Wood gasifier - fire basket

Abstract

Fire basket (1) with an inner wall (3), with an outer wall (2) opposite the inner wall (3), with a first opening (20) at the top of the fire basket (1), with a second opening (19) at the bottom or on the underside of the fire basket (1), with one or more holes (4) at the top in the inner wall (3) through which air can flow into an upper combustion zone of the fire basket (1), with one or more holes or openings (11, 12) at the bottom of the inner wall (3) through which air can flow into a lower combustion zone of the fire basket (1), wherein the one or more holes (4) present at the top in the inner wall (3) are arranged at the level of the upper third or at the level of the upper quarter (e / 4) of the height of the outer wall (2), characterized in thatthat the cross-section between the outer wall (2) and the inner wall (3) has a maximum between the one or more holes (4) at the top of the inner wall (3) and the one or more holes or openings at the bottom of the inner wall (3).

Description

The invention relates to a fire basket for outdoor use. Examples of outdoor areas include gardens or patios. A fire basket for outdoor use is known from German patent application DE 10 2021 209 754 A1. The fire basket has an approximately hemispherical outer wall with an upper and a lower opening. The fire basket includes a bowl into which fuel can be placed. When the bowl is inserted into the outer wall, it is completely enclosed in the lower part of the outer wall. The bowl has openings through which air required for combustion can flow into a combustion zone. Such a fire basket is less suitable for burning wood with very high efficiency because the gases produced during wood combustion can only be burned to a limited extent. To burn wood with very high efficiency, it can be burned in several stages. To achieve this, a first combustion zone of a wood-burning device can be loaded with wood. In this first zone, the wood burns with the supply of primary air, generating heat. Light wood gases are produced, which can combust in the first combustion zone. Less flammable components of the resulting wood gas are directed to a second combustion zone. In this second zone, the less flammable components can burn at a very high temperature with the aid of secondary air. Such wood-burning devices are known from German patent applications DE 20 2019 105 975 U1 and AT 525 531 B1. The publication DE 10 2023 100 774 A1 concerns a fireplace with an inner wall and an outer wall. An inner floor is connected to the inner wall. The inner floor has an airtight containment plate. The publication DE 10 2014 220 789 A1 discloses a cooking device with a double wall to avoid burns on a hot outer wall. From US patent 2020 / 0224879A1, a firebox is known that comprises a combustion chamber with a bottom and an opening at the top. It also includes a secondary chamber with a bottom, at least one air inlet, and at least one air outlet. The object of the invention is to create a fire basket with advantageous properties that can be used outdoors. Preferably, it should be possible to burn wood with very good efficiency. The object of the invention is solved by a fire basket which includes the features of the first claim. A fire basket is used to solve the problem. The fire basket has a first opening at its top. It also has a second opening at or near its bottom. The first opening is designed to allow fuel to be placed inside. Therefore, it can be the largest opening to facilitate the easy insertion of fuel. The second opening allows air to reach the fuel. Air can then flow through this opening into at least one area containing the fuel intended for combustion. The first opening at the top of the fire basket can thus be larger than the second opening at or near its bottom. The fuel can be a solid, such as wood, or a wood-based material.Wood can be in the form of logs, pellets, compressed wood shavings, or compressed wood flour. Wood can also be in the form of wood briquettes. The fire basket comprises an inner wall and an outer wall. The inner wall can be located entirely or at least predominantly within the outer wall. The outer wall can be the outermost wall of the fire basket, and therefore always visible from the outside, regardless of the viewing angle. The inner wall can be concealed by the outer wall depending on the viewing angle. The inner wall and / or outer wall can be continuous, for example, at least partially ring-shaped in cross-section. The inner wall and / or outer wall can then, for example, be cylindrical, at least partially. The inner wall and / or outer wall can be continuous, specifically square in cross-section. The inner wall can be at least partially the innermost wall of the fire basket. There may be no other wall or structure between the inner wall and the outer wall. The inner wall and / or outer wall can each be a single piece, i.e.,It is possible that the inner and / or outer wall parts were manufactured in a single step. However, it is also possible that two or more parts of the inner wall and / or outer wall were initially manufactured separately. These separately manufactured parts could then have been joined to form the inner or outer wall. The first opening at the top of the fire basket can be located on the top of the outer wall and / or the inner wall. The first opening at the top of the fire basket can also be the top opening of an attachment that is placed on the outer wall and / or the inner wall. The second opening can be an open underside of the outer and / or inner wall, i.e., an opening at the lower end of the outer and / or inner wall. The second opening can be formed by a hole in the outer and / or inner wall. There can be several second openings through which air can flow into the fire basket. Air can flow through at least one second opening into the area between the inner and outer walls. The inner wall can have one or more holes through which air can flow into a combustion zone of the fire basket. One or more holes or openings may be provided adjacent to the underside of the inner wall. The holes may be located within the inner wall itself. They may be situated in the lower third or lower quarter of the inner wall. The underside of the inner wall may be open, i.e., an opening. Air flowing in through the one or more holes in the lower third or lower quarter of the inner wall and / or through the open underside or opening can be directed to a primary, lower combustion zone within the fire basket to ignite fuel. One or more holes are provided adjacent to or near the top of the inner wall. These holes are located in the upper third or upper quarter of the inner wall's height. For example, if the inner wall is 30 cm high, the holes can be at least 20 cm above the bottom of the inner wall, thus placing them in the upper third of the wall's height. The fire basket can be designed so that air, previously heated by the inner wall, can flow through the holes in the upper third or upper quarter into a combustion zone. The holes are provided in the inner wall. One or more holes provided in the inner wall are positioned at the level of the upper quarter or the upper fifth of the outer wall's height. For example, if the outer wall is 40 cm high, the one or more holes can be located at least 30 cm above the underside of the outer wall, thus at the level of the upper quarter of the outer wall's height. This arrangement allows preheated air to flow into an upper combustion zone to burn difficult-to-ignite wood gases. In particular, the holes in the inner wall are oriented so that air can flow into the second combustion zone essentially horizontally or at a downward angle, ensuring the reliable combustion of even difficult-to-ignite gases in a central area of ​​the fire basket.The section of the inner wall containing these holes can be vertical, allowing air to flow essentially horizontally into the second combustion zone. Alternatively, the section of the inner wall containing these holes can taper upwards, allowing air to flow downwards into the second combustion zone. The air is directed in such a way that, on the one hand, it can burn, for example, wood or a wood-based material in a first combustion zone, and on the other hand, in a second zone, in its previously heated state, it can burn gases that are difficult to ignite and that have been produced by the burning of the wood. The second combustion zone is generally located spatially above the first. The one or more holes in the inner wall leading into the second combustion zone are always a significant distance from the one or more holes or openings in the inner wall leading into the first combustion zone. This significant distance can be at least 15 cm or at least 20 cm if standard-sized logs with a length of 25 cm or 33 cm are to be burned. For smaller pieces of wood, smaller distances may suffice, for example, at least 5 cm or at least 10 cm. This significant distance ensures that even difficult-to-ignite gases produced during wood combustion are reliably combusted. The distance is therefore chosen to be correspondingly large if the combustion of these difficult-to-ignite gases is to be successful. The maximum inner diameter of the inner wall is generally larger than the necessary distance to allow the combustion of difficult-to-ignite gases in a second zone. The maximum inner diameter of the inner wall can be 1.5 or 2 times larger than the necessary distance to allow the combustion of difficult-to-ignite gases in a second zone. The maximum inner diameter of the inner wall can also be 3 or 2.5 times smaller than the necessary distance to allow the combustion of