Conveyor oven

Abstract

A continuous oven (1) comprising an inlet and an outlet station (2, 3) between which an endlessly circulating belt (4) serving as a conveyor belt is arranged, wherein the upper run (5) of the circulating belt (4) serves to transport the baked goods and is guided through a continuous baking tunnel (6), characterized in that the continuous oven (1) is wood-fired, wherein the endlessly circulating belt (4) serving as a conveyor belt is designed as a stone slab belt, comprising several stone slabs (7) arranged side by side and fixed in a frame, wherein the stone slabs form the upper and lower runs (5, 8) of the stone slab belt (4), wherein the continuous oven (1) comprises at least one wood burner (9, 14) for generating bottom and top heat in the baking tunnel (6), the continuously generated hot air of which flows through several heating channels by means of at least one fan for the purpose of transferring heating energy to the conveyor belt (4).to be subsequently supplied to a chimney (10) or partly to the chimney (10) and partly via a duct system to the at least one wood burner (9, 14, 18), wherein, in addition to regulating the power output of the at least one wood burner (9, 14, 18) and supplying hot air to the at least one wood burner (9, 14, 18), a mixing valve (21) is provided in at least one heating duct for temperature control, by means of which fresh air can be mixed with the hot air generated by the at least one wood burner (9, 14, 18), wherein the mixing valve (21) can be controlled on the basis of the signals from two temperature sensors, wherein one sensor is arranged upstream of the mixing valve (21) in the direction of hot air flow and another sensor is arranged downstream of the mixing valve (21).

Description

[0001] The present invention relates to a wood-fired continuous baking oven according to the preamble of claim 1.

[0002] Conveyor ovens are known from the prior art, which are heated with oil, gas, or electricity for the purpose of implementing temperature control; the heat is transferred to the baked goods directly via hot air or indirectly via heating registers. Continuous ovens have an inlet and an outlet station, between which a continuously circulating belt is arranged, with the upper run of the circulating belt serving to transport the baked goods and being guided through a continuous baking tunnel. Above and below the circulating belt and thus the baked goods, there is usually a heating channel each, which can be exposed to hot air heated in a heating device. As it flows through the heating channels, this air transfers heat to the baking chamber as top or bottom heat via the wall of the heating channel facing the baking tunnel.According to the state of the art, the hot air is provided by the flue gases of an oil or gas burner, which are conveyed through the heating ducts via a flue gas circulation fan.

[0003] The present invention is based on the object of providing a wood-fired continuous baking oven.

[0004] This problem is solved by the features of claim 1. Further embodiments and advantages emerge from the subclaims.

[0005] Accordingly, a wood-fired continuous baking oven is proposed, comprising an inlet and an outlet station, between which an endlessly circulating belt serving as a conveyor belt (hereinafter also referred to as the conveyor belt) is arranged. The upper run of the circulating belt serves to transport the baked goods and is guided through a continuous baking tunnel. According to the invention, the endlessly circulating belt is designed as a stone slab belt, comprising a plurality of stone slabs arranged side by side, which are fixed in a frame, the stone slabs forming the upper and lower runs of the stone slab belt. The stone slabs are preferably stone slabs with high heat absorption capacity, such as ceramic or firebrick slabs.

[0006] A wood-fired continuous-flow oven according to the invention comprises at least one wood burner for generating top and bottom heat in the baking tunnel. The hot air generated during operation flows through several heating ducts by means of at least one fan to transfer heat energy to the stone slab belt. The air is then fed to a chimney or partially to the chimney and partially to the at least one wood burner via a duct system, thereby achieving optimal heat utilization. The at least one wood burner is mounted at the inlet or outlet station or on one side of the continuous-flow oven.

[0007] To regulate the temperature, in addition to regulating the power output of the at least one wood burner (this can be done, for example, based on the wood or pellet supply and the oxygen supply), a mixing valve is provided in at least one heating duct, by means of which fresh air can be added to the hot air generated by the at least one wood burner. The mixing valve is controllable based on the signals from two temperature sensors, one sensor being arranged upstream of the mixing valve in the direction of hot air flow, and another sensor downstream of the mixing valve. This allows the temperature at the sensor downstream of the mixing valve to be regulated to a setpoint.

