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Publication numberUS2512326 A
Publication typeGrant
Publication dateJun 20, 1950
Filing dateMar 6, 1947
Priority dateMar 6, 1947
Publication numberUS 2512326 A, US 2512326A, US-A-2512326, US2512326 A, US2512326A
InventorsHarrison James A
Original AssigneeHarrison James A
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Industrial gas-fired air heater
US 2512326 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

June 20, 1950 J. A. HARRISON INDUSTRIAL GAS FIRED AIR HEATER 2 Sheets-Sheet l Filed March 6, 1947 JNVENTOR. .J4/ves A HAAR/50N Arrow/Vs June 20, 1950 J. A. HARRISON 2,512,326

INDUSTRIAL GAS FIRED AIR HEATER Filed March 6, 1947 2 Sheets-Sheet 2 :ELE-E JNVENToR. JAMA-.s A. HAM/sow TIME QTTORNEYS zob Patented June 20, 1950 if INDUSTRIAL GAS-FIRED AIR HEATERv James A. Harrison, Southfield Township,

Oakland County, Mich.

Application March 6, 1947, Serial No. 732,746

This invention relates to industrial heating equipment and particularly to gas-fired heating apparatus for supplying heated air to process ovens or furnaces or for supplying tempered air to factory spaces in order to make up the air which is exhausted by Ventilating systems.

Heretofore, industrial air heaters of this character have been of two types, namely either pullthrough or blow-through. In the pull-through type, the air heater is installed on the inlet side of the systems air moving fan, and in the blowthrough type, when used, the air heater is installed on the discharge side of the fan.

Pull-through type heaters have been equipped with atmospheric type'gas burners which for temperature control purposes have turn-down ratios limited approximately three-to-one. Blowthrough type heaters have been equipped with blast type gas burner equipment requiring a combustion airblower to deliver the primary air at from 16 ounces to 32 ounces pressure. The turndown ratio of this blow-through type is limited to from four-to-one to siX-to-one. Due to the limited turn-down ratio of these two types of air heaters, it has been necessary that they be manufactured with a great number of gas burner sizes in order to answer the specific capacity needs and still have turn-down available for the control of the temperature of the air being heated. Likewise it has been necessary that the size of the air heater be quite accurately selected due to the limited range in turn-down.

An important object of this invention is to provide an improved air heater which is relatively inexpensive to manufacture and install, is highly efficient and more economical in operation, and has a considerably higher turn-down ratio than heretofore which enables the delivered air temperature to be accurately set and maintained.

Another important object of this invention is to provide an improved air heater construction including novel means for economically and eiliciently mixing the air and gas to form a combustible mixture, and burning this combustible mixture to heat the air forced through the combustion zone, with burners interchangeable for wide increases or decreases in heater capacity.

A further important object of the invention is to provide the air heater with burners which will eiliciently operate when air is blown through the air heater by the systems ian without the necessityof using a separate costly combustion airblower and still have ya turn-down ratio far in excess of that available with existing air heaters,

14 Claims. (Cl. 263-19) A further important object of this invention is to provide an air heater that can be employed in either a blow-through or pull-through type of system without change other than adjustment.

A further important object of the invention is to provide an air heater which has adjustable air passages so thatnot only the total passage can be adjusted for air handling capacity but the passages can be individually adjusted to distribute the air equally on both sides of the flames of combustion.

A further important objectjof thisinvention is to provide an air heater with adjustable air passages so that the passages can be' partly closed when the air heater is rst lighted and the air passing therethrough is cold and heavy thus eliminating the necessity `of employing an oversize motor for operating the circulatory air fan.

A stillA further important object ofthe invention is to provide a novel control mechanism for the apparatus which provides a large turn-down ratio a'nd enables the apparatus to be adjusted within a line degree of accuracy to provide the desired temperature in the chamber, oven or furnace into which the heated air is directed. Other objects, advantages and meritorious features will become more fully apparent rfrom the vfollowing specification, appended claims andy accompanying drawings wherein:

Fig. 1 is a schematic view of a system embodying the features of the invention showing the manner of :heating and circulatingv the air through a treatment chamber,

Fig. 2 is a cross sectional view through the air heating apparatus taken along line 2-2 of Fig. 1,

Fig. 3 is a longitudinal sectional view of the air heating apparatus taken along line 3--3 of Fig. 2, A

Fig. 4 is a schematic view showing the manner of controlling and delivering gas to the heating apparatus, and

Fig. 5 is a graph illustratingthe operation of the invention.

