US2968148A - Vanadium-containing residual fuels modified with zinc and alkali metal compounds - Google Patents

Description

leum fuels. clermg non-corrosive those residual fuels which contain VANADIUM-CONTAINING RESIDUAL FUELS MODIFIED WITH ZINC AND ALKALI METAL COMPOUNDS Albert G. Rocchini, Oakmont, and Charles E. Trautman,

'Cheswick, Pa., assignors to Gulf Research & Developmeut Company, Pittsburgh, Pa., a corporation of Delaware Filed Apr. 16,1958, Ser. No. 728,904

6 Claims. (Cl. 60-35.6)

This invention relates to vanadium-containing petro- More particularly, it is concerned with renfurnaces, boilers and gas turbines the ash resulting from combustion of the fuel oil is highly corrosive to materials of construction at elevated temperatures and attacks such parts as boiler tubes, hangers, turbine blades and the like. These effects are particularly noticeable in gas turbines. Large gas turbines show promise of becoming an important type of industrial prime mover. However, economic considerations based on the efliciency of the gas turbine dictate the use of a fuel for this purpose which is cheaper than a distillate diesel fuel; otherwise, other forms of power such as diesel engines become competitive with gas turbines.

One of the main problems arising in the use of residual fuel oils in gas turbines is the corrosiveness induced by those residual fuels containing sutficient amounts of vanadium to cause corrosion. Where no vanadium is present or the amount of vanadium is small, no appreciable corrosion is encountered. While many residual fuel oils as normally obtained in the refinery contain so little vanadium, or none, as to present no'corrosion problems, such non-corrosive fuel oils arenot always available at the point where the oil is to be used. In such instance, the cost of transportation of the non-corrosive oil to the point of use is often prohibitive, and the residual oil loses its competitive advantage. These factors appear to militate against the extensive use of residual fuel oils for gas turbines. Aside from corrosion, the formation of deposits upon the burning of a residual fuel in a gas turbine may result in unbalance of the turbine blades, clogging of openings and reduced thermal efiiciency of the turbine.

Substantially identical problems are encountered when using a solid residual petroleum fuel containing substantial amounts of vanadium. These fuels are petroleum residues obtained by known methods of petroleum refining such as deep vacuum reduction of asphaltic crudes to obtain solid residues, visbreaking of liquid distillation bottoms followed by distillation to obtain solid residues, coking of liquid distillation bottoms and the like. The solid residues thus obtained are known variously as petroleum pitches or cokes and find use as fuels. Since the vanadium content of the original crude oil tends to concentrate in the residual fractions, and since the processing of the residual fractions to solid residues results in further concentration of the vanadium in the solid residues, the vanadium corrosion problem tends to be intensified in using the solid residues as fuel.

The vanadium-containing ash present in the hot flue gas obtained from the burningof a-residual fuel containing substantial amounts of vanadium compounds causes catastrophic corrosion of theturbine blades and other metal parts in a gas turbine. The corrosive nature of United States Patent; 0 "ice meme, ,jifififi the ash appears to be due to its vanadium oxide content. Certain inorganic compounds of vanadium, such as vanadium oxide (V 0 which are formed on combustion of a residual fuel oil containing vanadium compounds, vigorously attack various metals, their alloys, and other materials at the elevated temperatures encountered in the combustion gases, the rate of attack becoming progressively more severe as the temperature is increased. The vanadium-containing ash forms deposits on the parts affected and corrosively reacts with them. It is a hard, adherent material when cooled to ordinary temperatures.

It has already been proposed to employ in corrosive residual fuels small amounts of certain metal compounds to mitigate the vanadium corrosion. Such compounds are of varying effectiveness and it has not always been possible to reduce vanadium induced corrosion to a minimum amount.

.It has now been discovered that residual petroleum fuels containing vanadium in an amount sufiicient to yield a corrosive vanadium-containing ash upon combustion can be rendered substantially non-corrosive by incorporating therein to form a uniform blend (1) a small amount of a vanadium-free zinc compound sutficient to reduce the corrosiveness of the ash but not in excess of that amount which will yield about 4 atom weights of zinc ,per atom weight of vanadium in said fuel, and (2) .asmall amount of a vanadium-free alkali metal compound su'fiicient to further reduce the corrosiveness of said ash to a minimum. In the fuel compositions of the invention the coaction of the two additive compounds is such that the corrosion is reduced to negligible amounts.

In the accompanying drawing the single figure shows an apparatus for testing the corrosivity of residual fuel oil compositions.

