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METHOD FOR REDUCING SOX EMISSIONS
DURING THE COMBUSTION OF
CROSS REFERENCE TO RELATED
The present application is a continuation-in-part of Applicants' prior copending application Ser. Nos. 10 780,783, filed Sept. 27, 1985, and 787,293, filed Oct. 15, 1985, which in turn, are a division and a continuation-inpart, respectively, of copending application Ser. No. 653,808, filed Sept. 24, 1984, which, in turn, is a continuation-in-part of application Ser. No. 547,892, filed 15 Nov. 2, 1983, (which issued as U.S. Pat. No. 4,618,348 on Oct. 21, 1986) all of which are incorporated herein by reference.
Hill, Inc., New York (1981)]. The total estimated figure for oil in place is 6200 XlO9 barrels. Venezuela heads the list with roughly half of this total, 3000 X109 barrels. Canada follows closely with 2950XlO9 barrels (this total includes hydrocarbon in bitumen), while the United States has an estimated 77 X 109 barrels. To put these figures in perspective, the total world reserves of oil lighter than 20° API is estimated to be about 660XlO9 barrels. Yet undiscovered reserves are estimated at 900XlO9 barrels. Thus, heavy crude is more plentiful than conventional oil by about a factor of four.
WORLD HEAVY OIL DEPOSITS (Billions of Barrels)
This invention relates to methods for burning high sulfur (S) content combustible compositions, wherein low, environmentally-acceptable, oxidized sulfur compound (SOX) emissions are realized. More particularly, this invention relates to the mixing of high sulfur con- 25 tent compounds with admixtures of soluble and insoluble sulfur sorbents. Use of such admixtures, it has been found, results in a far greater reduction on SOX emissions, than would be expected from the activity of each sorbent used alone, while exhibiting no deleterious ef- 30 fects on the combustion efficiency.
These admixtures can be used to control the SOX emissions from all high S content combustible materials including hydrocarbon oils and coal/water slurries. Extremely viscous hydrocarbons can be burned as 35 preatomized fuels, i.e., oil-in-water emulsions, the viscosity of which is greatly reduced in comparison with that of the starting hydrocarbon. Thus, a wide array of hydrocarbons previously unsuitable for use due to air pollution constraints can be burned. 40
2. BACKGROUND OF INVENTION
2.1. Viscous Hydrocarbons
While large quantities of high-quality, relatively inexpensive, light crude oils presently are recoverable from 45 world-wide geographical locations, ever-increasing consumption of petroleum fuels and other petroleum products and the energy crisis precipitated by such high demands have brought interest to bear on the enormous reserves of low-gravity, viscous hydrocarbons which 50 also exist throughout the world. Viscous hydrocarbons present in natural deposits have been generlly classified as viscous crude oils, bitumen or tar and have been variously called heavy crudes, native bitumen, natural bitumen, oil sands, tar sands, bituminous sands or depos- 55 its and natural asphalts, all of which materials are chemically gradational and nearly indistinguishable without standardized analyses. [For a discussion of the general characteristics of viscous hydrocarbons and the problem of precisely defining or classifying them, see Meyer, 60 "Introduction" in: The Future of Heavy Crude and Tar Sands, p. 1, Mining Informational Services, McGraw Hill, Inc., New York (1981). See also Section 6.2 infra.]
The geographical distribution of heavy crude reserves is given in Table I [abstracted from Meyer and 65 Dietzman (1981), "World Geography of Heavy Crude Oils," in: The Future of Heavy Crude and Tar Sands, pp. 16-28, Mining Informational Services, McGraw
It is clear that reserves of conventional light crudes are being depleted much faster than heavy crudes and that development of world reserves of viscous hydrocarbons will eventually become necessary to support world petroleum demands. Significant production of heavy crudes has begun, primarily by steam-assisted enhanced recovery methods. For example, recent estimates place production of heavy crude oil in California at 250,000 barrels per day. Future estimates [Barnea, "The Future of Heavy Crude and Tar Sands," in: The Future of Heavy Crude and Tar Sands, pp. 13-15, Mining Informational Services, McGraw Hill, Inc., New York (1981)] project that by the year 2000, production of heavy oil plus the bitumen from tar sands will increase to one-third of the world's total oil production. Such rapid development of heavy oil resources will extend the petroleum era and should: (1) allow products from heavy crudes to benefit from the existing energy infrastructure; (2) assure fuel supplies to the transportation sector and feed-stock to petrochemical plants; (3) be a stabilizing factor for world petroleum prices, increasing the number of oil producing countries; (4) reduce the strategic and political aspects of oil production; and (5) postpone the need for massive investments in coal conversion and other facilities for synthetic oil production.
