AT515122A4 - Process for the combustion of solid fuels - Google Patents

Abstract

The invention relates to a method for burning solid fuels - in particular biomass such as wood chips or pellets - in a furnace having at least one combustion chamber (1), wherein preferably the fuel in a combustion chamber upstream gasification chamber (4) is gasified, wherein the combustion Emerging ash is discharged via a movable grate (8) at intervals down by the grate (8) is opened. In particular, to burn fuels of lower quality reliably, with only low power loss, with high efficiency and low emissions, it is provided that before opening the grate (8) above the grate (8) an auxiliary grate (10) is inserted, the carburetor - or combustion chamber (4) of the furnace (1) closes down.

Description

The invention relates to a method for the combustion of solid fuels - in particular biomass, such as wood chips or pellets - in a furnace having at least one combustion chamber, wherein preferably the fuel is gasified in a gas chamber upstream of the gasification chamber, wherein the resulting ash during combustion over a movable grate at intervals downwards by the grate is opened. Furthermore, the invention relates to a furnace for solid fuels, in particular biomass, such as wood chips or pellets, with at least one combustion chamber, which is preferably upstream of a gasification chamber for receiving a fuel column, wherein the carburetor or combustion chamber is closed down by a grate, the is movably mounted between a closed position and an open position.

It is known to burn solid fuels, such as wood chips, but also fuel pellets or the like in so-called gasification boilers. In this combustion process, the combustion takes place in two stages, wherein in a first stage the fuel introduced from above into a gasification chamber and stacked in this fuel column is gasified in an ember bed and in an adjoining second stage the resulting gas in at least one of the Gasification chamber is burned to the top adjacent combustion chamber.

In the gasification chamber, a glow zone provides the energy needed for gasification. EP 2 397 756 A describes a furnace which operates according to such a method.

In known solutions, at certain intervals, when a sufficient amount of ash has accumulated below the ember bed, the grate below the gasification chamber is fully or partially opened to discharge the ash. For boilers designed for good quality fuel pellets, this is done, for example, by opening more or less large openings in the grate.

A solution for discharging the ash is thus that the grate has openings through which the ash is discharged downwards, wherein the openings are designed so that the fuel load is largely retained. In the combustion of fuel pellets of high quality is such

Procedures quite well suited and allows economic operation. Depending on the properties of the fuel, however, glazing and slag may form, that is to say stable structures are formed in the ember bed which are too large for the openings and therefore accumulate in the gasification chamber and cause problems in the longer term.

An alternative solution for discharging the ash in pellets of poor fuel quality, but especially in wood chips, is that the rust is pushed completely to the side, whereby the entire contents of the gasification chamber, which consist of ashes and also from the mentioned glazings and hard slag can, is discharged down. In order to avoid fuel losses, the process is carried out so that the fuel present in the gasification chamber can initially burn out to a large extent before the grate is opened.

However, in the case of low-grade fuels such as wood chips, it is necessary to ensure that this ash discharge is carried out relatively often to ensure reliable operation. At the same time, such fuels have a higher ash content, so that in terms of performance larger amounts of ash are dissipate. Operation according to the method described above causes a significant disturbance of normal operation in each discharge operation for ash, and each time causes a power deterioration, in addition a deterioration of the efficiency and an increase in exhaust emissions, in particular the particulate matter emissions. Especially in the partial load range, the burning out of the fuel takes considerable time, while only sub-optimal operation is possible.

The object of the present invention is to avoid these disadvantages and to provide a method with which also fuels of lower quality can be burned reliably, with only low power loss, with high efficiency and low emissions. Another object of the present invention is to provide a furnace with which this method can be carried out efficiently. It is also essential that exhaust emissions are minimized.

According to the invention, these objects are achieved in that before opening the grate above the grate an auxiliary grate is inserted, which closes the carburetor or combustion chamber down.

