WO1996030701A1 - Combustion plant - Google Patents

Abstract

The invention concerns a device for burning solid or pasty material (2) by means of a furnace grate (3, 4), said device comprising a closed combustion chamber (7) above the grate region (3, 4). The secondary combustion chamber (6) is arranged after the entire grate region (3, 4). The hot flue gases are thus guided out of the first grate region (3), in which the material for combustion (2) is actually burned, via the rear region of the grate (4). In this way, the residues of combustion (2') are melted in this rear region (4). The residues of combustion remaining after the combustion of domestic and commercial waste can thus be minimized, such residues being practically free from material which is still combustible and including heavy metals associated such that they are insoluble in water.

Description

Incinerator

The present invention relates to a device according to the preamble of claim 1 and a method for operating such a device.

Known such devices, i.e. Combustion or Firing systems can actually be divided into two categories.

The first category are the so-called grate firing systems. These are suitable for solid fuels, such as household waste, industrial waste, coal, etc. These fuels are burned on a grate. In a first phase, the fuel is dried and degassed. This is already partially done in the feed zone of the plant. This process is triggered by the radiation from the combustion chamber and by the addition of preheated air. The fuel is also ignited on its surface due to the flame radiation from the combustion chamber. In a second phase, the main combustion takes place, whereby the dried fuel ignites completely (not only on the surface). In this phase, more air is now supplied than in the first phase. Here, the conversion of solid carbon to gaseous products takes place, which through the firebox in the afterburning chamber. get the flue gas exhaust. The temperature in this section of the furnace is high. Depending on the calorific value of the fuel, the supply of the air quantity is controlled or. customized. However, there are limits to this adaptation, since the additionally supplied air also serves to cool the grate and, especially in the case of high-calorific fuel, an excess of air is generally used for precisely these reasons. The final phase is then the remaining combustion. Not yet Completely burned out fuel, ie the combustion residue, for example pressed paper, coarse materials and remaining solid carbon, is burned or burned here. to burn out. Since there should be as little heat loss as possible so that the residual combustion can be carried out as completely as possible, only a correspondingly small amount of air should be added here (because of the risk of the combustion re-starch cooling down).

The phases shown here are usually carried out separately in the incineration plant, conventionally for example on a movable grate, which slowly transports the fuel forward in the combustion chamber. Depending on the type of fuel, the transitions of the phases are fluid or not recognizable at all, especially with high fuel calorific values.

The disadvantage of this first category of incineration plants is, in particular, that the combustion residues obtained in solid form cannot be easily deposited due to their water solubility. These residues also still have a relatively high proportion of unburned material, and the heavy metals contained therein are not immobilized. This is because there is no melting of the residual fuel and residues in the burnout zone.

The second category of incinerators includes the melting processes, such as rotary kilns or melting chambers. The rotary kiln systems in particular are particularly suitable for the combustion of chemical waste in solid, pasty or liquid form. It is precisely these last two types of waste that cannot be used in grate firing systems because they cannot be stored or transported on the conventional grate. In the melting process the residues remaining from the combustion process are melted. This takes place through heat exchange between the residues and the hot flue gases from the combustion process in the rotary tube or the melting chamber. The slag that remains afterwards is fed to a water-cooled detoxifier and solidifies there to form a glazed granulate, which is easy to deposit due to its water-insolubility. In such plants, for example, residues from combustion plants of the first category can also be melted, although a very high energy input is necessary, since these residues are introduced in cold form and have to be heated up first.

Such systems, in particular rotary tube systems, are poorly suited for the combustion of large amounts of fuel, such as domestic and / or commercial waste, due to their low throughput. The additionally supplied combustion air is also difficult to press through such waste, with the result that the combustion temperatures required for melting cannot always or not reliably be achieved.

The object of the present invention was to provide an incineration plant which can also burn solid and / or pasty fuels with a high throughput and can melt the combustion residue.

According to the invention, this object is achieved by the features according to claim 1.

Due to the arrangement of the combustion chamber according to the invention. In the afterburning chamber, on a grate incineration plant on the last grate area, in conventional plants the burnout area, sufficiently high temperatures can be reached to remove the combustion residues to melt here. This ensures that the remaining residue is obtained as liquid and / or pasty slag, which can be cooled, for example, in a water bath, as is known in rotary kilns. Such a cooled slag now contains residual heavy metal residues in water-insoluble, glazed form and only has a very small proportion of combustible residual material. Such slags can now be easily deposited.

Further preferred embodiments of the invention are set out in dependent claims 2 to 16.

According to the invention, a method according to claims 17 to 21 is proposed for operating the device.

Such a device according to the invention is particularly suitable for the incineration of household and commercial waste.

Embodiments of the invention are explained in more detail below with reference to drawings. Show it

Figure 1 is a schematic longitudinal section of a conventional grate furnace with counterflow.

2 shows the schematic longitudinal section of a conventional grate combustion system with medium-flow combustion;

3 shows the schematic longitudinal section of a conventional grate combustion system with direct current combustion;

4 shows the schematic longitudinal section of a furnace according to the invention; Fig. 5 shows the schematic longitudinal section of a furnace according to the invention with a rotary tube.

The three known types of grate combustion plants are shown schematically in FIGS. 1 to 3. Basically, all of these systems have a feed device 1 with which the fuel 2 is introduced into the furnace. The systems generally have a firing grate 3 and a burnout grate 4. The fuel 2 is transported by devices on the grate 3 and 4 itself in the direction of the slag opening 5. For example, known movable grids such as roller grids, push-back grids, counter-thrust grates or counter-sliding grids are used for this purpose. The afterburner 6 is arranged in the counter-rom furnace, as shown in Figure 1, right at the beginning of the combustion chamber 7. This means that the flue gases are only partially guided over the fuel 2 against the direction of movement. However, the hottest flue gases from the actual main combustion area (indicated by arrows above the fuel 2) practically go directly into the afterburning chamber 6. Heat is extracted from the combustion residue 2 'on the burnout grate 4. This prevents the combustion residue 2 'from melting on the afterburning grate 4, and the residues 2' entering the slag fall opening 5 still have a relatively high proportion of combustible material and, moreover, are still liquid-soluble. Such waste cannot simply be landfilled, but must be handled separately as special waste; if necessary, they can be burned separately, for example in separate rotary kilns.

The same problem also occurs with medium-current firing, which is shown schematically in FIG. 2. The afterburning chamber 6 is in the middle of the grids 3, 4 arranged. Here too, the residues 2 ¹ cannot be melted on the burnout grate 4.

The direct current firing according to FIG. 3 does not bring any significant improvement in this regard either. Here, the afterburning chamber 6 is indeed shifted a little further in the direction of material flow, with essentially only the combustion chamber 7 'being slightly closed above the actual combustion zone by means of an edge 8 projecting into the combustion chamber. The burnout grate 4, on the other hand, is not or only slightly affected by the hot flue gases of the combustion zone.

Here, the arrangement of the combustion chamber 7 according to the invention, as shown for example in longitudinal section in FIG. 4, leads to the desired result. By forming the combustion chamber 7 behind the burnout grate 4 and preferably also narrowing it in this area, the hot flue gases are passed over the combustion residues 2 '. The narrowing causes an additional heating of these combustion residues, among other things also by additional heat radiation from the combustion chamber walls, with which the temperature required for the melting of these residues 2 ¹ can only be reached.

The combustion chamber is preferably provided with swirling edges 9 in the flue gas flow direction, which swirl the flue gases. This swirl also leads to better, i.e. homogeneous high flue gas temperature, which is reached in the afterburning chamber 6.

It is preferably provided according to the invention to additionally add high-calorific fuel, for example coal dust, between the combustion grate 3 and the burnout grate 4. This can preferably be done via feed openings take place, which are arranged in a stage 10 between the firing grate 3 and the burnout grate 4. This further increases the heat input. The residual fuel (combustible material, carbon) still contained in the combustion residues 2 ′ can thus be gasified and oxidized with little or no additional air supply, which can be supplied from below through the burnout grate 4. Such an additional air supply would remove heat again from the combustion residues 2 ', which is why this is actually undesirable. The combustion residues obtained in the form of liquid slag then pass through the slag fall opening 5 into a water-filled detoxifier, for example, and solidify to form a glass-like granulate. These granules are now insoluble in water, have practically no residual fuel and can therefore be landfilled without any problems.

