Presentation on Various Pump & Dicharge Side Control Schemes DD - Copy

Engineers & Technologist Pvt. Ltd.

SmartBrains

Pumps Selection, Sizing & Suction/Discharge side Flow/ Pressure

Regulation Control Guidelines

1.Pump 2 Control Valve-Pump Discharge Circuits

1.0 Pump1.1 Introduction The common types of pumps used in oil & gas industry are

centrifugal and positive displacement. CENTRIFUGAL PUMP Modern practice is to use centrifugal pumps because they are

usually less costly, require less maintenance, and less space. Conventional centrifugal pumps operate at speeds between

1200 and 8000 rpm. Very high speed pumps, which can operate up to 23000 rpm

and higher, are used for low capacity and high head applications.

Most centrifugal pumps will operate with an approximately constant head over a wide range of capacity.

POSITIVE DISPLACEMENT PUMP

Positive displacement pumps operate with approximately constant capacities over wide variation in head, and hence they are usually installed for services which require high head at moderate capacities.

A typical application of small reciprocating pump is for injection of fluids ( e.g. methanol and corrosion inhibitors) in to process streams where their constant capacity characteristic is desirable.

For procurement of a pump, it is necessary to furnish all pertinent process information.

Based on this information, Rotating Equipment group specialist will prepare pump specifications for pump vendor.

1.1.1 Different types of pumps and criteria for selection 1.1.1.1 Different types of pumps Pumps used are generally of following category: centrifugal positive displacement -They are of two types:-Reciprocating - piston, plunger or diaphragm type -Rotary - Gear, Screw or lobe type The problem is to select the size and type that most nearly fits

the service in question.

Centrifugal pumps are most widely used in chemical industry. For these pumps, there is a distinct relationship between head developed and capacity discharged for a centrifugal pump.

Positive displacement pump produces what ever head is imposed upon them. A safety valve is always required at discharge of the pump ( PSV is always in vendor’s scope of supply) .

1.1.1.2 Selection of Pump Type Though several parameters go in to the selection of type of

pump, capacity, head and viscosity are the major parameters, based on which a process engineer can decide the type of pump

It is further fine tuned with close cooperation between vendor and rotating equipment specialist.

Preliminary selection is however done by process engineer. Figure-12.3 from GPSA should be referred for selection of pump type based on head-capacity requirements.

Centrifugal pumps can handle liquids having viscosity up to 200 C S. For higher viscosity, specify screw, gear or reciprocating pumps.

Past commissioned jobs are best reference for selection of pumps.

 Another important criteria which dictates selection of pump is NPSHA.

For low NPSHA, special pump like Sundyne or equivalent or vertical barrel pump are used. Major features of different types of pumps are given as Table-1.

In spite of centrifugal pumps being most preferred, Rotating Equipment group’s, input on availability of centrifugal pump should be obtained.

References of centrifugal pumps handling fluids of viscosity up to 4000 CS are available.

When solids are present in the pumped fluid, internal passages should have adequate dimensions and hence type of pump should be finalized after interactions with Rotating Equipment group and feedback based on past jobs.

Past commissioned jobs are best reference for selecting such type of pump.

1.2 Procedure to fill each item on the pump data sheet 1.2.1 Item No. As in equipment list/ PFD A/B or A/B/C- to be added if operating philosophy is (1+1) or

(n+ m) respectively. Number of pumps in operation/ stand by is decided based on

following factors: Availability of pumps based on required capacity / head. Multiple operation when one case requires one pump where

as another case needs multiple pumps in operation Turndown requirements

For (n + m) pumps, n pumps in operation & m pumps as stand by . The capacity indicated is total capacity to be delivered by n pumps operating in parallel. Up to 3 pumps in operation one pump is taken as stand by and with 4 and more pumps, two pumps are taken as stand by. 

1.2.2 Service Name of pump as given in Equipment List / PFD 1.2.3 Type Centrifugal / Metering / Reciprocating / Screw /

Vertical submerged centrifugal , etc Metering pumps are small reciprocating pumps which can

deliver variable capacity by stroke adjustment. Large reciprocating pumps ( generally flow above 5 m3/ hr or

high discharge pressures ) are constant capacity pumps and any requirement of variation in flow will have to be handled outside the pump by spill back control.