difficult-to-ignite gases in a second zone. However, this does not preclude the possibility that the maximum inner diameter of the inner wall can be smaller than the necessary distance to allow the combustion of difficult-to-ignite gases in a second zone. One or more holes in the inner wall can be elongated. One or more holes in the inner wall can be circular or rectangular. Holes in the inner wall can be arranged in a ring. Elongated holes can extend along the ring shape, i.e., parallel to the ring shape. Holes can be produced, for example, by punching, milling, or drilling. Between the holes in the inner wall at the top and the one or more holes or openings at the bottom, there may be one or more further holes in the inner wall. However, it is preferable that the area of ​​the inner wall between the one or more holes or openings at the bottom and the one or more openings at the top is closed, so that no air can flow through it. A closed area of ​​the inner wall between the one or more holes or openings at the bottom and the one or more openings at the top can extend over a length of at least 5 cm or at least 10 cm to allow sufficient heating of secondary air. Over a distance of at least 5 cm or at least 10 cm, air can then flow adjacent to the inner wall and be heated without being able to flow into the interior of the inner wall. The distance and / or cross-section between the inner and outer walls narrows towards the one or more holes leading into the second combustion zone, which are located on the upper surface of the inner wall. This advantageously results in an increased flow cross-section and, consequently, a higher airflow velocity as the air approaches these holes. Air can then flow into the second combustion zone at a relatively high velocity, ensuring thorough mixing with difficult-to-ignite gases and thus optimizing their combustion. It is particularly advantageous if the outer wall tapers towards the one or more openings on the top, at least in its upper section, in order to direct the airflow so that it can pass through the openings at a particularly high velocity, thus further improving combustion. For this reason, the outer wall can taper conically towards the one or more openings on the top. However, a curved taper, such as a semi-spherical shape, is preferable in order to change the direction of the airflow gradually and in a more aerodynamically efficient manner. Starting from a central area, the fire basket can taper downwards to allow for particularly secure placement in a stand or tripod with a lower center of gravity. This taper can also be straight or curved. For the aforementioned reasons, the outer wall can preferably be semi-spherical. The distance and / or cross-section between the inner and outer walls can gradually taper towards the one or more holes leading into the second combustion zone. The distance and / or cross-section between the inner and outer walls should ideally not taper in a stepped manner to minimize air turbulence. This prevents detrimental air turbulence that could negatively reduce the flow velocity. The outer and / or inner walls can run in a straight line towards the aforementioned one or more holes, at least in their upper section, to avoid steps. If air escapes from the upper holes in the inner wall, air turbulence is desirable. Therefore, it can be advantageous to provide a large number of small holes instead of a smaller number of larger ones. Thus, more than 30, more than 50, or more than 70 holes can be provided, for example, arranged in a ring along the top of the inner wall. The number of holes in the upper part of the inner wall may be limited to 500 or 300 due to space constraints. The diameter of the holes can be less than 5 cm or less than 3 cm. The diameter of the holes can be greater than 0.5 cm or greater than 1 cm. The cross-section between the outer and inner walls exhibits a local maximum between the one or more holes at the top of the inner wall and the one or more holes or openings at the bottom of the inner wall. This allows the airflow velocity between the inner and outer walls to initially decrease, then accelerate again after passing through this cross-sectional maximum. This ensures that the air flows particularly slowly when heat can and should be transferred to the air via a heated inner and / or outer wall, in order to ignite difficult-to-ignite gases. Curved and / or straight profiles of the inner and / or outer walls are possible to avoid detrimental air turbulence. For example, the outer wall can be curved to reduce the distance to the inner wall and thus the flow cross-section. To ensure that the distance and / or the cross-section between the inner and outer walls gradually decreases, the outer wall can be curved, at least in the area of ​​this reduction. The outer wall can be shaped, at least in this area, like part of a sphere, part of an oval, or part of an egg. In other words, the outer wall can curve outwards, as is the case with part of a sphere, part of an oval, or part of an egg. The inner wall can be straight in this area. For example, the upper part of the inner wall can be shaped like a cylinder or a truncated cone.Alternatively or additionally, the inner wall can have a lesser curvature than the outer wall, so that the spacing and / or the cross-section gradually tapers towards the one or more holes or openings. The aforementioned truncated cone can taper downwards. The taper of the truncated cone can be slight. The curvature of the outer wall can favorably alter the airflow direction towards the second combustion zone. Preferably, the outer wall is shaped like part of a sphere so that air can be guided from an inlet opening towards the second combustion zone with minimal turbulence. Furthermore, the cross-sectional area between the outer and inner walls can be designed to have a maximum between the one or more holes on the upper surface of the inner wall and the one or more holes or openings on the lower surface. This allows the airflow velocity between the inner and outer walls to initially decrease, enabling the heat to be absorbed by the heated inner wall.Following this, the flow rate of the now highly heated air can be accelerated again, so that highly heated air can advantageously exit at high speed from the one or more openings at the top of the inner wall. The maximum diameter of the sphere can be limited to, for example, 100 cm or 80 cm. The minimum diameter of the sphere can be, for example, at least 9 cm, at least 14 cm, at least 40 cm, or at least 50 cm. Preferably, the outer wall is convex and connected to the inner wall in such a way that a lower section of the outer wall is prestressed towards the top of the outer wall by the inner wall, i.e., pulled upwards. This mechanically stabilizes the fire basket. Thin material thicknesses are then sufficient for the inner and / or outer walls to provide a stable fire basket. As a result, the fire basket can be relatively light and therefore handled without much effort. To properly brace the inner wall against the outer wall, the inner wall can be cylindrical or frustoconical, at least in sections. Furthermore, the shape of the inner wall can follow the shape of the outer wall and run approximately parallel to it. At least one section of the inner wall can therefore also be curved. A curved section of the inner wall can form the underside of the inner wall or be part of the underside of the inner wall. Thus, the inner and outer walls can run parallel, at least in sections, or at least substantially parallel, in a lower region. The shape and dimensions of the upper edge of the inner wall can correspond to the shape and diameter of the upper edge of the outer wall, enabling a connection between the inner and outer walls at the top. Thus, the top of the outer wall can be connected to the top of the inner wall. The connection between the upper edge of the outer wall and the upper edge of the inner wall can be positive-locking, material-locking, and / or force-locking. The connection can be such that no air can flow through it, or at least virtually no air can. Air then flows, at least predominantly, only through the one or more holes in the upper region of the inner wall into a combustion zone. The connection between the top of the outer wall and the top of the inner wall can be designed for tensioning. For example, the upper edge of the inner wall can rest on the upper edge of the outer wall in a prestressed state. A sufficiently high degree of airtightness can be achieved by prestressing, for example, in a ring-shaped contact of the upper edge of the inner wall against the upper edge of the outer wall. Thus, an airtight seal is possible. It is possible that an additional material bond, such as an adhesive bond or a weld, is present. However, an additional material bond may be unnecessary. It is also possible that a sealing ring is present between the upper edge of the inner wall and the upper edge of the outer wall to ensure a particularly reliable airtight connection.The sealing ring can be made of a sufficiently heat-resistant material. By clamping the top surface of the outer wall to the top surface of the inner wall, a stable assembly can be created from two relatively unstable parts, as a profile is clamped. Out-of-roundness can be eliminated by clamping. Clamping can be particularly advantageously achieved over a conical surface. The upper edge of the inner wall can rest at an angle against the upper edge of the outer wall, pre-tensioned in such a way that the upper edge of the outer wall is pressed outwards. This compensates for manufacturing inaccuracies in the shape of the outer wall that affect