US2986454A

US2986454A - Tubular catalytic converter

Info

Publication number: US2986454A
Application number: US673668A
Authority: US
Inventors: Joseph E Jewett
Original assignee: American Cyanamid Co
Current assignee: Wyeth Holdings LLC
Priority date: 1957-07-23
Filing date: 1957-07-23
Publication date: 1961-05-30
Anticipated expiration: 1978-05-30

Description

y 1961 J. E. JEWETT 2,986,454

TUBULAR CATALYTIC CONVERTER Filed July 25, 1957 2 Sheets-Sheet 1 BENZENE- AIR MIXTURE FIG. I

COLD TUBE SHEET 2 25 27 COOL HOT AIR T0 MIXER RADIANT HEAT 3 REFLEG HOT TUBE SHEET CIRCULATING GOOLANT BATH l0 l8 l9 INVENTOR. MALEIC ANHYDRIDE GASES J.E.JEWETT ATTORN EY May 30, 1961 Filed July 23, 1957 J. E. J EWETT TUBULAR CATALYTIC CONVERTER 2 Sheets-Sheet 2 AIR-BENZ 30 2o ROLL COLD FLARE l/8" IO TUBE SHEET ISOLATING 2 TAPER REAM BOTH SIDES F 2 TUBE |.30"O.D., AIR CHAMBER #24GA. 23 Ifor example) HOT TUBE sI-IEET ROLL WITH ROUND FAOE ROLLER N ITRE 8" L5" 0.0. BATH I i |.3l" I.D. sPAcE CAT. TUBE, ROLLED, AND WELDED (for example) FIG. 3

FLOW I 40 REOOROER I F.R. I I 31 I 25 I l I FLOW I 38 I 43 MEASURING l 39 ORIFICE I MIXER ORIFIGE I 35 F I AIR 1 CONTROLLER v I l I r I I BYPA$S4| 36 I 1 26 4 I I |I J' 12 7 42 I) F.x 44 I '-a I .JI J GSHS CONVERTER NOT SHOWING 42 VAPOR BATH CIRCULATION INVENTORf J. E. JEWETT MWW ML/ I ATTORNEY United States Patent TUBULAR CATALYTIC CONVERTER Joseph E. Jewett, Larchmont, N.Y., assignor to American Cfyafiamid Company, New York, N.Y., a corporation 0 arm Filed July 23, 1957, Ser. No. 673,668

6 Claims. c1. 23-288 This invention relates to catalytic converters of the tubular type in which the catalyst is retained in a number of tubes mounted between tube sheets within a converter shell and surrounded by a recirculating temperature regulating bath which usually functions to remove the heat of reaction. Converters of this type are used commercially for exothermic catalytic reactions such as the oxidation of naphthalene or of ortho-xylene to phthalic anhydride, the oxidation of benzene, toluene, cresols and the like to maleic anhydride and the oxidation of anthracene to anthraquinone.

In such converters the hydrocarbon-air mixture entering the catalyst tubes is usually brought into contact with the tube sheet supporting their ends. It is therefore necessary to keep this tube sheet at a temperature low enough to avoid pre-ignition of the reaction gas mixture and to minimize the formation of deposits of a pyrophoric character which could cause fires or explosions in the inlet chamber. It is a principal object of the present invention to provide a catalytic converter wherein contact of the entering gas mixture with a hot tube sheet is avoided, thereby avoiding such pre-ignition problems.

In relatively small converters having low rates of bath circulation it is possible to avoid excessively high tube sheet temperatures adjacent the gas inlet chamber by keeping the surface of the bath liquid some distance below the top tube sheet. However, it is not practical to adopt this expedient in large converters, due to piling up of the bath liquid on the entry side of the top pass at the high flow rates that must be used. Furthermore, excessive stresses are created in the catalyst tubes when the top tube sheet is substantially cooler than the topmost baffle. It is a further object of the invention to provide a converter in which the main tube sheet on the gas inlet end can be operated at substantially the same temperature as that of the recirculating bath and the adjacent bathe, thus preventing internal stresses, while avoiding pre-ignition of the entering reaction gas mixture.

In accordance with the invention the above and other objects are accomplished by providing across the gas inlet chamber a secondary tube sheet containing a set of isolating tubes fitted into the ends of the main catalyst tubes of the converter together with means for cooling this secondary tube sheet. The additional tube sheet and the isolating tubes are preferably of thin metal and take the temperature of the incoming gas mixture, and stresses due to temperature difference with the main hot tube sheet are avoided by pivotal connections between the isolating tubes and the main catalyst tubes. The medium used to cool the secondary tube sheet is preferably part of the air used for the catalytic oxidatron.

