JP3826085B2 - Exhaust gas denitration method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a denitration method and a denitration apparatus for radicalizing a denitration agent such as ammonia and removing the nitrogen oxides by blowing the radicalized denitration agent into a combustion furnace or exhaust gas.
[0002]
[Prior art]
When fossil fuels such as oil and coal are burned, nitrogen oxides (hereinafter referred to as NOx) are generated. Since NOx changes into sulfuric acid and nitric acid in the atmosphere and causes acid rain, a flue gas treatment that suppresses the amount of NOx generated or removes NOx in the exhaust gas is performed.
Here, as a method of suppressing the generation amount of NOx, there are a low NOx burner and two-stage combustion. As a method for removing NOx from exhaust gas, ammonia (NH ₃ Catalytic denitration equipment using a catalytic reduction method or the like using a catalyst as a catalyst.
[0003]
However, in the above-described catalytic reduction method, the concentration of NOx discharged from the combustion furnace (usually about 100 to 300 ppm) can be suppressed only to about 15 to 45 ppm, and the removal efficiency remains at about 85%. This is the current situation. Therefore, in order to make the concentration of 10 ppm or less expected to be required in the future, that is, the removal efficiency of 90% to 97%, the amount of catalyst used in the denitration apparatus must be increased, and the denitration cost increases. There is a problem.
[0004]
In recent years, therefore, a non-catalytic denitration apparatus and denitration method that eliminates the need for a catalyst by utilizing a radical reaction such as a denitration method by electron beam irradiation or a corona method has been proposed.
As such a non-catalytic denitration apparatus and denitration method, for example, “Denitration Method and Apparatus for Combustion Exhaust Gas” and Japanese Laid-Open Patent Publication No. 8-5051 disclosed in Japanese Patent Laid-Open No. 8-173753 are disclosed. Known are a “denitration device for combustion exhaust gas”, an “exhaust gas treatment method” disclosed in JP-A-1-99633, a “NOx removal method” disclosed in JP-A-1-11628, and the like.
[0005]
However, in such a conventional non-catalytic denitration method and apparatus, since it is necessary to irradiate the entire exhaust gas with an electron beam or to perform discharge, enormous energy is required, and equipment costs and operation are reduced. There is a problem of increasing costs. Further, even with such a non-catalytic denitration method and apparatus, it is difficult to achieve the target of NOx removal efficiency of 90% or more and emission of 10 ppm or less, which is expected to be required in the future. There's a problem.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned problems. Denitration of exhaust gas that can improve the removal efficiency of NOx discharged from a combustion furnace and suppress the amount of NOx discharged at low equipment cost and operation cost. The present invention provides a method and a denitration apparatus, and further provides an exhaust gas denitration method and a denitration apparatus that can increase NOx removal efficiency to 90% or more and can suppress the emission amount to 10 ppm or less. For the purpose.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the inventors of the present invention have focused on a radical injection method in which a radical chain reaction is generated by blowing a pre-radical denitration agent (denitration radical) into a combustion furnace or exhaust gas. . The radical injection method has an advantage that a high denitration rate can be obtained with low energy.
To cause the radical chain reaction, a high concentration of NH ₂ It is necessary to blow radicals into the combustion furnace and exhaust gas. However, if the denitration agent is simply passed through the discharge field, the denitration agent will mainly generate N radicals. ₂ It is not easy to generate radicals efficiently.
As a result of intensive research conducted by the inventors of the present invention, ammonia (NH ₃ NH) from denitration agents such as ₂ It has been found that radicals including radicals, NH radicals and N radicals are generated. Furthermore, denitration agent is blown again in the vicinity of the end of the discharge field and collided with the radicals, so that a high concentration of NH ₂ It has been found that radicals including radicals can be generated.
[0008]
Specifically, the invention described in claim 1 is a denitration method in which exhaust gas is denitrated with a radicalized denitration agent, wherein the denitration agent is radicalized to produce a denitration radical, A second radical generating step that is provided after the first radical generating step and generates the second radical by blowing the denitration agent into the first radical; and using the second radical, And / or a step of generating a denitration reaction in the reaction region outside the combustion furnace.
