US2456787A - Process and apparatus for heating hydrocarbon fluids - Google Patents

Description

Dec. 21, 194s.

L. KNIEL 2,456,787

PROCESS AND APPARATUS FOR HEATING HYDROCARBON FLUIDS Filed March 9, 1946 2 She'ets-Sheet 1 Dec. 2l, 1948. L. KNIEL 2,456,787

PROCESS AND APPARATUS FOR HEATING HYDROCARBON FLUIDS Filed March 9, 1946 2 Sheets-Sheet 2 TEMPERATURE DEGREES F.

I6 '7 REACTOR COIL- TUBE Patented Dec. 2l, 1948 PROCESS AND APPARATUS FOR HEATING HYDROCARBON FLUIDS Ludwig Kniel, Scandale, N. Y., assignorto The Lummus Company, New York, N. Y., a corporation oi' Delaware Application March 9, 1946, Serial No. 653,289

9 Claims. (Cl. 196-110) This invention relates to an apparatus and a method for heating a hydrocarbon fluid by passage of the fluid through banks of tubing within a furnace chamber in which the uid is heated predominantly by radiant heat. More particularly, the invention relates to an apparatus and a method in which the tubes which are subjected to the greatest heat are protected from overheating by passing through them fluid at a rela.- tively lower temperature than the fluid in other parts of the-same tube bank. This application is directed to improvements over the disclosure of copending application, Serial Number 594,410, filed May 18, 1945, by Ludwig Kniel, Pierre Lambert and Herbert R. Treat,for Heating of hydrocarbon fluids.

An important object of this invention is to provide a heating apparatus of high thermal efilciency in the heating of a hydrocarbon fluid, and also to effect economy in the apparatus.

Another .object of the invention is to provide an apparatus for heating a hydrocarbon fluid in which the flow of fluid is so arranged as to limit the maximum temperature which the hottest tubes in the apparatus attain.

Another object of the invention is to provide an apparatus and a method for heating a hydrocarbon fluid in which the life of the tubes is at a maximum, and in which coke deposition within the tubes is minimized.

' Further objects will be obvious from a reading of the following description in connection with the accompanying drawings in which:

Figure 1 is a vertical transverse section of a furnace embodying my invention:

Figure 2 is a partial vertical section on the line 2-2 of Figure 1;

Figure 3 is a graph showing the temperature of the fluid as it passes through each of the various tubes vin `my apparatus; and

Figure 4 is a graph showing the rate of heat input-into the fluid as it passes through the tubes inthe central or` reactor tube bank of my apparatus:

-Myinvention is of particular utility in the thermal cracking of propane to obtain ethylene as a desired end product, as in the case of the furnace described in the aforementioned copending application. In furnaces of this type the `hydrocarbon fluid is passed through banks` of tubes which are heated primarily by radiant heat. The central or reactor bank, or banks, of tubes being subjected on both sides to radiant heat, rather than onone side as in the case of side Wall tubesfhave a much greater heat input rate than Astraight countercurrent relation to the combustion gases, the tubes nearest the burners have been exposed to especially high temperatures,

which has the undesirable effect of reducing the tube life and necessitating frequent shut downs for replacement of tubes or fortheir repair. Such a condition obviously reduces the efficiency of a furnace in requiring its being shut down for such replacement or repairs and in the cost of tubes. My invention is designed to eliminate this condition, or at least substantially to reduce it so as to give increased tube life and to minimize the frequency of required shut downs for repairs.

Referring to the .mbodiment of the invention shown in Figures 1 and 2 of the drawing, the furnace chamber I0 is a box-like form having a fiat iioor or hearth II, a flat roof I2, opposite side walls I3, and vertical end walls I4 and I5. The lower portions of the side walls I3 are vertical, and the upper portions I3a converge upwardly to the roof. The chamber is constructed of blocks or slabs of refractory material sheated with heat insulation I6. The furnace is supported in a position elevated from the ground or from a foundation by a metal frame structure comprising columns Il and upper and lower girders I8 and I 9.

