Chemical Wall-Treatment Method That Reduces the Formation of Coke

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 chemical surface treatment stage, during which at least a part of the carbides initially present in the alloy is dissolved by electrolytic decomposition, under conditions suitable for dissolving at least a part of these carbides, in particular chromium carbides.

1 .- 15 . (canceled) 
     
     
         16 . 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 chemical surface treatment stage, during which at least a part of the carbides initially present in the alloy, in particular at the surface, is removed by electrolytic dissolution. 
 
     
     
         17 . The process according to  claim 16 , 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. 
     
     
         18 . The process according to  claim 16 , in which the chemical treatment stage is carried out under conditions suitable for dissolving at least a part of the carbides chosen from chromium carbides, niobium carbide, when the alloy contains niobium, and carbonitrides, when the alloy contains nitrogen. 
     
     
         19 . The process according to  claim 16 , in which the chemical treatment stage is carried out in an electrolysis cell comprising an aqueous solution chosen from a solution of an alkali metal hydroxide and a sulfuric acid solution. 
     
     
         20 . The process according to  claim 16 , 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. 
     
     
         21 . The process according to  claim 16 , 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.   
     
     
         22 . The process according to  claim 21 , in which the electrochemical dissolution of the chromium carbides is carried out and then the electrochemical dissolution of the niobium carbides is carried out. 
     
     
         23 . The process according to  claim 16 , characterized in that it additionally comprises, after the chemical surface treatment stage:
 a mechanical stage of impact surface treatment, during which the surface of the wall which has been subjected to the chemical treatment is hammered by projection of particles under conditions suitable for obtaining a permanent plastic deformation of the surface.   
     
     
         24 . The process according to  claim 23 , 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. 
     
     
         25 . The process according to  claim 23 , in which the particles used during the mechanical treatment stage have a mean diameter of 100 to 500 μm. 
     
     
         26 . The process according to  claim 23 , in which, during the mechanical treatment stage, the particles are projected by a gaseous fluid under a pressure of 200 to 400 kPa. 
     
     
         27 . The process according to  claim 16 , in which 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. 
     
     
         28 . The process according to  claim 16 , characterized in that it comprises, after the chemical treatment stage and optionally after the mechanical surface treatment stage, when it is carried out:
 an oxidation stage carried out under conditions suitable for forming a layer of oxide(s) on the surface which has been subjected to the chemical treatment and optionally the mechanical treatment, in particular a layer containing one or more chromium oxides.   
     
     
         29 . 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 claim  15  so as to reduce the formation of a coke deposit. 
     
     
         30 . A process for the treatment of hydrocarbons according to  claim 29 , in which the hydrocarbons are brought into contact with the surface of the metal wall at a temperature of 800 to 900° C.