JP3885272B2 - Denitration equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a denitration apparatus for removing nitrogen oxides (NO _x ) contained in exhaust gas in an internal combustion engine or the like.
[0002]
[Prior art]
Conventionally, NO _x treatment technology has been required in various fields and has been put to practical use as flue gas denitration technology as a general treatment method. The flue gas denitration technology is roughly divided into a dry method and a wet method. At present, the selective catalytic reduction method, which is one of the dry methods, is technically advanced, and has attracted attention as a powerful denitration method.
[0003]
The main reaction of the selective catalytic reduction method is as follows.
[0004]
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1)
In this reaction, ammonia, hydrocarbons, and carbon monoxide are used as a reducing agent. In particular, ammonia selectively removes NO _x even in the presence of oxygen, so NO contained in exhaust gas from diesel engines and the like. Effective for removing _X. This reaction contains precious metals such as platinum as denitration agents, alumina and titanium oxide (TiO ₂ ) as main components, and contains oxides and double salts such as vanadium (V), molybdenum (Mo), tungsten (W) as additives. A catalyst is used.
[0005]
Among these, the V ₂ O ₅ / TiO ₂ catalyst is effective in terms of activity, selectivity, and durability, and has been used for exhaust gas with a high content of SO _{x and} dust in addition to the NO _x. Is shown.
[0006]
[Problems to be solved by the invention]
The selective catalytic reduction method can treat NO _x with a simple system, obtain a high NOx removal rate, and decompose NO _x into harmless nitrogen gas (N ₂ ) and moisture (H ₂ O). Therefore, there is an advantage that waste liquid treatment is unnecessary. Ammonia gas or ammonia water is used as a reducing agent, but ammonia is expensive, and therefore a method using urea water has been studied from the viewpoint of cost.
[0007]
When urea water is used as the reducing agent, as shown in the following formula (2), means for decomposing urea by heating and evaporating urea water and generating ammonia as the reducing agent is used.
[0008]
(NH ₂ ) ₂ CO + H ₂ O → NH ₃ + CO ₂ (2)
However, depending on the decomposition conditions, urea does not decompose into ammonia but changes to other high melting point substances (cyanuric acid, melamine, isocyanic acid, etc.), and there are cases where decomposition efficiency decreases and harmful substances are generated, There may be problems in terms of cost and safety.
[0009]
The present invention has been made in view of the above, and obtains a denitration apparatus capable of efficiently decomposing urea water into ammonia without generating high melting point substances or harmful substances when decomposing urea water. It is for the purpose.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the denitration apparatus of the present invention includes a vaporizer container filled with zeolite particles in a pipe through which exhaust gas flows, and the vaporizer container is a liquid into which urea water is injected. The vaporizer vessel discharges ammonia obtained by decomposing urea by heating with heat supplied from exhaust gas into the pipe as a reducing agent. The ammonia and the exhaust gas are mixed and then contacted with the denitration catalyst, and a temperature measuring means for measuring the temperature in the vaporizer vessel is provided, and the vaporizer is based on the measurement signal from the temperature measuring means. The amount of water supplied into the vaporizer vessel is adjusted so that the temperature in the vessel is always 90 ° C. or higher and 162 ° C. or lower .
[0011]
The liquid feeding pipe and the water pipe are either configured as a double pipe structure in which the liquid feeding pipe is arranged inward, or the water feeding pipe is directly connected to the liquid feeding pipe.
[0013]
As a denitration catalyst, a zeolite carrier is used as a main raw material, a denitration catalyst is produced by degreasing, firing and honeycomb forming, and a denitration catalyst in which cobalt is supported on the catalyst carrier is used.
[0014]
According to such a denitration device, when urea water is injected into the vaporizer vessel from the liquid feed pipe and at the same time an appropriate amount of water is injected from the water pipe, urea is decomposed by the heat supplied from the exhaust gas and the decomposition action of the zeolite, Ammonia (NH ₃ ) and carbon dioxide (CO ₂ ) as reducing agents are generated. The ammonia and carbon dioxide flow into the exhaust gas pipe from the hole opened in the vaporizer vessel, mix with the exhaust gas, and contact with the denitration catalyst in the reactor in the next stage. Based on this, nitrogen oxides are removed.
