Thumb Rules for Chemical Engineer

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THUMB RULESParticulars

PIPING PRESSURE DROP : For Raynold's no 2100 to 106

EQUIVALENT LENGHTS for Pressure drop in the system

MAXIMUM ALLOWABLE FLOW OF STEAM THROUGH PIPE 41, 12 & 2" only

ALLOWABLE VELOCITIES FOR PROCESS FLUIDS

SONIC VELOCITY CALCULATION

PERMANENT HEAD LOSS THROUGH ORIFICE

VENTURI Pressure Drop

FLOW RECTANGULAR WEIR

CONTROL VALVE SIZING

RELIEF VALVE SIZING FOR LIQUID EXPANSION

STORAGE VESSEL VOLUMES

NPSH

Pressure Drop in Pipeline

TUBESIDE PRESSURE DROP IN SHELL & TUBE HEAT EXCHANGER

MOTORS kVA

MOTORS AMPS ETIMATE

CENTRIFUGAL COMPRESSOR HP

CENTRIFUGAL COMPRESSOR HEAD

TEMPERATURE RISE IN COMPRESSION

PUMP EFFICIENCY

PUMP HORSE POWER

RELATION OF HP, IMPELLER DIA & SPEED

RELATION BETWEEN PUMP HEAD, IMPELLER DIA & SPEED

CHANGE IN PUMP CAPACITY WITH IMPELLER DIAMETER

TUBESIDE PRESSURE DROP IN AIR COOLED HEAT EXCHANGER

MOTOR HP OUTPUT

MOTOR TORQUE

GAS EXPANDERS : AVAILABLE ENERGY

POWER FACTOR

SELECTION OF TYPE OF VACUUM EQUIPMENT

FAN / BLOWER OR COMPRESSOR

SPRAY WATER FOR PRDS

MAXIMUM AVAILABLE ENERGY (EXERGY)

FUEL TO AIR RATIO

COOLING TOWERS : WINDAGE LOSSES

COOLING WATER CONCENTRATION RATIO

APPROXIMATE EFFICIENCIES OF COMPRESSORS

Physical Properties

PIPING PRESSURE DROP

viscosity m cp

Flow rate W lb/hr

Density rinternal pipe diameter d Inch

Frictional pressure loss, #DIV/0!

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For Raynold's no 2100 to 106 :

lb/ft3

DPF psi/100 equivalent ft of pipe

EQUIVALENT LENGHTS

Nom

inal p

ipe s

ize (

in)

Glo

be v

/v o

r ball

check

v/v

Angle

valv

e

Sw

ing c

hek

valv

e

Plu

g c

ock

Gate

or

ball

valv

e

Elb

ow

45

°

Short

rad

Long r

ad

Hard

T

Soft

T

90° miter bend Enlargement Contraction

2 m

iter

3 m

iter

4 m

iter

sudden std sudden

Equiv. Length in terms of small d

d/D

= 1

/4

d/D

= 1

/2

d/D

= 3

/4

d/D

= 1

/2

d/D

= 3

/4

d/D

= 1

/4

d/D

= 1

/2

d/D

= 3

/4

1.5 55 26 13 7 1 1 3 2 8 2 5 3 1 4 1 3 2 1

2 70 33 17 14 2 2 4 3 10 3 7 4 1 5 1 3 3 1

2.5 80 40 20 11 2 2 5 3 12 3 8 5 2 6 2 4 3 2

3 100 50 25 17 2 2 6 4 14 4 10 6 2 8 2 5 4 2

4 130 65 32 30 3 3 7 5 19 5 12 8 3 10 3 6 5 3

6 200 100 48 70 4 4 11 8 28 8 18 12 4 14 4 9 7 4

8 260 125 64 120 6 6 15 9 37 9 25 16 5 19 5 12 9 5

10 330 160 80 170 7 7 18 12 47 12 31 20 7 24 7 15 12 6

12 400 190 95 170 9 9 22 14 55 14 28 21 20 37 24 8 28 8 18 14 7

14 450 210 105 80 10 10 26 16 62 16 32 24 22 42 26 9 20 16 8

16 500 240 120 145 11 11 29 18 72 18 38 27 24 47 30 10 24 18 9

18 550 280 140 160 12 12 33 20 82 20 42 30 28 53 35 11 26 20 10

20 650 300 155 210 14 14 36 23 90 23 46 33 32 60 38 13 30 23 11

22 688 335 170 225 15 15 40 25 100 25 52 36 34 65 42 14 32 25 12

24 750 370 185 254 16 16 44 27 110 27 56 39 36 70 46 15 35 27 13

30 312 21 21 55 40 140 40 70 51 44

36 25 25 66 47 170 47 84 60 52

2 30 30 77 55 200 55 98 69 64

48 35 35 88 65 220 65 112 81 72

54 40 40 99 70 250 70 126 90 80

60 45 45 110 80 260 80 190 99 92

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Contraction

Std

Equiv. Length in terms of small d

d/D

= 1

/2

d/D

= 3

/4

1

1

2

2

3

4 1

5 2

6 2

7 2

MAXIMUM ALLOWABLE FLOW OF STEAM THROUGH PIPE :

