US20200016724A1 - Mechanical Wall-Treatment Method That Reduces Coke Formation, and Hydrocarbon Treatment Method - Google Patents

Mechanical Wall-Treatment Method That Reduces Coke Formation, and Hydrocarbon Treatment Method Download PDF

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US20200016724A1
US20200016724A1 US16/471,024 US201716471024A US2020016724A1 US 20200016724 A1 US20200016724 A1 US 20200016724A1 US 201716471024 A US201716471024 A US 201716471024A US 2020016724 A1 US2020016724 A1 US 2020016724A1
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Prior art keywords
carbides
treatment
stage
process according
weight
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Inventor
Christel Augustin
Sophie Cazottes
Nicolas Vaché
Philippe Steyer
Claude Duret Thual
François Dupoiron
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Centre National de la Recherche Scientifique CNRS
Universite Claude Bernard Lyon 1 UCBL
Institut National des Sciences Appliquees de Lyon
TotalEnergies Raffinage Chimie SAS
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Centre National de la Recherche Scientifique CNRS
Universite Claude Bernard Lyon 1 UCBL
Institut National des Sciences Appliquees de Lyon
Total Raffinage Chimie SAS
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Assigned to TOTAL RAFFINAGE CHIMIE, INSTITUT NATIONAL DES SCIENCES APPLIQUEES DE LYON (INSA LYON), UNIVERSITE CLAUDE BERNARD LYON 1, CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE (CNRS) reassignment TOTAL RAFFINAGE CHIMIE ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: DUPOIRON, FRANÇOIS, DURET THUAL, Claude, STEYER, Philippe, VACHÉ, Nicolas, CAZOTTES, Sophie, AUGUSTIN, Christel
Publication of US20200016724A1 publication Critical patent/US20200016724A1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
    • B24C1/10—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods for compacting surfaces, e.g. shot-peening
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
    • B24C3/00—Abrasive blasting machines or devices; Plants
    • B24C3/32—Abrasive blasting machines or devices; Plants designed for abrasive blasting of particular work, e.g. the internal surfaces of cylinder blocks
    • B24C3/325—Abrasive blasting machines or devices; Plants designed for abrasive blasting of particular work, e.g. the internal surfaces of cylinder blocks for internal surfaces, e.g. of tubes
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G75/00—Inhibiting corrosion or fouling in apparatus for treatment or conversion of hydrocarbon oils, in general
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G75/00—Inhibiting corrosion or fouling in apparatus for treatment or conversion of hydrocarbon oils, in general
    • C10G75/04—Inhibiting corrosion or fouling in apparatus for treatment or conversion of hydrocarbon oils, in general by addition of antifouling agents
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G9/00—Thermal non-catalytic cracking, in the absence of hydrogen, of hydrocarbon oils
    • C10G9/005—Coking (in order to produce liquid products mainly)
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00—Electrolytic etching or polishing
    • C25F3/02—Etching
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
    • C10G2300/40—Characteristics of the process deviating from typical ways of processing
    • C10G2300/4075—Limiting deterioration of equipment

Definitions

  • the invention relates to a process for the surface treatment of a metal wall which has the effect of reducing the formation of coke at the surface of this wall. More specifically, the invention relates to a process for the surface removal of carbides from a wall made of metal alloy, in particular by mechanical treatment. The invention also relates to the use of a metal wall treated by the treatment process in a process for the treatment of hydrocarbons.
  • the walls of the reactors of some units of the petrochemical or chemical industry are sometimes subjected to very severe operating conditions which can result in phenomena of coking.
  • the manufacture of alkenes, monomers valued in the polymer industry is obtained by cracking oil-derived hydrocarbons at temperatures of the order of 800 to 900° C.
  • a mixture of hydrocarbons and steam is circulated at high speed in reactors, generally formed of metal tubes, often made of alloys rich in nickel and in chromium.
  • the reactors are thus subjected to high temperatures and to complex aggressive atmospheres and the formation of carbon (coke) is observed at the surface of the walls of the tubes, this formation being catalysed by the iron and the nickel present in the metal alloy forming the walls.
