US3910347A

US3910347A - Cooling apparatus and process

Info

Publication number: US3910347A
Application number: US072765A
Authority: US
Inventors: Herman N Woebcke
Original assignee: Stone and Webster Engineering Corp
Current assignee: Stone and Webster Engineering Corp
Priority date: 1966-06-13
Filing date: 1970-09-16
Publication date: 1975-10-07
Anticipated expiration: 1992-10-07

Abstract

An apparatus and process for effecting heat exchange between hot effluent and a coolant. The heat exchange apparatus is substantially tubular in shape and is provided with a divergent inlet section having an angle of divergence less than 10*, and preferably 4* to 7*.

Description

United States Patent Woebcke Oct. 7, 1975 1 COOLING APPARATUS AND PROCESS [75] Inventor: Herman N. Woebcke, Wayland, [56] References Cited Mass- UNITED sTATEs PATENTS [73] Assignee: Stone & Webster Engineering 779,741 1/1905 Scheubner 165/156 Corporation, Boston, Mass 1,884,583 10/1932 Lucke et a1 165/157 1,884,778 8/1965 Hood, Jr. et al.... 165/135 [22] Filed: Sept. 16, 1970 2,904,400 9/1959 Asendorf et a1. 23/288 X 1 pp 72,765 FOREIGN PATENTS OR APPLICATIONS Related [1.8. Application Data 184,231 5/1907 Germany 165/158 [60] Continuationin-part of Ser. No. 802,790, Feb. 27, i

1969, abandoned, and a continuation-in-part of Ser. im ry Drummer-Charles J- Myhre No. 877,575, Nov. 26, 1969, which is a division of Assistant Examiner-Theophie W. Streule, Jr. Ser. No. 802,790, Feb. 27, 1969, abandoned, and a continuation-in-part of Ser. No. 729,878, May 10, 1968, abandoned, which is a division of Ser. No. [57] ABSTRACT 5 5, u 1966, Pat 3,722. An apparatus and process for effecting heat exchange between hot effluent and a coolant. The heat ex- 1 CL 165/147; 165/16 change apparatus is substantially tubular in shape and 23/277 R is provided with a divergent inlet section having an [51] Int. Cl F2811 7/12; F28f 13/08 angle of divergence less than 10, and preferably 4 to [58] Field of Search 165/142, 1, 157, 158,141, 7

18 Claims, 9 Drawing Figures US. Patent Oct. 7,1975 Sheet2of5, 3,910,347

FIGZ

INVENTOR. HERMAN N. WOEBCKE U.S Patent Oct. 1,1975 Shem of5 3,910,347

INVENTOR.

R: m! E I 070.. ET I v L, W/ 6 4, w M x 5 3 a. m E El Cl a 7 i 22 V. FIG. 4

I/ERMAN ,N- WOE'BC'K' B Y WW Wi U.S. Patent Oct. 7,1975 Sheet4 0f5 3,910,347

INVENTOR. HERMAN IV. WOE'BCKE US. Patent 0a. 7,1975 Sheet5 of5 3,910,347

INVENTOR. HER/m Al WOEBCAE BY Arran e g COOLING APPARATUS AND PROCESS CROSS REFERENCES TO RELATED APPLICATIONS This application is a continuationin-part of applications Ser. No. 802,790 filed Feb. 27, 1969 and Ser. No. 877,575 filed Nov. 26, 1969 as a divisional application of Ser. No. 802,790, now abandoned. Application Ser. No. 802,790 is a continuation-in-part of application Ser. No. 729,878 filed May 10, 1968 now abandoned which is a divisional application of application Ser. No. 557,005 filed June 13, 1966 now US. Pat. No. 3,403,722 granted Oct. 1, 1968. Additional applicants and patents which are relevant to the subject matter of the present invention and which have a common assignee therewith are: HEATING APPARATUS AND PROCESS, US. Pat. No. 3,407,789 filed June 13, 1966 granted Oct. 29, 1968 COOLING APPARATUS AND PROCESS, U.S. PAT. No. 3,403,722 filed June 13, 1966 granted Oct. 1, 1968; and COOLING APPARA- TUS AND PROCESS US. Pat. No. 3,583,476 filed Feb. 27, 1969 granted June 8, 1971.

The present invention relates generally to an apparatus and process for cooling a fluid and, in particular, to an apparatus and process for rapidly cooling a fluid. The apparatus and process of the present invention are especially suitable for rapidly cooling furnace effluent issuing from a hydrocarbon cracking furnace.

