Method and device for aerodynamicaliy forming a mixture in a premix burner and an inlet forecourt for a burner

Abstract

The invention relates to a method and a device for pneumatically forming a mixture for a burner (3) by means of a blower (2) for generating an air flow, which is delivered to the burner (3) via a throttle point (6), wherein a combustion gas can be mixed before or in the throttle point (6) via a combustion gas regulating valve (9), wherein a reference pressure measuring point (13) is located in an inlet upstream (8) of the throttle point (6) between the blower (2) and the throttle point (6) which influences the air flow, which is connected to the combustion gas regulating valve (9) via a control line (14). The invention enables a reduced reference pressure (Pref) to be achieved in the heating device (1) for regulating the combustion gas supply, so that a pressure loss in the exhaust gas discharge device (10) of the heating device (1) no longer has a negative effect.

Description

Background Technology

[0001] This invention relates to a method and apparatus for aerodynamically forming a stable mixture in a premixed burner for igniting combustion gases and ambient air. Known burners, particularly in so-called gas combustion value devices / gas condensing boilers, supply ambient air via a blower / fan and mix it with combustion gases in a pre-given amount via a combustion gas regulating valve. This invention relates to an apparatus in which fuel mixing is achieved on the pressure side of a blower. This mixture is then ignited in a combustion chamber and subsequently used to generate heat in stable, controlled combustion, typically for supplying hot water and / or heat to a heating system. A mixture of air and combustion gases burns safely and environmentally friendly only when the air-to-combustion gas mixture ratio (air coefficient λ / Lambda) is within a flammable and environmentally friendly range. If this is not the case, then (partially) unburned combustion gases may enter the environment, which may also include carbon monoxide and / or even, in undesirable locations, the accumulation of flammable mixtures, potentially posing an explosion hazard. Therefore, special attention should be paid to the formation of the mixture of ambient air and combustion gases.

[0002] According to existing technology, to initiate the combustion process, a blower is first turned on, which delivers a pre-defined airflow to the burner through a throttling device (especially a Venturi nozzle). At the combustion gas inlet, typically before or within the Venturi nozzle, the combustion gas mixes with this airflow, achieved by opening a combustion gas shut-off valve and via a combustion gas regulating valve. To ensure that the combustion gas is not mixed prematurely during blower startup or mixed in the wrong amount during operation, a control circuit is provided that transmits a reference pressure Pref obtained between the blower and the combustion gas inlet to the combustion gas regulating valve. This valve opens only when sufficient air is delivered by the blower, allowing a proportional amount of combustion gas to flow within a certain regulation range, or setting a pressure Pout at the outlet of the regulating valve equal to the reference pressure Pref. Here, Pout = Pref holds true. Conversely, if, for some reason, sufficient air is no longer delivered, the combustion gas regulating valve closes because the reference pressure becomes too low. However, it also goes out of the adjustment range when the difference between the reference pressure and the supply pressure of the combustion gas (which may be, for example, about 15 mbar) is too small, or when the reference pressure becomes too large proportionally.

[0003] Among the many influencing factors, the pneumatic regulation also depends on the quality or type of the reference pressure measurement. In cases of very large pressure losses (depending on the corresponding burner power, this could occur, for example, in the exhaust vent / exhaust path), the reference pressure formed in this way can be very large, such that it almost reaches the input pressure Pin (e.g., 15 mbar) provided by the combustion gases at the combustion gas regulating valve and thus falls outside the regulation range. As a result, the combustion gas flow mixed into the airflow tends to be zero, and therefore insufficient combustion gases are provided to the burner for combustion, which can lead to undesirable consequences or even system shutdown. Summary of the Invention

[0004] For this pneumatic regulation according to the prior art, the object of the present invention is to change the reference pressure drop so that the effects, especially due to the pressure loss downstream of the throttling section (Venturi nozzle), do not have a significant impact on the reference pressure, and to provide as reliably as possible during operation the pressure difference between the reference pressure and the supply pressure of the combustion gas, which is at least required for regulation.

