METHOD AND ARRANGEMENT FOR INCREASEING THE LOAD CARRIER CONCENTRATION NEAR AN IONIZATION ELECTRODE IN A HEATING APPLIANCE

Description

[0001] The invention relates to a method and an arrangement for increasing the charge carrier concentration near an ionization electrode, which is used in a heating device that can be operated with a (solid, liquid and / or gaseous) fuel, such as oil, hydrogen and / or a hydrogen-containing fuel gas, and in particular for controlling a gas-air mixture and / or monitoring flames.

[0002] Hydrogen as a fuel gas or as an additive to fuel gases is becoming increasingly important, and significant efforts are being made to adapt new and existing heating appliances for its operation. This includes not only large systems but also wall-mounted units for heating water and, more generally, heating appliances for building heating and / or hot water supply.

[0003] Some fuels, such as hydrogen, differ from conventional fuel gases in several ways during combustion. In particular, the ionization in the resulting flame is much lower. There are far fewer charge carriers available for ionization measurement. Consequently, the established ionization measurement principle for flame detection in a combustion chamber, often used with conventional fuel gases, is not readily applicable to heating appliances when these are operated with fuels that produce a lower charge concentration at the ionization electrode. This applies, for example, to the use of pure hydrogen or fuel gases consisting of more than 50%, and especially more than 95%, hydrogen.For reliable evaluation of ionization measurements, a minimum concentration of charge carriers (ions and electrons) near the ionization electrode is required in all operating conditions. These charge carriers must be able to be moved by applying a voltage and thus generate an ionization current. This is not always the case in hydrogen flames.

[0004] An important function of ionization measuring devices is to detect the presence of a stable flame (a so-called flame detector); another is to adjust the ratio of combustion air to fuel gas suitable for reliable, stable, and environmentally friendly combustion (lambda value control). Both require certain minimum ion currents, which are not always available when hydrogen is used as the fuel gas.

[0005] JP S61 208418 A discloses a gas burner, proposing that, to achieve a sufficient flame flow rate for flame detection and low NOx generation, uniformly spaced secondary air inlet openings be provided at a distance from the flame opening of the gas burner on the underside of an auxiliary combustion chamber. A flame rod is located at the flame opening, and since the secondary air is directed from the secondary air inlets into the area of ​​the rod, flame ionization can be promoted.

[0006] 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 provide a method and an arrangement that increase the charge carrier concentration near an ionization electrode when flames are to be observed in a combustion chamber, wherein the arrangements are to be simple and suitable for everyday operation of a heating appliance.

[0007] 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.

[0008] The following method contributes to increasing the charge carrier concentration near an ionization electrode, and is particularly useful for controlling a gas-air mixture and / or monitoring flames in the combustion chamber of a heating appliance. A mixture of air and a fuel, especially a fuel gas with more than 50% hydrogen content, is supplied to the heating appliance through openings in a burner body. Furthermore, it is provided that at least one substance that promotes ionization is supplied, possibly added, and / or the proportion of this substance is increased, at least in the vicinity of the ionization electrode.

[0009] Upgrading existing ionization measurement systems for fuels with low charge carrier concentrations in the flame region, such as hydrogen as a fuel gas, is possible if sufficient charge carriers (permanently or temporarily) can be provided and / or generated during operation, at least in the vicinity of the ionization electrode, that are not (directly) generated during or from the combustion of the actual air-fuel gas mixture. It is proposed here to provide an additional substance that supplies (additional or combustion-external) charge carriers under the conditions prevailing in the vicinity of the ionization electrode (flames of more than 1,000 K [Kelvin]).To achieve a higher yield of charge carriers and thus a larger, more easily evaluable ion current, it is sufficient to increase the charge carriers in the vicinity of the ionization electrode, but the density of charge carriers can also be increased throughout the flames if this is technically easier to achieve.

[0010] In this process, a coating of titanium dioxide (an ionizing agent) is applied to existing components or an additional component containing titanium dioxide is added in the vicinity of the ionization electrode. Alternatively or cumulatively, a coating of aluminum oxide (an ionizing agent) is applied to existing components or an additional component containing aluminum oxide is added in the vicinity of the ionization electrode. Titanium dioxide and aluminum oxide have the desired property of releasing electrons under ultraviolet radiation and are suitable as coatings for metallic components. Therefore, they can be applied to existing components near the ionization electrode, and / or an additional component, such as a rod or sheet, can be added.