[0009]
According to this method, when the first radical is generated by barrier discharge or the like and then blown and collided with the denitration agent, the second radical having a high concentration is generated. And by blowing this high concentration 2nd radical in a combustion furnace or exhaust gas, a radical can be produced in a chain in exhaust gas.
Thus, in the present invention, it is not necessary to excite the entire mass of exhaust gas to radicalize the denitration agent as in the past, or to perform denitration using a large amount of catalyst, dramatically improving energy efficiency, In addition, the denitration rate can be improved.
[0010]
The invention described in claim 2 is a method in which a step of mixing a carrier gas and the denitration agent is provided before the first radical generation step and / or the second radical generation step.
By the carrier gas, a stable discharge field (plasma) can be formed at a low voltage, and the generation of the first radical can be promoted. Examples of the carrier gas include argon (Ar), xenon (Xe), krypton (Kr), nitrogen (N ₂ ) Can be used. These gases may be used alone or mixed as appropriate.
Since these carrier gases generate plasma at a low voltage, the discharge energy is small, and the denitration agent is not decomposed to N radicals, and is effective for the chain reaction of radicals. ₂ NH radicals effective for radicals and denitration reaction can be generated efficiently, and the denitration rate can be further increased. As the carrier gas, other than the above can be used, but Ar (ionization voltage is about 15.8 eV), Xe, Kr or N ₂ It is preferable to use an ionization voltage that is the same as or lower than the above.
[0011]
The invention according to claim 4 is a method in which a reaction region outside the combustion furnace is provided at an exhaust gas outlet of the combustion furnace.
According to this method, NOx can be decomposed with denitration radicals without the need to heat the exhaust gas.
[0012]
The invention according to claim 5 is a method in which the denitration agent is one or a mixture of two or more of nitrogen compounds and hydrocarbons.
Thus, as the denitration agent, nitrogen compounds such as urea containing N and H, and hydrocarbons such as methane containing C and H can be used. These may be used as a single species or as a mixture of a plurality of species.
As described in claim 6, the denitration agent is NH. ₃ It is good. In this case, as described in claim 7, the first radical is NH. ₂ It is preferable to include at least one of a radical, NH radical, and N radical.
Among the above radicals, especially NH ₂ Since radicals cause radical chain reactions, NH ₂ By blowing radicals into the combustion furnace and exhaust gas, NH ₂ The radical is regenerated. Therefore, NH was blown ₂ Even if the lifetime of the radical is short, NH reaches the center of the reaction region. ₂ It becomes possible to make radicals reach, and the denitration rate can be improved.
So NH ₂ The radicals are passed through a low voltage plasma and the first radical (NH ₂ , NH, N radicals), and again the first radical has NH ₃ Collide. NH radicals or N radicals are bombarded with NH ₃ High concentration of NH due to the property of extracting H from ₂ Can generate radicals.
[0013]
The invention according to claim 8 is a concentration parameter of the denitration agent to be radicalized, a flow rate parameter of the denitration radical, a discharge voltage parameter for generating the denitration radical, a temperature parameter of exhaust gas during a denitration reaction, This is a method for obtaining the relationship between the nitrogen oxide concentration parameter and the oxygen concentration parameter in the exhaust gas and the denitration rate, and selecting the parameter that maximizes the denitration rate from the parameters.
The denitration agent is NH ₃ The reaction temperature is 390 ° C. to 900 ° C., the oxygen concentration is 0.5% to 10%, the applied voltage is 7 kV to 15 kV, NH ₃ Denitration should be performed under a molar ratio of NO to NO of 0.9 to 1.2.
Further, according to the present invention, in the present invention, the position where the denitrating agent is blown into the first radical is within the reaction region, in the vicinity of the blowing port through which the first radical is blown into the reaction region, or Any of the inside of the entrance may be sufficient. Immediately before the first radical is blown into the reaction region, it is preferable to cause the denitration agent to collide with the first radical so that the second radical generated thereby is blown into the reaction region.
[0014]
The above method can be realized by the following denitration apparatus.
That is, the invention described in claim 11 is a denitration apparatus for denitrating exhaust gas by using a radicalized denitration agent, and a denitration agent supply means and a first radical that radicalizes the denitration agent to generate a first radical. A radical generating means; a first blowing conduit for blowing the denitration agent into the first radical produced by the first radical producing means; and mixing the first radical and the denitration agent; The second radical generated by blowing the denitration agent into the first radical is configured to have a second blowing conduit that guides the second radical to the reaction region inside the combustion furnace and / or the reaction region outside the combustion furnace. .
