Process and Apparatus for Steam Cracking Hydrocarbon Feedstocks

Abstract

The present disclosure provides a process for treating a hydrocarbon feedstock comprising: (a) feeding the hydrocarbon feedstock at a linear velocity equal to or less than 0.9 m/s to a first preheating zone in the convection section of a steam cracking furnace; (b) preheating the hydrocarbon feedstock in the first preheating zone to vaporize less than 99 wt. % of the hydrocarbon feedstock to form a vapor-liquid mixture; (c) separating at least a portion of the vapor-liquid mixture to form a vapor fraction and a liquid fraction; and (d) feeding at least a portion of the vapor fraction to the steam cracking furnace.

1 . A process for treating a hydrocarbon feedstock comprising:
 a. feeding said hydrocarbon feedstock at a linear velocity equal to or less than 0.9 m/s to a first preheating zone in the convection section of a steam cracking furnace;   b. preheating said hydrocarbon feedstock in said first preheating zone to vaporize less than 99 wt. % of said hydrocarbon feedstock to form a vapor-liquid mixture;   c. separating at least a portion of said vapor-liquid mixture to form a vapor fraction and a liquid fraction; and   d. feeding at least a portion of said vapor fraction to said steam cracking furnace.   
     
     
         2 . The process of  claim 1 , wherein said hydrocarbon feedstock is fed in substantially liquid phase. 
     
     
         3 . The process of  claim 1 , wherein said first convection section comprises multiple banks of heat exchange tubes and said hydrocarbon feedstock flows inside said tubes. 
     
     
         4 . The process of  claim 1 , wherein said linear velocity is in the range of 0.05 to 0.85 m/s. 
     
     
         5 . The process of  claim 1 , wherein said linear velocity is in the range of 0.1 to 0.80 m/s. 
     
     
         6 . The process of  claim 1 , wherein said first preheating zone comprises a first preheating section and a second preheating section, wherein said hydrocarbon feedstock is supplied to said first preheating section at a pressure in the range of 790 to 1480 kPa-a and a temperature in the range of 25 to 250° C. to form a preheated hydrocarbon product exiting said first preheating section at a temperature in the range of about 100 to 350° C., and then at least a portion of said preheated hydrocarbon product is supplied with a first diluent stream to said second preheating section to form said vapor-liquid mixture exiting said first preheating section at a temperature in the range of 350 to 500° C., at least 1 wt. % said vapor-liquid mixture based on the total weight of hydrocarbons in said vapor-liquid mixture is in liquid phase, and at least 60 wt. % said vapor-liquid mixture based on the total weight of hydrocarbons in said vapor-liquid mixture is in vapor phase. 
     
     
         7 . The process of  claim 1 , wherein 10 to 99.99 wt. % of said hydrocarbon feedstock boils below 590° C. measured according to ASTM D-2887. 
     
     
         8 . The process of  claim 1 , wherein said preheated hydrocarbon product is in substantially liquid phase. 
     
     
         9 . The process of  claim 1 , wherein said vapor-liquid mixture has a temperature in the range of 400 to 500° C. and comprises at least 2 wt. % liquid based on the total weight of hydrocarbons in said vapor-liquid mixture and wherein 50 to 99.99 wt. % of said hydrocarbon feedstock boils below 590° C. measured according to ASTM D-2887. 
     
     
         10 . The process of  claim 1 , wherein said vapor-liquid mixture has a temperature in the range of 450 to 500° C. and comprises at least 5 wt. % liquid based on the total weight of hydrocarbons in said vapor-liquid mixture and wherein 10 to 99.99 wt. % of said hydrocarbon feedstock boils below 590° C. measured according to ASTM D-2887. 
     
     
         11 . The process of  claim 1 , further comprising mixing a secondary diluent stream with said vapor-liquid mixture prior to said step (c). 
     
     
         12 . The process of  claim 11 , wherein a secondary diluent stream comprises steam. 
     
     
         13 . A process for cracking a hydrocarbon feedstock in a steam cracking furnace having a convection section, said convection section comprises a first bank, a second bank and a third bank of heat exchange tubes, said process comprising:
 a. feeding said hydrocarbon feedstock having at least 1 wt. % low volatile components and at least 0.1 wt. % coke precursors to said first bank of heat exchange tubes provided in said convection section, with an inlet linear velocity equal to or less than 0.9 m/s;   b. preheating said hydrocarbon feedstock to form a preheated hydrocarbon product having a temperature below 350° C.;   c. supplying at least a portion of said preheated hydrocarbon product with a first diluent stream to said second bank of heat exchange tubes to vaporize at least a portion of said hydrocarbon feedstock to form a vapor-liquid mixture having a temperature in the range of 350 to 500° C. and comprising at least 1 wt. % liquid based on the total weight of hydrocarbons in said vapor-liquid mixture;   d. separating at least a portion of said vapor-liquid mixture from step (c) to form a vapor fraction and a liquid fraction; and   e. feeding at least a portion of said vapor fraction from step (d) to said third bank of heat exchange tubes.   
     
     
         14 . The process of  claim 13 , further comprising mixing a second diluent stream to said vapor-liquid mixture prior to step (d). 
     