In FPS : In SI :

600 175 30 41

Density (lb/ft3)0.88 0.41 0.10

Density (kg/m3)14.08

3 7.5 3.6 1.2 3 3.4

4 15 7.5 3.2 4 6.8

6 40 21 8.5 6 18.2

8 76 42 18 8 34.5

10 130 76 32 10 59.1

12 190 115 58 12 86.4

14 260 115 87 14 118.2

16 360 220 117 16 163.6

18 300 166 18

20 227 20

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Nominal pipe size (in)

Maximum lb/hr x 10-3 at Pressure (psig) Nominal pipe size (in)

Maximum T/hr at Pressure (barg)

12 2

6.49 1.62

1.6 0.5

3.4 1.5

9.5 3.9

19.1 8.2

34.5 14.5

52.3 26.4

52.3 39.5

100.0 53.2

136.4 75.5

227

Maximum T/hr at Pressure (barg)

ALLOWABLE VELOCITIES FOR PROCESS FLUIDS

Fluid ft/s m/s

Water 10 3.0

air 100 30.5

Dry gas 100 30.5

wet gas 60 18.3

high pressure steam 150 45.7

low pressure steam 100 30.5

Average liquid process 4 - 6.5 1.2 -2

Pump suction (non-boiling) 1 - 5 0.3 - 1.5

Pump suction (boiling) 0.5 - 3 0.2 - 0.9

BFW 4 - 8 1.2 - 2.4

Drain lines 1.5 - 4 0.5 - 1.2

Liquid to reboiler (no pump) 2 - 7 0.6 - 2.1

Vapor to condenser 15 - 80 4.6 - 24.4

Gravity separator flow 0.5 - 1.5 0.2 - 0.5

Vapours 326 99.4

Hot oil headers 1.5 psi/100 ft

Ref : "Rules of thumb for chemical engineers"

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SONIC VELOCITY

Sonic velocity Vs Ft/s 0

Absolute temperature T °R

ratio of sp. Heats (usually = 1.4) K 1.4

Accelearion by gravity g ft/s2 32.2

Universal gas constant R /mol wt 1544


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PERMANENT HEAD LOSS THROUGH ORIFICE :

Do/Dp Permanent loss

0.2 95

0.4 82

0.6 63

0.8 40

For orifice :

Where

Uo = Velocity through orifice (ft/s)

Up = Velocity through pipe (ft/s)

Orifice pressure drop (ft of fluid)

D = Diameter

Co = Coefficient

(0.6 for typical applns)


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Permanent loss = Dh (1-Co)

(Uo2 - Up2)1/2 = Co(2gDh)1/2

Dh =

Compiled by : Ms Gauri

VENTURI Pressure Drop

Venturi pressure drop (ft of fluid) #DIV/0!

Permanent Head loss (ft of fluid)* #DIV/0!

Velocity through orifice (ft/s) Uo

Velocity through pipe (ft/s) Up

Diameter D

Coefficient Co

(0.98 for typical applns)


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(Uo2 - Up2)1/2 = Co(2gDh)1/2

Dh =

* Permanent head loss @ 3 - 4 % of Dh


RECTANGULAR WEIR

Flow over weir ft3/s Fv 0

Width of weir ft L

Height of liquid over weir ft H


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CONTROL VALVE SIZING

For liquids :

Hence if control valve specs are known, Q can be calculated as :

Flow rate m3/hr Q 85

Body differential pressure psi 3.5

Specific gravity G 1

Liq. Sizing coeff Cv 2


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Cv = Q (G/DP)1/2

DP


RELIEF VALVE SIZING FOR LIQUID EXPANSION

Required capacity (gpm) = #DIV/0! #DIV/0! m3/hr

Heat input (Btu/hr)

0.0008 3

Specific gravity

Specific heat (Btu/lb°F)


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Coefficient of volumetric expansion per °F (Select fluid)


STORAGE VESSEL VOLUMES

For Horizontal Cylindrical vessel :

Choose Type of head : 4

Liquid hold up (m3) = #DIV/0!

