US2638879A - Apparatus for heat treatment of fluent substances - Google Patents

Description

F. O. HESS May 19, 1953 APPARATUS FOR HEAT TREATMENT OF FLUENT SUBSTANCES Filed June 30, 1947 5 Sheets-Sheet 1 INVENTOR.

F O HESS ATTO RNEY May 19, 1953 F. o. HESS v 2,538,379

- APPARATGS FOR HEAT TREATMENT OF FLUENT SUBSTANCES Filed June 30, 1947 -s Sheets-Sheet 2' INVENTOR. I F. o. HESS F. O. HESS Ma y 19, 1953 APPARATUS FOR HEAT TREATMENT OF FLUENT SUBSTANCES- Filed June 30, 1947 3 Sheets-Sheet 3 FIG- 7 JNVENTOR.

F. O. HESS ATTORNEY FIG. 6

Patented May 19, 1953 UNITED .S'iA'i ES TUB. "HEAT I REZATMEN I' F ELUENT SUBSTANCES Frederic 0. Hess, l fhfiladel jlija, Ta assignor 't'o Se'l'as Corporation of America,Pliiladelphiafla a corporation of Pennsylvania Aimlicalfiidh 51111930, 1945, YSliaLNO. 758;!)22

(Cl. T22 355) 9 Claims. 1

This invention relates to heating, and more .particularly to a method and apparatus zfor heating fiuent material as it is passing througha-concdtti t.

The invention is particularly concerned with thezpr'ovision of the necessary or freq-uiredamoimt of :heat appropriate to the particular use :for which iii; :is employed and to the control =of such heat generally and in localized areas to-ca dei-gree heretofore unattainable for producing a '1 desired heating effect, "thus controlling within very :small limits the overall temperature :and the temperature .in different specific localities .-or zones throughout the area heated.

lhis application is :a continuation-impart or 1 mycoapending application Serial Number 3263613, tiled March 29, 1940, now abandoned.

an many -modern processes, it is necessary that the material is various portions of a conduit :be

accurately heated to different temperatures, :and

that these temperatures he zrapidlyandzaccnrate- 1y changed from :timeto time. 'With lone -flame burners and large W211 surfaces that are *ordrnarily used-it is impossibleto obtaiinioealized:tem

perature control ,along various portions :'of the other hand, the axis of the-flameis at right angles to the object to be heated, varying the .iiame length may move the hottest portion of the name "toward the object and might actually 'ti'u'chit, ormay o "beyond 'itin which case the object would be actually at a lower temperature on account of being "within -the -cooler portion of 'thefiame.

In an attempt to ofi-set this "effect of'long- 'il'aines and to obtain good heat distribution throughout the furnace chamloer, it iscus'tomary to use a'Ve'r37 large-amount or excess a'i-r tin can- "junction "with a rich name. This ractice, hesides failing to accomplish the desired heating, adds a fire hazard in the furnace. It is Jsohappensthat-combustilile material is passin through tneconuuit and arraeturethercof 'occurstheimato :utilize the beneficial effects of radiant heat has met with little success 'because there has been no Way to control its utilization in individualaones. The large heated wall has caused each portion of the co it to be heated substantially to the te,.- u-:-erature. This is true even though the angle at which the flame Aim;- .-pi-n ges upon the wall may be varied and even though the length of the flame may .be i' aried. It is noted that long flames and large volurnes cf combustion-air *go hand in hand whether the flames are used to heat the conduit directly 'or indirectly through heating the furnace walls.

stated alcove, rapid change of temperature is necessary in order to control the refined, high temperature processes in use today. not he sol-one where :large Wall sur-fiaoes are heated or where large amounts of combustion air, are used :becauseof the thermal iag. So .much heat is stored in the furnace walls and in the .-productsof combustion and excess air with-in the f-ur-nace chamber that a -rapid increase or decrease :of temperature cannot be obtained.

From the above it will beseen that to obtain accurate 'zone control of the heating of rluid in a conduit several things are necessary-among which the following are noted. The excess fair and the large volumes of air andgas used to obtain convection heating must be eliminated. Radiant heat in controllable form must be .-applied to the conduit rather than that obtained Jay the haphazard manipulation on directionalrchange of .burners. The :heat source tor effective zone control ';must he :close to the heated object.

