US3329139A - Radiant heating apparatus - Google Patents

Description

July 4, 1967 L. A. VEZZOLI RADIANT HEATING APPARATUS Filed July 16, 1964 Fig.2

Fig. 3

INYENTOR LOUIS A. VEZZOLI ATTORN Y 8 Claims. (61. 126-92) The present invention concerns an apparatusfor heating by radiation and convection, which com-prises a radiant gas burner or radiating panels and is adapted to operate with either liquid or gaseous fuel.

There are presently known apparatus for heating by convection and by the radiation of a high percentage of infra-red rays. Such apparatus which operate either with gaseous fuel or with liquid fuel, comprise at least one radiation burner including generally a metallic or ceramic plate consisting of at least one element such as a plate pierced with holes for allowing the passage of the gaseous fuel mixture fed from a mixing device, said fuel mixture burning adjacent the surface of the plate and maintaining the radiating surface at the required temperature.

These known apparatus operate under pressure, since, on the one hand, the air/ gas mixing chamber of the burner or burners is under pressure and, on the other hand, the burners are mounted in apparatus the flue system of which is generally under overpressure relatively to the atmosphere.

In this connection, it should be noted that:

(a) In the case of a gaseous fuel, the flow speed of the air/gas mixture through the radiating plate depends on the pressure prevailing in the mixing chamber preceding the plate, said pressure being the higher as the supply pressure is greater and the holes in the plate smaller and/ or less numerous.

(b) In the case of a liquid fuel, the pressure in the mixing chamber is a similar one, but it is furthermore necessary for the fuel to be vaporized and to provide mechanical appliances in order to establish the necessary pressure for the air and/ or the fuel.

In the known apparatus operating under pressure, wherein a pressure is exerted directly on the fuel mixture or on one of its constituents, it is found that the flow speed of said mixture and the draft of air decrease when the mixture temperature increases (since the viscosity increases as a function of the temperature), i.e. when the apparatus comes to normal operation. The flow speed thus will decrease toward the critical speed at which backfire may occur through the plate, from the time of igniting until the normal operating temperature is reached; and the attendant decrease of the air draft results moreover in an increase of the value of said critical speed. Of course, the air draft must be suflicient when starting the use of the apparatus to enable the formation of an ignitable fuel mixture, and both the speed of the fuel mixture and the air draft are dependent upon certain constructive features of the injection system and the pressure of the fuel supply.

Further, the presently known forms of heating apparatus equipped with radiation burners are unable to operate at will with gaseous and/or liquid fuel without first undergoing substantial change in certain of the burner parts; the sizes of the passage openings in the plate can not present a constant single value for maintaining satisfactory results. It is however highly important, both for industry and household use, to provide, in a simple and reliable manner, for one and the same apparatus to operate satisfactorily with either a liquid or a gaseous fuel. It is also important that the apparatus operate satis- United States Patent 3,329,139 Patented July 4, 1967 factorily in case the supply of gaseous fuel undergoes pressure variations or changes of composition, as frequently occurs in the use of town gas.

According to the present invention, I have found it possible to substantially eliminate the above mentioned drawbacks by causing the flow circuit of the fuel mixture and the burned gases to operate under controlled suction; I have found that furthermore the natural draught of the hot burned gases is generally sufficient to produce a suitable suction. In fact, since the force of this draught increases from the point of ignition up to the normal operating condition of the whole circuit, it can be utilized to prevent the decrease of the flow speed through the plate which commonly occurs, in the pressure controlled apparatus, due to the temperature increase of the burner.

When operating with under-pressure or subatmospheric pressure, as just mentioned, the air draft is no longer dependent upon the fuel supply pressure and structural characteristics of the injection system as above indicated; Since the mixing chamber is under suction, a simple selec tion of the size of the gas and air openings will enable the same apparatus to operate satisfactorily with gaseous fuels and with most of the liquid fuels, without any modifications in the apparatus being necessary and, more particularly, without it being necessary to change the radiation plate. I have found moreover that this arrangement does not increase the backfire risks but, on the contrary, tends to reduce the risk of backfire.

