US2857256A - Reducing corrosiveness of residual fuel oil ash - Google Patents

Description

United States Patent-O REDUCING CORROSIVENESS F RESIDUAL FUEL OIL ASH Raymond W. Walker, Union, and George S. Tobias,

Watchung, N. J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Application July 9, 1956 Serial No. 596,385

3 Claims. (Cl. 44--68) This invention pertains to a method for reducing the corrosiveness of the ash thatresults from the combustion of residual type hydrocarbon fuels. It further concerns improved residual fuel compositions which form substantially non-corrosive ash when they are burned. It especially relates to the treatment of residual petroleum fuels containing vanadium whereby the ash derived from these fuels is substantially non-corrosive towards iron, steel, steel alloys, and other ferrous metals. This treatment involves the addition of arsensic-containing materials to such fuels.

The present application is a continuation-impart of copending application Serial No. 315,408, filed October 17, 1952, and now abandoned.

Residual fuels derived from petroleum find wide use in marine and stationary steam power plants where the high B. t. u. content and low cost of such fuels per gallon make them very attractive economically. These fuels may be the residual products or blends thereof, obtained from refiningoperations such as the distillation of crudes, the flashing or distillation of cracked products and redistilla tion operations. They may consist of either virgin or cracked hydrocarbons or both. Inasmuch as the viscosity of a residual fuel, is one of its more important properties, it is sometimes necessary, where a particular residuum is too viscous, to. dilute it with a low viscosity distillate fraction. It is apparent then that residual fuels may contain distillate fractions as well as residues but in general they consist primarily of residual material.

Residual fuel oils are also known in the trade as bunker fuel 'oils. They are characterized roughly as boiling above 400 F. The United-States Department of Commerce recognizes two grades of residual fuel, No. 5 and No. 6, in its classification system for petroleum fuels. The No. 5 grade is essentially adistillate fuel with small amounts of residual materials. It contains relatively little ash-forming material. The No. 6 fuel is usually a true residual fuel containing a substantial amount of ash, up to 0.10% by weight, or more. It is with this grade thatthe present invention is primarily concerned. The No. 6 or bunker fuel grade has a gravity range of about 9 to 15 A. P. I., a viscosity range ofabout 3 0 to 300 seconds (Saybolt Furol) at 122 F., and a minimum flash point of 150 F.

This invention is directed primarily toward modification of the ash present in residual or bunker fuel oils. The amount and type of ash formed by a residual fuel oil during combustionfwill vary according to the ash content and the origin of the crude oil from which the fuel was derived. Crude oils when burned may form up to about 1% by weight of ash and the ash-forming constituents are concentrated almost entirely in the residua byrefining operations performed on the crudes. Residual ice sten. Of primary interest here is ,the vanadium content,

which may be up to calculated as V 0 by weight of an ash. The vanadium content of ash derived from domestic crude oils will range in general from about 0 to 20%. Residual fuel oils obtained from Middle East crudes produce ash with vanadium contents of 14 to 45%, while in the case of South American crudes the value may be as high as 80%. (In all cases calculated as V50 At the present time it is not known exactly what chemical forms or compounds of vanadium actually exist in these oils. In some crude oils the vanadium has been found to exist in the form of metallo-organic porphyrins.

The amount of ash in a residual fuel oil, and, in particular, its vanadium content (generally expressed, conventionally in the results of chemical analysis, as vanadium pentoxide content) have recently become a matter of great importance. This is particularly true in the power generation field where the vanadium contained in the fuels employed has been found to cause extensive corrosion in power equipment that operates at high temperatures. Examples of such high temperature equipment include the gas turbine, the mercury boiler and extremely high temperature and pressure steam boilers. All of these installations havemetal parts which are exposed at temperatures above 1000 F. directly to the gases produced by the combustion of residual fuel. In the case of the boilers,- the metallic parts include such items as the boiler tubes andsuperheater tubes. y In the case of the gas turbine, the burner chamber, turbine nozzles, and blading are among the parts subjected to these conditions. In general, extensive corrosion of all of these parts has occurred, particularly when a residual fuel forming an ash of high vanadium content was employed.

In an effort to combat the corrosion described above, stainless steels and other heat resistant alloys have been used in the construction of the parts aifected, but little success has yet been achieved along these lines. With this in mind, efforts are now being directed toward improving the quality of the fuels. All of the studies made in this direction have shown conclusively that the corrosion is directly caused by vanadium compounds which form a component of the ash formed when the fuel is burned.

