The present invention relates to a combustion head for atomized fuel oil burners, and which, according to the invention, produces a low-temperature flame.
In burners of the type referred to in the present invention, combustion of the combustible fluid and fluid combustion supporter mixture is brought about by means of a combustion head, which substantially comprises a tubular air conduit into which the fluid combustion supporter, e.g. air, is blown and mixes with the combustible fluid, in this case atomized oil, fed into the same tubular air conduit by means of a mixing device; and combustion is initiated by an ignition device igniting the fuel/combustion supporter mixture.
As anyone skilled in the art knows, one of the major problems posed by combustion heads, in terms of ecological impact, is the emission into the atmosphere of nitric oxides Nox produced during the combustion process.
For instance, in
However, the devices described in
Thus, the main object of the combustion head according to the present invention is to further improve conventional methods of reducing the nitric oxide content of combustion products.
The combustion head according to the present invention therefore provides for an exothermic combustion reaction producing fumes with a very small nitric oxide content.
It is a further object of the present invention to reduce the emission into the atmosphere of other polluting agents (carbon monoxide, unburned hydrocarbons, smoke, etc.).
According to the present invention, there is provided a combustion head for burners, as claimed in Claim 1.
A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which:
As stated, the present invention relates to a combustion head for burners, and which provides for a low-temperature flame.
The combustion head 10 shown in Figure 1 substantially comprises a tubular air conduit 11 into which the fluid combustion supporter, e.g. air, is fed by a blower (not shown) and mixes with a combustible fluid, e.g. atomized oil, fed into tubular air conduit 11 by a mixing device (see below). Downstream from the air-fuel mixing region, an ignition device 12 ignites the mixture to initiate combustion.
Combustion head 10 is fixed to a blower assembly (not shown) in turn fixed to the wall of a combustion chamber (not shown) by means of a connecting flange (not shown).
Near the end inserted inside the combustion chamber, tubular air conduit 11 has a substantially disk-shaped flame deflector 13 positioned perpendicularly to the air flow direction, which, for the sake of simplicity, is parallel to a longitudinal axis of symmetry S, as shown by arrow F. The periphery of flame deflector 13 integral with tubular air conduit 11 is normally fitted with pipes 14 arranged symmetrically and which define the flow section for a certain amount of tertiary air A3 (see below). In the example described, pipes 14 are four in number, though only two are shown in Figure 1.
Pipes 14 are located downstream from flame deflector 13 in the direction of arrow F; the central portion of flame deflector 13 has a substantially circular central opening 15 symmetrical with respect to axis S; and a pipe 16 for the insertion of a flame detector (not shown) is fixed upstream from flame deflector 13.
Tubular air conduit 11 houses a spray-holder 17 coaxial with axis S and which provides for feeding highpressure fuel to an oil nozzle 18 where the fuel is atomized.
Spray-holder 17 is fitted concentrically with a propeller device 19 and an air nozzle 20 to form a unit 21, which, as will be seen, may be moved axially along axis S. Unit 21 is located upstream from flame deflector 13, which also provides for effectively protecting unit 21 from excessively high temperatures in the flame region. Unit 21, which, as stated, comprises spray-holder 17, propeller device 19 and air nozzle 20, is centered with respect to both tubular air conduit 11 and central opening 15 of flame deflector 13 by a support 22 comprising a locating sleeve 23 supporting air nozzle 20, and one or more wings 24 for fixing locating sleeve 23 to flame deflector 13.
The end of air nozzle 20 facing flame deflector 13 converges slightly.
As shown in Figure 1, the position of unit 21 with respect to flame deflector 13 can be adjusted, as will be seen, using means 25, 26.
In the example shown, means 25 comprise a screw engaging an eye on flame deflector 13 to adjust the position of sleeve 23 with respect to flame deflector 13; and means 26 comprise a screw engaging a threaded hole on support 22.
Means 25 and 26 therefore provide for adjusting the position of unit 21 with respect to central opening 15.
The positions of propeller device 19 and spray-holder 17 with respect to air nozzle 20 determine the flow rate of primary air A1 at the outlet section of air nozzle 20.
Whereas, as stated, adjusting the position of air nozzle 20 with respect to central opening 15 of flame deflector 13, by moving unit 21 axially in the direction of arrow F using means 25, 26, defines the flow section of secondary air A2.
As shown in Figure 1, tubular air conduit 11 comprises a front portion 11a and a rear portion 11b, with an annular gap 27 in between for the recirculation of fumes R; and rear portion 11b is fixed firmly to front portion 11a by members 28, only one of which is shown in Figure 1.
