412 FOSSIL FUEL CLEANING PROCESSES
inorganic (pyritic and sulfate) matter. The organics may be
removed by various cleaning processes, but little reduction
in organic sulfur has been found to occur by physical clean-
ing methods. Currently an extraction process, followed by
hydrogenation, is being tried. Some coals have been reduced
to S contents below 2%, and typical sulfur reduction esti-
mates are in the range of 20–40% reduction. 5,6,7 Even if these
reduced levels are achieved, a need for further removal of
sulfur from the fl ue gases might exist. Cleaning, when com-
bined with fl ue gas desulfurization as a method of SO 2 con-
trol, could eliminate the need for reheat and considerably
reduce the sludge handling requirements of the plant.Fuel Oil Desulfurization (General)Before the ecological need for fuel oil desulfurization was
recognized, oil stocks were desulfurized for a number of
other reasons:1) To avoid poisoning and deactivation of platinum cat-
alysts used in most catalytic reforming processes.
2) To reduce sulfurous acid corrosion of home burner
heating equipment.
3) To demetalize crude stocks (sulfur removal from
crude is generally accompanied by a concomitant
removal of such trace metals as sodium, vanadium
and nickel).
4) To recover pure sulfur.
5) To reduce or eliminate final product odor.By defi nition, hydrodesulfurization is the removal of
sulfur by a catalytic reaction with hydrogen to form hydrogen
sulfi de. As carried out in the petroleum industry, the hydrode-
sulfurization process is not a specifi c chemical reaction.
Various types of sulfur compounds (mercaptans, sulfi des,
polysulfi des, thiophenes) with varying structures and molecu-
lar weights are treated. Obviously, they react at various rates.TABLE 1
Ash content and ash fusion temperatures of some U.S. coals and ligniteRankLow Volatile
Bituminous High Volatile Bituminous Subbituminous LigniteSeam Pocahontals No. 3 No. 9 Pittsburgh No. 6
Location West Virginia Ohio West Virginia Illinois Utah Wyoming Texas
Ash, dry basis, % 12.3 14.10 10.87 17.36 6.6 6.6 12.8
Sulfur, dry basis, % 0.7 3.30 3.53 4.17 0.5 1.0 1.1
Analysis of ash, %
by wt———————SiO 2 60.0 47.27 37.64 47.52 48.0 24.0 41.8
Al 2 O 3 30.0 22.96 20.11 17.87 11.5 20.0 13.6
TiO 2 1.6 1.00 0.81 0.78 0.6 0.7 1.5
Fe 2 O 3 4.0 22.81 29.28 20.13 7.0 11.0 6.6
CaO 0.6 1.30 4.25 5.75 25.0 26.0 17.6
MgO 0.6 0.85 1.25 1.02 4.0 4.0 2.5
Na 2 O 0.5 0.28 0.80 0.36 1.2 0.2 0.6
K 2 O 1.5 1.97 1.60 1.77 0.2 0.5 0.1
Total 98.8 98.44 95.74 95.20 97.5 86.4 84.3
Ash fusibility — — — — — — —
Initial deformation
temperature, F
Reducing 200+ 2030 2020 2000 2060 1990 1975
Oxidizing 2900+ 2420 2265 2300 2120 2190 2070
Softening
temperature, F
Reducing 2450 2175 2160 2180 2130
Oxidizing 2605 2385 2430 2220 2190
Hemispherical
temperature, F
Reducing 2480 2225 2180 2140 2250 2150
Oxidizing 2620 2450 2450 2220 2340 2210
Fluid temperature, F
Reducing 2620 2370 2320 2250 2290 2240
Oxidizing 2670 2540 2610 2460 2300 2290C006_002_r03.indd 412C006_002_r03.indd 412 11/18/2005 10:27:09 AM11/18/2005 10:27:09 AM