dpm lect 1 unit 3

8/9/2019 DPM Lect 1 Unit 3

1/54

Samarth D. Patwardhan


2/54

y UNIT 3y Pumps, Valves and compressors

y Introduction to mud circulation system

y

Design consideration for pipelines in O&Gtransportation

y UNIT 6y Agitators and their design

y Introduction to O&G storage facility

y Types and design of storage tanks


3/54


4/54

y A device used to move / displace fluid by the use ofphysical or mechanical action

y They do not create pressure

y The resistance to the flow is what creates pressurey Classification of pumps

y Positive displacement pumps

y Centrifugal pumps


5/54

y Moves fluid by trapping a fixed amount of it

y Discharging the trapped volume on the discharge side

y Classified as two main types:y Reciprocating types

y Plunger pumps

y Diaphragm pumps

y Rotary types


6/54

y Plunger pump consists of a cylinder with a reciprocatingplunger in it

y Suction strokey Suction valve opens, plunger retracts, and the fluid is sucked

into the cylindery Discharge stroke

y Plunger pushes the liquid forward, discharge valve opens andfluid is discharged

y When the plunger is in the end position, we have zero flow

y When the plunger is in the middle position, we havemaximum flow

y Lot of energy is wasted in the acceleration of fluid


7/54

y The positive displacement principle applies to:y rotary lobe pumpy progressing cavity pumpy rotary gear pumpy piston pumpy diaphragm pumpy screw pumpy gear pumpy

Hydraulic pumpy vane pump

y Never to be operated against a closed valve


8/54

y We have a rotating element in the pumps, and operatein a circular motion

y Displace a constant amount of liquid with eachrevolution of the pump shaft

y Very efficient (tight clearances dont allow liquid to slipback from discharge to suction side of the pump)

y Types of rotary pumps are:y gear pumpsy lobe pumpsy vane pumpsy screw pumps


9/54

y Differ from rotary pumps

y Rely on kinetic energy (than on mechanical energy) tomove liquid

y Liquid enters at the center of a rotating impeller, andgains energy, as it moves towards the outer diameter ofthe impeller

y Liquid is forced out of the pump by the energy it

obtains from the rotating impellery The kinetic energy of the fluid is first increased, and

then converted to potential / pressure energy


10/54

y Classified as eitherradial or axial f lowpumps

y Radial f lowy Fluid enters the center

of the rotating wheeland is propelledradially to the outsideby the centrifugal

forcey Within the impeller,

velocity is increased,and is converted topressure


11/54

y Axial pumpsy Flow is parallel to the axis of the shaft

y Velocity is imparted by the impeller vanes, which are

shaped like airfoils


12/54

y High viscosity many centrifugal pumps are rated atviscosities higher than 1000 cp, PD pumps are a betterchoice

y Variations in pressure PD pumps maintain their flowrate with variations in pressure; centrifugal pumps are

very sensitive to pressure variation

y Variation in viscosity PD pump is a better choice, asvariation in viscosities also result in variations in

pressuresy High pressures PD is the clear choice when high

pressures are required


13/54

y The pressure discharged by a pump is usuallyexpressed as head

y The head required to pump a fluid between two pointsis calculated from a derivation from Bernoullis law:

y Where,y Hp is head required for the pump, fty H1 is the total fluid head at point 1, fty H2 is the total f luid head at point 2, fty Hf is total head lost due to friction, between pts 1 and 2,

ft

12 HHHH fp !


14/54

y By rearranging the terms, we have:

y Where,y Rho is the density of f luid in lbs/ft3

y P1 and P2 are pressures in psiy V1 and V2 are velocities in ft/secy G is 32.2 ft/sec2

y

If Hp is 0, then pipeline is in equilibrium, and no pumpenergy is required to obtain the desired flow

y If Hp


15/54

y HHP (hydraulic horsepower) is given by:

y

Where,y HHP is hydraulic horsepower (1 HHP=550 ft-lb/sec)y Hp is pump head in fty Rho is density in lb/ft3

y Q is Flowrate in ft3/sec

y Q1 in bpd, Delta-P in psi

550

QHHHP

pV!

