WO2001098437A1

WO2001098437A1 - Use of nickel compounds as vanadium corrosion inhibitors

Info

Publication number: WO2001098437A1
Application number: PCT/FR2001/001681
Authority: WO
Inventors: Michel Moliere; Emmanuel Rocca; Pierre Steinmetz
Original assignee: Ge Energy Products France Snc
Priority date: 2000-06-19
Filing date: 2001-05-30
Publication date: 2001-12-27
Also published as: US20030159338A1; FR2810341A1; CN1271179C; AU2001274160A1; CN1330134A; FR2810341B1; EP1292656A1; MA25946A1

Abstract

The invention concerns inhibition of vanadium corrosion of thermal equipment materials burning vanadium-contaminated liquid fuels using nickel compounds. The invention is applicable in particular to liquid fuel combustion in gas turbines.

Description

Use of nickel compounds as inhibitors of vanadic corrosion

The present invention relates, in general, to the inhibition of vanadic corrosion of thermal equipment materials burning liquid fuels contaminated with vanadium.

It turns out to be economically interesting to be able to exploit medium quality oil extracts, such as for example products variously contaminated with impurities.

The presence of organic vanadium compounds in liquid fuels burned in various thermal equipment, such as boilers, diesel engines, gas turbines, etc. , is likely to cause high temperature corrosion of metallic materials in contact with combustion gases. This so-called vanadic corrosion can be more or less severe depending on the type of metal or alloy of the thermal equipment, the very type of this thermal equipment, the operating temperature range, the duration and the operating conditions.

This corrosion is caused by the formation in combustion gases of low-melting vanadic derivatives, such as vanadium pentoxide (N ₂ O ₅ ) (pure vanadic corrosion), and eutectic mixtures of N ₂ O ₅ -Νa -SO. (vanadium-sodium corrosion) capable of inducing, under the temperature conditions prevailing on the surface of the metal parts concerned, electrochemical attacks developing in the medium of molten electrolyte and in the presence of oxidants, in particular the oxygen contained in the fumes and sulfate ions formed from the fuel sulfur. As potassium has a corrosive effect similar to sodium, the term "sodium" will mean in the following description "sodium or potassium". Metallic materials are subject to two main corrosion mechanisms:

- Type I corrosion, or high temperature corrosion, which typically occurs at temperatures between 800 and 900 ° C. - Type II corrosion, or corrosion at low temperature, which typically occurs at temperatures between 550 and 750 ° C.

Type I corrosion is an acid attack in a hot oxidizing environment of metallic materials by molten electrolytes such as those rich in vanadium pentoxide. Type II corrosion is generally associated with the formation of eutectics comprising Na ₂ SO ₄ and another metal (eg vanadium and cobalt). In most thermal equipment, there are two types of corrosion risks. Indeed, it should be noted that sodium sulphate is generally present in the form of traces in thermal equipment. This sodium sulphate results from the reaction between the sodium contained in the combustion air and the sulfur derivatives present in the fuels. Thus, in a gas turbine comprising several successive stages, the first stage of the turbine is in contact with the combustion gases at high temperature and is exposed to type I corrosion, while the last stage sees combustion gases pass less hot and is exposed to IL-type corrosion. To fight against vanadic corrosion in gas turbines, it is essential to master the two corrosion mechanisms.

The corrosive power of these vanadic compounds can be inhibited by chemically "trapping" N ₂ O ₅ within refractory compounds. This removes the corrosive molten electrolyte medium. The classic vanadium inhibitors are represented by the aline-earth salts, such as the calcium salts and the magnesium salts, the latter being the most commonly used. Under certain conditions of temperature and dosage of the inhibitor, the vanadium forms with it refractory alkaline earth orthovanadates, of the M ₃ N ₂ O _{g type} , where M represents an alkaline earth metal.

The dosage of the inhibitor must be sufficient to allow all of the vanadium present in the fuel to be trapped and avoid the formation of vanadates of lower stoichiometry, such as pyro vanadates (M ₂ N ₂ O-) or metavanadates (MN ₂ O ₆ ), which are insufficiently refractory to ensure the targeted inhibition effect.

