System for steam-cracking hydrocarbons and transfer-line exchanger therefor

A system for cooling a gaseous product, containing ethylene, obtained directly from the steam-cracking of hydrocarbons at an elevated temperature, which comprises:

• passing said gaseous product upwardly and divergingly through the lower chamber of a bottom zone having an upper chamber and the lower chamber, each chamber having an upwardly diverging bottom wall with conical configuration;
• passing the gaseous product upwardly from the lower chamber of the bottom zone as separate vertical streams through the upper chamber of the bottom zone in indirect heat exchange relationship with steam and then upwardly through a longer intermediate zone in indirect heat exchange relationship with an aqueous fluid coolant;
• combining the streams of gaseous product in a top zone having an upwardly converging top wall;
• removing the combined gaseous product from the top zone;
• passing the aqueous fluid coolant upwardly through the intermediate zone for the indirect heat exchange relationship with the gaseous product streams passing upwardly through that zone;
• providing steam into the upper chamber of the bottom zone for the indirect heat exchange relationship with the gaseous product streams passing upwardly through the chamber;
• and
• passing steam from the upper chamber of the bottom zone downwardly into the lower chamber of the bottom zone for admixture with the gaseous product introduced into the bottom zone and for passage of the steam upwardly with the streams of the gaseous product through the upper chamber of the bottom zone and the intermediate zone in indirect heat exchange relationship with steam and aqueous fluid coolant, respectively.

A system, as an apparatus, for steam-cracking hydrocarbons to produce a gaseous steam-cracked product containing ethylene, which comprises:

• a first furnace for steam-cracking a heavy hydrocarbon feed, said first cracking furnace having a pipe with an inlet for entrance of the heavy hydrocarbon feed with water and an outlet for gaseous cracked product;
• a second furnace for steam-cracking a lighter hydrocarbon feed, said second cracking furnace having a pipe with an inlet for entrance of the lighter hydrocarbon feed with water and an outlet for gaseous cracked product;
• a mixer having first inlet, a second inlet and an outlet, said first inlet being connected to said outlet of said pipe of said first furnace;
• a first transfer-line exchanger having an outlet connected to said second inlet of said mixer and an inlet connected to said outlet of said pipe of said second furnace;
• and
• a second transfer-line exchanger having an inlet connected to said outlet of said mixer,
• whereby, in the use of the apparatus, the gaseous cracked product from the lighter hydrocarbon feed is cooled by passage through said first transfer-line exchanger and then mixed with the gaseous cracked product from the heavy hydrocarbon feed before that product from the heavy hydrocarbon feed is passed through the second transfer-line exchanger.

A system, as a process, for steam-cracking hydrocarbons to produce a gaseous steam-cracked product containing ethylene, which comprises:

• steam-cracking a heavy hydrocarbon feed at an elevated temperature to produce a first gaseous steam-cracked product containing ethylene;
• separately steam-cracking a lighter hydrocarbon at an elevated temperature to pro-uce a second gaseous steam-cracked product containing ethylene;
• cooling the second gaseous steam-cracked product by passing it through a transfer-line exchanger in indirect heat exchange relationship with an aqueous fluid coolant;
• mixing the cooled second gaseous steam-cracked product with the first gaseous steam-cracked product;
• and
• passing the mixture through a second transfer-line exchanger for indirect heat exchange relationship with aqueous fluid coolant.

A transfer-line exchanger, useful in a system for steam-cracking hydrocarbons to produce ethylene, which comprises:

• a vertical tank having:
• a cylindrical intermediate portion with side openings adjacent the top and bottom ends to withdraw and introduce, respectively, fluid coolant;
• a conical bottom entrance end portion connected to the bottom end of said intermediate portion;
• and
• a conical top exit end portion connected to the top end of said intermediate portion;
• a horizontal top tube sheet having a number of openings and supported by said tank at the top end of said intermediate portion of said tank;
• a horizontal bottom tube sheet having a number of openings corresponding to and in vertical alignment with said openings in said top tube sheet and an additional opening, said bottom tube sheet being supported in said tank at the bottom end of said intermediate portion of said tank;
• a horizontal sheet below and thinner than said horizontal bottom tube sheet and having a number of smaller openings corresponding to and in vertical alignment with said number of openings in said bottom tube sheet and having an additional opening corresponding in size and in vertical alignment with said additional opening in said bottom tube sheet;
• a conical shield having its vertex below its base and supported within said conical bottom entrance end portion of said tank to provide an upper chamber between said shield and said horizontal thinner sheet and a lower chamber between said shield and the bottom part of said conical bottom entrance end portion, said conical shield having a number of openings corresponding in size and number to and in vertical alignment with said number of smaller openings in said horizontal thinner sheet and said conical shield has the diameter of its base such that the periphery of said shield is spaced from said conical bottom entrance end portion of said tank to provide an annular space communicating said upper chamber above said conical shield with said lower chamber below said conical shield;
• a number of first vertical tubes corresponding in number to the said number of openings in said horizontal top and bottom tube sheets, said number of first vertical tubes extending into and between and being supported by said top and bottom tube sheets and said first vertical tubes closing said number of openings in said top and bottom tube sheets;
• and
• a number of second vertical tubes having thinner walls than said first vertical tubes and having the same inner diameter as that of said first vertical tubes, said second vertical tubes extending into said number of smaller openings in said thinner horizontal sheet and into said number of openings of said conical shield,
• said horizontal thinner sheet, said second vertical tubes and said conical shield being a subassembly supported in position with said horizontal thinner horizontal sheet abutting said horizontal bottom tube sheet.