766,58

1 PQHHP (!


16/54

y The brake horsepower is the input horsepower to theshaft of the pump, and is given by:

BHP = HHP / E

y Where, E is the pump efficiency


17/54

y We lived submerged at thebottom of an ocean of theelement air EvangelistaTorricelli

y weight of this air exerts aforce on earth, called asatmospheric pressure

y When vacuum is applied,the tube draws the mercuryinside

y Weight of the column ofmercury is the same asweight of the air outside thetube (atm. pressure)


18/54

y Fluid flows from areas of high pressure to areas of lowpressure

y Pumps operate by creating a low pressure at its inlet,which allows liquid to be pushed into the pump byatmospheric or head pressurey Pressure of the liquids surface being above the center-

line of the pump

y For the mercury barometer above,y

Even with perfect vacuum at the pump inlet,atmospheric pressure limits how high the liquid is lifted

y There is a physical limit to the pump operation, basedon the pressure external to the pump


19/54

y NPSH can be classified into two parts:y NPSHA the absolute pressure at the suction port of the

pumpy Function of the system, and needs to be calculated

y NPSHR the minimum pressure required at the suctionport to keep the pump from cavitatingy Function of the pump, and the manufacturer provides it

y NPSHAmust be greater than NPSHRy More suction side pressure should be available than

what the pump requires


20/54

y Vapor pressure is the pressure required to boil aliquid at a given temperature

y Soda water high vapor pressure liquidy At room temp, CO2 entrained is released

y In a closed can, soda is pressurized, vapor isentrained

y Cavitation occurs when the pressure in thepump inlet drops below the vapor pressure ofthe liquidy Vapor bubbles are formed at the inlet of the

pump, moved towards the discharge side,collapse on the surface, and eat away smallpieces of pump


21/54

y Loud noisy pump operation

y Loss of capacity (bubbles taking up space than liquids)

y Pitting damage to pump parts

y Many people / engineers take this as corrosiony Corrosion affects the material throughout, whereas

pitting is at selective places


22/54

y NPSHAis calculated as:

NPSHA= HA+(-) Hz HF + Hv Hvpy Where,

y HAis absolute pressure on the surface of the liquid insupply tank

y Hz is vertical distance between surface of the liquid andthe pump centre-line

y

HF is friction losses in the suction pipingy Hvis the velocity head at the pump suction port

y Hvp is the absolute vapor pressure of the liquid at thepumping temperature


23/54

y HA typically atmospheric pressure, always positive,altitude affects this value

y Hz can be positive (static head) if liquid level is

above the center-line of the pump, otherwise negative(suction lift)

y HF piping and fittings cause pressure drop, acting asrestrictions

y Hv very small value, mostly ignoredy Hvp must be subtracted in the end, to make sure the

inlet pressure stays above the vapor pressure


24/54


25/54

y Valves that activate automatically to relieve pressureare called relief valves

y One of the most important safety devices

y

Ensure that the pipes, fittings and other equipmentscan handle pressures higher than their designedpressures

y Essential device in a surface facility system

y Most of them are spring-loaded, and open fully, when

requiredy 2 types of relief valves conventional, balance-

bellowed


26/54

y Conventional can be usedanywhere where that the back-pressure in the relief header is

lowy Onshore they are used on

individual pipe lines

y Offshore mainly used for fire

and thermal relief


27/54

y Balanced bellows usedwhen the backpressure ratingis a little high (more than 10%

of the set pressure)y Used where conventional

valves cant be used

y Advantage bellows protect

the spring from process fluidy Disadvantage bellows can

fatigue out


28/54


29/54

y Service conditions

y Material to be used

y Load requirement

y Back-pressure variationsy Maximum allowable pressure drop across valve

y Location of valve-setting

y Type of application (fluid)