Within the furnaces chamber a pair of outer tube banks, 20 and 2I, are supported in vertical positions directly inwardly of the vertical portions of the side walls I3, and a central, or intermediate, tube bank 22 is supported in a vertical position between said outer banks. bank is arranged parallel to the outer banks. A relatively low wall 23 extends upwardly from the floor of the furnace chamber. This wall is formed of refractory blocks or slabs and internal metal structures 24 spaced along the wall. central tube bank extends from the wall 23 substantially to the roof I2, and together with said wall divides the furnace' chamber into two comf bustion zones,vA and B. At the bottom of each of said zones, there arerows of burners 25, the rows extending longitudinally along the furnace chamber and the burners being in staggered positions in the rows and directed upwardly through ports in the floor. The burners are adustable to vary the heat input in the two zones. The roof of the furnace chamber has two outlets. 23 and 21, opening from the zones A and B into This central TheA exhaust ducts 28 and 29, discharging products of combustion from the furnace chamber. The outlets 26 and 21 and the ducts 28 and 29 preferably extend substantially thev length of the furnace. chamber, and the ducts have dampers 30 and 3| for adjusting the draft through the furnace.

Each of the three tube banks comprises a single nections 34, said outlets are joined to the inlet of the central bank at its lower end. At a few tubes from the bottom of the central bank,

preferably an odd number of such tubes, a crossover or transfer line 36 conducts the fluid to the top tube of the central bank, and thereafter the fluid iiowsjdownwardly through the remainder of the tube bank until it finally exits from the furnace, as through the dischargeline 31. All of the banks, including their return bends, are conned within the furnace chamber and extend throughout most of the length of the chamber.

The tubes of the central bank are subjected to greater heat than the tubes of the outer banks, and they consequently require more frequent 'servicing and replacement. Therefore, provision is made for ready renewal of the central bank. The frame structure which supports the furnace carries a horizontal track 38 extending over the top of the furnace. 'I'his track lies in thev vertical plane of the central tube bank and', through a plurality of suspension connections 39, the bank is supported by the track. The suspension connections extend through slots 40 in the roof I2.

Hinged closures 4| close the portions of the slot between the suspension connections 39 and also close the portions adjacent the ends of the furnace chamber. These closures are formed on their inner sides of refractory material. The end wall |'4 of the furnace chamber has a vertically elongated aperture or slot 42 in register with the adjacent side edge of the bank 22 and meeting the slot 40 through the roof. The slot 42 is normally closed by a hinged closure or door 43 formed at its inner side of refractory material. After de taching the pipe connections 34 and 31 and open ing the top doors 4| and side door 43, the tube bank 22 may be pulled along its track outwardly through the slot 42 to the exterior of the furnace chamber where it may be conveniently serviced. f

In Figure 3, I have shown the temperaturev of the ,fluid as it passes through the various tube coils in the furnace. In the graph, the side wall tube banks have been assumed to have eight tubes each, and the central or reactor tube bank and that any other paths oi' ow of the fluid through the side wall banks may be employed, such, for example, as having the fluid enter the bottoms of said tube banksand flow upwardly through them. Within the banks the charge is qiuckly preheated predominantly by radiant heat, including that received directly from combustion within the zones A andBtalndfthat received through re-radiation from the wall l23. While the tubes of these banks are heated predominant-- ly -upon one side, there is no danger of coke deposition, since the charge is cool when it enters the banks and does not remain therein long enough to reach a coking temperature. The provision oi these banks avoids the requirement for the' customary bonvection heating bank and the chambercontaining such a bank and effects more eilicient and quick preheating than can be attained by convection heating.

The preheated charge is passed from the lower ends of the banks 20 and 2| through the connections 33, 34, and 35 to the lowr end of the central tube bank 22. This central tube bank is subjected to radiant heat directly from the products of combustion in zones A and B and also to heat reradiated from the walls I3, including their upper, sloping portions |3a. This bank.. particularly in its upper tubes, may also be 'subjected to heat of convection as one of the dampers 30 and 3| is normally closed and the other one open, so that the products of combustion in both zones A and B exit through the same outlet 26 or 21.' Thus, the products of combustion in one zone,A

21 and there would be'substantially no ow ofgases through the tubes in central bank .22.

' In the bank 22, the charge passes progressively upward, preferably through an odd number of tubesv to the crossover connection 36 through which it passesto the upper tube of the bank 22, and then vpasses progressively downward through the remainder of bank 22 to dischargeconnection' 31. The number of tubes vincludedbetween the connection 35 and 36 in the lower, and i'lrst,

. section of bank 22 is preferably an odd number for the reason that the inlet 35 and the outlet 31 of said bank 22 preferably pass through the same end wall I5 of the furnace, as indicted in Figure 2. 'I'here being no connection of the central tube bank-l 22 to the other end wall I4 of the furnace, provision is thereby made for expansion and contraction of the tubes with changes in temperature. By virtue of passing ,the preheated uid first through the lower tubes of'the intermediate bank 22 while the uid is still at a relatively low temperature, the lower tubes, which are subjected to the greatest degree of heat, are prevented from has been shown ashav'lng fourteen tbes, the

lower three of which are the rst ones into whic uid from the side wall tubes flows.