the shape of its upper edge. For example, the outer wall is at least predominantly or entirely shaped like part of a sphere. Ideally, the upper edge of the outer wall is then circular. Due to manufacturing inaccuracies, the upper edge of the outer wall may deviate from this ideal circular shape and, for example, be slightly oval. If the inner edge of the inner wall is circular, the oval shape of the upper edge of the outer wall will also be pressed into a circular shape. For this reason, the upper edge may be at least partially conical or widen upwards in a funnel shape.Even if the inner edge of the inner wall is not perfectly circular, it is still possible to press the upper edge of the outer wall into a more circular shape. This can affect the overall shape of the outer wall. Therefore, it is possible to manufacture the outer wall from a particularly thin material in a technically very simple way, without having to worry about excessively high manufacturing tolerances. This is of particular interest for the outer wall because the material expenditure or surface area of ​​the outer wall generally exceeds that of the inner wall. It is therefore a significant advantage that the outer wall can be manufactured with minimal material expenditure and / or in a technically very simple way.The inner wall can therefore be manufactured with a greater wall thickness compared to the outer wall, allowing the outer wall to deform without itself being deformed. The inner wall then experiences minimal deformation. For the same reason, the inner wall can alternatively or additionally be made of a mechanically more stable material than the outer wall. The inner wall may be manufactured using more complex techniques than the outer wall, resulting in lower manufacturing inaccuracies. This also contributes to the ability to press the outer wall into a desired, ideal shape even in the event of manufacturing inaccuracies. The inner wall is preferably manufactured by deep drawing to achieve relatively high manufacturing accuracy. At least one preform can be produced by deep drawing. The outer wall can be manufactured using a technically simpler rotary forming process, which may result in higher manufacturing inaccuracies. The outer wall can also be produced using a deep-drawing process, even with an undercut, by means of an elastomer core. This core allows a pre-drawn blank to be transformed into a spherical shape with an undercut. The core can then be removed from the spherical form. For tensioning, a lower section of the inner wall can be rigidly connected to a lower section of the outer wall, for example, by a screw connection. A screw connection is particularly suitable because the desired preload can be created in a technically simple way by tightening a screw or nut. A bowl may be inserted into the inner wall. This bowl may be designed to hold fuel for burning. It may also be designed to collect ash. The bowl may have openings and / or holes through which air can flow into it, thus supplying the fuel with oxygen for combustion. One or more holes in the shell can be elongated. One or more holes in the shell can be circular or angular. Holes in the shell can be arranged in a ring. Elongated holes can extend along the ring shape. The bowl can be loosely inserted into the inner wall, allowing it to be grasped and removed without having to loosen any connections. To facilitate this loose insertion, the inner wall can taper downwards. For this reason, the inner wall can be curved downwards. To make insertion particularly easy, the upper edge of the bowl can be circular, and the tapered section of the inner wall can be shaped, for example, like a partial sphere. The upper edge of the bowl can then rest on the inside of the inner wall. No special orientation is required. If the bowl can be removed from the inner wall, this can be intended to allow for easy ash disposal. This eliminates the need to handle the entire fire pit to empty the ash. The height of the bowl is small compared to the height of the inner and / or outer walls. The height of the inner wall, for example, can be at least twice the height of the bowl. The bowl can preferably be inserted into the inner wall in such a way that a lower section of the bowl projects downwards from the inner wall. Holes and / or openings in the bowl can then also be located below the inner wall. These can be ring-shaped holes or openings arranged below the inner wall. This allows air to flow into the bowl particularly freely for burning fuel. The holes in the bowl can be arranged so that they are surrounded by the inner wall when the bowl is inserted into the inner wall. The bowl can then be positioned so that air can flow into the bowl through these holes to burn the fuel. Since the outer and inner walls can be braced against each other, unlike in a shell, their wall thicknesses can be smaller than the shell's wall thickness. Specifically, the wall thicknesses of the outer and inner walls can be 10%, 15%, or 20% smaller than the shell's wall thickness. For example, the shell's wall thickness can be at least 0.5 mm or at least 0.8 mm, and the maximum wall thicknesses of the outer and inner walls can be 0.9 mm or 0.8 mm, respectively, if the outer wall is braced against the inner wall. Particularly thin wall thicknesses, for example down to 0.7 mm, are especially preferred. These very thin walls heat up quickly, allowing for rapid secondary combustion. A grate can be inserted into the bowl. Fuel can then be placed on the grate to burn. Ash falls through the grate and is collected in the bowl below. This prevents ash from interfering with the combustion of the fuel. Openings in the mesh are preferably sized so that even standard-sized wood pellets cannot fall through them. Wood pellets with a diameter of 6 to 8 mm are most common. Sometimes, wood pellets with a diameter of 4.5 or 10 mm are also used. The maximum opening size in the mesh can therefore be, for example, 5.5 mm or 4 mm. However, the maximum opening size can also be 10 mm or 8 mm to ensure that pellets can barely pass through. The minimum opening size in the mesh can therefore be, for example, at least 3 mm or at least 4 mm. The bars can be at least 4 mm or at least 5 mm high. The bars can be at least 4 mm, at least 5 mm, or at least 6 mm high and / or wide. The bars can be a maximum of 12 mm, at most 10 mm, or at most 8 mm high and / or wide. A mesh dimensioned in this way is easy to manufacture and ensures good airflow. The grid may be loosely placed on top so that it can be easily removed from the bowl without tools. Removing the grid may also be intended to make it easier to subsequently remove ash from the bowl. The bowl can have one or more holes and / or openings above and below the grate to direct air towards the grate for combustion. Fuel can then be supplied with air from both the top and bottom, which favors combustion. One or more holes and / or openings below the grate can be covered by a cover so that ash cannot, or at least hardly can, fall out of the bowl through the opening. The cover can be inclined towards the center of the bowl to direct ash towards the center. The bowl and cover can be shaped so that their elements interlock, similar to a labyrinth seal. Air can pass through these interlocking elements, while ash can be retained by them. At least 30, 40, or 50 holes can be provided above the grate to create desired air turbulence. For space reasons, the number of holes may be limited to 200 or 100. It may be advantageous for burning wood if these holes, located above an inserted grate, have a smaller diameter than the holes that may be provided in the upper part of the inner wall. The grid can be placed on the cover. For example, a flat area can be provided within the tray on which the grid can be placed. The cover, which may slope downwards and inwards, can then adjoin this flat area. The grid can be formed from rods, which can be arranged in a lower and an upper plane. The rods of the upper plane can form an angle with the rods of the lower plane, i.e., they can intersect. The angle can be at least 70°, for example, 90°. The rods within a plane can run parallel. By arranging rods in different planes, the air supply from below to the fuel can be further improved, thus further enhancing combustion. The bars of the lower level can be bonded to the bars of the upper level, for example, by a material bond. The grid, and thus the interconnected bars, can have been manufactured by die casting in a single operation. The maximum distance between two bars on a level can be 5.5 mm or 4 mm to prevent wood pellets from falling through the mesh. Nevertheless, logs can still be adequately supplied with air from both above and below for combustion. The bowl can include a handle for removing it from the inner wall. The handle can be a bar or a rod. The rod can have a knob or widening at one end to facilitate removal. The handle can be attached to the bottom of the bowl beneath an inserted grid. The grid can have an opening through which the handle passes when the grid is inserted into the bowl. This is particularly feasible if the handle is a rod or a rod with a knob. Such a rod-shaped handle is therefore especially preferable, as it requires very little space, leaving ample room for fuel. The rod can be positioned in the center of the bowl's base to prevent imbalances when lifting the bowl. The bowl may be made of an upper and a lower part, which are welded together, for example, to create suitably large openings in a technically simple way. The bottom of the bowl is generally closed to prevent ash from falling out. A lower opening in the outer wall can include