FR2810341A1 - Nickel compounds for inhibiting vanadium corrosion of thermal equipment burning vanadium-containing fuels are used in the form of aqueous or liposoluble solutions - Google Patents

Abstract

Nickel compounds are used for inhibiting vanadium corrosion of metallic materials of thermal equipment such as a gas turbine burning vanadium-containing fuels, where the mass ratio of nickel to vanadium contaminant is at least 1.74 Preferred Features: Combustion of a combustible liquid contaminated with vanadium includes the introduction of at least one nickel compound, where the mass ratio of nickel to vanadium is 1.9-2.5, most preferably 2.25, into the thermal equipment The thermal equipment is a gas turbine, preferably a gas turbine having a flame temperature above 1100 deg C, more preferably 1100-1300 deg C. Combustion may take place in the presence of sodium. The combustion process also includes lixiviation of nickel compound ash by a reducing organic acid, preferably oxalic acid. An Independent claim is given for the utilization of the nickel compounds for inhibiting vanadium corrosion of metallic materials of thermal equipment burning vanadium-containing fuels, where the nickel compound is liposoluble or water-soluble, in the form of an emulsion or microemulsion water-in-oil or oil in water, or in the form of an aqueous or organic suspension. Organic or inorganic nickel salts such as nickel nitrate or sulfate can be used. The process can be used for inhibiting vanadium corrosion of type I and type II metallic materials.

Description

The use of nickel compounds as vanadium corrosion inhibitors and combustion method using such compounds of the present invention relates generally to the inhibition of vanadic corrosion of vanadium-contaminated liquid fuel burning equipment materials. .

It is economically interesting to be able to exploit the oil extracts of average quality, such as for example products contaminated with various impurities.

presence of vanadium organic 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 the metallic materials in contact with the 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 same type of this thermal equipment, the operating temperature range, the duration and the operating conditions.

This corrosion is caused by the formation in the flue gases of vanadium derivatives with a low melting point, such as vanadium pentoxide (V205) and eutectic mixtures of V205 Na2SO4, which can induce, under the prevailing temperature conditions of the surface of the metal parts concerned, electrochemical attacks developing in molten electrolyte medium and in the presence of oxidants, in particular the oxygen contained in the fumes and sulfate ions formed from the sulfur of the fuel.

The corrosive potency of these vanadic compounds can be inhibited by chemically "trapping" V205 within refractory compounds. This eliminates the corrosive medium of molten electrolyte. Conventional vanadium inhibitors are represented by alkaline earth salts, such as calcium salts, magnesium salts, the latter being the most commonly used. Under certain conditions of temperature and dosage of the inhibitor, vanadium forms with it refractory alkaline earth orthovanadates, of the type M3V208, where M represents an alkaline earth metal.

The dosage of the inhibitor must be sufficient both to trap all the vanadium present in the fuel and to avoid the formation of vanadates of lower stoichiometries such as pyrovanadates or metavanadates, which are insufficiently refractory to ensure the effect of targeted inhibition.

The vanadates resulting from this inhibition process produce ashes suspended in the combustion gases, a portion of which is deposited on the walls of the combustion chambers and combustion apparatus components downstream thereof. This causes a gradual fouling of the combustion apparatus as its operation and causes a consequential 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 these deposits can be eliminated as completely as possible, without loading the economic balance sheet 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, particularly 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.

Washing with water is based on circulation inside the appliance when it is stopped, hot water and free of corrosive salts. The hot water dissolves the MS04 sulphates that form during the operation in parallel with the insoluble vanadates.

The dissolution of the sulphated phase results in the mechanical destabilization of all the insoluble solid phases associated with it in the deposit, in particular the alkaline earth vanadates. The wash water causes the deposit in partially dissolved form partially suspended therein.

In what follows, magnesium is taken as an example of conventional 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, parallel to that of orthovanadate, requires that in order to "trap" all the vanadium, a large excess of magnesium is added relative to the stoichiometry of the reaction with, in practice, a mass ratio. vanadium magnesium greater than or equal to 3.

This excess of inhibitor consumption leads to a direct cost of exploitation.

moreover, the combustion equipment is more rapidly fouled, resulting in accelerated degradation of performance and the need for more frequent removal, particularly with water, to ensure adequate operation.

Another disadvantage associated with the use of conventional alkaline earth based inhibitors, especially magnesium, concerns "de-scaling" of the thermal equipment used. "Decarriage" is understood to mean that the flame temperature of the gas turbines subjected to such inhibition treatment must be reduced with respect to the nominal value of the gas turbine model in question.