     
         15 . The process of  claim 13 , further comprising mixing said vapor fraction with a third diluent stream comprising steam prior to step (e). 
     
     
         16 . The process of  claim 13 , wherein 10 to 95 percent of said hydrocarbon feedstock boils below 590° C. measured according to ASTM D-2887. 
     
     
         17 . The process of  claim 13 , wherein said hydrocarbon feedstock comprises one or more of steam cracked gas oil and residues, gas oils, heating oil, jet fuel, diesel, kerosene, gasoline, coker naphtha, steam cracked naphtha, catalytically cracked naphtha, hydrocrackate, reformate, raffinate reformate, Fischer-Tropsch liquids, Fischer-Tropsch gases, Fischer-Tropsch waxes, distillate, crude oil, atmospheric pipestill bottoms, vacuum pipestill streams including bottoms, vacuum gas oils, heavy gas oil, naphtha contaminated with crude, atmospheric resid, heavy resid, C 4 's/residue admixture, naphtha residue admixture, and low sulfur waxy resid. 
     
     
         18 . A process for cracking a hydrocarbon feedstock to light olefins in a steam cracking furnace having radiant section burners and a convection section, said convection section comprises a first bank, a second bank and a third bank of heat exchange tubes, said process comprising:
 a. feeding said hydrocarbon feedstock at a pressure in the range of 790 to 1480 kPa-a and a temperature in the range of 25 to 250° C. to said first bank of heat exchange tubes provided in said convection section, with a linear velocity equal to or less than 0.9 m/s;   b. preheating said hydrocarbon feedstock to form a preheated hydrocarbon product having a temperature less than 350° C.;   c. supplying at least a portion of said preheated hydrocarbon product with a first diluent stream to said second bank of heat exchange tubes to vaporize at least a portion of said hydrocarbon feedstock to form a vapor-liquid mixture having a temperature in the range of 350 to 500° C. and comprising at least 1 wt. % liquid based on the total weight of hydrocarbons in said vapor-liquid mixture;   d. separating at least a portion of said vapor-liquid mixture from step (c) to form a vapor fraction and a liquid fraction; and   e. feeding at least a portion of said vapor fraction from step (d) to said third bank of heat exchange tubes.   
     
     
         19 . The process of  claim 18 , wherein said vapor-liquid mixture has a temperature in the range of 400 to 500° C. and comprises at least 2 wt. % liquid based on the total weight of hydrocarbons in said vapor-liquid mixture and wherein 50 to 99.99 wt. % of said hydrocarbon feedstock boils below 590° C. measured according to ASTM D-2887. 
     
     
         20 . The process of  claim 18 , wherein said vapor-liquid mixture has a temperature in the range of 425 to 500° C. and comprises at least 3 wt. % liquid based on the total weight of hydrocarbons in said vapor-liquid mixture and wherein 40 to 99.99 wt. % of said hydrocarbon feedstock boils below 590° C. measured according to ASTM D-2887. 
     
     
         21 . The process of  claim 18 , wherein said vapor-liquid mixture has a temperature in the range of 450 to 500° C. and comprises at least 5 wt. % liquid based on the total weight of hydrocarbons in said vapor-liquid mixture and wherein 10 to 99.99 wt. % of said hydrocarbon feedstock boils below 590° C. measured according to ASTM D-2887. 
     
     
         22 . The process of  claim 18 , wherein the total pressure drop for said first bank of heat exchange tubes is less than 100 kPa calculated by subtracting pressure at the inlet point of said first bank of heat exchange tubes from the exit point of said first bank of heat exchange tubes. 
     
     
         23 . The process of  claim 18 , wherein the total pressure drop for said second bank of heat exchange tubes is less than 500 kPa calculated by subtracting pressure at the inlet point of said second bank of heat exchange tubes from the exit point of said second bank of heat exchange tubes. 
     
     
         24 . Apparatus adapted for steam cracking a hydrocarbon feedstock to light olefins, comprising:
 a. a steam cracking furnace comprising radiant section burners adapted to provide radiant heat and hot flue gas and a convection section having a first bank, a second bank and a third bank of heat exchange tubes;   b. means for feeding said hydrocarbon feedstock to said first bank of heat exchange tubes with a linear velocity equal to or less than 0.9 m/s;   c. means for maintaining said hydrocarbon feedstock exiting said first bank of heat exchange tubes at a temperature less than 350° C.;   d. means for supplying a first diluent stream together with at least a portion of the preheated hydrocarbon product from (c) to said second bank of heat exchange tubes adapted to vaporize less than 99 wt. % of said hydrocarbon feedstock to form a vapor-liquid mixture;   e. means for maintaining said vapor-liquid mixture exiting said second bank of heat exchange tubes at a temperature in the range of 350 to 500° C.;   f. a vessel adapted to separate at least a portion of said vapor-liquid mixture from step (e) in to form a vapor fraction and a liquid fraction; and   g. means for feeding at least a portion of said vapor fraction from step (f) to said third bank of heat exchange tubes.   
     
     
         25 . The apparatus of  claim 24 , further comprising means for mixing a second diluent stream to said vapor-liquid mixture prior to (f).