JP3795114B2 - Waste incinerator exhaust gas treatment method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a waste incinerator exhaust gas treatment method for reducing the amount of NO _{x in} exhaust gas discharged from a waste incinerator.
[0002]
[Prior art]
In a waste incinerator that incinerates waste, the concentration of NO _{x in} the exhaust gas discharged tends to change suddenly, and therefore it is difficult to effectively reduce NO _x . FIG. 3 shows a conventionally used exhaust gas treatment method.
[0003]
FIG. 3 is a system diagram of exhaust gas treatment of a conventional waste incinerator. In FIG. 3, three types of system diagrams (a), (b), and (c) are shown. FIG. 3A shows, for example, means proposed in Japanese Patent Laid-Open No. 58-45723, and includes a waste incinerator 1, a baghouse (dust removal device) 2, and a chimney 3. Is a non-catalytic denitration method in which a reducing agent such as urea or ammonia is blown into the waste incinerator 1, that is, an in-furnace denitration method, which is used as a simple treatment method.
[0004]
FIG. 3B shows, for example, “3rd Environmental Engineering Symposium Lecture Collection (1993.7.2)”, “Waste Society 4th Research Presentation Lecture Collection (1993.10.13)”. In the apparatus including the waste incinerator 1, the baghouse 2, and the chimney 3, a denitration tower 4 is provided in the downstream of the baghouse 2, and denitration is performed by the denitration tower 4. An initial denitration rate of 50-75% is obtained at 165-260 ° C.
[0005]
FIG. 3C shows, for example, the means proposed in Japanese Patent Application Laid-Open No. 4-219124. In the apparatus provided with the waste incinerator 1, the bag filter type reactor 5, and the chimney 3 , A system using a denitration bag filter in which a filter part is impregnated with a denitration catalyst. In the system using this catalyst, ammonia gas or ammonia water is blown upstream of the flue,
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1)
NO _x is reduced and removed by this reaction.
[0006]
In the selective catalytic reduction method using NH ₃ as a reducing agent, the reduction reaction of NO _x by NH ₃ is known to be a reduction reaction by the following two reaction formulas in addition to the reaction by the above reaction formula.
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (2)
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O (3)
Of the above two reaction equations, the NO _x removal effect obtained by the reaction equation (2) has a reaction rate twice that of the reaction equation (1) when the NO / NO ₂ molar ratio is 1 or more. From this, for example, as disclosed in JP-A-6-53211, means for reducing nitrogen oxides by reducing NO _{2 in} waste gas as NO and contacting the catalyst has been proposed.
[0007]
[Problems to be solved by the invention]
The method shown in (a) of FIG. 3 has a limit in reducing the NO _x concentration, and cannot cope with the current situation where the regulation value of NO _x is being strengthened. In the case of municipal waste incinerators, it is difficult to select the reducing agent injection point because the furnace temperature and gas concentration distribution vary greatly. Experimental results have been obtained that the NOx removal rate is improved by spraying the reducing agent uniformly in a high temperature range of 900 to 1050 ° C. However, if the temperature is too high, NO _x is burned by the combustion of the ammonia compound of the reducing agent. In addition, if the temperature is too low, the denitration rate decreases and the ammonia leak concentration increases, so in practice, the denitration agent / NO _x ratio cannot be increased.
[0008]
The method shown in FIG. 3 (b) shows that the current catalyst has low activity at low temperatures, and it is necessary to increase the amount of catalyst used and the temperature in order to improve the denitration rate. For this reason, the pressure loss of the reaction tower 4 increases, and the attraction fan needs to be enlarged. This creates a need to replace the induction fan to add a catalyst denitration device to the existing equipment.
[0009]
Also in the method shown in FIG. 3C, it is necessary to increase the amount of catalyst used and the temperature in order to improve the denitration rate. However, the heat-resistant temperature of felts such as glass fiber woven fabric, polyphenylene sulfide, and polyimide used as bag filters is about 200 to 250 ° C., and there is a limit to increasing the temperature. Further, various problems associated with an increase in filter pressure loss exist as in the case of the method shown in FIG. Further, there is a problem that the catalyst is contaminated by sulfate in the exhaust gas, the active surface of the catalyst is blocked, and the denitration rate is lowered.
