EP0919771B1 - Combustion process for solid material on a water-cooled sliding grate as well as gratebar and grate for carrying out the process - Google Patents

Abstract

The combustion method uses a moving combustion grid with a number of baffle elements (10) supported by the top surfaces of the grid plates (1-4), for deflection of the primary combustion air supplied to the combustion bed via the combustion grid. An Independent claim is also included for a moving combustion grid for solid fuel combustion.

Description

The invention relates to a method for burning solids on a water-cooled Thrust combustion grate, such as that used in waste incineration plants Installation is coming. Furthermore, it is about a specific grate plate and one made of such Rust plates built up rust, as is necessary to carry out the process. With the too burning solids can be a wide variety of types of solids, be it lignite, sawdust, wood and rubber chips, all sorts of residual goods, Industrial waste, sewage sludge, hospital or household waste or rubbish, etc. etc.

In the conventional thrust combustion grates, which are installed in waste incineration plants, and which consist of step-like grate steps, each second of which is movable in the thrust direction, the primary air is blown through from below the grate through the grate into the combustion bed. In the case of the cast grids still in use, in which the individual grate levels consist of a series of cast grate bars lying loosely next to one another or screwed together, the primary air reaches the top of the grate through recesses in the cast grate bars on the side and / or in the head region. The primary air is conveyed through the grate by building up corresponding overpressures of the order of magnitude of approx. 40 mm to 250 mm water column in the zones below the grate by means of large fans. For each grate surface, around 2% is provided as a free passage cross-section for the primary air, and up to 2,500 m ^{3 of} air per hour are conveyed through the grate per square meter of grate surface to give an idea of the magnitude of the air flow. The speed of the air flowing through reaches peaks of over 30m / s. This air flowing through the grate serves as primary air for the fire and also as cooling air for the cast grate. A disadvantage of this concept is that the air gets into the combustion bed quite unbalanced. If, for example, a wire or other small part is jammed between two adjacent grate bars, the distance between them is increased at the expense of the distances between the other grate bars. The consequence of this is that the disproportionately greater amount of air flows through this gap than through the slots between the other grate bars. Another disadvantage is that with high calorific values of the firing material and locally thin firing bed, as occurs repeatedly in the course of the firing material transport, the primary air flow acting there breaks through the firing bed, generates a high flame and thus takes dust and ash far up into the boiler room without completely releasing the oxygen to the fire. You then have a locally excessive excess of air, which is detrimental to the flue gas quality.

A significant improvement in the combustion process could be achieved with water-cooled Rusting of hollow and preferably made of sheet metal grate plates can be achieved extend advantageously over the entire grate width. The grate plates then have primary air supply channels on, for example, primary air supply pipes passing through the grate plate, which can also taper towards the top, or are the primary air supply channels formed by recesses for the passage of primary air, so that the primary air that is, it can be conducted from below the grate through it onto its upper side. As a result the grate plates that run across the width can no longer slag between individual Grate elements fall under the grate, as is the case with grate levels consisting of several loose parts adjacent grate bars is the case. This makes slag diarrhea practical prevented. The big advantage of a water-cooled grate is in fact too see that the air it conveys is solely the function of the air supply for combustion has to fulfill, and does not have to have any cooling function. This allows the Air flow rate drastically reduce, resulting in a much quieter and better optimized fire leads. The distribution of the primary air over the individual primary air supply channels remains largely even. However, one disadvantage is still seen in that especially in the case of high calorific values and / or a locally thin combustion bed Primary air jet, which flows out through the mouth of the primary air duct there, the Can break through the burning bed.

In general, there are increasing demands on the combustion process posed. Because the composition and thus the calorific value as well as the resulting volume For example, household waste fluctuates strongly regionally and seasonally, and so does that physical properties such as specific weight, piece size distribution, air permeability, Humidity, ash content, proportion of non-ferrous metals, etc. vary widely, it is not easy, always a good burnout of the combustion gases and the slag if adhered to to achieve the legally prescribed values. The aim is an even one Temperature distribution within the gas flow in the boiler room, including a controlled one and uniform combustion on the grate and in the combustion chamber above the grate cardinally is. The finite number of primary air supply lines or orifices, at times Clogging of individual mouths, the irregular bulk volume and the resulting varying layer height of the firing material and its fluctuating calorific value often lead uneven combustion.

