Oil & Gas Processing Plants Design and

Operation
Training Course

AKEEL AKRAM – CHEMICAL ENGINEERING DEPARTMENT

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 ROTATING EQUIPMENT

DGEP/SCR/ED/ECP ~ 6th - 17th October 2003

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CONTENT

1. Pumps
2. Compressors
3. Turbo-Expanders
4. Gas Turbines

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PUMPS

• Pumps classification

• Positive displacement pumps

• Centrifugal pumps performance

• Pumps in operation

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PUMPS CLASSIFICATION

• Volumetric (Positive Displacement)

- Low/moderate capacity & high differential head
- Either reciprocating or rotary.
- Reciprocating pumps include piston, plunger, and
diaphragm types. (Chemical lnj : TEG Circulation, ...)
- Piston plunger may be single or double acting (Simplex,
Duplex, Triplex).
- Rotating (Lube oil, Viscous fluids, ...)

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PUMPS CLASSIFICATION

- Rotating
• depends on the close clearance between both rotating and
stationary surfaces to seal the discharge from the suction.
- Diaphragm pumps
• deliver a small, precisely controlled amount of liquid at a
moderate to very high discharge pressure. Used as
chemical injection pumps because of wide range of
materials in which they can be fabricated, and their
inherent leakproof design.

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DIAPHRAGM PUMP

Applications: Metering pumps

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CENTRIFUGAL: END SUCTION PUMP

Applications: Reflux, circulation, booster, boiler feed

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GEAR PUMPS

Applications: Diesel oil transfer and lube oil distribution

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SCREW PUMPS

Applications: Slop oil, viscous fluids

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 HORIZONTAL ‘ IN-LINE ’ PUMPS

Applications:Reflux, circulation, booster, boiler feed

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MULTISTAGE

Applications: seawater injection, condensate injection, pipeline transfer,

HP Amine

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 MULTISTAGE

SHAFT

impellers

Casing

HP Amine pump in South Pars Acid Gas Removal unit

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VERTICAL ‘ IN - LINE ’ PUMP

Applications: Reflux, circulation, booster, boiler feed

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‘ HEAVY PROCESS ’ - PUMP -

Applications: crude oil lift, transfer and/or boosting

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VERTICAL ‘ BARREL ’ OR ‘ CANNED ’ PUMP

Applications: Loading, transfer, pipeline booster, boiler feed

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Volumetric pumps

• Dynamic (Variable Head)

- Centrifugal (General Process, Liquid Exports, ...)
- Axial (Very high flowrate : Cooling water, ...)

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Volumetric pumps

Advantages of centrifugal pumps:

• less costly,
• require less maintenance,
• less space
• deliver an uniform (non-pulsating) flow.
• Due to their high reliability and inherent flexibility over a wide
range of operational cases, plus the wide range of pumps
available covering very different performance requirements, the
centrifugal pump (in some cases the axial pump) is the pump
most frequently used in the petroleum industry.
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PUMPS

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Centrifugal pumps

• Horizontal vs vertical pumps

• Vertical pumps :
- more compact
- often used for liquids at their bubble-point temperature
(The vertical distance from the suction flange down to the
inlet of the first stage impeller provides additional NPSHA).

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DETERMINATION OF PUMPING CHARACTERISTICS

• Characteristics of the liquid

• Pumping characteristics

• Mechanical characteristics

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 Characteristics of the liquid

• Nature (hydrocarbons, water,...),

• Corrosive elements presents in the liquid (H2S, salts...),
• Erosive elements presents in the liquid (solids and sludges)
• Pumping temperature,
• Density or relative density at pumping temperature,
• Vapour pressure at pumping temperature,
• Minimum and maximum operating gas pressure above liquid
level in suction vessel,
• Maximum operating gas pressure above liquid level in discharge
vessel.

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 Pumping characteristics

• Normal flowrate (volume of fluid actually delivered per unit of

time at the stated operating conditions indicated in the material
balance established for the nominal operating conditions).
• Rated capacity or design flowrate (maximum flowrate required to
take in account the variations of operating conditions to adapt
the installation to the new field yields).
• Rated capacity is equal to the normal flowrate increased by the
overcapacity factor or pump design factor.
• Maximum discharge pressure required at rated capacity.
• Minimum suction pressure available at rated capacity.
• Net Positive Suction Head Available (NPSHA) at rated capacity.
• Determined by No of pumps operated simultaneously.