[0015]
In this case, as described in claim 12, the tip of the first blowing conduit is positioned in the reaction region, in the vicinity of the inlet of the second blowing conduit or in the inside of the inlet. It is preferable to do so.
According to this configuration, the first radical generated by the low voltage plasma collides with the denitration agent blown from the first blowing conduit. Thereby, the 2nd radical containing a high concentration predetermined radical is produced | generated. Then, by blowing the second radical into the reaction region from the second blowing conduit, a radical chain reaction occurs in the reaction region. By this radical chain reaction, denitration radicals are generated one after another, and a denitration reaction can be caused over the entire reaction region. Thereby, the denitration rate can be improved.
[0016]
The invention described in claim 13 is configured such that a carrier gas supply means for supplying a carrier gas to the denitration agent is provided before the denitration radical generating means.
The carrier gas promotes the generation of the first radical by low voltage discharge. As a carrier gas, in addition to Ar which generates a discharge at a relatively low voltage, Xe, Kr, N ₂ Etc. can be used.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.
First, an example of combustion equipment to which the present invention is applied will be described with reference to FIG. The combustion facility in FIG. 1 is a power generation facility that generates power by burning fossil fuels such as coal and oil. In FIG. 1, the structure of such a combustion facility 1 is shown by a simple block diagram.
[0018]
The combustion facility 1 includes a combustion furnace 2 that burns fossil fuels such as coal and oil, a heat exchanger 5 that is provided downstream of the combustion furnace 2 to preheat the combustion air by preheating the exhaust gas, and in the exhaust gas. A dust collector 6 that collects contained dust through an electrode charged with a high-voltage DC voltage, and SO ₂ And a chimney 8 that discharges exhaust gas that has been subjected to denitration, dust collection, and desulfurization into the atmosphere.
The combustion furnace 2 is a combination of a low NOx burner and two-stage combustion to suppress NOx emissions. In this embodiment, the denitration apparatus 10 of the present invention is provided in the combustion furnace 2 and the exhaust gas outlet 3 from which the exhaust gas is discharged from the combustion furnace 2.
[0019]
The position where the denitration apparatus 10 is provided is preferably provided at a position where NOx in the exhaust gas can be most efficiently removed, that is, a position where the denitration rate is maximized. As will be described later, this position indicates various conditions when performing denitration, such as the concentration of denitration agent, the flow rate of denitration radicals, the discharge voltage for generating this denitration radical, the temperature of exhaust gas during the denitration reaction, the exhaust gas It can be determined by conditions such as the concentration of nitrogen oxides in the inside and the oxygen concentration in the exhaust gas.
[0020]
Furthermore, the combustion facility 1 of this embodiment has a catalyst-type denitration device 4 between the heat exchanger 5 and the exhaust gas outlet 3, and NH ₃ The residual NOx that could not be removed by the denitration apparatus 10 can be further removed from the exhaust gas by the contact catalyst system using NOx as a denitration agent. Since this catalyst-type denitration apparatus 4 can remove almost NOx in the exhaust gas by the denitration apparatus 10 of the present invention, it can be smaller than the conventional one, and the amount of catalyst used is also reduced. be able to. Of course, if the NOx removal device 10 according to the present invention can remove NOx almost completely, it is not necessary to provide such a catalyst-type denitration device 4.
[0021]
Next, the denitration apparatus 10 of this embodiment will be described with reference to FIG. The denitration apparatus 10 generates denitration radicals (hereinafter, denitration radicals generated in the discharge tube 12 are referred to as “first radicals”) from the denitration agent in the discharge tube 12, and then the first radicals. Denitration agent is blown from the right angle (cross flow injection), and the denitration agent and the first radical collide with each other to obtain a high concentration of NH necessary for radical chain reaction. ₂ A denitration radical containing radicals (hereinafter, a denitration radical generated from the first radical is referred to as a “second radical”) is generated, and this second radical is generated in a reaction region in the combustion furnace 2 or exhaust gas. By blowing, denitration treatment is performed while causing a radical chain reaction.