The type of residual fuel oils to which the invention is directed is exemplified by No. S, No. 6 and Bunker C fuel oils which contain a suffici'ent amount of vanadium to form a corrosive ash upon combustion. These are residual type fuel oils obtained from petroleum by methods known to the art. For example, residual fuel oils are obtained as liquid residua by the conventional distillation of total crudes, by atmospheric and vacuum reduction of total crudes, by the thermal cracking of topped crudes, by visbreaking -heavy petroleum residua, and other conventional treatments of heavy petroleum -oils. *Res'idua thus obtained are sometimes diluted with distillate fuel oil stocks, known as cutter stocks, and the invention also includes residual fuel oils so obtained, provided that such oils contain sufiicient vanadium normally to exhibit the corrosion characteristics described 1 by weight for some of the high vanadium stocks, ex-' hibiting severe corrosion.

The type of vanadium-containing solid residual fuels to which the invention is directed is exemplified by the coke obtained in known manner by :the delayed thermal coking or flui'clized cokingof topped or reduced crude oils and by the pitches obtained in known manner by the deep vacuum reduction of asphaltic-crudes to obtain solid residues.

These "materials have ash contents -of the :order of 0.18.

percent by weight, more or less, and :contain corrosive amounts of vanadium when :prepared from stocks containingsubstantialamountsofvanadium. Atypical pitch exhibiting corrosive characteristics upon combustion had a softening point of 347 F. and a vanadium content, as vanadium, of 578 parts per million.

Any zinc compound, organic or inorganic, which is free from vanadium is used as the zinc additive of the invention. Similarly, any organic or inorganic vanadium-free alkali metal compound is employed. The alkali metals include sodium, potassium, lithium, cesium and rubidium; sodium and potassium compounds are preferred. Such inorganic alkali metal and zinc compounds as the oxides, hydroxides, acetates, carbonates, silicates, oxalates, sulfates, nitrates, halides and the like are successfully employed. In this connection, the mixture of salts present in sea water, as disclosed in our copending application Serial No. 654,812, filed April 24, 1957, comprises a suitable alkali metal compound. Zinc oxide is a preferred inorganic zinc compound. The organic compounds of zinc and the alkali metals include the oil-soluble and oildispersible salts of acidic organic compounds such as: (1) the fatty acids, e.g., valeric, caproic, Z-ethylhexanoic, oleic, palrnitic, stearic, linoleic, tall oil, and the like; (2) alkylaryl sulfonic acids, e.g., oil-soluble petroleum sulfonic acids and dodecylbenzene sulfonic acid; (3) long chain alkyl sulfuric acids, e.g., lauryl sulfuric acid; (4) petroleum naphthenic acids; (5) rosin and hydrogenated rosin; (6) alkyl phenols, e.g., iso-octyl phenol, t-butylphenol and the like; (7) alkyl phenol sulfides, e.g., bis(isooctyl phenol)monosulfide, bis(t-butylphenol)disulfide, and the like; (8) the acids obtained by the oxidation of petroleum waxes and other petroleum fractions; and (9) oil-soluble phenol-formaldehyde resins, e.g., the Amberols, such as t-butylphenol-formaldehyde resin, and the like. Since the salts or soaps of such acidic organic compounds as the fatty acids, naphthenic acids and rosins are relatively inexpensive and are easily prepared, these are preferred materials for the organic additives.

When employing in residual fuels the inorganic additives of the invention, it is desirable to use finely-divided materials. However, the degree of subdivision is not critical. One requirement for using a finely-divided material is based upon the desirability of forming a fairly stable dispersion or suspension of the additives when blended with a residual fuel oil. Furthermore, the more finelydivided materials are more efiicient in forming uniform blends and rendering non-corrosive the relatively small amounts of vanadium in a residual fuel, whether the fuel be solid or liquid. The inorganic additives are therefore employed in a particle size range of less than 250 microns, preferably less than 50 microns. However, where the inorganic additives are water-soluble, for example, in the case of zinc sulfate, sodium carbonate, and the like, it is not necessary to employ finely-divided materials since, if desired, the additives can be dissolved in water to form a more or less concentrated solution and the water solution emulsified in the fuel.

The organic additives of the invention are oil-soluble or oil-dispersible and are therefore readily blended with residual fuels to form uniform blends. Since on a weight basis in relation to the fuel, the amounts of the additives are small, it is desirable to prepare concentrated solutions or dispersions of the organic additives in a naphtha, kerosene or gas oil for convenience in compounding.

