RU2576555C2 - Gas-air mixer for combustible gas with premixing - Google Patents

Abstract

FIELD: power engineering.

SUBSTANCE: claimed mixer comprises the blower assembly (6) with impeller (7) provided with radial vanes (8) driven about rotational axis (X) and with axial inlet section (9) and radial opposite outlet section (10), pipe (11) to house the blower impeller, and the first air feed channel (15). Note here that said first channel is aligned with said axis (X) and has the end part (15a) converging nearby the inlet section (9). The second tubular has flow feed channel (16) at the end of end section (15a) features the minimum cross-section. Note here that the second tubular section is aligned with the first channel (15) to allow the airflow to be mixed with gas flow upstream of the blower inlet section (9). The impeller vanes (8) extend from the impeller datum surface (12). Note here that every vane (8) has the leading edge (13) located in said inlet section (9). Note also the said leading edges make the inlet holes of appropriate vane channels between the pairs of vanes extending between inlet section (9) and outlet section (10). Pipe (11) with the profile (14) of leading surface is located ahead of impeller vanes (8) and spaced therefrom. In compliance with this invention, claimed device comprises the extra appliance (20) extending from the first channel (15) in direction from said axis (X) and located outside said first channel (15). Said extra appliance extends into the area confined simultaneously by the profile of the first channel end part (15), extension of end part (15a) to the impeller datum surface (12) datum surface side nearby the appropriate edges (13), leading edges (13) of the vanes, and profile (14) of the pipe front surface (11) ahead of the vanes (8 nearby the leading edges (13).

EFFECT: stabilised combustion, decreased emission of carbon dioxide.

7 cl, 7 dwg

Description

FIELD OF TECHNOLOGY

The present invention relates to a pre-mixed gas burner mixer device having the characteristics described in the introduction to claim 1, which is the main point.

TECHNOLOGICAL LEVEL OF TECHNOLOGY

The invention relates, in particular, but not exclusively, to the technical field of the technology of steam boilers for domestic use, designed for space heating and / or water heating.

In this technical field, steam boilers for home use must meet various requirements, including some related to user comfort and safety. Safety requirements include measures in response to any interference that may occur in the exhaust chimney.

A steam boiler can usually be considered as a system in which gas and cold water are supplied to the inlet, and hot water and combustion products created by the combustion of gas and air are obtained at the outlet. The combustion products are removed through a channel or chimney, which transfers them outward relative to the building in which the equipment is installed, and displaces them into the external environment.

The chimney, as a rule, is a cylindrical pipe with one end connected to the combustion chamber and the other end connected to an external terminal. Since the terminal is an external environment, it can become clogged or blocked by external factors, such as birds building nests, or objects carried by the wind and landing on the terminal. In such conditions, in other words, if the terminal is blocked, the steam boiler must be turned off or should work with the output of carbon monoxide reduced below the limits established by the norms.

The combustion process in a steam boiler occurs in a combination of air and combustible gas, while air is supplied to the inside of the equipment by a fan. Before reaching the fan, the intake air enters the mixer and creates a vacuum, thereby sucking in combustible gas. In compact systems, the mixer is made in the form of a converging channel, and the vacuum is created in the part with the smallest cross-section. Gas is introduced into the air stream through a channel coaxial with the converging channel.

In other systems where compactness is not required, a diverging channel, whose length is at least equal to the length of the converging channel, is set downstream of the section with a minimum cross section.

The amount of gas sucked in by a vacuum is controlled by a gas valve that keeps the ratio of gas to air constant if the fan speed changes.

If the exhaust chimney is clogged, the flow of air supplied by the fan decreases even if the speed of the fan remains the same, and therefore the gas flow also decreases.

In an ideal system, the gas-to-air ratio should remain constant when the air flow rate falls below the minimum required flow rate. Thus, the combustion process continues, while the carbon monoxide output is kept within, and below a certain level of thermal energy, the steam boiler turns off. The steam boiler switches off either because the flame can no longer remain stable, or because the steam boiler safety system, which detects the presence of a flame by means of an electrode, measures the ionization current in the flame, which is lower than the control limit set in the electronic circuit board of the steam boiler, and therefore triggered by closing the gas valve.

Mixer systems having only a converging duct, such as those described above, generally fail when the chimney is clogged. As the channel becomes clogged, the gas-to-air ratio tends to increase, leading to greatly exceeding the carbon monoxide yield limits established by the standards.

