In the world of air gas production, capacities and product purities are increasing while plants are getting smaller and smaller all the time. Though this trend may be an observation of air separation plants (ASUs) and large-scale production, there is undoubtedly an intrinsic link to the proliferation of pressure swing adsorption (PSA) technologies.
PSA plants are on the rise, globally. Capable of producing gases in the range of 90-96% purity and generally boasting more mobility and lower energy intensity, these systems are often the most cost-effective means of production for smaller scale applications or ‘pop-up’ uses such as in mobile military medical services.
PSA processes are based upon the static separation of ambient air – comprised of 21% oxygen, 78% nitrogen and just under 1% of argon – via a given adsorbent capable of extracting a target gas at high pressure. As a general rule, the higher the pressure, the more gas is adsorbed; when that pressure is reduced, the gas is desorbed (released).
Different surfaces are more adept at attracting different gases, meaning target-rich gases can be attained by selecting the most suitable material – and differences in properties such as molecular structure, size and mass are exploited to achieve the desired degree of product purity. Carbon Molecular Sieve technology, for example, separates nitrogen and oxygen and is able to adsorb oxygen under pressure and allow nitrogen to pass through as the product. Oxygen concentrators are mainly comprised of two separation vessels – zeolites – filled with molecular sieve absorbers that essentially retain nitrogen and release oxygen straight to the generator outlet. Exercising two adsorbent vessels warrants almost permanent production of the target gas.
The content of oxygen produced by PSA concentrators has typically been between 94-96% purity, though advanced versions of PSA technology feature a double-stage separation process and are capable of oxygen purities of 99-99.5%. For nitrogen, purity of 98% is generally attainable, while double-state separation can achieve a final product purity of up to 99.999%. All the while, these small plants are capable of delivering supply of up to 25 tonnes per day (tpd).
It is PSA’s inherent advantage in flexibility and scale that is driving increasing uptake of such plants across a range of end-user applications.
One of the foremost applications for PSA plants is in the medical field, where PSA oxygen generation is fast growing as an alternative to centrally produced and distributed oxygen. This has been particularly prevalent in the last 20 years and with an undoubted need for oxygen in healthcare, it will likely be sustained.
PSA systems offer the kind of mobility that addresses the varying requirements of the hospital and healthcare sector, while ever-squeezing margins in healthcare sectors are driving interest in this cost-effective means of medical oxygen generation and its proliferation has been facilitated by ‘monographs’ that deem the use of oxygen in the range of 90-96% purity acceptable.
Introducing a PSA generating system can represent significant savings and in most cases, pay-back time is expected to be 6 months to two years, gasworld understands. Such is the significance of PSA gas generation in the medical sector that Danish PSA manufacturer Oxymat A/S had more than 3,300 installations in operation worldwide as of mid-2015, and around 25% of these were in medical applications.
Such numbers are thought to be increasing in Europe following the passing of the Oxygen 93 Monograph in 2011, a major market evolution that gave official recognition for medical oxygen produced by on-site concentrators to become an accepted alternative to traditional methods of supply – and ultimately paved the way for greater autonomy in the region’s healthcare sector, and significant demand for PSA technologies. Despite this, the potential for PSA systems in Europe is still thought to be far from realised; the introduction of a PSA oxygen generator in the hospitals of more established economies involves changing long-standing consumption habits.
In developing countries however, where compressed cylinder of bulk cryogenic supply is not always feasible, PSA technology is vital to ensuring that hospitals and healthcare services get the oxygen they need. As the oxygen is produced onsite, without delivery and storage, medical oxygen generators have convinced many medical facilities in North America, Africa, Middle East, and Asia that this means is the way forward.
Oxymat had more than 230 installations of medical oxygen in the Middle East alone last year, and expects more to come as expected growth – and population – rates in the region are attained. The company is also known to have been tapping into the large potential market in the South East Asian healthcare sector in recent years.
We also see many other examples of PSA technologies in play in the medical markets of developing countries, with the Indian Government understood to be seriously looking at establishing such systems in its health institutions and the state of Himachal Pradesh in particular considering the installation of oxygen generators at all of its hospitals. And last year in China, local news reported that the first PSA unit for oxygen generation had been installed in an ambulance in the country and put into service. The system was specifically designed for an ambulance from a Shanghai hospital, with the aim to replace the use of oxygen cylinders in ambulances as either traffic issues or long distance journeys could lead to tragedy at present.
Uptake of PSA-based air gas generation is on the rise across a range of other applications, with food and beverages, pulp and paper, and manufacturing operations known to be adopting these systems.
Linde Gases announced in November (2015) that it was providing its PSA-based ECOVARTM range of plants to two companies in Finland’s pulp and paper industry, one primarily for the supply of nitrogen and the other for the supply of oxygen. Meanwhile, this summer the Turkish branch of The Linde Group – Linde Gaz A.S. – signed a deal to supply an onsite nitrogen PSA plant to a commercial air springs manufacturer in the country, with the system set for start-up at the end of 2016.
PSA is on the move in Japan’s food and beverages business too. Earlier this year, The Gas Review reported that the food industry is becoming a major platform for small-scale onsite gas generation as the quality and control of food freshness places growing demand on nitrogen and oxygen supply, while small levels of carbon dioxide consumption are being used in the extermination of harmful insects in strawberry plants – PSA generators and membrane separators more than adequate to meet demand.
It was also noted this summer that the number of nitrogen filled containers sailing across the Pacific Ocean has increased recently, with the sustainability of fresh fruit and vegetables during shipping processes becoming a hot topic in Japan. Shipping services using controlled atmosphere (CA) containers, which are filled with N2, are becoming more popular in the country, with PSA system demand rising as a result. In Aomori and Nagano for example, which are famous apple producing regions in Japan, apples are currently being stored in warehouses which use nitrogen PSA generators to maintain optimum levels of 90% nitrogen, 5% oxygen, and 5% carbon dioxide in the atmosphere.
With flexibility, mobility, cost benefits and increasing purities in its armoury, PSA gas generation is clearly intensifying as a compelling choice for a growing number of applications and is, quite literally, on the move.