Lecture Slides CPE 676_Supporting Equipment

8/2/2019 Lecture Slides CPE 676_Supporting Equipment

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Chapter 9 :Supporting equipments:

Pumps

Mixing Equipment

Drying Equipment


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Todays lesson:

Pumps

Centrifugal PumpsOperating principles

Safety : - Cavitation

- BackflowNPSH

- NPSHA

AND NPSHR


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Today's lesson objectives :

By the end of the class, the students are

expected to be able :

To explain the operating principles of

centrifugal and positive displacement pumps.

To describe the safety design and operationof pumps.

To determine the Net Positive Suction Head

(NPSH) required and available.

LESSON OBJECTIVES :-


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PumpsIntroductionBy principle, pumps areused to transferfluids from one point to other point over adistance and also it is meant to do work.

Pumps can be divided into 2 major groups; Centrifugal Positive displacements - reciprocating

or rotary


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PumpsIntroduction

The classifications of these groups are madebased on way the energy being delivered to

the liquid.

The centrifugal pumps uses centrifugalforces to transfer liquid meanwhile positivedisplacement pumps transfer the liquid bymeans of pressurizing the liquid bydisplacement.


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PumpsOperating Principles

There are numerous advantages of the centrifugalpumps that allow the wide range of usage in refineryand petrochemical industry.

Among the advantages of the centrifugal pumps are: Economical due to low cost

Capability to be operated in wide range ofvolume and pressure (head) outputs.

Require less maintenance works Ability of handling liquids that contaminated

with heavy particles.

Need less space as it is considered small.


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PumpsOperating Principles


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PumpsOperating Principles At point A, the fluid is feed to the inlet of the pump

known as suction side.

Then, the fluid will enter to the center of the pumpsat the rapidly rotating fan-shaped impeller eyeindicated by point B.

Afterwards, the fluids are flung radially along theimpeller (point C) due to the generated centrifugalforces that accelerates the fluids towards thedischarge area.

Finally, at point D, the pressurized fluids aredischarged from the pumps due to the conversion

from kinetic energy to pressure energy.


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Pumps Safety: Cavitation

In designing a pump, one of the most importantconsiderations that need to be taken into

account is the cavitations problem.

Cavitations problem occurs when the pressureof the liquid is less than its vapor pressure at

the same temperature, which resulted in theformation of vapors bubbles.


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PumpsCavitation

The formations of these bubbles vapors create low-pressure region in the impeller area.

This condition will encourage the highpressure

liquid to enter to these lower pressure regions createdby the vapors bubbles and causing the bubbles actinglike bullets that will hit and collapse on the bladesand consequently damaging the impeller.

The formation of the vapor bubbles will also createnoise and cause the pumps to vibrate and for worsecases the impeller might be break off into smallpieces.


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PumpsSafety: Cavitation

To overcome this problem it is vital to have theavailable NPSHA (Net Positive Suction HeadAvailable) of the pump is greater than or equal

to the required NPSHR (Net Positive SuctionHead Required).

NPSHA > NPSHR

To stop the cavitations it can be done also byraising the suction pressure of the pumps(NPSHA) or decreasing the pumping rate(decreasing NPSH

R).


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PumpsSafety: Cavitation


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PumpsSafety: Backflow

One of the major safety aspects that have beenconsidered in the operation of pumps isprevention of the backflow condition of

process fluids.

This backflow phenomenon will create severeimpact on the pumps particularly on theimpeller blades.

As the protection, a check valve is usuallyinstalled at the outlet of the discharged side ofthe pumps.


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For a check valve, there is a flipper thatoperating based on the concept of pressuredifference.

If the pressure of the discharged pumps ishigher than pipeline pressure then this flipperwill be opened towards the pipeline flow.


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PumpsSafety : Backflow

Conversely, if thedischarged pressureof the pumps is

lower thanpipelinepressure thus theflipper will be tend tobe closed towardsthe direction to thepump.


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To avoid the backflow situation from beingexperienced by the pumps, it is essential toensure that the pumps will have minimumflow at the suction side of the pump.

Usually, there is a spill back lineprovided atthe suction side of the pumps in order to addup any shortage of the flow to the pumps.


Lecture Slides CPE 676_Supporting Equipment

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