TM 5-810-15
fired units may be specified for boilers with
oil characteristics are similar to natural gas. Even
capacities of 100,000 pph and above. Field erected
though oil contains little ash, other constituents
atmospheric circulating fluidized bed boilers
such as sulfur, sodium and vanadium present
(ACFB) are 80,000 pph or larger. Gas and oil fired
problems. These concerns include emission of
boilers and field erected for capacities of 200,000
pollutants, external deposits and corrosion.
d. Fuel oil analysis. Historically petroleum re-
pph or larger. Field erected units are the only
boilers available for any of these technologies
fineries have produced five different grades of fuel
above 200,000 pph.
oil. Fuel oils are graded according to gravity and
viscosity as defined by ASTM standard specifica-
tions with No. 1 being the lightest and No. 6 being
3-4. Available fuels.
the heaviest. Table 3-2 lists typical analyses of the
a. Natural gas. Natural gas is the cleanest
various grades.
burning of the widely used commercially available
e. Coal types. For the purpose of boiler design,
fuels. It contains virtually no ash which reduces
domestic U.S. coals are divided into four basic
design, building and operating costs. This also
classifications: lignite, subbituminous, bituminous,
eliminates the need for particulate collection
and anthracite. Anthracite, however, requires spe-
equipment such as baghouses or electrostatic pre-
cial furnace and burner designs due to its low
cipitators. Thorough mixing with combustion air
volatile content and is not normally used in the U.S.
allows low excess air firing. The high hydrogen
for boiler fuel. Note the following illustrations,
content of natural gas compared to the oil or coal
figures 3-1 and 3-2. In general, these coal
causes more water vapor to be formed in the flue
classifications refer to the ratio of fixed carbon to
gas. This water takes heat away from the combus-
volatile matter and moisture contained in the coal,
tion process, making less heat available for steam
which increases with the action of pressure, heat,
generation which lowers the boiler efficiency.
and other agents over time as coal matures. The
b. Natural gas analysis. Two types of analyses of
changes in this ratio over the stages of coal
natural gas are commonly used. Proximate analysis
information are illustrated in figure 3-3. Volatile
provides the percentage content by volume of
matter consists of hydrocarbons and other com-
methane, ethane, carbon dioxide and nitrogen.
pounds which are released in gaseous form when
Ultimate analysis provides the percentage content
coal is heated. The amount present in a particular
coal is related to the coal*s heating value and the
oxygen. Table 3-1 gives natural gas analyses from
rate at which it burns. The volatile matter to fixed
selected United States fields.
carbon ratio greatly affects boiler design, since the
c. Fuel oil. Compared to coal fuel oils are rela-
furnace dimensions must allow the correct retention
tively easy to handle and burn. Ash disposal and
time to properly burn the fuel.
emissions are negligible. When properly atomized
Table 3-1. Analyses of Natural Gas from Selected United States Fields.
Pittsburg
So. Cal.
Birmingham
Kansas City
Los Angeles
Proximate, % by Volume
Methane CH4
83.40
84.00
90.00
84.10
77.50
Ethane C2 H6
15.80
14.80
5.00
6.70
16.00
Carbon D.C02
--
0.70
0.80
6.50
0.50
5.00
8.40
--
Nitrogen N2
0.80
Total
100.00
100.00
100.00
100.00
100.00
Ultimate % by Weight
Hydrogen H2
25.53
23.30
22.68
20.85
20.35
Carbon C
75.25
74.72
69.26
64.84
69.28
Nitrogen N2
1.22
0.76
8.06
12.90
1.41
10.37
1.22
--
Oxygen 02
--
Total
100.00
100.00
100.00
100.00
100.00
Sp Gr (Air= 1.0)
0.610
0.636
0.600
0.630
0.697
HHV Btu/ft3*
1,129
1,116
1,000
974
1,073
Btu/lb
23,170
22,904
21,800
20,160
20,090
Fuel lb/10,000 Btu
0.432
0.437
0.459
0.496
0.498
Theoretical Air lb/10,000 Btu
7.18
7.18
7.50
7.19
7.18
Total Moisture lb/10,O00 Btu
0.915
0.917
0.971
0.933
0.911
*At 60 degree F and 30 in. Hg
3-2
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