Where to use metering or reciprocating pump Metering pump is specified where variable capacity is

required and reciprocating type is specified where fixed capacity is required.

1.2.4 Liquid handled If service indicates type of fluid like naphtha/diesel/sour water

then hydrocarbon / water should be mentioned. If service does not indicate type of fluid but mentions main

fractionators reflux / Debutanizer reflux / Absorber reflux then Naphtha / LPG/Light hydrocarbon are mentioned.

Information on internals / type of seal is required by rotating / vendor to decide type of pump. 

1.2.5 Pumping Temperature   The normal temperature is to be indicated. Range needs to be indicated when there is wide variation. Process engineer to review start up, shut down, pump out

cases w. r. to change in temp, fluid, and source/destination. A note indicating name of fluid, temp, properties, vapor

pressure, capacity, discharge pressure, suction pressure, NPSH, and duration envisaged is to be provided by process engineer.

Capacity or pump discharge pressure is left to be decided by rotating group / vendor because various cases to be considered are not rigid case of operation e.g. pump out can take longer time hence discharge pressure is must but capacity can be less or during start up, capacity requirement is rigid but discharge pressure can be low due to lower circuit pressure drop.

However requirement of both capacity and discharge pressure as judged by process engineer should be mentioned with note that “Rotating Equipment to confirm”.

 1.2.6 Viscosity at pumping temperature   Range (if variation is wide) / viscosity at pumping

temperature from simulation / curves. For highly viscous fluids where screw pumps have been

specified, lowest viscosity envisaged is very important as problems of low efficiency, slippage, etc occur.

1.2.7 Vapor Pressure at pumping temperature       For liquids in equilibrium with vapor, pumps taking

suction from columns, flash vessels, etc, the operating pressure of vapor above the pumped liquid is the VP at pumping temperature.

For sub cooled liquids like in feed surge drum and blanketed drums, VP shall be estimated from simulations /curves.

Process to ensure sufficient margin in calculation/ estimation of vapor pressure.     

For slightly sub cooled liquids in reflux drums (like naphtha splitter reflux drum, crude fractionator reflux drum) or in column bottom(vacuum column or Visbreaker fractionator bottoms due to quench) , VP is operating pressure of vapor above pumped liquid and should not to be lowered for slight sub cooling

Vapor pressure for water being pumped from reflux drum boot/feed surge drum/compressor inter stage KOD shall be VP of water at operating temp from steam table / simulation and not at the operating pressure.

1.2.8 Liquid density at pumping temperature Shall be taken from simulation/curves/pure component

properties. If range is wide, both high and low values shall be reported.  

1.2.9 Presence of corrosive / toxic components If present, “yes” shall be filled and a note indicating type

and quantity ( if known) is to be added. If absent, “Absent” shall be filled

The general corrosive / toxic components encountered are sulfur / H2S / NH3 / phenols / sulfides/cyanides etc. Quantity of corrosive / toxic present should be taken based on past pump data sheet / past experience.

1.2.10 Solids in suspension If present, “yes” shall be filled and a note indicating type of

particles e. g. de-generated products, coke, etc and size of particles based on past similar job / as identified in Technology manuals shall be added in data sheet.

1.2.11 Flow Rate Normal flow rate shall be filled based on material balance

and considering multiple cases of operation along with operational flexibility required

Maximum flow rate shall be indicated based on standard over design factor ( 110% for feed and products, 115 % for pump around and 120 % for reflux, re-boiler service, and compressor inter stages.

Minimum flow shall be indicated based on turn down requirements for the unit as given in design basis / as required from process angle for the specific pump.

The Automatic Recirculation Control (ARC ®) Valve This valve provides bypass flow control, pressure reduction, and reverse flow pump protection all within a single unit. This single valve combines the functions of the check valve, pressure reducing orifice, pipe tee, control instrumentation flow meter, and bypass control valve that are all required in the instrumented control loop bypass system. Valves can be designed to provide either “Modulated” or “On-Off” bypass control. The operation of all

Centrifugal pumps Generally a turndown of 30% of rated capacity is achievable. If

required is less then 30% then add minimum flow provision and a note in data sheet.

For other cases of min flow >30%, add min flow provision based on old jobs / rotating group input and add a note to that effect in the data sheet.