  • a protective oxide layer can in particular be obtained by the use of appropriate alloys, for example rich in chromium or in aluminium, or by oxidation pretreatments.
  • the metal alloy comprising in particular, within its structure, carbides, some of which can show on the surface.
  • the metal alloy contains at least 5% by weight of iron, at least 18% by weight of chromium, at least 25% by weight of nickel and at least 0.05% by weight of carbon.
  • operation conditions favourable to coking is understood to mean conditions liable to bring about the formation of coke on the surface.
  • the parameters influencing the coking comprise, for example, the temperature, the nature of the liquid or gaseous fluids circulating inside the reactor and in contact with the surface, the flow conditions of the fluids (turbulences).
  • the process comprises a mechanical stage of impact surface treatment, during which a surface of the wall is hammered by projection of particles under conditions suitable for obtaining covering of the carbides initially present at the surface by permanent plastic deformation of the surface.
  • the surface treatment renders the surface dented and rough, with covering of the carbides initially showing on the surface and/or close to the surface. This removal of the carbides from the surface of the metal alloy makes it possible to reduce the formation of coke.
  • Such a stage of impact surface treatment exhibits the advantage of being easy to carry out and relatively inexpensive.
  • the process according to the invention can advantageously be carried out in order to treat a wall of a reactor after the manufacture of the reactor and before bringing it into service.
  • a stage of oxidation of the wall can be envisaged, which makes it possible to further reduce the formation of coke.
  • the surface treatment appears to promote the formation of a homogeneous oxidized layer and to thus reduce the formation of coke.
  • the invention is more particularly suited to treating a wall of a steam cracking reactor (furnace) or of any other plant in which there is observed the formation of coke catalysed by iron, nickel and optionally by other catalysing metal elements present in the metal alloy of which the reactor is composed.
  • the invention thus also relates to a process for the treatment of hydrocarbons under conditions capable of bringing about the formation of coke, characterized in that the hydrocarbons are brought into contact with a surface of a wall made of Fe—Ni—Cr metal alloy, the said surface of the metal wall being pretreated by a treatment process according to the invention so as to reduce the formation of a coke deposit.
  • the metal alloy is preferably a metal alloy containing at least 5% by weight of iron, at least 18% by weight of chromium, at least 25% by weight of nickel and at least 0.05% by weight of carbon.
  • the process for the treatment of the hydrocarbons can be a cracking process, in which the hydrocarbons are brought into contact with the wall as a mixture with steam.
  • a treatment is, for example, carried out in a steam cracking reactor.
  • the hydrocarbons can be brought into contact with the surface of the metal wall at a temperature of 800 to 900° C., in particular as a mixture with steam.
  • the treatment process according to the invention is intended for the treatments of Fe—Ni—Cr metal alloys containing in particular carbides within their structure. These carbides can show on the surface, in other words be in contact with the gaseous medium surrounding the alloy, and/or can be located in the immediate proximity of the surface, for example from a depth of 1 ⁇ m or more.
  • Such carbides are formed by precipitation during the manufacture of the wall. They can also appear in part in operation.
  • carbides which are particularly stable chemically, are formed from the carbon present in the metal alloy. These carbides can in particular be observed for a carbon content of the metal alloy of at least 0.05% by weight.
  • This type of metal alloy is suitable in particular for use at high temperature (heat resistant alloys).
  • the alloys treated are alloys exhibiting an Fe—Ni—Cr matrix, optionally an austenitic matrix, within which precipitate chromium carbides (Cr x C y ), indeed even niobium carbides (NbC), when niobium is present, and/or carbonitrides, when the alloy contains nitrogen, and/or other carbides optionally.
  • Such alloys thus comprise:
  • iron at least 5% by weight of iron, preferably from 10% to 50%, in a preferred way from 12% to 48%, by weight,
  • chromium at least 18% by weight of chromium, preferably from 19% to 42% by weight,
  • At least 25% by weight of nickel preferably from 31% to 46% by weight.