The present invention comprises an apparatus and process which is used to rapidly cool hot fluids. The apparatus comprises a means whereby a hot fluid is contacted on cooling surfaces to provide rapid decrease in the temperature of the hot fluid. The cooling means is suitable for cooling fluids at elevated pressures. The apparatus of the present invention can be used to rapidly cool hot gases without substantial pressure change.

The cooling means has particular and advantageous application when used in conjunction with a process for the production of olefins by cracking hydrocarbon feeds at high temperature and short residence time, using a high radiant heat furnace having relatively short conduits of small diameter. The cooling means is used to provide rapid reduction in the effluent product gas temperature from the furnace without substantial pressure drop.

Cracking furnace effluent gas temperatures are very high, and at these high temperatures the cracking reactions proceed at a rapid rate. In order to substantially stop the reactions in the effluent gas and to minimize the production of undesirable by-products, it is necessary to rapidly cool the effluent gas after it leaves the reactor to a temperature at which the reactions substantially cease. There are several means available for doing this, most of which have one or more drawbacks. Conventional means of cooling, e.g., a shell and tube heat exchanger, result in substantial pressure loss of the effluent gas. This type of heat exchanger employs multiple tubes and is fitted with an inlet head. The residence time of the hot gases in this head alone at the temperatures employed is significant and results in product degradation and the formation of coke precursors and coke, either of which can accumulate in the heat exchanger.

In cooling high temperature hydrocarbon gas efflu' ents from a hydrocarbon cracking process used to produce olefins, the temperature of the cooling means be sufficiently low to cool the gases the desired amount and sufficiently high to prevent condensation of high boiling hydrocarbon by-products on the cooling surfaces.

Cooling techniques and apparatus of the present invention are particularly useful in cooling the effluent gases from a process for the thermal cracking of hydrocarbons. In the thermal cracking of hydrocarbons, in the process described hereinafter, the hydrocarbon feed can be heated to high temperature, maintained at high temperature for a short residence time and selectively converted to desired products. In accordance with the present invention, the hot gas reaction products are rapidly quenched or cooled in such a manner that the conversion is substantially stopped after the desired residence time.

The quenching apparatus and process of cooling of the present invention is particularly suitable for use in cooling the hot gas effluent issuing from a pyrolysis furnace. However, the concept used can be readily applied to other processes for cooling hot product streams, for heat recovery and/or for heating fluids. The cooling means and process can be used for rapidly cooling hot gaseous products from other cracking processes. The quenching apparatus provides indirect cooling on surfaces. The apparatus is simple in design and easy to operate. The apparatus can be of any size and is normally designed for a specified service. The apparatus can be horizontally or vertically disposed. The cooling unit rapidly cools hot fluilds while not substantially changing the pressure of the fluid. That is, the pressure of the cooled fluid at the outlet of the cooling unit is substantially the same as the inlet pressure. The material to be cooled can be upflow or downflow. The operation of the unit can be such that the coolant circulation rate can be self-regulating and within limits adjust itself to the heat load. Alternatively, the coolant circulation rate can be controlled by suitable auxiliary pumping means.

SUMMARY OF THE INVENTION Basically, the heat exchanger of the present invention is comprised of a passage for the flow of hot fluid therethrough and at least one coolant passage. The hot fluid passage and the coolant passage or passages are arranged with common walls through which indirect heat exchange occurs. The inlet of the hot fluid passage is configured in the form of a diverging nozzle having an angle of divergence of from 4 to 10, and preferably 4 to 7.

A variation of the basic heat exchanger design con sists essentially of three concentric pipes,, pipes, walls of which form two annular chambers and one central chamber. The cooling fluid can be fed into the top of the unit and flow into the central chamber. The central chamber at the end opposite from the inlet thereof is in communication with the first annular chamber. The cooling fluid can flow downwardly in the central chamber and upwardly in the first annular chamber and exit through an opening at or near the top of the first annular chamber. The outer wall of the second concentric pipe forms a cooling surface. The hot gaseous material to be cooled can enter at the bottom of the cooling device through an opening in the third concentric pipe and pass upwardly through the second annular chamber and be cooled by direct contact with the cooling surface. The cooled material can pass out of the cooling device through an outlet located near the top of the second annular chamber.

