US2432885A - Furnace - Google Patents

Description

Dec. 16, 1947. R, L HASCHE FURNACE Filed Dec. 8, 1945 Patented Dec. 16, 1947 PAT assigner to Tennessee Eastman; Corp oraticn,

Kingsport, Tenn., Va Vcorpora'trl Yirg'iniaf Applicatin'Deceber 8, 1945,! Serial No. 633,839

y s claims. (c1.

u- My invention relates `to regenerative furnaces, thatis, to furnaces containingf a regenerative mass which is first heated by passing hot combustionA products therethrough, and which is then used to: heatrgases that are passed therethrough, the heat stored in the mass being given up, toathe gases so heated. The furnace is particularlydesigned to process `gases A*which must be very-quickly -heated to a high temperature and very `quickly cooled after `reaching 'the desired maximum temperature; for` example, `itis designedfor use in processes in which acetylene is made-fromrnethane. A-furnace for this purpose must be not only a furnace in which the methane is heatedasanear the highest ,temperature to which thefurnace lining, such, for example, as Carborundummay Vbe heated, for evample, to 300i)Q F., but the furnace must provide that the methane be heated in yasshorta time as is practicable, for example, ra second or preferably less, and-.be asmquickly cooled asis practicable, to a temperature at whichthe acetylene is Astablafor example, to 900 F.

I-t-is an object of'` my invention to provide a furnace capableof producing acetylene in the manner above described. Such a furnace has other uses, the manufacture of acetylene from methane beinggiven to illustrate only one use of myggnvention.-`

In any furnaceof this type, in which a mass of Carborundum or `other heat-refractory substance isheld at temperatures lin excess; .of 2800] F., sometimes for @period'fof seyeral months, :the problem of supporting the incandescent mass vof Carborundurnuisa troublesome one, and it is a further `object of theinvention ,to provide means f oriraisingthel temperature of certain portions of. the regenerative mass to atemperaturehigher than .-theniaxirnumtemperature to which it is desiredto heat the gases to be proces-sed, for example, toa maximum-temperature `of 3000 F., and toprovide aconstructionwhichwill permit tneifcooler portionof lthe regenerative mass to besupported on steel supports in such a manner that thesesupports `will notbe weakened by high 1i-fis' a fel-ther Object- Ofthe invention to provide means by-Whichfthe regenerativelmass is Aso heatedl that, a1thoughfthe gases are heated ,to this llglrtemperatlire,0.1228009` F., noportion of the regenerative mass will besubjected to an excessivetemper'ature, 'forexarnpla inexcess of 30070 E., `vidiich temperature is `close to the `maximum temperature at-'which` Carborundum can rbe e'conomicallyusedl-.

i;flt; s agfurtherobject of myinvention to provide-.inf such a-iurnace means for recovering` and putting to practical-useaconsiderable portion of; thefheat used to-heatlthe gas to a high enough temperature` to produce the desired changein the gas beingused as raw material, for example,

inconvertingmethaneto acetylene.

`It: 's ,f-.urther'obiei 0f my invention t0 Pf6* vide,afurnacewhichmay Abeoperated on a re'- eurrent "cycle in which` theA regenerative mass, einen bananen ,brought up to the maximum temp eraturev `that can be .maintained `without 'too rapiddetericration of the regenerative mass. is subjected to a recurrent cycle consisting 'ofa treating period, in whichthe `gas to be treated. QreXampIeQmethane or a mixturel of gases con-` tainingrnethane, passes in one direction through p,assagesr` in `said mass, thus reducing the temperatureof the.. mass; a. heating period during which Ahightemperature gases, usually products of combustion, are passedthrough said passages for asuiiicient period to restore the mass to the maximum. temperature; and a purging period during which the interior of the furnace is cleared of .products of combustion before the cycle vis repeated. l

Itis afurther object of my invention to provide a Vfurnace which may be operated on a cycle as above described in such a manner that no portioncf theregenerative mass is subjected to excessivefchanges inpreSSure during said cycle. Such changes in pressure Yare destructive to regenerative material and should not be in excess of., 5. pounds per square inch. If, for example, anyy portion ofthe regenerative mass is never at an absolute pressure below 16 pounds per square inch, that portion of the mass should neverb'e subjected to. an absolute press-ure in excess of 21 pounds persquare inch. It is a further object of my invention to provide a furnacestructurewhich will allow rapid purging of the interior of the furnace at the conclusion of the heating period so that hot combustion gases left in ,the passages in the mass at, the end of the heating period are not carried overwith and do not contaminate the gas heated during the treating period.

