JPH04358521A - Denitration device and its operation method - Google Patents

Abstract

PURPOSE:To enhance the decomposition rate of a solid nitrogen containing component and the conversion rate to ammonia by sensing the ammonia concentration at an outlet of a reducer gasification means and/or the concentration of a nitrogen oxide in exhaust gas and controlling the reducer feeding amount to be fed to the reduer gasification means and the reducer decomposition reaction temperature therein. CONSTITUTION:Urea or the like is decomposed on a decomposition catalyst layer 3 in the atmosphere containing water vapor to prepare ammonia to be used for denitration of exhaust gas. At that time, for the purpose of decomposing a reducer such as urea and converting the same securely to ammonia, at least it is required to control the reducer feeding amount to a reducer gasification means 4 and the reducer decomposition reaction temperature therein. For that purpose, the ammonia concentration at the outlet of a reducer gasification means 4 and/or the concentration of a hydrogen oxide in exhaust gas are sensed and controlled. As a result, the decomposition rate of a solid hydrogen containing compound and the conversion efficiency to ammonia are enhanced and a denitration device or superior response to the variation of exhaust gas condition is provided.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to flue gas denitrification technology using a catalytic reduction method, and in particular to the denitrification reaction using a solid nitrogen-containing compound that is safe and easy to handle as a raw material for a reducing agent. This invention relates to a suitable denitrification device and its operating method.

0002

[Prior Art] Nitrogen oxides (NOx) from fixed sources such as thermal power plants are substances that cause photochemical smog.
The selective catalytic reduction method using a reducing agent is widely used.

[0003] Recently, cogeneration systems using diesel engines, gas turbines, etc. have been increasing mainly in urban areas. As NOx emission regulations are being tightened for this cogeneration system, there is an urgent need to install exhaust gas denitrification equipment. The use of liquefied ammonia as in large-scale plants is inappropriate for such consumer denitrification equipment. Therefore, as an alternative reducing agent for liquefied ammonium, a method using solid nitrogen-containing compounds such as urea, melamine, biuret, cyanuric acid, and ammonium carbonate, which generate ammonia species by decomposition, is attracting attention.

0004

Problem to be Solved by the Invention When using the solid nitrogen-containing compound described above as an alternative reducing agent for liquefied ammonia, a technical problem is how to efficiently decompose it and convert it into ammonia. For example, if the exhaust gas composition changes due to changes in the load of a diesel engine, and the conditions for the decomposition reaction of nitrogen-containing compounds do not quickly follow this change, the decomposition rate of solid nitrogen-containing compounds and the conversion rate to ammonia will decrease.
There has been a problem in that solid nitrogen-containing compounds and their converted substances other than ammonia are deposited as scale in the reducing agent supply device or on the denitrification catalyst, making it difficult to operate the denitrification equipment.

An object of the present invention is to provide a denitrification device that has a high decomposition rate and a high conversion rate to ammonia of the solid nitrogen-containing compound, and has excellent responsiveness to fluctuations in exhaust gas conditions, and a method for operating the same. .

[0006]

