MXPA98003001A - A gas device to heat liquid - Google Patents

Abstract

The present invention relates to a gas apparatus for providing heat transfers to a fluid with at least one premixed atmospheric burner arranged to operate under natural draft, the burner includes: fuel supply means for receiving a flow of gaseous fuel from a source thereof and operate in response to the fuel flow to exhale and mainly combine ambient air to form an air-fuel mixture to supply a plenum chamber, the plenum chamber has a burner head with a plurality of flame openings arranged for closing one another ensure cross ignition, means of ignition associated with the flame openings to ignite the air-fuel mixture to generate flames, a combustion chamber having a surface that includes the outer surface of the burner head and which is connected to a discharge duct in fluid communication with the environment and in heat exchange relation with the fluid, the gas apparatus comprises a cavity in fluid communication with the external environment and a wall which is connected to the plenum chamber and is arranged to separate the plenum chamber from the cavity, furthermore characterized in that the wall has a plurality of additional openings, so that the communication of fluids between the plenum chamber and the cavity is limited to the flame openings and the additional openings, the ratio between the general area of the additional openings of flame and opening and the energy input to the Burner is a value that comprises between 200 and 500 mm2 / kW to obtain flames detached from the outer surface of the burner head so that the heat transfer is substantially convective and the width / depth ratio of each of the flame openings and of additional openings are selected to prevent the return of the

Description

A GAS DEVICE FOR HEATING LIQUIDS The present invention relates to a device that operates gas to provide the transfer of a substantially convective heat to a liquid, and which operates with at least one premix atmospheric burner, arranged to operate under a natural current; said burner includes means for supplying fuel to provide a mixture of gaseous fuel and air to a plenum chamber having a burner head with a plurality of flame openings, ignition means for igniting the air-fuel mixture, and a combustion chamber with a surface that includes the burner head and a discharge conduit in communication of the liquid with the environment and in a heat exchange relationship with said fluid.

The liquid heating devices of the aforesaid structural configuration are well known and of usual household use. They include devices for heating water exclusively for sanitary use (also commonly known as heaters or water heaters), devices for producing hot water for sanitary use and for heating rooms REF: 27319 (also called combination heaters) and also heaters to produce hot air (known as "stoves").

To satisfy the constant demand of the customers, so that we obtain the maximum security when we use the devices of which we speak here, at present great attention is paid to improving the security in cases in which the environment that surrounds the device contains substances volatile flammables. This happens quite frequently in some countries, including the United States, where in many houses liquid heating devices are installed in basements, garages, or other areas that also serve to store fuel or other flammable substances: in case you are Flammable substances spill for some reason, their vapors would surround the heating device, creating the risk of producing a fire.

In fact, such vapors produce, with the air, an explosive or highly flammable mixture that, to reach the combustion chamber could be burned by the pilot's flame or by the flames of the main burner when it is ignited; The harmful consequences of an explosion are easily imaginable. In the event that the flammable mixture in the combustion chamber is ignited, the flame will spread to the flammable liquid spilled and its containers, threatening to set the house on fire.

It should also be noted that the risk of flammable vapors entering the combustion chamber is greater in the case of liquid heating devices with a storage tank. In this case, the hot water that is contained in the tank of said device exchanges heat with the air in the exhaust duct and can heat it as to create the "chimney effect" in the duct, even if the burner is off. As a result of this, flammable vapors in the environment surrounding the device would be absorbed into the combustion chamber with all the disastrous consequences described above.

Various models of heating apparatuses are known having the above-described purpose of satisfying the demand for greater safety and avoiding the risks that have been described; they include devices that prevent the liquid from being exchanged with the surrounding environment; the air is absorbed, and the exhaust gases leave, through the pipes that pass in the walls of the room and communicating with the outside. The main disadvantage of these devices is that they require structural modifications of the gas devices, with the significant increase in costs. The device must be air-tight, to allow exhaust gases to escape and enter air, normally a fan or a blower must be installed.

