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Oil & Gas Processing Course1

AKEEL AKRAMCHEMICAL ENGINEERING DEPARTMENT

Oil & Gas Processing Plants Design and

Operation

Training Course

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

ROTATING EQUIPMENT

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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

HP Amine pump in South Pars Acid Gas Removal unit

SHAFT

impellers

Casing

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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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Oil & Gas Processing Course 19

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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Characteristics of the liquid

Pumping characteristics

Mechanical characteristics

DETERMINATION OF PUMPING CHARACTERISTICS

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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 dischargevessel.

Characteristics of the liquid

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Normal flowrate (volume of fluid actually delivered per unit oftime at the stated operating conditions indicated in the materialbalance established for the nominal operating conditions).

Rated capacity or design flowrate (maximum flowrate required totake 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.

Pumping characteristics

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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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Type of driver.

- Most are electrical motors (usually fixed speed induction motor)

- Nameplate rating

125% rated power if 22 KW and 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 EVOLUTIONIN A CENTRIFUGALPUMP

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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 .

CALCULATION OF PUMP CHARACTERISTICS

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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.

CALCULATION OF PUMP CHARACTERISTICS

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Pressure Head difference : the difference in staticpressure between the starting point and the finishing

point of the system.

Static Head difference : the difference in levelsbetween the starting point of the system.

Frictional Resistance : the head due to the resistance

to flow as the liquid moves through the system.

DIFFERENTIAL HEAD

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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.

STEPS FOR ESTIMATING PRESSUREDIFFERENTIAL

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DIFFERENTIAL HEAD

Hmt = ---------------------- + (Zr - Za) + Hfa + Hfr(Pr - Pa)

g@ P,T

SYSTEM RESISTANCE CURVE

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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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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.

POWER

p

sd

w

PPQP

.36

)( minmax

p

sd

wPPQP

.36)( minmax

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ESTIMATION OF CENTRIFUGAL PUMPS EFFICIENCY

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RELATIONSHIP POWER - FLOW

C O / S S

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Formation and collapse of vapour cavities in a flowingliquid.

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 toform 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 theimpeller often results.

CAVITATION / NPSHNet Positive Suction Head

THE EFFECT OF VAPORIZATION ON THE HEAD FLOW CURVE

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THE EFFECT OF VAPORIZATION ON THE HEAD-FLOW CURVE

THE DIFFERENCE BETWEEN REAL AND APPARENT CAVITATION

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THE DIFFERENCE BETWEEN REAL AND APPARENT CAVITATION

CAVITATION / NPSH N t P iti S ti H d

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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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Net Positive Suction Head available (NPSHA)- Determine by pump purchaser

Net Positive Suction Head required (NPSHR).

- Function of physical dimensions of casing, speed and typeof impeller.

- Increases as the pump speed increases.

- For this reason many critical suction condition

installations use relatively slow speed pumps.


NPSH il bl

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NPRHA= ------ + -------- - --------Po Co2

2gPVt

NPRHA = ----------------------------- + Za - Hfa(Pa - PVt)

g@ P,T

NPSH available

NPRHA = NPRHR + 1 m

Where:

Po = Dynamic press. at pump inletCo = Fluid velocity at pump inletP1 = Minimum pressure in pumpPa = Pressure in upstream vessel (bar)PVt = Vapor pressure of fluid @ T (bar)= densityG = gravity constantZa = Liquid level in upstream vessel (m)Hfa = Suction pressure losses (m)P, T = Pumping conditions

THE DIFFERENCE BETWEEN NPSH absolute AND NPSHR

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THE DIFFERENCE BETWEEN NPSH absolute AND NPSHR

MEASURED USING AERATED WATER


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Ways of increasing NPSHA:

- Reduce the pressure drop in the pump suction piping by increase of the linediameters and the decrease of the number of pipe components (bends,...).

- Increase the liquid suction static head by elevation of the suction vessel levelof by lowering the pumping station grade level.

- Reduce the vapour pressure value of the pumped liquid with the use of acooler installed on the pump suction piping (this solution is not oftenfeasible).

- Locate pump as close as possible to suction vessel.

