US2776192A - Acetic acid cracking furnace - Google Patents

Description

E. S. PAINTER ET AL ACEITIC ACID CRACKING FURNACE Jan. 1, 1957 2 Sheets-Sheet l Filed Dec. l0, 1952 INVENTORS J uw .Q @am 2.

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United States Patent O AGETIC ACID. CRACKLING FURNACE,

EdwinA S. Baintenlinasport, and Louis G- Haller, Johnson City', Tenir., assignors to Eastman Kodak Company, Rochester,-N'. YL, ak corporation or' New `I ersey 4Application December 10, 1952, Serial No.1325,0861

2 Claims.v (Cl. 23--277) This: invention relates to.` apparatus for the pyrolysis of organici, compounds andv particularly toV apparatus havingI increasedl capacity for; the pyrolysis of ketenizable compounds such asacetone, acetic;acid:anditheliketotproduce hetgene.,` higherhomologs of ketene or. other valuable products.

Apparatustforthe pyrolysisof ketenizable organic com-` i'pounds. is;1 described in prior Patent 2,541,471 to Hull and Saunders, Other details of the process are'described.` in prior Patent 2,258,985l to Hopkinson and: in other. publicat-ions mentioned therein.

The,pyrolysis furnace described by` IfI-ulll andY Saunders comprises: three heat-exchangechambers and one burner chamber. The heatrexchange chambers4 are designated, respectively as the preheat chamber, the super-heat chamber and` Pyrolysis chamber. Three4 coils ofY metal tubing-,are connectedinseries and theorganiccompounds to, -beprocessed' are passed through the tubing,` ,lirst through-g the4r coill in the preheatA chamber, vthen lthrough i the coil in the super-heatl chamber and: finally through *the coilvin the pyrolysis chamber, being heated' to. a higherv degree in.l each successive chamber, thence out to` the coolers and absorbers which are not shown in the ,Hull andSaunders patent.- but; which'rare .welb known. in the art` and?. differ. in detail.. according; to the.` iinali product which is desired; The fuel, which is` usually producer .gas or natural*4 gas, is burnedfi ina burner chamber from whence thehot combustion gasespassthrough the pyrolysis chamber from bottom to. top, through the super-heat chamber from'` top to; bottom. and finally through the prerheat chamber from bottom to. top and` down again through athollow core inside :the coil' andaout to thestack.`

'lhus` the combustiongases and' the compounds `being pyrolyzed ow, through the heating chambers in opposite directions. ThefHull and Saunders patent describescertain structural features of the heateexchange chambers whereby the heat4 exchange is mademoreeicient.

Saunders furnace and preferably retains these, detailsof structure including-ceramic cores within the coils which ketene, while keeping down the expense and use of:criticalimaterials.

Another objectv of the invention isto provider novel pyrolysis furnace constructions giving unusually. high production rates compared to known furnaces.: of `similar construction.

A further object of the invention is to provide a novel The -present invention is an improvementon the Hull' and inneroved.` by: providingy two` parallel paths of ll/z coils eachinplac e'0fi ausingle pathof three coils* for the corn- 2,776,192 Fanti-enter!v Jan.. 1, 957

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method. ofcoudlcting azketenizable substance through a pyrolysis process so as to; obtain unusually high yields;

Previous. suggestions; along this line, while somewhat similar, Werefound to be unworkable. One plan was to preheat all Athe :material together and then divide the ilow into branches; This failed in the present process because tiow meters` are not available for use at: 60G'D C., and without regulators' the vapor feed wouldnot divide properly.y Another suggestionhad-` to do with the form of the divided coils and proposed that the divided coils be interwound in each` chamber like multiple threads on a screw. Theoretically, this would be very eliicient and shouldgive nicely-equalized heating in the separate paths. The practical difficulties; of installing and repairing the coils, however, make this,v scheme impractical.

According to the present inventiomthe'ketene production capacity of a furnace of the Hull andSaunders type isincreased` by; thefsurprising amount: of about 3G percent andialsot-hequa-lity oftheketene-,andithe acetic anhydride manufactured.r -fromfvthe ketene produced inl the unit is pound; bcing-pyrolyzed We have discovered: that the capacity ofthefurnace: is limited! both by pressure drop vin `thetubing; and by'the'heat inputi to the furnace. The

pressure;` dropoyer a, conventional 3-coil furnace is about 700 mm.of; mercuryfrom. the` entrance of the first coil to the discharge ofl ,the third coil into the condenser. By: arranging. thecoils -in twoparallel. paths, the pressure drop: iscousiderably,decreased and. the total iiow through the. furnacev increased:

the; fullz coil;` ina the adjacent'` chamber. heretofore known as the super-heat chamber, While the: other half-coil .in the pre-heat: chamber is' connectedwith the coil in: the hottest O f the three; chambers, previously known as: the pyrolysis;chamber.` It' will: be noted that in accordance with-this change, both thechambers that have full coils now. operate. as: pyrolysis chambers.