When head required is very high but capacity very low, such pumps are not easily available and there may be case when pump selected would be such that minimum continuous bypass flow is greater than max flow required. Caution: In such pumps continuous bypass is required. For such pumps based on rotating input, pump suction / discharge hydraulics including NPSHA calculations should be redone based on Rotating groups input on pump MCF. To prevent heating of liquid due to circulation, bypass should be put up stream of cooler / condenser.

Reciprocating Pumps They are constant flow pumps so only max flow is specified.

Any turn down / variation is taken care by providing spill back.

For normal and minimum flow, a note is put on the pump data sheet that provision for spill back is required to take care of normal / minimum flow requirements.

Metering Pumps Generally 20-100 % variation in flow by stroke adjustment

(Automatic / manual) is possible. Less than 20% is possible but with loss of accuracy.

1.2.12 Suction Pressure Suction pressure = Source pressure +static head –(∆P in pump

suction side) where

Source pressure = operating pressure above liquid level in the source vessel / column / tank

Static head = static pressure difference due to liquid head between pump center line(normally one meter) and vessel /column BTL

For source vessel / columns, where there is no process requirement for elevation and ‘min for piping” is indicated in P&ID / Data Sheet, then 1 meter for vessels, 2 meters for columns and 6 meters for column when max suction pressure calculation is required and BTL of vessel is not known.

∆P in pump suction = ∆P in suction line + ∆P in suction strainer + ∆P in suction control valve / heat exchangers / other instruments if any in suction side.

∆ P in suction line = line loss in suction line

For estimating line loss, equivalent length should be calculated based on proposed location of source vessel and pump.

Charts 1,2,3 may be used to estimate equivalent lengths between two equipments or between an equipment and instrument.

Caution -While estimating suction ∆P in very high pressure services,

the line thickness / rating correction should be applied since pipe thickness for higher rating is quite significant.

For critical pumps like column bottom-high temp pumps, Process to review and approve isometrics.

∆P in suction strainer For basket strainers, the allowable ∆P as per process data sheet is too less ( say 0.05 kg/cm2) then process to check its availability from mechanical group.

∆P in Heat Exchangers / Control valves / instruments

As reported / proposed to be reported in respective process data sheets

1.2.13 Maximum Suction Pressure Centrifugal Pumps Maximum suction pressure = ----kg/cm2g Required for the purpose of pump shut off pressure

calculation.  For positive displacement pumps Maximum suction pressure

= ---- kg/cm2g To be used as max back pressure for safety valve at pump

discharge. Maximum suction pressure = Maximum source pressure +

static head where Maximum source pressure = Design pressure of source

vessel / column bottom.

For column bottom Top design pressure + tray DP + static head (HLL) in bottom

section. Reflux pump, reflux drum and condenser are designed with

column top design pressure. For vessels open to atmosphere, design pressure is

atmospheric Static head = static pressure difference due to liquid

head between source vessel/column HLL and pump center line. If two cases are reported, higher density should be used.

For a pump taking suction from an upstream pump discharge, maximum suction pressure = upstream pump shut off pressure

1.2.14 Discharge pressure, Differential pressure & Differential head

Discharge pressure = Destination pressure + static head + (∆P in pump discharge circuit) + contingency

where Destination pressure = B/L pressure for run down circuits,

operating pressure of destination vessel/ column etc For pumps whose destination point is another pumps discharge,

estimation of destination pressure should take in to consideration the max pressure possible say at turn down.

For pumps pumping to a vessel/column through a feed distributor, the distributor ∆P to be considered and confirmed from specialist department.

Static Head = static pressure due to liquid head between final destination point and grade.

For product run down circuits where destination pressure is B/L pressure, static head should not be considered.

For static head of vessel/column, height up to HLL For static head of destination vessel/column where no process

requirement for elevation and min for piping is indicated in P&ID/data sheet, BTL of 6 meters should be considered and counter checked with lay out.

For circuits where static head of final destination is lower than static head of an intermediate point e.g. final destination is vessel at grade and air cooler at intermediate point, it should be ensured that pressure at intermediate point (pump discharge-circuit loss till that intermediate point) is sufficient from process considerations i.e. above vapor pressure.

∆P in pump discharge = ∆P in discharge line + ∆P in flow instruments + ∆P in heat exchangers + ∆P in control valves + ∆P in any other item

Where, ∆P in pump discharge line =line loss in discharge line. For estimating line loss, equivalent length shall be calculated based on proposed lay out.