The invention will be better understood and made more apparent when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic flow diagram of an overall thermal cracking system with the gas cooling apparatus of the present invention embodied therein;

FIG. 2 is a cross-sectional elevational view of an embodiment of the cooling or quench apparatus;

FIG. 3 is a cross-sectional view of the cooling apparatus of FIG. 2 taken through line 33 showing a cross section of the concentric pipes and cooling tubes;

FIG. 4 is a cross-sectional elevational view of another embodiment of the cooling or quench apparatus of the present invention;

FIG. 5 is a cross-sectional view of the cooling apparatus of FIG. 4 taken through line 55 showing the concentric pipes and cooling fins;

FIG. 6 is a cross-sectional elevational view of another embodiment of the cooling or quench apparatus of the present invention;

FIG. 7 is a cross-sectional view of the cooling apparatus of FIG. 6 taken through line 77;

FIG. 8 is a cross-sectional elevational view of another embodiment of the cooling or quench apparatus of the present invention;

FIG. 9 is a cross-sectional view of the cooling apparatus of FIG. 8 taken through line 9--9;

The heat exchanger of the present invention will be described as part of a system for thermally cracking hydrocarbons to produce olefins. Basically, the heat exchanger of the present invention is an indirect heat exchanger having a passage for the flow effluent therethrough and at least one coolant chamber with a common wall therebetween.

The cooling apparatus can use any desired cooling fluid. The cooling fluid can be a liquid that, on heating, partially or completely vaporizes. The preferred cooling fluids are liquids. Suitable liquids are Dowtherm, water, etc.

The preferred cooling liquid is water. In the present embodiment, the cooling apparatus is used to produce high temperature, high pressure steam. The heat energy recovered in cooling can be used for power generation or heating service.

A typical reactor furnace and cooling unit will be described with reference to FIG. 1 of the drawings. A petroleum naphtha fraction boiling in the range of 90 to 375 F. is fed through line 1 into convection preheat section 7 wherein it is heated from about ambient temperature to a temperature of about l000 to l l00 F. Steam, at a ratio of steam to hydrocarbon of about 0.4 to 0.8 by weight, is introduced into preheat section 7 through lines 8 and/or 9 at a point where the naphtha feed is approximately 80% vaporized. The preheated hydrocarbon and steam and steam mixture at about IOO0 to 1 100 F. is then fed to manifold 2 and subsequently into the inlets of coils 3-6. The feed is heated in the coils from about l000 to 1 100 F. to a coil outlet temperature of about l650 F. Under the recited conditions the hydrocarbon partial pressure at the coil outlet is about 12 to 14 PSIA. The residence time of the fluid in the radiant section of the furnace is about 0.20 to 0.25 seconds. The mass velocity of the hydrocarbon and steam in the coils is about 18 to 26 pounds per second, per square foot of cross-sectional area of the coil.

The radiant coil inlet pressure is about 45 PSIA and the coil outlet pressure of the effluent gases is about 25 PSIA. The hot effluent gases are fed from the outlet manifold 11 through line 12 to the cooling apparatus 14 at a gas velocity of about 800 ft./sec. The hot gases are introduced into the cooler through inlet 13 at a temperature of about l650 F. The cooled gases are withdrawn from the cooler through outlet 15 which is in communication with line 16. The gases are cooled rapidly in about l0-20 milliseconds to a temperature of about 1200 to 1400 F. and may be conveyed to a conventional cooling means for further cooling and to a conventional olefin separation plant for separation and recovery of ethylene. The gas pressure in line 16 is about 25 PSIA.

Basically, the heat exchanger 14 of the present invention can be adapted to rapidly cool the furnace effluent by to 600 F.; that is, from about 1500 to l650 F. down to about I000 to l400 F. The cooling step is carried out very rapidly after the effluent leaves the radiant section of the furnace in about 1 to 30 milliseconds, preferably in about 5 to 20 milliseconds. The rapid cooling step is critical in the high temperature, short residence time process for cracking hydrocarbons to produce olefins. It is found that if the cooling step takes substantially more than about 30 milliseconds, there may be substantial coke deposits in interior passages of the cooling unit and downstream equipment.

When high temperature and short residence time are used to crack hydrocarbon to form olefins, it is necessary to rapidly cool the furnace effluent sufficiently below the reaction temperature to substantially stop the reaction. If this is not done, the reaction continues after the effluent has left the reaction zone and can result in degradation of product, reduction of ethylene yield, and increased production of polynuclear aromatics and/or compounds of low volatility. Such products tend to cause deposition of coke on the walls of the downstream equipment. At l600 F. reaction rates are so high that the .residence time in a quench zone at times as short as 50 milliseconds results in a significant amount of reaction taking place. It is, therefore, important to quench the effluent very soon after it leaves the furnace to a temperature at which substantially no deleterious reaction takes places, e.g. below 1 100 to 1400 F.

