All hydrocarbon processing facilities have storage tanks.
However, water (H2O) can enter during processing and
handling operations such as loading or transportation,
through a leaking roof or by condensation and then
settle to the tank's bottom. Thus, it is necessary to prevent
bottom plate corrosion and product degradation by draining
bottom H2O periodically.
By observing a tank's product and
H2O withdrawal flows, it can be seen that flows may
become stratified if slowed down or if the velocity is limited.
This makes it possible to selectively withdraw products and
H2O with limited-flow velocity through different
outlet pipes. Generally, the product outlet pipe and the
H2O drain pipe are at the lowest shell course and
the tank's bottom, respectively. It may be constructed as in
Fig. 1 or other designs.1