US2147662A

US2147662A - Heating of fluids

Info

Publication number: US2147662A
Application number: US120013A
Authority: US
Inventors: Lev A Mekler
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1937-01-11
Filing date: 1937-01-11
Publication date: 1939-02-21
Anticipated expiration: 1956-02-21

Description

Feb. 21, 1939. L, A. MEKLER '2,147,662

HEATING OF FLUIDS Filed Jan. ll, 1937 2 Sheets-Sheet l @f wwf@ egim? ,N

L11 l. A. MEKLER 2,147,662

HEATING OF' FLUIDS Feb. 2H,

Filed Jan. ll, 1937 2 Sheets-Sheet 2 7 7? Je?? for: [6M Mele/Z672 Patented Feb. 21, 1939 UNITED STATES HEATING F FLUIDS Lev A. Mekler, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application January 11, 1937, Serial No. 120,013

Claims.

This invention is directed to an improved means for heating fluids. The features of the invention are particularly advantageous as applied to the heating of hydrocarbon oils to the high temperatures required for their pyrolytic conversion with relatively high rates of heat transfer to the oil undergoing treatment. This specific adaptability of the invention is due to the cooperative relation between the various features of the invention which lends the apparatus a high degree of flexibility with respect to independent control of the rates of heating which may be employed in different portions of the fluid conduit through which the oil undergoing treatment is passed, regulating the portions to employ either substantially uniform and high rates of heat input throughout the fluid conduit or to so vary the rates of heating at different points along the path of flow of the oil through the fluid conduit so as to obtain any desired type of heating curve which may be selected to suit the particular requirements ofthe type of oil undergoing treatment in order to obtain the best results.

The furnace herein disclosed is of the general type ordinarily known asa combination radiant and convention heater and embodies the advantages ofthe best and more expensive forms of this type of heater so far developed in a simple and efficient form of furnace structure which is favorably comparable in first cost and less expensive to operate than the less advantageous forms of conventional heaters. In addition, the improved furnace of the present invention offers Va certain cooperative combination of advantageous features not found in even the best c'onventional furnaces. y l

The furnace structure of this invention employs a vertical refractory wall opposite and substantially parallel to the fluid conduit, which wall is directly heated to a highly radiant condition and functions as a major source of radiant heat energy for the fluid conduit. Due to the method 'of firing and the manner in which this radiant Wall is employed, it isqheated not only by radiation from Athe flames and h ot combustion gases, but also by conduction and convection therefrom, whereby a substantially greater portion orf the total available heat is extracted from the gases and transmitted by radiation from this wall to CTI 55 functions as a reservoir of heat and thereby the fluid conduits disposed substantially parallel thereto before the main stream of said gases con-` largely compensates kfor minor and uncontrollable variations in the nrlng, so as to maintain a substantially uniform rate of heating about the fluid conduits except when deliberate and substantial changes are made in the firing conditions. 5 Also, due to this wall and its relation to the other structural features of the furnace and the method of firing, thev operator is enabled, when desired, to maintain a substantially uniform and high rate of heating throughout the fluid con- 10 duit which more nearly approaches themaximum permissible rate than that obtainable in other furnaces or by other methods.

By employing the features'of the present invention theA restriction encountered in prior fur- 15 naces with respect to the sequence of flow through various portions of the fluid` conduit and with respect to the possible variations in the heating curve is eliminated, since excessively high rates `of heating are avoided in that portion of the fluid conduit which first comes into contact with the main stream of hot combustion gases and it may, therefore, be located at any `desirable point in the path of flow of the oil through the fluid conduit. Although, with the present invention, that portion of the fluid conduit which flrst comes into direct contact with the main stream of hot combustion gases may, when desired, employ the maximum rate of heating utilized in any portion of the fluid conduit, there need not be and prefer- 30 ably is not the Wide variation between the rates of heating in this zone and the rates of heating in other portions of the fluid conduit. This better equalization of the rates of heating in dierent portions of the fluid conduit results in greater efficiency of heat treatment, since higher average rates `of heating throughout the fluid conduit may be obtained with the same or `(alien a lower maximum rate.