30/54


31/54

y Positive displacement compressorsy Reciprocating

y rotary

y

Centrifugal compressors


32/54

y Compression is accomplished by movement of adisplacing element

y Two main types of PD compressors are:y

Reciprocating compressory Rotary compressor


33/54

y Compressing and displacing element is a pistonmoving linearly within a cylinder

y Each cylinder assembly includes:y

A pistony Cylinders

y Cylinder heads

y Suction and discharge valves

y N

ecessary parts to convert rotary motion toreciprocating motion


34/54

y Can deliver large volumes of gasy Up to 30,000 cubic feet / min

y Large discharge pressure 10,000 psig

y

Main advantagesy Non-lubricating

y High-pressure ratios through multi-staging

y Variable capacity

y

Disadvantagesy High maintenance

y Pulsation created by unbalanced forces


35/54


36/54


37/54

y Positive displacement is accomplished by the positiveaction of rotating elements

y Two or three stage units

y Advantagesy Does not produce pulsating action

y Less space requirement

y Disadvantages

y Uses more oily Less discharge pressure


38/54


39/54

y Accomplish compression through a rotating screw

y By adjusting the inlet and outlet port sizes, gas iscompressed and discharged continuously

y Lower initial and installation costs, as compared toreciprocating compressors

y Popular for reducing well-head pressures to increasegas production


40/54

y Advantagesy Ability to handle dirty gas

y Flexibility to use different materials

y

Variable capacity controly Disadvantages

y Low efficiency

y Limited pressure range


41/54

y The rotating impellers impart a velocity head to thefluid which is converted to pressure head

y Few moving parts

y

Only impeller and shaft rotatey Provide continuous delivery, without any cyclic

variations

y Low maintenance and oil consumption costs


42/54

y Advantagesy High capacity

y Virtually oil free operations

y High pressure capability

y Low maintenance

y Disadvantagesy Relatively expensive

y Inflexible in change in pressure ratios and capacities

y Extremely sensitive to vibrations


43/54


44/54

y Based on the laws ofThermodynamics

y Applies to both positive displacement and continuousflow compressors

y

For gas, three types of compressions are possibley Isothermal

y Adiabatic

y Polytropic


45/54

y Using ideal gas law, if temperature is constant, therelation between p and V is given by:

pV = constant

yIn practice, isothermal compression is approached

when the operation is carried out slowly, so that,through heat transfer, T can be maintained constant


46/54

y In adiabatic compression, no heat transfer is allowedduring the compression

y In this case, the relationship is given by

pVk

= Constanty Where k is the specific heat ratio (Cp/Cv)

y For adiabatic processes,

tconsTp kk

tan

1

!


47/54

y Polytropic compression is given by

pVn = constant

y Value of n is between 1 and k, if the process is between

isothermal and adiabatic processy n>k, if it is below the adiabatic process

y Using ideal gas law, the relationship between p and Tis given by:

tconsp nn

tan

1

!


48/54

y The work required to compress the gas is given by thearea within the cycle

y Isothermal compression is the most efficient in termsof compressing the gasy Heat is not always removed as easily as when it is

compressed

y Adiabatic and polytropic compression is used, in apractical sense

y

For positive displacement pumps, adiabatic process isclosely approached, but for centrifugal compressors,polytropic process is a better indicator


49/54

y Compressor Ratio is defined as the ratio of the dischargepressure over suction pressure

y Rt = Pd / Psy Gas compressors typically have an overall compression ratio

between 5 and 20y Factors for specifying a compressor:

y Typey Stages of compressiony Horsepower required

y Information neededy

Volume of gasy Suction and discharge pressuresy Suction temperaturey Specific gravity of gas


50/54

y Its a cyclical problemy Horsepower and number of stages of a compressor

depends on the choice of compressory Type of compressor, partly depends on horsepower and

number of stagesy As a 1st step number of stages can be estimated

assuming a compression ratio between 3 and 4

y And, BHP can be estimated by

BHP = 22RnFQg

n

Ps

PdR

/1

!


51/54

y Where,y R ratio per stage

y N number of stages

y F allowance for inter-stage pressure dropy 1.0 for single-stage

y 1.08 for two-stage

y 1.10 for three-stage

y Qg flowrate in mmscfd

y Once the required horsepower and number of stages isestimated, a choice of compressor can be made


52/54


53/54

y ExxonMobil sets drilling recordsy 7000 ft below sea level, more than 6 miles Hz

y Reliance entersMarcellus Shale

y

China on the prowly In 2009, spent $60 billion

y Canada moves towards green goalsy 90% of power from carbon-free resources by the end of

decadey The race for Arctic


54/54

y Introduction to mud circulation systems

y Design consideration for pipelines in O&Gtransportation

dpm lect 1 unit 3

Documents