The invention is based on the basic idea that, after a certain burning time, stratification occurs in the gasifier or combustion chamber, so that below the actual ember bed there is a layer with burnt-out fuel, ie essentially ashes. The auxiliary grate allows the ember bed to be retained while the ash is discharged by opening the grate. It is possible to produce a complete opening of the carburetor or combustion chamber down, so that the content is discharged under the auxiliary grate in any case. In addition, the insertion of the auxiliary grate leads to a mechanical destruction of any glassy structures and slag, which may form on the underside of the ember bed.

A significant advantage of the present invention is that it is not necessary to carry out any major interventions in the boiler operation before carrying out the discharge process for ashes.

It has also surprisingly been found that a substantial reduction of the particulate matter content in the exhaust gas can be achieved by the method according to the invention. This effect is essentially due to the fact that the recurrent introduction of the auxiliary grate destroyed larger-scale structures and the ash - especially the fuel supply in the gasification chamber - are compressed. In this way, a more compact structure is achieved, which suppresses the formation of hazardous aerosols.

It is particularly advantageous if the content of the gasifier or combustion chamber is cut through substantially horizontally by the insertion of the auxiliary grate. This optimally takes into account the generally horizontal stratification of the contents of the gasification chamber.

It is preferably provided that primary air is introduced laterally above the grate into the gasifier or combustion chamber. In principle, primary air can also be supplied from below through the grate. However, this is on the one hand disadvantageous because the necessary openings of the grate are prone to blockages. In connection with the solution according to the invention, a further disadvantage of such a procedure is that the air supply is obstructed when the auxiliary grate is inserted, so that optimum boiler operation is not possible during the discharge of ash.

In a particularly preferred manner, an ash receiving space is provided in the lower region of the gasification or combustion chamber, which is intended to receive ash, wherein the insertion of the auxiliary grate and the opening of the grate is carried out each time when the ash receiving space is filled with ash. The ash receiving space is that part of the gasification or combustion chamber which is intended to receive the not yet discharged ash. It is obvious that immediately after discharging the ash, the ash receiving space first receives the lower part of the ember bed and the ash layer builds up gradually. However, the method according to the invention is carried out such that the ash layer normally never extends beyond the ash receiving space.

As stated above, it is not absolutely necessary to specially prepare the process of discharging the ash. In some cases, however, it has turned out to be favorable if the combustion is throttled immediately before the insertion of the auxiliary grate and the opening of the grate. As a result, for example, the emissions of the boiler can be minimized or temperatures in the gasification chamber can be lowered slightly to reduce the load on the individual components, in particular the auxiliary grate.

The present invention also relates to a furnace for solid fuels, in particular biomass such as wood chips or pellets, with at least one combustion chamber, which is preferably upstream of a carburetor chamber for receiving a fuel column, wherein the carburetor or combustion chamber is closed down by a grate, the is movably disposed between a closed position and an open position.

According to the invention it is provided that above the grate at least one auxiliary grate can be inserted into the carburetor or combustion chamber, which closes the carburetor or combustion chamber down in an inserted position. This auxiliary grate, as well as the rust can consist of several parts. As a result, the thermal distortion can be minimized.

In particular, it is provided that the auxiliary grate is arranged parallel to the grate. This allows a uniform ash layer to be discharged.

A particularly favorable embodiment of the present invention provides that the auxiliary grate can be inserted laterally into the gasifier or combustion chamber and has a front edge with a cutting edge. The cutting edge makes it possible to destroy the structures present in the movement path of the auxiliary grate with the least possible effort.

In order to save space, auxiliary grate and grate can be inserted from the same side into the carburetor or combustion chamber. The grate and the auxiliary grate can be moved over in each case at least one displacement device.

The carburetor or combustion chamber has at least one, preferably sealable, lateral slot for receiving the auxiliary grate, wherein preferably the slot extends over a circumferential region of at least 150 ° about the vertical axis of the carburetor or combustion chamber. The slot can be arranged in a subsequent to the carburetor or combustion chamber down separate housing part.

