A pulse compensating device, in particular for gas-fired boilers for autonomous heating

Abstract

 Pulse compensating device (1), in particular gas-fired boilers for autonomous heating, comprising a combustion circuit (2) that is hermetically sealed relative to the installation environment. Said device (1) further comprises an elastic element (3) so shaped as to define a part of said combustion circuit (2), in order to absorb the pressure waves generated by flame pulses and means (4) for dissipating the energy associated to said pressure waves. Said means (4) are operatively interacting with the elastic element (3).

Description

[0001] The present invention relates to a pulse compensating device, in particular for gas-fired boiler for autonomous heating, of the type comprising a hermetically sealed combustion circuit.

[0002] As is well known, a combustion circuit that is hermetically sealed relative to the installation environment is usually obtained by means of a hermetically sealed chamber, within which are located, next to each other, the fuel/combustion supporter mixing chamber and the combustion chamber. Typically, the mixing chamber is separated from the combustion chamber by a thin metal lamina whereon are obtained slots, or else holes, necessary for flame propagation.

[0003] The hermetically sealed chamber is further provided with at least a first conduit for introducing the air supporting the combustion and with at least a second conduit for the exhaust of the combustion by-products.

[0004] Such gas-fired boilers are generally assisted by an electrical fan to facilitate the intake of the combustion-supporting air and the exhaust of the combustion by-products.

[0005] Such boilers are frequently affected by considerable vibrations caused by rapid pressure variations which are started by the pulsing of the flame. The intensity of such vibrations is also influenced by the length of the intake and exhaust conduits of the boiler itself. In particular, for boilers provided with electrical fan, when the volumes of the combustion circuit are traversed by determined masses of air and/or combustion by-products, under the thrust of the centrifugal electrical fan, an effect multiplying the peak pressure generated by the pulsing flame of the burner is activated.

[0006] Flame pulsing is an intrinsic phenomenon of atmospheric boilers, where the mixing chamber is separated from the combustion chamber only by a thin metal lamina. The contiguity between the mixing chamber and the combustion chamber determines a continuous displacement of the flame source plane (area where the mixture is ignited), in particular when the heat load of the burner is reduced by intervention of ignition ramps or through the modulation of the gas flow rate.

[0007] Other conditions that may induce flame pulsing in an atmospheric burner, in particular of the type with fixed flame geometry, are temperature and density variations of the air; such variations cause a continuous shift from situations of carbureting flame to situations of oxidising flame (insufficient and excessive quantity of air in the mixture).

[0008] For the aforementioned reasons, the propagation velocity of the flame does not exhibit a stationary profile over time; consequently, the flame front is unstable and continuously moves from the source plane, entailing strong pressure oscillations inside the combustion circuit.

[0009] This instability is still more accentuated in hyper-stoichiometric atmospheric burners, which use a limited supply of secondary air in order to reduce the polluting emissions of combustion by-products. While secondary air is unfavourable to reduce carbon monoxide emissions, it does enhance flame stability, thereby limiting its pulsing.

[0010] The pressure oscillation caused by the pulsing of the burner flame can be amplified by resonance phenomena caused by the compressibility of the air and fume masses inside the combustion circuit. Such resonance phenomena may even lead to an anomalous behaviour of the control organs tasked with stabilising the flow rate and pressure of the gas to be sent to the burner. The pressure waves, amplified by the resonance phenomena, are discharged in the form of violent vibrations on the metal structure of the box containing the combustion circuit of the boiler, simultaneously altering combustion with negative effects on carbon monoxide emissions. Such vibrations are very noisy and thus are annoying and unacceptable for the user.

[0011] In the prior art, the attempt to solve the vibration problems was made by mechanically stiffening the box of the combustion circuit, increasing plate thickness and/or using a higher number of fastening points.

[0012] However, this solution achieves scant results and causes a needless increase in fabrication costs.