  • these alloys comprise carbon, in particular from 0.05% to 1% by weight of carbon, preferably from 0.08% to 0.6% by weight.
  • the nickel or the iron can be the predominant element.
  • the iron content is the remainder to 100% of the contents of the other elements present in the alloy.
  • the treated metal alloys can comprise other elements. They can in particular comprise one or more of the following elements:
  • the metal alloy used can preferably be suitable for centrifugal casting. It can in particular observe Standard EN 10295 relating to heat-resistant steel castings.
  • This technique consists in pouring the liquid metal into a mould driven with a rotational movement around its main axis. Generally, the mould rotates at a speed such that it creates a mean acceleration of the order of several hundred and up to 1000 m/s 2 or more, in some cases.
  • the moulds can be made of sand or of metal die, fitted to machines having a horizontal, vertical or oblique axis. The parts obtained by centrifugation have very good physical and mechanical characteristics.
  • the treated wall can thus advantageously be produced by centrifugal casting.
  • This impact surface treatment is obtained by hammering the surface by projection of particles under conditions suitable for obtaining a permanent plastic deformation of the surface, in particular under conditions suitable for obtaining covering of the carbides initially present at the surface by permanent plastic deformation of the surface.
  • the carbides initially present at the surface can show on the surface and/or be located in the immediate proximity of the surface, in particular located at a depth of 1 ⁇ m and more from the surface.
  • the objective of this type of impact surface treatment is to compress the substance under the impacted surface: this compressed substance tends to regain its initial volume, resulting in high residual compressive stresses. This makes it possible to significantly increase the lifetime of a part made of alloy as virtually all of the fatigue and corrosion failures under tension are initiated at the surface of such parts.
  • the impacts caused by the projectiles will cover the surface with a uniform layer in compression, exhibiting a reduced content of carbides in comparison with the intact internal structure of the wall. This is because covering of the carbides initially present at the surface, in other words covering of the carbides showing on the surface and/or located in the immediate vicinity of the surface before the mechanical treatment, is observed.
  • shot peening use of beads
  • sand blasting alumina blasting
  • alumina blasting use of corundum particles
  • such a treatment makes it possible to cover the carbides initially present at the surface (showing on the surface and/or located in the immediate proximity of the surface) and to reduce the formation of coke.
  • the particles can be diverse in nature (inorganic, metallic, and the like) and of varied shapes (spherical or angular) and dimensions.
  • the particles can thus be chosen from aluminium oxide (for example white or brown corundum) particles, metal particles, beads made of material which is inert under the operational conditions of use of the wall made of metal alloy, for example made of glass or of aluminium oxide, or nesosilicate particles.
  • aluminium oxide for example white or brown corundum
  • metal particles beads made of material which is inert under the operational conditions of use of the wall made of metal alloy, for example made of glass or of aluminium oxide, or nesosilicate particles.
  • the nesosilicate (garnet) particles exhibit a general formula A m B n (SiO 4 ) t , where A is a transition metal or an alkaline earth metal and B is a transition metal or a rare earth metal.
  • A can be chosen from Mg, Ca and Mn and B can be chosen from Y, Ce and La.
  • the particles can exhibit a mean diameter of 100 to 500 ⁇ m.
  • Use may be made, by way of example, of glass beads with a mean diameter of 100 to 200 ⁇ m, of aluminium oxide particles with a mean diameter of 250 to 500 ⁇ m.
  • the particles can be projected by a gaseous fluid, for example air, argon or other, under a pressure of 200 to 400 kPa (2 to 4 bars), preferably of 250 to 350 kPa (2.5 to 3.5 bars).
  • a gaseous fluid for example air, argon or other
  • a pressure of 300 to 350 kPa can be used.
  • pressures of 270 to 320 kPa can be used.
  • the projection distance can be from 5 to 25 cm, for example from 10 to 20 cm.
  • the projection time can be from 0.2 to 3 minutes, preferably from 0.5 to 2 minutes (in particular for a surface area of a few cm 2 ).
