US2843467A - Fuel oils - Google Patents

Description

United States Patent i search & Development Company, Pittsburgh, Pa., a corporation of Delaware N0 Drawing. Application May 10,1954

Serial No. 4Z,84 2

This invention relates to vanadium-containing fuel oils. More particularly, it is concerned with rendering noncorrosive those residual fuel oils which contain such an amount of vanadium as normally to yield a corrosive vanadium-containing ash upon combustion.

It has been observed that when a residual type fuel oil containing substantial amounts of vanadium is burned in furnaces, boilers and gas turbines, the ash resulting from combustion of the fuel oil is highly corrosive to materials at elevated temperatures and attacks such parts as boiler tubes, hangers, turbine blades, etc. 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 efficiency of the gas turbine dictate the use of a fuel for this purpose which is cheaper than 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 cheap residual fuels in gas turbines is the corrosiveness induced by those residual fuels containing sufficient amounts of vanadium to cause corrosion problems. 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 con tain so little vanadium, or none, as to present no corrosion problem, such non-corrosive fuel oils are not 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. All of these factors appear tomilitate against the extensive use of residual fuel oils. for gasv turbines.

The vanadium-containing ash present in the hot flue gas obtained from the burning of a residual oil containing. substantial amounts of; vanadium compounds causes catastrophic oxidation of the turbine. blades in a gas. turbine. The corrosive nature of the. ash appears to be- Vanadium oxide (V 0 which is formed on combustion of aresidual due to its vanadium oxide: content.

fuel oil containing vanadium compounds, vigorously attacks various metals, their alloys, and other materials at the elevated temperatures encountered in combustion, the rate of attack becoming progressively more severe as the temperature is increased. The vanadium containing ash.

be distinguished from the type of corrosion occurringatatmospheric or slightly elevated temperatures, generally in the presence of air and moisture. Under. the latter conditions, an ash containing vanadium oxide lias no significant corrosive effect; The corrosion problem de- 2,843,467 Patented July 15, 1958 2 scribed herein may therefore properly be termed a problem of hot corrosion.

The economic factors involved preclude any extensive treatment of vanadiumcontaining residual fuel oils to remove the vanadium therefrom or to mitigate its effects. This is due in large part to the fact that the vanadium is apparently bonded into organic macro-molecules which behave much like asphaltenes. The vanadium compounds in residual oils are therefore not removed by centrifuging or by the conventional chemical refining treatments.

I have now discovered that residual fuel oils containing vanadium in' an amount sufficient to yield a corrosive vanadium-containing ash upon combustion canbe rendered non-corrosive, notwithstanding the normally corrosive vanadium content, by incorporating in the fuel oil a small amount, sufficient to retard the corrosiveness of said ash, of an oil-soluble or oil-dispersible organic silicon compound. In accordance with my invention, residual fuel oils thus prepared exhibit'a substantial retardation or elimination'of hot corrosion.

While I do not desire to be bound by any theory as to the action taking place, it is my present belief that the organic silicon compound reacts during combustion of the fuel oil with the vanadium component thereof to form a stable, high-melting, relatively non-corrosive vanadium compound which is not decomposed to vanadium oxide under the conditions of combustion. It is my further belief that this reaction takes place prior to the time any substantial amount of vanadium oxide ash comes into contact with the parts of the equipment otherwise corrosively affected. In any event, I have demonstrated that the addition of an oil-soluble or oil-dispersible organic silicon compound to a residual typepetroleum fuel oil normally yielding a corrosive vanadium-containing ash completely changes the character of the ash from a hard, adherent, slag-like deposit to a loose, light, fluffy powder which. is easily blown out by the combustion draft ina turbine, furnace or boiler, or which falls to the floor of a. furnace, or boiler. I have also demonstrated that the addition of the organic silicon compound eliminates or materially retards the corrosion normally obtained from C" fuel oils which contain a sufficient 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 re-' duction of total crudes, by the thermal cracking of topped crudes, by vis-breaking heavy petroleum residua, and other conventional treatments of heavy petroleum oils. Residua 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 sufficient vanadium normally to exhibit the corrosion characteristics described herein. Itshould, beunderstood that distillate fuel oils -themselyes contain either no vanadium or such small amounts as to present no problem of hot corrosion. The total ash from commercial residual fuel oils usually ranges from about 0.02" to 0.12 percent by weight. The vanadium pentoxide (V 0 content of such ashes ranges from zero t to trace amountsup to about 5 percent by weight for low vanadium stocks, exhibiting no significant vanadium corrosion problem, to as much as percent by weight for some of the high vanadium stocks, exhibiting severe corrosion.

