Why does a PSA plant need an oxygen receiver?

In a PSA plant, the oxygen produced in the adsorption towers is supplied to a buffer storage tank connected to the medical gas pipeline, as a USAID RISE operating procedure for PSA plants, written for hospitals in India, describes it. WHO's interim technical specifications for PSA oxygen plants (8 June 2020, superseded by WHO's technical specifications of 31 December 2024) listed an oxygen tank (receiver or buffer tank) with a bacterial outlet filter among the plant components, and WHO's Foundations of medical oxygen systems (2023) shows a product or buffer tank, followed by a bacteria or sterile filter and the oxygen analyser, in its typical PSA configuration. The PATH and CHAI brief on PSA plants (July 2021) notes that, depending on the manufacturer's recommendations, a compressed air surge tank and/or an oxygen receiver tank may be required.

How the buffer is sized

AIGA 113/20, the Asia Industrial Gases Association edition of EIGA Doc 195 on on-site oxygen 93, sets criteria rather than a volume:

• Demand variation: the buffer capacity is designed to take account of the variations in pipeline demand at the output of the concentrator unit.
• Short-term peaks: the buffer is designed and sized to take account of short-term consumption peaks.
• Start-up of a standby unit: where a concentrator unit is the secondary source, the duration of its start-up is taken into account in sizing its buffer, which must be able to supply the nominal flow rate at the required pressure throughout the start-up, the worst case being considered.
• No reserve at changeover: it is not acceptable to use the reserve source of supply when switching from the primary source to the secondary source or back.

The same document asks for the oxygen buffer to have a pressure relief valve and a means of purging. For the capacity of the supply system as a whole, it lists current average demand, daily activities, consumption peaks and future requirements, such as extensions or new activities.

Operating with the receiver

In the USAID start-up procedure, the receiver's inlet and outlet valves are kept closed at first. Once the oxygen pressure exceeds 4.2 bar and the display shows a purity of 93% ± 3%, the operator waits 5 minutes and then fully opens the receiver outlet valve if the plant is connected to the hospital pipeline. The daily inspection includes the oxygen pressure in the air receiver tank, the adsorption towers and the oxygen buffer tank, and a pressure relief valve is fitted in all the pressure vessels.

ULTRAOX plants include one or more air tanks and one or more oxygen tanks in their basic configuration, according to the ULTRAOX SC and ULTRAOX ST datasheets. The ULTRAOX 2022 datasheet describes a vertical oxygen storage tank with a medical grade oxygen coating, an oxygen safety valve and a calibrated and certified pressure gauge, and lists a high efficiency particulate filter for medical oxygen among the oxygen filters. The plant starts and stops oxygen production automatically in response to demand from the downstream distribution system.