[Means for Solving the Problems] The above objects of the present invention are achieved by the following configuration. That is, in a denitrification device that catalytically reduces nitrogen oxides in exhaust gas using a reducing agent made of a solid nitrogen-containing compound at normal temperature and normal pressure, at least one of heated gas and water vapor and the reducing agent are combined. a reducing agent supplying means for supplying the reducing agent together with a reducing agent transporting gas to the vaporizing means; A heated gas supply means for supplying at least one of heated gas and water vapor while heating; an ammonia concentration detection means for detecting the concentration of ammonia produced by decomposition of a reducing agent in the vaporization means; a nitrogen oxide concentration detection means for detecting the concentration of nitrogen oxides; a reducing agent supply amount control means for controlling the reducing agent supply amount of the reducing agent supply means based on the detected value of the nitrogen oxide concentration detection means; heating amount control means for the heating gas supply means that controls the heating amount of the heating gas supply means based on a detection value of at least one of the ammonia concentration detection means and the nitrogen oxide concentration detection means; or a reducing agent decomposition catalyst layer heating means for heating the reducing agent decomposition catalyst layer of the vaporization means, omitting the heating amount control means of the heated gas supply means according to claim 1, and an ammonia concentration detection means. heating amount control means for the reducing agent decomposition catalyst layer heating means that controls the heating amount of the reducing agent decomposition catalyst layer heating means based on the detected value of at least one of the detection means among the nitrogen oxide concentration detection means; The denitrification device additionally provided, or the denitrification device according to claim 1, includes a reducing agent decomposition catalyst layer heating means for heating the reducing agent decomposition catalyst layer of the vaporization means, an ammonia concentration detection means, and a nitrogen oxide concentration detection means. Denitrification further comprising heating amount control means for the reducing agent decomposition catalyst layer heating means, which controls the heating amount of the reducing agent decomposition catalyst layer heating means based on the detected value of at least one of the detection means. The operating method for any of the above denitrification equipment comprises comparing each detection value of the device or the ammonia concentration detection means and the nitrogen oxide concentration detection means and operating the heating amount control means based on the higher detection value. be.

[0007] Examples of the solid nitrogen-containing compounds include urea, melamine, biuret, cyanuric acid, ammonium carbonate,
Ammonium hydrogen carbonate or the like is used.

Further, a metal oxide is used as a decomposition catalyst for decomposing the reducing agent made of a nitrogen-containing oxide used in the present invention. As a metal oxide, alumina (A
l2O3), silica (SiO2), silica alumina (
SiO2-Al2O3), titania (TiO2), magnesia (MgO), calcia (CaO), etc. are used, but in order to promote the hydrolysis reaction, those with strong solid acidity or solid basicity are effective. Some metal oxides may be used in combination, or metal oxides such as tungsten, vanadium, iron, molybdenum, copper, cobalt, tin, nickel, chromium, sulfur, magnesium,
Components such as boron, barium, and lanthanum may also be added. The metal oxide is used in the form of pellets shaped into spheres, hollow cylinders, cylinders, etc., but it is also effective to use it in the form of foam or lattice-shaped monoliths.

[0009]Heating the vaporizing means used in the present invention is carried out by heating a gas such as air or a mixture of air and water vapor and supplying the heated gas to the vaporizing means and/or a reducing agent decomposition catalyst, as described above. Using layer heating means. The latter structure is preferably one that can heat the reducing agent decomposition catalyst layer with good response and has little pressure loss when sending the generated ammonia to the denitrification catalyst layer. Therefore, a wire mesh, lattice, or spiral shape is used to improve gas circulation. Then, heating means is installed inside and/or above the packed bed of the reducing agent decomposition catalyst.

[0010] Here, if the material of the reducing agent decomposition catalyst layer heating means is likely to cause an oxidation reaction of nitrogen-containing compounds or ammonia produced by decomposition thereof, this is not preferable because nitrogen oxides will be produced. It is necessary to use a heating means made of a ceramic material that does not easily cause such reactions and/or a heating device coated with ceramics. Furthermore, the effect will be even greater if this ceramic is selected from metal oxides that are reducing agent decomposition catalysts, and the heating part of the heater is shaped like a wire mesh, a lattice, or a spiral. If the heating means for the reducing agent decomposition catalyst layer of the vaporizing means is integrated with the reducing agent decomposition catalyst, the device will be more compact and more effective.

[0011]

[Function] For example, taking urea as a nitrogen-containing compound, urea forms alumina, silica, etc. when mixed with water at a temperature of 300°C or higher.
It is known that silica reacts on metal oxides such as alumina and titania and decomposes catalytically. This decomposition reaction is not simple; thermal decomposition and hydrolysis reactions occur simultaneously, producing various compounds. (NH2)2CO → NH3+HNCOH
NCO+H2O → NH3+CO2(NH2
) 2CO+H2O → 2NH3+CO2 If ammonia can be obtained by the hydrolysis reaction, it is preferable because conventional denitrification technology can be applied in the following process. In the case of a thermal decomposition reaction, substances other than ammonia are also produced, but these can also be ultimately hydrolyzed and converted to ammonia.

[0012] In order to decompose urea and obtain ammonia, temperature control on the metal oxide is important. According to the studies of the present inventors, for example, as a metal oxide, the average particle size is 4 m.
When granular urea is decomposed in an air atmosphere containing water vapor using alumina pellets of
It is known that 100% of urea is converted to ammonia at 0 to 400°C. Below this rate, the rate of hydrolysis reaction is insufficient, and above that rate, thermal decomposition reaction becomes dominant and the specified conversion rate (conversion rate from urea to ammonia) is reached.
is not obtained.

In the case of urea, the hydrolysis reaction is an endothermic reaction, and the temperature of the reducing agent decomposition catalyst layer is significantly lowered in the areas that often come into contact with urea, so a heating means is installed in the reducing agent decomposition catalyst layer. , the temperature is controlled to be within the above temperature range of 350 to 400°C.

The optimum decomposition reaction temperature for the reducing agent depends not only on the type of the reducing agent decomposition catalyst but also on various reaction conditions such as its filling method, the amount of the reducing agent and steam supplied, and the flow rate of the transport gas. It doesn't necessarily mean it will be the same. Furthermore, if a predetermined amount of ammonia concentration cannot be obtained by detecting only the ammonia concentration, it is impossible to determine whether the cause is because the reaction temperature is low or high. Therefore, in order to decompose the reducing agent and reliably convert it into ammonia, it is necessary to control at least the amount of reducing agent supplied to the reducing agent vaporization means and the reducing agent decomposition reaction temperature. Therefore, the concentration of ammonia at the outlet of the reducing agent vaporization means and/or the concentration of nitrogen oxides in the exhaust gas are detected and controlled.

There are three types of control methods as follows. First, the amount of reducing agent supplied from the reducing agent supply means to the vaporizing means is determined in accordance with the exhaust gas nitrogen oxide concentration, and the concentration of ammonia generated by decomposition of the reducing agent in the vaporizing means and/or the exhaust gas nitrogen oxide concentration is adjusted. This is a method of controlling the heating temperature of heated gas based on a reference. Note that using the reducing agent supply amount as a standard instead of the nitrogen oxide concentration in the exhaust gas becomes a substantially equivalent factor, and this case is also included.

[0016] Furthermore, for example, in a cogeneration plant using a diesel engine, DSS operation is most common, and the denitrification equipment installed there can be started early and has good responsiveness that follows the operating pattern of the diesel engine. It has to be something. Since the temperature control of the reducing agent decomposition catalyst layer heating means of the vaporization means has faster response than the heating control of the heated air supply means, The second method is a method of controlling the reducing agent decomposition catalyst layer heating means of the vaporization means.

Furthermore, the third method is to control the heating amount of the reducing agent decomposition catalyst layer heating means based on each detected value of the ammonia concentration and/or nitrogen oxide concentration, and to control the heating temperature of the gas in the heating gas supply means. This method provides the most appropriate control. In addition, in the heating control of the heated gas and/or the reducing agent decomposition catalyst layer in each configuration of the present invention, the heating amount (for example, 80
%) is maintained at a constant value, and the remaining heating amount (e.g. 2
0%) may be controlled respectively.

The present invention is a denitrification device that can carry out these control methods.

[0019] By controlling the heating temperature of the heating means for the heating gas and water vapor or the heating temperature of the heating means of the vaporization means based on the higher detected value of the nitrogen oxide concentration and the ammonia concentration, Easy heating control is possible.

[0020]

EXAMPLES Next, the present invention will be explained in more detail using examples, but the present invention is not limited to these examples. Example 1 FIG. 1 shows a system diagram of a denitrification device for a 200 kW diesel power generation facility according to this example. Exhaust gas from diesel engine 1 (gas amount 1200m3/h, NOX = 600ppm)
is sent to the denitrification catalyst layer 3 through the flue 2. On the other hand, solid nitrogen-containing compounds are filled with metal oxides and have a temperature of 3.
Ammonia is gasified in a vaporization decomposer 4 maintained at 50° C. to 450° C., and the generated ammonia is injected into the flue 2 through an injection nozzle 5. Nitrogen oxides in the exhaust gas are reduced and removed on a denitrification catalyst using ammonia as a reducing agent. The vaporizing decomposer 4 can be installed either inside or outside the flue 2. This embodiment is an example in which the vaporizing decomposer 4 is provided inside the flue 2.

FIG. 4 shows the structure of the vaporizing decomposer 4 in detail. The reducing agent decomposition catalyst layer 6 is filled with spherical γ-alumina having an average particle diameter of 6 mm as a metal oxide. A wire mesh-like vaporizer decomposer heater 7 is installed in the upper layer. As shown in the figure, the vaporization decomposer heater 7 is made by overlapping lattice shapes A and B, and the heater 7 has a γ-
coated with alumina. Three thermocouples 8 are installed on the vaporizer heater 7 to detect the temperature of the heater 7. A sampling port 9 for measuring ammonia concentration is installed at the outlet of the reducing agent decomposition catalyst layer 6. Further, the vaporization decomposer 4 is provided with a supply pipe 10 for a solid nitrogen-containing compound and a carrier gas (air), and a pipe 12 for air and steam as a heating gas. As shown in FIG. 1, the nitrogen-containing compound is transferred from the reducing agent feeder 11 to the feeder motor 16
It is supplied in the form of powder, granules, etc. At this time, the reducing agent is carried by the carrier gas from the line 25 and sprayed toward the reducing agent decomposition catalyst layer 6. When obtaining steam, it is economical to partially utilize the exhaust heat of the exhaust gas, but when starting up the exhaust gas generation source such as a boiler, the exhaust heat and vaporization cracker heater 7 are used to generate enough steam to vaporize nitrogen-containing compounds. If a temperature atmosphere cannot be obtained, the mixture of water supplied from the water supply pump 14 and carrier gas obtained from the air compressor 15 can be heated by the heater 13.

[0022] In this case, the atmospheric temperature (500°C) before urea injection necessary for the above-mentioned urea hydrolysis is as follows: diesel engine load is 100%, gas amount is 1200Nm3/
h. Calculate the amount of urea injection necessary to obtain a denitrification rate of 80% under the condition of 600 ppm of NOx at the inlet, and calculate the temperature drop due to heat absorption when this urea vaporizes and decomposes (approximately 100°C).
), and the temperature of the reducing agent decomposition catalyst layer during the reaction is set to 35
The amount of heating was set so that the temperature ranged from 0 to 450°C.

Once the denitrification device is started, the outlet N is adjusted as shown in FIG.
A signal from the Ox monitor 18 is output to the inverter 20 of the feeder motor 16 of the reducing agent feeder 11, and the rotational speed of the feeder motor 16 is set to supply an amount of reducing agent that can maintain a constant amount of outlet NOx in the exhaust gas. controlled as follows.

Here, the decomposition of urea in the vaporization decomposer 4 does not always correspond to the amount of urea supplied from the reducing agent supply device 11. The concentration of ammonia generated by the decomposition of urea in the vaporizing decomposer 4 is monitored by an ammonia monitor 21 installed at the ammonia sampling port 9 downstream of the vaporizing decomposer 4.
It is measured in Therefore, the higher one of the measured values of the NOx concentration at the exhaust gas outlet and the ammonia concentration in the vaporization decomposer 4 is selected by the high-level selector 23, and the heating temperature of the air (steam) heating heater 13 is selected via the adder 22. Take control.

Embodiment 2 The outline of this embodiment is shown in FIG. 2, which is a modification of the apparatus shown in FIG.

