gas general

Know the gas laws 258Calculate gas properties from a gas analysis 260Physical properties of selected hydrocarbons and

other chemicals and gases 264Nomograph for calculating density and specific

volume of gases and vapors 272

Considerations for Selecting EnergyMeasurement Equipment 273Facts about methane and its behavior 279Conversion table for pure methane 283Categories of natural gas and reserves terminology 284Glossary of common gas industry terms 285

9: Gas—General

Know the gas laws

The symbols that will be used in the mathematicalexpression of the various gas laws are:

V1 = Volume of the gas in cubic ft with original conditionsV2 = Volume of gas in cubic ft under the second set of

conditionsTx = Initial temperature of the gas in 0R (0F+ 460)T2 = Temperature of gas under second conditions 0RPi = Pressure of gas in psia under original conditionsP2 = Pressure of gas in psia under second conditions

Any other symbols used in mathematically expressing thegas laws will be explained at the time of their introduction.

Boyle's law. If the temperature remains the same, thevolume of a given quantity of gas will vary inversely as theabsolute pressure. This may be expressed mathematically as:

Vi = P2V2 Pi

Inasmuch as in the application of Boyle's Law we aregenerally interested in the volume at a second set of pressureconditions, a rearrangement of the formula more readilyused is:

V 2 = V 1 X ^ (1)

Example. A quantity of gas at a pressure of 42 psig hasa volume of 1,000 cubic ft. If the gas is compressed to100 psig, what volume would it occupy? Assume thebarometric pressure to be 14.2 psia and the temperature toremain the same. Substituting in the second arrangement ofthe formula for Boyle's Law above would give:

= 492.1 cubic ft

Charles' law (sometimes called Gay-Lussac's Law).If the pressure remains the same, the volume of a givenquantity of gas will vary directly as the absolute temperature.

This may be expressed mathematically as:

Yi=ZiV2 T2

Again, since we are usually more interested in the volumeat a second set of temperature conditions than any other

information, an arrangement of the formula that would behandy is:

V 2 = V 1 X ^ (2)Ii

A second part of Charles' Law is: If the volume of aquantity of gas does not change, the absolute pressure willvary directly as the absolute temperature.

Expressed mathematically this is:

P i = T i

P2 T2

In this instance, we would probably be more interested inthe pressure at a second temperature condition, which couldbe expressed as:

P2 = P i X ^ (3)Ti

Example. A given weight of gas has a volume of 450 cubicft when the temperature is 45° F and the pressure is 10 psig.If the pressure remains the same, but the temperature ischanged to 900F, what will be the volume of the gas?

Table 1Molecular Weights of Hydrocarbons and Other

Compounds Associated with Natural Gas

Compound

MethaneEthanePropaneButanePentaneHexaneHeptaneCarbon DioxideNitrogenOxygenWaterAir

Atomic Formula

CH4

C2H6

C3H8C 4H 1 0

CsH12

C 6H 1 4

CyH16

CO2

N2

O2

H2O

MolecularWeight

16.04330.07044.09758.12472.15186.178

100.20544.01128.01632.0018.01628.967

Note: Molecular weights based on following values of atomic weights:hydrogen 1.008, carbon 12.011, nitrogen 14.008, oxygen 16.000, andargon 39.944. Air was assumed to consist of 78.09% nitrogen, 20.95%oxygen, 0.93% argon, and 0.03% carbon dioxide.

Substitution in the formula for the first part of the Charles'Law gives:

(90 + 460)

= 490 cubic ft

It is desired to determine what the new pressure would befor the gas in the above example if the volume remains thesame and the temperature changes from 45° F to 900F asindicated. (Atmospheric pressure is 14.4 psia.)

Substitution in the formula gives:

= 26.6 psia or 12.2 psig

A convenient arrangement of a combination of Boyle's andCharles' laws that is easy to remember and use can beexpressed mathematically as:

PiVi P2V2

-7^r- = -^r- (4)Ii I2

One can substitute known values in the combination for-mula and solve for any one unknown value. In cases whereone of the parameters, such as temperature, is not to beconsidered, it may be treated as having the same value onboth sides of the formula, and consequently it can becancelled out.

Avogadro's law. This law states that equal volumes ofall gases at the same pressure and temperature conditionscontain the same number of molecules.

From this it may be seen that the weight of a given volumeof gas is a function of the weights of the molecules and thatthere is some volume at which the gas would weigh, inpounds, the numerical value of its molecular weight.

The volume at which the weight of the gas in poundsis equal to the numerical value of its molecular weight(known as the "mol-volume") is 378.9 cubic ft for gases at atemperature of 6O0F and a pressure of 14.73 psia. Table 1gives the atomic formula and molecular weights forhydrocarbons and other compounds frequently associatedwith natural gas. Reference to the table reveals thatthe molecular weight for methane is 16.043. Going backto the mol-volume explanation shows that 378.9 cubic ft ofmethane at 6O0F and a pressure of 14.73 psia would weigh16.0431b.

Avogadro's law ties in closely with what is usually knownas the ideal gas law.