U.S. Patent No. 5,317,992, discloses a gas heater in which combustion occurs at, or near, a combustion surface maintained at a subatmospheric pressure, using a surface burner that acts in a combustion chamber sealed under a natural current. This heater does not solve the problem of the ignition of flammable vapors; When the main burner is lit, the combustion surface in contact with the flame reaches temperatures high enough to ignite the mixtures of flammable fuel-air vapors on the outside of said combustion surface, and the flame will spread to the flammable liquid and its containers, threatening to set the house on fire. In addition, the combustion surface, as wide as to maintain the combustion load at levels of 500 to 2000 Joules / m2 hr. and made of metallic wire, preferably inconel 601, or ceramics to resist high temperatures, is very expensive compared to the aluminized steel sheet that is used in the usual water heaters.

The object of the invention is to provide a gas device for heating liquids that is safe even when used in an environment containing volatile fuel substances, in addition to avoiding the disadvantages of previous modern devices, while obtaining reduced emissions of oxides of nitrogen (NOX), and carbon monoxide (CO).

This object is achieved, according to the invention, because the gas device as defined above further comprises a wall connected to the plenum chamber and arranged to separate the combustion chamber from the environment, to limit the communication of liquids with the openings of the flame and with additional openings, if any, in said wall and that the ratio between the general area of the openings and the energy intake to the burner is between 200 and 500 m2 / kw, the width / depth portion of each opening is selected to avoid the flame return and the openings are arranged so close to each other that they guarantee cross ignition.

If additional openings are not provided, the amount of primary air is large enough to form a hyperestiquiometric air-fuel mixture, i.e., a mixture in which the primary air exceeds the amount necessary to provide complete combustion of the fuel.

If additional openings are provided, the amount of primary air is less than the amount required to complete the combustion and the primary air is induced to enter the combustion chamber through said additional openings. These additional openings also have the function of causing any flammable vapor from the environment to be ignited in the combustion chamber, as explained in more detail below.

The discharge conduit in the fluid communication with the environment is arranged to produce a substantially atmospheric to subatmospheric pressure in the combustion chamber, depending on the embodiment of the invention and the operating conditions. This effect is due to the flow from the combustion chamber to the environment of combustion products when the burner is on, or there is hot air between heating cycles.

Subatmospheric pressure, if any, cooperates with the plenum pressure in the burner mixing chamber to cause a mixture of air / gas, or secondary air / vapors, if additional openings are provided to flow through the openings of the flame to the combustion chamber.

Preferably, the openings of the flame, plus the additional openings, when presented, have a general area to obtain an average air transit speed or mixtures, above 0.5 m / sec.

Any mixture, air-fuel, air-fuel-flammable vapors, flammable air-vapors that are introduced into the combustion chamber, are immediately ignited by at least one ignition element and, due to the speed of the exit, the flames are separated from the surface of the burner head or the separation wall, so that the temperature of the burner head and the wall never reaches a value such as to burn any mixture on the other side.

In the case of a fully premixed burner, ie a burner with a combustion chamber substantially sealed to the environment, the flames would rise without specific flame-holding methods, due to the high speed of the mixture flowing from the openings of the flame. the flame and the low burning speed. To prevent flame instability, different methods are used in the embodiments of the invention described below.

In order to better understand the invention, its features and its advantages, a few embodiments thereof are described below, by way of non-limiting examples in connection with the accompanying drawings, in which Figure 1 is a longitudinal section of a device for heating liquids to gas, according to the invention; Figure 2 is an enlargement of a detail of figure 1; Figure 3 is a sectional view of the device of Figures 1 and 2, taken from III-III of Figure 2 with an enlarged part; Figure 4 is a longitudinal section of a variant of the device of the invention; Figure 5 is an enlargement of a detail of Figure 4; Figure 6 is a section of the device of Figures 4 and 5, taken from VI-VI of Figure 5; Figure 7 is a longitudinal section of another variant of the device of the invention; and Figure 8 is an enlargement of a detail of Figure 7, with an enlarged part; Figure 9 is an enlarged section of the device of Figures 7 and 8, taken from IX-IX of Figure 7; Figure 10 is an enlarged section of the device of Figures 7 and 8, taken from XX, of Figure 7. With reference to the drawings mentioned herein, a gas device for heating liquids in accordance with the invention. The gas device 1 is of the self-supporting type, that is, it can be placed on the ground or other surface, is elliptical about an axis L, and includes a storage tank for hot water 3, which surrounds an exhaust duct 5 and exchanges heat with it. In this example, and in the variants that are offered later in this description, the device of the invention has the purpose of heating water; however, as explained above, it can also be used to heat air, only with a different dimension of the surface that transmits heat to said air. The tank 3 has a side covering 4 which is thermally insulated by a layer 6, constituted in this embodiment by an insulating foam, and covered by an external sheet which is not shown in the drawings. A deflector 8 is installed in the duct 5 to agitate the exhaust gases that rise through the duct 5 and improve the heat exchange between the exhaust gases and the tank 3 liquid.

