US2151386A - Furnace - Google Patents

Description

March 21, 1939. L. DE FLoR'Ez 2,151,386

FURNACE v Filed April 16, 1929 2 sheets-shewb 2 Snowdon Patented Mar. 21 1939 FURNACE Luis de Flores, Pomfret, Conn., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application April 1e,

a4 claims.

My invention relates to furnaces, more particularly to tubular oilA heaters used in processes involving the heating' or cracking of oils, and has for its principal object the provision of a furnace of this type by means of which a liquid such as oil can be thoroughly heated in a minimum of time,`the apparatus therefore taking up but a relatively small amount of space.

The use oi tubular oil heaters has developed rapidly in recent years, due to the fact that adequate turbulence can' be attained in these'tubes by high velocity and that the surface can be disposed at will to permit comparatively even distribution of heat. In tubular heaters, especially where economizers are used which consist of tubes placed across the ueto be heated Iby the outp flowing gases, it has been difficult to maintain the gases at a velocity which will insure sufficient draft through the heater. One of the features of my invention lies in the construction of an econo- 1 mizer, wherein provision is made for increasing the velocity of the gases as they pass through the flue.

In carrying out my invention in one form, with the above objects in view, I have provided a tubular oil heater which comprises what may be termed a main radiant section, a secondary radiant section, and an economizer section. The -main radiant section is constructed in the form of a vertical cylindrical shell, the walls of which are lined with vertically disposed tubes. Fuel is admitted to a burner located at one end of the vertical chamber and the products oi.' combustion are discharged atthe other end and carried to the economzer section through a horizontal flue. In this horizontal flue is arranged a second unit of 'tubes positioned so as to be subjected tothe hot gases or products of combustion passing to the economizer. .'I'his last mentioned unit may be termed a secondary radiant heater. The economizer consists of a series of horizontal tubes arranged at right angles to the path of the gases. A plurality of horseshoe-shaped strips are hung over certain of the tubes in a manner to 4.3 reduce the size of the passage progressively toward the upper tubes whereby the velocity of the gases is increased as the gases pass through the economizer.

My invention will be better understood from the following description taken in -connection with the accompanying drawings and its scope will be pointed out in the appended claims.

In the drawings Fig. 1 is a side elevation in section through a furnace embodying my invention;

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Fig. 2 is a sectional elevation through the econo- 1929, serial No. atasco (ci. 19o-11o) mizer and secondary radiant section, and Fig. 3 is an enlarged -section through somje of the economizer tubes.

Referring to the drawings, I have illustrated a furnace comprising a main radiant heating section 5 I Il, a secondary radiant heating section I I and an economizer I2. A metallic wall or shell I3, preferably cylindrical in shape, defines the main heating chamber I4, the sides of this chamber being lined with suitable heat insulating, refractory l0 material i5. The wall or shell I3 is supported by a suitable framework I6 resting on bases Il. An arch I9 of 'heat insulating material forms a major part of the upper wall of the chamber I4, this arch being supported by suitable radial meml5 bers Isa from the framework I5. Located upon the arch I9 and directly over the center of the cylindrical chamber I4 is a. burner 20, and suitable inlets 2| and 22 may be provided respectively for the gas and oil, while a third inlet 23 allows 20 the admission of compressed air to the burner. Since the particular type or form of burner does not form part of my invention, I have shown this dlagrammatically only. At the center of the lower portion of the chamber I4 and directly op- 25 posite. the burner 20 is an outlet iue 28, leading downwardly and then horizontally to the4 lower part of the economizer I2. It will thus be observed that upon the admission of fuel and air to the burner and ignition thereof, a flame will be 30 produced and directed downwardly through the center-of the chamber I4, the hot gases of combustion therefrom passing into the fiue 2t.

