US3521986A - Aspirated radiant tube combustion apparatus - Google Patents

Description

ASPIRATED RADIANT TUBE COMBUSTION APPARATUS Filed Aug. 23, 1968 P. M. ECKSTROM July 28, 1970 2 Sheets-Sheet l v INVENTOR. Pence M. EcKsneaM BY i7 A r raeusy July 28,1970 P. M. ECKSTROM 3,521,986

ASPIRATED RADIANT TUBE COMBUSTION APPARATUS Filed Aug. 23, 1968 2 Sheets-Sheet 2 I NVEN TOR. 55752 M. fc/(snean Arrofirv'r United States Patent Ohio Filed Aug. 23, 1968, Ser. No. 754,876 Int. Cl. F231 17/00 US. Cl. 431-157 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a tube type combustion apparatus having an eductor at one end of the tube and a burner at another end thereof. An ambient air inlet opening is provided adjacent the upstream end of the eductor. The opening has a valve means for varying its effective size so that the apparatus internal operating pressure and the analysis of its flue gas may be adjusted to desired levels, even though constant input burners and eductors are used. Ambient air drawn through the opening dilutes the hot combustion gases and maintains the eductor at a cooler temperature.

BACKGROUND OF INVENTION Most heating apparatuses of the radiant tube type use a plurality or bank of radiant tube elements rather than a single radiant tube element. Generally, fuel is supplied to the burner of each radiant tube element from a corn-v mon source or manifold and is regulated by a master valve. Usually the burners are not provided with individual fuel control means. Also, combustion air is supplied at a constant rate to prior tube heating apparatuses by an eductor means which is not readily adjustable, especially with respect to each individual eductor. Due to the fact that the components of the heating tube assemblies may vary slightly from one another, the cumula tive effect of these variances may cause a substantial difference between the aerodynamic performances of conjoining tube assemblies. As a result of these possible variances, individual adjustability of each tube assembly is required so that uniform optimum performance may be obtained.

The prior art means for adjusting the performance of an inefficiently operating tube assembly involved removing the eductor spud or orifice member and substituting therefor one of a different size. Although the replacement spud size could normally be selected so as to give an improved result, burner efficiency was not optimized every time by the first replacement. This process was time consuming and could not be performed while the apparatus was in operation or even immediately after shut-down while the eductors were still hot. On occasions, the first replacement did not produce satisfactory results and the apparatus had to be shut down for one or more subsequent changes. Since the number of available standard spud or orifice sizes was limited, optimum performance was often compromised when it could be obtained only with a non-standard size. The problem of adjustment occurred during the initial operation of the apparatus and recurred whenever the fuel input to the burners was "ice changed to meet substantially different operating temperature requirements.

Overheating of the eductor assembly is another problem that has not been satisfactorily solved by prior art heating tube assemblies. The problem is more acute in jet pump eductors having high entrainment ratios between the volume of hot combustion gases educted and the volume of cool educting air. It is acute also when a fan type eductor is subjected to an excessively hot environment. In each instance, the eductor assembly had to be made of a more heat resistant and costly material due to the lack of adequate cooling. Furthemore, the heat given off by the hot eductors, located on the outside of the heating apparatus or furnace, makes the Working conditions around the furnace less tolerable to the operator and may even present a fire hazard.

OBJECTS AND ADVANTAGES It is an object of this invention to produce an aspirated tube type combustion apparatus having an adjustable vent means, between the burner and the eductor, for fine tuning the apparatus to obtain maximum combustion efficiency.

It is another object to produce such an apparatus which is vented adjacent its eductor so that ambient air is drawn through the vent for cooling the eductor and subjacent parts without an equivalent drop in the efliciency of its hot gas eduction.

It is another object of this invention to produce an aspirated heating tube which is particularly adapted for use in a 'bank of such tubes having a common or master control.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of a tube type combustion apparatus of this invention with end portions broken away to show the burner and interior details of the jet pump eductor.

FIG. 2 is an enlarged perspective view of the vented jet pump eductor assembly shown in FIG. 1 illustrating a throttle member confronting the ambient air vent opening and mounted so that it may be moved towards and away from this opening to vary its effective size.

