Rotating Equipment

Pumps

n

Introduction

=

Pump

Curves

-

Head versus Capacity

-

WSH

u

Single-Stage Centrifugal Pwmp Design

-

Pump Components

Pumps

(continued)

m

Reliability

8

Fan Laws

a

Hydraalics

8

Pump Control

i..

r

S d e s s

h p s

r

h

p

Selection

and

PerEomance

r Doizble

Suction, Mujti-Stage,

and

Sundyne funips

"

pd46"S"

phq?!

This is a typical pump curve. The pump curve gives information on how the pump will perform, the NPSH required by the pump, and the impeller

size m g e for the casing. AH p m p manufacturer's c m e s are similar so, if you

can

read one nnanufiictwer's curve, you can read anybodys.

0 400 800 1200 I W 2000 2400

Gallons Per Minme

Head-capacity curve. Once this curve is established based on the impeller diameter and speed, the pump wig1 always operate on this curve. Note how the curve rises

as

the Row goes down. This is a charactexistic of d l centrifugal pumps.

Single Stage Centrifagal

Pump

Mechanical Seal

Shaft

f

~ k l i n ~ Deflector 'L 0 3 Levef BoHe

Sleeve Met Ring

Single stage centrifugd pump. As the centrifugil force of the impeller throws the fluid out towards the cstsing, the velocity of the fluid goes up.

-4s the fluid leaves the p m p , this velociQ energy is changed to pressure energy.

I

L

Identical

Pumps Handling Liquids

of Dgferent Specific

CrasoEioc. S.G. = 0.75 Waxer, S.G. = f .O Brine, S.G = 1.2

Pump perfomance is measured in feet or meters of head. Head i s the height of the column that the pump

cm

move the fluid.

Pump

head is a

function of impeller diameter and sped. It is not a function of the density

or specific gravity of &e pumped fluid.

Here

are three identical. pumps

pumping out of three identical tanks. Note that the head or column height

is

Galbns Per ,Minute

Each pump casing size can handle more than one size impeller. This pump ' casing can handle impeller diameters between 9 and J 1 inches. Also, the

impeller can be trimmed to any size between 9 and 11 inches to meet the

sated opemxing point. The impeller diaeter does not have to be a whale inch size.

-

0

L2

E; .

-

z

cr?

2

o

400

aw

1200 ISOO 2000 ~rl.00

CaXlons Per Minute

The pump m ealso gives the NPSH required by the pump. Note how %he

A B

Puhc Along Liquid Pit&

The fluid loses pressure in the pump before the pressure starts to rise. As the fluid enters the pump, these are entrance and friction losses. As the

ff

aid enters the rotating impeller, $here are turbulence and friction Iosses at the vane tips. If this pmssure drop is enough to drop the pressure of the fluid below its vapor pressure point, flashing will occur. This phenomena, called caviation, will quickly destroy an impeller and a pump. The h?SH

The NPSH avaifable is a function of the pumping sysxem. WSW avail able is the pressure at the pump suction minus the fluid vapor presswe. Xtis the pressure thaz can be lost in the pump inlet

area

before

Washing

or catritaeon begins. For a bubble point or vapor pressure point fluid, the &iSH

0 300 800 1200 1600 2000 2400

Galtoas Per &ate

The pump curve shows the efficiency of tfxe pump at any operating point. Note that the efficiencies rise with rising Bow to the best efficiency point

(BEP), and then quickly drop off. Optimum pump operation is at or near

best

efficiency point.

0 400 800 lGZOO 1600 2000 2300

Gallons Per Minute

Pwnp

curves also show the

FP

requirement for the pump. Do not use these

curves. CAU3UX,AE W. These

FP

c w e s only appfy if the specific

gravity of the fluid is 1.0. Also, it i s difficult to get a good, accurate

Pump Selection

Y

60 Cycle C m n t

3550 rlmn

I

Two Sage Prmss

Singk Sxcion Uoubit. Suction

35% r/min S550 r h n

I

Double Sumon

Pump Cap~ciry, gpm

This chart shows the approximate head-capacity ranges of single stage fuX1 and half speed pumps, doable suction pumps, and two and &ti-stage pumps. Low Bow, high head applications are Sundynes.

AE

API

pumps today are centerline mounted. The centerline mounx allows

the pump casing to p w both up and down

as

the casing hears up. This

keeps the shaft in the horizontal plane and helps prevents seal leaks and shaft mis-alignment.

Impellers

All API pumps today have closed impellers with covers or shrouds on both sides of the vanes. This gives the fluid a more defined path through the

pump

and raises efficiency. The flow splitter in the outlet or double volute equalizes the radial forces around the impeller and minimizes the load on

Single Suetion Enclosed Impeller

Siagle Suction impeller

Large single suction impeller. Note

tee

impeller vanes at the inlet md

outIet, This is a half speed impeller. Full speed impellers are only allowed up to 15 inches in diameter to control tip speeds,

Suction

Specific Speed

PV*P

J.

