JPS58128126A - Method for introducing reducing agent - Google Patents

Abstract

PURPOSE:To effectively remove nitrogen oxides (NOx) from an effluent gas, by allowing an excess reduing agent to have been adsorbed in advance to a catalyst filled in a denitrator in the course of an effluent gas duct. CONSTITUTION:A combustion waste gas effluent from a boiler 6 is denitrated with a reducing agent introudced from an introduction pipe 7 installed on the upstream of a denitrator 8 located in the course of an effluent gas duct 4. Denitration is accelerated by a catlayst 9 filled in the denitrator 8 to remove NOx contained in the effluent gas. At that time, the start time of introduction of said agent is selected from before stop of the feed of the effluent gas to the denitrator 8 at latest to the same time as start of the denitrator 8, thus allowing an excess of the reducing agent to have been adsorbed to the catalyst 9 in advance, and consequently, NOx to be effectively removed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for injecting a reducing agent, and particularly to a method for injecting ammonia (N) as a reducing agent into a dry denitrification device for removing nitrogen ironides (hereinafter referred to as NOx) from exhaust gas. The present invention relates to a method for injecting a drug.

In recent years, in Japan, due to the tight supply of heavy oil, in order to correct the dependence on oil, there has been a shift from traditional heavy oil-burning to coal-fired fuel, and in particular, large-capacity coal-fired thermal power is being used for commercial boilers. A power plant is being built.

However, since coal fuel has poor fuel properties compared to petroleum fuel, NO contained in exhaust gas and unburned substances are likely to be generated, so flame splitting, exhaust gas recirculation, and two-stage measures are required to reduce %KNOx. Combustion and in-furnace denitration are also employed to achieve slow combustion and reduce NO.

In these coal-fired thermal power plants, there are few cases in which the boiler load is always operated at full load, and the load is 80% load,
A transition is being made to thermal power plants that handle intermediate loads, such as increasing and decreasing the load to 50% load, 25% load, or stopping operation.

On the other hand, so-called combined plants, which combine a gas turbine with good startup characteristics and an exhaust heat recovery boiler, are also used for intermediate-load thermal power generation, and are operated only during the day when there is a high demand for electric power.
There is a plan to build something that will shut down at night.

However, with the tightening of regulations on the concentration of NO and NOx in these coal-fired intermediate-load boilers and gas turbines, in addition to conventional combustion improvements, dry-type denitration using NH as a reducing agent and denitration in the presence of a catalyst has been introduced. An increasing number of plants are installing catalytic reduction denitrification equipment.

This is because in coal-fired boilers, the combustibility of the fuel is unstable, which increases the amount of NOx, and in gas turbine plants, the amount of oxygen is high and high-temperature combustion is performed, so as with coal-fired boilers, a large amount of NOx is produced in the exhaust gas. Therefore, a denitrification device 8 as shown in FIG. 1 is installed.

Figure 41 shows a conventional smoke and air duct system for a boiler in which a denitrification device 8 is installed.

The combustion air in the air duct 1 is pressurized by the forced draft fan 2, heated by the exhaust gas from the exhaust gas duct 4 in the air preheater 3, and then supplied from the wind box 5 to the boiler 6.

The exhaust gas combusted in the boiler 6 is denitrated by NH in the exhaust gas duct 4 and NH from the injection pipe 7, and the denitrification is promoted in the catalyst 9 in the denitrification device 8 disposed downstream. NOx is removed and the air preheater3.
Dust collector10. It is pressurized by the il ventilation side 11 and released into the atmosphere.

However, although the reaction temperature range of such a denitrification device 18 differs depending on the type of catalyst 9, the temperature 1@ which is the most efficient is
The ambient temperature is relatively high at 300 to 400°C, and the temperature range is quite narrow. Therefore, in boilers for intermediate-load thermal power plants and gas turbines that are constantly operated at partial load, the exhaust gas temperature fluctuates due to load fluctuations. However, there is a drawback that the catalyst 90 is outside the usable range.

In this case, if the temperature of the gas used in the catalyst 90 is too high, the catalyst 90
The structure of the catalyst changes and its function as a catalyst is impaired, and if the gas temperature used is too low, the anhydrous sulfur present in the exhaust gas!
(SOs) and the catalyst function deteriorates.

Therefore, the temperature of the exhaust gas during these partial loads is controlled by a gas bypass system, afterburning, etc., or denitration during partial loads is being solved by improving catalyst performance.

However, the disadvantages of denitrification equipment for intermediate-load thermal power boilers and gas turbines are that these boilers and gas turbines/
If it repeatedly starts and stops at St+*, a large amount of NO will be generated immediately after starting, and it will take several hours for the denitrification activity to reach a steady state after NH3 is injected. The amount of NOx emitted immediately after startup has become a new problem.