The device has a glass fiber cover 9. A lower part 10 of the insulating coating is also made of glass fiber. At the bottom of the device, the fiberglass is sealed to a base 11 to be air-tight. The base 11 has a series of feet 12, on which the device rests on the ground.

The lower part of the tank 3, from which the duct 5 extends, is vaulted and defines the roof of a combustion chamber 20, which have the shape of a substantially spherical cover. This chamber is closed at its bottom, that is to say in front of the spherical cap, by a partition wall 21 having a composite metal profile (see Figure 2) formed by sections, for example of laminated metal, with different functions which are now will describe in detail.

The wall 21, which is elliptical in this case, includes an annular part 21a, which extends radially from the liner 4 towards the axis L of the device, and is joined to a frusto-conical part 21b, which in turn is traced by an elliptical part 21c . An upper disc portion 21d closes the central part of the wall 21. In this embodiment, the portions 21a and 21b of the wall 21 are formed in one piece, while the portions 21c and 21d are adjusted to form the composite metal structure of the wall 21. All the joints between the various parts of the wall 21 are air tight. The part 21c of the wall has the property of extending the slot-shaped openings, or the openings of the flame 39 so that the gas-air mixture enters the combustion chamber so as to be ignited by an ignition element. More specifically, the openings of the flame 39 are placed in groups, like a crown, around the periphery of the elliptical part 21c, with the part 21c itself constituting the head of a plenum chamber of a burner 22 into which the above-described gas-air mixture, by means of an induction conduit 23, which may also be made of a metal foil. In this embodiment and in the variants described, only one main burner is used. However, the invention also applies to gas devices having more than one main burner. The frustoconical portion 21b of the wall 21 has a group of additional openings or grooves 50 that have substantially the same shape and dimensions as the openings of the flame 39.

In the invention of the device, a cavity 28 is defined behind the wall 21 which is in fluid communication with the external environment by means of an opening 33 in the lower part 10 of the cladding 4.

The cavity 28 contains the final portions of the two conduits 37 and 38 that carry gas to the nozzles 34 and 36 to release gas to the burner 22 and to the ignition element 25, which in this case is a pilot burner. For this purpose, the latter also has an induction conduit 35, which is functionally equivalent to the induction conduit 23 of the burner 22, is sealed to the parts 21a of the wall 21 and has a flame opening, not shown, of dimensions similar to each of the openings of the flame 39. A thermocouple is provided for the control of the flame, but it is not illustrated. A gas control unit 40 includes an effective valve in both conduits 37 and 38 to regulate gas flow therethrough, and is connected to a thermometer 41 to measure the water temperature in tank 3.

In a preferred embodiment of the invention, in a wall 21 of a metal sheet having a thickness of between 0.4 and 0.6 mm, the maximum width of the slots 50 and the openings of the flame 39 varies between 0, 4 and 0.5 mm and its space, that is to say the distance between the centers of the adjacent slots or openings of the same group, is between 1 and 1.5 mm; furthermore, the distance between groups of adjacent slots 50 or openings 39, should be a maximum of about 15-20 mm for reasons that will be better explained later, in the description of the operation of the device.

In another embodiment of the invention, the openings of the flame and / or the additional openings are circular holes having a diameter comprised between 0.4 and 0.9 mm. In any of the embodiments, the depth of the openings is the same as the thickness of the wall 21.