Diameter (m)

Height of liquid in vessel (m)

Depth of head (m)

Length of straight portion (m)

* For spherical vessels same formula can be used with length of straight portion = 0

Ref. : Calc & shortcut deskbook, Chemical engg

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A11

Gauri: from liquid level calibration


NPSH

Net Positive Suction Head = NPSH #DIV/0!

Where,

Suction head Feet

Vessel abs pressure Psia

Vapor pressure (pumping) Psia

specific gravity

Suction friction losses Ft of fluid


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A11

Gauri: can be calculated from earlier sheet


PRESSURE DROP IN PIPELINE

Pressure drop, Pa = #DIV/0!

Laminar flow :

f = Fanning friction factor = #DIV/0!

Enter :

Fluid viscosity, kg/m-s

D = Pipe diameter, m

L = Pipe length, m

e = Pipewall roughness, m

Q =


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DP =

r = Fluid density, kg/m3

m =

Volumetric flowrate m3/s


TUBESIDE PRESSURE DROP IN SHELL & TUBE HEAT EXCHANGER

I. Straight tube loss :

viscosity m cp

Flow rate through one tube W lb/hr

Density rInternal tube diameter d Inch

Length of tube L ft

No. of tubes n

Velo.in pipe leading to & from HE ft/s

Number of tube passes N

Frictional pressure loss in tubes psi #DIV/0!psi 0psi #DIV/0!

psi#DIV/0!

Total tubeside pressure drop psi #DIV/0!


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lb/ft3

DP by Entering & exiting the HE

DP by Entering & exiting the tubes

DP by end losses in tubesidebonnets & channels


MOTORS kVA

Current Amps

Line to line voltage V

kVA kVA 0


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MOTORS AMPS ETIMATE

Motor horse power HP 6900000

Line to line voltage V 11000

Motor efficiency fraction 0.8

Power factor fraction 0.86

Motor amps :

For three phase motor : 393.15218321

For single phase motor : 680.15327696


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CENTRIFUGAL COMPRESSOR HP

Suction temperature T1 °R

Suction pressure P1 psia

Discharge pressure P2 psia

Flow W lb/min

Adiabatic efficiency Ea fraction

Avg compressibility factor Z 1


Adiabatic component K Cp/Cv 1.4

Adiabatic Head Had (ft) = #DIV/0!

Horse power = #DIV/0!


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CENTRIFUGAL COMPRESSOR HEAD




Polytropic efficiency Ep fraction 0.8

Avg compressibility factor Z 1



polytropic component N =KEp/(KEp-K+1) 1.6

Polytropic Head Hpoly (ft)= #DIV/0!

Adiabatic Head Had (ft) = #DIV/0!


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TEMPERATURE RISE IN COMPRESSION





Adiabatic : Disch Temp (°C)= #DIV/0!


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PUMP EFFICIENCY

SI units

Developed head m Applicable for :

Flow m3/hr Head = 15 - 92 m

Efficiency % 80 Flow = 23 - 227 m3/hr

fps units :

Developed head ft Applicable for :

Flow GPM Head = 50 - 300 ft

Efficiency % 80 Flow = 100 - 1000 GPM


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PUMP HORSE POWER

SI units :

Flow rate m3/hr 1.5

Discharge pressure bar 7.5

Suction pressure bar 1

Pump efficiency % 80

Pump power HP 20.0211

FPS units :

Flow rate GPM

Discharge pressure psi

Suction pressure psi

Pump efficiency %

Pump power HP #DIV/0!


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RELATION OF HP, IMPELLER DIA & SPEED

Initial impeller diameter (m) = 0.383

Initial speed (rpm) = 1782

Initial HP = 130

New impeller diameter (m) = 0.401712New speed (rpm) = 1782 #DIV/0!New HP = 150 #DIV/0!


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U canCalculate any one by specifying other two parameters in column B


U canCalculate any one by specifying other two parameters in column B


RELATION BETWEEN PUMP HEAD, IMPELLER DIA & SPEED

Initial impeller diameter (m) =

Initial speed (rpm) =

Initial head (m) =

New impeller diameter (m) = #DIV/0!New speed (rpm) = #DIV/0!New head (m) = #DIV/0!


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U canCalculate any one by providing other two parameters in column B


U canCalculate any one by providing other two parameters in column B


CHANGE IN PUMP CAPACITY WITH IMPELLER DIAMETER

Initial diameter (m) =

Initial capacity (m3/hr) =

New diameter (m) =

New capacity (m3/hr) #DIV/0!