When a residual fuel containing vanadium compounds is burned, the vanadium apparently reacts with oxygen to form compounds'such as vanadium oxides (e. g. V 0 and vanadates. These materials are carried along .with the flue gas and are in contact with and partly deposit on the metal parts of the gas turbines and boilers described earlier. Inasmuch as vanadium pentoxide has a melting point of 1470 F., this material very often is present in its liquid form and has a substantial vapor pressure at the temperatures existing in gas turbine or boiler installations. Experimental work shows that vanadium pentoxide is extremely corrosive toward toward even the most corrosion-resistant alloy steels at temperatures of 1200 F. and up. It has further been shown that this chemical compound is most corrosive when it is present as a fluid. It appears that vanadium pentoxide or other vanadic acids not only destroy the oxidation-resistant surface layer 2,857,256 Patented Oct. 21, less which normally exists. on, alloy steels, but they also appear to act as catalysts for the oxidation of iron at temperatures above 1000 F. thereby markedly increasing the rate of corrosion once it has started.

Accordingly, an object of the present invention is to treat vanadium-containing residual fuel oil compositions so that the ash formed on burning will be substantially non-corrosive toward steel and steel alloys at tempera.- tures of '1000 F. and higher. It is 'a particular object toprovide vanadium-containing, residual fuel oil compositions which when burned in installations such as gas turb nes, and'the' furnaces of mercury boilers or highpressure steam boilers, etc. are virtually non-corrosive toward the ferruginous alloys used therein. It is a further objectof'the present invention to furnish a method of forming arsenic compounds directly within a vanadiumcontaining residual fuel oil or directly within a petroleum fraction which can subsequently be added to such a fuel. Broadly stated, the present invention comprises treatingvanadium-containing residual fractions with oxides of arsenic. It is desired that a vanadium-containing fuel be treated to an extent such that the ratio of the number of mols of arsenic, in the ash produced by burning the fuel, to the number of mols of vanadium calculated as vanadium pentoxide in the ash (e. g. mols As/Mols V be at least about 2:1 and preferably between 2:1

and :1; The invention is particularly attractive for preventing corrosion when the ratio of the mols of arsenic to the mols of such vanadium pentoxide is between 3:1 and 6:1.

When a fuel that contains both vanadium and arsenic compounds is burned and an ash thereby formed, it appears that a reaction involving the vanadium and arsenic occurs to form a stable complex of undetermined composition. This complex is substantially non-corrosive towards ferruginous metals even at temperatures of 1200 F. and above. It is of further interest that this complex causes the vanadium to lose its activity as an oxidation promoter. i

For the purposes of this invention, the percentage by weight of vanadium (expressed as vanadium pentoxide) in a residual-tyne fuel may be in the range of about 0.001 to 1.0%. Fuels containing 0.005 to 0.15% by weight of vanadium pentoxide are particularly contemplated. It will be noted that vanadium is not necessarily present as vanadium pentoxide in a residual fuel or in the fuel ash, but it is more convenient to consider that such is the case. Throughout the description of this invention, the vanadium content of an oil or of an ash is considered to .be the equivalent vanadium pentoxidecontent of the oil or ash. Similarly, the number of mols of vanadium in a fuel or an ash is actually expressed as theequivalent number of mols of vanadium pentoxide.

The arsenic-containing residual fuel compositions described above may be arrived at in several ways. It should be noted first, that the vanadium is present in the fuel as a result of either natural association or contamination. In any event, it is not part of the present invention to add further vanadium to a fuel. The methods described below for the incorporation of arsenic are merely representative andare not to be considered as limiting the invention in any manner.

A particularly attractive method for the arsenization of a vanadium-containing residual fuel oil consists in the direct reaction of an oxide of arsenic with the fuel. Alternatively, the oxide of arsenic is caused to react with a petroleum fraction to form an arsenic-containing composition which is then mixed withthe residual fuel. Examples of such petroleum fractions include crude mineral oils of generally parafiinic, naphthenic or asphaltic type and products derived from them, e. g. bright stocks, kerosenes, neutral or pale oils, steam refined oils, fuel oils, gas oils, cracked petrolatum, cracked paraflin wax, oil tars, clarified oil tars, naphthenic acids; and solvent extracted fractions.

It is preferred, however that a vanadium-containing residual fuel oil be directly reacted with the oxide of arsenic, e. g. As O or A5 0 In other words, the desired soluble arsenic-containing organic compounds are formed in situ in the residual oil.