As an additional means of reducing the rates 40 of heating in that portion of the fluid conduit located adjacent the point of entrance of the combustion gases into the fluid heating zone, the invention provides for spacing the tubular elements in this portion of the fluid conduit further apart than the tubular elements in subsequent portions of the fluid conduit, thereby reducing the gas velocity and the intimacy of contact between the gases and the tubes at this point. This yprovision also serves the useful purpose of retaining a greater amount of fluid heat in the gases which is thereby made available for portions of the fluid conduit located further along the path of flow of the combustion gases, whereby the rates of heatinguin the latter portion of this fluid conduit may be increased. Therefore. the same or even a greater amount of fluid heat may be recoveredfrom the combustion gases in the present furnace without employing excessively high rates of heating at any point in the fluid conduit.

Although I am unable to oifer any conclusive explanation for the following, I have found that more pronounced changes in the relation between the rates of heating obtained in diiferent portions of the fluid conduit result from smaller' changes in the firing conditions, particularly with respect to the amount of excess air employed, as compared with other combination radiant and convection heaters of this general type. This results in a higher degree of flexibility for the present furnace with respect to control of the rates of heating about diiferent portions of the fluid conduit and, in. combination with the many permissible variations in the sequence of different portions of the fluid conduit relative to their location along the path of flow of the oil undergoing treatment, permits practically an unlimited choice of heating curves which may be selected to suit the particular type of oil undergoing treatment.

It should also be noted that the furnace structure of the invention possesses the advantage of that type of furnace now generally known as the double-end fired heater since the lower portion of the furnace is divided by the central firing wall into two independently controlled combustion and heating zones wherein the firing conditions and the rates of heating obtained about the fluid conduits in each zone are controlled independently of those in the other zone. With the fluid conduits in these two connected in series. this permits accurate and positive control of the heating conditions to which the oil is subjected at different stages in its heat treatment. With parallel flow through the conduits in these two zones, separate streams of the same oil may be subjected therein to substantially identical heat treatment or separate streams of different oils may be subjected therein to different heating conditions regulated to suit the requirements of the particular oil in each stream.

In the accompanying diagrammatic drawings, comprising Figs. 1 to 6 inclusive, Fig. 1 illustrates a sectional elevation of one specific form of the improved furnace structure, while Figs. 2 to 6 inclusive illustrates some of the many possible alternative, but non-equivalent arrangements of fluid conduits and flows which may be employed in this improved form of furnace structure.

Referring to Fig. l side walls I and end walls, which latter are not illustrated in this particular view of the furnace. define the lower portion comprising the combustion and heating zones of the furnace. The side walls slope inwardly at their upper ends to provide sloping side wall or roof portions 2. and flue heating zone 3 defined by side walls 4 and end walls, not illustrated, as positioned above the sloping walls 2 of the furnace. The flue heating zone is surmounted by flue 5 leading to a suitable stack, not illustrated. A floor 6 is provided in which firing blocks 'I having burner ports 8 are situated and a central firing wall 9 extending between the end walls of the furnace divides the lower portion of the furnace into two separate combustion and heating zones I0 and II.

Two banks I3 and I4, each comprising a plurality of horizontally disposed tubes I2, are located adjacent to side walls I on opposite sides y .aumen of wall l. Preferably adjacent tubes in each of the banks I3, Il, Il, II, IfI and Il are connected in series at their opposite ends by means of suitable return bends located outside the heating zone and not here illustrated. It is, of course, also within the scope of the invention to connect various tube banks, or a portion or all of the tubular elements in any or each of the various banks in parallel. Also the various tube banks may be interconnected in any desired sequence. Some of the many possible variations in ow are illustrated in Figs. 2 to 6 inclusive and will be later described. v

In the particular case here illustrated, tube banks I3 and I4 each comprise a single vertical row of tubes although, when desired, two or more rows may be employed in one or both of these banks, in which case the tubes in adjacent rows are preferably arranged in staggered formation so that opposite sides of each are exposed to heating by radiation.