In the practice of the invention with vanadium-containing residual fuel oils, the mixture of additives is uniformly blended with the oil in the disclosed proportions. This is accomplished by suspending the finely-divided dry additives in the oil, emulsifying or dispersing a concentrated water solution of the water-soluble inorganic additives in the oil, or dissolving or dispersing the organic additives in the oil. If desired, suitable surface active agents, such as sorbitan monooleate and monolaurate and the ethylene oxide condensation products thereof, glycerol monooleate, and the like, which promote the stability of the suspensions or emulsions can be employed.

In the practice of the invention with the solid residual fuels, incorporation of the additives of the invention is accomplished in several ways. The additives can be suspended, emulsified or dissolved in the liquid vanadiumcontaining residual stocks or crude oil stocks from which the solid residual fuels of the invention are derived, and the mixture can then be subjected to the refining process which will produce the solid fuel. For example, in the production of a pitch by the deep vacuum reduction of an asphaltic crude oil, the additives or a concentrate thereof are slurried with the oil in proportion to the vanadium content thereof, and the whole subjected to deep vacuum reduction to obtain a pitch containing the additives uniformly dispersed therein. As still another alternative, particularly with a pitch which is withdrawn in molten form from the processing vessel, the additives can be mixed with the molten pitch and the mixture allowed to solidify after which it is ground to the desired size.

In the case of either liquid or solid residual fuels, the additives can be separately fed into the burner as concentrated solutions or dispersions. In such a case, it is preferred to meter the additives into the fuel line just prior to the combustion zone. In a gas turbine plant where the heat resisting metallic parts are exposed to hot combustion gases at temperatures of the order of 1200 F. and above, the additives can be added separately from the fuel either prior to or during combustion itself, or even subsequent to combustion. However they may specifically be added, whether in admixture with or separately from the fuel, the additives are introduced into said plant upstream of the heat resisting metal parts to be protected from corrosion.

The zinc compounds and the alkali metal compounds are both employed in small, corrosion retarding amounts with respect to the fuel, and in such amounts with respect to each other as to minimize the corrosiveness of the ash. In order to obtain the desired coaction with the alkali metal compound, the zinc compound is employed in a small amount sufiicient to retard the corrosiveness of the ash but not in excess of an amount which yields about 4 atom weights of zinc per atom weight of vanadium in the fuel. In larger amounts than about 4 atom weights of zinc per atom weight of vanadium, the coaction with the alkali metal compound is not obtained, the zinc compound appearing to act independently. With the amounts of zinc compound stated, the alkali metal compound is employed in a small amount sutficient to minimize the corrosiveness of the ash. For example, when the zinc compound is employed in the amount of 4 atom weights of zinc per atom weight of vanadium, ordinarily an amount of alkali metal compound yielding about 1 atom weight of alkali metal per atom weight of vanadium is sufiicient to reduce the corrosion to negligible amounts. In the compositions of the invention, an atom weight ratio of zinc to vanadium of 4:1 and an atom weight ratio of alkali metal to vanadium of 1:1 are preferred.

The following examples are further illustrative of the invention.

EXAMPLE I With a residual fuel oil uniformly blend 0.12 percent by Weight of zinc oxide and 0.02 percent by weight of sodium carbonate. The residual fuel oil employed has the following inspection:

The .resulting composition has an atom weight ratio of zinc to vanadium of 4:1 and an atom weight ratio of sodium to vanadium of 1:1. The additives are stably dispersed in the fuel oil.

EXAMPLE II To a residual fuel oil, add and uniformly blend 0.63 percent by weight of a solution in naphtha of zinc salt of petroleum naphthenic acids containing '8 percent by weight of zinc and 0.6 percent by weight of sea water made up in accordance with the composition and preparation for synthetic sea water shown in ASTM Test D665-54 published in ASTM Standards on Petroleum Products and Lubricants, November 1954, by The American Society for Testing Materials, Philadelphia, Pennsylvania. The resulting'fuel oil composition has an atom Weight ratio of zinc to vanadium of 4:1 and an atom weight ratio of sodium to vanadium of 0.8:1. The residual fuel oil employed in this example has the following inspection:

Melt a solid petroleum pitch obtained from the deep vacuum reduction of an asphaltic crude. This pitch has a softeningpoint of 347 F. and a vanadium content of 578 parts per million. While the pitch is in molten form, add and uniformly blend therein 0.37 percent by weight of zinc oxide and 0.1 percent by weight of potassium sulfate. Upon cooling and solidification, grind the mixture to about 150 mesh. The resulting fuel has an atom weight ratio of zinc to vanadium of 4:1 and an atom weight ratio of sodium to vanadium of 1:1.