[0015]
During such operation, the temperature in the vaporizer vessel is measured by the temperature measuring means, and the amount of water flowing into the water pipe is adjusted so that this temperature is always 90 ° C. or higher and 162 ° C. or lower. As a result, the temperature of urea does not increase excessively, so that urea can be efficiently decomposed into ammonia, and the action of solidifying urea and preventing clogging of the liquid feed pipe due to solidification can be obtained.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Various specific examples of the denitration apparatus according to the present invention will be described below. First, urea decomposition characteristics as a basis of this embodiment will be described with reference to FIGS. FIG. 5 is a graph showing the decomposition characteristics when urea is rapidly heated at a rate of 50 ° C. per minute using a parallax thermobalance, line A shows the thermogravimetric change (TG,%) of urea, Line B shows the change in reaction heat (DTA, converted from thermocouple measured value μv). The melting point of urea is 135 ° C.
[0017]
The change in line B from 136 ° C represents the evaporation of urea, and the change in line B at 263 ° C represents the melting point of melamine. Furthermore, the change of line A from 344 ° C. represents the decomposition of cyanuric acid. The temperature range C indicates a region where a high melting point substance is generated, and the generation of a high melting point substance was confirmed at a temperature exceeding 162 ° C. A temperature range D indicates a decomposition region of the high melting point substance.
[0018]
As understood from the line A, about 71.5% of urea is directly vaporized by heat, and about 28.5% is changed to melamine and cyanuric acid which are high melting point substances.
[0019]
Therefore, when urea water is sprayed into a pipe of exhaust gas at a high temperature of about 350 ° C. to 450 ° C. using a nozzle or the like, urea is vaporized or changed into a high melting point substance by the same heating reaction as described above. Therefore, there is a concern that urea is wasted.
[0020]
FIG. 6 is a graph showing temperature and thermogravimetric change (TG) when zeolite powder and urea are mixed. In general, zeolite is a substance mainly composed of an oxide of aluminum and silicon, which has been conventionally used as a catalyst support, and the zeolite has pores of about 5 to 10 angstroms.
[0021]
In this experiment, urea was dissolved in water, mixed well with zeolite powder, excess water was removed, and measurement was performed using a parallax thermobalance. Line E in FIG. 6 is a graph showing the decomposition characteristics when the temperature is rapidly increased at a rate of 50 ° C. per minute using only urea as in the example of FIG. 5, and line F is obtained by adding zeolite powder to urea. A graph showing the decomposition characteristics when the temperature is raised at a slow rate of 2 ° C. per minute, and line G is a graph showing the decomposition characteristics when the zeolite powder is added to urea and the temperature is raised at a rate of 50 ° C. per minute.
[0022]
According to FIG. 6, even when the urea water is rapidly heated at a rate of 50 ° C./min (line G) due to the coexistence of the zeolite powder, the generation ratio of the high melting point substance is reduced to about 16%. It can be seen that zeolite has an action of promoting the decomposition of urea.
[0023]
The reason is considered that urea is adsorbed on the surface of zeolite because it is a highly polar substance and decomposes into ammonia and carbon dioxide on the zeolite surface. When the temperature of the urea water is increased at a slow rate of 2 ° C./min (line F), the generation ratio of the high melting point substance is further reduced to about 6%. This is because the decomposition of urea is finished. This is probably because urea is decomposed before the reaction time is secured and the temperature reaches a temperature at which a high melting point substance is formed. In the case where the temperature is rapidly increased using only urea water at a rate of 50 ° C. per minute (line E), the generation ratio of the high melting point substance is about 28.5%.
[0024]
Therefore, when injecting urea water into the exhaust gas, urea can be efficiently decomposed into ammonia if a temperature condition that does not generate a high melting point substance as described above is ensured. When urea water is sprayed directly into the exhaust gas using a nozzle employed as a spraying means, the water is vaporized first, and the reaction represented by the above formula (2) does not occur.
[0025]
Therefore, this embodiment is characterized in that a vaporizer described below is used in order to efficiently decompose urea water into ammonia.
