US3322412A - High temperature quench method - Google Patents

Description

May 30, 1967 M. M. YURKo ETAL HIGH TEMPERATURE QUENCH METHOD Filed Feb. 1, 1963 United States Patent O 3,322,412 HIGH TEMPERATURE QUENCH METHOD Malvin M. Yurko, Whippany, NJ., Vernon 0. Bowles, Bedford, and Alphonse A. Corona, Jr., Hempstead, N.Y., and Walter F. Read, Westfield, NJ., assgnors to Mobil Oil Corporation, a corporation of New York Filed Feb. 1, 1963, Ser. No. 255,569 5 Claims. (Cl. 261-128) The present invention relates to an improved method for quenching the gaseous eiiiuents of high temperature reactions. It is more particularly concerned with cooling the hot etiiuent products of vapor phase reactions of hydrocarbons and, more specically, with quenching the effluent from the high temperature thermal hydrodealkylation of alkyl aromatic hydrocarbons.

Various devices have been proposed for quenching hot reaction products, usually in vessels separated from the reaction vessels. Although the quenching of reaction products within the actual reaction vessel is known, trouble has sometimes been encountered with the undesirable cooling of the reactants which are still reacting and often diii'iculty is experienced from the deposition of carbon at an excessive rate. Accordingly, there is a demand for quenching systems which are free from these diiculties.

Quenching within the reactor is important in the case of the thermal hydrodealkylation of alkyl aromatic compounds as the high temperature reaction eiiiuents contain substantial'quantities of hydrogen and lower hydrocarbons, such as methane. Such eiiiuents can rapidly cause metal dusting at temperatures above about 12757 F. at pressures of the order of 500 pounds per square inch. Metal dusting is a form of catastrophic corrosion that is believed to involve carburization of steels, including many types of stainless steel, and this attack is often so fast that it is impractical to even attempt to calculate a corrosion allowance. Also, the strength of metals, including heat-resistant stainless steel alloys, is greatly reduced at high temperature levels, and it is customary to compensate for this by using equipment with thicker walls at a higher cost. However, equipment with heavier walls introduces additional problems by reason of-the greater stresses set up in thermal expansion and contraction. The present invention is particularly intended to alleviate these diculties by rapid cooling of such eiiiuents before they leave the reactor.

An object of the invention is to provide an improved method of quenching high temperature gaseous materials.

Still another object of the invention is to minimize or prevent metal dusting by the etliuent from a high temperature reaction.

A still further object of the invention is to substantially reduce the weightand cost of the heat resistant equipment utilized downstream of a reactor for handling the products of a high temperature reaction.

Yet another object of the invention is to substantially reduce the stresses and strains created in equipment handling the effluent of a high temperature reaction.

Other objects and advantages of the invention will be apparent to those skilled in the art upon consideration of the detailed disclosure which follows.

This invention is concerned with a process which comprises quenching the hot effluent of a gaseous phase reaction at high temperature within the confines of an enclosed reaction vessel by passing said effluent upwardly in a confined space within said vessel through a permeable member flooded with a vaporizable quench liquid at a sutiiciently high gas flow rate with respect to the number and size of the openings in said permeable member to retain at least a major portion (preferably substantially all) of the vaporizing quench liquid above said permeable member. In one embodiment of the invention, the quenched eiiiuent is subjected to vortical flow during withdrawal through an outlet passage to vaporize any entrained droplets of quench liquid by impingement against a hot wall of said passage.

For a better understanding of the nature and objects of this invention, reference should be had to the accompanying drawing in which the ligure is a fragmentary sectional view taken along the longitudinal axis of the lower part of a reactor and showing a preferred embodiment of a quenching device. For greater clarity, a number of minor construction details have been omitted, particularly fastenings, such as bolts or studs, rivets, etc.

The drawing shows the lower part of a thermal hydrodealkylation reactor for the production of benzene from an alkyl benzene, such as toluene, and hydrogen. This reactor may also be employed for the production of naphthalene from various alkyl naphthalenes. In the production of both benzene and naphthalene, the ternperature of the etiiuent reaction products is typically of the order of 1200 to 1400 F. and after passing through the quenching device described hereinafter, the temperature of those reaction products is reduced about Z50-400 to a temperature level where metal dusting and/or the reduction in metal tensile strength are no longer problems.

The drawings shows the bottom of a reactor having a heavy shell 2 of relatively low alloy steel inasmuch as the layer of refractory insulation 4 protects the shell from direct exposure to the hot gaseous reaction mixture. However, the structural elements of the quench device are not similarly protected; and it is recommended that these be constructed of an austenitic stainless steel, such as type 304, one of the 18% chromium and 8% nickel alloys.

The quench assembly consists of an enclosure made up of cylindrical housing 6 attached to a base plate 8 which prevents liquid from contacting the refractory insulating cement in order to avoid the deterioration of this refractory material. The cover 10 is riveted to the flange 12 which is fastened to housing 6. This joint, like the other joints in the quench device, is not subjected to any significant pressure differential and therefore need not be made pressure tight.

Arched openings 14 are regularly spaced around the circumference of the wall 6 at its lower end to admit downwardly owing reaction products in even distribution into the enclosure and allow them to rise through the foam and sprays of quenching liquid described hereinafter. The space enclosed by the housing 6 and top 10 is divided into a lower chamber 16 and an upper chamber 18, usually of greater height than chamber 16, by a permeable member, such as perforate plate 20, which is attached by rivets to welded flange 22 on wall 6 and to welded iiange 24 on the 8-inch outlet pipe 26. For a gas flow in the range of 800,000 to 1,500,000 standard cubic feet per hour, plate 20 is drilled with 284 holes 28 of 1 diameter spaced evenly in the form of a grid with the center lines approximately 2.5 apart.

A quench liquid is pumped into the extremely hot gaseous product of the reator in the upper chamber 18 as the product is on its way out ofthe reactor. The quench liquid enters a supply pipe (not shown) which branches into a curved or Y-branch manifold 30 having two armsv extending on opposite sides of the outlet line 26 and termminating in the nozzles 32 which are disposed 180 apart relative to the circular plate 20. These nozzles, which are merely unrestricted orifices at the ends of the pipes in this illustration, are directed downwardly, since it is desired that the cooling action of the vaporizing liquid be primarily utilized to cool the gases which have already left the active reaction space in the reactor. In the case of an endothermic reaction, it is desirable to avoid contact of the cooling liquid with quench chamber top so far as may be practicable, for such contact would cool the top and allow it to absorb heat from the reacting gases in the reaction space thereabove. This cooling of the reactants would not only require a greater degree of heating or preheating of the charge but would slow down the reaction rate and increase the cost of pumping sufficient liquid for the quenching operation.

To break up the jets of quench liquid and distribute them over the surface of the perforate plate 20, a circular distributing or splash plate 34 is suspended below each nozzle 32 about half of the distance downward towards plate 20. Each splash plate hangs from three straps 36 which are welde-d to the side of the pipe nozzle 32 and to plate 34. These straps 36 are radially disposed at 120 intervals around the nozzles and splash plates with the intervening spaces open to permit the liquid to be freely distributed over the surface of perforate plate 20.

The Y-branch manifold 30 is supported on a U-shaped bracket 38 which extends around half of the pipe 26 to which it is secured by welding or bolts and the open end of the U projects out under the manifold.

The quench liquid employed in this invention is desirably a product of the present process in either crude or purified state, for example benzene; this eliminates contamination and the necessity for fractionating the quenched effluent. For example, in the thermal hydrodealkylation of toluene into benzene, it is preferred to use condensed reactor eflluent as the quench liquid. However, other high boiling liquids inert to the gaseous material -being quenched can be used for the purpose, if so desired.

There are a number of optional but highly desirable features of the novel device. Among these is the dam or shield 40 open at the top 42 and surrounding the lower chamber 16 and the lower part of the upper chamber 18 approximately to the level of the nozzles 32. This dam serves to prevent the passage of any quench liquid which reaches the floor 8 of the lower chamber from emerging into the main reaction space of the reactor and from contact with the surrounding insulation.

Another optional but generally desirable feature is the swirl baille assembly 44 located in the outlet conduit 26 to induce a swirling or vortical motion in the exit stream of quenched material passing downward in the line 26 sufficient to direct any entrained droplets of liquid of substantial size onto the walls of the conduit where they are quickly vaporized by the relatively hot surface of the pipe 26. This baille is made up of three semi-elliptical sections 46 of stainless steel plate welded to a short length of l-inch pipe 48 at an angle of 50 with the longitudinal axis of pipe 26. The three baille sections are spaced equidistantly or 120 apart around the tube 48, and the entire assembly is fastened in place by welding it to the pipe 26.

Other types of swirl baflles may also be employed including a twisted strip of sheet metal. In fact, any design may be used that imparts a centrifugal component to the motion of the quenched eflluent products passing therethrough. This baflle is desirably located well within the pressure bearing shell 2 of the reactor in order that any froth or drops `of entrained liquid will impinge on a wall section outlet conduit that is also located within the reactor shell and therefore not subject to a substantial pressure differential. It is preferable to avoid the sudden and perhaps random chilling of a pipe wall under heavy pressure caused by rapid vaporization of a relatively cool liquid.

In operating one modification of the present invention, the gaseous products of a thermal dealkylation reaction taking place at an average reaction temperature of 1260 F. in converting toluene by reaction with hydrogen in excess into benzene and methane reach the bottom of the reactor. This effluent passes over the upper end 42 of the shield 40 and then enters the lower chamber 16 through the openings 14. Next, the gaseous products rise vertically through the hole 28 in the perforate plate 20 and enter the upper chamber 18. Crude benzene product is discharged from nozzles 32 as the quench liquid and produces in chamber 18 a spray or foam in which the rising gases are cooled by evaporation of the liquid. The discharge rate -of the benzene product is 1.5 lbs. per lb. of toluene feed charged. After passing through the upper cell, the quenched effluent enters the line 26 and passes around swirl baflle assembly 44 where any entrained liquids is thrown by centrifugal force onto the interior surface of pipe 26 to vaporize. The temperature of the cooled effluent leaving baffle 44 is 950 F.

In a preferred embodiment, no substantial quantity of quenching liquid is allowed to reach the lower chamber; and the principal quenching action occurs in the sprays splashing ofl of the plates 34 in all directions as well as in the resulting mixed phase foam of gaseous products bubbling through the vaporizing liquid of which at least a major portion is located above the perforate plate 20. The retention of the liquid and mixed phases essentially as foam in upper chamber 18, is accomplished by selecting the number and diameter of the holes 28 relative to the rate of gaseous flow through plate 20 to create a gas velocity through the holes 28 of at least about 10 feet per second while providing suflicient openings for intimate contact between the liquid and gaseous phases and to avoid an excessive pressure drop across the plate. In general, relatively large openings are provided throughout the device to minimize difliculties from possible carbon formation. For that reason, nozzles with large single orifices discharging onto horizontal distributing plates are preferred to nozzles with a plurality of smaller orifices discharging horizontal jets of liquid.

It will be apparent to those skilled in the art that the invention may be utilized in many forms other than that illustrated in the drawing especially with apparatus of different configuration to provide other suitable sprays, passages and chambers of various shapes which will accomplish the sarne purpose. For instance, the device could easily be installed at the top instead of at the bottom of a reactor by rearranging outlet pipe 26 to lead the quenched products upward from chamber 18 and by sealing the central openings in plates 8 and 20 which were provided for a downwardly extending pipe 26. A variety of permeable members may be substituted for plate 20, as for example a woven screen of thick wire or small rods, or one or more layers of parallel flat bars, channel or angle sections, alternate layers being preferably oriented at right angles to adjacent layers. However, a flat plate perforated with holes of selected size and distribution is preferred as affording better control in maintaining a maximum of the liquid in the upper chamber. Where there is any tendency for the gaseous material to be significantly reheated by heat received from the cover 10 immediately after that material has been quenched in the upper chamber, this difliculty, may be overcome by afiixing a layer of refractory insulation to the cover to greatly reduce the transmission of heat therethrough. Accordingly, the invention should not be considered as limited in any other respects than the language of the appended claims and as may be Irequired by the prior art.

We claim:

1. In a process for the reaction of materials in the gaseous phase at high temperatures in a confined reaction zone within an enclosed reaction vessel followed by the quenching of the resulting hot gaseous effluent of said reaction, the improvement which comprises introducing a vaporizable quenching liquid above a permeable member having openings of predetermined number and size into a separate confined quenching zone within said vessel at a rate Suicient to quench the gaseous eflluent of said reaction to a substantially lower temperature upon the.

evaporation of said liquid in contact with said effluent, quenching the hot gaseous reaction eluent within said quenching zone by passing said gaseous eflluent upwardly through said permeable member into contact with said liquid at a suiciently high flow rate with respect to the number and size of the openings through said permeable member to retain at least a major portion of the Vaporizing quench liquid above said permeable member and withdrawing the quenched eluent from said vessel.

2. A process according to claim 1 in which the number and area of openings through said permeable member are suiciently restricted and the ow rate of gaseous effluent upwardly through said member is suiciently high to substantially eliminate the passage of quench liquid downward through said permeable member.

3. A process according to claim 1 in which said gaseous effluent comprising a dealkylated aromatic compound in admixture with methane and hydrogen is quenched from a reaction temperature exceeding 1200 F. to a temperature below about 1000 F. by the introduction at a temperature substantially below 1000 F. of a quench liquid comprising a portion of said `dealkylated compounds.

4. A process according to claim 1 in which said quenched elluent is subjected to vortical ow in an outlet passage from said reaction vessel having a wall of said passage maintained at a temperature substantially above the boiling point of said quench liquid under the prevailing conditions to impinge any entrained droplets of quench liquid on the wall of said outlet passage and Vaporize said droplets during withdrawal of said quenched eHuent from said vessel.

5. A process according to claim 4 in which said vessel is maintained at a high internal pressure and vortical ow is initiated and said vaporization -of entrained droplets occur within a section of the outlet passage located within said vessel.

References Cited UNITED STATES PATENTS 1,483,348 2/1924 Hayes et al 55-257 X 1,920,623 8/1933 Becker 261-108 2,781,251 2/1957 Howell 23--277 3,213,150 10/1965 Cabbage 260-672 X 3,219,419 11/1965 Braconier et al 23-277 HARRY B. THORNTON, Primary Examiner. R. R. WEAVER, E. H. RENNER, Assistant Examiners.

Claims (1)

1. IN A PROCESS FOR THE REACTION OF MATERIAL IN THE GASEOUS PHASE AT HIGH TEMPERATURES IN A CONFINED REACTION ZONE WITHIN AN ENCLOSED REACTION VESSEL FOLLOWED BY THE QUENCHING OF THE RESULTING HOT GASEOUS EFFLUENT OF SAID REACTION, THE IMPROVEMENT WHICH COMPRISES INTRODUCING A VAPORIZABLE QUENCHING LIQUID ABOVE A PERMEABLE MEMBER HAVING OPENINGS OF PREDETERMINED NUMBER AND SIZE INTO A SEPARATE CONFINED QUENCHING ZONE WITHIN SAID VESSEL AT A RATE SUFFICIENT TO QUENCH THE GASEOUS EFFLUENT OF SAID REACTION TO A SUBSTANTIALLY LOWER TEMPERATURE UPON THE EVAPORATION OF SAID LIQUID IN CONTACT WITH SAID EFFLUENT, QUENCHING THE HOT GASEOUS REACTION EFFLUENT WITHIN SAID QUENCHING ZONE BY PASSING SAID GASEOUS EFFLUENT UPWARDLY THROUGH SAID PERMEABLE MEMBR INTO CONTACT WITH SAID LIQUID AT A SUFFICIENTLY HIGH FLOW RATE WITH RESPECT TO THE NUMBER AND SIZE OF THE OPENINGS THROUGH SAID PERMEABLE

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