Pumps and NPSH: Avoid problems and improve reliability
- Process Consulting Services Inc., Grapevine, TX (United States)
Process engineers routinely specify and check pumps even though their understanding of the subject is often rudimentary compared to a machinery specialist. In the standard process plant, machinery specialists (if any) usually focus on the delicate, expensive and critical equipment: typically compressors, expanders, centrifuges, rotary driers, etc. Hence, despite the process engineer`s lack of appropriate knowledge and experience, the pump specification often goes directly to the pump vendor without the information required to select proper equipment. Proper equipment specification refers to more than the simple volume and head requirements of the service. Reliability, onstream time, maintenance manpower, maintenance cost and safety can be compromised by not understanding the criteria for pump selection. The most commonly used pump type in process plants is the centrifugal. Criteria vital for proper centrifugal pump selection include net positive suction head (NPSH) available, flowrates, fluid properties, head required, pump performance characteristics and variability in each of these areas. Process engineers understand that the interaction between suction specific speed and seal thermodynamics; pump reliability; and the impact of process variability from fluid flowrates, properties, and conditions (to mention a few items) may be outside their expertise. Here, they should solicit advice from a competent mechanical consultant. Misunderstanding even an apparently simple concept such as NPSH can often lead to unfortunate consequences. The paper uses two examples to illustrate these concepts: a primary fractioner overhead drum and solvent recovery system.
- OSTI ID:
- 231168
- Journal Information:
- Hydrocarbon Processing, Vol. 75, Issue 5; Other Information: PBD: May 1996
- Country of Publication:
- United States
- Language:
- English
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