FIG. 2 is a block diagram showing the configuration of the denitration apparatus 10 of this embodiment.
The denitration apparatus 10 is NH that is a denitration agent. ₃ NH to supply ₃ A supply unit 11; an Ar supply unit 14 for supplying Ar as a carrier gas; and NH. ₃ Mixer 15 for mixing Ar and Ar, and NH supplied from this mixer 15 ₃ / Ar, and a discharge tube 12 having a double tube structure for generating a first radical.
[0022]
The discharge tube 12 includes a grounded outer electrode 12 a and an electrode 12 b that is disposed concentrically with the electrode 12 a and connected to the plasma power source 13. The outer peripheral surface of the electrode 12b faces the inner peripheral surface of the electrode 12a with a gap of a predetermined dimension. NH supplied from the mixer 15 ₃ / Ar flows through the gap between the two electrodes 12a and 12b, and is discharged by the discharge between the electrode 12b on the plasma power source 13 side and the electrode 12a on the ground side. ₃ Is radicalized and NH ₂ A first radical containing a radical, NH radical and N radical is generated.
[0023]
In this embodiment, NH ₃ The reason why the carrier gas is supplied to is to generate plasma at a low voltage in the discharge tube 12 and thereby generate the first radical. In addition, Ar is used as a carrier gas because Ar has a low ionization voltage of about 15.8 eV, and plasma is generated at a relatively low voltage, so that the discharge energy can be smaller than that of other carrier gases. Furthermore, this is because there is an advantage that the concentration of denitration radicals generated is higher than that of other carrier gases.
[0024]
Further, in this embodiment, a conduit 25 that connects the discharge tube 12 and the combustion furnace 2 or the exhaust gas outlet 3 is connected to a conduit 22 that is connected to the mixer 15 from the lateral direction, and the first flowing in the conduit 25 From a direction substantially perpendicular to the radical, NH ₃ / Ar can be blown in. The tip of the conduit 22 is preferably positioned in the vicinity of the inlet 25a where the conduit 25 opens into the reaction region S.
Thereby, the first radical generated in the low voltage plasma is NH, which is a denitration agent blown from the conduit 22. ₃ High concentration of NH ₂ A large amount of second radicals including radicals and NH radicals are generated. This is because the first radical contains a large amount of NH radicals and N radicals, and NH radicals or N radicals collide with each other. ₃ This is because it has a characteristic of extracting H from the surface.
[0025]
High concentration of NH ₂ The second radical including the radical and the NH radical is blown into the reaction region S from the blow port 25 a of the conduit 25. The second radical causes a radical chain reaction in the reaction region S. By this radical chain reaction, denitration radicals are generated one after another, the denitration reaction can be caused over the entire reaction region S, and the denitration rate can be improved.
[0026]
Thus, according to the present invention, denitration can be performed with high efficiency over almost the entire reaction region S, and a denitration method and a denitration apparatus excellent in energy efficiency, facility cost, and operation cost can be obtained. In addition, according to the present invention, it is possible to obtain a denitration method and a denitration apparatus capable of setting the denitration rate to 90% or more and the NOx concentration to 10 ppm or less.
[0027]
[Example]
Next, specific examples of the present invention will be described.
FIG. 3 is a schematic configuration diagram showing an example of an experimental apparatus used in this embodiment.
[Experimental device]
The experimental apparatus 100 includes a discharge tube 112 that generates a first radical, a plasma power source 113 that applies a voltage to an electrode 112b inside the discharge tube 112, a cylindrical reaction furnace 130 that performs a denitration reaction, and simulated exhaust gas. NO / NO to adjust ₂ Gas supply part 115, N for supplying ₂ Gas supply unit 117 and O ₂ / N ₂ , A gas blender 116a for mixing the gases supplied from the gas supply units 115, 117, 118, and NH for adjusting the denitration agent ₃ A gas supply unit 114 that supplies / Ar, a gas supply unit 119 that supplies Ar as a carrier gas, a gas blender 116 b that mixes the gas supplied from each of the gas supply units 114 and 119, and the reactor 130. And a NOx meter 131 for measuring the concentration of NOx.