S

=

rpm

( g ~ r n ) ~

/ frvPSItr)3J4

r

Can

range

between 3000

-

20000

The suction specific speed relates

rpm,

gpm,

and NPSH required. UOP ' limits the suction specific speed to 11000. If a pump manufacturer w a s to

reduce the NPSH required of a certain pump, he can increase the impeller eye m a to reduce fiction drop and reduce IWSW required. This increased eye

area

increases the internal circulation in rhe suction

area

of the pump.

This can buitd up heat which can also flash the fluid and reduce pump reliability. This also reduces the sable operating range of the pump. As the flow is reduced, the p m p becomes less efficient and

more

heat is built up in the pump. At

higher

suction,. specific speeds this can promute cavitation.

Model 3735

High

TmperatuteMigh Pressure Process Pumps

Heavy Duty

Design

Features

to

Meet the Total

Range

of Process Indu:stries

Intpetier Sealing Renewable Stuffing Box

Wearing Rings Refiability Froat Bushing

b

1

,-

Heavy Cast

t Y Large Cooling

Duaf IWfficient _Jacket

Voiate Mechanical Casing Sealcooijng

This is a single stage (one impeller), single suction (one entry into the

impeller), overhung (impeller is cantilevered on one set of bearings) pump.

This is c d k d a Process pump. The metdfwgy is

as

follows:

Casing

Carbon

Steel

Impeller Carbon Steel

<50Q°F,

1 1-13% Cr

>50O0F

Shaft Carbon Steel Wearing rings 11-1.396

Cr

Throat bushing il-13%

Cr

1

Single

Stage Overhung Pump

Single stage, single suction, overhung p m p . Note the vent connection

on

Single Stage Pump

Single stage, single suction, overhung pump. This pump is self-venting as

Before there were mechanical seals, pumps were sealed by "stuffing" an absorbent material caned packing wound Ehe shaft. Since the process fluid had to lubricate &e surface between the

stu%h,a

and the shaft, the packing had to leak, typically a b u t 200 cchr for a new application. Over time, &e

packing would become sitmated with fluid and the leakage would increase

until the pump had to be shut down m d &e packing replaced. Today, UOP does not specify any

pumps

with packing.

Single Mechanical Seal

I

Single mechanical seal. Mlost

A H

pumps today have single mechanical seals. The single mechanical pusher type seal has two members, a rotating member md a stationary member. The main sealing takes place due to the friction between the rotating seal face and the stationary seal face. Since the pumped fluid lubricated this seal face, the si-qle mechanical seal does leak. Typical leak rates are about 2 ccfhr or about f

00 p p

of emissions in the air sumunding the se& As the seal faces wear, springs in the rotating member keep a t i a t fit between %he two seal faces.

O-rings

prevent X&age between the seal

and

the shaft

and

between she seal and the pump

Connection A (refer to appropriate Connection B (refer io appropriate primary seal piping arrangement) \xiliary seal piping m g e m c n t )

Seal Box

-

Sleeve -.-w- Rotatiag Seal .Member Seal End Plate / sealing device

Single Mechanical Seal

Here is another view of the single mechanical seal. Note the yellow process fluid coming from rhe pump discharge to the process side seal face. The mbbing seat faces generate heat.

If

the pumped Ruid

is

at vapor pressure or

bubble point and. heat is added, the fluid could Aash around the sea$

and

the seal faces codd b e their lubricant- Process fluid flows

fron

the discharge of the p m p &-ou&

an

usifice. The pmsswe is kept high enough momd

the

seal to

stay above the vapor pressure point even though with the seal faces

are

adding heat.

Welded Carbon or Tungsten Carbide

Puller

Metal Betitows vs. SteIlite Sealing Faces

Croove

Solid &.eel Rotating _Stationary

W v e Lags Sestf

seat

]Bellows seals are specified for high temperature applications, above 5S0°F.

Bellows seals have two members9 a rotating member and a stationary

f

Cap S

-

X*FICOZI

When the seal face wears on a bellows seal, the metal beljlows expands like

an accordion. The o-rings bemeen the seal and the shaft do not move dong

Ehe shaft as they do in a pusher type seal. Since the xing material starts to break down at higher temperatures, pusher type seak are temperame limited due to h e dynamic

o-ring.

Since the o-ring

on

the bellows seal

is

m

~1000

ppm

(Most

<I00 ppm)

m

Comply wigh Regulations

in

Most

Cases

Liquid

Taadem

Seals

(Unpressarized

Dual

Seals)

=

c50

ppm

(Most

<I0 ppm)

r

Vent to Flare

1

r

Diesel

Buffer

Liquid

8 3+

Years Life

Tandem seals are now referred

to

as

mpxessurized dual seals. The buffer between the two seals is vented to flare and is unpressurized. Leakage of

process fluid is greatly reduced

from

the single mechanical seal. Any process fluid that leaks across &e inner seal is contained by the outer seal.