The vanadates resulting from this inhibition process produce ash suspended in the combustion gases, part of which is deposited on the walls of the combustion chambers and of the components of the combustion apparatus situated downstream thereof. This causes a gradual fouling of the combustion apparatus as and when it is operated and results in a correlative and progressive loss of its energy performance.

Also, in order to ensure an adequate exploitation of the equipment treated with these vanadic inhibitors, it is essential that these deposits (1) are formed in minimal quantities and (2) can be eliminated as completely as possible, without loading the economic balance of the exploitation. Thus, the cost of the cleaning operation and the downtime of the equipment must be minimal.

Two cleaning methods are commonly used, notably in the case of gas turbines, dry cleaning and washing with water. Dry cleaning consists in introducing into the equipment kept in operation a slightly abrasive material, free from corrosive compounds and without ash.

In water washing, hot water is circulated inside the turbine, the flames being extinguished but the rotor being rotated at reduced speed to ensure mixing of the surfaces to be cleaned. The dissolution of the sulfated phase leads to the mechanical destabilization of all the insoluble solid phases associated with it in the deposit, in particular the alkaline earth vanadates. The washing water results in the deposit in partially dissolved form and partially in suspension therein.

In what follows, magnesium is taken as an example of a classic inhibitor because, its sulfate being very soluble, it is more widely used industrially than calcium, for example, whose sulfate is poorly soluble. The formation of magnesium sulphate, in parallel with that of orthovanadate, requires that in order to "trap" all of the vanadium, a large excess of magnesium is provided relative to the stoichiometry of the reaction with, in practice, a ratio mass of vanadium magnesium greater than or equal to 3.

This excess consumption of inhibitor leads to a direct additional cost of operation.

In addition, magnesium orthovanadate is not very stable in the presence of sodium with which it reacts to form salts with low melting points. This leads to increasing the dosage of magnesium in the presence of sodium. Thus, a mass ratio of magnesium to vanadium of 10 is required when the sodium contamination represents 20% of the mass vanadic contamination.

Furthermore, there is a faster fouling of the combustion equipment, leading to an accelerated degradation of performance and the need for more frequent cleaning, especially with water, to ensure adequate operation.

Another drawback linked to the use of conventional inhibitors based on alkaline earth metals, and in particular on magnesium, relates to the "de-scaling" of the thermal equipment used. We hear by

"derating" the fact that the flame temperature of gas turbines subjected to such inhibition treatment must be reduced compared to the nominal value of the model of gas turbine under consideration. The flame temperature is defined as the temperature of the hot gases at the inlet of the first stage of movable blades of the turbine and constitutes one of the parameters conditioning in essence the energy performance of the turbine.

The reason for this "derating" is due to the fact that at high temperatures, there is a desuif atation of magnesium. Knowing that the rate of desulfation, on the one hand, and the rate of desulfation at equilibrium of the reaction, on the other hand, increase with temperature and that the magnesium oxide, product of desulfation, is moreover insoluble in water, it happens that beyond a certain value of flame temperature and a certain duration of continuous operation, the proportion of sulfate remaining in the deposit becomes insufficient to ensure the correct removal of the deposit by washing with water.

Currently, combustion in gas turbines of fuels contaminated with vanadium and using magnesium as an inhibitor, results in limiting the flame temperature to around

1100 ° C.

The need to limit the flame temperature prohibits, for economic reasons, the use of gas turbines of recent technology. These have nominal flame temperature levels above 1100 ° C and have higher yields.

However, their purchase prices per electric kW are higher than those of turbines with a flame temperature of around 1100 ° C (so-called “E” class machines), so that their operation at reduced flame temperature n is not economical. Furthermore, when the flame temperature is fixed near this limit value of 1100 ° C., rather than at a lower level, with a view precisely to maximizing the energy performance of the gas turbine, the faster desulfation of magnesium requires more frequent washing, which reduces the availability of equipment. > Thus, in view of the drawbacks observed with conventional inhibitors, it appears desirable to have inhibitors of vanadic corrosion, in particular against type I corrosion and type II corrosion, which can be used in particular during the combustion of liquid fuels contaminated with vanadium, in particular in the presence of sodium, giving reduced fouling of the thermal equipment used and therefore better availability thereof, in particular when it comes to gas turbines.