  • Use may be made, by way of example, of a plant which can contain approximately 40 litres of particles, projected using a nozzle with a diameter of 7 to 8 mm, with compressed air under a pressure of 2.5 to 3.5 bars.
  • the surface of the wall to be treated can be pretreated by the chemical treatment stage described below.
  • This stage makes possible the at least partial dissolution of the carbides, in particular of the chromium carbides, and brings about the formation of cavities.
  • the permanent plastic deformation obtained by the implementation of the mechanical treatment stage makes it possible to fill these cavities in again, at least partially.
  • covering of the carbides present at the surface which have not been dissolved by the chemical treatment stage is also observed. This modification of the surface, which limits the access to the carbides trapped inside the metal alloy, also makes it possible to reduce the formation of coke.
  • the impact surface treatment stage can be carried out under conditions suitable for obtaining covering of the carbides, indeed even also the closing of the cavities formed during an electrochemical dissolution stage when it is present, over a depth of at least 20 ⁇ m, preferably over a depth of at least 30 ⁇ m.
  • This mechanical stage is preferably carried out “under cold conditions”, in other words at ambient temperature, namely a temperature ranging from 5 to 35° C.
  • this stage is preferably carried out before the mechanical surface treatment stage described above. More specifically, this stage is an electrochemical stage, in particular a selective dissolution electrochemical stage.
  • this stage is advantageously carried out under conditions suitable for dissolving at least a part of these carbides over a depth of at least 10 ⁇ m (from the treated surface), preferably of at least 20 ⁇ m, more preferably of at least 30 ⁇ m, indeed even of at least 40 ⁇ m.
  • the electrolytic dissolution conditions can advantageously be suitable for dissolving one or more carbides chosen from chromium carbides, niobium carbides, when the alloy contains niobium, carbonitrides, when the alloy contains nitrogen, indeed even other carbides, preferably chromium carbides.
  • the process according to the invention can comprise at least one other chemical treatment stage, during which at least a part of the carbides initially present in the alloy, in particular at the surface, and not dissolved during a preceding chemical treatment stage is removed by electrolytic dissolution.
  • a washing stage can be provided between two successive chemical treatment stages under conditions capable of removing the traces of electrolytes from the treated surface. It can be one or more stages of rinsing the wall with water, preferably distilled water, optionally followed by one or more stages of rinsing with an alcohol, for example ethanol. This washing can be followed by a drying under conditions which make it possible to remove the rinsing fluid or fluids from the wall to be treated.
  • the electrochemical dissolution of the chromium carbides is carried out and then the electrochemical dissolution of the niobium carbides is carried out.
  • the chemical stage is carried out by placing the wall to be treated at the anode of an electrolysis cell, the cathode being formed of a conductive part (for example made of metal or graphite), and by applying an electric potential through the electrolysis cell.
  • a conductive part for example made of metal or graphite
  • the chemical treatment stage can be carried out in an electrolysis cell comprising an aqueous solution of an alkali metal hydroxide or an aqueous sulfuric acid solution.
  • the electrolytic solution can thus comprise an aqueous solution of a soluble metal hydroxide.
  • This metal can be an alkali metal, such as Na, K or Li, for example Na.
  • the electrolytic solution can comprise from 100 to 200 g/l of alkali metal hydroxide, preferably from 120 to 150 g/l.
  • the chloride content of the solution is less than 10 ppm by weight.
  • niobium carbides A procedure for the dissolution of niobium carbides is, for example, described in “Anode dissolution characteristics of titanium, niobium and chromium carbides”, 1971, V. Cihal, A. Desestret, M. Froment and G. H. Wagner.
  • the electrolytic solution can thus be an aqueous sulfuric acid solution, the sulfuric acid concentration of which can be from 1 to 10 mol ⁇ l ⁇ 1 , preferably from 2 to 9 mol ⁇ l ⁇ 1 .
  • the invention is not limited to these specific conditions: a person skilled in the art is in a position to determine other suitable concentrations of sulfuric acid, indeed even to use other suitable electrolytic solutions.