FIG. 5 shows the time required for the denitrification device to start up when the heating means is changed using the system of this embodiment. Curve (a) in FIG. 5 shows the case where heating is performed only with the air (steam mixing) heater 13, and curve (b) shows the case where heating is performed only with the vaporization decomposer heater 7. This figure shows that the surface temperature of the 6 mm diameter reducing agent decomposition catalyst layer 6 in the vaporizer 4 is the temperature required for hydrolysis of urea (approximately 40 mm).
It can be seen that the time required for the temperature to rise to 0° C. is significantly faster in the method in which the heater is installed on the upper surface of the reducing agent decomposition catalyst layer 6, and is suitable for early start-up. This shows that heat transfer using heated gas as a heating medium has its own limits.

FIG. 6 shows the responsiveness of the reaction temperature on the γ-alumina layer 6. 200kw diesel engine load is 50% (gas amount 700Nm3/h, inlet N
Ox450ppm) to 100% (gas amount 1200Nm
3/h, inlet NOx 600ppm), the amount of urea injected to obtain a denitrification rate of 80% is 300 to 400 g/h and 700 to 850 g/h, respectively.
Therefore, the temperature decrease due to this increase in injection amount is 20 to 40
℃. Assuming that this temperature decrease is 40°C, and looking at the time required to raise the temperature by 40°C, this embodiment in which the vaporizing decomposer heater 7 is installed on the reducing agent decomposition catalyst layer 6 in the vaporizing decomposer 4 is effective. I understand that. The curve (a) in FIG. 6 shows the case where heating is performed only by the air (steam mixture) heating heater 13, and the curve (b) shows the case where heating is performed only by the vaporization decomposer heater 7.

Therefore, in this embodiment, by mainly controlling the vaporizing decomposer heater 7, the amount of ammonia produced is adjusted to an appropriate amount commensurate with the amount of urea supplied corresponding to the concentration of nitrogen oxides. The difference between this example and Example 1 is that the outlet NOx
The signal from the monitor 18 is not outputted to the heated gas, that is, the air (steam) heater 13, but instead is outputted to the heater load variable device 17 of the vaporization decomposer 4. Therefore, the signal having a higher value among the signals from the NOx monitor 18 and the NH3 monitor 21 is output as the temperature control signal for the heater 7 of the vaporization decomposer 4.

Embodiment 3 This embodiment shown in FIG. 3 is a combination of the processes of Embodiment 1 and Embodiment 2, in which both the heating gas heater 13 and the vaporization decomposer heater 7 are used to control the NOx concentration and NH3 concentration. It is controlled by concentration.

In the above embodiment, the NOx monitor 18 is installed in the exhaust gas duct on the downstream side of the denitrification device, but it may be installed in the exhaust gas duct on the upstream side. By adopting this system, the temperature of the decomposition catalyst layer can be controlled more quickly, and the heater installed above or inside the reducing agent decomposition catalyst layer can be made more compact.

In each of the above embodiments, an example is shown in which the vaporizing decomposer 4 is installed inside the flue 2, but as shown in FIG. As,
The generated ammonia may be injected into the flue 2 on the upstream side of the denitrification catalyst layer 3 from the injection nozzle 5.

Furthermore, the vaporizing decomposer 4 shown in FIG. 8 may be used instead of the vaporizing decomposer 4 shown in FIG. The vaporizing decomposer 4 shown in FIG. 8 has a ceramic foam made of cordierite (#13 manufactured by Bridgestone Corporation) as the reducing agent decomposition catalyst layer 6.
The material is coated with γ-alumina. A vaporizer heater 7 shown in FIG. 4 is installed between the ceramic foams.

In addition, in the heating control of the heated gas and/or the reducing agent decomposition catalyst layer in each of the above embodiments, the base heating amount (for example, 80%) of the heated gas and/or the reducing agent decomposition catalyst layer is kept at a constant value. Alternatively, the remaining heating amount (for example, 20%) may be controlled.