[0028]
The discharge tube 112 is NH ₃ The / Ar mixture is radicalized with low-temperature plasma by barrier discharge or the like, and denitration radicals are blown into the reaction furnace 130, and is formed from a quartz tube having a length of about 300 mm and a thickness of about 2 mm.
Inside the discharge tube 112, an outer electrode 112a formed in a cylindrical shape and a cylindrical inner electrode 112b disposed concentrically with the electrode 112a are provided. A plasma power supply 113 is connected to the inner electrode 112b, and the outer electrode 112a is grounded.
The gap between the two electrodes 112a and 112b is 1.5 mm, and plasma is generated in this gap. And NH ₃ When the / Ar mixture passes through the gap, a first radical is generated by the plasma.
[0029]
The reaction furnace 130 is for causing a denitration reaction, and has two quartz tubes with a diameter of about 50 mm and a length of about 500 mm arranged on the left and right. In each of the left and right quartz tubes, NO / O which is simulated exhaust gas supplied from the gas supply unit 115 is provided. ₂ / N ₂ A heater 132 is provided for heating the heater. A reaction chamber 134 is provided between the two quartz tubes, and NO / O supplied from one (left side of the drawing) quartz tube. ₂ / N ₂ Is denitrated in the reaction chamber 134 and then sent to the NOx meter 131 from the other (right side) quartz tube.
[0030]
The discharge tube 112 configured as described above and the reaction chamber 134 are connected by a conduit 125. The first radicals generated in the discharge tube 112 are blown into the reaction chamber 134 through the conduit 125.
The plasma power source 113 is a power supply device that can apply a high voltage up to 40 kV to the electrode 112a and a high-frequency pulse voltage up to 40 kHz to the electrode 112a.
[0031]
The gas blender 116a is provided with NO / NO supplied from the gas supply devices 115, 117, and 118. ₂ , N ₂ And O ₂ / N ₂ It is a gas blender with a mass flow control that can be mixed at any ratio. In addition, the gas blender 116b is NH supplied from the gas supply devices 114 and 119. ₃ / A gas blender with mass flow control that can mix Ar and Ar at any ratio.
The gas blender 116a and the reactor 130 are connected by a conduit 126, and the NO / O blended by the gas blender 116a. ₂ / N ₂ Is supplied to the reaction furnace 130 via the conduit 126.
The discharge tube 112 and the gas blender 116b are connected by a conduit 121, and NH ₃ / Ar is supplied to the discharge tube 112 from the gas blender 116b.
[0032]
Further, a conduit 123 is provided by branching the conduit 121 in front of the discharge tube 112. A valve 124 is provided in the middle of the conduit 123, and NH ₃ / Ar supply and stop, NH ₃ / Ar supply amount can be adjusted. The distal end of the conduit 123 is connected to a conduit 122 attached to the side surface of the conduit 125 at a substantially right angle. Therefore, when valve 124 is opened, NH flowing in conduit 121 ₃ A part of / Ar is blown from the right angle direction to the first radical in the conduit 125 generated in the discharge tube 12 through the conduit 123 and the conduit 122.
In this embodiment, in order to measure the denitration rate, the gas composition before denitration and the gas composition after denitration are continuously measured. NO / NOx is obtained by chemiluminescence. ₂ Is magnetic, N ₂ O was measured by an infrared method.
[0033]
[Denitration agent and carrier gas]
As described above, the denitration agent supplied to the discharge tube 112 is ammonia (NH ₃ ). The carrier gas used was argon (Ar) that generates plasma at a low voltage. And NH ₃ The concentration of was changed by adjusting the fraction with the carrier gas.
The exhaust gas denitrated by radical reaction is NH ₃ NO / NOx / O with a Shimadzu NOA-7000 type continuous analyzer (Shimadzu NOA-7000 type) equipped with a scrubber ₂ Was measured. N ₂ O was measured with an APNA-360 type manufactured by Horiba. The NOx removal rate can be determined by measuring the concentration of NOx initially introduced and the NOx concentration in the exhaust gas after the denitration reaction.