FIG. 1 of the drawing illustrates the thermosiphon cooling embodiment of the present invention. Coolant water from steam drum 17 is introduced through line 18 at a temperature of about 600 F. and a pressure of about l600 PSIA. The coolant flows through line 18 into a torus 19 and upwardly in tubes 20, in which tubes the water is partially converted to steam. The steam and water mixture flows into torus 21 and through line 22 back to steam drum 17. The water being more dense than the mixture of steam and water sets up a thermosiphonflow of coolant water through the cooling apparatus. Within design limits the cooling apparatus is selfregulating and the higher the temperature and flow rate of gases into the cooling unit the faster will be the coolant liquid circulation rate.

Saturated steam at a temperature of about 600 F. and a pressure of about 1600 PSIA can be withdrawn from steam drum 17 through line 23 and the heat energy recovered. Boiler feed water is fed to steam drum 17 through line 24.

The heat exchanger of the present invention can be used in other known processes but it is particularly suitable for service in a hydrocarbon cracking system. However, it will be obvious that the cooling apparatus has many uses for cooling process streams, heat exchange, and other uses that will appear to those skilled in the art.

The heat exchange apparatus of the present invention comprises a means whereby the hot furnace effluent is cooled in a heat exchanger passage. If the heat exchanger passage is annular, either or both of the surfaces comprising the annular passage can be a heat transfer surface. This cooling apparatus is particularly adapted to rapid quench of hot gas with a small decrease or substantially no change in the pressure of the fluid being cooled while generating high pressure steam economically.

One basic embodiment of thepresent invention is depicted in FIGS. 2 and 3. Basically, the heat exchanger 14 is an indirect heat exchange apparatus which cools furnace effluent or similar hot fluid and generates high pressure steam. Also, the inlet end of the heat exchanger is designed to gradually lower the velocity of the furnace effluent steam so that the velocity head or kinetic energy is converted to static pressure. The pressure recovery realized can partially or entirely offset the friction pressure drop through the device depending upon the specific dimensions of the apparatus and the conditions under which it is operated. Rapid cooling of the gas if effected by passing the gas through a tubular passage which is cooled.

The heat exchanger 14 is comprised of a centrally disposed pipe 25 that extends about the length of the apparatus and terminates in an outlet 26. The inner wall 27 of the pipe 25 defines the passage or chamber 28 through which the effluent passes to be quenched. At the top of the pipe 25 there is provided connecting means 29 to connect the heat exchanger 14 to the transfer line pipe.

The wall of pipe 25 can be provided with a multiplicity of equally spaced tubes 20 which tubes are connected to and are in close contact with the outer wall 31 of the pipe 25. These tubes run the approximate length of the wall and, at the upper and lower ends, flare outwardly by

curved portions

32 and 33 respectively, and are in communication with torus 21 at their upper end and torus 19 at their lower end. Torus 19 has a connecting conduit 36 through which coolant fluid passes through inlet 37 into the torus 19 and flows upwardly through tubes 20. Tubes 20 are in communica-' tion with upper torus 21 and the cooling fluid flows out of torus 21 through outlet 38 and conduit 39.

Pipe 25 at a position proximate to the end at which effluent enters the quench apparatus tapers inwardly to form inlet opening 40. The cross-sectional area of inlet 40 is such that the passage 28 gradually increases in cross-sectional area from inlet 40 to the quench chamber to form an inlet diffuser section 41.

The cooling apparatus can be disigned and sized to accommodate any desired cooling service. Suitable apparatus for use in the present invention can have an overall length of the cooling apparatus from gas outlet 26 to hot gas inlet 40 of to 50 feet. The inside diameter of the pipe 25 can be 2.5 to 5 inches. Tubes can be about 1 to 2 inches in inside diameter. The inside diameter of tori l9 and 21 can be about 3 to 6 inches. The cross-sectional area of gas inlet 40 can be about 3 to 14 square inches, gradually increasing in crosssectional area to about 4 to 20 square inches in the straight portion of pipe 25. The total coolant flow through tubes 20 can be about 10 times the flow of hot effluent gases based on weight.