Broadly speaking, vanadium-containing residual fuels are treated in accordance with this invention to the extent that the ratio of the mols of arsenic to the mols of vanadium pentoxide in the fuel ash is at least about 2:1 and preferably between 2:1 and 10:1. To treat the fuel it is merely necessary to first determine the amount of vanadium that is present in the ash when a sample of the fuel is burned and then treat the fuel with sufficient of the oxide of arsenic to produce in the ash an arsenicto-vanadium ratio within the defined range. When the arsenic oxide is reacted directly with the fuel, it is, generally necessary that the mixture be heated until a reaction takes place. In general, it has been found that for treating a residual fuel oil containing distillates like kerosene or gas oil a temperature. of to 350 F. is suitable. A temperature in the range of to 200 F. is especially preferred for this type of blended fuel. Reaction times may vary considerably, but generally speaking about one-half hour to about fourhours is ordinarily sufficient for effective arsenization. In some instances a small amount of sediment may be formed. This may be removed by settling, filtration or any conventional method.

Where desirable, the arsenic oxide may be reacted with one component of the residual fuel oil. For example, where a distillate oil is blended with a residual oil to form a residual fuel oil, it may be preferable to treat the distillate fraction rather than the residual material. Likewise, when residual fractions from 'more than one refining operation are being blended to form a residual fuel oil, it may be preferable to treat merely one of these fractions with the oxide of arsenic." It isnecessary, however, that the ratio of arsenic to vanadium in the final residual fuel oil blend be such that the mol ratio of arsenic to vanadium pentoxide in the fuel ash be in the range of ratios given earlier.

In reacting an arsenicoxide with a residual component of a fuel oil, reaction temperatures of about 300 F. to 600 F. and preferably 400 F. to 500 F. may be employed. In the case of a distillate component, reaction temperatures of about 100 F. to 300 F. and particularly about, 150 F. to 200 F; may be used, as mentioned previously. In either case reaction times of about onehalf hour to four hours or more may be employed.

The treatment of a residual fuel oil with an oxide of arsenic may be carried out in any conventional refining equipment suitable for this purpose. Apparatus such as' heated storage tanks, treating tanks, mixing tanks, orifice mixers and the like may be employed; If odoriferous products are formed, it may be desirable to air blow the fuel oil before marketing it.

Evidence of the beneficial effect of treating vanadium-v containing residual fuel oils with arsenic oxides has been obtained by means of a static oil ash corrosion test. This test, which has been found to correlate very well with full scale operation in boilers and gas turbines, is carried out in the following manner:

Place 3 grams of fuel oil ash in a No. 1 Coors Crucible, place a weighed steel test specimen (25 chromium/20 nickel alloy) in the crucible so as to be partially immersed in the ash, place the crucible set-up in a muffle furnace for 48 hours at 1500 F. and displace the furnace atmosphere with air on alvolume basis of approximately 100:1/hour throughout the testperiod. At the end of thetest period, remove the crucible set-up from the furnace, descale the'steel test specimen electrolytically in molten caustic, wash, dry andweigh. Calculate the percent weight loss directly.

When it is desired to test the effect of an additive on the fuel ash itself, av weighed quantity of the additive may be mixed directly with the ash in the crucible before insetting the steel specimen. When the additive to be tested is added to the fuel oil or when the fuel is to be modified by reaction with an additive, the treated fuel or the fuel oil and additive mixture is reduced to ash in a separate crucible, first, by coking at a low temperature (below 1000 F.) and finally by placing in a mufiie furnace for one hour at 950 F. The resulting ash is removed from the furnace and pulverized and 3 grams of the powder are then added to the crucible containing the steel specimen for quantitative test of corrosion. 1

EXAMPLE 1 The effect of vanadium content on the corrosiveness of the ash produced by the combustion of a residual fuel oil containing naturally occurring vanadium is amply demonstrated by the data presented below in Table I. It will be noted that corrosiveness increased with increase in vanadium content. As indicated, these data were obtained using the static oil ash corrosion test described above. A test withpure V is listed for comparison with the tests on ash. A blank test in which the steel specimen was heated in an empty crucible is also listed for reference.

