DE4435103A1 - Process and device to improve the effectivity of catalytic redn. devices - Google Patents

Abstract

Process to improve the effectivity of SCR (Selective Catalytic Redn.) De-NOx devices (1) by automatic matching of the amt. of redn. material injected to the local NOx concn. in the flue gas stream of combustion devices. The supply of redn. material to the nozzles or groups of these (12,14,16,18), which are distributed upstream of the catalyst arrangement (4) across the flue gas channel cross-section (2) and are fixed to the redn. material supply (32), each individually controlled according to the measured local NOx and redn. material concn. in the channel or the difference of both. Also claimed is a device to carry out the above process.

Description

The invention relates to a method and a system for improving the effectiveness of SCR DeNO _x systems. DeNO _x systems are systems that preferably break down nitrogen oxides carried in gases. The abbreviation SCR stands for Selective Catalytic Reduction.

The exhaust gases generated during combustion processes also contain various nitrogen oxides. These are considered environmental toxins and also have toxic effects on the human and animal organism. In power plant operations, it is common practice to convert these nitrogen oxides into the environmentally friendly and harmless products nitrogen (N₂) and water (H₂O). For this purpose, the SCR process has established itself worldwide. (Compare the German patent applications P 43 09 891.6, P 43 10 926.8 and P 43 15 278.3). A suitable reducing agent, generally ammonia, is added to the flue gas and this NH 3 flue gas mixture is contacted at 300 ° C to 450 ° C with so-called SCR-DeNO _x catalysts. For the complete transformation, it is necessary that the reactants NH 3 and NO _{x are present} on the SCR catalyst in the correct stoichiometric ratio.

In order to set the correct stoichiometric ratio over the entire cross-section of the flue gas duct, it is known in power plants to install pipe grids equipped with injection nozzles in the flue gas ducts, via which the reducing agent is distributed relatively evenly over the flue gas duct and injected into the flue gas flow. This injection device is generally located a few meters upstream of the SCR catalysts of the DeNO _x system, so that the injected reducing agent - generally ammonia - has time to mix evenly with the flue gas and the SCR catalysts from one evenly with ammonia flowed through flue gas.

In addition, because the velocity profile of the flue gas flow in the flue gas ducts is uneven due to the geometrical conditions of the flue gas duct and because the NO _x profile across the flue gas duct cross-section is uneven, it is known to use throttle points in front of the individual injection nozzles or injection nozzle groups switch, which are set manually by hand during the commissioning of the power plant so that despite different flow velocities or NO _x concentrations in the flue gas duct, a uniform ratio of reducing agent, generally NH₃, to NO _{x is} established across the entire cross section. This setting of the individual throttle positions is usually carried out at the nominal load of the power plant. It is quite time-consuming, because every change in the throughput in one nozzle also has an effect on neighboring nozzles of the injection system and, because of the mixing effect, also has an effect on adjacent flow threads of the flue gas.

Now it has been shown that not only the total amount of NO _x in the flue gas and thus the stoichiometrically required injection quantity of reducing agent or NH 3 changes, but also that the local flow conditions in the flue gas duct are changed . This creates, even with an overall adjusted amount of reducing agent injector, both current filaments in which too much in relation to the NO _x content and current filaments in which too little reducing agent is contained. This leads to problems in downstream system parts such as air preheaters or flue gas desulfurization systems.

Furthermore, it is known that by dust accumulation on the Injectors and dust deposits in the flue gas duct  local flow changes occur over time, which the Originally set even dosing of the Reduk agents in the flue gas change over time and so zones with too much and too little reducing agent in the flue gas let others arise. So far, this has only been possible through renewed manual setting of all throttling points can be corrected. This was time consuming and costly.

The invention is therefore based on the object to show a way, such as without a cumbersome readjustment of the throttle assigned to the injection nozzles for the reducing agent, the locally to the NO _x amount in the flue gas is fitted stoichiometric reduction amount injected and how this injection amount without great effort can be continuously adapted to changing local conditions. At the same time, this stoichiometric correct injection quantity of the reducing agent should be adaptable to the temporally and locally changing conditions in the flue gas duct with little effort when the combustion system changes load.