Unpressurized Dual Seals

Connection C (refer to appropriate

randem seal piping m n g e m n t )

fe Bushing (mechaaical seal Seal Member shing) or auxiliary s e a h g device

Unpressusized dud mechanicd sed. Used for following:

-

Light hydrocarbons

-

Vapor pressure over 30 psig

* 1 wt % Benzene

25 wt % C6-c9 ~O-CS

5 mol% H,S

Buffer fluid is circulated

from

the seal

pot to

the buffer area and back to the seal pot with pumping rings on the shaft. Leakage

of

process fluid is into the buffer area. The seal pot has a pressure dann for Bashing fluids and a level aIann

fur

non-flashing, fluids to warn of

an

inner seal leak.

Mufti-stage pump with unpressurized dual sears. Note the two seal pots the ' the API Plan 52.

Disc

Suction

.tion Tube

Sealless canned motor pump. Zero fugitive emissions. The motor windings

turn a magnet on the pump shaft across a containment barrier. The process

fluid

lubricate the bearings

on

the pump shaft and remove heat from the

mom

windings. Therefore, %he pump cannot be run

dry

(bearings will not

be lubric&ed]

or be

fun blacked in (heat will not be removed from a e

motor). UOP specifies insmmentation (alarm and shutdowns) to prevent

Sealless canned pump. Yote the process fluid circulating from the pump

discharge to the back end of the

pump.

The nuid rhen travels though the

p m p , Iszbricafing the shaft bearings and removing heat from the motor windings.

. If &e process fluid is comsivc, ( E F acid) the bearing fluid could be from

an

external source.

s&

Sedfess canned pump.

For

this type, the process fluid i s circulating back

Magnetic Drive Pamp

Sedless magnetic drive

pump.

Magnets on the motor shaft twn mapets

on

the pump shaft across a contaiment barrier. This is

an

altemte design to the canned motor p m p . Process ffuid still Iubpicates the p u p sha& bearings. Zero fugitive emissions.

Magnoseal

"

Standard Features

i ASMWANSI 13'mensions Magnetic Coupiings to 100 IfP Engineered Composite andMetal Containment SkUs

m Precision Cast Semi-

Open

Impeller

Wear Resistant Silicon Carbide Bearing System

Sealless magnetic (Mag) drive pump. Note that the magnetic couplings

are

Reliability and Maintenance

What

is

ReliabiXitv?

The main

objective of reliability is to achieve the

highest

plant availability

at

the

lowest possible cost

in order to maximize prof~t,

The

goal

is

t o achieve f i e

World

Ciuss

target

Reliability

and Maintenance

;

.Critical

Equipment

-

Centrifugal

Compressors,

Some pumps

-

Unspared

-

Continuous

Monitoring

System

.Pumps,

Reciprocating

Compressors

-

Spared

-

Periodic Monitoring o f Vibration b t a

-

CoIleci and Analyze

Reliability and Maintenance

Equipment

Specs

and

Standards

Vendor

Selection

Design and Testing

Process Considerations

Reliability and Maintenance

95%

on-kne availability for pumps, 5 year

MTBR

1. Reactive

-

Run

to failure

2.

Preventative

-

Time-based maintenance

t

Reliability and Maintenance

1

Reactive

-

Run

%o Failure

Process Interruption

m

N o

Opportunity

for

Diagnosis

Frequent failures

r

Other Pasts

are

Effected

Reliability and Maintenance

Pre'ventative

-

Time-based Maintenance

r N o

UppurtuniSy f o r Diagnosis

Reliability

and Maintenance

Proactive

-

Condition-based Maintenance

m

Repair

Before

Pump

Fails

m

Replace

Only

Bad

Parts

.Reliability and Maintenance

Unbalance

RPMx

1

Steady

Bent Shaft

W M

x

I. or 2,

Axial

high

Cavitation

Random

Fluctuating

Misalignment

R3PN

x

1

and 2

Pardlel

Radial

Angular

High

Axial

Reliability

and Maintenance

Prucuremerzt

EPC

during

vendor/contractor

proposal

review

"I

am

concerned

with 3

things:

Reliability

and

Maintenance

1.

Price

Reliability and Maintenance

Procurement

Main

Air Blower quits

Cost up

to $500,0001day in

lost production

1.

Functionality

2.