[0034]
[Plasma power supply]
As the plasma power source 113 for generating plasma, an impulse type high frequency power source (PHF-2X-2V type manufactured by HEIDEN Laboratory) consisting of two sine waves was used. Then, a sinusoidal pulse voltage (one cycle T ₀ = 10 μs) was repeatedly repeated, and a voltage was applied at a cycle T1. This application state is shown in FIG. In FIG. 4, the vertical axis represents voltage, and the horizontal axis represents time (period).
As shown in FIG. 4, as a characteristic of the plasma power supply 113, the sinusoidal pulse of the applied voltage has a waveform in which the negative half-wave peak voltage is larger than the positive half-wave peak voltage. For this reason, the reference value of the applied voltage is Vpp which is the difference between the maximum value and the minimum value of the sine wave pulse voltage.
[0035]
[Set various conditions]
In the radical injection which is the premise of the present invention, the relationship between the concentration of the denitrating agent to be radicalized, the flow rate of the denitrating radical, the plasma voltage, the temperature of the exhaust gas during the reaction, the concentration of NOx in the exhaust gas, and the oxygen concentration in the exhaust gas. It is closely related to the denitration rate of exhaust gas.
In view of this, first, denitration by radical injection, which is a premise of the present invention, was performed with the valve 124 closed, and various values of the above parameters were changed to verify the optimum conditions.
[0036]
[Relationship between reaction temperature and applied voltage]
FIG. 5 is a change graph of the denitration rate with respect to the applied voltage for each reaction temperature.
This graph shows the oxygen concentration O in the exhaust gas. ₂ = 2.0%, NH ₃ Molar ratio of NO to NO ₃ The reaction temperature was changed to 320 ° C., 390 ° C., 410 ° C. and 450 ° C. under the condition of /NO=2.2.
As can be seen from the graph of FIG. 5, when the reaction temperature is 450 ° C., when the applied voltage Vpp exceeds 5 kV, the denitration reaction starts abruptly and the denitration rate reaches 90%.
[0037]
However, thereafter, at any reaction temperature, the applied voltage Vpp increases and the denitration rate tends to decrease. The lower the reaction temperature, the greater the effect.
For example, when the reaction temperature is 450 ° C., the denitration rate of about 85% is maintained until the applied voltage Vpp = 20 kV, but at the reaction temperature of 390 ° C., the denitration rate decreases to 80% or less when the applied voltage Vpp = 15 kV or more.
From this graph, it can be seen that the relationship between the applied voltage Vpp and the reaction temperature has a great influence on the denitration rate. These phenomena occur when the applied voltage Vpp is small. ₃ To NH ₂ Is likely to be generated, and the denitration reaction is likely to occur, but when the applied voltage Vpp increases to some extent, NH ₃ Is decomposed to radicals such as N and NH, and it is considered that the denitration rate decreases.
From the graph of FIG. 5, it is understood that the applied voltage Vpp is preferably about 7 to 15 kV and the reaction temperature is preferably 390 ° C. or higher. A preferred range is 400 ° C. or higher. Since the denitration rate increases as the reaction temperature increases, the upper limit of the reaction temperature, that is, NH ₃ It is possible to increase the temperature to 900 ° C. at which thermal denitration of NO is started.
[0038]
[Relationship between oxygen concentration temperature and applied voltage]
FIG. 6 is a change graph of the denitration rate with respect to the applied voltage for each oxygen concentration. Reaction temperature is 410 ° C, NH ₃ The molar ratio of NO to NO is NH ₃ A graph was created by changing the oxygen concentration to 2.0%, 5.6%, and 0% under /NO=2.2.
As can be seen from the graph of FIG. 6, the denitration reaction starts at a lower applied voltage Vpp as the oxygen concentration increases. However, when the oxygen concentration increases to 5.6%, the denitration rate remains at about 60%. When the oxygen concentration is 2%, a denitration rate of about 90% can be obtained.
[0039]
However, in a state where there is no oxygen (0%), almost no denitration reaction occurs, and it can be seen that the presence of oxygen is important for the denitration reaction. That is, in order to obtain a high denitration rate, it is necessary to select an appropriate oxygen concentration.
This is because OH and NH generated from oxygen at an appropriate oxygen concentration ₃ NH ₂ This is thought to be due to the oxidation reaction that occurs when oxygen is excessive.