Furthermore, it also appears desirable to be able to use, without prior "derating", or with minimal derating, the new technology turbines operating at high flame temperature for better energy yields.

From another point of view, it also appears desirable to make the use of fuels contaminated with vanadium more efficient and economically more profitable. Finally, it appears particularly desirable to remedy the drawbacks associated with the use of conventional inhibitors, in particular during the combustion of liquid fuels contaminated with vanadium. The Applicant has now found that it is possible and particularly advantageous to use nickel-based compounds, the mass ratio of nickel to contaminating vanadium being greater than or equal to 1.74, to inhibit vanadic corrosion of metallic materials, in particular thermal equipment burning liquid fuels contaminated with vanadium, even at high temperature. The present invention therefore relates to the use of nickel-based compounds for inhibiting vanadic corrosion of metallic materials, characterized in that the mass ratio of nickel to contaminating vanadium is greater than or equal to 1.74. The metallic materials whose corrosion can thus be inhibited are of any type and in particular ferrous metallic materials (unalloyed, weakly to highly alloyed, stainless steels) or superalloys (based on chromium and / or nickel and / or cobalt ). This application to any type of metallic material is due to the nature of the inhibition in which the vanadium, trapped by nickel, is removed from the medium as a corrosive agent.

By thermal equipment is meant any type of combustion device such as diesel engines, boilers, gas turbines, etc. According to a preferred implementation of the invention, metallic materials of vanadic corrosion are protected gas turbines.

These nickel-based inhibitors can be substituted for those based on alkaline earth metals in any application where the latter can be used, regardless of the type of combustion device and of vanadium-containing fuel, while overcoming the drawbacks linked to the use of these alkaline earth metal inhibitors. Indeed, the Applicant has established that certain chemical compounds of nickel combine with the vanadium contained in the fuels to form, under appropriate temperature and stoichiometric conditions, nickel orthovanadate (Ni ₃ N ₂ O _g ). Nickel orthovanadate is a refractory, non-corrosive compound capable of inhibiting vanadic corrosion at high temperatures of metallic materials.

In the temperature range prevailing on the surface of the thermal equipment materials to be protected, nickel, unlike magnesium, does not form sulphate, which eliminates the need for the overdose of inhibitors linked to the formation of this salt.

The vanadic corrosion protection offered by these nickel-based inhibitors is very effective since nickel orthovanadate is not only thermally stable, but also chemically inert in the temperature range prevailing on the surface of the parts of the equipment to be protected, even in the presence of sodium sulphate.

Under the same conditions, a significant fraction of magnesium, when it is used as an inhibitor, combines with sodium sulfate to form eutectics MgSO.-Na-.SO. low melting point, and therefore potentially corrosive. The protection against vanadic corrosion provided by nickel-based inhibitors is therefore greater than that provided by magnesium inhibitors, in particular in the presence of sodium which is liable to be introduced into the thermal equipment, either via the fuel circuit, either via combustion air. This is due to the fact that nickel orthovanadate is very stable in the presence of sodium and does not form salts with a low melting point. The use of vanadium is therefore particularly suitable for inhibiting vanadic corrosion of metallic materials by a liquid fuel contaminated with vanadium and in the presence of sodium. Sodium can be supplied by the fuel and / or by the combustion air. Thus, a Ni / V mass ratio of 2.25 provides effective protection against compositions containing sodium and vanadium, with a sodium concentration less than or equal to 0.1 ppm in the combustion gas, equivalent to 5 ppm in the fuel.

The use of nickel-based compounds as inhibitors also has the additional advantage of reducing the soot particles in thermal equipment by the action of atomic nickel in hydrocarbon flames.

