EP2245370B1

EP2245370B1 - Inlet device for an air/gas flow in a fan unit, particularly for gas burners with pre-mixing

Info

Publication number: EP2245370B1
Application number: EP08869957.4A
Authority: EP
Inventors: Antonio Ranalli; Rosalino Usci; Michele Marcantoni
Original assignee: Sit SpA
Current assignee: Sit SpA
Priority date: 2008-01-08
Filing date: 2008-12-18
Publication date: 2017-04-26
Anticipated expiration: 2028-12-18
Also published as: WO2009087041A2; ITPD20080006A1; WO2009087041A3; EP2245370A2

Description

Technical field

The present invention concerns an inlet device for an air/gas flow in a fan unit, particularly for pre-mixed gas burners, having the characteristics mentioned in the preamble of claim 1.

Technological background

Devices of the aforesaid type are used particularly, although not exclusively, in gas burner apparatuses with pre-mixing, in which a combustible air/gas mixture is pre-mixed upstream of the combustion head of the burner.
An inlet device for an air/gas flow having the features outlined above is known from EP 896191 A2 .
Typical applications provide for the use of Venturi-effect mixers, in which the combustible gas is injected into the restriction section of a Venturi tube arranged for conveying to the burner the predetermined flow of air for combustion.
Other known applications provide for air/gas pre-mixing upstream of a fan unit intended to supply, at the delivery side, the pre-mixed air/gas flow to the burner. In the solutions relating to the latter application, the combustible gas is typically fed to an inlet device, and in particular in proximity to an axial zone of the device, with reference to the axis of the impeller of a centrifugal fan associated with the inlet device. The device, provided in general with stator blades intended to impart a rotational component to the pre-mixed flow, is fed with a flow of air which is then mixed, in the device, with the gas injected axially, to form a combustible mixture to be conveyed to the intake section of the fan.

Description of the invention

The principal aim of the invention is that of providing an inlet device for an air/gas flow which is structurally and functionally designed to improve the capacity thereof for mixing the flows of air and gas introduced and also to facilitate the conveyance thereof to an intake section of a fan unit associated with the device.

Brief description of the drawings

These and other aims which will become clear hereinafter are achieved by the invention by means of a device produced according to the attached claims.
Further characteristics and advantages of the invention will become clearer from the following detailed description of a preferred exemplary embodiment thereof, illustrated by way of non-limiting example with reference to the appended drawings, in which:

Figure 1 is a perspective view of a device produced according to the invention,
Figure 2 is a front view of the device of Figure 1,
Figure 3 is a diagrammatic side view of the device according to the invention in combination with a fan of a pre-mixed burner apparatus.

