Ignition device, ignition device system and combustion system for solid biomass fuels, and method for igniting solid biomass fuels

Abstract

One aspect of the invention relates to an ignition device (13) for solid biomass fuels in combustion and gasification systems. The ignition device (13) comprises at least two electrodes (25, 28) for generating an arc by means of which the biomass fuels can be ignited. In addition, the ignition device comprises a movement mechanism for moving the two electrodes (25, 28) into and out of a combustion chamber (8).

Description

[0001] Tomas Zadravec

[0002] Ignition device, ignition device system and combustion plant for solid biomass fuels and a method for igniting solid biomass fuels

[0003] The invention relates to an ignition device, an ignition device system and a combustion plant for solid biomass fuels and a method for igniting solid biomass fuels.

[0004] Such ignition devices and ignition systems are used in particular in combustion plants for solid biomass fuels, such as logs, pellets, bricks or wood chip heating systems.

[0005] Solid biomass fuels are characterized by the fact that they require initial ignition, a process that is more complex than, for example, ignition of gas in gas heating systems. This requires a sufficiently large amount of energy to be supplied to the solid biomass fuel.

[0006] Such an ignition process, which ignites the solid biomass fuels, can, unlike gas heating systems, extend over a longer period of 5 to 15 minutes.

[0007] Ignition devices are known in which a specific portion of the combustion air stream is heated to a sufficient temperature. This portion is called ignition air. The ignition energy is transferred from the ignition air to the fuel particles of the biomass fuel via convective heat transfer. The resulting heating of the fuel particles causes them to dry and release volatile combustible components. Upon reaching the flash point of the gaseous mixture, spontaneous ignition occurs, thus ending the ignition period. Air heating elements used in such ignition devices have an average nominal electrical power range of 300–1000 W. These systems are referred to below as ignition air devices.

[0008] A disadvantage here is that the ignition time, which can be up to 20 minutes, is perceived as long by users. High electrical power (typically over 1000W) and a high inrush current (typically over 10A) are required. Further disadvantages include high environmental impact, as incompletely combusted pollutants are released into the environment via the ignition air, and low efficiency of the ignition process; that is, a large amount of energy is expended, only a fraction of which is used to heat the solid biomass fuel particles. Previous systems have shown that a high inrush current leads to an initially high power consumption, which drops to the rated power after some time. The resistance of the heating element increases during operation, thus stabilizing the power output.The increase in temperature and resistance depends on the heat transfer system, which means that the actual ignition energy is higher than is usually calculated theoretically.

[0009] Therefore, energy consumption is higher in the first few seconds and then decreases. This stabilization phase accounts for a significant portion of the total ignition energy. Under real-world conditions, it takes longer to reach the rated power, resulting in higher energy consumption. Conventional heating elements thus require more time to reach their rated power in cold systems or systems with higher temperature losses.

[0010] For example, the inrush current can drop from four times the rated current to the rated current within 60 seconds. The energy consumed during this inrush phase accounts for approximately one-third of the total energy required during those 60 seconds.

[0011] Furthermore, the combustion air stream is usually heated in tightly packed areas to increase convective heat transfer to the combustion air. Simultaneously, the hot ignition air is guided through narrow channels in the burner assembly, which must be made of metallic materials to withstand the high thermal capacities (usually boiler steel). These components are often at a lower temperature than the combustion air at the start of the ignition process. These metal parts are cold at room temperature at the start of the ignition process, which means the heated air stream intended to warm the fuel particles is cooled again. This prolongs the ignition time and requires more ignition energy to ignite the fuel.

[0012] Furthermore, the fuel particles are primarily heated by the convection heat of the hot ignition air. Due to the physical limitations of air velocity and the air's residence time at the fuel particles, not all of the ignition air's energy can be transferred to the fuel particles. As a result, some of the ignition energy is released into the environment. This limitation in energy transfer extends the ignition time and requires more ignition energy to ignite the fuel.

[0013] PL69347Y1 discloses a device with electrodes for generating an electric arc to ignite solid fuels. One electrode is movable for adjusting the electric arc.

[0014] Documents WO2023173152A1, US20100261128A1, US4881472, and EP1359372A2 each describe a combustion device in which two electrodes are rigidly arranged in a combustion chamber to ignite a fuel. DE102007041156A1 describes a coal scuttle with a mechanical device for the continuous removal of ash and residues, wherein the bottom of the coal scuttle rotates to move the residues towards a discharge channel.

[0015] DE20321670U1 relates to a burner for pellet fuel. In a combustion chamber, hot combustion gases flow in a longitudinal direction (F). A grid inside the chamber supports the fuel and is inclined backwards relative to the longitudinal flow direction (F). Air supply devices blow air onto the pellet fuel located on the grid, causing partial gasification of the fuel. The air supply devices have cylindrical nozzles that are closed at the top and have openings on the side surface. The nozzles are arranged so that they supply primary gasification air over the entire surface of the grid. AT526024A1 describes a combustion plant for burning biomass, such as wood pellets. The combustion plant comprises a combustion chamber with a nozzle base above which a fluidized bed of solid particles, preferably quartz sand, is arranged.An ignition unit comprises two ignition electrodes or a spark plug to generate an electric arc. The tips of the two ignition electrodes or the tip of the spark plug are arranged vertically in the combustion chamber above the fluidized bed (which is stationary when the engine is off) and below a fuel supply inlet.

[0016] DE338521C relates to an electric high-voltage fire starter that uses an electric arc for ignition, which is generated between two electrodes, e.g., carbon rods. The starter comprises the first electrode, which is manually brought close to the second electrode to initiate the arc. Subsequently, driven by spring force, the first electrode is moved away from the second electrode until it reaches a stop, thereby increasing the arc's extent.

[0017] Patent CH594220A5 describes a heating device and a method for its operation. The heating device comprises a fluidized bed of refractory particles and a body to be heated, to which heat can be transferred from the fluidized bed through contact of its particles with the body's surface. During start-up, air and fuel are supplied to the fluidized bed at a velocity such that the fluidized particles are not thrown upwards against the surface of the body. Once the operating temperature is reached, air and fuel are supplied to the fluidized bed at the same velocity, so that the particles are thrown upwards against the surface of the body due to the higher gas velocity.

[0018] AT412419B describes a method for verifying the ignition function of a high-voltage ignition system for an oil or gas-fired heating burner, whereby the ignition is activated as soon as heat is requested by the oil or gas burner. The power consumption or current draw or output of the high-voltage ignition system is measured during a pre-ignition period before the fuel supply begins. To prevent premature fuel release, the fuel supply to the heating burner is released at a variable time, depending on when a predefined threshold value of the measured power consumption and / or current draw or output is reached or exceeded.

[0019] German patent DE 102016002533A1 describes a contact ignition device for a biomass combustion system, in particular a pellet stove. The contact ignition device comprises a heating element designed for direct contact with the fuel to ignite it. In an operating position, the heating element is in direct contact with the fuel, and in a resting position, the heating element is not in direct contact with the fuel.

[0020] W02008104012A1 describes an ignition device for igniting lumpy fuel or fuel with a high ignition temperature, especially firewood. Contact between the ignition device and the fuel is maintained by means of a contact element throughout the entire ignition process, or until ignition occurs.

[0021] DE334523C describes an electrical ignition device for combustion systems in which electrically conductive fuels (coal, coke or mixtures) are connected as a resistor in an ignition current and are ignited locally by means of an ignition pin or several ignition pins with the supply of compressed air.

[0022] DD105050A1 deals with an automatic ignition device for coal stoves and ranges. An electrical resistor, powered by mains electricity via a transformer and protruding into a combustion chamber, ignites the fuel or a special match. Outside the combustion chamber, but heatable by the heat from the stove, a bimetallic strip is located. When heated, this strip moves the heating resistor out of the combustion chamber and closes a feedthrough for the heating resistor with a cap. CNI 08731028A describes an electromagnetic telescopic safety device for an ignition system. The ignition system is located in the slag cleaning plate and moves with it into a fuel hopper. A return spring allows the slag cleaning plate, with the ignition system, to be moved back out of the fuel hopper.

[0023] FR2721096A1 describes an automatic ignition and loading system for a wood-fired boiler. Logs are pushed into a burner and ignited by two electric resistance heating elements. A contactor is located next to the heating element and is connected to position detectors, which control the loading and ignition process.