It is favorable to provide an ash receiving space in the lower area of the gasification or combustion chamber which is intended to receive ash, the auxiliary grid being arranged above the ash receiving space.

The supply of primary air for the combustion of the resulting charcoal takes place in the area of the grate, either through the grate plates themselves or through the lateral enclosure. The problem of a possible blockage of the air inlets can be minimized in particular by the fact that laterally open into the carburetor or combustion chamber primary air supply openings. In this case, primary air openings above the auxiliary grate and / or between the grate and the auxiliary grate-viewed in each case in their closed positions-can be arranged.

In this way it can also be avoided that the primary air is passed through the ash layer and entrains fine dust. It is particularly advantageous in this context if the primary air supply openings are arranged above the auxiliary grate. In this way, an influence on the combustion by the auxiliary grate is reliably avoided.

Another way to avoid clogging is that the cleaning of the air openings through the grate or a part of the grate mechanism by mechanically cleaning the air openings.

A high level of operational reliability can be achieved in that the grate and / or the auxiliary grate is formed substantially completely flat. The substantially smooth rust thus not only avoids blockages, but is also not prone to, for example, registered with the fuel nails or the like.

A particularly favorable design of the furnace is characterized in particular in that the combustion chamber is arranged directly above the gasification chamber.

A largely automatic operation can be represented by the fact that below the grate a receiving chamber for ashes is provided, in which a screw conveyor for removing the ash is arranged.

In the following, the present invention will be explained in more detail with reference to the embodiments illustrated in FIGS.

Show it

1 shows a furnace according to the invention with a partially cut carburetor chamber,

2 shows an ash disposal device of a furnace according to the invention in a section along the line II-II in FIG. 3 in a first embodiment variant of the invention, FIG.

3 shows this ash disposal facility in a plan view,

4 shows an ash disposal device of a furnace according to the invention in a side view in a second embodiment of the invention,

5 shows this ash disposal facility in a plan view,

6 shows an ash disposal device of a furnace according to the invention in Fig. 7 in a third embodiment of the invention in a section along the line VI - VI and

Fig. 7, this ash disposal facility in a plan view.

Functionally identical parts are provided in the embodiment variants with the same reference numerals.

The illustrated in Fig. 1 according to the principle of a countercurrent gasification firing 1 comprises a boiler body 2 with a carburetor part 3, which connects at the top of an unillustrated burner part with at least one combustion chamber.

The carburettor part 3 has a carburetor chamber 4 for the solid fuel supplied from above via the charging device 5, wherein at least one primary air supply 6a and one ash disposal device 7 are arranged in the bottom region of the carburettor part 3 in the lower third of the carburettor part 3. Optionally, at least one secondary air supply 6 may also be provided in the region of the middle or upper region of the jacket 3a of the carburetor part 3. The vertical axis 4a of the gasification chamber 4 is arranged substantially vertically in the embodiment. Via the charging device 5 solid fuel from a not further illustrated container is conveyed into the carburetor part 3. The solid fuel formed, for example, by fuel pellets is introduced, for example, with a not further evident stoker screw via the charging device 5 in the carburetor part 3 up to a maximum filling level. In the carburetor part 3, the solid fuel forming a fuel column in the carburetor part 3 is gasified in a glow zone of the carburetor chamber 4, whereby in the lower region of the carburettor part 3, for example 5 cm above the bottom of the carburetor part 3, an air ratio λ of about 0.3 is established , The gases generated in the glow zone and exiting upward from the gasification chamber 4 are burnt in the combustion chamber of the burner part, not shown, by supplying secondary air. The ash resulting from the decomposition of the fuel is removed by the ash disposal device 7. The ash disposal device 7 may be arranged as a separate unit below the carburetor part 3.

The ash disposal device 7 has in the bottom region of the gasification chamber 4 a grate 8, which is displaceable between a closed and an open position transversely to the vertical axis 4a, preferably substantially in the horizontal direction, by a first displacement device 9, for example a linear drive.

