JPH0275326A - Denitrification process - Google Patents

Abstract

PURPOSE:To reduce the quantity of a charge of denitrification catalyst and also reduce the quantity of catalyst for replenishment and replacement by applying ultraviolet rays to unreacted ammonia at the outlet of a denitrification apparatus to effect decomposition and removal thereof. CONSTITUTION:A light source 1 for emitting ultraviolet rays having a wavelength of 170-230mm is provided on the outlet side of a denitrification apparatus 2 wherein ammonia is used as a reducing agent. When ultraviolet rays from said light source are applied to the rare unreacted ammonia at the outlet of the denitrification apparatus 2, the ammonia is efficiently and completely decomposed and removed. In this manner, the quantity of a charge of denitrification catalyst can be reduced and further the quantity of catalyst for replenishment and replacement can be reduced. Consequently, denitrification can be accomplished economically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for decomposing unreacted ammonia in a denitrification device using ammonia as a reducing agent.

[Conventional technology]

Recently, due to environmental regulations, dry type flue gas denitrification equipment, which removes nitrogen oxides from flue gas emitted from various combustion equipment by catalytic reduction in the presence of ammonia, has been gaining popularity as it has many advantages over wet type denitrification equipment. came into use.

Among them, denitration equipment that uses nitrogen oxide removal catalysts in honeycomb, lattice, or plate structures have a simple structure, have little pressure loss, and are less likely to be clogged by the dust contained in the exhaust gas. It has many excellent advantages such as, so it is the most widely used in practical use.

However, in the above method, NOx and ammonia are reacted in the presence of a catalyst, and when removing NOx, ammonia and N
It is very difficult for Ox to react completely. Furthermore, the performance of catalysts used for denitrification generally deteriorates as they are used, and as the performance deteriorates, the concentration of unreacted ammonia at the outlet of the denitrification device increases. In addition, when SOx, especially KSO, is present, such as in heavy oil waves and coal-fired exhaust gas, it reacts with unreacted ammonia to form acidic ammonium sulfate, which can cause problems such as clogging of heat exchangers such as air preheaters. Ammonia concentration is above a certain level (approximately 5 ppm to 10 ppm)
This is considered to be the end of the catalyst's lifespan.

[Problem to be solved by the invention]

As shown above, in order to reduce unreacted ammonia,
It became necessary to increase the required amount of catalyst, or to add or replace it, which resulted in an increase in the amount of denitration catalyst packed, and the problem that it became necessary to add or replace the catalyst frequently, making the work complicated. .

The present invention provides an economical denitrification device that decomposes unreacted ammonia at the exit of the denitrification device, thereby reducing the amount of denitrification catalyst packed and the amount of additional and replacement catalysts. This is what we provide.

[Means to solve the problem]

In order to reduce the amount of unreacted ammonia at the outlet of the denitrification device, which greatly affects the life of the denitrification device, especially the catalyst, the present invention installs a light source that emits ultraviolet light in the range of 170 nm to 230 nm on the exit side of the denitrification device. , and reduce unreacted ammonia.

[Effect]

That is, in the present invention, in a denitrification apparatus using ammonia as a reducing agent, it is possible to easily maintain a constant denitrification efficiency by increasing the amount of ammonia injected (generally, NH,/NOx molar ratio).

However, in order to increase the total smol ratio shown in FIG. 1, unreacted ammonia will increase.

Unreacted ammonia is limited by acidic ammonium sulfate clogging of heat exchangers such as air preheaters installed downstream of the denitrification equipment and by emission standards, which determines the lifetime of the catalyst. Furthermore, the performance of denitrification catalysts is generally degraded by poisonous components contained in exhaust gas. In this case as well, unreacted ammonia will increase, and as a countermeasure, it will be necessary to add or replace the catalyst.

From the above, it is possible to design an economical denitrification device by decomposing unreacted ammonia at the denitrification device outlet.

Various methods can be considered to decompose unreacted ammonia at the outlet of the denitrification equipment, but unreacted ammonia usually has a very dilute concentration of 10 ppm or less, and treating it by increasing the denitrification catalyst is the first method. As shown in Figure 3, a huge amount of catalyst is required, which is not economical.

However, when photochemical reactions are used, NHs can be efficiently decomposed using ultraviolet light of 170 nm to 230 nm without being affected by gas concentration. In other words, denitrification is performed using ammonia in the presence of a denitrification catalyst,
The most efficient method is to treat the dilute unreacted ammonia generated at that time with ultraviolet light.

Ammonia is applied at a current of 170 nm to 230 nm as shown in Figure 2.
It absorbs ultraviolet light and decomposes by the reaction shown in the following formula.

NH, +hν→NH*+H Ammonia decomposed according to the above formula reacts with NOx in the exhaust gas and is finally decomposed into nitrogen and water.

The reaction formula is as follows: No + NH, →! 'L+Ha After satisfying the NOx concentration at the outlet of the denitration equipment by 0 or more, it is possible to reduce the unreacted ammonia to the required concentration or less.

〔Example〕

FIG. 4 shows an overall configuration diagram of the experimental apparatus used to carry out the method of the present invention, and tests for gas, gas, COI, O8, NH, etc., adjusted to an arbitrary flow rate with a gas flow rate controller 4. The gases are uniformly mixed in a gas mixer 5 and enter a reactor 2 having irradiation windows 3 made of synthetic quartz at both ends. H in test gas
IO is supplied by a humidifier 6. The test gas coming out of the reactor 2 is passed through a filter 7 for the purpose of collecting reaction products.
, is guided to an NH equipped with a recorder 10, an analyzer 9, and is released into the atmosphere. The gas mixer 5, reactor 2, etc. are housed in a constant temperature bath, and the temperature is 35 cm, assuming the outlet of the denitrification equipment.
The temperature was 0°C. Although a low-pressure mercury lamp or an excimer laser can be used as the ultraviolet light source, in this apparatus, an excimer laser (1) was used to irradiate ultraviolet light of 193 nm. The composition of the supply gas used in the experiment was as follows.

NOs: 50ppm NH, 26.5ppm
Ox:5% Cot 10%u*o:to%
N: In order to confirm the decomposition and removal of NH by residual ultraviolet light, the above-mentioned feed gas was passed through the reactor 2 at a space velocity of 3,000 h-' and irradiated with excimer laser light of 193 nm. The results are shown in FIG. 5, and it was found that NH was completely decomposed and removed by laser irradiation.

〔Effect of the invention〕

As described in detail above, in the present invention, there is a
By installing a light source that irradiates ultraviolet light of 70 nm to 230 nm and decomposing and removing unreacted ammonia, which has the greatest effect on the life of the denitrification catalyst, the amount of filling of the denitrification catalyst and the amount of additional or replacement catalyst can be reduced. This makes it possible to achieve a more economical denitrification method than conventional methods.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the denitrification rate, unreacted ammonia concentration, and ammonia injection amount, Figure 2 is a diagram showing the ultraviolet absorption spectrum of NH, and Figure 3 is a diagram showing leaked NH and the required amount of catalyst. FIG. 4 is a cross-sectional explanatory diagram showing the experimental apparatus of the present invention, and FIG. 5 is a diagram showing the results of ammonia decomposition using 193 nm ultraviolet light.

Claims (1)

[Claims] 1. A denitrification method using ammonia as a reducing agent, which comprises installing a light source that emits ultraviolet light of 170 to 230 nm on the outlet side of the denitrification device to decompose and remove unreacted ammonia.