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Conceptual Process Design

An introduction atwww.cpcsimulation.com


Basic process steps

Basic Engineering package FEED Residual process engineering Detail engineering Basic core process documents

Process design basis, PFD, P &ID, Datasheets, Line lists, Safety study


Agenda for this presentation

Workflow for conceptual process design PFD Development P & ID Development Line sizing Control Valve sizing Pump Head calculations PSV sizing Area classification


Conceptual process designDESIGN BASIS Why to prepare a design basis? Any guess on what this document consists of? Can a P&ID be made without knowing basis? Two different plants same product. Can P & IDs

be absolutely same? Two different plants same product. Can control

valve and safety valves be exactly same? If Yes why and if no why? Same product with same capacity: plant in India

and plant in Russia- will it be exactly same?


Conceptual process designDESIGN BASIS P & IDs for same product are different

because. Different licensor philosophies and design

specifications Different Legends Different plant capacity Different climatic conditions Different utility availability Different logistics requirements Different plot layouts Different equipment/ Instrument manufacturers


Conceptual process designDESIGN BASIS Equipment design margins Standard design philosophy Controls and instrumentation levels

(DCS/PLC, SIL study) Safety philosophy: (Fire, F&G, Flare) Isolation and sparing philosophy Battery limit conditions Environmental norms


Conceptual process engineering Focus on process flow diagram

development (Example.reflash column) Generate a mass and energy balance Chemicals and catalyst summary Development of conceptual P & IDs Critical equipment sizing Estimate utility requirements Operating instructions


Conceptual process engineering Not part of conceptual engg.. Pump head checks Control valve sizing Safety valve sizing Safety valve sizing Vendor package information Utility distribution drawings HAZOP study


DOUGLAS METHODOLOGY


BATCH VS. CONTINUOUS Production rate: > 45000 T/yr, use continuous

process Product demand: seasonal products batch Multiproduct plant Batch plant Significant gas recycle continuous plant Reaction behavior: High temperature or highly

exothermic reactions, continuous plant Significant opportunities of heat integration

continuous plant


RECYCLE STRUCTURE

Decide reactants to be recycled / purged

Decide purity / separation feasibility

Check effect of recycle on reaction chemistry e.g. recycle of poisons etc

Check effect of compression cost on feasibility


BLOCK FLOW DIAGRAM

Major equipments on block flow diagramEvaluate cost based on major equipments and

approximate operating costUse ratio method for cost estimationShortlist alternatives for further evaluationProcess simulation will help fix process

conditions, utility loads etcPinch analysis for energy and area saving, but

keep operational issues in mind


Any Questions so far?


PFD developement

Show only process flow lines Start up lines, pump recycle lines need

not be shown Utility streams shown in short Standby equipment and working

equipment depiction Which streams to number? Where to place stream number

diamond?


PFD Development

All equipments tagged Equipment title block added Exchanger symbol is generic and not as

per its TEMA type Start/stop switches for motors not shown All bays of air cooler are not shown Local temperature and pressure guages

not shown


Control valve Selection and SizingControl valve Selection and Sizing


F (kg/hr)Ti (oC)

To (oC)

Ms (kg/hr)TS (oC)

Thermometer

Human Brain

Hand

COMPONENTS OF CONTROL SYSTEM

Measuring element (thermometer)

Controller Final control

element (control valve)


V1

Process

__1__p + 1

Final ControlElement

__1__v + 1

Controller

Kc {1+(1/ I)+ d}

MeasuringInstrument

__1__m + 1

eR

C

P C

CONTROL SYSTEM BLOCK DIAGRAM


Controller sends the output signal of the order of 4 to 20 mA.

The i/p converter changes the signal to 3 to 15 psi and sends to Actuator.

The Actuator moves the plug relative to the stationary valve seat.

CONTROL VALVE SYSTEM


POSITIONER

Measures valve stem position and compares with set point

Makes sure control valve opening is as required by controller

Corrects for effect of packing friction due to dirt, lack of lubrication etc


VALVE TYPES AND SELECTION

Globe valve Workhorse of industry Multiple ports available Large pressure drop Size limited to about 12

Butterfly valves Low pressure drop Large sizes available

Ball valves Low leakage Quarter-turn


CONTROL VALVE SIZING- 1 Need to fix following:

Minimum, normal and maximum flow Corresponding pressure drop Required flow characteristics i.e. linear or quick

acting etc Control valve flow coefficient Cv used as sizing

parameter

Cv is flow of water in m3/hr through valve at 1 bar pressure difference across valve


HOW TO ASSIGN PRESSURE DROPS? For pump systems:

50-60% of total frictional loss excluding control valve OR

15% of pump differential head OR 0.7 kg/cm2

For process systems Difference of pressure between upstream and

downstream system Should give better controllability Smaller the pressure drop, bigger the valve


