US2781005A

US2781005A - Method of reducing vanadium corrosion in gas turbines

Info

Publication number: US2781005A
Application number: US233796A
Authority: US
Inventors: Taylor Tristram Allan; Macfarlane John James; Stephenson Norman
Original assignee: Power Jets Research and Development Ltd
Current assignee: Power Jets Research and Development Ltd
Priority date: 1950-06-28
Filing date: 1951-06-27
Publication date: 1957-02-12
Anticipated expiration: 1974-02-12
Also published as: GB731242A; CH306059A; FR1045851A

Description

Feb. 12, 1957 T. A. TAYLOR ETAL METHOD oF REDUCING VANADIUM coRRosIoN IN GAS TURBINES Filed June 27. 1951 3 Sheets-Sheet l bk; A ttorn eyJ' P61112, 1957 .T. A. TAYLOR' Em. 2,781,005

METHOD OF REDUCING VANADIUM CORROSION IN GAS TURBINES Filed June 27. 1951 3 Sheets-Sheet 2 Ri E 1b.; Aitor-nay.;

Feb. 12, 1957 T. A. TAYLOR ErAl. 2,781,005

METHOD oF REDUCING VANADIUM coRRosIoN. 1N GAS TURBINES 3 sheets-sheet '3' Filed June 27. 1951 oooo'o Invenlars `miA United States Patent C NIETHOD F REDUCING VANADIUM CORROSION iN GAS TURBINES Tristram Ailan Taylor, Countesthorpe, Leicester, .lohn James Macfariane, Cove, Farnborough, and Norman Stephenson, Narborough, near Leicester, England, assignors to Power .lets (Research and Development) Limited, London, England, a British Vcompany Appiication June 27, 1951, Serial No. 233,796

Claims priority, application Great Britain June 28, 1950 16 Ciaims. (Cl. L10-f1) This invention relates to fuel oils containing vanadium and to the treatment and combustion of such oils.

It is desirable from an economic point of view to use natural and low grade residual fuel oils ininternal cornbustion power plant, but it is found that Vsuch yfuels produce an ash which, if it comes `in contact with metals at elevated temperatures, of the order of -65 0 C. and above, causes a greatly increased rate of corrosion, due at least in part to oxidation of the metal. This occurs even inthe case of metals and alloys which 'normal circumstances would be resistant to lheatat such temperatures. lt would appear that there are few, if any, metals or alloys which are able to Vresist corrosion under these circumstances Vfor any substantial Alength of time. This roxidation both weakens the metal by reduction of its cross-section and also reduces its creep and fatigue resistance. It is also found that ceramic and refractory substances are similarly attacked.

lt is found that the acceleratedoxidation is mainly due to the vanadiumcontent of the oil. Low grade residual fuel oils nearly always containa quantity of vanadium in the form of complex vanadium ,compounds which, on combustion decompose to yield vanadium pentoxide. It is believed that the accelerated corrosion is due tothe fact that the vanadium pentoxirde exercises 1a ,uxing action on the protective oxide films ofparts exposed to the combustion gases. In this way the'lm on Y'die surface .of the parts exposed is destroyedfso thatfurthcr oxidation can take place. This effect is ,accelerated at high temperatures of Vtheorder Aof 650 C. and above, ,since the ash and its vanadium ,pentoxide content is in a liquid or semi-liquid state and is thus able to come into intimate contact with the protective film. The problem is thus particularly acute in gas turbine plant since turbine inlet temperatures in excess of 600 C. and ,the use .of ,low grade fuel oil `are both desirable from the point of view of economy. YIn particular 'the blades are subject to high stresses and hence it is highly desirable to provide some means of protection for them. Vlt is found that turbine blades made of iron-base alloys are particularly liable to attack.

According to the invention, .thecorrosion of parts in high temperature plant due to the vanadium content Vof fuel oils being burnt therein is reduced Vby the addition of an additive with which the vanadium `will react inv preference to the material of said parts. I

Preferably the additive is selected from ,thegroup consisting of: Y

(a) Magnesium and zinc.