an upward-projecting collar. This collar prevents ash that has unintentionally entered the outer wall from escaping. The fire basket can have an attachment above the outer and / or inner wall, which can be mounted on the outer and / or inner wall. This attachment can further improve the combustion of flammable gases. The attachment can be shaped like a nozzle, tapering towards its outlet. Thus, when mounted, the attachment can taper upwards to further enhance combustion. In particular, the secondary combustion of flammable gases resulting from wood burning in a second combustion zone can be further improved by the attachment. The attachment can also serve as a windbreak to protect the combustion of flammable gases from wind disturbances. The attachment can be at least 4 cm or at least 8 cm high to improve combustion.The fire basket attachment cannot be higher than 20 cm or 15 cm to avoid unnecessarily high material costs. An excessively high fire basket attachment also impairs optimal operation, for example, by obscuring the flame. The maximum diameter of the fire basket attachment can be at least 100 cm or 80 cm. The minimum diameter of the fire basket attachment can be at least 20 cm or 30 cm. The fire basket attachment can be loosely placed on top to allow for the removal of a bowl inside the fire basket, or at least to make it easier to remove. The fire basket attachment can then be removed without having to loosen any connections beforehand. The aforementioned outer wall and / or shell can be made of or comprise steel. A type of steel other than stainless steel may be selected. The steel can be coated internally and / or externally. This coating could, for example, consist of enamel. The outer wall can thus be manufactured with minimal technical effort. The inner wall can be made of a different type of steel than the steel used for the outer wall and / or shell. For example, the inner wall can be made of or incorporate stainless steel to improve its resistance to heat and / or corrosion. The grate can be made of iron or an iron alloy. The grate can be made of iron or an iron alloy. The fire basket cover can advantageously be made of aluminum or copper. Due to their good thermal conductivity, aluminum or copper heat up very quickly, which can improve the early combustion of difficult-to-ignite gases in an adjacent secondary combustion zone. However, the fire basket cover can also be made of another metal, such as stainless steel, and / or of ceramic and / or glass. The fire basket cover can be manufactured by die casting with very low manufacturing tolerances. A simpler manufacturing process is to use coiling followed by a pressure casting process. The fire basket cover can also be made of stainless steel or another type of steel. The steel can be coated. The fire basket can include a frame. The outer wall can be placed on the frame. There can be a loose connection between the outer wall and the frame, allowing the fire basket to be removed from the frame without tools. The frame can be, for example, a tripod. The frame can be formed by at least one wire. The frame can include a heat-shielding wall, such as a sheet of metal, to protect the surface underneath from heat. The heat-shielding wall can be shaped like a bowl or a flat plate. The heat-shielding wall is particularly useful when the frame is low. The invention is explained in more detail below with reference to the figures. The figures show: Fig. 1: Fire basket 1; Fig. 2: Frame with heat-protective wall; Fig. 3: Section through a fire basket; Fig. 4: Section through the fire basket from Fig. 3 showing the airflow path; Fig. 5: Detail of the top of the fire basket; Fig. 6: Detail of the bottom of the fire basket; Fig. 7: Grate; Fig. 8: Bowl; Fig. 9: Fire basket attachment; Fig. 10: Fire basket with tripod; Fig. 11: Section through the outer and inner walls; Fig. 12: Section through a fire basket; Fig. 13: Section through a fire basket; Fig. 14: Grate; Fig. 15: Cross-section of grate bars; Fig. 16: Transition between grate bars; Fig. 17: Frame; Fig. 18: Detail of a fire basket. Fig. 19: Fire basket with stand; Fig. 20: Section through fire basket with wood pellet attachment; Fig. 21: Bowl with wood pellet attachment and lifting tool; Fig. 22: Bowl with wood pellet attachment and lifting tool; Fig.23 : Section through fire basket with fire basket attachment; Fig. 24 : Section through fire basket with spark guard and lid. Fig. 1 shows a fire basket 1. The fire basket 1 can comprise an outer wall 2. The outer wall 2 can be shaped like part of a sphere, as shown in Fig. 1. The fire basket 1 can comprise an inner wall 3. The outer wall 2 can be opposite the inner wall. Holes 4 can be provided at the upper edge of the inner wall 3. Heated air can flow through the holes 4 into a second combustion zone to burn gases that are difficult to ignite. The fire basket 1 can have a fire basket attachment 5, which is placed on the outer wall 2 and / or on the inner wall 3. The fire basket attachment 5 can taper towards the top. The fire basket attachment 5 can complete the outer shape of a sphere, i.e., be correspondingly domed. The fire basket 1 can comprise a frame 6 onto which the outer wall 2 can be loosely placed. The frame 6 can be manufactured by bending and welding at least one wire. The frame 6 can comprise a heat-shielding wall 7, i.e., a wall firmly connected to the rest of the frame. Alternatively, the heat-shielding wall 7 can simply be inserted. The heat-shielding wall 7 can be shaped at least substantially like a bowl. The heat-shielding wall 7 can be oriented substantially parallel to the surface such that the surface below the heat-shielding wall 7 is protected from heat. Figure 2 shows an example of a frame 6 with a heat-shielding wall 7 inserted therein. The heat-shielding wall 7 can be shaped similarly to a bowl, as shown. Hooks 8 may be present on the outer edge. The heat-shielding wall 7 can be hung in the frame by means of the hooks 8. Figure 3 shows a section through a fire basket, as shown in Figures 1 and 2. It can be seen that the inner wall 3 is opposite the outer wall 2. A bowl 9 can be inserted into the inner wall 3 of the fire basket 1. The bowl 9 can be loosely inserted, so that simply lifting it is sufficient to remove it from the inner wall 3. No connection needs to be broken to remove the bowl 9 from the inner wall 3. When inserted, the bowl 9 can extend through the opening that forms the underside of the inner wall. Thus, as shown in Figure 3, the bowl 9 can be inserted into the inner wall 3 such that a lower section of the bowl 9 projects downwards from the inner wall 3. The upper edge of the bowl 9 can be circular. The upper edge of the bowl 9 can rest on the inside of the inner wall 3, specifically in a curved area of ​​the inner wall 3. A grid 10 can be inserted into the bowl 9. The grid 10 can be placed loosely inside, so that lifting it is sufficient to remove it from the bowl 9. Therefore, no connection needs to be broken to lift the grid 10. Fuel, such as wood, can be placed on the grid 10 for subsequent burning. Above the grid 10, holes 11 may be present in the tray. The holes 11 may be arranged in a ring. Air can flow through the holes 11 to the fuel. The top of the fuel placed on the grid 10 can thus be exposed to airflow. The holes 11 in the tray 9 may be arranged such that, as shown in Fig. 3, they are surrounded by the inner wall 3 when the tray 9 is inserted into the inner wall 3. Below the grid 10, for example, slotted openings or elongated holes 12 may be present in the tray 9. Air can flow into the tray 9 through these slotted openings or elongated holes 12. The holes and / or openings 12 in the tray may be located at least partially below the inner wall 3 when the tray 9 is inserted into the inner wall 3. A cover 13 may be provided to cover the slotted openings or elongated holes 12, preventing ash from falling through them. Ash cannot then fall out of the tray 9. Some of the air flowing into the tray 9 through the slotted openings or elongated holes 12 may pass under the cover 13.This portion of the air can then flow from below through the grid 10, thus supplying air to the underside of any fuel placed on the grid. The other portion of the air, which flows into the bowl 9 through the, for example, slit-shaped openings or elongated holes 12, can then flow to the openings or holes 11. The interior of the bowl 9 forms a first combustion zone in which wood and some of the resulting gases can burn. To allow air to flow into the bowl 9, the underside of the inner wall 3 is open. The underside of the inner wall 3 thus forms an opening. The distance a between this opening of the inner wall 3 and the holes 4 on the upper side of the inner wall 3 is, for example, at least 10 cm, so that gases that are difficult or difficult to ignite, which are produced during wood combustion, can be reliably burned in the upper combustion zone. A rod-shaped handle 14 can be attached to the base of the bowl 9. The rod-shaped handle 14 can have a knob on its upper side to ensure a secure grip. The rod-shaped handle 14 can extend beyond the outer edge of the bowl 9 to allow for easy grasping even when the bowl 9 is full of ash. The upper edge of the inner wall 3 can be bent outwards so that it rests on the outer edge of the outer wall 2. In a lower region of the outer wall 2, webs 15 and / or clips, rivet nuts, or sleeves inserted into the webs can be provided. The webs 15 and / or clips, rivet nuts, or sleeves can be attached to the inside of the outer wall 2. The webs 15 and / or clips, rivet nuts, or sleeves can, for example, be welded to the outer wall 2 and thus secured. The