Flame temperature is defined as the temperature of the hot gases at the inlet of the first stage of turbine blades and is one of the parameters that in essence determines the energy performance of the turbine.

The reason for this "derating" is that at high temperature, desulfation of magnesium is observed. Knowing that the desulfation rate, on the one hand, and the equilibrium desulfation rate of the reaction on the other hand, increase with temperature and that the magnesium oxide, product of the desulphatation, is otherwise insoluble in the water. water, it happens that beyond a certain flame temperature value of a certain continuous running time, the proportion of sulphate remaining in the deposit becomes insufficient to ensure the correct disposal of the deposition by washing at the same time. water.

At present, combustion in vanadium-contaminated fuel gas turbines using magnesium as an inhibitor leads to limiting the flame temperature to around 100 ° C, which is also the Mg3V208 melting temperature.

The need to limit the flame temperature prohibits, for economic reasons, the use of gas turbines of recent technology. The latter have nominal flame temperature levels above 1100 C and have higher yields. But their purchase prices per kW electrical are higher than those turbines whose flame temperature is of the order of 1100 C (so-called class machines <B> E), so that their operation flame temperature reduced is not economical.

Furthermore, when the flame temperature is set near this limit value of 1100 C, rather than at a lower level, precisely to maximize the energy performance of the gas turbine, the faster desulfation of magnesium requires more frequent washes, which reduces the availability of equipment.

Thus, in view of the drawbacks observed with conventional inhibitors, it appears desirable to have vanadium corrosion inhibitors, used especially in the combustion of liquid fuels contaminated with vanadium, conferring a reduced fouling of the thermal equipment used and therefore better availability of it, especially when it comes to gas turbines.

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

From another point of view, it also seems desirable to make the use of vanadium-contaminated fuels more efficient and economically more profitable. Finally, it appears to be particularly desirable to remedy disadvantages related to the use of conventional inhibitors, especially during the combustion of contaminated liquid vanadium fuels.

The Applicant has now found that it is possible and particularly advantageous to use nickel-based compounds to inhibit the vanadic corrosion of metallic materials, including thermal equipment burning liquid fuels contaminated with vanadium, even at high temperature.

The metallic materials whose corrosion can thus be inhibited are of any type and in particular ferrous metal materials (nonalloyed, low to high 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 vanadium, trapped by nickel, withdraws from the medium as a corrosive agent.

By thermal equipment is meant any type of combustion apparatus such as diesel engines, boilers, gas turbines, etc.

According to a preferred embodiment of the invention, the metal materials of turbines are protected from vanadium corrosion. These nickel-based inhibitors can be substituted for those based on alkaline-earth metals in any application in which they can be used. this regardless of the type of combustion apparatus and fuel containing vanadium, while overcoming the disadvantages associated with the use of these alkaline inhibitors, reux.

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, the nickel orthovanadate 3v208). Nickel orthovanadate is a refractory and corrosive compound capable of inhibiting the high temperature vanadium corrosion of metallic materials.

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

The protection against vanadic corrosion offered by these nickel-based inhibitors is very effective because nickel orthovanadate is not only thermally stable, but also chemically inert in the temperature range prevailing on the surface of the parts of the nickel. 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 sulphate to form MgS04-Na2SO4 eutectics with a melting point, and therefore potentially corrosive. The protection against vanadic corrosion provided by the nickel-based inhibitors is therefore greater than that provided by the magnesium inhibitors, especially in the presence of sodium which is likely to be introduced into the thermal equipment, either via the fuel circuit or via combustion air.

The use of nickel-based compounds as inhibitors also has the additional advantage of reducing soot particles within the 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, and in particular of thermal equipment materials, and more particularly superalloys of industrial gas turbine turbines. liquid fuels contaminated with vanadium.

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

The combustion according to the invention can be carried out at high temperature, especially greater than 1100 C, and more particularly of the order of 1300 C.

In fact, the melting and decomposition temperatures of the nickel orthovanadate (Ni 3 V 2 O 8) are formed respectively at 13 ° C. and about 2000 ° C.

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

The minimum mass ratio of nickel to vanadium necessary for complete inhibition of vanadium corrosion is at least 1.74. It is preferred to work in a range of 1.9 to 2.5 for this ratio. On the one hand, in order to provide an acceptable margin of safety in industrial application. On the other hand, a nickel excess leads to the formation of refractory nickel oxide, non-corrosive and slightly abrasive, which plays a role of self-cleaning of the 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 regulate this self-cleaning power of the inhibitor.