Also in the particular case here illustrated, tube banks I5 and I6, each comprising a single row of horizontally disposed tubes I2, are located adjacent the sloping roof 2 of the furnace on opposite sides of the plane of the vertical center line passing through wall 9. Either or both of the banks I5 and I6 may, when desired, comprise two or more rows of tubes preferably arranged in staggered formation.

Another tube bank I'I comprising two horizontal rows of horizontally disposed tubes I2 arranged, in the case here illustrated, in staggered formation is disposed at the inlet end of fluid heating zone 3 and immediately above tube banks I5 and I3.

Another tube bank I8, comprising a plurality of rows of horizontally disposed tubes I2, is located in combustion and heating zone 3. Aithough the tubes in adjacent horizontal rows of this bank are arranged in staggered formation, they may, when desired, be arranged in vertical rows and, as here illustrated, are preferably more closely spaced than the tubes of bank i1.

Suitable burners I9 communicate with firing ports 8 and are provided beneath floor 8 or opposite sides of wall 9 and supply a combustible supply of fuel and air to each of the combustion and heating zones I II and II. Although gas burners are here illustrated, suitable oil burners may be substituted or both oil and gas burners may be employed. It is also possible to fire the furnace with pulverized solid fuel, or liquid or gaseous fuel, if preferred. The-volume of fuel supplied to each of the combustion and heating zones I0 and II as well as the fuel-air ratio employed in each zone are independently controlled so as to independently control the combustion and heating conditions on opposite sides of wall 9 and, by varying the quantity of excess air employed in each of the combustion and heating zones, the relative amounts of heat supplied to tube banks I3 and Il as compared to the heat supplied to the tubular elements in the upper portion of the furnace may be varied to suit requirements. Regulated quantities of air are supplied to each of the burner compartments between floor 6 and the sub-floor or foundation 2i, through suitable air inlet ports 22, regulated by suitable sliding dampers or the like, such as indicated, for example at 23. Regulated quantities of the total air supplied to the combustion and heating zones may be premixed with the fuel in burners I9 by means of suitable air regulating devices 2| and the remaining quantity of total air may be supplied to the combustion and heating zones through burner ports 3 by providing spaces 2i between the tips of the burners and the ports 9.

The burners on opposite sides of the firing wall 9 are preferably arranged at spaced intervals in one or a plurality of rows, so that the flames and resultant hot combustion gases issuing therefrom form a substantially continuous curtain or layer on each side of wall 9. As in the case here illustrated, burners I9 are preferably inclined at a slight angle toward the opposite faces of wall 9, so that the flames and hot combustion gases impinge against the opposite faces of this wall and are directed upward thereover, heating the surfaces of the wall to a highly radiant condition. Preferably the opposite faces of wall 9 are roughened, for example by -allowing bricks or other refractory' shapes indicated at 2II to protrude therefrom. 'I'his assists combustion' and causes the flames and hot combustion gases to adhere more closely to the faces of wall 9 and increases the action of the gases so as to extract a greater amount of sensible heat.

Radiant heat is transmitted from the radiant surface of wall 9 and from the flames and hot combustion gases in zones I0 and II directly to the exposed surfaces of tubes I2 in banks I3 and I4 and also to the exposed surfaces of the tubes in banks I5 and I6. The shielded surfaces of tubes I2 in banks I3, Il, I5 and I6,which shielded surfaces face the refractory walls I and 2, are subjected to heating by reflected radiant heat from these walls. The tubes of banks I3, III, I5 and I6 are, of course, also heated, to some extent, by direct contact with hot combustion gases but, due to the design of the furnace, the method of ring described and the use of highly radiant wall 9, a substantially stream-line flow of combustion gases is obtained throughout the entire furnace and the impngement of the flames and hottest combustion gases against the tubes is prevented whereby heating by convection in banks I3 and I4, and to some extent in banks I5 and IB, is materially reduced as compared with that obtained in a similar furnace, not employing a ring wall such as wall 9.

The tubes of bank I1 are also subjected to Aappreciable heating by radiation from the hot combustion products in zones II'I and Il andabsorb a considerable amount of fluid heat from the hot combustion gases passing thereover on their way to fluid heating zone 3.

