Physical Properties

Property

Units

Water

Organic Liquids

Steam

Air

Organic Vapors

Heat Capacity

KJ/kg 0C

4.2

1.0-2.5

2.0

1.0

2.0-4.0

Btu/lb 0F

1.0

0.239-0.598

0.479

0.239

0.479-0.958

Density

kg/m3

1000

700-1500

1.29@STP
(1 bar, 0°C)

lb/ft3

62.29

43.6-94.4

0.08@STP
(14.696 psia and 60°F)

Latent Heat

KJ/kg

1200-2100

200-1000

Btu/lb

516-903

86-430

Thermal Cond.

W/m 0C

0.55-0.70

0.10-0.20

0.025-0.070

0.025-0.05

0.02-0.06

Btu/h ft 0F

0.32-0.40

0.057-0.116

0.0144-0.040

0.014-0.029

0.116-0.35

Viscosity

cP

1.8 @ 0 0C

**See Below

0.01-0.03

0.02-0.05

0.01-0.03

0.57 @ 50 0C

0.28 @ 100 0C

0.14 @ 200 0C

Prandtl Number

1-15

10-1000

1.0

0.7

0.7-0.8

** Viscosities of organic liquids vary widely with temperature

Liquid density varies with temperature by:

Materials of Construction

Material

Advantage

Disadvantage

Carbon Steel

Low cost, easy to fabricate, abundant, most common material. Resists most alkaline environments well.

Very poor resistance to acids and stronger alkaline streams. More brittle than other materials, especially at low temperatures.

Stainless Steel

Relatively low cost, still easy to fabricate. Resist a wider variety of environments than carbon steel. Available is many different types.

No resistance to chlorides, and resistance decreases significantly at higher temperatures.

254 SMO (Avesta)

Moderate cost, still easy to fabricate. Resistance is better over a wider range of concentrations and temperatures compared to stainless steel.

Little resistance to chlorides, and resistance at higher temperatures could be improved.

Titanium

Very good resistance to chlorides (widely used in seawater applications). Strength allows it to be fabricated at smaller thicknesses.

While the material is moderately expensive, fabrication is difficult. Much of cost will be in welding labor.

Pd stabilized Titanium

Superior resistance to chlorides, even at higher temperatures. Is often used on sea water application where Titanium's resistance may not be acceptable.

Very expensive material and fabrication is again difficult and expensive.

Nickel

Very good resistance to high temperature caustic streams.

Moderate to high expense. Difficult to weld.

Hastelloy Alloy

Very wide range to choose from. Some have been specifically developed for acid services where other materials have failed.

Fairly expensive alloys. Their use must be justified. Most are easy to weld.

Graphite

One of the few materials capable of withstanding weak HCl streams.

Brittle, very expensive, and very difficult to fabricate. Some stream components have been know to diffusion through some types of graphites.

Tantalum

Superior resistance to very harsh services where no other material is acceptable.

Extremely expensive, must be absolutely necessary.

Electric Motors and Turbines

A. Efficiencies range from 85-95% for electric motors, 42-78% for steam turbines

28-38% for gas engines and turbines

B. For services under 75 kW (100 hp), electric motors are almost always used.

They can be used for services up to about 15000 kW (20000 hp)

C. Turbines can be justified in services where they will yield several hundred

horsepowers. Otherwise, throttle valves are used to release pressure.

D. A quick estimate of the energy available to a turbine is given by:

Pressure and Storage Vessels

Pressure Vessels

A. Design Temperatures between -30 and 345 °C (-22 to 653 °F) is typically about

25 °C (77 °F) above maximum operating temperature, margins increase above this range

B. Design pressure is 10% or 0.69 to 1.7 bar (10 to 25 psi) above the maximum operating

pressure, whichever is greater. The maximum operating pressure is taken as 1.7 bar (25 psi)

above the normal operation pressure.

C. For vacuum operations, design pressures are 1 barg (15 psig) to full vacuum

D. Minimum thicknesses for maintaining tank structure are:

6.4 mm (0.25 in) for 1.07 m (42 in) diameter and under

8.1 mm (0.32 in) for 1.07-1.52 m (42-60 in) diameter

9.7 mm (0.38 in) for diameters over 1.52 m (60 in)

E. Allowable working stresses are taken as 1/4 of the ultimate strength of the material

F. Maximum allowable working stresses:

Temperature

-20 to 650 °F

750 °F

850 °F

1000 °F

-30 to 345 °C

400 °C

455 °C

540 °C

CS SA203

18759 psi

15650 psi

9950 psi

2500 psi

1290 bar

1070 bar

686 bar

273 bar

302 SS

18750 psi

18750 psi

15950 psi

6250 psi

1290 bar

1290 bar

1100 bar

431 bar

G. Thickness based on pressure and radius is given by:

where pressure is in psig, radius in inches, stress in psi, corrosion allowance in inches.