Accordingqtova preferred'form of the invention, comprisingza` variation; of the -form'` just described; each.. of thel three coils isdiyided into two separate halvesV and each; of the; two parallelA flow paths. passes through 4.one halfrcoil inffeactu-furnacechamber, Preferably, in order to.equalizextheheatptransfer' in the two, paths, onepath traverses' the' half-coil, in; the; hotter: end; of one chamber (i. e., the end` ati which the hot gases enter) and through the halfecoil; i'nethepcool'er end` off each of the other two chambers.` There isibutV littlerpreference as to which chamber-is reversed in this-regardwith respect tofthe other two.` 'lhemostf convenient arrangement is to'fpass one branch of the ilow through all the bottom half-coils and, theyother throught allzthetophalfrcoils. The two pathsV ofow are,v nicely-equalized byy making. the two halvesof the. c oil'inat least rone chamber unequal. in length.

To supply additional heat for the increasedcapacity, an auxiliary gas-firedl combustion chamber is optionally installed at' the rear of" the furnacethat isat the endin whichY the pre-heat chamber is located. The hot com bustion gases or'iiue gases'from the auxiliary burner are mixedi withfthe-vue -gasof' tlie'mainl burner inv the furnace at on neanthef.entrancetoithepre-heat chamber, that; is, at the bottom of the pre-heat chamber. The temperature of the gases in the pre-heat chamber is thus increased, allowing more heat to be transferred to the acid in this zone.

For a better understanding of our invention, reference will be made to the attached drawings forming a part of the present application, in which:

Fig. 1 is a semi-diagrammatic side elevational view largely in section and partly on exaggerated scale for clarity, showing a pyrolysis furnace in accordance with l one embodiment of the present invention.

Fig. 2 is a partial similar view of a furnace according to a slightly different form of the invention.

Fig. 3 is a diagrammatic plan view showing the connections to the coils.

Fig. 4 is a view corresponding to Fig. 1 and showing a preferred form of the invention.

In considering the drawings and in particular, Fig. l, it will be noted that many of the parts are the same as or similar to those described in the Hull and Saunders Patent 2,541,471 over which the present invention constitutes an improvement.

Referring to Fig. 1, the main body of the furnace is substantially as described in the Hull and Saunders patent. Within the furnace housing 11, there are a plurality of partition walls 12, 13, and 14, separating the furnace into a plurality of chambers 27, 28, and 29, connected t each other and to the burner chamber by passages 26, 33, and 35, all as described in the aforementioned patent. The burner chamber may be the same as in the prior art and so will not be described in detail here. The passageway 33 between chambers 28 and 29 preferably has a special shape described in the aforementioned patent for giving the combustion gases a turbulent ow as they enter the chamber 28. As in the prior art, the combustion gases flow from the burner chamber through chamber 29, 28, and 27 in that order, thence down through the pipe 21 in the center of the chamber 27 and out through the flue 24 to the stack (not shown).

In each chamber is located a coil of tubing preferably of stainless steel, extending substantially the full vertical length of the chamber. The coils 6 and 8 in chambers 28 and 29 may be the same and preferably are the same as in the prior art insofar as the structure of the coils themselves is concerned, and preferably the ceramic cores 22 and 23 extend the length of the coil as described in the aforementioned patent.

In accordance with one form of the present invention, two half- length coils 51 and 52, are arranged in the bottom half and the upper half, respectively, of pre-heat chamber 27 around the exhaust pipe 21. The half-coil 51 in the lower part of the chamber is connected by tubing 49 and through a flow control 53 (which is also conveniently a owmeter) to a source (not shown) of a ketenizable compound, and is connected by tubing 55 to the coil 6 in the second chamber 28. The half-coil 52 in the upper part of the pre-heat chamber is similarly connected by tubing 50 and through a flow control and meter 54 to the source of the ketenizable compound and is connected at its other end through tubing 56 to the coil 8 in the hottest chamber 29. The full coils 6 and 8 are connected at their other ends through tubing 57 and 58 respectively to a condenser 59 or other apparatus known in the prior art for utilizing the ketene produced in the furnace.

In order to supply the additional heat needed in reacting a larger quantity of material, a booster heating chamber 60 is optionally provided at or near the back end of the furnace, connected with the bottom of the pre-heat chamber 27 or preferably with the passage 26 between chambers 28 and 27, through a tunnel or passageway 61. The hot combustion gases from the booster heating chamber are mixed with the combustion gases from the' main burner at this point and increase the heat transfer which takes place in the pre-heat chamber. In furnaces for in- 4 dustrial use, the full coils have l5 to 15% turns and the two half-coils conveniently have 71/2 turns each.