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TUBESIDE PRESSURE DROP IN AIR COOLED HEAT EXCHANGER

viscosity of fluid m cp

Flow rate through one tube W lb/hr

Density rInternal tube diameter d Inch

Length of tube L ft

No. of tubes n

Number of tube passes N

Frictional pressure loss in tubes psi #DIV/0!

All other losses psi #DIV/0!

Total tubeside pressure drop psi #DIV/0!

Total tubeside pressure drop bar #DIV/0!


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lb/ft3


MOTOR HP OUTPUT

Motor power input kW

Motor efficiency fraction

HP output = 0

OR :

Torque

speed rpm

HP output = 0


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MOTOR TORQUE

Motor power HP

Speed rpm

Full load torque #DIV/0!


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GAS EXPANDERS : AVAILABLE ENERGY

SI units :Cp Btu/lb°C Cp kJ/kg°C

Inlet temperature °C Inlet temperature °C

Inlet pressure psia Inlet pressure barg

Outlet pressure psia Outlet pressure barg

K= Cp/ Cv K= Cp/ Cv

Actual available power Btu/lb #DIV/0! Actual available power kWh/kg


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###

###

###

#DIV/0!


POWER FACTOR

kW input kW

kVA input kVA

Power factor #DIV/0!


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A5

Gauri: calc in earlier sheet


SELECTION OF TYPE OF VACUUM EQUIPMENT

Reciprocating piston pump down to 1 torr

Rotary piston pump down to 0.001 torr

Two-lobe rotary pump down to 0.0001 torr

Steam jet ejectors 1 stage down to 100 torr

Steam jet ejectors 3 stages down to 1 torr

Steam jet ejectors 5 stages down to 0.05 torr

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FAN / BLOWER OR COMPRESSOR ??

Fans For 3% rise in pressure

Blowers For differential of 40 psig

Compressors Higher than 40 psig

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SPRAY WATER FOR PRDS (Pressure Reduction Desuperheating Stations)

Enthalpy of high pressure steam kJ/kg

Enthalpy of lower pressure steam kJ/kg

Enthalpy of the spray water kJ/kg

Spray water required T/T #DIV/0!


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MAXIMUM AVAILABLE ENERGY (EXERGY)

Receiver temperature To °C

Enthalpy at receiver conditions Ho kJ/kg

Enthalpy at source conditions H kJ/kg

Entropy at receiver conditions So kJ/kg°C

Entropy at source conditions S kJ/kg°C

Maximum available energy Ex kJ/kg 0Ex kWh/kg 0


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FUEL TO AIR RATIO

For fuel gas :

Density of fuel gas relative to air (i.e. MW/MWair) 0.78

Fuel gas / air ratio (mass/mass) 2145

For Fuel oil :

% Carbon

% hydrogen

Fuel oil / air ratio (mass/mass) #DIV/0!


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COOLING TOWERS : WINDAGE LOSSES

Type of cooling device

Spray pond 3

Atmospheric cooling tower 0.7

Mechanical draft cooling tower 0.2


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Windage loss as per centage of system circulating rate


COOLING WATER CONCENTRATION RATIO

Chloride concentration in make-up water

Chloride concentration in blow down

Concentration ratio #DIV/0!


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APPROXIMATE EFFICIENCIES OF COMPRESSORS

Efficiency Compression ratio

Reciprocating 65% 1.5

75% 2

80 - 85% 3.6

Large centrifugal 76 - 78%

Rotary compressor (except liquid liner type) 70%

Liquid liner type rotary 50%

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Physical Properties

Property Units Water Organic Liquids Steam Air

Heat Capacity KJ/kg °C 4.2 1.0-2.5 2 1

Btu/lb °F 1 0.239-0.598 0.479 0.239

Density kg/m3 1000 700-1500 1.29@STP

lb/ft3 62.29 43.6-94.4 0.08@STP

Latent Heat KJ/kg 1200-2100 200-1000

Btu/lb 516-903 86-430

Thermal Cond. W/m °C 0.55-0.70 0.10-0.20 0.025-0.070 0.025-0.05

Btu/h ft °F 0.32-0.40 0.057-0.116 0.0144-0.040 0.014-0.029

Viscosity cP 1.8 @ 0 °C varies with temp. 0.01-0.03 0.02-0.05

0.57 @ 50°C

Prandtl Number 1-15 10-1000 1 0.7

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0.28 @ 100°C

0.14 @ 200°C


2.0-4.0

0.479-0.958

0.02-0.06

0.116-0.35

0.01-0.03

0.7-0.8

Organic Vapors

Thumb Rules for Chemical Engineer

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