Although at least a major portion of the radiant heat and a substantial quantity of fluid heat is extracted from the combustion gases in the lower portion of the furnace and imparted to fluid conduits I3, Il, I5, IG and I1 they are still i at a relatively high temperature and contain a considerable amount of readily available fluid heat which is extracted therefrom as they pass over the tubes of bank I8 on their way to flue 5. Any available radiant heat remaining in these gases is also extracted therefrom in bank I8, although this is not ordinarily of any considerable amount.

The furnace illustrated and above described offers a considerably great degree of flexibility and efficiency as compared with a similar furnace employing no central firing wall. Even though separate sets of burners are employed on opposite sides of the furnace no satisfactory independent regulation of the heating conditions to which tube banks I3 and Il are subjected can be obtained without the use of some dividing structure such as wall 9. In addition to this utility, wall 9 functions as a heat absorbing and heat radiating body by means of which a considerably increased amount of radiant heat is transmitted to the tubes of banks I3 and Il. Therefore, without the wall 9 the tubes of banks I5, I8 and I'I would be exposed to excessively high rates of heating. Also turbulence in the lower portion of the combustion and heating zones would result in uncontrolled excessively high rates of heating in localized portions of banks I3 and Il. A higher average rate of heating may be obtained in the furnace of the present invention with the same or even lower maximum rate and without excessive localized heating. In the present invention the combustion gases in the upper portion of zones II) and II, adjacent tube banks I5, IG and I1, contain considerably less radiant heat than in a similar furnace not employing a firing wall such as Wall 9, and excessive heating of the tubes of these banks is therefore avoided. This also improves the fuel efficiency of the furnace since a lower flue gas temperature may be obtained without employing an excessively large fluid heating bank in zone 3.

Many alternatives and modifications of the specific form of furnace illustrated in Fig. l may be employed within the scope of the invention, particularly with respect tothe arrangement and size of the tubular elements of the fluid conduits, and the various tube banks may be connected in any desired sequence so as to obtain the heating conditions which are most advantageous for the particular type of oil undergoing treatment'.

To more clearly illustrate the flexibility of the furnace with respect to the flow of fluid through the va'rious tube banks, Figs. 2 to 6 inclusive, each diagrammatically-illustrating a specific flow, are shown in the drawings and will each be briefly described. In each of the figures of the drawings the same reference numbers are used to indicate corresponding portions of the furnace.

In Fig. 2 the oil to be treated enters the uppermost row of tube bank I8. flowing downwardly in series through the adjacent rows of this bank and in series through the adjacent tubes in each row. The oil is transferred from the lowermost row of bank I 8 into the lowermost tube of bank I3 and passes upwardly in series through the adjacent tubes of this bank and thence in series through theadjacent tubes of bank I5. The oil is then introduced into tube bank I1 wherein it flows in series and in criss-cross arrangement, as illustrated. through adjacent tubes of opposite rows of this bank and wherefrom it is supplied to the uppermost tube of bank I6, passing downwardly in series through the adjacent tubes of this bank and thence downwardly in series through the adjacent tubes of bank I4 to be discharged from the lowermost tube of bank I4 to succeeding portions of the cracking system, not illustrated.

The flow illustrated in Fig. 2 is advantageous for the treatment of light oils generally and permits adequate control of the heating curve to produce the desired results from various types of light oils by independent regulation of the heating conditions employed on opposite sides of the bridge wall. Ordinarily with this type of flow the oilv will be subjected to comparatively low and progressively increasing rates of heating in tube bank I8, higher and substantially uniform or progressively vincreasing rate of heating in tube banks I3 and I5, high and substantially uniform rates of heating in tube bank I'I' and in tube banks I6 and I4 may be subjected to substantially uniform or decreasing rates of either high. moderate or low intensity.