If the wall 21 is made of laminated metal parts, the openings of the flame 39 and the additional openings 50 can be formed as substantially parallel branches with bent lips having an Index of width / depth comprised between 1/5 and 1/10, depending of the thickness and thermal conductivity of the metal sheet. In this case, the central distance between two adjacent flame openings 39 or two adjacent additional openings 50, does not exceed 6.0 mm, and the distance between two openings 39 or two additional openings 50, measured along the direction longitudinal of the apertures, is less than 20.00 mm.

Finally, it should be appreciated, since the values expressed here may vary, depending on the construction of the device (shape, dimensions, etc.), it can be indicated, in general, that the Index between the general area of the openings of the flame 39 and the slots 50 and the burner's power outlet must be between 200 and 500 mm2 / k to obtain an average transit speed, of air or mixtures, above 0.5 m / sec.

With regard to the heating of the liquid, the operation of this embodiment and the variants that follow, will be explained later, but very briefly, since it is basically the same as for conventional devices, however, more attention will be paid to the characteristics that have to do with the safety of the device in the case of volatile flammable substances present in the surrounding environment.

The gas emitted from the nozzle 34 draws air, the so-called primary air, and forms a gas-air mixture in the plenum of the burner 22 as a result of the Venturi effect generated by the induction conduit 23. The gas-air mixture flows out through the openings 39 and ignited by contact with the flame of the ignition element 25, which is the flame of the pilot burner. The flames of the burner heat the water in the tank 3. As already indicated, the gas flow is regulated by the air control unit 40 in a known manner. This is all that needs to be explained at the moment of the way the device heats the water; it should simply be added that this embodiment of the invention in a device with an atmospheric burner of a partial premix type, i.e. in which the flame in the combustion chamber 20 burns both the primary gas-air mixture of which has spoken, generated by the Venturi effect, as the combustion air, the so-called secondary air, which gets into the combustion chamber 20 through the opening 33, and the slots 50, as a result of the subatmospheric pressure produced in the combustion chamber 20, by the thrust of exhaust gases or air, heated by the hot water that is in tank 3, flowing through conduit 5.

As regards the safety of the device, in the case of flammable volatile substances that are in the surrounding environment, two things can occur: first, when the main burner 22 is on, secondly when only the pilot burner 25 is on.

In the first case, the volatile flammable substances are brought to the cavity 28 from outside the device as a result of the chimney effect created by the main burner; a part of these substances is combined with the gas emitted from the nozzle 34 and passes through the openings 39 to the combustion chamber, where it is burned as explained above: in this case, the combustion that takes place it is not ideal for the burner, since the volatile substances will have altered the optimal gas-air mixture; however, it will not affect the overall operation of the device.

In addition, a second part of the volatile substances in the environment surrounding the device will enter the chamber 20 through the slots 50, and will also be ignited by the flames burning above the openings 39 and the pilot burner, due to the reciprocal position of the openings 39 and the slots 50. In addition to these two portions of volatile substances that enter the device, a third part also enters the combustion chamber 20 by the pilot burner which is always burning and whose operation is the same as that of the main burner.

The device of the invention is, therefore, clearly in conditions of maximum safety when the main burner is activated and doing its function of heating the fluid in the tank 3.

Returning to the case in which the volatile flammable substances fill the environment surrounding the device when the burner is not lit and there are no flames in the openings 39, events occur in this way.

Only the flame of the pilot burner 25 is burning in the combustion chamber, there is a natural current in the combustion chamber and in the exhaust gas discharge conduit 5, due to the heat generated by the pilot burner and the heat exchanged between the water in tank 3, and the air in conduit 5. Volatile fuel substances, mixed with air, and thus entrained within the device and within its own combustion chamber 20 by means of the only possible route, is to say by means of the slots 50 and the openings 39 in the annular part 21a and the elliptical part 21c, respectively of the wall 21.

