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Issue 209 September 2022 - LNG Issue
Gasworld US Edition, Vol 60, No 09 (September) - Equipment Issue
By Anthony Wright 2022-08-22T11:36:00+01:00
Used to generate industrial gases onsite, pressure swing adsorption (PSA) plants are an alternative to more traditional cryogenic air separation processes. Considered advantageous when it comes to producing smaller volumes of oxygen, PSA has seen increased uptake over the past two years for medical oxygen production as healthcare facilities across the world look to adopt PSA technology to treat patients suffering from Covid-19.
During the pandemic industrial gas producers in low- and middle-income countries (LMICs) ramped up their medical oxygen production capacity to treat those who required oxygen treatment.
By installing PSA systems at hospitals, countries with low medical oxygen capacities such as India were able to mitigate shortages and supply chain concerns associated with liquid oxygen storage and transport. In doing so, life-saving oxygen was supplied in larger quantities to those who needed it most.
With the outbreak of Covid-19 exposing the chronic nature of the country’s oxygen shortages, India has sought to ensure that oxygen is far more readily available. By hiking up its medical oxygen production rate, the Indian Government has funded more than a thousand new plants that are currently producing 1,750 metric tonnes of oxygen every day.
In addition to oxygen production, PSA systems come imbued with a range of other potential applications. The PSA process can be utilised to generate high purity nitrogen gas from compressed air, remove carbon dioxide (CO2) when synthesising hydrogen, and it can even be used to remove CO2 from biogas to make biomethane, a process known as biogas upgrading.
The process essentially involves separating gases through the pressure swing adsorption process. Adsorption is when a substance is separated from a particular phase – in this instance oxygen in its gaseous phase – before it accumulates or concentrates at the surface of another.
Adsorption is enabled using certain materials such as zeolite, a highly porous material with a large specific surface area. Zeolite, often a major component of molecular sieve, separates gas molecules, allowing the collection and concentration of high purity oxygen.
When used to generate medical oxygen, the process involves two vessels, each one containing a zeolite molecular sieve as an adsorber. Compressed air passes through one adsorber, at which point the sieve selectively adsorbs the nitrogen and the other various component gases, allowing oxygen and argon to pass through.
An inlet airflow is then switched to the second adsorber once the first adsorber becomes saturated with nitrogen. The first adsorber regenerates by desorbing nitrogen through depressurisation and purging with some of the product oxygen. This process is repeated while the pressure continually swings between a higher level to allow adsorption and a lower level to allow desorption.
US-based gas generation company AirSep – the commercial division of CAIRE Inc. (CAIRE) – uses such a process to produce onsite oxygen and nitrogen to commercial services across the globe. The company offers a range of solutions from standard generators delivering five litres per minute (LPM) to custom-built, large-scale industrial PSA oxygen systems.
In addition to providing oxygen to hospitals and healthcare facilities, the systems are commonly used in aquaculture, ozone generation, wastewater treatment, gold leaching, and oxygen lancing/decarbonisation.
Speaking to gasworld about the company’s oxygen delivery services, Lawrence J. Hughes, VP/GM at AirSep, stated that the advantages of its systems include the ability to produce oxygen on demand.
“This minimises a user’s dependency on costly and cumbersome liquid or cylinder oxygen equipment. There is a long-term price stability and the cost/ccf decrease as usage increases.”
“PSA system users eliminate concerns about losing product due to venting, contractual increases, hidden costs, or lost deliveries.”
There are also significant benefits when it comes to reducing the environmental impact of industrial gas generation. According to Hughes, PSA technologies reduce operating costs up to 60% and eliminate the need for heavy truck transport for delivery of oxygen cylinders, reducing emissions and the risk of injury when handling heavy containers.
PSA systems also eliminate the storage requirements of high quantities of combustive gases that are under pressure or in liquid cryogenic form, further enhancing safety.
Innovations spawned from PSA technology include double-stage PSA (DS-PSA), a variant developed for use in laboratory nitrogen generators. As its name suggests, after the air is passed through a carbon molecular sieve to produce pure nitrogen, the step is repeated and nitrogen is passed into a second sieve, allowing the nitrogen gas to reach a final purity up to 99.999%.
“The presence of DS-PSA technology-based systems for the generation of ultra-high purity oxygen should also develop greatly in applications specifically requiring high levels of oxygen purity.”
When used for increasing oxygen concentration, a carbon-based molecular sieve absorbs the residual nitrogen left over from the first adsorption in a reverse cycle, concentrating oxygen up to 99%.
“The presence of DS-PSA technology-based systems for the generation of ultra-high purity oxygen should also develop greatly in applications specifically requiring high levels of oxygen purity,” commented Valerie Bokobza, Marketing Director, NOVAIR.
Speaking about the DS-PSA services offered by NOVAIR, Bokobza said, “An exclusive patented new technology developed at NOVAIR, and based on the double-stage PSA onsite oxygen generation process, now makes it possible to produce outputs of up to 99.5% pure oxygen with exceptional stability.”
Traditionally using a ‘twin-tower’ approach, NOVAIR also offers modular PSA generators featuring multiple modules of molecular sieves, each implementing an optimised patented PSA process. According to Bokobza, production capacity can be easily adjusted onsite by simply adding or removing modules.
Another method, vacuum swing adsorption (VSA) uses a vacuum instead of pressure draw gas through the separation process. Operating at near-ambient temperatures and pressures, VSA separates gases from a gaseous mixture before swinging to a vacuum – generated by a blower – to regenerate the adsorbent material.
