EP0254321A2 - Stove for solid fuel - Google Patents

Abstract

A stove with air or water cooling, in particular a single-unit stove, tiled stove, tiled-floor stove, stack or heating boiler, heating tiled stove or heating stack, has for the burning of solid fuels a grating which is cooled or circulation-cooled and off-gas flues, which connect the ash cave to an off-gas collector in the upper part of the stove. The off gases are introduced through the chimney flue, with or without an off-gas extraction fan, through the glow bed into the ash cave and from the latter through the off-gas flues and the off-gas collector into the chimney. The sidewalls of the combustion chamber are provided with a lining of high-temperature-resistant material of low heat conductivity, preferably also great heat retention. In the lining there are channels, forming the off-gas flues, for secondary combustion and removal of the off gases from the ash cave into the off-gas collector. <IMAGE>

Description

The invention relates to an oven with air or water cooling, in particular single oven, tiled stove, fireplace or boiler, heated tiled stove, fireplace, for the combustion of solid fuels.

Although the combustion of solid fuels is one of the oldest technologies of mankind, the technically perfect combustion of solid fuels in modern furnaces is still a problem that is not completely solved. The Haputgrund is to be seen in the fact that the combustion of solid fuels creates a lot of floating gases that are not burned to a sufficient extent and then appear in colder parts of the furnace as soot, tar coating, soot gloss or the like. knock down.

From DE-PS 31 45 273 an open heating fireplace is known, in which the flue gases can get in a known manner both directly from the ember bed upwards into a flue gas collector, and through the ember bed into the ash fall chamber, from there through flue gas flues to the upper one Flue gas collector and from here into the chimney reach. From this prior publication it is known that the flue gases passing through the ember bed are particularly hot and can be used to regulate the chimney draft.

The invention has for its object to provide a furnace for the combustion of solid fuels, in which both the solid fuels and the resulting carbonization gases burn completely, as is the case with liquid and gaseous fuels.

To achieve the object, the invention is based on the prior art of an oven with air or water cooling, in particular a single oven, tiled stove, fireplace or boiler, heated tiled stove, fireplace, for the combustion of solid fuels, with an uncooled or cooled grate and flue gas that Connect the ash fall chamber to a flue gas collector in the upper part of the stove, the flue gases being introduced through the chimney draft, without or with a flue gas extraction fan, through the ember bed into the ash fall chamber and from there through the flue gas flues and the flue gas collector into the chimney. The invention consists in that the side walls of the combustion chamber are provided with a lining made of high-temperature-resistant material with low thermal conductivity and in the lining the flue gas channels for afterburning and discharging the flue gases from the ash fall chamber are present in the flue gas collector. The lining of the combustion chamber with a high temperature-resistant material with low thermal conductivity ensures that the combustion takes place at very high temperatures. These temperatures are around 1000 to 1300 ° C and are higher than in normal ovens. The combustion gases and the existing smoldering gases then flow through the ember bed through into the ash fall chamber and from there into the highly heated channels in the lining of the combustion chamber. In this way, any more combustible carbonization gases are burned.

The ash fall chamber preferably also has a lining made of high-temperature-resistant material with low thermal conductivity. This prevents cooling of the combustion and smoldering gases passing through the ember bed and the gases enter the channels at higher temperatures.

In a development of the invention, the grate is designed as a base plate made of high-temperature-resistant material with low thermal conductivity, the base plate having column-shaped or slot-shaped passage openings for the flue gases. This prevents the embers from cooling down from below. The column diameter or the slot width is preferably very much smaller than the thickness of the base plate.

To control the furnace output, part of the grate or the base plate can be covered by a relatively thin plate made of high-temperature-resistant material with low thermal conductivity.

A flap can be provided for the secondary air supply in the ash fall area. This makes it possible to regulate the afterburning.

When the stove is air-cooled, as is the case, for example, with a tiled stove, the channels can be open towards the side walls, so that there is increased heat transfer to the side walls.

