US3357485A - Cooler inlet device - Google Patents

Description

Dec. 12, 1967 T LLW ET AL 3,357,435

COOLER INLET DEVICE Filed April 21, 1965 2 Sheets-Sheet l INVENTORS Thomas F. O'Sullivon Jon Kramer Karl Buschmann Hermon Meyer Armin Schweitzer ATTORNEYS Dem 12, 1967 F OSULLIVAN ET AL 3,357,485

COOLER INLET DEVICE 2 Sheets-Sheet Filed April 21, 1965 lNVENTORS Thomas F. O'Sullivon Jon Kramer Karl Buschmonn Herman Meyer Armin SchweHzer BY 5133 72/21, 77km figanywmflu'a ATTORNEYS United States Patent COOLER INLET DEVICE Thomas F. GSullivan, Wilton, Conn, Jan Kramer, Voorschoten, Netherlands, and Karl Buschrnann, Neustadt an der Weinstrasse, and Herman Meyer and Armin Schweitzer, Ludwigshafen (Rhine), Germany, assignors to The Lummus Company, New York, N.Y., a corporation ofDeiaware Filed Apr. 21, 1965, Ser. No. 449,849 7 Claims. (Cl. 165-174) This invention relates to apparatus for production of olefins, with special reference to ethylene, by thermal cracking of hydrocarbons. It is known that olefinic hydrocarbons may be prepared by thermal cracking of gaseous or completely evaporable liquid hydrocarbons in metal tubes, ina mixture with steam, at temperatures above 750 C. This forms cracked gas rich in olefins, such as ethylene and propylene, and also containing higher olefins, diolefins, and other cracking products. To prevent secondary reactions, the highly reactive gas mixture must be quickly cooled. This cooling is in practice accomplishedby direct injection of coolants, as for instance liquid hydrocarbons, into the reaction mixture, or by indirect cooling, e.g. with the aid of water, in a crackedgas cooler.

In general, to improve heat recuperation, indirect cooling is preferred. A disadvantage of indirect cooling, however, is that deposits of coke or other cracking products are often formed, especially in the connecting duct between the cracking furnace and the cracked gas cooler, or in the individual cooling tubes of the cooler. These deposits increase the pressure difference in the system and interfere with the uniform distribution of the hot cracked gas on the cooling surfaces. The plant must then be shut down at longer or shorter intervals and the coking products must be cleaned out.

The connecting duct (between the cracking furnace and the cracked-gas cooler) used to deliver the cracked gas to the cooling tubes, is, in general, so designed that it gradually widens in diameter from the diameter of the cracking tube to the diameter of the cooler shell. To avoid vortices, which prolong the residence time in this area and thereby cause secondary reactions, the angle of the cone to the direction of flow must be kept as small as possible. When the cooler shell is of large diameter, however, the connecting line forms a relatively large space, and it has been found that the long residence time of the cracked gas in this space results in coking and decreased olefin yield.

To prevent condensing heavy polymers on the gas side of the tube, the tube wall temperature must be controlled. When the cooling medium is evaporating water, the pressure must be very high (80 to 100 atmospheres) to give the required tube wall temperature. One type of exchanger construction well suited to such pressure is double tube because it does not require excessively thick shell or tube sheet. However, high severity pyrolysis requires extremely rapid cooling and very low pressure drop across the cooler. This requires many parallel tubes of small diameter. A disadvantage of the double tube exchanger is that tubes can not be located on close centers. When many parallel tubes are required the volume of the inlet device becomes large, forming an adiabatic reactor, the same as a large or long transfer line. The adiabatic reaction reduces the temperature and causes coke formation, which increases the pressure drop and limits the length of operation between cleanings.

It is therefore an object of the present invention to provide an improved connector duct for heat exchangers wherein gas pressure is not substantially decreased, laminer flow is encouraged and vortices or eddys are discouraged.

3,357,485 Patented Dec. 12, 1967 Another object of the present invention is to provide a connection duct for heat exchangers in which the residence time of gases passing therethrough is minimized thus, in the case of connectors between cracking heaters and quench coolers, minimizing secondary reactions and coke formation, and thereby increasing yield.

Still another object of this invention is to provide an inlet device for the inner tube side of high temperature, high pressure double tube exchangers having many parallel tubes, that will have a very low volume.

Yet another object of this invention is to provide an inlet device which will convert the high velocity of the heater outlet (700 to 1000 feet per second) to the exchanger tube velocity (30() to 400 feet per second) with minimum pressure loss.