The invention may be embodied inl various forms and is herein illustrated as applied to a heat treatment oven or chamber from which air is drawn and heated and returned to heat the chamber. Referring to'Fig. 1, the heat treatment chamber is generallyindicated at l0 and is provided with an air inlet I2 at one end and an exhaust stack I4 at the other end. Both the inlet and exhaust openings may be varied in size by suitable valve control means. A circulatory system is provided for removing air from one portion of thelchamber, heating it and returning the heated air to another portion of the chamber. In operation, the inlet and exhaust openings are usually adjusted so that approximately 75% or more of the air is circulated through the system, the balance being introduced and discharged through the inlet and outlet openings.

The air circulatory system comprises a circular duct I6 generally mounted outside of the chamber and provided with a return air intake I8 entering the upper area of the chamber to draw air therefrom. The opposite discharge end of the duct I6 is provided with an air supply section 2li, entering another portion of the chamber, and constructed with a horizontal distributory section 22 having a series of discharge openings 24 for distributing the heated air over the lower area of the chamber as shown Iby the arrows in Fig. 1.

Although the duct l and the heating apparatus therein may be disposed inside the chamber, it is preferred for accessibility to locate the duct I6 outside the chamber over the' top as shown or along either side wall. The duct is provided with means in the form of an air blower or fan 26l for drawing air through the intake i8 and forcing it through the balance of the system. Provided in the duct l is a slightly reduced circular section 28 in which-the air heater islocated; In the illustrated embodiment of the invention, the air blower 26- is located on the inlet side of the air heater and the system typies a blowthrough type of apparatus. lit may, however, be locatedvon the outlet side of the casing andV pull air therethrough as in the pull-through types of apparatus. In the preferred construction, the air blower functions-todirect the air under pressure of one to fou-r inches of water column.

The reduced section 2B-is in the form-.of a hollow casing in which. is contained the air heater. The air heater includes a plurality of gas burner units of similar construction arranged in circularly spaced relation around the axisor the casing as shown in Figs. 2` and 3. Each burner. unit comprises a Venturi. tube 30 having the. constricted portion of' its passage preferably nearer 4 the inlet end than the outlet end. Air is forced by the blower 26 through the. entire length of each venturi, traveling at a greater rate of speed through the constricted area than any other portion of the venturi. At approximately the minimum diameter of the venturi, gas is admitted and mixedA with the air. The gas is. delivered separately to eachfburner unit. by a tube or pipe 32 preferably formed ofk copper. Each tube 32 opens. into the constricted passage of the venturi of' itsl respective burner unit as shown at 3A. Preferably, the discharge endsection of the gas delivery pipe is wound one or more turns around the Venturi tube as shown at 35 to thereby preheat the gas therein beforerit discharges. into the Venturi tube. The purpose or this. is. topreheat the raw gas before admission into, the burner units to thereby proportionately expand the volume of gas delivered asthe temperature of the air increases. Air forced: through each Venturi tube picks up the-gas admitted thereinto and carries it to the discharge end while it mixes therewith. At the discharge end of the Venturi tubes, the air'andgas flows therefrom in a combustible stream and in ignited condition for-ms the flame jets generallyv indicated at 36.

Asr previously mentioned, the Venturi tubes arearranged in circularly spaced relation around the axis of the casing. The seriesfof` Venturi tubes are mounted between two substantially coaxial sleeves 38 and 40 of unequal radii. The outer sleeve 38 is cylindrical and is less than the length of the casing 28 and preferably located closer to the inlet side of the casing than the outlet side thereof. The inner sleeve 40 is mounted substantially within the outer sleeve and is provided with a conical section l2 which flares slightly outwardly toward the flame jet area and then is shaped with a short cylindrical section 44 at its discharge end. Both the sleeves project a slight distance beyond the discharge end of the Venturi tubes as shown in Fig. 2. The inner sleeve 48 is opened at both ends and forms a relatively large passage for the flow of air through the duct'system. The outer sleeve 33 is spaced inwardly from the wall of the casing 28 and forms an annular passage d5 therearound for the ow of controlled amounts of air therethrough.