In either case, either passing through the openings 39, or of the slots 50 (see the relative relative positions of these parts in Figure 2), at least a fraction of the flow of the volatile fuel substances entering the device will immediately touch the flame of the pilot burner 25, this fraction will be ignited by the pilot burner, then generating a flame that will spread through the entire combustion chamber to the groups of openings 39 and slots 50. This result, ie , the expansion of the flame to all the openings and slots provided, according to the invention, is promoted by the arrangement of the openings in groups distributed around the frusto-conical part 21b and the elliptical part 21c of the wall 21, and is made particularly effective in this embodiment of the invention by the dimensions of the openings, as indicated.

The role of the additional openings or slots 50 should be emphasized in this context: the dimensions of the slots should be such as to prevent any return of the flame through the wall 21, which could leave the device with the unfortunate effects that may occur. detailed at the beginning of the description. For this reason, the grooves 50 have substantially the same dimensions as those of the openings of the flame 39, which are designed so as to prevent the phenomenon of return of the flame, since they act as escapes for the flames of the burner. The design of the openings in such a way as to prevent the return of the flame is well known to technicians with experience in the field. The openings with the width / depth, or diameter / depth indices as mentioned above, satisfy the requirements necessary to prevent the return of the flame.

An additional factor contributing to the safety of the device is represented by the fact that the mixture of air and flammable volatile substances is immediately ignited after the wall 21: this prevents the formation of dangerous explosive mixtures in the combustion chamber.

The relative position of the openings of the flame 39 and the secondary air, or the additional openings 50 must achieve two objectives: first, to contact, as soon as possible, any flammable mixture with flames of the main burner during ignition periods; Second, increase the air content of the primary fuel-air mixture to the front of the flame to reduce the NOX content, in the exhaust gases, also for burners, particularly premixes.

A variant of the embodiment of the invention described above is illustrated in Figures 4, 5 and 6 which show a device for heating liquids in which the components are the same from the structural and functional point of view, as those of the previous embodiment maintains the same reference numbers.

In this variant of the invention, the atmospheric burner is of a type of total premix, that is, of a type in which the combustion chamber 20 only burns a gas-air mixture, which is produced by means of a Venturi-type tube 60 which is housed in the body, or in the plenum chamber, 61. The tube 60 is the only form of fluid communication between the combustion chamber and the external environment, by means of the flame openings 39 in the body 61 on one side and an opening 63 on the lower part 10 of the device with its mouth closed to the lining (see Figure 4) on the other side, with this type of configuration, the flames in the combustion chamber 20 burn only the gas-air mixture provided by Venture tube 60, without the need for an additional flow of air in chamber 20, as required in the previous example. The pilot burner 25 is a copy of the main burner, with reduced dimensions and has a group of flame openings identical to the main burner.

In this embodiment of the invention, the combustion chamber is basically sealed with respect to the environment outside the device, and the burner body 61 is formed by a wall 61a, of which, the upper part has a number of openings 39 in adjacent groups arranged substantially the same as in the previous embodiment, as shown in Figure 3, but in an extended elliptical ring, and a flange 61b.

The Ventura tube 60 receives gas from a nozzle 34 and a pilot burner 25 goes inside the housing 61, together with associated openings 39.

The operation of this variant will also be considered only with respect to the safety of the device in the case of the presence of volatile combustible substances in the surrounding environment, since the heat of the water is transported in almost the same way as described previously; it only needs to be noted that in this variant the gas-air mixture produced in the Venturi tube 60 expands to the housing 61 and flows from there to the combustion chamber 20 via the openings 39 in the upper part of the wall 61a.

In the event that volatile flammable substances are present, in the environment surrounding the device, there are two possibilities also in this case: the first occurs when the water is being heated in the tank, and therefore the flames of the main burner are present in the combustion chamber, the second when only the pilot burner 25 is lit.

In the first case, the volatile substances are mixed with the gas leaving the nozzle 34 and pass through the Venturi tube 60 to the housing 61 and from there to the combustion chamber 20 by means of the groups of openings 39 that They act like the head of the burner. The mixture of gas, air and volatile flammable substances is burned to heat the water that is in the tank and, although this combustion is not ideal, for the reasons that have been explained, the operation of the device is not affected significantly.