Downstream from flame deflector 13, portion 11b of tubular air conduit 11 is fitted with a recirculating flame pipe 29, which is adjustable to narrow annular gap 27 for recirculating fumes R.
In actual use, to operate combustion head 10, a stream of combustion supporting air is fed by the blower (not shown) along tubular air conduit 11 to flame deflector 13, where it is divided into three distinct air sections A1, A2, A3 (primary, secondary and tertiary respectively) as explained above.
In the primary air A1 section, propeller device 19 rotates the combustion supporting air to produce, at the outlet of air nozzle 20, a swirling air jet which mixes with the oil atomized by oil nozzle 18, and the characteristics of which are exploited to control the stability of the flame and combustion intensity. The converging shape of air nozzle 20 provides for effectively mixing the air and oil by concentrating the air jet in the spray from oil nozzle 18; and combustion of the air/atomized fuel mixture so formed is initiated by ignition device 12 to create, close to air nozzle 20, a reducing zone where combustion is incomplete.
The flame produced in this zone is simultaneously confined by the combustion supporter issuing from secondary air section A2 at central opening 15 of flame deflector 13, the flow rate of which varies according to the adjustment of unit 21 - defined, as stated, by spray-holder 17, propeller device 19 and air nozzle 20 - with respect to central air opening 15 of flame deflector 13.
At this stage, the combustion process is also assisted by recirculating fumes R, which are drawn in through gap 27 for recirculating fumes R and defined by the position of recirculating flame pipe 29 with respect to tubular air conduit 11. The volume of recirculating fumes R drawn into recirculating flame pipe 29 through gap 27 depends on the speeds at which the combustion supporting air flows through the three distinct air sections A1, A2 and A3; which speeds create a low-pressure zone at annular gap 27 to assist intake of recirculating fumes R.
In short, the volume of recirculating fumes R may be said to depend on the speed and fluid-dynamic characteristics of the air divided into the three sections A1, A2, A3, and on the size of gap 27 between tubular air conduit 11 and recirculating flame pipe 29.
The flow rate of recirculating fumes R through gap 27 can therefore be controlled by adjusting the position of recirculating flame pipe 29 along axis S. This provides for optimizing the intake volume of recirculating fumes R, the main function of which is to lower the flame temperature, which is mainly responsible for the formation of Nox.
The position of recirculating flame pipe 29 with respect to tubular air conduit 11 is adjusted by adjusting a pin 30, integral with rear portion 11b of tubular air conduit 11, with respect to a sloping slot 31 formed in recirculating flame pipe 29. Obviously, to adjust the position of recirculating flame pipe 29 with respect to tubular air conduit 11, and so adjust the size of annular gap 27 for recirculating fumes R, the user, when the burner is off, need simply rotate pipe 29 about axis S with respect to tubular air conduit 11, so as to exploit the "screw effect" of pin 30 engaging sloping slot 31.
The next combustion stage takes place at the oxidizing zone, where the combustion supporting air from tertiary air section A3, defined by pipes 14, completes the combustion process inside recirculating flame pipe 29.
In the second embodiment of the present invention shown in Figures 2 and 3, sleeve 23 and the elements connected to it are replaced by a flame deflector 13 comprising a given number of fins 13a, e.g. four fins 13a spaced 90° apart, for loosely centering air nozzle 20 and all the elements connected to it. Air nozzle 20 and all the elements connected to it are pressed in between fins 13a; and the quantity of secondary air A2 is adjusted by adjusting the position of air nozzle 20 with respect to central opening 15. Obviously, enough space is left between one fin 13a and another to allow secondary air A2 to reach opening 15.
As regards primary and tertiary air A1 and A3, the same considerations apply as in the first embodiment in Figure 1.
In the second embodiment shown in Figures 2 and 3, recirculating flame pipe 29 comprises two portions 29a, 29b connected integrally to each other. Portion 29b has a number of slots 32 perpendicular to axis S and which, as before, define an annular gap 27 for recirculating fumes R. In this embodiment, pin 30 is integral with flame deflector 13, and sloping slot 31 is formed in portion 29b of recirculating flame pipe 29. In this case, too, to adjust the amount of fumes R recirculated through annular gap 27, the user, when combustion head 10 is off, simply turns recirculating flame pipe 29 one way or the other about axis S to exploit the "screw effect" of pin 30 engaging sloping slot 31.
In the second embodiment shown in Figures 2 and 3, ignition device 12 is advantageously fixed to the upstream face of flame deflector 13, to enable the user, when necessary, to remove ignition device 12 from the boiler side as opposed to the rear portion of combustion head 10.