[0026]
FIG. 1 is a schematic diagram showing the configuration of a first embodiment of a carburetor employed in the present invention. Reference numeral 1 is a pipe for exhaust gas G derived from an internal combustion engine (not shown). The pot 2 is disposed at the position as a vaporizer container. A large number of holes 2a, 2a for discharging the vaporized ammonia gas are opened on the upper wall surface of the pot 2, and the pot 2 is filled with zeolite particles 3, 3.
[0027]
4 is a liquid feed pipe for injecting urea water into the pot 2, and 5 is a water pipe. The liquid feed pipe 4 and the water pipe 5 are configured as a double pipe structure in which the liquid feed pipe 4 is inserted inward, and the double pipe penetrates the exhaust gas pipe 1 and is potted from the outside. 2 is inserted. 6 is a thermocouple inserted into the pot 2 from the outside of the pipe 1 as a temperature measuring means for measuring the temperature in the pot 2.
[0028]
The reason why the liquid feed pipe 4 and the water pipe have a double pipe structure is that the urea feed caused by excessive heating of the urea water by the exhaust gas G in the liquid feed pipe 4 is prevented, and the liquid feed pipe 4 This is to prevent the clogging phenomenon.
[0029]
According to the configuration of the denitration apparatus, when urea water is injected into the pot 2 from the liquid supply pipe 4 and an appropriate amount of water is injected from the water pipe 5 at the same time, the above formula (2) is obtained by the heat supplied from the exhaust gas G. Based on this, urea is decomposed to produce ammonia (NH ₃ ) and carbon dioxide (CO ₂ ) as reducing agents. The ammonia and carbon dioxide flow into the exhaust gas G pipe 1 from the holes 2 a and 2 a opened in the upper wall surface of the pot 2. After being mixed with the exhaust gas G, it flows down and comes into contact with the denitration catalyst.
[0030]
During the above operation, it is necessary to measure the temperature in the pot 2 with the thermocouple 6 and to control the temperature so that it is always 90 ° C. or higher and 162 ° C. or lower. This is because it has been confirmed that a high melting point substance is generated at a temperature exceeding 162 ° C., and it has been confirmed that the decomposition of urea into ammonia is performed from 90 ° C. in the configuration of the denitration apparatus. This temperature control is carried out by controlling the amount of water supplied from the water pipe 5, preventing the temperature in the pot 2 from rising excessively, preventing the formation of a high melting point substance and efficiently decomposing urea into ammonia. Further, it is possible to prevent the clogging phenomenon of the liquid feeding pipe 4 caused by solidification of urea.
[0031]
The configuration of the second embodiment of the vaporizer employed in the present invention will be described with reference to FIG. Since the basic configuration is the same as that of the first embodiment, the same reference numerals are given.
[0032]
In the second embodiment, an opening 1a is formed in the middle of the exhaust gas G pipe 1, and a bottomed cylindrical pot 2 as a vaporizer container is inserted through the opening 1a. 8 is a lid portion of the pot 2, and the lid portion 8 is fixed to a flange portion 7 formed in the opening portion 1 a of the pipe 1, whereby the opening portion 1 a of the pipe 1 is hermetically closed and the pot 2 is piped 1 is supported in a suspended state.
[0033]
The pot 2 is filled with zeolite particles 3 and 3, and a hole 2 b for discharging the vaporized ammonia gas is formed at one end of the side wall of the pot 2. In the illustrated example, the vaporized ammonia gas is set to be discharged toward the downstream direction of the exhaust gas G from the hole 2b.
[0034]
Reference numeral 4 denotes a liquid feed pipe for supplying urea water, and is provided extending from the outside through the lid portion 8 to the vicinity of the bottom wall of the pot 2. A water pipe 5 for supplying water for controlling the temperature in the pot 2 is directly connected to the liquid feed pipe 4 outside the lid portion 8. 6 is a thermocouple provided as a temperature measuring means for measuring the temperature in the pot 2.
[0035]
According to the vaporizer of the second embodiment, when urea water and water are merged into one liquid feed pipe 4 and injected into the pot 2, the above equation (2) is obtained by the heat supplied from the exhaust gas G. Based on this, urea is decomposed in the pot 2 to generate ammonia (NH ₃ ) and carbon dioxide (CO ₂ ). The ammonia and carbon dioxide are discharged from the hole 2b of the pot 2 in the downstream direction of the exhaust gas G, mixed with the exhaust gas G, and then flow down to contact the denitration catalyst.