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Mechanical characteristics

• Type of pump desired if there is a preference (for

spare parts standardisation for instance)
• centrifugal, Triplex, etc...,
• horizontal, vertical in-line, etc...
• Flange ratings, flange type if other than standard,
• Mechanical seal required,
• Preferred metallurgy of major parts,
• Type of driver.

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Mechanical characteristics

Type of driver.
- Most are electrical motors (usually fixed speed induction motor)
- Nameplate rating
• 125% rated power if <22 KW
• 115% if >22 KW and <55 KW
• 110% if > 55KW
• Material
- Usually cast-steel cases and cast iron internals (API 610)
• Seals (API-682)
- Consists of stationary and rotating face
- Requires cooling and lubrification

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LIQUID HYDRAULIC PATH IN A CENTRIFUGAL PUMP

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PRESSURE VELOCITY EVOLUTION IN A CENTRIFUGAL PUMP

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CALCULATION OF PUMP CHARACTERISTICS

• Need detailed isometric flow diagram to determine :

- the straight length and the diameter and the thickness of the different suction and discharge
pipe sections,
- the manifold characteristics and the number of piping components with their main
characteristics (bends, valves, tees,...),
- the process equipment (heat exchanger, heater,...)
- the liquid suction static head between the low liquid level in the suction vessel and the
centerline of the pump suction flange,
- the liquid discharge static head between the higher point reached by the liquid in the discharge
line or in the discharge vessel and the centerline of the pump discharge flange.

• If the isometric flow is not available, the process engineer must establish a simplified flow
diagram to show and estimate all characteristics indicated here above, in particular the
suction and discharge line profile .

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CALCULATION OF PUMP CHARACTERISTICS

• RATED CAPACITY

• It is equal to the normal flowrate corresponding to the nominal operating conditions

increased by the overcapacity factor (or pump design factor).

• Overcapacity factor (or pump design factor) recommended :

- 10 % volume for feed pumps and pumps transferring fluids between column or drums,

- 20 % volume for reflux pumps and circulating pump around circuits,

- 20 % volume for boiler feed water pumps.

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DIFFERENTIAL HEAD

• Pressure Head difference : the difference in static

pressure between the starting point and the finishing
point of the system.

• Static Head difference : the difference in levels

between the starting point of the system.

• Frictional Resistance : the head due to the resistance

to flow as the liquid moves through the system.

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STEPS FOR ESTIMATING PRESSURE DIFFERENTIAL

• Calculate system resistance (Conservatism : high static level and

pressure differential, and the highest expected pipe friction).

• Calculate system resistance (best case : low of static level and

pressure differential and the lowest pipe).

• Plot these curves as the extremes expected from the behaviour

of the system.

• Select pumping equipment that successfully meets all

reasonably expected operating conditions.

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SYSTEM RESISTANCE CURVE

DIFFERENTIAL HEAD
(Pr - Pa)
Hmt = ---------------------- + (Zr - Za) + Hfa + Hfr
g @ P,T
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DIFFERENTIAL HEAD

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RELATIONSHIP HEAD - FLOW

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PUMP AND SYSTEM CURVE

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 POWER

Q  ( Pd max  Ps min )
Pw 
36. p
Q  ( Pd max  Ps min )
Pw 
36. p
• pw = brake pumping power, kW,
• Q = rated capacity or design liquid flowrate, m3/h,
• PdMax = maximum discharge pressure at centerline of pump discharge flange, (bar abs),
• Psmin = minimum suction pressure at the centerline of the pump suction flange, (bar abs),

• p = pump efficiency .

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ESTIMATION OF CENTRIFUGAL PUMPS EFFICIENCY

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RELATIONSHIP POWER - FLOW

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CAVITATION / NPSH – Net Positive Suction Head

• Formation and collapse of vapour cavities in a flowing

liquid.
• Local pressure is reduced to that of the liquid vapour
pressure at the temperature of the flowing liquid.
• At these locations, some of the liquid vaporises to
form bubbles or cavities of vapour system.
• Collapse of bubbles begin when local pressure is
higher than the vapour pressure.
• Result in Noise, severe pitting, and erosion of the
impeller often results.

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THE EFFECT OF VAPORIZATION ON THE HEAD-FLOW CURVE

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THE DIFFERENCE BETWEEN REAL AND APPARENT CAVITATION

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CAVITATION / NPSH – Net Positive Suction Head

• NPSH definition:
- Total inlet pressure, in meters or feet of liquid pumped
determined at the pump suction connection (i.e. suction
flange), minus the vapour pressure of the liquid pumped in
meters or feet of liquid pumped at pumping temperature.
• Two NPSH definitions are used in pumping systems :
- Net Positive Suction Head available (NPSHA),
- Net Positive Suction Head required (NPSHR).