The invention will be further described with reference to the accompanying drawings wherein:

Fig. 1 is a vertical diametral section through a converter equipped with an embodiment of the invention;

Fig. 3 is a diagrammatic assembly illustrating the operation of the converter of Fig. 1.

Referring first to Fig. l of the drawings, reference numeral 1 indicates generally a tubular converter containing an embodiment of the invention. The converter is. made up of a preferably cylindrical converter shell 2, a pair of

main tube sheets

3 and 4, a topbaflle 5 and

lower baffles

6 and 7 and a set of catalyst tubes 8 welded at their opposite ends 9 and 10 in the

respective tube sheets

3 and 4. An inlet pipe 11 and an outlet pipe 12 are provided in the converter shell 2 for establishing a flow of a temperature regulating bath liquid through the converter, the bafiies causing the liquid to pass transversely over the catalyst tubes in the direction ii dicated by the arrows.

A gas inlet chamber 15 is provided at one end of the- 19. This arrangement, however, would entail contact of the unreacted gas mixture with the tube sheet 3 and would create the difficulties discussed above.

In accordance with the present invention a secondary tube sheet 20 is mounted across the inlet chamber 15,-

preferably being retained by

flanges

21 and 22 in the converter shell. A set of isolating tubes 23, equal in number to the number of catalyst tubes, extends from this tube sheet into the catalyst tubes 8 and serves to conduct the incoming gas mixture into thesev catalyst tubes while avoiding contact with the hot tube sheet 3.

Pre-ignition of the entering reaction gas mixture by contact with this tube sheet is thereby avoided.

In order to ofiset the transfer of heat from the catalyst tubes to the secondary tube sheet by conduction along the tubes 23 an air chamber 24 provided with,

inlet and

outlet pipes

25 and 26 is provided. This permits the passage of relatively cool air across the sec.- ondary tube sheet 20 and the isolating tubes 23. If desired, the transfer of heat from the hot tube sheet 3 to the cold tube sheet 20 by radiation may be reduced by the provision of one or more radiant heat reflectors 27 which may consist of light gage polished stainless steel or

aluminum sheets

28 and 29 held separated by spacers and placed above the hot tube sheet 3.

The construction and arrangement whereby the isolating tubes 23 are attached to the secondary tube sheet 20 and the catalyst tubes 8 in a pivotable yet gas-tight arrangement constitutes an important feature of the invention. As is shown on Fig. 2 of the drawings, the walls 30 of the openings in the secondary tube sheet 20 which receive these isolating tubes are given a slight taper so that there is substantially a line contact between the tube and the tube sheet. The upper ends 31 of the tubes are flared, and are rolled to a close fit into the tapered openings in the tube sheet.

isolating tube can be expanded into pivotal frictional engagement with the inner wall of the catalyst tube. This is preferably done by rolling the thin-walled isolating tube with a round-faced roller. The fact that the roll: ing is well below the end of the catalyst tube, and therefore opposite the metal of the tube sheet, will ensure Patented May 30, 1961 The lower ends of the isolating tubes 23 are fitted into the open ends 9 of the catalyst tubes 8 and preferably project therein for a suflicient distance so that a portion of each minimum temperature difference between the catalyst tube and the rolled surface of the isolating tube when the converter is at its operating temperature and thus will ensure a sufiiciently gastight joint.

A preferred embodiment of a benzene oxidation process using the invention is illustrated diagrammatically in Fig. 3. A pipe supply compressed air is indicated by numeral 35 while 36 is an orifice in. this pipe providing a pressure drop, 37 is a branch pipe on the upstream side of the orifice, 38 is a mixer on its downstream side and 42 is a pipe supplying benzene vapor to the mixer. Pipe 39 connects the mixer with the gas inlet pipe 17 of the converter while pipe 37 is connected with the inlet pipe 25 of air chamber 24. Outlet pipe 26 from this chamber connects with pipe 39 and contains a bypass valve 41 to control the maximum quantity of air that can pass through chamber 24. This arrangement prevents the leakage of benzene vapors into the air chamber 24 by circulating a portion of the oxidizing air through this chamber under a slightly higher pressure than that in the inlet chamber 15 and catalyst tubes 8 while simultaneously cooling the secondary tube sheet 20 and isolating tubes 23.

The catalyst used in the converter may consist of granular polysurface pellets of sintered silicon carbide spray-coated with 16% V 2.2% Ag O, 6.6% M00 and 0.63% A1 0 the balance being the silicon carbide carrier. A suitable temperature regulating bath may be a eutectic mixture containing 40% by weight of sodium nitrite and about 7% of sodium nitrate, the balance being substantially all potassium nitrate, and this bath may be maintained atthe operating temperatures of 440450'C. shown in the drawings by means of an external air cooler or by any other appropriate cooling means.