(b) Oxides of such metals.

(c) Compounds of such metals yielding the voxide at combustion temperatures;

In the preferred form of .the invention, the additive is introduced into the fuel before use. lfilternatively =4it can be added separately immediatelyprior .to Aor duringcom- Patented Feb. 12, 1957 'ice bustion, or even subsequent to combustion, but upstream of the parts exposed to corrosion.

It is believed that in the resulting reaction, the vanadium pentoxide content of the oil tends to combine with the additive to form a stable vanadate in preference -to attacking the oxide film ofthe parts exposed to corrosion. Moreover the resultant ash is normally of a dry friable nature and does not tend to adhere to such parts.

The effective part of the additive appears in each case l0 to be the oxide. Thus if a metal is added to the oil, complex compounds are formed which break down at combustion temperatures to yield the oxide. lf the metal itself is added during combustion it will immediately burn to form the oxide. Alternatively in either case a suitable metallic compound which will yield the oxide at combustion temperatures may be used.

The invention will now be more fully described with reference to specific examples and to the accompanying drawings of which:

Figure l shows a test apparatus in which conditions in a gas turbine plant can be simulated.

Figure 2 shows curves obtained vin a test carried out in the apparatus of Figure 1.

Q Figure 3 shows a gas turbine plant using residual fuel -0 oil.

Figure 4 is a detail of the arrangement of Figure 3.

The eiciency of various additives in neutralising the corrosive effect of vanadium on various alloys can be assessed by laboratory tests now described. The additive and vanadium pentoic'de, both inthe form of a line powder are roasted together and mixed with a suitable binder, such as Canada balsarn, to form a smooth paste. The paste is then spread over the surface of a test specimen which consists of a cylindrical rod of the alloy in 30 question. The binder is .burnt oit and the specimen is maintained at high temperature in a furnace for a suitable period of time. The specimen can then be weighed and analysed to ascertain the extent and nature of the Vcorrosion.

Example I Pastes of various compositions were applied to specimens of a heat resisting nickel-base alloy having the following composition.

The specimens were maintained at a temperature of 700 C. for 100 hours, and the table below shows the amounts of alloy oxide formed in veach case. The rst column shows the equivalent composition of the paste and the second column shows the weight gain in milligrams due to oxide formation, there being one milligram 6g of vanadium pentoxide in .the paste applied per square centimeter of surface of the specimen.

1 Uneoated 0.5 ings.

The comparative amounts of corrosion with no coating of paste and'with a coating of `vanadium pentoxide `only are given for comparison. The figure for zinc is shown as being negative. This is Vdue to the fact that the ash formed tends to ake off the specimen duel to its /friable A nature. In each case the corrosion is reduced to au extent comparable to the natural corrosion which would take place in the absence of vanadium.

V Although from the above series of testsrit would appear that a ca-lcium compound would be the mostsuitable additive from an economic point ofl View, it 'is' found in practice that certain difficulties arise in the use of this element. Most residual fuel oils also contain a certain amount of sulphur and there isa tendency for the calcium to react with the sulphurV to form calcium sulphate in preference to Iforming a vanadium compound. Hence calcium will only be suitable for use with'sulphur free oils, or in cases where some means of removing the sulphur is used. It is found howeverV that zinc and magnesium are not subject to this disadvantage, probably because theirV sulphates are unstableV at thetemperatures concerned. f Y

It will be seen that the composition of the paste in each case corresponds to the orthovanadate of the metal concerned; i. e. a salt having the formula MSOJOQZ for a divalent element such as zinc or magnesium. lf a smaller quantity yof the additive is introduced, the rate of corrosion is not greatly reduced, probably because a certain amount of free vanadium pentoxide willstill be present inthe ash. v

A test approximating more closely to the conditions actually'existing in a gas turbine plant will now be described with reference to Figure l of the accompanying drawings.