Hot gases at a velocity of 700 to 800 ft./sec. enter the cooling apparatus through inlet 40 and pass into chamber 28 where they are slowed to about 400 to 500 ft./sec. and pass out of the apparatus at the end of the chamber through outlet 26. Coolant Water enters the bottom torus 19 through inlet 37 and flows upwardly in tubes 20 providing indirect contact cooling for the hot furnace effluent gases at the inner wall surface 27 of pipe 25. The inner surface 27 of pipe 25 provides the cooling surface for the hot gas.

The mixture of steam and water moves upwardly in tubes 20 into torus 21 and through outlet 38.

The inlet diffuser section 41 provides for gradual increase in cross-sectional area of the gases entering through inlet 40 which gradually increases the pressure of the hot gases as the gas velocity is reduced. The diffuser section 41 insures uniform gas distribution over the cooling surface 27 without the production of large eddy currents in the gas flow. In accordance with the present invention, the pressure increase in the gas caused by the gradual increase in cross-sectional area in the inlet compensates for a substantial portion of the pressure loss in the gas due to friction. The cooled outlet gas pressure will be about the same as the hot inlet gas pressure. Passage 28 is sized to provide the gradual increase in cross-sectional area through which the hot gases flow. The gradual increase is provided by the tapered shape of the wall of diffuser section 41.

The gradual increase in cross-sectional area provides a gradual decrease is gas velocity which is accompanied by an increase in gas pressure to conserve total energy.

The total angle of divergence of the entering pipe of the diffuser section 41 is in the range of 4 to 10, preferably 4 to 7, e.g. 5.

FIG. 3 shows a cross section of the cooling apparatus taken through line 3-3 of FIG. 2. FIG. 3 shows an end section of tubes 20 and the manner in which they are connected by welds 42 to the outer wall of pipe 25. A suitable heat transfer material 43 can be used to fill the space between tubes 20 in order to improve the heat transfer between the hot gases and coolant.

Another embodiment of the cooling apparatus is illustrated by FIGS. 4 and 5 of the drawings. In this embodiment cooling of the hot gases is provided by direct contact with the outer wall of the concentric pipe 25. In order to improve the heat transfer between pipe 25 and the cooling fluid, pipe 25 can possess a multiplicity of cooling fins 44 which project into the coolant passage 45.

The diffuser section 41 immediately adjacent the cooling chamber inlet 40 is again formed of an entering pipe section which makes a total divergence angle of between 4 and 10, preferably 4 to 7.

The coolant chamber 45, however, completely surrounds the inner quenching chamber 28 thereby providing direct exposure of the tube 25 with the fluid passing through the cooling chamber or jacket 45. Coolant enters inlet 46 which is near the hot effluent inlet 40, passes through chamber 45 and discharges through outlet 47 thereby providing cooling of the chamber 28 from the inlet 40 to the discharge opening 26.

Another embodiment of the cooling apparatus is depicted in FIGS. 6 and 7 of the drawings. Referring to FIG. 6 of the drawings, the cooling device can comprise three concentric cylinders or pipes which are vertically disposed, the outer cylinder of which is provided with a multiplicity of equally spaced tubes. The hot effluent gases are introduced into the coolant apparatus and rapidly cooled by indirect heat exchange by contact with two cooling surfaces.

The central concentric pipe 132 has an inlet 173 at its upper end and depends downwardly to form the central passage 131. The second concentric pipe 134 at its upper end just short of inlet 173 curves inwardly and abuts and terminates at the wall of central pipe 132. The outer wall of pipe 132 and the inner wall of pipe 134 form annular space 133. Spacers 148 maintains pipe 132 equidistant from the inner wall of pipe 134. Pipe 134 at its lower end forms a rounded chamber terminating in rounded end member 137. The third concentric pipe 136 extends about the length of the apparatus and terminates short of the top of pipe 134. Above the point at which pipe 136 terminates, conduit 174 is in communication with annular space 133 through outlet opening 175. The inner wall of pipe 136 and the outer wall of pipe 134 form the second annular chamber 135. Near the top of annular passage 135 there is provided baffle ring 146 which prevents stagnant product gases from accumulating in the upper end of the annular chamber. Also near the top of annular chamber 135 there is provided connecting means 144 which is in communication with annular passage 135 through outlet opening 145. Baffle ring 146 and spacers 147 maintain concentric pipe 134 in the center of annular chamber 135.

