EP2138766B1 - Method for feeding material through a nozzle into a boiler of a garbage incineration facility - Google Patents

Description

The present invention relates to a method for injecting a substance into a boiler of a waste incineration plant according to the preamble of claim 1 and to an apparatus for carrying out the method according to the preamble of claim 9.

Generic methods are used for example for the selective non-catalytic reduction (SNCR) of gaseous nitrogen oxides (NO _x ), such as those incurred in waste incineration. Such SNCR methods are roughly in the DE-A-4139862 and in the WO 2006/053281 described.

In the SNCR process, reducing agents in aqueous solution (eg ammonia water or urea) or gaseous (eg ammonia) are usually injected into the hot flue gases flowing through the boiler in order to reduce nitrogen oxides to molecular nitrogen according to the following equations.

4NO + 4NH ₃ + O ₂ -> 4N ₂ + 6H ₂ O

2NO ₂ + 4NH ₃ + O ₂ -> 3N ₂ + 6H ₂ O

Depending on the flue gas composition, the optimum temperature range is approximately between 850 ° C and 950 ° C. The corresponding area of the boiler is also referred to as a secondary combustion chamber.

Above the optimum temperature range, ammonia is oxidized to an increasing extent, with nitrogen oxides arise, resulting in an undesirable excess consumption of ammonia. Below the said temperature range, only an insufficient reduction of nitrogen oxides takes place.

In order to remove nitrogen oxides efficiently from the flue gas, it is thus necessary to inject ammonia into the boiler in the first place, where said optimum temperature range is given.

Accordingly, for example, in WO 91/17814 discloses a method according to which a means for the reduction of pollutants is injected at a temperature in a flue gas passage, in which the pollutants are effectively reduced. The nozzles are arranged in different, distributed over the height zones.

Alternatively, in DE-C-3722523 proposed a nozzle assembly on a vertically displaceable lance stick over which the location of the ammonia feed can be adjusted.

In the WO 91/06506 discloses a system for reducing nitrogen oxides in the exhaust gas from the combustion of a carbonaceous fuel. In this case, a treatment agent is introduced into the exhaust gas by means of injectors which are fed by a mixer.

For an efficient reduction of nitrogen oxides, however, aggravating the fact that the temperature at the individual points in the boiler is usually subject to uneven and strong temporal variations.

In this regard, in DE-A-4434943 discloses a method in which the optimal temperature for the reduction temperature level is determined in the boiler via temperature sensors and the nozzles for supplying the reducing agent are aligned accordingly.

However, an optimal reduction of the nitrogen oxides is only possible in practice if the amount of reductant to be supplied can be adjusted individually for each nozzle in order to take into account the local temperature differences in the boiler.

In this context, the DE 20 2006 013 152 a conduit arrangement for several atomizer lances on a boiler, through which an additive is fed into the boiler. In this case, the feed quantity of the additive for each atomizing lance is set in a distributor.

All of the nozzles or lances of the documents cited above of the prior art are so-called two-substance nozzles or two-substance lances.

So be in the in the DE 20 2006 013 152 described arrangement admixed the additive and the pressure medium immediately before feeding into the boiler in a connection piece associated with the atomizer lance, which allows independent dosing of the blowing agent and the additive.

Since every single two-substance lance or two-fluid nozzle has its own feed for the additive and its own feed for the compressed air, its construction is relatively complicated. Moreover, two-substance lances or two-substance nozzles have relatively large dimensions, which makes their installation in the boiler of an incinerator difficult.

If, as customary in the SNCR process, ammonia is injected, then in the systems based on two-substance nozzles it is usually present in a very dilute solution in the form of ammonia water in order to produce a to ensure uniform distribution of the ammonia to the individual two-fluid nozzles. For this purpose, softened water is generally used in order to minimize lime deposits in the nozzle or in the liquid line leading to it.