Fig. 2 is a partial showing of a modified form of the furnace embodying the invention. Only the pre-heat chamber 27a is shown. In this case the top 11 of the furnace has been taken apart, extensions 62 built onto the vertical walls surrounding the pre-heat chamber, and a raised top 63 built over this chamber to take the place of the portion of the top wall 11 which was removed. This higher chamber accommodates two half-coils 51a and 52a, of 91A. turns each. Otherwise the furnace shown in Fig. 2 is the same as that shown in Fig. 1.

Fig. 3 is a partial plan view of the coils and their connecting tubes showing one convenient arrangement of the connecting tubes. The flow of the starting material is regulated by the controls 53 and 54. Tracing the two parallel paths separately (Figs. l and 3), the ow through the tube 49 enters the upper end of the lower half-coil 51 and around 71/2 turns (Fig. 1) or 9% turns (Fig. 2) to the bottom, thence up and through the tube 55 to the lower end of the coil 6 in the second chamber, then out the top of that coil and through the tube 57 to the condenser 59. The other path is through the tube 50 to the top of the upper half-coil 52, then through 71/2 or 91/2 turns of this half-coil and out through the connecting tube 56 to the top of the coil 8 in the hottest chamber 29, then out of the bottom of this coil and through the tube 58 to the condenser. The two outlet tubes 57, 58 may be joined through a Y-connection or may enter the condenser separately as may be found more convenient. Separate condensers could also be used, of course.

Fig. 4 is a partial view corresponding to Fig. 1 and showing the preferred arrangement of half-coils (separate upper and lower coiled tubes) in the heating chambers. Aside from the omission of the booster heating chamber (60) and passageway (61), the parts of the furnace itself are the same as in Fig. 1 and are either numbered the same as in Fig. 1 or not shown in Fig. 4. The pre-heat chamber may optionally be oversized as in Fig. 2, with correspondingly longer half-coils. The coils in all three chambers are divided into upper halfcoils 52, 76, and 78 and lower half- coils 51, 75, and 77 in the preheat, super-heat and pyrolysis chambers 27, 28, and 29 respectively. The connecting pipes and the outlet pipes are arranged so that one path of flow is through inlet pipe 50, top coil 52, connecting pipe 84, top coil 76, connecting pipe 86, top coil 78 and outlet pipe 88 to the condenser 59, and the other path of flow is through inlet pipe 49, lower coil 51, pipe 83, lower coil 75, pipe 85, lower coil 77 and outlet pipe 87 to the condenser.

In order to equalize the flow in the two branches, the top coils (i. e., the coils in the cooler end) in the rst and third chambers are made longer and the bottom coils shorter in the ratio of 81/2 to 61/2 and 91/2 to 51/2 in the respective chambers. The ceramic cores 22, 23 are inconvenient to use with divided coils and we prefer to omit them in this form of the invention.

In a furnace for the regular production of acetic anhydride by the cracking of acetic acid and mixing the ketene product in controlled proportions with acetic acid and having three coils of l5 turns each in accordance with Figs. 1 and 3, that is, with the first coil divided into two sections of 71/2 turns each, the ow rates were found to approximate 1100 pounds per hour through the bottom of the first coil and the second coil and 900 pounds per hour through the other branch, making a total of 2000 pounds per hour for the unit. The pressure drop across such a furnace is about 350 mm. Hg.

As another example, in an acetic acid cracking furnace in accordance with Fig. 2 with the pre-heat chamber enlarged to accommodate a coil of 20 turns divided into two sections of 91/2 turns each, the flow rates achieved were found to approximate 1400 pounds per hour through the bottom section of the rst coil and through the second coil and 900 pounds per hour through the other branch, making a total feed of 2,300 pounds per hour. 'lli'he pressure drop across this furnace is about 400 mm.

In both cases the differences in the quantity of feed as between the two branches of the tubing corresponds to the difference in the heating conditions of the two branches. The lower half-coil is in a higher temperature zone and has a higher rate of heat transfer than the upper half-coil.

By way of comparison, the maximum feed rate to the conventional 3-coil furnace is 1500 to 1600 pounds per hour and the pressure drop is about 700 mm. Hg across the three coils connected in series.

Thus it will be seen that the embodiments of Figs. 1 and 2 are very successful and represent distict improvements over the prior art, but in operating them there still seemed to be room for further improvement, as the operation was somewhat uneven, left something to be desired in ease of control, and the number of cracking coil failures continued at a high rate. Also, as could be expected, the heat from the booster burner was not efficiently utilized, although it did achieve its aim of an immediate increase in total production from the furnace.