Poor primary air supply on air-cooled grates can lead to overheating on the grate. The burnout zone is extended and unsatisfactory slag burnout is the result. The lack of air in the combustion chamber affects the gas burnout and the flow conditions in the boiler room. This in turn leads to excessive contamination of the boiler walls. If individual primary air supply openings become clogged, this leads to an increase in the air outlet speeds in the open mouths and where the primary air jet breaks through the combustion bed (blow-through), to streaks in the combustion chamber, to increased CO and NO _x formation and increased dust ejection. If, as a result of the consistency of the firing material, some or all of the orifices are clogged on one side of the grate, this results in an uneven firing bed that burns out only on one side.

The way in which primary air is introduced into the combustion bed of a thrust combustion grate and especially a water-cooled thrust combustion grate is out the above reasons of the utmost importance for the combustion and therefore it applies to significantly improve this primary air supply.

From the PATENT ABSTRACTS OF JAPAN, vol. 007, no.104 (M-212), May 6, 1983 a grate has become known, in which the grate bars each consist of two nested profiles are shaped so that the air flowing through the rods passes through the attached ones Longitudinal profiles flow horizontally and laterally. However, the air diverted in this way is not pure primary air, but primarily cooling air, and the grate is not water-cooled Thrust combustion grate.

In FR 2'574'160 (ELECTRICITE DE FRANCE), June 6, 1986 there will be a special tour reveals the cooling and primary air on an air-cooled grate. The Grate bars protruding upwards, which have an inclined side towards the front, which is perforated so that the air on the inclined grate is effectively horizontal through these holes exit.

Finally, EP 0'019'652 A (SULZER AG), December 10, 1980 shows a grate for a fluidized bed firing, which consists of water flowing through, parallel to each other at a distance arranged pipes, which are welded to each other with an intermediate web are. The primary air flows through the intermediate webs through air arranged therein Slits or holes upwards and flows around cover plates. However, these are not on a thrust combustion grate, and especially not on a water-cooled thrust combustion grate realized and can not be transferred directly to one.

It is therefore the object of the present invention to specify a method with which breaking through the combustion bed with primary air, as well as clogging or clogging largely of primary air supply openings in water-cooled thrust combustion grates is preventable, and which has a lower air flow rate, better combustion and thus also enables better flue gas qualities. It is also the task the invention, a grate plate and a grate constructed from such grate plates on which this procedure can be carried out.

This object is achieved by a method for burning solids a water-cooled thrust combustion grate, which is characterized by the fact that the primary air fed into the combustion bed through the water-cooled thrust combustion grate after flowing through the grate plates of the thrust combustion grate on guide elements strikes, which over the mouths placed in the front of the grate plates are arranged, and is deflected by each such guide element, so that the deflected primary air - in comparison with its speed in the direction of the Sliding grate surface emerging primary air flow - at a slower speed flows diffusely into the firing material.

Furthermore, the object is achieved by a grate plate for consisting of a water-cooled thrust combustion grate for burning solids from a flow-through hollow body with connection piece for the supply and discharge of Cooling water, as well as primary air supply channels penetrating the grate plate from bottom to top, which is characterized by the fact that on the front of the grate plate placed the mouths of the primary air supply ducts on the grate plate surface are arranged, on which the primary air emerging from the mouth is intended to encounter.

And finally, the problem is solved according to claim 9 by one stair-shaped water-cooled thrust combustion grate for burning Solids consisting of grate plates lying one on top of the other according to one of claims 4 to 8 exists and is characterized by that each grate level consists of one or more such grate plates.

In the figure drawings are different variants of grate plates for the structure of a thrust combustion grate, which is suitable for carrying out the method. Based on these drawings, the method and the device are described and their advantages explained.

It shows:

Figure 1:

A cross-section of a thrust combustion grate seen from the side, with Guiding elements over the mouths of the primary air supply channels leading through it;

Figure 2:

A grate plate with a design of the guide elements in the form of welded, bow-shaped baffles;

Figure 3:

A grate plate with a design of the guide elements in the form of welded on flat baffles;

Figure 4:

A grate plate with a design of the guide elements in the form of a welded-on, sawtooth-shaped steel sheet;

Figure 5:

A grate plate with a design of the guide elements in the form of screwed on Muzzle caps;

Figure 6:

A grate plate with a design of the guide elements in the form of welded-in Cap-shaped tubes;

Figure 7:

A diagram for the discussion of the flue gases G and the system efficiency E as a function of the O ₂ content in the flue gas G.