The test rig consists essentially ofY a combustion chamber adapted to burn heavy fuel oil and a test section containing dummy blades of the material to be tested. Cornpressed air is blown under pressure and preheated if necessary through duct 1 into the primary combustion zone 2 of a combustion chamber 3 of the cyclone or vortex type. This chamber is of the type described in British Patent No. 639,468 and will'not therefore be further described here. The combustion gases leave through an axial outlet 4 and then passes through vloute-5 into Vthe rectangular test section 6. Mounted within this sect-ion are test pieces 7 lwhich are similar in shape to normal gas turbine blades but are uncambered. The combustion gases are then discharged to atmosphere.

With this apparatus heavy fuel oil of any desired cornposit-ion can be burnt. After a test of suitable duration, the dummy blades can be removed and weighed and analysed and hence the extent and nature of the corrosion ascertained. 1

Example II In a series of tests using the above apparatus, a fuel oil having a viscosity of 100 F. or 536 Redwood seconds and the following composition was used.

lIt was found that this ash began to melt at a temperature of about 650 C.

The dummy blades were of the nickel base heat resisting nickel-base alloy mentioned above.

' This fuel was burnt in the apparatus of Figure l and the amount of oxidation of the dummy blades ascertained by analysis. The experiment was repeated with zinc naphthenate added to the oil in a quantity giving the equivalent of 3ZnO.VzO5. In each case the test duration was 50hours. 1 Y

The resulting rates ofoxidation are shown in the curves A and B/of Figure 2. The* ordinate represents the alloy oxide formed in mgs./sq. cm./hr. and the abscissa the blade temperature in degrees C. The upper curve A represents the combustion of fuel without the additive and the lower curve B with the additive. lt will'be seen for example that at 750 C., the corresponding rates of oxidation are respectively 0.1755 and 0.0125. The additive thus reduces the corrosion to about 7% of its normal value, and it is believed that this approximates to the rate of corrosion which would loccur even if no vanadium were present.

Gther organic compounds such as the corresponding oleate, stearato, or linolcate could be used, all being soluble in oil. From an economic point of View it would be preferable to add the oxide, hydroxide or carbonate dissolved `or suspended in oil, water or other `liquid medium. in some cases it is possible to add the powdered metal itself, since for example, certain residual oils will attack zinc directly to form complex organic compounds.

Magnesium can be added in the same way. Y

As stated above the additive may alternatively be directly introduced-into the combustion chamber or Yinto the vicinity of the parts exposed to corrosion. This applicat-ion of the invention is illustrated with reference to Figures 3 and 4 of the drawings. The compressor and turbine in Figure 3 are shown partly in section.

Figure 3 shows diagrammatically a gas turbine plant suitable for burning residual fuel oil. Air enters through duct 1-1 as indicated by arrow A and then passes into the axial flow multistage compressor 12. The compressor rotor 13 is mounted in bearing 14 and is connected by shaft 15 to the turbine rotor 16. The compressed air passes from the compressor 12 through

ducting

17, 18 and 19 into a cyclone or vortextype ycombustion chamber 20, which twill be more fully described below. The combustion gases then pass through an annular duct 21 to the turbine 22 and are discharged through exhaust duct 23.

The combustion chamber 20 is generally of the type described in said British Patent No. 639,468, and comprises a primary flame tube 31, shown in section in Figure 4, leading tangentially into a vortex chamber 32. The air is delivered from the duct 19 as indicated by arrow B, and the flow is then divided by an inner duct33 supported co-axially within the flame tube by rings of

vanes

34 and 35. Part of the airis delivered directly into the combustion zone 36 of the ame tube through the annular space v'between the duct 33 and the wall of the ame tube, whilethe remainder passes through the interior of the duct 33. Mounted within this duct is a perforated substantially frusto-conical ilame stabilizing baie 37. Part of the remainder of the air passes through swirl vanes 38 at the Yupstream end of the baie37'while the rest passes through the holesv in the bafe.

Since heavy residual oil Iis to be used, it is desirable to inject the fuel by means of an air blast burner 39, by which is meant a burner in which atomisation ofthe fuel is effected by. meansV of a blast of compressed air. Fuel and compressed air are respectively supplied to the burner through pipes'40 and 41.

