EP0437759A2 - Grate and fuel fired boiler incorporating such a grate - Google Patents

Abstract

A grate for a fuel boiler consisting of stepped plates (10, 11), each second (11) of which can be moved back and forth and is provided with a corresponding drive, combustion air being allowed to pass through spaces between the plates (10, 11) controlled and complete combustion of the fuel when the fixed plates (10) are fastened to a common first holder (20) and the movable plates (11) are fastened to a common second holder (29) and when the fastening of each plate (10, 11 ) on its holder (20, 29) is adjustable in height. In this case, preferably only air is used for the combustion of the fuel which has passed through the spaces between the plates (10, 11), and has preferably been sucked through.

Description

The invention relates to a grate for a fuel boiler consisting of plates arranged in steps, each second of which can be moved back and forth and is provided with a corresponding drive, combustion air passing through spaces between plates. The invention further relates to a boiler with such a grate.

In combustion furnaces to which the fuel is fed continuously or intermittently, the aim is to burn the fuel as completely as possible in order to keep the ash accumulation as small as possible. For this it is necessary to let the fuel stay on the grate for a relatively long time in order to provide the burning time required for complete combustion. In order to produce uniform combustion conditions, it is necessary to transport the fuel on the grate from one end to the other so that fresh fuel can be replenished so that a reasonably uniform state is achieved. When transporting the fuel from one end of the grate to the other, it should be striven for that no fuel portion can fall through the grate before reaching the ash-side end of the grate, since the fuel that has passed through may not yet be completely burnt.

A grate of the type mentioned at the outset is known from a brochure from Vyncke. It consists of fixed plates arranged in steps, between each of which a movable plate is arranged. The movable plates are hollow and flowed through with water, which is intended to protect the plate material. Primary air for combustion flows through spaces between the movable and stationary plates, while secondary air can enter through the side openings of the boiler wall at the level of the fuel bed. Due to the movement of the movable plates of the grate, the fuel moves down the steps of the grate until it falls into an ash container at the lower end of the grate. The combustion in the combustion chamber is supported by a flame directed towards the grate from a side wall of the boiler, which flame is fed by another fuel, for example gas. In order to achieve an air supply which is adapted to the fuel quality changing when walking over the grate, various chambers are provided below the grate, into which combustion air can be blown in different amounts, which then exits through the associated interstices of the grate. A water-cooled heat shield arranged at an angle above the grate ensures that the combustion gases above the grate cool down relatively quickly. The arrangement of the movable plates and fixed plates of the grate is such that only one gap is created between two stationary plates because a stationary plate and a fixed plate are in direct contact with each other.

The known grate has a number of disadvantages. The use of primary and secondary air does not allow for fully controlled combustion. The same applies to the water cooling of the movable grate plates, which completely burn a more difficult to burn fuel, for example waste, not allowed. The movable plates mounted on the fixed plates are subject to considerable wear, since solid particles of the fuel damage the surface of the two plates lying on top of one another as a result of the relative movement. Another disadvantage of the known boiler is that the fuel falls onto the grate via a slope. It is therefore entirely a matter of chance how far the fuel rumbles down on the grate until it stops. It can be seen that this results in completely different residence times for fuel parts on the grate.

The known boiler therefore does not allow complete and adequately controlled combustion of the fuel. In addition, the known boiler does not make it possible to significantly reduce the pollutant content in the combustion gases.

The problem on which the invention is based is to create a grate or a boiler which enables a controlled and complete combustion of the possibly problematic fuel, for example garbage.

Based on this problem, a grate of the type mentioned is characterized in that the fixed plates are fastened to a common first holder and the movable plates are fastened to a common second holder and that the fastening of each plate on its holder is adjustable in height.