So that the liquid slag on the burnout grate 4 can reach the slag fall opening 5 without falling down into the supply air area, this burnout grate 4 is preferably inclined, preferably approximately 20 ° from the horizontal, and preferably also has a concave cross section. So that the slag flows in the middle of the burnout grate 4 against the slag fall opening 5.

So that the grates 3.4 are not worn out or destroyed too quickly by the great heat, and still rely on additional air supply for combustion or. the melting process can be dispensed with, it is preferably provided according to the invention to cool the grids 3, 4 through cooling channels in the grates themselves. The cooling can be done by gaseous or liquid coolants. The choice of the coolant and also its temperature can on the one hand prevent the destruction or excessive wear of the grate 3, 4 and on the other hand also influence the combustion process in the main combustion area become. It is now also possible to achieve an approximately constant stoichiometric combustion in this area, which also develops the hottest flue gases. This cannot be guaranteed with conventional grate furnaces, since the additional air also serves to cool the grates 3, 4. Especially with high-calorific fuels, this means that there must be combustion with excess air in order to cool the grate 3, 4 sufficiently.

Due to the arrangement of the combustion chamber according to the invention, the burnout grate 4 actually becomes a melting grate. The advantage of the molten slag, as already explained above, lies in the practically complete burnout of the material, the destruction of toxic substances such as dioxin and furans, the immobilization of pollutants such as heavy metal and the reduction in the specific volume of the combustion residues themselves compared to a burnout.

In order to achieve the remaining gas burnout required in this area in the afterburning chamber 6 in each case, blowing nozzles 11 are further provided according to the invention for blowing in flue gas. These nozzles have plates 12 in front of their nozzle openings, preferably made of ceramic material. A swirling of the injected smoke gases is achieved by these plates 12, which leads to good gas burnout and self-cleaning of the nozzles 11. Without such swirling, the nozzles would clog in a short time due to the soot particles contained in the flue gas. In the further course, as usual, secondary air is added via the nozzles 11 'in order to ensure the gas burnout and the required oxygen content.

So that liquid substances can now also be burned with this device, the invention provides for a rotary tube 13 to be connected to the burnout grate 4 to arrange, as can be seen from Figure 5. Liquid fuels can now be introduced directly into this rotary tube 13 through correspondingly arranged feed openings 14 and burned there. The great advantage here is that the hot flue gases are guided out of the combustion chamber 7 via the burnout or combustion chamber. Melting grate 4 in the rotary tube 13 in which very high temperatures can be reached right from the start. The length of the rotary tube 13 can thus also be much shorter in comparison to conventional rotary tube systems. In particular, pasty or solid fuels with a very low calorific value can be applied to the melting grate 4 in front of the rotary tube 13. These are then dried and degassed there very quickly and then already get very hot into the rotary tube 13 for melting. Such a device according to the invention can be used universally for the combustion of all fuels, it being possible for the first area with the rust combustion to achieve a very high throughput, in particular also for solid fuels.

Finally, the walls 7 'of the combustion chamber 7 can be constructed from cooled masonry, as can also be seen in FIG. 4. For example, air channels are present in the masonry. Cooling air can now be guided through these channels and, if appropriate, subsequently fed to the combustion chamber 7 as combustion air. This is particularly advantageous when a fuel 2 with a low calorific value has to be burned, in which heat loss through the combustion chamber walls 7 'is to be prevented, so that the melting of the slag is promoted.

The temperature of the walls 7 ¹ , ie the masonry, is preferably kept within a predetermined value by a correspondingly regulated or controlled supply of the cooling air. According to the invention, this temperature value is said to be just below the melting temperature of the the walls for depositing fly ash resp. Slag parts are kept. Especially in the case of fuel 2 with a high calorific value, temperatures in the combustion chamber 7 higher than this slag melting temperature are achieved with a device according to the invention. Appropriate cooling of the combustion chamber walls causes the fly ash to melt, respectively. Prevents slag. The molten slag would severely affect the masonry. Through the adjustability of this temperature, the thickness of the slag layer can moreover be adjusted, preferably only a very thin slag layer is aimed for.