The oil-soluble or oil-dispersible organic silicon compounds used in accordance with my invention are themselves well known in the art. They include such materials as the organosilanes, i. e.,deri'vatives of the silanes, Si I-I in which one or more of the hydrogen atoms are replaced by hydrocarbon or substituted hydrocarbon radicals, for example:

Tetrapropyl silane Tetraphenyl silane Tripropyl, amyl silane Tripropyl, chloroamyl silane Dimethyl, dihydroxymethyl silane Hexapropyl disilane Triisobutyl silane, etc.

I A particularly suitable class of organic silicon compounds is the organosiloxanes, which includes such types of compounds as (R SiO),,, etc. This class includes, for example, the liquid silicone" polymers such as dimethyl silicone, methyl phenyl silicone, etc., also known as methylpolysiloxanes and methylphenylpolysiloxanes. Other suitable classes of organic silicon compounds include: (1) the organosilanols, R Si(OH) examples of which are ethylpropylphenyl silanol, tripropyl silanol, triisoamyl silanol, phenylbenzylsilane diol, etc.; (2) the silicate esters and their polymers, e. g., tetramethyl orthosilicate, tetraethyl orthosilicate, the higher secondary alkyl orthosilicates, tetraphenyl orthosilicate, glycol orthosilicate, etc.; (3) the silazanes, R SiNH R SiNHSiR etc. containing the linkage NSiC-; (4) the aminosilanes, as shown in U. S. Patent 2,566,363, e. g., (RO) Si(NH di-tertiarybutoxydiaminosilane, including hydrolysis produits and polymers thereof; and (5) the dior tri-hydrocarbonoxysilanes, e. g., alkoxyand aroxysilanes of the type R Si(OR) hexaalkoxydisilanes, etc.

The above-described organic silicon compounds are liquids or solids. Both liquid and solid materials are readily dissolved or dispersed in the vanadium-containing residual fuel oils. The requirement for oil-solubility or dispersibility of the organic silicon compounds is to insure uniform blending of the compounds throughout the body of the fuel oil to which they are added. It would obviously be undesirable for the bulk of the additive to be concentrated in a small portion of the fuel oil while the remainder of the oil contained little or no additive. The requirement for uniform blending of the organic silicon compounds is therefore satisfied by the use of oil-soluble or oil-dispersible compounds. As will be apparent to those skilled in the art, the distinction between oil-solubility and oil-dispersibility is a matter of degree, it being sufiicient for the purposes of this invention that a fairly stable dispersion of the dispersible additives be obtained, or that redispersion of a settled additive can be easily accomplished by simple agitation.

In the practice of my invention, therefore, the organic silicon compound can be admixed with the vanadiumcontaining residual fuel oil to form a solution or a relatively stable suspension or dispersion; if any settling takes place, redispersion can be satisfactorily accomplished by simple agitation. Alternatively, the additive can be separately fed to the fuel oil line just prior to the burner, or even directly into the flame. In such instances, the organic silicon compound is preferably employed as a concentrated solution or dispersion in a naphtha or heavy fuel oil and is metered into the combustion device in the proportions required.

As I have stated, the oil-soluble or oil-dispersible organic silicon compound is employed in a minor amount with respect to the vanadium-containing fuel oil, sufficient to retard the corrosiveness of the ash from the fuel oil. It is desirable to employ such an amount of the additive as to result in at least about one atom weight of the silicon therein per atom weight of the vanadium in the fuel oil. Preferably, the atom weight ratio of the silicon to the vanadium is 2:1. While larger amounts of the organic silicon compounds can be used, it is ordinarily unnecessary to exceed an atom weight ratio of silicon to vanadium of 3:1.

The following specific examples are further illustrative of my invention.