The height adjustability of the individual plates of the grate allows the setting of different gaps for the passage of the combustion air, so that the gaps can be adapted to different fuels on the one hand and can be adjusted differently over the length of the grate on the other to generate a desired flow profile for the combustion air through the grate. According to the invention, a sub-stoichiometric carbonization can be set in this way at the beginning of the grate, while over-stoichiometric complete combustion can take place at the end of the grate. For this purpose, the spaces between the plates can be enlarged towards the end of the grate.

The grate according to the invention is designed in a particularly preferred manner so that the combustion takes place exclusively with the primary air passing through the intermediate spaces between the plates and that no secondary air is permitted. By mounting the fixed plates on the one hand and the movable plates on the other hand on respective common brackets, the adjacent fixed and movable plates are supported independently of one another. This eliminates the need to allow plates of one type to rest on plates of the other type, which results in considerable mechanical stresses. According to the invention, there are air gaps between a fixed plate and two adjacent movable plates or a movable plate and two adjacent fixed plates. Due to the common holder for the movable plates, their drive for the back and forth movement can be easily realized by moving the entire holder back and forth.

The movable plates are preferably arranged so that they overlap with both adjacent fixed plates even in their extreme positions of the reciprocating movement. This prevents fuel from falling through the grate.

In a structurally simple and preferred embodiment, the plates rest on vertically standing plate-shaped supports which are attached to the common brackets so as to be adjustable in height.

The common second holder of the movable plates is preferably designed as a channel which is approximately U-shaped in cross section, on the side walls of which the vertically standing supports for the movable plates are fastened. The movable plates can be connected to the vertical supports by means of a screw connection.

On the other hand, the vertically standing plate-shaped supports, which are connected to the common first holder, have a stepped upper edge, through which a depression is formed, which receives the associated plate. The recess can be open to the previous support in the direction of inclination, so that the fixing of the fixed plates is carried out by two plate-shaped supports resting against one another.

The vertical supports are preferably arranged close to one another and the air supply takes place within the vertical supports. In this way, the supply of secondary air from the side can be reliably avoided.

The boiler according to the invention, equipped with a grate as described above, works with combustion air which only passes through the spaces between the plates. The combustion air is preferably moved through the intermediate spaces by a suction source arranged downstream of the combustion chamber. The combustion chamber is therefore under negative pressure, which leads to the extraction of combustion air through the spaces between the grate plates. With the help of the vacuum, very defined combustion conditions can be set. It is particularly preferred to maintain a low fuel bed temperature, which ensures that any acid builders that are incorporated through the addition of basic additives remain in the ash and do not break down into the gaseous state due to excessively high fire bed temperatures and pollute the combustion gases as pollutants.

The boiler according to the invention can preferably be designed with an afterburner chamber in which very high temperatures arise due to radiant heat and good insulation, which thermally decompose any unbound pollutants into harmless gases.

The boiler according to the invention works without an additional flame, since the amount of fuel can be reliably regulated at any time due to the metered fuel supply and due to the metered transport on the grate, as a result of which temperatures and combustion conditions which are well defined in terms of the properties of the fuel can be achieved.

A defined supply of the fuel to the start of the grate is achieved in that a feed tray is arranged at the height of the start of the grate and serves as a supply device for the fuel to the grate.

Figur 1 -

eine schematische Darstellung eines Verbrennungsofens, insbesondere für Müll

Figur 2 -

eine Einzeldarstellung eines Rostes in dem Verbrennungsofen in Figur 1

Figur 3 -

eine im Querschnitt U-förmige Halterung für die bewegbaren Platten

Figur 4 -

eine mit Bohrungen versehene Profilschiene zur (einseitigen) Halterung der festen Platten

Figur 5 -

einen Rost großer Breite, aufgebaut aus drei nebeneinander aufgebauten Einzelrosten gemäß Figur 2

The invention will be explained in more detail below with reference to exemplary embodiments shown in the drawing. Show it:

Figure 1 -

a schematic representation of an incinerator, in particular for waste

Figure 2 -

an individual representation of a grate in the incinerator in Figure 1

Figure 3 -

a U-shaped bracket in cross section for the movable plates

Figure 4 -

a profiled rail with holes for (one-sided) mounting of the fixed plates

Figure 5 -

a grate of large width, constructed from three individual grids built next to one another according to FIG. 2

Fuel is supplied to the incinerator shown schematically in FIG. 1 via a flap 1 arranged in the ceiling. The fuel is preferably mixed homogeneously with a basic additive in order to bind acid generators into harmless salts by means of a neutralization reaction. The fuel falls on a moving floor 2, which is equipped with sawtooth-shaped wedges 3, at least some of which can be moved back and forth by a drive 4. Since the fuel can migrate over the flat slope of the sawtooth-shaped wedge 3, but is pushed forward by the steep slope, the fuel migrates to the front edge 4 of the moving floor and pushes a hinged flap 5 to the side and falls on a floor 6 on which a Slide plunger 7 is moved back and forth by a drive 8. Through the ceiling A basic additive in liquid form can be added to the fuel lying on the floor 6 through the incinerator, as indicated by the two arrows in FIG. 1. This addition is superfluous if the fuel has been homogeneously mixed with a basic additive.

At the same height as the floor 6 is the beginning of a grate 9, which consists of step-like fixed plates 10 and movable plates 11 arranged between them. The movable plates 11 are shown in FIG. 1 in their retracted position in which they overlap somewhat with the fixed plate 10 arranged below them. By a back-and-forth movement, which is caused by the same drive 8 as for the sliding plunger 7, the fuel on the grate 9 is moved obliquely downwards until it falls completely burned into an ash container 12, from which the ash, for example, with the aid of a Screw conveyor 13 is transported away. The combustion chamber 14 arranged above the grate 9 is delimited towards the floor 6 and sliding floor 2 by a wall 15 which is held in a holder 16 arranged somewhat above the start of the grate. The combustion gases pass through a passage 17 arranged below the ceiling to the outlet 18 of the boiler. If the boiler walls are well insulated and have a high heat capacity and can possibly emit heat radiation, the space above the grate 9 can heat up to very high temperatures and thus contaminants contained in the combustion gases can be broken down into harmless components. At the outlet 18 of the boiler, heat exchangers, filters or similar can be installed. connect.

The structure of the grate is explained below with reference to Figure 2. The movable plates 11 extend - like the fixed plates 10 - over the entire width of the grate. Within this width, two U-shaped profile pieces 19 are arranged, which act as the first common holder 20, specifically for the fixed plates 10. A profile piece 19 is in detail Figure 4 shown. It has eight pairs of holes 21, to each of which a plate-shaped support 22 is screwed. The plate-shaped supports 22 have two elongated holes 23, 24, one of which is T-shaped and thus offers an adjustment possibility in the vertical and in the horizontal direction. By screwing the plate-shaped supports 22 in their elongated holes 23, 24, the supports 22 on the first common bracket 20 are adjustable in height. The supports 22 have a step 25 on their upper edge, through which a recess 26 is formed which is open to the support 22 preceding in the conveying direction. The associated fixed plate 10 is inserted into the recess 26 and thus rests on two vertical plate-shaped supports 22 arranged near the opposite boiler walls. In FIG. 2, eight vertical plate-shaped supports 22 adjoin one another closely and form joints 27.

A groove 28 with a U-shaped cross section is arranged within the first common holder 20 and forms the second common holder, namely for the movable plates 11. The channel 28 is shown as a detail in FIG. 3 and consists of a rectangular base 30 and two side walls 31, the height of which decreases in accordance with the inclination of the grate 9 in the conveying direction. The side walls 31 are provided with pairs of holes 32 which are aligned with one another. With the help of a pair of holes 32, a vertical plate-shaped support 33 is attached to the respective side wall 31 of the channel 28. Here, too, the attachment takes place via pairs of elongated holes 34, 35, so that the vertical supports 33 can be adjusted in height. A movable plate 11 is supported on each of its upper edges 36 and is screwed to the support 33 with the aid of a fastening angle. The movable plates 11 are thus also supported by two vertical plate-shaped supports 33, the distance between the support points being somewhat less than the distance between the support points for the fixed plates 10 due to the associated vertical supports 22. The vertical supports 33 also adjoin one another closely and form joints 37.