webs 15 and / or clips, rivet nuts, or sleeves can, for example, be screwed or riveted to the outer wall 2 and thus secured. Threads can be provided or screwed into the inner end of the webs 15 and / or in the clips, rivet nuts, or sleeves. The threads can extend vertically or substantially vertically upwards.A screw 16 could have been screwed into each thread through an opening in the inner wall 3. This could have firmly connected the inner wall 3 to the outer wall 2. This type of fastening avoids thermal stresses that could damage the connection between the inner wall 3 and the outer wall 2. Thermal stresses can therefore be compensated for without causing damage. Webs 15 could have been made from a strip of sheet metal. Clamps, rivet nuts, or sleeves could have been made of metal. Plastic is conceivable, but rather unfavorable for thermal reasons. The dimensions can be chosen such that screwing screws 16 into the corresponding threads clamps the inner wall 3 to the outer wall 2, thus pulling the upper edge of the outer wall 2 slightly downwards and pre-tensioning it. Preferably, this also achieves centering. The fire basket attachment 5 of the fire basket 1 can comprise a circumferential wall 17 and a projection 18 extending inwards from the circumferential wall 17, for example, a circumferential protrusion. The inner end of the protrusion 18 can be inclined downwards. The inner end of the protrusion 18 can extend into the inner wall 3. The fire basket attachment 5 can thus be reliably held in place. Lifting the attachment 5 can then be sufficient to remove the fire basket attachment 5. The outer wall 2 or the fire basket 1 can have a lower opening 19 on its underside, through which air can flow into the fire basket 1. The fire basket 1 or the fire basket attachment 5 can be open at the top, i.e., have an upper opening 20, through which the previously flowing air, possibly along with smoke, can exit the fire basket 1. Fuel can be added to the fire basket through this opening 20. A collar 21 can protrude upwards from the edge of the lower opening 19. The collar 19 can retain ash that has unintentionally entered the area between the outer wall 2 and the inner wall 3. The inner wall 3 can initially be cylindrical in its upper region. From this cylindrical region, the inner wall 3 can taper downwards and, in this region, run parallel to the outer wall 2 at approximately the same distance or in this direction. The outer wall 2 can be shaped almost entirely like part of a sphere. This allows air to flow particularly advantageously as shown in Fig. 4. Air first enters the fire basket 1 through the lower opening 19, as indicated by arrows 22. Air then flows along the outer wall 2. At the level of the slotted openings or elongated holes 12, some of the air flowing into the fire basket 1 flows into the bowl 9, as indicated by arrows 23.This division of the airflow slows down the flow velocity of the portion of air entering the fire basket that now reaches the particularly heated area of ​​the inner wall 3, as indicated by arrows 24. The flow velocity of this portion of air also slows down at the level of arrows 24 because the cross-sectional area of ​​the airflow increases. This increase occurs because the diameter of the fire basket 1 increases upwards at the level of arrows 24, without the distance between the inner wall 3 and the outer wall 2 changing, or changing significantly. The slower flow velocity at the level of arrows 24 provides sufficient time for the air indicated by arrows 24 to heat up considerably. This portion of the incoming air can therefore heat up advantageously, partly due to its relatively low flow velocity. Highly heated air eventually reaches the level indicated by arrows 25. At the level indicated by arrows 25, the distance between the outer wall 2 and the inner wall 3 decreases. Furthermore, the cross-sectional area of ​​the airflow also decreases because the diameter of the fire basket 1 narrows towards the top at the level indicated by arrows 25. The airflow velocity at the level indicated by arrows 25 advantageously increases again towards the top. Additionally, the direction of the airflow changes, as indicated by the direction of arrows 25, obliquely inwards, so that air can flow at high velocity through the openings 4 into the upper second combustion zone. The one or more holes 4 present in the inner wall 3 at the top are located at the level of the upper quarter of the height of the outer wall 2.Since the distance between the inner wall 3 and the outer wall 2 gradually decreases upwards at the level of arrows 25, and the flow cross-section also gradually becomes smaller, detrimental air turbulence is minimized. In the second combustion zone, the gases that are difficult to ignite due to wood combustion can thus be burned. This combustion of difficult-to-ignite gases is further supported by the fire basket attachment 5, as tests have shown. The air that has flowed into bowl 9 can flow out of fire basket 1 along arrows 27, i.e. through the inner wall 3 and then through the fire basket attachment 5. Figure 5 shows a section of the fire basket 1. It can be seen that the upper edge 28 of the outer wall 2 can be bent inwards in a semicircular shape in cross-section. The upper edge 28 of the outer wall 2 may thus have been mechanically stabilized. The upper edge 29 of the inner wall 3 can extend outwards and obliquely upwards, resting on the upper edge 28 of the outer wall 2. If the inner wall 3 is now pulled downwards by the screws 16, the upper edge 28 of the outer wall 2 is thereby pressed both downwards and outwards. It can be seen that the circumferential wall 17 of the attachment 5 can, for example, rest on the upper edge 28 of the outer wall 2. Alternatively or additionally, the projection 18 can rest on the upper edge 29 of the inner wall 3. Figure 6 shows a section of the fire basket 1. It can be seen that the grid 10 can have bars 30 in a first level and bars 31 in a second, underlying level. The bars 30 can, for example, run transversely to the bars 31. The upper edge 32 of the inserted bowl 9 can be curved in a semicircular shape in section to stabilize the upper edge 32 of the bowl 9. It can also be seen that the sloping cover 13 can have a collar 33 angled downwards from the cover 13. The collar 33 further improves the prevention of ash from escaping the bowl 9 through the slotted openings or elongated holes 12. The collar 33 and the cover 13 can be made from a single piece, for example, from a sheet of metal such as steel.It can be seen that a rivet nut or sleeve 15a is inserted into the end of the web 15 furthest from the outer wall 2, into which a screw 16 is screwed. Fig. 7 shows a perspective view of the grid 10. It can be seen that the grid 10, in addition to the bars 30 and 31, can have a circumferential rim 34. The circumferential rim 34 can be ring-shaped. The circumferential rim 34 can protect against injuries and damage. Furthermore, the circumferential rim can mechanically stabilize the grid 10. With the grid 10 shown in Fig. 8, it is not necessary to pay attention to which way the grid is inserted into the tray 9. Basically, the grid 10 includes an opening in the center for the insertion of a rod-shaped handle. Fig. 8 shows a perspective view of the bowl 9. With the exception of the holes 11 and / or the, for example, slit-shaped openings or elongated holes 12, the bowl 9 may have no further openings or holes on its exterior. In particular, the bottom of the bowl 9 may be completely closed to prevent ash from falling out. The section of wall adjacent to the bottom of the bowl 9 and extending to the, for example, slit-shaped openings or elongated holes 12 may also be completely closed to prevent ash from falling out. A support 35 for the grid 10 may be provided inside the bowl 9. The support 35 may be circumferential. The support 35 may be annular. The support 35 may have a flat surface on which the grid can be placed. The cover 13 may be attached to the support 35.The support 35 and the cover 13 may have been manufactured from a single piece, for example from a sheet of metal such as a steel sheet. The support 35, the collar 33 and the cover 13 may have been manufactured from a single piece, for example from a sheet of metal such as a steel sheet. Figure 9 shows a perspective view of the fire basket attachment 5. The fire basket attachment 5 is particularly well suited for stamping an emblem 36 into it, for example, the inscription "höfats". Once an emblem has been stamped in, it is heat-resistant. Furthermore, a fire can be seen through the emblem, providing an additional visual effect. Figure 10 shows that the fire basket 1 can include a tripod 37 onto which the outer wall 2 can be loosely placed. The tripod 37 can have three legs 38, which can be connected to each other, for example, by a joint 39. If a joint 39 is present, the legs can be pivoted into a transport position. In the transport position, the legs 38 are parallel to each other. The tripod 37 cannot include a heat-shielding wall because the distance between the outer wall 2 and a surface can be relatively large. Figure 11 shows a cross-sectional view of the outer wall 2 and the inner wall 3. The underside of the inner wall 3 is essentially open and thus has a lower opening 40. The upper side of the inner wall 3 is also open and has an upper opening 20. The upper opening of the outer wall 2 is slightly larger than the upper opening 20 of the inner wall, so that the edges 28 and 29 of the outer wall 2 and inner wall 3 can be easily joined. Figure 11 shows that the outer wall 2 can be shaped like part of a sphere. This part of the sphere