In order to cvercorne the above-mentioned deficiencies in prior types oi heating equipment it has beenifound zin accordance 'With the present invention that the desired results may he rob- .t'a'in'ed by utilizing number of accurately .posi tione'd and reg-ulatable sources of radiant heat for producing the required heating zeftect. Since the ikieat rays from a radiant heat source travel straight lines, can be directed :by the "com accretion of hehea't-source, thedistrib'ution of such radiated heat may he directed over desire'd area. Also utilizing a murautyaf such sources in which-the heated area's overlap, rate and close control cf the heat area may be obtained by simple adjustment or the fuel "input to theraciiant burners.

F'With radiant heating it is aisopossihleto iresignfheating devices with the heat -source located close to the heated areas without the danger of flame impingment or highly idealized heating, since with this type of "heat "source no a-ctualflame extends beyond-the conflines,of the burner, 'The temperature can thus he critically controlled willie "$6111 :mairitafmn max-imam burner efficiency and resulting fuel eccncxrfir at any given adiust'inerit thereof.

It will therefore be apparent that among the objects of the invention is to provide a method of and apparatus for heating fluent streams simply, efficiently, economically and continuously, with flexible control susceptible of critical adjustment of temperatures within desired heating areas or zones.

A specific object of the invention is to provide an improved method of and apparatus for heating fluent material flowing through a bank of tubes, by means of gas burners of such character and so disposed that a large portion of the heat liberated in their operation is radiated to the tubes, from the burning gases and from incandescent refractory portions of the gas burners, without subjecting the tubes to flame imtemperature regulation so that injury thereto can be avoided. This includes the use of brittle substances such as quartz and other materials as the conduit through which the material to be heated passes.

By the use of such materials for conduits new processes requiring temperatures above the range to which metal tubes can be subjected and the heating of highly corrosive materials may be accomplished.

A further object of the invention is to provide heating apparatus in which the heat is radiated from surfaces having such configuration and relative location that the heat will be uniformly distributed over a predetermined area and in which the control of the radiant heat source will accurately control the temperature in the area receiving the heat.

A further object of the invention is to provide heating equipment and a method of heating capable of both localized and properly distributed heating, and in which the temperature in any selected area or zone can be accurately controlled over the total temperature range, in order to obtain desired temperatures within the heated area, whether such temperatures be 200 F., 2000" F., or any other desired temperature or temperatures.

Another object of the invention is to provide a process of heating in which accurate control of the heat input in selected zones or areas can be obtained, and in which the heat input in such zones may be reduced to zero or therebelow by the introduction of cooling effects in these zones while maintaining the desired heating effect in closely adjacent or other zones.

Another object of the invention is to provide heating apparatus in which all parts are accessible for inspection and in which the heating means can be shut off and air introduced therethrough to effect uniform cooling of the entire furnace or any portion thereof for repair, inspection, or other purpose.

Another object of the invention is to provide a process of heating applicable to the treatment of fluent materials in which reactions may occur rendering necessary the accurate control of heat input at any given point in the travel of the material thereof, and also may require reducing such heat input to the extent of cooling when the reaction of the material heated makes it desirable.

Still another object of the invention is to provide a heating apparatus and process adaptable for use in treating fluent materials continuously, and in which the heat necessary for such treatment varies in accordance with different characteristics of the material during the heating process, and to apply the required heat in different areas or zones during the continuous movement of the material and the changes which occur therein.

The invention is thus well adapted for use in known processes including superheating of steam, heating an organic fluid to a high temperature, oil cracking, or the like, as the material flows continuously in an elongated flowpath, to effect changes in the chemical composition of the fluid which require, or make desirable for optimum results, different rates of heat transmission to the fluid passing through different portions of said path.

In a fluid heater constructed in accordance with the present invention, there is no risk of injuriou flame impingement against the tubes, and with burners suitably distributed in the furnace chamber, heat may be transmitted at a relatively high rate to tubes separated only a foot or so from said wall, and with such regulation of heat distribution as to avoid risk of local overheating of any tube or tube portion. The use in a fluid heater of the multiplicity of burners characteristic of the present invention, permits any control or regulation of the heat distribution which may be practically desirable, to be effected by suitable regulation of the rate of fuel supply to the different burners.