A still further object of this invention is to provide an inlet device which will have very little or no dead space where the gas flow can form an eddy resulting in long residence time.

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

It has now been found that these disadvantages do not appear, and that .a particularly high olefin yield is obtained, if suitable baffies or guides are installed in the connecting piece between cracking tube and cracked-gas cooler. This prevents the velocity of the cracked gas in the connecting piece from falling below its velocity at admission to the cooling tubes.

According to one embodiment of the invention, a diverter or baffle, preferably attached .to the cooler shell, is installed in the conical connecting duct between cracking tube and cracked-gas cooler. It is advantageous for this diverter to have channels conducting the hot cracked gas to the individual cooling tubes. The diverter may also advantageously have a hydrodynamically favorable shape so that atall points of the connecting duct the flow velocity of cracked gas shall not fall below the velocity at admission to the cooling tubes.

With the present double tube exchangers, tube spacing is over 3 times the gas tube I.D. giving an area of tube sheet approximately 10 times the flow area of the exchanger. Since the ar a of the heater outlet tubes is about one half of the exchanger tubes, with conventional inlet devices the volume is approximately /3 that of the heater coil. Since this occurs at maximum temperature, the adiabatic reaction is rapid, having significant affect on the yields and promoting coke formation. The present invention reduces the volume to less than that of the heater coil, thus reducing the adiabatic reaction to an insignificant amount.

The fluid velocity between the heater outlet to the exchanger inlet is inversely proportional to the flow area. With the areas resulting from conventional construction the velocity is decreased by a factor of twenty and then increased by a factor of ten. This results in a pressure loss of about 1.0 times the exit velocity head plus 0.5 times the entrance velocity head. This is about 2.8 p.s.i. for operating conditions in use today, and would be greater for more severe conditions which can be obtained with use of this invention. This invention avoids most of the pressure loss, thus permitting operation at higher outlet pressure or greater velocity in the exchanger or heater outlet, or any combination of the three which results in improved product yield and greater thermal efficiency.

Moreover, conventional inlet devices have abrupt changes in cross sections where the gas flow can develop eddies resulting in long residence time for some of the gas. This permits polymerization and dehydrogenation 3 resulting in coke formation. The invention eliminates such areas thus preventing the undesired reactions.

It has been found advantageous to provide the diverter and connecting duct with good thermal insulation, so that the cracked gas is cooled only when it reaches the cooling tubes. The connecting line between cracking tube and the cooling tubes of the cracked-gas cooler should be kept as short as possible, sothat the cracked gas is distributed to the cooling tubes in the connecting duct as in a diffuser and Without eddying.

A better understanding of the device of the invention will be gained by referring to the accompanying drawings, wherein:

FIGURE 1 is a cross-sectional view of a first embodiment of the invention;

FIGURE 2 is a cross-sectional view of a second embodiment of the invention; and

FIGURE 3 illustrates two alternative constructions of the embodiment of FIGURE 2.

With reference to FIGURE 1, the outlet pipe or flange from the cracking heater 2 is connected as by welding to a conventional cone-shaped connecting duct 4 which is attached at flange 6 to a similar flange 8 on the end of the quench cooler 10. The inner, gas side cooling tubes 12, are surrounded by outer water side tubes 13, and this assembly is connected at each end of the cooler to suitable tube sheets 14. In this embodiment, the diverter or baflie of the invention, indicated generally at 16, comprises an outer conical shell 18, passages or tube extensions 20 extending therethrough and connecting those of tubes 12 which are covered by diverter 16 to orifices on the surface of shell 18 and insulation 22 packed between the tube extensions 20 and the shell 18. The insulation is, of course, optional, and in certain applic'ations'air is sufiicient. The diverter 16 can be attached to exchanger in any convenient manner.

The diverter may be constructed as a unit assembly, with suitable provision being made for attaching tube extensions 20 to the appropriate tubes 12, or tubes 12 may be extended, and shell 16 merely fitted thereover, the tubes then being cut oif to provide a flush orifice on the surface.

As can be seen from FIGURE 1, gases passing through conical conduit 4 will, due to diverter 16, lose much less pressure and have a more generally laminar flow in traversing the distance and entering tubes 12.

