JP3638638B2 - Denitration equipment using solid reducing agent - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a denitration technique using a selective catalytic reduction method, and relates to a denitration apparatus that suitably performs a denitration reaction using a solid reducing agent that is easy to handle.
[0002]
[Prior art]
Hazardous nitrogen oxides are contained in exhaust gas discharged from boilers or internal combustion engines using fossil fuels such as coal, oil or gas, which is one of the main causes of air pollution.
Of these sources of nitrogen oxides, large-scale boilers that release large volumes of exhaust gas into the atmosphere have a strong reduction in emissions due to stricter regulations on nitrogen oxides in the country and region. In addition, a denitration apparatus using a selective catalytic reduction method using combustion technology and / or liquefied ammonia as a reducing agent is used.
On the other hand, even in a small power generation facility where the installation of a denitration device has been rare so far, it is necessary to install a denitration device in the same manner as a large plant due to stricter emission regulations.
The NH ₃ in a conventional denitration apparatus is used as a reducing agent, since it is supplied from the high-pressure gas container, subject to the Pressurized Gas Control Law requires great care during transport and storage and the NH ₃ There was a risk of secondary pollution due to leaks.
[0003]
In recent years, a method of evaporating an aqueous solution of a reducing agent (an aqueous solution of a nitrogen-containing compound such as water and urea) that is easy to handle instead of using the above-described liquefied NH ₃ using heat of an electric heater or exhaust gas, or A method using a hydrolysis reaction of a catalyst has been proposed.
In this case, when the water is used, it is uneconomical especially in terms of transportation cost because the commercially available water for industrial use has a concentration of about 30 wt% at the most, and a large tank is necessary for storage. Installation space was required.
Compared to this, when using an aqueous solution of nitrogen-containing compounds such as urea, the aqueous solution can be prepared as needed at the site, so it is economically superior, and the development of a method that effectively uses these reducing agents Is expected.
It is known that the aqueous urea solution undergoes a hydrolysis reaction at a temperature of 80 ° C. or higher, and the reaction is promoted in the presence of an appropriate decomposition catalyst. In particular, when a catalyst is used, the reaction proceeds at a relatively low temperature (80 to 350 ° C.), which is an advantageous method.
[0004]
FIG. 3 shows a conventional denitration process using urea. An aqueous solution a of urea d is fed from the storage tank 1 by the pump 2 and led to the hydrolysis reactor 4 filled with the catalyst 3. The hydrolysis reactor 4 is provided with a heater 5 for heating urea d inside the reactor 4 to 80 to 100 ° C. The aqueous solution c containing the hydrolyzed gas b passes through the line 8 as it is and is injected into the flue gas flue 11 which is the gas to be treated discharged from the exhaust gas generation source 10 through the injection nozzle 9 to react NOx and NH ₃ . It is used as a reducing agent for the denitration reaction on the denitration catalyst 12 for detoxifying NOx.
However, regarding the hydrolysis method of these solid reducing agent (urea d) aqueous solutions in the denitration technique shown in FIG. 3, the aqueous solution c containing undecomposed compounds is transported from the hydrolysis reactor 4 to the aqueous solution c (or gas b). Since it is injected into the gas to be processed from the injection nozzle 9 through the means, there is a possibility that a polymer compound is formed in the conveying means or the gas flue 11 to be processed.
Even if the 100% decomposition reaction proceeds, a large amount of moisture is contained, so that even if a large amount of heat is applied, it is still difficult to vaporize, so that drainage is formed in the flue 11 or is located downstream. The denitration catalyst 12 has a problem such as having an adverse effect.
[0005]
[Problems to be solved by the invention]
Conventional denitrification techniques that utilize hydrolysis reaction of the solid reductant aqueous solution is undecomposed compounds due to adhering to the flue solid or not been sufficient consideration to the point of complete vaporization of liquefied NH ₃ When compared with the denitration technology used, there was a problem in terms of long-term stable operation.
