EP1647770A2 - Method of influencing the properties of incineration residues of an incineration plant - Google Patents

Abstract

The process involves burning of material on a burning grate. Melting or sintering methods are regulated in burner bed. Refeeding is carried on only till the time and in such quantity that specified changes of basic combustion parameters lie in pre specified tolerance limit. The combustion conditions of burning process are objectively changed in order to counteract the change of burning parameters due to refeeding.

Description

The invention relates to a method for influencing the properties of combustion residues from an incinerator, in particular a waste incineration plant, in which the fuel is burned on a furnace grate and accumulating ungeschmölzene and / or unsintered combustion residues are fed back into the combustion process. The combustion residues usually come from the ash content of the fuel and fall as a grate ash - often called slag - in the purifier. But it can also be fly ash from the boiler or the exhaust filter system. The Rostaschen can also contain metals, glass or ceramic parts.

A method of this kind is known from DE 102 13 788.9 A 1. In this method, the combustion control is performed so that in the combustion bed of the main combustion zone, a portion of the combustion residues melts and / or sintered and the non-molten and / or sintered combustion residues are deposited at the end of the combustion process and fed back to the combustion process.

Furthermore, it is known from EP 0 862 019 B1 to meter dusts into the high-temperature region of the incinerator in which the temperature is above the melting or sintering temperature of the flue-dust. The dosage The fly ash occurs there depending on particular combustion conditions in which to a greater extent toxic organic pollutants such as PCDD / PCDF and / or precursor compounds, ie precursor compounds of PCDD and PCDF arise.

These methods do not take into account that the recirculation of combustion residues can have a significant impact on the combustion process. Of particular importance here are the metering of the proportion of combustion residues in the fuel mixture and the change in the material composition of the combustion residues.

The recirculation of combustion residues, for example, by increasing the proportion of combustion residues in the fuel mixture to a lowering of the fuel bed temperature. In turn, due to the lower fuel bed temperature, the proportion of unmelted and / or sintered components in the combustion residues will increase. If now, e.g. According to DE 102 13 788.9 A1, these components are recycled unregulated, this will lead to another - in this case disadvantageous - lowering the fuel bed temperature.

In addition, the material composition of the combustion residues may change as a result of their recycling. Non-molten and / or sintered combustion residues in the form of slag fine fraction have, for example, higher calcium oxide contents and lower iron oxide contents than the average composition of the combustion residues. This means that can be increased by the made according to DE 102 13 788.9 A1 feedback of slag fine fraction of the average lime content of the combustion residues over time.

• einerseits
  durch die stoffliche Zusammensetzung des Brennstoffes und der rückgeführten Verbrennungsrückstände, die wiederum ausschlaggebend für die Schmelztemperatur bzw. die Reaktivität bei Sinterreaktionen ist
• und andererseits
  durch die Verbrennungsbedingungen, die ausschlaggebend für die Brennbetttemperatur oder andere wesentliche Verbrennungsparameter sind. Die Verbrennungsbedingungen sind bestimmt durch die Zugabemenge des Brennstoffgemisches, den Ort der Zugabe, die Schürung durch den Feuerungsrost sowie die Mengen an Luft, Sauerstoff oder rückgeführtem Abgas und deren Temperatur.

The melting and / or sintering process is determined:

• on the one hand
  by the material composition of the fuel and the recirculated combustion residues, which in turn is decisive for the melting temperature or the reactivity in sintering reactions
• and on the other hand
  by the combustion conditions that determine the fuel bed temperature or other significant combustion parameters. Combustion conditions are determined by the amount of fuel mixture added, the location of the addition, the stoke caused by the combustion grate and the amounts of air, oxygen or recirculated exhaust gas and their temperature.

In the following, a distinction is made between the combustion conditions and combustion parameters. This is to be understood that the combustion conditions are the settings that can be directly influenced or adjusted by control devices. These are e.g. the amount of the fuel mixture supplied (fuel mixture = fuel + recycled combustion residues), the place of addition, and the amount of supplied air, supplied oxygen or recirculated exhaust gas and their temperature.