[0011] In this context, "near or in the vicinity of an ionization electrode" does not necessarily mean the entire combustion chamber or the entire flame-filled area of ​​the combustion chamber, but rather refers specifically to the area that can be influenced by an ionization electrode and the voltage applied to it. This is particularly the area between the ionization electrode and the counter electrode (e.g., a porous burner body, possibly made of a metallic or ceramic material) and / or a (particularly cylindrical) area of ​​up to 10 cm [centimeters], especially up to 5 cm, around the ionization electrode. The surrounding area can also include the surface of the ionization electrode.

[0012] The proposed method, in particular the increase in the proportion of the substance, can also be carried out (only) if the heating appliance is (temporarily) operated in predetermined (with regard to ionization unfavorable) conditions, for example at (a) low heat loads (e.g., < 20% Qn, where Qn represents the normal heat load or the primary operating point of the heating appliance) and / or (b) lean gas-air mixture (e.g., lambda > 1.6). If these operating ranges are exited, the addition of the substance can be reduced or discontinued.

[0013] Air is indeed such a substance, particularly its nitrogen and carbon dioxide content. This is especially true for hydrogen or fuel gas with more than 50% hydrogen content, because a higher proportion of carbon dioxide and nitrogen increases ionization, which would not result in a temperature increase. Therefore, an additional supply of air, for example through air-fed openings in a burner body, is advantageous. This locally alters the lambda value, but has only a minor effect on the overall combustion process. Using additional carbon dioxide (possibly instead of air) is also very effective because this substance can provide many charge carriers. If sufficient carbon dioxide is available, it can simply be mixed with the air and / or the fuel. For lower consumption, it may be beneficial to provide an additional supply only in the vicinity of the ionization electrode.Equivalent substances can be used with other fuels, such as suitable petroleum gases (propane, butane, etc.).

[0014] Another possibility is that the substance promoting ionization is one that can be ionized by ultraviolet radiation and is placed in the vicinity of the ionization electrode. Hydrogen flames generate intense ultraviolet radiation, which can be used to produce charge carriers if a substance that releases electrons under this irradiation is irradiated with it. This substance is not consumed, or only very slowly, and eventually recaptures electrons, thus remaining permanently available for the emission of charge carriers. Certain metal oxides that are stable under the conditions prevailing in a combustion chamber are particularly suitable.

[0015] Another possibility is to introduce a substance with low ionization energy, which releases valence electrodes at flame temperature, into the vicinity of the ionization electrode. Suitable substances of this type that promote ionization include, for example, some salts that exist in solid form (as crystals) at the temperatures encountered here. They decompose (albeit very slowly) under the influence of flames, so that replenishment at certain intervals or a continuous supply is necessary.

[0016] Sodium chloride (NaCl) is particularly suitable as a substance with low ionization energy. It is readily available at low cost, and its crystals can be formed into any desired shape and are therefore easy to add.

[0017] For this purpose, it is advantageous if the substance with low ionization energy is supplied in solid form via a feeding mechanism (continuously, at least over a predefinable operating period). The mechanism can be very simple and, for example, replace material consumed at the tip of a rod by pushing it forward with a spring.

[0018] The solution to the problem is also provided by an arrangement for increasing the charge carrier concentration near an ionization electrode (for controlling a gas-air mixture and / or monitoring flames) in a combustion chamber of a heating appliance, to which a mixture of air and a fuel, in particular a fuel gas with more than 50% hydrogen content, can be supplied through openings in a burner body, wherein at least in the vicinity of the ionization electrode means are available for providing or increasing a proportion of a substance that promotes ionization.

[0019] The components in this case are made of or coated with a substance that can be ionized under ultraviolet radiation, in particular titanium dioxide.

[0020] The means referred to here can be a device for the on-demand provision of the substance. These means can include storage, conveying, and / or dispensing components. It is possible that at least one means is permanently or permanently attached to the ionization electrode. It is possible that the means is a component or coating made of the substance that promotes ionization, which is specifically provided on or attached to the ionization electrode. The means are positioned, in particular, on the ionization electrode up to a definable environmental boundary. The environment is, in particular, an area between the ionization electrode and the counter electrode and / or a (particularly cylindrical) area of ​​up to 10 cm [centimeters], in particular up to 5 cm, around the ionization electrode.