In order to use to the fullest extent the radiant heat produced by the ame in chamber I4, I have provided a plurality of tubes 25 arranged vertically in a pair of concentric circles around the periphery of the heating chamber I 4. The tubes 25' are preferably supported or suspended from their upper extremities from a flat annular tube sheet 26, this tube sheet 26 resting at its inner edge upon the arch I9 and at its outer edge upon the refractory lining I5, thus forming the remaining part of the top wall of the chamber I4. The upper and lower ends of adjacent tubes 25 are connected together by means of return bends 28 in a manner such that a continuous path for liquid to be heated is formed through the tubes. In other words, the liquid to be heated enters one of the tubes 25 through an inlet pipe 29 50 and then passes from tube to tube around the chamber I4, finally leaving the Atubes through an outlet 30. While I have illustrated and described the tubes as being connected in series, it is to be understood that they may be connected in parallel be connected between one pair of headers so that the liquid will pass through them al1 in the same direction at the same time, or small groups of the tubes may be connected in parallel and these groups connected in series.

Annular discs of heat insulating material 3i form part of the lower wall of the chamber I4 and serve to hold the tubes 25 in proper spaced relation. An annular cover member 38 rests upon the framework supporting the arch I9 directly above the tubes 25, and by removing this cover member access may be had to the tubes 25 for cleaning purposes or for removal and .replacement of the tubes. That-portion of the furnace described up to`this point is substantially the same as described in my co-pending application, Serial. Number 120,067, filed July 2, 19261, now U. S. Patent 1,717,334, issued July 11, 1929.

The horizontal part of the outlet flue 24 is preferably circular in section and is lined with a layer of suitable heat insulating materialll. 'I'he outer end of the horizontal flue 24 opens upwardly into the economizer I2. In the lower half of the flue 24 is arranged a plurality of tubes 38 extending horizontally and arranged preferably in the form of a semi-circle as is shown more clearly in Fig. 2. 'I'hese tubes 38 are interconnected at their ends, thus forming a continuous passage for the liquid entering one of the tubes from the economizer. In the arrangement illustrated, the liquid having been preheated in the economizer, passes through the tubes 38 in the flue 24, then through the pipe 29 to the tubes 25 in the main radiant heating section and iinally out of the heater through the pipe 30. The tubes 38 will thus be heated by the hot gases passing through the flue both by radiation and by partial convective contact. The horizontal unit of tubes may thus be termed a secondary radiant heating section.

A plurality of tubes 39 are supported horizontally in the heating chamber of the economizer and liquid entering these tubes through an inlet 40 passes downwardly through the tubes to an l outlet 4I the liquid in the passage thus absorbing heat from the hot gases passing upwardly through the economizer around the tubes. A flue 42 at the top of the economizer preferably leads to a stack (not shown) and a pair of dampers 43 in this flue are adapted to control the draft through the economizer. A door 44 at each end of the horizontal flue 24 provides access to the interior.

In order to increase the velocity of the hot gases passing upwardly through the economizer I2, I have provided a plurality of metallic strips 45, each strip being bent into the shape of a horseshoe or hair pin. 'I'hese strips`45 are hung upon and depend from the tubes 39 and are thus directly in the path of the hot gases. The nurnber of strips increases progressively toward the top of the economizer, as will be observed withreference to Fig. 2 and hence it will be evident that the space through which the hot gases pass in traveling through the economizer decreases in inverse proportion to the increase in number of the strips 45. The velocity-of these gases will thus be increased as the gases flow upwardly through the economizer. Since the strips 45 are of metal, they aid considerably in transferring or in series parallel; i. e., all of the tubes may mizer I2 and the inlet of the vertical tubes 25. 'I'he bent strips 45 provide a simple and effective means for increasing the velocity oi' the flue gases in the economizer and thus materially increase the efficiency of the furnace. A

While I have described my invention as embodied in concrete form in accordance with the provisions oi' the patent statutes it should be understood that I do not limit my invention Y thereto, since various changes and modifications may be made without departing from the'scope of the invention as defined by the accompanying`r in another of said zones disposed substantially entirely below the point-oi' generation of said` hot gases and the point of entry and withdrawal of said gases passing therethrough, exposing substantially all of said fluid in said other zone to radiant heat derived directly from said gases and heating said fluid preponderantly by radiation.