The ideal gas law. Although expressed in manyslightly different arrangements, this law is most frequentlyexpressed as:

pV = nRT

where: p = Pressure of the gasV = Volume of the gasn = Number of lb-mols of gasR = The universal gas constant, which varies

depending upon the units of pressure, volume,and temperature employed

Since the number of lb-mols of a gas would be equal to theweight of the gas divided by the molecular weight of the gas,we can express the ideal gas law as:

WpV = 10.722 x — x T (5)

M

where: p = Pressure of the gas, psiaV = Volume of the gas, cubic ft

W = Weight of the gas, IbM = Molecular weight of the gasT = Temperature of the gas, 0R

The constant 10.722 is based upon the generally usedvalue for the universal gas constant of 1,544 when thepressure is expressed in lb/sq. ft absolute.

This formula can be used in many arrangements. Anarrangement that may be used to determine the weight of aquantity of gas is:

W = 0 . 0 9 3 3 x ^ 2 (6)

when the symbols and units are as above.

Example. It is desired to find the weight of a gas in a1,000-cubic-ft container if the gas is at a pressure of 150 psigand a temperature of 900F. The molecular weight of thegas is known to be 16.816, and the barometric pressure is14.3 psia.

Substitution in the formula gives:

^7 .0933 x 16.816 x 1,000 x (150 + 14.3)YY —

(90 + 460)

= 468.71b

The formula above may be used when the molecularweight of a gas is known; however, at times it is desirableto determine the weight of a given volume of gas when the

molecular weight is not known or cannot be readilydetermined. This may be accomplished if the specific gravityof the gas is known by using the formula:

GVD

W = 2 . 6 9 8 x - ^

where G = the specific gravity of the gas (air equals 1.000)and the other symbols and units are as previously given.

Example. If the molecular weight of the gas in thepreceding example was unknown, but the specific gravitywas known to be 0.581, substitution in the formula wouldgive:

W = - 5 ^ ? 3

= 468.31b

Calculate gas properties from a gas analysis

In most practical applications involving gas calculations,the gas will consist of a mixture of components. Properties ofthe components are known; however, the properties of themix must be determined for use in other calculations, suchas compressor performance calculations. The gas molecularweight, K-value (isentropic exponent), and compressibility ofthe gas mix will be determined in the calculation to follow.Other data that may be needed for compressor performancedetermination will likely come from the process design andfrom the manufacturer's data.

Sample calculation 1

Given: A gas mixture at 30psia and 600F consisting of thefollowing components:

Table 1

cpGas MoI % MoI wt Pc T c Ibm-mol- R

Ethane 5 30.070 706.5 550 12.27Propane 80 44.097 616.0 666 17.14n-Butane 15 58.123 550.6 766 22.96

Total 10C)

Table 2Individual Component Contributions

Gas MoI % MoI wt Pc T c cp

Ethane 5 1.50 35 28 0.61Propane 80 35.28 493 533 13.71n-Butane 15 8.72 83 115 3.44

Total 100 45.5 611 676 17.76

Therefore, the properties of the mix will be:

Molecular weight = MW = 45.5Critical pressure = Pc = 611Critical temperature = Tc = 676Specific heat at constant pressure = cp = 17.76

The ratio of specific heats for the mixture are calculatedfrom Equation 1.

kmix-cpmix/(cpmix-1.986) (1)

kmix = 17.76/(17.76 -1.986)

= 1.126

Determine the compressibility of the mix by calculatingthe reduced pressure and reduced temperature by usingEquations 2 and 3.

Pr = P/Pc (2)

Tr = T/Tc (3)

Pr = 30/611

= 0.049

Tr = (60 + 460)/676

= 0.769

Refer to Figure 1 to determine the compressibility usingthe values of P1. and Tr. Z = 0.955.

If the mixture of components is given in mols of compo-nent or mass flow of components, these must be convertedto mol % before calculating the properties of the mix.


MoIs of components are given:

Ethane 400 mols/hrPropane 4,800 mols/hrn-Butane 900 mols/hrTotal Flow 6,100 mols/hr

MoI % ethane = 400/6,100 = 6.56%

Table 3

Component Mol/hr MoI %

Ethane 400 6.56Propane 4,800 78.69n-Butane 900 14.75

Totals 6,100 100.00

The mol % values listed in Table 4 can be used to calculatethe properties of the mixture following the proceduredetailed in Sample Calculation 1.


Mass flow of components is given.

Table 4

Component

EthanePropanen-Butane

Totals

Mass flow(kg/h)

15,000150,00035,000

MoI wt

30.07044.09758.123

MoI flow(kmol/h)

4993,402

602

4,503

MoI %

11.0875.5513.37

100.00

MoI flow of ethane = 15,000/30.07

= 499

MoI % of ethane = 499/4,503

= 11.08%

When a dry gas is saturated with water, it will be necessaryto consider the effects of the water on the molecular weightof the mixture. The water will also affect the total mass flowof the mixture.


Given: Compress 1,000 lbm/min dry CO2, which is initiallywater saturated. MW = 44.01, P inlet = 16psia, Tinlet = 1000F.