The combustion parameters are to be understood here to be those quantities which are not set directly via control devices but result from the combustion conditions. These include, for example, fuel bed temperature, combustion chamber temperature, steam production and O 2 content in the exhaust gas. The fuel composition (calorific value, Water content, ash content) is considered as a combustion parameter because it can not be directly influenced or adjusted in the case of waste.

The object of the invention is to provide a method by means of which the sintering and / or melting process of substantially all solid combustion residues in the fuel bed can be ensured.

• die Rückführung wird nur so lange und in einer solchen Menge durchgeführt, solange die hierdurch bedingten Veränderungen wesentlicher Verbrennungsparameter in vorher festgelegten Toleranzgrenzen liegen
• es werden die Verbrennungsbedingungen des Verbrennungsprozesses gezielt verändert, um den durch die Rückführung bedingten Veränderungen der Verbrennungsparameter entgegen zu wirken
• es wird durch eine Rückführung ausgewählter Fraktionen der Verbrennungsrückstände die stoffliche Zusammensetzung der Verbrennungsrückstände so verändert, dass der Schmelz- und/oder Sinterungsvorgang der Verbrennungsrückstände beeinflusst wird
• es wird durch die Zugabe von Zuschlagstoffen die stoffliche Zusammensetzung der Verbrennungsrückstände so verändert, dass der Schmelz- und/oder Sinterungsvorgang der Verbrennungsrückstände beeinflusst wird.

This object is achieved in a method according to the preamble of claim 1 according to the invention in that the melting and / or sintering operations are controlled in the fuel bed after at least one of the following process steps:

• the recirculation is carried out only so long and in such an amount, as long as the thereby caused changes of essential combustion parameters lie within pre-determined tolerance limits
• the combustion conditions of the combustion process are deliberately changed in order to counteract the changes in the combustion parameters caused by the return
• it is by recycling selected fractions of the combustion residues, the material composition of the combustion residues changed so that the melting and / or sintering process of the combustion residues is affected
• the addition of aggregates changes the material composition of the combustion residues so that the melting and / or sintering process of the combustion residues is influenced.

Of course, already reaches one of the specified steps in the process to solve the problem initially posed. The more of these process steps are used together, the better the combustion conditions and the more combustion residues can be recycled.

In an advantageous embodiment of the invention, the selected fractions of the combustion residues have a particle size of 2 mm to 10 mm.

In connection with the change in the material composition, it is possible to proceed in such a way that the combustion bed composition on the firing grate is changed in such a way that melting and / or sintering processes are accelerated or proceed even at lower temperatures. For this purpose, substances can be admixed with the fuel or with the combustion residues to be returned, which cause a lowering of the melting point. These may be silicate compounds, such as borosilicate and similar compounds, in principle therefore already known for such effects substances.

In an advantageous embodiment of the invention, scrap metal and in particular iron scrap is used as an additive. This scrap can be recovered from the grate ash by known separation techniques or from an external source.

Advantageously, the metal scrap is comminuted prior to addition. The crushed metal scrap can have a grain size of 1 to 20 mm.

wobei x jeweils der Molbruch des oxidischen Bestandteils bezogen auf eine durchschnittliche Zusammensetzung der Verbrennungsrückstände ist. Eine besonders bevorzugte Art der Rückführung ist dann gegeben, wenn die Zugabe von Metallschrott so dosiert wird, dass die Basizität B der Verbrennungsrückstände zwischen 0,3 und 0,7 liegt. Eine bevorzugte Art der Metallschrottzugabe ist gegeben, wenn die Basizität der Verbrennungsrückstände durch die Intensität der Zerkleinerung des als Zuschlagstoff zugegebenen oder rückgeführten Schrottes geregelt wird. In diesem Fall wird beispielsweise die Zerkleinerung des Metallschrottes intensiviert, wenn die Basizität der Verbrennungsrückstände über einem vorgegebenen Grenzwert zwischen 0,3 und 0,7 liegt.The combustion or partial combustion of this scrap produces metal oxides and locally strong heat releases, which have an advantageous effect on the melting and sintering behavior impact. This is especially the case when the basicity of the combustion residues is thereby reduced. The basicity can be defined as simplified $$\mathrm{B}=\left({\mathrm{X}}_{\mathrm{Ca}\mathrm{O}}+{\mathrm{X}}_{\mathrm{Fe}\mathrm{O}}\right)/\left({\mathrm{<figure-callout\; id="2"\; label="X\; Si\; O"\; filenames="imgf0002.png"\; state="\{\{state\}\}">X\; </figure-callout>}}_{\mathrm{Si}\mathrm{O}}+{\mathrm{X}}_{\mathrm{Fe}2\mathrm{O}3}\right).$$

