JPH04358519A - Gasification device for denitration reducer - Google Patents

Abstract

PURPOSE:To provide a gasification device gasifying a solid reducer in a short time and prevent the formation of scale because of decomposition, polimerization or the like. CONSTITUTION:Reduer powder composed of solid nitrogen containing component is dropped from a piping 15 onto a gasified face 16 of a reduced heating means 3 at the normal temperature and under the normal pressure, gasification is performed at explosively fast speed only at the point of bringing the reducer into contact with the gasified face 16 which shortens the required time for gasification and controls the progress of secondary reaction such as decomposition, polymerization or the like. The reduer, therefore, is not changed in its quality to reduce the danger of formation of scale.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an exhaust gas denitrification device.
In particular, the present invention relates to a denitrification reducing agent vaporization device suitable for supplying a nitrogen oxide selective reducing agent in solid form, vaporizing it, and mixing it with exhaust gas.

0002

BACKGROUND OF THE INVENTION Since combustion exhaust gas from coal and oil contains nitrogen oxides that are harmful to animals and plants, their emission into the atmosphere is regulated. This exhaust gas emission regulation is strictly applied to sources that generate a large amount of exhaust gas, such as large boilers in industrial areas where the air is easily polluted. In large boilers, we first suppressed the amount of nitrogen oxides generated by improving the combustor, and then used exhaust gas denitrification equipment to reduce nitrogen oxides in the exhaust gas with ammonia gas added to the exhaust gas, converting it into harmless nitrogen. Later, technology for releasing it into the atmosphere was established and is now in practical use.

[0003] However, regulations on combustion exhaust gas from small boilers and diesel engines in urban areas have traditionally been lenient, and it has been rare to install exhaust gas denitrification equipment. Recently, however, air pollution in urban areas has not been improved, and in fact tends to worsen, so regulations have been tightened and exhaust gas denitrification equipment is becoming increasingly necessary. Ammonia gas, which has been conventionally used for exhaust gas denitration, is dangerous and cannot be used in such small devices. Ammonia gas is a hazardous substance whose use is regulated by the High Pressure Gas Control Law, Poisonous and Deleterious Substances Control Law, Air Pollution Control Law, Offensive Odor Control Law, Fire Service Law, etc., and cannot be used in crowded areas or in small equipment that is not adequately managed. If it is used in an ammonia aqueous solution, it will not be subject to the High Pressure Gas Control Law and will be slightly less dangerous, but it will still be harmful.

It is known that nitrogen-containing compounds are effective as reducing agents in place of ammonia in conventional denitrification equipment, and among nitrogen-containing compounds, solid reducing agents such as urea are harmless to humans and animals and are easy to obtain and handle. Therefore, many methods using urea etc. have been reported.

[0005]

[Problems to be Solved by the Invention] When the present inventors tested a denitrification device that uses urea, which is a typical solid reducing agent, it was found that complete vaporization of urea was not easy, and adhesion caused by byproducts of urea heating. There is a problem in that scale tends to accumulate in the vaporizer, exhaust gas flue, and denitrification reactor.

Granular urea is used instead of an aqueous solution because it is easier to handle and store in the denitrification equipment, but as the particles become larger, the scale adhering to the above-mentioned parts of the denitrification equipment tends to increase. By the way, 1 g of urea is separated into a crucible,
Electric furnace temperature range 350℃~600℃, heating time range 0
．． The scale weight on the remaining crucible after heating for 5 to 4 hours was measured, and the results are shown in FIG. At 350° C., which is the temperature of the denitrification reactor, 9% by weight of scale remains after heating for 0.5 hours. This scale does not decrease much even if the heating time is increased, and it only decreases to 3% by weight after 4 hours of heating. The X-ray diffraction diagram of this substance is shown in FIG. 8, and it has a peak different from that of urea, which is presumed to be a polymer.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reducing agent vaporizer for denitrification that prevents scale formation during vaporizing a reducing agent such as urea.

