US2079191A - Heating apparatus and method - Google Patents

Description

May 4, 1937. D. l.. THOMAS HEATING APPARATUS AND METHOD Filed Sept. 13, 1933- 3 Sheets-.Sheet l INVENTOR DONALD L. THON/1S BY m.

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INVENTOR DVLD L. THNS BYM )m ATTORNEY Cil Patented May 4, 1937 2,079Jtl PATENT vOFFICE N `IIIEA'IING APPARATUS AND Donald L. Thomas, `New York, N. Y., assignor to Gasoline Products Company,

Incorporated,

Newark, N. J., a corporation 'o'f Delaware Application September 13, :1933, VSerial No.'689,253

9 Claims. "(01. 19e- 116) This invention relates in general to an improved type of oil furnace and more particularly to a radiant type of oil furnace such as is commonly employed in oil cracking processes.

Inmy copending application Serial No. 576,518, led November .21., 1931, I have illustrated and described a form of furnace wherein the main radiant heating section is made up of a series of widely spaced depending loop-shaped rows of tubes located in the upper free space of thecoml bustion chamber.

In Figure 3 of my copending application there is disclosed a box-type of furnace with a central combustion chamber having radiant tubes thered in and two convection chambers with tubes therein located one on each side of the combustion chamber behind bridge walls, the bridge walls themselves carrying an -additional series of tubes located in recesses formed in the front surfaces thereof. The present invention relates to this particular type of furnace and the major object thereof is to present a more developed type of furnace of this character in which efficient heating of the fluid bycontrol of the products of combustion are accomplished.

Other objects of my invention will clearly hereinafter appear as the description thereof progrosses.

In order to make my invention more clearly understood, I have shown in the accompanying drawings, means for carrying the same into practical eflect without limiting the` improvements in their useful applications tothe particular constructions which, for the purpose of explanation, have been made the subject of illustration.

Figure 1 is a transverse verticalsection of a box-type of furnace embodying my invention. p

Figure 2 is Aa vertical longitudinal section of the furnace taken along line 2-2 of Figure `1.

Figure 3 illustrates a particular type of hanger for supporting the successive vertical rows of tubes in the radiant heat section of the furnace. l

Figure 4 is a horizontal cross-section of the furnace taken along lines 4-4 of Figure 1.

Figure 5 .is an enlarged view of the damper control mechanism illustrated in Figure 4.

Referring to the several views shown in the drawings wherein the same reference characters designate like parts throughout and Amore particularly to Figures 1 and 2, -there is shown a furnace l, which may comprise a `combustion chamber 2 and two convection heating sections 3 separated from the combustion chamber 2 by suitable bridge walls 4. Burners 5 :and 5 `for the combustion chamber may be located at opposite 'en'ds thereof and may be arranged for opposed firing as shown in: Figure 2.

. The radiant heat section of the .furnace is designated generally by the numeral and may comprise a series of vertical depending rows of tubes -61 to 510, inclusive, and -a row of tubes. 511 positioned above the depending rows to function as reaction tubes `'for the oil being heated, as will hereinafter appear.. While I have shown ten rows of vertical depending tubes and a single row of reaction tubes, it is to be clearly understood that this is merely for illustrative purposes as any number of `rows of tubes and any number of tubes in each row may 4be Yused without departing from the scope -or spirit of my invention.

The convection heating sections 3 of my improved ftype of furnace may be `identical and the particular tube arrangement in each may be the same. Only one convection sect-ion will be described, it being understood that the description relating thereto is equally applicable to the other convection section. As shown in Figure 1, oil to be preheated may be introduced through an inlet pipe 1 suitably connected to a preheating coil 8 arranged in the `lower part of the convection heating sections and forming a part of the convection banks of tubes therein. Suitably connected to the preheating coil section 8, by means of a line 9, is an economizer coil section Il located in the upper portion of the convection heating section 3.