• Fig. 1 einen senkrechten Schnitt durch einen Ofen nach der Linie I - I von Figur 2,
• Fig. 2 einen horizontalen Schnitt durch den Ofen nach der Linie II - II von Figur 1,
• Fig. 3 einen senkrechten Schnitt durch den Ofen nach der Linie III - III von Figur 2,
• Fig. 4 einen senkrechten Schnitt durch einen Ofen mit einem ausgekleideten Aschefallraum nach der Linie IV - IV von Figur 5,
• Fig. 5 einen horizontalen Schnitt durch den Ofen nach der Linie V - V von Figur 4,
• Fig. 6 einen senkrechten Schnitt durch den Ofen nach der Linie VI - VI von Figur 5,
• Fig. 7 einen senkrechten Schnitt durch einen Ofen mit einem ausgekleideten Aschefallraum und einer Bodenplatte nach der Linie VII - VIII von Figur 8,
• Fig. 8 einen horizontalen Schnitt durch den Ofen nach der Linie VIII - VIII von Figur 7,
• Fig. 9 einen senkrechten Schnitt durch den Ofen nach der Linie IX - IX von Figur 8,
• Fig. 10 einen horizontalen Schnitt durch einen Ofen mit einer vorgesetzten Auskleidung,
• Fig. 11 einen senkrechten Schnitt durch einen Heizkessel nach der Linie XI - XI von Figur 12,
• Fig. 12 einen horizontalen Schnitt durch den Kessel nach der Linie XII - XII
• Fig. 13 einen senkrechten Schnitt durch einen Kachel-­Grundofen.
• Fig. 14 einen senkrechten Schnitt nach der Linie XIV - XIV von Figur 15 durch einen Ofen wie Figur 7 mit einem Sekundärluftkanal und Leitblechen,
• Fig. 15 einen horizontalen Schnitt durch den Ofen nach der Linie XV - XV von Figur 14,
• Fig. 16 einen senkrechten Schnitt durch den Ofen nach der Linie XVI - XVI von Figur 15,
• Fig. 17 einen senkrechten Schnitt nach der Linie XVII - XVII durch einen Ofen wie Figur 7 mit einer Nachverbrennungskammer und einem Sekundärluftkanal,
• Fig. 18 einen Schnitt durch den Ofen nach der Linie XVIII - XVIII von Figur 17,
• Fig. 19 einen senkrechten Schnitt nach der Linie IXX - IXX von Figur 20 durch einen Ofen wie Figur 7 mit sich nach unten erweiternden Durchtrittsöffnungen,
• Fig. 20 einen Schnitt durch den Ofen nach der Linie XX - XX von Figur 19,
• Fig. 21 einen Schnitt durch den Ofen nach der Linie XXI - XXI von Figur 20,
• Fig. 22 einen senkrechten Schnitt durch einen Ofen wie Figur 1 mit einem hohl ausgebildeten Rost und Abgasleitblechen,
• Fig. 23 einen senkrechten Schnitt durch einen Heizkessel nach der Linie XXIII - XXIII von Figur 24,
• Fig. 24 einen horizontalen Schnitt durch den Kessel nach der Linie XXIV - XXIV von Figur 23 und
• Fig. 25 einen senkrechten Schnitt durch den Kessel nach der Linie XXV - XXV von Figur 24.

Exemplary embodiments of the invention are shown in the drawings. Show it:

• 1 is a vertical section through an oven along the line I - I of Figure 2,
• 2 shows a horizontal section through the furnace along the line II-II of FIG. 1,
• 3 shows a vertical section through the furnace along the line III - III of FIG. 2,
• 4 shows a vertical section through an oven with a lined ash fall area along the line IV-IV of FIG. 5,
• 5 shows a horizontal section through the furnace along the line V - V of FIG. 4,
• 6 is a vertical section through the furnace along the line VI - VI of Figure 5,
• 7 shows a vertical section through an oven with a lined ash fall area and a base plate along the line VII-VIII of FIG. 8,
• 8 is a horizontal section through the furnace along the line VIII - VIII of Figure 7,
• 9 is a vertical section through the furnace along the line IX - IX of Figure 8,
• 10 is a horizontal section through an oven with a facing lining,
• 11 is a vertical section through a boiler along the line XI - XI of Figure 12,
• Fig. 12 is a horizontal section through the boiler along the line XII - XII
• Fig. 13 is a vertical section through a basic tile stove.
• 14 shows a vertical section along the line XIV-XIV of FIG. 15 through an oven like FIG. 7 with a secondary air duct and baffles,
• 15 shows a horizontal section through the furnace along the line XV-XV of FIG. 14,
• 16 shows a vertical section through the furnace along the line XVI - XVI of FIG. 15,
• 17 shows a vertical section along the line XVII - XVII through a furnace as in FIG. 7 with a post-combustion chamber and a secondary air duct,
• 18 shows a section through the furnace along the line XVIII - XVIII of FIG. 17,
• 19 shows a vertical section along the line IXX - IXX from FIG. 20 through an oven like FIG. 7 with passage openings widening downward,
• 20 shows a section through the furnace along the line XX-XX of FIG. 19,
• 21 shows a section through the furnace along the line XXI-XXI of FIG. 20,
• 22 shows a vertical section through an oven like FIG. 1 with a hollow grate and exhaust gas baffles,
• 23 is a vertical section through a boiler according to the line XXIII - XXIII of Figure 24,
• 24 is a horizontal section through the boiler along the line XXIV - XXIV of Figure 23 and
• 25 shows a vertical section through the boiler along the line XXV - XXV of FIG. 24.