Example 1.-In 99.8 parts by weight of a No. 6 residual fuel having a vanadium content of 305 parts per million, as vanadium, there was dispersed 0.2 part of the liquid dimethyl silicone polymer known as D. C. Fluid 200. A similar dispersion was prepared in the identical proportions, but using the aminosilane known as Sylon. This aminosilane is disclosed in Example I of U. S. Patent No. 2,566,363. Two hundred (200) gram portions of each of the dispersions were then placed in 4" diameter 18-8 stainless steel dishes. The dishes were heated until the fire temperature of the oil had been reached and the oil ignited. After the oil had burned itself out, the dishes containing the residue from the ignition were placed in a muflie furnace and heated for 14 days at 1350 F. At the end of this time, the dishes were allowed to cool slowly and the nature of the ash was determined by inspection. The ash was then removed from the dishes, the dishes wiped clean with steel wool, and the bottoms and the walls of the dishes were examined for corrosion in the form of etching or pitting. The following table shows the results obtained, the identical residual fuel oil without the addition of metal having beenrun for purposes of comparison.

Additive Nature of Ash Corrosion None Hard and crusty. Heavy corrosion with deep pitting. D. O. Fluid 200 Light and fluffy No pitting. Sylon do Do.

Example 2.In order to demonstrate the corrosiveness of a residual fuel oil ash containing high amounts of vanadium and to demonstrate the corrosion inhibiting effects of the additives of this invention, the following tests Were performed. An Eastern Venezuela No. 6 fuel oil was fired at 1600 F. to obtain an ash having a vanadium content, determined by analysis, of 36.75 percent. Strips of ,6 inch thick 19-9 DL stainless steel sheet were cleaned by sand blasting in order to insure clean and uniform surfaces. The strips were then roasted in contact with the vanadium-containing ash for seven days in-an electrically heated muflie furnace held at 1350 F. At the end of seven days heating the specimens were allowed to cool and were then examined for corrosion. Tests were made on the ash alone and on ash containing the additives disclosed herein. In order to insure complete removal of all organic or carboniferous material, the ash was roasted for two hours at 1350 F. prior to being employed in the tests. In cases where an additive compound was also employed, it was added to the ash and well mixed prior to this preliminary heating. The addi-- tives were employed in amounts of 10 percent weight of their mixture with the ash. The following table shows the results obtained.

Additive Appearance of Metal After Test None -Q Very heavy corrosion with large area of metal eaten away. Very light etching; no pitting. Very light pitting.

As is apparent from the preceding description, the use of the additives of my invention strikingly changes the taining ash upon combustion, and a small amount, sufiicient to retard the corrosiveness of said ash, of a compound selected from the class consisting of oil-soluble and oil-dispersible organic silicon compounds.

2. The composition of claim 1, wherein said organic silicon compound is selected from the class consisting of organosilanes, organosiloxanes, organosilanols, silicate esters, and aminosilanes.

3. The composition of claim 1, wherein said organic silicon compound is employed in an amount suflicient to yield at least about 1 atom weight of silicon per atom weight of vanadium in said oil.

4. The composition of claim 1, wherein said organic silicon compound is an aminosilane.

5. The composition of claim 1, wherein said organic silicon compound is a siloxane.

6. The composition of claim 5, wherein said siloxane is a liquid dimethyl silicone polymer.

7. A fuel oil composition comprising a major amount of a residual fuel oil yielding a corrosive vanadium-con taining ash upon combustion, and a small amount, suflicient to retard the corrosiveness of said ash of a compound selected from the class consisting of oil-soluble and oil-dispersible silicate esters.

8. The composition of claim 7, wherein said silicate ester is tetraethyl orthosilicate.

References Cited in the file of this patent UNITED STATES PATENTS 2,432,109 Zisman et a1. Dec. 9, 1947 2,527,987 Caron et a1 Oct. 31, 1950 FOREIGN PATENTS 697,101 Great Britain Sept. 16, 1953 697,619 Great Britain Sept. 23, 1953 502,159 Belgium Apr. 14, 1951

Claims (1)

1. A FUEL OIL COMPOSITION COMPRISING A MAJOR AMOUNT OF A RESIDUAL FUEL OIL YIELDING A CORROSIVE VANADIUM-CONTAINING ASH UPON COMBUSTION, AND A SMALL AMOUNT, SUFFICIENT TO RETARD THE CORROSIVENESS OF SAID ASH, OF A COMPOUND SELECTED FROM THE CLASS CONSISTING OF OIL-SOLUBLE AND OIL-DISPERSIBLE ORGANIC SILICON COMPOUNDS.