On the axis of the casing is a conical shaped member or plug 46, preferably diamond shaped in longitudinal cross section, which is mounted for longitudinal adjustable movement. rIhe plug 46 is mounted within a xed subsidiary sleeve 4B supported by brackets or otherwise centrally Within the casing. The sleeve is preferably provided` with tapering conical end sections lili- 50 which preferably converge toward the axis of thecasin-g at thesame angle of inclination as the conical sides of the plug. The plug is xed on an axially extending rod 52 which is mounted by spacedv supports Sli-54 for longitudinal movement. One end section of the rod is provided with rack teeth meshing with a pinion 58 fixed on a transversely extending control shaft 60. The latter is; provided with any suitable means, such as the hand wheel 52, for eifecting rotation oi the shaft, which will advance or retract the plug relative to the sleeve 48 to vary the air flow as will be more particularly described hereinafter. The maximum diameter of the plug bears such a relation to the sizes of the end openings of the sleeve 48 that when adjusted to the extreme positions of its longitudinal movement it substantially closes off the now of air through the sleeve. Movement of theV plug toward closing position at either end of the sleeve will build up a pressure differential between inlet and outlet sides of the air heater. The pressure differential or drop should be greater than 1/4 inch water column to prevent nash back in the burner tubes 3o.

The annular passage 4,5 formed between the casing 218 and the sleeve 38 allows a flow of a oontrolled amount of air from the inlet side to the outlet side of the heater. This is preferably accomplished by providing an annular plate 64 on the. inlet side having a series oi equally spaced apart openings or ports GB circularly arranged around the axis of the casing 28 and concentric thereto.y These openings are spaced apart from oneanother approximately their circumferential dimensions as shown in Fig. 2. Overlying the plate. S4 is asecond annular plate 63 which is substantially thesame size as theformer and similarly provided with a series. of openings or ports corresponding in size to the openings 66. This second annular plate is mounted for rotatable adjustment relative to the rst plate from one extreme position in which the openings of the two plates. are incomplete registration to the other extreme position in which the openings are completely out of registration and no air will flow. therethrough. The plate 58 may be adjusted to 1g any intermediate position between these extreme positions and thereby regulate the amount of air flowing through the annular passage 45.

The rotatable plate may be either manually' or automatically adjusted and is herein shown as automatically adjustable in response to the temperature changes in the treatment chamber. As shown in Fig. 2 an adjusting rod 10 is provided for this purpose which extends substantially tangentially through an opening 12 in the casing 28 and has one end pivotally connected as at 14 to the annular plate A68. The opposite end is connected by linkage, such as that shown at 16 in Fig. 1, to an electric motor 18 or other suitable operating device. The latter -is provided With a thermal responsive control element 80 projecting into the treatment chamber or other heated space and as is conventional practice the control element in response totemperature changes opens and closes electrical switches and causes the motor to turn over in one direction or the other and either pull or push the linkage system and rod to vary the overlapping relationship of the openings or ports in the two annular plates B4 and 68.

The air passing through the Venturi tubes forms the primary air of the combustible mixture. The air passing through the annular passage and the annular passages formed by the innermost pair of sleeves 40 and 48 forms the secondary air of the combustible mixture. By virtue of this arrangement, secondary air is supplied to both the. outer and inner sides of the llames of combustion represented at 36 and an efficient burning operation results. Adjustment of the plug 46 and the size of the ports 66 will not only vary the air handling capacity of the heater but vary the distribution of the air so that if desired an equal amount of secondary air may be provided on both sides of the burning mixture issuing from the tubes 30.

Moreover, by adjusting the air handling capacity of the heater it is possible to reduce the amount of air flowing therethrough when the air is cold and increase the capacity progressively with the increase in temperature. The motor 18 and its thermal responsive control element are so related to the temperature in the treatment chamber that when the air therein is relatively cold, the size ofthe ports 66 are adjusted to approximately their minimum size to thereby reduce the volume of air passing through the heater unit.l As the temperature of the air in the treatment chamber and in the duct system increases, the motor is controlled to open the ports 65 Wider until at the maximum temperature for which the apparatus is set is attained at which time the ports will be opened approximately their widest extent. By vitrue of such a control, it is possible to use a low horse power motor for the blower ian 25 because when the air passing therethrough is cold and heavy its volume is cut down, but as the air temperature increases and the air becomes lighter in weight the capacity of the heater increases proportionately.