[0034]

Effects of the Invention According to the present invention, the decomposition reaction of solid nitrogen-containing compounds such as urea as an alternative reducing agent for liquefied ammonia occurs efficiently, and ammonia can be obtained with high efficiency. , scale cannot be deposited in the flue or on the denitrification catalyst. Furthermore, when the exhaust gas composition changes due to changes in the load of the diesel engine, it becomes possible to control the decomposition reaction conditions with good responsiveness. With such highly efficient operation, the metal oxide packed bed can be kept to the minimum necessary, making it possible to make the device more compact and save energy.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a denitrification device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a denitrification device according to an embodiment of the present invention.

FIG. 3 is a diagram showing a denitrification device according to an embodiment of the present invention.

FIG. 4 is a structural diagram of a reducing agent vaporization decomposer according to an embodiment of the present invention.

FIG. 5 is a diagram showing the time required to start up the denitrification device according to the embodiment of the present invention.

FIG. 6 is a diagram showing the responsiveness of the vaporization decomposer according to the embodiment of the present invention.

FIG. 7 is a diagram showing a denitrification device according to an embodiment of the present invention.

FIG. 8 is a structural diagram of a reducing agent vaporization decomposer according to an embodiment of the present invention.

[Explanation of symbols]

1 Diesel engine 2 Exhaust gas flue 3 Denitration catalyst layer 4 Vaporization decomposer 6 Reducing agent decomposition catalyst layer (γ-alumina layer) 7
Vaporizing decomposer heater 9 Sampling port 10 for measuring ammonia concentration Reducing agent supply pipe 12 Air (steam) supply pipe 13 Air (steam) heater

Claims (4)

[Claims] 1. A denitrification device that catalytically reduces nitrogen oxides in exhaust gas using a reducing agent made of a solid nitrogen-containing compound at normal temperature and normal pressure, in which at least one of heated gas and water vapor and the a vaporizing means having a reducing agent decomposing catalyst layer that brings the reducing agent into contact with the reducing agent over a reducing agent decomposing catalyst to produce ammonia; a reducing agent supplying means that supplies the reducing agent to the vaporizing means together with a reducing agent conveying gas; a heated gas supply means that supplies at least one of heated gas and water vapor to the vaporization means while heating; an ammonia concentration detection means that detects the concentration of ammonia produced by decomposition of the reducing agent in the vaporization means; Nitrogen oxide concentration detection means for detecting the concentration of nitrogen oxides in exhaust gas; and reducing agent supply amount control for controlling the reducing agent supply amount of the reducing agent supply means based on the detected value of the nitrogen oxide concentration detection means. heating amount control of the heating gas supplying means for controlling the heating amount of the heating gas supplying means based on a detection value of at least one of the ammonia concentration detection means and the nitrogen oxide concentration detection means; A denitrification device characterized by comprising means. 2. The heating amount control means of the heated gas supply means according to claim 1 is omitted, and the reducing agent decomposition catalyst layer heating means for heating the reducing agent decomposition catalyst layer of the vaporization means, the ammonia concentration detection means, and the nitrogen oxide A heating amount control means of the reducing agent decomposition catalyst layer heating means is added, which controls the heating amount of the reducing agent decomposition catalyst layer heating means based on the detected value of at least one of the detection means among the concentration detection means. A denitrification device characterized by being equipped with. 3. The denitration apparatus according to claim 1, further comprising at least one of a reducing agent decomposing catalyst layer heating means for heating the reducing agent decomposing catalyst layer of the vaporizing means, an ammonia concentration detecting means, and a nitrogen oxide concentration detecting means. Denitrification characterized by additionally comprising a heating amount control means of the reducing agent decomposition catalyst layer heating means for controlling the heating amount of the reducing agent decomposition catalyst layer heating means based on the detected value of the detection means. Device. 4. The heating amount control means is operated based on a higher detected value by comparing the detected values of the ammonia concentration detecting means and the nitrogen oxide concentration detecting means. or 3. How to operate the denitrification equipment.