[0021] In a preferred embodiment, the means comprise at least one additional inlet for a gaseous substance, such as, in particular, air, carbon dioxide, or petroleum gas (propane, butane, etc.). If premixing of air and fuel takes place downstream of a blower, air can be diverted before mixing and supplied to an area near the ionization electrode. This increases the proportion of nitrogen and carbon dioxide in that area, thus enhancing ionization. The same effect can also be achieved by introducing carbon dioxide.

[0022] In another embodiment, a feeding mechanism is provided for a solid substance with low ionization energy, which releases valence electrodes at flame temperature. This can be, in particular, sodium chloride (NaCl).

[0023] Particularly preferred is the feed mechanism arranged between the ionization electrode and the burner body, comprising a metallic tube for supplying rod-shaped sodium chloride crystals, the tube being thermally connected to a housing of the combustion chamber for cooling. As will be explained in more detail with reference to the drawing, such a feed mechanism can be of simple design and effect a continuous supply of sodium chloride by means of spring force, whereby sodium chloride not exposed to the flames is protected by the metallic tube, which can be cooled via its connection to a housing.

[0024] The explanations of the procedure can be used to further characterize the setup, and vice versa. The setup can also be configured to carry out the procedure. It should also be noted that the various measures for increasing ionization can be used individually or in any combination. They have an additive effect and can therefore be used together in difficult cases.

[0025] Schematic embodiments of the invention, to which it is not limited, and the functioning of the method are explained in more detail with reference to the accompanying drawing. These depict: Fig. 1: schematically a section of a longitudinal section through a combustion chamber of a heating device in the area of ​​an ionization electrode, Fig. 2: schematically the arrangement of an additional inlet into a combustion chamber for a gaseous substance that promotes ionization, and Fig. 3: schematically the arrangement of a component that promotes ionization in the vicinity of an ionization electrode.

[0026] Fig. 1 Figure 1 schematically shows a section of a longitudinal section through a combustion chamber 1 of a heating appliance that can be operated with hydrogen or a hydrogen-containing fuel gas. A mixture G of air L and fuel gas enters the combustion chamber 1 from a burner interior 15 through openings 3 in a burner body 2 and combusts there, forming flames 4. The flames 4 ionize the mixture and / or the resulting gaseous combustion products. However, since only water is produced during the combustion of hydrogen, and both are hardly ionizable under the given conditions, the yield of charge carriers during hydrogen combustion is very low, making reliable observation of the flames 4 using an ionization measurement system not readily possible.In order to nevertheless generate a sufficiently large ion current by means of an ionization electrode 5, means for increasing the concentration of charge carriers are present in its vicinity 13 (in particular between the ionization electrode 5 and a counter electrode, which is usually formed by the burner body, or in a radius of 2 to 10 cm around the ionization electrode 5). In the present embodiment, this is a feed mechanism 9, 10, 11, 12 for a substance that releases charge carriers under the influence of flames 4 (essentially by thermal ionization). Salts, especially sodium chloride (NaCl), are particularly suitable for this purpose. Thus, in a guide tube 9, a salt crystal rod 8 is pressed against a lid 10 by means of a compression spring 12, whereby a small part of the salt crystal rod 8 is exposed to the flames 4 through at least one window 11.This part is consumed over time, and the remaining salt crystal rod 8 is then advanced by the compression spring 12. At certain maintenance intervals, the salt crystal rod 8 can be replaced from outside the combustion chamber 1. Preferably, the ionization electrode 5 is attached to a so-called burner door 7 by means of an electrically insulating bushing 6. The burner door 7 is part of a housing (not shown) surrounding the combustion chamber. The burner body 2 is also attached to it, and the supply of a relatively cold mixture G keeps the burner door 7 at a much lower temperature during operation than the temperature in the combustion chamber 1 (and especially in the flames 4). This can be used to keep the salt crystal rod 8 at a lower temperature, except in the area of ​​the window 11, thus extending its service life.For this purpose, the guide tube 9 (which is generally made of metal) can be coupled to the burner door 7 by means of a heat-conducting connection 18.

