US3449212A - Cyclonic cracking vapor heat exchanger inlet for solids removal - Google Patents

Description

June 10, 1969 R. K. DORN 3,449,212

CYCLONIC CRACKING VAPOR HEAT EXCHANGER INLET FOR SOLIDS REMOVAL Flled Jan 9, 1967 Sheet of 2 INVENTOR. Rolf K. Dorn WZa/un 54W ATTORNEYS June 10, 1969 DORN 3,449,212

CYCLONIC CRACKING VAPOR HEAT EXCHANGER INLET FOR SOLIDS REMOVAL Filed Jan. 9, 1967 Sheet 2 orz IN V EN TOR.

Rolf K. Dorn ATTORNEYS United States Patent 3,449,212 CYCLONIC CRACKING VAPOR HEAT EXCHANGER INLET FOR SOLIDS REMOVAL Rolf K. Dorn, Berkeley Heights, N.J., assignor to The Lummus Company, New York, N.Y., a corporation of Delaware Filed Jan. 9, 1967, Ser. No. 608,159 Int. Cl. B01d 45/12; F28f 19/00; ClOg 9/18 US. Cl. 196-136 3 Claims ABSTRACT OF THE DISCLOSURE Particles of coke entrained in the efiluent gases from petroleum cracking heaters tend to clog the transfer line heat exchangers where the gases are quenched. Exchanger inlet designs are herein proposed which impart a cyclonic motion to the gases, creating centrifugal forces which throw the coke particles outwardly, where they are collected before they can enter the heat exchanger.

This invention relates generally to the removal of particulate solid material from gas streams and, more particularly, the invention relates to the separation of coke particles from the gaseous hydrocarbon effiuent streams issuing from high severity cracking heaters. In accordance with the invention, the coke is separated from the hot gas just ahead of the transfer line exchanger which cools the gas. Considered from a different aspect, the invention relates to a novel inlet device connecting the output of one or more cracking heaters with the inlet of a transfer line heat exchanger, wherein entrained coke particles are separated.

In the production of olefins from normally gaseous hydrocarbons by thermal cracking or in the steam reforming of naphtha and the like, it is necessary that the reaction products be cooled very quickly from the cracking temperature to a temperature below the point where secondary reactions can proceed. Such secondary reactions decrease yield and cause coke formations which decrease the length of time a heater can be kept in service. In conventional practice, the heater efl luent is passed in a conduit to an insulated inlet cone which is in direct communication with either the crack gas side or the shell side of a transfer line exchanger (also referred to as a cracked gas cooler), the cone being necessary because of the substantially larger diameter of the exchanger. The insulation, which may be internal or external, is provided in an attempt to keep the gas as hot as possible until it actually reaches the exchanger. It is also possible to cool the effluent directly by injection of a suitable cooling medium, but while this effects the desired cooling very rapid- 1y, it results in a significant loss of recovered heat, e.g., as high pressure steam. As a result, indirect cooling in a transfer line exhanger is generally preferred.

Operating experience has demonstrated that for certain feedstocks, particularly ethane and propane, and for high severity naphtha cracking, the inlet tone is a most critical zone for coke buildup in the entire heater-transfer line system. Coke buildup will cause blockage of gas flow through a portion of the exchanger. Further, it is difficult to distribute the flow to all of the exchanger tubes equally; tubes with low gas flow resulting from coke deposits tend to foul quickly. Ultimately, the resulting high pressure drop or reduced cooling duty of the exchanger requires that the hole heater-exchanger system be shut down and cleaned out.

It is thus a general object of the present invention to remove entrained coke from cracked gas in the inlet cone between a heater and a transfer line exchanger.

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Another object of the invention is to provide an im proved inlet cone for connecting a heater to a transfer line exchanger wherein entrained coke particles are removed.

Yet another object of the invention is to provide means for passing cracked gas from a heater to a transfer line exchanger which effectively removes entrained coke.

A still further object of the invention is to pass cracked gas from a heater to a transfer line and remove coke therefrom, without reducing yield, without loss of heat recovery potential, and without requiring large volumes of steam.

Various other objects and advantages of the invention will become clear from the following detailed description of two embodiments thereof, and the novel features will be particularly pointed out in connection with the appended claims.

In essence, the device of the present invention accomplishes the foregoing objects by imparting a cyclonic motion to the cracked gas as it enters the inlet, which creates centrifugal forces acting to push the coke particls against the walls of the inlet. The device is provided with one or more outlets particularly placed so as to receive these coke particles, and these outlets are connected to conventional cyclone classifiers which separate the coke particles from the accompanying gas. The cyclones are purged with steam to prevent clogging.

In the operation of cracking heaters and the like, it is quite conventional to pass the effluent stream from two heaters to a single transfer line exchanger, a Y connection being employed to combine the two streams. Although two inlets are discussed hereinbelow, the present invention does not require two or more inlet gas streams in order to impart the necessary cyclonic motion to the gas. In one embodiment the two inlets are entirely separate and in a second embodiment the two streams pass into a single inlet conduit through a specially designed Y connection. However, a single inlet can be employed.