[0010]
An object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a waste incinerator exhaust gas treatment method that can efficiently reduce NO _x at low temperatures and can be easily applied to existing equipment. It is in.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an exhaust gas treatment method for a waste incinerator that reduces the amount of NOx in the exhaust gas by introducing the exhaust gas discharged from the waste incinerator to the denitration treatment device. Introducing and adding N ₂ O produced by vaporizing and decomposing an ammonium nitrate aqueous solution into the upstream flue or the denitration treatment apparatus, bringing it into contact with nitrogen compounds in the exhaust gas together with a reducing agent such as ammonia, at low temperature It is characterized by improving the denitration rate.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on the illustrated embodiments.
FIG. 1 is a system diagram illustrating an exhaust gas treatment method for a waste incinerator according to an embodiment of the present invention. In this figure, 10 is a waste incinerator, 11 is a denitration device, 12 is a suction blower for attracting exhaust gas, 13 is a flue between the waste incinerator 10 and the denitration device 11, and 14 is a denitration device 11 and a suction blower 12. Reference numeral 15 denotes a gas cooler for cooling the exhaust gas from the denitration device 11. 16 is a liquid supply tank for storing ammonium nitrate aqueous solution, 17 is a liquid feed pump for sending out the liquid in the liquid feed tank 16, 18 is a liquid feed heater for heating the liquid from the liquid feed pump 17, and 19 is a denitration device 11. This is an NO _x analyzer for analyzing the NO _x concentration at the inlet and outlet.
[0013]
During operation of the garbage incinerator 10, the ammonium nitrate aqueous solution in the feed tank 16 is sucked up by the feed pump 17, heated and vaporized and decomposed by the feed heater 18, and the flue 13 upstream of the denitration device 11. To be introduced. The introduced ammonium nitrate aqueous solution promotes catalytic reduction denitration reaction in the catalyst denitration apparatus 11 even under a low temperature condition of 180 to 250 ° C.
[0014]
The above reaction will be described in more detail. Most of the NO _{x in} the combustion exhaust gas from the waste incineration facility is NO. Therefore, denitration is actually performed according to each of the above-described reaction formulas. For example, in order to improve the denitration rate of denitration by the reaction formula (2), it is necessary to introduce NO ₂ into the exhaust gas to cause a catalytic denitration reaction. In the present embodiment, with reference to this method, attention is paid to a compound that generates N ₂ O having a different oxidation number from NO and NO ₂ , such as ammonium nitrate, and a catalytic denitration apparatus while vaporizing these aqueous solutions. 11 is introduced into the flue 13 upstream, and the denitration rate is improved at a low temperature by the following reaction similar to the above reaction formula (2).
[0015]
First, NH ₄ NO ₃ (ammonium nitrate) undergoes the following decomposition reaction to generate N ₂ O.
NH ₄ NO ₃ = N ₂ O + 2H ₂ O + 10 kcal mol ⁻¹ (at 250 ° C.) (4)
In this case, an aqueous solution of about 0.1 to 10% of ammonium nitrate ammonium is prepared, and the aqueous solution is heated and vaporized and decomposed at 180 to 300 ° C., particularly in the vicinity of 250 ° C., and the flue upstream of the denitration device 11 13 is desirable.
[0016]
The generated N ₂ O causes a denitration reaction in the presence of a catalyst according to the following reaction formula (5) or (6). This reaction is an exothermic reaction from the heat of reaction (−ΔH) and the activation free energy (ΔG), and has the same reaction rate as the reaction formulas (2) and (3).
2NO + N ₂ O + 2NH ₃ → 3N ₂ + 3H ₂ O (5)
-Δ = 214 kcal mol ^-1 (exotherm), ΔG = -222 kcal mol ^-1
3N ₂ O + 2NH ₃ → 4N ₂ + 3H ₂ O (6)
-Δ = 254 kcal mol ^-1 (exotherm), ΔG = -246 kcal mol ^-1
In particular, the effect of improving the denitration rate can be obtained by the reaction of reaction formula (5).
[0017]
In the description of the above embodiment, an example in which ammonium nitrate is used as a reaction activator has been given. In addition to the production of N ₂ O using such ammonium nitrate, for example, The use of substances is also possible.
(I) Reduction of nitrate / nitrite with tin (II) chloride / sodium amalgam (ii) Oxidation of ammonia, potassium sulfate / dinitrogen oxide generated from saturated potassium hydroxide solution of potassium nitrite + nitric oxide K ₂ SO ₄ N ₂ O) is treated with a dilute acid.