Calculate the molecular weight of the mixture and thetotal mass flow for the required 1,000 lbm/min of dry CO2.

MoI fraction of water vapor = y = Pw/P (4)

Pw = partial pressure of water vapor. It is exactly equal to thesaturation pressure if the gas is saturated.

MWmix = yMWmix + (1 - y) x MWdg (5)

where w = water vapordg = dry gas

mtotai = IDd8[I + (MWW x Pw)/(MWdg x Pdg)] (6)

Saturated pressure of water vapor at 1000F is equal to0.95 psia, and since the mixture is saturated, the partialpressure is also equal to 0.95 Asia.

Calculate mol % of water vapor using Equation 4.

y = 0.96/16 = 5.94 mol % water vapor

Calculate MWmix using Equation 5.

MWmix = 0.0594(18.02) + (1 - 0.059) x 44.01 = 42.48

Calculate the mass flow of the mix using Equation 6.

Mtotai = 1,000[I + (18.02 x 0.95)/(44.01 x (16 - 0.95))]

= 1,026 lbm/min

compressibility factor, Z = Pv/RT

reduced pressure, Pr

Figure 1. Compressibility chart for very low values of reducedpressure. Reproduced by permission of Chemical Engineering,McGraw Hill Publications Company, July 1954.

compressibility factor, Z = Pv/RT


Figure 2. Compressibility chart for low values of reduced pressure. Reproduced by permission of Chemical Engineering, McGrawHill Publications Company, July 1954.

+ compressiDllity factor, Z = Pv/RT '


Figure 3. Compressibility chart for low to high values of reduced pressure. Reproduced by permission of Chemical Engineering,McGraw Hill Publications Company, July 1954.

co

mp

ressib

ility

facto

r, Z

= P

v/R

T

Co

mp

ress

ibili

ty F

acto

r


Figure 4. Compressibility chart for low to very high values of reduced pressure. Reproduced by permission of ChemicalEngineering, McGraw Hill Publications Company, July 1954.

Pressure - PSIA

Compressibility Chart for Natural GasBased on ° - 6 0 Specific Gravity(A) American Gas Association Research.(B) Compressibility Charts for Natural Gas. The Pipeline Engineer,

August 1957. Ingersoll-Rand Company, 1966

Pressure - PSIAKILO Pascals

Figure 5. Compressibility chart for natural gas. Reprinted by permission and courtesy of lngersol Rand.

Physical properties of selected hydrocarbons and other chemicals and gasesPhysical Constants *See the Table of Notes and References.

Nu

mb

erSee Note No. - >

Compound

Fo

rmu

la

A.

Mo

lar

mas

s

(mo

lec

ula

r w

eig

ht)

B.

Bo

ilin

g p

oin

t.0F

14

.69

6

ps

ia

Vap

or

pre

ssu

re,

psia

100

0F

C.

Fre

ezin

g p

oin

t,0F

14

.69

6

ps

ia

0.

Re

fra

cti

ve

ind

ex,

TVQ

60

0F

C r i t i ca l constants

Pre

ss

ure

, p

sia

Te

mp

era

ture

,0F

Vo

lum

e,

ft3/l

bm

•

eZ

MethaneEthanePropaneIsobutonen-Butane

Isopentanen-PentaneNeopentane

n-Hexane2-Methylpentane3-MethylpentaneNeohexane2,3-DimethyI butane

n-Heptane2-MethyIhexane3-MethyIhexane3-Ethylpentane2,2-Dimethy I pentone2.4-0imethylpentane3,3-OimethylpentaneTriptane

n-OctaneDi isobutylIsooctanen-Nonanen-OecaneCyclopentaneMethy i eye IopentaneCyclohexaneMethyI eye Iohexane

Ethene(Ethylene)Propene(PropyIene)1-Butene(ButyIene)cis-2-Butenetrons-2-ButeneIsobutene1-Pentene1,2-Butodiene1,3-ButadieneIsoprene

AcetyleneBenzeneTolueneEthyl benzeneo-Xylenem—Xy Ienep-XyIeneStyreneIsopropyI benzene

Methyl alcoholEthyl alcoholCarbon monoxideCarbon dioxideHydrogen sulfideSulfur dioxide

AmmoniaAirHydrogenOxygenNitrogenChlor meWaterHeliumHydrogen chloride

CH4C2H6C3H8C4 H ioC4Hi0

C5Hi2C5Hi2C5Hi2

C6Hi4C6Hi4C6Hi4C6Hi4C6Hi4

C7H16C7Hi6C7Hi6C7Hj6C7Hi6C7Hi6C7Hi6C7Hi6

C8Hi8C8Hi8C8Hi8CgH2OCi0H22C5Hi0C6Hi2C6Hi2C7Hu

C2H4C3H6C4H8C4H8C4H8C4H8C5Hi0C4H6C4H6C5H8

C2H2C6H6C7H8C8HiOC8HiOC8HiOC8HiOC8H8C9Hi2

CH4OC2H6OCOCO2H2SSO2

NH3N2-I-O2H2O2N2C l 2H2OHeHCI

12/12/86NOTE: Numbers in this table do not have accuracies greater than 1 part in 1,000; in some cases extra digits have been added to

calculated values to achieve consistency or to permit recalculation of experimental values.

