Heating device with a gas-air mixing device

Abstract

The invention relates to a heating device (1) comprising a conveying device (2) which supplies a mixture of fuel gas and combustion air to a burner (3), and a one-piece gas-air mixing device (15) comprising a line element (19) which can be inserted into a flow path of the heating device (1) and at least one mixing element (20) which projects into a flow cross-section of the line element (19) and has at least one gas outlet opening (21).

Description

[0001] The invention relates to a heating device with a gas-air mixing device.

[0002] Heating devices for burning a fuel gas, such as natural gas or hydrogen, generally create a combustion mixture of fuel gas and combustion air with a predetermined combustion air ratio (also known as lambda or air ratio) and feed this mixture to a burner for combustion. Such heating devices are also known as premix burners. Various processes are known for forming the combustion air ratio. Heating devices with a pneumatic gas-air connection record a control pressure in the area of a throttle point (Venturi nozzle) in the combustion air supply, which allows a conclusion to be drawn about the supplied mass flow of combustion air. Using the reference pressure, the gas valve adds a mass flow of fuel gas corresponding to a predetermined combustion air ratio. The fuel gas is often mixed with the mass flow of combustion air in the area of the throttle point, which can be designed as a gas-air mixing device for this purpose.The advantage of pneumatic mixture formation is that it does not require complex sensors and is therefore very robust in application and simple in construction.

[0003] In such heaters, the heating output is controlled, or a modulation point is reached, by means of the fan speed, which adjusts the mass flow of combustion air to be supplied, to which the gas valve, based on the control pressure, adds a flow rate of fuel gas corresponding to a predetermined combustion air ratio. For this purpose, the requirements for heaters with regard to their modulation range—for example, the heaters must be operable at an output of 10% of the rated output—pose a challenge for the design of the mixing device. Thus, the mixing device (the throttle point) must generate sufficient intake pressure for mixture formation at low outputs, but at high outputs, the pressure drop at the throttle point must not be too high.A large pressure drop at high power levels is accompanied by a number of disadvantages, such as the need for a large fan, high noise emissions and a risk of flushing the heater's siphon due to the high pressure.

[0004] To utilize the intake pressure of the throttle point, gas is usually added in the area of the smallest flow cross-section of the throttle point. For example, EP 3 488 148 B1 shows a gas-air mixing device with at least six gas pockets for adding fuel gas, arranged in the area of the narrowest flow cross-section of the throttle point. However, this mixing device can also only be used for a limited modulation range. Thus, gas-air mixing devices can often achieve stable and precise formation of the combustion mixture at low power levels. However, at high power levels, the suction effect from the radial channels can become excessive, meaning that high power levels cannot be achieved cleanly and evenly or may not be achieved at all.

[0005] DE 10 2017 216 966 A1 describes a gas-air mixing device designed to cover a wide modulation range. For this purpose, adjustable openings for combustion air and fuel gas are provided, which can be adjusted using a controllable adjustment device. This mixing device has a complex, multi-part design.

[0006] Based on this, the object of the invention is to propose a gas-air mixing device for a heater and a heating device that at least partially overcomes the described problems of the prior art. In particular, the mixing device should enable safe operation of the heater within a wide modulation range, for example, a modulation range with a lower limit of 10% of the heater's rated power.

[0007] In addition, the invention should at least not significantly increase the complexity of a mixing device or a heating device and the mixing device should be easy to manufacture.

[0008] These objects are achieved by the features of the independent patent claims. Further advantageous embodiments of the solution proposed here are specified in the independent patent claims. It is pointed out that the features listed in the dependent patent claims can be combined with one another in any technologically expedient manner and define further embodiments of the invention. Furthermore, the features specified in the patent claims are further specified and explained in the description, with further preferred embodiments of the invention being presented.

[0009] A heating device contributes to this, at least having a conveying device which supplies a mixture of fuel gas and combustion air to a burner, and a one-piece gas-air mixing device, comprising a line element which can be inserted or is inserted into a flow path of the heating device and at least one mixing element which projects into a flow cross-section of the line element and has at least one gas outlet opening.

[0010] The heater can, in particular, be a gas heater. This can have a conveying device, in particular a fan, which can convey a mass flow (or volume flow) of combustion air. The combustion air can be supplied via a combustion air supply. The gas valve can add a mass flow of fuel gas corresponding to a predetermined combustion air ratio to the mass flow of combustion air. The heater can, in particular, be a wall-mounted heater and be equipped with condensing technology. The heater can form a pneumatic gas-air connection in which a control pressure of the air supply, in particular in the area of a throttle point (Venturi nozzle), is transmitted to the gas valve, which releases a corresponding mass flow of fuel gas.A pneumatic gas-air system enables robust adjustment of a specified combustion air ratio, particularly since the fuel gas mass flow is dependent on the effective combustion air mass flow. The heater can form an electronic gas-air system, in which the signal from a flame monitor, for example, an ionization current measurement of the flame, is used to adjust the combustion air ratio. The invention can be used with a pneumatic and an electronic gas-air system.