- Select a draw-off location on the suction vessel where the least opportunityfor vapour entertainment exists, and provide a vortex breaker within thesuction vessel.

- Avoid potential air or vapors traps ; eg : use flat-top reduces, avoid invertedloops, etc

- Arrange suction piping to slope continuously downward, avoiding any highpoints (minimum slope : 2 %).


Centrifugal pump with inducer

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Centrifugal pump with inducer

TYPICAL CENTRIFUGAL PUMP PERFORMANCE CURVES

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TYPICALCENTRIFUGAL PUMP PERFORMANCE CURVES

Performance correction chart for viscous flow

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Performance correction chart for viscous flow

AFFINITY LAWS

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AFFINITY LAWS

Change of speedfrom N1to N2Change of diameterfrom D1to D2

New Flowrate

New Head

New Power

1

212

D

DQQ

1

212

N

NQQ

2

1

212

N

NHH

2

1

212

D

DHH

3

1

212

DDPP

3

1

212

NNPP

MINIMUM FLOW

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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

MINIMUM FLOW

FLOW CONTROL

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Throttling control

- By throttling valve in discharge piping.

- Consumes energy since it artificially increases the systemresistance to flow .

Speed control- Not frequently done because most pumps are driven by fixed - speed

motors.

- Adjusting the rotational speed often consume substantially lessenergy.

- 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 variablespeed pump drivers.

FLOW CONTROL

HEAD CAPACITY AND PIPING SYSTEM RESISTANCE CURVE

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HEAD-CAPACITY AND PIPING SYSTEM RESISTANCE CURVE

FLOW CONTROL BY VARYING PUMP SPEED

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FLOW CONTROL BY VARYING PUMP SPEED

FLOW CONTROL

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Recirculation control

- Used more frequently for positive displacement pumps

- Caution for centrifugal pumps, because a wide-openbypass may result in a head so low that the pumped fluidwill be circulated back to the suction at an extremely highrate, causing high power consumption, increase in fluidtemperature, and possibly cavitation, as well as possibleoverloading the driver.

- For many types of centrifugal pumps manufacturersstipulate minimum flow requirements to prevent pump

damages. It is recommended to circulate the pumped fluidnot back to the suction pump but back to the suctionvessel

FLOW CONTROL

LOW FLOW RECIRCULATION BY FIC

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LOW FLOW RECIRCULATION BY FIC

LOW FLOW RECIRCULATION BY OUTLET CHECK VALVE

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LOW FLOW RECIRCULATION BY OUTLET CHECK VALVE

PARALLEL SERVICE

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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 systemcharacteristic, the flow will not necessarily increase in proportion to the number ofpumps added.

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

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

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

- Use of multiple pumps may allow investment savings, i.e. for high capacity servicesthree 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, itmay be preferable to have a service pump and its spare operate in parallel, rather thandesign each for the full over-normal flow rate.

- To increase plant safety and (or) reliability.

PARALLEL SERVICE

PUMPS IN PARALLEL SERVICE

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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

PUMPS IN PARALLEL SERVICE

SERIES SERVICE

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When?

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

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

SERIES SERVICE

PUMPS IN SERIES OPERATION

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Multiphase Production

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Before

When the development a marginal field or a group of remote wells is consideredtogether with an existing central gathering system the traditional options for fielddevelopment 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 transportedover long distances without the need for prior separation. .

- Interest for multiphase production, which leads to simpler and smaller in-fieldinstallations, is primarily dictated by the need for more a cost effective productionsystem

- Capable of handling liquid/vapor fraction ranging from 0% to 100%

Multiphase Production

Multiphase pumps

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Multiphase pumps

The standardized Sulzer MPP pump rangeincorporates 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 thepump can handle any void fractions without

phase separation occcuring whilst also being

very tolerant of sand particles.

Multiphase pumps

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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 characteristicsduring the production life of the field

Multiphase pumps

NAUTILUS PROJECT

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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 forthepump/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 remotefields.

NAUTILUS PROJECT

INSTALLATION FACILITIES

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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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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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OPERATION

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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

Y2 PUMPS

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