Furthermore, the ash disposal device 7 above the grate 8 by a second displacement device 11, for example a linear actuator, actuatable auxiliary grate 10 which is laterally inserted into the gasification chamber 4, and which closes the gasification chamber 4 in the inserted state down. Grate 8 and auxiliary grid 10 are arranged to be movable parallel to one another.

In the exemplary embodiment illustrated in FIGS. 3 to 3, the ash disposal device 7 has an annular housing part 12 adjoining the lower end face 3b of the carburetor part 3, onto which the carburetor part 3 is placed, in particular flanged. Along the lower end face 12a of the housing part 12 facing away from the carburetor part 3, the grate 8 is moved back and forth between its open and its closed position shown in FIGS. 1 to 3 by the first displacement device 9. In order to enable a displacement of the auxiliary grate 10, the housing part 12 has a side slit 13 arranged, for example, in a normal plane ε, through which the auxiliary grate 10 can be pulled in or out. The slot 13 extends through an angular range 13a of at least 150 ° about the vertical axis 4a of the carburetor or combustion chamber 4 on the circumference of the cylindrical housing part 12. At the slot 13 to the outside then a guide 14 for the auxiliary grate 10 is arranged on the housing part 12. In order to avoid in particular in the open position of the auxiliary grate 10 an ingress of false air, are provided for the slot 13 - not shown - sealing means.

In the area of the jacket of the housing part 12, more primary air openings can be arranged between the grate 8 and the auxiliary grate 10, as shown in FIG. 2.

As can be seen from FIGS. 2 and 3, the grate 8 is flat and preferably consists of several segments in order to avoid thermal distortion. It closes the gasification chamber 4 in the closed state down - in particular airtight - from. The auxiliary grate 10 is flat and preferably designed in several parts.

The auxiliary grate 10 has on its second displacement device 11 facing away from the front edge 15 on a cutting edge 16, with which the contents of the gasification chamber 4 can be cut horizontally.

In the first embodiment shown in FIGS. 1 to 3, first and second displacement devices 9, 11 are arranged on the same side of the housing part 12, the grate 8 and the auxiliary grate 10 are pushed to the same side in the open position.

The second and third embodiments shown in FIGS. 4, 5 and 6, 7 differ from the first embodiment in that both the grate 8, and the auxiliary grate 10 are formed in two parts and each of two halves 8 a, 8 b; 10a, 10b are made, which come to lie in the open position on different sides of the housing part 12 and are displaced from these opposite sides in the closed position. The supply of the primary air takes place here from below through openings 6c, 6d in the grates 8, 10.

In the second exemplary embodiment illustrated in FIGS. 4 and 5, the first and second displacement devices 9, 11 are arranged on different sides of the housing part 12. The drive is in each case via not further apparent gears and racks with guide shafts 17. Grate 8 and auxiliary grate 10 are each in a closed position.

In the third embodiment shown in FIGS. 6 and 7, for each of the halves 8 a, 8 b, 10 a, 10 b of the grids 8, 10 own first displacement devices 9 a, 9 b and 11 a, 11 b are provided on different sides of the housing part 12. The drive of the guided grates 8, 10 can also be done here on not further apparent gears and racks.

The invention has been explained with reference to furnaces 1 with a combustion chamber upstream carburetor chambers 4. However, it is by no means limited to furnaces 1 with carburetor chambers 4 and, of course, can also be used advantageously in furnaces 1 without pre-chambers 4, for example woodchip furnaces. In these cases, the ash disposal device 7 closes with the grate 8 and the auxiliary grate 10 down directly to a combustion chamber and not to a gasification chamber.