**Weld Efficiency can usually be taken as 0.85 for initial design work

Storage Vessels

I. For less than 3.8 m3 (1000 gallons) use vertical tanks on legs

J. Between 3.8 m3 and 38 m3 (1000 to 10,000 gallons) use horizontal tanks on concrete supports

K. Beyond 38 m3 (10,000 gallons) use vertical tanks on concrete pads

L. Liquids with low vapor pressures, use tanks with floating roofs.

M. Raw material feed tanks are often specified for 30 days feed supplies

N. Storage tank capacity should be at 1.5 times the capacity of mobile supply vessels.

For example, 28.4 m3 (7500 gallon) tanker truck, 130 m3 (34,500 gallon) rail cars

Piping

A. Liquid lines should be sized for a velocity of (5+D/3) ft/s and a pressure drop of

2.0 psi/100 ft of pipe at pump discharges

At the pump suction, size for (1.3+D/6) ft/s and a pressure drop of 0.4 psi/100 ft of pipe

**D is pipe diameter in inches

B. Steam or gas lines can be sized for 20D ft/s and pressure drops of 0.5 psi/100 ft of pipe

C. Limits on superheated, dry steam or gas line should be 61 m/s (200 ft/s) and a pressure drop of 0.1 bar/100 m or 0.5 psi/100 ft of pipe.  Saturated steam lines should be limited to 37 m/s (120 ft/s) to avoid erosion.

D. For turbulent flow in commercial steel pipes, use the following:

E. For two phase flow, an estimate often used is Lockhart and Martinelli:

First, the pressure drops are calculated as if each phase exist alone in the pipe, then

F. Control valves require at least 0.69 bar (10 psi) pressure drop for sufficient control

G. Flange ratings include 10, 20, 40, 103, and 175 bar (150, 300, 600, 1500, and 2500 psig)

Pumps

A. Power estimates for pumping liquids:

kW=(1.67)[Flow (m3/min)][Pressure drop (bar)]/Efficiency

hp=[Flow (gpm)][Pressure drop (psi)]/1714 (Efficiency)

**Efficiency expressed as a fraction in these relations

B. NPSH=(pressure at impeller eye-vapor pressure)/(density*gravitational constant)

Common range is 1.2 to 6.1 m (4-20 ft) of liquid

C. An equation developed for efficiency based on the GPSA Engineering Data Book is:

Efficiency = 80-0.2855F+.000378FG-.000000238FG^2+.000539F^2-.000000639(F^2)G+

.0000000004(F^2)(G^2)

where Efficiency is in fraction form, F is developed head in feet, G is flow in GPM

Ranges of applicability are F=50-300 ft and G=100-1000 GPM

Error documented at 3.5%

D. Centrifugal pumps: Single stage for 0.057-18.9 m3/min (15-5000 GPM), 152 m (500 ft)

maximum head; For flow of 0.076-41.6 m3/min (20-11,000 GPM) use multistage, 1675 m (5500 ft)

maximum head; Efficiencies of 45% at 0.378 m3/min (100 GPM), 70% at 1.89 m3/min (500 GPM),

80% at 37.8 m3/min (10,000 GPM).

E. Axial pumps can be used for flows of 0.076-378 m3/min (20-100,000 GPM)

Expect heads up to 12 m (40 ft) and efficiencies of about 65-85%

F. Rotary pumps can be used for flows of 0.00378-18.9 m3/min (1-5000 GPM)

Expect heads up to 15,200 m (50,000 ft) and efficiencies of about 50-80%

G. Reciporating pumps can be used for 0.0378-37.8 m3/min (10-100,000 GPM)

Expect heads up to 300,000 m (1,000,000 ft).

Efficiencies: 70% at 7.46 kW (10 hp), 85% at 37.3 kW (50 hp), and 90% at 373 kW (500 hp)

Compressors and Vacuum Equipment

A. The following chart is used to determine what type of compressor is to be used:

B. Fans should be used to raise pressure about 3% (12 in water), blowers to raise to less than 2.75 barg (40 psig),

and compressors to higher pressures.