2. 'Ihe method o-f heating hydrocarbon uid to elevated temperature, which comprises generating hot combustion gases, flowing hot combustion gases through a furnace, in an upper zone of said furnace applying heat derived from said gases to the petroleum by convection, and in another zoneof said furnace,.below the firstnamed zone and below the point of generation of said gases and the point of entry and withdrawal of said gasespassing through said other zone, exposing substantially all of said petroleum in said other zone to radiant heatderived directly from said gases and heating said petroleum preponderantly by radiation and thereby limiting the temperature rise of the petroleum'in said first-named zone. 4

3. 'I'he method of heating hydrocarbon fluid to elevatedtemperaturawhich comprises generating hot products of combustion, flowing said hot products of combustion through different heating zones, passing a stream of hydrocarbon fluid through one of said zones and therein applying heat derived from said gases flowing therethrough to said stream by convection, passing said stream through another of said heating zones in a path substantially entirely below the point of generation of said hot products of combustion and the point of entry and withdrawal of said hot products of combustion flowing throughsaid other zone, and exposing substantially all of said fluid in said other zone to radiant heat derived directly from said hot products of combustion and heating said fluid preponderantly by radiation.

4. The method of heating hydrocarbon fluid to elevated temperature, which comprises generating hot'prcducts of combustion in a separate combustion zone wherein at least partial combustion takes place, flowing said hot products of combustion through different heating zones, passing a stream of hydrocarbon fluid through one of said zones and therein applying heat derived from said gases flowing therethrough to said stream by convection, passing said stream through another of said heating zones in a path substantially entirely below `the point of generation of said hot products of comaromas bustion and the point of entry and withdrawal of said hot products of combustion iiowing through said other zone, and exposing substantially all of said iiuid insaid other zone to radiant heat derived directly from said hot products of combustion and heating said fluid preponderantly by radiation.

y5. Oil heating apparatus ior heating oil to conversion temperature comprising separate heat-absorption structures for conveying oil being heated disposed in dierent zones, means for producing a current of hot combustion gases throughsaid zones in series and for heating the absorption structure in one 4oi? said zones by convection, the heat-absorption structure of another of said zones disposed-substantially entirely below said means for producing said hot gases andthe point oi entry and withdrawal of gases with substantially all of sali second-mentioned heat-absorption structure being exposed directly to radiation from said gases and heated preponderantly by radiation.

6. Oil heating apparatus for heating oil to conversion temperature comprising separate heat-absorption'structures disposed in different' zones, means for producing a current of hot combustion gases `through said zones in series and for heating the absorption structure in one of said zones by convection, the heat-absorption structure of another of said zones horizontally disposed substantially entirely below said means for producing said hot gases and the point of entry of gases therein and substantially entirely below the point of withdrawal of gases therefrom, with substantially all of said last-mentioned heatabsorption structure being exposed directly to radiation from said gases and heated preponderantly by radiation, and means for conducting the 'oil from the heat-absorption structure in one of said zonesto the heat-absorptionstructure in the other of said zones.

7. Oil heating apparatus for heating oil to conversion temperature comprising a heating chamber, means for introducing combustion gases into said chamber to effect a current of hot gases through said chamber, said chamber arranged to cause said combustion gases to flow through a substantial part thereof in a substantially rectilinear flow, heat-absorption structure in another chamber reoeiving said gases from the rst-mentioned chamber adapted to absorb heat by convection from said gases, and means for reducing the temperature of said gases to prevent excessive temperature of said heat-absorption structure comprising heat-absorption structure horizontally disposed in said first-mentioned chamber substantially entirely below said means for introducing combustion gases and the point of entry and withdrawal of said combustion gases passing through said first-mentioned chamber with substantially all of said heat-absorption structure being exposed directly to radiation from said gases and absorbing heat preponderantly by radiation, and means for connecting said heat-absorption structures for passage of the oil therethrough in succession.

8. Heating apparatus for heating hydrocarbon uid to conversion temperature comprising a plurality of chambers, means for producing a current of hot gases through said chambers in succession, oil-conducting tubes disposed in one of said chambers to absorb heat from said gases preponderantly by-convection, and oil-conducting tubes, connected to said first-named tubes,

lhorizontally disposed adjacent the bottom of I another ot said chambers substantially entirely below said means for producing said hut gases and the pointof entry and withdrawal of the current of gases, with substantially all o! said second-mentioned oil conducting tubes being exposed directly to radiation from said gases and heated preponderantly by radiation.