Furthermore, the character of the burner employed and the fact that the radiation is directly from the burner combustion space through the open side of the latter, permit of a high radiation temperature and higher rate of heat radiation in a heater for fluent material constructed in accordance with the present invention, than are practically possible of attainment in known types of heaters havin a heat conducting and radiating wall of carborundum or of a refractory metallic alloy between a combustion or heating gas space and a space including tubes containing fluent material to be heated. As is well known, the rate of heat transfer by radiation from a high temperature source of heat to a colder body to be heated is proportional to the difference between the fourth powers of the absolute temperatures of the source and body.

Further objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a perspective of a heating apparatus constructed in accordance with the present invention and with parts broken away for greater clarity;

Fig. 2 is a section on the line 2-2 of Fig. 3 and showing the internal structure of a modified form of heating apparatus;

Fig. 3, a side elevation on the line 33 of Fig. 2;

Fig. 4, a fragmentary diagrammatic view showing how a cooling medium may be introduced to the burners;

Fig. 5, a fragmentary perspective of a different type of heat radiating wall for use with the furnace;

ii: Cooling for certain portions of the tube bank after.,heating= may be easily accomplished with the present apparatus by the introduction of cold air. through the burners in desired selected cations One means for accomplishing this is shown in Figure 4 in which the gas and vair suppliedato a manifold I! from control valve 65 passes-through a three way valve 68, the other .or third branch ofthe valve leading to a pipe 69 throughwhich air may be supplied to the burners. In the normal operation of the system, the three-way valve 68 will be adjustedso that the air and gas mixture passesthrough the valves 65- and 68 to the manifold 11. When, however, it isdesired to reduce the temperature of that portion of the furnace which is heatedby the burners supplied by the manifold H, the threewayvalve 68 isadjusted so that air can pass through the manifold I1 and through the burners to cool those tubes which are normally heated by these burners. A similar arrangement can be provided to supply cooling air to each burner individually, if desired. Cooling air to each burner can be introduced through all of the burners in order to rapidly cool the furnace in case this may be necessary.

Tubes I2 of the tube bank may be of material appropriate for the particular use to which the tube bank is placed, for example, stainless steelor other appropriate metal may be used in certain processes, although the invention contemplatesand is particularly-adapted for the use of other materials, such as quartz or the like because of its high resistance to chemical reaction and the high temperature to which it can be heated. It has not been previously commercially feasible to employ quartz tubes and other sub-- stances which were subjected to high temperatures because of brittleness or other characteristics which would not withstand uneven stresses caused byuneven heating of the furnace itself. The close temperature control possible with the present invention makes it possible to maintain atemperature control within plus of minus 5 F., although in normal applications the control of temperature-within 1% is all that is necessary. {This accurate control is entirely possible and practical over a, range from approximately 200 F. to 2000? F. Such accurate zone control of temperature can only be obtained where the heat is supplied from a radiant source because if there .were anyappreciable convection heating, there would be. no adequate control over the heating eifect produced by the convection currents and consequently no accurate zone control for the total heating effect.

An added advantage of the structure described above resides in the fact that when it is necessaryto. shut down the apparatus, for cleaning, repair or the, like, it is only necessary to introduce cold air through all of the burners in order to obtaina relatively quick cooling of the complete structure; it being possible by this method to cool the'structure sufficiently for workmen to enter to make repairs within a matter of or minutes, whereas in conventional structures, two or three days were often required for the necessary cooling, I While for many applications, the burners of the type shown in Fig. 1 of the drawing and. described in my prior Patent No. 2,215,079 are provided, other types of radiant burners, as mentioned above, may also be used. For example, a furnace wall may be made of a plurality of burners of the type shown in Fig. 5 ofthe drawing. In this figure there is a furnace wall formed of a series of compartments, each of which has afloor 'II through which extends a burner 12 of a type disclosed in Patent No. 2,287,245. This type-of burner has a comparatively short flame which may be readily controlled. This flame impinges upon a sloping wall I3 that lies directly above the floor II of each compartment. These sloping walls are heated to incandescence by the flame within the compartment in which complete combustion occurs. Each compartment wall radiates heat to the tubes in front of the same, the interior furnace wallas a whole being composed of a series of similar compartments so that all portions of the tubes in the furnace are heated by radiant heat projected from the sloping walls I3. The walls themselves are composed of a series of refractory blocks so shaped that the various compartments are produced by properly laying the blocks in relation to each other. The compartments are separated from each other by partitions 14, also of suitable refractory material. As shown in the drawing, the various compartments are symmetrical with one compartment directly above the other. The compartments may be arranged in any desired manner although at times it may be desirable to arrange them so that one row of compartments is staggered with respect to the adjacent row, as shown in Fig. 1. This prevents any possibility of a cold spot in the tube for containing the material to be heated because of the location of partitions 14.