From the graph of FIG. 6, it can be seen that the oxygen concentration should be greater than 0%, preferably 0.5% to 2.5%. In the present invention, even if the oxygen concentration is high to some extent, a high denitration rate can be obtained as compared with the conventional radical injection, and the present invention can be applied if the oxygen concentration is up to about 10%. .
[0040]
[Molar ratio NH ₃ / Relationship between NO and applied voltage]
FIG. 7 shows the molar ratio NH. ₃ It is a change graph of the denitration rate with respect to the applied voltage according to / NO. The reaction temperature was 410 ° C., the oxygen concentration was 2.0%, and the molar ratio NH ₃ The graph was created by changing / NO to 2.2, 1.2, 0.8, and 0.6.
As can be seen from the graph of FIG. 7, the smaller the molar ratio, the lower the applied voltage Vpp at which denitration is started. However, when the molar ratio is about 0.8, the denitration rate also decreases. In addition, the smaller the molar ratio, the narrower the width of the applied voltage Vpp at which a high NOx removal rate can be obtained.
From the graph of FIG. 7, it is understood that the molar ratio is preferably larger than 0.8 and smaller than 2.2 in the optimum applied voltage Vpp range of 7 kV to 15 kV.
[0041]
As described above, the optimum range of each condition in the radical injection which is the premise of the cross flow injection of the present invention can be obtained.
Next, the valve 124 is opened to verify the denitration effect of the cross flow injection. By opening valve 124, the first radical in conduit 125 is NH ₃ / Ar is blown.
[0042]
[Denitration effect of cross flow injection]
FIG. 8 compares the denitration effect of cross flow injection with the denitration effect of normal flow (without blowing into the reaction chamber). In FIG. 8, the horizontal axis represents the molar ratio NH. ₃ / NO.
In the case of cross-flow injection, a denitration rate of 79.5% is obtained at a molar ratio of 0.8, confirming an improvement of the denitration rate of about 8% compared to the normal flow (when the valve 124 is closed). We were able to. It can also be seen that when the molar ratio exceeds 1.0, the denitration rate reaches almost 100%.
[0043]
From the above experimental results, according to the denitration method of this example, reaction temperature = 400 ° C. to 450 ° C., oxygen concentration = 0.5% to 2%, applied voltage Vpp = 7 kV to 15 kV, molar ratio NH ₃ By setting / NO to be 0.9 or more, the denitration rate can be made 90% or more. In particular, the molar ratio NH ₃ By setting / NO to 0.95 to 1.2, 95% to 100% could be achieved, and the denitration rate by the above-described radical injection method could be greatly improved.
[0044]
Although a preferred embodiment of the present invention has been described, the present invention is not limited to the above-described embodiment.
For example, in the above description, the denitration apparatus 10 is provided in both the combustion furnace 2 and the exhaust gas outlet 3, and the cross flow injection is performed by both of them. However, the cross flow injection is performed by either of them. Also good.
[0045]
In the above description, Ar is used as an example of the carrier gas. However, other carrier gases having an ionization voltage equivalent to or lower than Ar, such as xenon (Xe), krypton (Kr), nitrogen ( N ₂ ) Etc. can also be used.
Furthermore, ammonia (NH ₃ However, it is also possible to use other denitration agents, for example, nitrogen compounds such as urea containing N and H, and hydrocarbons such as methane containing C and H.
Further, in the above embodiment, the denitration agent is blown in the conduit 25 connecting the discharge tube 12 and the combustion furnace 2 or the exhaust gas outlet 3 as shown in FIG. The denitration agent may be blown into the reaction region S of the exhaust gas outlet 3, and the denitration agent is blown in the vicinity of or inside the blow port 25a through which the denitration radical is blown into the reaction region from the conduit 25. May be. Further, NH, which is a denitration agent, from a substantially perpendicular direction to the first radical flowing in the conduit 25. ₃ However, as long as the second radical can be efficiently generated, it may be blown from an oblique direction as well as a right angle direction.
[0046]
【The invention's effect】
Thus, according to the present invention, the denitration efficiency can be remarkably improved with low equipment costs and operation costs. In addition, the denitration efficiency can be increased to 90% or more, and NOx in the exhaust gas can be suppressed to 10 ppm or less.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an example of combustion equipment to which the present invention is applied.