Physical Constants *See the Table of Notes and References.

Num

ber

Rel

ativ

e de

nsity

Density of Iiquid14.696 psio, 600F

(spe

cific

gra

vity

)

Ibm

/gal

.

ga

l./I

b m

ole

Tem

pera

ture

co

eff

icie

nt

of

de

ns

ity

, 1/

°F

Ac

en

tric

fac

tor,

OJ

Com

pres

sibi

lity

fact

orof

re

al

ga

s. Z

14.6

96

ps

ia.

60

0F Ideal gas14.696 psio, 6O0F

Rel

ativ

e de

nsity

(spe

cific

gra

vity

)A

ir

- 1

ft3

gas

/lb

m

ft

ga

s/g

al.

Iiq

uid

Specific Heat600F

14.696 psiaBtu/(Ibm-0F)

CP.Idealgas

Liquid

Num

ber

12/12/86NOTE: Numbers in this table do not have accuracies greater than 1 part in 1,000; in some cases extra digits have been added tocalculated values to achieve consistency or to permit recalculation of experimental values.

Physical Constants

Num

ber

See Note No. ->

Compound

K.Heoting value. 600F

Btu

/ft3

Ide

al g

as

,14

,696

p

sio

Btu

/lbm

Liq

uid

Btu

/ft3

idea

l g

as

,14

.696

p

sio

O m

Btu

/lbm

L i q

uId

Btu

/ga

lL

iqu

id

L. M.

.«? oft

!*« t|%o <o • »- 3 —

I S R < 8"z

Flommobilitylimits.vol X

inai r mixture

Low

er

Hig

her

ASTMoctanenumber

Mot

or m

etho

dD

-357

Neee

oion

met

nod

D-9

08

•.O

mZ

MethaneEthanePropaneIsoDutanen-Butane

Isopentonen-PentaneNeopentane

n-Hexane2-MethyI pentone3-MethylpentaneNeohexane2,3-DimethyI butane

n-Heptane2-MethyI hexane3-MethyIhexane3-EthyIpentone2,2-Dimethylpentane2.4-0imethylpentane3,3-DimethylpentaneTriptane

n-OctaneDi isobutylIsooctonen-Nonanen-DecaneCyclopentaneMethyI eye IopentaneCyclohexaneMe t hyI eye Ionexane

Ethene(Ethylene)Propene(Propylene)1-Butene(Butylene)cis-2-Butenetrans—2-ButeneIsobutene1-Pentene1,2-Butadiene1t3-6utadieneIsoprene

AcetyleneBenzeneTolueneEthyl benzeneo-XyIenem-XyIenep-XyIeneStyreneIsopropytbenzene


AmmoniaAirHydrogenOxygenNi troaenChlorineWaterHeliumHydrogen chloride

12/12/86NOTE: Numbers in this table do not have accuracies greater than 1 part in 1,000; in some cases extra digits have been added tocalculated values to achieve consistency or to permit recalculation of experimental values.

*See the Table of Notes and References.

(Cont'd)NOTES AND REFERENCES FOR THE TABLE OF PHYSICAL CONSTANTS

Num

ber

See Not* No. - >

Compound

Form

ula

A.

Mo

lar

mas

s(m

ole

cula

r w

eig

ht)

B.

Bo

ilin

g p

oin

t.0F

14.6

96 p

sia

Vapo

r p

ress

ure

, p

sia

100

0F

C.

Fre

ezin

g p

oin

t,0F

14.6

96 p

sia

D.

Ref

ract

ive

inde

x, 7

IQ60°F

C r i t i c a l constants

Pre

ss

ure

, p

sia

Te

mp

era

ture

,0F

Vo

lum

e,

ft3/l

bm

•E3Z

MethaneEthaneProponeIsobutonen-Butane

Isopentonen-PentaneNeopentane

n-Hexane2-Methylpentane3-MethylpentoneNeohexone2.3-Oimethylbutane

n-Heptane2-Methylhexane3~Methylhexane3-Ethylpentane2,2-Dlmethy I pentone2,4-Oimethylpentane3,3-OimethylpentaneTriptane

n-OctaneDlisobutylIsooctonen-Nonanen-DecaneCyclopentaneMe thy I eye IopentaneCycIohexaneMethy IcycIohexone

Ethene(Ethylene)Propene(Propylene)i-Butene(Butylene)cls-2-Butenetrans-2-6uteneIsobutene1-Pentene1,2-Butodiene1,3-ButodieneIsoprene

AcetyleneBenzeneTolueneEthyl benzeneo-XyIenem-Xylenep-XyIeneStyreneIsop ropy I benzene