[0008] According to a further development of the invention, the proportion of hot air supplied to the at least one wood burner can be regulated via a valve, wherein the proportion of hot air supplied to the at least one wood burner can be determined as a function of the desired power output of the at least one wood burner and optionally additionally as a function of the soot content in the hot air. For this purpose, a soot sensor is provided whose signals are evaluated, whereby the higher the soot content of the hot air, the lower the proportion of hot air supplied to the at least one wood burner. The valve can be designed, for example, as a flap valve.

[0009] According to a further development, if increased soot formation is detected, i.e., if the soot content exceeds a predetermined, adaptable threshold, the oxygen supply to the at least one wood burner is increased, thereby improving combustion. The oxygen supply to the at least one wood burner can also be regulated based on the desired power output and the soot content.

[0010] Furthermore, due to the design, in the continuous baking oven according to the invention a large part of the ash produced in at least one wood burner is burned in the hot air according to the catalyst principle via the stones of the stone slab belt, wherein according to one embodiment the continuous baking oven has collecting trays below the conveyor belt for receiving the residual ash in the heating channels, wherein alternatively or in addition to the collecting trays below the conveyor belt collecting channels are provided for receiving the residual ash in the heating channels, wherein the residual ash received in the collecting channels can be discharged via a screw system.

[0011] According to an advantageous development of the invention, the continuous baking oven according to the invention has nozzles for compressed air cleaning of the heating channels, wherein collecting channels are provided for receiving the residual ash in the heating channels, wherein the residual ash received in the collecting channels can be discharged via a screw system.

[0012] According to an advantageous embodiment, for the purpose of cleaning the stone slab belt of residual ash, a cleaning brush can be provided, for example, below the lower run of the conveyor belt on the side of the furnace facing the inlet station, which cleaning brush can optionally have an integrated suction device.

[0013] Optionally, it can further be provided that the continuous baking oven has externally arranged steam generators through which steam is supplied to the baked goods in the conveying direction downstream of the inlet station in a manner known in the art, wherein at least one steaming zone is provided which is delimited by Teflon curtains; the steam removal takes place according to the state of the art via a steam removal system comprising at least one steam removal channel.

[0014] Preferably, at least one wood burner is designed as a pellet burner with a screw feed. The number of wood burners depends on the dimensions of the stove.

[0015] According to the invention, it is provided that the hot air generated during operation, for the purpose of generating the required bottom heat, flows through a first heating duct by means of at least one fan, the upper side of which is formed by part of the lower run of the conveyor belt and the other sides of which are thermally insulated, wherein the first heating duct is followed by a second heating duct which is fluidically connected to the first heating duct and runs between the upper run and the lower run of the conveyor belt, through which residual heat is released directly to the underside of the upper run and the upper side of the lower run of the conveyor belt, before the hot air is blown out via the chimney or the hot air is fed partly to the chimney and partly via a duct system to the at least one wood burner.

[0016] According to one embodiment of the invention, a third heating channel is provided to generate the required top heat. This third heating channel runs above the upper run of the conveyor belt, is thermally insulated on the side facing away from the upper run, and opens into the chimney. The third heating channel can be supplied with hot air from the first heating channel and / or with hot air heated by at least one wood burner assigned to the third heating channel, using at least one fan.

[0017] According to a further embodiment of the invention, in order to generate the required top heat in the baking tunnel, a second endlessly rotating belt designed as a stone slab belt is provided, the dimensions of which correspond to the dimensions of the conveyor belt and the lower run of which is arranged above the upper run of the conveyor belt and parallel thereto at a defined distance which is greater than the maximum height of the baked goods, wherein at least one wood burner associated with the second stone slab belt is provided, which can be attached to the inlet or outlet station or to one side of the continuous baking oven and whose hot air generated during operation flows through a fourth heating channel by means of at least one fan for the purpose of generating the required top heat, the underside of which is formed by the upper run of the second stone slab belt and the other sides of which are thermally insulated, wherein the fourth heating channel is followed by a fifth,A heating duct fluidically connected to the fourth heating duct, which runs between the upper and lower runs of the second stone slab belt, is connected. The residual heat is transferred directly to the upper side of the lower run of the second stone slab belt before the hot air is discharged through the chimney or the hot air is fed partially to the chimney and partially to the at least one wood burner via a duct system. In this way, the heating energy is transferred directly to the second stone slab belt during continuous operation.

[0018] The first and second stone slab belts, as well as optionally the respective wood burners and heating channels associated with the stone slab belts, can be arranged mirror-symmetrically, with an imaginary plane running parallel to the upper and lower slabs of the stone slab belts serving as the plane of symmetry. Furthermore, the first and second stone slab belts can each be driven in the same direction, either at the same speed or at different speeds.

[0019] The first and - if provided - the second stone slab belt are guided over deflection rollers in a manner known from the prior art and can preferably be driven by a drive in the area of ​​a deflection roller.

[0020] For the purpose of cleaning the second stone slab belt of residual ash, a cleaning brush can be provided below the lower run of the second stone slab belt on the side of the furnace facing the inlet station, which cleaning brush optionally has an integrated suction system.

[0021] According to a further development of the invention, the upper and lower runs of the conveyor belt and, if provided, of the second stone slab belt are guided through a compensation zone extending from the inlet station towards the outlet station over a predetermined distance, in which no heating energy is transferred to the stone slab belt, whereby the absorbed heating energy is compensated in the stone slabs.

[0022] The continuous baking oven according to the invention comprises a control system in which parameters important for operation, such as the wood or pellet supply and the oxygen supply to the at least one wood burner, the proportion of hot air that is supplied to the at least one wood burner and the proportion of fresh air that is added to the hot air generated by the at least one wood burner, are regulated or adjusted on the basis of the desired setpoints during operation, for example the setpoints for the temperature in the baking tunnel and for the soot content.

[0023] The invention is explained in more detail using the accompanying figures. The general structure and the principle underlying continuous ovens, such as the drive and the loading of the belts, are well known to those skilled in the art, so only the components relevant to the invention are described below. They show: Fig. 1: A schematic side sectional view of a first embodiment of a continuous baking oven according to the invention; and Fig. 2: A schematic sectional view of a second embodiment of a continuous baking oven according to the invention.

[0024] According to the invention and referring to Fig. 1, a wood-fired continuous baking oven 1 according to the invention comprises an inlet and an outlet station 2, 3, between which an endlessly circulating belt 4 serving as a conveyor belt (hereinafter also referred to as conveyor belt) is arranged, wherein the upper run 5 of the circulating belt 4 serves to transport the baked goods and is guided through a continuous baking tunnel 6. According to the invention, the conveyor belt 4 is designed as a stone slab belt, comprising a plurality of stone slabs 7 arranged side by side, which are fixed in a frame, wherein the stone slabs 7 form the upper and lower runs 5, 8 of the conveyor belt 4. The conveying direction of the baked goods is illustrated by the arrow.

[0025] The continuous baking oven 1 further comprises at least one wood burner 9 mounted on the inlet or outlet station 2, 3 or on one side of the continuous baking oven 1 for generating top and bottom heat in the baking tunnel 6. In the example shown, the at least one wood burner 9 is designed as a pellet burner with a screw feed.

[0026] In the continuous-flow oven 1 according to the invention, the hot air continuously generated in the at least one wood burner 9 during operation flows through several heating channels by means of at least one fan for the purpose of transferring heat energy to the conveyor belt 4, in order to then be fed to a chimney 10 or partially to the chimney 10 and partially via a duct system (not shown) to the at least one wood burner 9. Preferably, the at least one wood burner is designed as a pellet burner with a screw feed.

[0027] In the Fig. 1, it is provided that the hot air generated during operation, for the purpose of generating the required bottom heat, flows through a first heating duct 11 by means of at least one fan (not shown), the upper side of which is formed by part of the lower run 8 of the conveyor belt 4 and the other sides of which are thermally insulated, wherein the first heating duct 11 is followed by a second heating duct 12 which is fluidically connected to the first heating duct 11 and runs between the upper run 5 and the lower run 8 of the conveyor belt 4. Residual heat is advantageously released directly to the underside of the upper run 5 and the upper side of the lower run 8 of the conveyor belt 4 through the second heating duct 12, before the hot air is blown out via the chimney 10 or is fed partly to the chimney 10 and partly via a duct system (not shown) to the at least one wood burner 9.

[0028] Furthermore, the Fig. In the example shown in Figure 1, a third heating channel 13 is provided to generate the required top heat in the baking tunnel 6. This third heating channel runs above the upper run 5 of the conveyor belt 4. The third heating channel 13 is thermally insulated on its side facing away from the upper run 5 and is fluidly connected to the chimney 10. In the example shown, the third heating channel 13 can be supplied with hot air heated by at least one wood burner 14 assigned to the third heating channel by means of at least one fan. According to a further embodiment, the third heating channel 13 can additionally or alternatively be supplied with hot air from the first heating channel 11.