Charts 1,2,3 shall be used to estimate equivalent lengths between two equipments or between an equipment and instrument.

∆P in Heat Exchangers/flow =As reported / process data sheets ∆P in control valves = As per pump calculations for varying

flow rates Contingency = 1.0 kg/cm2 to take care of any unforeseen

additional requirement of ∆P in discharge circuit.

Differential pressure = Discharge pressure – suction pressure where

Differential head = [Differential pressure in kg/cm2)/ (in meters ) (density in kg/m3)]x 104 .

If for multiple cases of operation, hydraulic pressures are not very different, a single discharge pressure can be considered. Since centrifugal pump develops fixed head for a given flow, it is advisable to report head based on lower density.

If for two different cases of operation, hydraulic pressure drops in the circuit are very different, (due to large variation in viscosities) two separate circuit hydraulic calculations are to be performed & differential head calculated based on density of respective cases.

1.2.15 NPSHa NPSHa = [source pressure –vapor pressure-suction losses +

elevation of liquid level- pump centre line] in meters of liquid =[(suction pressure-vapor pressure) in kg/cm2] / [Density in

kg/m3] x 104

NPSHa (reported in data sheet) should be 0.5 meter less than calculated figure. If NPSHa is greater than 8 meters then write > 8 meters.

NPSHa reported should be consistent with past jobs. Typical min NPSHa for centrifugal pump is 3 meters except

for water pumps where 2 meters is acceptable (also for flare KOD pump, NPSHa of 2 meters is acceptable). The source vessel/column BTL elevation shall be adjusted to ensure this.

Suction line size may be increased to achieve required NPSHa, over sized suction line leads to excessive loads on piping/pump and should be avoided. If suction line size increase is only option because BTL elevation can not be increased (revamp ) then higher size only for initial portion (i.e. towards the source vessel/column )and a reduced line size towards pump.

For positive displacement pumps: The following note must be added in all positive displacement

data sheets. NPSHa reported does not include acceleration head loss.

Suction line straight length = -- meters, suction line size = -- inches and suction line equivalent length = -- meters. Straight length and equivalent length are based on proposed lay out.

For vertical submerged centrifugal pumps: Flooded shall be written e.g. for CBD pumps. Vertical

submerged centrifugal pumps are pumps whose impeller is in horizontal plane.

Vertical barrel pumps: Where NPSH is very low, vertical barrel pumps may be

considered. These pumps are similar to vertical submerged centrifugal pumps but with in built barrel against an independent vessel.

NPSH estimated by process will stay, and additional NPSH due to depth of barrel would be estimated by Rotating group / vendor.

1.16 Capacity Control for Volumetric Pumps It is for metering pumps i.e. for small reciprocating pumps

which can deliver variable capacity by stroke adjustment.

1.16.1 Continuous/Discontinuous/Manual/Automatic Manual is specified when stroke adjustment is by manual

means Automatic is specified if stroke adjustment is automatically

achieved by signal from say level of source vessel. Continuous/Discontinuous is never specified.1.16.2 Type Where automatic is specified, a note shall be added indicating

type of automatic control e.g. stroke adjustment by level signal from LT/LIC ---(tag no)

1.16.3 Range 20-100% shall be specified as 0-100% is not accepted. 1.16.4 Precision at min rate To be left blank

1.17 Mechanical Data: 1.17.1 Design Pressure: Design pressure is maximum discharge pressure that pump can

develop at pump shut off. For Centrifugal pumps Design pressure = Max suction pressure + Max Differential

Pressure(DP) where Max Suction Pressure = As above Max Differential Pressure (single stage pumps) = 1.2 x DP Max DP (For multi stage pumps) = 1.3 x DP Max DP (For variable speed pumps) = 1.32xDP For positive displacement pumps Design Pressure = 1.1 x Discharge Pressure (in kg/cm2g) or (Discharge Pressure +2.0) whichever is higher

1.17.2 Design Temp Design temp of source vessel/column For quenched columns (DCU quench column, main

fractionators of Delayed Coker / FCC, etc ) and Column bottom pumps = pump operating temp + 25 0C

1.18 Casing/Impeller material Shall be reported as suggested by Material specialist/ past jobs

/ Material Flow Diagram. If CI (Cast IRON) casing / impeller is specified as MOC then

reconfirmation from Rotating Equipment group is to be obtained as CI pumps are generally not available.  