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CAVITATION / NPSH – Net Positive Suction Head

• Net Positive Suction Head available (NPSHA)

- Determine by pump purchaser

• Net Positive Suction Head required (NPSHR).

- Function of physical dimensions of casing, speed and type
of impeller.
- Increases as the pump speed increases.
- For this reason many critical suction condition
installations use relatively slow speed pumps.

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NPSH available
2
Po + --------
NPRHA = ------ Co - --------
PVt
 2g 
(Pa - PVt)
NPRHA = ----------------------------- + Za - Hfa
g @ P,T
NPRHA = NPRHR + 1 m

Where:

Po = Dynamic press. at pump inlet

Co = Fluid velocity at pump inlet
P1 = Minimum pressure in pump
Pa = Pressure in upstream vessel (bar)
PVt = Vapor pressure of fluid @ T (bar)
 = density
G = gravity constant
Za = Liquid level in upstream vessel (m)
Hfa = Suction pressure losses (m)
P, T = Pumping conditions

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 THE DIFFERENCE BETWEEN NPSH absolute AND NPSHR
MEASURED USING AERATED WATER

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CAVITATION / NPSH – Net Positive Suction Head

• Ways of increasing NPSHA:

- Reduce the pressure drop in the pump suction piping by increase of the line
diameters and the decrease of the number of pipe components (bends,...).
- Increase the liquid suction static head by elevation of the suction vessel level
of by lowering the pumping station grade level.
- Reduce the vapour pressure value of the pumped liquid with the use of a
cooler installed on the pump suction piping (this solution is not often
feasible).
- Locate pump as close as possible to suction vessel.
- Select a draw-off location on the suction vessel where the least opportunity
for vapour entertainment exists, and provide a vortex breaker within the
suction vessel.
- Avoid potential air or vapors traps ; eg : use flat-top reduces, avoid inverted
loops, etc…
- Arrange suction piping to slope continuously downward, avoiding any high
points (minimum slope : 2 %).

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Centrifugal pump with inducer

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TYPICAL CENTRIFUGAL PUMP PERFORMANCE CURVES

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Performance correction chart for viscous flow

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AFFINITY LAWS

Change of speed Change of diameter

from N1 to N2 from D1 to D2

New Flowrate N2 D2
Q 2  Q1  Q 2  Q1 
N1 D1
New Head 2
 N2
2
 D2 
H 2  H 1   H 2  H 1  
 N1   D1 
New Power 3
 N2
3
 D2 
P 2  P1    P 2  P1   
 N1   D1 

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MINIMUM FLOW

• If discharge is shut-off, all energy converted to heat

• Liquid heats up rapidly and eventually vaporises
• Can result in catastrophic failures

- Pump vendor shall specify minimum flow requirements

to ensure adequate flow

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FLOW CONTROL

• Throttling control

- By throttling valve in discharge piping.

- Consumes energy since it artificially increases the system
resistance to flow .

• Speed control
- Not frequently done because most pumps are driven by fixed - speed
motors.
- Adjusting the rotational speed often consume substantially less
energy.
- Used for large, powerful pumps, because it allows to follow as
closely as possible the area of highest pump efficiency.
- An hydraulic coupling variable speed driver is used with a constant
speed electric motor,
- For large units gas and steam turbines are ideally suited as variable
speed pump drivers.
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HEAD-CAPACITY AND PIPING SYSTEM RESISTANCE CURVE

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FLOW CONTROL BY VARYING PUMP SPEED

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FLOW CONTROL

• Recirculation control

- Used more frequently for positive displacement pumps

- Caution for centrifugal pumps, because a wide-open
bypass may result in a head so low that the pumped fluid
will be circulated back to the suction at an extremely high
rate, causing high power consumption, increase in fluid
temperature, and possibly cavitation, as well as possible
overloading the driver.
- For many types of centrifugal pumps manufacturers
stipulate minimum flow requirements to prevent pump
damages. It is recommended to circulate the pumped fluid
not back to the suction pump but back to the suction
vessel

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LOW FLOW RECIRCULATION BY ‘ FIC ’

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LOW FLOW RECIRCULATION BY OUTLET CHECK VALVE

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PARALLEL SERVICE

• Pumps may be designed for parallel operation for any of the following typical reasons :

- Capacity increase for an existing pumping service. Due to the existing discharge system
characteristic, the flow will not necessarily increase in proportion to the number of
pumps added.