where x is the mole fraction of the oxidic constituent based on an average composition of the combustion residues. A particularly preferred type of recycling is given when the addition of scrap metal is metered so that the basicity B of the combustion residues is between 0.3 and 0.7. A preferred type of metal scrap addition is given when the basicity of the combustion residues is controlled by the intensity of comminution of the scrap added as an aggregate or recycled. In this case, for example, the crushing of the metal scrap is intensified if the basicity of the combustion residues is above a predetermined threshold between 0.3 and 0.7.

In a further advantageous embodiment of the invention, the return of the combustion residues can be carried out directly into the combustion chamber. It is advantageous if the recirculation of the combustion residues takes place on the Feuerungsrost.

A particularly preferred type of recycling is given when the recirculation of the combustion residues is carried out on the feed table. With this procedure, on the one hand a very rapid determination of the influence of the combustion process is possible and on the other hand, this Rückführungsart designed advantageous because not yet prevail on the feed table, the high temperatures as in the main combustion zone, whereby the device for recycling is not subject to high temperature loads.

The influencing of the combustion process can be carried out in a particularly advantageous manner by observing a significant combustion parameter which can be seen in the position of the burn-out zone. For example, if the burnout zone travels toward the discharge end of the furnace grate, which is a consequence of the decreasing calorific value of the fuel / residue mixture present on the furnace grate, then less combustion residue will be added. In contrast, the amount of combustion residue to be recycled can be increased as the burnout zone migrates toward the feed end.

When changing or monitoring significant combustion parameters, many options are available to the person skilled in the art.

An essential combustion condition is the fuel mass applied per unit time. In connection with the fuel mass, an important combustion parameter is the fuel calorific value and also the moisture and the ash content of the fuel.

If the fuel calorific value drops, less combustion residue will be returned and vice versa.

The moisture of the fuel can be determined before reaching the combustion chamber, for example, by using a microwave detector, which is arranged in the region of the feed chute for the fuel. At high moisture content decreases with the same composition of the fuel whose calorific value, so that less combustion residues can be led back and vice versa.

Another important combustion parameter is the height of the fuel bed temperature and the temperature distribution on the fuel bed. This combustion parameter can z. B. be monitored by means of an infrared camera. Higher temperatures of the fuel bed give the possibility of recycling higher amounts of combustion residues and vice versa.

Another essential combustion condition is the amount of combustion air, both the primary and the secondary combustion air amount and optionally the amount of recirculated exhaust gas.

Another essential combustion condition is the temperature of the combustion air, which is set by means of an air preheater, for example.

With the help of the further essential combustion condition, the oxygen content of the combustion air, the combustion process can be greatly influenced, as can be exerted on the regulation of the oxygen content, a significant influence on the primary combustion and in particular on the Brennbetttemperatur.

Another essential combustion condition is the location of the combustion air supply. Here, a particularly sensitive control can be achieved in that the combustion grate is subdivided both in the longitudinal direction and in the transverse direction into several sub-wind zones, which are acted upon by respectively adjusted amounts of primary air and oxygen.

Another essential combustion condition with which the combustion process can be significantly influenced is the speed of rusting and the rusting rate Duration of the stoke resulting in the recirculation rate of the fuel within the fuel bed. For this purpose, in particular, a reverse slide inclined in the direction of the discharge end, in which, for example, every second step of the grate can be moved and the intermediate grate steps are made stationary. In this design, the fuel is constantly circulated on its way from the task end to the discharge end, so that fuel parts that were on the top of the fuel bed for a certain length of stay, get down again on the rust, creating a good mixing of already glowing fuel with fresh abandoned fuel in the initial area and good ventilation and loosening in the lower area, towards the discharge end, located area is achieved.