In Fig. 3 the oil to be treated is supplied to the uppermost row of tube bank I8 and flows in a general downward direction-in series through the succeeding rows of this bank and in series through the adjacent tubes of each row. The oil is transferred from the lowerrnost row of tube bank I8 to the lowermost tube of bank I3. The oil flows upwardly in series through the adjacent tubes of banks I3 and I5 and enters the uppermost row of bank Il', flowing in series and in criss-cross arrangement, through adjacent tubes in opposite rows of this bank wherefrom it is discharged into the uppermost tube of bank I6 which, in this particular case, comprises two parallel rows of tubes in staggered formation. The oil flows in series through adjacent tubes in opposite rows of bank I 6 in a general downward direction and continues therefrom in series flow through adjacent tubes in the opposite parallel rows of' tube bank I4', being discharged from the lowermost tube of this bank to other portions of the cracking system, not illustrated.

The now illustrated in Fig` 3 is particularly desirable for reforming service and for cracking light oils generally when it is desired to maintain the oil at or near the maximum cracking temperature employed for a considerable predetermined length of time, this being accomplished in the present case by means of a soaking section which comprises tube banks I6' and I 4'. It will be noted that with the improved form of furnace structure herein provided the heating conditions employed in the soaking section may be controlled independently of those employed on the opposite side of the bridge wall and will ordinarily be of a somewhat milder nature. The use of two rows of tubes in banks I4' and I6' serve to give the oil undergoing treatment a longer time period in the soaking section.

In Fig. 4 tube banks I1 and I8 are connected in sequence, the oil entering the uppermost row of bank I 8, flowing downwardly in series through adjacent rows of both banks and in series through adjacent tubes in each row and thence flowing downwardly in series through adjacent tubes in banks I5 and I3, being transferred from the lowermost tube of bank I3 to the lowermost tube of bank I 4 and flowirg upwardly in series through the adjacent tubes of banks I4 and I5 to be discharged from the uppermost tube of' bank I6 to subsequent portions of the cracking system, not illustrated. f

The flow illustrated in Fig. 4 is particularly advantageous for the treatment of relatively heavy oils. It will be noted that the heating conditions employed in banks I3 and I5 may be controlled independently of those utilized in banks I4 and I6. Ordinarily the oil is subjected to progressively increasing rates of heating in tube banks I8, I1', progressively decreasing rates or substantially uniform rates of heating in banks I 5 and I3 and progressively increasing or substantially uniform rates in tube banks I4 and I6.

In Fig. 5, as in Fig. 4, tube banks I8, I1', I5 and I3 are connectedjn the sequence given and the flow of oil through these tube banks is the same as that described in connection with Fig. 4. Tube bank I6', to which the oil undergoing treatment is transferred from the lowermost tube of bank I3,

comprises two parallel rows of tubes arranged in l staggered formation, with adjacent tubes in opposite rows connected in series, and the oil passes downwardly through this bank into tube bank vstrued as limitations.

I4". which in this particular case, comprises three parallel rows of tubes with the adjacent tubes in the different rows connected in series. 'I'he oil passes in a general downward direction through tube bank I4" and is discharged from the lower portion of this bank to subsequent portions of the cracking system, not illustrated.

The flow illustrated in Fig. 5, like that of Fig. 3, is advantageous for reforming service and is similar to the flow illustrated in Fig. 3 except for the sequence of tube banks I3, I5, II' and I8 which, in the case of Fig. 5, is better adapted to the use of progressively decreasing rates of heating in banks I5 and I3, as well as in banks I6 and I4", with progressively increasing rates in banks I8 and Il. It will be noted that in Fig. 5 the use of three rows of tubes in bank I4' provides a longer soaking time for the oil in this zone than in bank I4' of Fig. 3.

In Fig. 6 tube banks I'I and I8 are each divided into right-hand and left-hand sections, the opposite sections of each bank containing an equal number of tubes. One stream of oil is supplied to the uppermost row of the left-hand section of bank I8, passing downwardly in series through the adjacentrows of this section and in series through the adjacent tubes of each row and thence in series through the adjacent rows of the left-hand section of bank II, continuing downwardly from this point in series through adjacent tubes of banks I5 and I3 to be discharged from the lowermost tube of bank I3.