In order to provide an extensive radiant heating surface within the combustion chamber 2, I have shown in Figure 1, two tube rows I2, the individual tubes of each -of which may be located in suitable recesses formed in the face `of the bridge walls 4 which separate the combustion chamber -of the furnace from the convection heating sections. The lower end of each tube row l2 may be connected by means of a line I3 to the inlets Lof the radiant heating section t. The radiant heating section 6 may be divided into two oil heating circuits, as will be explained.

rl'he radiant heat section of the furnace may be made up of widely spaced downwardly depending rows of tubes of rib-like conformation disposed in the upper free space of the combustion chamber. The number of tubes employed to makeup each row, depends upon the amount of radiant heat surface required in the furnace. These downwardly depending rows of tubes may extend from one third to one half of the height of the combustion chamber, if necessary, and in accordance with the preferred form of construction, should preferably be spaced apart from inches to 24 inches on centers in order to absorb the greatest amount of radiant heat as explained in my aforementioned copending application.

Each of the downwardly depending rows of tubes 61 to 65 may be connected in series to the adjacent row by tubes 612, Figure 2, to permit series flow of the oil therethrough. The rows 66 to 610 may be similarly connected. Each of these groups of rows may in turn be joined in series to one half of the row of tubes 611 of much larger size. The object of making the tubes 611 of much larger size is to have them serve as the digestion or reaction part of the oil cracking circuit to eliminate large sized reaction chambers which are usually placed outside of the furnace. While the tubes have been described as connected in series, they may be connected for parallel flow, if desired.

My invention provides a furnace structure particularly adapted for heating two separate and distinct streams of oil. As shown on the left hand side of Figure 1, one stream of oil may be passed through the preheating coil 8, thence by transfer line 9 through the economizer coil I I. The heated oil may then be passed from the economizer coil II, by a line II', through the radiant row of tubes I2 located within the recesses in the bridge wall 4. The oil may then be passed, by transfer line I3 to the inlet of the radiant tube sections 61 to 65, thence to the left hand half of reaction tubes 611 and finally leaves the furnace through a suitable outlet pipe I4.`

The circuit for the other stream of oil may be identical to that described and the oil may be passed, on the right hand side of Figure 1, through the preheating and economizer coils, thence through the radiant row of tubes located in the recesses in the right hand bridge wall 4, thence through the radiant tube section 66 to 610, thence through the right hand half of the reaction tubes 611 and finally through a suitable outlet pipe I5. It will be clear from the description of the furnace arrangement that the two oil streams are heated independently of each other and it is possible to heat two different types of charging stock in the furnace at the same time.

As shown in the figures, my invention provides for utilizing part of the space within the furnace for superheating steam. In each of the convection sections 3 there may be provided a convection heated superheater coill I6 having a suitable inlet pipe I'I connected thereto. The upper ends of the superheating coils I6 may be connected by means of a steam transfer line I8 to a radiant heat superheater designated generally by the numeral I9 and located in the upper portion of the radiant heating section of the furnace. The superheater I9 may comprise headers 2| and 22 suitably connected together by a plurality of pipes 23. It will thus be seen from this arrangement that my invention provides for superheating steam by passing it through a convection steam superheating section connected in series with a radiant steam superheating section. The plurality of pipes 23 connecting the inlet header 2I with the outlet header 22 are arranged in parallel relation to each other so that the steam makes only a single pass through the tubes in going from the inlet pipe I'I to the outlet header 22 of the radiant heat superheater. The tubes comprising the convection steam superheater I6 may be connected together in series so that the steam passes through each tube individually in succession. This particular arrangement for the steam superheater is particularly adapted to give a high superheat to the steam under all conditions of furnace operation. The steam thus superheated may be used in any part of a cracking process or wherever desired.

The tubes forming the convection coils of the furnace may be supported at their outer ends in a tube plate supporting structure which closes the ends of the furnace and which in this particular arrangement may be formed by a hollow structure or casing 23. Spaced tube openings are provided for the passage of the convection tubes through the sides of the casing in the regular manner, but in my arrangement the convection tubes where they pass through the hollow casing are supported in short lengths of large sized tubing that are used to connect the front and backsides of the casing. These short lengths of tubing may be rolled or welded into the side plates of the hollow casing and practically convert it into a type of heat interchanger or air heater, as in accordance with my invention, it is contemplated to draw a small quantity of sccondary air through the hollow space of the casing and discharge it into the main combustion chamber of the furnace. To accomplish this, the bridge walls 4 may be hollow, as shown at 24, thus enabling the walls to be cooled by air passing therethrough. An opening 25, see Figure 1, connects the hollow wall space of the bridge wall with the top of the casing interior while a series shown, is provided in the lower part of the outer face of the casing 23 for air admission thereto. Air cooling the furnace headers in this manner will greatly prolong their life, obviate warping thereof as well as bending of the parts and will greatly conserve the loss of heat from the still at these points. It should be understood from the description that the top, bottom and sides of the air headers are closed except for the openings herein specied. My invention has been illustrated in Figure 4 with a casing 23 at each end of the convection section 4 and two intermediate casings. Obviously the number of casings may be varied as desired. The combustion gases passing through the convection heating sections 3 are conducted through passages defined by the casings 23.