1 shows a vertical section along the line I - I of FIG. 2 through an oven 1 for solid fuels according to the invention. The stove 1 can be, for example, a single stove or a heating insert for a tiled stove, basic tiled stove or fireplace. The furnace 1 has a combustion chamber with the side walls 11 and a load-bearing insert 12 which is inserted into the ash fall chamber 16 and on which the grate 13 is placed. The side walls 11 of the combustion chamber above the grate 13 are provided with a lining 14, which consists of a high-temperature-resistant material with low thermal conductivity. It is of great advantage if the high-temperature-resistant material with low thermal conductivity, from which the lining 14 is made, is at the same time a material with a high heat storage capacity. This has the advantage that the heat given off by the furnace is compensated for and takes place continuously, so that only very slight temperature fluctuations occur in the furnace 1. Molded parts made of fireclay, for example, can be used as a common refractory furnace material.

The liner 14 is also placed on the insert 12. The liner 14 is covered at the top by a plate 141. The plate 141 can be made of the same material like the lining 14, but it can also be a metal plate. In the lining 14 there are channels 15 which connect the ash fall chamber 16 to a flue gas collector 17 in the upper part of the furnace, which in turn is connected to a chimney via a flue gas nozzle 18.

In the above example, a furnace 1 with a combustion chamber has been described, which has a rectangular cross section in the horizontal section according to FIG. The rectangular cross-section of the combustion chamber is the most common cross-sectional shape. However, it goes without saying that a round cross-sectional shape, for example in the form of a standing cylinder, is also possible. In principle, any cross-sectional shape of the combustion chamber is possible which has vertical side walls 11 in which the channels 15 run. This also applies to all ovens 2, 3 and 4 and boiler 5 and basic tile oven 6 described below.

The channels 15 lie in the surface of the liner 14 and preferably have a rectangular cross section with rounded corners, three channel walls 151, 152, 153 being formed from the material of the liner 14 and the fourth channel wall 111 from the side wall 11. The channels 15 However, they can also be round on the inside. On the strip-shaped duct wall 111, the flue gases come into direct contact with the side wall 11 and can give off the heat to the side wall 11 here.

As a result of the chimney draft, the flue gases enter through the ember bed 131 lying on the grate 13 into the ash fall chamber 16, through the channels 15 into the flue gas collector 17 and then into the chimney. The lateral limitation of the ember bed by the lining 14 made of high temperature resistant material with low thermal conductivity initially causes the combustion of the solid fuels to take place at a high temperature. The passage of the flue gases through the ember bed 131 and the highly heated channels 15 results in afterburning of those gaseous carbonization gases which have not yet been completely burned, both in the ember bed 131 and in the ash fall chamber 16 and in the channels 15. As a result, this leads to very clean soot-free and soot-free combustion. A flap 161 can be used to supply secondary air to the ash fall chamber 16, as a result of which both the combustion residues in the ember bed 131 and the afterburning in the ash fall chamber 15 and the channels 15 can be regulated. It is understood that, if the chimney draft is not sufficient or if a higher draft is desired, a flue gas extraction fan, not shown in the drawings, can be switched on between the flue gas connector 18 and the chimney.

A flap 142 is provided in the cover plate 141 for heating the furnace 1. If a flammable heating material has caught fire on the grate 13, the flap 142 is closed. In the heating phase, furnace 1 works as a burn-through furnace.