[0036]
At the same time, the temperature in the pot 2 is measured by the thermocouple 6 and the temperature in the pot 2 is controlled so that this temperature is always 90 ° C. or higher and 162 ° C. or lower. This temperature control is performed by adjusting the amount of water flowing in the water pipe 5 that joins the liquid feed pipe 4, and this adjustment of the water amount prevents the urea water in the pot 2 from being excessively heated. The generation can be prevented and urea can be efficiently decomposed into ammonia, and the clogging phenomenon of the liquid feeding pipe 4 due to solidification of urea can be prevented.
[0037]
As another use method of the water pipe 5 used in the second embodiment, only water is poured through the water pipe 5 without flowing urea water into the liquid feed pipe 4 when the internal combustion engine is stopped. The liquid feed pipe 4 can be easily cleaned.
[0038]
Next, an actual example of a denitration apparatus using the vaporizer described in the present embodiment will be described with reference to FIG. In the figure, 11 is a sealed reactor, 12 is an internal combustion engine such as a diesel engine, 11a is an introduction part of exhaust gas G flowing through the pipe 1 led out from the internal combustion engine 12, and 11b is the exhaust part. . A vaporizer 13 (corresponding to the second embodiment) is disposed in the middle of the pipe 1. 15 is a water tank and 16 is a tank of urea water.
[0039]
In the reactor 11, denitration catalysts 14 and 14 formed in a honeycomb shape are stacked. As the denitration catalyst 14, 14, a zeolite carrier (ZSM-5) is used as a main raw material, and the zeolite is degreased, calcined and formed into a honeycomb to produce a catalyst carrier, and this catalyst carrier is supported with cobalt by ion exchange. Using.
[0040]
Reference numerals 17 and 18 _denote , for example, adjustment of the urea water supply amount according to the load condition of the internal combustion engine 12, the amount of NO _x in the exhaust gas, etc., adjustment of the water supply amount by the measurement signal of the thermocouple 6, the urea water 16 and the water 15 A control panel and a controller for controlling a supply amount and performing various settings and operations.
[0041]
In FIG. 3, in order to clearly show the supply control mechanism of water and urea water to the vaporizer 13, the configuration of the control mechanism is taken out separately from the enlarged portion of the vaporizer 13 and shown in the center part in the figure. It is.
[0042]
According to such a denitration apparatus, ammonia gas generated by the decomposition of urea water from the vaporizer 13 by the above-described operating principle flows into the exhaust gas G generated from the internal combustion engine 12 and is mixed with the exhaust gas. 11 is fed into the reactor 11 from the introduction part 11a and passes through the denitration catalysts 14 and 14. At this time, nitrogen oxide (NO _x ) contained in the exhaust gas G is removed by a uniform denitration reaction based on the main reaction of the selective catalytic reduction method (see the above-mentioned formula 1), and the discharge unit 11b From the outside.
[0043]
According to the vaporizer 13, since the urea is efficiently decomposed into ammonia and the ammonia is supplied to the exhaust gas G in a gas state, the exhaust gas G and the reducing agent are mixed well. The length of the piping from the reactor 13 to the reactor 11 can be greatly shortened, and the denitration apparatus can be downsized.
[0044]
Further, if necessary, a disc-like or ellipse-like shielding plate 19 proposed in Japanese Patent Application No. 8-183904 may be provided at a position facing the introduction portion 11a in the reactor 11. By providing this shielding plate 19, the exhaust gas G containing ammonia collides with the shielding plate 19 in the reactor 11, and at this time, the exhaust gas G and ammonia are mixed more favorably. It is possible to further reduce the size of the denitration device, such as shortening, and the exhaust gas G can be uniformly brought into contact with the denitration catalysts 14 and 14 by the rectification action of the post-vortex generated after passing through the shielding plate 19. Efficiency can be further improved.
[0045]
FIG. 4 is a graph showing the denitration characteristic change by the reducing agent injection method based on the conventional example and the present example. The line H is a case where urea water is sprayed from the nozzle into the pipe, and the line I is used in this example. The case where a vaporizer is used is shown respectively. The experiment was performed by injecting urea water into a pipe connecting a 100 kW diesel engine generator and a denitration device. The horizontal axis of FIG. 4 are shown as the number of moles of urea injected against moles of the NO _X discharged from a diesel engine.