Linear

Quick opening

Equal %

FLOW CHARACTERISTICS Inherent characteristics Quick acting / linear / equal percentage


SELECTING CHARACTERISTICS: LEVEL

Level control: very slow response (remember tanks in series experiment)

Mostly linear


SELECTING CHARACTERISTICS: FLOW

Whenever in doubt, use equal percentage


CAVITATION AND FLASHING Cavitation is collapse of

bubbles Damages trim Special trim designs

available Flashing not as dangerous

as cavitation Needs to be specified to

vendor


CHOKING Occurs for gaseous systems when downstream

pressure less than about 50% of inlet pressure Can occur at much higher % for two-phase

systems Fluid accelerated to sonic velocity in valve Formation of shock waves Avoided by use of multiple valves or use of ROs


FAIL- SAFE POSITION Action for valve when air supply fails Three options

Fail open Fail close Fail last

Energy adding valves to be fail closed e.g. steam Energy removing valves to be fail closed e.g.

cooling medium


Line sizing

An introduction


Flow rate basis for line sizing

PFD and mass balance Utility summary and utility flow diagrams Design margin: General

considerations For all process lines 10% Start up, intermittent flow 5% Utility lines 15% Utility main header 20%


Line sizing basis

For revamp, basis differs. Circulating fuel oil system-design ring main for

125 to 150% of flow Pipe wall roughness basis Carbon steel, new- 0.047 mm Brass, aluminum, Copper, Plastics, Glass

0.03 mm Stainless steel 0.025 mm Rusty steel 0.2 mm Galvanized steel 0.13 mm


Normal pipe size

Avoid 30NB,65NB,125NB, 550NB Nominal pipe size for process lines shall

be 25mm Pipe rack lines shall be minimum 40NB Schedule number as per pipe

specification index Piping length estimate based on project

status-preliminary or plot plan/equipment layout based or isometrics based


Equivalent length calculations: Le/D values Globe valve 450 Angle valve 200 Gate valve 13 Ball Valve 18 90Deg Elbow 30 Conventional check valve 135 Globe lift check valve 450 45 degree elbow 16 Flow through run 20 Flow through branch 60


Pressure drop calculations

Preliminary line size based on velocity criteria Actual pressure drop to be verified with

allowable pressure drops as per process design General criteria: Pump suction line delp is

0.085kg/cm2 per 100m of pipe General criteia: Pump discharge line delp is

0.15 to 0.6 kg/cm2 per 100 mtr pipe Reynolds number: Try to be in turbulant region

or laminar region. Avoid transition region(2300 to 4000 Nre)


Cooling water lines

DeltaP per 100 mtr is generally 0.3 kg/cm2 Flow possible through various pipes- in m3/h based on

above criteria 25 1.5 40 3.8 50 8.5 80 26 100 51 150 160 200 350 250 640 300 1000


Gravity lines

The maximum recommended velocity for gravity lines is 1 m/s

The minimum line size for gravity lines within process area to be 40mm

Sizing of self venting lines- velocity at about 0.3 to o.7 m/s

Column draw off lines based on static head available


Compressible fluid line sizing

If pressure drop is less than 10% of the upstream pressure, use density and average linear velocity based on either inlet or outlet conditions

If pressure drop is between 10%-40% of the upstream pressure, use density and average linear velocity based as averages of inlet and outlet conditions

First estimate- v= c/row; c is 13 to 24


Tower overhead lines

For pressure between, 0 to 0.7 kg/cm2g, use velocity range as 40 to 60 m/s and max allowable pressure drop of 0.011 kg/cm2 for 100 mtr pipe

For pressure between, 0 to 3.5 kg/cm2g, use velocity range as 18 to 30 m/s and max allowable pressure drop of 0.033 kg/cm2 for 100 mtr pipe

For pressure between, 3.5 to 15 kg/cm2g, use velocity range as 12 to 15 m/s and max allowable pressure drop of 0.15 kg/cm2 for 100 mtr pipe


Special services

Recommended velocity in m/s for special services:

Concentrated H2So4 1.2Salt water 1.8Caustic solution 1.2Plastic pipe 4.5Liquids with suspended solids 0.9 min.Liquid lines to chillers 1.8Refrigerant lines 1.2Liquid from condenser 2.1Reboiler trap out 1.2


HAZARDOUS AREA CLASSIFICATIONHAZARDOUS AREA CLASSIFICATION


OBJECTIVE OF AREA CLASSIFICATION Fire triangle: Oxygen / Fuel / Ignition source Oxygen: Air abundantly available Plant leak: Fuel supply started A minor spark and EMERGENCY Different fluids, different thresholds Area classification makes sure that ignition

source is not available


ZONES: HOW TO DECIDE Zone 0 normally means vapour space above continuous

vents, storage tanks, open tanks of volatile materials Zone 1 normally have following locations