In Figure 4, I have used the same tube numbering in showing the rate oi heat input, but only for the tubes in the central' or reactor tube bank.

In the operation of this furnace, the' charge to be heated is continuously introduced into the upper ends of the outer tube banks 20 and 2| and passed progressively downward therethrough in parallel. It is to be understood that this arrangement is not an essential part of my invention,

A tion of heat is graphically illustrated in Figure 4,

where it will be seen that the rate of absorption' of *heat in the lower and first tubes numbered 3,

Il and Il, in central bank 22. is much greater than that in the other tubes of the reactor coil. numbered l2 through 22.

This arrangement of fluid flow makes possible an unusually enlcient and reliable-furnace requiring a minimum of upkeep. As described in the previously mentioned copending application, the provision of side wall tube banks 2l and 2l permits rapid preheatlng of the charge. but at the same time does not permit coking in the side wall tubes, as the fluid does not attain a sufficiently high temperature for coke to form.

"The exit temperature from the side wall tube bank is kept below approximately 1000 F. Due to the fact that they are kept relativelycool, the side wall tubes can be made of low carbon steel and hence are of comparatively low cost. The tubes in the center row are made of allow steel to withstand the higher temperatures to which they are subjected.

Coking is also minimized in other parts of the furnace, because the tubes are sovdisposed that there are few, if any, relatively cold spots where coke deposition wiuld be likely to occur. Coking or carbon deposition is inhibited by the tubes in which the fluid fis at a high enough temperature for carbon deposition, that is. those in the central or reactor coil, being heated substantially uniformly about their peripheries.

The exit from the lower part of the center 'row of tubes through the transfer tube is arranged to take place at `a temperature just before coking tends to occur. Up to this temperature, the amountof ,coke `which may form is sufficiently low so that the velocity of vapors through the transfer tube will effectively carry all of it to the top of the tubes, after which it will pass through the tubes aided by graviy and, therefore, 'without tending to clog the tubes.

Another advantage of my invention isthat feeding of the preheated uid first into the hottest tubes of the reactor coil accomplishesa rapid rise in the temperature of the fluid to a cracking temperature. This can be seen from an inspection of Figure 3, in which the steepest rise of the temperature curve is at tubes 9, Ill and il, and of Figure 4, which shows that in those tubes the rate of heat absorption is greatest. This rapid rise of temperature is important because it suppresses carbon deposition, which occurs more readily when the temperature rise is slower.

Finally, in the furnace of my invention, I overcome a disadvantage found to occur in prior constructions of this general type, namely, the tendency of tubes which are subjected to the greatest heat to fail frequently and to require replacement or repair.'

It is to be understood that the embodiment shown in the accompanying drawings and described above is merelyillustrative, and that my invention may take other specific forms, such, for example, as a furnace having three combustion Ychambers and two intermediate tube walls, as shown in the above-mentioned copending appli` cation. Forms and embodiments otherthan those shown in this and the previous application, are likewise within the scope of my invention, and are to be considered as included by it where they are within the scope of the appended claims.

Having thus clearly described my invention, what I claim as new and desire to secure by Letters Pattent is:

l. The method of heating a hydrocarbon fluid, comprising conducting combustion within two side-by-side zones to eil'ect a high degree of heating within regions of one end of, the zones and progressively diminishing heating toward the opposite end of the zones. conductingsaid fluid in separate streams along confined courses within said highly heated regions and at the remote sides thereof and, within said courses, effecting preheating of the fluid predominantly by radiant heat, uniting said -streams of the fluid thus preheated and conducting the pre-- heated fluid along a relatively short confined course'between said highly heated regions and in substantially. equal exposure to radiant heat from said regions simultaneously andfrom the two regions,v together around substantially the entire cross section of the course, conducting the fluid from said relatively shortcourse to a point between regions of the opposite-end ofthe zones and-thence along a longer confined course between the zones and in substantially equal exposure to radiant heat from said zones simultaneously and from l the vtwo zones together around substantially the entire cross section of the course, and, in said longer course, advancl ing the uid progressively toward said highly;v

heated regions, and conducting combustion gases of at least one of said zones over said longer course t-o heat the fluid therein by con-l vection also.