Each of the burners used with a furnace wall of this type is supplied individually through a pipe IS, the flow through which is controlled by a manually adjustable, valve I6. These pipes I5 are connected to manifolds 'I'I located along the outer walls of the furnace in a manner similar to that of the manifolds I'I. As in Fig. 1, it is generally desirable to have all of the compartments in a single horizontal row or in adjacent rows serviced by the same manifold so that as the intensity of the gas flame is changed in one row of compartments the heat projected by the radiant Walls in a single horizontal plane can be changed. In this way the tubes extending horizontally at different levels in the furnace chamber can be heated to different temperatures and zone control thereby obtained. Provision may be made for'supplying cooling air as indicated in Fig. 4.

There is shown in Fig. 8 the detailsof a short flame burner I2 which may be used in the structure of Fig. 5. While this particular burner may be advantageously employed, it is to be understood that any suitable short flame type burner may be used in this application, as it is only necessary that the burner heat the wall portion 13 and that complete combustion take place within the space 1 I.

From the foregoing it will be readily apparent that the fluent material to be heat treated is introduced into the tubes I2 adjacent the upper end of the tube bank and flows through the preheating portion I5 of the passage I4. This preheats the fluent material to a temperature somewhat below that at which it is desired to treat the material, but utilizes the heat which would otherwise pass out of the furnace and be wasted. As the material to be treated passes into the tubes within the furnace chamber II, it is subjected to the desired heat controlled by the particular burners heating that particular area of the tube bank, it being necessary in various processes of treating streams of fluent materials tovary the aeaasm 9 heat input thereto. at'frequent intervals throughout. the. cycle.

The burners may be individually adjusted to provid the desired heat input. at any location in. the travel at. the material. through the tube L2- in accordance with the heat treating processbeing followed. As indicated above, if it is desirable: because of an: exothermic reaction: in thematerial, or for other reason, to.- cool said ma terial, cold air may be admitted through the appropriate burner orburners in order tome-imtain; the desired temperature. As the materialpasses: from. this region additionalheat may be supplied by other burners in order to completethe process. By utilizing radiant type burners as. described: above toobtain a radiant. wall, there will. be no flame impingementon: the tubesrorming the tube bank and therefore no. localized over-heating resulting. in the" formation. of. coke or other deposits within the tubes.

There is a further advantage in utilizing this type of burner in that no excess air' is. required since complete combustion takes place: within: the burner combustion space and: consequently there is insufficient oxygen within the furnace chamber H to support combustion therein. When combustible material is flowing through the tube bank and a rupture occurs, there is little danger of fire as the oxygen in the chamber is insufiicient to support combustion. The small volume of heated gas-in the furnace chamber increases the speed and accuracy of control.

A modified form of theinvention is illustrated in Figures 2 and 3 in which a furnace is pro .vided having an outer shell 42 and a lining Mi of refractory material defining" a furnace chamber 44, openings 45" being provided in the top of the chamber 44 to permit escape of the-products of combustion. Mounted in the opposing side walls of the chamber are a plurality of burners 6-8,, which may be of the; radiant type described above or which may be of any other desiredtypewhich provides a purely radiant heat I source.

A tube bank M is disposed within the cham'-- ber in a vertical arrangement and defines a serpentine path for the material treated in order to. permit exposure of the maximum external surface area of the. tubes" to the heat emanating from. the radiant burners; This tube bank differs from. that shown in Fig 1 in that the tubes, are so arranged that they. form, in effect; three vertical rows instead of the two rows as disclosedinthat figure. The tube arangement; is thesame that. of; Fig. 1' to the extent. that. the tubes-are. so positioned. vertically that each tube: can. receive radiation. directly from. both furnace walls. This. insures that the, tube passes or lengths. willlbe. evenly heated around". their circumferences. As. in the embodiment of Fig. 1",. fuel; for the. burners, may be. supplied through headers. i8, controlled by. valves. 4.9... each burner being, fedfromapipe Edi tapped into the. adjacent hea. er and controlled by the valve. 51"..

