US2949008A

US2949008A - Residual fuels

Info

Publication number: US2949008A
Application number: US711829A
Authority: US
Inventors: Albert G Rocchini; Charles E Trautman
Original assignee: Gulf Research and Development Co
Current assignee: Gulf Research and Development Co
Priority date: 1958-01-29
Filing date: 1958-01-29
Publication date: 1960-08-16
Anticipated expiration: 1977-08-16

Description

RESIDUAL FUELS Filed Jan. 29, 1958K, Ser. No. 711,829

6 Claims. (Cl. Gil-35.6)

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.

This :application is a continuation-impart of our copending application Serial No. 701,845, tiled December 10, v1957, and assigned to the same assigneeas the instant application and now abandoned. Y

It has been observed that when a residual type fuel oil ,containing substantial amounts Aof vanadium is burned in furnaces, boilers and gas turbines, the ash resulting vfrom combustion of the fuel oil is highly corrosive to .materialseof construction at elevated temperatures and .attacks such parts as boiler tubes, hangers, turbine blades, -and the like. These .effects are particularly noticeable Vin gas turbines. Large gas turbines show promise of becoming an important type of industrial prime mover. Howeven economic considerations based on the efficiency of the gas turbine dictate the useof a fuel for this purpose which is cheaper Vthan a distillate diesel fuel; otherwise, .otheruforms-of powersuch as diesel engines be Vcome competitive with gas turbines. Y l

One of the main problems arising in the use of residual fuel oils in Agasturbines is the -corrosiveness induced by those residual fuelsY containing suficient;v amounts of vanadium to cause .,corrosion. lWhere no vanadium is presentor the amount of vanadium is small, no appreciable corrosion is encountered. While many residual fuel oils as normallyobtained inthe refinery contain so little fvanadium, or none, as to present noV corrosion problems,

such` non-corrosiveV fuel oils are not always available at' .the point where the oil is to be used. In such instance, the cost of transportation ofthe non-corrosive oil to the point of use is often prohibitive, and the residualoil `loses its competitive advantage. These factors appear to militate against the extensive use` of Yresidual fuel oils for gas turbines. VAside f1-om, corrosion, .theformation of deposits lupon the burning of `a, residual'fuel in a gas turbine-may result in unbalance of the turbine blades, `clogging of openings and reduced thermal eiciency of Ythe turbine. p l n ASubstantially identical problems are encounteredwhen using a-solid residual petroleum fuel ontainingsubstantial amounts of vanadium. Thesefuels'are petroleum 'residues obtained by-known methods YofV petroleum re- 'Vning such as'deep vacuum Vreduction of asphaltic crudes toiobtain solid'residues, -visbreaking ofeliquid distillation bottoms followed'bydistillation to obtain solid` residues, coking--of liquidl distillation bottoms, and the like. The solid residues'thus obtained are known variously as petro- -leum pitchesorcokes vand -iind use as fuelsj' Sincen the vanadium contentofvthe original crude oilltends to concentrate in thezresidual fractions,` and since the' processing of atheresidual fractions to `solid residues results in fur,-

f 2 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 burning of -a residual fuel containing substantial amounts of vanadium compounds causes catastrophic corrosion of the turbine blades and other metal parts in a gas turbine. The corrosive nature of the -ash appearsto be due to its vanadum oxide content. such as vanadium oxide (V205), 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 formsv deposits on the parts affected and corrosively reacts with them. yIt 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. f

It has now been discovered that residual petroleum fuels containing vanadium in an amount suflicient to yield a corrosive vanadium-containing ash upon combustioncan be rendered substantially non-corrosive by incorporating therein to form a uniform blend (1) an amount of a vanadium-free magnesium compound yielding about 1 atom weight of magnesium per atom Weight of vanadium in said fuel, and (2) 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. 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 Van apparatus for testing the corrosivity of residual fuel oil compositions.

The .type of residual fuel oils to which the invention is directed is exempliiied 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 from petroleum by ther concentration of the vanadiumin .the solidresidues, Y.

methods known to the art. For example,'residual fuel oils are obtained asliquid 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, yand other conventional treatments of heavy petroleum oils. Residua thus obtained are sometimes diluted with distillate fuel oil stocks, known as cutter stocks, and

Ythe 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 Vas to present no problem of corrosion. The total ash yfrom commercial residual fuel oils usually ranges from about 0.02 to 0.2 percent by weight. The vanadium pentoxide (V205) content of such ashes ranges 'from zero to trace amounts up to about 5 percent by weight yfor 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 vanadiumcontaining solid residual fuels .to which the invention is directed is exemplified by the .coke .obtainedin known manner bythe delayed thermal 2,949,008l Patented Aug. ..16, 196G- Certain inorganic compoundsl of vanadium,

coking or fiuidized 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, kof 578 parts per million.