Reliability

3. Utilities

Reliability and Maintenance

Procurement

Reliability and Maintenance

Life Cycle

Costs

i

₁

_Reliability

_and

_Maintenance

I

E

Besi Psactices

-

Pump and

Sys?ern Design

Suction Specific

Speed

4

11000

m

L3/b4

<

60

(inches)

-6b

rj~-k+

1%

m

Design system for

operation

a t

or

near

BEP

m

5

faot

NPSH

margin

M i n i m

5 pipe

diameters

shvtight

pipe on

r

1mtafl APX Flush

?Ian

23

if

pumping

Reliability and Maintenance

,

Best Practices

-

Pump

Operation

=

Do not start and stop often Check cooling water and seal

-

Do

not nm pump dry flush temps

1

Operate at or near BEP B Inspect and change bearing

m V i i y iinhpect pump often 0.2 (3-6 months)

(once per shift) r Do not "hose down'' pumps

r M;easummd record D

Report

problems immed.iately

Reliability and Maintenance

Best

Pmtices

-

Pump Reliabifitv

r Alignment

-

~ 8 k e e

8 Bearings

w b b e oil

Reliability and Maintenance

I

Reliable

Reciprocating Compressor

Design

Limit

Piston

Speed

m

Lianit

3Pis;tonRPM

,

.'

Limit CyHnder

Size

8

L M t Discharge

Temp

(250°F)

H f i r

Lubricate

Cylinders

i

=

coat

~isttyx

R U ~

m

Vibration

and

Temperature

Moni^tor

Relkbility

and

Maintenance

Reliable Centrifugal Compressor

Design

I

m

Limit b4axi.m-

Impeller Yield Strength

!

r ~q

as

Seals

i

r

Report all

Operating

Cases

r

Voting Type Sha*down

Affinity Relationships

Q

=

Capacity, gpm

N

=

Rotative Speed, rpm

H

=

Head, feet

]HIP

=

Horsepower

D

=

Impeller Diameter

Affinity relationships or fan laws.

The flow varies proportionaI to the speed variation md the head varies pfoportionaI

to

the square of the speed. These laws explain why high flows and low heads are achieved wjth law speed p m g s and low flows and high heads ate achieved with high speed (Sundym) pumps.

d

I _{GP.M x Head x $13.}

_CR

_-

-

Ib / nin x Head

BHP

=

-

-

GPM x PSI

3960 x E g 33,000 x E# 1714 x Efl

When using pump curves for

60

cycle

and

the pumps wi3I be in a m n t y with 50 cycle power, &e Row, head, md NPSH required must be corrected before a pump can be selected,

Horsepower in Field

Measure

imp draw of motor

Watts = b p s

x

Volts

BHP=1.73 x Amps x VoRs

x

motor eff x motor power factor

i 746

Motor eff

=

0.95 (Approx)

Motor power factor

=

0.90

(Approx)

Horsepower

in

Field

Power Factor

Power factor is the

ratio

between the KW and the

KVA

drawn by

an

electricat load where the KW is

the

actual load power

and

the KVA is the apparent

load power.

Xt

is a measure of how effectively the current is

being converted into usem work output and

more

partZculariy

is a

good indicawr of

the

effect: of the

load cmsent on

&e

eMicienty

of

the supply system*

I

Horsepower in Field

i ExayXe ~ n r ~ s ' = 30 Volts = 360 BKP = 1.73 ( 30) (360) (0.95) (090)/746 i

_BHP

_{= 21.4}

GPM

= 300 P2 = 170

Eff

= (300) (1'70-95)/(1714)(21.(t)

System Resistance

Curve

q3

~ s i g

200 G P M ,

₃₃

%

Flow

I

30

psig

mH

=

i&

&

-

_1.5

_psi

>

-a

-

0 5

psi

0.5

psi

I

1

psi

1

psi

70 psig

7

System

Resistance Curve

Pump Performance Curve

Twu Centrifgal Pumps

in

_Parallel

Capacity gpm

When pumps s e operated in parallel, the combined performance curve is obtaiaed by adding horizontally the capacities of the same heads. it is preferred that the head-capacity curves rise to shtrtoff: If the curves droop

and if the second pump comes on-line at low flow, the pruryi, cuufd "hunt"

Two

Centr?ugaI Pumps

in

Series

Capacity gpm

t P D W D B i P D M Y

For series opesation, the combined performance curve is abtained by adding vertically the heads at the same capacities. Note that the maximum

suction

pressme of the

&wnswem

p a p is the shutoff pressure of the upstream

Typical

Mo.tor/Motor Spare Pump

A m g e m e a t

Discharge

9

Typically, there are nxro pumps insQlled, one operating and one spare. If a pump goes out of service,

an

operator has to corne out and srart up the spare pump. Pumps are typiaEy started with the &scharee valve closed or pinched open. The bast amount, of starting torque req&red by the motor to

Typical

Motor-Auto Cut-In Turbine

Spare Pamp Arrangement

Discharge

.---.---.-- _{"I Slow Roll}

:

I

I

i

,

EZY-P~SS

!

h7

i

/

Control

Exhaust Steam 3.5 Kg/m2g

Critical service pumps are on mtomaric start. Examples of critical service pumps

are

Boiler Feedwater, Surface Condenser Condensate, Compressor

Lube

Oil, and

HI?

