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Materials Handling - Liquids and Gasses

Large storage tanks have been in use since ancient times, usually for holding water or liquids such as beer and wine. With the development of an industrial economy the advantages of bulk movement and storage prompted the development of relatively large tanks in a range of industries.

Most notable of these was the coal tar industry, initially based on tar recovered at gas works, and by the 1850s these works were using large metal bodied tanks of relatively modern appearance. When bulk petroleum oil appeared on the scene in the 1880s large tanks were built to store the oil, although most inland movement was in wooden barrels until the 1920s.

Early large tanks did not have domed tops, the top was made up of triangular sections, each made up of several sheets of metal. Domed tank tops appeared in the 1920s and became the norm by the mid 1930s.

Liquids will flow down hill of course, and it was often possible to arrange for the storage tanks to be mounted higher than the plant they supplied. Having said which you still had to pump the liquid into the tank. The earliest pumps were piston types, usually called 'reciprocating' pumps, In the 1930s centrifugal rotary pumps were developed but these run into difficulties when the flow becomes intermittent such as when a tank is emptying. If the fluid flow breaks up with air or a vacuum forming you get fluid on one side of the turbine and not on the other. This throws it out of balance which can destroy the bearings. Also the pump will over-speed if it starts pulling air or a vacuum which causes the bearings to over heat. Even on modern oil tankers the centrifugal pumps are shut down as the tank level drops and the final 'stripping' is done with steam powered reciprocating pumps.

In the oil industry a lot of gasses are produced which are stored in pressurised tanks. The spherical pressurised tank was developed in the later 1930s and by the time of the second world war there were a few quite large examples in use, mainly associated with fertiliser factories where they held ammonia. They only became common after the war however and in the 1970s concrete replaced petal plates as the most common method of construction.

Spherical tanks stand on stubby legs, on metal types these were often grouped under the tank, reaching up perhaps a quarter of side of the tank, The concrete types are supported closer to the 'equator' of the tank. Similar tanks are seen at petrochemical installations and the only difficulty in modelling them is in finding a smooth ball of suitable size. Small tanks of this type would need to be about two inches (50mm) in diameter, larger concrete tanks used in LPG installations since the 1970s could be up to eight inches (200mm) in diameter.

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