[0024] The object of the present invention is to create an ignition device that is energy-efficient and fast, without polluting the environment.

[0025] The problem is solved by the subject matter of the independent claims. Advantageous further developments and preferred embodiments form the subject matter of the dependent claims. One aspect of the invention relates to an ignition device for solid biomass fuels in combustion and gasification plants. The ignition device comprises at least two electrodes for generating an electric arc with which the biomass fuels can be ignited. It also comprises a movement mechanism for extending and retracting the two electrodes into and out of a combustion chamber.

[0026] The ignition zone of an electric arc is smaller than that of prior art systems using an ignition air stream (ignition air devices), because these systems incorporate an ignition lance. With arc ignition, the ignition zone is limited to the area around the arc.

[0027] The movement mechanism allows the ignition area of ​​the arc to be freely positioned within a predetermined area, thus covering a similar and even a larger volume than is the case with known ignition air devices.

[0028] Furthermore, the power output is constant across the entire range in which the electrodes are moved. With air-ignition devices, there is a gradient in ignition power because the heating power decreases away from the inlet of the hot air stream. This is partly due to the fact that the heating power is increasingly transferred to the material being ignited along the path of the electrodes, even if the material is already ignited. This can lead to a situation where fuels located further away cannot be ignited.

[0029] The ignition device exhibits a very high stability of the ignition process, as the generated arc produces a very high temperature, often several thousand degrees Celsius, resulting in a very reliable and rapid ignition of the biomass fuel.

[0030] Arc ignition, especially in combination with the movement mechanism, allows for precise control of the ignition point. This makes it possible to set very accurately where the initial ignition should begin. Furthermore, the ignition timing and ignition energy can be precisely controlled via the current flow. This leads to improved combustion control.

[0031] Almost all the energy of the electric arc is transferred to the biomass fuel, resulting in ignition. By adjusting or switching off the arc, no energy needs to be transferred to already ignited biomass. This makes the ignition device very efficient.

[0032] The ignition energy can be easily adjusted to the requirements of the specific fuel and operating conditions by adjusting the current.

[0033] The high temperatures of the electric arc promote complete combustion of the fuel, resulting in better energy efficiency and lower emissions. This efficient combustion reduces the formation of carbon monoxide (CO), hydrocarbons (HC), and particulate matter.

[0034] The ignition device, with its arc igniter, has few mechanical parts and is therefore less susceptible to wear. Because the electrodes can be extended from a combustion chamber by the movement mechanism, they are not constantly exposed to higher temperatures, resulting in a longer service life.

[0035] The ignition device can be used in a wide variety of combustion and gasification systems because the ignition current and the movement mechanism allow the precise application of the correct energy to the ignition point. With previous systems, oversized ignition devices in very small combustion systems could damage the area around the heating element and even the combustion chamber walls, as the ignition air temperature is too high and the dimensions of the spacers are too small to reliably shield more sensitive components.

[0036] It can also happen that state-of-the-art heating elements are damaged if they are placed too close to biomass fuel.

[0037] On the other hand, it is also conceivable that undersized ignition devices from the prior art do not provide sufficient power. In very large combustion plants, this could result in insufficient energy being supplied to ignite the corresponding biomass. Alternatively, the biomass might only be ignited at the edges, which could lead to an undesirable flame distribution.

[0038] In some prior art ignition devices, due to limited space, the heating elements may be placed close to the combustion chamber. In these cases, glowing particles and / or ash particles could reach the heating elements and damage them.

[0039] The present ignition device requires, if at all, a smaller opening than is usual in the prior art, so that it is less likely that glowing or burnt particles can penetrate it.

[0040] However, by moving the electrodes, the present ignition device can find the optimal ignition point in a large number of different combustion systems.

[0041] The present ignition device is also flexible with regard to the fuel. The fuel can vary depending on its density, material, and size, whether it be biomass or fuel particles. Depending on the type of fuel used, the ignition device can be easily adjusted to achieve higher or lower ignition points. With previous ignition devices, it was possible that an ignition device was only suitable for certain fuel materials, while with others, insufficient energy transfer or inadequate ignition occurred.

[0042] The mechanical movement of the electrodes also removes deposits and impurities that accumulate on the electrodes over time.

[0043] The two electrodes can be spaced at the point of arc generation with a distance of at least 1 mm, preferably at least 5 mm, and particularly preferably at least 2 cm. The two electrodes can also be spaced at a distance of at most 3 cm, preferably at most 2 cm, and particularly preferably at most 1 cm.

[0044] The smaller the distance, the less energy is required to generate an arc. The breakdown voltage and resistance of the arc decrease. This increases the current and the electrodes become hotter.

[0045] Larger distances require more energy, but the resulting larger arc allows a larger area of ​​the biomass fuel to be ignited.

[0046] Such a distance has proven to be optimal, as a compromise between the size of the contact area with the biomass fuel, which is varied by the distance, and the energy required to create such an arc.

[0047] The ignition device may include an airflow device which can generate an airflow with which a generated arc can be blown away from the movement mechanism towards the biomass fuels.

[0048] This arc can be directed straight onto the fuel, enabling a more efficient transfer of heat energy to the fuel. This can then lead to faster and more reliable ignition.

[0049] The airflow can also actively prevent biomass fuel and other particles from entering the ignition device itself, as these are pushed away from the opening by the airflow.

[0050] Furthermore, a targeted airflow can ensure that sufficient oxygen is available to promote complete combustion, which in turn reduces the emission of carbon monoxide and burnt hydrocarbons.

[0051] The airflow also prevents smoke or hot gases from escaping through the ignition device. The airflow can also have a cooling effect on the electrodes, lowering their temperature and reducing potential wear. This can extend the electrodes' service life and reduce maintenance costs. Simultaneously, heat is transferred to the airflow, drying the biomass fuel and aiding ignition.

[0052] Furthermore, cooled electrodes are less susceptible to overheating and erosion, resulting in more stable arc formation and therefore reliable ignition.

[0053] The airflow blows deposits and particles away from the electrode surface, improving ignition conditions and reducing the risk of short circuits. The airflow can be adjusted to optimize the ignition of different fuels, increasing the flexibility and versatility of the ignition system.

[0054] By controlling the airflow, the ignition energy can be regulated even more precisely to meet the specific requirements of the fuel under operating conditions.

[0055] However, the airflow must be fundamentally distinguished from the combustion airflow of the prior art, as the combustion airflow is significantly stronger, i.e., it contains more air particles per cross-section than the arc airflow presented here. The arc airflow only needs to move the arc, whereas the combustion airflow of the prior art must transport large amounts of energy and carry it further into the combustion chamber.

[0056] The airflow device may include a heating element to pre-dry the fuel and / or assist degassing.

[0057] The heating element is integrated into the airflow channel, so that the air flowing through it is heated. The heated air then reaches the fuel. The heating element can be, for example, a heating wire, a heating tape, and / or a ceramic heating element.

[0058] A temperature control system regulates the temperature of the heating element.

[0059] The power output is significantly lower than the ignition airflows known from the prior art and is generally no more than 200 W, preferably a maximum of 100 W, and in particular a maximum of 60 W.

[0060] Preheating the air can dry moist or wet fuel, which increases its ignitability, as dry fuel is easy to ignite.

[0061] Furthermore, heating the fuel promotes the outgassing of volatile and highly flammable components, resulting in faster and more efficient ignition. Pre-drying and pre-heating the fuel reduces the energy required for vaporization and ignition, which can increase the overall efficiency of the system.

[0062] Dry and preheated fuel produces less ash and residue, simplifying cleaning and maintenance. The system can be easily adapted to different fuels by using a heating element, as the optimal ignition conditions for various fuels are easier to achieve.

[0063] The electrodes may have a coating of a non-oxidizing material.

[0064] Alternatively, the entire electrodes can be made of this non-oxidizing material.

[0065] Non-oxidizing materials are resistant to chemical reactions with oxygen at high temperatures, such as those occurring during the formation of electric arcs. This prevents the formation of oxide layers, which in turn could impair the performance of the electrodes. Because oxide layers are prevented or reduced, the electrode surfaces remain smooth, which can extend the lifespan of the electrodes.

[0066] Furthermore, the electrical conductivity of non-oxidizing materials remains constant, as oxide layers can have an insulating effect that could impede current flow. This ensures consistent and reliable ignition performance.