FIG. 3 is a view of another embodiment of an eductor similar to that shown in FIG. 2, but with a pivoted plate means for varying the effective size of the vent opening.

FIG. 4 is another embodiment of a tube type combustion apparatus similar to that of FIG. 1, but with a fan type eductor having a vent with a plurality of openings around the periphery of the upstream end of the eductor. The effective size of these openings may be varied by moving a cooperating sleeve having matching openings.

DETAILED DESCRIPTION OF THE DRAWINGS Referring to the drawings, particularly to FIGS. 1 and 4, there are shown combustion apparatuses 10 and 12, respectively, each having a tubular combustion chamber 14 with a burner 16 adjacent one end and an eductor assembly 18 or 20 coupled to another end. It is to be understood that, although the invention is shown and described with reference to a single straight radiant tube, it may be used on tubes having other forms, such as U- shaped tubes or tubes having three legs, as disclosed by 3 assignees Pat. 2,860,864 by P. L. Knight issued Nov. 18, 1958. Also, the tubes may be operated at lower than radiant temperatures or used as immersion tubes for heating liquids.

The rate at which fuel is fed to the burner 16 may be constant and preset to provide the desired operating temperature. Normally the air for combustion is drawn into the tube 14 through an open annulus between the burner body and the tube by means of negative pressure produced by the eductor assembly 18 or 20. With this arrangement, the amount of combustion air flowing into the tube is controlled by the eductor assembly 18 or 20. In installations where the opertting pressure within the combustion tube would be excessively low, if the combustion air were supplied solely by the negative pressure of the eductor, combustion air may be supplied under positive pressure at the burner end of the tube.

The jet pump type eductor 26 shown in FIGS. 1 and 2 and the fan type eductor 28 shown in FIG. 4 are com monly used to produce the low or negative pressure at the outlet end of the combustion tube 14. The jet pump eductor 26 preferably comprises a 90 elbow having a long radlus bend of the type commonly called a sweep elbow. One end of the elbow is fastened to an outlet end of the combustion tube by means of a coupling such as a clamp band 30 made of heat resistant material. The outlet end of the eductor may be coupled to an elongated throat member 32 which has a gradually increasing crosssectional area from its elbow end to its outlet end. Adjacent the heel of the elbow bend, an apertured boss 34 is provided to contain a spud 36 for injecting the eductor air into the body of the eductor. The spud 36 is removably fastened in the aperture, such as by threaded means, so that the outlet end of the spud is recessed from the flow lines of the gases entering the eductor upstream from this spud. The outlet end of the spud is level with the centerline of the eductor inlet. Also, the axis of the spud is aligned with the centerline of the eductor outlet so that the eductor air is directed outwardly along this latter centerline. The inlet end of the spud 36 is connected to a supply line 38 for furnishing educating air or gases under positive pressure to the eductor. The spud orifice size and the pressure at which the educting air or gases are supplied to the spud are selected so as to draw preferably about 50 to 100% excess of combustion air at the burner when the eductor venting means is closed.

.The venting means 39 for the eductor 26 is located at least slightly upstream from the eductor spud and comprises One or more openings 40 in the eductor body having a closure member 42 for adjusting the effective size of these openings 40 (see FIG. 2). The closure member 42 is a circular metal disk which has an upturned edge and which is of suflicient size to completely cover the openings 40. It is mounted in confronting relationship to the openings by means of a threaded stud or cap screw 44 which is screwed into a threaded aperture in the web between the two openings 40. The total effective size of these openings may be varied by rotating the disk so that it moves either towards or away from these openings. A locking means such as self locking threads holds the disk firmly in its set position.

The eductor assembly 56 shown in FIG. 3 has a jet pump type eductor similar to that shown in FIGS. 1 and 2 but with a different adjustable venting means. Its venting means 58 comprises a closure plate 60 which may be pivotally or slidably mounted on the eductor so that it may be laterally positioned partially or wholly in front of the vent opening 62 by means of a handle lug :64 integrally attached to the plate 60. A set screw 66 is provided to lock the plate 60 in any desired position.

