The present invention relates to a boiler for generating hot water or steam.

Boilers in general, and steam generators in particular, are known which comprise a substantially cylindrical outer enclosure, which defines a heating chamber that contains water that, in steam generators, is heated at least until it reaches its vaporization temperature.

In particular, a furnace body is axially accommodated inside the heating chamber and is in a position to exchange heat with the water to be heated and defines, internally, a combustion chamber, inside which the flame bursts, produced by the combustion head of a burner, located at one end of the combustion chamber and, usually, associated with a door to close the boiler.

The hot combustion gases generated in the combustion chamber are channeled into heat exchange tubes that axially pass through the heating chamber, so that the hot exhaust gases can exchange heat with the water contained in the heating chamber, until they lead out into an exhaust gas chamber, from which the exhaust gases exit by way of a flue.

Typically, steam generators of this type are provided with burners that use a non-premixed laminar flame.

"Premix" burners also exist which operate with gaseous fuels, and they have, upstream of the combustion head, a device for mixing air and gas which is constituted by a Venturi tube provided with an axial inlet connected to an air supply duct, a lateral inlet connected to a gas supply duct and controlled by an adjustable gas inflow valve, and an axial outlet, which is arranged at the opposite end of the Venturi tube with respect to its axial inlet and connected to the combustion head by way of the interposition of a fan, which makes it possible to continue the mixing of air and gas which is done inside the Venturi tube and to send the air/gas mixture under pressure to the combustion head. Owing to such structure, traditional premix burners are known as "press" burners, since, by way of their fan, they increase the pressure in the combustion chamber with respect to the ambient pressure, and as a consequence steam generators made in this way are called, in the jargon, "pressurized".

The steam generators described above have some drawbacks.

In the event of obstructions in the flue, serious problems can occur owing to a buildup of unburned material in the furnace in the ignition phase.

Furthermore, with the steam generators described, flame backflows are possible toward the external environment, or smoke leaks through the gaskets arranged in the door and in the fume collection chamber.

Another drawback of pressurized steam generators is constituted by the risk of propagation of a pressure wave, which translates to a sound wave, toward the external environment during the ignition phases.

A further drawback of pressurized steam generators is the high space occupation at the door owing to the presence of the premix burner and, more specifically, of its fan and of its Venturi tube.

The aim of the present invention is to provide a boiler for generating hot water or steam that is capable of overcoming the drawbacks of the known art indicated above, while at the same time ensuring a high yield and extremely low pollutant emissions, constituted by carbon monoxide and nitrogen oxides, by virtue of a better combustion of the gas.

Within this aim, an object of the present invention is to provide a boiler for generating hot water or steam that has a combustion system that is capable of preventing a buildup of unburned material in the event of an increase in resistance in the flue.

Another object of the present invention is to provide a boiler for generating hot water or steam that is not affected by problems whereby exhaust gases exit toward the external environment.

Another object of the present invention is to provide a boiler for generating hot water or steam that sends a considerable decrease of NOx to the flue.

Another object of the present invention is to provide a boiler for generating hot water or steam, in which there is no damaging propagation of pressure waves, which are the cause of noise both in the ignition phase and during normal operation.

Another object of the present invention is to provide a boiler for generating hot water or steam that has smaller encumbrances at the door with respect to the known art.

Another object of the present invention is to provide a boiler for generating hot water or steam which, in addition to offering the widest guarantees of reliability and safety in operation, is of very simple construction so as to also be competitive from a purely economic viewpoint.

This aim and these and other objects which will become better apparent hereinafter are achieved by a boiler for generating hot water or steam, according to the invention, as defined in claim 1 .

Further characteristics and advantages of the invention will become better apparent from the description of some preferred, but not exclusive, embodiments of the boiler for generating hot water or steam, according to the invention, which are illustrated, by way of non-limiting example, in the accompanying drawings wherein:

Figure 1 is a schematic longitudinal cross-sectional view of the boiler for generating hot water or steam according to the invention;

Figure 2 is a schematic longitudinal cross-sectional view of a device for premixing air and gas present in the boiler for generating hot water or steam according to the invention;

Figure 3 is a schematic view of a portion of the boiler for generating hot water or steam according to the invention, in a possible embodiment.

With reference to the figures, the boiler for generating hot water or steam, according to the invention, generally designated with the reference numeral 1 , comprises a substantially cylindrical containment enclosure 2, which defines a heating chamber 3, which is intended to contain water to be heated to the desired temperatures.

It should be noted that, in the examples shown in the figures, the water contained inside the heating chamber 3 is intended to be heated at least up to its vaporization temperature, in order to allow the production of steam, but more generally, the boiler according to the invention can also be used for the production of hot water.

Conveniently, in the upper part of the containment enclosure 2 there is an outlet 4, through which the steam produced exits from the heating chamber 3, as in the example shown in Figure 1 , or optionally the hot water produced.

As illustrated, the heating chamber 3 axially accommodates a furnace 5, which defines, internally, a combustion chamber 6 in which the flame produced by a burner 7 is burned.