AmmoniaAirHydrogenOxygenNltro9«nChlorineWaterHeliumHydrogen chloride

CH4C2H6C 3 H,C4Hi0C4Hi0

C 5HuC 5 HuC5Hi2

C 6 HuC 6HuC 6 HuC 6HuC 6Hu

C7Hj6C7Hi6C7Hi6C7Hi6C7Hi6C7Hi6C7Hi6C7H16

CiHi 8CsHisCsHisC9H20Ci0H2 2C5Hi0C6Hi2C6H12C7H14

C2H4C3H6C4H8C4HsC4H8C4H8C5Hi0C4H6C4H6C5H8

C2H2C6H6C7H8CsHioCsH10CsH10CsH10CsH8C9H12

CH4OC2H6OCOCO2H2SSO2

NH3N2 +O2H2O2N2Cl 2H2OHeHCI

12/12/86


Num

ber

E. F.

Density of Iiquid14.696 psio. 6O 0F

Rel

ativ

e de

nsity

(spe

cific

gra

vity

)eo

°F/6

0°F

Ibm

/gal

.

ga

l./I

b m

ole

Tem

per

atu

rec

oe

ffic

ien

tof

d

en

sit

y.

1/0F

OA

ce

ntr

icfa

cto

r,

a

XC

ompr

essi

bilit

y fa

ctor

of

rea

l g

as

, Z

14

.69

6 p

sia

, 60

0F

X.Ideal gas

14.696 psia, 600F

Rel

ativ

e de

nsity

(spe

cific

gra

vity

)A

ir -

1

ft3

go

s/lb

m

ft

ga

s/g

al,

liq

uid

JSpecific Heat

6O0F14.696 psioBtu/( IbIi-0F)

Cp.Idealgas

CP.Liquid

Num

ber


Num

ber

See Note No. ->

Compound

K.Heating value. 600F

Net

Btu

/ft3

Ide

al

ga

s.

14.6

96 p

sia

Btu

/lbm

Liq

uid

Btu

/ft3

idea

l g

as

,14

.696

pa

ia

Gross

Btu

/lbm

Liq

uid

Btu

/ga

l.L

iqu

id

L.

Hea

t o

f va

pori

zatio

n14

.696

psi

a at

bo

ilin

gp

oin

t, B

tu/l

bm

M.

Air

re

qu

ire

d f

or

com

bust

ion

idea

l gas

ft3(a

ir)/

ft3(g

<»

)

Fl ammabiIi tyI imits.vol %

inai r mixture

Low

er

Hig

her

ASTMoctanenumber

Mot

or m

etho

dC

K35

7

Res

earc

h m

etho

dD

-908 •

E3Z

MethaneEthanePropaneIsobutanen-Butane

Isopentanen-PentaneNeopentane

n-Hexane2-Methylpentone3-MethylpentaneNeohexane2,3-Dimethy I butone

n-Heptane2-Methylhexane3-Methylhexane3-EthyI pentone2f2-0imethy I pentone2,4-0imethyIpentane3,3-DimethylpentaneTriptane

n-OctoneDi isobutyiIsooctonen—Nononen-OecaneCycI opentoneMethyI eye IopentaneCyclohexaneMethylcyclohexane

Ethene(Ethylene)Propene(PropyIene)i-Butene(Butylene)cis-2-Butenetrans-2-ButeneIsobutene1-Pentene1.2-Butadfene1,3-ButadieneIsoprene

AcetyleneBenzeneToIueneEthyl benzeneo-XyIenem-Xylenep-XyIeneStyreneIsopropy I benzene


AmmoniaAirHydrogenOxygenNi trogenChlorineWaterHeliumHydrogen chloride

5757575757

575757

5757575757

5757575757575757

575757575757205720

57575757575757575757

575757575757572057

62628

18

58

58

8

(Cont'd)

NOTES FOR THE TABLE OF PHYSICAL CONSTANTS

a. Values in parentheses are estimated values.b. The temperature is above the critical point.c. At saturation pressure (triple point).d. Sublimation point.e. The + sign and number following specify the number

of cm3 of TEL added per gallon to achieve the ASTMoctane number of 100, which corresponds to that ofIsooctane (2,2,4-Trimethylpentane.)

f. These compounds form a glass. An earlier investiga-tor [12] reported a value of-2440F for the freezingpoint of 3-Methylpentane.

g. Average value from octane numbers of more than onesample.

h. Saturation pressure and 600F.i. Index of refraction of the gas.j . The temperature difference correction from [51].k. Densities of the liquid at the normal boiling point,

m. Heat of sublimation,n. Equation 2 of the reference was refitted to give:

a = 0.7872957; b = 0.1294083; c = 0.03439519.p. Normal hydrogen (25% para, 75% ortho).

q. The vapor pressure [5] at the critical temperature[43].

r. An extrapolated value.s. The value for the critical point of helium depends

upon the temperature scale chosen. See reference 7.t. Gas at 600F and the liquid at the normal boiling

point.u. Fixed points on the 1968 International Practical

Temperature Scale (IPTS-68).v. Densities at the normal boiling point are: Ethane,

4.540 [34]; Propane, 4.848 [33]; Propene, 5.083 [5];Hydrogen Chloride, 9.948 [56]; Hydrogen Sulfide,7.919 [30]; Ammonia, 5.688 [56]; Sulfur Dioxide,12.20 [56].

w. Technically, water has a heating value in two cases:net (-1060. Btu/lbm) when water is liquid in the re-actants and gross (+50.313 Btu/ft*) when water isgas in the reactants. The value is the ideal heat ofvaporization (enthalpy of the ideal gas less the en-thalpy of the saturated liquid at the vapor pressure).This is a matter of definition; water does not burn.

x. Extreme values of those reported by ret 24.