The air supply takes place within the U-shaped channel 28, specifically by means of a negative pressure generated above the grate 9, through which air is sucked between the plates 10, 11. Due to the air flow caused by a vacuum, an extraordinarily uniform air flow is created, which can be controlled by different distances between the plates 10, 11 at the grate end compared to the grate start, so that a substoichiometric carbonization is caused at the grate start, while an over-stoichiometric combustion at the grate end arises, which does not lead to an inadmissible increase in the fuel bed temperature, because the fuel is already largely incinerated at the grate end, so that a temperature increase cannot occur despite the excess air available combustion air. The excess oxygen can favor or enable the thermal decomposition of pollutants in the post-reaction chamber.

Since the plates 10, 11 are only supported, as shown, on two lines near the end of the plates by the edges of the vertical supports 22 and 33, only plates of a certain maximum length can be used, otherwise the plates 10 will bend , 11 - and thus undefined combustion air supplies - would be risked. If a grate of greater width is to be used due to the desired performance of the incinerator, it can be composed of several individual grates 9, as is shown schematically in FIG. The plates 10, 11 of the 3 individual gratings 9 in the exemplary embodiment shown can complement each other without any noticeable space to the desired overall width of the grate, so that larger grate widths can also be realized without the risk of the plates 10, 11 bending.

Claims (13)

Grate for a fuel boiler consisting of stepped plates (10, 11), each second (11) of which can be moved back and forth and is provided with a corresponding drive, combustion air passing through spaces between the plates (10, 11), characterized that the fixed plates (10) are attached to a common first holder (20) and the movable plates (11) are attached to a common second holder (29) and that the attachment of each plate (10, 11) to its holder (20, 29) is adjustable in height. Grate according to claim 1, characterized in that the movable plates (11) are arranged to overlap with both adjacent fixed plates (10) even in their extreme positions of the reciprocating movement. Grate according to claim 1 or 2, characterized in that the plates (10, 11) rest on vertically standing plate-shaped supports (22, 33) which are attached to the common holders (20, 29) so as to be adjustable in height. Grate according to claim 3, characterized in that the common second holder (29) of the movable plates (11) is designed as a channel (28) which is approximately U-shaped in cross-section, on the side walls (31) of which the vertically standing supports (33) for the movable plates (11) are attached. Grate according to claim 4, characterized in that the movable plates (11) are screwed together with the associated vertically standing supports (33). Grate according to one of claims 3 to 5, characterized in that the vertically standing plate-shaped supports (22) connected to the common first holder (20) have a stepped upper edge and that the depression (26) formed by the step (25) has the associated one fixed plate (10). Grate according to claim 6, characterized in that the recess (26) is open to the support (22) preceding in the direction of inclination. Grate according to one of claims 3 to 7, characterized in that the vertical supports (22, 33) adjoin one another closely and in that the air is supplied within the vertical supports (22, 33). Boiler with a grate according to one of claims 1 to 8, characterized in that the combustion air only passes through the spaces between the plates (10, 11). Boiler according to claim 9, characterized in that the combustion air is moved through the intermediate spaces by a suction source arranged downstream of the combustion chamber. Boiler according to claim 9 or 10, characterized in that the spaces between the plates (10, 11) for setting a predetermined flow profile through the grate (9) are set at different heights. Boiler according to claim 11, characterized in that the height of the intermediate spaces increases towards the end of the grate. Boiler according to one of claims 9 to 12, characterized by a feed bottom (6), which is arranged at the level of the grate start, as a feed device for the fuel to the grate (9).

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