US2913319A

US2913319A - Fuel oils

Info

Publication number: US2913319A
Application number: US603609A
Authority: US
Inventors: Charles E Trautman
Original assignee: Gulf Research and Development Co
Current assignee: Gulf Research and Development Co
Priority date: 1956-08-13
Filing date: 1956-08-13
Publication date: 1959-11-17
Anticipated expiration: 1976-11-17

Description

NOV. 17, 1959 c, TRAUTMAN 2,913,319

FUEL OILS Filed Aug. 13, 1956 IAL Al? MILL-75 34 22 23 TESTSPEC/MEN #45 ATrOQ/VEY United States Patent FUEL OILS Charles E. Trautman, Cheswick, Pa., assignor to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware Application August 13, 1956, Serial No. 603,609

14 Claims. (CI. 4450) This invention relates to vanadium-containing petroleum fuels. More particularly, it is concerned with rendering non-corrosive those residual fuels 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 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 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 residual fuel oils in gas turbines is the corrosiveness induced by those residual fuels containing sufiicient 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 are not always available at the point where the oil is to be used. 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 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 reducing thermal efficiency 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. 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 flu gas obtained from the burning of a residual fuel containing substantial amounts of vanadium compounds causes catastrophic corrosion of the turbine blades and In such Since Patented Nov. 17, 1959 "ice other metal parts in a gas turbine. The corrosive nature of the ash appears to be due to its vanadium oxide content. such as vanadium oxide (V 0 which are formed on combustion of a residual fuel oil containing vanadium compounds, vigorously attack various metals, their al-- loys, 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 is to be noted that the corrosion of materials at high temperatures by the hot ash resulting from the com bustion of a vanadium-containing residual fuel 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 con ditions, an ash containing vanadium oxide has no significant corrosive effect. The corrosion problem described herein may therefore properly be termed a problem of hot corrosion.

The economic factors involved preclude any extensive treatment of vanadium-containing residual fuels to remove the vanadium therefrom or to mitigate its effects. The vanadium compounds in residual oils are not removed by centrifuging or by the conventional chemical refining treatments.

I have now discovered that residual petroleumfuels" containing vanadium in an amount sufficient to yield a corrosive vanadium-containing ash upon combustion can be rendered substantially less corrosive, notwithstanding the normally corrosive vanadium content, by incorporating therein in a small amount suflicient to retard the corrosiveness of the ash a compound of a didymium rare earth element. In the fuel compositions of the inven: tion, corrosion due to the vanadium-containing ash is substantially retarded.

The single figure of the drawing shows an apparatus for testing the corrosiveness of residual fuel oil compositions.

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 suflicient 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. 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. It should be understood that distillate fuel oils themselves 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 0.2 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.

The type of vanadium-containing solid residual fuels to which the invention is directed is exemplified by the Certain inorganic compounds of vanadium,

coke obtained in known manner by the delayed thermal coking or fluidized coking of 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 containing substantial amounts of vanadium. A typical pitch exhibiting corrosive characteristics upon combustion had a softening point of 347 F. and a vanadium content, as vanadium, of 578 parts per million.

As has been stated, the corrosion retarding additives of the invention are compounds of a didymium rare earth element. As known commercially, the didymium elements are the rare earth elements of atomic numbers 57 to 71, inclusive, with the exception of cerium. The didymium elements thus include lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutecium.

Commerical ores of the rare earth elements are primarily monazite and bastnasite. Monazite is an orthophosphate of the rare earth elements and thorium. Bastnasite is a cerium earth fluorocarbonate. In the Working of these ores to separate the thorium and cerium, the remaining didymium elements are obtained. Generally, the ores are opened by heating with sulfuric acid, the thorium is separated, the rare earths are isolated, and the cerium is separated from the rare earths to obtain a mixture of the didymium elements, all in accordance with known methods. The following table shows the composition of rare earths in typical commercial didymium salts.