Itis a further object of my invention to produce a furnace which will operate over long priodswithout need of repairs, and in which the productivecapacityis high as compared with the bulk and cost `of the furnace. l

Further objects andadvantages willbe made evident hereinafter. ,i y 1 Referring to the drawing, in Which Iillustrate a preferred form of furnace embodying my invention:

Fig. 1 is a vertical cross section through the furnace, shown somewhat schematically, various valves, punnps, etc., ordinarily used with the furnace but readily supplied by one skilled in the art, being omitted; p

Fig. 2 is a section through the boiler shown in Fig. l, this section being viewed in the direction of the arrows adjoining the line 2-2 of Fig. 1, this line identifying the horizontal plane of the section shown in Fig. 2; and

Fig. 3 is a section of the furnace shown in Fig. 1, this section being viewed in the direction of the arrows adjoining the line 3-3 of Fig. 1, this line identifying the horizontal plane of said section shown in Fig. 3.

The preferred form of furnace shown in the drawing includes a regenerative mass II above which a heat exchanger I2 is supported, if necessary, by a structure external to the furnace, and not shown. The regenerative mass II may be formed of loose Carborundum bricks so placed as to provide vertical, substantially straight, and open primary passages I3 which extend through the mass II and connect a primary space I4 below the mass with a secondary space I5 above the mass. The heat exchanger I2 is somewhat similar to a fire tube boiler, consisting of a steel shell I6 having a ,lower head I'I, an intermediate head Illa, and an upper head I8. Secured at their lower ends in the lower head I'I and at their upper ends in the intermediate head I8a are a series of tubes I9, these tubes providing secondary passages 20 through the heat exchanger I2, these secondary passages providing open passages between the secondary space I5 and a tertiary space 2I inside the shell I6 and between the heads I8 and Ia. The space inside the shell I6 around the tubes I9 is kept filled with water. Steam with some entrained water flows through a pipe 22 to a steam drum 23 in which the steam separates from the water. The usual boiler feed devices are provided, but not shown, to keep the inside of the heat exchanger full of water at all times as the water is boiled away in the form of steam. Steam is taken from the drum 23 through a pipe 24, and, due to thermo-Siphon and gravity action, water flows from the drum 23 through a pipe 25 back into the shell I6 near its lower end.

For convenience in illustration, the passages I3 and tubes I9 are somewhat simplified in the drawing, being much more numerous and of greater area in proportion to the diameters of the mass Il and the heat exchanger I2 in the actual furnace than they are shown in the drawing.

The regenerative mass is so constructed that it can be supported wholly on a steel structure 25a in the primary space I4. This space I4, as will be understood from the description appearing later herein, never contains gas at a temperature which will substantially impair the strength of steel, and the lower end of the regenerative mass II never reaches such a destructive temperature.

Surrounding the upper end of the regenerative mass I I is an annular combustion chamber 30, which is in communication with the secondary space I5 through an uninterrupted annular throat 3 I. Combustion in this space is provided by five equally spaced burners 32, each fed with gas from a fuel gas manifold 33. lThe combustion products in the space I5 may have a temperature of 32003400 F. The burners 32 discharge through openings 34 in the lower wall of the combustion space 36, these openings connecting the combustion space 30 with pipes 35 forming part of each burner. A steel shell 36 surrounds the mass II and the combustion chamber 30. Surrounding the mass I I inside the shell 36 is an annular layer of heat-insulating material 31. Surrounding the upper end of the regenerative mass II is a ring of Carborundum 39. The heat exchanger I2 and various pipes may also be heat-insulated eX- ternally by heat-insulating material, not shown. Air is supplied to the pipes 35 from an air manifold 40, and steam is admitted into the burners 32 from a steam manifold 4I.

I prefer to line the inside of the combustion chamber 30 with Carborundum brick, but 'it should be understood that Carborundum is merely a preferred refractory material and wherever I have specified its use any refractory material having satisfactory characteristics may be used. In fact, in actual furnace construction I do not use Carborundum as the material for the annular layer 31, in which a low thermal conductivity is desirable.

