# US 4,397,740 A · Method and apparatus for cooling thermally cracked hydrocarbon gases > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,397,740 A - Document ID: US4397740A - Status: Granted - Kind: A - Application number: 06/429,717 - Filed: 1982-09-30 - Granted: 1983-08-09 - Earliest claimed: 1982-09-30 - Assignees: Phillips Petroleum Company - Inventors: Stephen L. Koontz - Web page: https://patentgrep.com/patent/US4397740A ## CPC - C07C 4/04: Thermal processes {(C07C4/025 takes precedence)} - C10G 9/002: {Cooling of cracked gases} - F28D 7/163: {with conduit assemblies having a particular shape, e.g. square or annular; with assemblies of conduits having different geometrical features; with multiple groups of conduits connected in series or parallel and arranged inside common casing (F28D7/1615 takes precedence)} - F28F 19/00: Preventing the formation of deposits or corrosion, e.g. by using filters {or scrapers} - Y10S 585/95: Prevention or removal of corrosion or solid deposits - C07C: ACYCLIC OR CARBOCYCLIC COMPOUNDS - C10G: CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION (cracking to hydrogen or synthesis gas C01B; cracking or pyrolysis of hydrocarbon gases to individual hydrocarbons or mixtures thereof of definite or specified constitution C07C; cracking to cokes C10B); RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES - F28D: HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT (fluid heaters having heat generating means and heat transferring means F24H; furnaces F27; details of heat-exchange apparatus of general) - F28F: DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION (water and air traps, air venting F16) - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS ## Abstract The flow of cracked gases, for example, from an ethylene plant through the tubes of a transfer line heat exchanger is equalized by employing larger cross-section tubes in the outer portion of the exchanger and smaller cross-section tubes in the inner portion of the exchanger thereby preventing, or substantially minimizing, build-up of coke deposits in the exchanger, especially in the inlets of the tubes in the outer portion where coke formation conventionally occurs. ## Claims ### Claim 1 A method for minimizing a formation of coke during cooling of a thermally cracked hydrocarbon stream in a shell-tube heat exchange zone which comprises passing a thermally cracked hydrocarbon stream through a plurality of tubular flow paths surrounded by a heat exchange fluid in the shell portion of said heat exchange zone, equalizing the rate of flow of said stream through the flow paths in said heat exchanger by providing a plurality of flow paths in a central portion of said heat exchanger with each of said flow paths having a smaller cross-sectional area than the flow paths in an annular or peripheral section surrounding the flow paths in the central portion, and thereby minimizing the amount of coke deposition in said heat exchange zone. ### Claim 2 (depends on 1) A method according to claim 1 wherein the total cross-sectional area for the flow paths in the central portion of said heat exchange zone is about 95 to 290%, the total cross-sectional area of the flow paths in the said annular or peripheral section. ### Claim 3 (depends on 1) A method according to claim 1 wherein the total number of flow paths in said central portion of said heat exchange zone comprises about 65 to about 85 percent of the total tubes and the total number of flow paths in said annular or peripheral section comprises about 35 to about 15 percent of the total number of flow paths. ### Claim 4 (depends on 3) A method according to claim 3 wherein the individual flow paths in said central portion and said annular section are of substantially uniform cross-sectional area throughout the length of each of the flow paths. ### Claim 5 (depends on 1) A method according to claim 1 wherein the number of flow paths in said central portion is approximately 80 with each having an inner diameter of about 1.3 inches and the number of flow paths in the annular or peripheral section is about 25 with each having an inner diameter of about 2 inches. ### Claim 6 A method of cracking hydrocarbons to produce a gaseous cracked product with a minimum of coke formation during quenching or cooling which comprises cracking a hydrocarbon feed at an elevated temperature to produce a gaseous cracked product comprising olefins and coke-forming hydrocarbons, cooling the gaseous cracked product by passing it through a multi-tubular transfer line exchanger in indirect heat exchange relationship with a heat exchange fluid wherein the tubular flow paths positioned in the central or core portion of said transfer line exchanger are of smaller cross-section area than the outer flow paths arranged in an annular pattern around the tubular flow paths in the central portion of the exchanger so that the rate of flow of gaseous cracked product through all flow paths is about the same, thereby minimizing build-up of coke in the transfer line exchanger. ### Claim 7 (depends on 6) A method according to claim 6 wherein the total cross-sectional area for the flow paths in the central portion of said heat exchange zone is about 95 to 290% the total cross-sectional area of the flow paths in the said annular section. ### Claim 8 (depends on 6) A method according to claim 6 wherein the total number of flow paths in said central portion of said heat exchange zone comprises about 65 to about 85 percent of the total tubes and the total number of flow paths in said annular or peripheral section comprises about 35 to about 15 percent of the total number of flow paths. ### Claim 9 (depends on 8) A method according to claim 8 wherein the individual flow paths in said central portion and said annular section are of substantially uniform cross-sectional area throughout the length of each of the flow paths. ### Claim 10 (depends on 6) A method according to claim 6 wherein the number of flow paths in said central portion is approximately 80 with each having an inner diameter of about 1.3 inches and the number of flow paths in said annular section is about 25 with each having an inner diameter of about 2 inches. ### Claim 11 A system for cracking hydrocarbons and cooling the cracked effluent with minimum coke deposition in a multi-tubular indirect quench-cooling heat exchanger which comprises: (a) a furnace for cracking a hydrocarbon feed, said furnace having an inlet pipe for entrance of the hydrocarbon feed to the furnacre and an outlet pipe for removal of gaseous cracked product, (b) a conduit means connected to said outlet pipe and in open communication with the inlet of a multi-tubular shell-tube indirect heat exchanger, (c) inlet conduit means and outlet conduit means connected to the shell of said heat exchanger for introduction and withdrawal of heat exchange fluid surrounding the tubes within said heat exchanger, (d) an outlet pipe connected to said heat exchanger for withdrawal of cooled gaseous product, and (e) an inlet tube sheet and an outlet tube sheet positioned within said heat exchanger with each tube sheet being connected to a plurality of tubes for passage of gaseous product from said furnace through said heat exchanger in indirect heat exchange relationship with heat exchange fluid in the shell side of said heat exchanger, said tubes being so-sized that the rate of flow of gaseous product throughout each of the tubes is substantially equal and so-arranged that tubes of smaller diameter are positioned within a central portion of said heat exchanger and tubes of larger diameter are positioned in annular section surrounding the tubes in the central portion with the proviso that the total number of tubes in said central portion comprises about 65 to about 85 percent of the total tubes and the number of tubes in the annular section comprises about 35 to about 15 percent of the total number of tubes. ### Claim 12 (depends on 11) A system according to claim 11 wherein the total cross-sectional area for the tubes in the central portion of said heat exchanger is about 95 to about 290 percent of the total cross-sectional area of the flow paths in the annular section. ### Claim 13 (depends on 11) A system according to claim 11 wherein the number of tubes in the central portion is about 80 with each having an inner diameter of about 1.3 inches and the number of tubes in the annular section is about 25 with each having an inner diameter of about 2 inches.