can be larger than a hemisphere. The lower opening 19 of the outer wall 2 can be much smaller than the upper opening of the outer wall, since only air is intended to flow through the lower opening 19. The diameter of the upper opening of the outer wall 2 can be at least twice or at least three times the diameter of the lower opening 19. The diameter of the sphere of the outer wall 2 can be greater than 40 cm or greater than 45 cm. The wall thickness of the outer wall 2 can be less than 2 mm or less than 1 mm. The wall thickness of the outer wall 2 can be at least 0.5 mm.The outer wall 2 can be at least 30 cm or at least 35 cm high. The outer wall 2 cannot be higher than 70 cm or not higher than 60 cm. The inner wall 3 can include an upper section 42, which may be cylindrical or frustoconical. If the upper section 42 is shaped like a frustocone, the frustocone tapers only slightly. A section 43 adjoining the upper section 42 downwards can be curved, for example, parallel to the spherical shape of the outer wall 2. The underside of the inner wall 3 can include a stabilizing rim 41, which may be shaped like a perforated disc. The opening 40 on the underside of the inner wall 3 can be larger than the opening 19 on the underside of the outer wall 2 to allow a sufficiently large shell 9 to be inserted into the inner wall 3, partially through the opening 40. The distance between the inner wall 3 and the outer wall 2 in the region of section 43 can be at least 2 cm or at least 3 cm.The distance between the inner wall 3 and the outer wall 2 in the area of ​​section 43 cannot exceed 6 cm or 5 cm. The inner wall 3 can, for example, be at least 10 cm or at least 15 cm high. The inner wall 3 can, for example, be no higher than 40 cm, 30 cm, or 25 cm. The wall thickness of the inner wall 3 can be less than 2 mm or less than 1 mm. The wall thickness of the inner wall 3 can be greater than 0.5 mm. The wall thickness of the inner wall 3 can be greater than the wall thickness of the outer wall 2. Figure 12 shows an embodiment with elongated holes 4 in the inner wall 3, through which heated air can flow into the upper combustion zone. Particularly good combustion of difficult-to-ignite gases in the case of wood combustion can be achieved by suitable conditions. The height b between the top of the grate 10 and the upper opening 20 of the fire basket 1 can therefore be advantageously less than the maximum diameter d of the inner wall 2. The ratio height b / diameter d can, for example, be advantageously greater than 0.5 or greater than 0.6 and / or less than 0.9 or less than 0.8. The height of the inner wall 3 can be less than the maximum width d of the inner wall 3. The ratio of the height of the inner wall 3 / maximum width d can be between 0.3 and 0.7 or between 0.4 and 0.6 in order to reliably ignite even difficult-to-ignite gases from wood combustion. Advantageously, the area of ​​opening 20 is smaller than the opening of the inner wall 2 at its upper surface. Thus, the diameter c of the circular opening 20, and therefore its area, can be smaller than the diameter d of the upper circular opening of the inner wall 3, or its corresponding area. The ratio of diameter c to diameter d can be, for example, greater than 0.7 or greater than 0.8 and / or less than 0.95 or less than 0.9, in order to ignite even difficult-to-ignite gases from wood combustion. The corresponding area ratio between the two openings can, for example, be between 0.5 and 0.9. The opening 19 on the underside of the fire basket 1 can be significantly smaller than the opening on the top side of the inner wall 3, while still allowing sufficient air to enter the fire basket 1. The area of ​​the opening 19 on the underside of the fire basket can be four or five times smaller than the opening on the top side of the inner wall 3. Both openings can be circular. In this case, the diameter d of the opening on the top side of the inner wall 3 is correspondingly larger than the diameter of the opening 19 on the underside of the fire basket. The area of ​​the opening 19 on the underside of the fire basket can be at least 5% of the area of ​​the opening on the top side of the inner wall 3 to ensure sufficient airflow into the fire basket. The sum of the areas of the elongated holes 4 (i.e., the flow cross-sections) in the inner wall 3 can be significantly smaller than the sum of the areas of the openings 12 through which air can flow to the bowl 9. This advantageously allows considerably more air to flow into the bowl 9 during operation than into the upper region of the inner wall 3, which is beneficial for the most complete combustion of wood possible. The ratio of the sum of the areas of the elongated holes 4 in the inner wall 3 to the sum of the areas of the openings 12 through which air can flow to the bowl 9 can be at least 1.1 and / or not more than 2.1. In Fig. 12, e is the height of the outer wall 2. Fig. 12 shows that the one or more holes 4 present in the inner wall 3 at the top are arranged at the height of the upper quarter e / 4 of the height of the outer wall 2. Figure 13 shows that the walls 2, 3 of the fire basket 1 can also be shaped differently so that the airflow velocity between the outer wall 2 and the inner wall 3 initially decreases, and then accelerates again towards the openings 4 in the inner wall 3. Arc-shaped profiles are not necessary. For example, the outer wall 2 can be shaped in cross-section similarly to part of a rhombus. The underside 44 of the outer wall 2 can be flat to prevent the fire basket 1 from being excessively tall. Legs 45 can be attached to the underside 44 for standing the fire basket. Fig. 14 shows a perspective view of another embodiment of a grid 10. The cross-section of a rod or ring 46, 47, 48, 49, 50 of the grid 10 can be such that the cross-section widens from an outer surface, i.e., top or bottom, of the grid 10 towards the middle plane of the grid. If the outer surface of the grid 10 is the top surface during operation, then the cross-section of the rod 46, 47, 48, 49, 50 widens downwards. If the outer surface of the grid 10 is the bottom surface during operation, then the cross-section of the rod 46, 47, 48, 49, 50 widens upwards. A mechanically stable rod or ring 46, 47, 48, 49, 50 can be provided, which can taper towards the outside of the grid 10, for example, similarly to a pitched roof, so that ash cannot accumulate on the rod or ring 46, 47, 48, 49, 50 as much as possible. The cross-section of rods or rings 46, 47, 48, 49, 50The rings 46, 47, 48, 49, 50 can therefore be shaped like a point on the outer sides of the grid 10. Such rods or rings 46, 47, 48, 49, 50 are shown in Fig. 14. The cross-section of a rod or ring 46, 47, 48, 49, 50 of the grid 10 can be such that the cross-section widens from an outer surface of the grid 10 towards the central plane of the grid 10 in such a way that no surfaces parallel to the central plane of the grid 10 are present on which ash could accumulate. The cross-section can therefore widen in an arc or in a straight line from the outer surface of the grid 10 towards the central plane. Fig. 14 shows the straight course of the widening towards the central plane. The cross-section of a rod or ring 46, 47, 48, 49, 50 of the grid 10 can be mirror-symmetrical such that there is no preferred orientation for placing the grid 10. The central plane of the grid 10 can be the plane of symmetry. Regardless of which outer surface of the grid 10 is at the top or bottom, the grid 10 then always acts in the same way with respect to ash, which cannot or can only barely remain on such shaped rods or rings 46, 47, 48, 49, 50 of the grid. Thus, during operation, ash can slide down along the widening of the rods or rings 46, 47, 48, 49, 50 due to gravity. The cross-section of a rod or ring 46, 47, 48, 49, 50 of the grid 10 can, for example, be rhombus-shaped or square. The cross-section of a rod or ring 46, 47, 48, 49, 50 of the grid 10 can also be oval. However, cross-sectional shapes that taper to a point towards the outside are preferable, as ash can then slide off particularly reliably and evenly. A large number of bars or rings 46, 47, 48, 49, 50, or all bars and rings 46, 47, 48, 49, 50 of the grid 10 can have identical cross-sectional shapes. However, the thickness and / or width of the bars or rings 46, 47, 48, 49, 50 can differ, for example, for reasons of stability. One or more bars or rings 47 that define the outer boundaries of the grid 10 may have a greater height than other bars or rings 46, 48, 49, 50 of the grid 10. This can improve the retention of fuel on the grid 10. One or more bars or rings 47 that define the outer boundaries of the grid can, for example, be straight, curved, or ring-shaped. Figure 14 shows a ring 47 that forms the outer boundary of the grid 10. Several rods can also be joined together to form a polygon similar in shape to the ring 47. A multitude of rings 46, 47, 50, 50a of the grid can be arranged concentrically. Concentric rings 46, 47, 50, 50a of the grid 10 can have equal spacing between them, as shown in Fig. 14. The distances between two adjacent concentric rings 46, 47, 50, 50a of the grid 10 are then always the same. Fuel can then be held uniformly on the grid. For reasons of stability, one or more inner rings 50, 50a of the grid may be larger than other bars and / or rings 46, 48, 49 of the grid 10, i.e., thicker and / or wider. Such a ring 50 may, for example, run in a ring-like shape around the center of the grid 10, as viewed from above. Concentric rings 46, 47, 50 of the grid 10 can be connected to each other by rods 48, 49 running transversely to them. Transverse rods 48, 49 can