Thrust combustion grates have stationary and movable grate levels made of grate plates or from a series of grate bars, the grate steps being stepped on one another lie on. These sliding combustion grates can be installed so that the combustion bed in the is essentially horizontal, or inclined, with inclinations of up to 20 degrees or more are common. EP-0'621'449 describes a water-cooled thrust combustion grate known. Its grate plates are made of sheet steel and form board-shaped hollow bodies that extend across the width of the entire grating track and through which water is passed as a cooling medium. Every second grate plate is movable and can therefore perform a stoking or transport stroke. If it is a feed grate acts, the movable grate plates can be fired with their end face Push it onto the next lower grate plate. On the other hand, a push-back grate forms a somewhat wrong built-in, inclined staircase. The end faces of the Movable grate plates transport the one behind them in a rear grate Firing material back, after which it rolls down again in the direction of the tendency to rust. The movable grate plates, i.e. between two stationary grate plates arranged grate plates are usually collectively back and forth in the direction of their inclination emotional. This ensures that the burning rubbish lying on the grate at a long dwell time of 45 to 120 minutes constantly rearranged and even on the grate is distributed.

An advantageous construction of this thrust combustion grate with its essential elements can be seen in Figure 1, in which a portion of a thrust combustion grate is shown using a cross section. The grate consists of stairs Grate levels, which are each formed by a hollow, water-cooled grate plate 1,2,3,4. Every second grate level, in the figure the grate plates 2 and 4, is designed to be movable while the intermediate grate plates are suspended on cross tubes 5. The moveable Grate plates 2.4 are each laterally mounted on a roller 6 and lie with it Rear part on vertical rollers 7, which are arranged on the laterally delimiting planks are. Each movable grate plate 2.4 is from its own hydraulic piston-cylinder unit 8 driven. At the front of each grate plate open through the grate plate extending pipes 9 for the supply of primary air from the area below the Rust. These primary air supply pipes 9 open somewhat above the surface of the grate plate and have an elongated cross-section, as will be shown later becomes. In this way it has already been avoided that excessive amounts of these tubes Slag falls through. The mouths of these primary air pipes 9 or corresponding primary air supply channels are as shown here with guide elements 10 in the form of muzzle caps made of bow-shaped baffles that are simply welded onto the top of the grate plate are. The upper section of the baffles is V-shaped in cross section. The of The primary air jet hitting the bottom of these guide plates is therefore from the guide plates divided and distracted laterally. At the same time, the bow-shaped baffles cover the mouth in the thrust direction of the grate, so that the fired material is guided around the baffles and does not directly cover the primary air outlets.

In Figure 2 is a part of the front edge of a grate plate with a design of the guide elements in the form of welded bow-shaped guide plates 10 in a perspective view shown. One sees the elongated primary air supply pipes 9, which one to open a few millimeters above the surface of the grate plate. Over these estuaries the mouth or nozzle caps 10 are welded in the form of the bow-shaped guide plates 10. These baffles 10 consist of sheet steel and form seen from the side, if they are welded on, a trapezoidal shape, the piece of sheet metal which the forms the upper side of the trapezoid, is V-shaped in cross section, which is indicated by a simple folding can be achieved. With this shape, the one that hits from below becomes Primary air flow divided into two as indicated by the arrows and deflected laterally and thereby also swirled. The effect is that the air at a significantly reduced speed and penetrates diffusely into the kiln. The air passing through in a row arranged primary air orifices flows in, the combustion bed in its entirety Diffuse penetration wide, so that the atmospheric oxygen much more homogeneous than before Combustion is supplied. Instead of the shape shown here, the bow-shaped Baffles can also form a semicircular arc, or one Angle welded onto the grate plate like a gable above the mouth. The Mounting direction can be chosen arbitrarily, so that the angular plane also in right angle to the direction of thrust. If the sheets as in the figure shown, this also ensures that the primary air supply openings are not clog.