In addition to the high expense associated with central dilution of ammonia with softened water, dual-fluid nozzle systems often have the disadvantage that the control is sluggish, i. that only with a strong delay on temporal temperature changes in the boiler can be reacted. In particular, the known systems generally do not allow adequate reaction to short-term temperature peaks in the boiler.

The object of the present invention is thus to provide a simple method for injecting a substance which is a reducing agent for the reduction of nitrogen oxides into a boiler of a waste incineration plant, which makes it possible to set the desired amount of substance for individual injection sites in a targeted manner and this setting rapidly adapt.

In particular, it should allow the procedure with the least possible expenditure on equipment, to ensure optimal reduction of nitrogen oxides with minimal consumption of reducing agents taking into account both the local temperature differences and the temporal temperature changes in the boiler in SNCR process.

The object is achieved according to the invention by the method of claim 1. Advantageous embodiments are listed in the dependent claims.

According to claim 1, the substance to be injected is passed, starting from at least one distributor, via lines which branch off from the distributor to a respective nozzle assigned to the respective line. The quantity of substance to be passed to the respective nozzle is set in the distributor.

Due to the fact that, in accordance with the invention, the substance to be injected and the propellant are combined by the distributor before the diversion of the respective line, a mixture containing the substance and the propellant is already present before the branching. Consequently, structurally simple and robust single-fluid nozzles can be used, as they are approximately in the EP-A-0 364 712 are described, the contents of which are hereby incorporated by reference.

So far, it has been assumed that adjusting the einzudüsenden amount of material for each individual nozzle can be accomplished only using two-fluid nozzles.

It has now surprisingly been found that it is also possible using single-fluid nozzles to set the einzudüsende amount of substance for each nozzle individually.

The method of the present invention is used primarily for the above-mentioned SNCR methods. As a rule, the substance to be injected is therefore a reducing agent for the reduction of nitrogen oxides, in particular ammonia or urea.

The invention makes it possible to individually set the amount of reducing agent to be injected as a function of the prevailing temperature profile in the boiler for each nozzle. This can ensure that the reducing agent is mainly injected there, where the optimum temperature range for the reduction exists. This means that at a high reduction rate of nitrogen oxides, the slip and thus also the consumption of reducing agent is minimized, resulting overall in a very economical and ecological operation.

According to an embodiment of the invention, when the change in the setting of the amount of the substance to be fed to the respective nozzle is made, this change is made steplessly, i.e., in a state of change. continuous, performed.

In general, the nozzles are arranged in a plurality, preferably at least three horizontal (and thus generally aligned transversely to the flow direction of the flue gas) nozzle planes. According to the above embodiment of the method, the amount of substance to be injected can be shifted continuously from a first nozzle plane to a further nozzle plane, i. that it is infinitely reduced in a first horizontal nozzle level and simultaneously increased continuously on a further horizontal nozzle level. This makes it possible to respond optimally to temporal temperature fluctuations in the case of SNCR methods, which is not possible in the case of an abrupt nozzle level changeover and the resulting undefined transition states in this manner.

The invention further makes it possible to carry out said stepless change or displacement very quickly. Among other things, this is made possible by the fact that, according to the method according to the invention, a central dilution of the substance, as is carried out, for example, in the two-substance nozzle-based SNCR method, is not necessary is. Thus, the present invention allows itself to adequately respond to short-term temperature changes.

As a rule, the total quantity of reducing agent to be injected is regulated as a function of the nitrogen oxide content present in the flue gas after the boiler. For this purpose, means for determining the nitrogen oxide content are arranged downstream of the boiler. The determined nitrogen oxide content is compared to control the required total amount of reducing agent with a predetermined setpoint.

In order to ensure the highest possible nitrogen oxide reduction rate with minimal consumption of reducing agent, the amount of reducing agent to be passed to the respective nozzle is generally controlled as a function of the temperature profile in the boiler. Thus, it can be ensured that the reducing agent is mainly injected where the optimal temperature range for the reduction exists.

For the determination of the temperature profile is in principle any temperature measuring device in question, which is suitable for this purpose. Corresponding temperature measuring devices are known to the person skilled in the art. So-called radiation pyrometers, which allow an accurate measurement of the gas temperature, are particularly preferably used as temperature measuring devices.

