Conventional pumps using external electric motors, mechanical seals and conventional lubrication oil (or grease systems) have created reliability, safety and operational challenges for downstream units, refineries, and chemical and petrochemical facilities. In some applications, they are employed in a “1+1” configuration—one operating and another on standby—because of maintenance concerns. These challenges have caused some to consider other options for modern pumping systems in today’s plants and facilities. Modern submerged electric motor pumps can be an alternative to these conventional pumps. In a submerged electric motor pump, the pump and electric motor are mounted on a common shaft and the combined unit is submerged in the pumped liquid. At first glance, it may seem unsafe or unreliable to submerge the electric motor with the pumped liquid, which could be flammable or explosive. However, this arrangement is both safe and reliable. Conventional centrifugal pump units couple a pump casing to an external electric motor. This conventional pump should have a shaft seal—often two seals—to allow the shaft to extend outside of the pump casing. Seals are susceptible to failure. Risks and operational problems can result from an external pump concept, the pump seals, leaking the pumped liquid to the atmosphere and conventional lubrication systems. These issues can cause unscheduled shutdowns and serious safety issues. For many services and pumped liquids, a good method for safe pumping is to completely submerge the combined pump and electric motor in the pumped liquid. The unit is then isolated from air; motor gaps and voids are filled with the pumped liquid; and the need for seals and couplings is eliminated. The system is intrinsically safe and reliable. Submerged electric motor pumps are used in a wide range of midstream and downstream applications.
This equipment can be a good alternative to conventional centrifugal pump units.
Rotating Machinery Consultant
05/03/2017