[0011] The gas valve can, in particular, be a magnetic gas valve that releases a mass flow of fuel gas according to a suction effect or negative pressure occurring at the gas-air mixing device. The gas valve can open a path for the fuel gas and, by means of the set opening cross-section (flow cross-section available for the flow of the fuel gas), adjust the amount of fuel gas flowing out. In this respect, the fuel gas, which is under slight overpressure at the inlet of the gas valve, is guided through an adjustable opening cross-section to the outlet of the gas valve. The suction effect of the delivery device should be taken into account here. The delivery device can be arranged in the immediate vicinity of the outlet of the gas valve or the gas-air mixing device, so that the suction effect of the delivery device has a significant influence on the amount of gas flowing out of the gas valve.In this case, the suction effect can cause an excessively large outflow of fuel gas, causing the gas valve to reduce its opening cross-section to prevent an excessive outflow of fuel gas and thus a reduction in the target combustion air ratio (air ratio, lambda). This can occur with gas-air mixing devices, even though the modulation is increased due to an increased heat demand, thus increasing the opening cross-section of the gas valve. The invention enables a mitigation of the problem described above.

[0012] The combustion mixture of combustion air and fuel gas can be fed via a mixture duct to a burner located in a combustion chamber, where it is combusted. Viewed in the flow direction of the heater, an exhaust duct located within a housing of the heater can be arranged downstream of the combustion chamber, which can be connected to an exhaust system.

[0013] Such a heater can adapt its heating output to a heat requirement, also known as modulation. This can be done within a modulation range specified for the heater. To avoid frequent, wear-inducing switching of the burner on and off, modern heaters can be operated in a wide modulation range, for example from 2.4 kW [kilowatts] to 24 kW (corresponding to 10% to 100% of the nominal output). A wide modulation range places high demands on the gas-air mixing device, which must generate sufficient suction pressure for the escaping mass flow of fuel gas at low power levels, but must have the lowest possible flow resistance (pressure loss) at high power levels and thus a flow with a high mass flow of combustion air.

[0014] The gas-air mixing device can thus comprise a line section (e.g., a pipe section) that can be or is integrated into the flow path of the heater. The line section can, in particular, have the same (external) shape and size of the flow cross-section as the flow path surrounding the line section or as the lines of the heater surrounding the gas-air mixing device.

[0015] According to one embodiment, the conduit section can have a constant flow cross-section over its length through which the air can flow in the direction of flow through the heater. In other words, a gas-air mixing device proposed here does not comprise a throttle device, i.e., no tapering of the flow cross-section. For clarification, it is noted that the constant flow cross-section relates to the conduit section, and a reduction in the flow cross-section due to the protruding mixing element is not considered. The flow cross-section of the conduit element can, in particular, have a circular shape. However, the invention can, in principle, be implemented with any cross-sectional shape of the conduit element.

[0016] According to one embodiment, the mixing element can be a tubular element that is aligned (largely) perpendicular to a flow direction of the heater. The mixing element can thus also be understood as a lance that protrudes into or flush with the flow cross-section or flow path of the heater. The mixing element designed as a tubular element can have a circular cross-section and an inner and / or outer diameter that is largely constant over its length. In particular, the mixing element can be a tubular element that is (completely) straight in the axial direction and is aligned perpendicular to the line part or a flow direction thereof. An opening of the mixing device can have an outflow direction that is aligned perpendicular to the line element or a flow direction thereof.

[0017] According to one embodiment, the mixing element can extend / collapse into a central region of the flow cross-section. The central region here refers to a range from 20 percent to 80 percent, or in particular 40 percent to 60 percent, relative to the diameter of the pipe element. The pressure drop caused by the mixing element must also be taken into account, which can increase with the depth of the projection. A suitable depth of projection of the mixing element into the flow cross-section can be determined for a specific heater or reference heater in laboratory tests.

[0018] According to one embodiment, the mixing element, designed as a tubular element, can have a diameter ranging from 20 millimeters to 60 millimeters. The tubular element can have a circular cross-section. The diameter can also be selected depending on the installation location of the gas-air mixing device. For example, a smaller diameter can be selected for installation in the immediate vicinity of the conveying device, and a larger diameter can be selected for installation in the combustion air supply. A suitable diameter can also be determined in laboratory tests on a reference heater.