[0008]

Means for Solving the Problems The above objects of the present invention are achieved by the following configuration. In other words, in a reducing agent vaporization device used in a denitrification device that reduces nitrogen oxides in exhaust gas and converts them into nitrogen using a reducing agent made of a solid nitrogen-containing compound at room temperature and normal pressure, a space continuous with the exhaust gas flue is used. a reducing agent heating means having a vaporizing surface in which the reducing agent contacts and vaporizes;
reducing agent powder supply means for supplying the reducing agent to the vaporization surface of the reducing agent heating means at an arbitrary predetermined supply rate; This is a reducing agent vaporization device for denitrification, which is provided with temperature control means for the heating means to maintain the heating means at an arbitrary predetermined temperature selected from the temperature range above the temperature at which the vapor pressure becomes the pressure of the heating surface atmosphere or above.

[0009] Here, the vaporization surface of the reducing agent heating means can be integrally made of a highly thermally conductive material, and the temperature detection end of the temperature control means can be provided on or inside the vaporization surface. Further, the vaporizing surface of the reducing agent heating means can be provided with an uneven surface that holds the reducing agent powder and the reducing agent melted into droplets.

[0010] When using urea powder as a reducing agent,
The temperature control means controls the vaporizing surface temperature of the reducing agent heating means to 360°C.
The temperature is controlled within a range of 450° C. or higher.

[0011] The denitrification reducing agent supply device for the combustion device may be provided with a reducing agent decomposition catalyst layer in the exhaust gas flue downstream of the vaporization surface of the denitrification reducing agent vaporization device.

0012

[Operation] According to the present invention, the reducing agent powder is dropped onto the vaporizing surface of the reducing agent heating means, and the unevaporated reducing agent is pushed up and suspended by the vapor generated on the vaporizing surface, and vaporized. Vaporization occurs at an explosive rate only at the point of contact with a surface. Direct contact between the reducing agent powder and the vaporization surface heats the reducing agent, shortens the time required for vaporization, and suppresses the progress of side reactions such as decomposition and polymerization. Therefore, there is less risk of the reducing agent deteriorating and forming scale.

For example, if urea is used as a reducing agent,
Since the melting point of urea is as low as 132°C, urea powder turns into droplets on the vaporization surface, but as the droplets move violently on the vaporization surface, the inside of the droplet is agitated, and intermediate products that promote polymerization are produced. It is also possible that the concentration of intermediate products in the diluted liquid urea decreases, making it difficult to polymerize. Also, if this is the case,
Even if substances that are difficult to vaporize due to polymerization are generated, or even if substances that do not vaporize due to trace impurities such as iron in urea remain, the urea droplets themselves remain suspended from the vaporization surface and vaporize. Scale does not adhere to the vaporizing surface and remains only as loose powder. When the present inventors tested urea powder, it vaporized without scale formation at a vaporization surface temperature of 360° C. or higher. However, when the temperature exceeds 450°C, the jump of the urea powder becomes large, so the number of times the vaporizing surface and the urea powder come into contact decreases, and the time required for vaporization increases. Furthermore, if the temperature exceeds 650°C, the risk of ignition increases. Therefore, in the case of urea powder, the vaporization surface temperature should be set at 360°C or higher and 450°C.
It is preferable to select from the range below ℃.

[0014] Nitrogen-containing compounds other than urea, such as cyanuric acid, melamine, ammonium bicarbonate, biuret, etc., can be rapidly vaporized by heat transfer through contact with the vaporizing surface, and vaporized at the point of contact at a pressure higher than the pressure of the vaporizing surface atmosphere. generate,
Vigorous movement of the nitrogen-containing compound powder eliminates the risk of scale formation.

In the present invention, it is important to maintain the temperature of the vaporization surface of the reducing agent heating means within a predetermined temperature range. It is preferable to suppress the distribution within a narrow range, install a temperature detection end in the same block, and control the amount of heat to heat the block based on the temperature detection value. When copper is used as the material of the block, it is preferable to cover the vaporized surface with ceramics such as alumina. If copper metal is exposed, the catalytic action of copper oxide may oxidize some of the urea and produce nitrogen oxides.