Understanding of the invention will be facilitated by referring to the accompanying drawings, in which:

FIGURE 1 is an elevation view, taken along line 11 of FIGURE 2, partly in section, showing one embodiment of the invention as attached to a heat exchanger;

FIGURE 2 is a simplified, schematic plan view taken along line 2-2 of FIGURE 1;

FIGURE 3 is a view similar to FIGURE 1 of a second embodiment of the invention, and taken along line 33 of FIGURE 4;

FIGURE 4 is a view similar to FIGURE 2, and taken along line 4-4 of FIGURE 3;

FIGURE 5 is taken along line 5-5 of FIGURE 3, and illustrates the Y connection of the two inlet conduits; and

FIGURE 6 illustrates a Y connection having convergent inlets.

In FIGURES 1 and 3 a conventional shell and tube heat exchanger is indicated generally at 10. It consists of a steel shell 12, a tube sheet 14 and a plurality of tubes 16 mounted therein. A flange 18 and suitable gaskets (not shown) are provided for attachment of the inlet device. It will be understood that the invention is applicable to essentially any heat exchanger of this general type.

With reference to the embodiment illustrated in FIG- URES 1 and 2, the inlet device is indicated generally at 20. A circular sidewall 22 of about the same diameter as exchanger 10 is flanged for attachment to flange 18 thereof, a suitable gasket (not shown) being provided therebetween. An inwardly-dished circular cover 24 defines, together with sidewall 22, a closed chamber 26 which is in direct fluid communication with the tube side exchanger 10. The central inward dishing ofcover 24 makes chamber 26 considerably larger near sidewall 22 than at the center.

Sidewall 22 is provided with two diametrically opposed tangential inlets 28, 30 for feeding cracked gas into chamber 26. Inlets 28, 30 are positioned so as to impart a cyclonic or circulatory motion to the cracked gas within chamber 26, most of the gas staying relatively near sidewall 22 due to the greater volume of the chamber in this area. The cyclonic motion of the cracked gas creates centrifugal forces which throw entrained coke particles against sidewall 22.

Sidewall 22 is also provided with two tangential outlets 32, 34 designed to allow the entrained coke to escape from chamber 26, centrifugal forces again being the motivating factor. Outlets 32, 34 communicate with a pair of conventional collection containers 36, 38 wherein the coke particles accumulate. Steam is injected into containers 36, 38 in lines 40, 42 for purging purposes and to prevent plugging of coke outlet 44 in the bottom. The steam, flowing with a very low velocity into chamber 26, prevents the cracked gas from entering containers 36, 38. The cracked gas passes into tubes 16 of exchanger 10.

In the embodiment illustrated in FIGURES 3-6, the heat exchanger and collection containers are as hereinabove described, and bear similar reference numerals. In many respects, this embodiment of the invention is similar to that described in FIGURES 1a-c and 23 of copending US. application Ser. No. 560,208 filed June 24, 1966. The inlet, indicated generally at 50, comprises a shell 52, insulation 54, a thin skirt or cover 56 to protect insulation 54, a flange 56 for attachment to the outlet of the cracking heater, and a flange 58 matching flange 18 on exchanger 10. It will be understood that flange 32 may be connected to intermediate piping, rather than directly to the heater outlet, as for example when one exchanger is connected to two heaters.

Insulation 54 and skirt 56 define the passage for cracked gases between flange '56 and tube sheet 14. In particular, the portion nearest flange 56 is defined by a cylindrical sleeve 60 of the same diameter as the connection from the heater or heaters. The adjoining portion of skirt 56 may or may not have a slightly and gradually enlarged diameter, but as it gets closer to the tube sheet it flares outwardly into dished annular section 62. The outer diameter of section 62 is approximately equal to the effective diameter of tube sheet 14. Sections 60, 56 and 62 define the trumpet bell portion of the passage, indicated generally at 64.

The foregoing features are all discribed in the abovenoted copending application.

For purposes of the present invention, it is necessary to impart a cyclonic or spiraling motion to the cracked gas as it flows through passage 64, and to create this motion a specially designed Y connection 66 is employed. As shown more clearly in FIGURE 5, two (or more) heater outlet conduits 68, 70 are joined to a single conduit 72 so that the gases impinge on opposite walls of the latter conduit and take on a spinning or spiraling cyclonic movement. As noted above, however, a single outlet conduit can also be employed. As shown in FIGURE 6, the heater outlet conduits 82, 84 may converge at the end where they communicate with the single conduit 80, so that the gases are accelerated as they pass through the conduit. As the gases proceed up passage 64 in this fashion, centrifugal forces are again created which throw particles of entrained coke against walls 60, 56. A slight discontinuity between sections 56 and 62 forms a spiraling groove 74, which catches the coke particles as they slide up the walls. As more clearly shown in FIGURE 4, groove 74 terminates at an opening 76 in wall section 62, opening 76 being shaped so that the coke particles sliding along groove 74 naturally fall thereinto.