In case there are volatile flammable substances, on the other hand, when the nozzle 34 does not carry gas to the Ventura 60 pipe and therefore there are no flames in the combustion chamber, but only the pilot burner 25 is ignited, the substances towards the combustion chamber by the "chimney effect" of form, and for the same reasons as explained above: they enter therefore the Venturi tube 60, the casing 61 and from there to the combustion chamber by means of grooves 39; at least a fraction of these substances will come into contact with the flame of the pilot burner and will also ignite in this case. The resulting flame will extend to all groups of openings 39 placed in a ring shape as described in the previous example, and therefore eliminating flammable substances.

In this second embodiment of the invention, the dimensions of the openings are again designed to prevent the return of the flame to the casing 61, both because they act as the head of the burner and because they prevent the flame from expanding to the flammable substances that they are outside the device.

The same numerical values that were treated in the previous example are also relevant in this case for the structure of the housing 61 and in particular for the thickness of the wall 61a, as well as the width of the openings 39 and the distances between the adjacent groups from the same.

The openings of the flame have a general area such as to obtain an average speed of transit, of air or mixtures, above 0.5 m / sec. to prevent flame instability, in this embodiment, the same method as that followed in U.S. Patent No. 5,385,467, of the same inventor, is used. This method comprises the steps of unloading the mixture from a perforated surface of a basically circular geometry comprising a peripheral grooved area and a basically solid central area, completing the combustion in a thin lamellar flame separated from the head of the burner, so that the temperature of the wall never reaches the value necessary to ignite any mixture on the other side.

Any mixture, air-fuel, air-fuel-flammable vapors, flammable air-vapors present in the combustion chamber, are immediately ignited by the pilot burner. To obtain this immediate ignition, the distance of the group of openings of the flame 39 furthest from the pilot burner 25 in the embodiment of the invention does not exceed 250 mm.

Finally, in addition to the two embodiments of the invention described so far, a third variant that combines some structural details and operating principles of the previous two is also described below; in this case, again, as shown in Figures 7 to 10, any component in terms of structure or operation, as in the first two embodiments, will have the same reference numbers. This third variant of the invention has a wall 81 with a composite metal profile similar to that of the wall 21 described above. This wall, again, includes an annular part 81a, which extends radially from the lower part 10, of the device, and is connected to a frustoconical part 81b, which in turn is traced by an elliptical part 81c; this part is closed by a disc upper part 81d. The portions 81c and 81d are connected to each other at a few connection points 82 along their peripheral edges. The connection points 82 are made of short pins, which keep said peripheral edges spaced apart at a distance of about 7 mm and support an intermediate metal ring 81c which is of a thickness of about 3mm, so as to form two flame openings in the form of ring with a width of approximately 2mm and a depth of approximately 15mm. The connection between the part 81b and the elliptical part 81c is gas-tight, and the annular part 81a of the wall 81 has no openings or slots. Therefore, the combustion chamber 20 is in fluid communication with a cavity 88 formed between the wall 81 and the base 11 of the device only through the above-mentioned ring-shaped openings.

In this case, therefore, the device functions as a "fully premix" type burner, in which the flames in the combustion chamber burn a gas-air mixture produced by the Venturi effect in the tube 60, of a form entirely similar to the view in the second embodiment of the invention. In this case, the ignition element 25 is an electrode with two functions at the same time: spark ignition electrode or an electrode for detecting the ionization current for flame control. In this context, it should be noted that the combustion air that is mixed in the Venturi tube 60 is carried by means of the air duct 89, which extends along a generatix of the device of the invention, incorporated in the insulating layer 6. of the same. The conduit 89 extends from a socket 87 adjacent the cover 9 of the device, to the intake of the Venturi tube 60. The nozzle 34 is disposed inside this conduit, frontally to the Venturi tube 60.

In this embodiment, when the burner goes out, the air that is heated in the same way in the duct 5 and in the duct 89, due to contact with the wall of the hot water tank, quickly reaches the same temperature in both ducts. Therefore, the thrust on both sides of the U-shaped duct 89 + 60 + 88 + 20 + 5 is balanced, and any air flow that will pass, is stopped, any flammable vapor intake in the chamber Combustion between heating periods and any risk resulting from fire are avoided in this way.