With regard to the method, this object is achieved in that the reducing agent injection quantity is automatically adapted to the local NO _x concentration in the flue gas flow from combustion systems, in which the inflow of reducing agents is arranged in the upstream of the catalyst arrangement over the cross section of the flue gas duct Injection nozzles or nozzle groups connected to a reducing agent supply are controlled individually depending on the measured local NO _x and reducing agent concentration in the flue gas duct or the difference between the two. For this purpose, a quantity of reducing agent is injected locally through the respective injection nozzle, which is adapted to the instantaneous NO _x concentration in the flue gas in the area of the responsible sensor. The result is that the amount of reducing agent adapts temporally and locally to the NO _x amount and thus also follows the complex, temporal and local changes in the flue gas composition when the incinerator is changed.

With regard to the arrangement, this object is achieved in that in the flue gas channel upstream of the catalyst arrangement of the SCR DeNO _x system, injection nozzles for reducing agents are arranged uniformly over the cross section of the flue gas channel and in the flue gas channel between the level of the injectors and the catalyst arrangement sensors are the reductant and / or NO _x measurement or egg ner difference measurement NO _x reducing agent concentration over the cross section of the flue gas channel are arranged distributed, the latter influx via one or more Signalauswertesy stems to control means for influencing the reducing agent or to the individual injectors Injector groups are connected. This will create an arrangement that not only injects the reducing agent evenly distributed over the cross sections of the flue gas duct, but also adjusts this quantity of injection both overall as a function of the NO _x content of the flue gas and locally individually to the current flow conditions in the flue gas duct.

The reducing agent and also NO _x concentration in the flue gas can advantageously be measured by sensors for NO _x and / or reducing agent or the difference from both arranged in the flue gas duct.

In a particularly advantageous embodiment of the invention the sensors each reduce the supply of reducing agent to one in arranged the same current path in the flue gas duct Injection nozzle or injection nozzle group via an evaluation control level. With this arrangement, the required Reduce the catalyst volume by 5 to 10% or the catalyst Extend gate life significantly.  

It can be cost effective if the injectors are used for that Reducing agents at least partially in groups captured and via a sensor-controlled actuator for each Reducing agent supply can be supplied with reducing agent. As a result, both sensors, actuators and evaluation fen saved.

In an advantageous embodiment of the invention, the catalyst assembly may also downstream tionsmittel- sensors for reductive or NO _x measurement or a differential measurement NO _x -Reduktionsmittelkonzentration each case over the cross section of the flue gas channel are arranged distributed and influencing via one or more Signalauswertsysteme to the control means to Be of the reducing agent flow to the individual injection nozzles or injection nozzle groups. This has the advantage that there are measured values of the actual state of the flue gas behind the catalytic converter level, which can also detect defects in the catalytic converter arrangement.

A more prompt and at the same time more precise tracking of the injected amount of reducing agent to the actual requirement can be achieved if sensors for reductant and / or NO _x measurement or a differential measurement NO _x reducing agent concentration between the individual catalyst layers are arranged and one or several signal evaluation systems are connected to the control means for influencing the reducing agent inflow to the individual injection nozzles or injection nozzle groups. As a result, an impending discrepancy is recognized and compensated for more quickly.

Further advantageous embodiments of the invention are the other subclaims.

Exemplary embodiments are explained with the aid of the figures. It demonstrate:  

Fig. 1 shows a schematic cross section through a flue gas channel with a DeNO _x plant,

Fig. 2 shows a section along the line II-II of Fig. 1,

Fig. 3 shows a schematic cross section of another injection device for a reducing agent,

Fig. 4 shows a section along the line IV-IV of Fig. 3,

Fig. 5 shows a cross section through the gas composition in flue gas channel at a plant according to the prior art, at rated load,

. Fig. 6 is a cross section through the gas composition in flue gas channel of Figure 5 drive according to the invention Ver at rated load;

Fig. 7 shows a cross section through the gas composition in the flue gas duct of Fig. 5 at partial load according to the prior art and

Fig. 8 shows a cross section through the gas composition in the flue gas duct of Fig. 7 at partial load in the method according to the Invention.

