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

Abstract

The invention relates to a process for the treatment of a wall made of Fe—Ni—Cr metal alloy of an industrial reactor which reduces the formation of coke on the said wall when it is subjected to operational conditions favourable to coking, the metal alloy comprising, within its structure, carbides, some of which show on the surface. 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, in particular of the chromium carbides.

1 .- 14 . (canceled) 
     
     
         15 . A process for the treatment of a wall made of Fe—Ni—Cr metal alloy of an industrial reactor which reduces the formation of coke on the said wall when it is subjected to operational conditions favourable to coking, the metal alloy comprising, within its structure, carbides, some of which can show on the surface, the process comprising:
 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 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. 
 
     
     
         16 . The process according to  claim 15 , in which the particles used during the mechanical treatment stage are chosen from aluminium oxide particles, metal particles, beads made of material which is inert under the said operational conditions, or nesosilicate particles. 
     
     
         17 . The process according to  claim 15 , in which the particles used during the mechanical treatment stage have a mean diameter of 100 to 500 μm. 
     
     
         18 . The process according to  claim 15 , in which, during the mechanical treatment stage, the particles are projected by a gaseous fluid under a pressure of 200 to 400 kPa. 
     
     
         19 . The process according to  claim 15 , characterized in that it additionally comprises, before the mechanical surface treatment stage:
 a stage of chemical treatment of the surface of the wall to be treated, during which at least a part of the carbides initially present in the alloy, in particular at the surface, is removed by electrolytic dissolution.   
     
     
         20 . The process according to  claim 19 , in which the chemical treatment stage is carried out under conditions suitable for dissolving at least a part of the carbides over a depth of at least 10 μm. 
     
     
         21 . The process according to  claim 19 , characterized in that the chemical surface treatment stage is carried out under conditions suitable for dissolving carbides chosen from chromium carbides, niobium carbide, when the alloy contains niobium, and carbonitrides, when the alloy contains nitrogen. 
     
     
         22 . The process according to  claim 19 , in which the chemical treatment stage is carried out in an electrolysis cell comprising a solution chosen from an aqueous solution of an alkali metal hydroxide and an aqueous sulfuric acid solution. 
     
     
         23 . The process according to  claim 19 , comprising 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. 
     
     
         24 . The process according to  claim 19 , in which:
 one chemical treatment stage is a stage of electrolytic dissolution of chromium carbides,   another chemical treatment stage is a stage of electrolytic dissolution of niobium carbides, the metal alloy containing niobium.   
     
     
         25 . The process according to  claim 24 , in which the electrochemical dissolution of the chromium carbides is carried out and then the electrochemical dissolution of the niobium carbides is carried out. 
     
     
         26 . The process according to  claim 15 , characterized in that it comprises, after the mechanical surface treatment stage:
 an oxidation stage carried out under conditions suitable for forming a layer of oxide(s) on the surface which has been subjected to the mechanical treatment, in particular a layer containing one or more chromium oxides.   
     
     
         27 . 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 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 said surface of the metal wall being pretreated by a treatment process according to claim  14  so as to reduce the formation of a coke deposit. 
     
     
         28 . A process for the treatment of hydrocarbons according to  claim 27 , in which the hydrocarbons are brought into contact with the surface of the metal wall at a temperature of 800 to 900° C.