(Iii) Decomposition of hydradium nitrite ([N ₂ H ₅ ] NO ₂ → N ₂ O + NH ₃ + H ₂ O
(Iv) Reaction of hydrazoic acid and nitrous acid (HN ₃ + HNO ₂ → N ₂ + N ₂ O + H ₂ O
(V) Discharge in a mixed gas of nitrogen and oxygen In the above embodiment, the denitration apparatus 11 has been described as an example of the denitration treatment apparatus. However, the present invention is not limited to this, and a denitration tower system (honeycomb / plate) Shape / particulate denitration catalyst), denitration bag filter method (surface / inner base fabric support method, catalyst fiber filter method, flue injection method) can also be used, and the catalyst component, shape and method of use are also selected appropriately be able to. Further, a reaction activator such as ammonium nitrate may be introduced into the denitration apparatus instead of the flue.
[0018]
【Example】
In the embodiment shown in FIG. 1, the ammonium nitrate aqueous solution diluted to 1.6% by weight was used and introduced into the flue at a flue NO _x concentration and an equivalent ratio of 0 to 1. Further, the temperature of the liquid supply heater 18 was set to 300 to 400 ° C., and the ammonium nitrate aqueous solution was heated to be vaporized and thermally decomposed. The NO _x concentration in the exhaust gas was 200 ppm on average, and the temperature in the denitration apparatus 11 was 230 ° C. NH ₄ NO ₃ while changing the (nitrate ammonium pneumo) concentration from 0 to _{200 ppm NH 3 / (NO +} NH 4 NO 3) was added NH ₃ so that the concentration ratio is 1.2, was measured for NOx removal efficiency. The result is shown in FIG.
[0019]
In FIG. 2, the horizontal axis represents the ammonium nitrate / NO 3 molar ratio, and the vertical axis represents the denitration rate. When not adding nitric acid ammonium pneumo (molar ratio = 0), relative to the inlet of the NO _X concentration 200 ppm, NO _X concentration at the outlet is next 86 ppm, the denitration rate was 57%. Upon introduction nitrate ammonium pneumo with NH ₄ NO ₃ / NO molar ratio 0.2, NO _X concentration at the outlet the inlet of the NO _X concentration with respect to 235 ppm is next 79 ppm, the denitration ratio was 66%. It was found that the denitration efficiency at this time was the largest.
[0020]
【The invention's effect】
As described above, in the present invention, a fluid reaction activator is introduced and added to the upstream flue of the denitration treatment apparatus or into the denitration treatment apparatus, and mixed with the nitrogen compound in the exhaust gas. Therefore, denitration can be performed efficiently, and complicated incidental equipment is not required, and application to an existing furnace is easy.
[Brief description of the drawings]
FIG. 1 is a system diagram illustrating an exhaust gas treatment method for a waste incinerator according to an embodiment of the present invention.
FIG. 2 is a graph showing the relationship between the molar ratio of NH ₄ NO _{3 to} NO in exhaust gas and the denitration rate.
FIG. 3 is a system diagram of exhaust gas treatment of a conventional waste incinerator.
[Explanation of symbols]
10 incinerator 11 denitrator 12 suction blower 13 flue 15 gas cooler 16 feed pump 17 feeding pump 18 serving solution heater 19 NO _X analyzer

Claims (2)

In a waste incinerator exhaust gas treatment method in which exhaust gas discharged from a waste incinerator is introduced into a denitration treatment apparatus to reduce the amount of NOx in the exhaust gas,
Introducing and adding N ₂ O produced by vaporizing and decomposing ammonium nitrate aqueous solution into the upstream flue of the denitration treatment apparatus or in the denitration treatment apparatus, and mixing contact with nitrogen compounds in the exhaust gas together with a reducing agent such as ammonia An exhaust gas treatment method for a waste incinerator characterized in that the denitration rate is improved at low temperatures . In a waste incinerator exhaust gas treatment apparatus provided with a flue through which exhaust gas discharged from a waste incinerator flows and a denitration treatment apparatus into which exhaust gas from the flue is introduced,
An apparatus for supplying N ₂ O obtained by vaporizing and decomposing an aqueous ammonium nitrate solution in the flue or the denitration treatment apparatus is provided,
A waste incinerator exhaust gas treatment apparatus characterized by mixing and contacting a nitrogen compound in exhaust gas together with a reducing agent such as ammonia to improve the denitration rate at a low temperature .

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