Table I EFFECT OF VANADIUM CONTENT ON OORROSIVENESS OF FUEL OIL ASH IN STATIC OIL ASH CORROSION TEST AT 1500 v To establish the ability of the static oil ash corrosion test to predict the corrosiveness of residual fuel oil ash, residual fuels of different vanadium contents were burned in an actual burner installation. In these tests a small capacity, low-pressure airatomization' burner capable of handling from 1 to 2 gallons of preheated residual fuel per hour was used. The fuel was burned with excess air to give an approximate air/fuel ratio of 23 to 1. The hot flue gases were conducted from the combustion chamber to a horizontal insulated flue pipe in which metal test specimens were positioned .by means of suitable holders. By placing the test specimens at intervals along the flue, various test temperatures could be investigated, the maximum test temperature, i. e. at the position nearest the combustion chamber, being controlled by adjusting the firing rate of the burner.

The corrosiveness of the ash produced by each of two fuels was determined in these burner tests by measuring the loss in weight experienced by steel test specimens (25 chromium/2O nickel alloy) exposed to the flue gases at a temperature of 1600 F. One fuel containing naturally occurring vanadium corresponding to 0.057% I V 0 caused a specimen weight loss of about 8% in 80 hours, while the other fuel containing naturally occurring vanadium in an amount corresponding to only 0.002% V 0 caused less than 0.30% loss in the same length of time. These results substantiate the results obtained by the static oil ash corrosion test.

EXAMPLE III The beneficial effects that may be obtained by treating a residual fuel oil containing vanadium with an oxide of arsenic are brought out in Table II below. The data were obtained by mixing a fuel oil ash containing 73 percent vanadium oxide with the various proportions of arsenic pentoxide stated in the table, each mixture of ash and additive beingsubjected to the static oil ash corrosion,

test described above.

Table [1 EFFECT OF ARSENIO CONCENTRATION ON OORROSIVE- NESS OF A FUEL OIL ASH CONTAINING 73% V205 Static oil ash corrosion test at 1500 F.

Mol Ratio, AS/VBOS in Venezuelan Fuel Ash 1 0:1 09:1 26:1 4.3:1

Specimen wt. Loss, Percent 20.0 39.0 2. 45 0.296 Relative Loss, Percent 100.0 195. 0 12. 2 1. 5

1 Arsenic present as AS205 in the ash.

A vacuum-reduced residual stock was found to produce, when burned, about 0.10% of an ash containing73% V 0 A 2000 gram sample of this stock was stirred and heated with 2 grams of AS205 for a period of thirty minutes at about 500 F. The residual stock had the following inspections:

' Inspection: Value Specific gravity at ,60" F 0.9972 Flash-Open Cleveland, F 445 Viscosity- Secs. Furol 122 F. 3612 Secs.'Furol F 1308 Secs. Furol F 268.4 Secs. Furol@ 210 F 107 Following the reaction period, the treated sample was filtered through a paper-type filter. About 25 grams of material failed to pass through the filter. This material contained about 0.24% of As O and 0.59%of ash by weight. The ash in turn contained about 7.9% of V 0 The filtered oil was analyzed and found to contain arsenic in an amount corresponding to about 0.10% by weight as As O and about 0.087 gram of ash. The ash in this instance had a V 0 content of about 72% by weight. These data demonstrate that arsenic can be incorporated into a residual fuel oil or one of its components to the extent required for the purposes of the present invention. The data also indicate that a portion of the vanadium is actually precipitated from the oil by the reaction.

It will be noted that the particular stock treated in this example can be employed directly as a fuel oil or as one component of a fuel oil. For the latter purpose it is diluted with about 25% of heavy gas oil merely to make it less viscous, that is to decrease its viscosity to about 300 seconds Saybolt Furol at 122 F. and to increase its API gravity from about 10 to 15. Since the gas oil 'is essentially vanadium-free, this blending operation will not disturb the arsenic-to-vanadium ratio of the fuel.

EXAMPLE V A quantity of vanadium naphthenate was added to one of four samples of a commercial gasoline; to a second sample was added a quantity of copper naphthenate; and to a third sample was added a quantity of residual fuel oil containing vanadium in its naturally occurring state. In each case suflicient material was added to provide four milligrams of the particular metal per liter of gasoline. Each of the three samples, as well as the sample to which no extraneous material had menace.

beenadded; was subjected to A. S. T. M. Oxidation- Test D-525-55. The following results were obtained:

These data demonstrate that the vanadium compounds that are present in residual fuel oils are of a different nature than the Compounds of'vanadium or copper that tend to catalyze the oxidative deterioration of petroleum products. The data presented above indicate that the vanadium compounds that are present in residual fuel oils do not catalyze oxidative deterioration. It is thereforeevident that the action of the arsenic in reducing the corrosiveness of the ash produced on combustion of vanadium-containing residual oils on ferrous metals is not ofthe samenature as the action of an arsenic-containing inhibitor in improving the oxidation stability of the fuel oil itself. I