A separate stream of the same or a different oil passes downwardly in sequence through the righthand section of tube banks I8 and I'I, passing in series through adjacent rows of these sections and in series through the adjacent tubes of each row and thence downwardly in series through the adjacent tubes of banks I6 and I4 to be discharged from the lowermost tube of bank I4.

The ow illustrated in Fig. 6 may be utilized for subjecting two separate streams of dissimilar oils to independently controlled cracking conditions and to independently controlled rates of heating, in a single furnace, and is also advantageous for subjecting two separate streams of substantially equal volume and of the same 011 to substantially equal cracking conditions in a single furnace and to substantially equal rates of heating in corresponding stages of their heat treatment. This parallel, two coil arrangement serves to decrease the loss of pressure due to friction through the fluid conduit thereby decreasing pumping costs and decreasing the'expense of the equipment by reducing the required pressure at the inlet of the heating coil.

It will be understo/od that the flows illustrated and above described are given only as typical eX- amples of the flexibility of the improved furnace of the present invention and are not to be con- Various other combinations and specific flows will be apparent to those skilled in the art from the teachings of the present invention and it is therefore, in lts broadest sense, not limited to any specic flow nor to any particular class of cracking service.

Neither is the specific form of furnace structure. illustrated in the accompanying drawings to be considered a limitation, since various modifications thereof will be apparent to those skilled in the art and are within the scope of the invention.

I claim as my invention:

1. A furnace for heating uids comprising, in combination, side and end walls defining the lower portion of the furnace, a central wall dividing si. i..

said lower portion of the furnace into separate combustion zones, fluid conduits disposed adjacent said side walls on opposite sides of said central wall, a fluid heating zone, of smaller crosssectional area than said lower portion of the furnace, disposed above said central wall and cornmunicating with said separate combustion zones, fluid conduits disposed in said fluid heating zone,

means for directing flames and resultant hot combustion gases upwardly at an angle against opposite faces of said central wall, and means for passing combustion gases from said separate combustion zones over the fluid conduits disposed in said fluid heating zone.

2. A furnace for heating fiuid comprising, in combination, side and end walls defining the lower portion of the furnace, a central wall dividing said lower portion of the furnace into separate combustion zones, fluid conduits disposed adjacent said side walls on opposite sides of said central wall, a fluid heating zone, of smaller cross-sectional area than said lower portion of the furnace, disposed above said central wall and communicating with said separate combustion zones, uid conduits disposed in said fluid heating zone, side and end walls defining said fluid heating zone, sloping walls connecting said side walls of the lower portion of the furnace with said side walls of the iiuid heating zone, uid conduits disposed adjacent said sloping walls, and means for directing combustible mixtures of fuel and air upwardly at an angle against opposite faces of the bridge wall.

3. A furnace for heating fluids comprising, in combination, side and end walls defining the lower portion of the furnace, a central wall dividing said lower portion of the furnace into separate combustion zones, fluid conduits disposed adjacent said side walls on opposite sides of said central wall, a uid heating 'zone communicating with said combustion zones, means for supplying combustible mixtures of fuel and air upwardly into said combustion zones at an angle against opposite faces of said central wall, means for transmitting radiant heat fromY said central wall directly to said side walls and to one side of each of said iiuid conduits disposed adjacent the side walls, means for supplying reiiected radiant heat from each of said side walls to the opposite side of said uid conduits adjacent the same, means for passing combustion gases from each of said combustion zones to said fluid heating zone, iiuid conduits disposed in the path of hot combustion gases passing from said combustion zones to said fluid heating zone, and means for passing said combustion gases over the 4last mentioned fluid conduits.

4. A furnace for heating fluids comprising, in combination, side and end walls defining the lower portion of the furnace, a central wall dividing said lower portion of the furnace into separate combustion zones, fluid conduits disposed adjacent said side walls on opposite sides of said central wall, a fluid heating zone communicating with saidseparate combustion zones, means for introducing combustion mixtures of fuel and air upwardly into said combustion zones at an angle against opposite faces of thebridge wall, means for transmitting radiant heat from the resultant flames and hot combustion gases and from said central wall directly to said side walls and to one side of each of the fluid conduits disposed adjacent the side walls, means for independently controlling the amount of heat supplied to the fluid conduits adjacent each of said side walls, a fluid conduit disposed in said iiui heating zone, and means for passing hot combustion gases from said separate combustion zones over the last mentioned fluid conduits to transmit uuid heat thereto from said gases.