[0029] Alternatively, to generate the required top heat by means of the third heating channel 13 according to Fig. 1 will be further developed and with reference to Fig. 2, based on the design according to Fig. 1 instead of the third heating channel 13 for generating the required top heat in the baking tunnel 6, a second endlessly rotating belt 15 designed as a stone slab belt is provided, the dimensions of which correspond to the dimensions of the conveyor belt 4 and the lower run 17 of which is arranged above the upper run 5 of the conveyor belt 4 and parallel thereto at a defined distance which is greater than the maximum height of the baked goods.

[0030] In this case, at least one wood burner 18 is provided which is assigned to the second stone slab belt 15 and which can be mounted at the inlet or outlet station 1, 2 or at one side of the continuous baking oven 1 and whose hot air generated during operation flows through a fourth heating channel 19 by means of at least one fan for the purpose of generating the required top heat, the underside of which is formed by the upper run 16 of the second stone slab belt 15 and the other sides of which are thermally insulated.

[0031] The fourth heating channel 19 is followed by a fifth heating channel 20 which is fluidically connected to the fourth heating channel 19 and runs between the upper run 16 and the lower run 17 of the second stone slab belt 15, through which residual heat is released directly to the upper side of the lower run 17 of the second stone slab belt before the hot air is blown out via the chimney 10 or the hot air is fed partly to the chimney 10 and partly via a duct system not shown to the at least one wood burner 18.

[0032] In the example shown, the conveyor belt 4 and the second stone slab belt 15 as well as the respective wood burners and heating channels assigned to the stone slab belts 4, 15 are arranged mirror-symmetrically, with an imaginary plane running parallel to the upper and lower slabs of the stone slab belts serving as the plane of symmetry.

[0033] According to the invention and referring to Fig. 1 and Fig. 2, it is provided that, in addition to regulating the power output of the at least one wood burner in at least one heating duct, a mixing valve 21 is provided for regulating the temperature, by means of which fresh air can be added to the hot air generated by the at least one wood burner, wherein the mixing valve 21 is controllable based on the signals of two temperature sensors, wherein one sensor is arranged upstream of the mixing valve 21 in the hot air flow direction and another sensor is arranged downstream of the mixing valve 21. As a result, the temperature at the sensor arranged downstream of the mixing valve can be regulated to a setpoint. In the embodiment according to Fig. 1, a mixing valve 21 is provided in the first heating channel 11 and in the third heating channel 13; in the embodiment according to Fig. 2, a mixing valve 21 is provided in the first heating channel 11 and in the fourth heating channel 19.

[0034] Furthermore, the proportion of hot air supplied to the at least one wood burner can be regulated via a valve (not shown), wherein the proportion of hot air supplied to the at least one wood burner can be determined as a function of the desired power output of the at least one wood burner and optionally additionally as a function of the soot content in the hot air. For this purpose, a soot sensor (not shown) is provided, the signals of which are evaluated, wherein the higher the soot content of the hot air, the lower the proportion of hot air supplied to the at least one wood burner. The hot air that can be supplied to a wood burner is hot air from a heating duct assigned to the wood burner. The valve can be designed, for example, as a flap valve.

[0035] According to a further development of the invention, if increased soot formation is detected, i.e., if the soot content exceeds a predetermined, adaptable threshold, the oxygen supply to the at least one wood burner is increased, thereby improving combustion. The oxygen supply to the at least one wood burner can be regulated based on the desired power output and the soot content, and if the target temperature in a heating channel is exceeded, the mixing valve is regulated accordingly.

[0036] In the Fig. 1 and Fig. In the examples shown in Figure 2, the upper and lower runs of the conveyor belt 4 and - if provided - of the second stone slab belt 14 are guided through a compensation zone 22 extending from the inlet station 2 in the direction of the outlet station 3 over a predetermined distance, in which no heating energy is transferred to the respective stone slab belt, whereby the absorbed heating energy in the stone slabs 7 is compensated before the baking process.