FIGS. 4, 5 and 6 show an oven 2 in which the invention shown in FIGS. 1, 2 and 3 has been further developed by an additional lining 22 of the ash fall chamber 26. The lining 22 consists of shaped blocks made of high-temperature resistant material with low thermal conductivity, in which there are rectangular deflection channels 221. This lining of the ash fall chamber 26 prevents the flue gases from cooling down in the ash fall chamber 26 after they have passed through the ember bed 231. They then also enter the deflection channels 221 and from there into the channels 25 at a higher temperature than is the case with the furnace 1 according to FIGS. 1, 2 and 3. As a result, the afterburning is again better and the heat losses in the ash fall chamber 26 are lower.

FIGS. 7, 8 and 9 show a furnace 3 with a further development of the invention according to the previous figures. While in the furnaces 1 and 2 the ember bed is on grates 13 and 23, in the furnace 3 the grate is replaced by a base plate 33 made of high temperature resistant material with low thermal conductivity. This provides thermal insulation of the ember bed 331 from below, which leads to a further increase in the combustion temperature. The base plate 33 has column-shaped or slot-shaped through openings 332 for ashes and flue gases. Here, the column diameter or the slot width is very much smaller than the thickness of the base plate 33. Since the base plate 33 is at a high temperature due to the direct contact with the ember bed 331, the afterburning takes place as soon as the gases pass through the slots 332 in FIG Base plate 33.

To control the furnace output, part of the grate 13, 23 or the base plate 33 can be covered by a relatively thin plate made of high-temperature-resistant material with low thermal conductivity.

In Figure 10 is a horizontal section through a Furnace 4 reproduced, which corresponds to the section through the furnace 1 of Figure 2. Figure 10 shows a modification of the previous furnace construction in such a way that the lining 44 does not abut the side walls 11 like the lining 14 with channels 15, but is at a distance from the side walls 41, so that a shaft is located between the side wall 41 and the lining 44 45 narrow width is available for the flue gases. The narrow width shaft replaces the channels 15 in FIGS. 1, 2 and 3, which are not present in the lining 44.

As can be seen from all of the preceding FIGS. 1 to 10, the flue gases flow through channels or shafts, the walls of which are at least partially formed from the metal outer wall parts 111, 211. The heat transfer from the flue gases then takes place particularly intensively on these metal wall parts. According to the invention, however, this direct contact between the flue gases and the metal wall parts is only possible if the stove has air cooling, for example as a tiled stove.

However, if there is a boiler, i.e. If the heat is not dissipated by air but by water, it is not possible due to the excessive cooling of the flue gases to let them come into direct contact with the metal walls.

FIG. 11 shows a vertical section through a boiler 5 along the line XI-XI from FIG. 12, and FIG. 12 shows a horizontal section through the boiler 5 according to the line XII-XII from FIG. The internal structure of the boiler 5 corresponds to that of the furnace 2, which has been shown in Figures 4, 5 and 6.

The boiler 5 has a water jacket 51. The inner walls of the boiler body are provided with a lining 54, which consists of a high-temperature-resistant material with low thermal conductivity, such as firebricks. Channels 55 are present in the lining 54, which connect the ash fall chamber 56 to a flue gas collector 57 in the upper part of the boiler, which in turn is connected to the chimney by a flue gas nozzle 58. In contrast to the furnaces 1, 2, 3 and 4 described above, the channels 55 lie completely in the lining 54 and are not open to the water-cooled boiler wall. The flue gases do not touch the inner wall of the boiler when they flow through the channels 55.

Wirbulators can be used in channels 15, 25, 35 and 55 in order to increase the heat transfer from the flue gas to the channel walls.

FIG. 13 shows a vertical longitudinal section through a basic tile stove 6. The combustion chamber 61 of the basic furnace 6 has the same structure as the furnace 3 according to FIGS. 7, 8 and 9. In contrast to the furnace 3, which has an outer casing made of metal, for example made of sheet steel or cast iron, the basic furnace 6 has a brick casing 62, which is plastered in a known manner or is still clad with tiles. Two flue gas flues are provided in the basic tile stove 6, namely a drop flue 63 and a riser 64. The control flap 66 can also be arranged on the top of the furnace 6. It is of course also possible to arrange the two trains 63, 64 horizontally. More than two trains are also possible. For the connection of the basic furnace 6 to a chimney, the flue gas opening 67 is provided see. The flow path of the flue gases is marked by several arrows R. R1 is the short-term path of the flue gases in the heating phase as long as the heating flap 68 is open, as has been described on page 7, lines 25 to 29 in relation to the furnace 1.

