US2843200A

US2843200A - Fuel oils

Info

Publication number: US2843200A
Application number: US428841A
Authority: US
Inventors: Albert G Rocchini
Original assignee: Gulf Research and Development Co
Current assignee: Gulf Research and Development Co
Priority date: 1954-05-10
Filing date: 1954-05-10
Publication date: 1958-07-15
Anticipated expiration: 1975-07-15

Description

United States Patent FUEL OILS Albert G. Rocchini, Springdale, Pa., assignor to Gulf Research 85 Development Company, Pittsburgh, Pan, a corporation of Delaware No Drawing. Application May 10, 1954 Serial No. 428,841

7 Claims. (Cl. 158-1175) This invention relates to vanadium-containing fuel oils. More particularly, it is concerned with rendering non-corrosive 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 sufiicient 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 contain 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 noncorrosive oil to the point of use is often prohibitive, and the residual oil loses its competitive advantage. All of these factors appear to militate against the extensive use of residual fuel oils for gas 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 appearsto be due to its vanadium oxide content. Vanadium oxide (V 0 which is formed on combustion of a residual 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 is a hard, adherent material which forms deposits on the parts affected and corrosively reacts with them.

It is to be noted that the corrosion of materials at high temperatures by the hot ash resulting from the combustion of a vanadium-containing residual fuel oil is to be distinguished from the type of corrosion occurring at atmospheric or slightly elevated temperatures, generally in the presence of air and moisture. Under the latter conditions, an ash containing vanadium oxide has no significant corrosive effect. The corrosion problem delem of hot corrosion.

2,843,200 PatentedJuly '15, 1958 The economic factors involved preclude any extensive treatment of vanadium-containing 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.

1 have now discovered that residual fuel oils containing vanadium in an amount sufficient to yield a corro sive vanadium-containing ash upon combustion can be 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 a finely divided precipitated hydrated calcium silicate. 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 hydrated calcium silicate-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 a hydrated calcium silicate to a residual type petroleum 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, fluify powder which is easily blown out by the combustion draft in a turbine, furnace or boiler, or which falls to the floor of a furnace or boiler. I have also demonstrated that the addition of a hydrated calcium silicate eliminates or materially retards the corrosion normally obtained from the ash of a residual type fuel oil containing substantial amounts of vanadium.

The type of residual fuel oils to which my invention is directed'is exemplified by No. 5, No. 6 and Bunker.

C fuel oils which contain a sufficient amount of vanadium to form a corrosive ash upon combustion. These are residual type fuel oils obtained frompetroleum 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 vis-breaking heavy petroleum residua,

'and other conventional treatments of heavy petroleum 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 to trace amounts up 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.

'l' he precipitated hydrated calcium silicates of my invention are obtained by a numberof different reactions,

such as the reaction of calcium chloride with sodium silicate in aqueous solution. The composition of the silicate, including both the proportion of calcium to silica and the amount of water of .hydrationpresent, varies widely according to the method of preparation employed. Suitable compounds of this character for use according to the present invention are represented by the general formula wherein n and m are integers from 1 to 10 and x is an integer from 1 to 5.

The degree to which the hydrated calcium silicate is subdivided is not critical. The requirement for using a finely divided material is based upon the desirability of forming a fairly stable suspension or dispersion of the hydratedcalciuin silicate in the vanadium-containing residual fuel oil so as to obtain a uniform blend with the oil, at least at the point Where combustion of the fuel oil occurs. Precipitated hydrated calcium silicates are ordinarily obtained in the form of particles ranging from about to 100 millimicrons in diameter. Any of such materials are eminently satisfactory, particularly when it is considered that the particles should not be of such size as to clog the fuel oil injection nozzle or other injection device into the combustion zone.

In the practice of my invention, therefore, the finely divided hydrated calcium silicate can be admixed with the vanadium-containing residual fuel oil to form a relatively stable suspension or dispersion; if any settling takes place, redispersion can be satisfactorily accomplished by simple agitation. Alternatively, the finely divided 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 hydrated calcium silicate is preferably employed as a concentrated flowable paste or slurry in a naphtha or heavy fuel oil and is metered into the combustion device in the proportions required.

As I have stated, the finely divided hydrated calcium silicate 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 total of calcium and silicon in the hydrated calcium silicate per atom weight of the vanadium in the fuel oil. Preferably, the atom weight ratio is 2:1. While larger amounts of the hydrated calcium silicate can be used, it is ordinarily unnecessary to exceed an atom Weight ratio of the calcium and silicon to vanadium of 3: 1.

The following specific examples are further illustrative of my invention.