Claims (19)

1. A method for burning solid fuels - in particular biomass such as wood chips or pellets - in a furnace having at least one combustion chamber (1), wherein preferably the fuel is gasified in a combustion chamber upstream of the gasification chamber (4), wherein the resulting during combustion Ash over a movable grate (8) is discharged at intervals downwards by the grate (8) is opened, characterized in that before opening the grate (8) above the grate (8) an auxiliary grate (10) is inserted , which closes the carburetor or combustion chamber (4) of the furnace (1) downwards. 2. The method according to claim 1, characterized in that by inserting the auxiliary grate (10) the contents of the gasifier or combustion chamber (4) is cut substantially horizontally. 3. The method according to any one of claims 1 or 2, characterized in that primary air and / or secondary air is introduced laterally above the grate (8) in the carburetor or combustion chamber (4). 4. The method according to any one of claims 1 to 3, characterized in that in the lower region of the carburetor or combustion chamber (4) an ash receiving space is provided, which is intended to receive ash, and that the insertion of the auxiliary grate (10) and the opening of the grate (8) is performed each time the ash receiving space is filled with ash. 5. The method according to any one of claims 1 to 4, characterized in that immediately before the insertion of the auxiliary grate (10) and the opening of the grate (8), the combustion is throttled. 6. firing (1) for solid fuels, in particular biomass, such as wood chips or pellets, with at least one combustion chamber, which is preferably upstream of a carburetor chamber (4) for receiving a fuel column, wherein the carburetor or combustion chamber (4) down through a grate (8) is closed, which is movably mounted between a closed position and an open position, characterized in that above the grate (8) at least one auxiliary grate (10) in the gasifier or combustion chamber (4) can be inserted, in an inserted position, the carburetor or combustion chamber (4) closes down. 7. furnace (1) according to claim 6, characterized in that the auxiliary grate (10) is arranged parallel to the grate (8). 8. furnace (1) according to any one of claims 6 or 7, characterized in that the auxiliary grate (10) laterally in the carburetor or combustion chamber (4) can be inserted and a front edge (15) with a cutting edge (16). 9. firing (1) according to one of claims 6 to 8, characterized in that the grate (8) and / or the auxiliary grate (10) in several parts, preferably at least two parts, is formed. 10. firing (1) according to one of claims 6 to 9, characterized in that auxiliary grate (10) and grate (8) from the same side in the carburetor or combustion chamber (4) can be inserted. 11. furnace (1) according to one of claims 6 to 10, characterized in that the carburetor or combustion chamber (4) has at least one, preferably sealable, lateral slot (13) for receiving the auxiliary grate (10), preferably the slot (13) extends over an angular range (13a) of at least 150 ° about the vertical axis (4a) of the carburetor or combustion chamber (4). 12. firing (1) according to claim 11, characterized in that the slot (13) in a to the carburetor or combustion chamber (4) downwardly adjoining the separate housing part (12) is arranged. 13. firing (1) according to one of claims 6 to 12, characterized in that in the lower region of the gasifier or combustion chamber (4) an ash receiving space is provided which is intended to receive ash, and that the auxiliary grate (10) is arranged above the ash receiving space. 14. firing (1) according to one of claims 6 to 13, characterized in that laterally into the carburetor or combustion chamber (4) at least one primary air supply opening (6a, 6b) and / or Sekundärluftzuführöffnung (6) opens. 15. furnace (1) according to one of claims 6 to 14, characterized in that at least one primary air supply opening (6a, 6b) above the auxiliary grate (10) and / or between the grate (8) and auxiliary grate (10) -betrachtet in the closed Positions - is arranged. 16. firing (1) according to one of claims 6 to 15, characterized in that the grate (8) and / or the auxiliary grate (10) is formed substantially flat. 17. firing (1) according to one of claims 6 to 16, characterized in that the grate (8) and the auxiliary grate (10) via at least one displacement device (9, 11) are displaceable. 18. furnace (1) according to one of claims 6 to 17, characterized in that the combustion chamber is arranged immediately above the gasification chamber (4). 19. furnace (1) according to one of claims 6 to 16, characterized in that below the grate (8) is provided a receiving chamber for ashes, in which a screw conveyor for removing the ash is arranged. 2013 11 07 Fu