C. The theoretical reversible adiabatic power is estimated by:

Power = m z₁ R T₁ [({P₂ / P₁}^a - 1)] / a

where:

T1 is the inlet temperature, R is the gas constant, z1 is the compressibility, m is the molar flow rate,

a = (k-1)/k , and k = Cp/Cv

D. The outlet for the adiabatic reversible flow, T2 = T1 (P2 / P1)a

E. Exit temperatures should not exceed 204 0C (400 0F).

F. For diatomic gases (Cp/Cv = 1.4) this corresponds to a compression ratio of about 4

G. Compression ratios should be about the same in each stage for a multistage unit,

the ratio = (Pn / P1) 1/n, with n stages.

H. Efficiencies for reciprocating compressors are as follows:

65% at compression ratios of 1.5

75% at compression ratios of 2.0

80-85% at compression ratios between 3 and 6

I. Efficiencies of large centrifugal compressors handling 2.8 to 47 m3/s (6000-100,000 acfm) at suction is about 76-78%

Heat Exchangers

A. For the heat exchanger equation, Q = UAF (LMTD), use F = 0.9 when charts for the LMTD correction

factor are not available

B. Most commonly used tubes are 3/4 in. (1.9 cm) in outer diameter on a 1 in triangular spacing at 16 ft (4.9 m) long.

C. A 1 ft (30 cm) shell will contains about 100 ft2 (9.3 m2)

A 2 ft (60 cm) shell will contain about 400 ft2 (37.2 m2)

A 3 ft (90 cm) shell will contain about 1100 ft2 (102 m2)

D. Typical velocities in the tubes should be 3-10 ft/s (1-3 m/s) for liquids and30-100 ft/s (9-30 m/s) for gases

E. Flows that are corrosive, fouling, scaling, or under high pressure are usually placed in the tubes

F. Viscous and condensing fluids are typically placed on the shell side.

G. Pressure drops are about 1.5 psi (0.1 bar) for vaporization and 3-10 psi (0.2-0.68 bar) for other services

H. The minimum approach temperature for shell and tube exchangers is about 20 °F (10 °C) for fluids and

10 °F (5 °C) for refrigerants.

I. Cooling tower water is typically available at a maximum temperature of 90 °F (30 °C) and should be

returned to the tower no higher than 115 °F (45 °C)

J. Shell and Tube heat transfer coefficient for estimation purposes can be found in many reference books

or an online list can be found at one of the two following addresses:

http://www.cheresources.com/uexchangers.shtml

http://www.processassociates.com/process/heat/uvalues1.htm

K. Double pipe heat exchangers may be a good choice for areas from 100 to 200 ft2 (9.3-18.6 m2)

L. Spiral heat exchangers are often used to slurry interchangers and other services containing solids

M. Plate heat exchanger with gaskets can be used up to 320 °F (160 °C) and are often used for interchanging

duties due to their high efficiencies and ability to "cross" temperatures. More about compact heat exchangers

can be found at:

http://www.us.thermal.alfalaval.com/

Tray Towers

A. For ideal mixtures, relative volatility can be taken as the ratio of pure component vapor pressures

B. Tower operating pressure is most often determined by the cooling medium in condenser or the

maximum allowable reboiler temperature to avoid degradation of the process fluid

C. For sequencing columns:

1. Perform the easiest separation first (least trays and lowest reflux)

2. If relative volatility nor feed composition vary widely, take products off one at time

as the overhead

3. If the relative volatility of components do vary significantly, remove products in order

of decreasing volatility

4. If the concentrations of the feed vary significantly but the relative volatility do not,

remove products in order of decreasing concentration.

D. The most economic reflux ratio usually is between 1.2Rmin and 1.5Rmin

E. The most economic number of trays is usually about twice the minimum number of trays.
    The minimum number of trays is determined with the Fenske-Underwood Equation.

F. Typically, 10% more trays than are calculated are specified for a tower.

G. Tray spacings should be from 18 to 24 inches, with accessibility in mind

H. Peak tray efficiencies usually occur at linear vapor velocities of 2 ft/s (0.6 m/s) at moderate pressures,

or 6 ft/s (1.8 m/s) under vacuum conditions.

I. A typical pressure drop per tray is 0.1 psi (0.007 bar)

J. Tray efficiencies for aqueous solutions are usually in the range of 60-90% while gas absorption and

stripping typically have efficiencies closer to 10-20%

K. The three most common types of trays are valve, sieve, and bubble cap. Bubble cap trays are

typically used when low-turn down is expected or a lower pressure drop than the valve or sieve

trays can provide is necessary.