Although. thetube bankin Fig. 2' is shown; as broken in. the. center, it is to. be understood. that. thispa-ut is omittedin order that the. arrangement. of. the. burners in. the side. walls. may be, clearly: seen whereas in fact thetube. comprising, the; bani-Lie. continuous from its inlet 5.21 to its. outlet Eiit. The burners. in. this embodiment. as. inthatof Fig. 1,.are so placed and; adjustedlthat'. the, desired. heat input. may be. obtained. at. any point along. therpath of. travel. of the. material. under. heatreatment. Suitable openingsare. pro-- 1%; vided in. the furnace. wall as shown at. Ma through, which thermocouples responsive to furnace temperature may extend.

The. operation of the furnace disclosed in Figs. 2 and 3 is very similar to that disclosed Fig. I,

that fluent. material. is admitted. to the inlet 52 and passesprogressively through the furnace. the heatv supplied thereto being controlled by each burner in. the zone served thereby and resulting in accurate control of the temperature of the fiuent material being treated. at. any position or zone in: the travel thereof through the: tube. bank. In this case, also, the various values 5t may be: manually adjusted it itis desired toad just manually the temperatures of the various zones oi the. furnace.

In Figs. 6 and 7 there is shown a further modified form of the invention inwhichthe. furnace is: substantially circular in cross-section and in which! the tube bank. is vertically arranged withboth the inlet and the: outlet thereto at the top of. the furnace; Thefurnace as shown in Fig. 6 comprises an-.outer-ca-sing 5.4:, an. inner wallestruc ture 5% of refractory material, and a plurality of radiant burners 5% arranged in a spiral pattern from: the bottom tothe top of the furnace inthe side" wall structure thereof. Central-lyof the furnace, thereis' provided. a: structure 51' of; refractory material which supports thetube. bank. which is a continuous tube: arranged in a; plu rality of vertical loops located about the einoil-Inference of the central refractory structure tiythe tube bank having an inlet 5a and" an outlet 591.-

The top: of. the furnace is closed: by a cap: or? cover 643 of refractory material and withv an outer casing. 61.- The cap. 86 is removably posttinned on the top of the cylindrical: outer portion of" the furnace in order to permit removal: of the i nner refractory structure ii -l and: the tube bank 55 for cleaning, or repairs or other purpose. The casing ii -t isprovi'dedwith an open ing filo; through which the products of combu's tion may pass.

Aisin the other forms of the invention materia-l passes through the tube of this furnace and is subjected tocontrolled heat from the variousradiant burners 56 installed the wall thereof an'dasbef'ore; the design of the burnersand' the spacing thereof from the tube bank and from each other is so correlated that the heat rays from eachburner overlap the heat raysfromgth'enext adjacent burner, resulting in the absence of cold" spots on" the tubebank. In this embofi'i-- ment also: it is possible to maintain accurate and close zone control of the heating effects on the tube bank. This is accomplished by connecting the various. burners; in one: position of the circumference of the furnace to a single manifold. The burners are connected vertically instead of horizontally in thisembo'diment because'the tubes are vertically arranged. If desired, the upper andlower groups of burners in each oircumferen ti'al section may be supplied. by separate man'- iiold's...

The temperature of the furnace is measured and controlled in response to the. internal temperature thereof as measured by thermocouples. extending into the furnace through circumferentially and vertically spaced openings the in the furnace wall. Inxthi's construction a1so,.the" furnace temperature invarious zones may be con-. trolled by the manual adjustment of individual valves. associated with each burner or by man ual' adjustment of valves similar to valves 55" controlling the supply of gas and air to the burners of each section.

Radiant walls of the type shown in Fig. may be used in the furnaces of Figs. 2 and 3 and Figs. 6 and '7, if desired.

It will of course be understood that any known controls may be used in connection with any of the above modifications in order to obtain completely automatic control of any particular process being followed.

It will be obvious to those skilled in the art that various changes may be made in the invention' without departing from the spirit and scope thereof and therefore the invention is not limited by that which is shown in the drawings and described in the specification but only as indicated in the appended claims.