[0067] The increased reliability of the electrodes results in fewer failures and malfunctions, and cleaning and maintenance will be required less frequently.

[0068] Non-oxidizing materials can be, for example, platinum, iridium, gold, tantalum, nickel, or an alloy of one or more of the above-mentioned materials.

[0069] Electrodes can also have a coating of tungsten or a tungsten alloy. Alternatively, they can be made entirely of tungsten or a tungsten alloy.

[0070] Tungsten has a very high melting point of approximately 3400 °C, making it an advantageous material for applications requiring high temperatures.

[0071] Tungsten alloys retain their mechanical and electrical properties even at very high temperatures, which improves their performance and reliability.

[0072] Tungsten alloys are characterized by high tensile strength and hardness, making the electrodes resistant to mechanical stress, deformation, wear, and abrasion. Since the electrodes must be inserted into the fuel-containing area to ignite the biomass fuel, this creates a corresponding mechanical stress on the electrodes. Hard electrodes, such as those made of tungsten or tungsten alloys, can tolerate these stresses more easily than electrodes made of softer materials. The thermal expansion of tungsten and tungsten alloys is low, which reduces stress and deformation. As a result, the distance between the two electrodes remains constant over a wider temperature range, ensuring a reliable electric arc.

[0073] The electrodes can have a detachable fastening, so that the electrodes are replaceable.

[0074] This makes it possible to replace the electrodes if they become worn, damaged, or become depleted.

[0075] Since the electrodes are the most prone to wear and tear, for example through combustion, replacing these electrodes can significantly extend the service life of the entire ignition system.

[0076] The electrodes can have an adjustable position relative to each other in order to vary the arc length.

[0077] For this purpose, both electrodes can be moved independently of each other by a movement device.

[0078] The movement mechanism of each electrode allows it to move along a specific direction.

[0079] However, it is also conceivable that the movement mechanism of one or each electrode could execute a movement in two or even three dimensions. Rotational movements are also imaginable.

[0080] This allows the electrodes to be adjusted to each other as desired.

[0081] The moving mechanism allows the electrodes to maintain a constant spark gap, ensuring consistent ignition performance. This remains true even if the electrodes shorten due to wear, for example. An optimal spark gap results in reliable ignition and improved combustion efficiency.

[0082] The movable electrodes can distribute the ignition energy better and promote the formation of a stable arc, which also increases the efficiency of the ignition.

[0083] The movable electrodes can adapt to different operating conditions, thus optimizing ignition performance under varying conditions. For example, if the electrodes expand due to heat, their spacing can be adjusted, which also improves reliability in changing environments. Furthermore, short circuits can be prevented, as this ensures that the electrodes are not too close together, even in the event of mechanical shocks or vibrations. A certain safety distance to the combustion chamber wall can also always be maintained.

[0084] Moving the electrodes, for example by rotating them, can lead to more even wear of the electrode surface, preventing hotspots and uneven burning, which in turn extends the service life of the electrodes.

[0085] The electrodes can be connected to the voltage source via an energy chain.

[0086] An energy chain is a mechanical system designed to safely and efficiently guide and protect flexible conductors, such as electrical cables. The current that generates the electric arc flows through these flexible conductors. The energy chain comprises a series of interconnected links to form a flexible yet robust structure that can move, at least in the direction of the movement mechanism.

[0087] Energy chains protect the contained cables, especially the power lines, from mechanical damage such as abrasion, bending, or entanglement that could be caused by the movement of the electrodes. By protecting the cables, their service life can be extended, reducing maintenance costs and increasing safety.

[0088] The energy chain guides the cables neatly and systematically, minimizing the likelihood of tangling or knotting. This orderly routing of the cables allows for efficient use of available space, thus saving room.

[0089] Nevertheless, the energy chain retains a high degree of flexibility to enable movement.

[0090] The position of the electrodes can be detected by integrated magnets and a reed sensor.

[0091] Small magnets are attached to a moving part of the motion mechanism. The magnets generate a constant magnetic field that varies depending on the position of the electrodes, i.e., how far they have moved. The reed sensor is positioned near the motion path of the mechanism, where it can detect the movement of the magnets. The reed sensor consists of two ferromagnetic reeds that close in the presence of a magnetic field and open when the magnetic field is removed. When one of the magnets approaches the reed sensor, the sensor closes a circuit, generating a signal. The exact position of the electrodes can then be determined from the position and state of the reed sensor. Reed sensors offer high precision in position detection because they are very sensitive to the magnetic field.

[0092] If several magnets are used, the position can be determined with high resolution by counting the magnets that pass the reed sensor.

[0093] A Hall sensor can also be used instead of a reed sensor.

[0094] However, other positioning mechanisms are also conceivable, such as camera monitoring, e.g., with linear encoder strips, or an ultrasonic distance sensor. It is also possible to use classic or capacitive limit switches or to count the rotations of the motor, especially a stepper motor.

[0095] Another aspect of the invention relates to an ignition device system comprising an ignition device as previously described, a high voltage source, and a control unit for controlling a high voltage and for controlling the movement mechanism.

[0096] The high-voltage source comprises at least one transformer with a primary winding for the low-voltage source, for example, 12 V, and a secondary winding designed to generate the high voltage. The turns ratio between the primary and secondary windings determines the voltage ratio.

[0097] There may also be high-voltage capacitors present that store electrical energy so that it can be released again at the appropriate time, e.g. to smooth and stabilize the output voltage.

[0098] The control unit can include a MOSFET switch, a power MOSFET switch, or a relay that can switch the voltages to generate the arc.

[0099] MOSFETs (metal-oxide semiconductor field-effect transistors) can switch very quickly, in the nanosecond or microsecond range, thus enabling efficient arc ignition. This high switching speed reduces energy losses during switching, thereby increasing the overall system efficiency. MOSFETs have a very high input impedance, allowing them to be operated with only a small control current. This simplifies control and reduces the load on the control electronics. Furthermore, MOSFETs are robust against electrical interference and voltage flashovers, which extends their lifespan.

[0100] Power MOSFETs are designed to switch high voltages and currents, allowing the high energy pulses required for arcing to be switched directly. Alternatively, an IGBT (Insulated Gate Bipolar Transistor), a TRIAC (Triode for Alternating Current), or another type of transistor can be used. It is also conceivable to use a triode, i.e., a vacuum tube.

[0101] The control unit may include a programmable microcontroller to adjust the operating parameters of the arc.

[0102] The operating parameters may include:

[0103] Electrode spacing, electrode position, voltage intensity, current frequency, arc duration, airflow intensity, and / or airflow temperature.

[0104] This allows a wide variety of different combustion systems and fuel types to be used without having to provide a new system for each application.

[0105] For example, the electrode spacing can be adjusted to the size of the biomass particles or pellets, which also necessitates adjustments to the voltage and, if applicable, the current frequency. The electrode spacing can be individually adjusted if both electrodes are independently movable, or a spacer of a predetermined length can be selected.

[0106] Depending on the moisture content of the biomass particles, especially the pellets or pieces of wood, the airflow temperature can also be adjusted to enhance the drying effect.

[0107] Another adjustment concerns the movement of the electrodes. It has been shown that, after reaching the ignition position—the position at which ignition can occur—it can be advantageous to move the electrodes slightly back and forth. This allows the biomass fuel to move forward locally and thus be compacted, increasing the probability of contact between a generated arc and the biomass fuel.

[0108] Furthermore, it is conceivable that the duration of an electric arc can be regulated.

[0109] Operating parameters that influence arc generation can include, among others:

[0110] Energy (W),

[0111] Frequency (f),

[0112] Power (P), Inductance (L),

[0113] Pulse time (t), peak current (Ip), and / or supply voltage (V).

[0114] The following connection exists: and dip

[0115] V = L . dt

[0116] The frequency can be between 10 and 200 kHz, especially above 20 kHz, as this makes the frequencies inaudible to humans and reduces sound emissions.

[0117] Another aspect of the invention relates to a combustion plant for biomass fuels, in particular wood pellets, comprising:

[0118] - an ignition device system as described above.

[0119] The incineration plant may also include:

[0120] - a conveying mechanism for feeding the biomass fuel into the combustion plant,

[0121] - a combustion chamber in which the biomass fuels are burned with a supply of oxygen,

[0122] - a gasification chamber connected to the combustion chamber in which the gases produced during combustion are converted into synthesis gas under reduced oxygen supply,

[0123] - an exhaust system for removing the exhaust gases produced during combustion and gasification,

[0124] - a control unit for regulating, in particular, the supply, combustion and / or gasification, and

[0125] - a heat transfer unit for utilizing the heat energy generated during combustion and gasification.

[0126] The control unit can manage the ignition and regulate the combustion, ensuring it is stable, modulated, or burns out. It can also regulate safety aspects, such as emergency situations.

[0127] The control unit can utilize control algorithms, which can include constant and sensor-dependent, variable parameters. In principle, with regard to combustion, the control unit can control the fuel supply by regulating the mass flow, the exhaust fan by regulating its speed, ash removal by regulating the motors and actuators, air supply by regulating the valves, and / or recirculation by regulating a valve.

[0128] The oxygen supply can include a simple air supply, oxygen-enriched air, or a supply of pure oxygen.

[0129] Control parameters that can be measured by sensors include, for example: exhaust fan speed, combustion chamber temperature,

[0130] Chimney pipe temperature, O2 concentration and / or emission concentration (e.g., CO), fuel supply speed, combustion chamber negative pressure,

[0131] Air supply (primary, secondary and tertiary) velocity measured by an anemometer or differential pressure sensor.

[0132] Modulation control can be achieved by varying the fuel mass flow rate and regulating the air supply and / or the ratio of the airflows.

[0133] In addition, the control unit can also control the ignition by activating the ignition device.

[0134] The control system can monitor switches on doors or flaps and the negative pressure in the combustion chamber to ensure that no door or flap is open during operation. This can also occur during the ignition process, as it can be dangerous for a user to reach into the combustion chamber at the time of ignition.

[0135] The control unit can, for example, increase the feed rate or reduce the combustion rate based on the combustion speed, for example by reducing the air intake. It can also control the gasification process.

[0136] Another aspect concerns a method for igniting solid biomass fuels in combustion and gasification plants using an ignition device as previously described, whereby the following steps are carried out:

[0137] - Extension of the two electrodes into the combustion chamber,

[0138] - Generation of an electric arc between the electrodes to ignite the solid biomass fuel and

[0139] - Retraction of the two electrodes from the combustion chamber.

[0140] By moving the electrodes in and out of the combustion chamber, the desired ignition point can be precisely reached. This is usually the center of the combustion chamber. Retracting the electrodes from the combustion chamber removes them from the heat zone, thus extending their lifespan.

[0141] The arc duration can be at least 5 seconds, preferably at least 15 seconds and especially preferably at least 25 seconds.

[0142] This ensures that there is enough time to ignite the biomass.

[0143] An airflow can be generated with which the generated arc can be blown away from the movement mechanism and onto the biomass fuel.

[0144] This allows the electric arc to come into direct contact with the biomass fuel.

[0145] The invention is explained in more detail below by way of example, using the examples shown in the drawings.

[0146] The drawings show schematically:

[0147] Figure 1 shows a wood pellet combustion plant in an open partial view.

[0148] Figure 2a shows an ignition device in the retracted state in a perspective side view.

[0149] Figure 2b shows the ignition device of Fig. 2a in the extended state in a perspective side view,

[0150] Figure 3 shows the ignition device of Fig. 2a in the retracted state in a cross-section,

[0151] Figure 4 shows the ignition device of Fig. 2a in the extended state in a cross-section,

[0152] Figures 5a-c show the ignition device of Fig. 2a in cross-section in a partial view.

[0153] Figure 6 shows the tip of the ignition device in cross-section in a partial view.

[0154] Figure 7 shows a circuit diagram for a high-voltage module.

[0155] Figure 8a-d shows a method for igniting biomass fuel in an open partial view.

[0156] Figure 9 shows a circuit diagram of the process for igniting biomass fuel,

[0157] Figure 10 shows a partial view of the path of an airflow in the ignition device.

[0158] Figure 11 shows the effect of airflow on an electric arc.

[0159] Figure 12 shows the position of an energy chain in the ignition device in a partial view.

[0160] Figure 13a shows an ignition device of a second embodiment in the retracted state in a perspective oblique side view.

[0161] Figure 13b shows the ignition device of the second embodiment in the retracted state in a perspective side view,

[0162] Figure 13c shows the ignition device of the second embodiment in the extended state in a wood pellet combustion plant in a perspective side view.

[0163] Figure 13d shows the ignition device of the second embodiment in the extended state in a perspective side view,

[0164] Figure 14a shows the ignition device of the second embodiment in the retracted state in a perspective side view, Figure 14b shows the ignition device of the second embodiment in the extended state in a perspective side view,

[0165] Figure 14c shows the ignition device of the second embodiment in the retracted state in a perspective side view,

[0166] Figure 14d shows the ignition device of the second embodiment in the retracted state in a perspective semi-open side view,

[0167] Figure 15a shows the ignition device of the second embodiment in the retracted state in a second perspective side view,

[0168] Figure 15b shows the ignition device of the second embodiment in the retracted state in a second perspective semi-open side view,

[0169] Figure 15c shows the ignition lance of the second embodiment in a perspective side view,

[0170] Figure 15d shows the ignition lance of the second embodiment in a perspective semi-open side view,

[0171] Figure 15e shows the ignition lance of the second embodiment in a second perspective semi-open side view,

[0172] Figure 16a shows the ignition lance of the second embodiment in a side view,

[0173] Figure 16b shows the ignition lance of the second embodiment in cross-section,

[0174] Figure 16c shows the ignition lance of the second embodiment in a semi-open

[0175] View from below

[0176] Figure 16d shows the ignition lance of the second embodiment in a semi-open side view,

[0177] Figure 16e shows the ignition lance of the second embodiment in a semi-open top view,

[0178] Figure 16f shows the ignition lance of the second embodiment in a semi-open, magnified view from below.

[0179] Figure 17 shows a circuit diagram for an ignition device,

[0180] Figure 18a shows a wood combustion plant in its retracted state in an open partial view.

[0181] Figure 18b shows a wood combustion plant with the ignition device in the extended position in an open partial view.

[0182] Figure 19a shows an ignition device in the retracted state in a perspective side view,

[0183] Figure 19b shows the ignition lance of the ignition device in a perspective view.

[0184] Side view,

[0185] Figure 20a shows the ignition lance in cross-section,

[0186] Figure 20b shows the ignition device of Fig. 19a in the retracted state in a cross-section,

[0187] Figure 20c shows the ignition device of Fig. 19a in the extended state in a cross-section,

[0188] Figure 21a shows the ignition lance in cross-section,

[0189] Figure 21b shows the ignition device of Fig. 19a in the extended state in a semi-open view from below,

[0190] Figure 21c shows the ignition device of Fig. 19a in the extended state in a semi-open, magnified view from below, Figure 22a shows a circuit diagram of the method for cleaning the ignition device, and

[0191] Figure 22b shows an alternative circuit diagram of the method for igniting biomass fuel.

[0192] The wood pellet combustion plant 1 (see Fig. 1) comprises a pellet storage 3 in which wood pellets 2, hereinafter also referred to as pellets 2, are stored and constitute the biomass fuel, and are burned; a conveying system 4 to transport the pellets 2 from the pellet storage 3; an exhaust system 5 for removing flue gases produced during combustion; a water or air circuit (not shown) to dissipate generated heat; a heat exchanger 6 to transfer the heat generated by combustion to a heating medium such as water or air; an ash container 7 in which the ash produced by the combustion of the pellets 2 is collected; and a combustion chamber 8 in which the actual combustion of the pellets 2 takes place. The pellets 2 are conveyed by the conveying system 4 from the pellet storage 3 into the combustion chamber 8 and filled there to a predetermined level.Here, the pellets are ignited and burned.

[0193] Furthermore, the wood pellet combustion plant 1 includes a control unit 9 for monitoring and controlling the combustion plant 1. The control unit 9 regulates the operation of the conveying system and the actual combustion, for example by controlling the temperature.

[0194] The combustion chamber 8 comprises a combustion chamber wall 10 made of heat-resistant material such as fireclay or ceramic to withstand the high temperatures during combustion and to store heat, and a combustion chamber floor 11, which may be designed as a grate or have several holes through which the pellet ash can fall. The combustion chamber floor 11 is made of heat-resistant material and ensures a sufficient supply of air from below into the combustion chamber 8.