1.19 Seal Type It shall be single / double mechanical seal for hydrocarbon

service and packing for slurry services and positive displacement pumps.

Type of seal shall be revised based on pump specialist input. Refer API-610 for various types of seal flush plans. For external seal flushing (dirty / congealing pump fluids),

following note is added ----(name of flushing fluid like HGO,HVGO) is available at --- 0C and ---kg/cm2g for seal flush. Density and viscosity at

operating T,P is -----kg/m3 and -----cp/cst respectively. Input from Rotating Equipment on pressure required for seal

flush fluid. 1.20 Line Rating Pump suction and discharge line rating shall be reported based

on suction and discharge design pressure and temperature e. g. 150# / 300# (Though pump suction and discharge nozzle rating would both be 300#).

1.21 Driver It is usually decided during design basis. Motor or steam turbine shall be specified for centrifugal or

positive displacement pumps. Steam turbines are specified where greater reliability is

required e.g. BFW pumps or steam balance calls for steam turbine drive. Extraction type turbine is normally provided due to less space requirement.

1.22 Steam Turbine data: Inlet and outlet steam pressure levels shall be as decided in design basis.

1.22.1 Inlet pressure Minimum steam pressure as in design basis - ISBL losses.

Normal/Max steam pressure as in design basis shall be reported. The following note shall be added:

The pressure reported is upstream of governor (control valve, which is in vendor scope). Minimum pressure shall be used to calculate steam requirement.

1.22.2 Inlet TemperatureMin/nor/max temp to be reported1.22.3 Design Pressure As per design basis1.22.4 Design Temperature As per design basis1.22.5 Exhaust pressure Max pressure plus ISBL loss up to exhaust steam header,

normal/min are also reported. 1.22.6 Line rating-For both in and out, the rating shall be

reported as a control valve at the outlet of turbine will be there and rating would be reduced only downstream of this valve.

1.2 Notes Apart from the notes that are mandatory as highlighted, the following notes shall be included where applicable.

Pour Point A note” Pour point of pumping fluid = ---0C” shall be added for all pumps whose pour point is greater than or near ambient temp. It shall be taken from crude assay / pilot plant runs / as indicated in respective units

Auto Start Requirement For pump which require auto start, following note is added.

“Pump/motor to be designed for auto start with discharge open”. It is generally required for BFW, seal flush fluid pumps, etc

Discharge Dampeners For positive displacement pumps where discharge dampeners

are required from process angle, the following note shall be added. “Discharge dampener to be provided “.

1.24 Typical Sample Calculations Typical process data sheet for pump duly filled and calculation

sheet are enclosed as ready reference

2.0 Control Valve-Pump Discharge Circuits 2.1 Purpose This guideline will cover how differential pressure across

control valve, in pump discharge circuits, at min/nor/rated flow shall be specified.

Scope: To estimate pressure drop for control valve circuits in pump discharge. The min/nor/rated flows and the properties , temperature, pressure and other parameters are outside the scope of this guideline and shall be specified based on PFD/material balance/design basis/pump or other equipment data sheet.

2.2 Definitions Qrated = Rated flow in m3/hr Q nor = Normal flow in m3/hr Qmin = Minimum flow in m3/hr

del PCVmin = Control valve del P at rated flow in kg/cm2

del PCvnor = Control valve del P at normal flow in kg/cm2

del PCvmax = Control valve del P at minimum flow in kg/cm2

del Prated = Pump differential pressure at rated flow kg/cm2

del Pnor = Pump differential pressure at normal flow kg/cm2

del Pmin = Pump differential pressure @ mini. flow kg/cm2

del Pckt rated = Circuit dynamic frictional losses at rated flow in kg/cm2 , i.e. not including static head, control

valve del P and contingency. (The dynamic losses are frictional losses which vary with flow through the circuit)

del Pckt nor= Circuit dynamic frictional losses at normal flow in kg/cm2

del Pckt min = Circuit dynamic frictional losses at minimum flow in kg/cm2

Cvmax = 1.17 x Qmax {(Density at op.temp.)/(del PCV min)}1/2

Cvmin= 1.17 x Qmin {(Density at op.temp.)/(del PCV max)}1/2

2.3 Procedure Control valves in pump discharge circuits broadly fall under the

following categories: (Types A to G, and J, K are on centrifugal pump discharge while

H & I are on positive displacement pump discharge) A -Control valve in the governing circuit (from pump

differential pressure requirement angle) e.g. FV-1203 in Fig-1. B -Control valve in parallel circuit to a different destination i.e.

not in governing circuit e.g. FV-1202 in Fig 1.