9. Oil heating apparatus for heating oil to conversion temperature comprising separate heat-absorption structures disposed in dierent zones, means for producing a current oi' hot combustion gases for passage through said Azones in series and for heating the absorption structure in one of said zones by convection, bare tubular heat-absorption structure, in another of said zones, horizontally disposed below substantially the entire convectively heated absorption structure and said means for producing said hot gases and substantially entirely below the point of entry and withdrawal of combustion gases passing through said last-mentioned chamber, with substantially all of said last-mentioned heat-absorption structure being exposed directly to radiation from said gases and heated preponderantly by radiation, and means for connecting said absorption structures for passage oi' the oil therethrough in succession.

10. Heating apparatus for heating hydrocarvbon fluid to conversion temperature comprising by convection, another of said zones being arranged to cause said hot combustion gases passing therethrough to flow through a substantial part thereof in a substantially rectilinear path, the heat-absorption structure of said last mentioned zone being disposed substantially horizontally and substantially entirely below said means for producing said hot gases and the point of entry and withdrawal of gases passing through said last-mentionedl zone, with substantially al1 of said second-mentioned heat-absorption structure being exposed directly to radiation from saig gases and heated preponderantly by radiatio 11. A furnace for heating hydrocarbon fluid to conversion temperature comprising a heating chamber, means for producing hot gases for passage through said chamber, another heating chamber traversed by said hot gases, heat-absorption structure disposed in said second-mentioned heating chamber to receive heat -from the gases by convection, another heat-absorption structure disposed in said first-mentioned heating chamber substantially entirely below said means for producing hot gases and the point of entry and withdrawal of said hot gases passing through the first-mentioned heating chamber with substantially all of saidlast-mentioned structure being exposed to radiation from said gases and heated preponderantly by radiation, and means for connecting said heat-absorption structures for passage of the fluid to be heated.

l2. In a furnace for heating hydrocarbon uids to conversion temperature, a heating chamber. means for producing hot combustion gases for passage through said heating chamber, conduit elements for conveying hydrocarbon fluid being heated in said heating chamber disposed substantially entirely below said means and the point of entry and withdrawal of said hot gases passing through said chamber, with substantially all of said conduit elements being exposed directly .to radiation from said gases and heated prcponderantly by radiation, and other conduit elements for conveying hydrocarbonfluid being directly exposed to said hot combustion gases and heated preponderantly by radiation.

13. In a furnace for heating hydrocarbon oils to conversion temperature, a radiant heating section, heat-absorbing tubes therein for conveying oil to beheated, means for producing hot products of combustion to heat said tubes by radiant heat, another radiant heating section positioned below said combustion producing means and in communication with said rstmentioned heating section for the passage of hot products of combustion, separate heat-absorbing tubes for conveying oil being heated within said second-mentioned heating section horizontally disposed substantially entirely below the means for producing hot products of combustion and the point of entry and withdrawal of said products of combustion passing through said second-mentioned heating section, with at least a part of said tubes being adjacent the floor and with substantially all of them being exposed directly to radiation from said products of combustion .and heated preponderantly by radiant heat, and means for connecting the heat-absorbing tubes in one section to those of the other heating section.

14. In a furnace for heating hydrocarbon oils to conversion temperature, a heating section, heat-absorbing tubes therein adapted to be heated by radiation,another heating section below.

said first-mentioned heating section, Ameans for producing hot products of combustion for passage through said heating sections, separate heatabsorbing tubes in said second-mentioned heating section horizontally disposed substantially entirelyl below said combustion producing means and the point of entry and withdrawal of said hot gases passing through the second-mentioned heating chamber, with at least a part of said tubes being adjacent the floor and with substantially all of them being exposed directly to radiation from said products of combustion and heated preponderantly by radiant heat, and means for connecting the 'heat-absorbing tubes in one section to those of the other heating section.

