JP4760702B2 - Leak ammonia reduction method in non-catalytic denitration of non-transfer type ash melting furnace exhaust gas - Google Patents

Description

  The present invention is a non-catalyst using high concentration nitrogen oxide (NOx) in a gas discharged from an ash melting furnace using a non-transfer type plasma torch using air as a working gas as a heating source, and ammonia as a reducing agent. In which the unreacted ammonia is decomposed and removed on the downstream side of the non-catalytic denitration zone.

A Europlasma ash melting system equipped with a non-transfer ash melting furnace is shown in FIG. Air is generally used as a working gas for a non-transfer type plasma torch. In the plasma torch, since the working gas air is heated to a high temperature exceeding 3000 ° C., nitrogen in the air is oxidized by oxygen, and high concentration NOx exceeding 30000 ppm is generated. In order to decompose this high-concentration NOx, advanced exhaust gas treatment technology is required. Therefore, it has been necessary to use wet exhaust gas treatment, waste water treatment equipment capable of treating high-concentration nitric acid-based nitrogen, and a large amount of denitration catalyst (see Patent Documents 1, 2 and 3).
Japanese Patent Laid-Open No. 8-215536 (Non-catalytic denitration of a waste incinerator) JP 52-39834 A (injecting ammonia gas as a reducing agent into the free board portion on the fluidized bed of the fluidized bed furnace (0.1% or less in the exhaust gas) JP 7-39720 A (suppression of NOx and CO production by ammonia oxidation reaction)

  In order to solve the above problems, if the NOx concentration is to be reduced with high efficiency by the non-catalytic selective denitration method before the exhaust gas is introduced into the exhaust gas treatment device, the amount of ammonia blowing increases, Leakage increases. Since this leaked ammonia cannot be reduced by dry exhaust gas treatment, wet exhaust gas treatment is required.

  In view of the above situation, the present invention supplies a combustible gas to the downstream side of the non-catalytic denitration zone and combusts it when subjecting the NOx-containing exhaust gas discharged from the non-transfer type plasma ash melting furnace to the non-catalytic denitration treatment. The present invention provides a method for reducing leakage ammonia in non-catalytic denitration of non-transfer type ash melting furnace exhaust gas, characterized in that exhaust gas after denitration is heated to decompose and remove unreacted ammonia.

The non-catalytic denitration, NH ₃ and a method of selectively reducing and removing NOx in the exhaust gas with NH ₃ donor such as urea.

  In the present invention, propane, natural gas, or the like is used as the combustible gas.

  The exhaust gas residence time in the non-catalytic denitration zone is preferably 1 to 2 seconds. Below this range, the denitration efficiency is poor, and beyond this range, leaked ammonia increases rapidly.

  The reaction temperature in the non-catalytic denitration zone is preferably 800 to 870 ° C. If it is less than this range, the denitration efficiency is poor, and if it exceeds this range, the leaked ammonia concentration decreases to non-detection, but NOx is generated due to ammonia decomposition, so there is a disagreement that the denitration performance deteriorates.

The residence time of the exhaust gas in the ammonia decomposition zone is preferably 0.83 to 2 seconds. Below this range, the ammonia decomposition efficiency is poor, and even above this range, there is no difference in ammonia decomposition efficiency.

  The reaction temperature in the ammonia decomposition zone is preferably 900 to 1000 ° C. If it is less than this range, the ammonia decomposition efficiency is poor, and if it exceeds this range, the leaked ammonia concentration decreases to non-detection.

  According to the first aspect of the present invention, NOx can be reduced with high efficiency up to a concentration capable of being discharged into the atmosphere by non-catalytic selective denitration, and the leaked ammonia is reduced to a concentration at which white smoke does not occur. Therefore, the exhaust gas treatment is further simplified.

  In addition, the purification load on the exhaust gas treatment system installed downstream can be reduced.

  According to the second aspect of the present invention, since the exhaust gas stays at 800 to 1000 ° C. for 2 to 4 seconds in the non-catalytic denitration zone and the downstream ammonia decomposition zone, the effect of reducing dioxins can also be achieved.

  Next, in order to specifically explain the present invention, some examples of the present invention and comparative examples for showing comparison with the examples will be given.

Comparative Example 1
A high temperature exhaust gas containing NOx exceeding 30,000 ppm is discharged from a non-transfer type plasma torch that uses air as a working gas. In the test device (3) equipped with the non-catalytic denitration zone (1) and ammonia decomposition zone (2) shown in Fig. 6, the exhaust gas is diluted with air before flowing into the non-catalytic denitration zone (1) Was adjusted within the range of 750 to 900 ° C. Ammonia diluted about 10 times with air was injected into the exhaust gas to perform non-catalytic denitration. The test results are shown in FIGS. FIG. 1 shows the relationship between NH ₃ / NOx molar ratio, denitration rate, and leaked ammonia at a residence time of 2 seconds. As can be seen from the figure, a denitration effect exceeding 99% was obtained under favorable conditions. 2 to 4 show the results of the same test in relation to residence time, denitration rate, and leaked ammonia for each temperature.

  From these test results, the following was found.

  ○ In order to promote non-catalytic denitration with high efficiency, it was necessary to dilute the supplied ammonia to a concentration below its flammable concentration range.

