METHOD AND ARRANGEMENT FOR INFLUEDING A VOLUME FLOW THROUGH A FLOW PATH FOR FUEL GAS TO A HEATING APPLIANCE

Description

[0001] The invention relates to a method and an arrangement for influencing a volume flow rate through a fuel gas valve of a heating appliance, which is particularly suitable for operation with hydrogen and / or a hydrogen-containing fuel gas. Hydrogen as a fuel gas or as an additive to fuel gases is becoming increasingly important, and considerable efforts are being made to adapt new or existing heating appliances for operation with it. This applies not only to large systems, but also to wall-mounted units for heating water and, more generally, to heating appliances for heating buildings and / or providing hot water.

[0002] WO 2020 / 182 902 A1 discloses methods for operating modulating, surface-stabilized premixed gas burners, and in particular burners in which the fuel gas contains at least 20% hydrogen by volume. The aim is to prevent flashback under normal operating conditions and to minimize the impact on the overall efficiency of the heat exchanger. The probability of flashback can therefore be significantly reduced or even eliminated by increasing the air-to-fuel-gas ratio at lower load levels. This increases the exit velocity of the premixed gas flowing from the burner deck at lower loads, reduces the flame velocity, and cools the burner deck.

[0003] For many years, pneumatic gas valves, such as those described in DE 38 41 86 A1, have been used in heating appliances that operate with air and fuel gas. These gas valves are located in a flow path for the respective fuel gas and release it as needed. The mixture ratio of fuel gas to combustion air is mechanically determined in pneumatic gas valves, for example, by pre-tensioning control diaphragms via springs. Due to the physical and technical material properties of such a system, a control diaphragm has a relatively narrow operating range; that is, a possible minimum volume flow cannot fall below a certain limit, because otherwise, at correspondingly lower control pressures, this diaphragm would no longer be able to regulate the applied pressures reproducibly.At operating points with higher flow rates, these gas valves have proven their worth, so that even today this robust mechanical solution is often preferred to electronically controlled valves, which require combustion-related sensors. The exact design is not important in this case, as long as such a gas valve has a valve body in the flow path.

[0004] EP 0 379 759 A1 discloses a proportional control valve for a fluid, in particular a proportional control valve for controlling the gas supply to a gas-fired water heater used to supply hot water for a bath, a shower, and in a kitchen. The control valve comprises a valve section with a flap and a magnetic element located near the valve section and integrally attached to the main passage. A movable body, located within and actuated by the magnetic element, is also provided to displace the flap of the valve section directly or indirectly. Furthermore, an electrical control element is provided, which is connected to a sensing element for acquiring characteristic data to be controlled, thereby controlling the movable body in accordance with the acquired data.

[0005] WO 2021 / 078 949 A1, as prior art according to Article 54(3) EPC, discloses a method for starting a burner. A shut-off element is arranged in an air supply and / or gas supply of the burner, which, when the burner is started, reduces the gas flow supplied to the burner and / or increases the air flow supplied to the burner. A disadvantage is that a defect in the shut-off element can lead to unsafe operating conditions of the burner.

[0006] The ignition process is a particularly critical step in heating appliances and, in appliances with pneumatic gas valves, is generally carried out at loads of 50–80% of the rated load for which the heating appliance is designed. When igniting hydrogen-air mixtures, or mixtures of hydrogen-containing fuel gases and air, it is often advisable to lean out the fuel-air mixture ratio, i.e., reduce the amount of fuel, to ensure reliable ignition. Pure hydrogen or hydrogen admixtures, for example, in the range of 10–30%, in a fuel gas make a mixture with air very easy to ignite. If ignition is even slightly delayed after the mixture is introduced into a combustion chamber, violent deflagrations (so-called hard ignitions) can occur, which is undesirable.However, the leaner the mixture is made during ignition, the less violent the ignitions will be. The risk of flame flashback into a burner body also decreases. Mixtures of air and hydrogen with an air-fuel ratio (lambda) of, for example, 3 to 10 can still be ignited, allowing for a wide margin for leaning out the mixture. After successful ignition, components relevant for stable combustion heat up due to the presence of a flame, allowing for a lower air-fuel ratio to be set, which is usually significantly lower than during the ignition process. A change, for example, from lambda = 3 to 10 during ignition to lambda = 1.2 to 2 during normal operation can be achieved by adjusting the so-called offset (setting the preload of a control diaphragm, for example).Ignition in a pneumatic gas valve (using a stepper motor) is not possible with a stepper motor alone, because it primarily has an effect at low control pressures acting on the gas valve, i.e., at partial load of the heating appliance. However, as mentioned above, the ignition process in appliances with pneumatic gas valves takes place at a relatively high load (50-80% of the rated load). Since the fuel-to-air mixture ratio is mechanically predetermined in a pneumatic gas valve, it is not readily possible to exert a significant, time-limited influence on the mixture ratios during the ignition process.

[0007] The object of the present invention is to at least partially solve the problems described with reference to the prior art, and in particular to create a method and an arrangement for influencing a volume flow through a flow path in a pneumatic fuel gas valve of a heating appliance, wherein the arrangement should be simple and suitable for everyday operation of a heating appliance.