In the arbitrary determination of the tolerance limits within which a recirculation of combustion residues is carried out, on the one hand, the heat release and on the other hand the pollutant emission can be used, which influence these tolerance limits.

Figur 1:

ein Flussdiagramm eines Basisverfahrens und

Figur 2:

eine schematische Darstellung einer Verbrennungsanlage zur Durchführung des Verfahrens.

The invention will be explained in more detail below with reference to a flowchart and an exemplary embodiment of a combustion plant. In the drawing show:

FIG. 1:

a flowchart of a basic method and

FIG. 2:

a schematic representation of a combustion plant for carrying out the method.

According to FIG. 1, 1,000 kg of waste, with an ash content of 220 kg, are placed on a grate furnace and thereby burned in such a way that a proportion of 25 to 75% of the incineration residues produced is already converted into completely sintered slag. The total combustion residues, including those already returned are 340 kg. Of these 320 kg fall into a wet slagger, and are deleted in this and discharged. By a separation process, which includes a screening and optionally a washing process and a magnetic metal deposition, 190 kg of fully sintered inert material and 30 kg of scrap iron are separated. The granules and part of the scrap iron are sent for recycling. The amount of scrap iron that is recycled depends on the basicity of the combustion residues. In this example, 10 kg of scrap iron are recycled and 20 kg recycled. 110 kg combustion residues, which are not yet sintered, are returned to the combustion process. The fly ash leaving the combustion chamber with the flue gases is 20 kg. It is recycled in this example to 50% and fed to 50% on a separate disposal route.

The combustion system shown schematically in FIG. 2 comprises a feed chute 1 into which the fuel is fed, a feed table 2 with a feed element 3, which conveys the fuel into the combustion chamber 4. 3a designates a controllable drive device which makes it possible to regulate the feed quantity as a function of a combustion parameter. There, the fuel denoted by 5 falls on a Feuerungsrost 6, which is designed as a back pressure grating and 7 performs Schürbewegungen by a drive. For this purpose, the drive 7 acts on the transmission member 8 with which each second grate stage is connected, so that each stationary grate stage is followed by a stationary grate stage. A control device 7a allows a controllable drive in order to be able to regulate the speed of quenching as a function of other combustion parameters. In the illustrated Feuerungsrost five different sub-chambers 9a - 9e are provided in the longitudinal direction, which also still divided in each case in the transverse direction are so that the primary combustion air can be adjusted in terms of quantity and distribution to the respective requirements on the firing grate. The supply of the primary combustion air via a schematically indicated blower 10 and the control of the amount of combustion air via not shown valves in the individual supply lines 11a - 11e. The control of the amount of combustion air takes place via a control device designated 10a. 12 and 13 are secondary air nozzles, which emanate from a supply line 14 and 15 and introduce secondary air into the combustion chamber 4.

At the lower end of the firing grate, the slag and other combustion residues fall into a wet slagger 16, from which they are fed to a separating device 17. The non-sintered or unmelted residual slag is then added via a line 18 in the task area above the feed table 3 the fuel and thus passes back to the Feuerungsrost. The separating device denoted by 17 is intended to symbolize only in a schematic way the separation process explained in connection with Figure 1. An infrared camera 19 monitors the combustion process on the grate 6. A central control unit 20 influences various control devices 3a for the control of the task quantity, 7a for the quenching speed, 10a for the primary air quantity and 21a for the amount of oxygen, which via a distributor 21 the individual primary air chambers 9a -. 9e is supplied.