Figure 3 shows a grate plate with a design of the guide elements in the form of welded flat baffles 12. This variant also fulfills the intended purpose, namely the deflection of the primary air and its diffusion, which in turn is indicated by arrows is. These flat bars 12 can serve a further purpose. they seem namely as barbs and take each time the movable plates are pushed forward the firing material lying in front of the area of the flat iron 12 while pulling it back release this again and then the primary air flows back to the flat iron 12 and it cools. That lying on the grate in the vertical direction above the flat iron 12 Firing material is separated from the underlying material by this take-away, so that A horizontal shift of the combustion bed layers takes place with this solution too Avoid clogging or clogging the primary air supply openings, because if there is the next succeeding grate step, seen relatively, from the feed openings moved away, this also resolves during the previously opposite relative movement at most under the flat iron 12 clamped material and releases the mouth again.

FIG. 4 shows a further variant for a guide element, in this case a sawtooth-shaped one Sheet 13, similar to the shape of a cutter bar knife, across the width of the grate on the The front edge of the grate plate is welded on. The saw teeth each protrude above a nozzle the primary air supply, so that the emerging primary air flow onto one sawtooth each strikes and is deflected by this towards the front and the two sides. With this too Execution a horizontal displacement of the bed layers is achieved, and at the same time, clogging of the primary air supply openings is avoided.

FIG. 5 shows an embodiment with screwed-on orifice caps 14. The primary air supply ducts or pipes are circular in this case and the pipe openings, which protrude slightly from the ros have an external thread. The nozzle cap 14 is screwed onto this. These nozzle caps 14 are standard fittings with hexagonal outer shape, which are used for this purpose be provided with radial bores 15. The fittings are only a small one Part of their thread screwed on, so that the primary air is unhindered by the radial Holes 15 can emerge. It is therefore after the pipe mouth of the fittings deflected and radially flows out through the six holes shown in the example, whereby it diffuses on all sides into the surrounding firing material, as indicated by the arrows. Clogging of the mouths arranged all around is due to the relative movement of the Mouth and nozzle caps 14 to the transported firing material impossible. Such nozzle caps can of course also have other shapes and are welded on instead of being screwed on.

FIG. 6 shows a further embodiment variant for the guide elements. These exist here from tubes 16 with an elongated cross section 17. These tubes 16 are at one end closed and there form a rounded cap 18. With its open side down these tubes 16 are directed into corresponding elongated holes in the upper and lower grate plate used and sealed in these elongated holes. They are there longer than the grate plate thickness and with its lower end flush with the underside welded into the grate plate so that it can then be Exceed the grate plate surface at the end. On both sides of the grate overhanging the grate Section of the tubes 16 are below, the caps 18 in the flat areas Slots 19 are provided, which are directed in the tube 16 from the inside outwards towards the bottom. First, the air is thereby deflected in the cap 18 and then flows depending on Execution of the slots 19 in the caps 18 upwards, horizontally or obliquely downwards through them onto the garbage bed, and secondly, the slots 19 are through this arrangement largely protected against constipation from fired goods, because they only move lengthways of the kiln and, as I said, are directed downwards. Because of the rounded Caps 18 can the pipe sections that protrude beyond the grate plate surface with the move the moving grate plates through the firing material, or the firing material can touch it Pipe sections are pushed past without getting stuck on sharp edges and a pipe 16 may be deformed or even torn thereby.

Basically, such guide elements described for the figures can be on the top the grate can only be realized on water-cooled grates, because these remain in operation at a low temperature so that most of the heat comes from the guide elements the rust is drained off. On the other hand, such elements would be innate on air-cooled grates burn in no time.

A thrust combustion grate built up from water-cooled grate plates can also such guiding elements and then basically allows that through the shear combustion grate on the combustion bed supplied primary air after the outlet the sliding grate surface is first deflected. The resulting diffusion of the primary air and consequently its more homogeneous penetration of the combustion bed turns out to be enormously beneficial for the quality of the combustion. The influences of the Qualitative discussion of oxygenation:

In this regard, FIG. 7 shows a diagram for assessing the quality of the combustion, the flue gases G and the system efficiency E being plotted as a function of the O ₂ content in the flue gas G. The CO value is regarded as a superordinate measure of the quality of combustion. Now you can see from this diagram that the CO limit value (CO _max ) is maintained over a relatively wide range of the O ₂ content in the flue gas. With a decreasing O ₂ proportion, the NO _x proportion also decreases and the efficiency E of the incineration plant increases with a simultaneously decreasing gas volume flow V. However, if the O ₂ proportion is further reduced to a certain extent, the CO increases -Very suddenly steep. The aim of the combustion control must therefore be to keep the O ₂ value so low that the NO _x content becomes minimal and at the same time the CO limit value is just maintained. Such an ideal working point is shown in the diagram. In addition to the flue gas values to be achieved, it also guarantees high system efficiency. Because of the optimized oxygen input with the present method, less air has to be blown through the firing material. This brings you closer to the basic goal of stoichiometric combustion. You also have less dust ejection. The dust particles are also less fast. This reduces the erosion of the boiler walls. Fast and many dust particles treat the boiler walls like sandblasting.

