US 4981667 A
The sulfur in petroleum pitches and cokes can be converted to calcium sulfate instead of sulfur dioxide during combustion when calcium oxide or calcium carbonate is added to the molten pitch before burning.
1. A method for burning a sulfur continuing molten carbonaceous material by adding sufficient calcium oxide or calcium carbonate to convert the sulfur content of the carbonaceous material to calcium sulfate during the burning, said carbonaceous material comprises petroleum pitch containing about 40 percent petroleum coke dissolved therein.
2. A method for burning a sulfur containing molten carbonaceous material by adding sufficient calcium oxide or calcium carbonate to convert the sulfur content of the carbonaceous material to calcium sulfate during the burning, said carbonaceous material comprises petroleum pitch containing about 25 percent sawdust dissolved therein.
This invention relates to a method or process for converting the sulfur content of the flue gas from carbonaceous fuels into a solid by adding lime to the fuel before burning it.
The high carbon content fuels such as petroleum pitch, coal tar pitch and coke are among the cheapest source of energy. Their use is precluded however if they contain sulfur, 3% usually being the upper limit in most applications. When these sulfur containing materials are used for fuel, current restrictions on SO2 in flue gas emission make it mandatory to employ scrubbers or some other method to remove the sulfur.
Berg, U.S. Pat. No. 4,687,647 described the use of high sulfur pitch in the conversion of molybdenite ores. Berg, U.S. Pat. No. 4,806,319 used high sulfur pitch to recover gaseous SO2 and NOx from inert gases. In neither of these uses did the presence of the sulfur in the pitch have a deleterious effect on the process.
The obeject of this invention is to provide a method or process to convert the sulfur when present in pitches and cokes into a solid form when employed as a fuel.
The objects of this invention are provided by a process for converting the sulfur in pitches and cokes into a solid form by adding lime to the pitch or coke before combustion.
We have discovered that when lime, either as calcium oxide or calcium carbonate, is added to molten high sulfur petroleum pitch, coal tar pitch or petroleum coke, when this mixture is burned in the usual manner, the lime reacts in the combustion zone to form solid calcium sulfate with the sulfur in the pitch. This comes out of the combustion zone as a fine solid powder much as ash does in a coal burner. We have also found that the molten pitch is a good conveyor of solid fuels such as fluid petrolem coke and sawdust and that the presence of CaO or CaCO3 in the molten pitch will effectively combine with the sulfur these and convert it into solid CaSO4. Petroleum pitch has a has a viscosity of about 350 Centistokes at 350° F., the temperature at which it should be heated in order to pump it into the furnace. We found that with coarse fluid petroleum coke, about 40% coke, 60% pitch was a mixture that could still be pumped. With dry sawdust, 25% sawdust, 75% pitch was pumpable. These ratios could be improved somewhat by grinding to a finer perticle size the fluid petroleum coke or the sawdust.
High sulfur content petroleum pitches and cokes are precluded from commercial use as fuels because upon combustion, the sulfur is converted into gaseous sulfur dioxide, a compound with which it is prohibited to emit into the atmosphere. These pitches and cokes possess a high Btu content and are abundant and cheap. This invention employs lime mixed with the pitch to convert the sulfur to CaS4 instead of S2, a material which is a solid and is easily to dispose of or put to use. This invention presents an economically attractive way to employ high sulfur pitches and cokes, which are both high Btu content and low cost, as a fuel without introducing SO2 into the flue gas.
TABLE 1______________________________________Results of the Combustion of Pitch Mixtures Sulfur Calcium Content Ash Compound Of SulfurMaterial Btu/lb. Used Mixture, % Content, %______________________________________Petroleum Pitch 17,100 CaO 5 3.95Petroleum Pitch 17,100 CaCO3 5 4.2Pitch + Fluid 14,340 CaCO3 6 4.1CokePitch + Saw- 15,239 CaCO3 3.7 3.93dust______________________________________ Table 1 summarizes the data obtained in the working examples.
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