Brian Wildey, Soeren Schmitz and Tom Saari discuss the rise of onsite oxygen generation as a reliable and cost-effective solution for the high demands of the medical market.

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).

In the 1970s Pressure Swing Adsorption (PSA) to produce oxygen was commercialized. Operating at atmospheric temperature, nitrogen is adsorbed using a molecular sieve material. PSA systems utilize commonly available components, that greatly reduces the CAPEX. Because the oxygen is generated onsite there is no delivery cost. However, the power consumption is very high, resulting in a high OPEX.

The other consideration is that the PSA process produces oxygen at a purity of 93 +/-3 percent so the process can only be used for applications that do not need the higher purity oxygen produced by the cryogenic process.

Further, sub-optimal delivered oxygen cost limits the penetration of PSA systems to small requirements such as homecare oxygen therapy.

Onsite gas generation,PCI,Oxygen

Source: PCI

Fig 1

To lower the operating costs, several companies developed a variant of the PSA process that uses a vacuum cycle rather than high pressure. This significantly lowers the operating cost, but at the expense of a higher capital cost as it requires larger adsorber beds and a separate air blower and vacuum pump. This variant is known as VPSA.

In 2001 PCI was asked by the US Military to supply an oxygen generator to meet the needs of its field hospitals in the Gulf War. Their requirement was for a systemthatwas easily deployable, robust, simple to operate and with low operating and maintenance costs.

To meet this requirement PCI developed the Expeditionary Deployable Oxygen Concentration System (EDOCS 120 superseded by the EDOCS 120B) which is shown in Fig 1 (above, right).

Besides generating oxygen, the Expeditionary Deployable Oxygen Concentration System (EDOCS 120) has the capability to fill cylinders and also has a built-in cylinder bank. Therefore, with these capabilities, the EDOCS 120 ensures the hospitals always get the oxygen they need including those needs for peak requirements and during times when the generator was down for power failure and/or maintenance. These units have now been used by the US military for over 10 years.

PCI DOCS 200,onsite gas generation

Fig 2

In 2007, PCI recognized that there was a market need for a line of commercial oxygen generators that from a market perspective would fit between the PSA and VPSA systems (Fig 2, right). Maintaining the concept of a simple design that has low operating and maintenance costs, the Deployable Oxygen Concentration System (DOCS) design evolved. The DOCS 200, shown in Fig 2, 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 LP, 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 in the following references [1][2].

By utilizing VFD drives on both the air blower and the oxygen compressor, the DOCS efficiently adjust the production to match the end-user process needs. Fig 3 shows the typical turndown performance. This is very important for hospital supply systems as the oxygen requirement varies greatly through any 24-hour period.

PCI Chart SGR Q3 2012

Source: PCI

Fig 3

Further 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 reducing costs and improving on-stream performance.

PCI’s initial focus for the DOCS was the supply of oxygen to hospitals. It has designed and manufactures three DOCS sizes for medical applications that produce 80, 200 and 500 lpm 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 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 [3][4][5]&[6] have lead 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. The FDA also cleared the DOCS 66, 200 and 500 units for use as a back-up supply for disaster relief, crisis response and ambulatory patient use in the US.

In 2010, the Europe Community issued an Oxygen 93 monograph allowing non-cryogenic generated oxygen to be used in hospitals. Further, to ensure that the patient’s safety and wellbeing cannot be compromised, it added limits to the allowable concentrations for SO2 and oil.

With these two major health bodies accepting the use of oxygen in the range of 90 percent to 96 percent in hospitals, it will only be a matter of time before other MoH organizations around the world will follow suit.

An ISO standard that recommends the required system for an onsite oxygen supply for hospitals - ISO 10083 (oxygen concentrators for use with medical gas pipeline systems) - has been published. 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 this varying need. In many cases the peak requirement may be three to four times the average 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. The second source can be another generator, vaporized LOX or a cylinder bank. The third source must be a dual cylinder bank with automatic switching between the banks.

With a DOCS system PCI can provide a cylinder filling compressor that can refill all the 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. Fig 4 shows an example of such a system.

PCI Chart SGR Q3 2012

Source: PCI

Fig 4



No two hospitals are the same, so it is very important to analyze the oxygen needs before designing the appropriate system. Therefore it can be stated that 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 50 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.

About the author
Brian Wildey is PCI Sales Director.
Soeren Schmitz is PCI Vice-President & General Manager Commercial Oxygen Solutions.
Tom Saari is PCI Manager RA/QC.
Detailed information on PCI and all of its products can be found on the PCI website at: www.pcigases.com

 

References
[1] D. Schneider et al ‘Onsite Oxygen Generation’ CryoGas International August/September 2010
[2] D. Schneider et al ‘PSA v’s VSA’ CryoGas International February 2011
[3] The World Health Organization ‘Informal Consultation on Clinical Use of Oxygen’ Meeting report October 2/3, 2003
[4] M. B. Dobson et al ‘Oxygen Concentrators and Cylinders’ Int J Tuberc Lung Dis 5 (6): 520-523
[5] R. M. Friesen et al ‘Oxygen Concentrators: A primary Oxygen Supply Source’ Can J Anesth 1999,46:12, pp. 1185-1190
[6] L. Walker ‘Effects of Oxygen Concentrators on Ventilator Oxygen Delivery’ Can J Anesth/JCan. Anesth (2010) 57: 708-709