5. A furnace for the heating of fluids com prising, in combination, side and end walls delining the lower portion of the furnace, a vertical wall extending between said end walls and disposed ventrally in relation to said side walls, fluid conduits disposed adjacent each of said side walls, a floor containing firing ports disposed on opposite sides of said central wall, and burners communicating with said firing ports, said burners and firing ports being so disposed as to direct combustible fuel mixtures at an angle against and over opposite faces of said central wall in a general upward direction.

6. A furnace for the heating of uids comprising, in combustion, side and end walls deflning the lower portion of the furnace, a vertical wall extending between said end walls and disposed centrally in relation to said side walls, fluid conduits disposed adjacent each of said side walls, a door containing firing ports disposed on opposite sides of said central wall, burners communicating with said firing ports, said burners and firing ports being disposed to direct combustible fuel mixtures against' and over opposite faces of said central wall in a general upward direction, a iiuid heating zone of smaller cross-sectional area than said lower portion of the furnace andV communicating therewith, said fluid heating zone being located above said central wall and disposed centrally in relation to said side walls, and fluid conduits Vdisposed. in said fluid heating zone.

'7. A furnace for the heating of fluids corn-V fining the lower portion of the furnace, a Vertical wall extending between said end walls and disposed centrally in relation to said side walls, fluid conduits disposed adjacent each of said side walls, a floor containing firing ports disposed on opposite sides of said central walls, burners communicating with said firing ports,said burners-and ring ports being disposed to direct combustible fuel mixtures against opposite faces of the bridge wall, side and end walls defining a iiuid heating zone of smaller cross-sectional area than said lower portion of the furnace and communicating therewith, said fluid heating zone being located above said central wall and disposed centrally in relation to said lower portion of the furnace, sloping walls disposed above the side walls of said lower portion of the furnace and connecting the latter with the side walls of said fluid heating zone, fluid conduits in said fluid heating zones, and fluid conduits disposed adjacent each of said sloping walls.

8. A furnace for the heating of fluids cornprising, in combination, side and end walls defining a lower portion of the furnace, a vertical wall extending between said end walls and disposed centrally in relation to said side walls, uid conduits disposed adjacent each of said side walls, a oor containing firing ports disposed on opposite sides of said central wall, burners communicating with said ring ports, said burners and firing ports being disposed to direct combustible fuel mixtures against opposite faces of the bridge wall, side and end walls defining a uid heating zone of smaller cross-sectional area than said lower portion of the furnace and communicating therewith, said fluid heating zone being located above said central wall and disposed centrally in relation to said lower portion of the furnace, sloping walls disposed above the side walls of said lower portion of the furnace and connecting the latter with the side walls oi.' said fluid heating zone, iiuid conduits in said duid heating zones, fluid conduits disposed adjacent each of said sloping side walls. and fluid conduits disposed immediately beneath said uid heating zone and above the fluid conduits adjacent said sloping walls.

9. A fluid heating furnace comprising a pair of side walls, an inner wall disposed in a vertical ,plane between and spaced from said side walls, horizontal heating tubes adjacent one of the side walls opposite the inner wall and disposed in a common vertical plane, additional horizontal heating tubes adjacent the other of said side walls opposite the inner wall and disposed in a aumen second .common vertical plane, and means for directing dames and combustion gases in a vertical direction along the opposite faces oi' said inner wall.

l0. A uid heating furnace comprising a pair of side walls, an inner wall disposed in a vertical planev between and spaced from said side walls. horizontal Vheating tubes adjacent one of the side walls opposite the inner wall and disposed in a common vertical plane, additional horizontal heating tubes adjacent the other of said. sidewalls opposite the inner wall and disposed in a second .'common vertical plane, and means for impinging dames angularly against and .for passing resultant combustion gases in a vertical direction over the opposite faces of said inner wall.

LEV V A. MEKLER.