[0016] The vaporization surface preferably has an uneven shape. Compared to a flat surface, the number and area of contact with the reducing agent powder increases, and the time required for vaporization becomes shorter.

Although the vaporization surface of the present invention alone can speed up the vaporization of the reducing agent and increase the reliability of reducing agent vaporization, if a catalyst layer for decomposing the reducing agent vapor is provided downstream of the vaporization surface of the vaporization device, , the reliability of the serious vaporization device can be further increased. If the reducing agent vapor is hydrolyzed in the decomposition catalyst layer by the water vapor in the carrier gas flowing through the serious vaporization device and converted into ammonia, the reducing agent such as urea will precipitate and scale even if the surface temperature of the piping drops. will not be generated.

[0018]

EXAMPLES The present invention will be explained using examples. Example 1 Urea powder with a diameter of 2 mm was dropped into a groove on an aluminum metal block maintained at a predetermined temperature, the vaporization state was observed, and the weight of the unevaporated residue was measured. Figure 1 shows the results of measuring the weight of the residue by dropping the urea powder at a rate of 10 g/h·cm2 per bottom area of the groove and varying the block surface temperature between 320°C and 500°C. The boundary of residue formation is 350
℃ and 370℃. temperature 400
FIG. 3 shows an X-ray diffraction chart of the material recovered by condensing the vapor generated in the temperature test. In the figure, the peak marked with the symbol ○ coincided with the peak of urea. From this, it is clear that when urea is rapidly vaporized by the method according to this example, most of the urea is vaporized without being altered by decomposition or polymerization.

Example 2 Changes in the time required for vaporization depending on the uneven shape of the vaporization surface were tested. In the test, urea powder with a diameter of 1.5 mm is dropped onto an aluminum metal plate maintained at a specified temperature or into a circular groove with a diameter of 8 mm, and the time required for one particle of the powder to completely vaporize is measured. did. The results are shown in Figure 4. The curve indicated by A in the figure is the time required for urea vaporization on a flat plate, and the curve indicated by B is the time required for vaporization in a groove with a diameter of 8 mm. It is clear that the time required for vaporization is shortened by processing the vaporization surface into irregularities. Curves A and B both have temperatures of 400°C and 450°C.
It is also clear that there is a region in which the time required for vaporization varies greatly between degrees Celsius, and that it is necessary to maintain the temperature at 450.degree. C. or lower in order to shorten the time required for vaporization.

Observation during the test showed that the urea powder collided violently with the wall surface in the groove formed by the unevenness and was reflected. Since the number of collisions is large, the time required for vaporization is shorter than that using a flat plate. In addition, when the temperature exceeds 400℃, the tendency of urea powder to float from the vaporization surface increases,
It becomes noticeable at temperatures above 50°C. This is considered to be the cause of the phenomenon that the time required for vaporization increases as the temperature rises.

Next, an embodiment of a denitrification apparatus using the denitrification reducing agent vaporization apparatus of the present invention will be described. Example 3 The denitration apparatus of this example is shown in FIG. FIG. 5 shows a urea vaporization device according to the present invention that supplies reducing gas to exhaust gas from an exhaust gas generation source 8 through a flue 9, purified in a denitrification reactor 10, and released into the atmosphere from a chimney 12. It is a flow diagram.

Urea in the storage tank 1 is extracted at a predetermined rate by the granular material quantitative feeder 2, and is delivered to the vaporizer 3 via the urea transport pipe 15. Air is supplied from an air blower 13 via a carrier gas conduit 14 to assist in urea movement within the urea transport tube 15 and urea dispersion within the vaporizer 3 . In the vaporizer 3, the urea powder falls onto an aluminum heating block 4 maintained at a temperature of 360° C. or higher and 450° C. or lower, where it is vaporized. Although the decomposition catalyst 5 is not necessarily required in the vaporizer 3, if a porous alumina catalyst is used as the catalyst and water vapor is mixed into the carrier gas, all of the vaporized urea can be converted into ammonia gas. Using ammonia gas rather than urea reduces the risk of scale formation in downstream piping. The gas generated from urea is injected into the flue 9 as a gaseous reducing agent 7 from the injection nozzle 6, mixed with the exhaust gas, and then reacted with nitrogen oxides in the exhaust gas on the denitrification catalyst in the denitrification reactor 10. Detoxifies nitrogen oxides.