In particular, the burner 7 has a combustion head 8, which is accommodated in the combustion chamber 6 and is designed to emit the flame into the combustion chamber 6, and a device 9 for premixing air and gas which is connected to the combustion head 8, in order to supply it with a mixture of air and gas.

Conveniently, the combustion head 8 is inserted in a door 10 that closes an axial end of the combustion chamber 6.

The combustion chamber 6 is, in turn, connected to a plurality of heat exchange tubes 11 which are designed to be passed through by the hot combustion gases generated by the flame emitted by the combustion head 8.

In particular, the heat exchange tubes 11 pass through the combustion chamber 6 longitudinally, so as to enable the heating of the water contained in it, and lead out into a fume collection chamber 12, which is connected to a flue, through which the combustion gases are evacuated outside.

It should be noted that the combustion chamber 6, at the opposite end with respect to the combustion head 8, is, conveniently, closed by a bottom wall 14 of the furnace 5 which enables the combustion gases to be returned toward the combustion head 8 and the door 10.

In particular, at the door 10 there is, advantageously, a chamber 15 for redirecting the exhaust gases which makes it possible to channel the combustion gases originating from the bottom wall 14 of the furnace 5 into the heat exchange tubes 1 1.

According to the invention, the premixing device 9 comprises an air supply duct 17, connected with the outside environment and connected to the combustion head 8, inside which a mixer body 16 is axially accommodated, which is struck by the flow of air that flows inside the supply duct 17.

In particular, such mixer body 16 has, on its front side directed against the stream of air that arrives from the supply duct 17, a contoured portion 16a that is adapted to create, between the internal side walls of the supply duct 17 and the lateral surface of the mixer body 16, an intake region 18 that has a transverse air passage cross-section that is narrower than the air passage cross-section defined by the supply duct 17 upstream of the mixer body 16, along the direction of the air stream in the mixer body 17.

In the mixer body 16, substantially at the intake region 18, at least one gas delivery opening 19 is defined, which is connected to a feed channel 20, which is defined, at least partially, inside the mixer body 16 and connected to a fuel gas source.

Also according to the invention, means are provided that are adapted to create a lower pressure in the combustion chamber 6 with respect to the external ambient pressure, and which comprise, advantageously, at least one fan 21 , controlled by a corresponding electric motor 22, which is accommodated in the exhaust gas collection chamber 12 and has, in particular, an intake connected to the exhaust gas collection chamber 12 and a delivery connected to the flue 13. With reference in particular to Figure 2, the contoured portion 16a of the mixer body 16 has, conveniently, a lateral surface that progressively approaches the internal side walls of the supply duct 17, proceeding in the direction of the air stream that flows inside the supply duct 17.

More specifically, the contoured portion 16a of the mixer body 16 is, advantageously, substantially ogive-shaped.

As can also be seen in Figure 2, the mixer body 16 is, advantageously, provided with a plurality of gas delivery openings 19, which are distributed about an axis of extension 16b of the mixer body 16 that is substantially parallel to the axis of the supply duct 17.

Conveniently, the gas delivery openings 19 defined in the mixer body 16 are open toward the rear side of the mixer body proper.

Advantageously, the feed channel 20 also extends in the rear portion of the mixer body 16, and is connected, conveniently, to the gas source by way of a delivery duct 23, which extends, with one of its portions, outside the supply duct 17 and is controlled, advantageously, by a valve 24, preferably controlled pneumatically.

Preferably, the contoured portion 16a of the mixer body 16 is internally hollow and the delivery openings 19 can be, advantageously, defined between a section of the contoured portion 16a directed toward the rear side of the mixer body 16 and a portion of wall of the mixer body 16 that merges from the rear into the contoured portion 16a and in which a section of the feed channel 20 is internally defined, which leads into the cavity of the contoured portion 16a, from which the gas is deviated toward the delivery openings 19.

Conveniently, as better shown in Figure 3, the combustion head 8 is of the type with an internal flame.

More specifically, the combustion head 8 is cylindrical and hollow with a cylindrical side wall 8a and an end wall 8b which are provided, on their surface directed inward, with a plurality of flame-emitting nozzles. Also with reference to Figure 3, advantageously, along the supply duct 17, in a position interposed between the mixer body 16 and the combustion head 8, there can be one-way valve means 25 the function of which is to contrast the transmission of pressure waves from the combustion chamber 6 toward the supply duct 17, which could disturb the pressure values in the intake region 18 and, therefore, the regular flow of gas through the delivery openings 19 of the mixer body 16.

In particular, such valve means comprise a flap check valve that has, conveniently, a flow control body 26 eccentrically pivoted about a pin 27, so as to considerably increase the moment of inertia of the flow control body 26 with respect to its rotation axis, but creating only minimal resistance upon opening.

More specifically, the flow control element 26 has, proximate to the pin 27, a counterweight 26a that enables the flow control element 26 to oppose a considerable mechanical inertia at the moment of being switched on, while keeping the flow control element perfectly balanced.

There is, furthermore, an abutment element 32, integral with the supply duct 17, against which the flow control element 26 can rest in the closed condition.