Add pumps. If a critical service pump goes out of

service, equipment, personnel, or caalysr codd be damaged before an operator corxld get the spare p m p in opedon. Therefore, the spare pump

Rolling Element (Ball) Bearings

Double Axial

Rolling Element Bearings

r

Per APX 610

Minimum

Requirements

r

23M0

horn

(3

yrs)

at

rated

capacity

Bearings

Enemies

rr

Wrong

02

level

Wa$er

Bearings Oil Level

8

Just Right

-

Half way up bottom

bearing

Too

Low

-

Inadequate

Lubrication

f"

-!+

bq

Too

High

-

Excessive

Heat

-+

k9

+&

-*Q

w-

8

Per

SKI",

oil has useful life

of 30

yrs

@

30°C (80°F)

Cug in

half

for every

1

0°C

( 1 8

"F)

rise

Bearings Water

Where Does It Come

From?

fCiq,.&,

A h

b a i .

?LAC)

a

House

Cleaning

Seal Gland

Quench

i-

Aspiration

N

Open Oil Cans

Bearings Water What

Are

Problems?

i

fitting

and Corresion

increase fatigue

Free a t d e

X.f,

camas hydrogen exnbnittlexnent

acce~eralhg

fatigue

Water/oil

emulsion

is

poor fabricant

Bearings Solids

Where

Do They Come From?

Seal Cage

and

Bearing Box Seal Wear

m

Oil

Flinger

Ring

r,

Soofids

in

contamhated

02

1

Air borne partides

Oil

Mist

Wrong

03

Ievds, water eontamination, solid

abrasion

all

go away with oil

mist

lubrication

Pure

Oil

M'st

Engineered for large Process

units:

rn

Serve up to 80 Pumps

with

Drivers

Required Maimum of 30 SCFM of

Air

m

Consume

Less

than

2

Gallons

of

Oil per

Day

. .

,justifying

use

of

Synthetic

Oils

for Mzulimm Benefits

Oil

Mist Benefits

a

The

Proper Amount of Clean Oil

is

Applied

Continuously

a

Clean

Oace

Thfough

Lubrication

B e a ~ g

Housings are

Pressurized

Preventing

External Contamination

m

Internal

Metal

Surfaces

are

Always

Coated

114th

oil

which Prevents

Corrosion

(Important For

Stand-by

E q n i p a t )

n

L,, Bearing Life

$3

Extended

by a Factw of

6

Source: Texas

A&M

Unrivemity

Research

Oil Mist BeneJits

~ekring

fdures reduced up to

90%

Dirt

particles are not delivered to the bearings

m

Dirt pantides do not accumulate in the oil sump

W y r particles are carried away

m

hearings operate 18

to

27°F cooler

m

Bearings

see

onjly fresh oil

Double Suction

Single stage, double suction between bearing pump.

Single Stage Double Stlction

Two Stage Single Suction

Between Bearing

8

Stage Centrtyugal P a q

Opposed linpellers

Mechanical Wear _Cross

Seal

Quench 7

J

~ z & s Over f m

Discharge _{4th Stage Discharge to 5& Stage Suction}

Inside of hurizontal11y split mufti-stage pump. The impeXlers are opposed to each other. The first stage is on the

far

left of &e

pump.

The fluid travels to f$e left for the first four stages. m e r the fourth stage, the fluid crossed over ta the far right and travels to fhe right for the 5th through 8th stages. This is to balance the axid thrust on the bearings.

Six stage, axidly split pump. Note the cf.ossover piping internal

to

the

Double Case Ceatr~ugal

Pamps

Radially split multi-stee pump. Radially split .multi-stage pumps are more expensive and take longer to repair

&an

axidly split multi-stage pumps. The axidZy split rnuki-stage pump has a large casing split. Therefore, to reduce &e possibility of process fluid Je&age, APT

610

does not

allow

the

use of axidly split muki-stage pimps if the panping temperature is over

400°F,

the discharge pressure is over 1450 psig or the specific gravity is under 0.7.

Mrclti-Stage Pump

with

Balancing

Drum

Suction

Inside a radially split multi-stage p m p . Note that the impellers are all

facing the same direction. This is because the design of she forged, barrel

type casing does not allow for the cross over piping. To bdance the axial thrusts, a balance d m atmched to a line at suction pressure is installed on

the discharge side. This drum absorbs the axial thrust. Also, this enables both seals to sed against suction pressure.