Having in view the results above referred to, my invention provides a radiation and convection heating apparatus of the type mentioned comprising, in a suitable frame enclosure, ducts for carrying away the burned gases and forming heat convection surfaces, at least one radiation burner, said burner including at least one plate formed with openings for the passage of the fuel mixture, controllable means for supplying fuel to the burner and igniting means for the fuel. The frame enclosure comprises opposite to said burner a surface transparent to the infrared radiations, which surface .is tightly sealed in said enclosure, and adjacent to the burner, for instance above the burner, a fuel vaporizing tube or fuel pre heating chamber is inserted in a sealed manner in the path' i of the burned gases. The fuel is admitted into this tube through controllable injection means; the tube is open at one of its ends for admitting the air; and it extends into the mixing chamber directly upstream the radiation plate, to enable the air and gas or vapor mixture to pass through said plate. Further, an electrical resistance is arranged under the vaporizing tube to enable preheating of the fuel-air mixture when starting the operation of the apparatus and to assure the initial ignition of the mixture on the surface of said plate. The arrangement is such that the burner and the flue ducts are under suction during the heating operations; and this suction may be either direct or indirect.

In such an apparatus, at least one adjustable opening may be provided at the outlet of the vaporizing means or on the bottom of the mixing chamber, in order to take in a supplemental flow of fresh air, this additional air being adapted, under the increasing influence of the suction, to limit the temperature increase of the fuel mixture when the apparatus is in normal running condition.

This latter arrangement is particularly advantageous for operation with liquid fuels. The supplemental air intakes are less numerous and larger the farther they are spaced apart from the radiation plate, being at the outlet through.

Through any usual means, with the possible insertion above the apparatus of a known type of draft-cutter, the burned-gas discharge duct opens either directly into the atmosphere or into a chimney or hood. The apparatus according to my invention may also comprise a perforated screen, such as a grid for instance, arranged in front of and adjacent to the refractory plate as taught in United States Patent No. 3,107,720, this arrangement enabling the efficiency to be substantially improved and, more particularly, the radiating power of the radiation panels.

The admission of fuel may be adjusted, for instance by means of a carburetor, a pump, a venturi system or also by means of a pressure fluid, or better still, by means of calibrated perforations arranged under the header.

In order to obtain a correct igniting and combustion, the apparatus of the invention is operated as follows:

The electric resistance is first turned on, to heat the tubular supply and/or vaporizing enclosure during the preheating period required, said period being determined experimentally for the various fuels to be used and according to the proper characteristics thereof (vaporization temperature, etc.). This period is the longer as the fuel vaporizes at a higher temperature; for the gaseous fuels, the period is zero. When the preheating is sufficient, the fuel is admitted at the normal operating flow so as to become mixed with the air sucked in by the draft due to the electric resistance heat, and provides a combustible mixture which ignites upon passing through the refractory plate and contacting the electric resistance. Since in the use of liquid fuel the fuel tank may be simply under load, there is no need for any mechanical movable appliance for the fuel or air feeding. The combustion takes place adjacent the surface of the refractory plate: the electrical resistance may then be cut off and the apparatus will normally operate under subatmospheric pressure, without risk of backfire as the temperature increases, owing to the gradual increase of the value of the suction until the normal working condition is reached.

It has been found that, generally, to obtain a correct combustion and performances, the suction should attain a value of from 0.5 to 1.5 mm. of water column directly in front of the burner where the combustion is effected; as a rule, the required suction should be the greater as the fuel utilized is heavier. The excess of air required for the combustion and for avoiding the backfire risk is thus adjusted under the best conditions. The necessary draught, at the outlet of the apparatus, corresponds to this suction plus the pressure loss due to the flue circuits; this may therefore be adjusted up to 1 to 2.5 mm. of water column, approximately, and the higher as the fuel used is heavier. With the device according to the invention, it is therefore possible, at the point of sale of the apparatus or of a given use, to immediately adjust the apparatus for a given gaseous or liquid fuel. It is simply necessary to readily adjust the supply orifice of the fuel and the airsuction opening or openings to the values corresponding to said fuel, which are marked once for all as a function of preliminary tests effected in the workshop. It is of course no longer necessary to modify the radiation plate of the burner, since it has been found that, whatever the fuel utilized, whether gaseous or liquid, a correct operation and satisfactory results can be obtained with a constant size of the orifices for the passage of the combustible mixture; in the case of orifices of circular crosssection, their common diameter is preferably comprised between 1 and 1.5 mm. In all cases, these orifices are provided as numerous and close together as possible, account being taken of the construction technique and of the mechanical resistance desired for the radiation plate, so that the resistance of the latter will be as low as possible to the passage of the combustible mixture.