In addition, in this range, it has been found that the amount of ash formed by the nickel-based compound was at least half as much as the amount of ash formed by a magnesium-based compound.

This can be explained in particular by the non-adhering nature of the nickel-based ash particles under the temperature and speed conditions prevailing within the combustion zones in the vicinity of the protected parts, and also by the slightly abrasive nature of these particles, which tend to erode any deposit arising from the surface of the fixed and moving parts of the thermal equipment.

Thus, the frequency of the cleaning operations the thermal equipment is greatly reduced and the equipment is therefore more available.

injection modes of this nickel-based inhibitor are similar to those of conventional inhibitors. It can be injected as a fat-soluble additive directly mixed with the liquid fuel in the storage tanks or in line before the fuel injection into the combustion chamber. It can also be used as a water-soluble additive, emulsified online in liquid fuels before injection into the combustion chamber or injected separately into the thermal equipment.

According to the method of adding 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 microemulsion, or in form of a suspension.

When it is in liposoluble form, the nickel-based compound is chosen in particular from organometallics such as sulphonates, carboxylates or alkanoates of nickel 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 the liquid fuel.

When it is used in a water-soluble form, the nickel-based compound is in particular constituted by an aqueous solution of an organic or inorganic salt of nickel, such as a nitrate, a sulphate, etc.

When the nickel-based compound is used in the form of a water-in-oil emulsion or microemulsion, it is then an aqueous solution of at least one organic or inorganic salt of nickel, which a nitrate or sulphate, emulsified in a solvent compatible with the fuel to be treated, by emulsifying means 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 long-term stability of the emulsion required for industrial applications can be enhanced by the addition of a co-solvent such as oleic acid introduced in a small proportion.

When it is used in the form of an oil-in-water emulsion or microemulsion, it is an organic solution of a nickel sulfonate, a carboxylate or a nickel alkanoate emulsified in an aqueous solution using an emulsifier having a suitable lipophilic / hydrophilic balance of the same type as described above and introduced in appropriate concentration. A co-solvent can also be added.

When the nickel-based compound is used in suspension form, it is a solid compound such as an oxide, a partially hydrated oxide, a hydroxide or a super nickel base, in particulate form, suspended in a solution. aqueous or in an organic solvent compatible with the fuel to be treated.

Nickel compounds in liposoluble form used directly and easily miscible fuel to be treated are often preferred.

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

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

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

Another aspect of the invention relates to a method of combustion of a vanadium-contaminated liquid fuel which, in addition to the known conventional steps accompanying the combustion, comprises a step of introduction into the thermal equipment, separately or in admixture. with the contaminated liquid fuel, a nickel-based additive.

Nickel supply is in such proportions that the mass ratio of nickel to contaminating vanadium is greater than or equal to 74 and preferably between 1.9 and 2.5.

More particularly, according to a preferred embodiment of the invention, this method is applied to combustion in gas turbines.

non-stick refractory nature of the nickel-based ash particles, the resulting low fouling rate of the turbine parts and the removal of the need to form a water-soluble fraction of sulfated ash, makes it possible to increase substantially the flame temperature of turbines burning vanadium-contaminated liquid fuels. This results in the possibility of advantageously implementing gas turbines of the latest technologies, more efficient, whose nominal flame temperatures are greater than 100 C and in particular of the order of 1300 C.

The nickel-based compound may be in the forms defined above, which depend in particular on its mode of addition. This is performed according to conventional methods described above. The liquid fuel may be of any type of liquid fuel contaminated with vanadium, and in particular those described above.

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

The chemical leaching of ash instead of just 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 improve the energy performance of the latter during the cycle. following operation.

According to this embodiment, any nickel-based deposits which may accumulate in the thermal equipment, and in particular the turbine, for example, over long periods of non-stop operation, are eliminated by means of a solution based on nickel. reducing organic acid. The reducing organic acid is preferably formic acid or oxalic acid. It can be used hot and supplemented with an acid corrosion inhibitor of carbon steels and cast irons, such as thiourea optionally supplemented with benzotriazole or tolytrazole.

In order to illustrate the invention, two embodiments are described below: <U> First embodiment </ U> In a traditional "second generation" or "E" type gas turbine, one burns heavy fuel heavily contaminated with vanadium. Class "E" gas turbine means a gas turbine which has a nominal flame temperature of between 1100 and 1150 and a combustion temperature in the flame of 2100 to 2200 C. The heavy fuel oil used a residue from the atmospheric distillation of petroleum which contains between 70 and 100 ppm of vanadium.