As previously explained, the combustion chamber 2 may be red from both ends, Figure 2. the combustion gases therefrom being divided and passed over the bridge walls 4 to heat the tubes 4 in the convection heating section 3 by contact therewith. The height of the bridge walls 4 should be kept as low as possible for efcient operation of the furnace, in order to utilize, to the greatest possible extent, the radiant heat surfaces of the depending rows of radiant heat tubes whose ends extend over the convection bank of heat tubes on each side of the furnace. By keeping the bridge walls low, radiant heat from the burners may reach practically all of the parts of these rows, more or less directly, as well as the incandescent combustion gases developed in the furnace which iiow in the chamber-like spaces or passages between the tube rows in the convection section at each side. of the furnace chamber. A centrally placed flue 29, or group of flues, controlled by a damper 28, or group of dampers, is arranged as yan outlet at the bottom of the convection heating sections 3 for the removal of the waste gases therefrom. The ues 29` are in communication with underground cross-fines 3|, which lead to a specially constructed central flue, now to be described.

The central flue, indicated by the numeral 32, may consist of a ceramic or other type ofrefractory structure, which is subdividedfinto a series of chambered passages shown in Figure l. As shown, there are two central passages 33 and 34, forming a double-decked combination on each side of which may be located rectangular flues 35. The rectangular lues 35 are adapted to receive combustion gases from the cross-flues 3l and convey them to a suitable chimney for the furnace, not shown. The object of the central passage 34 of the main ueis to provide means for enabling recirculation of all or a part of the waste combustion gases, if desired. The recirculated furnace gases may. be returned to the combustion chamber 2, from the flue 34, by means of a plurality of recycled gas tubes 36, from which they are discharged into the combustion chamber in a direct central line with the still burners, as is clearly shown in Figure 2. This central discharge of the gases permits of extremely close temperature control of the furnace under all conditions of operation. The passage. 33 may be used for supplying preheated air to the furnace burners by means of vertical breaching 31, which may be employed for carrying the burners 5 and 5 and which may be connected at the bottom with the air passages 33. The heated air for the burners may be obtained from a suitable air preheater, the heat for which may be derived from the combustion gases leaving the furnace. The dampers 28, located in the passages 29 leading from the. convection sections 3, may be used for controlling the still draft and, if desired, these dampers may be automatically operated, as will more specifically hereinafter be explained. Suitable openings k38 may be provided on each side of the furnace to enable easy access to the underground flues for cleaning and repairing operations when necessary. Removable doors 39 for closing the openings 38, when the still is in operation, are also provided. It will be noted that the combustion gases leaving the furnace through the rectangular flues 35 `impart additional heat to the air and recycled gases passing through the central passages 33 and 34, respectively, by conduction through the walls of these passages.

As previously explained, air that has been preheated by passing in heat exchange relation with.

the combustion gases removed from the furnace, may be introduced into the combustion chamber through the passages 33. A portion of the cornbustion gases, after passing through any suitable air preheater, may be recycled back into the combustion chamber 2, by means of a suitable conduit connected with the passage 34.

In Figure 3, I have shown a particular type of tube support for the depending rows of tubes in the radiant heat section of the combustion chamber 2, and which make up part of the radiant heat surfaces for the furnace. In supporting the tubes in accordance with my invention, the use of horizontal bars is eliminated, and each tube row may be supportedby its own individual hanger or hangers which may be suitably secured to the usual I-beams at the roof of the furnace. As shown in Figure 3, the hanger maybe constructed from a single continuous tube 4|', bent-to the sinuous shape shown in the figure and suitably welded together at points 42'., This particular type of hanger permits of cooling and, as shown,

a cooling fluid may be introduced into one branch (a) andl passed throughout the entire length of Athe tube forming the hanger, thereafter emerging from the branch (b). It` is preferred thatl these hangers be made from corrosion-resistant metalsuch-as chromium alloy piping, but,:.if desired, any suitable metal or alloy may be used. The particular hanger shown in Figure 3, is merely for illustrative purposes and' it is to be clearly understood that the Y number of loops formed for supporting the various tubes passing through the hanger and resting at the welded points 42 will depend upon the number of tubes that are used in each depending row. The enlarged reaction tubes 611 may be supported from the roof of the furnace in any desired conventional manner.