A somewhat different solution to the problem is illustrated in FIGURE 2, wherein parts similar to those in FIGURE 1 are indicated with prime numerals. In this embodiment, what in effect is done is provide extensions 20 for all of the tubes 12', extensions 20' terminating in a second, dished tube sheet, indicated schematically at 24, of much smaller diameter than tube sheet 14. Tube sheet 24 may be as small, and may be brought out as far, as it is possible to do and still have space available to accommodate the ends of tube extensions 20. Thus, the face presented by tube sheet 24 to the gases is almost all tube openings and very little supporting structure. The gases thus lose only a very small amount of pressure in passing into extensions 20', and after that they lose no pressure or velocity in going into quench cooler 10.

An alternative arrangement involves bringing the tubes 20' into actual outside contact and, rather than employing a tube sheet at all, merely filling the void space with a solid refractory material which both provides insulation and also excludes gas from what would otherwise be void space.

Such an arrangement is shown in FIGURE 3, which ineludes two variations of the invention. On the right side, the tubes 20" are in actual contact with refractory 22 filling the void space. On the left side of FIGURE 3, conduit 4 terminates at tube sheet 24, and tubes 20" are left exposed.

It will be noted that the embodiments of FIGURES 2 and 3 differ in degree rather than kind from the embodiment of FIGURE 1, in that the conical portion of diverter 16 is merely expanded to become part of duct 4, and as a result all of the tubes 12 are covered.

It will be understood that various changes in the steps, materials, details and arrangements of parts, as described hereinabove, may be made by those skilled in the art without departing from the scope of the invention as defined in the appended claims.

What is claimed is;

1. A connector duct for the tube side of a heat exchanger that comprises:

a generally conical conduit connectable at its larger end to said heat exchanger around the periphery thereof;

a generally conical diverter axially located within said conduit and having its larger end connectable to said heat exchanger; and

a plurality of passages within said diverter coaxially connectable to the individual tubes of said exchanger covered by the larger end of said diverter so as to be in fluid communication therewith, said passages terminating at their opposite ends at the surface of said diverter.

2. The connector duct as claimed in claim 1, and additionally comprising thermal insulation material within said diverter and surrounding said passages.

3. A connector duct for the tube side of a heat exchangcr that comprises:

a generally conical conduit connectable at its larger end to said heat exchanger around the periphery thereof; a plurality of extension tubes coaxially connectable to each of the tubes of said heat exchanger so as to be in fluid communication therewith, said tubes extending into the narrower portions of said conduit, and

means securing the ends of said extension tubes within said narrower portion of said conduit and adapted to maintain only said extension tubes in fluid communication with said conduit.

4. The connector duct as claimed in claim 3, wherein said extension tubes are in direct contact with each other and with said conduit at the end furthest from said heat exchanger and additionally comprising refractory insulation material between said contacting ends and said heat exchanger and surrounding said extension tubes.

5. The connector duct as claimed in claim 3, wherein said securing means comprise a tube sheet.

6. In combination with a cracking heater and a shell and tube quench cooler, a connector conduit that comprises:

a generally conical conduit connected at its larger end to said cooler around the periphery thereof and connected at its smaller end to the outlet of said heater:

a generally conical diverter axially located within said conduit and having its larger end connected to said cooler; and

a plurality of passages within said diverter, said passages being equal in number to and. in fluid communication with the individual tubes of said cooler covered by said diverter at one end thereof and in fluid communication with the interior of said conduit at the other end.

7. The combination as claimed in claim 6, and additionally comprising thermal insulation material within said diverter and surrounding said passages.

References Cited UNITED STATES PATENTS 2,862,694 12/1958 Lortz 134 3,001,766 9/1961 Laist 165135 FOREIGN PATENTS 1,249,001 11/1960 France.

ROBERT A. OLEARY, Primary Examiner.

CHARLES SUKALO, Examiner.

Claims (1)

1. A CONNECTOR DUCT FOR THE TUBE SIDE OF A HEAT EXCHANGER THAT COMPRISES: A GENERALLY CONICAL CONDUIT CONNECTABLE AT ITS LARGER END TO SAID HEAT EXCHANGER AROUND THE PERIPHERY THEREOF; A GENERALLY CONICAL DIVERTER AXIALLY LOCATED WITHIN SAID CONDUIT AND HAVING ITS LARGER END CONNECTABLE TO SAID HEAT EXCHANGER; AND A PLURALITY OF PASSAGES WITHIN SAID DIVERTER COAXIALLY CONNECTABLE TO THE INDIVIDUAL TUBES OF SAID EXCHANGER COVERED BY THE LARGER END OF SAID DIVERTER SO AS TO BE IN FLUID COMMUNICATION THEREWITH, SAID PASSAGES TERMINATING AT THEIR OPPOSITE ENDS AT THE SURFACE OF SAID DIVERTER.

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