[0019] According to one embodiment, the mixing element can be configured to allow a mass flow of fuel gas to flow through it. The fuel gas can thus be guided through a wall of the conduit element into the interior of the mixing element. To achieve good mixing, the fuel gas can advantageously be introduced into the flow cross-section of the conduit element, thereby improving mixing across the entire modulation range.

[0020] According to one embodiment, the mixing element can penetrate a wall of the line element and have an inner and an outer region, wherein the outer region can be configured for connection to a gas fitting or a gas valve or also a fuel gas line.

[0021] According to one embodiment, a fastening means for a gas fitting can be arranged on the outside of the line element. The fastening means can, for example, consist of a projecting tab with a hole for receiving a screw.

[0022] According to one embodiment, the mixing element can have an open (axial) end region as a gas outlet opening. In other words, the mixing element can have two ends, one of which can be connected to the wall of the conduit element or can be arranged outside the conduit element, and the other end can be arranged freely in the flow path or flow cross-section within the conduit element and can be at least partially open. According to one embodiment, the axial end region can also be completely closed.

[0023] According to one embodiment, the mixing element can have at least two (radially arranged) gas outlet openings arranged such that a mass flow of combustion air flowing through the gas-air mixing device can flow through the mixing element. The at least two gas outlet openings in the mixing element can be arranged on a front side, which is oriented such that the mass flow of combustion air impinges on it, and on a rear side, which is oriented in the direction of the flow. It is understood that more than two openings can also be arranged.

[0024] The gas-air mixing device is constructed as a single piece and can be made of a plastic or a metallic material, for example. It can be manufactured using an injection molding process, for example. The gas-air mixing device can be manufactured using an aluminum die-casting process, for example.

[0025] The details, features, and advantageous embodiments discussed in connection with the gas-air mixing device can also be found in the heater presented here, and vice versa. In this respect, reference is made in full to the explanations therein for a more detailed characterization of the features.

[0026] This therefore provides a gas-air mixing device for a heater and a heater that at least partially solve the problems described with reference to the prior art. In particular, the gas-air mixing device and the heater contribute to enabling safer operation of a heater across a wide modulation range. In particular, the heater can be operated safely and robustly both at minimum and maximum power.

[0027] In addition, a gas-air mixing device proposed here can be easily used on a state-of-the-art heater and could therefore also be retrofitted to existing heaters.

[0028] The invention and the technical environment are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments cited. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts explained in the figures and combine them with other components and findings from the present description. In particular, it should be noted that the figures, and in particular the proportions shown, are only schematic. They show: Fig. 1 : a heater proposed here, and Fig. 2 : a gas-air mixing device proposed here, Fig. 3 : another view of the gas-air mixing device, and Fig. 4 : a representation of the gas-air mixing device integrated into a flow path of the heater.

[0029] Fig. 1 shows, by way of example and schematically, a heater 1 proposed here, comprising a housing 18. This can have an air supply 4 for combustion air. A gas-air mixing device 15 can be arranged in the air supply 4. Viewed in a flow direction 16 of the heater 1, a conveying device 2 designed as a fan, which can convey a mass flow of combustion air, can be arranged downstream of the gas-air mixing device 15. A gas valve 5 can, by means of the gas-air mixing device 15, add a mass flow of fuel gas to the mass flow of combustion air conveyed by the conveying device 2. For this purpose, the gas valve can be connected to a gas supply 8. The combustion mixture of fuel gas and combustion air can be fed via a mixture channel 12 to a burner 3 arranged in a combustion chamber 26 and burned there.A heat exchanger 13 can be arranged on the burner 3, which can transfer heat generated during combustion to a heating circuit 14 with a flow 6 and a return 9.

[0030] Downstream of the burner 3, an exhaust pipe 10 arranged within the housing 18 can supply combustion products to an exhaust system 11 outside the housing 18. A control and regulating device 7 of the heating device 1 can be electrically connected at least to the gas valve 5 and the conveying device 2.

[0031] A flame monitor 17 can be arranged on the burner 3, configured to check for the presence of a flame at the burner 3. A signal from the flame monitor 17 can also be used to detect the current combustion air ratio during combustion. The flame monitor 17 can be an ionization electrode or a UV (ultraviolet) sensor, which is used particularly in heaters 1 powered by hydrogen as a fuel.