A benzene-air ratio of about 1.2 to 1.5 mole percent of benzene is maintained during the converter operation by means of the diaphragm-controlled

valves

43 and 44 operated by an air flow controller PC, a benzene flow controller FX and a recorder-controller RC. The air flow controller functions in response to the pressure differential across a flow measuring orifice 46 and operates valve 43 to maintain a constant air flow. The flow of benzene vapor is measured by FX and is communicated to the recorder-controller which also receives the flow signal from the orifice 46; the control valve 44 in the benzene vapor line operates in accordance with the combined signals. The pressure dilferential between the air chamber 24 and the gas inlet chamber 15 may like Wise be controlled by means of a diaphragm-controlled valve 40 in the branch pipe 37 operated by a differential pressure recorder DPC.

From the foregoing description of a preferred embodiment of the invention it will be seen that all of the objects thereof are accomplished. Catalytic converters of the type dealt with by the invention customarily operate with bath temperatures of about 400 450 C. or somewhat higher and may contain as many as several thousand catalyst tubes which may be of carbon steel or low alloy but are frequently made of austenitic stainless steel such as the well known 316 nickel-chromium-iron alloy. Stainless steel alloys of this type have an expansion coeflicient, over the range in which catalytic converters are operated, which is about 50% greater than that of carbon steel or low alloy steel. The difierence in expansion of a tube sheet at about 200 C. (the approximate temperature of the entering gases) and the adjacent top bafile 5 (at a bath temperature of 450 C.) is such that with 1%" tubes of No. 13 gage thickness and a tube nest having a maximum radial dimension of about 5 ft. it would be necessary to maintain a distance of almost 3 ft. between the baflie and the tube sheet. level of the bath liquid would have to be some distance below the tube sheet to attain the 200 C. temperature,

Since the top 4 for the-reasons discussed above, an additional two feet would have to be added to the length of the catalyst tubes. This additional expense is avoided by the present invention, which substitutes an inexpensive structure of thin gage metal.

What I claim is:

1. A catalytic converter comprising in combination a converter shell containing a set'of catalyst tubes mounted at their ends in a pair of main tube sheets and a set of baflles fitting closely around the catalyst tubes for directing the flow of a temperature regulating liquid across said tubes, a gas inlet chamber at one end of said shell, a secondary tube sheet across said inlet chamber, a set of isolating tubes each having one end supported in said secondary tube sheet and the other end pivotally attached to one of said catalyst tubes to permit rocking in response to differences in thermal expansion between said mainand' secondary tube sheets, and means for cooling said secondarytube sheet and isolating tubes whereby pre-ignition of'an entering reaction gas mixture is avoided.

2. A catalytic converter comprising in combination a converter shell containing a pair of main tube sheets having inner and outer sides, a set ofcatalyst tubes extending throughand having open ends rigidly supported in said tube sheets, a set of bafiles fitting closely around the catalyst tubes for directing the flow of a temperature regulating liquid across said tubes, at gas inletchamber at oneend of said shell, a secondary tube sheet across said' inlet chamber and spaced from the outer side of one of said main tube sheets, a'set of isolating tubes each having an outer end supported in said secondary tube sheet and an inner end in pivotal frictional engagement with the inner wall of'one of said catalyst tubes to permit rocking in response to difierences in thermal expansion between said main and secondary tube sheets, and means for passing a cooling gas across said secondary tube sheet and said isolating tubes whereby preignition of an intering reaction gas mixture is avoided.

3. A catalytic converter comprising in combination a converter shell containing a pair of main tube sheets having inner and outer sides, a set of catalyst tubes extending through and having open ends rigidly supported in said tube sheets, a set of bafiles fitting closely around the catalyst tubes for directing the flow of a temperature regulating liquid across said tubes, a gas inlet chamber at one end of said shell, a secondary tube sheet across said inlet chamber spaced from the outer side of an adjacent main tube sheet and having openings in alignment with the ends of the catalyst tubes therein, a set of isolating tubes each having an outer end supported in one of said openings in the secondary tube sheet and an inner end inserted into the catalyst tube in alignment therewith and having an enlarged portion in pivotal frictional engagement with the inner wall thereof to permit rocking in response to differences in thermal expansion between said main and secondary tube sheets, and means for passing a cooling gas across said secondary tube sheet and said isolating tubes between said main and secondary tube sheets whereby pre-ignition of an entering reaction gas mixture is avoided.