The gas delivery tubes 32 Which separately open into the burner tubes communicate with a common source of gas maintained at the desired pressure. Referring to Fig. 4, the gas delivery tubes represented by the lines 32 extend to a common control unit which is operable to progressively increase or decrease the number of lighted burners. The control unit comprises a circular housing 82 having a rotary valve member 84 therein. The latter is secured to a shaft 86 which is operatively coupled to a reversely op- '6 erated electric motor 88 of the type shown at 18. The motor 88 in turn Ais controlled by a thermal responsive control element 89 similar to 88 which extends into the treatment chamber or is in thermalr'elation to the air therein.

Each gas delivery line 32 has a separate inlet port opening into the housing 82 as indicated at 90. These openingsor ports are located in one side Wall 92 of the casing over which the valve member 84 sweeps.` When the valve member overlies a port it cuts off the delivery of gas to the line 32 communicating with this port, The ports 90 are arranged in a semi-circular series and the valve member is generally in the formation of a semi-circular segment adapted in one position, such as that shown in Fig. 4, to overlie and close all the ports with the exception of one port. The single exception is indicated at 94 and the valve member is cut away as at 96 in order that when the valve'member is in the maximum closed position shown in Fig. 4 the single port 84 remains open for the delivery .of gas to burner with which it is connected. This burner will serve as the pilot and be continuously lighted. Suitable stop'means may be provided on the valve member or the shaft 86 limiting the rotation between the maximum closed position shown in Fig. 4 and themaximum open position Where all the ports`90 are open for feeding gas to all the burners, or the motor 88 may be so controlled as to limit the rotation between these two limits. In addition, if desired, individual manually controllable valves may be installed in each gas delivery line 32. Such valves are represented at 98 in Fig. 4.

Any suitable detent means may be provided for causing the valve member to move in step by step manner so that no port is only partially opened and partially closed. As shown in Fig. 4, the side 92 of the housing is provided with a series of recesses |08 into which a ball ||0 indicated in dotted outline may drop thereinto. The ball is mounted in a cavity on the underside of the valve member and is carried around therewith when the latter rotates. The balland the recesses are so located with respect to the inlet ports 9D that when the valve member moves to open or close another port the ball falls into a recess following complete opening or closing or the port and thereby resistingly checks further rotation .of the valve member.

Raw gas is delivered to the valve control housing 82 by means of a delivery line or pipe which opens into the housing on the side opposite to the series of inlet ports 90. Preferably this gas is delivered at a substantially constant pressure, which pressure may be regulated by a control device generally indicated at |00. Such device includes the valve |02 connected by a valve stem to a Apressure responsive member such 'as the diaphragm |04. The diaphragm is responsive to differential pressures exerted against the opposite sides thereof. One side is exposed to the pressure of the raw gasadmitted by valve |02 and delivered therefrom to the distributing device enclosed within the `housing 82. The opposite side of the diaphragm is exposed to the pressure of air delivered thereto by the conduit |06 which as shown in Fig. 1 opens into the air duct It at some point between the fan 26 and the air heater 28. This vair pressure falls as the temperature increases, thus the same falling pressure can be imparted to the raw gas due to the regulating action of the control device |00.y This air pressure is relatively constant. If the pressure of the raw gas iiowing through the control device lull should fall, such as by the opening of more inlet portsr 90; the change in the diierential pressures exerted on the diaphragm will cause the valve IGZ to open further and admit more raw gas to distributing control device in the housing 82. Should the pressure of the raw gas increase beyond the desired amount, the change in the diierential pressure will lift the diaphragm and cause the valve |02 to move toward closed position thereby reducing the amount of raw gas supplied to the housing 82.

The air heater portion of the apparatus enclosed within the casing 28 forms a separate installable unit of theA air circulating duct system. As previously mentioned it may be installed on thedischarge side of air blower and function as a blow-through type of air heater, or it may be installed on the inlet side of the systems air moving fan. To facilitate installation and removal as a separate unit, the casing 28 of the air heater is provided with outwardly extending'radial flanges {l2-l I2 at the opposite ends thereof. Each flange is provided with a series of circumferentially spaced openings or holes rIlll through which fastening means such as bolts or rivets may extend to secure the unit between comparable end portions of the sections making up the duct system I6. The air heater may thus be separately manufactured and installed without difficulty wherever it may be desired in the air circulating system.

