A tank is simply a piece of equipment used to store liquids, gasses or mixtures of the two. A liquid or liquid/gas tank is generally larger in vertical cross section than in horizontal to make it easier to retrieve just one phase. This is known as vertical placement. Gas tanks are generally of the opposite proportions, and are known as horizontal tanks. Tanks may be used as a source for a unit operation and have only an out flow stream. They may be used to store a final product and only have an input stream. They may also be used as an overflow reservoir between two unit operations and have both an input and output stream. In this case it is generally advisable to size an overflow reservoir to be half full after five minutes of full input with no output, starting with an empty tank.
The basic schematic of several tanks are shown below:
