US3292913A

US3292913A - Quench system and chamber

Info

Publication number: US3292913A
Application number: US455921A
Authority: US
Inventors: Robert G Craig
Original assignee: Air Products and Chemicals Inc
Current assignee: Air Products and Chemicals Inc
Priority date: 1965-05-14
Filing date: 1965-05-14
Publication date: 1966-12-20
Anticipated expiration: 1983-12-20

Description

Dec. 20, 1966 CRAIG QUENCH SYSTEM AND CHAMBER Filed May'14, 1965 INVENTOR. Aofierf a. (wi

AT TORNEY.

United States Patent 3,292,913 QUENCH SYSTEM AND CHAMBER Robert G. Craig, Wilmington, Del., assignor to Air Products and Chemicals, Inc., Philadelphia, Pa., a corporation of Delaware Filed May 14, 1965, Ser. No. 455,921 Claims. (Cl. 261149) This invention relates to high temperature reaction systems and particularly to systems requiring quenching of the reaction eflluent so as to arrest any further reaction which might occur at the higher temperatures and to prevent reactions leading to formation of products of an undesired nature and which possibly could adversely affect the operation of down stream equipment. This invention has particular utility in hydrocarbon conversion systems, for example in a dehydrogenation system where the quenching of the reactor effluent prevents the polymerization of dehydrogenated hydrocarbons and diminishes the danger of possible coking of the down stream equipment.

In present day operations in hydrocarbon conversion systems the quench is customarily performed in separate or combined prequench and quench towers. Thus it is the practice to pass the reactor efliuent at its emergent high temperature into a prequench area as rapidly as possible and therein to eifect a rapid initial temperature decrease, such as from about =1100 F. to about 300 F., by contact with a relatively cool quenching medium in order to reduce the possibilities of loss of dehydrogenated product to undesirable polymer. The partially cooled eflluent is region wherein more thorough and eflective temperature reduction is obtained by more extensive contact with a relatively cooler quench liquid which may be the same or different from the quench liquid employed in the prequench section. Thus in a relatively short time period the temperature of the stream from the reactor to its exiting from the quench system may be reduced from above about -1100 F. to 125 F. more or less as desired and/or required. Such quench systems are shown in US. Patent Nos. 2,935,541 and 3,080,153.

As is well known in the art of dehydrogenating hydrocarbons to less saturated products, such as for instance dehydrogenation of C saturates and olefins to diolefins, by contact with a dehydrogenation catalyst such as the well known 20% chromia on alumina at temperatures in the order of about 1100 F., improved yields and operating conditions generally result when the reaction pressure is less than atmospheric. There is measurable increase in yield of desired products as the pressure is decreased down to the practical operating pressures obtainable with present commercial equipment. Such pressure is generally in the range of about 5 to 7 inches Hg absolute. Pressures lower than this and even at the lower indicated range have certain advantages but are obtained and maintained with such a degree of difficulty that under normal operating conditions the advantages are outweighed by the disadvantages such as increased power costs, size and cost of equipment, etc.

One of the factors contributing to the difficulties of obtaining lower operating pressures is the well known bugaboo of pressure drop throughout the system. An area contributing a relatively high degree of pressure drop is the present type of prequench and quench system which 0 passed from the prequench region into the main quench may easily account for up to 2" Hg or more of pressure drop between the inlet to the prequench tower and the outlet from the main quench tower. 7

It has been found now that a substantial reduction in the pressure drop difliculties is obtained by quenching such efiluent gases in a quench system and at quenching conditions which differ both in apparatus and flow of materials from systems previously employed.

In accordance with the invention the efiluent gases are transferred into a horizontally extending quench area wherein they are immediately contacted by the prequench fluid under conditions to eflFect a substantial and substantially immediate temperature reduction by contact with the quench medium moving substantially across the direction of flow of the efliuent gases. After separation of the bulk of the quench fluid from the partially cooled gases the gases then enter an area for further cooling and quenching, again through the medium of a relatively cooler quench medium passed also at substantially cross flow with relation to the flow pattern of the reactive gases. By thus eliminating the normal cascade trays and many of the flow baflles in normal quench tower operation much of the cause leading to the higher pressure drop situation is alleviated. It is also possible to reduce the structure height substantially in that the present structure is horizontally disposed and eliminates the need for tower systems that generally rise over feet above the ground. This in turn permits reduction in the length of pipe runs and in other substantial savings attendant to low rise structures.

A fuller understanding of the invention may be had through reference to the following description and the drawing in which FIGURE 1 is a schematic representation of a typical embodiment suitable for use in a hydrocarbon dehydrogenation operation; and FIGURE 2 is an enlarged view of one area of initial contact of reactor efliuent with the first quench medium.