[0008] To solve this problem, a method and an arrangement according to the independent claims are provided. Advantageous embodiments and further developments of the invention are specified in the respective dependent claims. The description, particularly in conjunction with the drawing, illustrates the invention and provides further exemplary embodiments.

[0009] This involves a method for influencing the volume flow through a fuel gas flow path to a heating appliance, wherein the flow path includes a pneumatic fuel gas valve and wherein an additional electromechanical actuator, located inside or outside the fuel gas valve, influences the flow path and narrows and / or limits its free cross-section. The actuator is designed such that, in a rest position, it (practically) does not affect the flow path or the fuel gas valve, while when electrically actuated, it (significantly) narrows and / or limits the cross-section of the flow path. When actuated, it results in a considerably leaner mixture until it is deactivated. This is used when igniting a mixture of air and hydrogen or a hydrogen-containing fuel gas by reducing the volume flow at least until the mixture ignites when the heating appliance is started.In this way, ignition is less violent (with regard to the formation of pressure surges, noises, etc.) and even with a slightly delayed ignition, no damage occurs due to a possible deflagration.

[0010] In a preferred embodiment, the additional actuator acts directly or indirectly on a valve body of the fuel gas valve, limiting or reducing its opening. In the simplest case, the actuator can be a plunger that presses on the valve body, limiting or counteracting its movement (and opening). The plunger may, but need not, be rigidly connected to the valve body.

[0011] An arrangement for influencing a volume flow through a flow path for fuel gas to a heating device also contributes to solving the problem, wherein the flow path has a pneumatic fuel gas valve and wherein an additional electro-mechanical actuator is present inside or outside the fuel gas valve, which can narrow and / or limit a cross-section of the flow path, wherein the actuator acts directly or indirectly on a valve body of the fuel gas valve in the flow path.

[0012] In particular, the actuator can assume at least two positions: one without a narrowing of the cross-section and one with a narrowing of the cross-section. This is the simplest and easiest-to-control variant; however, it is also possible to implement not only such a switching function, but also intermediate positions or continuous adjustment.

[0013] In a preferred embodiment, the actuator is movable by a magnetic coil in conjunction with a permanent magnet or a magnetizable component. The magnetic coil moves the permanent magnet or the magnetizable component and thus the actuator (e.g., against a spring force). Switching a current through the magnetic coil activates the actuator, and switching it off deactivates it. Optionally, the position of the actuator can also be adjusted by varying the strength of the current in the magnetic coil.

[0014] In the present case, the actuator is connected to a control unit which is set up to control an ignition process of the heating device and the actuator.

[0015] The explanations of the procedure can be used to further characterize the arrangement, and vice versa. The arrangement can also be set up in such a way that the procedure is carried out using it.

[0016] Schematic embodiments of the invention, to which it is not limited, and the functioning of the method will now be explained in more detail with reference to the drawing. These depict: Fig. 1: a pneumatic fuel gas valve with integrated actuator, and Fig. 2: a fuel gas flow path with fuel gas valve and an actuator for narrowing a cross-section.

[0017] Fig. 1 Figure 1 schematically shows a flow path 6 for fuel gas (pure hydrogen or fuel gas with a hydrogen content) through a pneumatic fuel gas valve 1. The exact design and details of the fuel gas valve 1 are not important in this case. In any event, it must have a valve body 2 which, in conjunction with a valve seat 14, can open or (partially) close a flow cross-section Q. Thus, with the cross-section Q open, a volume flow 11, 12 (indicated by arrows at an inlet and an outlet) can flow through the fuel gas valve 1. In a pneumatic fuel gas valve 1 (control valve), this volume flow is matched to an air flow, which, together with the fuel gas flow, feeds a heating device (not shown).While such fuel gas valves do offer an adjustment for the air-to-fuel gas ratio, this adjustment is not suitable for large changes in this ratio in all operating situations, particularly not for a significant leaning of the mixture when igniting a heater. Therefore, in the present embodiment, a rod-shaped actuator 3 is provided, which is electromechanically movable and acts on the valve body 2. In a rest position P1, it does not affect the movement of the valve body 2 or moves freely with it. In a starting position P2, however, it limits the movement of the valve body 2 so that it can only open a limited cross-section Q for the volume flow 11, 12. This results in less fuel gas relative to air flowing to the heater (at least with large airflows), which is particularly desirable when starting the heater for the reasons described above.After the heating device has started, the actuator 3 can be moved back to its rest position P1. The movement of the actuator can be effected in any manner that can be triggered by a control unit 16. In the present embodiment, the movement is effected by a moving coil 4 in a housing 5. This contains a magnetic coil 8, which can be supplied with current from a power source 10 via leads 13 and a switch 9. The control unit 16 closes and opens the circuit according to the described requirements. A permanent magnet 7 is drawn into the magnetic coil 8 when the switch 9 is closed (e.g., against the force of a spring, not shown) and moves the actuator 3 from the rest position P1 to the start position P2. This also works analogously with a magnetizable component (e.g., made of soft iron) instead of a permanent magnet 7.The actuator 3 can (but does not have to) be rigidly connected to the permanent magnet 7 and the valve body 2 (and move with both). Alternatively, it can be designed as a free-floating plunger, so that it only has direct, rigid contact with the permanent magnet 7 and the valve body 2 in the starting position P2. In principle, any intermediate positions between P1 and P2 can also be set by adjusting the corresponding current in the solenoid coil 8, but this is not necessary in the present case. The actuator 3 must be guided within the fuel gas valve 1 by sealing devices (not shown) to prevent fuel gas from escaping.