Frequent maintenance, leakage prone area Areas where frequent upstream upsets mean downstream

released to atmosphere Location adjacent to zone 0 area

Zone 2 normally means areas like Accidental failure of gaskets/packings etc Zone adjacent to zone 1 area


FUEL PROPERTIES

Classification based on minimum ignition energy Fluids classified as either IIC or IIB or IIA IIC fluids very sensitive. Explode at slightest spark

energy. E.g. acetylene, hydrogen IIB / IIA rather less sensitive No difference between electric equipments for IIB

and IIA Basically fluid group either IIC or IIA/IIB


TEMPERATURE CLASS Makes sure that

temperature of electrical equipment surface does not exceed fluid autoignition temperature

85185T6

100212T5

135275T4

200392T3

300572T2

450842T1

oCoFTemperature Code


EXTENT OF ZONES Defined by codes Depends on whether source of hazard is lighter or heavier

than air Depends on location of source i.e. near ground / above

ground, open or closed space etc


ELECTRIC EQUIPMENT SPECIFICATIONS Method of containment: contain explosion within

confines of electric equipment e.g. Flameproof apparatus (Ex d)

Method of segregation/separation: Separate spark from fuel e.g. Oil immersion (Ex o)

Method of prevention: Provide just sufficient energy and reduce faulty conditions e.g. Increase Safety (Ex e)

Identified on electric equipment by notations


Pressure Relief


WHAT IS THE ROLE OF PSV?

Makes sure that vessel pressure does not exceed vessel design pressure

Pressure increase in a system occurs due to imbalance of either energy or flow i.e. input is not equal to output Relief events

Example of energy imbalance = Fire Example of material imbalance = Blocked outlet Imbalance corrected by releasing material out of the

system (to atmosphere or flare)


STEPS IN PSV SYSTEM SIZING

Identify relief events Calculate relieving capacity required Select type of valve to be used Calculate PSV orifice area Select Standard orifice having area more than calculated

orifice area Fix PSV inlet and outlet line size based on rated capacity Design flare system (if any) considering worst case

scenario for entire plant


ACCUMULATIONAccumulation allowed by API:

3% for fired and unfired steam boilers 10% for vessels equipped with a single pressure

relief device in non-fire case 16% for vessels equipped with multiple pressure

relief devices 21% for fire contingency

PSV overpressure should be such that at no instant relieving pressure is reached

Consider vessel operating at 1.5 bar (g)


What are Relief Events? External fire Control valve failure leading to uncontrolled

flow of fluid or energy Blocked outlet Cooling water failure Power failure Exchanger tube rupture


OTHER RELIEF EVENTS Blocked outlet case: relief flow is flow into the system

(credit can be taken for pump curve shift) Control valve failure case: Vendor certified full open

control valve flow (corrected for relieving pressure) Cooling water / power failure: uncondensed vapour

minus vapor normally exiting the system Tube rupture: Calculated based on orifice theory All calculations at relieving pressure


RELIEF DEVICE TYPES Pressure Safety Valves

Conventional spring operated valves Balanced bellows valves Pilot operated valves

Rupture Devices Rupture discs Rupture pin devices


CONCEPT OF BACKPRESSURE Backpressure = pressure from valve outlet which tries to

close the valve i.e. forces disk down

Superimposed backpressure: backpressure on disc before valve opens

Superimposed backpressure can be constant or variable

Built-up backpressure: backpressure developed due to flow after valve opens


BALANCED BELLOWS VALVE

Balanced bellows work on similar principle of spring tension, but bellows takes care of problems of backpressure

Conventional valves okay if backpressure limited to 10% of set pressure

Balanced bellows can go easily upto 30% backpressure and upto 50% at reduced capacity

Problem of bellow rupture due to fatigue etc


RUPTURE DISC Nonreclosing device Once ruptured, material

loss continues Used in place of or

upstream of PSV in corrosive, viscous services etc

Reduce capacity of valve if upstream of PSV


PSV INLET AND OUTLET LINE

PSV inlet line size should atleast be equal to PSV inlet flange

PSV inlet line size pressure drop limited to 3% of set pressure avoids chattering

3% limit not applicable to pilot operated valves PSV outlet line size should atleast be equal to PSV outlet

flange PSV outlet line size selected to meet backpressure

requirements 10% of set pressure for conventional valves 30 50% of set pressure for balanced bellow valves Max. 90% for pilot operated valves possible


THANK YOU

process design,cv,line size,hazard,safety valve guide

Documents

process conditions

different plants

safety studywww

safety valves

sil study safety philosophy

estimate utility requirements

continuous production

conceptual engg