The primary space I4 is provided with an inlet pipe 42 through which the gas to be processed may be supplied to the space I4, and steam or other inert diluent gas may be supplied to the primary space I4 through a pipe 43. The pipes 42 and 43 are provided with valves, as are the pipes that supply fuel gas to the pipes 35, and as is the pipe supplying steam to the burners 32, these valves also not being shown. The primary space I4 also has an outlet pipe 45 through which combustion gases are conducted to a stack 46 through a valve 41. Processed gases are taken from the tertiary space 2I through a valve 48 to a pipe 49, these gases being the product desired.

It is important that the lower head I1 of the heat exchanger I2 be evenly spaced from and close enough to the top of the mass II to readily absorb radiant heat passing from the mass II through the secondary space I5 to the head I1, the purpose being to prevent the upper portion of the refractory mass II and the ring 39 from closely approaching combustion temperature and thus becoming overheated.

The operation of the furnace may be manually controlled by operating the various valves, but in practice these valves are automatically controlled by mechanism forming no part of the furnace and hence not described or shown.

The operation in producing acetylene from methane will be described, as such an operation is typical of many uses for which the furnace may be utilized. The furnace is operated in a periodically recurring cycle consisting of a heating, a purging, and a treating period. At the beginning of the heating period, the valve 48 is closed, and the valve 41 is open, and during this heating period no gas or diluent is supplied to the primary space I4 through the pipe 42,

Fuel gas is supplied to the burners 32 from the manifold 33, and air for combustion is supplied to the pipes 35 from the manifold 40. It is important to so regulate the flow of air and gas that each of the burners will produce combustion products of about the same volume and at about the same temperature. In the drawings, I show ve burners 32, but in large furnaces more than five burners are desirable. The burners may be inserted through the side walls of the combustion chamber 30, their exact location being somewhat a matter of convenience. If the burners are properly operated, the combustion chamber 30 is filled with an annular ring of combustion gases arisasssz at a'fairly uniform temperature of 3200 F.'to 3400 F. I have' found that in a properly designed furnacev a heat liberation of '150,000 to 1,000,000 B. t. u.s per hour for each cubic foot of combustion space is possible. This ring of combustion products surrounds the upper end of the ring 39 andtends to heat it. The combustion products flow evenly through the throat 3|, which is constricted toan area perpendicular to the gas flow of at least 1/3 of the area on a horizontal plane of the combustion space 30. This constriction tends to promote `an even iiow of combustion products through the throat 3 I. Combustion productsilow thro-ugh the throat at a rather uniform velocity and temperature al1 around the throat, and this velocity is lowered in the space I5 before the gases change direction and flow downwardly through the primarypassages I3. The changes in velocity and direction of the combustion' gases in passing from thecombustion chamber 30 to the spacel5 tendgtomixcthe gasesand produce a very uniformtemperature of the gases entering each ofthe passagesy I3, which is highly desirable, as itvis my purpose to uniformly heat the regenerativemass to themaximum temperature at which it can be used in practice.

The lower head I1the lower end of the heat exchanger I2, is placed ,closeto the upper end of the refractory mass .II and absorbs the heat therefrom and prevents overheating of the top of the'imass. Carborundu-m stands up well at temperatures materially below 3000 F. but deteriorates rapidly at temperatures materially above 3000 F. I prefer to operate the furnace so .that no portion ofthe regenerative mass is at a temperature above 3000 F., in order to prevent rapid deterioration of the Carborundum, and to operate as close as is practicable to this temperature in order to improve the degree of conversion of the methane to acetylene. A uniform heating of the mass II can only be accomplished by uniformity of temperature of the combustion products in the combustion chamber 30 and a uniform flow of gases through the throat 3l. Radiant heat from theV upper end of the mass is absorbed bythe lower head of the heat exchanger and is thus savedfor use in the steam produced by the heat exchanger I2.