The temperature gradient falling in the flow direction of the flue gas can be determined by means of an algorithm known to the person skilled in the art. By determining the temperature at a defined point, the be determined in the boiler temperature profile in the flow direction.

In addition, by determining the temperature at a further point, it is possible to determine the temperature profile also transversely to the flow direction via interpolation between the two temperature points. Thus, determining the temperature at two different points allows one to determine the entire temperature profile in two dimensions. Accordingly, the temperature profile in the boiler is particularly preferably determined by means of at least two temperature measuring devices. It is conceivable, for example, that at least two temperature measuring devices are provided per distributor.

The amount of locally required reducing agent also depends on the local flow rate, since at a high flow rate more reducing agent is needed than at a low flow rate. In this regard, it is conceivable additionally to regulate the amount of reducing agent to be passed to the respective nozzle as a function of the flow velocity distribution of the flue gas in the boiler. It is usually sufficient to determine the flow rate once.

The adjustment of the reducing agent quantity to be conducted to the individual nozzles takes place according to the invention in the distributor. Specifically, the metered reducing agent is supplied to the propellant stream and that according to the invention before the branching of the line leading to the respective nozzle. Thus, therefore, before the branching there is a mixture containing the blowing agent and the reducing agent.

In addition, according to the invention, a distribution of the amount of blowing agent takes place. In this case, a first amount of blowing agent is set for the nozzles acted upon by the reducing agent, while a second blowing agent quantity for cooling the said nozzles is set for the nozzles not acted upon by the reducing agent.

For distribution, the means known to those skilled in the art are suitable, which are suitable for the corresponding purposes. For example, the amount of reducing agent or blowing agent can be adjusted by means of control valves.

The reducing agent is preferably in aqueous solution. In the case of dissolved ammonia is therefore called ammonia water. Preferably, about a commercial ammonia solution is used, e.g. a 25% ammonia solution. However, any other solution is also conceivable which liberates ammonia at the temperatures present in the vessel, e.g. a solution containing an ammonium salt such as ammonium carbonate, ammonium formate and / or ammonium oxalate.

The blowing agent used is preferably air or steam.

If, for example, air is used as propellant, then the ammonia water to be injected is atomised into droplets when it is fed into the air stream and then distributed immediately afterwards to the individual nozzles or to the respective lines leading to the nozzles. Any coalescing droplets are atomized again in the sonic nozzle.

In the treated with the ammonia water nozzle nozzle pressure of about 1 to 5 bar is usually set so that the ammonia water or evaporating in the boiler ammonia can penetrate far enough into the flue gas stream. Those nozzles that are not in operation, i. are not acted upon with ammonia, are flowed through for cooling with a smaller amount of air. Before the branching of the lines leading to the respective nozzles thus a first air flow is adjusted for the nozzles acted upon by the ammonia water, while for those nozzles which are not in operation, another, compared to the first air flow lower air flow is set.

The branching from the manifold, leading to the respective nozzles lines are usually in the form of tubes, as they are known in the art for the corresponding purposes. As nozzles, for example, round jet nozzles or fan nozzles can be used, with other suitable nozzles are known in the art. In particular, an alternate arrangement of round jet nozzles with fan nozzles is conceivable.

• Fig. 1 eine rein schematische Darstellung einer einem Kessel einer Müllverbrennungsanlage zugeordneten erfindungsgemässen Vorrichtung ist, welche insgesamt neun Düsen umfasst, die auf drei Düsenebenen verteilt sind; und
• Fig. 2 ein Diagramm ist, in dem in Abhängigkeit der Kesselhöhe (Ordinate) der jeweilige Temperaturbereich (Abszisse) aufgetragen ist und die resultierende Fläche der Temperaturverteilung im Kessel in Überlagerung mit dem dunkel schraffiert dargestellten, optimalen Temperaturbereich des SCNR-Verfahrens aufgezeichnet ist.

