US2631929A - Stabilizing vanadium containing fuel oils - Google Patents

Description

Patented Mar. 17, 1953 UNITED STATES i TENT OFFICE STABILIZING' VANADIUM. CONTAININ G FUEL OILS No Drawing.

Application December 6, 1949, Se-

rial No. 131,506. In Great Britain October 21,

2 Claims.

The present invention relates to improved'hydrocarbon fuel oils of the type which contain vanadium compounds, which compounds are liable to be deposited as solid vanadium pentoxide on combustion.

Heavy residual fuel oils have, for a long time, been used in steam-raising boilers and the like. Combustion systems of this type are comparatively crude and the deposition of ash from the fuel inside the system, while reducing its overall efficiency, is not a problem of major importance. More recently residual fuels have been proposed for use in more sensitively adjusted systems such. as gas turbines and diesel engines, and in systems such as these where the tolerance between moving parts is small and where restriction to gas flow must be avoided, the build-up of deposits'is a serious problem.

Residual fuel oils from certain crudes, especially Venezuelan, contain substantial amounts of vanadium. While some of the ash-forming constituents are present as solid impurities and may be largely removed by such methods as filtration or centrifuging, it appears that the vanadium is present in oil-soluble form, probably as vanadium naphthenates, and accordingly cannot be removed by simple mechanical methods;

When such fuels are burnt in boiler furnaces through. atomizing burners of conventional type, it is found that deposits containing a very large proportion of vanadium pent'oXide are formed in the system. These deposits are undesirable since they reduce the thermal emciency and probablyhelp to catalyze the reaction 2SOz+Oz- 2SO3, which is generally considered to be the cause of flu gas corrosion. Nevertheless, the deposits may be cleaned off periodically without undue difiiculty, and their presence does not prevent the furnace from working.

In contrast to this, when. vanadium-containing oils are burnt in gas turbines or diesel engines. the deposits tend to build up on the turbine. blades or round the exhaust valves respectively, and in due course this may reduce the eificiency of the engine to an extent which necessitates dismantling and cleaning it. Furthermore, with. high vanadium fuels this. necessity may arise-with uneconomic frequency.

In summary, therefore, the. presence of Vanadium compounds in residual fuels is alway disadvantageous and the disadvantages become more pronounced as the degree of precision of the equipment in which they are used increases.

The object of the present invention is to provide an improved fuel in which this disadvantage 2 is alleviated or obviated altogether, and the useof which will tend to remove existing vanadium oxide deposits when used in equipment in which they have already been formed, and accordingthereto there is incorporated in the vanadiumcontaining fuel oil a minor proportion of an oilsoluble organic halogen compound. Also included within the scope of the invention is the method of operating combustion apparatus in which vanadium-containing fuel oil is burnt which comprises carrying out the combustion in the presenceof a minor proportion of an oil-soluble organic halogen compound. In this method of opcrating there may be used the improved fuel already'described, or the vanadium-containing fuel may be used unblended, and the organic halogen. compound, e. g., in the form of a relatively concentrated solution in mineral oil, injected into-thefuel system either before or into the combustion: chamber, the main thing being to ensure that the halogen compound is present during the actual combustion of the fuel. As a modification of: the process, volatile inorganic compounds such as HCl could be employed in this manner.

The halides and oxyhalides of vanadium are reasonably volatile at the combustion temperatures involved (QM-1200" F.) and it appears that they are probably formed in preference to vanadium oxide, provided that the halogen is present during the combustion. While it is not intended to be bound by the accuracy or otherwise of any theory put forward, it is considered that injection of the halogen compound at a later stage of the combustion. cycle, or in other. words into the hot exhaust gases would be considerably less eflici'ent. Nevertheless, particularly in thecase of furnaces, there maybe no clear out line of demarcation between combustion and flue gases, and it is within the scope of the present invention to inject the halogen compound into'the gas stream at any point where the temperature is sufficiently high to cause substantial scavenging of the vanadium. As already indicated, however, it is preferred to have the halogen present inthe fuel before combustion.

The amount of halogen compound to. beadded will depend upon the amount of vanadium present and in general should be in excess of the amount theoretically required. At the sametima. the question of corrosion of the turbine or furnaceshould be considered, so that excessive. amounts of, halogen should. not be used. For any normal fuel it will be found that an amount of additive equivalent to /2 chlorineby weight will provide a substantial theoretical excess, and'that quantities of the order of 0.1% or even less will still provide ample halogen for eifective scavenging. Owing to the low cost of fuel oil, it is desirable that the amount of additive be kept as low as practicable, and for the same reason it is preferred to use relatively available highly halogenated compounds such as carbon tetrachloride, ethylene dichloride, chloroform and hexachlorethane. Other compounds such as chlorobenzenes may be used but the aliphatic compounds appear to be more effective. While the use of halogens other than chlorine is theoretically practicable, they are undesirable on economic grounds, and their physical properties are less wel1 suited to the purpose of the invention than are those of the chlorides and oxychlorides.