' 15. In a furnace for heating hydrocarbon oils to conversion temperature, a combustion chamber having means for producing hot products of combustion associated therewith, a heating chamber connected to said combustion chamber for receiving hot products of combustion therefrom for passage therethrough and conduit elements for conveyingoil being heated in said heating chamber disposed substantially entirely below said means for producing hot products of combustion and the point of entry and withdrawal of hot -products of combustion passing through said heating chamber with substantially -all of said conduit elements being'exposed directly to radiation from said products of combustion and heated preponderantly by radiation.

16. A system for transferring heat to a hydrocarbon fluid passed through heat-absorption structures to be heated therein to conversion temperature, comprising a combustion chamber, means for producing hot gases associated with said combustion chamber, a heating chamber into which said combustion chamber discharges hot gases, another heating chamber extending upwardly above the outlet of said combustion chamber and traversed by said hot gases, heattherethrough of the fluid to be heated.

17. `A system for transferring heat to a hydrocarbon fluid passed through heat-absorption structures to be heated therein to conversion temperature, comprising a combustion chamber. means for producing` hot gases associated with said combustion' chamber, a heating chamber into which said combustion chamber discharges hot gases, another heating' chamber traversed by said hot gases, heat-absorption structure disposed within said second-mentioned chamber in the current of gases to receive heat therefrom preponderantly by convection, a separate floor tube section disposed in said mst-mentioned heating chamber substantially entirely below said means for producing said hot gases and the point of entry and withdrawal of said hot gases passing through the first-mentioned heating chamber with substantially all of said floor tube section being exposed directly to radiation from said gases and heated preponderantly by radiation, and means for connecting said iloor tube section' and heat-absorption structure for passage therethrough of the fluid to be heated.

18. In a furnace for heating hydrocarbon oils to conversion temperature, a combustion chamber having means for producing hot products of combustion associated therewith, a heating chamber connected to said combustion chamber for receiving hot products of combustion therefrom for passage therethrough, conduit elements for conveying oil being heated in said heating chamber and horizontally disposed substantially first-mentioned heating chamber to be heated preponderantly by convection heat from, said hot products of combustion.

19. In a furnace for heating hydrocarbonbils to conversion temperature, a combustion chamber having means for producing hot products of combustion associated therewith, a heating chamber connected to said combustion chamber for receiving hot products of combustiontherefrom, said heating chamber arranged to cause said hot products of combustion to ow through a substantial part of said heating chamber in a substantially rectilinear path, and horizontally disposed conduit elements for conveying oil being heated in said heating chamber arranged in parallel relationship to each other and disposed subanimee stantially entirely below said means for producing said hot products of combustion and the point of entry and withdrawal of hot products of combustion passing through said heating chamber with substantially all ot said conduit elements being eixpos'ed directly `,to radiation from said gases and heated preponderantly by radiation.

20. In a lfurnace for heating hydrocarbon oils to conversion temperature, a combustion chamber having means for producing hot products of combustion associated therewith, a heating chamber connected to said combustion chamber for receiving hot products of combustion therefrom, said heating chamber arranged to cause said hot products ol combustion to ow through a substantial part of said heating chamber in a substantially rectilinear path, conduit elements for conveying oil being heated in said heating chamber and horizontally disposed substantially entirely below said means for producing said hot products of combustion and the y point of entry and Withdrawal of hot products of combustion passing through said heating chamber with substantially all of said conduit elements being exposed directly to radiation from said gases and heated preponderantly by radiation, another heating chamber connected to said first-mentioned heating chamber for receiving products of combustion therefrom, and conduit elements in said heating chamber connected to said first-mentioned heating chamber to be heated preponderantly by convection heat from said hot products of combustion.

2l, A system for heating petroleum to conversion temperature comprising a chamber arranged to cause combustion gases to ow through a substantial part thereof in a substantially rectilinear iiow, a combustion chamber discharging combustion gases into said chamber. means for producing hot gases associated with said combustion chamber, heat-absorbing structure in said first-named chamber horizontally disposed substantially entirely below said means for producing said hot gases and the point of entry and discharge of gases passing through said firstmentioned chamber, with substantially all oi said heat-absorption structure being exposed directly to radiation fromk said gases and heated preponderantly by radiation, another heat-absorbing structure in said system to absorb heat by convection from said combustion gases, and connections for passing the petroleum through said heat-absorbing structures in succession.