N. The most common weir heights are 2 and 3 in and the weir length is typically 75% of the tray diameter

O. Reflux pumps should be at least 25% overdesigned

P. The optimum Kremser absorption factor is usually in the range of 1.25 to 2.00

Q. Reflux drums are almost always horizontally mounted and designed for a 5 min holdup at half of the

drum's capacity.

R. For towers that are at least 3 ft (0.9 m) is diameter, 4 ft (1.2 m) should be added to the top for vapor

release and 6 ft (1.8 m) should be added to the bottom to account for the liquid level and reboiler return

S. Limit tower heights to 175 ft (53 m) due to wind load and foundation considerations.

T. The Length/Diameter ratio of a tower should be no more than 30 and preferrably below 20

U. A rough estimate of reboiler duty as a function of tower diameter is given by:

Q = 0.5 D² for pressure distillation

Q = 0.3 D² for atmospheric distillation

Q = 0.15 D² for vacuum distillation

where Q is in Million Btu/hr and D is tower diameter in feet

Packed Towers

A. Packed towers almost always have lower pressure drop than comparable tray towers.

B. Packing is often retrofitted into existing tray towers to increase capacity or separation.

C. For gas flowrates of 500 ft3/min (14.2 m3/min) use 1 in (2.5 cm) packing, for gas flows

of 2000 ft3/min (56.6 m3/min) or more, use 2 in (5 cm) packing

D. Ratio of tower diameter to packing diameter should usually be at least 15

E. Due to the possibility of deformation, plastic packing should be limited to an unsupported

depth of 10-15 ft (3-4 m) while metallatic packing can withstand 20-25 ft (6-7.6 m)

F. Liquid distributor should be placed every 5-10 tower diameters (along the length) for pall rings

and every 20 ft (6.5 m) for other types of random packings

H. Packed columns should operate near 70% flooding.

I. Height Equivalent to Theoretical Stage (HETS) for vapor-liquid contacting is 1.3-1.8 ft

(0.4-0.56 m) for 1 in pall rings and 2.5-3.0 ft (0.76-0.90 m) for 2 in pall rings

J. Design pressure drops should be as follows:

Service

Pressure drop (in water/ft packing)

Absorbers and Regenerators

Non-Foaming Systems

0.25 - 0.40

Moderate Foaming Systems

0.15 - 0.25

Fume Scrubbers

Water Absorbent

0.40 - 0.60

Chemical Absorbent

0.25 - 0.40

Atmospheric or Pressure Distillation

0.40 - 0.80

Vacuum Distillation

0.15 - 0.40

Maximum for Any System

1.0

**For packing factors and more on packed column design see:

Packed Column Design

Reactors

C. For homogeneous stirred tank reactions, the agitor power input should be about

0.5-1.5 hp/1000 gal (0.1-0.3 kW/m3), however, if heat is to be transferred,

the agitation should be about three times these amounts.

D. Ideal CSTR behavior is usually reached when the mean residence time is 5-10 times

the length needed to achieve homogeneity. Homogeneity is typically reached with

500-2000 revolutions of a properly designed stirrer.

E. Relatively slow reactions between liquids or slurries are usually conducted most

economically in a battery of 3-5 CSTR's in series.

F. Tubular flow reactors are typically used for high productions rates and when the

residence times are short. Tubular reactors are also a good choice when significant

heat transfer to or from the reactor is necessary.

G. For conversion under 95% of equilibrium, the reaction performance of a 5 stages

CSTR approaches that of a plug flow reactor.

H. Typically the chemical reaction rate will double for a 18 °F (10 °C) increase in

temperature.

I. The reaction rate in a heterogeneous reaction is often controlled more by the rate of

heat or mass transfer than by chemical kinetics.

J. Sometimes, catalysts usefulness is in improving selectivity rather than increasing

the rate of the reaction.

Refrigeration and Utilities

A. A ton of refrigeration equals the removal of 12,000 Btu/h (12,700 kJ/h) of heat

B. For various refrigeration temperatures, the following are common refrigerants:

Temp (°F)

Temp (°C)

Refrigerant

0 to 50

-18 to -10

Chilled brine or glycol

-50 to -40

-45 to -10

Ammonia, freon, butane

-150 to -50

-100 to -45

Ethane, propane

C. Cooling tower water is received from the tower between 80-90 °F (27-32 °C)

and should be returned between 115-125 °F (45-52 °C) depending on the size

of the tower. Seawater should be return no higher than 110 °F (43 °C)

D. Heat transfer fluids used: petroleum oils below 600 °F (315 °C), Dowtherms

or other synthetics below 750 °F (400 °C), molten salts below 1100 °F (600 °C)