[0013] Alternatively, the attempt to reduce vibrations is made by throttling the mass flow rate of the combustion by-products and/or drilling through holes on the box of the hermetically sealed chamber, in order to attenuate the pressure spikes that develop in its interior.

[0014] This technique has the drawback of modifying the starting characteristics of the boiler, both in terms of performance and of its tightness relative to the installation environment. An aim of the present invention is to eliminate the aforesaid drawbacks making available a pulse compensating device, in particular for gas-fired boilers for autonomous heating, that is able to absorb and dissipate the pressure waves generated by the flame pulsing, without letting them interfere with the metal parts constituting the combustion circuit.

[0015] Another aim of the present invention is to propose a pulse compensating device, in particular for gas-fired boilers for autonomous heating, that is able to meet the requirements set by current standards pertaining to safety and polluting emissions.

[0016] A further aim of the present invention is to obtain a pulse compensating device that does not influence on the performance of the boiler.

[0017] Said aims are fully achieved by the pulse compensating device, in particular for gas-fired boilers for autonomous heating, of the present invention, which is characterised by the content of the claims set out below.

[0018] These and other aims shall become more readily apparent from the following description of a preferred embodiment illustrated, purely by way of non limiting example, in the accompanying drawing tables, in which:

• Figure 1 shows a global view of a first embodiment of a pulse compensating device, in particular for gas-fired boilers for autonomous heating, according to the present invention;
• Figure 2 shows a lateral view of a detail of the device illustrated in Figure 1;
• Figure 3 is a section view of the detail illustrated in Figure 2;
• Figure 4 shows a global view of a second embodiment of a pulse compensating device, in particular for gas-fired boilers for autonomous heating, according to the present invention;
• Figure 5 shows a lateral view of a detail of the device shown in Figure 4;
• Figure 6 is a section view of the detail shown in Figure 5.

[0019] With reference to Figures 1 and 4, the pulse compensating device, in particular for gas-fired boilers for autonomous heating, is globally indicated with the number 1, highlighting in both figures the path followed by the air destined to sustain combustion and by the combustion by-products.

[0020] The device 1 is inserted in a combustion circuit 2 that is hermetically sealed relative to the installation environment. The device 1 comprises a substantially elastic element 3 so shaped as to define a part of the combustion circuit 2, in order to absorb the pressure waves generated by flame pulses inside the mixture. The elastic element 3 operatively interacts with means 4 so shaped as to dissipate the energy associated to the pressure waves.

[0021] The combustion circuit 2 comprises a combustion chamber 5 that is hermetically sealed relative to the external environment. Inside said hermetically sealed chamber 5 are present a chamber 6 for mixing fuel with combustion supporter and a combustion chamber 7 operatively connected to said mixing chamber 6. The combustion circuit 2 further comprises at least a first conduit 8 for introducing a pre-determined flow rate of air into the combustion chamber 7 and at least a second conduit 9 to expel the combustion products from said chamber. to facilitate the intake of air and the exhaust of the combustion by-products, an electrical fan 10 is inserted in the combustion circuit 2.

[0022] In the first embodiment shown in Figures 1 through 3, the elastic element 3 is substantially a membrane shaped in such a way as to define at least a portion of a wall 5a of the hermetically sealed chamber 5. The means 4 for dissipating the energy associated to said pressure waves comprise at least an expansion chamber 11 positioned externally or internally to the hermetically sealed chamber 5 in correspondence with the membrane. Said expansion chamber 11 is provided with at least a through hole or otherwise an opening 12, in order to allow the exterior air to enter and exit the chamber, thereby dissipating energy. The membrane is fastened, possibly in removable fashion, to the hermetically sealed chamber 5 in correspondence with the edges of the expansion chamber 11. In the illustrated embodiment, said edges in fact constitute the elements for fastening the membrane.