Six stage radial1 y spjitjt pump. Note the double suction suction

erst

stage for

Power lini t Gearbox Integral Centrifugal Separator Diffuser Pump Casing

Mbdel

LiMV-

21

Sundyne

Process

Pump

Mechanicai Seal

Sundyne pump. This is a high speed, integrally geared pump used for low

flow, high head appXica~ions. Sundyne is the only manufacturer having good success with this design of p m q . This pump is built to MI 610

standards. It

can

achieve high heads using high speed rather

than

multiple

Sundyne with single

gem

between motor shafl and impeller shaft. This type gear box is good to 50 hp.

Purchasing Pumps

Technical Evalaation

Does

it meet flow and head?

Check completed API data sheets line by

line. Does it meet the spec?

Parchasing Pumps

Technical Evaluation

5. Suction Specific Speed

6. Seals

7. Materials

8- Efficiency

9 Exceptions to Specs and Standards

PROBLEMS

"

Problem I

I

I

Liquid is at bubble point. Friction loss is 2 psig. (6 feet)

npsha = (26 - 3) - 6 = 17 feet

Two existing pumps (operating and spare) Byron Jackson 4 x 6 x 13

j$

L (curve attached)

Present pump duty Flow 600 gpm Head 500 ft

npshr 14 ft

Sp Gr 0.80 Temperature 150°F 60 Cycle

New conditions require flow to be increased to 780 gpm.

PROBLEM I

-

MSWER

Methods to increase available npsh:

I

Raise minimum liquid level

Modify piping to reduce friction loss Reduce pump centerline elevation Operate both pumps in parallel

Purchase new pump with lower npsh required Cool vessel liquid to reduce vapor pressure

Problem I11

1. Make the best pump selection fiom the attached curves.

P/IM/J;~:@&

4 x 6 ~ -

T O C

2. How many stages?

6

d + F

3. What is the efficiency?

*%

s/fjQ

--

C X

4. What is the horsepower?

%

3

F

5. What is the required npsh?

Effective FEE. 65

Byron United

WGp

w/lP hternational, hc. Jacksonm Centrifugalm

Pwnp Divisim Pumps Pumps

---.

Senion 1-130

-

Byron United

Effective FEB. 65 Pumps Pumps

Page 1-730-47

Effective FEB. 65

Byron United

wGP

w/IP International, Inc. Jackson@ CentrifugalN

, Pump Division Pumps Pumps Section 1-730

'

Effective May 65 Supersedes February 6!

Byron United

WGInY

BWIIP ~niernatbnal, IN. Jacksona centrifugalm Pmp Division Pumps Pumps

Section 73 0

Section 1-73 Byron United

, PumpDivlslon Pumps Pumps

Effective February 65 Effective February 65

Byron United

wqIF

BWN) lntemtional, inc Jackson@ Centrifugal"

Pllmp oivision Pumps Pumps

S e ~ t i 0 n 730

Effective Februarv 65

Byron United

w*p

m p Internatbnal, Inc. Jackson* CentrifugaP

Pump Oivision Pumps Pumps Sectia n 73 0

Best pump selection - 4 x 6 x 9D 2604-2 Stages I - 7

Efficiency - 80% Horsepower - 750HP Required npsh - 17 feet

Types

of

Co~npressors

-

., , 0 .< %

Posj tive Displacement

Reciprocating

(Centrifugal) I

-

Compfessor $law is measuted in ACFM, Actual Cubic Feet per Minute,

or

inlet Ms/hr. ACT34 is the flow rate at atmospheric conditions (standard) correcxed for inlet gempernure and

pxessme.

Compressors

r

Basic

Theory

Hardware

i Case studies

3

Receiver cieAnce Volume 1 Discharge Iniet

Reciprocating Cornpressor Compression Cycfe

Compression (1 -2)

The piston compresses the gas inside the cylinder. When the pressure exceeds the suction pressure, the inlet valves close so the gas cannot escape h c k

to

the suction side. The piston continues to compress the gas until the discha-ge pressure is reached. At this point, the discharge vdves open.

Ex haust (2-3)

The piston continues in its forward stroke, pushing the gas out at discharge

Expansion

1 Pressure f

k

-

)

Stroke

,-A

Discharge 1 I. .:,.. 0 ' Inlet Expansion (3-4)

The piston completes its forward stroke. Some gas is left inside the cylinder. The piston moves back toward the crankcase. The gas inside the cylinder expands and the pressure drops. When the presswe inside the cylinder drops below discharge pressure, the discharge valves cXose. When the gas &ups bdow suction pressure, the suction valves open.

Receiver I .f Pressure

Discharge Inlet

Iritake (4-1)

As the piston .travels back toward the crankcase, the cylinder continues to fiE with gas.

Compressor Valves

The compressor valves are nothing more than check valves designed to open or close based on the differeaiaf pressure across the vafve. Since most of the maintenmce of reciprocating .compressors have to do with the valves, there 'has been

much

research and imprmmenw; in vdve types and mdexids. Channel valves have

been

used fox- a long time. ' h e channels move

up

and down

300-500

dxnes a nziau%e ad&nst the valve sptings. If any

liquid gets between the channel m d spring, the spring could break as liquid is inconrpressjble,

h

is important that the

gas

is kept clean and dry.