  • the difference in electric potential applied to the electrolysis cell can be from 4 to 8 volts or from 3 to volts, indeed even from 3 to 5 volts. It may be preferable to avoid greater differences in potentials in order not to generate too much heat.
  • the current flow passing through the electrolysis cell can vary according to the surface area to be treated.
  • the current density can typically be from 5 A/in 2 (7750 A/m 2 ) to 10 A/in 2 (15 500 A/m 2 ) of surface area of wall to be treated.
  • the duration of the treatment can be variable, for example from 4 to 50 hours or from 2 to 50 hours, for example from 2 to 30 hours, depending on the amount of carbides and/or on the depth of wall which it is desired to treat.
  • the temperature of the electrolytic solution can vary from ambient temperature up to approximately 85° C. However, it is preferable for the temperature of the solution to be kept below 60° C.
  • This stage is carried out after the mechanical surface treatment stage. It is carried out under conditions which make it possible to form a layer of oxide(s) on the treated surface of the wall, in particular a layer containing one or more chromium oxides.
  • the oxidation conditions can be those generally used to form a layer of oxide(s) on this type of alloy and known from from the prior art.
  • the oxidation can be carried out at a temperature of 800 to 1100° C., under partial molecular oxygen pressure of 10 ⁇ 6 atm to 0.2 atm, for a period of time of 30 min to 5 h.
  • FIG. 1 diagrammatically represents an electrolysis cell which can be used for the chemical surface treatment stage
  • FIGS. 2 and 3 represent SEM photographs of sections of two samples which have been subjected to a selective dissolution electrochemical treatment
  • FIGS. 4 to 7 are diagrammatic representations of the observations in section of samples which have respectively been subjected to: only a polishing ( FIG. 4 ), an electrochemical dissolution treatment ( FIG. 5 ), a mechanical surface treatment ( FIG. 6 ), an electrochemical dissolution treatment followed by a mechanical surface treatment ( FIG. 7 );
  • FIGS. 8 to 11 are SEM photographs with a secondary electron detector (applied acceleration voltage of 20 kV— FIG. 7-8, 10-11 , or 25 kV— FIG. 9 ) of sections of samples, according to two magnifications:
  • FIGS. 8 a , 8 b show photographs of a reference sample
  • FIGS. 9 a , 9 b show photographs of a sample which has been subjected to an electrochemical dissolution treatment
  • FIGS. 10 a , 10 b show photographs of a sample which has been subjected to a mechanical alumina blasting treatment
  • FIGS. 11 a , 11 b show photographs of a sample which has been subjected to an electrochemical dissolution treatment followed by a mechanical alumina blasting treatment.
  • FIG. 1 diagrammatically represents an electrolysis cell 1 .
  • a difference in electric potential is applied between two electrodes 2 , 3 immersed in an electrolytic solution 4 .
  • the positive terminal is the anode 2 , the site of an oxidation, and the negative terminal is the cathode 3 , the site of a reduction.
  • a direct current generator 5 connected to the anode 2 and to the cathode 3 , provides the current.
  • the substance to be dissolved has to be located on the anode 2 (+ terminal).
  • the space between the two electrodes 2 , 3 is, for example, approximately 1 cm.
  • a simple metal plate can be used for the cathode (the ⁇ terminal).
  • the electrolyte 4 will, for example, be a sodium hydroxide solution.
  • the samples used are plaques with dimensions of 8 ⁇ 30 mm (samples C1 to C5) and 8 ⁇ 25 mm (samples C6 to C9) and with a thickness of 2 mm obtained by electrical discharge machining to the core of 5 cm portions of new steam cracking tubes, with an initial thickness of 8 mm.
  • the initial surface state is a crude machining state.
  • the tubes from which the tested samples result were manufactured by centrifugal casting.
  • Each tested sample was polished by means of SiC-based abrasive papers in the following order of fineness: 600, 800, 1200 and 2400.
  • the sample is subjected to an electrolytic dissolution chemical treatment.