My invention will now be described by way of a nonlimitative example, with reference to the appended drawings, wherein:

FIG. 1 is a diagrammatic vertical cross-sectional view of an apparatus according to the invention, taken approximately along line I-I of FIG. 2;

FIG. 2 is a diagrammatic fragmentary cross-sectional view looking toward the front of the burner assembly, approximately along line IIII of FIG. 1; and

FIG. 3 is a fragmentary cross-sectional view taken approximately on line IIIIII of FIG. 2.

As illustrated in the drawing, the apparatus comprises an enclosure frame designated generally at 1, wherein is arranged a duct or flue 2 for conducting the burned gases to an outlet flue 2'. The duct or flue may be formed for instance of sheet metal and forms also much of the convection surface for delivering heat from the burned gases to the ambient atmosphere. The lower portion of the duct 2 is connected with a heating chamber 4 which comprises in its front wall an opening 5 into which is secured a sealed plate 6, for instance of glass, which is transparent to the infra-red radiation and is heat resistant. In spaced relation to said plate 6 and at the rear of the heating chamber is secured a sealed radiation panel 7 with its housing 8 forming the mixing or burner chamber which receives the combustible fuel mixture.

A fuel tank 9 is connected through a pipe 10 to a nozzle 11, a shut-off cook 12 being fitted on said pipe 10. The tank 9 is protected against heat by means of a baffle 13. When the fuel used is a gas, the tank 9 need not be used, and the pipe leading through cock 12 to the nozzle 11 is connected with a source of gaseous fuel.

A vaporizing tube, or preheating chamber 14 is tightly mounted in the path of the burnt gases, above the radiation plate 7. The inlet end 15 of tube 14 is vented to the atmosphere and accommodates also the admission of fuel through nozzle 11; the other end 16 of tube 14 opens into the inside of the mixing chamber and is provided with a supplemental air intake orifice 17.

An electric resistance 18 for preheating and igniting is arranged under the tube 14 in front of the upper portion of plate 7. The electric resistance may be substituted by any known convenient device for projecting and igniting alcohol on the radiating plate 7, thus serving both for preheating the tube 14 and igniting the combustible mixture having traversed plate 7.

In the example illustrated, a perforated metallic screen or grid 19 is arranged in front of the refractory plate, and at a very short distance therefrom, in order to increase the radiation power.

A draft regulator 20 is provided on the outlet flue 2' to stabilize the draught at the normal desired value, when necessary. The bottom of the casing may be formed with a (not illustrated) drain hole. The draft regulator or damper 20 may be substituted by a cap or hood arranged above the apparatus at a height such that it assures by itself the required draught.

The apparatus may carry a second cock means (not shown) for supplying it with gas, in order to allow switching from one type of fuel to the other by simply connecting or disconnecting the respective fuel lines.

I have used practically an apparatus comprising radiation elements (such as plate and grid) slanted towards the rear by 25 with respect to the vertical plane. The apparatus was operated easily with good results, with any one of the following fuels: kerosene, fuel-oil, natural gas, propane, butane-propane, town gas. I have found that by omitting according to the invention, the fan, the control box, the circuit-breaker, the thermostat and other operating and adjusting means necessary in the known apparatus, the operation under subatmospheric pressure was perfectly correct, the air/gas or air/vapor mixture being sufficiently cooled through the fresh-air intake of the pre-adjusted orifices 17.

It will be noted that, where regulations for the installation of gas heating apparatus provide for safety conditions which do not allow for a direct establishment of the required suction, it is possible to combine a pressure producing device with a pressure reducing device in the same apparatus.

The apparatus according to the invention may be used either for heating homes or for industrial heating purposes.

It is to be understood that various modifications may be brought to the apparatus as described above, Without departing from the spirit and scope of the invention. Thus, for instance, the vaporizer, instead of being arranged directly above the burner, may as well be located in any part of the discharge circuit of the burnt gases where it may heat up sufiiciently to assure the required heating for correct operation of the apparatus. It is also possible, on the other hand, by conveniently using the natural draught of the flues and the subatmos pheric pressure produced thereby (and by imparting to the same a smaller value than that mentioned hereinabove), to improve the results given by the known apparatus, operating under pressure; this improvement will be the more substantial as the fuel supply pressure is lower. Finally, in the case of a furnace or of a drying oven operating under a mechanical draught, it is sometimes possible to omit the plate transparent to the infra-red rays while maintaining under suction the front portion of the burner or burners.