In the known systems described above, the gas-to-air ratio increases when the chimney is clogged. The increase in the ratio is due to an increase in vacuum and, consequently, the amount of gas introduced. This phenomenon occurs due to various hydrodynamic conditions that are created in the region of the impeller opening (inlet section). Under these conditions, turbulences are created whose axes are coaxial with the axis of rotation of the impeller, with recirculation between the inlet and outlet of the inter-blade channel.

DETAILED DESCRIPTION OF THE INVENTION

A problem to be solved by the present invention is to provide a mixer device of the aforementioned type, which is structurally and functionally designed in order to overcome the limitations of the prior art described above.

This problem is solved by the invention by means of a gas-air device of a mixer made in accordance with the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will become apparent through the following detailed description of some preferred examples of its embodiment, illustrated for guidance and in a non-limiting manner with reference to the accompanying drawings, in which:

- figure 1 is a schematic view of the installation on which the device according to the invention will be used,

- figure 2 is a schematic view of a mixer device according to the prior art,

- figure 3 is a view corresponding to the view of figure 2 of the device according to the invention;

- figure 4 and 5 are schematic views in axial section of a detail of figure 3 in other embodiments,

- Fig.6 is a schematic front view of the device according to the invention shown in the preceding drawings, and

- Fig. 7 is a perspective view of a detail of a further exemplary embodiment of a device according to the invention.

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

As originally shown in FIG. 1, number 1 denotes a steam boiler with a combustible gas burner with pre-mixing of air and gas, for example, a steam boiler used to heat a medium 2 in which a combustion chamber (not shown) is connected through an exhaust channel 3 of combustion gases with an outlet terminal 4, shown schematically, located outside the environment.

The steam boiler 1 contains a burner, which is supplied with a combustible gas-air mixture pre-mixed in the mixer device 5, shown schematically in figure 2 in a known configuration. The device comprises a fan unit 6 with an impeller 7, driven around the rotation axis X, which is provided with radial blades 8 extending between the axial inlet section 9 and the radially opposite outlet section 10. The impeller 7 is placed in the housing 11, in which sections 9 and 10 are formed .

Each of the impeller blades 8 protrudes from the base surface of the impeller 12, extends perpendicularly to the X axis and has one edge 13 in the inlet section 9, while the pairs of adjacent edges define the boundaries of the leading edges or inlets of the respective inter-blade channels stretching between the pairs of adjacent blades along the extension blades between sections 9 and 10.

In the pipe 11 containing the impeller 7, a front surface is formed facing the sides of the blades opposite in the axial direction of the base surface 12, and the profile of this surface is indicated by number 14 in the axial section of FIG. 2.

Upstream of the fan inlet section 9, from which air is sucked in by the fan and sent to the burner, the mixer device comprises a tubular channel 15 designed to direct air, while this channel is aligned with the X axis and has a terminal portion 15a converging towards the inlet section 9, while the free end of this part has a minimum cross section. Vacuum is created in this section due to converging geometry and draws in a gas stream that is guided through the second tubular channel 16, formed at least partially, inside the channel 15 and coaxially with it. Alternatively, channel 16 may also extend beyond channel 15.

The amount of gas sucked in by a vacuum is controlled in the traditional way - a gas valve (not shown), which keeps the ratio of gas to air constant if the fan speed changes.

According to the main features of the invention, the device 1 also contains at least one additional device in the form of an element 20 of the stator blade protruding from the side profile of the channel 15 on the outer part of the channel from the X axis.

As shown in FIG. 3, assuming that the median section of the blade member 20 is represented in the axial section plane (page plane) in the drawing, the blade member extends into an area (shown by a dashed line) bounded simultaneously:

- the profile of the terminal part of the converging channel 15,

- the continuation of the terminal part to a point close to the surface 12, parallel to the X axis,

- part of the base surface 12 of the impeller in the immediate vicinity of the respective edges 13 of the blades,

- the corresponding leading edge 13 of the inter-blade channel,

- profile 14 of the surface, which encloses the impeller of the pipe 11, located frontally with respect to the blades 8 in the immediate vicinity of the corresponding edges 13.

In the region bounded, as described above, indicated by dashed lines in FIGS. 3-5, at least one blade member 20 may extend from the side profile of the converging member in order to occupy this region at least partially, while remaining at a distance from the impeller blades to avoid collision with these blades.