The combustion gases from the furnace, as previously explained, pass through the centrally placed ue or flues 29 at the bottom of the convection heating sections to the furnace chimney. Suitable underground cross flues may connectthe convection heating sections, each of which may be divided into threeV passages for het gases by means of the dividing tube header supports 23. These headers or tube supports may be in the form of narrow hollow chambers through which air may be drawn in from the lower part of the furnace. through the openings 2l and issue from the side opening near the top into the hollow bridge wall space 24 through the opening 25. 'Ihe air passing through the hollow bridge wall space may be drawn downwardly by the draft of the furnace and into the combustion chamber 2 through the distributing openings. 26 located in the bottom of the bridge walls.

'I'he divisional headers 23 may extend up to the top of the bridge walls 4 and their upper metal surfaces may be covered with a refractory protective layer of re brickv or suitable furnace cement to a depth of about 4 to 6" as a protection against the heat of the combustion gases coming from the combustion chamber of the furnace.

In accordance with my invention suitable means are provided below the convention coils in the convection heating sections 4 for regulating, either automatically or manually, the quantity of combustion gases passing through the convection heating sections. In this manner, the desired heating of the uids passing through the coInfection',sactionsV may be acomnlished, it being understood that more or less contact with combustion gases, as desired, may be accomplished by the regulating arrangement Referring to Figure 4, each of the passages dened by the spaces between the tube header supports 23 may be provided below the convection coils in the convection heating section 3 with the steel frame 4l having divisional cross bars or plates 42 which subdivide each frame into three equally sized spaces or openings designated by the numeral 43. Each of the openings I3 may be provided with a rotatable damper 29 for the purpose of regulating the quantity of combustion gases passing therethrough. There are thus provided three dampers in each frame 4I, the three dampers constituting a single unit which, in accordance with my invention, may be operated in. unison. It is to be clearly understood that while I have shown threepassages formed by the `tube header supports 23 for the passage of hot corn-` bustion gases from the combustion. chamber 2 the number of passages may be varied merely by 'ILOY changing the number of dividing tube and header supports 23. Moreover, the number of dampers for each chamber may be varied at will, the three shown being merely for illustrative purposes.

To operate the three dampers in unison in accordance with the embodiment of the invention illustrated in Figure 4, the central damper of each group of three may be the controlling member and may be connected by suitable means for actuating the other dampers of the group associated therewith. As shown, each damper may be provided with a shaft 44, the end ones of which are connected with the shaft of the central damper by means of a chain 45 and a sprocket wheel gear 46 associated with each of the end damper shafts 44. It will be clear from this structure that actuation of the central damper shaft will cause the other dampers to be moved in unison therewith through the connecting chain and sprocket arrangement. Actuation of the plurality of dampers for each passage formed below the convection heating coils may be done by hand, or, if desired, may be automatically controlled.

An arrangement for automatically controlling the group of dampers for each passage below the convection heating coils is clearly illustrated in Figures 4 and 5. As shown, there is located on the outer end of the shaft 44 of the central controlling damper, a planetary multiplying gear arrangement indicated by the numeral 41, and shown somewhat in detail in Figure 5.

The planetary gear arrangement 41 may comprise an outer sun wheel 48 which may be provided with internal teeth adapted to gear with three small spur gears 49 evenly spaced with respect to the circular sun wheel 48. The small spur gears 49 may gear with a central spur pinion 5| which is xedly secured to the shaft 44 of the central damper 29. The three small spur gears 49 may be loosely carried on a face plate 52 which may be loosely journaled on the damper shaft 44, the sun Wheel 48 likewise being loosely journaled on this shaft. 'Ihe sun wheel 48 may be provided with an outer set of teeth adapted to mesh with a suitable worm gear 53 provided with a long upstanding shaft 54 having a hand wheel 55 at the top thereof. The worm gear 53 prevents rotation or movement of the sun wheel 48 except as caused by rotation of the hand wheel 55 at the top of the shaft.