[0023] In the second embodiment illustrated in Figures 4 through 6, the elastic element 3 is substantially a sleeve so shaped as to define at least a portion of the first conduit 8 to introduce a pre-determined flow rate of combustion air into the combustion chamber 7. In an alternative embodiment, not shown herein, the possibility is provided of shaping, by means of said sleeve, also or only a portion of the second conduit 9. In the second illustrated embodiment, the means 4 for dissipating the energy associated to the pressure waves comprise at least an expansion chamber 13 placed in annular position relative to said sleeve. In this case, as well, the expansion chamber 13 is provided with at least a through hole or otherwise an opening 14, in order to allow the exterior air to enter and exit the chamber, dissipating energy.

[0024] The operation of the invention is as follows.

[0025] The energy of the pressure waves generated inside the combustion circuit 2 is absorbed by the deformation of the membrane or of the sleeve (depending on the embodiment) and dissipated by means of the exit of air through the openings 12, 14 of the expansion chambers 11, 13; the dissipation is made possible by the viscosity of the exterior air that is in contact with the elastic element 8.

[0026] The invention achieves important advantages.

[0027] Firstly, the use of an elastic element together with an external expansion chamber allows to absorb and dissipate pressure waves, without letting them interfere with the metal parts constituting the combustion circuit. In this way, the invention achieves the important advantage of eliminating the annoying noise of the boiler caused by the vibrations due to the violent impact of pressure waves on metal parts of the combustion circuit.

[0028] Advantageously, a pulse compensating device according to the present invention meets all requirements imposed by current standards in terms of safety and polluting emissions. A further advantage of the device according to the present invention is that it does not affect the performance of the boiler. In particular, the use of a membrane or of a sleeve as described and illustrated herein does not impinge on the hermetic seal of the combustion circuit and thus does not induce any release of burnt gases into the installation environment.

[0029] Advantageously, the embodiment with the sleeve, the latter defining a portion of an intake or exhaust conduit, provides for easy maintenance and it can also be installed on a pre-existing combustion circuit, without altering its type or performance.

[0030] A Pulse Compensating Device, in Particular for Gas-Fired Boilers for Autonomous Heating

Claims

1. Pulse compensating device (1), in particular for gas-fired boilers for autonomous heating, comprising a combustion circuit (2) that is hermetically sealed relative to the exterior environment, characterised in that it comprises:

an elastic element (3) so shaped as to define a part of said combustion circuit (2) to absorb the pressure waves generated by the flame pulses; and

means (4) for dissipating the energy associated to said pressure waves, said means (4) being operatively interacting with said elastic element (3).

2. Device as claimed in claim lcharacterised in that said elastic element (3) is substantially a membrane so shaped as to define at least a portion of a wall (5a) of a hermetically sealed chamber (5) which is part of the combustion circuit (2).

3. Device as claimed in claim 2, characterised in that said means (4) for dissipating the energy associated to said pressure waves comprise at least an expansion chamber (11) positioned externally to the hermetically sealed chamber (5) of the combustion circuit (2) in correspondence with the membrane, said expansion chamber (11) being provided with at least a through hole or opening (12) to allow the exterior air to enter it and exit it, thereby dissipating energy.

4. Device as claimed in claim 1, characterised in that said elastic element (3) is substantially a sleeve so shaped as to define at least a portion of a conduit (8) for introducing a pre-set flow rate of air to support combustion into a combustion chamber (7).

5. Device as claimed in claim 1 or 4, characterised in that said elastic element (3) is substantially a sleeve so shaped as to define at least a portion of a conduit (9) to expel the combustion by-products from a combustion chamber (7).

6. Device as claimed in claim 4 or 5, characterised in that said means (4) for dissipating the energy associated with the pressure waves comprise at least an expansion chamber (13) placed in annular position relative to said sleeve, said expansion chamber (13) being provided with at least a through hole or opening (14) to allow the exterior air to enter it and exit it, thereby dissipating energy.

7. Gas-fired boiler, with hermetically sealed chamber, characterised in that it comprises at least a device (1) according to any of the previous claims.

Drawing