EXAMPLE IV To the same residual fuel oil of Example I, add and uniformly blend 0.12 percent by weight of zinc oxide and 0.11 percent by weight of a solution in naphtha of the sodium salt of petroleum naphthenic acids containing 7 percent 'by weight of sodium. The resulting fuel oil composition has an atom weight ratio of zinc to vanadium of 4:1 and an atom weight ratio of sodium to vanadium of 1:1.

Similar compositions are prepared employing the other zinc and alkali metal compounds disclosed.

In order to test the elfectiveness of the additives of this invention under conditions of burning residual fuels in a gas turbine, the apparatus shown in the drawing is employed. As shown therein, the residual oil under test is introduced through line 10 into a heating coil 11 disposed in a tank of water 12 maintained at such temperature that the incoming fuel is preheated to a temperature of approximately 212 F. From the heating coil 11 the preheated oil is passed into an atomizing head designated generally as 13. The preheated oil passes through a passageway 14 into a nozzle 15 which consists of a #26 hypodermic needle of approximately 0.008 inch ID. and 0.018 inch OD. The tip of the nozzle is ground square and allowed to project slightly through an orifice 16 of approximately 0.020 inch diameter. The orifice is supplied with 65 p.s.i.g. air for atomization of the fuel into the combustion chamber 21. The air is introduced through line 17, preheat coil 18 in tank 12, and air passageways 19 and 20 in the atomizing head 13. The combustion chamber 21 is made up of two concentric cylinders 22 and 23, respectively,

welded to two end plates 24 and 25.

Cylinder 22 has a'diameter of 2 inches and cylinder 23 has a diameter of 3 inches; the length of the cylinders between the end ;'plates is 8 /2 inc-hes. End plate 24 has a central opening 26 into which the atomizing head is inserted. End plate '25 has a one (1) inch opening 27 covered by a baffle plate 28 mounted in front of it to prevent direct blast of flame on the test specimen 29. Opening 27 in end plate 25 discharges into -a smaller cylinder 3-0 having a diameter of 1% inches and a length of 6 inches. The specimen 29 is mounted near the downstream end of the cylinder approximately 1% inches from the outlet thereof. Combustion air is introduced by means of air inlet 31 into the annulus between cylinders 22 and 23, thereby preheating the combustion air, and then through three pairs of inch tangential air inlets 32 in the inner cylinder 22. The first pair of air inlets is spaced A inch from end plate 24; the second pair inch from the first;and the third 3 inches from the second. The additional heating required to bring the combustion products to test temperature is supplied by an electric heating coil 33 surrounding the outer cylinder 23. The entire combustion assembly is surrounded by suitable insulation 34. The test specimen 29 is a metal disc one inch .in diameter by 0.125 inch thick, with a hole in the center by means of which the specimen is attached to a tube 35 containing thermocouples. The specimen and tube assembly are mounted on a suitable stand 36.

In conducting a test in the above-described apparatus, a weighed metal specimen is exposed to the combustion products of a residual fuel oil, the specimen being maintained at a selected test temperature of, for example, 1350", 1450 or 1550 F. by the heat of the combustion products. The test is usually run for a period of hours with the rate of fuel feed being /2 pound per hour and the rate of atomizing air feed being 2 pounds per hour. The combustion air entering through air inlet 31 is fed at 25 pounds per hour. At the end of the test run the specimen is reweighed to determine the weight of deposits and is then "descaled with a conventional alkaline descaling salt in molten condition at 475 C. After descaling, the specimen is dipped in 6 N hydrochloric acid containing a conventional pickling inhibitor, and is then Washed, dried and weighed. The loss in weight of the specimen after descaling is the corrosion loss.

Tests are conducted in the apparatus just described using a 25-20 stainless steel as the test specimen. The tests are run for 100 hours at a temperature of 1450 F. under the conditions described above. Tests are made With the fuel oil compositions of Examples I and IV,

with fuel oil composition similar to those of these examples but containing only one of the additives in varying proportions, and with the uncompounded residual fuel oils of Examples I and II. The following table shows the corrosion and deposits obtained.

It will be seen from the above table that the zinc additives and the alkali metal additives unexpectedly coact to minimize corrosion and deposits. This is surprising when it is considered that, although the individual additives tend to reduce corrosion and deposits, they still permit considerable corrosion unless used in relatively large amounts.