As explained above there is a tendency for the turbine rotor and

stator blades

24 and 25 to be corroded by the vanadium content of Ythe fuel. To reduce this corrosion,` a suitable additive is introduced into the air blast through branch pipe 42 from a tank 43, the quantity introduced being determined by valve 44. The additive is thus entrained in they air and mixes with the fuel in the combustion chamber to neutralise the vanaditun as explained previously. Similar additivesmay be used to those which are mixed directly with the oil prior Vto combustion.

The introduction of additive into the oil before use'is also shown in Figure 4. The tank 43 containing the additive is connected to the fuel tank 45 by a pipe 46. After the fuel tank 45 is lled, a suitabler quantity of the additive is allowed to run in from tank 43by open.

ing vals/e747. In this case it will be unnecessary to introduce additive into the air blast.

We claims 1.*r'i lalgas turbine plant in which fuel oil containing vanadium 'and sulphur is burnt and which includes heatresisting metallicV 'parts exposed to the resultant stream of hot combustion gases at a temperature in excess of 650 C. and"normally liable to be corroded by the vanadium pentoxide content of the ash resulting from the combustion of said oil, the method of reducing said corrosion comprisin'gthe step of introducing into the plant upstream of saidparts an additive selected from the group consisting of magnesium and zinc oxides and magnesium and zinc compounds yielding the oxide at the temperature of said hot combustion gases, the quantity of additive introduced being such that the molecular ratio of the minimum oxide content thereof to the vanadium pentoxide content of the ash is 3 to l.

' 2. In a gas turbineplant in which fuel oil containing vanadium and sulphur is burnt and which includes heatresisting: metallic l ptartsexpose'd to the resultant stream of hot combustion gases at atemperature in excess of 650 C. and normally liable to be corroded by the vanadium p entoxide content of the ash resulting from the combustion of said oil, the method of reducing said corrosion comprising the step of introducing into the plant upstream of saidparts an oxide of a metal selected from the group consisting of magnesium and zinc, the minimum quantity of .oxide introduced b eing related to the quantity of vanadium pentoxide inthe ash in the molecular ratio 3 to l. T3. -ln a gas turbine plant in which fuel oil containing vanadium and sulphurisburnt and which includes heatresistingV metallicA parts exposed to the resultant stream of hot combustion gases at a temperature in excess of 650 C. and normally liable to be corroded by the vanadium Vpe'n'toxide content of the ash resulting from the combustion of said oil, the method of reducing said corrosion comprising the step of introducing into the plant upstream of said parts an additive selected from the group consisting of zinc oxide and zinc compounds yielding the oxide at the temperature of said hot combustion gases, the quantity of said additive introduced being such that the molecular ratio of the minimum zinc oxide content thereof to the vanadium pentoxide content of the ash is 3 to l.

4. In a gas turbine plant in which fuel oil containing vanadium and sulphur is burnt and which includes heatresisting metallic parts exposed to the resultant stream of hot combustion gases at a temperature in excess of 650 C. and normally liable to be corroded by the vansdium pentoxide content of the ash resulting from the combustion of said oil, the method of reducing said corrosion comprising the step of introducing zinc oxide into the plant upstream of said parts, the minimum quantity of zinc oxide introduced being related to the quantity of vanadium pentoxide in the ash in the molecular ratio 3 to 1.

5. A residual fuel oil containing sulphur and a small quantity of vanadium in the form of naturally occurring vanadium compounds which give rise to the presence of a quantity of vanadium pentoxide, V205, in the ash resulting from the combustion of said oil, which ash is normally liable to cause corrosion of heat-resisting metallic parts exposed to the combustion products of the oil at temperatures in excess of 650 C. and further containing a quantity of the oxide of a metal M selected from the group consisting of magnesium and zinc, whereby said corrosion is reduced, the minimum quantity of the oxide, MO, and the quantity of the Vanadium pentoxide in the ash being related in the proportion 3MOzV2O5.

