Tank farm pump
Tank farm pumps are submersible pumps which are used in tank farms for transporting liquid raw, intermediate and finished products in chemical and petrochemical plants as well as in refineries. Plant operators select the type of pump depending on the required operating data and on whether the fluid to be pumped is highly volatile, flammable or toxic.
Types of pump
- Horizontal single-stage or multistage pump
- Single or double suction pump (see Double-suction pump)
- Close-coupled pump in in-line design, see In-line pump
- Canned motor pump (see Wet rotor motor)
- Vertical submersible pump such as a vertical shaft submersible pump, seeFig. 2Vertical shaft submersible pump
In many cases, a specific type of pump is required to comply with the applicable national regulations. According to the regulations of some countries, for example, pumps for tanks containing flammable or toxic fluids must be either submersible pumps with a sealed passage of the pump shaft (see Shaft seal) out of the tank, self-priming pumps arranged on the tank, or submersible motor pumps.
For pumping highly volatile and flammable liquids ductile materials such as steel and nodular cast iron (see Material selection) are recommended for safety reasons and to prevent corrosion. With the exception of submersible pumps with a separate discharge line (see Pump system) whose shaft seal is not in contact with the fluid handled, pumps with conventional drives are generally fitted with mechanical seals. Submersible pumps are usually designed so they can be inserted into standardised manholes with the footplate of the pump covering the manhole.
The use of submersible pumps becomes problematic when the tank height requires large installation depths. This makes the maintenance of such pumps rather difficult as transportable lifting equipment is required for pulling out the pump. It can also lead to problems in the case of several product-lubricated intermediate bearings (see Plain bearing), low fluid levels and intermittent operation if the fluid pumped is very aggressive or tends to crystallise (e. g. sodium hydroxide and potassium hydroxide).
For pumping melts or highly viscous fluids (see Viscosity) tank farm pumps are often fitted with a heating jacket to keep the fluid within the pump in a pumpable condition. Liquefied gas tank farms require a special pump design (see Liquefied gas pump).