[0046]
The theoretical reaction between urea and NO _x is NO _x 1 and urea 0.5, but using the vaporizer employed in this example, it can be confirmed that the reaction proceeds as expected. It was.
[0047]
【The invention's effect】
As described in detail above, according to the present invention, urea is decomposed by heat supplied from exhaust gas by injecting urea water and water into a vaporizer vessel filled with zeolite particles, and the reducing agent. As a result, ammonia is generated and mixed with the exhaust gas, flows into the denitration catalyst in the reactor, and nitrogen oxides can be removed based on the selective catalytic reduction method.
[0048]
In addition, by efficiently decomposing urea into ammonia and supplying ammonia to the exhaust gas in a gaseous state, the exhaust gas and the reducing agent are mixed well, so the length of the pipe from the vaporizer to the reactor is long. Therefore, the denitration device can be downsized.
[0049]
By adjusting the amount of water so that the temperature in the vaporizer vessel is always 90 ° C. or higher and 162 ° C. or lower during operation, the temperature of urea is prevented from being excessively increased, and the decomposition efficiency of urea is prevented from being lowered. It is possible to prevent clogging of the liquid feeding pipe due to solidification of urea.
[0050]
In particular, in the present invention, it is not necessary to use expensive ammonia gas or aqueous ammonia which has been conventionally used as a reducing agent, which is effective from the viewpoint of cost. Therefore, according to the present invention, when the urea water is decomposed, a high melting point substance or a harmful substance is not generated, and the urea water can be decomposed into ammonia efficiently and supplied to the exhaust gas at a low cost. A denitration device is obtained.
[Brief description of the drawings]
FIG. 1 is a schematic view showing the configuration of a first embodiment of a vaporizer used in a denitration apparatus of the present invention.
FIG. 2 is a schematic view showing the configuration of a second embodiment of the vaporizer used in the denitration apparatus of the present invention.
FIG. 3 is a schematic diagram for entirely explaining an actual example of a denitration apparatus according to the present embodiment.
FIG. 4 is a graph showing changes in denitration characteristics by a reducing agent injection method based on a conventional example and this example.
FIG. 5 is a graph showing the decomposition characteristics of urea.
FIG. 6 is a graph showing the decomposition characteristics of urea with and without zeolite.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Pipe (exhaust gas G) 2 ... Pot 2a, 2a (as a vaporizer container) ... Hole 3 ... Zeolite particle 4 ... (Urea water) liquid feed pipe 5 ... Water pipe 6 ... Thermocouple 7 ... Flange 8 ... Lid 11 ... Reactor 11a ... Introduction part 11b ... Discharge part 12 ... Internal combustion engine 13 ... Vaporizer 14 ... Denitration catalyst 15 ... Water 16 ... Urea water 17 ... Control panel 18 ... Controller 19 ... Shield plate

Claims (4)

A vaporizer container filled with zeolite particles is placed in a pipe through which exhaust gas flows,
The vaporizer container includes a liquid feeding pipe into which urea water is injected, and a water pipe into which water is injected ,
The vaporizer vessel discharges ammonia obtained by decomposing urea by heating with heat supplied from exhaust gas into the pipe as a reducing agent, and contacts the denitration catalyst after the ammonia and exhaust gas are mixed. together and configured to,
Temperature measuring means for measuring the temperature in the vaporizer vessel is provided, and the vaporizer vessel is supplied to the vaporizer vessel so that the temperature in the vaporizer vessel is always 90 ° C. or higher and 162 ° C. or lower based on a measurement signal from the temperature measuring means. The denitration device is configured to adjust the amount of water to be discharged .   The denitration apparatus according to claim 1, wherein the liquid feed pipe and the water pipe are configured as a double pipe structure in which the liquid feed pipe is arranged inward.   The denitration apparatus according to claim 1, wherein a water pipe is directly connected to the liquid feed pipe. 2. A denitration catalyst in which zeolite is used as a main raw material, a catalyst carrier is prepared by degreasing, firing, and honeycomb forming the zeolite, and a cobalt carrier is supported on the catalyst carrier. The denitration device according to any one of items 2 and 3.

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