Example 1.--ln 99.9 parts by weight of a No. 6 residual fuel having a vanadium content of 305 parts per million, as vanadium, there was suspended 0.1 part by weight of a precipitated finely divided hydrated calcium silicate. This amount of hydrated calicum silicate is equivalent to 2.22 atom weights of the total of calcium and silicon in the calcium silicate per atom weight of vanadium in the oil. The hydrated calcium silicate employed is sold commercially under the trade name of Silene EF.. This material had a particle size of about 35 millimicrons average diameter, a specific gravity of 2.1 and a refractive index of 1.472. It analyzed 18.5 percent CaO, 64 percent SiO and had a loss on ignition of 16.5 percent indicating that it consisted principally of 1a hydrated calcium silicate of the formula A two hundred gram portion of the suspension was then placed into a 4" diameter 18-8 stainless steel dish. The dish was heated until the fire temperature of the oil had been reached and the oil ignited. After the oil had burned itself out, the dish containing the residue from the ignition was placed in a muffle furnace and heated '4' for 14 days at 1350 F. At the end of this time, the dish was allowed to cool slowly and the nature of the ash was determined by inspection. The ash was then removed from the dish, the dish wiped clean with steel wool, and the bottom and the walls of the dish 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 been run for purposes of comparison.

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 effect of the hydrated calcium silicate of this invention, the following test was 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 inch thick 19-9 DL stainless steel sheet were cleaned by sand blasting 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 muffle 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 hydrated calcium silicate. 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. Where the additive was also employed, it was added to the ash and well mixed prior to this preliminary heating. The hydrated calcium silicate, specifically Silene EF, was employed in an amount of 10 percent by weight of its mixture with the ash. This amount of hydrated calcium silicate is equivalent to 0.23 atom Weights of the total of calcium and silicon per atom weight of vanadium. The following table shows the results obtained.

Additive Appearance of Metal after Test As is apparent from the preceding description, the use of the hydrated calcium silicate of my invention strikingly changes the character of the vanadium-containing ash from a residual fuel oil to a light and fluffy powder, and substantially reduces the corrosiveness of the ash.

I claim:

1. A fuel oil composition comprising a major amount of a residual fuel oil yielding a corrosive vanadiumcontaining ash upon combustion, and a minor amount, sufficient to retard the corrosiveness of said ash, of a finely divided precipitated hydrated calcium silicate.

2. A composition according to claim 1, wherein the calcium silicate is employed in an amount suificient to yield at least about 1 atom weight of the total of calcium and silicon in said calcium silicate per atom Weight of vanadium in said oil.

3. A composition according to claim 1, wherein the calcium silicate is represented by the formula wherein n and m are integers from 1 to 10 and x is an integer from 1 to 5.

4. A composition according to claim 1, wherein the calcium silicate is CaSi O -3H O and the amount thereof is sufiicient to yield about 2 atom weights of the total of calcium and silicon in Said calcium silicate per atom weight of vanadium in said oil.

5. In a process for burning a residual fuel oil yielding References (Cited in the file of this patent a corrosive vanadium-containing ash, wherein the ash H corrosively attacks the materllls of the combustion Zone, FOREIGN PATENTS the method of retarding said corrosive attack which com- 445,506 Great Britain Apr. 14, 1936 prises uniformly blending with said fuel oil, at least at 5 697,101 Great Britain Sept. 16, 1953 the point of combustion thereof, a finely divided pre- 697,619 Great Britain Sept. 23, 1953 cipitated hydrated calcium silicate, and subjecting the 502,159 Belgium Apr. 14, 1951 blend to combustion. w

6. The process of claim 5, wherein the calcium silicate (HHER REFEREZNCES is suspended in the fuel oil prior to injection of the fuel 0 S osium n Corro ion of Materials at Elevated oil into the combustion Zone. Temperatures, A. S. '1". M. Bulletin No. 108, Iune 26,

7. The process of claim 5, wherein the is formed into a suspension and the s .02)

1950, Oil Ash Corrosion of Materials at Elevated Tern-- peratures, by C. T. Evans, in, pages 59, 60, 68, 97-99, with the fuel oil immediately prior to injection of the iuel complete arti le pages 59-105.

oil into the combustion zone. 15

Claims

5. IN A PROCESS FOR BURNING A RESIDUAL FUEL OIL YIELDING A CORROSIVE VANDIUM-CONTAINING ASH, WHEREIN THE ASH CORROSIVELY ATTACKS THE MATERIALS OF THE COMBUSTION ZONE, THE METHOD OF RETARDING SAID CORROSIVE ATTACK WHICH COMPRISES UNIFORMLY BLENDING WITH SAID FUEL OIL, AT LEAST AT THE POINT OF COMBUSTION THEROF, A FINELY DIVIDED PRECIPITATED HYDRATED CALCIUM SILICATE, AND SUBJECTING THE BLEND TO COMBUSTION.