[0195] The wood pellet combustion plant 1 also includes a primary air supply 12, which is blown into the combustion chamber 8 through the combustion chamber floor 11. The primary air supply 12 provides the fire in the combustion chamber 8 with the necessary air for the primary combustion of the wood pellets 2.

[0196] The wood pellet combustion plant 1 has an ignition device 13, which is arranged on the combustion chamber 8 such that it passes through the combustion chamber wall 10. The position can preferably be chosen such that the axis of the ignition device 13 intersects the center of a pile of wood pellets 2 in the combustion chamber 8 and that the axis is substantially radial to the combustion chamber wall 10. This allows the ignition device 13 to ignite the center. The radial arrangement ensures that the center is reached via the shortest path, thus saving material. The ignition device 13 comprises a protective cover 14 for protection outside the combustion chamber 8, a mounting flange 15 for attaching the ignition device 13 to the combustion chamber wall 10, and a mounting tube 16, which separates the ignition device 13 from the combustion chamber wall 10 and, depending on the embodiment, may project into the combustion chamber 8 (see Figure 2a).

[0197] The ignition device 13 further comprises an ignition lance 17, which in the rest state is arranged in the mounting tube 16 and can be extended from this into the combustion chamber 8 and with which the pellets 2 are ignited (Figure 2b).

[0198] The protective cover 14 of the ignition device 13 protects a fan 18, a control and high-voltage module 19 for regulating high voltages and a geared motor 20 with which the ignition lance 17 can be extended and retracted.

[0199] The control and high-voltage module 19 can generate a high-voltage current, which is conducted to the ignition lance 17 via a first insulated power cable 21 and a second insulated power cable 22. The first insulated power cable 21 is electrically connected to a U-shaped guide element 23. The guide element 23 can also be V-shaped or omega-shaped. Its shape allows the guide element 23 to guide the ignition lance 17 (Figure 3).

[0200] Furthermore, the control and high-voltage module 19 regulates the fan 18 and the geared motor 20 and communicates with the control unit 9.

[0201] The ignition lance 17 comprises a main body 24, which is designed as an elongated hollow insulating tube (Figure 4). The tube is made of a ceramic material that exhibits particularly good insulating properties.

[0202] A first electrode 25 is formed as an outer coating on the end face of the main body 24, which faces into the combustion chamber 8. The end face of the first electrode 25, which faces into the combustion chamber 8, forms a first electrode tip 26 (Figure 5a-c).

[0203] The first electrode 25 is electrically connected to the guide element 23 by a guide element 27 arranged on it and thus to the control and high-voltage module 19 via the insulated power cable 21.

[0204] The guide element 27 engages with the guide element 23 and ensures that, regardless of the position of the main body 24, the first electrode 25 is electrically connected to the control and high-voltage module 19.

[0205] The ignition lance 17 further comprises an elongated, rod-shaped second electrode 28, which is arranged centrally along its entire length within the main body 24 and has a mushroom-shaped second electrode tip 29 that points into the combustion chamber 8. The first electrode 25 thus forms an outer electrode and the second electrode 28 forms an inner electrode.

[0206] The second electrode tip 29 can also have other shapes and can also be designed as a rod or rounded rod.

[0207] The second electrode 28 is rigidly connected to the first electrode 25 via four insulating, rod-shaped spacers 30, which are arranged between the first electrode tip 26 and the second electrode tip 29. The spacers 30 are 5 mm long and made of a material with high dielectric strength. Examples include polyethylene terephthalate (PET) with a dielectric strength of 20 to 25 kV / mm, polymethyl methacrylate (acrylic / Plexiglas) with approximately 30 kV / mm, hard porcelain with 30 to 35 kV / mm, or quartz glass with 25 to 40 kV / mm. Other materials are also conceivable.

[0208] The smallest distance between the first electrode 25 and the second electrode 28 is 3 mm.

[0209] The spacers 30 can suppress the penetration of pellets 2 into the space between the second electrode 28 and the main body 24 (Figure 6).

[0210] The first electrode 25 and the second electrode 28 together form an arc generation point 31, whereby an arc 32 can be generated between the first electrode tip 26 of the first electrode 25 and the second electrode tip 29 of the second electrode 28. Accordingly, the shortest distance between the first electrode 25 and the second electrode 28 is between the first electrode tip 26 and the second electrode tip 29.

[0211] A threaded rod 33 is arranged around the second electrode 28 such that the thread of the threaded rod 33 engages in a thread of a threaded nut 34. The threaded nut 34 is fixedly connected to the main body 24.

[0212] The second electrode 28 can rotate freely within the threaded rod 33 and move back and forth. The second electrode 28 is electrically connected to the threaded rod 33 via a contact spring 35.

[0213] The material of the second electrode 28 and the threaded rod 33 is chosen in such a way that no cold fusion occurs.

[0214] The components of the ignition lance 17, i.e. the main body 24, the first electrode 25, the second electrode 28, the guide element 27, the threaded nut 34, the spacers 30 and the contact spring 35, are firmly connected to each other and form a machine part.

[0215] The geared motor 20 can transmit a rotary motion to the threaded rod 33 via a gearbox 36. The output torque of the gearbox 36 is transmitted from an output shaft of the gearbox 36 to the threaded rod 33 via a high-voltage insulating coupling 37.

[0216] The threaded rod 33 rotates within the threaded nut 34. The threaded nut 34 transmits the force to the main body 24 and thus to the first electrode 25 and the guide element 27.

[0217] Since the guide element 27 engages with the guide element 23 to form a rail mechanism, rotation of the ignition lance 17 itself is prevented.

[0218] A linear movement of the main body 24 and thus also of the first electrode 25 is achieved, whereby the linear movement is also transferred to the second electrode 28 via the spacers 30.

[0219] This allows the ignition lance 17 to be moved in and out of the combustion chamber 8.

[0220] The threaded rod 33 is electrically connected to the second insulated power cable 22 via a contact drum 38. This connects the second electrode 28 to the control and high-voltage module 19 via the contact spring 35, the threaded rod 33, the contact drum 38, and the second insulated power cable 22.

[0221] Thus, both the first electrode 25 and the second electrode 28 are electrically connected to the control and high-voltage module 19 independently of each other. However, they are mechanically connected by the spacers 30.

[0222] The control and high-voltage module 19 includes an adjustable signal generator 39, e.g., based on the component designated IC555 (see Figure 7). The signal generator 39 outputs a high-frequency square wave signal of approximately 40 kHz. This signal is fed to a power MOSFET 40, e.g., one with the trade name IRFP460.

[0223] The power MOSFET 40 circuit switches a 12 V DC supply voltage from a power supply 41 through a diode 42 and a high-voltage transformer 43. The high-voltage transformer 43 comprises a ferrite core with 6 primary and 400 secondary windings of enamel wire with a diameter of 0.25 mm. The high-voltage transformer 43 supplies a high-voltage alternating current of approximately 25 kV, which is insulated and routed to the first electrode 25 and the second electrode 28. This creates a continuous arc 32 between the electrodes. A volt-ampere meter 44 is connected in series with the first electrode 25 and the second electrode 28 to measure the current consumption during operation. The fan 18 is operated by means of an adjustable voltage module 45. Air is drawn in through the heat sink 41.A second embodiment (Figures 13-16) is described below, in which identical elements as in the first embodiment are designated with the same reference numerals. The explanations given above apply to identical elements unless otherwise stated below.

[0224] In the second embodiment, a wood pellet combustion plant 1 is again provided, as in the first embodiment. The main difference between the first and second embodiments lies in the ignition device 13.

[0225] The ignition device 13 also has a protective cover 14, a mounting flange 15 and a mounting tube 16.

[0226] A geared motor 20 moves an ignition lance 17 into the combustion chamber 8.

[0227] The ignition lance 17 comprises a ceramic main body 24, the main body 24 having a cross-sectional shape shaped like an arch. On the flat, short side of the main body 24, a rack 49 is incorporated into which a gear 50 of the geared motor 20 engages, enabling the ignition lance 17 to be pushed forward.

[0228] A first electrode 25 and a second electrode 28 are arranged parallel to each other. This arrangement differs from the first embodiment, where the first electrode was an outer electrode and the second electrode was an inner electrode.