According to the invention, in order to inhibit vanadium corrosion, an aqueous solution of nickel nitrate emulsified with a metal-free surfactant and with a mass of nickel in an organic solvent is added to the liquid fuel. by a middle distillate of kerosene type oil, miscible with petroleum fuel to be burned. The nickel nitrate emulsion is injected using a metering pump into the high pressure part of the liquid fuel circuit, and more precisely upstream high pressure filters. The amount of nickel nitrate emulsion injected is such that the nickel to vanadium ratio is equal to 2.

It is found that the use of nickel as an inhibitor according to the invention applied to the combustion of a heavy heavy-fuel oil vanadium in a gas turbine of reduced class by a factor of 2.5 the rate of deposition of ash with respect to use magnesium as an inhibitor. This represents an average electric power gain of the order of 4% for an equal fuel consumption. This gain can be estimated at about $ 200,000 (or $ 1.4 million in May 2000) for an annual production of $ 5 million (or $ 35 million in May 2000), which represents a considerable gain.

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

Furthermore, the thermal equipment is made more available since there is a multiplication by 2.5 of the continuous operating time of the turbine between two consecutive washing operations. This eliminates a cumulative stopping time of 60 hours over a period of 1000 hours, which represents an increase in availability of the order of 6% a. <U> Second Embodiment </ U> In a so-called "third-generation" or "F" -type turbine, a condensate of gas slightly contaminated with vanadium is burned. The class "F" gas turbine is one of the new-generation gas turbines mentioned earlier in the text and has a flame temperature of about 1300 C and a combustion temperature in the flame of between 2300 and 2400 C. The fuel used corresponds to the condensable fraction at ambient pressure temperature of the production of a natural gas well, after possible stabilization treatments (lowering of flash distillation vapor pressure), and softening (removal of H2S). These gas condensates may typically contain between 0.2 and 1.5 ppm vanadium.

The same nickel compound and the same mode of introduction into the turbine are used in the previous embodiment. It should be noted that gas condensates frequently contain small amounts of vanadium which either exceed the allowable specification (eg 0.5 ppm) for turbine operation without the use of a corrosion inhibitor, or if they do not exceed not this specification allowed, decrease the life of active hot parts of the machine when an inhibitor is not added. Because the conventional inhibitors, in particular magnesium-based, form very hard deposits not removable by washing, at high flame temperature, which one of the specificities of gas turbines class "F", the operation of a such a machine would lead to an irreversible fouling of the blades. Such fouling requires disassembly of the machine for manual cleaning. In addition, the magnesium orthovanadate begins to melt at 1100 C and corrosion protection would be questioned. These major disadvantages are removed when using according to the invention a nickel-based inhibitor.

A similar result is obtained if a heavy petroleum distillate is used as a fuel. This type of fuel, which is slightly contaminated, also typically contains between 0.2 and 1.5 ppm of vanadium.

Claims (1)

Use of nickel-based compounds to inhibit vanadic corrosion of metallic materials. Use according to claim 1, characterized in that it is applied to the high temperature combustion of a vanadium-contaminated liquid fuel. 3. Use according to claim 1 or 2, characterized in that the mass ratio of nickel to contaminating vanadium is greater than or equal to 1.74, and preferably between 1.9 2.5. 4. Use according to any one of claims 1 to 3, characterized in that the nickel-based compound is in liposoluble or water-soluble form, in the form of an emulsion or micro-emulsion water-in-oil or oil- in-water, or in the form of an aqueous or organic suspension. . Use according to any one of Claims 1 to 4, characterized in that the nickel-based compound is combined, in the form of a mixture in any proportion, with at least one other metal chosen preferably from chromium, silicon, aluminum, magnesium, iron and manganese. 6. Use according to any one of claims 1 to 5, characterized in that the liquid fuel is a fuel containing nickel as a significant metal contaminant. Process for the combustion of a liquid fuel contaminated with vanadium, characterized in that it comprises a step of introducing into the thermal equipment at least one nickel-based additive. 8. A method of combustion of a vanadium-contaminated liquid fuel according to claim 7, characterized in that the mass ratio of nickel to contaminating vanadium is greater than or equal to 1.74, and preferably between 1.9 and 2.5 . 9. A method of combustion of a vanadium-contaminated liquid fuel according to claim 7 or 8, characterized in that the thermal equipment is a gas turbine, and preferably a gas turbine having a flame temperature greater than 1100 C. 10. A method of combustion of a vanadium-contaminated liquid fuel according to any one of claims 7 to 9, characterized in that it comprises a leaching step of nickel-based ash with a reducing organic acid or one of its salts.