A. Molar mass (molecular weight) is based upon the following atomic weights: C = 12.011; H = 1.00794; O = 15.9994;N = 14.0067; S = 32.06, Cl = 35.453. The values were rounded off after calculating the molar mass using allsignificant figures in the atomic weights.

B. Boiling point: the temperature at equilibrium between the liquid and vapor phases at 14.696 psia.C. Freezing point, the temperature at equilibrium between the crystalline phase and the air saturated liquid at 14.696

psia.D. The refactive index reported refers to the liquid or gas and is measured for light of wavelength corresponding to

the sodium D-line (589.26 nm).E. The relative density (specific gravity): p(liquid, 60°F)/p(water, 600F). The density of water at 600F is 8.33718

lbm/gal.F. The temperature coefficient of density is related to the expansion coefficient by:

HSW(S),. ---"•'G. Pitzer acentric factor:

« =- log, 0 ( /yP e ) - I1 P at T = 0.7Te

H. Compressibility factor of the real gas, Z = (PV)/(RT), is calculated using the second virial coefficient equation.I. The density of an ideal gas relative to air is calculated by dividing the molar mass of the of the gas by 28.9625,

the calculated average molar mass of air. See ref. 39 for the average composition of dry air. The specific volumeof an ideal gas is calulated from the ideal gas equation. The volume ratio is: V(ideal gas)/V(Iiquid in vacuum).

J. The liquid value is not rigorously Cp, but rather it is Cs, the heat capacity at saturated conditions, defined by:

«•»-'(5),»When dealing with liquids far from the critical point, Cs * Cp.

K. The heating value is the negative of the enthalpy of combustion at 600F and 14.696 psia in an ideal reaction (onewhere all gasses are ideal gasses). For an arbitrary organic compound, the combustion reaction is:

CnHmO»S,Nfc(f,/,or*) + (n + j - ^+j)O7[g) — nCO2(g) + y H2O(^ or I) + ^N,(f) + )SO,(f)

where s, l,and g denote respectively solid, liquid and ideal gas. For gross heating values, the water formed is liquid;for net heating values, the water formed is ideal gas. Values reported are on a dry basis. To account for waterin the heating value, see GPA 2172. The Btu/lbm or gal. liquid column assumes a reaction with the fuel in theliquid state, while the Btu/ft3 ideal gas column assumes the gas in the ideal gas state. Therefore, the values arenot consistent if used in the same calculation, e.g., a gas plant balance.

L. The heat of vaporization is the enthalpy of the saturated vapor at the boiling point at 14.696 psia minus theenthalpy of the saturated liquid at the same pressure.

M. Air required for the combustion of ideal gas for compounds of formula CnHmOhSjNk is:

V(axr)/V(gaa) = (n + - - - + »/0.20946

COMMENTS

Units - all dimensional values are reported in terms of the following three units, which are defined in terms of thecorresponding SI units:

mass - pound (avdp), lbm = 0.45359337 kglength - foot, ft = 0.3048 mtemperature - degree fahrenheit, (t/°F) = 32 + [l.8(t/°C)JTemperature of the Celsius scale is defined bythe International Practical Temperature of 1968 (IPTS-68).

Other derived units are:volume - cubic foot, ft3 = 0.02831685 m3

gallon = 231 in3 = 0.003785412 m3

pressure - pound per square inch absolute = 6894.757 Paenergy - British thermal unit (I.T.), Btu = 251.9958 cal (I.T.) = 1055.056 J

Physical constants:gas constant, R = 1.98598 Btu(I.T.)/(°Rlb mol)

10.7316 ft3 psia/(°Rlb mol)8.31448 J/(K mol)

Conversion factors:1 ft3 = 7.480520 gal.1 lbm/ft3 = 0.1336806 lbm/gal = 16.018462 kg/m3

1 psia = 0.06804596 atm1 atm = 14.69595 psia = 760 Torr1 Btu (LT.) = 252.1644 calth

REFERENCES FOR THE TABLE OF PHYSICAL CONSTANTS1. Ambrose, D., National Physical Laboratory, Ted-

dington, Middlesex, England: Feb. 1980, NPL Re-port Chem 107.

2. Ambrose, D.; Hall, D. J.; Lee, D. A.; Lewis, G. B.;Mash, C. J., J. Chem. Thermo., 11, 1089 (1979).

3. Angus, S.; Armstrong, B.; de Reuck, K. M., Eds."Carbon Dioxide. International Thermodynamic Ta-bles of the Fluid State-3"; Pergamon Press: Oxford,1976.

4. Angus, S.; Armstrong, B.; de Reuck, K. M., Eds."Methane. International Thermodynamic Tables ofthe Fluid State-5"; Pergaroon Press: Oxford, 1978.