The primary passages I3,should be of such size, and the volume ofthe combustion products should be such, that the combustion products passing downwardly through the primary passages attain a high velocity, preferably in excess of 10,000 feet a minute. These products lose heat rapidly by convection; in fact, I have found that inaproperly designed and operated furnace the combustion products lose i about 80% of their sensible heat to the regenerative mass I I and the heat exchanger I2 in their passage from the throat 3l to the primary space I4. The products of combustion are drawn from the primary space I 4 through the pipe 45 and valve 41 into the stack 46, which provides a draft, thereby aiding in Withdrawing the products of combustion from the system. The regenerative mass I-I shouldbe of sufficient length to insure a temperature at the bottom of the mass of about 900F. when the top of the mass is at 3000 F., and when the mass reaches these temperatures the firing period terminates ,and the flow of gas to the burners 32 from the manifold 33 and the flow of air to the pipes 35 are both shut olf. This ring period, when the furnace is operating on the cycle, may be fromkl to 2 minutes.

apurgingperiod, which. `may require. 3 seconds, then zoccurs. The valve 48 isw opened and the valve 41 is closed at the end of the heating period. Steam or other purging agent is admitted to the primary space I4 from the pipe 42 and flows upwardly through the primary passages I3, the space I5, and the secondary passages 20 to the tertiary space 2|, and through the valve, 48 to the pipe 49. This flow purges the primary passages I3 of `combustion products Steam is at the same time admitted `to the burners 32 from the manifold 4I to purge'the combustion chamber 30 of combustion products, and a flow of steam from themanifold 4I is maintained until the end of the treating period, this steam preventing the gas :being treated during the treating period from entering the combustion chamber 30 andprotecting the burners 32 from injury by the combustion gases.

During the treating period, the gas to be treated, for example, a mixture containing methane, is delivered to the primary space III from the pipe 42 and flows upwardly through the primary passages I3, being heated by contact withhthe hot regenerative mass. In making acetyleneJ prefer not to heat the methane mixture before it enters the primary space I4. In itspassage upwardly through the primary passages, the mixture is heated to a temperature of about 2800 F. At or perhaps below this temperature, the methane is converted into acetylene, hydrogen being released. This reaction absorbs large quantities of heat which is obtained from the regenerative mass I I. At this high temperature the reaction isvery rapid,V taking not more than second, and it is important that the flow of gas should be such that the gas passes through the upper 10%V of the regenerative mass in considerably less than 1L., second- Acetylene is quite unstable, and it is important that the converted products of the primary passages be cooled quickly; this cooling is accomplished in the tubes I9 of the heat exchanger I2. The heat exchange tubes I9 should be so proportioned that the gases are cooled to about 900 F. in their passage through these tubes, and that the time required` should be ,-16 second, or less. This quick cooling can be secured if the heat exchange surface, that is, the area of the internal surface of the tubes I9, is from 0.2 to 0.4 times the area of the walls of the primary passages I3, andthe mass velocity of the cracked gas and steam mixture passing through the tubes is from 3 to 6 pounds per square foot of the tube cross section per second. It is not advisable to cool the gas much below 900 F. in the cooler I2, as at .lower temperatures any tars carried in the gases tend to condense and collect carbon, thus blocking the tubes. This tar and carbon can be removed in a scrubber after the gas leaves the pipe 49. The treating period continues until the regenerative mass I I cools to such a degree that it is not highly efficient in its conversion of methane to acetylene, when the treating period ends by shutting off the flow of the methane mixture into the primary space I4, by shutting off the flow of steam into the burners 32, and by opening, the valve 41 and closing the vale 48. The cycle is. then complete, and the firing period of the next cycle starts. The treating period may have been about 1 minute.

While I have described the use of my furnace in relation to producing acetylene from methane, it may be also used to produce butadiene and the olens, such as ethylene, propylene, and butylene, or the .aromatica suchas benzene, toluene, and

mylene, for `hydro'cyanic vacid l'from the vreaction of hydrocarbons and ammonia. All of these products are `endothermic :in nature, andthe 'speed of formation eis very rapid at high temperature. .All of Ithese products are Yalso unstable at high ternperatures .and must be quickly cooled -if they are to be preserved against disintegration. To successfully :produce `and preserve .each of these other `products, they .must be held at vformation temperatures no longer ythan :a fraction of a second,

While I have described lmy .furnace 4as using methane as a gas to .be processed, in 'practice it will be more often .used to process natural gas, which is :largely methane, waste hydrocarbon gases fromoil Arefineries or other sources which may or may not contain methane but contain other hydrocarbons such .as iethane, butane, propane, `or the like, Aor natural gasoline or other petroleum derivatives which are liquidat normal temperatures and which vmust be -fgasi'fied 'by heating prior to -being -delivered rto the primary space I4.

