Heats Of Combustion Correlations

There have been plenty of posts on Higher Heating Value (HHV) & Lower Heating Value (LHV) in the "Cheresources" forums including the difference between HHV and LHV and how it can be calculated or obtained. Online property databanks such as the NIST databook will provide you the HHV or LHV if you know which chemical or a mixture of chemicals you are dealing with.

What if you don't know the chemical composition of the fuel whose Heating Value (HHV & LHV) needs to be found based on just physical properties such as specific gravity (fuel gases) or API gravity (liquid fuels). Can you obtain the heating value of petroleum coke (solid fuel) based just based on the ultimate analysis of the petroleum coke in terms of weight percent of Carbon, Hydrogen, Sulfur and Ash present in it?

Well the answer to the above is yes. Certain empirical correlations are available to obtain the HHV & LHV based on specific gravity for fuel gases, API gravity for liquid fuels and ultimate analysis for soild petroleum coke. Today's blog entry provides the correlation equations for HHV and LHV with certain boundaries for fuel gases, liquid fuels and petroleum coke. Unfortunately the correlations I have compiled are only in USC units. Let us go to the correlations category wise:

Fuel Gases

HHV = 229.60 + 1321*SG +207.97*(SG)² - 57.084*(SG)³

LHV = 186.37 + 1219.3*SG + 206.93*(SG)² - 56.936*(SG)³

where:

HHV / LHV = Higher / Lower Heating Value of Fuel Gas, Btu / scf
SG = specific gravity of fuel gas, dimensionless (SG < 2)

Conversion of Btu / scf to Btu / lb

Btu / lb = Btu / scf * (379.5 / MW)

where:

MW = molecular weight of the fuel gas (= SG*28.96)

Constant 379.5 is the molar volume in cubic feet at standard conditions of 14.696 psia and 60°F

Reference: API Technical Databook GPA Publication 2145-82

Liquid Fuels

HHV = 17,721 + 89.08*°API - 0.348*(°API)² + 0.009518*(°API)³

LHV = 16,840 + 76.60*°API - 1.230*(°API)² + 0.008974*(°API)³

where:

HHV / LHV = Higher / Lower Heating Value of Liquid Fuel, Btu / lb

°API = API gravity of the liquid fuel (Range: 0 < °API < 60)

Reference: Maxwell's Databook on Hydrocarbons

Petroleum Cokes

HHV = 146.58*C + 571.38*H + 29.4*S - 6.58*ASH

LHV = 146.58*C + 476.58*H + 29.4*S - 6.58*ASH

where:

HHV / LHV = Higher / Lower Heating Value of Petroleum Coke, Btu / lb

C = weight percent of carbon in petroleum coke

H = weight percent of hydrogen in petroleum coke

S = weight percent of sulfur in petroleum coke

ASH = weight percent of ash in petroleum coke

Reference: API Technical Databook

Ratio of HHV to LHV for Fuel Gases (Fuel Gas SG: <1.6)

(HHV / LHV) = 1 + 0.0947*(SG)^-0.2484

Ratio of HHV to LHV for Fuel Gases (0.4 < SG <1)

(HHV / LHV) = 1 + 0.0938*(SG)^-0.2531

Ratio of HHV to LHV for Liquid fuels

(HHV / LHV) = 1.0525 + 0.000443*°API - 0.00000204*(°API)²

Reference for HHV / LHV Ratios: API Technical Databook

Well that is enough of equations for today. Hope the readers of my blog find these equations useful in determining HHV and LHV. Looking forward to comments from members of "Cheresources".

Regards,
Ankur.