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# 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.

sheiko
Good info.
But I would have also included latest ISO and ASTM equations...
ankur2061

Good info.
But I would have also included latest ISO and ASTM equations...

Thanks. Unfortunately, I do not have access to the ISO or ASTM equations. Could you share them or provide the title and number of these standards from where the equations could be obtained.

Regards,
Ankur
carlo
It seems to me that the equation for liquid fuel HHV is uncorrect.
The 3rd coefficient should be -0.348 instead of 348.

In addition to the above, why not tp refer to API Technical Data Book correlations?

Carlo Stegher
ankur2061

It seems to me that the equation for liquid fuel HHV is uncorrect.
The 3rd coefficient should be -0.348 instead of 348.

In addition to the above, why not tp refer to API Technical Data Book correlations?

Carlo Stegher

Carlo,

You are absolutely right and I stand corrected. The value should be 0.348 and not 348 as given in the formula. I have corrected the equation in the blog entry. Thank you very much.

Regards,
Ankur.
sheiko
Ankur,
For Fuel Oil: ASTM D4868 or ISO 8217
For Jet Fuel: ASTM D3338

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