22.,A system for transferring heat tofhydrocarbon fluid to raise said fluid to conversion temperature comprising a chamber arranged to cause combustion gases to flow through a substantial part thereof in a substantially rectilinear fiow, a `combustion chamber discharging combustion gases into said chamber, means for producing hot gasesassociated with said combustion chamber, heat-absorption structure horizontally disposed in said first-named chamber comprising tubes, at least somev of which are adjacent the discharge of said combustion cham'- ber and all of which are substantially entirely below said means for producing said Ahot gases and the point of entry and discharge of said hot gases passing through said rst-mentioned chamber, with substantially all of said heatabsorption structure being exposed directly to radiation from said gases and heated preponderantly by radiation, heat-absorption structure in another zone of the system adapted to absorb heat by convection from said combustion gases, and means for connecting said heat-absorption structures for passage of the fluid therethrough in succession.

23. A system for heating petroleum to conversion temperature, comprising a housing structure enclosing a plurality of heating zones, a piurality of heat-absorption structures disposed in different of said zones, means for connecting said absorption structures for passage of. the petroleumA therethrough in succession,a combustion chamber discharging hot combustion gases through said zones in succession, means for producing hot gases associated with said combustion chamber. a heat-absorption structure in one of said zones adapted to be heated by convection, and tubular heat-absorption structure in another of said zones, disposed substantially entirely below said means for producing said hot gases and the point of entry and withdrawal of the stream of gases passing through said other zone, with substantially all of said tubular heatabsorption structure being exposed directly to radiation from said gases and heated preponderantly by radiation.

24, Heat transfer apparatus for heating hydrocarbon fluid to conversion temperature comprising means for producing combustion gases, a heating chamber traversed by combustion gases, heat-absorption structure for conveying said fluid being heated disposed-in said chamber, another heating chamber traversed by combustion gases, other heat-absorption structure for conveying y said fluid being heated with at least a part thereof disposed adjacent the bottom of said lastmentioned chamber and with all of it disposed substantially entirely below said means for producing said combustion gases and the point of entry and withdrawal of said combustion gases passing therethrough, with substantially all of said heat-absorption structure being exposed directly to radiation from said gases and heated preponderantly by radiation and so disposed dilferently, in relation to the gas flow, from said first-named absorptionstructure that it absorbs sufllcient heat materially to reduce the temperature of said gases for protection ci said first heatabsorptionstructure, and means comprising a chamber for effecting at least partial combustion before introduction of said gases into said second-mentioned heating chamber.

25. Fluid heating apparatus for heating hydrocarbon iiuid to conversion temperature comprising a combustion chamber, means for producing hot gases associated with said combustion chamber, a heating chamber receiving hot gases formed in said combustion chamber. heat-absorption structure disposed in said heating chamber to receive heat by convection from the gases, another heating chamber in communication with the discharge end of the combustion chamber, heat-absorption structure in said last-mentioned heating chamber horizontally disposed adjacent the discharge end of the combustion chamber and substantially entirely below said means for producing said hot gases and the discharge end of said combustion chamber and the point of withdrawal of said hot gases from the first-mentioned heating chamber, with substantially all of said last-mentioned heat-absorption structure being exposed directly to radiation from said gases and absorbing heat preponderantly by radiation, for limiting the temperature to which the rstnamed heat-absorption structure is subjected,

and-means connecting said absorption structures for passage of fiuid therethrough in succession.