5. Angus, S.; Armstrong, B.; de Reuck, K. M., "Propy-lene (Propene). International Thermodynamic Ta-bles of the Fluid State-7"; Pergamon Press: Oxford,1980.

6. Angus, S.; de Reuck, K. M.; Armstrong, B., Eds."Nitrogen. Internationa] Thermodynamic Tables ofthe Fluid State-6"; Pergamon Press: Oxford, 1979.

7. Angus, S.; de Reuck, K. M.; McCarthy, R. D., Eds."Helium. International Thermodynamic Tables ofthe Fluid State-4"; Pergamon Press: Oxford, 1977.

8. Armstrong, G. T.; Jobe, T. L., "Heating Values ofNatural Gas and its Components," NBSIR 82-2401,May 1982.

9. Aston, J. G.; Szass, G. J.; Fink, H. L., J. Am. Chem.Soc, 65, 1135(1943).

10. Barber, C. R., Metrologia 5, 35 (1969).11. Boundy, R. H.; Boyer, R. F., (Eds.), "Styrene,

Its Polymers, Copolymers and Derivatives," A.C.S.monograph No. 115, Reinholt, N.Y., 1952.

12. Bruun, J. H.; Hicks-Bruun, M. M., J. Res. NBS, 5,933 (1930).

13. Chaiyavech, P.; Van Winkle, M., J. Chem. Eng.Data, 4, 53 (1959).

14. Chao, J., "Bensene," Key chemical data books,Thermodynamics Research Center, Texas A k. MUniversity, College Station, Texas (1978).

15. Chao, J., Hydrocarbon Processing, 59(11), 295(1979).16. Chao, J.; Hall, K. R., Thermochimica acta, 72, 323

(1984).17. Chao, J.; Hall, K. R.; Yao, J., Thermochimica acta,

64, 285 (1983).18. CODATA Task Group on Key Values for Thermody-

namics, CODATA Special Report No. 7, 1978.19. Commission on Atomic Weights and Isotopic Abun-

dances, Pure and Appl. Chem. 49, 1102 (1983).20. Cox, J. D.; Pilcher, G., "Thermochemistry of Or-

ganic and Organometallic Compounds," AcademicPress, London, 1970.

21. Dean, J. W., "A Tabulation of the Properties of Nor-mal Hydrogen from Low Temperature to 300 K andfrom 1 to 100 Atmospheres," NBS Tech. Note 120,November 1961.

22. Douslin, D. R.; Huffman, H. M., J. Am. Chem. Soc,68, 1704 (1946).

23. Edwards, D. G., "The Vapor Pressure of 30 InorganicLiquids Between One Atmosphere and the CriticalPoint," Univ. of Calif, Lawrence Radiation Labora-tory, UCRL-7167. June 13, 1963.

24. Engineering Sciences Data Unit, "EDSU, Engineer-ing Sciences Data," EDSU International Ltd., Lon-don.

25. Flebbe, J. L.; Barclay, D. A.; Manley, D. B., J.Chem. Eng. Data, 27, 405 (1982).

26. Francis, A. W., J. Chem. Eng. Data, 5, 534 (1960).27. Friedman, A. S.; Haar, L., J. Chem. Phys. 22, 2051

(1954).28. Ginnings, D. C; Furukawa, G. T., J. Am. Chem.

Soc. 75,522(1953).29. Glasgow, A. R.; Murphy, E. T.; Willingham, C. B.;

Rossini, F. D., J. Res. NBS, 37, 141 (1946).30. Goodwin, R. D., "Isobutane: Provisional Thermo-

dynamic Functions from 114 to 700K at Pressures to700 Bar," NBSIR 79-1612, July 1979.

31. Goodwin, R. D., "Hydrogen Sulfidc Provisional Ther-mochemica) Properties from 188 to 700 K at Pres-sures to 75 MPa1" NBSIR 83-1694, October 1983.

32. Goodwin, R. D.; Haynes, W. M., "ThermophysicalProperties of Isobutane from 114 to 700 K at Pres-sures to 70 MPa," NBS Tech. Note 1051, January

1982.33. Goodwin, R. D.; Haynes, W. M., "Thermophysical

Properties of Normal Butane from 135 to 700 K atPressures to 70 MPa," NBS Monograph 169, April1982.

34. Goodwin, R. D.; Haynes, W. M., "ThermophysicalProperties of Propane from 85 to 700 K at Pressuresto 70 MPa," NBS Monograph 170, April 1982.

35. Goodwin, R. D.; Roder, H. M.; Straty, G. C; "Ther-mophysical Properties of Ethane, 90 to 600 K atPressures to 700 bar," NBS Tech. Note 684, August1976.

36. Guthrie, G. B.; Huffman, H. M., J. Am. Chem. Soc,65, 1139 (1943).

37. Haar, L.; Gallagher, J. S.; KeIl, G. S., "NBS/NRCSteam Tables," Hemisphere Publishing Corporation,Washington, 1964.

38. Huffman, H. M.; Park, G. S.; Thomas, S. B., J. Am.Chem. Soc, 52, 3241 (1930).

39. Hust, J. G.; Stewart, R. B., "Thermodynamic Prop-erty Values for Gaseous and Liquid Carbon Monox-ide from 70 to 300 Atmospheres," NBS TechnicalNote 202, Nov. 1963.