[0005] The method, apparatus, and inlet preamplifier according to the independent claims are used to achieve this objective. Advantageous designs and modifications of the invention are given in their respective dependent claims. The invention is described in the specification, and in particular, in conjunction with the accompanying drawings, and other embodiments are given.

[0006] In the method according to the invention for forming a mixture of air and combustion gas for use in a premixed burner, a blower generates an airflow that is introduced into the burner through a throttling section, particularly a venturi nozzle, and the combustion gas mixes with the airflow before or during the throttling section via a combustion gas regulating valve. A reference pressure measuring section for obtaining a reference pressure between the blower and the throttling section is connected to the combustion gas regulating valve via control lines to transmit the reference pressure. The acquisition of the reference pressure is performed in the inlet pre-stage by a pressure reduction. Here, the reference pressure is always proportional to the static pressure before the throttling section caused by the blower, but the pressure is slightly reduced by using the inlet pre-stage, thereby relatively reducing the disruptive effect of pressure loss in the subsequent system. In the simplest case, this effect (reduction) of the reference pressure can be achieved by reducing the pressure at a point where the airflow is faster (and therefore lower) than at a conventional reference pressure measuring section. Typical nozzle shapes create these areas of faster flow. In this case, the reference pressure Pref obtained in the inlet stage is constituted by the formula Pref = Pstat + Pdyn, where Pstat is the static pressure representing the amount of air delivered by the blower before the throttling section, and Pdyn is the dynamic (negative) pressure related to the flow rate.

[0007] In a preferred embodiment of the invention, the inlet pre-stage is positioned directly upstream of the throttling section, which is obviously to facilitate flow. This design avoids unnecessary pressure loss at the connection points. The inlet pre-stage has a narrowing region where a reference pressure is obtained via at least one pressure acquisition opening. Because the flow is faster and the pressure is lower in the narrowing region, the desired reduction in reference pressure can be achieved. It has been shown that pressure losses and changes in flow conditions in subsequent equipment components no longer have a disruptive effect on the mixing of combustion gases, as the reduced reference pressure is almost solely related to the static component of the airflow generated by the blower.

[0008] Of particular advantage is that two or more pressure acquisition openings are located in the narrowing region and connected together to the reference pressure measurement site. This can be achieved, for example, by having all the pressure acquisition openings open into an annular space surrounding the narrowing region, and then also acquiring the reference pressure from that annular space.

[0009] The present invention also provides an apparatus for pneumatically forming a mixture for a burner that burns combustion gases with ambient air, wherein a blower is provided to generate an airflow that is introduced into the burner through a throttling section, particularly a venturi nozzle, wherein the combustion gases can be mixed via a combustion gas regulating valve before or within the throttling section, wherein a reference pressure measuring section is provided between the blower and the throttling section, the reference pressure measuring section being connected to the combustion gas regulating valve via a control line, and wherein the reference pressure measuring section is arranged upstream of the throttling section in an inlet pre-stage that influences the airflow. According to the present invention, the reference pressure measuring section is not located in a position where the flow is as uniform as possible, as is typically the case previously, but rather in an inlet pre-stage that alters the flow. Importantly, due to the presence of the inlet pre-stage, the reference pressure measuring section can be arranged in a region where the pressure is lower than the pressure of the undisturbed flow. Many structural forms exist that locally / locally cause a reduction in pressure, such as in the throttling section, nozzle, venturi nozzle, etc.

[0010] Therefore, preferably, the inlet preamplifier is suitably designed such that a reduced reference pressure is available at the reference pressure measurement point, which is then delivered to the fuel regulating valve. This is calibrated accordingly for a pressure range of variation in the reference pressure (but the reference pressure still maintains a desired proportion to the airflow) in order to continue mixing the desired amount of fuel into the airflow. Thus, the condition Pout = Pref is modified such that Pout > Pref generally holds, since Pout should remain constant, but Pref becomes smaller.