Thus, according to a first aspect of the invention, at least one nickel-based compound is used to inhibit the vanadic corrosion of metallic materials, in a mass ratio of contaminating nickel to vanadium greater than or equal to 1.74, and in particular of thermal equipment materials, and more particularly superalloys of industrial gas turbines burning liquid fuels contaminated with vanadium.

According to the invention, the fuel can be any type of liquid fuel contaminated with vanadium, and in particular a fuel slightly contaminated with vanadium, such as a gas condensate or a heavy petroleum distillate, or a fuel very highly contaminated with vanadium. In these two cases, the use of magnesium as an inhibitor led to significant fouling of active hot parts, detrimental to the proper functioning of the thermal machine.

The combustion according to the invention can be carried out at high temperature, in particular higher than 1100 ° C., and more particularly between 1100 ° C. and 1300 ° C. Indeed, the melting and decomposition temperatures of nickel orthovanadate (Ni AOA which forms are respectively 1310 ° C and about 2000 ° C.

These characteristics give the nickel-based inhibitor a potentially wider range of application than that of magnesium-based inhibitors, the orthovanadate of which melts at 1200 ° C. They contribute in particular to the substantial increase in the flame temperature of gas turbines burning fuels contaminated with vanadium, and make possible the combustion of such fuels in more efficient new technology gas turbine models.

The mass ratio of nickel to contaminating vanadium is preferably between 1.9 and 2.5 (a ratio of 2.25 is even more particularly preferred). On the one hand, in order to provide an acceptable safety margin in industrial application. On the other hand, an excess of nickel leads to the formation of refractory, non-corrosive and slightly abrasive nickel oxide, which plays a role of self-cleaning of thermal equipment favorable to the conservation of the energy performance of said equipment. An adjustment of the nickel to vanadium ratio makes it possible to adjust this self-cleaning power of the inhibitor.

Furthermore, within this range, it has been found that the amount of ash formed by the nickel-based compound is at least two times less than the amount of ash formed by a magnesium-based compound.

This is explained by two facts:

- the non-adherent nature of the ash based on nickel under the temperature and speed conditions prevail in the combustion gases in the vicinity of the surfaces to be protected, - the slightly abrasive nature of these particles, particularly those of nickel oxide which tend to erode any emerging deposit on the surface of fixed and moving parts of thermal equipment.

Thus the frequency of cleaning operations of the thermal equipment is greatly reduced and the availability of the equipment increased.

In addition, the Applicant has found that the nickel-based deposits, composed of orthovanadate and nickel oxide, are both extremely friable and of porous structure. This results in three beneficial effects in nickel ablation operations: a) particularly high efficiency of dry cleaning, thanks to the brittleness of the deposits, b) effectiveness of washing with water despite the insolubility of the nickel ash; indeed, during a washing with hot water, the water penetrates into the porous structure of the deposit, which by its low mechanical resistance, disintegrates under the combined effect of capillary forces and hydrodynamic forces caused by the circulation of the wash water (the stirring effect is particularly important in the case of a gas turbine due to the rotation of the blades). The wettability of the deposit can be further increased by the addition of a wetting agent, free of sodium to avoid the corrosive effect of this metal, such as a cationic or nonionic surfactant, c) increased reactivity compared to a possible chemical reagent. The invention also relates to the use of nickel - based compounds, in the proportions described above, for inhibiting type I corrosion of metallic materials, as well as for inhibiting type II corrosion of metallic materials.

According to another aspect of the invention, the nickel-based compounds are used to inhibit the vanadic corrosion of metallic materials by a liquid fuel contaminated with vanadium and in the presence of sodium. By "in the presence of sodium" is meant that sodium is present in the liquid fuel and / or in the combustion air.

Nickel-based compounds can also be used to inhibit vanadic corrosion of metallic materials when combusting a vanadium-contaminated liquid at temperatures above 1100 ° C. Preferably, the combustion temperature is between 1100 ° C and 1300 ° C.