40. Jones, F. E., J. Res. NBS, 83, 419 (1978).41. KeIl, G. S., J. Chem. Eng. Data, 20, 97 (1975).42. Kishimoto, K.; Suga, H.; Syuro, S., Bull. Chem.

Soc Japan, 46, 3020(1973).43. Kudchadker, A. P.; Alani, G. H.; Zwolinski, B. J.,

Chem. Rev. 68, 659 (1968).44. Marchman, H.; Prengle, H. W.; Motard, R. L., Ind.

Eng. Chem., 41, 2658 (1949).45. "The Matheson Unabridged Gas Data Book"; Math-

eson Gas Products; New York, 1974.46. McCarty, R. D.; Weber, L. A., "Thermophysical

Properties of Oxygen from the Freesing Liquid Lineto 600 R for Pressures to 5000 Psia", NBS TechnicalNote 384, July 1971.

47. Messerly, J. F.; Guthrie, G. B.; Todd, S. S.; Finke,H. L., J. Chem. Eng. Data, 12, 338 (1967).

48. Messerly, J. F.; Todd, S. S.; Guthrie, G. B., J. Chem.Eng. Data, 15, 227 (1970).

49. Miller, A.; Scott, D. W., J. Chem. Phys., 68(3), 1317(1978).

50. Miller, L.P.; Wachter, N. W.; Fried, V., J. Chem.Eng. Data, 20, 417(1975).

51. Ohe, S., "Computer Aided Data Book of Vapor Pres-sure," Data Book Publishing Co., Tokyo, Japan,1976.

52. Riddick, J. A.; Bunger, W. B., "Organic Solvents,Physical Properties and Methods of Purification,*1

Wiley-Interscience: New York, 1970.53. Roder, H. M., "Measurements of the Specific Heats,

C«, and C», of Dense Gaseous and Liquid Ethane,"J. Res. Nat. Bur. Stand. (U.S.) 80A, 739 (1976).

54. Scott, R. B.; Meyers, C. H.; Rands, R. D.; Brick-wedde, F. G.; Bekkedahl, N., J. Res. NBS, 35, 39(1945).

55. Sliwinski, P., Z. Physik. Chem. (Frankfurt) 63, 263(1969).

56. Stull, D. R.; Westrum, E. F.; Sinke, G. C, "TheChemical Thermodynamics of Organic Compounds,"John Wiley & Sons, Inc., New York, 1969.

57. "TRC Thermodynamic Tables - Hydrocarbons,"Thermodynamics Research Center, Texas AfeM Uni-versity System: College Station, Texas.

58. "TRC Thermodynamic Tables-Non-Hydrocarbons,"Thermodynamics Research Center, Texas A&M Uni-versity System: College Station, Texas.

59. Vargaftik, N. B.; "Tables on the ThermophysicalProperties of Liquids and Gases," Hemisphere Pub-lishing Corporation, Washington D.C, 1975.

60. Weast, R. C, "Handbook of Chemistry and Physics,"The Chemical Rubber Co: Cleveland, Ohio, 1969.

61. Wilhoit, R. C; Aljoe, K. L.; Adler, S. B.; Kud-chadker, S. A., "Isopropylbensene and l-Methyl-2-,-3-, and -4-isopropylbenxene," API Monograph Se-ries No. 722, American Petroleum Institute, 1984.

62. Wilhoit, R. C; Zwolinski, B. J., J. Phys. Chem. Ref.Data, 2, Suppl. no. 1 (1973).

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Reprinted with Permission—Gas Processors Suppliers Association, Tenth Edition Engineering Data Book.

Nomograph for calculating density and specific volume of gases and vapors

The density of a gas or vapor can be calculated from theequation for an ideal gas:

_ 1 4 4 P _ MP _2.70PSgP~ RT " 1 0 . 7 2 T " T

where: p = Density of gas, lb/cu ftP = Absolute pressure, psi (psig + 14.7)R = Individual gas constant (10.72/M)M = Molecular weight of gasT = Temperature, 0R

Sg = Specific gravity of individual gas relative to air(= to ratio of gas molecular weight to that of air)

The above equation and corresponding nomograph(Figure 1) can be used to calculate the density (or specificvolume) of gases at low pressures and high temperatures,where the ideal gas law holds. Note that the pressure scale is

calibrated in psi gauge so that the correction of 14.7 psi isnot needed when using the nomograph.

Example. What is the density of dry methane if itstemperature is 1000F and its pressure is 15 psig?

Connect With Mark or ReadM = 16 t = 100°F IndexIndex Mark P = 15 psig p = 0.08 lb/cu ft

Source

"Fluid Flow Through Pipe, Fittings and Valves,"Technical Paper No. 410, A-Il, Crane Company, Chicago,IL (1957).

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Figure 1. Weight density and specific volume of gases and vapors.

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