The invention further relates to an apparatus for carrying out the method described above. The method and the device will be further explained with reference to the appended figures, of which

• Fig. 1 a purely schematic representation of a device associated with a boiler of a waste incineration plant according to the invention, which comprises a total of nine nozzles, which are distributed on three nozzle levels; and
• Fig. 2 a diagram is in which, depending on the boiler height (ordinate) the respective temperature range (Abscissa) is plotted and the resulting area of the temperature distribution in the vessel is recorded in superimposition with the dark shaded optimum temperature range of the SCNR process.

According to Fig. 1 the device 2 is associated with a boiler 4 of a waste incineration plant, which is traversed by the flue gas combustion. The flow direction of the flue gas is shown by means of parallel arrows 6.

The device 2 comprises a distributor 8. In this opens a supply line 10 for supplying a substance, in particular a reducing agent for the reduction of nitrogen oxides, and a supply line 12 for supplying a propellant. A total of nine lines 14a-i branch off from the distributor 8, of which three lines 14a, 14b, 14c each lead to a nozzle 16a, 16b or 16c of a first horizontal nozzle plane, three lines 14d, 14e, 14f to a respective nozzle 16d, 16e 16f of a second horizontal nozzle plane and three lines 14g, 14h, 14i lead to a respective nozzle 16g, 16h or 16i of a third horizontal nozzle plane. In each case, three nozzles 14a, 14d, 14g and 14b, 14e, 14h and 14c, 14f, 14i are arranged one above the other and thus each in a vertical nozzle plane.

The distributor is also associated with two temperature measuring devices 18a, 18b, based on which the present in the boiler 4 temperature profile - as described above - is determined continuously in two dimensions.

When using the device in a SNCR method these are usually also means for determining the assigned to the boiler present nitrogen oxide content (not shown), by means of which the total amount is einzudüsendem reducing agent.

Depending on the temperature profile, the quantity of reducing agent to be passed to the respective nozzle 16a-i is set in distributor 2 and combined with the blowing agent. The propellant flow containing the metered amount of reducing agent is subsequently conducted via the respective line 14a-i to the nozzle 16a-i at the desired injection point where it is injected into the boiler 4. The non-pressurized with the reducing agent nozzles are cooled with a set also in the distributor 8, lower amount of blowing agent.

The reducing agents used in the described SNCR process are preferably ammonia water, which is supplied to a propellant stream of air or steam. The distribution of the ammonia water takes place in such a way that it is injected in the optimum temperature range of 850 to 950 ° C. for the reduction of nitrogen oxides.

This concept is in Fig. 2 illustrates further, according to which the temperature distribution for conventional boiler usually from about 1000 to 1100 ° C in the lowest part of the boiler, ie at about 2 to 4 m above the grate, to about 700 to 900 ° C in the uppermost region of the boiler, ie at about 20 to 40 m above the grid. The region overlapping with the dark shaded, optimal temperature range of the SNCR process corresponds to that region of the boiler in which the nozzles distributed on the three horizontal nozzle planes are for optimal reduction of nitrogen oxides should be in operation.

The location of these horizontal nozzle levels in the boiler is in Fig. 2 represented by dashed arrows. The nozzle levels are arranged at irregular intervals from each other. Depending on the boiler but also a regular arrangement of the nozzle levels is conceivable.

Thus, the diagram for a corresponding boiler provides information about the arrangement of the nozzle levels to be selected in order to ensure injection in the preferred temperature range.

example

A concrete embodiment for the metered addition of ammonia water for an SNCR process is shown in Table 1. According to this embodiment, the boiler is divided into four boiler sectors, namely a rear left (HL) boiler sector, a rear right (HR) boiler sector, a left front boiler sector (VL) and a front right boiler (VR) sector. The nozzles are arranged in the boiler sectors on three horizontal nozzle levels.

For each of the boiler sectors, the temperature is determined by means of a radiation pyrometer at a given point. By multiplication with a corresponding factor given in Table 1, the temperature of the individual nozzle levels in the boiler sectors can be determined on the basis of the respective measured temperature.