The face plate 52 may be provided with an extension arm 56 to which there is pivoted an operating arm 51 which is connected to the planetary gear arrangement 41 for each of the groups of dampers,

The operating rod 51 may extend outside of the furnace and may be connected to a suitable pres'- sure operated controlling member, indicated generally by the numeral 58. The pressure operated controlling member 58 may comprise a piston 59 having a piston rod 6I connected to the operating rod 51. Oil and preferably oil from the transfer line I3 may be introduced into the member 58 by means of a line 62. By introducing oil in this manner, the piston 59 acted upon by the oil under pressure thereby causing the piston to be moved downwardly. The pressure in the transfer line i3 closely follows the temperature changes of the oil passing through the furnace tubes and consequently, the still draft will follow the temperature requirements equally closely, thereby insuring equable draft under all conditions of operation. An adjusting spring 63, the tension of which may be adjusted by a hand wheel 64, may be suitably positioned between the underside of the piston 59 and the face of a member 65. The member 65 is connected to the hand wheel 64 and may be moved thereby to change the tension of the spring 63. As the piston 59 of the controller 58 is arranged to oppose the operating pressure of the oil delivered thereto by the line 62 by means of the adjustable spring 64, it is thus possible to vary the draft conditions differentially' as concerns the two sides of the furnace so that a greater quantity of combustion gases may be passed into one of the convection heating sections 3 than into the other. It will be clearly understood that the more the dampers: are open, the more combustion gases from the furnace are caused to flow through that particular convection heating section. In this manner, the stream of oil passing through one of the heating circuits previously described may be heated to a higher temperature than the oil passing through the other heating circuit on the opposite side of the still.

It is to be understood that the quantity and velocity of the combustion gases passing through each convection heating section is controlled by a separate planetary gear arrangement 41 associated with each group of dampers, and a separate pressure operating controlling members 58 on each side of the furnace. It will thus be seen that with two separate streams of oil passing sired to crack two different kinds of stock in sepf arate streams at the same time and in the same furnace. For instance, one stock, such as gasoline, to be reformed requires a higher temperature for cracking than gas oil which, in accordance with my invention, may at the same time be cracked in the other heating circuit at a lower temperature.

It is possible to alter the setting of the dampers in each of the subdivided convection passages by means of the upright shaft 54 which controls the sun wheel 48 so that an excess of combustion gases may be caused to flow from the furnace into any one or more of the convection passages dened by the casings 23, thus controlling the heat input of the oil passing through the convection tubes at these points to a greater or lesser extent. The combustion gases leaving the convection chambers exit from the furnace through the flues as already explained.

The dampers may be adjusted automatically to compensate for any variation in the temperature of either stream of oil from that desired. Thus, when the position of the piston is changed, there is a corresponding movement of the operating arm 51. The movement of the operating arm 51 is transmitted to the face plate 52 which is correspondingly moved about the damper shaft 44. This movement of the face plate effects a movement of the shaft 44 through the small spur gears 49 meshing with the central spur pinion 5l fixedly secured to the shaft 44. It will thus be seen that the setting of each damper is altered in response to any movement of the piston 59.

While I have shown a particular arrangement for automatically altering the damper settings, other arrangements may be employed. For instance, any suitable fluid may be automatically introduced into either of the pressure operated controlling members in response to variations of the temperature of either stream of oil leaving the furnace through the outlets I4 or I5.

The radiant heating section of the furnace as designated generally by the numeral 6 may, in accordance With my invention, be slightly modified in order to provide a larger number of tubes and at the same time impart intense radiant heat to both sides of the tubes in the manner described in my aforementioned copending application. In accordance with this modification, the depending rows of tubes maybe arranged in a triangular like formation, being arranged as equilateral triangular sections placed side by side With the apex ofl each triangular section being closest to the source of heat. As Will be evident, the triangular arrangement of the tubes permits more tubes to be inserted in the heating section and at the same time permits these tubes to be heated ron both sides :by the intense radiant heat of the furnace. Moreover, the upper` tubes of the triangular arrangement are not appreciably shielded from radiant heat at the bottoms thereof and accordingly receive a greater heat input. VWhen employing this arrangement, one or more rows of reaction tubes Ein may be provided, it being understood that half of the tubes arranged in triangular formation and half of the reaction tubes Will constitute one oil `heating circuit While the other half will constituteanother heating circuit.