2.2. Combustion of Oil-in-Water Emulsions
The vast majority of combustible emulsions known in the art are water-in-oil emulsions, primarily consisting of relatively small amounts of water (1-10% by volume) in oil to enhance combustion. Some combustible oil-in-water emulsions have been described [see e.g., U.S. Pat. Nos. 3,958,915; 4,273,611 and 4,382,802]. Notably, however, the oil phases used have been light, low viscosity fuels and other low viscosity oils, e.g., kerosene, gasoline, gas oil, fuel oils and other oils which are liquid at room temperature. Combustible thixotropic jet fuels and other safety fuels have been described in U.S. Pat. Nos. 3,352,109; 3,490,237 and 4,084,940. Under resting (stationary) conditions, these oil-in-water emul10
sions are in the form of gels with apparent rest viscosities of 1000 cps and preferably 50,000-100,000 cps. These thixotropic oil-in-water emulsions exhibit low viscosities under high pumping (high shear) rates.
2.3. Microbial Surface-Active Compounds
Many microbes can utilize hydrocarbon as their sole source or carbon for growth and energy production. The hydrocarbon substrates may be linear, branched, cyclic or aromatic. In order to rapidly assimilate such water-insoluble substrates, the microbes require a large contact area between themselves and the oil. This is achieved by emulsifying the oil in the surrounding aqueous medium. Hydrocarbon degrading microbes frequently synthesize and excrete surface active agents which promote such emulsification.
For example, the growth of Mycobacterium rhodochrous NCIB 9905 on n-decane yields a surface active agent which was reported by R. S. Holdom et al. [J. Appl. Bacterid. 32, 448 (1969)] to be a nonionic detergent. J. Iguichi et al. [Agric. Biol. Chem., 33 1657 (1969)] found that Candida petrophilium produced a surface active agent composed of peptides and fatty acid moieties, while T. Suzuki et al. [Agric. Biol. Chem., 33, 1919 (1969)] found trehalose lipid in the oil phase of culture broths of various strains of Arthrobacter, Brevibacterium, Corynebacterium and Nocardia. Wagner has reported the production of trehalose lipids by Nocardia rhodochrous and Mycobacterium phlei and their use in oil recovery [U.S. Pat. Nos. 4,392,892 and 4,286,660].
Torulopsis gropengiesseri was found to produce a sophorose lipid, while rhamnolipids are reported by K. Hisatsuka et al. [Agric. Biol. Chem., 35, 686 (1971)] to 35 have been produced by Pseudomonas aeruginosa strain S7B1 and by S. Itoh et al. [Agric. Biol. Chem., 36, 2233
(1971) ] to have been produced by another P. aeruginosa strain, KY4025. The growth of Corynebacterium hydrocarboclastus on kerosene was reported by J. E. Zajic 4^ and his associates [Dev. Ind. Microbiol., 12, 87 (1971); Biotechnol. Bioeng., 14, 331 (1972); Chemosphere 1, 51
(1972); Crit. Rev. Microbiol., 5, 39; U.S. Pat. No. 3,997,398] to produce an extracellular heteropolysaccharide which, among other properties, emulsified kero- 45 sene, Bunker C fuel oil and other fuel oils.
Gutnick et al. discovered that Acinetobacter calcoaceticus ATCC 31012 (previously designated Acinetobacter sp. ATCC 31012 and also called RAG-1) produces interfacially active extracellular proteinassociated lipopolysaccharide biopolymers called emulsans. These biopolymers are produced and build up as a capsule or outer layer around the bacterial cell during growth and are eventually released or sloughed off into the medium, from which they can be harvested as extracellular products. Acinetobacter calcoaceticus ATCC 31012 produces a-emulsans when grown on ethanol or fatty acid salts [U.S. Pat. Nos. 4,230,801; 4,234,689 and 4,395,354] and /J-emulsans when grown on crude oil or hexadecane [U.S. Pat. No. 3,941,692]. The a-emulsans and /3-emulsans can be derivatized to an O-deacylated form called psi-emulsans [U.S. Pat. No. 4,380,504]. The a-emulsans, /3-emulsans and psi-emulsans can be deproteinized to yield apo-a-emulsans, apo-/3-emulsans and apo-psi-emulsans, respectively [U.S. Pat. Nos. 4,311,830; 4,311,829 and 4,311,831, respectively].
