Heater 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 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

The invention relates to a heating device with a gas-air mixing device.Heating devices for burning a combustion gas, such as natural gas or hydrogen, generally form a combustion mixture of combustion gas and combustion air with a predefined combustion air ratio (also referred to as lambda or air ratio) and feed this to a burner for combustion. Such heating devices are also referred to as premixing burners. Various methods are known for forming the combustion air ratio. Heating devices with a pneumatic gas-air combination detect a control pressure in the region of a throttle point (Venturi nozzle) in the supply of the combustion air, which permits a conclusion to be drawn as to the mass flow of combustion air supplied. On the basis of the reference printer, the gas valve adds a mass flow of fuel gas corresponding to a predefined combustion air ratio. The admixture of the combustion gas into the mass flow of combustion air frequently takes place in the region of the throttle point, which can be designed for this purpose as a gas-air mixing device. Pneumatic mixture formation advantageously does not require any complicated sensor system and is therefore very robust in use and simple in construction.In such heating devices, the heating power is controlled or a modulation point is approached by means of the blower speed, which adjusts combustion air to a mass flow to be supplied, to which the gas valve uses the control pressure to add a flow rate of combustion gas corresponding to a predefined combustion air ratio. For this purpose, the requirements for heaters with regard to their modulation range, for example the heaters should be operable with a power of 10% [percent] of the rated power, represent a challenge to the design of the mixing device. Thus, the mixing device (the throttle point) must generate a sufficient intake pressure for the mixture formation at low outputs, but the pressure drop at the throttle point does not have to be too high at high outputs. A large pressure drop at high powers is associated with a number of disadvantages, for example the need for a large fan, high noise emissions and a risk of flushing the siphon of the heater due to the high pressure.In order to utilize the intake pressure of the throttle restriction, the gas is usually added in the region of the smallest flow cross section of the throttle restriction. For this purpose, EP 3 488 148 B1, for example, shows a gas-air mixing device having at least six gas pockets for adding fuel gas, arranged in the region 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, the gas-air mixing devices can frequently achieve a stable and precise formation of the combustion mixture at low powers, but at high powers the suction effect from the radial ducts can become too great, as a result of which high powers cannot be started up cleanly and uniformly or can no longer be achieved at all.Proceeding from this, it is an object of the invention to propose a gas-air mixing device for a heating device and a heating device, which at least partially overcome the described problems of the prior art. In particular, the mixing device should allow reliable operation of the heating device in a widely spread modulation range, for example a modulation range with a lower limit of 10% of the rated power of the heating device.In addition, the invention is not intended to increase the complexity of a mixing device and of a heating device at least substantially and to make the mixing device simple to produce.These objects are achieved by the features of the independent 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 desired, technologically meaningful manner and define further embodiments of the invention. In addition, the features specified in the patent claims are more precisely described and explained in the description, further preferred embodiments of the invention being presented.A heating device contributes to this, at least having a conveying device which feeds a mixture of combustion gas and combustion air to a burner, and a gas-air mixing device, comprising a line element which can be inserted or can be 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.The heating device can be, in particular, a gas heating device. This can have a conveying device, in particular a blower, which can convey a mass flow (or volume flow) of combustion air. The combustion air can be supplied with combustion air via a supply. The gas valve can add combustion air to the mass flow, which corresponds to a predefined combustion air ratio, to mass flow of combustion gas. The heating device can be in particular a wall-hanging heating device and equipped with calorific value technology. The heating device can form a pneumatic gas-air combination, in which a control pressure of the air supply, in particular in the region of a throttle point (Venturi nozzle), is transmitted to the gas valve and the latter delivers a corresponding mass flow of fuel gas. A pneumatic gas-air combination enables a robust setting of a predefined combustion air ratio, in particular since a mass flow of combustion gas takes place as a function of the effectively flowing mass flow of combustion air. The heating device can form an electronic gas-air composite, in which the signal of a flame monitoring system, for example an ionization current measurement of the flame, is used to set a combustion air ratio. The invention can be used with a pneumatic and an electronic gas-air composite.The gas valve can be, in particular, a magnetic gas valve which delivers a mass flow of fuel gas in accordance with a suction effect or a reduced pressure occurring at the gas-air mixing device. The gas valve can thereby open a path for the fuel gas and adjust the quantity of the outflowing fuel gas by means of the adjusted opening cross section (flow cross section available for the flow of the fuel gas). In this respect, the fuel gas 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. In this case, a suction effect of the conveying device should be observed. The conveying device can be arranged in the immediate vicinity of the outlet of the gas valve or of the gas-air mixing device, so that the suction effect of the conveying device has a considerable influence on the quantity of gas flowing out of the gas valve. In this case, the suction effect can bring about an excessively large, outflowing mass flow of fuel gas, as a result of which the gas valve reduces its opening cross section in order to prevent an outflow of an excessively large mass flow of fuel gas and thus a reduction in the ambient combustion air ratio (air ratio, lambda). This can occur with gas-air mixing devices, although due to an increased heat requirement the modulation is increased and thus