[0018] In Fig. 2 An alternative embodiment of the invention is shown schematically. Here, the volume flow 11, 12 in the flow path 6 is not influenced by intervention in the fuel gas valve 1, but rather upstream or downstream of it. Which of the two possibilities is chosen depends, among other things, on the available space at the respective device and location. The described effect of leaning out the air-fuel gas mixture when starting a heating device can also be achieved by a controlled narrowing of the cross-section Q of the flow path 6 upstream or downstream of the fuel gas valve 1. For this purpose, a simple narrowing membrane 15 is partially pressed into the flow path 6 by the actuator 3. In the rest position P1, the narrowing membrane 15 lies virtually flat against a wall of the flow path 6, but in the start position P2, it is pressed into the flow path by the actuator 3, thereby narrowing or limiting its free cross-section Q.The drive and control of actuator 3 can be determined exactly as above using . Fig. 1 describe and be realized.

[0019] The present invention makes it possible to selectively reduce the volume flow of hydrogen or hydrogen-containing fuel gas through a pneumatic fuel gas valve 1 for the starting process of a heating device using a simple and robust device, in order to make the ignition process safer and easier to control. Reference symbol list

[0020] 1 Pneumatic fuel gas valve 2 Valve body 3 Actuator 4 Immersion coil 5 Housing 6 Flow path 7 Permanent magnet 8 Solenoid coil 9 Switch 10 Power source 11 Volume flow (inlet) 12 Volume flow (outlet) 13 Supply lines 14 Valve seat 15 Constriction diaphragm 16 Control unit Q Cross-section P1 Rest position P2 Start position

Claims

1. Method for influencing a volume flow (11, 12) through a flow path (6) for fuel gas, namely hydrogen or a hydrogen-containing fuel gas, to a heating appliance when igniting a mixture of air and fuel gas, wherein the flow path (6) comprises a pneumatic fuel gas valve (1) with a movable valve body (2), characterised in that an additional electro-mechanical actuator (3) inside or outside the fuel gas valve (1) influences the flow path (6) and narrows and / or limits its free cross-section (Q), whereby in a rest position (P1) it does not influence the flow path (6) and the fuel gas valve (1) in a rest position (P1), and when it is electrically activated, it narrows or limits the cross-section (Q) , and wherein the volume flow (11, 12) is reduced at least until the mixture is ignited when the heating appliance is started, and after starting it is moved to the rest position (P1) so that the free cross-section (Q) is widened again.

2. Method according to claim 1, wherein the additional actuator (3) acts on the valve body (2) of the combustion gas valve (1) when the heating appliance is started and limits or reduces its opening.

3. Method according to claim 2, wherein the additional actuator (3) is rod-shaped and the valve body (2) in the rest position (P1) is no longer influenced in its movement by the electro-mechanical actuator (3).

4. Method according to claim 1, wherein the additional actuator (3) limits or reduces the cross-section (Q) of the flow path (6) upstream or downstream of the fuel gas valve (1) when the heating appliance is started.

5. Method according to claim 4, wherein the additional actuator (3) partially presses a constriction membrane (15) into the flow path (6) during start-up and, after start-up, the constriction membrane (15) rests flat against a wall of the flow path (6) in a rest position (P1).

6. Arrangement for influencing a volume flow (11, 12) through a flow path (6) for fuel gas to a heating appliance designed for igniting and combusting a mixture of air and fuel gas, namely hydrogen or a hydrogen-containing fuel gas, wherein the arrangement with the flow path (6) has a pneumatic fuel gas valve (1), wherein inside or outside the fuel gas valve (1), which can narrow and / or limit a free cross-section (Q) of the flow path (6), the additional actuator (3) is connected to a control unit (16) which is designed to control an ignition process of the heating appliance and the additional actuator (3) in accordance with a method according to one of the preceding claims, and wherein the additional actuator (3) acts on a valve body (2) of the fuel gas valve (1) in the flow path (6) or on a constriction diaphragm (15) upstream or downstream of the fuel gas valve (1) in the flow path (6).

7. Arrangement according to claim 6, wherein the additional actuator (3) can assume at least two positions (P1, P2), one (P1) without constriction of the cross-section (Q) and one (P2) with constriction of the cross-section (Q).

8. Arrangement according to one of claims 6 or 7, wherein the additional actuator (3) can be moved by a solenoid coil (8) in cooperation with a permanent magnet (7) or a magnetisable component.