The injection methods of this nickel-based inhibitor are similar to those of conventional inhibitors. It can be injected in the form of a fat-soluble additive in a mixture directly with the liquid fuel in the storage tanks or in line before the injection of the fuel into the combustion chamber. It can also be used in the form of a water-soluble additive, emulsified in line in liquid fuels before injection into the combustion chamber or else injected separately into thermal equipment. Depending on the mode of addition of the nickel-based compound to the liquid fuel, it may be in liposoluble or water-soluble form, in the form of a water-in-oil or oil-in-water emulsion or micro-emulsion, or in the form of a suspension. When it is in liposoluble form, the nickel-based compound is chosen in particular from organometallic compounds such as sulfonates, nickel carboxylates or alkanoates with a variable hydrocarbon chain comprising between 2 and 12 carbon atoms, and preferably 6 or 7 carbon atoms, dissolved in an organic solvent compatible with liquid fuel.

When used in a water-soluble form, the nickel-based compound is in particular constituted by an aqueous solution of an organic or inorganic nickel salt, such as for example a nitrate or a sulfate. When the nickel-based compound is used in the form of a water-in-oil emulsion or micro-emulsion, it is then an aqueous solution of at least one organic or inorganic nickel salt, such as that a nitrate or a sulfate, emulsified in a solvent compatible with the fuel to be treated, by means of an emulsifier having a suitable hydrophilic / lipophilic balance, such as for example a polyethoxylated nonylphenol of generic formula CH3- (CH2) 8- (C6H4) -O- (CH2CH2O) nH, and introduced in appropriate concentration. The compound of generic formula CH3- (CH2) 8- (C6H4) -O- (CH2CH2O) nH can represent up to 10% by mass of the solution. The long-term stability of the emulsion, essential for industrial applications, can be enhanced by the addition of a co-solvent such as oleic acid introduced in small proportion.

When it is used in the form of an oil-in-water emulsion or micro-emulsion, it is an organic solution of a nickel sulfonate, a carboxylate or an alkanoate emulsified in an aqueous solution by means of an emulsifier having a suitable lipophilic / hydrophilic balance of the same type as described above and introduced in an appropriate concentration. A co-solvent can also be added. When the nickel-based compound is used in the form of a suspension, it is a solid compound such as an oxide, a partially hydrated oxide, a hydroxide or a nickel super-base, in particulate form, suspended in an aqueous solution or in an organic solvent compatible with the fuel to be treated.

Preference is often given to nickel compounds in liposoluble form which are directly usable and easily miscible with the fuel to be treated.

The very high reactivity of nickel with respect to vanadium allows, according to a particular implementation of the invention, to use it in association, in the form of a mixture in any proportion, with one or more other metals. Thus, it is possible to envisage a combination with at least one or more metals having other corrosion-inhibiting functions, chosen in particular from chromium, silicon, aluminum, zinc and magnesium. It is also possible to envisage the association with at least one or more metals having a role of combustion catalyst, chosen in particular from iron, manganese and cerium.

According to another embodiment of the invention, the fuel contaminated with vanadium also contains nickel as a notable metallic contaminant.

The use of nickel-based inhibitors allows a particularly economical combustion of these fuels which contain nickel naturally. In fact, the quantity of inhibiting nickel to be added is then equal to the complement between the concentration corresponding to the ratio of nickel to targeted vanadium and the natural concentration of nickel in the fuel. Examples of this type of fuel include crude oils and distillation residues from certain oils, such as crude oils from China and Indonesia, "Low Sulfur Waxy Residuals" from the South Asian oil market.

Another aspect of the invention relates to a method of combustion of a liquid fuel contaminated with vanadium, which, in addition to the known conventional steps accompanying combustion, comprises a step of introducing into the thermal equipment, separately or as a mixture with the contaminated liquid fuel, at least one nickel-based compound.

The nickel is supplied in proportions such that the mass ratio of nickel to the contaminating vanadium is greater than or equal to 1.74 and preferably between 1.9 and 2.5. A mass ratio of 2.25 is particularly preferred.

According to a variant of the process of the invention, the nickel-based compounds are used to inhibit the vanadic corrosion of metallic materials by a liquid fuel contaminated with vanadium, the combustion taking place in the presence of sodium.