A conduit 78 communicates with opening 76 and the cake particles pass therethrough into drum 38. The

cracked gases, free of entrained coke, pass into tubes 16 of exchanger 10 in the conventional fashion.

Under conditions of severe cracking, the gas density is generally less than half the density of air so the separation is relatively easy, particularly as no extreme high degree of separation is required. A drum with unchanged bulk flow direction is preferred to minimize (or practically eliminate) additional pressure drop.

As can be seen from a velocity vector diagram, the actual gas velocity needs to be only a few percent higher than the axial velocity vector in order to obtain tangential velocity vectors in the range of 50 to ft./sec. as used in dust/ air cyclones. For example an axial velocity of 200 ft./sec. and tangential velocity of 70 ft./sec. results in an actual velocity of 212 ft./sec., only 6% more than the axial velocity (200 4-70 Usually, the cracked gas velocity is reduced in the transfer-line downstream of the heater outlet; thus normally no acceleration is required as could be obtained easily with a nozzle type Y.

An additional advantage of the embodiment of FIG- URES 3-6 is the more uniform axial velocity profile in the transfer-line downstream of the Y. The coke collecting drum should be steam purged to allow a slow steam flow into the transfer-line and to cool the coke. This drum could also be kept filled with water for better cooling, generating steam for purging by vaporization. Preferably this drum should have a steam or water inlet at the bottom to minimize the risk of plugging the bottom outlet, by keeping coke particles in motion. An auxiliary steam connection at the top is also preferred to insure steam flow if the bottom connection becomes plugged.

This drum could be used and should be connected accordingly for normal decoking. Due to the coke separation as close as possible to the transfer-line exchanger the invention improves also the operation within the exchanger. It is known that mass velocities about 50 kg./m. sec. are preferably employed. With this invention mass velocities in the range of 30 to 50 kg./m. sec., preferably between 35 and 45 kg./m. sec. can be used successfully.

Various changes in the details, steps, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as defined in the appended claims.

What is claimed is:

1. An inlet device for passing cracked gas from a cracking heater or heaters to a multitude shelf and tube heat exchanger and removing entrained solids therefrom comprising:

a circular chamber on the inlet side of said exchanger, said chamber having a cylindrical sidewall extending from said inlet side and an inwardly dished cover, said chamber being in fluid communication with the tube side of said exchanger;

at least one inlet in said sidewall;

a tangential inlet conduit in fluid communication with said heater or heaters and with each said inlet, positioned so as to impart, in cooperation with said dished cover, cyclonic motion to gas entering said chamber through said inlet, whereby entrained solids are thrown outwardly against said sidewall;

at least one outlet in said sidewall;

a tangential outlet conduit in fluid communication with each said outlet and positioned to receive entrained solids adjacent said sidewall; and

collector drum means in fluid communication with each said outlet conduit, wherein said entrained solids are collected, each said collector drum means being provided with means for circulating a low-velocity fluid therein for preventing substantial passage of said gas in said drums.

5 6 2. An inlet device for passing cracked gas from a 3. The inlet device as claimed in claim 2, and addicracking heater or heaters to a multitube shell and tube tionally comprising: heat exchanger and removing entrained solids therefrom a generally spiral groove in said primary conduit adaptcomprising: ed to retain entrained solids adjacent the side of a single primary conduit in fluid communication with said primary conduit and direct same to said outlet.

the inlet of said heat exchanger, said primary con- 5 duit having a flaring portion of general trumpet bell References Clted configuration adjacent said exchanger inlet; UNITED STATES PATENTS at least two secondary conduits in fluid communication with said heater or heaters and with said pri- 2 Tingieren 5 1 mary conduit, the junction of said primary and sec- 2607438 8/1952 1 6 a '6 5 X ondary conduits being of a general Y configuration 2698672 1/1955 31 2; I" 208 161 X and adapted to impart a spiraling, cyclonic motion 2776931 1/1957 Chane at 55:459 X to gas passing from said secondary conduits into 2799354 7/1957 Bore y 55 345 X said primary conduit, whereby entrained solids are 2880169 3/1959 g g 161 X thrown against the wall of said primary conduit; 3213015 10/1965 g 'g 196 116 X the diameters of said secondary conduits being reduced 3357485 12/1967 Usunivan et 165:178 X in converging fashion near said junction, whereby 275988O 8/1956 Brown 208 158 X the velocity of gas entering said primary conduit is 3090746 5/1963 Market 5;; 208 127 X increased;

at least one outlet in the flaring portion of said pri- 3374832 3/1968 Tucker 165-134 mary conduit positioned to receive solids adjacent FOREIGN PATENTS the sidewall of said primary conduit; 554 831 7/1943 Great Britain a tangential outlet conduit in fluid communication with 8,391 7/1956 Germany each said outlet; and

collector drum means in fluid communication with each O N D O Primary Examiner said outlet conduit, wherein entrained solids are collected, each said collector drum means being pro- DRUMMONDAmSm' Examiner vided with means for circulating a low-velocity fluid U S Cl X R therein f r preventing substantial passage of said gas into said drums. '208-127, 157; l-l34; 5S-345

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