[0229] In the parallel arrangement, the first electrode 25 and the second electrode 28 are spaced apart by a protrusion 51 of the main body 24. The protrusion 51 also serves as an insulator between the first electrode 25 and the second electrode 28.

[0230] Below the protrusion 51 a cavity 52 is arranged through which an airflow 47 can flow.

[0231] The first electrode 25 and the second electrode 28 are connected via a plug connection to the first insulated power cable 21 and the second insulated power cable 22 respectively.

[0232] A first electrode tip 26 and a second electrode tip 29 can be slightly bent away from the protrusion 51 and towards each other (see Figure 15E).

[0233] The following defines various parameter settings for arc generation, some of which were simulated.

[0234]

[0235] The calculation model shows that for case 1 with a supply voltage of 12 V, the power is 10 W, the frequency is 40 kHz, the duty cycle (DC) is 80%, the current is 2.67 A, and the output voltage is approximately 25 kV.

[0236] In case 2, the frequency is set to 100 kHz. To keep the 12 V constant, the power drops to 4 W, the current to approximately 1 A, and the output voltage to 10 kV.

[0237] In case 3, where the frequency is reduced to 20 kHz, the power increases to 20 W, the current to 5 A, and the output voltage to 50 kV. Therefore, the energy density and voltage of the arc can be controlled by adjusting the frequency.

[0238] In case 4, the DC is set to 90%. As a result, the power increases to 13 W, the current to 3 A, and the output voltage to approximately 30 kV.

[0239] In case 5, the DC voltage is further reduced. This reduces the power and the output voltage drops to 19 kV. Therefore, the DC voltage is also an influencing parameter for the arc energy density and the output voltage.

[0240] The transformer can have an inductance of 88 mH ± 10% and a coil resistance of 180 mQ in the primary coil and an inductance of 330 mH ± 10% and a coil resistance of 450 Q in the secondary coil.

[0241] The procedure begins with step S1 (Figures 8a and 9).

[0242] In the next step (S2), the ignition lance 17 is extended (Figure 8b). During this process, the geared motor 20 rotates, and consequently, so does the threaded rod 33. The rotational movement is converted into a linear movement, causing the ignition lance 17 to advance towards the center of the combustion chamber 8. The movement ceases as soon as the second electrode tip 29 reaches approximately the center of the wood pellets 2 within the combustion chamber 8.

[0243] Alternatively, the arc generation point 31 can also be moved slightly beyond the center of the pile of pellets 2 in order to later pass through the center when the ignition lance 17 is withdrawn and ignite the pellets 2 along the entire path.

[0244] By extending the arc generator 31, it can be moved to the predetermined position in order to ignite the pellets 2 at the most advantageous point within the combustion chamber 8.

[0245] Then the wood pellets 2 are lit (step S3) (Figure 8b).

[0246] Here, the control and high-voltage module 19 generates a high voltage such that an electric arc 32 is created between the first electrode tip 26 and the second electrode tip 29. This electric arc 32 is in close proximity to or in contact with the wood pellets 2. The heat energy of the electric arc 32 is thus transferred to the wood pellets 2, generating significant heat and releasing combustible substances. As soon as these combustible substances reach their flash point and sufficient oxygen is present, they ignite. The electric arc 32 can act as an ignition source for the combustible gas mixture released from the pellets 2. The burning gases then support the further ignition process, causing the fire to spread from the ignition point.

[0247] This method ignites the pellets with less energy compared to ignition air devices.

[0248] Step S4 follows, in which the ignition lance 17 is retracted (Figure 8c). Similar to step S2, the geared motor 20 is set into rotation, but in the opposite direction, so that the resulting linear movement is also reversed. The ignition lance 17 is then pushed back into the mounting tube 16. The electric arc 32 may still be partially present during this process, allowing a larger quantity of wood pellets 2 to be ignited. The high voltage is then stopped to extinguish the electric arc 32 when the arc generation point 31 reaches a predefined distance from the combustion chamber wall 10. Alternatively, the high voltage can also be stopped after a predetermined fixed time.

[0249] The procedure ends with step S5 (Figure 8d).

[0250] In an alternative embodiment, the ignition device 13 can comprise an airflow unit 46 which is arranged inside the protective cover 14 (Figure 10).

[0251] The airflow unit 46 generates an airflow 47, which is guided past the control and high-voltage module 19 through an inlet of the ignition device 13, thereby cooling it. The airflow 47 is then directed forward between the first electrode 25 and the second electrode 28 to the arc generation point 31. The airflow 47 is strong enough to force any resulting arc 32 outwards, thus more easily igniting the wood pellets 2 (Figure 11).

[0252] Furthermore, the airflow 47 ensures that sufficient oxygen is supplied to the arc generation point 31 to facilitate ignition.

[0253] A third advantage is that the airflow 47 prevents wood pellets 2 and flue gases from entering the ignition lance 17 between the first electrode 25 and the second electrode 28, which could cause a short circuit or damage the ignition lance 17.

[0254] Another possibility is to heat the airflow 47 using a heating module (not shown) in order to preheat and / or dry the wood pellets 2. This makes ignition easier.

[0255] One possibility is that the waste heat from the control and high-voltage module 19 causes such heating.

[0256] Alternatively, heating wires or heating tapes can be used. The power output of such a heating module is in the range of a few tens of watts, e.g., 50 W.

[0257] An additional possibility is that the ignition of the wood pellets 2 is detected by a sensor, for example by an infrared sensor which reacts to heat, so that the arc 32 is automatically switched off after a predetermined time after such ignition is detected and / or that the ignition lance 17 is retracted, as described in step S4.

[0258] In an alternative embodiment, the first insulated power cable 21 and the second insulated power cable 22 are guided within an energy chain 48, thereby protecting them (Figure 12).

[0259] Another possibility is that magnets are arranged on the energy chain 48 and a reed sensor (not shown) in the ignition lance 17 detects the position of the integrated magnets of the energy chain 48 and transmits the measured values ​​to the control and high-voltage module 19. This makes it possible to determine the position of the ignition lance 17 and thus the arc generation point 31.

[0260] An alternative version of the electrode arrangement is the parallel arrangement of the first electrode 25 and the second electrode 28. This allows for easier adjustment of the distance between them, provided a suitable motor is available. In an alternative embodiment, the fan 18 can be designed as a pump. A pump includes a backstop function so that smoke and hot air cannot escape unintentionally from the combustion chamber 8 through the ignition device 13.

[0261] Another possibility is that the airflow 47 is heated by a heating unit (not shown).

[0262] This heating unit can be located directly at the fan 18, at the high-voltage module 19, or as part of the ignition lance 17.

[0263] According to an alternative embodiment, the main body 24 can be made of a ceramic material. Ceramic material exhibits very good convective heat transfer, which means that air heated by a heating unit can also heat the pellets 2 through the ceramic. Furthermore, ceramic material is a very good insulator that also absorbs very little moisture.

[0264] Another possibility is to monitor motor parameters, such as the motor current. A change in the motor current can indicate a change in the resistance that the ignition lance 17 experiences, for example, due to the pellets 2. From this, the position of the ignition lance tip can be determined.

[0265] According to another embodiment, the control and high-voltage module 19 can include an ignition detection module that detects the ignition of the pellets 2. For example, the arc can be extinguished and reignited at predetermined intervals. Once the pellets 2 are ignited, they are surrounded by a flame, which is a plasma. Plasma has a significantly lower resistance than air, so the initial current is considerably higher when the arc is reignited. If this initial current exceeds a predetermined threshold, the pellets 2 are considered ignited.

[0266] According to an alternative embodiment, the control and high-voltage module 19 can control an actuator module 53, which includes a geared motor 20 and a read sensor 54. (See Figure 17) Alternatively, it can also control the ignition lance 17 with an air inlet 55 into the ignition lance 17, the heating element 56, and / or a temperature monitoring system 57 for the first electrode 25 and the second electrode 28.

[0267] According to one embodiment, the control and high-voltage module 19 can include a microcontroller 58, for example, an ESP32S2 Mini. Within the control and high-voltage module 19, this microcontroller controls an Ha-Bridge module 59 for the direction of rotation and speed control of the geared motor 20 within the actuator module 53. Furthermore, the microcontroller 58 controls the fan 18, an optocoupler 60 for the fan 18, a power control module 61 for the heating element 56, a temperature control module 20 for temperature monitoring 57, as well as the signal generator 39, the power MOSFET 40, and the transformer 43 for the first electrode 25 and the second electrode 28. Another possibility is to introduce aerosols into the ignition lance 17, which are then transported by the airflow 47 into the combustion chamber 8 and accelerate ignition there.