An important feature of the cooling apparatus is the nose cone 138. The nose cone 138 is arranged axially with the pipe 134, the base of the nose cone 138 being attached to the rounded end member 137 and the apex extending in the direction of the inlet opening 143. The concentric pipe 136 at a position proximate to the end of the straight portion of concentric pipe 134 tapers inwardly in the general direction of the nose cone 138 to form inlet opening 143. The cross-sectional area of inlet 143 is such that the annular passage 140 gradually increases in cross-sectional area from inlet 143 to the annular space formed by the walls of

pipes

134 and 136.

The outer wall of concentric pipe 136 can be provided with a multiplicity of equally spaced tubes 161 defining passages 167, which tubes are connected to and are in close contact with outer wall 136. These tubes run the approximate length of outer wall 136 from about the bottommost portion of wall 136 up to conduit 144. Tubes 161 at the upper and lower ends flare outwardly by

curved portions

160 and 162, respectively and are in communication with torus 150 at their upper end and torus 149 at their lower end. Torus 149 has a connecting conduit 164 through which coolant fluid passes through inlet 163 into the torus 149 and flows upwardly through tubes 161. Tubes 161 are in communication with upper torus 150 and the cooling fluid flows out of torus 150 through outlet 166 and conduit 165.

The cooling apparatus can be designed and sized to accommodate any desired cooling service. Suitable apparatus for use in the present invention can have an overall length of the cooling apparatus from coolant inlet 173 to hot effluent gas inlet 143 of 20 to 24 feet. The inside diameter of the third concentric pipe 136 can be 8 to 10 inches. Tubes 161 can be about one to two inches in inside diameter. The inside diameter of

tori

149 and 150 can be about 3 to 4 inches. The crosssectional area of central chamber formed by pipe 132 can be 7 square inches. The length of the central chamber can be l8 to 20 feet. The cross-sectional area of the first annular chamber 33 can be about 12 square inches and can have a length of about 18 to 20 feet. The crosssectional area of the second annular chamber can be about 20 square inches and the chamber can have a length of about l6-l8 feet, excluding the inlet section. The cross-sectional area of gas inlet 143 can be about 12 to 13 square inches, gradually increasing in cross-sectional area to about 19 to 20 square inches in the straight portion of pipe 134. Tapered nose cone 138 can have an angle at its apex of about 28 to 30. The total cross-sectional area of tubes 161 can be about 10-1 1 square inches. The total coolant flow through tubes 161 and first annular passage 133 can be about 10 times the flow of hot effluent'gases based on weight.

Hot gases at a velocity of 700 to 800 ft./sec. enter the cooling apparatus through inlet 143 and pass into second annular chamber 135 where they are slowed to about 400 to 500 ft./sec. and pass out of the apparatus at the end of the chamber through outlet 145. The coolant water is introduced through inlet 173 and flows downwardly in the central chamber 131 of concentric pipe 132 and a mixture of water and steam flows upwardly in first annular passage 133 and passes out near the top of the first annular passage through outlet opening 175. Coolant water enters the bottom torus 149 through inlet 163 and flows upwardly in tubes 161 providing indirect cooling for the hot furnace effluent gases at the inner wall surface of pipe 136. The inner surface of pipe 136 and the outer surface of pipe 134 provide the two cooling surfaces for the hot gas.

The mixture of steam and water move upwardly in tubes 161 into torus 150 and through outlet 166.

The inlet diffuser formed by wall 139 and nose cone 138 provides for gradual increase in crosssectional area of the gases entering through inlet 143 which gradually increases the pressure of the hot gases as the gas velocity is reduced. The diffuser 140 ensures uniform gas distribution between cooling

surfaces

136 and 134 without the production of large eddy currents in the gas flow which would reduce the extent of pressure increase. In accordance with the present invention, the pressure increase in the gas caused by the gradual increase in cross-sectional area in the inlet compensates for a substantial portion of the pressure loss in the gas due to friction. The cooled outlet gas pressure will be about the same as the hot inlet gas pressure. Passage 140 is sized to provide the gradual increase in cross-sectional area through which the hot gases flow. The gradual increase is provided by the tapered shape of nose cone 138 and the converging wall 139 of pipe 136.

The gradual increase in cross-sectional area provides a gradual decrease in gas velocity which is accompanied by an increase in gas pressure to conserve total energy.

