PSA System – O2 generation

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Oxygen injection & monitoring system–H2S REDUCTION

Hydrogen sulphide is formed during the anaerobic digestion of organic material containing sulphur. Its presence significantly reduces the lifetime of pipework, instrumentation, analytical equipment, CHP, blowers, compressors, or even the absorbent material from biogas upgrading processes.

H2S can be removed from biogas using various chemical, physical and biological processes. Air injection with a blower is currently the method used to supply O2 into the different H2S reduction processes, but for sites wishing to upgrade biogas to biomethane, there are several downsides, not least that most upgrading technologies are not able to remove N2 from CH4.

The solution

Using an integrated combination of PSA technology (to create pure O2), highly accurate gas analysis, and mass flow measurement, we overcome the problems of conventional air blowers. Further, the system enjoys low operating costs and is supported throughout the UK with our existing, expert service team.

The specifics

Oxygen generation using VSA and PSA system

PSA system enables the production of pure oxygen from air by selective adsorption of N2 on a special molecular sieve material. As a result, only O2 is injected in the bioprocess for H2S reduction, avoiding biogas dilution with contaminants.

Proprietary O2 injection systems use proportional valves injecting 02 as a function of external process variables such as the H2S content in the raw biogas, raw biogas flow, or even a combination of both.

Oxygen production cost per Nm3 of biogas treated, is extremely low, ranging from £0.0005 to £0.0010. We offer a wide range of O2 injection systems (PSA and VSA) covering anaerobic digestion plant capacities between 20 Nm3/h and 2000 Nm3/h of raw biogas.


  • Safe delivery & independence from external gas suppliers and O2 market price fluctuations
  • Suppression of logistic operations; handling of cylinders, liquid O2, and supply management
  • Modular, flexible, and low maintenance
  • Low power demand; -<0.5 kWh/Nm3 @ 90% O2
  • O2 purity up to 93% (dew point < -50˚C @ 0 barg)
  • Compression up to 8 barg available
  • O2 sensor & output signal for remote monitoring
  • Skid or container mounted for mobility
  • VSA for larger flows and lower power demand


psa system

The summary

One integrated solution, supported throughout the UK

Allison Engineering has a long track record of delivering process solutions, going back to 1979. We support over one hundred and fifty Anaerobic Digestion sites with supply, installation, commissioning and service support with a variety of technical process solutions.

This oxygen injection system gives considerable advantages to AD sites wishing to reduce H2S and deliver gas to the grid. Further, our gas upgrader range offers further benefits.

We welcome the opportunity to discuss your specific application and look forward to hearing from you.