Fig. 1 shows a schematic representation of an _x in the range of 1 DeNO Plant cut flue gas channel 2. The DeNO _x system is located with its catalyst arrangement 4 in a downward branch 6 of the flue gas duct 2 , where, however, the upstream injector arrangement 8 for the reducing agent - in the present case for ammonia - is installed in a horizontal branch 10 of the flue gas duct 2 . Such kinked flue gas ducts with catalyst arrangements arranged in the downward branch are customary in power plants, because the gas ducts in the catalyst arrangement do not tend to become clogged by entrained dust particles with vertical gas flow, as with horizontal gas guidance.

In the illustration in FIG. 1, a total of four injection nozzles 12 , 14 , 16 , 18 for ammonia can be seen, which are on a common ge, through a gas-tight partition 20 in two sections 22 , 24 divided supply line 26 are ruled out. The two sections of the supply line 26 are each connected to an ammonia line 32 by a separate supply line 28 , 30 . Each supply line contains its own motorized control valve 34 , 36 . Between the injection nozzles 12 , 14 , 16 , 18 and the catalyst arrangement 4 , two groups of two sensors 37 , 38 and 40 , 41 can be seen. In the exemplary embodiment, these sensors detect the NH 3 content or the NO _x content in the flue gas. Of these four sensors, a group of two sensors is assigned to the upper section of the flue gas duct 2 or the lower section of the flue gas duct in FIG. 1. In the downward branch 6 of the flue gas duct 2 in the flow direction behind the catalyst arrangement 4 , two groups of four sensors 43 , 44 , 45 , 46 and 47 , 48 , 49 , 50 for detecting ammonia and NO _{x are again} to be recognized, one of which Group of sensors 43 , 44 , 45 , 46 the path of the flue gas in the horizontal section of the flue gas channel 2, the two upper injectors 12 , 14 and the other group of sensors 47 , 48 , 59 , 60 the path of the flue gas of the im horizontal section of the flue gas channel 2 is assigned to the lower two injection nozzles 16 , 18 .

Like the sectional view of FIG. 1 shows, there is a Kata lysatoranordnung of an upper catalyst layer 52 and lower egg ner catalyst layer 54, both of c region by a Zvi 56 are separated from each other. In this space two groups of four sensors 58 , 59 , 60 , 61 and 62 , 63 , 64 , 65 for ammonia and NO _x can be seen again. The signal lines 66 of all sensors which are assigned to the flue gas path in which the upper nozzle group is also located are in the evaluation stage 68 and the signal lines 70 of all sensors which are assigned to the flow path of the flue gas to which the lower nozzle group is also assigned, are connected to evaluation stage 72 . The evaluation stage 68 is connected with a control line to the engine valve 34 , which controls the flow through the supply line 28 leading to the upper nozzle group, and the evaluation stage 72 is connected via a control line to the engine valve 36 , which controls the flow through the supply line 30 , which leads to the lower nozzle group.

Like the sectional view shown in Fig. 2 along the line II-II of Fig. 1, the flue gas channel 2 are across the width upper and lower supply lines with each with four injection nozzles 12, 14, 16, 18 and 80 to 99 be set supply lines 26 , 100 , 102 , 104 , 106 , 108 see easily. Each of these supply lines, like the supply lines 28 and 30 in FIG. 1, is assigned a motor-adjustable control valve 36 , 110 , 112 , 114 , 116 , 118 for the control of the reducing agent metering. The sensor groups Sen, which can be seen in FIG. 1 in the drawing plane, are repeated together with the associated evaluation stages, not shown here, in the width of the flue gas duct.