Tests in a waste incineration plant have shown that using this method the overpressure under the grate is reduced to a third of the otherwise necessary value could be met, and the required flue gas qualities nevertheless maintained become. So there are no longer such large amounts of air flowing at high speed and locally uncontrolled by the grate and the firing material, but it is in a targeted amount Oxygen very gently, that means with low flow velocity into the firing material diffuses. As a result, no unnecessary flue gas volume is generated, the flue gas speed is significantly reduced and thus the generation of fly ash. The small The proportion of fly ash is also no longer swirled up into the boiler. All of this allowed it, the boiler and all downstream system components are smaller and thus dimensioned more cost-effectively.

Claims (9)

1. Process for incinerating solids on a water-cooled thrust combustion grate, characterized in that the primary air supplied through the water-cooled thrust combustion grate to the combustion bed after flowing through the grate plates of the thrust combination grate impacts against deflector elements (10,12,13,14,16) disposed over the openings on the front side of the grate plates and is deflected by each said deflector element so that the deflected primary air flows diffusely into the combustible material at a reduced speed in comparison with its speed in the direction of the primary air flow exiting the surface of the thrust grate.
2. The process according to claim 1, characterized in that the primary air flow flows through pipes (16) welded into the grate plate (1-4) which project beyond the surface of the grate plate and are sealed at the top like caps, and have slots (19) in their sides oriented obliquely upwards, downwards or horizontally so that the primary air exiting through the slots (19) flows diffusely into the combustible material where it contributes to the creation of a homogeneous, low speed airflow.
3. The process of one of claims 1 to 2, characterized in that the primary air flow, after exiting from the thrust grate surface, impacts against bow-shaped deflector plates (10) which are disposed over openings shaped like oblong holes running in the direction of thrust and form an arch over these openings, and in that the primary air flow exiting from each opening is divided and deflected by the local deflector plate (10), so that the primary air flows diffusely into the combustible material where it contributes to creating a homogeneous, low speed airflow.
4. A grate plate for a water-cooled thrust combustion grate for the incineration of solids comprising a permeable hollow element (1-4) with connection pieces for supplying and draining away cooling water, and with primary air supply ducts (9) which pass through the grate plate from bottom to top, characterized in that deflector elements (10,12,13,14,16) are disposed on the surface of the grate plates over the openings of the primary air supply ducts (9) on the front side of the grate plates, against which the primary air exiting from the opening is intended to impact.
5. The grate plate of claim 4, characterized in that the deflector elements (16) are formed in that pipes (16) with a cross-section (17) like an oblong hole, which are sealed at one end to form a rounded cap (18), are inserted with their open end downward into corresponding oblong holes (17) in the top and bottom grate plate sheets and welded impermeably into these oblong holes, with their cap ends (18) projecting beyond the grate plate surface, and on both sides of the section projecting beyond the grate plate have slots (19) below the caps (18) in the straight areas, which are contrived in the pipe (16) to run from inside to outside and are oriented downwards, upwards or horizontally.
6. The grate plate of claim 4, characterized in that deflector elements in the form of bow-shaped deflector plates (10) or flat plates (12) projecting beyond the openings at an oblique angle are welded on over the openings of the primary air supply ducts (9), against which plates the primary air exiting from the openings is intended to impact.
7. The grate plate of claim 4, characterized in that a sawtooth shaped steel sheet (13) is welded along the front edge of the grate plate, each of whose sawteeth projects over a primary air supply duct opening at an oblique angle, against which the primary air exiting from the openings is intended to impact.
8. The grate plate of claim 4, characterized in that deflector elements in the form of opening or nozzle caps (14) with radial holes (15) for diffusing the primary air that impacts against them are mounted over the circular openings of the primary air supply ducts (9).
9. A stairway-like thrust combustion grate for incinerating solids comprising grate plates (1-4) that rest on top of each other according to one of the claims 4 to 8, characterized in that each grate layer consists of one or several such grate plates (1-4).

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