Composition of Rare Earths, Weight Percent As the above table shows, the didymium elements are obtained by present commercial processing methods as mixtures. Such mixtures are particularly useful in the practice of this invention. Although the individual didymium elements can successfully be employed, as will be shown hereinafter, compounds of the individual elements are expensive because of the dificulty of further separation of the didymium mixture.

Any compound of a didymium element or mixture thereof is employed in the practice of the invention. This includes inorganic as well as organic compounds. For example, the commercially available carbonates, oxides, hydroxides, oxalates, acetates, sulfates and nitrates are suitable. Salts of acidic organic compounds, which can be prepared by reaction of the didymium element oxide or carbonate with the corresponding acidic organic compound or by metathesis of a didymium element nitrate or other water soluble salt thereof with an alkali metal salt of an acidic organic compound, are also suitable. Representative examples of acidic organic compounds useful in preparing oil-soluble or oil-dispersible didymium salts include (1) the fatty acids, e.g., valeric, caproic, Z-ethyihexanoic, oleic, palmitic, 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 alkylsulfuric acids, e.g., Iauryl sulfuric acid; (4) petroleum naphthenic acids; (5) rosin and hydrogenated rosin; (6) alkyl phenols, e.g., iso-octyl phenol, t-butylpheuol and the like; (7) alkylphenol sulfides, e.g., bis(iso-octyl phenol)- monosulfide, bis(t-butylphenol)disulfide, and the like; and (8) 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 easily prepared, these are preferred materials.

When employing the inorganic didymium compounds in residual fuels, it is desirable to use finely divided materials. However, the degree to which the materials are subdivided 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 inorganic didymium compounds when blended with a residual fuel oil. Furthermore, the more finely-divided materials are more efficient 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 didymium compounds are therefore employed in a particle size range of less than 250 microns, preferably less than 50 microns.

The organic didymium compounds of the invention are oil-soluble or oil-dispersible and are therefore readily blended with residual fuels to form uniform blends.

In the practice of the invention with vanadium-containing residual fuel oils, the selected didymium compound is uniformly blended with the oil in proportion to the vanadium content thereof. Since on a weight basis in relation to the fuel the amounts of additive are small, it is desirable to make concentrated dispersions or solutions of the additive in a naphtha or heavy, oil for convenience in compounding.

In the practice of the invention, with the solid residual fuels, incorporation of the didymium additives is accomplished in several ways. The additive can be suspended or dissolved in the liquid vanadium-containing 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 didymium element additive is slurried with the oil in proportion to the vanadium con tent thereof, and the whole subjected to deep vacuum. reduction to obtain a pitch containing uniformly dis persed therein the additive. Alternatively, particles of the solid residual fuels in question can be coated or impregnated with a concentrated naphtha solution of the additive in the proportion required in relation to the vanadium content, and the aggregate then dried to obtain solid fuel particles impregnated with the additive. As still another alternative, particularly with a pitch which is withdrawn in molten form from the processing vessel, the additive can be mixed with the molten pitch and the mixture allowed to solidify after which it is ground to the desired size. Of course, in the case of either liquid or solid residual fuels, the additive can be separately fed into the burner as a concentrated solution or dispersion, preferably in admixture with the fuel.

As has been stated, the didymium compounds are employed in a small amount with respect to the vanadiumcontaining residual fuel, suificient to retard the corrosiveness of the ash. Ordinarily, to achieve practical corrosion retardation, it is desirable to employ such an amount of additive as to result in at least about 0.5 atom weight of the didymium element or mixture thereof per atom weight of the vanadium in the fuel oil. Preferably, the atom weight ratio, didymium element or elements to vanadium, is 2:1, although larger amounts of the additiv'e, say 3:1 or higher, can be employed. It is to be noted that, when using a mixture of didymium elements,

the average atomic Weight of the total elements in the mixture is employed in determining the atom weight ratio of didymium elements to vanadium.

The following specific examples are further illustrative of my invention.