[0011] In a preferred embodiment of the invention, the inlet preamplifier includes a narrowing region with at least one pressure acquisition opening connected to a reference pressure measurement point. Such pressure acquisition openings have historically been mostly orifices, but other shapes can be manufactured using modern manufacturing techniques. The key is the ability to reliably obtain the fluid pressure at the opening.

[0012] In one particular embodiment, each pressure sampling opening has a chamfer at least on its downstream edge. This is particularly advantageous if, as expected, laminar flow does not form in the narrowing region. The inclination of each upstream edge thus helps to avoid additional eddies and pressure fluctuations. Because the pressure sampling openings can also be located in regions that extend obliquely (i.e., tapered) relative to the flow direction, it is particularly advantageous to chamfer at least the downstream inner edge of the pressure sampling opening. However, the entire edge can also be chamfered.

[0013] Preferably, the inlet preamplifier is positioned directly upstream of the throttling section, and a nozzle or venturi nozzle is formed through a narrowing region, to which the throttling section is conveniently connected for flow. In this way, the combination of the inlet preamplifier and the throttling section can be constructed compactly with minimal flow disturbance. Alternatively, both can be integrated into a single component.

[0014] The present invention also relates to an inlet preamplifier for a burner, wherein the inlet preamplifier has a narrowed region from which at least one pressure acquisition opening branches and connects to a reference pressure measurement site. The narrowed region can, for example, reduce the cross-sectional area available for airflow by 5% to 40%, preferably 10% to 20%. This inlet preamplifier can be easily retrofitted or integrated into new equipment and allows for a reduced reference pressure less affected by subsequent pressure losses within the equipment, using which a combustion gas regulating valve can be reliably controlled. Attached Figure Description

[0015] The illustrative embodiments of the present invention and the operation of the method according to the present invention will be described in detail below with the aid of the accompanying drawings, including but not limited to the illustrative embodiments of the present invention. Wherein:

[0016] Figure 1 An apparatus for pneumatically forming a mixture according to the present invention is shown, and

[0017] Figure 2 Show Figure 1 The details show the shape of the pressure acquisition opening. Detailed Implementation

[0018] Figure 1The apparatus according to the invention, namely heating device 1, is schematically shown, with details crucial for understanding the invention. A blower 2 draws in ambient air via an air suction pipe 4 and delivers it to a burner 3. Behind the blower 2 and in front of the burner 3, the air flows through a throttling section 6, specifically in the form of a venturi nozzle, where combustion gases mix with the airflow. The combustion gases, at a supply pressure Pin, travel from the supply line to a combustion gas regulating valve 9 via a combustion gas shut-off valve 5, and from there to the throttling section 6 at an outlet pressure Pout. The combustion gas regulating valve 9 is connected via a control line 14 to a reference pressure measuring section 13. The reference pressure Pref obtained there determines whether the combustion gas regulating valve 9 is open and to what extent, in order to mix the amount of combustion gases corresponding to the airflow. A control unit 7 controls and regulates the process operating in the heating device via signal lines (not shown). The flame exiting the burner 3 heats a heating circuit (not shown) and / or a domestic water circuit via a heat exchanger 11. The generated exhaust gases are discharged into the environment through an exhaust exhaust device / exhaust path 10.

[0019] According to existing technology, the reference pressure Pref can be easily obtained between the blower 2 and the throttling section 6. According to the invention, this process takes place in the inlet pre-stage 8, which has a narrowing region 16. The reference pressure Pref is collected there through at least one pressure acquisition opening 12. The reference pressure is lower due to the faster flow in the narrowing region 16. As mentioned above, different conditions in the burner 3 and / or exhaust gas outlet 10 (or different environmental conditions or different burner power) can lead to pressure losses, but due to the effect of the narrowing region 16 and the resulting lower reference pressure Pref, adverse consequences are no longer possible. The lower reference pressure Pref can be balanced by correspondingly calibrating the combustion gas regulating valve 9. However, there is no longer a risk that the reference pressure Pref will approach the combustion gas supply pressure Pin, so even if the pressure loss in the gas path system 10 is relatively high, there is no need to worry about an insufficient supply of combustion gas.