26. In a furnace comprising -a vertically arranged substantiallyy cylindrical combustion chamber, a heating coil composed of a plurality of vertically disposedv interconnected heat absorbing tubes adjacent to the wall ofthe combustion chamber and disposed on an annular pitch circle, the center of which substantially corresponds with the center of the combustion chamber, means for directing burning fuel and the products of combustion thereof in a central longitudinal and unobstructed path through said chamber and substantially out of contact 'with said tubes, an insulated flue section free from heat absorbing tubes and leading from one end of said combustion chamber, a substantially cylindrical outlet flue connected with said iiue section, and a plurality of tubes arranged longiconnected heat absorbing tubes adjacent to the wall of the combustion chamber and disposed on an annular pitch circle the center of which substantially corresponds with the center of the combustion chamber, a burner located at one end of the chamber so positioned centrally with respect to said tubes as to impel its flame and the products of combustion in an unobstructed vertical path substantially parallel to and out of direct contact with said tubes, an insulated flue section free from heat absorbing tubes and leading from the end of said combustion chamber opposite to said burner, a horizontal outlet flue connecting with said flue section, and a plurality of tubes arranged longitudinally in the shape of a semi-circle in the lower part of saidA outlet iiue and forming a secondary heat absorbing'unit.

28. In a furnace for heating oil, walls deilning a substantially cylindrical heating chamber, a plurality of tubes arranged vertically around the inner periphery of said walls, means located in the upper central portion of said chamber` for producing and directing downwardly a high temperature radiant flame whereby radiant heat may be absorbed by said tubes, an lnsulated'ilue section free from heat absorbing tubes leading from the lower part of said chamber, a horizontal outlet iiuel connecting with said flue section, and a plurality of tubes arranged longitudinally in the shape of a semi-circle in the lower part of said outlet iiue and adapted to be heated by said hot gases.- thereby forming a secondary radiant heat absorbing unit.

29. A furnace comprising a vertical heating section, a horizontal heating section, an economizer chamber, a plurality of interconnected heat absorbing tubes in said heating sections and economizer chamber, means for-projecting a flame into said vertical section, means for directing the hotproducts of combustion through said horizontal section and through said economizer chamber, and separate insulated ue sections connecting said vertical section and said horizontal section, and said horizontal section and said economizer chamber, respectively.

30. In a furnace comprising a vertically arranged substantially cylindrical combustion chamber, a heating coil composed of a plurality of vertically disposed interconnected heat absorbing tubes adjacent to the wall of the combustion chamber and disposed on an annular pitch circle, the center of which substantially corresponds with the center of the combustion chamber, means for directing burning fuel and the products of combustion thereof in a central longitudinal and unobstructed path through said chamber and substantially out of contact with said tubes, an insulated flue section free from heat absorbing tubes and leading from the lower part of said combustion chamber, an outlet flue connected wtih said flue section, and a plurality of heating tubes all arranged longitudinally within said outlet flue and connected to said iirst mentioned tubes, forming a secondary' heat absorbing unit.

3l. A furnace for heating oil, comprising walls forming a down draft radiant heating chamber, an insulated flue section free from heat absorbing tubes and leading from the lower part of said heating chamber, an outlet flue connecting with said flue section and extending substantially at right angles to said chamber, an economizer chamber, a second insulated fiue section free from heat absorbing tubes connecting said economizer chamber and said outlet flue, means for directing a flame downwardly in said heating chamber, a

series of heat absorbing tubes in said heating the `velocity of the products of combustion passing through said economizer.

32. In a furnace, a heating chamber, heat-absorbing tubes therein, heat producing means for heating said heat absorbing tubes by radiant heat, an insulated flue section leading from one end of said heating chamber, another heatingl chamber connected with said flue section, and a plurality of heat absorbing tubes connected to around thesurface of said last mentioned heating chamber and adapted to be heated by radiant and partial convection heat.

33. In a furnace, a heating chamber, heat absorbing tubes therein, heat producing means for heating said heat absorbing tubes by radiant heat, an insulated flue section leading from one end of said heating chamber, another heating chamber connected with 'said flue section, and splurality of heat absorbing tubes connected to said first mentioned tubes disposed longitudinally around a portion of the surface of said last mentioned heating chamber and adapted to be heated by radiant and partial convection heat.

34. In a furnace, a heating chambenheat absorbing tubes therein, heat producing means for heating said heat absorbing tubes by radiant heat,`

' radiant and partial convection heat, and an economizer section having heat absorbing tubes therein connected to said second mentioned heating chamber,'the aforementioned heat absorbing tubes being connected to form a continuous path for a fluid to be heated.

' LUIS nl FLOREZ.

Ysaid first mentioned tubes disposed longitudinally

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