6. A residual fuel oil containing sulphur and a small quantity of vanadium in the form of naturally occurring vanadium compounds which give rise to the presence of a quantity of vanadium pentoxide, V205, in the ash resulting from the combustion of said oil, which ash is normally liable to cause corrosion of heat-resisting metallic partsrexpoisejd` to .the combustion ,products ofv the oil at temperatures in excess of '650 C. ,ant/:l further containing Ya'quantity of lzinc oxide whereby said corrosionis reduced, the proportion of the minimum quantity of zinc oxide to the quantity of vanadium pentoxide in the ash being 3ZnOzV2O5.

7. A residual `fuel oil containing sulphur and a small quantity of Vanadium in the form of naturally occurring vanadium compounds which give rise to the presence ot a .quantity of vanadium pentoxide, V205, in the ash resuiting from the combustion of said oil, which ash is normally liable to cause corrosion of heat-resistingmetallic parts exposed to the combustion products of the oil at temperatures in excess of 650 C. and further containing a quantity of magnesium oxide whereby said corrosion is reduced, the proportion of the minimum` quantity of magnesium oxide to the quantity of vanadium pentoxide in the ash being 3MgO:V2O5.

.8. A fuel oil containing sulphur and a small quantity of vanadium in the form of naturally occurring vanadium compounds which give rise to the presence of a quantity of vanadium pentoxide in the ash resulting from the combustion of said oil, which ash is normally liable to cause corrosion of heat-resisting metallic parts exposed to .the combustion products of the oil at temperatures in excess of 650 C. andrfurther containing a quantity of a compound yielding at'temperatures in excess of 650 C. the oxide of a metal selected from the group Aconsisting of magnesium ^and zinc whereby said corrosion is reduced, the molecular ratio of the oxide content of the cornponnd to the quantity of vanadium pentoxide in the ash ,being at least '5 to l.

9. In a gas turbine plant in whichvfuel oil containing vvanadium and sulphur is burnt and which includes heat resisting metaly parts exposed to the resultant stream of hot combustion gases at a temperature in .excess of 650 C. and normally liable to be corroded by the vanadium pentoxide content of the ash resulting from combustion of said oil, the method of reducing said corrosion comprising the step of introducing into the plant upstream of said parts a compound yielding at temperatures in excess of 650 C. the oxide of a metal selected from the group consisting of magnesium and zinc, the quantity of said compound introduced being such that the molecular ratio of the minimum oxide content thereof to the vanadium pentoxide content of the ash is 3 to l.

l0. A method as claimed in claim 9 wherein said compound is an oil-soluble organic compound of a metal selected from the group consisting of magnesium and zinc.

ll. in a gas turbine plant in which fuel oil containing vanadium and sulphur is burnt and which includes heat resisting metal parts exposed to the resultant stream of hot combustion gases at a temperature in excess of 650 C. and normally liable to be corroded by the vanadium pentoxide content of the ash resulting from the combustion of said oil, the method of reducing said corrosion' comprising the step of introducing into the plant upstream of said parts a magnesium compound yielding magnesium oxide at temperatures in excess of 650 C., the quantity of said compound introduced being such that the molecular ratio of the minimum magnesium oxide content thereof to the vanadium pentoxide content of the ash is 3 to l.

l2. In a gas turbine plant in which fuel oil containing vanadium and sulphur is burnt and which includes heat resisting metal parts exposed to the resultant stream of hot combustion gases at a temperature in excess of 650 C. and normally liable to be corroded by the vanadium pentoxide content of the ash resulting from the combustion of said oil, the method of reducing said corrosion comprising the step of introducing into the plant upstream of said parts a zinc compound yielding Zinc oxide at temperatures in excess ot 650 C., the quantity of said compound introduced beino such that the molecular ratio of the minimum zinc oxide content thereof to the vanadium pentoxide content of the ash is 3 to 1.