The angle of the nose cone 138 and the entering pipe 139 are selected so that the increase in cross-sectional area of the annular space formed between cone 138 and pipe 139 per unit length is equal to the increase in cross-sectional area per unit length of a conical pipe having an angle of divergence of 4 to l, preferably 4 to 7, e.g. 5. The angle of the cone 138 and extent to which converging wall 139 corresponds to the angle of cone 138 provide the necessary gradual increase in cross-sectional area. The nose cone angle can be 25 to 30. The angle of converging wall 139 if taken to an apex can be 20 to 25. The length of cone 138 can be 8 to 12 inches. The cooling chamber that is the second annular chamber 135 has the same cross-sectional area throughout its length.

FIG. 7 shows a cross section of the cooling apparatus taken through line 7-7 of FIG. 6. FIG. 7 shows an end section of tubes 161 and the manner in which they are connected by welds 170 to the outer wall of concentric pipe 136. A suitable heat transfer material 171 can be used to fill the space between tubes 161 and to improve the heat transfer between the hot gases and coolant.

Another embodiment of the cooling apparatus is illustrated by FIGS. 8 and 9 of the drawings. in this embodiment cooling of the hot gases is provided primarily by direct contact with the outer wall of concentric pipe 134. In order to improve the heat transfer between pipe 134 and the hot gases, pipe 134 can contain a multiplicity of cooling fins 156 which project into the hot gases in annular space 135.

The cooling apparatus or quenching unit of the present invention provides rapid cooling for hot fluids by indirect heat exchange on cooling surfaces. The heat exchanger can be used to cool liquids or gases and/or for heat recovery and generation of steam. Typically, when used to cool a hot gaseous hydrocarbon effluent from a cracking furnace, the inlet gas temperature to the quench unit will be about l350 to 1650 F. While in the heat exchanger the effluent will be cooled by 100 to 600 F. The hot gases are fed to the quench unit at a velocity of 350 to 1000 ft./sec., and preferably at 500 to 900 ft./sec. The heat flux at the inlet to the cooling apparatus can be as high as 80,000 BTU/hr./sq. ft. and the cooling apparatus can have an average heat flux of about 40,000 BTU/hr./sq. ft. in the operation of the unit, at the pressures described below, about 10 to lbs. of water are circulated for each pound of steam produced. The design and operation of the unit can provide that there be substantially no decrease in pressure between the hot gas inlet and the quenched gas outlet. The pressure decrease of the fluid to be cooled can be kept down to 3 PSI and preferably less than 1 PS1. The water is introduced to the unit at a pressure of 200 to 2000 PSIA and at a temperature of about 388 to about 635 F. and preferably, the coolant water is introduced at a pressure of 1500 to 1800 PSlA and at a temperature of about 595 to 620 F. In the embodiment of the invention where the coolant circula' tion is provided by thermosiphon effect, the circulation rate can be self-regulating within design limits and automatically adjusts for variations in cooling service required.

When cooling high temperature hydrocarbon streams which contain some relatively high boiling con stituents, it is necessary to maintain the cooling surfaces at a temperature high enough to prevent condensation and deposition of the high boiling constituents on the cooling surfaces, but it is also necessary to maintain the cooling surfaces cold enough to carry out the rapid cooling of the effluent stream that is required.

1 claim:

1. A heat exchange apparatus comprising:

a divergently shaped inlet section for the flow of hot fluid therethrough configured with a total divergence angle between 4 and 7;

a downstream section for the flow of hot gases passing from the inlet section which downstream section extends from the downstream end of the inlet section and has a constant cross-sectional. area equal to the cross-sectional area of the downstream end of the divergently shaped inlet section;

means for cooling the hot fluid flowing through the heat exchanger apparatus;

whereby the flow of the hot gases is substantially turbulence-free during the passage thereof through the heat exchange apparatus.

2. The apparatus of claim 1 wherein the total angle of divergence of the inlet section is 5.

3. The apparatus of claim 1 wherein the passage for the flow of hot fluid is a centrally disposed tubular structure and the means for cooling the hot fluid flowing therethrough is a cooling chamber arranged therearound.

4. The apparatus of claim 1 wherein the passage for the flow of hot fluid is a centrally disposed tubular structure and the means for cooling the hot fluid flowing therethrough is comprised of an annular array of tubes arranged in direct contact with the outer surface. of the centrally disposed chamber.

5. The apparatus of claim 4 further comprising cooling manifolds at each end of the heat exchanger and wherein the annular array of tubes arranged in direct contact with the surface of the centrally disposed chamber communicate with the manifolds.

6. The apparatus as in claim 5 where the cooling manifolds arranged to communicate with the annular array of tubes are toroidal in configuration.