During operation of the combustion system, the flue gases flow in the illustration of FIG. 1 from left to right through the ho rizontalen branch 10 of the flue 2 and then be deflected at guide plates 120 by 90 ° downwards and so then flow through the upper and lower layers 52 , 54 of the cata- tor arrangement 4 and on the sensor groups 43- 50 behind it further down. When passing through the upper and lower injection nozzles 12 , 14 , 16 , 18 , the NO _x -containing flue gas is enriched with a reducing agent, here ammonia, and the two sensor groups behind these injection nozzles measure the ammonia or NO _x content of the flue gas. In the present case, they form a signal which corresponds to the value concentration NO _x - concentration NH₃. This signal corresponds approximately to the desired residual NO _x value behind the catalyst arrangement. The respective evaluation stages 68 , 72 for the upper and lower sensor groups 37 , 38 and 40 , 41 are set so that they open the motor-controlled control valves 34 , 36 on the supply lines 28 , 30 somewhat when the ammonia content in the flue gas is below the stoichiometric Amount that is required to reduce the nitrogen oxides measured in the flue gas and vice versa. When the flue gas channel 2 continues to flow through, the flue gases enriched with ammonia are deflected downward on the guide plates 120 and flow through the catalyst arrangement 4 from top to bottom. In the illustration of FIG. 1 below the catalyst arrangement they flow through the arranged there sensor groups 43 to 46 and 47 to 50, which in turn measure the ammonia and NO _x content of the flue gases. The measurement result is passed on via the signal line 66 , 70 to the two evaluation stages 68 , 72 . As soon as an excess of ammonia is measured, the control valve responsible for this path of the flue gas flow is throttled further, and if an excess of NO _x and no ammonia is detected, the corresponding control valve is opened a little further. In this way, changes in the NO _x content in the flue gas, which are attributable to a change in performance of the combustion system, are automatically taken into account. Because of the - shown in Fig. 1 - division into a lower and an upper strand also local irregularities of the NO _x content in the flue gas as they can arise from displacement and turbulence of the smoke gas flow, for these two flue gas strands separately compensated . This also applies to malfunctions in the ammonia injection, which are generated either by partial blockages of the injection nozzles and / or by changing the flow conditions in the flue gas duct.

In the illustration of FIG. 1 can be seen in the intermediate space 56 between the upper and lower catalyst layer further sensors 58 to 65 for ammonia and NO _x. These can, especially when changing the performance of the incinerator, changes in the ammonia and NO _x content even before the catalytic converter arrangement downstream sensors 43 to 50 determine and thus contribute to countermeasures by the control valves at an earlier point in time. This previous countermeasure can also dampen or even avoid excessive regulation.

In FIGS. 3 and 4 is another type of the assignment of A spray nozzles 124 to 139 to the individual power supply strands 140, 142, 144, 146, 148, 150 nen to erken in the flue gas channel 122. Each supply line is provided with a motorized control valve 152 to 157 , which - as shown in FIG. 1 - is controlled by an evaluation stage 68 , 72 which is connected to the sensors assigned to the same flue gas path. In this case, the sensors or sensor groups must be arranged strictly in the flue gas path of the respective injectors and connected via the evaluation stage to the respective control valves which are responsible for these injectors. This type of matrix-like assignment of the injection nozzles to the individual supply lines running at right angles to one another makes it possible to apply ammonia to adjacent nozzles to different extents. Such an injector field allows a better adjustment of the metered amount of ammonia over the cross section of the flue gas duct to under different NO _x concentrations than when the injectors are assigned to the individual supply lines in the flue gas duct as shown in FIGS . 1 and 2.

FIGS. 5 and 6 show a comparison of the flue gas together reduction in cross section of the flue gas channel 161, 167 on either side of a catalytic converter assembly 163, 165. In FIG. 5, a flue gas channel is schematically indicated 161 and shown in FIG. 6, a flue gas duct 167, where the two flows the flue gas from top to bottom. In the upper area of the flue gas duct, an injection device 8 for ammonia is indicated in both figures. Below this, the NO _x profile 160 is schematically drawn over the cross section of the flue gas duct and below it the ammonia profile 162 or 168 over the cross section of the flue gas duct in each case above the catalytic converter arrangement 163 or 165 . Below the catalyst arrangement, the NO _x profile 164 or 170 and then the ammonia profile 166 or 172 are again displayed. In FIG. 5, showing the conditions in a plant according to the prior art, the NO _x -profile 160 is upstream of the catalyst arrangement 163 over the cross-section of the flue gas channel across a wavy line, which caused for example by a different operation of the burner in the boiler can be.