It iIJ also possible, in accordance with my invention, to p-rovide heat absorbing tubes around the four Walls of the furnace defined by the front and back Walls and the bridge Walls 4. These tubes may be `arranged for duplex oil circuits and are positioned `around the four Walls in the form of a double threaded spiral, the tubes of each spiral being slightly inclined from the horizontal order to forml a continuous coil section for the two streams of'oil being heated therein. In this manner the tubes so placed receive intense radiantkheat and"a1so protect the four wallsof the furnace, as described.

From the foregoing it will be apparent that I have invented a novel type of `furnace structure in Whichftwo separate' streams of oil may be independently heated. It Will also be evident that I have provided a novel damper arrangement for either automatically or, manually controlling theow of the combustion gases whereby the tWo streams of oil may be independently heated to different temperatures. The furnace arrangement disclosed is particularly adapted for handling large quantities of oil to be heated with the `combustion gases formed in the single combustion Zone being apportioned, one portion of which passes through a separate convection section on one side of the furnace and the other portion of which passes through another separate convection section on the other side of the furnace. y

Obviously, many modifications and variations of the invention as hereinbefore set forth may be made Without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

What I claim is:

l. The method of heating a plurality of separate continuous streams of hydrocarbon oils passing through heat absorbing tubes in a heating apparatus having a plurality of convection heating chambers separated from a combustion chamber by a plurality of bridge Walls Which comprises, producing hot products of combustion for the combustion chamber, passing separate streams of oil through heat absorbing conduits in the combustion chamber and heating each stream of oil passing therethrough preponderantly by radiant heat from the hot products of combustion, passing each of said streams of oil through separate heat absorbing tubes in separate convection heating chambers, distributing a portion of the hot products of combustion after passing through the combustion chamber to each of said separate convection heating chambers, heating the stream of oil passing through heat absorbing tubes in each convection heating chamber by the portion of hot products of` combustion distributed thereto and imparting more heat to one ofl the streams of oil passing through the heat absorbing tubes in one of the convection heating chambers relative'to another by varying the quantity of the hot products of combustion distributed to each of the separate convection heating chambers for the oil streams in question. Y

2. A method in accordance ,With claim 1 in which the quantity of-hot products of combustion distributed to `each of the separate convection heat chambers is automatically regulated.

3. The method of heating a plurality of separate continuous streams of hydrocarbon oils passing through heat absorbing tubes in a heating apparatus having a plurality of convection heating chambers separated from a combustion chamber by a `plurality of bridge walls which comprises, producing hot products of combustion for the combustion chamber, Vpassing a separate stream of oil through heat absorbing tubes positioned upon each of the bridge Walls separating the combustion chamber from the convection chambers and vheating each stream during its flow therethrough preponderantlyby4 radiant heat from the hot products of combustion, passing each of said streams of oil through separate heat absorbing tubesin separate convection heating chambers, distributing a portion of the hot products of combustion after passing through the combustion chamber over the'bridge Walls to each of said separate convection heating chambers, heating the stream of oil passing through heat absorbing tubes in each convection heating chamber by the portion of hot products of combustion distributed thereto and imparting more heat to one of the streams of oil passing through the heat absorbing tubes in one of Vthe convection heating chambers relative to another by varying the quantity of the I hot products of combustion distributed to each of the separate convection heating chambers for the oil streams in question.

ll. In a heating apparatus for heating separate streams of hydrocarbon iiuid to cracking temperature, a combustion chamber, means associated with said combustion chamber for producing hot products of combustion, heat absorbing tubes within said combustion chamber adapted to be heatedpreponderantly by radiant heat from said hot products of combustion, a plurality of convection heating chambers for receiving a portion of the hot products of combustion from said combustion chamber, a plurality of bridge walls separating said convection heating chambers from said combustion chamber, heat absorbing tubes in each convection heating chamber adapted to be heated by the hot productsl of combustion from the combustion chamber, connections between the tubes in each convection heating chamber and separate tubes in the combustion chamber for passage of separate streams of hydrocarbon fluid being heated to cracking temperature, and means associated with each convection heating chamber for causing a greater quantity of hot products of combustion to pass through one of the convection heating chambers than the others.