radiate outwards in a star shape, for example, radiating from a ring 50, to which transverse rods 48, 49 can be connected. To prevent the openings of the grid 10 adjacent to the outer surface of the inner ring 50 from becoming too small, only some transverse rods 49 can be connected to the inner ring 50, for example, only every second transverse rod 49. Other transverse rods 48 can be connected to another, for example, an adjacent ring 50a. Transverse bars 48, 49 of the grid can have equal spacing between them. The distances between two adjacent transverse bars 48, 49 of the grid are then always the same. Exactly three transverse bars 49 can project outwards in such a way that they can serve as a wobble-free three-point support. The ends 51 of these transverse bars 49 can therefore project from a bar 47 at the edge. The ends 51 then form supports with which the grid 10 can be placed inside the fire basket 1. The transition between rods and rings 46, 48 may be rectangular. However, a rounded transition 52, as shown in Fig. 14, is preferable. The grid 10 is then better able to withstand thermal stresses, as tests have shown. The grid 10 shown in Fig. 14 may, for example, have been produced by a casting process, such as die casting or sand casting. Fig. 15 shows preferred cross-sections 53, 53a of rods or rings 46, 47. The cross-sections 53, 53a of the rods or rings 46, 47 can be of the same shape and can initially widen in a pointed, roof-like shape from the outside towards the central plane 54 of the grid 10, as shown in Fig. 15. The pointed, roof-like widenings can merge into parallel sides or into sides with draft angles, as shown in Fig. 15. The draft angles can then terminate at the central plane 54, from which demolding then takes place. No ash can remain on such a rod or ring 46, 47. Furthermore, the rod or ring 46, 47 is very stable. The height and width of the cross-section 53a of the outer rod or ring 47 can be greater than the height and width of the cross-sections 53 of the rods or rings 46, as shown in Fig. 15. The distances between the rods or rings 46 and 47 can be equal, as shown in Fig. 15. Fig. 16 shows an enlarged top view of a rounded transition 52 between two rods / rings 46 and 48, which is preferable for thermal reasons. Fig. 17 shows a frame 56 that can include a ring element 57. The ring element 57 can be circular, as shown in Fig. 17. However, it is also possible for the ring element 57 to be, for example, a polygon. The upper surface 58 of the ring element 57 can be concave to securely hold a corresponding convex underside of the fire basket 1. The curvature of the upper surface 58 of the ring element 57 can be spherical, particularly if the convex underside of the fire basket 1 is also spherical. The radius of the curvature of the ring element 57 can then match the radius of the curvature of the underside of the fire basket 1, so that the underside of the fire basket 1 can be securely and evenly held by the ring element 57.The radius of the curvature of the ring element 57 can only approximately match the radius of the curvature of the underside of the fire basket 1, meaning that the underside of the fire basket 1 cannot be held in place by the ring element 57 across its entire surface. While the ring element 57 does not directly contribute to holding the fire basket, it is advantageous that the ring element 57 does not protrude excessively far downwards from the fire basket. The frame 56 can include legs 59, for example, exactly three legs 59 for a wobble-free setup. The legs 59 can be evenly distributed and attached to the ring element 57. The legs 59 can be formed by profiles, for example, U-profiles, T-profiles, or H-profiles, so that the legs 59 are stable yet lightweight. In the case of Fig. 17, the legs are formed almost entirely by U-profiles with legs 60, which is preferable for cleaning purposes. The height of the legs 60 can decrease towards the bottom, as shown in Fig. 17, so that the lower end 61 of the legs 59 can be narrow, enabling the frame 56 to be set up easily and reliably without wobbling. The lower end 61 of the legs 59 can also be rounded, as shown in Fig. 17, to ensure easy and reliable wobble-free setup.The lower end 61 can be rounded in several directions to reliably prevent the legs 59 from resting on easily damaged edges. Looking from the ring element 57, the legs 59 can project obliquely outwards, as shown in Fig. 17, to increase the contact area for stability. This also makes it easier to grasp a leg 59 of the frame 56, which is placed on a surface, in order to handle the frame 56. Each leg 59 can be L-shaped, i.e., it has a long leg 62 and a short leg 63 connected to it at an angle. The short leg 63 can be attached to the ring element 57. This allows the support surface for the fire basket 1 to be increased without having to provide a ring element 47 with a large diameter. The outer surface of a short leg 63 can be concavely curved so that a correspondingly curved underside of the fire basket 1 can rest flat on the short leg 63 for support. The underside of the fire basket 1 can rest flat on the short legs 63 of the legs 59. Alternatively, the underside of the fire basket 1 can rest only on the outer surface of the short legs 63 of the legs 59. If there are only three legs 59, the three legs provide a stable three-point support for the fire basket 1. Due to manufacturing tolerances, it is advantageous that the curvature of the contact surface between the base 56 and the fire basket 1 is not identical. If the curvature of the base 56 is slightly less, a stable three-point support is achieved. This means that the fire bowl 1 rests on the short legs at only three points. If the legs 59 are not excessively long or short, the frame 56 can be manufactured in a single step in a single operation, for example, using a casting process such as die casting or sand casting, in a particularly simple technical manner. Such a single-piece manufacturing process is especially possible if the height of the frame 56 is less than its maximum diameter. Such a frame is shown in Fig. 17. If the frame 56 does not have excessively long legs, its height can be less than the height of the fire basket 1. If a frame 56 with longer legs 59 is desired, at least the ring element 57 together with the short legs 63 can be manufactured in one piece in a single operation, for example by casting such as die casting or sand casting. The long legs 62 can then be attached to the short legs 63, for example by means of screws or by welding. In this way, a suitable frame 56 with long legs 59 can still be manufactured in a technically simple manner. If the legs 59 are longer in this sense, then the height of the frame 56 can be greater than the height of the fire basket 1. A frame 56 can be made of a metal, such as steel. After manufacturing, one or more protective layers and / or coatings may have been applied to the surface of the frame 56. A protective layer could, for example, consist of enamel or powder coating. Fig. 18 shows a section of a fire basket with a grid 10, as shown in Fig. 14, and a frame, as shown in Fig. 17. Fig. 18 shows that the underside of the fire basket can only rest on the outside of the legs 63. Three legs 63 ensure a wobble-free hold. The tray 9 may have a few retaining holes 64 above the holes 11 for holding a wood pellet attachment. These retaining holes 64 may be evenly spaced at the same height. The wood pellet attachment may have pins that extend into the holes 64 to stabilize its position. One retaining hole 64 may be provided for a threaded insert to attach the wood pellet attachment to the tray 9 by means of a screw connection. To ensure a particularly suitable attachment of a bridge 15, it can have a foot 65 whose shape is adapted to the contour of the inner side of the outer wall 2. The foot, adapted to the contour of the inner side, ensures an even distribution of the load. The foot 65 can be several centimeters long, for example, at least 2 cm or at least 3 cm. Along the length of the foot 65, one or more tabs 66 can be bent on the underside and attached to the inner side of the outer wall, for example, by soldering or welding. Several tabs 66 are preferable to avoid excessive point loads on the outer wall, particularly with regard to the attachment. The remaining part of the bridge 15 can project upwards from the foot 65, vertically upwards when the fire basket is in its intended position. A reinforcement 67 for receiving the screw 16 can be provided, which may be located above the inner wall 3. The handle 14 can be fastened to the base of the shell 9 by a screw 68. One or two washers 69 can stabilize this fastening of the handle 14. Figure 18 illustrates that the bowl 9 and the cover 13 can be interlocked by the shaped elements 33 and 12 in such a way as to create a kind of labyrinth seal. Ash would have to travel the back-and-forth curved path 70 to be able to leave the bowl 9. This is a difficult obstacle for ash to overcome. Fig. 19 shows a fire basket 1 with a frame 56, which, unlike the frame 56 from Fig. 17, has long legs, so that the frame 56 cannot be manufactured in one piece in a single operation (except for optional coatings). The height HG of the frame 56 is slightly greater than the height HK of the fire basket 1. The height HG of the frame 56 is greater than the maximum diameter of the frame 56. Figure 20 shows a section through a fire basket 1 with a wood pellet feeder 71. The wood pellet feeder 71 increases the volume of the bowl 9 for receiving fuel and fuel residues, which can occur in greater quantities with pellets. The wood pellet feeder 71 prevents free-flowing fuel such as