Claims

claims 1. Device for the combustion of solid and / or pasty material (2), which has a material supply (1), a firing and burnout grate (3,4), means for supplying combustion air to the grate area, one over at least one area of the grate arranged combustion chamber (7) and an afterburner chamber (6) connected to it, characterized in that the combustion chamber (7) is arranged closed over the entire grate area (3, 4) and at the earliest at the end of the grate area (3,) away from the material feed (1). 4) opens into the afterburning chamber (6). 2. Device according to claim 1, characterized in that the grate (3, 4) has transport means for conveying the fuel (2). 3. Device according to one of claims 1 to 2, characterized in that the combustion chamber (7) before the confluence with the afterburning chamber (6) has at least one swirl edge (9) which is directed against the grate area (3, 4). 4. Device according to one of claims 1 to 3, characterized in that the firing grate (3,4) is divided into at least two areas, a first combustion area (3) and a subsequent melting area (4). 5. The device according to claim 4, characterized in that the combustion chamber (7) over the melting area (4) has a smaller cross section, preferably a smaller height, than over the combustion area (3). 6. The device according to claim 4 or 5, characterized in that the grate in the combustion area (3) at least 5 ° from the horizontal against the afterburning chamber (6) is inclined. 7. Device according to one of claims 4 to 6, characterized in that the grate (4) in the melting area is at least 5 °, preferably 25 °, inclined from the horizontal towards the afterburning chamber (6). 8. Device according to one of claims 4 to 7, characterized in that the grate between the combustion area (3) and the melting area (4) has a step (10). 9. Device according to one of claims 4 to 8, characterized in that the grate in the melting area (4) is inclined more from the horizontal than the grate in the combustion area (3). 10. Device according to one of claims 4 to 9, characterized in that the grate in the melting area (4) is concave in cross section. 11. The device according to one of claims 1 to 10, characterized in that at least part of the grate (3,4) has cooling channels for receiving coolant. 12. Device according to one of claims 1 to 11, characterized in that in addition to the primary material feed (1) at least one further material feed is provided, which is arranged within the grate area (3, 4). 13. Device according to one of claims 4 to 11, characterized in that at least one additional material supply between the combustion (3) and the melting area (4) is provided. 14. Device according to one of claims 1 to 13, characterized in that in the afterburning chamber (6) blowing nozzles (11) for the supply of secondary air and / or recycled flue gas are arranged, which in front of their Outlet openings have plates (12), preferably made of ceramic material. 15. Device according to one of claims 1 to 14, characterized in that after the firing (3) and burnout grate (4) a rotary tube (13) is provided, and that the afterburning chamber (6) is arranged only after this rotary tube (13) The outlet opening of the combustion chamber (7) is arranged in such a way that the flue gases generated therein are passed completely through the rotary tube (13) before they reach the combustion chamber (7). 16. The apparatus according to claim 15, characterized in that means (14) for introducing liquid fuel through the combustion chamber (7) into the rotary tube (13) are provided. 17. A method for operating a device according to one of claims 1 to 16, characterized in that - fuel (2) is brought to the beginning of the grate (3) by means of a feed device (1), - That the fuel (2) by means of moving parts of the grate (3,4) from the feed device (1) is transported away through the combustion chamber (7). - An approximately stoichiometric combustion is achieved by supplying additional air at least in the first grate area (3), - That the combustion air in the combustion chamber (7) is guided over the entire grate area (3,4) to the afterburning chamber (6). 18. The method according to claim 17, characterized in that in the rear grate area (4) high-calorific fuel, preferably in the form of dust, liquid or granules, is fed to the combustion residues in order to support the melting process in this area (4). 19. The method according to claim 17 or 18, characterized in that fly ash is added to the combustion residues (2 *) located in the rear grate region (4). 20. The method according to any one of claims 17 to 19, characterized in that the combustion chamber walls (7 ') are cooled to a predetermined temperature and the cooling air is passed into the combustion chamber (7) as combustion air after flowing through the combustion chamber walls (7 ¹ ). 21. The method according to any one of claims 17 to 20, characterized in that the combustion chamber walls (7 ') are kept at a temperature by controlled or regulated supply of cooling air, which is only slightly lower, preferably at most 50 °, than the melting temperature of the fly ash or slag material to be deposited on the combustion chamber walls. 22. Use of a device according to one of claims 1 to 16 for the combustion of household and commercial waste and melting of the combustion residues.