[0027] Fig. 2 The diagram schematically illustrates the following: Since an increase in the charge carrier concentration can also be achieved by increasing the concentration of carbon dioxide and / or nitrogen, at least in the vicinity 13 of an ionization electrode 5, an additional inlet 14 for air L is provided, so that the mixture G of air and fuel gas is directed through the burner interior 15 into the entire combustion chamber 1, while additional air enters the vicinity 13 of the ionization electrode 5. This air can be drawn off by a blower or supplied by other means. Instead of air, additional carbon dioxide can also be supplied. This can be added to the air L, the fuel gas, or the mixture G. However, the least amount of carbon dioxide is required when it is supplied solely through the additional inlet 14.Carbon dioxide can be stored in a pressure vessel (not shown) and metered in when the heating unit is started, meaning that, depending on the size of the pressure vessel, carbon dioxide only needs to be refilled at scheduled maintenance intervals. Alternatively, a system using pressure cartridges, similar to those used in the preparation of carbonated beverages, can be implemented.

[0028] Fig. 3 Figure 16 schematically shows an embodiment of the invention in which a surface of an existing or additionally installed component 17 near the ionization electrode 5 consists of, or is coated with, a material that releases electrons under ultraviolet radiation. A suitable coating 16 can, for example, consist of titanium dioxide. Since hydrogen flames emit strong ultraviolet radiation, additional charge carriers are released, which enhance ionization.

[0029] The present invention makes it possible to use cost-effective ionization measurement systems for monitoring flames and / or controlling a combustion process, even when using hydrogen-containing fuel gas or pure hydrogen as fuel gas in a heating appliance. Reference symbol list

[0030] 1 Combustion chamber (of a heating appliance) 2 Burner body 3 Openings 4 Flames 5 Ionization electrode 6 Electrically insulating bushing 7 Burner door (part of a housing) 8 Salt crystal rod 9 Guide tube 10 Cover 11 Window 12 Compression spring 13 Surroundings 14 Air inlet 15 Burner interior 16 Coating (titanium dioxide) 17 (Additional) component 18 Heat-conducting connection G Mixture (air and fuel gas) LAir

Claims

1. Method for increasing the charge carrier concentration in the vicinity of an ionisation electrode (5) in a combustion chamber (1) of a heating device, to which a mixture (G) of air (L) and a fuel is supplied through openings (3) in a burner body (2), wherein at least in the vicinity (13) of the ionisation electrode (5), at least one substance promoting ionisation is provided or the proportion of this substance is increased, wherein a coating (16) of titanium dioxide or aluminium oxide is applied to existing components or an additional component (17) of titanium dioxide or aluminium oxide is applied as the substance in the vicinity (13) of the ionisation electrode (5).

2. Method according to claim 1, wherein the provision of a further substance takes place after setting a low heat load of the heating device and / or a leaner gas-air mixture.

3. Method according to claim 1 or 2, wherein the heating device is operated with fuel gas containing more than 50% hydrogen.

4. Method according to one of the preceding claims, wherein a further substance is air (L) or carbon dioxide.

5. Method according to one of the preceding claims, wherein a further substance is a substance that can be ionised under ultraviolet radiation, which is arranged in the vicinity (13) of the ionisation electrode (5).

6. Method according to claim 1, wherein a further substance (8) with low ionisation energy, which releases valence electrons at flame temperature, is supplied in the vicinity (13) of the ionisation electrode (5).

7. Method according to claim 7, wherein the further substance (8) with low ionisation energy is sodium chloride (NaCl).

8. Method according to claim 6 or 7, wherein the further substance (8) is supplied in solid form via a supply mechanism (9, 10, 11, 12).

9. Arrangement for increasing the charge carrier concentration in the vicinity of an ionisation electrode (5) in a combustion chamber (1) of a heating device, to which a mixture (G) of air (L) and a fuel can be supplied through openings (3) in a burner body (2), wherein at least in the vicinity (13) of the ionisation electrode (5), means for providing or increasing a proportion of a substance that promotes ionisation are provided, wherein the means comprise components made of or coated with a substance that can be ionised under ultraviolet radiation.

10. Arrangement according to claim 9, wherein the means comprise at least one additional inlet (14) for a gaseous substance.

11. Arrangement according to claim 9 or 10, wherein the substance ionisable under ultraviolet radiation is titanium dioxide.

12. Arrangement according to one of claims 9 to 11, wherein a feed mechanism (12) for a solid substance with low ionisation energy is provided, wherein the solid substance releases valence electrons at flame temperature.

13. Arrangement according to claim 12, wherein the feed mechanism is arranged between the ionisation electrode (5) and the burner body (2) and has a metallic tube (9) for feeding rod-shaped sodium chloride crystals (8), wherein the tube (9) is thermally connected to a housing (7) of the combustion chamber (1) for cooling purposes.