  • the sample to be tested is placed at the anode of an electrolysis cell, such as described in FIG. 1 , the cathode being a metal plate made of stainless steel or of graphite, with dimensions similar to or greater than those of the sample.
  • the anode and cathode are separated by a distance of approximately 1 cm, the plates being substantially parallel inside the electrolysis cell.
  • An electrolytic solution is prepared by dissolving, with mechanical stirring, 135 g of NaOH (in the form of pellets) in 11 of distilled water and then the electrolysis cell is filled with the solution obtained.
  • the chloride content of the solution is less than 10 ppm by weight.
  • a potential difference is applied between the anode (sample) and the cathode.
  • the current intensity does not appear to influence the depth of dissolution of the chromium carbides, unlike the duration of the dissolution.
  • FIGS. 2 and 3 are photographs of the sample C4 dissolved for 15 h ( FIG. 2 ) and of the sample C5 dissolved for 20 h ( FIG. 3 ).
  • the acceleration voltage applied for the measurement is 15 kV
  • the magnification is 619 ⁇ ( FIG. 2 ) and 629 ⁇ ( FIG. 3 )
  • the scale is 10 ⁇ m.
  • cavities are observed over a depth of approximately 40 ⁇ m, which appears to indicate the existence of interconnected carbide networks.
  • the cavities extend over a depth of 80 ⁇ m. Chromium carbides still exist between 50 and 80 ⁇ m, which appears to indicate that the network of carbides is not completely interconnected.
  • Table 2 indicates, for the samples C6 to C9, the maximum depth down to which dissolution of the chromium carbides was observed.
  • FIGS. 4 and 5 diagrammatically represent typical observations of a section of an untreated sample ( FIG. 4 ) and of a sample which has been subjected to a chemical treatment ( FIG. 5 ).
  • the black parts correspond to the chromium carbides and the grey parts to the niobium carbides.
  • Niobium carbides are observed in the cavities.
  • the solution might spread by dissolving the chromium carbides resulting from the interconnected networks but while retaining the niobium carbides (NbC).
  • NbC niobium carbides
  • a polished HP 25-35 alloy sample is subjected to shot peening in a sleeve sandblasting chamber.
  • the parameters used are as follows:
  • a sample M1 is obtained.
  • a polished HP 25-35 alloy sample is subjected to alumina blasting in a sleeve sandblasting chamber.
  • the parameters used are as follows:
  • a sample M3 is obtained.
  • FIG. 6 diagrammatically represents the typical observation of a section of a sample which has been subjected to a mechanical treatment. It is noted that the chromium carbides are no longer in direct contact with the surface.
  • Example 1 The sample C4 of Example 1 is subjected to the same shot peening treatment as that described in Example 2. A sample CM4 is obtained.
  • Example 1 The sample C4 of Example 1 is subjected to the same alumina blasting treatment as that described in Example 3. A sample CM5 is obtained.
  • FIG. 7 diagrammatically represents the typical observation of a section of an alloy sample which has been subjected to a chemical and mechanical treatment. It is noted that the chromium carbides are no longer in direct contact with the surface and that the cavities formed by the electrochemical dissolution have been at least partly closed for the majority of them.
  • Coking tests were carried out on the samples C4, M2, M3, CM4 and CM5 prepared in Examples 1 to 5, and also on a reference sample simply polished.
  • the samples were brought to high temperature in the presence of a mixture of light hydrocarbons and of steam (similar to industrial conditions). They were thus subjected to conditions favouring the formation of coke.
  • FIGS. 8 a and 8 b are photographs (magnifications 35 ⁇ and 150 ⁇ respectively) of the surface of the reference sample which has not been subjected to any specific treatment besides the initial polishing. The formation of coke at the surface is observed.
  • FIGS. 9 a and 9 b are photographs of the sample M1-shot peened (magnifications 35 ⁇ and 150 ⁇ respectively)
  • FIGS. 10 a and 10 b are photographs of the sample M2-alumina blasted (magnifications 35 ⁇ and 150 ⁇ respectively)
  • FIGS. 11 a and 11 b are photographs of the sample CM5 (magnifications 35 ⁇ and 150 ⁇ respectively).