By "in the presence of sodium" is meant that sodium is present in the liquid fuel and / or in the combustion air. Due to this presence, the combustion gases contain sodium. More particularly, according to a preferred embodiment of the invention, this method is applied to combustion in gas turbines. In fact, in a gas turbine, performance is closely linked to the state of cleanliness of the components of the expansion turbine. In addition, the Applicant has found that the nickel oxide, stable above 650 ° C., under partial pressure conditions of

SO _3, prevalent in combustion gases, is mainly available as a self-cleaning agent in the hottest areas, that is to say precisely where deposits are most difficult to remove. These zones are the flame tubes, the transition pieces and the first expansion stages (essentially the first and second stages).

Three advantages of nickel-based inhibitors allow a substantial increase in the flame temperature of gas turbines burning liquid fuels contaminated with vanadium. It's about :

- the refractory and non-adherent nature of the nickel-based ash particles,

- the low fouling rate of the turbine parts which results therefrom, - the elimination of the need to form sulphated ash which is soluble in water.

This results in the possibility of advantageously applying the process to the most recent, more efficient technology gas turbines, the flame temperatures of which are higher than

1100 ° C and are in particular between 1100 ° C and 1300 ° C.

The nickel-based compound can be in the forms defined above, which depend in particular on its mode of addition. This is carried out according to conventional methods described above.

The liquid fuel can be any type of liquid fuel contaminated with vanadium, and in particular those described above.

According to a particular embodiment of the method of the invention, the method of combustion of liquid fuels contaminated with vanadium also comprises a step of leaching of the ash based on nickel with a reducing organic acid.

The chemical leaching of the ash instead of simple washing with water makes it possible to optimize the state of cleanliness of the hot parts of the turbine at the end of cleaning and, thereby, to improve the energy performance of the latter during the cycle of following exploitation.

In accordance with this embodiment, any deposits based on nickel which could accumulate in the thermal equipment, and in particular the turbine, are eliminated, for example over long periods of non-stop operation, by means of a solution to reducing organic acid base.

Indeed, the applicant has established that a reducing organic acid which is particularly suitable is oxalic acid. This acid remarkably dissolves the solids Ni ₃ N ₂ O ₈ , ΝiO, and CaSO ₄ , as well as their mixtures. The dissolution reactions are as follows:

(1) Νi ₃ N ₂ O ₈ + 4H ₂ C ₂ O ₄ + 4H ⁺ → 3ΝiC ₂ O ₄ l + 2CO ₂ + 2VO ²⁺ + 6H ₂ O

(2) NiO + H ₂ C ₂ O ₄ → NiC ₂ O ₄ i + H ₂ O (3) CaSO ₄ + H ₂ C ₂ O ₄ → CaC ₂ O ₄ l + 2H ⁺ + SO ₄ ^{2 "}

Reaction (1) is essential because orthovanadate is the main phrase and requires both the reduction of vanadium from the degree of oxidation N to IN under acidic conditions and the formation of an insoluble salt of nickel in order to displace the left to right reaction. Oxalic acid combines these properties and also has the advantages of being weakly corrosive, very soluble in water and of moderate cost.

Thus, a 0.5 M aqueous solution of oxalic acid at 80 ° C, obtained from commercial H2C2O4, 2 H2O, ensures a dissolution rate of 90% after three hours of leaching.

Oxalic acid can be used with an inhibitor of the acid corrosion of carbon steels and cast irons, such as thiourea, benzotriazole or tolyltriazole in order to protect the ferrous alloys present in the mechanical structures of the turbine. .