4. A catalytic converter comprising in combination a converter shell containing a pair of main tube sheets having inner and" outer sides, a set of catalyst tubes extending through and having open ends supported rigidly in said tube sheets, a set of bafiles fitting closely around the catalyst tubes for directing the flow of a temperature regulating liquid across said tubes, a gas inlet chamber at one end of said shell, asecondary tube sheet across said inlet chamber spaced from the outer side of an adjacent main tube sheet and having tapered openings in alignment with the ends of the catalyst tubes therein, a set of isolating tubes each having a flared outer end set into 'one of said tapered openings and an inner end inserted into the catalyst tube in alignment therewith and having a rounded enlargement in frictional engagement with the inner wall thereof opposite said adjacent main tube sheet to permit rocking of said isolating tube in rezponse to differences in thermal expansion between said main and secondary tube sheets, and means for passing a cooling gas across said secondary tube sheet and said isolating tubes whereby pre-ignition of an entering gas mixture is avoided.

5. A catalytic converter comprising in combination a converter shell containing a pair of main tube sheets having inner and outer sides, a set of catalyst tubes extending through and having open ends supported in said tube sheets, a set of baflies fitting closely around the catalyst tubes for directing the flow of a temperature regulating liquid across said tubes, a gas inlet chamber at one end of said shell, a radiant heat reflector adjacent the outer side of the main tube sheet nearest said inlet chamber, a secondary tube sheet across said inlet chamber and spaced from said radiant heat reflector, a set of isolating tubes extending through said radiant heat reflector each having one end fastened in said secondary tube sheet and the other end inserted into the adjacent end of one of said catalyst tubes and in pivotal frictional engagement therewith to permit rocking in response to differences in thermal expansion between said main and secondary tube sheets, and means for passing a cooling gas between said secondary tube sheet and said radiant heat reflector and across said isolating tubes whereby preignition of an entering reaction gas mixture is avoided.

6. A converter system for the catalytic vapor phase oxidation of a hydrocarbon-air mixture comprising in combination a tubular converter having at one end thereof a gas inlet chamber provided with a reaction gas inlet pipe in communication with a mixer for mixing compressed air with a hydrocarbon to be oxidized, a first main tube sheet having an outer side adjacent said inlet chamber, a seecond main tube sheet at the opposite end of said converter and a set of catalyst tubes mounted at their ends in said tube sheets, a secondary tube sheet across said inlet chamber and forming with said first main tube sheet an air chamber, a set of isolating tubes across said air chamber each having one end supported in said secondary tube sheet and the other end attached to one of said catalyst tubes, a compressed air pipe attached to said mixer and having a branch pipe leading to said air chamber, an outlet pipe connecting said air chamber with said reaction gas inlet pipe, and a throttling valve in said compressed air pipe. between said branch pipe and said mixer for establishing a difference in pressure therebetween and thereby causing a flow of air through said gas chamber whereby said secondary tube sheet and isolating tubes are cooled and pre-ignition of the hydrocarbon-air mixture by contact therewith is avoided.

References Cited in the file of this patent UNITED STATES PATENTS 1,847,743 Anderson Mar. 1, 1932 1,848,939 Dempsey Mar. 8, 1932 1,909,358 Jaeger May 16, 1933 2,037,316 'Fenske Apr. 14, 1936 2,164,628 Sibley July 4, 1939 2,802,725 Kappel Aug. 13, 1957 FOREIGN PATENTS 309,106 Great Britain Apr. 2, 1929 1,126,765 France July 30, 1956 1,134,275 France Nov. 26, 1956

Claims

1. A CATALYTIC CONVERTER COMPRISING IN COMBINATION A CONVERTER SHELL CONTAINING A SET OF CATALYST TUBES MOUNTED AT THEIR ENDS IN A PAIR OF MAIN TUBE SHEETS AND A SET OF BAFFLES FITTING CLOSELY AROUND THE CATALST TUBES FOR DIRECTING THE FLOW OF A TEMPERATURE REGULATING LIQUID ACROSS SAID TUBES, A GAS INLET CHAMBER AT ONE END OF SAID SHELL, A SECONDARY TUBE SHEET ACROSS SAID INLET CHAMBER, A SET OF ISOLATING TUBES EACH HAVING ONE END SUPPORTED IN SAID SECONDARY TUBE SHEET AND THE OTHER END PIVOTALLY ATTACHED TO ONE OF SAID CATALYST TUBES TO PERMIT ROCKING IN RESPONSE TO DIFFERENCES IN THERMAL EXPANSION BETWEEN SAID MAIN AND SECONDARY TUBE SHEETS, AND MEANS FOR COOLING SAID SECONDARY TUBE SHEET AND ISOLATING TUBES WHEREBY PRE-IGNITION OF AN ENTERING REACTION GAS MIXTURE IN AVOIDED.