Ring valve. T d a y the

i n s

are made out of a high temperawre

Two

Stage Compression

Volume

-

Staging

Reciprocating compressors have a discharge temperature constraint. Due so mechanical considerations, the discharge temperature of a gas compressor should not exceed 27S°F. Discharge temperamre is a function of compression ratio and sucGozl temperature. Xf the process demands a compression ratio resulting in

an

unacceptable discharge temperature, the compression can be staged. The compressor shown above has a suction pressure of 15 psia and a discharge pressme of 115 psia. This coxnpsession ratio of 7.7 will resub in

an

unacceptably high discharge temperature.

Therefore, the compression is divided into two stages with intercoofing.

The first-stase cylinder(& raise the pressme up to 40 psia. The gas is then cooled back down to

XOO°F.

The second-stage cylinder(s) then raise the pressure up FO If5 psia. At

no

time does the gas temperature exceed

limitations.

Staging also saves power consu3nption. Cooling the gas after partial compression to a temperature equal to the original intake temperature reduces the power required in the second stage. (HP is a function of m a s flow times differential head. Head is a function of temperature.) Occasional! y. even if discharge temperature is not a consideration, intercooling is used to save power. The power savings has to offset the utility consumption of the intercooler.

Reciprocating Compressor Control

r

Saction

Valve Unfoaders

r

Cyfinder

Pockets

w

Bypass

Capacity is controlled with suction valve unfoadefs, cylinder cIearance

Finger

Type

Unlouder

Unloaders hold fie suction valves open

so

no compression can take place.

If one side of a double acting cylinder is unloaded, the capacity goes down by 50% for that cylinder. A one cylinder cornpressor can unload to 50% and

0% capacity. A two cylinder compressor can unload to 75%, 50%- 25% and

Clearance Pocket

In

addition to suction valve unloaden, head end fixed cleaance pockets are also used for capacity controI. The head end of the cylinder has a pocket that can be opened. When opmed, the total cylinder clearance increases.

On

the intake part of the stroke, the gas thax fifills the clearance pocket expands and less gas enters fie cylinder. When the pocket is opened, the capacity DECREASB. Typically, the pocket is sized

for

10% capacity. With the pockex closed. the compressor is at rated capacity of 110% nonnal pmcess requirement. with the pocket opened, the compressor is a XOO%

process capacity.

Variable capacity pockets are not recommended. The plunger in the variable pocket tends to leak, making the pocket useless.

Clearance

Pocket

I

Nore 2 compartment disrance piece, piston packing, piston sings, and rider

Cut-away of tbe two cylinder compressor. Note how the connecting rod between the crankshaft and the piston rod is connected to the piston sod at

the crosshead. Tfne piston rod screws i ~ t o the crosshead. A pin attaches the connecting rod to the crosshead.

Single Cylinder

Reciprocating

Compressor

250

BHP Frame Rating

Single cylinder compressor. Double acting with one hlet md oudet vdve

on each side. The box mounted on the f m e is the crankshaft driven cylinder ~ubxicatur. The oif lines from tbe f~brktit~r

to

the cyiinder can be seen. Typically, tfie packing box is

dso

lubricated by

this

lubricator.

Two Cylinder Balanced-

Opposed

Reciprocating Compressor 400 BHP

Frame Rating

Two cylinder, two-stage compressor. The larger first-stage cylinder is an the right. The fist-stage cylinder has 92 valves total, the second-stage

cylinder has four vdves total. Again, note the cylinder a d packing lubricator mounted on the crankcase-

Pump to

Point Cylinder Lubricator

Two cylinder, two-stage compressor. The larger first-stage cyXinder i s on

the right. The first-stage cylinder fits 12 valves roM. the second-stage cylinder has four vaEves t a d . Again, note &e cylinder and packing lubricator mowted

on

the crankcase.

Cut-away of the two cylinder compressor. Note how the connecting rod between the crankshafi and

tEre

pistun rod is connected to the piston rod at the crosshead. The piston rod screws into the crosshead. A pin attaches the connecting rod to the crossbead.

Crankshaft

Cut-away of the two cylinder compressor. Note how the connecting rod between the crankshaft and the piston rod i s connected to the piston rod at the crosshead. The pism rod screws into the crosshead. A pin attaches the connecting rod ro the crosshead.

Connecting

Rod

Cut-away of the two cylinder compressor. Xote how the connecting rod

between the crankshaft and the piston rod is connected to the piston rod at the crosshead. The piston rod screws into the crosshead. A pin attaches the connecting rod

to

the crosshead,

Cms

Head

Cut-away of the two cylinder compressor. Note how the connecting rod

between the crankshdt and the piston rod is connected to the piston rod at the crosshead. Tfae piston

md

screws into the crosshead. A pin attaches the

Cut-away of the two cyfinder compressor. Note how the connecting rod between the crankshaft and the piston rod is connected to the piston rod at the crosshead. The piston rod screws into the crosshead, A pin attaches the connecting rod to the crosshead.