2. The method of heating a hydrocarbon fluid, comprising conductingr combustion within two sideby-side zones to effect a high degree heating within regions at one end of the zones and progressively diminishing heating toward the opposite end of thezones, conducting said fluidiri separate streams along confined courses within said highly heated regions and at the 'rfmote` sides thereof and, within said courses, effecting preheating of the fluid predominantly by radiant heat, uniting said streams of the fluid thus preheated and conducting the preheated fluid along a relatively short confined course between said highly heated regions and in substantially equal exposure to radiant heat from said regions simultaneously and from the two regions together around substantially the entire cross section of the course, and conducting the fluid from said relatively short course to a point between regions of the oppositeA end of the zones and thence along a longer conllned course between the zones and in substantially equal exposure to radiant heat from said zones simultaneously and from the two zones together around substantially the entire cross section of the course, and, in said longer course, advancing` comprising conducting; combustion predoml-.

nantly within lower regions of two slde-by-side zones, passing said fluid in two separately confined streams and in the same general vertical direction along two substantially coextenslve serpentine courses at the opposite outer sides of said zones to preheat the fluid predominantly bv radiant heat, combining said streams after passage through said courses, passing the fluid of the combined streams along a relatively short confined course between said lower regions and substantially midway between said flrst courses. passing the fluid from said relatively short course to a point a substantial distance above the latter and thence downwardly along a relatively long serpentine course between said zones and substantially midway between said vfirst courses,

substantially symmetrically with respect to said plane, adjacent opposite side walls of the chamber and defining first courses for the uid, a

- single row of spaced substantially parallel tubes located within said plane between said outer banks and dividing the chamber into two substantially duplicate combustion zones, a minor number of tubes of said row atone end ofthe row beingf serially connected and deiining a second course forthe iiuid with an inlet and an outlet, and the remaining tubes ofthe row being serially connected and defining a third course for the fluid with an inlet at the opposite end of the row and an outlet adjacent said second course, a fluid delivery connection betweenleach outer bank and the inlet of said second course,

a fluid delivery connection between the outlet of said'second course and the inlet of said third course, burnermeans arranged to conduct combustion within regions of said zones adjacent said second course and at oppositesides thereof, and outlet means disposed for passing products of said combustion from regions adjacent the inlet end of said third course.

6. A heater for hydrocarbon uid comprising a furnace chamber, a pair of outer banks of tubes within -said chamber, adjacent opposite side walls thereof and defining rst courses for the uid, aj single row of spaced substantially parallel tubes located within a plane substantial- 1yl midway between said outer banks and dividing the chamber into .two side-by-side combustion zones, a minor number of tubes of said row at one end of the row being serially connected and defining a second course for the fluid with an inlet and an outlet and the remaining tubes of the row being serially connected and defining a third course for the fluid with an inlet at the opposite end of the row and an outlet adjacent said second course, a fluid delivery connection between each outer bank and the inlet of said second course, a uid delivery connection between the outlet of said second course and the inlet of said third course, burner means arranged to conduct combustion within regions of said z'ones adjacent said second course at opposite sides thereof, and outlet means disposed for passing products of said combustion from regions of said zones adjacent the inlet end of said third course.

7. A heater as claimed in claim 6 wherein the portion of said row of tubes defining Vsaid third course extends materially beyond said outer banks, and the oppositewalls of the chamber' have portions thereof disposed to reflect radiant heat of said combustion predominantly upon opposite sides of the tubes defining said third course.

8. A heater as claimed in claim 6 wherein thel said burner means comprises a plurality of burners within each zone spaced longitudinally of the tubes of said row and directed toward the regions adjacent the inletend of said third course.

9. A heater for hydrocarbon fluid comprising a combustion chambersubstantially symmetrical with respect to a central plane, a single row of spaced substantially parallel tubes within said plane and dividing the chamber into a pair of substantially duplicate combustion zones, a minor lnumber of tubes of the row at one end of the row being serially connected and defining a relatively short course for the fluid with an'inlet and an outlet, and the remaining tubes of the row being serially connected and defining a relatively long course for the uid with an inletv at the opposite end of the row and an outlet adjacent said short course, means to deliver the fluid to the inlet of said short course, a uid delivery connection between the outlet of said short course and the inlet of said long course,

Vand burner means arranged for combustion of radiant heating of the tubes of the row, the individual tubes ofthe row being exposed transversely around substantially their entire circum ference to receive radiant heat from both zones simultaneously and substantially equally, and outlet means disposed for passing products of said combustion from regions of said zones adjacent the inlet end of said longer course.

' LUDWIG KNIEL.

REFERENCES CITED The following references are of record in the leof this patent:

. UNITED STATES PATENTS Number I

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