With reference to FIGURE 1, there is shown a diagrammatic representation of a multiplicity of reactors R. Five reactors (R1 to R5) have been illustrated. Each of these reactors is individually piped and valved for operation separately or in combination with any or all of the other reactors in accordance with well known and well established practice which forms no part of the present invention. For simplicity of consideration the further description is to the operation of a single reactor (R.1) particularly as it is concerned with the present invention.

When the reactor is on stream, charge is introduced through valved line shown generally as 26 and reactor eflluent passes through valved line 21 directly into the quench area at 22. The effluent in so doing passes through a suitable spray mist or the like of quench fluid introduced through line 23 in the direction of efliuent flow for initial prequench cooling and flows thence into expanded area 24 wherein it may be, if so desired, contacted Withfurther quantities of prequench medium introduced through one or more of the other prequench inlet system lines 23. During the horizontal passage of reactor eflluent through

areas

22 and 24 the bulk of the quench medium, which is preferably of relatively high density with respect to the gaseous efiiuent, is separated by gravity and flows along the bottom of

areas

22 and 24 for removal through line 31 positioned before internal baflie or weir 32. The dropout of most of the remaining cooling quench fluid from the efiluent gases, upon their entry into the further expanded chamber area 38, is aided by the presence of bafile 51 positioned and sized to cause no substantial increase in pressure drop while simultaneously creating a circular or eddy type pattern of the flowing gases contributing to a centrifugal effect tending to throw the quench fluid out of the gas for collection and flow along the walls of the cooling area. A demister or similar liquid droplet removal system may be employed down stream it necessary or desirable. This collected quench liquid may be removed through line 42 for combination with the liquid in line 31 and then moved by pump 33 into and through suitable heat exchange means 34 for temperature adjustment, and from thence through line 36 into distributing manifold 37.

The precooled gaseous fl-ow exiting from expanded chamber area 24 is further cooled in chamber area 38, both by expansion and by cross flow contact with quench fluid introduced through lines 39, to the desired temperature and is removed through exit line 41 for further down stream processing as may be desired and required but which forms no substantial part of the present invention.

The quench medium'introduced at the top of chamber area 38 for cross flow downward contacts the efiluent gases which are moving generally horizontally at relatively low velocity such that lateral displacement of the quench liquid is relatively limited and which under the influence of gravity collects in a lower region of chamber area 38 for removal through lines 43 which lead into line 44 and pump 46 for transfer through line 47 which may or may not include suitable heat transfer devices, not shown, for adjustment of temperature as may be desired or required. The quench medium from line 47 in turn passes for recycle use, as controlled by suitable valves into lines 23.

In chamber area 38 widely spaced baffles, such as doughnut baEfle members 48 and disc baffie members 49 which may be of varying sizes, with large free flow areas therebetween provide a mild mixing and flow direction change for the low velocity gases While presenting relatively little pressure drop.

Quench fluid may be either removed from or supplied to the quench system by any suitable means, not shown, to meet operational requirements.

In FIGURE 2 an expanded schematic drawing of one embodiment of the preliminary quench system is shown. Reactor eflluent passes through line 21a and open valve 21b and exit line 21c into chamber area 22 at which point it is contacted with the cool quench liquid introduced through line 23a for discharge through suitable nozzle means 52.

All of the quench fluid omission nozzles in chamber area 38 are designed to give a vertical spray curtain effectively normal to the flow direction of the reactor eflluent. The disc and doughnut bafiie members at no point occupy a cross sectional area within the substantially horizontal quench region of less than 50% and preferably their area is in the order of 55% of the cross section in said region. The separation of these disc and doughnut baflle members on their lateral dimension is such that not less than 120% of the cross sectional opening around the disc member or in the doughnut member is available for It should be noted that for systems involving only one to three reactors, normal operation of these reactors would not require chamber area 24 to be enlarged over chamber area 22.

Apparatus designed and operated in accordance with this invention in a system having a throughput yielding approximately 100,000 STYP butadiene can operate at reaction pressures as low as Hg absolute or less with no change in the auxiliary equipment previously required to provide operation at 7" Hg absolute. A pressure re duotion of this magnitude would result in an increase in yield of up to 20 percent of desired product or a reduction of feed requirements of up to 10 percent over. dehydrogenation systems operating at 7" Hg pressure.

Example Comparative nuns were made in a large scale pilot plant at simulated commercial plant operation. The catalyst was standard chromia (18.5 wt. percent) on alumina (81.5 wt. percent) dehydrogenation catalyst which had been removed from a commercial dehydrogenation plant after 205 days of use. The operating conditions of the several comparative runs were substantially similar with the exception of variations in liquid hourly space velocity (LHSV) and variations in pressure 1 as shown in the table below.