To overcome these difficulities, the preferred arrangement of coils shown in Fig. 4 was conceived and tested without a booster burner. It gave almost as great a rate of production as the furnace of Fig. l and ran 165 days without interruption, which was a record run. Thus, with what appears to be only a slight variation of the prior art structure, increased production, far exceeding what could be expected, was obtained, and yet long coil life was obtained, thus providing an operation of extremely high economic desirability.

Furnaces according to the present invention operate in the usual temperature range of 700 to 750 C. The ideal temperature for the reaction in the pressure range from 100 mm. mercury absolute to atmospheric pressure is about 740 C. The invention should operate equally well in furnaces fired by natural gas or other gaseous fuels.

We claim:

1. Apparatus for pyrolysing a ketenizable substance to form ketene, comprising a furnace wall structure defining a plurality of vertically elongated pyrolysis chambers, means for passing hot combustion gases initially into one end chamber, said wall structure having openings connecting the chambers in series for passage of the hot gasses in zig-zag fashion therethrough, passing last through the other end chamber, separate upper and lower coiled tubes located respectively in the upper and lower ends of each chamber, tubular conduit means connecting each coiled tube in the upper end of each chamber serially with a coiled tube in the upper end of each of the other chambers, tubular conduit means connecting each coiled tube in the lower end of each chamber serially with a coiled tube in the lower end of each of the other chambers, whereby two separate tubular flow paths through said chambers are provided, means for removing ketene from the coiled tubes located in said one end chamber, means for passing a ketenizable substance into each of the coiled tubes located in said other end chamber.

2. Apparatus for pyrolysing a ketenizable substance to form ketene, comprising a furnace wall structure deining a plurality of vertically elongated pyrolysis chambers, means for passing hot gases initially into one end chamber, said wall structure having openings connecting the several chambers for the passage of hot gases through the chambers, seperate upper and lower coiled tubes located, respectively, in the upper and lower ends of each chamber, conduit means connecting one coiled tube in `each chamber with one coiled tube in each of the other chambers to provide a flow path for a ketenizable substance, conduit means connecting the other coiled tube in each chamber with the other coiled tube in each of the other chambers to provide a second path for a ketenizable substance, the respective conduit means so connecting the coiled tubes in the upper and lower ends of the chambers that each flow path contains coils which are first swept over by the hot gases entering a chamber and coils which are swept over last by hot gases passing through a chamber, means for removing ketene from the coiled tubes located in said one end chamber, and means for passing a ketenizable substance into each of the coiled tubes located in said other end chamber.

References Cited in the le of this patent UNITED STATES PATENTS 2,232,705 Hull Feb. 25, 1941 2,393,778 Hull Jan. 29, 1946 2,536,949 Livingood Jan. 2, 1951 2,541,471 Hull et al Feb. 13, 1951

Claims (1)

1. APPARATUS FOR PYROLYSING A KETENIZABLE SUBSTANCE TO FORM KETENE, COMPRISING A FURNACE WALL STRUCTURE DEFINING A PLURALITY OF VERTICALLY ELONGATED PYROLYSIS CHAMBERS. MEANS FOR PASSING HOT COMBUSTION GASES INITALLY INTO ONE END CHAMBER, SAID WALL STRUCTURE HAVING OPENINGS CONNECTING THE CHAMBERS IN SERIES FOR PASSAGE OF THE HOT GASSES IN ZIG-ZAG FASHION THERETHROUGH, PASSING LAST THROUGH THE OTHER END CHAMBER, SEPARATE UPPER AND LOWER COILED TUBES LOCATED RESPECTIVELY IN THE UPPER AND LOWER ENDS OF EACH CHAMBER, TUBULAR CONDUIT MEANS CONNECTING EACH COILED TUBE IN THE UPPER END OF EACH CHAMBER SERIALLY WITH A COILED TUBE IN THE UPPER END OF EACH OF THE OTHER CHAMBERS, TUBULAR CONDUIT MEANS CONNECTING EACH COILED TUBE IN THE LOWER END OF EACH CHAMBER SERIALLY WITH A COILED TUBE IN THE LOWER END OF EACH OF THE OTHER CHAMBERS, WHEREBY TWO SEPARATE TUBULAR FLOW PATHS THROUGH SAID CHAMBERS ARE PROVIDED, MEANS FOR REMOVING KETENE FROM THE COILED TUBES LOCATED IN SAID ONE END CHAMBER, MEANS FOR PASSING A KETENIZABLE SUBSTANCE INTO EACH OF THE COILED TUBES LOCATED IN SAID END CHAMBER.

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