It is to be understood that in addition to treatment of the fuel oils of the present invention with oxides of arsenic, other known additives for fuel oils may be incorporated therein in the usual manner. Thus for example rust inhibitors, cloud-point or pour-point depressors, sludge dispersers, demulsifiers, antioxidants, and the like may be included. 7 Also small amounts of colloidal fixing agents such as high boiling amines, amine soaps, petroleum sulfonates, etc. may be added to, a residual fuel to keep a finely divided insoluble arsenic composition in a state of suspension within the fuel.

In conclusion, the present invention discloses that when a residual fuel oil containing vanadium is treated with an oxide of arsenic there is produced a new fuel composition which, upon combustion, will form an ash which is non-corrosive at temperatures of 1000 F. and above. This invention further describes a process whereby the corrosiveness of the ash produced by the combustion of a vanadium-containing residual fuel oil may be markedly reduced by treating the residual fuel with an oxide of arsenic.

What is.claimed' is: t

1. A fuel composition eomprisin'g-a-rrnajor portion of liquidv petroleum.hydrocarbons,.'including at least some residual petroleum oil; said-:corrlposition containing from about 0.001. to 1.0;percent by weight of naturally occurring. vanadium, calculated as vanadium pentoxide, to which composition has been added an amount of arsenic, in; the. form of the reaction product of an oxide of arsenic Withga. petroleum fraction, such that the ash produced upon combustion of thefuel will contain between about 2 and 10 mols of arsenic for each mol of vanadium, calculated as vanadium pentoxide, said reaction product being obtained by reaction of said oxide of arsenic with said petroleum fraction at a temperature in the. range of from 100 to 600 F. for a period of about /2' to 4 hours.

2. A fuel composition as defined by claim 1 wherein the ash contains between about 3 and 6 mols of arsenic per mol of vanadium, calculated as vanadium pentoxide.

3; A. fuel composition comprising a major proportion of liquid petroleum hydrocarbons, including at least a portion of residual petroleum oil hydrocarbons, and containing from about 0.001 to 1.0 percent by weight of naturally occurring vanadium, calculated as vanadium pentoxide, and a minor proportion of arsenic-containing material produced by reaction of anoxide of arsenic with a petroleum fraction, said arsenic-containing material being present in sufficient quantity to provide, in the ash produced on combustion of the fuel, from about 2 to about. 10 mols of arsenic per mol of vanadium, calculated as vanadium pentoxide, said reaction product be: ing obtained by reaction of said oxide of arsenic with said petroleum fraction at a temperature in the range of from l00to 600 F. for a period of about /2 to 4 hours.

References Cited in the file of this. patent UNITED STATES PATENTS 2,506,847 Tom May 9, 1950 2,781,005 Taylor et a1. Feb. 12, 1957 FOREIGN PATENTS 498,777 Belgium Nov. 14, 1950 a f r-

Claims (1)

1. A FUEL COMPOSITION COMPRISING A MAJOR PORTION OF LIQUID PETROLEUM HYDROCARBONS, INCLUDING AT LEAST SOME RESIDUAL PETROLEUM OIL, SAID COMPOSITION CONTAINING FROM ABOUT 0.001 TO 1.0 PERCENT BY WEIGHT OF NATURALLY OCCURRING VANADIUM, CALCULATED AS VANDIUM PENTOXIDE, TO WHICH COMPOSITION HAS BEEN ADDED AN AMOUNT OF ARSENIC, IN THE FORM OF THE REACTION PRODUCT OF AN OXIDE OF ARSENIC WITH A PETROLEUM FRACTION, SUCH THAT THE ASH PRODUCED UPON COMBUSTION OF THE FUEL WILL CONTAIN BETWEEN ABOUT 2 AND 10 MOLS OF ARSENIC FOR EACH MOL OF VANADIUM, CALCULATED AS VANADIUM PENTOXIDE, SAID REACTION PRODUCT BEING OBTAINED BY REACTION OF SAID OXIDE OF ARSENIC WITH SAID PETROLEUM FRACTION AT A TEMPERATURE IN THE RANGE OF FROM 100 TO 600*F. FOR A PERIOD OF ABOUT 1/2 TO 4 HOURS.