[0268] According to an alternative embodiment, the monitoring system can also monitor the motor speed, for example, to derive resistance or load on the motor, which in turn can provide information about the presence of pellets 2. Devices may also be provided that control and monitor the airflow 47, the high-voltage transformer 43, and the temperature in the combustion chamber 8 and / or the airflow 47. It could also be useful to measure environmental parameters such as humidity and temperature, or fuel parameters such as the moisture content of the pellets 2, and to take these into account when setting the ignition parameters.

[0269] A further embodiment of an ignition device for a wood-burning plant 69 is described below. Identical parts of the ignition device are identified by the same reference numerals as in the preceding embodiments. The explanations given above apply to these parts unless otherwise stated below.

[0270] The wood combustion plant 69 comprises a combustion chamber 8, an ignition device 13, a control and high-voltage module 19, and a control unit 9. Like the embodiments described above, it is also equipped with a heat exchanger 6 and an exhaust gas system 5.

[0271] The combustion chamber 8 serves to hold pieces of wood 63, which are hereinafter also referred to simply as wood 63. These pieces of wood represent a biomass fuel that is to be burned. They rest on a combustion chamber floor 11 in the combustion chamber 8. The combustion chamber 8 is bounded by a surrounding combustion chamber wall 10. Openings are formed in the combustion chamber floor 11 so that a primary air supply 12 can take place from below the combustion chamber floor 11.

[0272] The ignition device 13 is arranged in a mounting tube (not shown) located outside the combustion chamber 8 and connected to the combustion chamber wall 10. An approximately cylindrical protective cover 14 of the ignition device 13 is fixedly connected to the mounting tube via a mounting flange 15. The protective cover 14, which also forms part of the housing of the ignition device 13, is thus fixedly arranged with respect to the combustion chamber 8.

[0273] The protective cover 14 contains a permanent magnet 64 (Fig. 20b), which is tubular and thus defines a hollow cylindrical space. A lance tube 17 is axially displaceable within the permanent magnet 64. The lance tube 17 has a circumferential annular projection 70 at its rear end, with a spring 67 (here: a coil spring) extending between the annular projection 70 of the lance tube 17 and a corresponding inwardly directed annular projection 71 of the protective cover 14. The spring 67 thus exerts a force on the lance tube 17, pushing it backward, i.e., away from the combustion chamber 8 or away from the adjacent combustion chamber wall 10.

[0274] Coil windings 68 are arranged around the outer circumference of the lance tube 17, forming an electrical coil 68. When this coil 68 is energized, it generates a magnetic field that, through interaction with the permanent magnet 64, causes the lance tube 17 to be pushed towards the combustion chamber 8 or towards the adjacent combustion chamber wall 10. This movement is directed against the action of the spring 67.

[0275] The lance tube 17 has a threaded section on its outer circumference at the front end. A threaded nut 34 is meshed with this threaded section, and a main body 24 is fastened to the main body 24 within the lance tube 17 by means of this nut. The main body 24 is a ceramic body with an approximately tubular cavity 52 that extends longitudinally and axially through the entire main body 24. The main body 24 thus has a continuous opening through which air can flow. A first electrode 25 and a second electrode 28 are embedded in the main body 24, each forming a first and second electrode tip 26, 29 at its front end. In this embodiment, the electrode tips 26, 29 are set back from the front end of the main body 24. This prevents the electrode tips 26, 29 from directly contacting a biomass fuel if the front end of the main body 24 should come into contact with such a fuel.Moist biomass fuels can cause a short circuit between the two electrodes 25 and 28.

[0276] The rear ends of the first and second electrodes 25, 28 form plug connections which are inserted into corresponding plug connections 66 attached to the lance tube 17. The plug connections 66 are each connected to a cable 21, 22 that leads to the control and high-voltage module 19.

[0277] An air inlet body 55 is arranged at the rear end of the lance tube 17. This air inlet body has a tubular passage, allowing air to flow through it axially. The tubular passage is conically shaped at the rear end, widening towards the rear.

[0278] The protective cover 14 has a valve body 65 at its rear end, which is conically complementary to the conical opening of the air inlet body 55. The valve body 65 is arranged such that when the lance tube 17 is fully retracted, it completely closes the passage through the lance tube 17. The valve body 65 and the air inlet body 55 thus form a valve with a variable opening degree for controlling the airflow in the axial direction through the ignition device 13. The two electrodes 25 and 28 are each electrically connected separately to one of the cables 21, 22 via one of the connectors 66, but are mechanically fastened as a unit to the lance tube 17 by means of the threaded nut 34.

[0279] The entire movable unit, comprising the lance tube 17, the air inlet body 55, the main body 24, the threaded nut 34, and the electrodes 25, 28, represents a movable lance which, in the initial state, due to the spring 67, strikes the valve body 65 with the air inlet body 55 (Figure 20b) and which, when the coil 68 is excited, can be moved forward a short distance so that the lance with its main body 24 protrudes into the combustion chamber 8 (Figure 20c).

[0280] The permanent magnet 64 and the coil 68 form an electromagnetic actuator that provides the movement mechanism for the lance. This electromagnetic actuator can be controlled so that it is always in one of its end positions (Figure 20b, Figure 20c). However, it is also possible to control the electromagnetic actuator in a metered manner so that it can assume any intermediate position. This is achieved, for example, by stimulating the coil using PWM (pulse width modulation). This allows the lance to be inserted to varying degrees into the combustion chamber 8, and also allows the rear opening for controlling the air supply to be opened to varying degrees.

[0281] The control and high-voltage module 19 has a feedback diode 72 (Figure 7) which is arranged in parallel to the primary coil of the transformer 43. A voltage measuring device 73 is arranged on the positively polarized supply line of the primary coil of the transformer 43, in particular in the area adjacent to the primary coil or to the feedback diode 72.

[0282] If no power is drawn from the secondary coil of the transformer 43, for example because there is no arc between the electrode tips 26, 29, then the magnetic field in the primary coil collapses and generates voltages which are short-circuited via the feedback diode 72. This leads to a voltage increase, which can be detected with the voltage measuring device 73. Conversely, if the electrode tips 26, 29 are short-circuited, for example by a moist fuel element, this leads to a voltage reduction, which can also be detected with the voltage measuring device 73.

[0283] The nominal voltage of the voltage module 45 is, for example, 12 V. Under normal operating conditions, the voltage measuring device 73 measures a voltage value of approximately 80 V due to the voltage boost caused by the clocking. If the circuit on the secondary side is interrupted, the voltage value measured by the voltage measuring device 73 can be 100 V or more. In the event of a short circuit, the measured voltage value is typically around 45–60 V. This allows for the detection of an incorrect operating condition (short circuit or open circuit). The control unit is designed so that in the event of a short circuit, the power supply is immediately interrupted, and appropriate countermeasures can be initiated. These countermeasures can include, for example, interrupting the power supply and / or moving the lance, in particular retracting the lance, so that the short circuit is cleared.After the lance is moved, it is re-energized and tested to see if the short circuit is still present. If not, the ignition process can continue normally.

[0284] If an interruption is detected, this state is maintained for a predetermined duration to ignite the arcs between electrode tips 26 and 29. If this is unsuccessful, an error message is displayed.

[0285] It can also be useful to apply such a low voltage to electrodes 25 and 28 before igniting the arc that ignition is impossible. This low voltage can be used for a short-circuit test, because if a short circuit exists between electrodes 25 and 28, it can be detected on the primary side by the voltage measuring device 73. This prevents ignition in the event of a short circuit. Ignition due to a short circuit can damage the electrodes or other electrical components.

[0286] This monitoring device also makes it possible to determine the quality of the arc. Even with a flickering arc that is repeatedly interrupted and then reignites spontaneously, the interruption of the arc can be detected by an increase in the voltage value on the primary side.

[0287] The operation of this ignition device 13 is explained below.

[0288] First, 8 pieces of wood 63 are fed into the combustion chamber and piled up inside.

[0289] The electromagnetic actuator is then actuated in such a way that the lance enters the combustion chamber 8, thereby simultaneously opening the supply of the axial airflow through the ignition device 13.