The object of the present invention is to use a solid reducing agent that is easier to handle than liquefied NH ₃ as the reducing agent for the denitration reaction, eliminate scale adhesion to the flue, and perform the same denitration reaction as the liquefied NH ₃ method. It is to provide a possible denitration device.
[0006]
[Means for Solving the Problems]
The above object of the present invention is achieved by the following configuration. That is, a solid reducing agent that performs a denitration reaction by injecting a reducing agent composed of a nitrogen-containing compound that is solid at normal temperature and pressure into a gas to be treated containing nitrogen oxides, and then contacting with a catalyst containing a transition metal. in denitration apparatus using a mixing vessel for mixing the water solid reductant was discharged the reducing agent in the mixed solution discharged from the mixing vessel and hydrolyzing the hydrolysis reactor, the hydrolysis reactor reduction A heating type gas-liquid separation container having means for heating the aqueous solution of the agent; means for returning the water or aqueous solution discharged from the heating type gas-liquid separation container to the mixing container; This is a denitration apparatus using a solid reducing agent provided with a nozzle for injecting it into a processing gas . May be used treated gas as a means for heating the pressurized water decomposed reducing agent aqueous solution.
[0007]
[Action]
The operation of the denitration apparatus using the solid reducing agent of the present invention will be described with urea as an example. A part of the aqueous solution is obtained by introducing an aqueous solution of urea supplied from the storage tank into the hydrolysis reactor, passing the catalyst layer in a low temperature range of 80 to 100 ° C., and proceeding the solid-liquid contact hydrolysis reaction. Is hydrolyzed to obtain NH ₃ water. Here, the solubility of NH _{3 in} water decreases as the liquid temperature increases as shown in FIG. 4, and becomes almost zero at 100 ° C. Therefore, the aqueous solution (including NH ₃ water) obtained by the hydrolysis reaction of urea is introduced into a heating type gas-liquid separation container using heat such as a heater or exhaust gas, and is heated to 90 to 100 ° C. Dissolved NH ₃ in the aqueous solution can be taken out as a gas. The obtained NH ₃ gas is injected into the flue from the nozzle through the conveying means.
[0008]
According to this method, the reducing agent injected from the nozzle is the same as the NH ₃ gas used in the prior art, and does not contain a large amount of moisture, so that it is a small amount compared with the case of vaporizing and evaporating in the flue. The amount of heat, ie, the use of a hydrolysis catalyst, forms NH ₃ water, so the amount of heat required to raise the NH ₃ solubility characteristics to only 100 ° C. is sufficient, and no latent heat of vaporization of water is required. . Therefore, it is not necessary to consider complete vaporization / evaporation in the flue, and there is no possibility that undecomposed compounds adhere to the flue and adversely affect the denitration catalyst installed downstream. Meanwhile, the hot water discharged from the reducing agent solution the heating means is returned to the storage tank again aqueous urea solution, is used in the preparation of the urea aqueous solution. Therefore, the water for preparing the aqueous solution can be minimized. Furthermore, since warm water is returned to the tank, the temperature of the solution in the tank rises, the solubility of urea as a solute increases (see FIG. 5), and a high-concentration urea aqueous solution can be prepared. An excellent device.
[0009]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
Example 1
FIG. 1 shows an example of a denitration process using a solid reducing agent according to the present invention.
An aqueous solution a of urea d, which is a solid reducing agent, is fed from the storage tank 1 by a pump 2 and is subjected to hydrolysis catalyst 3 (one or more carbonates and / or water in alkali metals, alkaline earth metals or rare earth elements). It is led to a hydrolysis reactor 4 filled with an oxide or an ammonium salt of a mineral acid. The hydrolysis reactor 4 is provided with a heater 5 for heating urea d inside the reactor 4 to 80 to 100 ° C. The hydrolyzed aqueous solution is separated into a gas b and a liquid c by a heating type gas-liquid separation container 7 having a built-in heater 6, and the obtained gas b is discharged from an exhaust gas generation source 10 through a supply line 8 and through an injection nozzle 9. is injected into the flue 11 of the exhaust gas, it is used as a reducing agent for denitration reaction on the denitration catalyst 12 to detoxify the NOx by reacting NOx with NH _3.