[0037] Furthermore, the conveyor ovens Fig. 1 and Fig. 2 below the conveyor belt 4 collecting trays for receiving the residual ash in the heating channels, wherein alternatively or in addition to the collecting trays below the conveyor belt 4 collecting channels 23 are provided for receiving the residual ash in the heating channels, wherein the residual ash received in the collecting channels 23 can be discharged via a screw system.

[0038] In addition, the continuous baking ovens according to the invention Fig. 1 and Fig. 2 nozzles 24 for compressed air cleaning of the heating channels, wherein collecting troughs are provided for collecting the residual ash in the heating channels, wherein the residual ash collected in the collecting troughs can be discharged via a screw system.

[0039] According to an advantageous embodiment of the invention, for the purpose of cleaning the conveyor belt 4 from residual ash, a cleaning brush can be provided below the lower run 8 of the conveyor belt 4 on the side of the furnace 1 facing the inlet station 2, which cleaning brush optionally has an integrated suction device. In the embodiment according to Fig. 2, for the purpose of cleaning the second stone slab belt 15 of residual ash below the lower run of the second stone slab belt, a cleaning brush can be provided, for example on the side of the furnace facing the inlet station 2, which cleaning brush optionally has an integrated suction device.

[0040] In the examples shown, the continuous baking oven 1 has externally arranged steam generators through which steam is supplied to the baked goods by means of steaming pipes 25 in the conveying direction downstream of the inlet station 2, wherein at least one steaming zone is provided which is delimited by Teflon curtains 26; the steam removal takes place according to the prior art via a steam removal system comprising at least two steam removal channels 27.

