Page 185 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Chapter

Pumping of Liquids

Pumping of liquids is almost universal in chemical and 5. determine the important avaiZab2e net positive suc-
petrochemical processes. The many different materials tion head (NPSHJ for the pump suction side
being processed require close attention to selection of mechanical system, and compare this to the manu-
materials of construction of the various pump parts, shaft facturer’s required net positive suction head
sealing, and the hydraulics of the individual problems. A (NPSHR) by the pump itself. This requires that the
wide variety of types and sizes of pumps have been devel- designer make a tentative actual pump selection of
oped to satisfy the many special conditions found in one or more manufacturers in order to use actual
chemical plant systems; however, since all of these cannot numbers.
be discussed here, the omission of some does not mean 6. make allowable corrections to the pump’s required
that they may not be suitable for a service.
NPSH (using charts where applicable) and com-
In general, the final pump selection and performance pare with the available NPSH. The available must
details are recommended by the manufacturers to meet always be several feet greater than the corrected
the conditions specified by the process design engineer. It required.
is important that the designer of the process system be
completely familiar with the action of each pump offered 7. make fluid viscosity corrections to the required per-
for a service in order that such items as control instru- formance if the fluid is more viscous than water.
ments and valves may be properly evaluated in the full 8. examine specific speed index, particularly if it can
knowledge of the system. be anticipated that future changes in the system
This chapter presents information on rating, sizing, may be required.
and specifjmg process pumps. The emphasis will be on 9. if fluid being pumped is at elevated temperature
centrifugal pumps, which are by far the most widely used (usually above 9O”Fk), check temperature rise in
in the process industries; however, applications of other pump, and the minimum flow required through
types of pumps will also be discussed (see Table 3-1). the pump.
To properly accomplish a good and thorough rat-
ing/sizing of a centrifugal pump, the plant system design- 10. make pump brake horsepower corrections for flu-
ids with a specific gravity different than water.
er should at a minimum:
Select actual driver (electric motor, usually) horse-
power in order that horsepower losses between the
1. understand the fundamentals of performance of the driver and the pump shaft will still provide suffi-
pump itself. cient power to meet the pump’s input shaft require-
2. understand the mechanical details required for a ments.
pump to function properly in a system. 11. if the pump has some unique specialty service or
3. calculate the friction and any other pressure losses requirement, recognize these in the final sizing and
for each “side” of the pump, suction and discharge, selection. Consult a reliable manufacturer that pro-
(see Chapter 2). duces pumps for the type of service and applica-
4. determine the suction side and discharge side heads tions and have them verify the analysis of your sys-
for the mechanical system connecting to the pump. tem’s application (s) .

160