- Very high reliability is required without total reliance on the functioning of an autostart
mechanism.

- Required capacity exceed capacity of any pump or driver model.

- Required capacity exceed the utility energy supply available for a single driver or driver
type.

- Use of multiple pumps may allow investment savings, i.e. for high capacity services
three 50 % sized pumps may require lower total investment than two 100 % sized pumps.

- To meet a requirement for flow capacity higher than normal on an infrequent basis, it
may be preferable to have a service pump and its spare operate in parallel, rather than
design each for the full over-normal flow rate.

- To increase plant safety and (or) reliability.

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 PUMPS IN PARALLEL SERVICE

WHEN ‘ HALF CAPACITY ’ PUMPS ARE

IN PARALLEL SERVICE

QR1 = Rated capacity of each half capcity ’s pump

Qmax1 = Maximum capacity of single pump
Qmax2 = Maximum operating flow obtained by two half capacity pumps in service
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SERIES SERVICE

• When?

• Unusually high NPSHR, i.e. operating at a high differential head - design flow
point requires a "booster" pump to pressure the suction of the high pressure
pump.

• Head requirement exceeds the capability of a single pump and the flowrate
is beyond the economic reciprocating pump range.

• The differential pressure requirement is low enough at times that one of

several pumps in series can be turned off, as in transportation pipelines.

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PUMPS IN SERIES OPERATION

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Multiphase Production

• Before

• When the development a marginal field or a group of remote wells is considered

together with an existing central gathering system the traditional options for field
development were:
• natural flow,
• artificial lift,
• In-field separation with crude oil pumps and gas compression systems

Multiphase pumping offers a fourth solution:

- Imparts energy to the unprocessed effluent enabling liquid/gas mixture to be transported
over long distances without the need for prior separation. .
- Interest for multiphase production, which leads to simpler and smaller in-field
installations, is primarily dictated by the need for more a cost effective production
system
- Capable of handling liquid/vapor fraction ranging from 0% to 100%

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Multiphase pumps

• The standardized Sulzer MPP pump range

incorporates the latest 2nd generation helico-
axial Poseidon developed by IFP for the
poseidon group (IFP, Total and Statoil) and
subsequently licensed to Sulzer pumps.

• The MPP pump is a multi-stage pump with each

stage or compression cell comprising a rotating
helico-axial flow impeller and a stationary
diffuser.

• The poseidon hydraulic design ensures that th

epump can handle any void fractions without
phase separation occcuring whilst also being
very tolerant of sand particles.

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Multiphase pumps

• Advanced hydraulic design allied to simple modular concept

• Duplex metallurgy for corrosion resistance and H2S service
• Flow homogenizer for smoother mechanical running when sudden transient
phenomena such as severe slugging are likely to occur
• Hydraulic flexibility and wide range of duties
• Easily retrofitted to take account of changing reservoir characteristics
during the production life of the field

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 NAUTILUS PROJECT

Nautilus is a subsea 1.3 MW electrically driven

multiphase booster station.

The development of this project is being led by

TOTAL with Sulzer having overall responsibility for
thepump/motor unit.

Nautilus has been designed for installation up to

about 60 km (37 miles) from the receiving platform
which is therefore expected to improve significantly
the economic viability of subsea satellite or remote
fields.

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INSTALLATION FACILITIES

• Temporary strainers
• Used for the protection during the initial operating period
of new plants to collect weld beads, pipe scale, and any
other foreign matter
• Permanent strainers
• Used where solids or foreign matter are a normal
constituent of the pump fluid.
• cleaned when pressure drop reaches maximum allowable
limit.

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INSTALLATION FACILITIES

• Reciprocating pump pulsation dampeners

• Pressure pulsations can lead to pipe failure

• Pulses reduced by:
• Using a multiple cylinder pump such as duplex or triplex,
• by installing bladder-type accumulators (pulsation
dampeners) in the pump discharge lines, or by a change of
driver speed.

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INSTALLATION FACILITIES

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OPERATION

• Typical starting sequence

- Ensure all valves in auxillary sealing, cooling and flushing
are open and that systems are functioning properly.
- Close discharge valve
- Open suction valve
- Vent gas from pump and associated piping
- Energize driver
- Open discharge valve slowly
- On large, multistage pumps, flow is established in a matter
of seconds thanks to the minimum flow recirculation

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