the opening cross section of the gas valve is increased. The invention enables the above-described problem to be alleviated.The combustion mixture of combustion air and combustion gas can be supplied via a mixture duct to a burner arranged in a combustion chamber and burned there. Viewed in a flow direction of the heating device, an exhaust gas duct which is located within a housing of the heating device and which can be connected to an exhaust gas system can be arranged downstream of the combustion chamber.Such a heating device can adapt its heating power to a heat requirement, also referred to as modulating. This can take place within a modulation range predetermined for the heating device. In order to avoid frequent, wear-promoting switching on and off of the burner, modern heating devices can be operated in a large modulation range, for example from 2.4 kW [kilowatts] to 24 kW (corresponding to 10% to 100% of the rated power). A large modulation range makes high demands on the gas-air mixing device, which must generate a sufficient suction pressure for the emerging mass flow of combustion gas at low powers, but must have as low a flow resistance (pressure loss) as possible at high powers, and thus a flow with a high mass flow of combustion air.The gas-air mixing device can thus comprise a line part (for example a pipe piece) which can be integrated or is integrated into the flow path of the heating device. The line part can in this case in particular have the same (outer) shape and size of the flow cross section as the flow path surrounding the line part or as the lines of the heating device surrounding the gas-air mixing device.According to one embodiment, the line part can have a constant flow cross section over its length through which flow can take place in the direction of flow of the heating device. In other words, a gas-air mixing device proposed here does not comprise a throttle device, i.e. no narrowing of the flow cross section. For clarification, it is noted that the constant flow cross section relates to the line part and a reduction of the flow cross section by the protruding mixing element is not taken into account. The flow cross section of the line element can in particular have a circular shape. However, the invention can in principle be realized with all cross-sectional shapes of the line element.According to one configuration, the mixing element can be a tubular element which is (largely) oriented perpendicularly to a flow direction of the heating device. The mixing element can thus also be understood as a lance which protrudes or extends flush into the flow cross section or the flow path of the heating device. The mixing element designed as a tubular element can have an inner and / or outer diameter that is as constant as possible over its length.According to one configuration, the mixing element can protrude / project into a central region of the flow cross section. The middle range here denotes a range from 20 percent to 80 percent or in particular 40 percent to 60 percent, based on the diameter of the line element. Here, the pressure drop which arises due to the mixing element and which can increase with the engagement depth is also to be taken into account. A suitable engagement depth of the mixing element into the flow cross section can be determined for a specific heating device or reference heating device in the context of laboratory tests.According to one configuration, the mixing element designed as a tubular element can have a diameter which lies in a range from 20 millimeters to 60 millimeters. The diameter can also be selected depending on the installation location of the gas-air mixing device, so that when installed in the immediate vicinity of the conveying device, a smaller diameter can be selected and when installed in the supply of combustion air, an increased diameter can be selected. A suitable diameter can also be established in the context of laboratory tests on a reference heater.According to one configuration, the mixing element can be configured to be flowed through by a mass flow of fuel gas. The fuel gas can thus be conducted through a wall of the line element into the interior of the mixing element. Advantageously, in order to achieve good mixing, the combustion gas can thus be introduced into the flow cross section of the line element, whereby the mixing can be improved in the entire modulation range.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 else a fuel gas line.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 consist, for example, in a projecting tab with a hole for receiving a display screen.According to one configuration, the mixing element can have an open end region as a gas outlet opening. In other words, the mixing element can have two ends, one end of which can be connected to the wall of the line element or can be arranged outside the line element and the other end can be arranged freely in the flow path or flow cross section inside the line element and can be at least partially opened.According to one embodiment, the mixing element can have at least two gas outlet openings which are arranged in such a way that a mass flow of combustion air flowing through the gas-air mixing device can flow through the mixing element. In this case, 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 thereon, and on a rear side which is oriented in the direction of the flow direction. It is understood that more than two openings can also be arranged.According to one embodiment, the gas-air mixing device can be formed in one piece and can consist, for example, of a plastic or a metallic material. Production can be effected by way of example by means of an injection molding process. The gas-air mixing device can be produced, for example, by means of an aluminum die casting process.The details, features and advantageous embodiments discussed in connection with the gas-air mixing device can correspondingly also occur in the heating device presented here, and vice versa. In this respect, reference is made to the full extent of the details given there for more detailed characterization of the features.Thus, a gas-air mixing device for a heating device and a heating device are provided here which 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 a heater to be operated more safely in a wide modulation range. In particular, the heating device can be operated reliably and robust both in the range of the minimum power and in the range of the maximum power.In addition, a gas-air mixing device proposed here can be used without problems on a heating device according to the prior art and could therefore also be retrofitted on existing heating devices.The invention and the technical field are explained in more detail below with reference to the attached figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments listed. 