Reduced fouling from the convection section of a cracker

Abstract

Crackers for hydrocarbon such as naphtha and C2-C4 paraffins contain a radiant section and a convection section. The exhaust gases leaving the radiant section pass through the convection. Generally fouling from the convection section was low relative to fouling (e.g., coke build up) in the radiant section. With improved metallurgy and operating conditions, the time between decokes of the radiant section has increased and now there is a need to reduce fouling from the convection section. This may be achieved by using stainless steel, and particularly high nickel, high chrome stainless steel in the passes in the convection section.

What is claimed is: 
     
         1 . A convection section of a furnace to treat hydrocarbons wherein not less than 50% of the coil length upstream from the feed outlet of the convection section, comprise less than 66 wt. % of Fe and the balance a mixture of 23 to 26 wt % of Cr; 19 to 22 wt. % of Ni; and one or more components selected from C, Mn, Si, P, and S. 
     
     
         2 . A convection section of a furnace wherein not less than 75% of the coil length upstream from the feed outlet of the convection section have the composition of  claim 1 . 
     
     
         3 . The convection section of a furnace to treat hydrocarbons according to  claim 1 , wherein the coils further comprise 0.08 to 0.2 wt. % C; 1.5 to 2.5 wt. % Mn; 1.5 to 3 wt % of Si, 0.04 to 0.05 wt. % P; and 0.25 to 0.35 wt. % of S. 
     
     
         4 . The convection section of a furnace according to  claim 3 , wherein the hydrocarbons comprise one or more from C 2 -C 4  paraffins. 
     
     
         5 . A method to reduce fouling in the convection section of a furnace to treat hydrocarbons wherein not less than 50% of the coil length from the feed outlet of the convection section comprises less than 66 wt. % of Fe and the balance a mixture of 23 to 26 wt. % of Cr; 19 to 22 wt. % of Ni; and one or more components selected from C, Mn, Si, P, and S. 
     
     
         6 . The method according to  claim 5 , wherein not less than 75% of the coil length from the feed outlet of the convection section have the composition of  claim 5 . 
     
     
         7 . The method according to  claim 6 , wherein the coils further comprise 0.08 to 0.2 wt. % C; 1.5 to 2.5 wt. % Mn; 1.5 to 3 wt. % of Si, 0.04 to 0.05 wt. % P; and 0.25 to 0.35 wt. % of S. 
     
     
         8 . The method according to  claim 6 , wherein the hydrocarbons comprise one or more from C 2 -C 4  paraffins. 
     
     
         9 . The method according to  claim 8 , wherein the hydrocarbon is ethane.