Cooper and Zajic [Adv. Appl. Microbiol. 26:229-253 (1980)] have reviewed the production of surface active
2.4. Reduction of SOX in Combustion Gases
Within the past few years there has been an increasing concern with the immediate and long-term effects of atmospheric pollution produced during the burning of hydrocarbon fuels. During this time, substantial amounts of money and effort have been spent to combat this problem. Additionally, the governmental agencies, on the federal, state, and local levels have issued environmental regulations which severely limit the amount of pollutants which can be released into the atmosphere, consequently forcing users of these fuels to make the choice of burning the more expensive, "clean-burning", fuels or, as the supply of such fuels is shrinking, to seek methods to reduce the emissions released by the combustion of the higher-polluting fuels.
A class of pollutants that has, recently, become a major concern is that of gaseous sulfur compounds such as H2S, COS, SO2, SO3 and the like. When released into the atmosphere, these compounds, it has been postulated, can react with atmospheric moisture and oxygen to form sulfuric acid, which results in "acid rain", severely corrosive precipitation that is detrimental to plant and animal life. For this reason, particularly stringent restrictions have been placed upon the amount of gaseous sulfur compounds, notably the oxidized forms of sulfur produced during sulfur burning, SOX, which can be released into the atmosphere during combustion of fuels. Such restrictions have made it nearly impossible to utilize high sulfur content fuels in standard applications. Since many of the viscous hydrocarbon fuels discussed supra, and much of the world's coal reserves, have high sulfur content, use of a significant portion of the world's petroleum and coal reserves presents difficult environmental and economic problems. As the world's hydrocarbon reserves are shrinking, the use of these other fuels becomes necessary.
For this reason, scientists have attempted to lower the gaseous sulfur emissions of high sulfur content fuels. Three main approaches have been used. In the first, the combustion gases are channelled through an SOX absorbent prior to release into the atmosphere, resulting in reduced SOX levels in the effluent gas. This method, also known as "scrubbing" is the most common method in use today; however, it suffers from the major draw20
back of requiring significant capital outlay for the design and construction of the system. Nonetheless, this is the principal SOX control method in use today.
An alternative approach involves the removal of the sulfur from the fuel prior to the combustion. This may 5 be accomplished by extracting the sulfur components into solvents having a stronger affinity for the sulfur compounds than the fuel. Such solvents are, however, expensive and often will extract significant amounts of combustible fuel components along with the sulfur. For 10 these reasons, this method has proven to be impractical.
More useful, in the case of petroleum hydrocarbons, is hydrogen addition to convert the sulfur in the sulfur compounds to hydrogen sulfide (H2S), which can be separated from the petroleum fraction. However, this 15 process also requires significant capital outlay.
In the third approach, the fuel is mixed with sulfur sorbents which act to remove the sulfur and the oxidized sulfur compounds during the combustion process. A particular advantage of this approach is that solid compounds can be utilized as sorbents. Such compounds will remain in the solid phase during combustion, thus facilitating the ultimate collection of the sulfur-sulfur sorbent conjugates. Also, because the reac- ^ tion occurs in the combustion zone, the temperatures are quite high rendering the sorbent species quite reactive; thus, the kinetics of the absorption are directed in favor of the SOX binding.
A major drawback of this method, however, is the 3Q lack of adequate sulfur sorbents, thus making efficient sulfur removal difficult. For example, Cottell (U.S. Pat. No. 3,941,552) found in experiments using coal/water slurries that when lime (CaO) is present in a 50% excess of the stoichiometric requirement (to achieve 100% S 35 removal), a 50% reduction in SOX levels is observed; this increases to 80% when twice the stoichiometric requirement of lime is used. Dooher et al. (Fuel, 59, Dec, 1980, pp. 883-891) conducted burn experiments on water-in-oil emulsions of high sulfur oil utilizing 40 soda ash ... as a sorbent and claimed to have found somewhat better results (50% of the stoichiometric requirement of ... achieved a 45% SO2 removal). However, in a commercial boiler, the use of high concentrations of sodium salts is undesirable due to 45 the well-known side effect of fouling, which necessitates frequent cleaning of the boiler.
There exists, therefore, a real need for efficient sulfur sorbent agents which can effectively limit SOX emissions, yet which will not exhibit deleterious effects such 50 as fouling.
3. SUMMARY OF INVENTION
It is an objective of this invention to provide a method whereby a reduction in the oxidized sulfur 55 (SOX) emissions during the burning of high sulfur content hydrocarbons and coals can be achieved. More particularly, it is an objective of this invention to provide a method whereby sulfur-containing materials, including hydrocarbons, coals, coal/water slurries and 60 hydrocarbon-in-water emulsions, can be burned safely and efficiently, in an environmentally-acceptable manner wherein the SOX emissions are reduced to a value below the permissible local regulatory standard.