C Control valve in a parallel circuit i.e. not in the governing circuit, but to same destination. e. g. FV-1401 in Fig 2. D Control valve in series with main control valve in the governing circuit. e. g., FV-1502 A in Fig 3.E Control valve in parallel in a part of the circuit. e. g., FV-1502 B in Fig 3.F Pump minimum flow control valve for centrifugal pump. e.g. FV-1201 in Fig.1.G 3-way valve. e.g., TV-1701 in Fig 4.H Control valve at positive displacement (constant flow) pump discharge. e. g., FV-1601 in Fig 5, LV-1601 in Fig 5. I Spill back control valve for positive displacement pump. e. g., PV-1601 in Fig 5.

J Pressure control valve for fuel oil to furnaceK Back pressure control valve in fuel oil circulation lineL Control valve at pre heat inlet like FV-1801/ HV-1801 in Fig 6 M Control valve at heater pass inlet like FV-1901 Fig 6N Pressure control valve on pump discharge as in pipeline application. e. g., PV-2001 in Fig 7. O Mixing valves e. g., at desalter / caustic wash inlet

2.4 Estimation of del PCV min del PCV min is estimated as part of pump hydraulic calculations. del PCV min is taken as 0.7 kg/cm2 as an initial estimate. NOTE:- del PCV min for any control valve shall be 0.7 kg/cm2

minimum. However this may be relaxed for special cases, like revamp jobs if pump discharge rating increases only due to control valve del P. Engineering confirmation on availability of control valve needs to be obtained before finalizing pump in such cases.

Step-1: del Pckt is proportional to Q2 ---------------1 del Pckt + del PCV = constant -----------------2 From equations 1 and 2 above, since del Pckt max and del Pcv min

are known from pump hydraulic calculations, del Pckt min , del PCVmax , del Pckt nor and del P CV nor can be calculated.

Step 2: However above equation-2 does not consider that pump

discharge pressure increases with decrease in flow for a centrifugal pump. Hence del PCV max and del PCV nor calculated in

step1 above is to be corrected for this extra head developed by the pump.

A 20 % higher head is considered to be developed at shut off i. e., at zero flow, del P developed at normal /minimum flow can be estimated as given below assuming linear relation between flow vs head developed.

del Pnor = del Pnor+ 0.2 x del P rated (Qrated – Qnormal)/Qrated

del Pmin = del Pmin + 0.2 x del P rated (Qrated – Qmin)/Qrated

The increased control valve inlet pressure due to higher head developed at normal/minimum flows is also to be estimated and reported in the process datasheet.

Step 3: Using the corrected del PCV max as estimated in step 2 and del

PCVmin , Cv max and Cv min are calculated. Generally Cv selected for control valve is around 110 % of Cv max .

To ensure controllability of the valve the following two criteria are to be met.

Criterion 1: Cv max/Cv min is lower than 13 Criterion 2: del PCV nor is greater than or equal to

0.3 x del Pckt nor i. e. , 30 % of dynamic losses in the circuit at normal flow (does not include static head, control valve del P and contingency)

If the above two criteria are met ,del PCV max, del PCV nor and del

PCV min can be reported in the datasheet. Otherwise del PCV min is

to be increased to such a value and steps 1 to 3 are to be repeated till the above two criteria are met. Generally criterion 1 is fulfilled with a del PCV min = 0.7 kg/cm2 where del PCV max is less

than 5 kg/cm2.

If there are multiple cases, del PCV min reported in data sheet shall

be corresponding to that case which gives max Cv max .and del PCV

max reported in data sheet shall be corresponding to that case

which gives the minimum C v min. del PCV nor reported shall be

that corresponding to the case which is a more probable normal operating case.

