered oxygen costs for 10 years using an ISO 10083 configured system DOCS against oxygen delivered from PSA, vaporized LOX, and cylinder systems. The computation includes capital equipment, depreciation, duties, sales tax, and operating costs of power and maintenance.

As shown in this example, with the right DOCS system design any hospital in the world can have a reliable oxygen supply with a delivered oxygen cost at least 20 percent (and as high as 80 percent) less than from any alternate source.

Besides hospitals there are many other applications that can benefit from a reliable cost effective oxygen supply. Many processes that currently use air as an oxidant can benefit from a conversion to oxygen that improves productivity and/or reduces NOx emissions.

Other potential markets include steel production, oil refining, chemical processing, mineral processing, pulp and paper, glass, ground water remediation, disaster preparedness, military medical, aquaculture, water treatment, oxygen enrichment, and clean energy, and PCI offers larger oxygen generators to meet these needs.