Details of the vaporizer 3 are shown in FIG. The upper surface of the heating block 4 holds the fallen urea and has an upwardly uneven surface so as to contact and heat the urea. A built-in heater 17 and a temperature detection terminal 18 are embedded inside, and the temperature of the heating block 4 detected by the temperature detection terminal is sent to a temperature regulator 20 via a temperature signal line 19, so that it reaches a preset value. Heater power is supplied to the built-in heater 17 via the heater power line 21 to generate heat.

[0024]

According to the present invention, since the reducing agent is completely vaporized on the vaporizing surface of the reducing agent heating means, scale is not accumulated in the vaporizing section, the flue, or the denitrification reactor. Furthermore, by controlling the heating temperature of the vaporization surface, the reducing agent can be vaporized smoothly.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the vaporization surface heating temperature and the amount of unevaporated residue when the present invention is applied to urea.

FIG. 2 is a diagram showing the appearance of a residue depending on the vaporization surface temperature shown in FIG. 1;

FIG. 3 is an X-ray diffraction chart of a substance recovered by cooling and condensing the vapor generated at a heating temperature of 400° C. in FIG.

FIG. 4 is a diagram showing the influence of the shape of the heating surface on the time required for urea vaporization.

FIG. 5 is a diagram showing the flow of a denitrification device to which the vaporizer according to the present invention is applied.

FIG. 6 is a diagram showing details of the carburetor in FIG. 5;

FIG. 7 is a diagram showing the relationship between heating temperature and heating time of unevaporated residue during heating of urea.

FIG. 8 is an X-ray diffraction diagram of the residue obtained by heating at 350° C. for 4 hours in FIG. 7.

[Explanation of symbols]

1 Storage tank 2　　　Powder quantitative feeder 3. Vaporizer 5 Decomposition catalyst 7. Gaseous reducing agent 10 Denitrification reactor 13 Air blower 15 Urea transport tube 17 Built-in heater 18 Temperature detection end

Claims (5)

[Claims] Claim 1: In a reducing agent vaporization device used in a denitrification device that reduces nitrogen oxides in exhaust gas and converts them into nitrogen using a reducing agent made of a solid nitrogen-containing compound at room temperature and normal pressure, A reducing agent heating means having a vaporizing surface in which the reducing agent contacts and vaporizes in a continuous space, and a reducing agent powder supplying means for supplying the reducing agent to the vaporizing surface of the reducing agent heating means at an arbitrary predetermined supply rate. and heating to maintain the temperature of the vaporizing surface of the reducing agent heating means at an arbitrary predetermined temperature selected from a temperature range that is below the ignition temperature of the reducing agent and at least the temperature at which the vapor pressure of the reducing agent is equal to or higher than the pressure of the atmosphere of the heating surface. A vaporizing device for a reducing agent for denitrification, characterized in that it is provided with a temperature control means. 2. The vaporization surface of the reducing agent heating means is integrally made of a highly thermally conductive material, and the temperature detection end of the temperature control means is provided on or inside the vaporization surface. The vaporization device for the reducing agent for denitrification described above. 3. The reduction for denitrification according to claim 1, wherein the vaporizing surface of the reducing agent heating means is provided with an uneven surface for holding the reducing agent powder and the reducing agent melted into droplets. Agent vaporization device. 4. When using urea powder as a reducing agent, the temperature control means controls the vaporizing surface temperature of the reducing agent heating means to 36°C.
The vaporizing device for a reducing agent for denitrification according to claim 1, wherein the temperature is controlled within a temperature range of 0° C. or more and 450° C. or less. 5. A reducing agent supply device for denitration, characterized in that a reducing agent decomposition catalyst layer is provided in the gas flow path downstream of the vaporization surface of the vaporization device for a reducing agent for denitration according to claim 1.