Page 230 - Mechanical Engineers' Handbook (Volume 4)

5 Fuels and Combustion 219

HHV Btu/scf
(specific gravity) 0.5

The fuel gas industry was originally developed to supply fuel gas for municipal and
commercial lighting systems. Steam was passed through incandescent coal or coke, and fuel
oil vapors were added to provide a luminous flame. The product had a heating value of
around 500 HHV, and a high carbon monoxide content, and was replaced as natural gas or
coke oven gas became available. Coke oven gas is a by-product of the manufacture of
metallurgical coke that can be treated to remove sulfur compounds and volatile tar com-
pounds to provide a fuel suitable for pipeline distribution. Blast furnace gas can be used as
an industrial or steam-generating fuel, usually after enrichment with coke oven gas. Gas will
be made from replaceable sources such as agricultural and municipal wastes, cereal grains,
and wood, as market economics for such products improve.
Heating values for fuels containing hydrogen can be calculated in two ways:

1. Higher heating value (HHV) is the total heat developed by burning with standard air
in a ratio to supply 110% of net combustion air, cooling products to ambient tem-
perature, and condensing all water vapor from the combustion of hydrogen.
2. Lower heating value (LHV) is equal to HHV less heat from the condensation of
water vapor. It provides a more realistic comparison between different fuels, since
flue gases leave most industrial processes well above condensation temperatures.
HHV factors are in more general use in the United States, while LHV values are more
popular in most foreign countries. For example, the HHV value for hydrogen as fuel is 319.4
Btu/scf, compared to a LHV of 270.2.
The combustion characteristics for common fuels are tabulated in Table 3, for combus-
6
tion with 110% standard air. Weights in pounds per 10 Btu HHV are shown, rather than
corresponding volumes, to expedite calculations based on mass flow. Corrections for flue
gas and air temperatures other than ambient are given in charts to follow.

Table 3 Combustion Characteristics of Common Fuels
6
Weight in lb/10 Btu
Fuel Btu/scf Fuel Air Flue Gas

Natural gas (SW U.S.) 1073 42 795 837
Coke oven gas 539 57 740 707
Blast furnace gas 92 821 625 1446
Mixed blast furnace and coke oven gas:
Ratio CO/BF 1/1 316 439 683 1122
1/3 204 630 654 1284
1/10 133 752 635 1387
Hydrogen 319 16 626 642

Btu/lb
No. 2 fuel oil 19,500 51 810 861
No. 6 fuel oil 18,300 55 814
With air atomization 869
With steam atomization at 3 lb/gal 889
Carbon 14,107 71 910 981