In any consideration of the furnace -it should be understood that `the heat 'exchanger not only acts as a very'eicient means forquickly-extracting heat from the gas after 'this gas leaves the regenerative mass, but lthat it also acts as a steam boiler, producing steam. This :function is of considerable value, as steam finds aready use in connection with the plant in which any Lsuch furnace is operated.

The general dimensions of the regenerative mass in regard tothedimensions of the primary passages therethrough and the thickness ofthe Walls therebetween may be -those set forth inthe Hasche et al. 4Patents No. 2,318,688, issued May 11, 1943, and No. 2,319,679, issued May 18,1943.

Other modifications of the apparatus ofthe pres-v ent invention are shown anddescribe'd in applicants copending applications Serial Numbers 633,844 and 633,845, filed December 8, l1945.

Quantitative statements as given above, in so far as they depend upon any definite size of furnace, relate to a furnace having 4a lregenerative mass with a diameterof'l/g fee't, a length'of v15 feet, atotal surface of primary vregenerative passageway 'of approximately 8000 vsquare feet, a Volume of total primary passageway of regenerative mass of approximately "115 cubic lfeet, Aand having a steam boiler, `the outside diameter yof which is 5.feet, with alength 'of A15 feet, and-total surface of the boiler tubes approximately 2400 square feet. vIn such a furnace the'lineal velocity of `gas through the tubes should be20,000 to 30,- 000 feet per minute.

To obtain the best results, vthe area of the walls of the primary passages should be approximately equal tothe area ofthe walls ofthe secondary passages, and the total cubical volume of thespace included in the secondary space -and the secondarypassages should not vbe over twice the -volume of the space'included'in the primary passages.

AI claim as my invention:

1. A regenerative-furnace comprising an outer shellenclosing an elongated upright regenerative mass having passageways extending lengthwise therethrough, a chamber surrounding one end of said regenerative mass forming a substantially annular colnbustionspace about the end portion of said regenerative mass, an annular throat constituting a communication between said annular combustion space and a space adjacent said end of said mass'into vwhich said 'passageways open, a plurality of burners opening into said .annular combustion space, a second chamber providing a primaryspace in direct communication with .said passageways at the opposite end of said regenerative imass, :an inlet communicating with said second chamber for admitting gas to be treated during a treating cycle, and an outlet communicating with said second chamber for the 'escape of products of combustion during a heating cycle.

2. .A regenerative furnace comprising an outer shell enclosing an elongated upright regenerative mass vhaving passageways extending lengthwise therethrough, :a chamber surrounding one end ofsaid .regenerative mass forming a substantially annular :combustion-space about Vthe end portion of said :regenerative mass, an annular throat constituting .a communication between said annular combustion space rand a space adjacent said end `of said ymass yinto which said `passageways open, a, :plurality of burners opening into said annular combustion space, a second chamber providing a primary .space in direct communication With-'said passageways at the opposite end of said .regenerative mass, an inlet communicating with said second vchamber for admitting vgas to be .treated'during la treating cycle, an youtlet communicating with said second chamber for the escape of products of combustion during a heating cycle and .heat exchange means in substantially axial communication with said passageways in said lregenerative mass at the end thereof surrounded by said annular combustion chamber.

'3. Aregenerative furnace comprising an outer shell enclosing an elongated upright regenerative mass Ahaving passageways extending lengthwise therethrough, a chamber surrounding one end of said regenerative vmass forming a substantially annular combustion space about the end :portion of said regenerative mass, an annular 'throat constituting a communication between said yannular combustion spaceand arspace adjacent said end of said mass into which said passageways open. a plurality of burners opening into said annular combustion space, a second chamber providing a 'primary space in direct vcommunication with said passageways at the opposite end of said regenerative mass, an inlet communicating with said second chamber for admitting gas to be treated during a treating cycle, an outlet cornmunicating with said second chamber for the escapeof -products of combustion during a heatingfcycle and heat exchange means in substantiallyfaxial communication with said passageways in -said regenerative vmass at'the end thereof surrounded by said l*annular combustion chamber, said heat exchange means embracing tubular passageways disposed ina casing, said casing being adaptedtoreceive fluid for heat exchange with gases lflowing through said tubular passageways.

4l'tUDOlllPI-I LEONARD HASCHE.

REFERENCES 'CITED l'Baumann et al. July 4, 1939 Poindexter Aug. 9, 1921 FOREIGN -PATENTS Country Date France fFeb. 10, 41925 Nuniber Number

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