The eductor assembly 20 shown in FIG. 4 has a fan type eductor 28 with a centrifugal fan in a fan housing 70. The capacity of the fan may be selected so that the eductor assembly 20 is capable of serving more than one combustion tube 14. In any case, a venting means 72 is provided between each combustion tube end and the eductor 28. The venting means 72 may comprise a plurality of openings 74 around the periphery of the upstream end of the eductor assembly 20. The ambient air entering through the peripherally disposed vent openings tends to remain adjacent the inner perimeter of the subjacent eductor duct to provide improved cooling thereof. A clamp band or movable sleeve 76 having corresponding openings is circumposed over the openings 74 so that by moving the sleeve 76 the effective size of the openings 74 may be varied readily. Preferably the sleeve is firmly held in its selected position by a set screw or the like. It is to be understood that, although each specific venting means 39, 58, or 72 is shown and described with reference to a specific eductor, its use is not restricted to that specific eductor. These venting means may be interchanged and used on either type eductor or on similar eductors.

The eductor assemblies 18, 20, and 56 are engineered so that about 50 to excess of air for combustion will be supplied to the burners 16 when the venting means 39, 58, and 72 is fully closed. The vent openings are sized so that when the vent closure members 42, 60, and 76 are in their fully open position, the theoretical oxygen content of the flue gases would be zero. This permits the venting means for each combustion tube to be adjusted so that the oxygen content in the flue gases, measured at the exit end of the tube, will be ideally from 1-3%.

Under normal operating requirements, the capacity of the eductor and the size of the vent openings are established to produce a ratio, between the ambient air flowing through the venting means and the combustion gases flowing out of the tube, of about 1-3 parts ambient air to 1 part combustion gases measured at standard temperature and pressure. In installations having high fuel input requirements, the capacity of the eductors and the size of the vent openings may be increased so as to provide adequate cooling of the eductor assemblies.

While the best modes known to us to carry out this invention have been described in connection with specific arrangements of parts, it should be expressly understood that various modifications of the above will be apparent to those skilled in the art without departing from the scope of the invention which is defined only by the appended claims.

I claim:

1. A tube type combustion apparatus compnsing an elongated combustion chamber tube having at least two ends, a burner at one end of said tube for supplying combustible fuel to said tube, a jet pump type eductor in fluid communication with an opposite end of said tube for causing combustion air to flow into the burner end of said tube and for educting hot combustion gases from said tube, and a vent means adjacent said opposite end for the admission of ambient air, said vent means including a closure member cooperating with a vent 01ifice, said closure member being movable to an infinite number of fixed positions for varying the effective size of said orifice to control the amount of combustion air flowing into the burner end of said tube.

2. A tube type combustion apparatus comprising an elongated combustion chamber tube having at least two ends, a burner at one end of said tube for supplying combustible fuel to said tube, an eductor at an opposite end of said tube for causing combustion air to flow into the burner end of said tube and for educting hot combustion gases from said tube, and a vent means adjacent said opposite end for admission of ambient air, said eductor having suflicient capacity to provide combustlon an at a rate of 50-100 percent in excess of stoichiometric proportions with respect to said fuel at the burner when said vent means is fully closed, said vent means being sized so that the amount of combustion air may be reduced to provide an oxygen content in the flue gases of 5 6 only about 1-3 percent, said vent means including a clo- References Cited sure member cooperating with a vent orifice, said closure UNITED STATES PATENTS member being movable to fixed positions for varying the 1,144,785 6/1915 Rector 431 157 effective SiZe 0f Said vent orifice. 2 220 5 2 1 1940 Ruckstahl 2 9 3. An apparatus according to claim 1 wherein the ca- 5 ,22 31 12 1940 Hepburn 91 pacity of said eductor and the size of said vent means 3,163,202 12/1964 Schmidt et a1. 431--157X are such that under normal operating conditions the ratio between the volume of combustion gases educted and EDWARD Pnmary Exammer the volume of ambient air measured at standard tem 10 US CL perature and pressure is between about 1:1 and 1:3. 126 91 ;43 1 3 53

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