Used mostly in portable oxygen concentrators, rapid pressure swing adsorption (RPSA) works by rapidly cycling the pressure while alternately venting opposite ends of the column at the same rate. This process allows for non-adsorbed gases to get pushed through the column at a faster rate.
In 2016, medical technology special GCE Healthcare (GCE) announced the launch of its pioneering portable oxygen therapy device, Zen-O Lite. A lighter weight alternative to its existing Zen-O range of POC’s, the Lite version aimed to reduce both weight and noise of portable oxygen solutions.
Weighing in at just 2.5kg, the POC allows users greater mobility for supplemental oxygen therapy. Delivering oxygen on demand at an output of 1,050ml per minute, the device automatically responds to a patient’s breath rate. If a patient carrying the concentrator begins exerting themselves and requires more oxygen, the device detects this and automatically increases the amount delivered to ensure optimal oxygen levels.
By enabling the localised production of onsite medical oxygen, PSA systems were found to be invaluable during the Covid-19 pandemic, especially in low and middle-income (LMIC) countries. Coordinated by NGOs across the globe, thousands of systems were delivered to healthcare facilities directly affected by oxygen shortages and supply chain issues.
Stating that demand for NOVAIR solutions increased ‘massively’ during the pandemic, Bokobza added that its systems were shipped all over the world. “In some regions strong affected by the pandemic, the traditional sources of oxygen, liquid or bottled, were not responding to the tremendous need, mostly due to the heavy logistics required for them,” she said.
“Onsite solutions have proven to be the smartest and most appropriate choice. Hundreds of PSA oxygen generators have recently been installed, providing long-lasting autonomy to numerous healthcare facilities worldwide.”
Following Russia’s invasion of Ukraine earlier this year, supply chains were massively impacted, causing a dearth in medical oxygen supplies and concerns over shortages. In February, the World Health Organisation (WHO) released a warning stating that the country was running ‘dangerously low’ on its supplies of medical oxygen.
Essential for treating and range of common conditions such as pneumonia, sepsis and COPD to pregnancy complications and childbirth, oxygen shortages were compounded by a scarcity of zeolite.
According to gasworld’s Business Intelligence department, Ukraine’s medical oxygen demand more than doubled during the pandemic, increasing from between 140–150 metric tonnes per day to 350–380 metric tonnes per day. To help satiate the country’s need for oxygen NOVAIR responded by sending several containerised medical oxygen plants from its factories in France to healthcare facilities in Ukraine.
Having had a close relationship with its Ukraine distributors throughout the years, CAIRE and its AirSep division has continued its communication with the country, which it admits has been challenging.
“Today, communications with our contacts have been challenging as the country feels the impact of the conflict and upheaval,” said Hughes. “We have been in contact with global medical aid organisations and other entities working to provide oxygen equipment in war zones.”
In these volatile environments, AirSep opts for its self-contained PSA oxygen generators such as its Reliant and Centric products, of which 220 V versions – available for export only – are used primarily for medical oxygen supply.
In addition to helping improve the quality of life for ourselves, PSA technology could help improve the quality of life for our planet. With the consensus that CO2 produced from fossil fuel usage is the main cause of global warming now widely accepted, many technologies have been developed in recent years to separate and recover CO2 by capturing and/or storing it.
Carbon capture and storage (CCS) and its utilisation form (CCUS) enables the capture of harmful emissions through pre and post-combustion and oxyfuel methods, including techniques such as the use of liquid solvents (or chemical absorption) to separate CO2 from the flue gas of industrial processes before capture and direct air capture (DAC) which captures the gas directly from the atmosphere.
Ongoing research has shown that PSA has strong potential for both pre and post-combustion carbon capture. Researchers from the Norwegian University of Science and Technology tested different adsorbent materials and process configurations to evaluate the efficacy of integrating PSA for post-combustion processes in power plants. Although deemed potentially suitable for retrofitting old plants and having not encountered ‘significant’ issues, the team found that feasibility could be impacted by the excessively large footprint of the separation unit.
For pre-combustion, the team discovered that PSA presents a promising alternative. According to the research, the performance, in terms of CO2 separation, energy efficiency, and footprint of the technology, revealed results ‘slightly lower’ than that of a plant using absorption as a CO2 capture method, indicating an immature technology with a window for future improvements.
PSA has also been explored by space agencies to help purify the spacecraft cabin air of the International Space Station (ISS). Onboard, the system enriches and recovers the CO2 to make it suitable for use in a Sabatier reactor, which converts a mixture of CO2 and hydrogen into methane and water.
The two-stage system concentrates metabolic CO2 from about 0.2667 vol% to about 40 to 60 vol% in Stage 1, with Stage 2 further enriching the CO2 product up to >97 vol% CO2, recovering at least 95% of it. This is equivalent to removing 4kg of CO2 per day.
By continuing to invest in and scale up technology that utilises PSA as its core process, industry could continue to improve the lives of countless patients requiring oxygen treatment, in addition to helping pioneer nascent technologies in carbon capture and the purification of air within spacecrafts and spacesuits.
As Covid-19 cases continue to increase across the globe, advanced gas process system manufacturer Oxair is offering its oxygen pressure swing adsorption (PSA) to those who need a continuous oxygen supply.
A potential worldwide shortage of medical oxygen supplies due to the coronavirus pandemic could be alleviated by installing Pressure Swing Adsorption (PSA) systems in healthcare facilities, says Oxair.
PKU Pioneer has revealed that it is to build the world’s largest PSA-CO (carbon monoxide) plant to serve a 400,000 tonnes per annum ethylene glycol plant, which is using the by-product coke oven crude gas from a project of the Xinjiang Guanghui Coke Cleaning and Refinery Co. Ltd.
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