Incinerator system

Abstract

The invention relates to an incinerator system for burning biomass, in particular wood pellets, comprising a combustion chamber (1) with a nozzle bottom (2) above which a fluidized bed (3) comprising a bulk quantity of solid particles, preferably quartz sand, is arranged, an ignition unit (4), a combustion air supply (5) and a fuel supply (6). The ignition unit (4) comprises two ignition electrodes (7) or a spark plug for generating an arc, the tips of the two ignition electrodes (7) or the tip of the spark plug being arranged in the combustion chamber (1) in the vertical direction above the fluidized bed (3), which is stationary in the switched-off state, and substantially below an inlet opening (8) of the fuel supply (6).

Description

Technical field

[0001] The invention relates to a combustion furnace system for the combustion of biomass, in particular wood pellets, comprising a combustion chamber with a nozzle base above which a fluidized bed of a bed of solid particles, preferably quartz sand, is arranged, an ignition unit, a combustion air supply, and a fuel supply. State of the art

[0002] Fluidized bed combustion systems are most commonly used in large-scale installations, such as power plants, where they operate around the clock. However, in smaller systems, for example, for heating, hot water preparation, and electricity generation in single-family homes, these systems do not run continuously but cyclically and therefore must be reignited periodically. EP 2827059 A describes an example of such a combustion system for residential use. Here, the air supplied for the start-up process is preheated, for example, by an electric hot air blower to reach the ignition temperature for the fuel.

[0003] The ignition of biomass in pellet stoves, when automatic ignition is used, is usually achieved with heating elements or hot air. The ignition devices used require around 600 to 1000 W and are subject to considerable wear and tear due to the high temperatures.

[0004] German patent DE 20321670 U discloses a burner for pellet fuel which is ignited by a discharge electrode in a guide tube. The electrodes themselves remain at a distance from the pellets. The design is correspondingly complex and unsuitable for use in a fluidized bed combustion chamber.

[0005] US 4436037 A discloses a combustion furnace system with a fluidized bed for thermoplastic polymers, wherein an ignition unit is arranged above the fuel supply located in the fluidized bed.

[0006] US patent 2011 / 083593 A1 describes an electric heating element in the nozzle plate of a fluidized bed. Description of the invention

[0007] The object of the present invention is to improve a combustion furnace system, such as that described in EP 2827059 A1, in such a way that the ignition process, which is frequently necessary in private use, can be carried out much more energy-efficiently. The device should be simple and inexpensive to construct and have a long service life with low maintenance requirements.

[0008] This problem is solved according to the invention by the ignition unit comprising two ignition electrodes or a spark plug for generating an electric arc, wherein 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 ignition is switched off, and substantially below an inlet opening of the fuel supply. In the proposed solution, the tips of the ignition electrodes or the tip of the spark plug project directly into the combustion chamber and generate an electric arc when a voltage is applied. The fuel, which is introduced into the combustion chamber via the fuel supply, comes to rest on the stationary fluidized bed precisely between the two ignition electrodes or near the tip of the spark plug and is ignited by the plasma of the electric arc. For example, only about 150 W are required for the ignition device to reliably ignite the fuel.

[0009] Another advantageous feature is that the tips of the ignition electrodes or the spark plug are located within the moving fluidized bed during operation of the combustion furnace. Once the combustion furnace is started, the surface of the fluidized bed, now permeated by air, is higher than the surface of the stationary fluidized bed and thus also surrounds the tips of the ignition electrodes or the spark plug. This has the advantage that any soot produced during the ignition process is removed from the tips of the ignition electrodes by the solid particles of the fluidized bed, ensuring that the ignition electrodes are always completely soot-free and clean after each new start-up, thereby reducing the frequency of maintenance.

[0010] Furthermore, it is a preferred feature that the inlet opening for the combustion air supply is also arranged substantially above the tips of the ignition electrodes or the tip of the spark plug, and that the incoming airflow is thus oriented substantially perpendicular to the surface of the fluidized bed when the system is switched off. The introduced combustion air facilitates the ignition process and extends the arc towards the fluidized bed, so that the resulting plasma can efficiently surround and ignite the fuel.

[0011] Finally, another preferred feature is the provision of a control unit by which the starting process during commissioning of the combustion furnace system can be controlled, wherein for the starting process the control unit first directs fuel into the combustion chamber, which comes to rest on the stationary fluidized bed, then generates an arc via the ignition electrodes or via the spark plug, which ignites the fuel located between the tips of the ignition electrodes or near the tip of the spark plug, wherein the combustion air supply can optionally be controlled via the control unit in order to extend the arc towards the fluidized bed by means of the incoming airflow, and wherein after ignition of the fuel the ignition electrodes or the spark plug can be deactivated again by the control unit and the air supply through the nozzle base can be activated in order to set the fluidized bed in motion.It is advantageous to control the entire starting process via a dedicated control unit. This allows individual parameters for the specific system to be saved and adjusted as needed. Possible adjustable parameters include the amount of fuel injected, the ignition duration, the quantity and velocity of the combustion air injected, the point at which the air supply is switched on through the nozzle base to fluidize the fluidized bed, and so on. Brief description of the drawings

[0012] The invention will now be described in detail with reference to an exemplary embodiment and the accompanying figures. Fig. 1 a schematic lateral sectional view through the combustion chamber of a combustion furnace system according to the invention and Fig. 2 a schematic cross-sectional view through the combustion chamber of a combustion furnace system according to the invention. Way(s) to implement the invention

[0013] In Fig. 1A combustion chamber 1 of a combustion furnace system according to the invention is shown schematically in a side sectional view. The combustion chamber 1 contains a fluidized bed 3, shown here in its switched-off state, which is formed from a bed of, for example, quartz sand. A nozzle plate 2 is provided below the fluidized bed 3, which is connected to an air supply 9 via a plurality of openings. The air supply 9 serves to fluidize the fluidized bed 3 and to supply combustion air during operation of the system. The air supply 9 is arranged externally along the combustion chamber 1 so that the incoming air is preheated via heat exchanger surfaces before entering through the nozzle plate 2.

[0014] An ignition unit 4 is arranged above the fluidized bed 3, with the tips of the ignition electrodes 7 located above the surface of the stationary fluidized bed 3. Directly above the tips of the ignition electrodes 7 is the inlet opening 8 for the fuel supply 6, through which fuel, for example in the form of wood pellets, is introduced. In the example shown, the combustion air supply 5 is also routed into the combustion chamber 1 via the same pipe as the fuel supply 6, with a common inlet opening 8.

[0015] In the Fig. 2 is the system made of Fig. 1 The schematic cross-sectional view shows the area of ​​the common pipe for the combustion air supply 5 and fuel supply 6. It is understood that the fuel supply 6 can also be designed separately and the combustion air supply 5 can be arranged, for example, next to it or in a ring around it.

[0016] When the system is switched off, the introduced fuel comes to rest in the area between the tips of the ignition electrodes 7. When the ignition electrodes 7 are switched on, an arc is created between the two tips, whereby the resulting plasma is blown by the air introduced via the combustion air supply 5 towards the fuel or the surface of the fluidized bed 3, thus efficiently igniting the fuel.

[0017] Significantly less energy is consumed for the ignition process than with conventional ignition devices. Once sufficient fuel has been ignited, the fluidized bed 3 can be activated. The movement of the sand bed in the fluidized bed 3 causes the tips of the ignition electrodes 7 to enter the fluidized bed 3 and be cleaned of any soot that may have accumulated during the ignition process. This ensures that the electrodes are completely clean for the next ignition and thus remain fully functional even after repeated ignitions.

Claims

1. Incinerator system for the combustion of biomass, in particular wood pellets, comprising a combustion chamber (1) with a nozzle base (2), above which a fluidised bed (3) consisting of a bed of solid particles, preferably quartz sand, is arranged, an ignition unit (4), a combustion air supply (5) and a fuel supply (6), characterized in that the ignition unit (4) comprises two ignition electrodes (7) or an ignition plug for generating an arc, the tips of the two ignition electrodes (7) or the tip of the spark plug being arranged in the combustion chamber (1) in the vertical direction above the fluidised bed (3) at rest in the switched-off state, and essentially below an inlet opening (8) of the fuel supply (6).

2. Incinerator system according to claim 1, characterized in that the tips of the ignition electrodes (7) or the tip of the spark plug lie within the moving fluidised bed (3) during operation of the incinerator system.

3. Incinerator system according to claim 1 or 2, characterized in that the inlet opening of the combustion air supply (5) is also arranged essentially above the tips of the ignition electrodes (7) or the tip of the spark plug and the incoming air flow is thus aligned essentially perpendicular to the surface of the fluidised bed (3) at rest in the switched-off state.

4. Incinerator system according to one of claims 1 to 3, characterized in that a control unit is provided, via which the starting process can be controlled when the incinerator system is put into operation, wherein for the starting process the control unit first feeds fuel into the combustion chamber (1), which fuel comes to rest on the resting fluidised bed (3), then an arc is generated via the ignition electrodes (7) or via the spark plug, which ignites the fuel located between the tips of the ignition electrodes (7) or near the tip of the spark plug, wherein the combustion air supply (5) can be controlled via the control unit, if necessary, in order to stretch the arc in the direction of the fluidised bed (3) by the incoming air flow, and wherein, after ignition of the fuel, the ignition electrodes (7) or the spark plug can be deactivated again by the control unit and the air supply through the nozzle base (2) can be activated in order to set the fluidised bed (3) in motion.

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