Any magnesium compound, organic or inorganic, which is free from vanadium is used as the magnesium additive of the invention. Similarly, any organic or inorganic vanadium-free alkali metal compound is employed. The alkali metals include sodium, `potassium, llithium, cesium and rubidium; sodium and potassium `compounds are preferred. Such inorganic alkali metal and magnesium compounds as the oxides, hydroxides, ac'etates, 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. Magnesium oxide and talc are preferred inorganic magnesium compounds. The organic compounds of magnesium and the alkali metals include the oil-soluble and oil-dispersible salts of acidic organic compounds such as: (l) the fatty acids, eg., valerie, caproic, Z-ethylhexanoic, 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., lauryl sulfuric acid; (4) petroleum naphthenic acids; (5) rosin and hydrogenated rosin; (6) alkyl phenols, eg., iso-octyl phenol, t-butylphenol and the like; (7) alkylphenol suliides, e.g., bis(isooctyl phcnol)monosulde, bis(t-butylphenol)disulfide, and the like; (S) 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-butylphenolformaldehyde 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 inely-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 finely-divided materials are more eflicient in forming uniform blendsand 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 eX- ample, in the case of magnesium sulfate, sodium carbonate, and the like, it is not necessary to employ finelydivided materials since, if desired, the additives can be dissolved in Water to form a more or less concentrated solution and the Water solution emulsied 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 Vamounts of the .additives are small, it is desirable to prepare concentrated solutions or dispersions ofthe organic additives in a naphtha, kerosene or gas oil for convenience in compounding.

In the practice of the Yinvention with vanadium-con- :taining 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, emulsiiied 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 Vconcentrate thereofV 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 Vis 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 s1ze.

In the case of either liquid or solid residual fuels, the additives can be separately ffed 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 vto or Vduring 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 meta-l parts to be protected from corrosion.

The magnesium 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. For example, when the magnesium compound is employed in the amount of 1 atom weight of magnesium per atom Weight of vanadium, ordinarily yan amount of alkali metal compound yielding about 1 -atom weight of alkali metal is suicient to reduce the corrosion to negligible amounts.V

'Ihe following examples are further illustrative of `the invention.

EXAMPLE I With a residual fuel oil uniformly blend 0.015 percent vby weight of magnesium oxide 4and 0.11 percent by weight of a solution of sodium ypetroleum naphthenate in naphtha con-taining 7 percent by weight of sodium.Y The residual fuel `oil employed Ihas the following inspection:

Sodium: ppm. of oil 2 The resulting composition has Aan atom weight ratio of magnesium to vanadium of 1:1 and an atom weight ratio `of sodium to vanadiumof v1:11.

A. EXAMPLE 1I Uniformly'blend withithe same residual fuel oil of Example I,Y0.15 percent by weight of a solution of the magnesium soap of tall oil in naphtha containing 6 percent by weight of magnesium and 0.03 percent by weight of potassium carbonate. The resulting fuel oil composition has an .atom weight ratio of magnesium to vanadium of y1:1 and an atom weight ratio of potassium to vanadium of 1:1.

.. l. Y. EXAMPLE III To the same residual -fuel oil of Example I, add and uniformly blend `0.035 percent by Weight of the same talc used in the composition of Example V and 0.02 percent by weight of sodium carbonate. The resulting fuel oil composition has an atom Weight ratio of magnesium to vanadium of 1:1 and an -atom weight ratio of sodium to Vvanadium of 1:1;

In` order Vto test the effectiveness 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 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 I.D. and 0.018 inch O.D. The tip of the nozzle is ground square and allowed to project slightly through an oriice 16 of approximately 0.020 inch diameter. The oriiice 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 l17, preheat coil 18 in tank 12, and air passageways 19 and 20 in the -atomizing head 13. The ycombustion 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 Z3 -has a diameter of 3 inches; the length of the cylinders between the end plates is 81/2 inches. End plate 24 has a central opening 26 into which the atomizing head is inserted. End plate 25 has a one (l) inch opening "27 covered by a bale plate 28' mounted in front of -it to prevent direct blast of llame on the test specimen 29. Opening 27 in end plate 25 discharges into a smaller cylinder 30 having a diameter of 11/2 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 iby means of air inlet 31 into the annulus between cylinders 22 'and 23, thereby preheating the combustion air, and then through three pairs of 1%6 inch tangential air inlets 32 in the inner cylinder 22. The iirst pair of air inlets is spaced 1A inch from end plate 24; the second pair 3%; inch from the rst; 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 100 hours with the rate of fuel feed being 1/2 pound per hour and the rate of atomizing air feed being 2 pounds peflioui. "I'he Ycombustion air entering through air inlet V31is"fed at 25 ypounds 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'molte/n condition at 475 C. After descaling, the specimen isdipped in 6 N hydrochloric acid containing a conventional pickling inhibitor, and is then washed, dried and weighed. 'I'he loss in weight of the Vspeciinenafter descaling is the corros-ion loss.