What I claim is:

1. An apparatus for heating by radiation and convection, comprising a frame, an enclosure therein forming a heating chamber and flue means for conducting burned gases away from said chamber, at least one radiant gas burner, said burner including a chamber to receive a combustible mixture of air and a fuel in either gaseous or vaporized form and at least one refractory plate having orifices formed therethrough for conducting from said burner chamber streams of said mixture to be burned at the face of said plate, a fuel-air mixing tube having at one end thereof an opening admitting ambient air thereinto, having a portion thereof disposed in the path of flow of hot burned gases from said plate to said flue and having a leg thereof extending from said portion into said burner chamber, means for introducing fuel into said one end of said tube for admixture with air drawn thereinto, and means in said heating chamber for preheating said tube portion and igniting said streams to start the operation of said burner, there being means constituted at least in part by said flue means for producing and maintaining at the face of said plate a suction continuously drawing air and fuel through said tube, said burner chamber and said orifices.

2. An apparatus according to claim 1, said heating chamber having in a wall thereof opposite to said burner plate a sealed window transparent to infra-red radiations.

3. An apparatus according to claim ll, said preheating and igniting means comprising an electrical resistance element extending along and adjacent to said tube portion and the face of said burner plate.

4. An apparatus according to claim 1, said fuel introducing means comprising a nozzle for delivering into said tube a liquid fuel to be vaporized by heat in said tube portion.

5. An apparatus according to claim 1, said fuel introducing means comprising means for delivering into said tube either a gaseous fuel or a liquid fuel to be vaporized by heat in said tube portion, or a. mixture of such fuels.

6. An apparatus according to claim 1, further comprising air intake means for admitting a regulated supplemental flow of air into the passageway for said mixture between said tube portion and said burner plate.

'7. An apparatus according to claim 6, said air intake means comprising at least one adjustable orifice opening into said leg of said mixing tube.

8. An apparatus according to claim 1, further comprising a heat-resistant metal screen overlying the face of said refractory plate in closely spaced relation thereto for increasing the operating temperature and the radiation of said plate.

References Cited UNITED STATES PATENTS 1,760,319 5/1930 Risinger 126--95 2,153,379 4/1939 Lucas 12695 X 2,969,787 1/1961 Dupler 126-92 3,152,634 10/1964 Schotsman 158-71 3,199,568 8/1965 Baumanns et al. 126-92 3,203,413 8/1965 Hartzell et al. 12692 FOREIGN PATENTS 398,880 1/ 1909 France. 634,881 3/1950 Great Britain.

FREDERICK L. MATTESON, IR., Primary Examiner ROBERT A. DUA, Examiner.

Claims (1)

1. AN APPARATUS FOR HEATING BY RADIATION AND CONVECTION, COMPRISING A FRAME, AN ENCLOSURE THEREIN FORMING A HEATING CHAMBER AND FLUE MEANS FOR CONDUCTING BURNED GASES AWAY FROM SAID CHAMBER, AT LEAST ONE RADIANT GAS BURNER, SAID BURNER INCLUDING A CHAMBER TO RECEIVE A COMBUSTIBLE MIXTURE OF AIR AND A FUEL IN EITHER GASEOUS OR VAPORIZED FORM AND AT LEAST ONE REFRACTORY PLATE HAVING ORIFICES FORMED THERETHROUGH FOR CONDUCTING FROM SAID BURNER CHAMBER STREAMS OF SAID MIXTURE TO BE BURNED AT THE FACE OF SAID PLATE, A FUEL-AIR MIXING TUBE HAVING AT ONE END THEREOF AN OPENING ADMITTING AMBIENT AIR THEREINTO, HAVING A PORTION THEREOF DISPOSED IN THE PATH OF FLOW OF HOT BURNED GASES FROM SAID PLATE TO SAID FLUE AND HAVING A LEG THEREOF EXTENDING FROM SAID PORTION INTO SAID BURNER CHAMBER, MEANS FOR INTRODUCING FUEL INTO SAID ONE END OF SAID TUBE FOR ADMIXTURE WITH AIR DRAWN THEREINTO, AND MEANS IN SAID HEATING CHAMBER FOR PREHEATING SAID TUBE PORTION AND IGNITING SAID STREAMS TO START THE OPERATION OF SAID BURNER, THERE BEING MEANS CONSTITUTED AT LEAST IN PART BY SAID FLUE MEANS FOR PRODUCING AND MAINTAINING AT THE FACE OF SAID PLATE A SUCTION CONTINUOUSLY DRAWING AIR AND FUEL THROUGH SAID TUBE, SAID BURNER CHAMBER AND SAID ORIFICES.

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