The NH₃ profile 162 has been manually adjusted to this NO _x profile 160 when the power plant is started up under nominal load, so that it essentially follows this NO _x profile. To make sure that no ammonia escapes from the chimney in the event of changes in performance or other malfunctions, the ammonia profile 162 has been set somewhat substoichiometrically. It follows that a substantially balanced, reduced NO _x profile 164 and a very low, substantially balanced ammonia profile 166 can be detected behind the catalyst arrangement 163 . In the ge marked with the circle A in profile 162 in FIG. 5, however, an injection nozzle is partly set by flying dust for explanation. This disturbance has an effect behind the catalytic converter arrangement in that the NO _x profile 164 here shows an inverse disturbance and that the ammonia profile 166 has a maximum inverse to the NO _x profile. Such a local emission of ammonia is very undesirable, since it has a very disruptive effect on downstream system parts.

In the exemplary embodiment in FIG. 6, which shows the situation comparable to that in FIG. 5 in a system according to the invention, the sensors 169 are indicated between the ammonia injection device 8 and the NO _x profile 160 , which have the NO _x or the ammonia profile 168 measure up. These sensors therefore measure the disturbance of the ammonia profile assumed in circle A in this exemplary embodiment at the same location as in FIG. 5 and can therefore compensate this disturbance by testing the corresponding control valves accordingly. As a result, behind the catalyst arrangement 165, despite the same fault as in FIG. 5, a completely balanced NO _x profile 170 is created and the ammonia profile 172 is minimized. Since in this arrangement according to the invention a constant metering of ammonia is guaranteed corresponding to the NO _x profile, the catalyst arrangement 165 can also be reduced in volume by approximately 5% compared to embodiment 5 without having to be afraid getting excessive ammonia breakthroughs at any point.

FIGS. 7 and 8 correspond to Figs. 5 and 6 and zei gene, only the ratios, the plants at the same force would result at part load. It can be seen in FIG. 7 - which illustrates the prior art - that at partial load the NO _x profile 174 is significantly more uneven compared to that state at full load and one can see the fault point at A in the ammonia profile 162 , which is already shown in FIG. 5 was presented. Since the setting of the throttle points on the supply lines during the transition to part-load operation that was carried out during commissioning has not been changed, the ammonia profile is unchanged from that in FIG. 5. As a result, one gets behind the catalyst arrangement 163 a strongly distorted NO _x profile 176 and an even more distorted ammonia profile 178 , which because of the flue gas flowing in front of the catalyst arrangement with a locally lower NO _x concentration behind the catalyst arrangement also has a very large amount increased ammonia emissions.

In the inventive equipment of the flue gas duct 167 with a sensor arrangement, which is indicated in Fig. 8 under the Ammo niakeindüsvorrichtung 8 , not only the fault point at A, which is caused by the nozzle partially covered with dust, is compensated, but also Ammonia output from the nozzles in the remaining areas adapted to the inflowing, modified NO _x profile 174 . As a result of this adjusted ammonia profile 180 , the NO _x profile 182 behind the catalytic converter arrangement 165 is again strongly compensated and the ammonia profile 187 is minimized as that at full load in FIG. 6. Here too, because of the better stoichiometric adaptation of the reducing agent, Ammonia, on which the NO _x contents of the flue gas are worked on with a catalyst volume reduced by approximately 10%.

This has been assumed in the present exemplary embodiments went that ammonia is used as a reducing agent. The invention can equally well be used with other Reduk tion agents, such as CO, H₂ or convertible into ammonia fe, such as urea, are used. The procedure is also just as well for systems with horizontally arranged kata lysator channels - as they occur with dust-free gases - applicable.

Claims (11)