It should be noted that the flow control element 26 is opened by virtue of the flow of air and gas that is returned toward the combustion chamber 6 and the combustion head 8 and which, in passing, is capable of generating a lift effect that makes it possible to keep the flow control element 26 open.

Conveniently, in order to enable the flow control element 26 to be able to positively take advantage of such lift effect, optionally the flow control element 26 can also have a wing profile shape, for example of the NACA type.

Advantageously, in the exhaust gas collection chamber 16 there is an exhaust gas heat exchanger 28 which is struck externally by the exhaust gases channeled toward the flue 13 and is connected internally in input with the water mains, by way of a pump 29, and in output to a water supply line 30 to the heating chamber 3, so as to enable the recovery of any residual heat in the exhaust gases by way of preheating the water that is sent to the heating chamber 3.

Conveniently, in the exhaust gas collection chamber 12 there can also be a bulkhead 29 that makes it possible to channel the exhaust gases coming from the heat exchange tubes 1 1 toward the flue 13, forcing them to strike the condensing device 26.

Advantageously, as shown in Figure 1 , the premixing device 9 can be accommodated within a housing 31 , integral with the door 10 and having at least one access for air and for the gas source.

Operation of the boiler according to the invention is the following.

The heating chamber 3 is supplied with water by way of the supply line 30.

Once the fan 21 is activated, a lower pressure is created in the combustion chamber 6 which makes it possible to suck air into the supply duct 17 from the external environment.

The flow of air that flows in the supply duct 17 undergoes an increase in speed and a consequent decrease in pressure, by the Venturi effect, at the intake region 18 created by the presence of the mixer body 16.

Such decrease in pressure causes the valve 24 to open with consequent inflow of the gas into the delivery duct 23 and emission of the same gas from the delivery openings 19 of the mixer body 16, so that it can mix with the flow of air originating from the supply duct 17.

The gas mixture thus obtained fuels the combustion head 8 which is then ignited so as to generate a flame inside the combustion chamber 6.

Any pressure waves that may be generated during ignition of the combustion head 8 and which could disturb the regular flow of air and gas are obstructed by the one-way valve means 25. In particular, the flow control element 26 opposes, at the moment of ignition, a considerable mechanical inertia to the pressure wave that is propagated by the furnace 5 in the opposite direction to the flow of air and gas that feeds the combustion head 8.

With the combustion head 8 ignited, the hot combustion gases, once they have reached the bottom wall 14 of the furnace 5, are redirected toward the door 10 where they are channeled into the heat exchange tubes 11 , so as to heat the water contained in the heating chamber 3.

Once they have passed through the heat exchange tubes 11, the combustion gases reach the exhaust gas collection chamber 12 where they are channeled toward the flue 13, which they reach after having passed through the exhaust gas heat exchanger 28.

The steam or hot water produced inside the heating chamber 3 exits through the outlet 4.

The heating chamber 3 is resupplied with water by the supply line 30 which receives preheated water from the heat exchanger 28.

In practice it has been found that the invention is capable of fully achieving the set aim.

It must be pointed out in particular that, with the boiler for generating hot water or steam according to the invention, it is not possible to have backflows of flame toward the external environment, or leaks of exhaust gases through the gaskets arranged in the door and in the exhaust gas collection chamber, since the combustion chamber and the exhaust gas collection chamber are kept at low pressure.

Furthermore, given that the suction fan remains inside the exhaust gas collection chamber, any resistance of the flue is interpreted by the system as a loss of performance of the fan with consequent automatic decrease of the flame power, thus giving the combustion system a characteristic self- regulating operation that does not modify the combustion parameters in any way but only the power burned.

Another advantage of the boiler according to the invention consists since the premixing device provided with a mixer body inserted in the air supply duct makes it possible to take advantage of the principle of the Venturi effect, i.e. of the decrease in the pressure owing to an increase in the speed of the air, like conventional burners that premix air and gas, but making it possible at the same time to obtain a closer air/gas mixing with consequent advantages for the reduction of NOx and an obstacle to the propagation of the pressure wave toward the external environment during the ignition phases, also facilitated by the presence of the one-way valve means.

Another advantage is constituted by the fact that the boiler according to the invention has an extremely reduced space occupation in front of the door, since the premixing device and the gas valve can be installed in the door, while the suction fan, which is decidedly more cumbersome, is located inside the exhaust gas collection chamber of the boiler proper.

All the characteristics of the invention, indicated above as advantageous, convenient or similar, may also be missing or be substituted by equivalent characteristics.

The individual characteristics set out in reference to general teachings or to specific embodiments may all be present in other embodiments or may substitute characteristics in such embodiments.

The invention, thus conceived, is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

Thus, for example, with the same concept, one can provide not only steam generators and boilers for the production of steam in general, but also boilers for hot water, traditional or condensation, industrial boilers using superheated water or diathermic oil and so on.

In practice the materials employed, provided they are compatible with the specific use, and the dimensions and shapes, may be any according to requirements. Moreover, all the details may be substituted by other, technically equivalent elements.

Where the technical features mentioned in any claim are followed by reference numerals and/or signs, those reference numerals and/or signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference numerals and/or signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference numerals and/or signs.