Transfer line exchanger with thermal spray coating

Abstract

The present disclosure refers to transfer line exchangers with improved cooling capacity, equipped with a thermal spray coating in crackers and a method for the maintenance of transfer line exchangers with the help of a thermal spray coating. In some embodiments, the thermal spray coating is obtained from a spray material formed of Cr3C2 and a NiCr alloy. Preferably, the spray coating material comprises at least 60 wt.-%, preferably at least 70 wt.-% of Cr3C2, based on the total weight of the spray material.

1 . A transfer line exchanger with cooling tubes through which the gas to be cooled is processed, wherein the inner surface of each cooling tube is at least partially equipped with a thermal spray coating obtained from a spray coating material comprising Cr 3 C 2  and a NiCr alloy. 
     
     
         2 . The transfer line exchanger of  claim 1 , wherein the spray coating material comprises at least 60 wt.-% of Cr 3 C 2 , based on the total weight of the spray coating material. 
     
     
         3 . The transfer line exchanger of  claim 1 , wherein the gas inlet side of each cooling tube, which is impacted by gas as the gas enters the cooling tube, is equipped with the thermal spray coating. 
     
     
         4 . The transfer line exchanger of  claim 1 , wherein the thermal spray coating extends at least 100 mm into the cooling tube from the gas inlet side. 
     
     
         5 . The transfer line exchanger of  claim 1 , wherein the thermal spray coating has a thickness of 0.1 to 0.5 mm. 
     
     
         6 . The transfer line exchanger of  claim 1 , wherein the thermal spray coating is directly applied on-site to the surface of the cooling tube. 
     
     
         7 . The transfer line exchanger of  claim 1 , wherein the thermal spray coating is a weldable coating. 
     
     
         8 . The transfer line exchanger of  claim 1 , wherein the thermal spray coating is applied by HVOF (High Velocity Oxy-Fuel Spraying), Combustion Flame Spraying, Plasma Spraying, Vacuum Plasma Spraying, or Two-Wire Electric Arc Spraying. 
     
     
         9 . The transfer line exchanger of  claim 1 , wherein each cooling tube is secured by a tube plate at both ends of the tubes and the tube plate at the gas inlet side is equipped with a thermal spray coating. 
     
     
         10 . The transfer line exchanger of  claim 1 , wherein at least one cooling tube comprises at least two tube segments welded to each other at a welding area and at least one segment is provided with the thermal spray coating adjoining to the welding area. 
     
     
         11 . An apparatus for the production of olefins comprising the transfer line exchanger of  claim 1 . 
     
     
         12 . A process for cracking hydrocarbons, comprising the steps of:
 (i) feeding a feedstock of hydrocarbons into a cracking coil located inside a thermal reactor;   (ii) heating the feedstock, thereby obtaining a cracking gas; and   (iii) ‘introducing the cracking gas into a transfer line exchanger for cooling, wherein the transfer line exchanger is a transfer line exchanger of  claim 1 .   
     
     
         13 . The process for cracking hydrocarbons of  claim 12 , further comprising a maintenance phase comprising the steps of:
 (iv) detecting faults on the inner surface of the cooling tubes; and   (v) applying the thermal spray coating to the faults,   wherein the cooling tube has a process side and a water side.   
     
     
         14 . The process of  claim 13 , wherein the step of detecting of faults is conducted by measuring the wall thickness of the cooling tube on the process side. 
     
     
         15 . The process of  claim 13 , wherein the water side surface of the cooling tubes of the transfer line heat exchanger is monitored by measuring the wall thickness of the cooling tubes on the process side of the tubes.