It is also an objective of this invention to provide 65 clean burning combustible compositions which, during combustion, will produce lower sulfur emissions than the neat hydrocarbons or coals.
This invention provides a method for decreasing SOX emissions during combustion of high sulfur content hydrocarbons and coals by adding to such materials an admixture of insoluble and soluble sulfur sorbents prior to the burning. It has been found that, remarkably, this admixture of sulfur sorbents provides a higher degree of SOX emission reduction than would be predicted on the basis of the reduction efficiency of each sorbent individually, i.e., the admixture components exhibit a catalytic effect on the SOX removal efficiency of each other. By use of these sorbents, the SOX emissions during combustion of high sulfur content hydrocarbons (including coals) can be brought within environmentally acceptable levels, making such materials commercially useful.
This invention also provides methods for reducing the SOX emissions during the combustion of viscous, high sulfur content hydrocarbons by forming preatomized fuels (hydrocarbon-in-water emulsions) and adding the insoluble/soluble sorbent admixture to the preatomized fuels. As with the unemulsified fuel compositions described above, the admixture achieves a remarkable reduction in SOX emissions when the preatomized fuel is burned. Similar reductions can be seen using coal/water slurries treated with the sorbents as fuels.
This invention also provides fuel compositions comprised of sulfur-containing combustible compounds, including preatomized fuels and coal slurries, and admixtures of soluble/insoluble sulfur sorbents, which exhibit reduced SOX emissions when burned.
The term "hydrocarbosol" is defined as any bioemulsifier-stabilized hydrocarbon-in-water emulsion wherein the individual hydrocarbon droplets are essentially surrounded or covered by water-soluble bioemulsifier molecules predominantly residing at the hydrocarbon/water interface, which bioemulsifier molecules form an effective barrier against droplet coalescence and hence promote the maintenance of discrete hydrocarbon droplets suspended or dispersed in the continuous, low-viscosity aqueous phase.
The term "water-soluble" is defined to include waterdispersible substances.
The term "viscous hydrocarbon" is defined as any naturally occurring crude oil or any residual oil remaining after refining operations which is generally characterized by a viscosity of about 102-106 centipoise or greater and otherwise generally, but not necessarily, characterized by an API gravity of about 20° API or less, high metal content, high sulfur content, high asphaltene content and/or high pour point. The term "viscous hydrocarbon," it is to be understood, also encompasses the following nomenclature: vacuum residuals, vis-breaker residuals, catalytic-cracker residuals, catalytic hydrogenated residuals, coker residuals, ROSE (residual oil supercritical extraction) residuals, tars and cut-back tars, bitumen, pitch and any other terms describing residuals of hydrocarbon processing.
The term "pre-atomized fuel" is defined as any hydrocarbosol and any viscous hydrocarbon-in-water emulsion formed by methods described herein for use as a combustible fuel.
The term "bioemulsifier" is defined as any biologically derived substance which, by virtue of any combination of characteristics including, but not limited to, high molecular weight, polymeric nature, highly spe7
cific three-dimensional structure, hydrophobic and hydrophilic moieties and sparing solubility in hydrocarbons, binds tightly to the hydrocarbon/water interface and essentially covers the surface of individual hydrocarbon droplets in hydrocarbon-in-water emulsions, 5 effectively maintaining discrete droplets and preventing coalescence, and thereby imparting substantial stability to hydrocarbon-in-water emulsions. An example of a bioemulsifier is a-emulsan.
The term "biosurfactant" is defined as any biologi- 10 cally derived substance which reduces the interfacial tension between water and a hydrocarbon and, as a result, reduces the energy requirement (mixing energy) for creation of additional interfacial area. An example of a biosurfactant is a glycolipid. 15
The term "surfactant package" is defined as any composition useful for forming hydrocarbon-in-water emulsions of viscous hydrocarbons generally characterized by a paraffin content of about 50% by weight or less and an aromatic content of about 15% by weight or 20 greater with viscosities of about 100 centipoise or greater at 150° F., which composition may comprise a chemical surfactant or a combination of chemical cosurfactants or a combination of co-surfactant(s) and biosurfactant(s) or a combination of chemical surfac- 25 tant(s) and bioemulsifier(s) or a combination of chemical surfactant(s), biosurfactant(s) and bioemulsifier(s), and which may also include chemical emulsion stabilizers, and which may be in aqueous form.