The operation of the system is generally understood from the previous description. When the system is iirst started up, the air in the chamber, oven or space to be heated is relatively cold and heavy and normally without any control of the capacity of the air` heater, a considerable load will be imposed on the motor driving the air moving fan 26. However, the control motor 'I3 of the present system in response to the relatively cool temperature of the treatment chamber will have shifted the annular plate E8 until the openings 66 for the annular passage 6.5 are substantially closed thereby reducing the volume of air capable of passing through the air heater. Moreover, the plug 46 may be adjusted by the control 52 to substantially its closed position in the sleeve 48. This will reduce the load on the fan motor thereby enabling a motor of a lower horse power rating to be used. At the same time the control motor 88 in response to the temperature in the treatment chamber will have moved the valve member 84 in a counterclockwise direction in Fig. 4 to substantially the maximum open position. As a result substantially all the burner units 30 will receive raw gas for operation. The combustible mixture owing from all these burners will be ignited by the single continuously operated pilot burner and the air heater will be functioning at substantially its maximum heating effectiveness.

As the temperature rises in the treatment chamber or other space being heated by the system, the control motor 'I8 will function to rotate he annular plate 68 so that the openings 65 are progressively opened in proportion to the rise in temperature. More air is admitted into the air heater increasing the amount of air moving through the air heater. The conical plug 46 may be adjusted to open the passage through the innei-most sleeve 43 thereby further increasing the air capacity of the air heater and providing an amount of secondary air approximately equal to thatsupplied by way of the annular passage 5.

8 As the temperature continues to rise the control motor 88r will function to rotate the valver member 84 in a clockwise direction in Fig. 4 toward its positionsuccessively cutting off the delivery of gas to the burners and thereby reducing in step by step manner the number of burners in operation.

Ii the controls are set to provide a limit to the rise in temperature in the heat treatment chamber, for example 450 F., as this temperature is approached the number of burners in operation will be reduced until the temperature levels off at this desired limit. The graph in Fig. 5 represents the operation of the system from a start in cold condition.. Ii' 450F; is the desired temperature, the controls may be set so that the teinperature curve begins to level orf atY this degree level. If it should go above as indicated in the graph, one or more burners will be cut oithus reducing the eiectiveness of the air heater. This will cause the tempera-ture of the air in the treatment chamber to fall and if it should go below the desired degree, one or more burners will bel out in. In actual practice, the temperature curve after approximating the desired limit will iluctuate slightly above and below the desired degree as shown in the graph and the cutting in or out of one burner` by the valve member 84 will suice to hold the temperature at substantially the desired level.

During the operation of the air heater, the raw gas delivered to the burners will be preheated as it passes through the coils 35 just prior to admission tothe Venturi tubes. This will expand the volume of gas proportionately to the temperature of the air heated. The volume of gas delivered tothe Venturi tubes therefor maintained proportionate to the volume of air flowing through Venturi tubes. Since the gas, is admitted into the Venturi tubes at substantially their point of minimum dia-meter, the action of the air passing these inlet ports 34 induces a suction which obviates the necessity of maintaining the gas under high pressure. The gas need only .be under a suicient amount of pressure to feed it to the burners.

What I .claim is:

l. An air heating apparatus comprising, in combination, a generally circular casing, a series of' gas burner units in the form of Venturi tubes arranged in the interior of the casing in a substantially lcircular relation around the axis of the casing, said Venturi tubes occupying less than the total cross sectional area, of the casing so as to provide one or more air passages between the` Venturi tubes for the uninterrupted ow of air through the casing, means for causing air to be heated; to ilow through the casing from one end to the other end thereof, said Venturi tubes having their-axes extending substantially parallel to the axis of the casing so that a part oi the air ilowing therethrough is caused to flow through the Venturi tubes, means for delivering gas to each burner unit and causing the gas to enter each Venturi tube at substantially the minimum cross sectional area thereof so that the gas mixes with the air owing through the Venturi tubes, means responsive to the temperature of the air heatedr by said burner units for cutting off the operation of one or more of the burner units to prevent increase in the temperature of the air beyond the desired temperature level, valve means for one of said air passages adjustable to vary the amount off air iloWing therethrough, and. means responsive to the temperature of the` air heated by said burner units for adjusting said valve means according to the temperature of the air.