Preliminary laboratory tests indicated that the reaction of organic halogen compounds, of the type mentioned above, with vanadium pentoxide started below red. heat and became more vigorous as the temperature was increased to red heat. In order to confirm that this result was representative of what would occur in practice, a pair of experimental runs were made on an open-cycle gas turbine. In such a turbine, the combustion gases pass through the turbine system, in contrast to a closed cycle turbine in which the operating medium is hot air. When run on gas oil, the unit can be run more or less indefinitely with satisfactory results.

For test, there was selected a fuel having a high ash content with the ash preponderantly vanadium. The fuel, a heavy fuel oil, had the following characteristics:

Specific gravity 0.9634 Redwood viscosity at 100 F secs 966 Ash "per cent 0.06 Sulphur do 2.2 Ash analysis:

Vanadium as V205 per cent 81.8 Iron as F8203 do 5.6

Nickel, calcium and sodium not determined In the first run, this fuel was used without any additive and starting with a clean turbine. The test terminated after hours running, with a steady power drop, which, when the test finished had reached (i. e., the final power output,

was of the initial power output).

On openin up the turbine for inspection, it

Deposit on Deposit on 151: and 2nd 3rd and 4th l'OW blades row blades Vanadium as V105 60.1%. Iron as FezOa 5.5%. Nickel as NiO. 4.3%. Calcium as CaO 14.3%. Sodium as NazO 8.3%. Sulphate as SOL. 8.3%. Moisture 4 Present.

From this result it will be quite apparent that the presence of the vanadium in the fuel oil has 4 rendered the turbine virtually inoperative in as short a period as 30 hours.

The turbine was then cleaned and the test run Was repeated using the same fuel but with the addition of /2% by weight of carbon tetrachloride. This additive has the merits of high chlorine content and ready availability, but its boiling point is rather low if the fuel is to undergo prolonged storage.

Using this modified fuel, the turbine ran perfectly normally for hours with no measurable power drop. Since it Was considered that any potential adverse effects would have begun to show themselves after 70 hours running, and since there was no trace of any such effect, the test was stopped deliberately after the '70 hours and the turbine opened for inspection.

In comparison with the first test the amount of deposit was extremely small and confined to the first row of stator and of rotor blades. Furthermore, What deposits there were on the blades were flaky and loose. No corrosion due to halogen was observed. For comparison with the previous deposits, analysis of the deposit from the first row of stator blades is given below:

Vanadium as V205 per cent 77.1 Iron as F6203 dO 3.6 Nickel as NiO d0- 5.1 Calcium as CaO do 1.7 Sodium as NazO do 2.1 Sulphate as S03 do 8.4 Chloride as Cl do 1.1 Moisture Present Owing to the construction of the turbine and the nature of the deposits it was not feasible to conduct the test on quantitative lines and relate the quantity of vanadium deposited on the engine in each run to that contained in the fuel burnt during the run. Nevertheless it was obvious to the eye that the amount of deposits in the second run was a, very small fraction of that of the first run, despite the fact that over twice as much fuel was burnt. In addition, there is the incontrovertible fact that in the first run, the engine was forced to a virtual standstill after only 30 hours running, whereas the second run could apparently have continued indefinitely.

It will be clear from this test that the improved fuel of the present invention does most effectively suppress vanadium deposition, and that equally beneficial results would be experienced when using it in steam boilers or diesel engines. When used for diesel engines,. in particular marine diesels, it is desirable that'the fuel should also be centrifuged (e. g., treated in a centrifugal purifier and/or clarifier) to remove oil-insoluble matter. Furthermore, when'used for gas turbines or furnaces it may be desirable to inject liquid water into the system periodicallyin order to remove deposits, primarily consisting of sodium salts, which may have built up.

What is claimed is:

1. A fuel composition consisting of a vanadiumcontaining heavy fuel oil and 0.5% by weight of an oil-soluble halogen compound chosen from the class consisting of carbon tetrachloride, ethyl ene dichloride, chloroform and hexachlorethane; 2. Composition according to claim 1 in which the halogen compound is carbon tetrachloride.

THOMAS CHARLES GORDON THORYPE. EDWIN MATHIESON DODDS.

(References on following page) 8 7 REFERENCES CITED Number Name Date Th follown references are of record in the 2,213,281 De Bidder 15, 1940 file :i this p at ent: 2,4 1,751 Bro-ggi May 18, 1928 2,460, L 1, 19 9 UNITED STATES PATENTS 5 yons Feb Number Name Date FOREIGN PATENTS 238,867 Draper Mar, 15, 1881 um r Country Date 1,098,412 Shaw June 2, 1914 ,506 Great Britain Apr. 14, 1936 1,637,007 North July 26, 1927 9 ,692 Great Britain Dec. 5, 1938 2,078,958 Lysholm May 4, 193 10

Claims (1)

1. A FUEL COMPOSITION CONSISTING OF A VANDIUMCONTAINING HEAVY FUEL OIL AND O.5% BY WEIGHT OF AN OIL-SOLUBLE HALOGEN COMPOUND CHOSEN FROM THE CLASS CONSISTING OF CARBON TETRACHLORIDE, ETHYLENE DICHLORIDE, CHLOROFORM AND HEXACHLORETHANE.