10 kg of ammonia water (25% ammonia solution) / h are injected per boiler sector. The distribution of the ammonia water to the individual nozzle levels is carried out as a function of the calculated temperature profile in such a way that ammonia water is mainly injected there where the optimal temperature range for the reduction of nitric oxide is present.

As can be seen from Table 1, for the nozzles supplied with ammonia water, a driving / cooling air amount of 100 kg / h is set, while for the non-treated with ammonia water nozzles, a reduced blowing / cooling air amount of 50 kg / h for cooling the said Nozzle is set. Table 1 HL MR VL VR Total Display Radiation Pyrometer (T) ° C 910 880 850 860 Temperature on 1st level (calculated 1.11 * T) ° C 1010 977 944 955 Temperature on 2nd level (Calculates 1.04 * T) ° C 946 915 884 894 Temperature on 3rd level (Calculates 0.97 * T) ° C 883 854 825 834 Dosage 25% ammonia water on 1st level kg / h 0.0 0.0 0.3 0.0 Dosage 25% ammonia water on 2nd level kg / h 0.0 1.4 9.7 7.3 40 Dosage 25% ammonia water on 3rd level kg / h 10.0 8.6 0.0 2.7 Driving / cooling air on 1st level kg / h 50 50 100 50 Driving / cooling air on 2nd level kg / h 50 100 100 100 950 Driving / cooling air on 3rd level kg / h 100 100 50 100

Claims (9)

1. Method for injecting a substance into a boiler (4) of a waste incineration plant, using a gaseous propellant, the substance being conducted, starting from at least one distributor (8), via lines (14a-i) which branch off from the distributor (8), in each case to a nozzle (16a-i) which is assigned to the respective line (14a-i) and by means of which the substance and the propellant are injected into the boiler (4), and the substance quantity to be conducted to the respective nozzle (16a-i) being set in the distributor (8), wherein the substance and the propellant are combined upstream of the branch-off of the respective lines (14a-i), and the substance is a reducing agent for the reduction of nitrogen oxides, characterized in that a first propellant quantity is set for the nozzles acted upon by the reducing agent, while, for the nozzles not acted upon by the reducing agent, a second propellant quantity is set for cooling said nozzles.
2. Method as claimed in claim 1, characterized in that, in the event of a change in the setting of the substance quantity to be conducted to the respective nozzle (16a-i), this change is carried out infinitely variably.
3. Method as claimed in claim 1 or 2, characterized in that the substance is ammonia or urea.
4. Method as claimed in claims 1 to 3, characterized in that the overall quantity of reducing agent to be injected is regulated as a function of the nitrogen oxide content, present downstream of the boiler (4), in the flue gas.
5. Method as claimed in claims 1 to 4, characterized in that the quantity of reducing agent to be conducted to the respective nozzle (16a-i) is regulated as a function of the temperature profile in the boiler (4).
6. Method as claimed in claim 5, characterized in that the temperature profile in the boiler is determined by means of at least two temperature measuring apparatuses (18a, b).
7. Method as claimed in claim 6, characterized in that the temperature measuring apparatuses (18a, b) used are radiation pyrometers.
8. Method as claimed in claims 1 to 7, characterized in that the propellant used is air or steam.
9. Apparatus for carrying out the method as claimed in claims 1 to 8, comprising at least one distributor (8), from which lines (14a-i) branch off which lead in each case to a nozzle (16a-i) for injecting the substance and the propellant into the boiler (4), the distributor (8) being assigned means for setting the substance quantity to be conducted to the respective nozzle (16a-i), wherein the apparatus comprises means for combining the substance and the propellant upstream of the branch-off of the respective line (14a-i) from the distributor (8), characterized in that the apparatus is configured in such a way as to set a first propellant quantity for the nozzles acted upon by the reducing agent and to set a second propellant quantity for the nozzles not acted upon by the reducing agent for their cooling.

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