7. The apparatus as in claim 3 wherein the cooling chamber has a coolant inlet located in proximity to the inlet of the centrally disposed chamber for hot fluid and an outlet located in proximity to the outlet of the centrally disposed chamber for hot fluid.

8. The apparatus of claim 7 wherein the cooling chamber surrounds the entire centrally disposed chamber for hot fluid.

9. The apparatus of claim 1 wherein the passage for the flow of hot fluid is annular.

10. The apparatus of claim 9 wherein the increase in cross-sectional area of the divergent inlet section is equivalent to the increase in cross-sectional area per unit length of a conical pipe having an angle of divergence of 5.

11. The apparatus of claim 9 wherein the means for cooling the hot fluid flowing through the annular passage is a cooling passage arranged concentrically with and interiorly of the inner wall of the annular passage.

12. The apparatus of claim 11 wherein the cooling passage arranged concentrically with and interiorly of the inner wall of the annular passage is comprised of a tubular central cooling chamber arranged axially in the heat exchanger, which central cooling chamber has an inlet at one end and an outlet at the opposite end; an annular cooling chamber defined by the outer wall of the tubular central chamber and the inner wall of the annular hot fluid passage; and communication means between the tubular central chamber and the annular cooling chamber.

13. The apparatus of claim 12 wherein the diverging inlet for the annular hot fluid passage is defined by a cone extending from the end of the inner wall of the annular hot fluid passage near the hot fluid inlet and a converging wall surrounding the cone, which converging wall extends fromthe outer wall of the annular hot fluid passage to the hot fluid inlet.

14. The apparatus of claim 13 wherein the cone has an angle of 25 to 30 and the converging wall extending from the outer wall of the annular hot fluid passage surrounding the cone has an angle of to 15. The apparatus of claim 9 wherein the cone has an angle of 25 to and the converging wall extending lar hot fluid passage into the outer cooling chamber.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO.

DATED October 7, 1975 Herman N. Woebcke It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line line 67, between Column 2, line Column 3, line of hot Column 5, line after "3" insert gas inlet 40 can Column 6, line [SEAL] l3, "applicants" should be application "means" and "be" insert must 52, delete second ,pipes,". 34, between "flow" and "effluent" insert Signed and Scalcd this Twenty-first Day Of June 1977 A lies I:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner oflarems and Trademarks

Claims

1. A heat exchange apparatus comprising: a divergently shaped inlet section for the flow of hot fluid therethrough configured with a total divergence angle between 4* and 7*; a downstream section for the flow of hot gases passing from the inlet section which downstream section extends from the downstream end of the inlet section and has a constant crosssectional area equal to the cross-sectional area of the downstream end of the divergently shaped inlet section; means for cooling the hot fluid flowing through the heat exchanger apparatus; whereby the flow of the hot gases is substantially turbulencefree during the passage thereof through the heat exchange apparatus.

2. The apparatus of claim 1 wherein the total angle of divergence of the inlet section is 5*.

4. The apparatus of claim 1 wherein the passage for the flow of hot fluid is a centrally disposed tubular structure and the means for cooling the hot fluid flowing therethrough is comprised of an annular array of tubes arranged in direct contact with the outer surface of the centrally disposed chamber.

10. The apparatus of claim 9 wherein the increase in cross-sectional area of the divergent inlet section is equivalent to the increase in cross-sectional area per unit length of a conical pipe having an angle of divergence of 5*.

13. The apparatus of claim 12 wherein the diverging inlet for the annular hot fluid passage is defined by a cone extending from the end of the inner wall of the annular hot fluid passage near the hot fluid inlet and a converging wall surrounding the cone, which converging wall extends from the outer wall of the annular hot fluid passage to the hot fluid inlet.

14. The apparatus of claim 13 wherein the cone has an angle of 25* to 30* and the converging wall extending from the outer wall of the annular hot fluid passage surrounding the cone has an angle of 20* to 25*.

15. The apparatus of claim 9 wherein the cone has an angle of 25* to 30* and the converging wall extending from the outer wall of the annular hot fluid passage surrounding the cone has an angle of 20* to 25*.

16. The apparatus of claim 14 further comprising cooling means arranged around the outer wall of the annular hot fluid passage.

17. The apparatus of claim 16 wherein the cooling means arranged around the outer wall of the annular hot fluid passage is a cooling chamber.

18. The apparatus of claim 17 further comprising cooling fins extending from the outer wall of the annular hot fluid passage into the outer cooling chamber.