The oxalic acid can also be added with a wetting agent such as a cationic or nonionic surfactant making it possible to accelerate the diffusion of the oxalic acid in the pores of the deposit and the dissolution of the latter. Finally, the ability of oxalic acid to also dissolve calcium sulphate is useful when the fuel is contaminated with calcium: petroleum fuels can contain calcium in water-soluble form (mineral salts contained in residual water droplets in emulsion in fuel) or liposoluble (organic calcium salts dissolved in the fuel phase). Indeed, the combustion of fuels contaminated with calcium forms calcium sulphate which is very slightly soluble in water, strongly adheres to the hot parts of the turbine and is likely to trap the other phases of the ash including those rich in nickel. In order to illustrate the invention, three embodiments are described below: First embodiment

In a traditional gas turbine called "second generation" or class "E", a heavy fuel oil highly contaminated with vanadium is burned. By gas turbine class "E" means a gas turbine which has a nominal flame temperature between 1100 and 1150 °. The heavy fuel oil used, with a composition typical of that of the Southeast Asian market, is a residue from the atmospheric distillation of petroleum which contains 50 ppm of vanadium and 30 ppm of nickel.

According to the invention, in order to inhibit vanadic corrosion, an aqueous solution of nickel nitrate emulsified with a metal-free surfactant and at a rate of 10% by mass of nickel is added to the liquid fuel. an organic solvent constituted by a middle petroleum distillate of the kerosene type, miscible with the petroleum fuel to be burned. The nickel nitrate emulsion is injected using a metering pump into the low pressure part of the liquid fuel circuit, and more precisely upstream of the high pressure filters. The quantity of nickel nitrate emulsion injected is such that the ratio of nickel to vanadium is equal to 2.25. This leads to injecting (2.25 * 50-30) = 82.5 mg of nickel per kg of fuel, while 3 * 50 = 150 mg of magnesium was required with traditional methods. Abrasive agents, such as nut shells, are periodically injected into the circuit for dry cleaning, which is particularly effective with nickel-based ash.

It can be seen that the use of nickel as an inhibitor according to the invention applied to the combustion of a heavy fuel highly contaminated with vanadium in a gas turbine of class "E", reduces by a factor 2.5 the rate of deposition of ash compared to the use of magnesium as an inhibitor. This represents an average electrical power gain of around 6% for an equal fuel consumption. We can put this gain at around 300,000 dollars (or 2.1 MF in May 2001) for an annual production of 5 million dollars (35 MF in May 2001), which represents a considerable gain.

The implementation of a chemical leaching step of the nickel-based ash optimizes the state of cleanliness of the hot parts of the turbine at the end of cleaning and, thereby, improves the energy performance of the latter during the cycle of next operation.

Furthermore, thermal equipment is made more available since there is a multiplication by a factor greater than 2.5 of the continuous operating time of the turbine between two consecutive washing operations. This eliminates a cumulative downtime of 60 hours over a period of 1000 hours, which represents a gain. availability greater than 6%.

Second embodiment

In a so-called "third generation" or class "F" gas turbine, installed for example in a maritime area where the air is contaminated with sodium, a "gas condensate" is very slightly contaminated with vanadium. The "F" class gas turbine is one of those new generation gas turbines mentioned above in the text which have a flame temperature of 1300 ° C. or more. The fuel used corresponds to the condensable fraction at ambient temperature and pressure of the production of a natural gas well, after possible stabilization treatments (reduction of the vapor pressure by flash distillation), and softening (removal of HJ3). These gas condensates can typically contain between 0.2 and 1.5 ppm vanadium. The sodium concentration is approximately 2.5 ppm, corresponding to a concentration of 0.05 ppm in air.

A nickel compound in liposoluble form is used, for example a nickel carboxylate, containing 8% by weight of nickel, with the same method of introduction into the turbine as in the previous application mode.

The Ni / N dosage ratio is 2.25. The flame temperature of the gas turbine is for example 1280 ° C. It should be noted that gas condensates frequently contain small quantities of vanadium which either exceed the permitted specification (for example 0.5 ppm) for operation of the turbine without having to use a corrosion inhibitor, or if they do not not exceed this permitted specification, decrease the service life of active hot machine parts when an inhibitor is not added. The fact that conventional inhibitors, in particular based on magnesium, form very hard deposits, which cannot be removed by washing, when the turbine is operated at high flame temperature, which is one of the characteristics of gas turbines of class "F ", the operation of such a machine would lead to irreversible fouling of the blades. Such fouling would in fact require disassembly of the machine for manual cleaning. In addition, magnesium orthovanadate begins to melt at 1100 ° C and the anti-corrosion protection would then be called into question. These major drawbacks are eliminated when a nickel-based inhibitor is used according to the invention, which also protects gas turbines from the harmful effects of possible incursions of sodium present in the air. The flame temperature can be adjusted to a value less than or equal to 1300 ° C.