2. An air heating apparatus comprising, in combination, a generally circular casing, a series of gas burner units in the form of Venturi tubes mounted in the interior of the casing in a substantially circular relation around theaxis of the cas-ing and in spaced relation to the inside surface of the casing to form an annular air passage therebetween, said Venturi tubes having their axes substantially parallel to the axis of the casing and their inlet and outlet openings in corresponding positions in the casing, means for causing air to be heated to flow through the casing at a relatively high velocity from one end to the other end thereof and causing part of the air to flow through the Venturi tubes and another part of the air to flow through the annular pass-age between the Venturi tubes and the inside surface of the casing, means for delivering raw gas to each burner unit and causing the gas to enter each Venturi tube substantially at the minimum cross sectional area thereof, means responsive to the temperature of the air heated by said burner units for cutting off the operation of one or more burner units to maintain the air at the desired temperature level, adjustable valve means controlling the amount of air flowing through said annular passage, and means responsive to the temperature of the air heated by said burner units for adjusting said valve means in accordance with the temperature of the air.

3. An air heating apparatus comprising, in combination, a generally circular casing, a series of gas burner units in the form of Venturi tubes substantially circularly arranged in the interior of the casing but in spaced relation to the axis of the casing and the inside Wall of the casing so as to form ,an axial air passage and an annular air passage, said Venturi tubes having their respective passages extending substantially parallel to ther axis of the casing, means for causing air to be heated to flow through the casing from one thereof to the other and to flow through said axial and annular passages and the passages of said Venturi tubes, means for separately delivering gas` to each burner unit and causing it to enter the passage of each Venturi tube at substantially the minimum diameter thereof, means responsive to the temperature of the air heated by the apparatus for varying the number of burner units in operation in order to maintain the lair at the desired temperature level, adjustable valve means for said annular passage and a separate adjustable valve means for said axial passage adapted upon adjustment to vary the amount of vair owing therethrough, and means responsive to the temperature of the air heated by the apparatus for adjusting at least one of said valve means so as to vary the amount of air flowing through the passage controlled thereby in direct proportion to the temperature f the all'.

4. An air heating apparatus for installation in a circulatory air system comprising, in combination, .a generally circular casing having means on the opposite ends thereof for securing the same in the system, a plurality of burner units in the form 'of lVenturi tubes arranged in a circular series in the interior of the casing in spaced relation to the axis thereof and the inner surface thereof to form an axial air passage vand an annular air passage therebetween,

said Venturi tubes being opened ended and having their respective passages extending substantially parallel to the axis of the casing, a gas delivery pipe for each burner funit adapted to communicate with an outside source of gas and opening into the Venturi tube passage of its burner unit at substantially the minimum cross sectional area. thereof, each gas delivery pipe being coiled one or more times about its burner unit prior to opening into the Venturi pass-age thereof, adjustable valve means for each of said axial and annular passages, and means for controlling the adjustment of said valve means in order to vary the air capacity of the heating apparatus.

5. An air heating unit adapted to be installed in a duct of an air circulating system comprising, in combination, a generally circular casing having means on the opposite ends thereof for securing the same to the open ends of two separated sections of an air duct, a pair of sleeves of different diameters mounted in the easing concentric with the axis thereof and forming an axial air passage through the inner sleeve and an annular air passage between the outer sleeve and the casing, a plurality of gas burner units arranged in circularly spaced apart relationship in the area between said sleeves, each burner unit having an open ended Venturi passage extended substantially parallel with the axis of the casing, a gas delivery pipe for each burner unit adapted to communicate with an outside source of gas and having its discharge end opening into the Venturi passage of its respective burner unit at substantially the minimum diameter thereof, each gas delivery pipe being coiled one or more turns about its respective burner unit for preheating the gas prior to discharge into the Venturi passage, valve control means for varying the amount of air adapted to be passed through said annular passage, valve control means for varying the amount of air adapted to be passed through said axial passage, and control means operable from outside of said casing for adjusting said two valve means.