The foregoing data demonstrate the desirability of the lower pressure operation. Not only is more of the desired butadiene produced but the selectivity to the desired product is better.

Obviously many modifications and variations of the.

invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, therefore only such limitations should be imposed as are indicated in the :appended claims.

What is claimed is:

1. A quench system for the gaseous effluent of a grouped plurality of reactors having an in-line arrangement of valved downflow eflluent outlets comprising:

(a) an elongated hollow vessel forming a chamber ex- I tending laterally below and beyond one end of the row of eflluent outlets, said chamber having at one end a prequench section communicating along its upper side with said efiluent outlets and at the other end a substantially enlarged quench section beyond the row of eflluent outlets;

(b) means for introducing a spray of prequench liquid 3 into said prequench section at locations adjacent and 1 individual to the discharge ends of said effluent outlets in a manner to effect .good heat exchange coni tact with the incoming effluent;

(c) first baflle means in the path of initial flow of the prequenched eflluent through said quench section to disengage entrained prequench liquid from the flowing eflluent stream;

(d) means for withdrawing prequench liquid from the bottom of said prequench section and from the initial portion of said quench section, cooling said liquid, and thereafter reintroducing the same as a spray of quench liquid into the enlarged quench l section of said chamber in a manner to eifect good heat exchange contact with the prequenched effiuent; (e) second baflle means in said quench section down stream of said first baflie means to provide low velocity, tortuous flow of said effluent and mild mixing thereof with said spray of quench liquid;

(f) means for withdrawing said quench liquid from the bottom of said quench section and recycling the same as prequench liquid into said prequench section;

(g) and means for discharging the cooled elfiuent from the down stream end of said chamber.

2. Apparatus as in claim 1, in which said first baffle means comprises a low weir at the juncture of said prequench and quench chamber sections.

3. Apparatus as in claim 1, in which said second baflle means comprises a doughnut-and-disc arrangement of bafifie members substantially prependioular to the direc tion of normal efiluent flow through said chamber.

4. Apparatus as in claim 3 in which said second bafile means occupies at least 50% of the cross sectional area of the quench chamber section.

5. Apparatus as in claim 3 in which said doughnut-anddisc bafile members are separated on their lateral dimensions such that at least 120% of the cross-sectional flow area around said members is available for cross flow.

References Cited by the Examiner UNITED STATES PATENTS HARRY B. THORNTON, Primary Examiner. T. R. MILES, Assistant Examiner.

Claims

1. A QUENCH SYSTEM FOR THE GASEOUS EFFLUENT OF A GROUPED PLURALITY OF REACTORS HAVING AN IN-LINE ARRANGEMENT OF VALVED DOWNFLOW EFFLUENT OUTLETS COMPRISING: (A) AN ELONGATED HOLLOW VESSEL FORMING A CHAMBER EXTENDING LATERALLY BELOW AND BEYOND ONE END OF THE ROW OF EFFLUENT OUTLETS, SAID CHAMBER HAVING AT ONE END A PREQUENCH SECTION COMMUNICATING ALONG ITS UPPER SIDE WITH SAID EFFLUENT OUTLETS AND AT THE OTHER END A SUBSTANTIALLY ENLARGED QUENCH SECTION BEYOND THE ROW OF EFFLUENT OUTLETS; (B) MEANS FOR INTRODUCING A SPRAY OF PREQUENCH LIQUID INTO SAID PREQUENCH SECTION AT LOCATIONS ADJACENT AND INDIVIDUAL TO THE DISCHARGE ENDS OF SAID EFFLUENT OUTLETS IN A MANNER TO EFFECT GOOD HEAT EXCHANGE CONTACT WITH THE INCOMING EFFLUENT; (C) FIRST BAFFLE MEANS IN THE PATH OF INITIAL FLOW OF THE PREQUENCHED EFFLUENT THROUGH SAID QUENCH SECTION TO DISENGAGE ENTRAINED PREQUENCH LIQUID FROM THE FLOWING EFFLUENT STREAM; (D) MEANS FOR WITHDRAWING PREQUENCH LIQUID FROM THE BOTTOM OF SAID PREQUENCH SECTION AND FROM THE INITIAL PORTION OF SAID QUENCH SECTION, COOLING SAID LIQUID, AND THEREAFTER REINTRODUCING THE SAME AS A SPRAY OF QUENCH LIQUID INTO THE ENLARGED QUENCH SECTION OF SAID CHAMBER IN A MANNER TO EFFECT GOOD HEAT EXCHANGE CONTACT WITH THE PREQUENCHED EFFLUENT;