Preferred embodiment of the invention

With reference to the drawings listed, the reference 1 indicates as a whole an inlet device for an air/gas flow in a fan unit (shown only diagrammatically), produced according to the present invention.
In particular, the device 1 is designed to admit the flows of air and combustible gas into a mixing zone so as to form a pre-mixed flow of a combustible air/gas mixture intended to be fed to the intake section of a centrifugal fan 2, which is arranged to supply, at its delivery side, the combustible mixture to a combustion head 3 of a gas burner 4. Figure 3 shows diagrammatically a preferred configuration in which the device 1, the fan 2 and the burner 3 are diagrammatically shown associated with one another, one after the other, in an axial direction X. The axis X moreover forms the axis of rotation of the impeller 2a of the fan, which is housed in a manifold 5 provided with an axial intake section 5a and a delivery section 5b which is located in a position remote from the axis, at the outside diameter of the impeller.
According to a principal characteristic of the invention, the device 1 comprises conveying means for conveying the fluid introduced into it, indicated as a whole by 6, which are of the centripetal type, i.e. are designed to convey the flow, admitted in a position remote from the axis X, in the direction of the axis itself, in a substantially centripetal movement, as will become clear from the following detailed description.
The conveying means 6 comprise a plurality of stator conveying ducts, all indicated by 7, which extend in directions having a predominant radial component, with respect to the axis of rotation X, and are angularly spaced from one another along a circumferential profile concentric with the axis X, as is clearly illustrated in Figure 1.
The ducts 7 are conveniently formed on a discoid base 8 having its main axis coaxial with the axis X, and from which rise in the same direction a plurality of walls 9, each pair of walls adjacent to each other defining a respective duct 7. Each of said ducts 7 is therefore delimited by a pair of opposed and facing walls 9, by the base 8 and, on the opposite side from the base, by at least part of the manifold 5.
As illustrated in Figures 1 and 2, each duct 7 is open at its opposed longitudinal ends, at which are respectively formed an opening 7a, remote from the axis X, constituting an opening for the entry of the flow into the device, and an opening 7b, close to the axis X, constituting an opening for the exit of the flow from the corresponding duct 7.
The openings 7a are therefore distributed along a common circumferential profile, in a position remote from the main axis X, and are conveniently angularly spaced at a regular pitch. Similarly, the openings 7b are also distributed at an equal angular pitch on a second profile, close to the axis X and concentric therewith.The passage cross-section of the flow in each conveying duct 7 has an amplitude which increases from the corresponding opening 7a in the direction of the opposed outlet opening 7b.
Furthermore, the walls 9 delimiting the plurality of ducts conveniently have a curved profile in the longitudinal direction predominantly directed radially, as is clearly illustrated in Figure 2. The curved profiles of the entire plurality of walls are moreover provided in a configuration in which they have a curvature of the same sign.
The reference 10 also defines a zone formed in the device, downstream of the ducts 7 and contained between the outlet openings 7b and the main axis X of the device, in which zone takes place the mixing of the flows conveyed, in a centripetal movement, along the ducts 7 and delivered at the outlet of the ducts.
In a typical application in which one or more ducts 7 are dedicated to conveying a combustible gas into the zone 10 and the remainder of the ducts are used for conveying air, in the same zone, the pre-mixing of air/gas takes place in the latter for the formation of a combustible mixture to be fed to the fan 2 and thence to the burner 4.
In this respect, the mixing zone 10, provided at least in part in the base 8 of the device, is arranged to be placed in fluid communication with the axial intake section 5a of the centrifugal fan 2, such that the fan is fed at the intake side with the pre-mixed air/gas flow.
Indicated in the figures by suitable arrows are the directions of the centripetal conveying movement of the flow inside the device.
It should be noted that the device, in functional terms, forms a kind of bladed stator placed at the intake side of the fan, in which the air/gas pre-mixing takes place downstream of the conveyance, with a centripetal motion, of the flows of air and gas admitted into the device.
Such a configuration offers advantages compared with the known solutions, in which the injection of the gas takes place centrally and in an axial direction in proximity to the main axis. One advantage, for example, is that of being able to manage the injection of the gas more easily and simply, since it is located in a position remote from the axis. This is reflected for example in the possibility of being able to position more easily and simply the valve unit intended to deliver the combustible gas to the mixing zone. Another advantage is that of being able to take advantage, in the centripetal radial movement, of the curvature of the ducts in order to impart a rotational component to the flow introduced into the device, this being advantageously made possible by the centripetal movement conveying the flow which characterizes the device according to the invention.
A further advantage is that of the rates of motion which are more similar to those of the gas nozzle: this is an advantage in the regularity of delivery of the gas in the case of a pneumatically-controlled valve.
It is further possible to obtain an advantageous silencing effect with suitable configuration of the system.

Claims

An inlet device for an air/gas flow, particularly for the admission of said flow into a centrifugal fan (2) of a pre-mixing burner apparatus, comprising flow conveying means (6) arranged for conveying the flow of air and/or gas to the intake section (5a) of the fan, said conveying means (6) being of the centripetal flow type and comprising a plurality of stator conveying ducts (7) extending in directions having a predominant radial component with respect to the axis of rotation (X) of the fan (2) and being angularly spaced from one another along a circumferential profile concentric with said axis, wherein each duct (7) of said plurality is delimited at least by a pair of opposed walls (9) facing each other and rising in the same direction from a discoid base (8) of said device arranged for coaxial mounting with the fan (2), the duct (7) being capable of being delimited, on the opposite side from the base, by at least part of the manifold (5) for housing the impeller, each duct (7) being open at the opposed ends of its length, with a first opening (7a) for the entry of the flow at one of the ends, in a position remote from the main axis of the base, and with a second opening (7b) for the exit of the flow at the other end, positioned in proximity to said axis (X), characterized in that the passage cross-section for the flow in each conveying duct (7) has an amplitude increasing from the entry opening (7a) in the direction of the outlet opening (7b) for the flow.
A device according to claim 1, wherein each pair of opposed walls (9) of said base (8) delimiting a respective duct (7) has a curved profile in the longitudinal direction and also radial with respect to the main axis (X) of said base (8).
A device according to claim 2, wherein the curved profiles of each pair of walls (9) facing each other and delimiting a corresponding duct (7) have a curvature of the same sign.
A device according to any one of the preceding claims, wherein downstream of each duct (7), with respect to the centripetal direction of the flow, between the outlet opening (7b) of the duct (7) and the main axis of the device, a mixing zone (10) is defined for the flows conveyed by said ducts (7) to the intake section (5a) of the fan (2).
A device according to claim 4, wherein said mixing zone (10) is arranged to be placed in fluid communication with an axial intake section (5a) of a centrifugal fan (2) with impeller coaxial with said device, such that the fan is fed at the intake side with the mixed air/gas flow coming from the mixing zone (10).
A device according to any one of the preceding claims, wherein one or more of said conveying ducts (7) are intended for the admission of a combustible gas to be conveyed to the mixing zone (10), the remainder of the ducts (7) of said plurality being intended to convey air to the mixing zone (10), such that in said zone the air/gas pre-mixing takes place for feeding the intake section (5a) of a fan arranged for supplying at the delivery side a flow of combustible mixture to a burner apparatus.