YTests are conducted in the yapparatus just described using a 25-20 stainless steel asthe test specimen. The 'tests lare run for 100 hours at a temperature of 1450 F. under theconditions described above. Tests are made with the fuel oil compositions of Examples I, V and V I, `with fuel oil compositions similar to those of theseexamples but containing only one of the additives in varying proportions, and with the uncompounded residual fuelf'oil of Example I., The following table shows lthe corrosion and deposits obtained.

.f Table l Y Atom Wt. Corrosion,

Fuel Y Ratm-Addi- Wt.I lossof Deposits, v tive MetalzV Specimen, Mg./Sq.ln.

Mg./Sq.ln.

,Y y m oundedFuel-'of Ex- Ugpl1t- 1, 580 1, 130 Fuei- Sodium N aphthenate. l 21g;

o Fuel Magnesium 0xide 1:1 940 228 D0 2:1 96 145 3:1 25 43 1:1 220 210 0 2:1 79 150 Compounded Fuel of Ex- M .Vzkl ample NV=1;1i i 0 57 Compounded Fuel of Example III (ulfgggg 16 10o It will be seen from the above'table that the magnesium additives and the lalkali metal additives unexpectedly coact to minimize corrosion and deposits. This -is surprising when it is considered that, although the 1ndividual additives tend to reduce corrosion and deposits, they still permit corrosion. 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 magnesium additive used alone requires at least 3 atom weights of magnesium per atom weight of vanadium before minimizing corrosion. With thecombination of additives disclosed, considerably smaller amounts of each additive can be employed and corrosion is nonetheless to negligible amounts. Similar results to those shovwn for the specific additives employed in the examples and in the above table are obtained when using the other magnesium 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:

scope of the appended claims.

We claim:

l. A fuel composition comprising a uniform blend of a major amount of a residual petroleum fuel yielding a corrosive vanadium-containing ash upon combustion, an`

amount of a vanadium-free magnesium compound yielding about 1 atom Weight of magnesium per atom weight of vanadium in said fuel and an amount of a vanadiumfree alkali metal compound yielding about 1 atom Weight Iof alkali metal per atom weight of vanadium `in said fuel.'

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

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

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

5. A fuel composition comprising a uniform blend of a major amount of a residual fuel oil yielding a corm l rosive vanadium-containing ash '-upon combustion, an

amount of talc yielding about l atom Weight of magnesium per atom Weight `of vanadium in said fuel oil and an amount of sodium carbonate yielding abou 1 atom Weight' of sodium per atom Weight of vanadium in said fuel oil.

6. ln a gas turbine plant in which arfuel oil containing vanadium is burned and which includes heat resisting metal-lic parts exposed to hot combustion gases and liable to be corroded by the corrosive Vanadium-containing asn resulting from combustion of said oil, the method of reducing said corrosion which comprises introducing into said plant upstream of said parts a small amount .of a vanadium-free mixture of ,a magnesium compound and an alkali metal `compound, the amount of said magnesium compound being suilicient kto yield about 1 atom Weight of magnesium per atom weight of vanadium in said fuel oil and the amount of said alkali metal compound being -sufiioient to yield about l Vatom weight of alkali metal per atom'weight of vanadium .in said fuel oil.

References Cited in the file of this patent FOREIGN PATENTS 498,777 Belgium Nov. 14, 1950 306,652 Switzerland Apr. 30, 1955 1,117,896 France 7..-- Mar. 5, 1956 UNITED STATES PATENT OFFICE CERTIFICATE 0F vCORRECTION Patent No. 2,949,008 August l6 1960 Albert G Rocchini et al.

It is hereby certified that error appears in the-printed Specification of' the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, lines 13 and l4, strike out "the same talc used in the composition of Example V1 and insert instead N- talc having a magnesium content of 1867 per cent by weight =f=g column lines 14 and l5,l strike out V and VI" and insert instead and lll Signed and sealed this llth day of April 1961.,

(SEAL) Attest:

ERNEST W. sgwlDER ARTHUR W. CROCKER Attesting Officer Acting Commissioner of Patents

Claims

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 INTO SAID PLANT UPSTREAM OF SAID PARTS A SMALL AMOUNT OF A VANADIUM-FREE MIXTURE OF A MAGNESIUM COMPOUND AND AN ALKALI METAL COMPOUND, THE AMOUNT OF SAID MAGNESIUM COMPOUND BEING SUFFICIENT TO YIELD ABOUT 1 ATOM WEIGHT OF MAGNESIUM PER ATOM WEIGHT OF VANADIUM IN SAID FUEL OIL 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 OIL.