Claims

[1] Continuous baking oven (1), comprising an inlet and an outlet station (2, 3), between which an endlessly circulating belt (4) serving as a conveyor belt is arranged, wherein the upper run (5) of the circulating belt (4) serves to transport the baked goods and is guided through a continuous baking tunnel (6), characterized bythat the continuous baking oven (1) is wood-fired, wherein the endlessly circulating belt (4) serving as a conveyor belt is designed as a stone slab belt, comprising a plurality of stone slabs (7) arranged side by side, which are fixed in a frame, wherein the stone slabs form the upper and lower runs (5, 8) of the stone slab belt (4), wherein the continuous baking oven (1) comprises at least one wood burner (9, 14) for generating top and bottom heat in the baking tunnel (6), the hot air of which, continuously generated during operation, flows through a plurality of heating ducts by means of at least one fan for the purpose of transferring heating energy to the conveyor belt (4), in order to then be fed to a chimney (10) or partly to the chimney (10) and partly via a duct system to the at least one wood burner (9, 14, 18), and wherein for regulating the temperature in addition to regulating the power output of the at least one wood burner (9, 14,18) and for supplying hot air to the at least one wood burner (9, 14, 18) in at least one heating channel, a mixing valve (21) is provided, by means of which fresh air can be added to the hot air generated by the at least one wood burner (9, 14, 18), wherein the mixing valve (21) is controllable based on the signals of two temperature sensors, wherein one sensor is arranged in the hot air flow direction upstream of the mixing valve (21) and another sensor is arranged downstream of the mixing valve (21). [2] Continuous baking oven (1) according to claim 1, characterized byin that the proportion of hot air which is supplied to the at least one wood burner (9, 14, 18) can be regulated via a valve, wherein the proportion of hot air which is supplied to the at least one wood burner (9, 14, 18) can be determined as a function of the desired power output of the at least one wood burner (9, 14, 18) and optionally additionally as a function of the soot content in the hot air, wherein a soot sensor is provided for this purpose, the signals of which are evaluated, wherein the higher the soot content of the hot air, the lower the proportion of hot air which is supplied to the at least one wood burner (9, 14, 18). [3] Continuous baking oven (1) according to claim 1 or 2, characterized bythat a large part of the ash is burned in the hot air according to the catalyst principle via the stones of the conveyor belt (4), wherein the continuous baking oven (1) has collecting troughs below the conveyor belt (4) for receiving the residual ash in the heating channels, wherein alternatively or in addition to the collecting troughs below the conveyor belt, collecting troughs (23) are provided for receiving the residual ash in the heating channels, wherein the residual ash received in the collecting troughs (23) can be discharged via a screw system. [4] Continuous baking oven (1) according to claim 1, 2 or 3, characterized by in that it has nozzles (24) for compressed air cleaning of the heating channels, wherein collecting channels are provided for receiving the residual ash in the heating channels, wherein the residual ash received in the collecting channels can be discharged via a screw system. [5] Continuous baking oven (1) according to claim 1, 2, 3 or 4, characterized bythat for the purpose of cleaning the conveyor belt (4) of residual ash below the lower run (8) of the conveyor belt on the side of the furnace (1) facing the inlet station (2) it has a cleaning brush, optionally with integrated suction. [6] Continuous baking oven (1) according to claim 1, 2, 3, 4 or 5, characterized by in that it has externally arranged steam generators through which steam is supplied to the baked goods by means of steaming pipes (25) in the conveying direction downstream of the inlet station (2), wherein at least one steaming zone is provided which is delimited by Teflon curtains (26) and wherein the steam removal takes place via a steam removal system comprising at least one steam removal channel (27). [7] Continuous baking oven (1) according to one of the preceding claims, characterized by that the at least one wood burner (9, 14, 18) is designed as a pellet burner with screw feed. [8] Continuous baking oven (1) according to one of the preceding claims, characterized byin that the at least one wood burner (9) is mounted at the inlet or outlet station or at one side of the continuous-flow oven and the hot air generated during operation of said burner flows through a first heating duct (11) by means of at least one fan for the purpose of generating the required bottom heat, the upper side of said first heating duct being formed by part of the lower run (8) of the conveyor belt (4) and the other sides of which are thermally insulated, wherein the first heating duct (11) is followed by a second heating duct (12) which is fluidically connected to the first heating duct (11), runs between the upper run (5) and the lower run (8) of the conveyor belt (4), through which residual heat is released directly to the underside of the upper run (5) and the upper side of the lower run (8) of the conveyor belt (4) before the hot air is blown out via the chimney (10) or the hot air is fed partly to the chimney (10) and partly via a duct system to the at least one wood burner (9). [9] Continuous baking oven (1) according to claim 8, characterized by in that a third heating channel (13) is provided in the baking tunnel (6) to generate the required top heat, the third heating channel running above the upper run (5) of the conveyor belt (4), being thermally insulated on the side facing away from the upper run (5) and opening into the chimney (10). [10] Continuous baking oven (1) according to claim 9, characterized by that the third heating channel (13) can be supplied with hot air from the first heating channel (11) and / or can be supplied with hot air heated by at least one wood burner (14) assigned to the third heating channel (13) by means of at least one fan. [11] Continuous baking oven (1) according to claim 8, characterized bythat, to generate the required top heat in the baking tunnel (6), a second endlessly rotating belt (15) designed as a stone slab belt is provided, the dimensions of which correspond to the dimensions of the conveyor belt (4) and the lower run (17) of which is arranged above the upper run (5) of the conveyor belt (4) and parallel thereto at a defined distance which is greater than the maximum height of the baked goods, wherein at least one wood burner (18) associated with the second stone slab belt (15) is provided, which can be mounted at the inlet or outlet station (2, 3) or on one side of the continuous baking oven (1) and whose hot air generated during operation flows through a fourth heating channel (19) by means of at least one fan for the purpose of generating the required top heat, the underside of which is formed by the upper run (16) of the second stone slab belt (15) and the other sides of which are thermally insulated,wherein the fourth heating channel (19) is followed by a fifth heating channel (20) which is fluidically connected to the fourth heating channel (19) and runs between the upper run (16) and the lower run (17) of the second stone slab belt (15), through which residual heat is released directly to the upper side of the lower run (17) of the second stone slab belt (15) before the hot air is blown out via the chimney (10) or the hot air is fed partly to the chimney (10) and partly via a duct system to the at least one wood burner (18). [12] Continuous baking oven (1) according to one of the preceding claims, characterized bythat the upper and lower runs (5, 8) of the conveyor belt (4) and, if provided, of the second stone slab belt (15) are guided through a compensation zone (22) extending from the inlet station (2) in the direction of the outlet station (3) over a predetermined distance, in which no heating energy is transferred to the stone slab belt, whereby the absorbed heating energy in the stone slabs (7) is compensated. [13] Continuous baking oven (1) according to claim 12, characterized by that the conveyor belt (4) and the second stone slab belt (15) and optionally the respective wood burners and heating channels assigned to the stone slab belts are arranged mirror-symmetrically, with an imaginary plane running parallel to the upper and lower slabs of the stone slab belts serving as the plane of symmetry.

Images