Chemical Technology August 2015

Pump selection and application guidelines– Part 1 by Neetin Ghaisas, ME, PEng, Director of Design Engineering and Rotating Equipment Group Leader at Fluor Canada, Calgary, Alberta, Canada

A pplication limits stated in this article for American Petroleum Institute (API) and The American Society of Mechanical Engineers (ASME B73) pumps were adopted from Process Industry Practice PIPRECP001. Similarly, some paragraphs in API 610, 10 th Edition, are referenced in the sections on Oil Lubrication and Couplings and Guards. Power recovery turbines and air operated pumps are excluded from the scope of this guideline. Selection and application Centrifugal pumps are widely used in most pumping appli- cations. By selecting appropriate materials of construction, speed, size and using available design configurations, cen- trifugal pumps can be applied in a variety of services includ- ing toxic, carcinogenic, highly corrosive and abrasive fluids. Rotary pumps are chosen for special services such as viscous fluids at fairly constant flowrate and discharge pressure. The pump internals are lubricated by the pumped fluid. Most rotary pumps are self priming and can handle entrained air or gas. In sub-atmospheric suction condi- tions, entrained gases in the fluid expand, affecting pump displacement, and thereby reducing its capacity. Rotary pumps with negative suction pressure require that the pump casing be filled with liquid to seal internal clearances and provide lubrication during starting. Direct acting (steam driven) reciprocating pumps are suitable for pumping relatively small volumes against high differential heads. Where process steam is required at dif- A standard set of considerations and best industry practices that Rotating Equipment Engineers apply in the selection of various types of pumps and their auxiliaries, is described. Typical services and limiting operating conditions of centrifugal and positive displacement pumps are included to aid in the selection process.

ferent pressure levels, a direct acting reciprocating pump can be used as a pressure-reducing device to save energy. Reciprocating pumps can be used to pump a wide variety of fluids including those with varying corrosive and erosive qualities. The centrifugal pump is usually the most preferred con- figuration in processing industries. But in certain applications and situations as listed below, centrifugal pumps may not be appropriate. • A: Low flow and high head pumping needs, such as in chemical injection. • B: Fluids containing volatile vapours. Presence of vapours undermines performance of centrifugal pumps. • C: Intermittent services or where a number of liquids of widely different viscosities are handled. • D: Multiple pumping operations including a range of flow rates and heads. • E: Constant capacity requirements with varying discharge pressures. • F: Large capacity and high head or low head or low net positive suction head available (NPSHA) applications. Performance characteristics of reciprocating pumps make them an ideal candidate for such applications. Some of the features, characteristics and limitations that engineers should consider when selecting a pump are: • A: Vertical pumps should be used in those applications where NPSHA or head/capacity make a horizontal pump less practical, or in those services (within the operating

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Chemical Technology • August 2015