Caution: If flashing occurs at control valve outlet, the following data are to be included in process data sheet: Weight % vapor at outlet, temperature at outlet, vapor properties at outlet, vapor pressure and liquid critical pressure.

sample calculations for pump discharge control valve circuit- Case-II

del PCVmin = 0.7 (initial estimate) del Pckt rated =1.88(LL) + 0.60 (3 FE ) + 6.00 (3 HE) = 8.48 del Pckt nor = 8.48 x (86.1/94.7)2 =7.0 del PCvnor =8.48+ 0.7-7.0 =2.18 or 2.2 del Pckt min = 8.48 x (43/94.7)2

=1.75 del PCvmax = 8.48+ 0.7- 1.75 =7.43 or 7.4

Correction for pump discharge pressure del PCvmax = 7.4+0.2 x 11.7 x{(94.7- 43)/94.7} =7.4+1.28 =8.68 or 8.7

del PCvnor = 2.2 + 0.2 x11.7x {(94.7- 86.1)/94.7} =2.2+0.2 =2.4Cvmax =1.17x 94.7x (968/0.7)0.5 =4120.3 Cvmin=1.17x 43x (968/8.7)0.5 = 530.7

Calculation for LV (case-1) From pump calculation sheet

del PCVmin =4.77 or 4.8

del Pckt rated = 3(For two HE)+0.6 (For two FE ) +0.4 (For line loss) =4.0

del Pckt nor =4 x (90.6/99.7)2 =3.3 del PCvnor =4+4.77-3.3 = 5.47 or 5.5

del Pckt min = 4 x (45.3/99.7)2 =0.826 del PCV max =4+4.77-0.826 =7.94 or 7.9

Correction for pump discharge pressure

del PCvnor = 5.5 + 0.2 x 11.1 x {(99.7-90.6) / 99.7} =5.71 or 5.7

del PCvmax =7.9+0.2 x 11.1x { (99.7-45.3) /99.7} = 9.11 or 9.1

Cvmax = 1.17 x 99.7 x {(920)/(4.8)}1/2 =1615

Cvmin= 1.17 x43 x {(920)/(9.1)}1/2 =506

Check Criteria

Cvmax case 2 / Cvmin case 1 =4120.3 / 506 = 8.14 < 13

del PCvnor case 2 / del Pckt nor case

2 = 2.4 / 7.0 = 0.34 >0.3 O Kdel PCVmin =0.7

del PCvnor =2.4

del PCV max =8.7

Check Criteria

Pump Calculation with 3-way valve & Heat Exchangers

del PCVmin = 0.7 (initial estimate)

del Pckt rated =1.1(LL) +0.3 ( FE ) =1.4 ( Del P of both HE’s and 3-way valve not to be included as

variation in HE del P due to flow is to be taken care by respective 3-way valve main port del P )

del Pckt nor =1.4 x (350.2/420.2)2 =0.97 del PCvnor = 1.4+0.7-0.97 =1.13 or 1.1

del Pckt min = 1.4 x (159.2/420.2)2 =0.2

del PCvmax = 1.4+0.7-0.2 =1.9

Correction for increased pump discharge pressure with decreased flow

Corrected del PCvnor =1.1+ 0.2x6.6x{(420- 350./420} =1.32 or 1.3del PCvmax = 1.9+0.2 x6.6 x {(420.2- 159.15)/420.2} =2.72 or 2.7Check of criteriaCvmax = 1.17 x {257( normal flow through FV) x 1.2} x { 694 /

0.7 }1/2

=11361.4Cvmin= 1.17 x {253.5x 0.5} x {704/ 2.7}1/2 = 2394.6Cvmax / Cvmin =4.74 which is less than 13del PCvnor/ del Pckt nor =1.3/0.97 = 1.34 > 0.3

del PCVmin =0.7del PCvnor =1.3del PCV max =2.7

Type A control valves: Estimation of del PCV min , del PCV nor , del PCV max are as presented in sample calculations.

Type B & C valves: For control valves not in the governing circuit , the del PCV min is to be increased by the difference in discharge pressure required for the two circuits. Subsequent steps for estimation of del PCV min , del PCV nor and del PCV max are same as for type A control valves.

Type D control valves: Procedure shall be similar to three way valves

Type E control valves: Procedure shall be similar as for bypass port of three way valves

Caution: control scheme where only a control valve in the exchanger bypass and no control valve upstream or downstream of the exchanger is provided as it is difficult to match exchanger and control valve pressure drops.