On the other hand, the water (or aqueous solution) c discharged from the gas-liquid separation container 7 is returned to the storage tank 1 for the aqueous solution of urea d by the liquid feeding pipe 13 and used for urea water preparation.
[0010]
【The invention's effect】
According to the present invention, the following effects can be obtained.
1) It is possible to prevent adhesion of a polymer compound generated in the process of vaporizing and decomposing the solid reducing agent into the flue.
2) It can be handled in the same way as the conventional liquefied NH ₃ method, there is no need to take measures against drainage, and there is no adverse effect on the denitration catalyst.
3) Since an aqueous solution with a constant concentration is used, it can be controlled by changing the flow rate of the pump according to the load of an exhaust gas generation source such as a boiler, a gas turbine, or a diesel internal combustion engine.
4) It is economical because it does not require the latent heat of water evaporation compared to direct spraying of an aqueous solution into the flue in consideration of complete vaporization and evaporation.
5) The warm water discharged from the reducing agent aqueous solution heating means is returned to the mixing container such as the urea aqueous solution storage tank and used for the preparation of the urea aqueous solution, and the aqueous solution preparation water can be minimized. Become. Moreover, the temperature of the solution in the mixing container such as a storage tank for urea aqueous solution rises, the solubility of urea as a solute increases, and a high concentration urea aqueous solution can be prepared, resulting in a more economical device.
[0011]
【The invention's effect】
According to the present invention, the following effects can be obtained.
1) It is possible to prevent adhesion of a polymer compound generated in the process of vaporizing and decomposing the solid reducing agent into the flue.
2) It can be handled in the same way as the conventional liquefied NH ₃ method, there is no need to take measures against drainage, and there is no adverse effect on the denitration catalyst.
3) Since an aqueous solution with a constant concentration is used, it can be controlled by changing the flow rate of the pump according to the load of an exhaust gas generation source such as a boiler, a gas turbine, or a diesel internal combustion engine.
4) It is economical because it does not require the latent heat of water evaporation compared to direct spraying of an aqueous solution into the flue in consideration of complete vaporization and evaporation.
[Brief description of the drawings]
FIG. 1 is a diagram showing a denitration process using a solid reducing agent of Example 1 of the present invention.
FIG. 2 is a diagram showing a denitration process using a solid reducing agent of Example 2 of the present invention.
FIG. 3 is a diagram showing a structural diagram of a conventional denitration apparatus using a solid reducing agent.
FIG. 4 is a graph showing the solubility of NH ₃ in water.
FIG. 5 is a graph showing the solubility of urea in water.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Storage tank, 2 ... Pump, 3 ... Catalyst, 4 ... Hydrolysis reactor,
5, 6 ... heater, 7 ... heated gas-liquid separation container, 9 ... injection nozzle,
DESCRIPTION OF SYMBOLS 10 ... Exhaust gas generation source, 11 ... Exhaust gas flue, 12 ... Denitration catalyst a ... Solid reducing agent (urea) aqueous solution, b ... Gas, c ... Liquid,
d: Solid reducing agent (urea)

Claims (2)

A solid reducing agent that performs a denitration reaction by injecting a reducing agent comprising a nitrogen-containing compound that is solid at normal temperature and pressure into a gas to be treated containing nitrogen oxides, and then contacting with a catalyst containing a transition metal was used. In denitration equipment,
A mixing vessel for mixing the solid reducing agent and water;
A hydrolysis reactor for hydrolyzing the reducing agent in the mixed solution discharged from the mixing vessel;
A heating type gas-liquid separation container having means for heating the reducing agent aqueous solution discharged from the hydrolysis reactor;
Means for returning water or an aqueous solution discharged from the heated gas-liquid separation container to the mixing container;
A denitration apparatus using a solid reducing agent, comprising a nozzle for injecting the obtained gaseous reducing agent into the gas to be treated. 2. The denitration apparatus using a solid reducing agent according to claim 1, wherein the means for heating the hydrolyzed reducing agent aqueous solution is a gas to be treated.

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