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 constituent parts and findings from the present description. In particular, it should be pointed out that the figures and in particular the size relationships illustrated are only schematic. The following are shown: FIG. 1 : shows a heating device proposed here, and FIG. 2 : a gas-air mixing device proposed here, FIG. 3 is a further view of the gas-air mixing device; and FIG. 4 : shows an illustration of the gas-air mixing device integrated into a flow path of the heating device.FIG. 1 shows, by way of example and schematically, a heating device 1 proposed here having a housing 18, which 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 heating device 1, a conveying device 2, which is designed as a blower and can convey a mass flow of combustion air, can be arranged downstream of the gas-air mixing device 15. A gas valve 5 can add a mass flow of fuel gas to the mass flow of combustion air conveyed by the conveying device 2 by means of the gas-air mixing device 15. For this purpose, the gas valve can be connected to a gas feed 8. The combustion mixture of combustion gas and combustion air can be supplied via a mixture duct 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 heat exchanger can transfer heat arising during the combustion to a heating circuit 14 with a feed line 6 and a return line 9.Arranged downstream of the burner 3, an exhaust pipe 10 arranged inside the housing 18 can supply combustion products arising to an exhaust system 11 outside the housing 18. A control and control unit 7 of the heating device 1 can be electrically connected at least to the gas valve 5 and the delivery device 2.A flame monitoring device 17 can be arranged on the burner 3 in order to check the presence of a flame on the burner 3. A signal of the flame monitoring system 17 can also be used to record a current combustion air ratio of the combustion. The flame monitoring device 17 can be an ionization electrode or a UV (ultraviolet) sensor, which is used in particular in heating devices 1 operated with hydrogen as fuel.FIG. 2 shows a more detailed illustration of the gas-air mixing device 15. a line element 19 can be configured to be integrated into the flow path of the heating device 1, for example between the air supply 4 and the conveying device 2.A mixing element 20 can penetrate a wall of the line element 19 and have fastening means 22 outside the line element 19 for fastening the gas valve 5. Within the line element 19, the mixing element 20 can have gas outlet openings 21, through which combustion gas can emerge into the line element 19. In this case, first gas outlet openings 27 can be arranged on a downstream side of the mixing element 20 and second gas outlet openings 28 on a side thereof arranged upstream of the mixing element 20, such that an air flow in the flow direction 16 flows through the mixing element 20.The gas-air mixing device 15 can comprise fastening means 23 for fastening to the conveying device 2, which can be designed, for example, as a flange and can comprise holes for receiving connecting means such as screws.FIG. 3 shows a further illustration of the gas-air mixing device 15 from FIG. 2, which shows the second gas outlet openings 28 in the direction of the flow direction 16 of the heating device 1 or of the gas-air mixing device 15.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. On the gas-air mixing device 15, the gas valve 5 is arranged on the fastening means 22 provided for this purpose. Arranged downstream of the conveying device 2 may be the mixture channel 12 which extends as far as a burner door 25, wherein the combustion mixture is conducted through the burner door 25 into a cavity of the burner 3 located in the combustion chamber 26.As a precautionary measure, it should be noted that the numerical words used here ("first", "second",... ) are primarily (only) used for distinguishing a plurality of articles, sizes or processes of the same type, that is to say in particular do not necessarily specify a dependence and / or sequence of these articles, sizes or processes with respect to one another. If a dependence and / or sequence is required, this is explicitly stated here or it is obvious to the person skilled in the art when studying the specifically described configuration. If a component can occur multiple times ("at least one"), the description of one of these components can apply equally to all or a part of the plurality of these components, but this is not obligatory.List of reference characters1 Heating device 2 Conveying device 3 Burner 4 Air supply 5 Gas valve 6 Flow line 7 Regulating and control device 8 Gas supply 9 Return line 10 Exhaust pipe 11 Exhaust system 12 Mixture channel 13 Heat exchanger 14 Heating circuit 15 Gas-air mixing device 16 Flow direction 17 Flame monitoring device 18 Housing 19 Line element 20 Mixing element 21 Gas outlet opening 22 Fastening means Gas valve 23 Fastening means Conveying device 24 Supply air pipe 25 Burner door 26 Combustion chamber 27 First gas outlet opening 28 Second gas outlet openingReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedEP 3 488 148 B1

[0004]

Claims

Heating device (1) having a conveying device (2) which feeds a mixture of combustion gas and combustion air to a burner (3), and a 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).Heating device (1) according to claim 1, wherein the line element (19) of the gas-air mixing device (15) has a substantially constant flow cross section over the entire length through which flow can take place in the flow direction (16) of the heating device (1).The heating device (1) according to any one of the preceding claims, wherein the mixing element (20) is a tubular element oriented perpendicular to a flow direction (16) of the heating device (1) of the gas-air mixing device (15).The heater (1) according to claim 3, wherein the mixing element (20) has a constant diameter along its length.Heating device (1) according to claim 3 or 4, wherein the mixing element (20) is configured to be flowed through by a mass flow of fuel gas.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).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 in such a way that a mass flow of combustion air flowing through the line element (19) flows through the mixing element (20).Heating device (1) according to one of the preceding claims, wherein the mixing element (20) extends as far as into a central region of the flow cross section of the line element (19).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).Heating device (1) according to one of the preceding claims, wherein the gas-air mixing device (15) is formed in one piece and consists of a plastic or a metallic material.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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