wood pellets from accumulating undesirably on the upper edge of the bowl 9 and / or prevents fuel residues from spilling out unintentionally above the grate 10. The wood pellet feeder 71 can taper downwards. For example, the wood pellet feeder 71 can taper downwards in a conical shape. The wood pellet feeder 71 can have a first section 72, which, for example, tapers downwards in a conical shape. The wood pellet attachment 71 can have a second section 73 that tapers downwards more sharply than the first section 72. The second section 73 can also taper conically.The maximum outer diameter of the wood pellet attachment 71 can be slightly smaller than the maximum inner diameter of the inner wall 3, so that the wood pellet attachment 71 can be supported against the inner wall 3. The underside of the wood pellet attachment 71 can be connected to the bowl 9, for example by means of screw connections 74. For stabilization purposes, the wood pellet attachment 71 can have an outwardly curved rim 75 on its upper side, for example, which can rest against the inside of the inner wall 3. Using the handle 14, the bowl 9 and the attached wood pellet attachment 71 can be removed from the fire basket 1, for example to fill it with wood pellets or to empty burnt ash. Figures 21 and 22 show a bowl 9 with a wood pellet attachment 15 and a lifting tool 76. The lifting tool 76 can be detachably connected, for example, to a knob 78 of the handle 14. The lifting tool 76 can include claws 77 into which the knob 78 can be hooked. Using the lifting tool 76, the bowl 9, optionally together with the wood pellet attachment 15, can then be lifted out of the fire basket 1 without risk of burns. The lifting tool 76 can, for example, be pivotally connected to the handle 14 or the knob 78 of the handle 14, so that the bowl 9 can be pivoted for emptying while the lifting tool 76 is held. A pivoting motion is shown in Figure 22. The tray 9 can have a drain opening 81 on its underside, which may be laterally bounded by a wall 82. Ash can fall out of the tray 9 through the drain opening 81 by tilting the tray 9. Particularly in the case of wood pellets, however, emptying can also be done through the opening on the top. The lifting tool 76 can have a lifting tool handle 79 on its upper side to enable the lifting tool 76 to be held safely and ergonomically. The claws 77 can be bent in a U-shape. Two such claws 77 can be arranged side by side. For example, the knob 78 can then be pivotally hooked between the two claws 77 from above. Figure 23 shows a section through a fire basket with a double-walled fire basket attachment 5 for further improving combustion. In addition to the circumferential outer wall 17, the fire basket attachment 5 can comprise an inner wall 80, 81. The inner wall can comprise an upper wall section 80 and a lower wall section 81. The two wall sections 80 and 81 can form an angle that can be, for example, at least 80°, at least 90°, or at least 95°. The angle can be less than 120°, less than 110°, or less than 105°. The lower wall section 81 can, for example, be connected to the circumferential projection 18 of the fire basket attachment 5. The lower wall section 81 can project inwards so that heat can accumulate above the openings 4 at the top in the inner wall 3 for improved combustion.When the fire basket 1 is set up as intended, the lower wall section 81 can be slightly inclined upwards to facilitate airflow out of the fire basket 1 and thereby further improve combustion. The upper wall section 80 can, for example, run parallel to the upper section of the inner wall 3. The upper wall section 80 can, for example, run vertically or at least approximately vertically when the fire basket 1 is set up as intended. Walls 17, 18, 80, 81 of the fire basket attachment 5 can enclose a cavity so that the heat near the openings 4 at the top is intensified in the inner wall (3), i.e., adjacent to the upper second combustion zone, to improve combustion, and the fire basket attachment 5 remains comparatively cool on the outside. Opposite a punched-out emblem 38, the inner wall 80, 81 can include a cutout 82 so that the light from the fire can be visible through the punched-out emblem 36. Figure 24 shows a partial section through a fire basket 1 with a spark guard 83 and a lid 84. The spark guard is an air-permeable grid or wire mesh, or comprises an air-permeable grid or wire mesh in such a way that air exchange is possible. The spark guard can be placed on the fire basket during combustion, as shown in Figure 24, and protects against flying sparks. The spark guard 83 can be semi-spherical. The radius of the spark guard 83 can correspond to the radius of the outer wall 2. The spark guard 83 can be reinforced at the edges, for example by folding over the grid or wire mesh or by a separate additional ring. The spark guard 83 can be made of metal. The cover 84 can also be semi-spherical. The cover 84 can have a larger radius than the spark guard so that the cover 84 can be easily fitted together with the spark guard 83 as shown in Fig. 24. The cover 84 can be made of metal. The cover 84 can be reinforced at its edges, for example by a forming that extends inwards in a semi-circular shape.

Claims

Fire basket (1) with an inner wall (3), with an outer wall (2) opposite the inner wall (3), with a first opening (20) at the top of the fire basket (1), with a second opening (19) at the bottom or on the underside of the fire basket (1), with one or more holes (4) at the top in the inner wall (3) through which air can flow into an upper combustion zone of the fire basket (1), with one or more holes or openings (11, 12) at the bottom of the inner wall (3) through which air can flow into a lower combustion zone of the fire basket (1), wherein the one or more holes (4) present at the top in the inner wall (3) are arranged at the level of the upper third or at the level of the upper quarter (e / 4) of the height of the outer wall (2), characterized in thatthat the cross-section between the outer wall (2) and the inner wall (3) has a maximum between the one or more holes (4) at the top of the inner wall (3) and the one or more holes or openings at the bottom of the inner wall (3). Fire basket (1) according to claim 1, characterized in that the outer wall (2) is shaped like part of a sphere or like part of an oval or like part of an egg. Fire basket (1) according to one of the preceding claims, characterized in that an upper area of ​​the inner wall (3) is shaped like a cylinder or a truncated cone. Fire basket (1) according to one of the preceding claims, characterized in that the outer wall (2) is curved outwards and is connected to the inner wall (3) in such a way that a lower area of ​​the outer wall (2) is prestressed towards the top of the outer wall (2) by the inner wall (3). Fire basket (1) according to one of the preceding claims, characterized in that the inner wall (3) and outer wall (2) run parallel or at least substantially parallel in a lower area. Fire basket (1) according to one of the preceding claims, characterized in that the top of the outer wall (2) is connected to the top of the inner wall (3) in an airtight or at least substantially airtight manner. Fire basket (1) according to one of the preceding claims, characterized in that the upper edge (29) of the inner wall (3) rests on the upper edge (28) of the outer wall (2) under prestress. Fire basket (1) according to the preceding claim, characterized in that the upper edge (29) of the inner wall (3) rests airtight on the upper edge (28) of the outer wall (2). Fire basket (1) according to one of the two preceding claims, characterized in that the upper edge (29) of the inner wall (3) is inclined and rests on the upper edge of the outer wall (2) in such a pre-tensioned manner that the upper edge (28) of the outer wall (2) is pressed outwards. Fire basket (1) according to one of the preceding claims, characterized in that a lower area of ​​the inner wall (3) is connected to a lower area of ​​the outer wall (2) by a screw connection such that the outer wall (2) can be pre-tensioned by tightening the screw (16) of the screw connection. Fire basket (1) according to one of the preceding claims, characterized in that a bowl (9) is loosely inserted into the inner wall (3). Fire basket (1) according to the preceding claim, characterized in that a grid (10) is loosely inserted in the bowl (9). Fire basket (1) according to the preceding claim, characterized in that the bowl (9) has one or more holes (11) and / or openings (12) above and below the grid (10) through which air can be directed to the grid (10) for combustion. Fire basket (1) according to the preceding claim, characterized in that the one or more holes and / or openings (12) below the grid are covered by a cover (13) which is inclined towards the center of the bowl (9). Fire basket (1) according to one of the preceding claims, characterized in that the fire basket (1) comprises a removable, upwardly tapered fire basket attachment (5) above the outer wall (2) and / or inner wall (3). Fire basket (1) according to the preceding claim, characterized in that the fire basket attachment (5) is made of aluminium or copper, a ceramic material or glass. Fire basket (1) according to one of the preceding claims, characterized in that the outer wall (2) is made of coated steel and the inner wall (3) is made of stainless steel. Fire basket (1) according to one of the preceding claims, characterized in that the fire basket (1) comprises a wood pellet attachment (71) which can be detachably connected to a bowl (9) of the fire basket (1).

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