On-Site Gas Production Considerations

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Supply Forms of Technical Gases

Nitrogen and Oxygen can be supplied in general from

  • Bottles and racks with up to 12 pressure cylindres of max. 50 L/300 bar
  • Cryogenic Tanks with up to 50.000 litres capacity
  • On-Site production plant (Air Processing Systems)
  • Combinations of these

Each of these alternatives have their specific advantages and disadvantages.

Major Decision Criteria

Pressure Cylinders are very compact, easy to handle and suitable for frequent use of small gas quantities of one or more required gas purities. But bottles are not recommended for higher consumption due to the highest cost per volume ratio of the gas compared with the other above alternatives.

Cryongenic tanks are the best choice when a high gas purity and a huge consumption are required at the same time. When the consumption is dropping or only frequent this supply form has reduced efficiency as the tank pressure drops due to overpressure release after heating of the gas in the tank by sun radiation.

An on-site production plant for nitrogen, oxygen and mixtures thereof has to be investigated more in detail as there are several criteria to be taken into account to discover the full benefit of such a system.

Considerations of On-Site Generation

Cost of On-Site Gas Production

Due to the specific process parameters cryogenic gas production supplies exclusively high gas purities with an enormous energy consumption. Today energy cost is driving the product cost directly. But very often the high purity of cryogenic nitrogen or oxygen is not needed for the application. Thus there can be a cost advantage when the required gas quality is produced on-site in an energy-saving way from compressed air at a level of e.g. 95 % vol. of nitrogen. A commercial calculation of the different supply forms can help to find out which is the most economic alternative. In general in this criteria there will a slight advantage for the on-site production of nitrogen versus cryogenic nitrogen due to the lower energy cost of the on-site production. The pressure cylindre in this comparison are much more expensive than any on-site production.

Space Requirement and Permissions

A cryogenic tank might not be possible everywhere due to limited space or no permission to install a big vertical tank. On-site production plants can be installed in a flexible arrangement as per customers' requirements also inside buildings and there are usually no limitations for the installation.

Logistic Limitations

Logistic reasons might recommend an on-site generation when a regular supply by truck is complicated and/or expensive due to the location is far from the cryogenic production or difficult to reach by road.

Power Supply Options

A permanent or on demand generation on site can be interesting if there is electric power available from reserve due to over capacities e.g. from solar or wind power plants.

Requirement for Variable Purity

If different gas purities for separate applications are required and suitable this can give an advantage for Nitrogen or Oxygen Generation Systems. On-site production plants are able to supply e.g. 95 % vol. and 99 % vol. of nitrogen purity with different parameter setup of the control system.

Efficient Use of Thermal Heat of Compression

While compressors directly emit approx. 90 % of the electric energy consumption of the motor as waste heat there is a huge potential to use the heat of compression for separate tasks. Thus it might be benefitial to look into an integrated concept of on-site gas production and combined heat recovery and supply to other consumers e.g. heating of the production site or for a certain technical process. So the cost for on-site gas production would be reduced due to improved energy efficiency.