The mode of action is explained below:

As already described in connection with FIG. 1, the aim of this method is to re-supply the unmelted or unsintered combustion residues to the combustion process. Thus, for example, by means of an infrared camera 19, the fuel bed observed and thereby the fuel mass distribution and the fuel bed temperature detected. Depending on these combustion parameters, the control device 3a is influenced via a central control unit 20, for example, in order to control the feed quantity. Furthermore, it is possible, starting from this central control unit to influence the control device 10a to change the amount of combustion air. Another influencing possibility, starting from the central control unit 20, is the ability to influence the control device 7a in order to change the speed of warping. A controller 21a, which is also influenced by the control unit 20, regulates the amount of oxygen that can be supplied to the individual sub-chambers 9a - 9e. In the illustrated embodiment, of course, not all control options are recorded schematically, but only a few particularly important control operations, with the help of which it is possible to control the combustion process so that as much combustion residues can be returned to the firing grate again.

Claims (23)

A method for influencing the properties of combustion residues from a combustion plant, in particular a waste incineration plant, wherein the fuel is burned on a furnace grate and resulting unmelted and / or unsintered combustion residues are fed back to the combustion process, characterized in that the melting and / or sintering operations be controlled in the fuel bed with at least one of the following process steps: - The return is carried out only as long as and in such an amount, as the resulting changes in essential combustion parameters are within predetermined tolerance limits - The combustion conditions of the combustion process are selectively changed in order to counteract the changes caused by the feedback of the combustion parameter - It is by a return of selected fractions of the combustion residues, the material composition of the combustion residues changed so that the melting and / or sintering process of the combustion residues is affected - It is changed by the addition of aggregates, the material composition of the combustion residues so that the melting and / or sintering process of the combustion residues is affected. A method according to claim 1, characterized in that the selected fractions of the combustion residues have a particle size of 2 mm to 10 mm. A method according to claim 1 or 2, characterized in that metal scrap and in particular iron scrap is used as an additive. A method according to claim 3, characterized in that the metal scrap is comminuted prior to addition. A method according to claim 4, characterized in that the crushed metal scrap has a particle size of 1 to 20 mm. Method according to one of claims 1 to 5, characterized in that the return of the combustion residues takes place directly in the combustion chamber. A method according to claim 6, characterized in that the return of the combustion residues takes place on the Feuerungsrost. A method according to claim 6, characterized in that the recycling of the combustion residues takes place on the feed table. Method according to one of claims 1 to 8, characterized in that an essential combustion parameter is the position of the Ausbrennzone. Method according to one of claims 1 to 8, characterized in that a substantial combustion condition is the per unit time discontinued fuel mass. Method according to one of claims 1 to 8, characterized in that an essential combustion parameter is the fuel calorific value. Method according to one of claims 1 to 8, characterized in that an essential combustion parameter is the moisture of the fuel. Method according to one of claims 1 to 8, characterized in that an essential combustion parameter is the height of the fuel bed temperature and the temperature distribution on the fuel bed. Method according to one of claims 1 to 8, characterized in that a substantial combustion condition is the amount of combustion air. Method according to one of claims 1 to 8, characterized in that a substantial combustion condition is the temperature of the combustion air. Method according to one of claims 1 to 8, characterized in that a substantial combustion condition is the oxygen content of the combustion air. Method according to one of claims 1 to 8, characterized in that a substantial combustion condition is the location of the combustion air supply. Method according to one of claims 1 to 8, characterized in that a substantial combustion condition is the scouring speed, that is the circulation speed fuel within the fuel bed. Method according to one of claims 1 to 8, characterized in that the tolerance limits are influenced by the heat release. Method according to one of claims 1 to 8, characterized in that the tolerance limits are influenced by the pollutant emission. Method according to one of claims 1 to 8, characterized in that the amount and type of aggregates or the selectively recirculated fractions of combustion residues is selected depending on the composition of the combustion residues. Method according to one of claims 1 to 8, characterized in that the amount and type of aggregates or the selectively recirculated fractions of combustion residues is selected depending on the basicity of the combustion residues. Method according to one of claims 1 to 8, characterized in that at a basicity above a tolerance to be selected between 0.3 and 0.7, the amount of supplied or removed from the grate ash and recycled metal scrap is increased and accordingly below this tolerance limit the amount is reduced.

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