Thus the use of a sodium additive alone in amounts yielding as much as 6 atom weights of sodium per atom weight of vanadium still permits corrosion, and the zinc additive used alone requires about 6 atom weights of zinc per atom weight of vanadium before minimizing corrosion. With the combination of additives disclosed, considerably smaller amounts of each additive can be employed and corrosion and deposits are nonetheless minimized to negligible amounts. Furthermore, the deposits are of a non-adherent powdery texture. Similar results to those shown for the specific additives employed in the examples and in the above table are obtained when using the other zinc and alkali metal compounds disclosed.

A typical analysis of the 25-20 stainless steel employed in the testing described is shown in the following table in percent by weight:

Resort may be had to such modifications and variations as fall within the spirit of the invention and the scope of the appended claims.

We claim:

1. A fuel composition comprising a uniform blend of a major amount of a residual fuel yielding a corrosive vanadium-containing ash upon combustion, an amount of a vanadium-free zinc compound yielding about 4 atom weights of zinc per atom weight of vanadium in said fuel and an amount of a vanadium-free alkali metal compound yielding about 1 atom weight of alkali metal per atom weight of vanadium in said fuel.

2. The composition of claim 1, wherein the fuel is a solid residual petroleum fuel.

3. A fuel composition comprising a major amount of a residual fuel oil yielding a corrosive vanadium-containing ash upon combustion, an amount of a vanadium-free of a vanadium-free sodium compound yielding about 1 atom weight of sodium per atom weight of vanadium in said fuel oil.

4. A fuel composition comprising a major amount of a residual fuel oil yielding a corrosive vanadium-containing ash upon combustion, an amount of zinc oxide yielding about 4 atom weights of zinc per atom weight of vanadium in said fuel oil and an amount of sodium naphthenate yielding about 1 atom weight of sodium per atom weight of vanadium in said fuel oil.

5. A fuel composition comprising a major amount of a residual fuel oil yielding a corrosive vanadium-containing ash upon combustion, an amount of zinc oxide yielding about 4 atom weights of zinc per atom weight of vanadium in said fuel oil and an amount of sodium carbonate yielding about 1 atom weight of sodium per atom weight of vanadium in said fuel oil.

6. In a gas turbine plant in which a fuel oil containing vanadium is burned and which includes heat resisting metallic parts exposed to hot combustion gases and liable to be corroded by the corrosive vanadium-containing ash resulting from combustion of said oil, the method of reducing said corrosion which comprises introducing in said plant upstream of said parts a small amount of a vanadium-free mixture of a zinc compound and an alkali metal compound, the amount of said zinc compound being sufiicient to yield about 4 atom weights of zinc per atom weight of vanadium in said fuel, and the amount of said alkali metal compound being sufficient to yield about 1 atom weight of alkali metal per atom weight of vanadium in said fuel.

References Cited in the file of this patent UNITED STATES PATENTS 2,706,149 Brenneman Apr. 12, 1955 2,781,005 Taylor et al Feb. 12, 1957 FOREIGN PATENTS 689,579 Great Britain Apr. 1, 1953 711,895 Great Britain July 14, 1954 744,141 Great Britain Feb. 1, 1956 745,621 Great Britain Feb. 29, 1956 759,826 Great Britain Oct. 24, 1956 761,378 Great Britain Nov. 14, 1956 781,581 Great Britain Aug. 21, 1957

Claims (1)

1. 6. IN A GAS TURBINE PLANT IN WHICH A FUEL OIL CONTAINING VANADIUM IS BURNED AND WHICH INCLUDES HEAT RESISTING METALLIC PARTS EXPOSED TO HOT COMBUSTION GASES AND LIABLE TO BE CORRODED BY THE CORROSIVE VANDIUM-CONTAINING ASH RESULTING FROM COMBUSTION OF SAID OIL, THE METHOD OF REDUCING SAID CORROSION WHICH COMPRISES INTRODUCING IN SAID PLANT UPSTREAM OF SAID PARTS A SMALL AMOUNT OF A VANADIUM-FREE MIXTURE OF A ZINC COMPOUND AND AN ALKALI METAL COMPOUND, THE AMOUNT OF SAID ZINC COMPOUND BEING SUFFICIENT TO YIELD ABOUT 4 ATOM WEIGHTS OF ZINC PER ATOM WEIGHT OF VANADIUM IN SAID FUEL, AND THE AMOUNG OF SAID ALKALI METAL COMPOUND BEING SUFFICIENT TO YIELD ABOUT 1 ATOM WEIGHT OF ALKALI METAL PER ATOM WEIGHT OF VANADIUM IN SAID FUEL.

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