6. An air heating apparatus comprising, in combination, an elongated generally circular casing, a series of gas burner units in the form of Venturi tubes shorter in length than the length of the casing, means mounting the Venturi tubes in the interior of the casing in spaced relation to the opposite ends thereof and with the axes of the Venturi tubes extending parallel to the axis of the casing and their inlet and outlet openings in corresponding positions in the casing, said mounting means further disposing the Venturi tubes in spaced-relation to the inside surface of the casing to form an annular air passage therebetween, means for ilowing air to be heated through the casing at a relatively high velocity from on-e end to the other end of the casing and causing a part of the air to 'ow through the Venturi tubes and another part of the air to iiow through the annular passage between the Venturi tubes and the inside surface of the casing, means for delivering gas to each burner unit and causing the gas to enter each Venturi tube substantially at the minimum cross sectional area thereof, and valve means in said annular passage controllable from outside of the casing for varying the volume of air flowing through the passage. l l 7. An air heating apparatus comprising, in combination, a generally circular elongated casing, a plurality of gas burner units in the form of open ended Venturi tubes shorter in length than 11 the length of the casing, means mounting the Venturi tubes in the interior of the casing in a circular series of less radius than the casing and forming a central passage on the axis of the casing and an annular passage between the Venturi tubes and the inner surface of the casing, said Venturi tubes being mounted in the same plane in the casing in spaced relation to the opposite ends of the casing and with their axes extending substantially parallel to the axis of the casing and with their inlet and outlet openings in corresponding positions in the casing, means for flowing air to be heated through the casing from one end to the other end thereof and causing a portion of the air to flow through the Venturi tubes and portions of the air to flow through the central and annular passages on either side of the Venturi tubes, means for delivering gas to each burner unit from outside of the casing and causing the gas to enter each Venturi tube substantially at the minimum cross sectional area thereof, and separate adjustable valve means in said annular passage and in said central passage for varying the volume of air flowing therethrough.

8. In a substantially closed circulatory air heating system including as parts thereof a chamber to be heated and a conduit opening at its opposite ends into communication with spaced areas of the chamber, a section of the conduit forming an air heater and provided in the interior thereof with a plurality of open ended tubular gas burners having their axes extending parallel to the axis of the section and occupying an area less than the total cross sectional area of the section to provide for the flow of air therearound, means for moving air through the system in one direction and causing the air passing through the air heater to divide and ow both through and around the gas burners, means for progressively increasing or decreasing the number of the gas burners in operation, and means responsive to the temperature of the air in said chamber for governing the action of said second mentioned means.

9. In a substantially closed circulatory air heating system including as parts ofthe circulatory system a chamber to be heated and a conduit opening at its opposite ends intocommunication with spaced areas of the -chamben'a section of said conduit forming an air lheater and having a plurality of open ended tubular gas burner units mounted inthe interior of the section and arranged in a group spaced radially inwardly of the surrounding wall portion of the section to form an annularly shaped air passage therebetween, an air impelling device adjacent to one end of the air heater operable to move air through said section and through said burner units and through said annular passage, means for delivering gas to said burner units from an outside source of supply to mix with the air flowing therethrough to form a combustible mixture, an adjustable valve in said annular passage for varying the volume of air flowing therethrough, means responsive to the temperature of the air in said chamber for lvarying the number or' burners in operation to maintain the air at the desired temperature, and .separate means responsive to the temperature of the air in the chamber for adjusting said valve.

10. An air heating apparatus comprising, in combination, a generally circular casing, a plurality of open ended tubular gasburner units in the interior of the casing having their axes extending substantially parallel to the axis of the casing and arranged :in `a group spaced radially inwardly on all sides thereof from the surrounding Wall portion of the casing to form an annularly shaped air passage therebetween, means for iiowing air to be 'heated through the casing to thereby cause a part of such air to ow through the burner units land another `part of such air to ow through the annular passage, means for delivering gas to each burner unit to form a combustible mixture with the air ilowing therethrough, a .pair of a-nnularly shaped plates disposed in said annular air passage in juxtaposition to one another, said plates each having a series of similarly shaped apertures spaced apart from one another approximately their'respective circumferential dimensions, and means operable from outside of-the casing for -circularly adjusting one of said plates relative to the other plate from a position in which the Aapertures of the plate substantially register with one another to a position in which the apertures are substantially out of registration with one another in order to vary the volume of air `flowing through the annular passage.