○ Under the above reaction conditions, denitration efficiency at 850 ° C. was the best, and about 99% of NOx could be decomposed at a molar ratio (NH ₃ / NOx) 2.

  However, the leak ammonia concentration at this time exceeds 200 ppm, and if the leak ammonia is not reduced by wet smoke washing or the like as it is, white smoke will be discharged from the smoke outlet.

  ○ The reaction temperature in the non-catalytic denitration zone was set to 800 ° C., 850 ° C., and 900 ° C., and the denitration rate and the leaked ammonia concentration with respect to the residence time of the exhaust gas in the non-catalytic denitration zone were determined. The results are shown in FIG. 2, FIG. 3 and FIG. From these figures, it can be seen that the denitration reaction is almost completed with a residence time of about 1 second.

  ○ When the reaction temperature reached 900 ° C., the oxidative decomposition reaction of ammonia was accelerated and the denitration efficiency was reduced, but the leaked ammonia concentration was reduced to about several ppm.

Example 1
Compared with the test equipment (3) with non-catalytic denitration zone (1) and ammonia decomposition zone (2) shown in Fig. 6 except that the denitration reaction temperature is 850 ° C and the residence time of the exhaust gas is about 2 seconds. Non-catalytic denitration was carried out in the same manner as in Example 1. Next, when the contact time in non-catalytic denitration reached about 1.2 seconds, propane gas was injected into the ammonia decomposition zone (2) through the nozzle (6) in the denitration reactor on the downstream side and burned. . The amount of propane injection was adjusted so that the reaction temperature in the ammonia decomposition zone (2) was 900 ° C. due to the combustion of propane. In FIG. 6, (4) is a test apparatus inlet sampling port, and (5) is a test apparatus outlet sampling port.

  In addition, the increase and decrease of the leak ammonia concentration were checked before and after the propane injection and before and after the stirring air injection.

  A test for determining the denitration rate and the leaked ammonia concentration was performed in the same manner as in Comparative Example 1. The experimental results are shown in Table 1.

Comparative Example 2
Non-catalytic denitration was performed in the same manner as in Example 1. When the contact time in the non-catalytic denitration was about 1.2 seconds, air was injected and injected through the nozzle in the denitration reactor in the downstream side. The reduction effect of leaked ammonia due to the stirring effect was measured.

  A test for determining the denitration rate and the leaked ammonia concentration was performed in the same manner as in Comparative Example 1. The experimental results are shown in Table 1.

Examples 2-4, Comparative Examples 2-4
The operation was performed in the same manner as in Example 1 except that the reaction temperature in the non-catalytic denitration zone was varied in the range of 750 to 900 ° C. and the propane supply amount was adjusted so that the reaction temperature in the ammonia decomposition zone was 900 to 1100 ° C. went.

A test for determining the denitration rate and the leaked ammonia concentration was performed in the same manner as in Comparative Example 1. The experimental results are shown in Table 1.

  In the table, zone (1) is a non-catalytic denitration zone, zone (2) is an ammonia decomposition zone, SNCR is a test device equipped with a non-catalytic denitration zone (1) and an ammonia decomposition zone (2), DXN is dioxin, post-combustion Means combustion of combustible gas in the ammonia decomposition zone, respectively.

  As is clear from Table 1, in each of the Examples, a high denitration rate was obtained, and the leak ammonia concentration could be remarkably reduced, and in addition, dioxin could be reduced.

Is a graph showing the molar ratio (NH 3 / _NOx) the relationship between the denitrification rate and leakage ammonia concentration. It is a graph which shows the relationship between the residence time in the denitration reaction temperature of 800 degreeC, a denitration rate, and leak ammonia concentration. It is a graph which shows the relationship between the residence time in the denitration reaction temperature of 850 degreeC, a denitration rate, and leak ammonia concentration. It is a graph which shows the relationship between the residence time in the denitration reaction temperature of 900 degreeC, a denitration rate, and leak ammonia concentration. It is a flow which shows the euro plasma type ash melting system provided with the non-transfer type ash melting furnace. It is a longitudinal cross-sectional view which shows the test apparatus provided with the non-catalyst denitration zone and the leak ammonia decomposition zone.

Explanation of symbols

(1) Non-catalytic denitration zone
(2) Ammonia decomposition zone
(3) Test equipment
(4) Test equipment inlet sampling port
(5) Test equipment outlet sampling port
(6) Nozzle

Claims (2)

When the NOx-containing exhaust gas discharged from the non-transfer type plasma ash melting furnace is subjected to non-catalytic denitration treatment using ammonia , flammable gas is supplied to the downstream side of the non-catalytic denitration zone and burned, and after denitration A method for reducing leaked ammonia in non-catalytic denitration of non-transfer ash melting furnace exhaust gas, wherein the exhaust gas is heated to decompose and remove unreacted ammonia. Flue gas residence time in the non-catalytic denitration zone is 1 to 2 seconds, the reaction temperature is from 800 to 870 ° C., the residence time of the exhaust gas in the ammonia decomposition zone is from 0.83 to 2 seconds, the reaction temperature is 900 to 1,000 The method of claim 1 wherein the temperature is ° C.

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