During the heating periods, first, a spark between the electrode 90 and the lips of the ring-shaped flame openings between the portions 81c and 81d ignite the existing mixture from the same openings with or without flammable substances, then the flames remain under the control of ionized current, carried by the same electrode 90, which is in electrical contact by means of an insulated wire 91 with a gas control unit 40 '. The control unit 40 'incorporates a control valve similar to the control valve of the previous embodiments, and an electronic flame and ignition control that operate by battery.

To reduce the resistance to air flow, air-gas mixtures and exhaust gases, in this embodiment a new design of the conduit 5 and the deflector 8 is provided, which, without changing the diameter of the connection of the Exhaust pipe, also improves the efficiency of the device in which the reduction to a minimum of losses in reserve is guaranteed by the U-shaped duct 89 + 60 + 88 + 20 + 5. Of course, a similar arrangement of the exhaust duct and baffle can advantageously be used in the other embodiments described above.

The exhaust gas line 5 is formed of an upper part with a reduced section and a lower part with an increased section. The two portions are connected by means of a frusto-conical part with four sharp notches. The lower part has a side wall with four longitudinal notches. The total surface of the duct is almost the same as that of the pipe, of the same length and with the same diameter as the lower part of said duct 5.

Within and concentrically with the conduit 5 is a deflecting pipe 8 having a lower cylindrical part, an upper part with a cross-section completely closed at the apex, an intermediate part with four sharp notches corresponding to the similar notches of the conduit 5, drilled with holes or slots 95 to allow the flow of exhaust gases from within the baffle 8 to the duct 5.

The very hot exhaust gases existing in the flow of the combustion chamber inside the duct 5 are then divided into two branches. A first branch enters into the baffle 8 and exchanges heat with the internal surface of the pipe 8. The pipe 8 becomes very hot and strongly radiates the surface of the duct 5, which is at a very low temperature due to contact with water. The second branch flows between the pipe 8 and the duct 5 and becomes cold rapidly due to the high heat exchange with the cold surface of the duct 5 and at the high speed. Approximately two thirds of the height of the conduit 5, the two branches come together again and create a turbulent flow that improves the heat exchange of the upper part of the conduit 5.

This disposition described here of the exhaust duct provides a substantial efficiency of improvement in heat exchange without reducing the capacity of the water tank. This is due to the shape of the duct 5, which has a surface area up to 50% larger than that of a cylindrical duct having a diameter equal to the diameter of the upper part of the duct 5 and the same length.

In addition, with reference to the ignition element, each of the embodiments of the invention could have a plurality of ignition elements: it has been verified that the spreading of the flames to all the openings and / or slots of the device, and therefore the elimination of volatile substances, is especially effective when the furthest opening, or the group of furthest openings is not more than 250 mm away from the ignition element. This means that it is not advisable to provide an additional ignition element when the distance exceeds this value. In general, the device of the invention provided will be specifically effective when volatile substances are ignited in all openings 39 and all slots 50, if any, in a maximum of 2 seconds.

Claims (16)

1. A gas device for providing a convective heat transfer to a liquid, with at least one pre-burned atmospheric burner, arranged to operate under a natural current, said burner includes: fuel supply means for receiving a flow of gaseous fuel from an external source and operating in response to the flow of fuel to suck and combine the primary air flow of the environment to form an air-fuel mixture to carry it to the plenum, said plenum chamber has a burner head with a plurality of flame openings, ignition means associated with the flame openings for igniting the air-fuel mixture to generate flames, a combustion chamber having a surface that includes the surface external of said burner head and that is connected to a discharge conduit in a communication relation with the liquid with the environment and in heat exchange with said fluid, characterized in that it comprises a wall that is connected to said plenum chamber, it has a plurality of additional openings and is arranged to separate said combustion chamber from the or, so as to limit the communication of the liquid from there to said flame openings and said additional openings, the ratio between the general area and the additional openings and the energy input to the burner is of a value comprised between 200 and 500 mm2 / k, the width / depth ratio of each of these flames and additional openings is selected to prevent the return of the flame and the openings are arranged on the burner head and on the wall so close to each other as to ensure cross ignition.