11. An air heating apparatus comprising, in combination, a generally circular casing, a pair of open ended sleeves of -diierent-diameters disposed inside of the casing `in Aco-afxial relationship to one another and to the axis of the casing, said sleevescooperating with the casing to form an annularly shaped air passage between the larger diameter sleeve and the casing and a central passage through the smaller diameter sleeve, a plurality of tubular burnerunits mounted in the space between said sleeves in circularly spaced apart relationship around the axis of the casing land having their respective axes extending parallel to the axis of the casing, means for delivering gas from a source of supply outside of the casing to each burner unit for mixture with the air therewithin, an air impelling device at one end of fthe casing operable to force air under relatively Vhigh velocity `through the casing and through said burner units and said annular and central passages, and means for adjusting the cross section areas of said annular and central passages ito Yvary the volume of air owing therethrough.

l2. In a gas-:red air heating system, the method of operating the system which comprises continuously circulating the air to be heated in a moving streamthrough the system, causing the air stream of the systemtoflow fthrough a combustion zone, `introducing raw gas into the combustion Zone at 4a 'plurality `of points separated from one another transversely'of the air stream flowing therethrough, utilizing 'the air in the air stream as lthesole source of primary and secondary-airfor the combustible mixture by dividing the vstream adjacent to-each Vpoint into an inner *core of 'primary -air for vimmediate mixture with the raw gas introduced aft-that point and into anlouter vlayer of secondary air for later mixture with the gas and primary air further along the stream, varying the volume of the air stream passing through the combustion zone in direct proportion to the temperature of the air stream, and varying-the amount of raw gas introduced into the combustion zone in inverse proportion to the temperature of the air stream.

13. In a circulatory-air heating system including a-combustion zone in-Which the air in the system is heated and-afchamber which is heated by theair inthesystem, the method of operating the system which Acomprises continuously moving an air stream under forced draft through the system in one direction, introducing iuel from an outside source of supply into the combustion zone, utilizing the air stream of the system flowing through the combustion zone as the sole source of air for forming a combustible mixture with the fuel introduced into the combustion zone, varying the amount of fuel delivered to the combustion zone in inverse proportion to the temperature of the air in the chamber, and varying the volume of air owing through the combustion zone in direct proportion to the temperature of the air in the chamber.

14. In a circulatory air heating system including a chamber to be heated by air and a combustion zone for heating the air, the method of operating the system which comprises continuously circulating an air stream under forced draft through the system in one direction, introducing a gaseous fuel from an outside source of supply into the combustion zone, utilizing the air stream of the system flowing through the combustion zone as the sole source of air for forming a combustible mixture with the gaseous fuel thus introduced, controlling the amount of gaseous fuel delivered to the combustion zone in inverse proportion to the temperature of the air in the cham- 14 ber, and controlling the pressure of the gaseous fuel thus introduced in accordance with the pressure of the air stream flowing through the combustion zone.

JAMES A. HARRISON.

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

UNITED STATES PATENTS Number Name Date 1,349,668 Good Aug. 17, 1920 1,958,913 DeCoriolis et al May 15, 1934 2,000,733 Avery May 7, 1935 2,097,544 Ames Nov. 2, 1937 2,120,803 Grant June 14, 1938 2,147,568 Barber Feb. 14, 1939 2,383,641 Focke Aug. 28, 1945 2,403,230 Nagel July 2, 1946 2,432,525 Kruse Dec. 16, 1947 2,447,482 Arnold Aug. 24, 1948 FOREIGN PATENTS Number Country Date 120,663 Great Britain Nov. 21, 1918 316,667 GreatI Britain May 22, 1930

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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2711310 *Jul 21, 1954Jun 21, 1955Morrill Byron SBaking and drying oven
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US6767206Sep 5, 2001Jul 27, 2004Outokumpu OyjArrangement and method for heating gas in a gas duct in connection with continuously operated sintering
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Classifications
U.S. Classification432/21, 432/48, 432/24
International ClassificationF23D14/00
Cooperative ClassificationF23D14/00
European ClassificationF23D14/00