What is claimed is:

1. Apparatus for the continuous heat treatment of fluent substance comprising wall structure of refractory material defining a relatively narrow chamber disposed with its axis in substantially horizontal position, said chamber having an outlet passage at the top thereof and eX-' tending substantially throughout its length, a serpentine pre-heating tube portion disposed within said outlet passage and communicating with a serpentine heat treating tube portion disposed lengthwise and centrally within said chamber whereby material treated will flow back and forth in a series of substantially horizontally disposed passes between the upper and lower portions of said chamber, a plurality of burners distributed over the interior of the walls of said chamber on opposite sides of the heat treating portion of said tube and throughout the length and heighth cf the same, the spacing of said burners relative to each other and the spacing of the same relative to said tube being in a manner to provide intimately overlapping radiant heat areas located throughout the length of the heat treating portion of said tube for providing uniform and continuous heat distribution, said burners and contiguous wall portions being constructed and arranged to be heated to incandescence for providing radiant heat, means for selectively controlling the fuel supplied to each burner whereby upon operation of said control means the heat output of the associated burner can be varied for modifying the temp rature of the tube portion receiving heat from that burner, the distance of the burners from said tube and spacing of the burners being so correlated that said burners operate at maximum efficiency at any setting of the fuel supply control, and means for selectively admitting air to each burner whereby the portion of the tube normally receiving heat from that burner may be cooled.

2. Apparatus for the continuous heat treatment of fluent substance comprising wall structure of refractory material defining a relatively narrow chamber disposed with its axis in substantially horizontal position, said chamber having an outlet passage at the top thereof and extending substantially throughout its length, a serpentine preheating tube portion disposed within said outlet passage and communicating with a serpentine heat treating portion disposed lengthwise and centrally within said. chamber whereby material treated will flow back and forth in a series of substantially horizontally disposed paths between the upper and lower portions of said chamber, a plurality of burners distributed in horizontal rows over the interior of the walls of said chamber on opposite sides of said tube and throughout the length and heighth of said tube, the spacing of said burners relative to each other and the spacing of said burners relative to said tube being in a manner to provide intimately overlapping radiant heat areas located throughout the length of horizontal sections of said tube for providing uniform and continuous heat distribution of said sections, said burners and contiguous wall portions being constructed and arranged to be heated to incandescence for providing radiant heat, means for selectively controlling the fuel supplied to each row of burners whereby upon operation of said control means the heat output of the associated row of burners can be varied for modifying the temperature of the tube section receiving heat from that row of burners, the distance of the burners from said tube and spacing of the burners being so correlated that maximum efliciency of said burners is obtained with any setting of the fuel supply control.

3. Apparatus for the continuous heat treatment of fluent substance comprising wall structure of refractory material defining a relatively narrow chamber said chamber having an outlet passage at the top thereof and extending substantially throughout its length, a pre-heating tube portion disposed within said outlet passage and communicating with a heat treating portion disposed centrally within said chamber, a plurality of burners distributed over the interior of the walls of said chamber on opposite sides of said tube and throughout the length and heighth of said tube, the spacing of said burners relative to each other and the spacing thereof relative to said tube being in a manner to provide intimately overlapping radiant heat areas located throughout the length of said tube for providing uniform and continuous heat distribution, said burners and the contiguous wall portions being constructed and arranged to be heated to incandescence for providing radiant heat, means for selectively controlling the fuel supplied to each burner whereby upon operation of said control means the heat output of the associated burner can be varied for modifying the temperatur of the tube portion receiving heat from that burner, the distance of the burners from said tube and the spacing of said burners being so correlated that maximum efficiency of said burners is obtained with any setting of the fuel supply control, and means for selectively admitting air to each burner whereby the portion of the tube normally receiving heat from that burner may be cooled.

4. Apparatus for the continuous heat treatment of fluent substance comprising wall structure of refractory material defining a relatively narrow chamber disposed with its axis in a substantially horizontal position, said chamber having an outlet passage at the top thereof and extending substantially throughout its length, a serpentine pre-heating tube portion disposed within said outlet passage and communicating with a serpentine heat treating portion disposed lengthwise and centrally within said chamber whereby material treated will flow back and forth in a series of substantially horizontally disposed paths between the upper and lower portions of said chamber, a plurality of burners distributed over the interior of the walls of said chamber on opposite sides of said tube and throughout the length and heighth of said tube, the spacing of said burners relative to each other and the spacing thereof relative to said tube being in a manner to provide intimately overlapping radiant heat areas located throughout the length of said tube for providing uniform and continuous heat distribution, means for selectively controlling the fuel supplied to each burner whereby upon operation of said control means the heat output of the associated burner can be varied for modifying the temperature of the tube portion receiving heat from that burner, and means for selectively admitting air to each burner whereby the portion of the tube normally receiving heat from that burner may be cooled.