Type F control valves: Procedure shall be similar as for type B and C control valves given above.

Type G control valves: The normal flow through main port is to be same as flow through the exchanger.

The minimum flow through bypass port is to be 10 / 20 % of flow through exchanger.

Caution: The exchanger is to be specified considering only 90/80 % of flow available to take in to consideration the 10/20 % of flow through the bypass port.

The rated flow for both main and bypass ports shall be the available rated flow for the exchanger circuit (to take care of total exchanger bypass). For the bypass port normal flow and del PCV nor need not be furnished.

The frictional losses through the exchanger circuit and bypass circuits across points C and D are always equal irrespective of flow.

del PCV min bypass port or del PCV max bypass port = del

P ckt max + del PCVmin main port assuming negligible

line losses in the bypass circuit.

Type H control Valves: Positive displacement pumps develop a discharge pressure equivalent to the back pressure at its rated (constant) flow.

Caution: Positive displacement pumps are fixed capacity machines unless provided with auto capacity control like stroke adjustment. If a control valve is envisaged in the positive displacement pump discharge (either through a FIC or LIC or both) a spill back control valve (normally a PIC) should be provided to prevent pump PSV from lifting. The spill back control is provided upstream of any control valve in the pump discharge circuit. This spill back control valve should be capable of pumping back the flow equivalent to rated flow of the pump.

a. For control valve where the pump discharges to a single destination:-

The del P through the control valve for all flows is to be specified as 0.7 kg/cm2 and the same 0.7 kg/cm2 should be used in pump hydraulic calculations.

b. For two different control valves in two different circuits discharging to two different destinations: e.g., FV-1601and LV-1601 in Fig-5.

---For the control valve in the governing circuit del Pcv min / nor / rated shall be 0.7kg/cm2 ---For the control valve in the not governing circuit the del Pcv min / nor / rated shall be 0.7 +Difference in (destination pressures + frictional losses + static heads in the two circuits)

If there is a possibility of only one circuit being in operation at a time, then since the pump would develop only the back pressure, the del Pcv min for the control valve in each circuit shall be 0.7 kg/cm2.

Warning: There have been instances of vibration problems when control valve has been provided in positive displacement pump discharge, and hence should be avoided if the system design permits.

Type I control valves: The spill back control valve for reciprocating pumps is a pressure control valve.

The maximum flow shall be indicated equal to the pump rated flow rate in the control valve data sheet and a note -“this control valve shall be normally in closed position“ shall be added. No normal flow/ delP shall be indicated.

The circuit frictional loss is only the line loss. del Pcv = pressure upstream of control valve –line loss in spill

back line - (source pressure at suction vessel + static head as in pump suction pressure calculation)

Pressure upstream of control valve is the pump discharge pressure less FE loss, if any , upstream of the control valve.

Suction line loss is not considered as it can be negligible during turn down etc.

Pdischarge rated = Destination pressure + del Pckt max +discharge

side static head + contingency

Pdischarge min = Destination pressure + del Pckt min+ discharge side static head.

Pressure upstream of control valve shall be estimated based on both Pdischarge rated and Pdischarge min and two del Pcv figures shall be reported for both rated and min flows.

Type J control valves: Since pressure control valve for fuel oil to furnace involves pressure requirements at burner during turndown, etc.

Type K control valves: Procedure shall be similar as for type B and C control valves given above.

Type L control valves: Procedure shall be similar as for type A control valves given above but Pckt shall be frictional dynamic losses up to FV-1901 inlet only as it is intended to ensure a fixed pressure of 2-3 kg/cm2 above bubble pressure of liquid at FV-1901 inlet to prevent 2-phase at control valve inlet which is not desirable for control.

Type M control valves: Procedure shall be similar as for type A control valves given above but del Pckt shall be the frictional dynamic losses downstream of FV-1901 only. But control valve upstream pressure is constant and variation in pressure with pumped flow is not to be compensated as it will be absorbed in FV-1801/HV-1801.

Type N valves: Procedure shall be similar as for type A control valves given above.

Type O control valves: del P at min/nor/max flows shall be the same and based on process requirement. This control valve del P being constant with flow, should not be included in del Pckt for estimating del P for the other control valve in the circuit.

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