Conventional stoves work with a large excess of air (air factor λ ≈ 2.0 to 3.0), while the stoves 1, 2, 3, 4, 5 and 6 described above according to the invention with little or no excess air (λ ≈ 1.0 up to 1.5) work at much higher temperatures from 1 000 ° C to 1 300 ° C. As a result, almost complete combustion with only a very small amount of ash is achieved.

FIGS. 14, 15 and 16 show the furnace 3 according to FIGS. 7, 8 and 9 with an additional secondary air combustion. In this case, the furnace 3 additionally has two exhaust gas baffles 341, 342 under the base plate 33, which run obliquely downwards, as can be seen from FIG. The purpose of the baffles 341, 342 is to direct the flame inwards and to lead past the nozzles 361 of a secondary air duct 36, so that the preheated secondary air flowing out through the fine nozzle openings 361 is fine in the entire flame front and along the entire length of the secondary air duct 36 distributed and thus a visibly better afterburning takes place again. Measurements of the chimney flue gases show a carbon monoxide content that is practically no longer measurable. The secondary air duct 36 can preferably consist of a tube made of ceramic or highly heat-resistant metal. A large ash fall box 37 can also be arranged in the lower part of the furnace 3.

17 and 18 show two sections through the furnace 3, in which the base plate consists of two partial base plates 333, 334, which are located at a distance from one another and form a post-combustion chamber 38. The secondary air duct 36 with the two exhaust gas guide plates 341, 342 is located in the afterburning chamber 38. The air preheated in the secondary air duct 36 leads to complete CO afterburning.

FIGS. 19, 20 and 21 again show the furnace 3 according to FIGS. 7, 8 and 9, but with a base plate 33 with passage-like openings 335 that widen downward in a nozzle-like manner, round, square or rectangular in cross-section. The columnar or slot-shaped through openings 332 according to FIGS. 7, 8 and 9 can be designed to widen downwards. The nozzle-shaped widening of the passage openings 332, 335 downwards causes an increase in the flow velocity (Laval nozzle) for the combustion gases that pass through, resulting in better and more intensive mixing and thus combustion of the gases. The secondary or post-combustion air is here through secondary air channels 363 that enter the Base plate 33 are poured or pressed, supplied and occurs directly at the passage openings 335. The base plate 33 consists of chamotte, ceramic, refractory concrete or high-alloy cast or metal. The side walls 31 and the rear wall 32 of the furnace 3 are designed here as a variant without trains. However, trains 35 according to FIGS. 7, 8 and 9 can also be provided. The amount of secondary air supplied can be regulated via a secondary air flap 362.

FIG. 22 shows a section through the furnace 1, but with the grate bars 13 running from front to back. The grate bars 13 are, for example, triangular or round in cross section, are hollow and have nozzle-shaped openings 132 on the underside. In addition, exhaust gas baffles 341, 342 are again present. The grate bars 13 are preferably made of highly heat-resistant metal or ceramic.

A boiler 5 is shown in FIGS. 23, 24 and 25. Parts of this boiler 5, which correspond to the corresponding parts of the boiler according to FIGS. 11, 12, are provided with the same reference numerals and are therefore not described again. In the combustion chamber inside the lining 54 and on the top of the base plate 541 there is a basket-shaped heat exchanger 59 made of pipes or hollow castings. The tubes or the hollow castings of the heat exchanger 59 consist, for example, of round or rectangular tubes made of highly heat-resistant material.

The heat exchanger 59 is water-bearing and is connected to the outer water jacket on its input and output sides. In order to achieve better water circulation, the lower basket parts 591 can be installed at an angle.

The purpose of installing the heat exchanger 59 is to achieve a more continuous power output while maintaining the economical, clean and environmentally friendly combustion of the boiler 5 according to FIGS. 11, 12. The exchanger base 591 and the side parts 592 serve as heat exchangers, with between the Pipes of the grid-shaped heat exchanger 59 is a relatively large distance to ensure a uniform temperature in the combustion chamber and thus a uniform heating of the lining 54. The connection of the heat exchanger 59 to the outer water jacket 51 takes place via the water inlets 597 and water outlets 598. The heat exchanger 59 is mainly necessary for the combustion of coal and coke.