Figures 4 and 5 show alternative configurations of the region defining the boundaries of the blade member 20 according to various frontal profiles of the pipe 11.

More specifically, the blade member 20 has a plate shape with opposing surfaces 20a defining the boundaries of the transverse thickness 20b.

In an exemplary embodiment, the stator blade member 20 extends radially with respect to the axis of rotation X, and its opposite surfaces 20a are flat. Obviously, other shapes or arrangements are possible. The number and angular positions of the blade members 20 may also vary.

In a further exemplary embodiment shown in FIG. 7, four blade members 20 are provided that are circumferentially spaced at equal angular intervals. The blade elements extend radially with a flat surface having a rectangular geometry.

Preferably, each of the blade members 20 has a thickness 20b greater than 0.2 mm and, for convenience, made equal to 1 mm, while the converging channel 15 has a wall with a thickness of 21 less than 3 mm at its end with a minimum cross section.

The functions of the stator blade element according to the invention are described in detail below.

When the chimney is at least partially clogged, the ratio of gas to air tends to increase. This increase is due to an increase in vacuum and, consequently, the amount of gas introduced. This phenomenon occurs due to various hydrodynamic conditions that are created in the region of the impeller opening. Under these conditions, turbulences are created whose axes are coaxial with the axis of rotation X, with recirculation between the inlet and outlet of the inter-blade channel. Providing at least one additional fixture or vane 20 located in the region described above tends to impede these hydrodynamic actions of the combustible mixture, leading to improvements in productivity during chimney clogging. Thus, the air-gas ratio tends to decrease when the clogging increases, leading to the steam boiler shutting down safely.

The solution described above makes it possible to maintain the compact configuration of the mixer, and in addition, reducing the gas-to-air ratio is an additional safety parameter, since when the gas-to-air ratio decreases, the flame also tends to extinguish due to instability, without leading to oxide formation carbon.

Thus, the invention solves the problem that has been proposed, and provides the described advantages over known solutions.

Claims (7)

1. A mixer device for combustible gas burners, comprising:
- a fan unit (6) with an impeller (7) having radial blades (8), driven around a rotation axis (X), and with an axial inlet section (9) and a radially opposite outlet section (10),
- pipeline (11) for accommodating the impeller of said fan,
- a first channel (15) for supplying an air flow to the inlet section, wherein said first channel is coaxial with the axis of rotation (X) and has an end portion (15a) converging close to the inlet section (9),
- a second tubular channel (16) for supplying a gas stream at the end of the end portion (15a) having the smallest cross-section, the second tubular channel being coaxial with the first channel (15) so that the air stream is mixed with the gas stream downstream of the inlet fan sections (9),
- impeller blades (8) protruding from the base surface (12) of the impeller, each blade (8) having a leading edge (13) located in the inlet section (9), and these leading edges form the inlet openings of the respective blade channels between adjacent pairs of blades passing between the inlet section (9) and the exhaust section (10) of the fan,
- pipeline (11) having a profile (14) of the front surface located in front of the impeller blades (8) and spaced from them, characterized in that it contains at least one additional device (20) that protrudes from the first channel (15) in the direction from said axis (X) and which is located outside the first channel (15), at least one additional device extends into the region bounded simultaneously by the profile of the end part of the first channel (15), extending the end part (15a) to the base surface (12) to stalk, by the side of the impeller base surface (12) near the respective edges (13) of the blades, the leading edges (13) of the blades, and the profile (14) of the front surface of the pipeline (11), which is located in front of the blades (8) of the impeller close to the corresponding leading edges ( 13) the blades. 2. The device according to claim 1, characterized in that at least one additional device (20) has the same shape as the stator blade element. 3. The mixer device according to claim 2, characterized in that at least one additional device (20) has a plate shape. 4. The mixer device according to claim 3, characterized in that at least one additional device (20) extends radially from the axis of rotation (X) and has flat opposite surfaces (20a). 5. The mixer device according to claim 2, characterized in that it contains at least four additional devices (20) located around the circumference at equal angular intervals. 6. The mixer device according to claim 5, characterized in that each of the additional devices (20) has a rectangular flat profile. 7. The mixer device according to claim 6, characterized in that each of the additional devices (20) has a thickness greater than 0.2 mm, measured between opposite surfaces (20a), while the channel (15) has a wall with a thickness of less than 3 mm by its end with the smallest cross section.

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