The chemical gases are the gases produced chemically and are defined in IMO's rules as condensed gases. Because of the gases' boiling point at atmospheric pressure and special requirements for temperature control, these gases must be carried on gas carriers as specified by the IMO gas code. Condensed gases are liquids with a vapour pressure above 2,8 bars at 37,8oC. Chemical gases that are mostly transported are Ethylene, Propylene, butadiene and VCM. Chemical gases that have to be transported by gas carriers are those mentioned in chapter 19 in IMO IGC code. There are, at all times, stringent demands for low oxygen content in the cargo tank atmosphere, often below 0,2% by volume. This involves that we have to use nitrogen to purge out air from the cargo compartment before loading those products.

In addition, even though the vapour pressure does not exceed 2,8 bars at 37,8 deg C such as, ethylene oxide and propylene oxide or a mixture of these, they are still in the IMO gas code as condensed gases. Gas carriers that are allowed to transport ethylene oxide or propylene oxide must be specially certified for this. Ethylene oxide and propylene oxide have a boiling point at atmospheric pressure of respectively 11oC and 34oC and are therefore difficult to transport on tankers without indirect cargo cooling plants. Ethylene oxide and propylene oxide can not be exposed to high temperature and can therefore not be compressed in a direct cargo cooling plant. Ethylene oxide must be transported on gas tanker type 1G.

Chemical gases like propylene, butadiene and VCM are transported with medium-sized atmospheric pressure tankers from 12000 m3 to 56000 m3. Semi-pressurised gas carriers are also used in chemical gas trade and then in smaller quantity as from 2500 m3 to 15000 m3.

Chemical gases are transported all over the world, and especially to the Far East where there is a large growth in the petro-chemical industry. Chemical gases are mainly utilised in the petro-chemical industry and rubber production.

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