In the upper part of the boiler 5, a primary air duct 593 with air outlet nozzles 594 is arranged. The primary air duct 593 ensures a uniform air distribution of the primary air in the boiler 5. Without the primary air duct 593, the front part of the boiler 5 burns faster than in the rear part of the boiler 5, which is undersupplied with combustion air, resulting in unburned carbonization gases. The amount of air supply can be controlled via a primary air damper 595. In addition, the supplied air is preheated in the primary air duct 593. The heating flap is preferably used to heat the boiler 5 when it has to be operated as a burn-through furnace in the heating phase. The primary air duct 593, 594 with the primary air flap 595 can also be used in all of the previously described air-cooled ovens.

The exhaust gas baffles 341, 342 and the secondary air duct 36 are located below the base plate 541. The function of the exhaust baffle plates 341, 342 and the secondary air duct 36 has been described in detail with reference to FIGS. 14, 15 and 16 and therefore need not be repeated.

The arrows inside the boiler 5 the The directions of flow of the combustion air are marked with "o2".

If water has been specified as the coolant in the boiler 5 according to FIGS. 23, 24 and 25, it goes without saying that, instead of water, other liquid coolants, such as thermal oils, for example, can also be used to achieve higher operating temperatures.

Claims (17)

1.Air with air or water cooling, in particular a single stove, tiled stove, basic tiled stove, fireplace or boiler, tiled stove, fireplace, for burning solid fuels with an uncooled or cooled grate and flue gas flues that connect an ash fall chamber with a flue gas collector in the upper part of the stove , whereby the flue gases are introduced through the chimney draft, without or with a flue gas exhaust fan, through the ember bed into the ash fall chamber and from there through the flue gas flues and the flue gas collector into the chimney, characterized in that the side walls (11) of the combustion chamber are lined (14) are made of high-temperature-resistant material with low thermal conductivity and in the lining (14) flue gas-forming channels (15) for after-combustion and discharge of the flue gases from the ash fall chamber (16) in the flue gas collector (17) are available. 2. Furnace according to claim 1, characterized in that the ash fall chamber (26) has a lining (22) made of high temperature resistant material with low thermal conductivity. 3. Oven according to claim 1 or 2, characterized in that the grate is designed as a base plate (33) made of high temperature-resistant material with low thermal conductivity, the base plate (33) having columnar or slit-shaped passage openings (332) for ash and flue gases. 4. Oven according to claim 3, characterized in that the column diameter or the slot width are very much smaller than the thickness of the base plate (33). 5. Oven according to claims 1 to 4, characterized in that part of the grate (13) or the base plate (33) can be covered by a relatively thin plate made of high temperature resistant material with low thermal conductivity to control the furnace output. 6. Oven according to claims 1 to 5, characterized in that the high temperature resistant material with low thermal conductivity also has a large heat storage capacity. 7. Furnace according to claims 1 to 6, characterized by fireclay as a high temperature resistant material with low thermal conductivity and high heat storage capacity. 8. Oven according to claims 1 to 7, characterized by a flap (161) in the wall to the ash fall chamber (16) for secondary air supply. 9. Oven according to claims 1 to 8, characterized in that the channels (15) to the side walls (11) are open when the oven (1) is air-cooled. 10. Oven according to claims 1 to 9, characterized in that a lining (44) without channels is arranged at a distance in front of the side walls (41) (Fig. 10). 11. Oven according to claims 1 to 8, characterized in that when the furnace (5) (boiler) is water-cooled, the channels (55) lie within the lining (54). 12. Oven according to claims 1 to 11, characterized in that under the base plate (33) or the grate bars (13) exhaust gas baffles (341, 342) are arranged which guide the exhaust gases to a secondary air duct (36) through which the secondary air Exhaust gases are fed for afterburning. 13. Oven according to claims 3 or 4, characterized in that the columnar or slot-shaped passage openings (332, 335) are designed to widen downward in a nozzle shape. 14. Oven according to claims 12 or 13, characterized in that the secondary air duct (363) is integrated in the base plate (33). 15. Oven according to claims 1 to 12, characterized in that the grate bars (13) are hollow from front to back and serve as secondary air channels. 16. Oven according to claims 11 to 15, characterized in that a grid-shaped heat exchanger (59) is arranged in the interior of the boiler (5). 17. Furnace according to claims 1 to 16, characterized in that in the upper part of the furnace (5) a primary air duct (593) is arranged for the uniform supply of combustion air.

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