The term "emulsans," which reflects the polysaccha- 30 ride structure of these compounds and the exceptional bioemulsifier activity of these materials, generically identifies those capsular/extracellular microbial protein-associated lipoheteropolysaccharides produced by Acinetobacter calcoaceticus ATCC 31012 and its deriva- 35 tives or mutants, which may be subdivided into the a-emulsans and the /J-emulsans. The name "apoemulsan" generically identifies those deproteinized lipopolysaccharides obtained from the emulsans.
The term "a-emulsans" defines those extracellular 40 microbial protein-associated lipopolysaccharides produced by Acinetobacter calcoaceticus ATCC 31012 and its derivatives or mutants in which the lipopolysaccharide components (i.e., without the associated protein) are completely N-acylated and partially O-acylated 45 heteropolysaccharides made up of major amounts of D-galactosamine and an aminouronic acid, the lipopolysaccharide components containing at least 5 percent by weight of fatty acid esters in which (1) the fatty acids contain from about 10 to about 18 carbon atoms; and (2) 50 about 50 percent by weight or more of such fatty acids are composed of 2-hydroxydodecanoic acid and 3hydroxydodecanoic acid. It follows, therefore, that the deproteinized a-emulsan are called "apo-a-emulsans."
The term "/3-emulsans" defines those extracellular 55 microbial protein-associated lipopolysaccharides produced by Acinetobacter calcoaceticus ATCC 31012 and its mutants in which the lipopolysaccharide components (i.e., without the associated protein) are completely N-acylated and partially O-acylated heteropoly- 60 saccharides made up of major amounts of D-galactosamine and an aminouronic acid, the lipopolysaccharide components containing less than 5 percent by weight of fatty acid esters in which (1) the fatty acids contain from about 10 to about 18 carbon atoms; and (2) less than 50 65 percent by weight of such fatty acids are composed of 2-hydroxydodecanoic acid. The deproteinized /3-emulsans are called "apo-/3-emulsans."
The term "psi-emulsans" defines the O-deacylated extracellular protein-associated microbial polysaccharides obtained from the emulsans, the protein-free components of such psi-emulsans being completely Nacylated heteropolysaccharides made up of major amounts of D-galactosamine and an aminouronic acid and containing from 0 to 1 percent of fatty acid esters in which, when present, the fatty acids contain from about 10 to about 18 carbon atoms. These protein-free components are called "apo-psi-emulsans," regardless of how they are prepared.
The term "polyanionic heteropolysaccharide biopolymers" defines those biopolymers in which (a) substantially all of the sugar moieties are N-acylated aminosugars, a portion of which is N-acylated-D-galactosamine and another portion of which is N-acylated aminouronic acid, a part of the N-acyl groups of such heteropolysacchardide being N-3-hydroxydodecanoyl groups; and (b) at least 0.2 micromoles per milligram of such heteropolysaccharide consist of fatty acid esters in which (1) the fatty acids contain about 10 to about 18 carbon atoms and (2) about 50 percent by weight or higher of such fatty acids are composed of 2-hydroxydodecanoic acid and 3-hydroxydodecanoic acid.
The term "SOX" defines all oxidized sulfur compounds produced during sulfur combustion without reference to the degree of oxidation.
The term "hydrocarbon" is defined as any naturally occurring petroleum crude oil, residue, or distillate, including coals.
The term "sulfur containing combustible compound" refers to all combustible compounds which contain measurable quantities of sulfur compounds and which, when burned, produce measurable amounts of SOX.
The term "high sulfur content" includes all compounds which, when burned, have a SOX emission level which exceeds the standard set by the local regulatory authority.
The term "slurry" includes all dispersoids wherein a ground or pulverized solid phase is dispersed in a continuous liquid phase.
5. BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a graphical representation of the Removal Efficiency as a function of % excess oxygen with the addition of 1% and 2% CaC03 as a S sorbent, at 30 and 50% furnace loads.
FIG. 2 is a graphical representation of the Removal Efficiency as a function of the % excess oxygen for three ... S sorbent systems at 30 and 50% furnace loads.
FIG. 3 is a graphical representation of the Removal Efficiency as a CaCO3/10% calcium acetate sorbent system at a 30 and 50% furnace load.
6. DETAILED DESCRIPTION OF THE
6.1. Surfactant Packages
The surfactant packages suitable for forming preatomized fuels can be formulated with a wide variety of chemical and microbial surface active agents and are preferably formulated with water-soluble surface active agents to provide for the formation of oil-in-water, as opposed to water-in-oil, emulsions. The surfactant packages can be formulated with numerous chemical surfactants, used alone or in conjunction with chemical co-surfactants of the same type (e.g., a combination of