Paeking Box

Cut-away of the two cylinder compressor. Note how the comecting rod between the crankshaft and the piston rod is connected to the piston rod at

the crosshead. The piston rod screws into the crosshead. A pin attaches the connecting rod to the crosshead.

Four cylinder, two-stage compressor. The smaller second-stase cylinders

Fow cyhder, two-stage, compressor in field. Note the suction pulsation bottles on top of the cylinders. There are also dischaage pulsation bottles

under the cylinders. The pulsation butdes danpen the pulses caused by rhe reciprocating action of the pistons and ease the pulsations on the piping and fuu~dation,

Large, eight cylinder, two-stage compressor. The four first-stage cylinders

' are on the right. Note Be total number of valves. Each first stage cylinder has eight suction and eight discharge vafves. Each second-mge cylinder has six suction arnd six discharge valves. The total number of valves is 112!

If

one vdve bm&, the compressor is down.

Recip.rocating Compressor Piston

Rod,

Two

Compariement

Distance Piece

Two compartment distance piece

and

crosshead connecting piston rod to connecting rod.

.

Reciprocating Compressor

Frame Oil System Lubricator

Crankcase wl& shaft driven f m e oil pump. Note the motor driven

ReeQroeah'ng

Compressor Piston

Piston Rings, Rider

Rings

After the $-hour shop mechanical

run,

the piston nod is disconnected from

the cross head and the piston is pulled .From the cyginder

for

inspection.

Recerocating Compressor Advantages

$

High

Compression

Ratios

i

Constant VolmeIWide Pressure Range

m

Molecdar Weight Flexibility

r

Fairly Basic Evolved

Teclunology

Reciprocating

Compressor Disadvantages

r

Foundation

and Piping Requirements

Pufsatin;:Fiow

r

Vulnerable to Dirt

and

Liquid

t

Maintenance

r

Plot

Area

n

Large Volumes Constraints

r

Lurbsieticta:

Contamhating Process

Torsional Xmplia.bions

The foundation and piping have to be designed to handle the pulsating Bow.

Niaintenance is higher than far centrif~tgaf compressors due to the parts with close clearances. Reciprocating compressors are typically spared.

Reciprocating compressors take up a lot more space &an centrifugal compressozs.

The cylinder lube oiE can con2runinare downstream catalyst

or

molecular sieve absorbents.

A reciprocating compressor driven by a steam turbine though a speed reducing gear is not recommended.

D i a p h a p s guide the gas

from

the discharge of one impeller to the suction

Recycle

Gas Compressor

5 Stage

CePttrifugZ

Compressor

Five-stage centrifugal compfessos. Note the seal

md

lube oil piping

connections. The labyrinth seals minimize the flow of gas back to a lower

Stress Corrosion Crack

Riveted impeller. This is an old manufacturing technique, now obsolete. Today, most impellers are machined. The cover is $hen welded in place. The stronger wheds result in higher achievable perfonnif~ce per stage.

Stress Corrosion Crack

Riveted impeller. T h i s is an old manufacturing technique, now obsolete. Today, most impellers are machined. The cover is %en welded in place. The stronger wheels resuft in higher achievable performance per stage.

Cen&i!ugal Compressor Control

=

Variablte Speed

r

Suction Throttle Valve

Centrifusal compressors are controlled with variable speed or for a singXe speed driver, suction tkxottling.

Centrifuga

E

Compressor Typical Variable

Speed Performance Curves

30

30 40 50 60 70 80 90 100 110 120 130

Percent Inlet Volume

IPD21k14/CD45

cD.RCc-12

For a variable speed driver, steam tusbine, or variable speed motor, the compressor speed can be varied to meet the head requirements along the system resistance curve. Most variable speed compression trains can opesate between

70%

md 105% of the design speed.

Centrifugal Compressor Typical Constant

Speed Performance Curve

Percent Inlet Volume

When a compressor is motor driven, there is only one head-capacity curve. When operating at off-design cases, pressure must be thjrotzled over a

Centrifugal

Compressor

Typical

Constant

Speed Performance

Curve

The throztle valve can go upstream or downstream of the compressor.

If

the valve goes on the discharge, the voJurnetric Row rate, A m , is directly proportional to the mass flow, lbslh~. 808 Ibshr will be achieved at 80%

ACEM.

Note that a% 80% ACFM, almost half the head pmduced by the

compressor is ti~oa1ed across the control valve. Since

HP

is a Emction of mass fiow time heasl, almost half &e

E

l

?

requirement of the compsessox is wasted across the control valve.