[0032] Fig. 2 shows a more detailed representation of the gas-air mixing device 15. A line element 19 can be designed to be integrated into the flow path of the heater 1, for example between the air supply 4 and the conveying device 2. The line element 19 can have a circular cross-sectional area.

[0033] A mixing element 20 can penetrate a wall of the line element 19 and have fastening means 22 outside the line element 19 for attaching the gas valve 5. Within the line element 19, the mixing element 20 can have gas outlet openings 21 through which fuel gas can exit into the line element 19. First gas outlet openings 27 can be arranged on a downstream side of the mixing element 20, and second gas outlet openings 28 can be arranged on an upstream side of the mixing element 20, so that an air flow flows through the mixing element 20 in the flow direction 16.

[0034] The gas-air mixing device 15 may comprise fastening means 23 for fastening to the conveying device 2, which may, for example, be designed as a flange and may comprise holes for receiving connecting means such as screws.

[0035] Fig. 3 shows a further illustration of the gas-air mixing device 15 from Fig. 2 . The second gas outlet openings 28 can be seen, which point in the direction of flow 16 of the heater 1 or the gas-air mixing device 15.

[0036] Fig. 4 shows a detailed view of the gas-air mixing device 15 installed in the heater 1 and adjacent components. The gas-air mixing device 15 is positioned between an air supply pipe 24, which can also be designed as a silencer, and the conveying device 2. The gas valve 5 is arranged on the gas-air mixing device 15 on the fastening means 22 provided for this purpose. The mixture channel 12 can be arranged downstream of the conveying device 2 and extends to a burner door 25, wherein the combustion mixture is guided through the burner door 25 into a cavity of the burner 3 located in the combustion chamber 26.

[0037] As a precaution, it should be noted that the numerals used here ("first", "second", ...) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and therefore do not necessarily specify any interdependence and / or sequence of these objects, quantities, or processes. Should a dependence and / or sequence be required, this is explicitly stated here or will be obvious to the person skilled in the art upon studying the specifically described embodiment. To the extent that a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or part of the majority of these components, but this is not mandatory. List of reference symbols

[0038] 1 Heater 2 Conveyor system 3 Burner 4 Air supply 5 Gas valve 6 Flow 7 Control unit 8 Gas supply 9 Return 10 Exhaust pipe 11 Exhaust system 12 Mixing duct 13 Heat exchanger 14 Heating circuit 15 Gas-air mixing device 16 Flow direction 17 Flame monitoring 18 Housing 19 Pipe element 20 Mixing element 21 Gas outlet opening 22 Gas valve fastening means 23 Conveyor system fastening means 24 Air supply pipe 25 Burner door 26 Combustion chamber 27 First gas outlet opening 28 Second gas outlet opening

Claims

1. Heating device (1), comprising a conveying device (2) which supplies a mixture of fuel gas and combustion air to a burner (3), and a one-piece gas-air mixing device (15) comprising a line element (19) which can be inserted into a flow path of the heating device (1) and at least one mixing element (20) which projects into a flow cross-section of the line element (19) and has at least one gas outlet opening (21).

2. Heating device (1) according to claim 1, wherein the line element (19) of the gas-air mixing device (15) has a largely constant flow cross-section over the entire length through which the gas can flow in the flow direction (16) of the heating device (1).

3. Heating device (1) according to one of the preceding claims, wherein the mixing element (20) is a tubular element which is oriented perpendicular to a flow direction (16) of the heating device (1) of the gas-air mixing device (15).

4. Heating device (1) according to claim 3, wherein the mixing element (20) has a constant diameter over its length.

5. Heating device (1) according to claim 3 or 4, wherein the mixing element (20) is designed to be flowed through by a mass flow of fuel gas.

6. Heating device (1) according to one of claims 3 or 4, wherein the mixing element (20) has an open end region as a gas outlet opening (21).

7. Heating device (1) according to one of the preceding claims, wherein the mixing element (20) has at least two gas outlet openings (21) which are arranged such that the mixing element (20) is flowed through by a mass flow of combustion air flowing through the line element (19).

8. Heating device (1) according to one of the preceding claims, wherein the mixing element (20) extends into a central region of the flow cross-section of the line element (19).

9. Heating device (1) according to one of the preceding claims, wherein a fastening means (22) for a gas valve (5) of the heating device (1) is arranged outside the line element (19) in extension of the mixing element (20).

10. Heating device (1) according to one of the preceding claims, wherein the gas-air mixing device (15) consists of a plastic or a metallic material.

11. Heating device (1) according to one of the preceding claims, wherein the gas-air mixing device (15) is arranged between an air supply pipe (24) and a conveying device (2) of the heating device (1).

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