Method and apparatus for quenching a hot gaseous stream

A process for cracking liquid hydrocarbon feed to produce cracked gaseous hydrocarbons, the process comprising the steps of:

• (a) feeding a liquid hydrocarbon feed stream to an olefins furnace;
• (b) cracking the liquid hydrocarbon feed stream in the olefins furnace to produce a hot gaseous cracked effluent stream having a temperature of about 1400 to about 1650° F.;
• (c) feeding the hot gaseous cracked effluent stream from the olefins furnace to the first section of a primary transfer line heat exchanger (TLE), which first section of said primary TLE comprises a shell-and-tube heat exchanger where the hot gaseous cracked effluent stream is indirectly cooled on the tube side while generating high-pressure steam from saturated steam on the shell side;
• (d) feeding the gaseous cracked effluent exiting the first section of the primary TLE to the tube side of a second section of the primary TLE, where a flow obstruction means is positioned in said tube side of the second section to create a low-pressure zone in said gaseous cracked effluent stream immediately downstream of said flow obstruction means, and where the gaseous cracked effluent stream is indirectly cooled on the tube side while generating saturated steam from boiler feed water on the shell side;
• (e) injecting a first wetting fluid tangentially into said gaseous cracked effluent stream at said low-pressure zone at a momentum sufficient to cause said wetting fluid to flow circumferentially around the inside surface of said tube side;
• providing a sharp interface between said gaseous cracked effluent stream and said first wetting fluid;
• and causing said first wetting fluid to contact and wet the downstream face of said flow obstruction means;
• and wherein the weight ratio of wetting fluid to the hot gaseous feed stream entering the tube side of a second section of the primary TLE is about 0.5 to about 2.0 and wherein the exit temperature of said gaseous effluent stream from the first section of said primary TLE is between about 1100° F. and about 1200° F. and the exit temperature of the second section of the primary TLE is approximately 50° F. above the temperature of the saturated steam being generated;
• (f) feeding the gaseous cracked effluent stream exiting from the second section of said primary TLE to a separator;
• (g) removing in the separator, a separator bottoms liquid stream comprising tar and heavier hydrocarbons and a separator product gas stream comprising an olefin rich product;
• (h) feeding the separator product gas stream exiting the separator to at least one secondary TLE where the separator product gas stream is indirectly cooled on the tube side to an exit temperature of between about 400 to about 500° F. while generating low-pressure steam on the shell side from boiler feed water and where a second flow obstruction means is positioned in said tube side of said secondary TLE to create a low-pressure zone in said product gas stream immediately downstream of said second flow obstruction means whereby a second wetting fluid is introduced at said low-pressure zone at sufficient flowrate to maintain the downstream internal surfaces in a wetted state;
• (i) feeding the gaseous cracked effluent stream exiting from said second TLE to a second separator;
• (j) removing from the second separator, a separator liquid bottoms stream comprising tar and heavier hydrocarbons and a separator product gas stream comprising an olefin rich product;
• and
• (k) recovering olefin product(s) from the separator product stream.