1.Procedure for improving the effectiveness of SCR-DeNO _x systems ( 1 ) by automatically adapting the amount of reducing agent to the local NO _x concentration in the flue gas stream from combustion systems, in which the flow of reducing agent to the upstream of the catalyst arrangement ( 4 ) over the cross-section of the flue gas duct ( 2 , 122 ) distributed on ordered, to a reducing agent supply ( 32 ) connected injection nozzles or injection nozzle groups ( 12 , 14 , 16 , 18 , 80 to 99 , 124 to 139 ) individually depending on the Measured local NO _x and reducing agent concentration or the difference between the two in the flue gas duct is controlled. 2. The method according to claim 1, characterized in that the Re duktionsmittel- and NO _x concentration in the flue gas from in the flue gas channel ( 2 , 122 ) arranged sensors ( 37 to 41 , 43 to 50 , 58 to 65 , 169 ) for NO _x and / or reducing agent or the difference between the two is measured. 3. The method according to claim 2, characterized in that the sen sensors ( 37 to 41 , 43 to 50 , 58 to 65 , 169 ) each have the re duction agent supply to an in the same current path in the flue gas duct ( 2 , 122 ) arranged injector or Control a spray nozzle group ( 12 , 14 , 16 , 18 , 80 to 99 , 124 to 139 ) via an evaluation stage ( 68 , 72 ). 4. The method according to any one of claims 1 to 3, characterized in that the one injection nozzles ( 12 , 14 , 16 , 18 , 80 to 99 , 124 to 139 ) for the reducing agent at least partially summarized in groups via a sensor-controlled adjusting means ( 34 , 36 , 110 , 112 , 114 , 116 , 118 , 152 to 157 ) for the reducing agents are supplied with reducing agents. 5. Plant for performing the method according to one of claims 1 to 4, characterized in that in the flue gas channel ( 2 , 122 ) upstream of the catalyst arrangement of the SCR-DeNO _x system ( 1 ) injection nozzles ( 12 , 14 , 16 , 18th , 80 to 99 , 124 to 139 ) for the reducing agent are arranged uniformly distributed over the cross section of the flue gas duct and in the flue gas duct between the level of the injection nozzles and the catalyst arrangement ( 4 ) sensors ( 37 to 41 , 169 ) for reducing agent and / or NO _x measurement or a differential measurement NO _x reducing agent concentration are distributed over the cross section of the flue gas duct, the latter via one or more signal evaluation systems ( 68 , 72 ) to control means ( 36 , 34 , 110 , 112 , 114 , 116 , 118 , 152 to 157 ) for influencing the reducing agent inflow to the individual injection nozzles or injection nozzle groups are connected. 6. Arrangement according to claim 5, characterized in that also downstream of the catalyst arrangement ( 4 ) sensors ( 43 to 50 ) for reducing agent or NO _x measurement or a differential measurement NO _x reducing agent concentration in each case over the cross section of the flue gas duct ( 2 , 122 ) distributed and arranged via one or more signal evaluation systems ( 68 , 72 ) to the control means ( 34 , 36 , 110 , 112 , 114 , 116 , 118 , 152 to 157 ) for influencing the reducing agent inflow to the individual injection nozzles or injection nozzle groups are connected. 7. An arrangement according to claim 5 or 6, characterized in that sensors (58 to 65) _x to the reductant and / or NO measurement or a differential measurement NO _x -Reduktionsmittelkonzentration also between the individual catalyst levels (52, 54) are arranged and are connected via one or more signal evaluation systems ( 68 , 72 ) to the control means ( 34 , 36 , 110 , 112 , 114 , 116 , 118 , 152 to 157 ) for influencing the reducing agent flow to the individual injectors or injectors groups. 8. Arrangement according to one of claims 5 to 7, characterized in that the individual sensors ( 37 to 41 , 43 to 50 , 58 to 65 , 169 ) each because of a reducing agent injection nozzle or injection nozzle group ( 12 , 14 , 16 , 18 , 80 to 99 , 124 to 139 ), which is arranged in the same current path in the flue gas duct ( 2 , 122 ), in that they each have a signal evaluation system ( 68 , 72 ) on the control means ( 34 , 36 , 110 , 112 , 114 , 116 , 118 , 152 to 157 ) are connected for the reducing agent supply. 9. Arrangement according to one of claims 5 to 8, characterized in that as Re Ductant ammonia (NH₃) is used. 10. Arrangement according to one of claims 5 to 9, characterized in that the set reducing agent and NO _x -detecting sensors are used ver. 11. Arrangement according to one of claims 5 to 10, characterized in that the control means ( 34 , 36 , 110 , 112 , 114 , 116 , 118 , 152 to 157 ) for influencing the reducing agent flow to the injection nozzles or groups of injection nozzles ( 12th , 14 , 16 , 18 , 80 to 99 , 124 to 139 ) are electromotive, pneumatic or hydraulic continuously adjustable valves.