[0020] The design of the inlet preamplifier 8 with one or more pressure acquisition openings 12 allows for greater design flexibility. In the present illustrative embodiment, two pressure acquisition openings 12 are exemplarily shown, both openings leading into and connecting to the reference pressure measurement section 13 via the annular chamber. The pressure acquisition openings 12 are positioned in a narrowing region 16 where airflow is faster. Here, the pressure acquisition openings 12 can be located in a conical, still-narrowing region or in a cylindrical, already narrowing region. Typically, but particularly advantageous in the first case, the inner edges of these pressure acquisition openings 12 are chamfered 15, at least on the downstream portion.

[0021] exist Figure 2 The design with chamfer 15 is shown again in a magnified view. There, the pressure collection opening 12 is located in the tapered portion of the narrowing region 16.

[0022] The present invention can obtain a reduced reference pressure for regulating the supply of combustion gas in the heating device, thereby eliminating the negative impact of pressure loss in the exhaust gas discharge device of the heating device and enabling reliable operation of the combustion gas regulating valve even when the pressure loss changes.

[0023] List of reference numerals

[0024] 1. Heating device

[0025] 2. Blower / Fan

[0026] 3. Burner

[0027] 4. Air suction tube

[0028] 5. Combustion gas shut-off valve

[0029] 6. Throttling point (Venturi nozzle)

[0030] 7 Control Unit

[0031] 8. Entrance pre-stage

[0032] 9. Combustion gas regulating valve

[0033] 10. Exhaust gas discharge device / exhaust gas path

[0034] 11 Heat Exchanger

[0035] 12 Pressure sampling opening

[0036] 13. Reference pressure measurement location

[0037] 14 Control circuit

[0038] 15 Chamfer

[0039] 16 Narrowing area

[0040] 17. The pressure acquisition opening is located at the downstream edge.

[0041] Pref reference pressure

[0042] Pin: Supply pressure of combustion gas

[0043] Pout is the outlet pressure of the combustion gas after the combustion gas regulating valve.

Claims

1. A method for forming a mixture of air and combustion gas for a burner (3), wherein, A blower (2) generates an airflow that is delivered to a burner (3) via a throttling section (6), and combustion gases are mixed with the airflow before or within the throttling section (6) via a combustion gas regulating valve (9), the throttling section (6) being a Venturi nozzle, wherein a reference pressure measuring section (13) for obtaining a reference pressure (Pref) between the blower (2) and the throttling section (6) is connected to the combustion gas regulating valve (9) via a control line (14) for transmitting the reference pressure (Pref), and the acquisition of the reference pressure (Pref) is carried out in an inlet preamplifier (8) in a pressure reduction manner; the inlet preamplifier (8) is located directly upstream of the throttling section (6) and has a narrowing region (16), in which the reference pressure (Pref) is acquired via at least one pressure acquisition opening (12).

2. The method according to claim 1, wherein, Two or more pressure acquisition openings (12) are arranged in the narrowed area (16) and connected together to the reference pressure measurement site (13).

3. An apparatus for pneumatically forming a mixture for a burner (3), said burner causing combustion gases to burn with ambient air, wherein, A blower (2) is provided to generate an airflow, which is delivered to the burner (3) via a throttling section (6). Combustion gases are mixed via a combustion gas regulating valve (9) before or within the throttling section. A reference pressure measuring section (13) is also provided between the blower (2) and the throttling section (6). The reference pressure measuring section is connected to the combustion gas regulating valve (9) via a control line (14). The reference pressure measuring section (13) is arranged upstream of the throttling section (6) in an inlet preamplifier (8) that influences the airflow. The inlet preamplifier (8) is designed such that a reduced reference pressure (Pref) can be obtained at the reference pressure measuring section (13). The inlet preamplifier (8) has a narrowing region (16) in which at least one pressure acquisition opening (12) connected to the reference pressure measuring section (13) is provided.

4. The apparatus according to claim 3, wherein, Each pressure acquisition opening (12) has a chamfer (15) at least on the downstream edge (17).

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