13. In a gas turbine plant in whichfuel oil containing vanadium and sulphur is burnt and which includes heat resisting metal parts exposed to the resultant stream of hot combustion gases at a temperature in excess of 650 C. yand normally liable to be corroded by the Vanadium Vmolecular ratio of the minimum magnesium oxide content thereof to the vanadium pentoxide content of the ash is 3 to l.

14. In a gas turbine plant in which fuel oil containing vanadium and sulphur is burnt and which includes heat resisting metal parts exposed to the resultant stream of hot combustion gases at a temperature in excess of 650 C. and normally liable to be corroded by the vanadium pentoxide content of the ash resulting from the combustion of said oil, the method of reducing said corrosion comprising the step of introducing magnesium oxide into the plant upstream of said parts, the minimum quantity of magnesium oxide introduced being related to the quantity of vanadium pentoxide in the ash in the molecular ratio 3 to 1.

l5. A residual fuel oil containing sulphur and a small quantity of vanadium in the form of naturally occurring vanadium compounds which give rise to the presence of a quantity of vanadium pentoxide in the ash resulting from the combustion of said oil, which ash is normally liable to cause corrosion of heat-resisting metallic parts exposed to the combustion products of the oil at temperatures in excess of 650 C., and further containing a quantity of a zinc compound yielding zinc oxide at temperatures in excess of 650 C. whereby said corrosion is reduced, the molecular ratio of the zinc oxide'content of the compound to the quantity of vanadium pentoxide in the ash being at least 3 to 1.

16. A residual fuel oil containing sulphur and la small quantity of vanadium in the form of naturally occurring vanadium compounds which give rise to the presence of a quantity of vanadium pentoxide in the ash resulting from the combustion of said oil, which ash is normally liable to cause corrosion of heat resisting metallic parts vexposed to the combustion products of the oil at temperatures in excess of 650 C., and further containing a quantity of a magnesium compound yielding magnesium oxide at temperatures in excess of 650 C. whereby said corrosion is reduced, the molecular ratio of the magnesium oxide content of the compound to the quantity of vanadium pentoxide in the ash being at least v3 to l. Y

References Cited in the iile of this patent UNITED STATES PATENTS 1,350,268 vSkinner V- Aug. 17, A1920 1,666,523 Bailey Apr. 17, 192s 2,401,285 Woodward et al. May 28, 1946 2,552,851 Gist May 15, 1951 2,579,614 Ray Dec. 25, 1951 FOREIGN PATENTS 445,506 Great Britain Apr. 14, 1936 496,692 Great Britain Dec. 5, 1938 OTHER REFERENCES Symposium on Corrosion of Materials at Eelevated Temperatures, Special Tech. pub. No. 108 pub. by American Society for Testing Materials, presented June 26, 1950, pp. 97-102, 44-6sv.

Claims

1. IN A GAS TURBINE PLANT IN WHICH FUEL OIL CONTAINING VANADIUM AND SULPHUR IS BURNT AND WHICH INCLUDES HEATRESISTING METALLIC PARTS EXPOSED TO THE RESULTANT STREAM OF HOT COMBUSTION GASES AT A TEMPERATURE IN EXCESS OF 650*C. AND NORMALLY LIABLE TO BE CORRODED BY THE VANADIUM PENTOXIDE CONTENT OF THE ASH RESULTING FROM THE COMBUSTION OF SAID OIL, THE METHOD OF REDUCING SAID CORROSION COMPRISING THE STEP OF INTRODUCING INTO THE PLANT UPSTREAM OF SAID PARTS AN ADDITIVE SELECTED FROM THE GROUP CONSISTING OF MAGNESUIM AND ZINC OXIDES AND MAGNESIUM AND ZINC COMPOUNDS YIELDING THE OXIDE AT THE TEMPERATURE OF SAID HOT COMBUSTION GASES, THE QUANTITY OF ADDITIVE INTRODUCED BEING SUCH THAT THE MOLECULAR RATIO OF THE MINIMUM OXIDE CONTENT THEREOF TO THE VANADIUM PENTOXIDE CONTENT OF THE ASH IS 3 TO 1.