Example 1 With a No; 6 residual fuel oil having an ash content of 0.037 percent by weight and containing 166 parts per million of vanadium, uniformly blend 0.08 percent by weight of finely powdered didymium carbonate similar in appearance to face powder. This yields an atom ratio, DizV, of 1:1. The didymium carbonate used in this example is a mixture of the cerium-free rare earth elements derived from monazite sand. It has the following typical rare earth oxide analysis in percent by weight:

Lanthanum oxide, Lazog 29.3 Cerium oxide, CeO- 0.5 Praseodymium oxide, Pr 7.1

Neodymium oxide, Nd O 24.5

Samarium oxide, Sm O 2.6 Yttrium rare earth oxides 0.3 Other rare earth oxides 0.7

Total rare earth oxides 65.0

Example 2 To the same residual fuel oil of Example 1, add 0.13 percent by weight of finely powdered lanthanum carbonate. This yields a La:V atom ratio of 1:1.

Example 3 To the same residual fuel oil of Example 1, add 0.11 percent by weight of finely powdered neodymium carbonater An atom ratio, NdzV, of 1:1 is obtained.

Example 4 Melt a solid petroleum pitch obtained from the deep vacuum reduction of an asphaltic crude. This pitch has a softening point of 347 F. and a vanadium content of 578 parts per million. While the pitch is in molten form, add and uniformly blend therein 0.2 percent by weight of finely powdered didymium oxide. Upon cooling and solidification, grind the mixture to about 150 mesh The resulting fuel has an atom ratio, DizV, of 1:1. The didymium oxide used in this example is a mixture of the cerium-free rare earth elements derived from monazite sand. It has the following typical oxide analysis in percent by weight:

Lanthanum oxide, Lagos 42.3 Cerium oxide, CeO 1.0 Praseodymium oxide, Pr O 10.2 Neodymium oxide, Nd O 35.4 Samarium oxide, Sm O 3.7 Yttrium earth oxides 0.4 Other rare earth oxides 1.0

Total rare earth oxides 94.0

Example 5 To a residual fuel oil having an ash content of 0.04 percent by weight and a vanadium content of 180 parts per million, add 6.2 percent by weight of a concentrate of didymium naphthenate in naphtha having a total metal content of 4 percent by weight. An atom weight ratio, DizV, of 0.5:1 is obtained. The oxide analysis of the didymium naphthenate is the same as that shown in the preceding example.

Example 6 I To the same residual fuel oil of Example 5, add

cient of a lanthanum tallate concentrated solution in naphtha to obtain an atom weight ratio, LazV, of 2:1.

Example 7 To the same residual fuel oil of Example 5, add a didymium rosinate concentrate in naphtha in an amount sufiicient to give a Di:V atom ratio of 3:1. The oxide analysis of the didymium rosinate is the same as that shown in Example 4.

Similar compositions are prepared using such didymium (element or mixture of elements) compounds as the nitrate, acetate, oleate, oxalate, stearate, octylphenolate, as well as the other compounds disclosed here- In order to test the effectiveness of the additives of this invention under conditions of burning residual fuels in a gas turbine, the apparatus shown inthe drawings is employed. As shown in the drawing, 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 needel of approximately 0.008 inch LD. 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 inches. 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 30 having a diameter of 1 /2 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 are spaced 4 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 4 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. The oil employed is a No. 6 residual fuel oil having an ash content of 0.037 percent and containing 166 parts per million of vanadium. Comparative tests are run with the same oil containing no additive and with the compositions of Examples 1, 2 and 3.

The efiectiveness of the additives of the invention in reducing corrosion and deposits is clear.

In conducting the experimental work on which the invention is based, it had been expected that all of the rare earth elements because of their close chemical similarity would be substantially equally effective as corrosion retarding additives. Surprisingly, however, it has been found that this is not the case. Cerium compounds or any mixture of rare earth compounds containing substantial amounts of cerium are considerably inferior to the didymium compounds as additives for retarding corrosion due to corrosive vanadium-containing ash. Furthermore, the cerium-containing additives produce more deposits of an adherent crusty nature, comparable to the deposits obtained upon combustion of a vanadium-containing fuel containing no additive.