[0290] Short-circuit tests are performed at low voltage to check whether a piece of wood 69 is in contact with the electrode tips 26, 29. If this is not the case, the voltage is increased and the arc is ignited.

[0291] The ignition of the electric arc heats the air in the combustion chamber 8, causing it to rise and draw in more air through the ignition device 13. The axial airflow pulls the arc formed between the electrodes a short distance out of the lance and into the combustion chamber 8, where it comes into contact with a piece of wood 63. This ignites the wood 63, intensifying the airflow and extinguishing the arc. This is detected as an interruption. If this interruption occurs after a predetermined, typical start time, it is considered a successful ignition, at which point the supply voltage is switched off and the actuator is deactivated.

[0292] The lance then returns to its starting position (Figure 20b). This closes the valve supplying the axial airflow. Further combustion in the combustion chamber 8 takes place without additional air supply via the ignition device 13.

[0293] This ignition device 13, according to the embodiment shown in Figures 18-21, is particularly suitable for combustion plants 69 for pieces of wood 63. Compared to the ignition device 13 described above, this ignition device 13 has a shorter travel distance, which is achieved with an electromagnetic actuator. This is sufficient for large pieces of wood 63, as these typically lie directly against a region of the combustion chamber wall 10.

[0294] It may be advantageous to provide several ignition devices 13 on a combustion chamber 8, for example, arranged around its circumference. Since the ignition devices 13 are very simple in design, they can be manufactured cost-effectively.

[0295] In the embodiment described above, the electrode tips 26, 29 are set back slightly from the front end of the main body 24 to prevent a short circuit. If an electrical short-circuit test is required, it is also advantageous for the electrode tips 26, 29 to protrude slightly from the main body 24, as this allows a potential short circuit to be detected before ignition.

[0296] The invention has been explained above with reference to different embodiments. Individual components of the embodiments can be interchanged. The control and high-voltage module 19 makes sense in all variants for all different mechanical embodiments of the ignition device 13.

[0297] Furthermore, the control unit 9 can be configured such that the lance is rapidly moved alternately forwards and backwards in a specific operating state. Since ash can accumulate on the electrodes, such rapid vibration of the lance can cause the ash to fall off the electrodes. This serves to clean the electrodes. With a small range of motion of the lance, as is the case, for example, in the embodiment shown in Figures 18-21, the full stroke can be used for this purpose. With a larger range of motion, it is advantageous to use only a partial stroke to vibrate the electrodes.

[0298] Such a control system for generating a vibration of the moving device is shown schematically in Figure 22a. The method can also be modified such that the lance is first inserted into the combustion chamber 8 with its maximum stroke, then ignited, and with a burning arc, moved successively, in stages, or even a short distance backward and a short distance forward again, and thus withdrawn from the combustion chamber 8. This is shown schematically in Figure 22b. Since the position of the burning fuel can change due to thermal influences, this prevents the fuel from continuously contacting the electrode tips 26, 29 and thus causing fouling and damage to the electrodes.

[0299] Reference sign

[0300] 1 wood pellet combustion plant 38 contact drum

[0301] 2 wood pellets 39 signal generator

[0302] 3 pellet storage 40 Power-MOSFET

[0303] 4 Conveyor system 41 Supply voltage source

[0304] 5 Exhaust system 42 Diode

[0305] 6 heat exchangers 43 high-voltage transformer

[0306] 7 ash containers, 44 volt-ampere meter

[0307] 8 combustion chamber 45 adjustable voltage module

[0308] 9 Control unit 46 Airflow unit

[0309] 10 Combustion chamber wall 47 Airflow

[0310] 11 Combustion chamber floor 48 Energy chain

[0311] 12 Primary air supply 49 Rack and pinion

[0312] 13 Ignition device 50 Gear

[0313] 14 Protective cover 51 Protrusion

[0314] 15 Mounting flange 52 Cavity

[0315] 16 Mounting tube 53 Actuator module

[0316] 17 Ignition lance 54 Reed sensor

[0317] 18 fans 55 air intake

[0318] 19 Control and high-voltage module 56 Heating element 57 Temperature monitoring

[0319] 20 geared motors 58 microcontrollers

[0320] 21 First insulated power cable 59 H Bridge module

[0321] 22 second insulated power cable 60 optocouplers

[0322] 23 Guide element 61 Performance control

[0323] 24 Main body 62 Temperature control module

[0324] 25 first electrode 63 pieces of wood

[0325] 26 first electrode tip 64 permanent magnet

[0326] 27 Guide element 65 Lead

[0327] 28 second electrode 66 plug connection

[0328] 29 second electrode tip 67 spring

[0329] 30 spacers 68 windings

[0330] 31 Arc generation point 69 Wood combustion plant

[0331] 32 arcs 70 circumferential ring projection

[0332] 33 Threaded rod 71 inwardly directed ring pre-

[0333] 34 Threaded nut jump

[0334] 35 Contact spring 72 Feedback diode

[0335] 36 Gearbox 73 Voltage measuring device

[0336] 37 Clutch

Claims

Claims 1. Ignition device (13) for solid biomass fuels in combustion and gasification plants comprising at least two electrodes (25, 26) for generating an electric arc (32) with which the biomass fuels can be ignited, and a movement mechanism for extending and retracting the two electrodes (25, 26) into and out of a combustion chamber (8).

2. Ignition device (13) according to claim 1, characterized in that the ignition device (13) has an airflow device by which an airflow (47) can be generated with which a generated arc (32) can be blown away from the movement mechanism towards the biomass fuels.

3. Ignition device (13) according to claim 2, characterized in that the airflow device comprises a heating element to pre-dry the fuel and / or to assist outgassing.

4. Ignition device (13) according to one of claims 1 to 3, characterized in that the electrodes (25, 26) have a coating of a non-oxidizing material, preferably tungsten or a tungsten alloy, and / or are formed from such a non-oxidizing material.

5. Ignition device (13) according to one of claims 1 to 4, characterized in that the electrodes (25, 26) have a detachable fastening so that the electrodes are replaceable.

6. Ignition device (13) according to one of claims 1 to 5, characterized in that the electrodes (25, 26) have an adjustable position relative to each other in order to vary the arc length.

7. Ignition device (13) according to one of claims 1 to 6, characterized in that, that the electrodes (25, 26) are connected to the voltage source by an energy chain.

8. Ignition device (13) according to one of claims 1 to 7, characterized in that the position of the electrodes (25, 26) is detected by integrated magnets and a reed sensor.

9. Ignition device system comprising an ignition device (13) according to one of claims 1 to 8 and a high voltage source and a control unit (19) for controlling a high voltage and for controlling the movement mechanism.

10. Ignition device system according to claim 9, characterized in that the control unit (19) comprises a21) a MOSFET switch or a power MOSFET with which the voltages for generating the arc (32) can be switched.

11. Ignition device system according to claim 9 or 10, characterized in that the control unit (19) has a programmable microcontroller to adjust operating parameters of the arc (32) and / or to perform a short-circuit test prior to ignition of the arc.

12. Combustion plant (1) for biomass fuel, in particular wood pellets, comprising: - an ignition device system according to one of claims 9 to 11 .

13. Incineration plant (1) according to claim 12, characterized in that the incineration plant (1) further comprises: - a conveying mechanism for supplying the biomass fuel to the combustion plant (1 ), - a combustion chamber in which the biomass fuels are burned with the supply of oxygen, - a gasification chamber connected to the combustion chamber in which the gases produced during combustion are converted into synthesis gas under reduced oxygen supply, - an exhaust system (5) for discharging the exhaust gases produced during combustion and gasification, - a control unit (9) for regulating in particular the supply, combustion and / or gasification, and - a heat transfer unit for utilizing the heat energy generated during combustion and gasification.

14. Method for igniting solid biomass fuels in combustion and gasification plants with an ignition device (13) according to any one of claims 1 to 8, wherein the following steps are carried out: - Extension of the two electrodes (25, 26) into the combustion chamber (8), - Generating an electric arc (32) between the electrodes to ignite the solid biomass fuel, and - retracting the two electrodes (25, 26) from the combustion chamber (8).

15. Method according to claim 14, characterized in that an airflow (47) is generated with which the generated arc (32) can blow away from the movement mechanism towards the biomass fuels.

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