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Encyclopedia of Marine and Energy Technology

Membrane type Nitrogen Generator System


Built in Japan at the Namura yard, the methanol carrier MILLENNIUM EXPLORER is equipped with the world largest ship-based nitrogen generator system. Designed by Permea Maritime Protection, the system is based on membrane technology, utilizing patented PRISMR membrane hollow fibres. The nitrogen is used to protect the methanol cargo during sea voyages as well as during cargo discharge operations.

With a rated capacity of 6250 m3/h, the nitrogen generator is about three times bigger than the previous largest one delivered by Permea. The system can produce 95% nitrogen purity and comprises feed-air compressors, a valve and control skid, a pre-treatment skid, and membrane skids.

Within the system, there are six oil-lubricated, water-cooled screw type feed-air compressors, supplied by Tamrotor of Finland, each with a 3-phase 363kW/440V motor. The compressors weight 4700kg each, measure 3100 x 1700 x 2200mm, and have been equipped with a special canopy to reduce the noise level down to approximately 80Dba.

Two compressed air filters, manufactured by Parker Hanifine, incorporate three filters in series, and each unit provides 50% of the system capacity. Elmess of Germany has supplied the two 40kW rated, stainless steel heaters for the compressed air units. The control system for the generator was manufactured by Permea in Norway, while the six membrane skids, each with a capacity of approximately 1065 m3/h of nitrogen were produced by Air Products in USA. The entire system was assembled and delivered from Parma’s plant in Kristiansand, Norway.

The nitrogen produced by PRISMR  systems is extremely dry, with dew points down to –70°C. When used for inert purging and blanketing of chemicals or other cargo, it does not only minimise the risk of explosion and fire, but also prevents degradation of cargo sensitive to oxygen, moisture or combustion by-products. Furthermore, with an ample onboard supply available, nitrogen can be used more extensively, without regard to cylinder supply. One example of such extended use is the purging of cargo lines between pumping of different cargoes, which, often at the expense of safety, is still frequently done with air. Super-dry nitrogen is also ideal as non-freezing, non-corrosive instrument gas, and for drying of void spaces like cofferdams, etc.