2. A gas device for providing a substantially convective heat to a liquid with at least one premix atmospheric burner arranged to operate under a natural stream, said burner includes: fuel supply means for receiving a gaseous fuel flow from a source thereof and operating in response to the flow of fuel to aspirate and combine the primary air of the environment to form a mixture of fuel-gas hyperestichrometric air to carry it to the plenum, said plenum chamber has a burner head with a plurality of flame openings, means of ignition associated with the flame openings for igniting the air-fuel mixture to generate flames, a combustion chamber having a surface including the external surface of said burner head, is connected to the discharge conduit in communication of the liquid with the environment and in heat exchange with said l liquid, and is substantially sealed from the environment, characterized in that the ratio between the general area of the flame openings and the energy input to the burner is of a value between 200 and 500 mm2 / k, the width / depth ratio of each of said openings is of a selected value to prevent the return of the flame and the openings are arranged on the burner head so close to one another as to ensure cross ignition.

3. The gas device, according to any of claims 1 and 2, characterized in that the discharge conduit and the number and area of the openings are so selected that the average air transit or air-gas mixture velocity through of the openings is greater than 0.5 m / sec.

4. The gas device, according to claim 1 or 2, characterized in that the openings of the flame and / or the additional openings are elongated grooves having a width comprised between 0.4 and 0.5 mm and a depth between 0.4 and 0.6 mm.

5. The gas device according to claim 1 or 2, characterized in that the openings of the flame and / or the additional openings are circular holes having a diameter comprised between 0.4 and 0.9 mm and a depth comprised within 0 , 4 and 0.6 mm.

6. The gas device, according to claims 1 or 2, characterized in that the central distance between two adjacent flame openings and / or the central distance between two adjacent additional openings is between 1.0 and 1.5 mm.

7. The gas device, according to claims 1 or 2, characterized in that the flame and / or the additional openings are arranged in groups spaced no more than 20 mm from each other, the central distance between two adjacent openings in a group is 1.0 and 1.5 mm.

8. The gas device, according to claim 1 or 2, characterized in that the head of the burner and / or the wall is a rolled metal and the flame and / or the additional openings are substantially parallel grooves with bent lips having a proportion of width / depth between 1/5 and 1/10, depending on the thickness and thermal conductivity of the metal sheet.

9. The gas device, according to claim 8, characterized in that the central distance between two adjacent flame openings or additional openings does not exceed 6.0 mm.

10. The gas device, according to claim 8 or 9, characterized in that the distance between two flame openings or two additional openings, as measured along the longitudinal direction of the openings is less than 20.0 mm .

11. The gas device, according to any of the preceding claims, characterized in that the ignition means comprise a plurality of ignition elements.

12. The gas device, according to claim 11, characterized in that at least one ignition element is a pilot burner functionally identical to said atmospheric burner.

13. The gas device, according to claim 12, characterized in that the pilot burner is incorporated in at least one atmospheric burner.

14. The gas device, according to any of the preceding claims, characterized in that it comprises a tank including said liquid and have a side coating and an air duct, at least one premix atmospheric burner is disposed below the tank and said primary air is induced to flow through said air duct, said air duct extends along the side lining from a port near the top of the tank to the atmospheric premix burner.

15. The gas device, according to any of the preceding claims, characterized in that it comprises a tank including said liquid and at least one premix atmospheric burner is disposed below the tank, wherein the discharge conduit has an upper part with a section reduced, a lower part with an increased section and a frustoconical part, connecting the upper and lower parts to each other, said lower part and said frustoconical part have notched walls, so that the total surface of the discharge duct is substantially the same as the surface of the pipe having the same length as the discharge conduit, and the same section as the section of said lower part, said discharge conduit comprises a baffle pipe, which is disposed within, and concentrically with the discharge conduit, it is closed at its upper end and is provided with perforations.

16. The gas device, according to any of the preceding claims, characterized in that it comprises a gas control unit that includes an electronic ignition and flame control device, said ignition means comprise an electrode for detecting the current of the gas. ionization for flame control.