5. In a heating apparatus for heating separate streams of hydrocarbon fluid to cracking temperature, a combustion chamber, means associated with said combustion chamber for producing hot products of combustion, heat absorbing tubes within said combustion chamber adapted to be heated preponderantly by radiant heat from said hot products of combustion, a plurality of convection heating chambers for receiving a portion of the hot products of combustion from said combustion chamber, a plurality of bridge walls separating said convection heating chambers from said combustion chamber, heat absorbing tubes in each convection heating chamber adapted to be heated by the hot products of combustion from the combustion chamber, connections between the tubes in each convection heating chamber and separate tubes in the combustion chamber for passage of separate streams of hydrocarbon fluid being heated to cracking temperature, and means associated with each convection heating chamber for automatically causing a greater quantity of hot products of combustion to pass through one of the convection heating chambers than the others.

6. In a heating apparatus for heating separate streams of hydrocarbon fluid to cracking temperature, a combustion chamber, means associated with said combustion chamber for producing hot products of combustion, heat absorbing tubes within said combustion chamber adapted to be heated preponderantly by radiant heat from said hot products of combustiom'a convection heating chamber positioned on each side of the combustion chamber for receiving a portion of the hot products of combustion from said combustion chamber, a plurality of bridge walls separating said convection heating chambers from said combustion chamber, heat absorbing tubes in each convection heating chamber adapted to be heated by the hot products of combustion from the combustion chamber, connections between the tubes in each convection heating chamber and separate tubes in the combustion chamber for passage of separate streams of hydrocarbon fluid being heated to cracking temperature, and means associated with each convection heating chamber for causing a greater quantity of hot products of combustion to pass through one of the convection heating chambers than the other.

7. In a heating apparatus for heating separate streams of hydrocarbon fluid to cracking temperature, a combustion chamber, means associated with said combustion chamber for producing hot products of combustion, heat absorbing tubes within said combustion chamber adapted to be heated preponderantly by radiant heat from said hot products of combustion, a plurality of convection heating chambers for receiving a portion of the hot products of combustion from said combustion chamber, a plurality of bridge walls separating said convection heating chambers from said combustion chamber, heat absorbing tubes in each convection heating chamber adapted to be heated by the hot products of combustion from the combustion chamber, connections between the tubes in each convection heating chamber and separate tubes in the combustion chamber for passage of separate streams of hydrocarbon uid being heated to cracking temperature, and means associated with each convection heating chamber for causing a greater quantity of hot products of combustion to pass through one of the convection heating chambers than the others, said means comprising a plurality of dampers associated with each of the convection heating chambers and means for actuating said dampers.

8. In a heating apparatus for heating separate streams of hydrocarbon fluid to cracking temperature, a combustion chamber, means associated with said combustion chamber for producing hot products of combustion, heat absorbing tubes within said combustion chamber adapted to be heated preponderantly by radiant heat from said hot products of combustion, a plurality of convection heating chambers for receiving a portion of the hot products of combustion from said combustion chamber, a plurality of bridge walls separating said convection heating chambers from said combustion chamber, heat absorbing tubes in each convection heating chamber adapted to be heated by the hot products of combustion from the combustion chamber, connections between the tubes in each convection heating chamber and separate tubes in the combustion chamber for passage of separate streams of hydrocarbon fluid being heated to cracking temperature, and means associated with each convection heating chamber for causing a greater quantity of hot products of combustion to pass through one of the convection heating chambers than the others, said means comprising a plurality of dampers associated with f each of the convection heating chambers, each of said dampers being connected together, and means for actuating the thus connected dampers as a unit.

9. In a heating apparatus for heating separate streams of hydrocarbon fluid to cracking temperature, a combustion chamber, means associated with said combustion chamber for producing hot products of combustion, heat absorbing tubes within said combustion chamber adapted to be heated preponderantly by radiant heat from said hot products of combustion, a plurality of convection heating chambers for receiving a portion of the hot products of combustion from said combustion chamber, a plurality of bridge walls separating said convection heating chambers from said combustion chambers, heat absorbing tubes in each convection heating chamber adapted to be heated by the hot products of combustion from the combustion chamber, connections between the tubes in each convection heating chamber and separate tubes in thecombustion chamber for passage of separate streams of hydrocarbon uid being heated to cracking temperature, and means associated with each convection heating chamber for causing a greater quantity of hot products of combustion to pass through one of the convection heating chambers than the others, said means comprising a plurality of dampers associated with each of the convection heating chambers, each of said dampers being connected together, and means for automatically actuating the thus connected dampers as a unit.

DONALD L. THOMAS.

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