Third embodiment

A similar result is obtained if a heavy petroleum distillate is used as fuel. This type of fuel, slightly contaminated, also typically contains between 1 and 1.5 ppm of vanadium. In addition, these fuels contain significant amounts of sodium salts dissolved in water droplets present in the fuel. The sodium concentration is typically between 1 and 1.5 ppm in such heavy petroleum distillates.

The use of nickel as an inhibitor thus makes it possible to protect effectively from vanadic corrosion the gas turbines of class "F", by using a heavy distillate, combustible whose use was until now considered as risky in class turbines F.

Claims

1. Use of nickel-based compounds to inhibit vanadic corrosion of metallic materials, characterized in that the mass ratio of nickel to contaminating vanadium is greater than or equal to 1.74.

2. Use according to claim 1, characterized in that the mass ratio of nickel to contaminating vanadium is between 1, 9 and 2.5.

3. Use according to claim 1 or 2, characterized in that the mass ratio of nickel to contaminating vanadium is equal to

2.25.

4. Use according to any one of claims 1 to 3, for inhibiting type I corrosion of metallic materials.

5. Use according to any one of claims 1 to 3, for inhibiting type II corrosion of metallic materials.

6. Use according to any one of claims 1 to 3, for inhibiting vanadic corrosion of metallic materials during combustion at temperatures above 1100 ° C

7. Use according to claim 6, characterized in that the combustion temperature is between 1100 ° C and 1300 ° C.

8. Use according to any one of claims 1 to 7, for inhibiting vanadic corrosion of metallic materials by a liquid fuel contaminated with vanadium and in the presence of sodium.

9. Use according to any one of claims 1 to 8, characterized in that the nickel-based compound is in liposoluble or water-soluble form, in the form of a water-in-oil emulsion or micro-emulsion or oil -in-water, or in the form of an aqueous or organic suspension.

10. Use according to any one of claims 1 to 9, characterized in that the nickel-based compound is associated, in the form of a mixture in any proportion, with at least one other metal preferably chosen from chromium, silicon , aluminum, magnesium, iron, manganese, zinc and cerium.

1 1. Use according to any one of claims 1 to 10, characterized in that the liquid fuel is a fuel containing nickel as a significant metallic contaminant.

12. Method of combustion of a liquid fuel contaminated with vanadium, characterized in that it comprises a step of introducing at least one nickel-based compound, the mass ratio of nickel to contaminating vanadium being greater than or equal to 1, 74.

13. A method of combustion of a liquid fuel contaminated with vanadium according to claim 12, characterized in that the mass ratio of nickel to contaminating vanadium is between 1.9 and

2.5.

14. A method of combustion of a liquid fuel contaminated with vanadium according to claim 12 or 13, characterized in that the mass ratio of nickel to contaminating vanadium is equal to 2.25.

15. Method of combustion of a liquid contaminated with vanadium according to any one of claims 12 to 14, characterized in that the combustion is carried out in the presence of sodium.

16. A method of combustion of a liquid fuel contaminated with vanadium according to any one of claims 12 to 15, characterized in that the thermal equipment is a gas turbine, and preferably a gas turbine having a flame temperature higher than 1100 ° C.

17. A method of combustion of a liquid fuel contaminated with vanadiu according to claim 16, characterized in that the flame temperature is between 1100 ° C and 1300 ° C.

18. A method of combustion of a vanadium-contaminated liquid fuel according to any one of claims 12 to 17, characterized in that it comprises a step of leaching the ash based on nickel with a reducing organic acid.

19. A method of combustion of a liquid fuel contaminated with vanadium according to claim 18, characterized in that it comprises a step of leaching of the ash based on nickel by oxalic acid.