5. Apparatus for the continuous heat treatment of fluent substance comprising wall structure of refractory material defining a relatively narrow chamber, a serpentine tube disposed centrally within said chamber whereby material treated will flow back and forth in a series of substantially horizontally disposed paths between the upper and lower portions of said chamber, a plurality of burners distributed over the interior of the walls of said chamber on opposite sides of said tube and throughout the length and height of said tube, the spacing of said burners relative to each other and the spacing thereof relative to said tube being in a manner to provide intimately overlapping radiant heat areas located throughout the length of said tube for providing uniform and continuous heat distribution, means for selectively controlling the fuel supplied to each burner whereby upon operation of said control means the heat output of the associated burner can be varied for modifying the temperature of the tube portion receiving heat from that burner,

and means for selectively admitting air to each burner whereby the portion of the tube normally receiving heat from that burner may be cooled.

6. Apparatus for the continuous heat treatment of fluent substance flowing in a confined path comprising wall structure of refractory material defining a relatively narrow chamber, a horizontally disposed serpentine tube disposed centrally within said chamber whereby material treated will flow back and forth in a series of substantially horizontally disposed passes between the upper and lower portions of said chamber, a plurality of horizontal rows of burners distributed over the interior of the walls of said chamber on opposite sides of said tube, the spacing of said burners relative to each other and the spacing thereof relative to said tube being in a manner to provide intimately overlapping radiant heat areas located throughout the length of said tube for providing uniform and continuous heat distribution, means for selectively controlling the fuel supplied to each row of burner whereby upon operation of said control means the heat output of the associated burners can be varied for modifying the temperature of the tube portion receiving heat from that burner.

'7. Apparatus for the continuous heat treatment of fluent substance comprising wall structure of refractory material defining a relatively narrow chamber, a serpentine tube disposed centrally within said chamber whereby material treated will flow back and forth in a series of passes between the walls of said chamber, a plurality of rows of radiant burners extending in the direction of said passes over the interior of the walls of said chamber on opposite sides of said tube and throughout the extent of said tube, the spacing of said burners relative to each other and the spacing thereof relative to said tube being in a manner to provide intimately overlapping 14 radiant heat areas located throughout the length of said passes for providing uniform and continuous heat distribution along said passes, means for selectively controlling the fuel supplied to each burner whereby upon operation of said con-- trol means the heat output of the associated burner can be varied for modifying the temperature of the pass receiving heat from that burner.

8. Apparatus for the continuous heat treatment of fluent substance flowing in a confined path comprising wall structure of refractory material defining a relatively narrow chamber, a horizontal serpentine tube disposed centrally within said chamber whereby material treated will flow back and forth in a series of substantially horizontally disposed paths between the upper and lower portions of said chamber, a plurality of radiant heat sources distributed in horizontal rows over the interior of the Walls of said chamber on opposite sides of said tube and throughout the length and height of said tube, the spacing of said sources relative to each other and the spacing thereof relative to tube being in a manner to provide intimately overlapping radiant heat areas located throughout horizontal portions of the length of said tube for providing uniform and continuous heat distribution along said portions and, means for selectively controlling the heat output of each of said radiant heat sources whereby upon operation of said control means the heat output of the associated radiant heat source can be varied for modifying the temperature of the tube portion receiving heat from that source.

9. Apparatus for the continuous heat treatment of fluent substan e flowing in a confined path comprising wall structure of refractory material def ning a chamber, a serpentine tube disposed within said chamber whereby material treated will flow back and forth in a series of substantially horizontally disposed passes between the upper and lower portions of said chamber, a plurality of burners disposed in said wall structure, the configuration of said burners and the spacing thereof relative to said tube being in a manner to provide intimate overlapping radiant heat areas for providing uniform and continuous heat distribution in the region of said tube, means for selectively controlling the fuel supplied to each burner whereby upon operation of said control means the heat output of the associated burners can be varied for modifying the temperature of the tube portion receiving heat from that burner, and means for selectively admitting air to each burner whereby the portion of the tube normally receiving heat from that burner may be cooled.

FREDERIC O. HESS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,046,897 Held July 7, 1936 2,105,820 Parsons Jan. is, 1938 2,127,815 Gullette Aug. 23, 1938 2,191,273 Denney Feb. 20, 1940 2,215,079 Hess Sept. 17, 1940 2,215,080 Hess Sept. 17, 1940 2,215,081 Hess Sept. 17, 1940 2,306,818 Lyster Dec. 29, 1942

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