In order to demonstrate the superiority of the additives of the invention, comparative tests are run under identical conditions with a corrosive vanadium-containing residual oil (ash 0.037 percent, vanadium 166 parts per million) and with the same oil containing rare earth carbonate (thorium-free derived from monazite), cerium carbonate, the didymium carbonate of Example 1 and lanthanum carbonate. The test specimens are 25-20 stainless steel, and as described above, the tests are run for 100 hours at a temperature of 1450 F. Each additive, 'i.e., the rare earth carbonate, cerium carbonate, didymium carbonatc and lanthanum carbonate, is employed in an amount sulficient to give an identical atom weight ratio of metal to vanadium of 1:1. The rare earth carbonate has the following typical oxide analysis in percent by weight:

The results obtained are shown in the following table:

The above results clearly show the superiority of the didymium compounds of the invention as compared to cerium compounds or mixtures containing substantial amounts of cerium. Not only is the amount of corrosion sharply reduced, but the amount of deposits is also reduced. Furthermore, the nature of the deposits is changed from the difiicultly removable adherent scale, as obtained without an additive, to a readily removable powdery material.

A typical analysis of the stainless steel employed in the above testing is shown in the following table in percent by weight:

25-20 Cr 25 Ni 20 C 0.08 Mn 2.0 Si 1.5 S 0.03 P 0.04 Fe Balance The preceding description clearly demonstrates the effectiveness of the additives of the invention in reducing the corrosivity of vanadium-containing residual fuels, and also in reducing the amount of ash deposits obtained. Furthermore, the character of the deposits has been radically changed from a hard adherent scale to a powdery material which is more readily blown out by the combustion draft in a turbine, furnace or boiler and which can more easily be removed from the affected parts.

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

I claim:

1. A fuel composition comprising a major amount of a residual petroleum fuel yielding a corrosive vanadiumcontaining ash upon combustion, and a small amount of a compound of a clidymium rare earth element sulficient to retard the corrosiveness of said ash.

2. The composition of claim 1, wherein the compound is employed in an amount sufficient to yield at least about 0.5 atom weight of didymium element per atom weight of vanadium.

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

4. The composition of claim 1, wherein the didymium rare earth element is lanthanum.

5. The composition of claim 1, wherein the didymium rare earth element is neodymium.

6. The composition of claim 1, wherein the didymium compound comprises a mixture of didymium rare earth elements derived from monazite.

7. A fuel composition comprising a major amount of a residual petroleum fuel oil yielding a corrosive vanadium-containing ash upon combustion and an amount of a compound of a didymium rare earth element sulficient to yield from about 0.5 to about 3 atom weights of didymium element per atom weight of vanadium in said oil.

8. The composition of claim 7, wherein the didymium compound comprises a mixture of didyrnium rare earth elements derived from monazite.

9. The composition of claim 8, wherein the didymium compound is an inorganic compound.

10. The composition of claim 8, wherein the didymium compound is a salt of an acidic organic compound.

11. The composition of claim 10, wherein the acidic organic compound is selected from the group consisting of fatty acids, naphthenic acids and rosins.

12. The composition of claim 11, wherein the acidic organic compound is petroleum naphthenic acids.

13. The composition of claim 11, wherein the acidic organic compound is tall oil.

14. The composition of claim 11, wherein the acidic organic compound is rosin.

References Cited in the file of this patent UNITED STATES PATENTS 2,781,005 Taylor et al Feb. 12, 1957 FOREIGN PATENTS 498,777 Belgium Nov. 14, 1950 502,159 Belgium Apr. 14, 1951 719,069 Great Britain Nov. 24, 1954 306,651 Switzerland July 1, 1955

Claims

1. A FUEL COMPOSITION COMPRISING A MAJOR AMOUNT OF A RESIDUAL PETROLEUM FUEL YIELDING A CORROSIVE VANADIUMCONTAINING ASH UPON CONBUSTION, AND A SMALL AMOUNT OF A COMPOUND OF A DIHYMIUM RARE EARTH ELEMENT SUFFICIENT OT RETARD THE CORROSIVENESS OF SAID ASH.