FIG. 2 is a diagram illustrating the configuration according to an embodiment of the denitration apparatus.
FIG. 3 is a schematic configuration diagram showing an example of an experimental apparatus.
FIG. 4 is a diagram showing a state of voltage application by a plasma power source.
FIG. 5 is a graph showing the change in the denitration rate with respect to the applied voltage for each reaction temperature.
FIG. 6 is a graph showing a change in denitration rate with respect to an applied voltage for each oxygen concentration.
FIG. 7: molar ratio NH ₃ It is a change graph of the denitration rate with respect to the applied voltage by / NO.
FIG. 8 is a graph comparing the denitration effect of cross flow injection and the denitration effect of normal flow.
[Explanation of symbols]
1 Combustion equipment
2 Combustion furnace
3 Exhaust gas outlet
10 Denitration equipment
11 NH ₃ Supply section
12 Discharge tube
13 Plasma power supply
14 Ar supply section
15 Mixer
22,25 Conduit (Blowing Conduit)
25a inlet
S reaction area

Claims (13)

In a denitration method in which exhaust gas is denitrated with a radicalized denitration agent,
A first radical generation step of radicalizing the denitration agent to generate a denitration radical;
A second radical generation step, which is provided after the first radical generation step, and generates the second radical by blowing the denitration agent into the first radical;
Using the second radical to cause a denitration reaction in a reaction region inside the combustion furnace and / or a reaction region outside the combustion furnace;
An exhaust gas denitration method comprising: 2. The exhaust gas denitration method according to claim 1, further comprising a step of mixing a carrier gas and the denitration agent before the first radical generation step and / or the second radical generation step. . The exhaust gas denitration method according to claim 2, wherein the carrier gas is any one gas of Ar, Xe, Kr, and N ₂ or a mixed gas of two or more. 4. The exhaust gas denitration method according to claim 1, wherein a reaction region outside the combustion furnace is provided at an exhaust gas outlet of the combustion furnace. The exhaust gas denitration method according to any one of claims 1 to 4, wherein the denitration agent is any one or a mixture of two or more of nitrogen compounds and hydrocarbons. The denitration method for exhaust gas according to claim 5, wherein the denitration agent is NH ₃ . The exhaust gas denitration method according to claim 6, wherein the first radical includes at least one of NH ₂ radical, NH radical, and N radical. The concentration parameter of the denitration agent to be radicalized, the flow rate parameter of the denitration radical, the discharge voltage parameter for generating the denitration radical, the temperature parameter of the exhaust gas during the denitration reaction, the concentration parameter of nitrogen oxides in the exhaust gas, and the exhaust gas The exhaust gas denitration method according to any one of claims 1 to 7, wherein a relationship between an oxygen concentration parameter and a denitration rate is obtained, and a parameter that maximizes the denitration rate is selected from the parameters. . Denitration is performed under conditions of a reaction temperature of 390 ° C. to 900 ° C., an oxygen concentration of 0.5% to 10%, an applied voltage of 7 kV to 15 kV, and a molar ratio of NH ₃ to NO of 0.9 to 1.2. The method for denitrating exhaust gas according to claim 6 or 7. In the reaction region, in the vicinity of the blow port for blowing the first radical into the reaction region or in the blow port, the denitration agent is blown into the first radical to generate a second radical. The denitration method for exhaust gas according to any one of claims 1 to 9. In denitration equipment that denitrates exhaust gas with radicalized denitration agent,
Denitration agent supply means;
A first radical generating means for radicalizing the denitration agent to generate a first radical;
A first blowing conduit for blowing the denitration agent into the first radical generated by the first radical generating means to mix the first radical and the denitration agent; and the denitration agent for the first radical. A second blowing conduit for guiding a second radical generated by blowing into one radical to a reaction region in the combustion furnace and / or a reaction region outside the combustion furnace;
An exhaust gas denitration apparatus characterized by comprising: The tip of the first blowing conduit is located in the reaction region, in the vicinity of the inlet of the second blowing conduit, or inside the inlet. Exhaust gas denitration equipment. The exhaust gas denitration apparatus according to claim 11 or 12, further comprising a carrier gas supply unit configured to supply a carrier gas to the denitration agent before the first radical generation unit.

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