  • the samples which have been subjected to a chemical treatment exhibit overall less coke than the reference sample. Coke is still observed over approximately 10% of the surface of the sample.
  • the sample which has been subjected to the most violent treatment exhibits a dented surface with numerous protrusions due to the impacts of the projectiles.
  • the samples which have been subjected to a mechanical treatment exhibit less coke than the reference sample.
  • the amounts of coke formed on the shot-peened sample (M1) and the alumina-blasted sample (M2) appear to be similar (see figures).
  • samples CM4 and CM5 A notable reduction in the amount of coke is also observed for the samples which have been subjected to a chemical treatment prior to the mechanical treatment (samples CM4 and CM5), as may be made out in FIGS. 11 a and 1 lb for the sample CM5.
  • the sample is subjected to an electrolytic dissolution chemical treatment in order to remove the niobium carbides.
  • the sample to be tested is placed at the anode of an electrolysis cell of the same type as that represented in FIG. 1 and described in Example 1.
  • a 7.2 mol ⁇ l ⁇ 1 electrolytic solution of sulfuric acid (H 2 SO 4 ) is prepared, with which the electrolysis cell is filled.
  • a first test was carried out on an HP 25-35 alloy with dimensions of 8 ⁇ 25 mm and with a thickness of 2 mm, which was polished before being placed in the sulfuric acid solution.
  • a potential difference of the order of 0.8 V is applied between the anode (sample) and the cathode for 2 hours.
  • the sample is subsequently rinsed with distilled water and then with ethanol, dried and stored in a case sheltered from scratches and from the air in a desiccator.
  • a second test was carried out under the same electrolysis conditions on a sample with the same dimensions and of the same alloy subjected beforehand to an electrolytic dissolution of the chromium carbides.
  • the latter is carried out with a current density of 5 A ⁇ in ⁇ 2 (0.775 A ⁇ cm ⁇ 2 ) for 2 hours in a NaOH solution (135 g in the form of pellets in 1 l of water).
  • the sample obtained is subsequently rinsed with distilled water and then with ethanol and dried before being introduced into the sulfuric acid solution for the dissolution of the niobium carbides.
  • the successive electrolytic decomposition of the chromium carbides and of the niobium carbides thus makes it possible to dissolve the NbCs at the surface.
  • the electrolytic dissolution of the M 23 C 6 /M 7 C 3 might come partially “to lay bare” the NbCs and to increase the free surface area in contact with the electrolyte of the second dissolution.

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US16/471,024 2016-12-20 2017-12-19 Mechanical Wall-Treatment Method That Reduces Coke Formation, and Hydrocarbon Treatment Method Abandoned US20200016724A1 (en)

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FR1662903A FR3060430B1 (fr) 2016-12-20 2016-12-20 Procede de traitement mecanique d'une paroi reduisant la formation de coke.
PCT/EP2017/083563 WO2018114960A1 (fr) 2016-12-20 2017-12-19 Procede de traitement mecanique d'une paroi reduisant la formation de coke et procédé de traitement d'hydrocarbures

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US3865634A (en) * 1973-08-13 1975-02-11 Exxon Research Engineering Co Heat resistant alloy for carburization resistance
US4851093A (en) * 1988-06-06 1989-07-25 United Technologies Corporation Selective decomposition of a chromium carbide coating from a chromium carbide coated nickel alloy substrate
FR2698576B1 (fr) * 1992-11-30 1995-02-17 Framatome Sa Procédé et dispositif de réparation d'une zone défectueuse de la paroi d'une pièce métallique et en particulier d'une pièce tubulaire.
FR2798939B1 (fr) * 1999-09-24 2001-11-09 Atofina Reduction du cokage dans les reacteurs de craquage
JP4183926B2 (ja) * 2001-04-19 2008-11-19 三井金属鉱業株式会社 タンタル／ニオブ含有の炭化物系原料からのタンタル／ニオブの回収方法
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