The present invention attempts to solve such conventional drawbacks,
Its purpose is to start and stop 111311H
The objective is to obtain a method for injecting a reducing agent that can efficiently denitrate immediately after startup, even in a repeating plant.

In short, the present invention allows the injection of the reducing agent to be started before the exhaust gas ventilation to the denitrification device is stopped and at the latest at the same time as the denitrification device is started, so that the reducing agent is adsorbed into the catalyst layer, and the reducing agent is adsorbed into the catalyst layer. The denitrification efficiency is kept at a steady value.

Examples of the present invention will be described below, starting with experimental examples conducted by the inventors prior to that.

The dishes of the present invention are as shown in FIGS. 2 and 3 (NH).

In the catalytic reduction denitrification method, the reason why it takes several hours for the denitrification efficiency to increase to a steady value after the start of NH1 injection was investigated from the viewpoint of the reaction mechanism, and as a result, the following conclusion was reached.

Note that the conditions are gas temperature 200'C% plane transverse velocity 1 [6 m
/h, gas is kerosene combustion gas, No value is 200p, N
H3 injection amount kt 200 ppm "11" A4° That is, as shown in FIG. 2 and FIG.

The amount of adsorption changes over time, and based on this,
When the relationship between #1 deoxidation X(-) and NH adsorption amount Q is investigated, the following relationship is established.

tn' = const, eQ According to this equation, the reason why the denitrification rate does not increase immediately after NHI is injected is because the supply amount of NHI is small, and it takes until the amount of NH adsorbed on the catalyst reaches a steady value. It took 44Jn that this was because it took time.

On the other hand, in order to increase the denitrification rate X, it is necessary to
All that is required is to increase Hst.

Regarding the properties of this adsorbed NH1, we found that the adsorbed N
It was also found that H,t'l is extremely stable, and that NH, once adsorbed on the catalyst, does not change even during the period when the denitration equipment is stopped and remains retained on the catalyst.

The present inventors have skillfully applied this extraordinary stability of adsorbed NH to a denitrification device.

Therefore, it is necessary to start the injection of NH before the start of the denitrification equipment, or at the same time as the start of the denitrification equipment, a large amount of NH, (an excess of NH compared to the NOx required for the denitrification reaction) is introduced in a short period of time. , ) onto the catalyst to increase the amount of NH adsorbed on the catalyst, denitrification can be performed efficiently immediately after startup in equipment that frequently starts and stops, such as gas turbines and intermediate load boilers. We have reached the conclusion that it is possible.

Based on this point, the present invention aims to start the injection of NH before the start-up time of the denitrification equipment, or at the start-up time, since gas turbines and intermediate-load boilers generate a large amount of NOx at the time of start-up. At the same time, a temporary large excess of N1
-11 is injected into the catalyst layer.The present invention will be described in detail below with reference to Examples.

The catalysts and conditions used in the test are as follows.2 Practical row 1 A Ti-based catalyst that was heated for 350'CK with a gas having the composition shown in Table 1, and then formed and sized into 10 to 20 meshes at the same temperature. The contact was carried out at a space velocity of 50,000h' and the contact was carried out for 30 minutes. After that, the NH concentration was increased to 300 ppm, and after maintaining the same condition for 30 minutes, exhaust gas ventilation was stopped.
It was immediately taken out into the atmosphere and left for 12 days. This catalyst was heated again from room temperature to 350'C as shown in Figure 4 while passing through a gas having the composition 1fi filled with reactive iFK. As shown by the double-dot chain curve A in the figure, the denitrification rate increases from the time of startup, and injecting an excessive amount of NOx before the exhaust gas 1 & air of the denitrification equipment stops increases the denitrification rate upon restart. It was concluded that it is most effective to do so.

Table 1 Implementation IF12. 3 A similar test was carried out under the same conditions as in Example 1 except that the NH concentration was changed from 300 ppm in Example J1-1 to 400 and 600 ppm, and the other conditions were the same as in Example 1.

At this time, the denitrification rate decreased over time from the time of startup, as shown by the dot-dash line curve B in Example 2 and the solid line curve C in Example 3.

Comparative Example 1 A similar test was conducted without performing the high NH3a& (300 ppm) treatment shown in Utility Model Application No. 1.

What is the change in the denitrification rate over time at this time, indicated by the dotted line in Figure 5? As shown by mD, the denitrification rate at startup was poor compared to curves A, B, and C, and it was not possible to obtain a high denitrification rate immediately after venting the exhaust gas at startup.

This is an example in which excess NH, fi is injected before the exhaust gas ventilation to the denitrification equipment is stopped, but below, we will discuss the case where this excess NH, @ is injected before or at the same time as the denitrification equipment is started. explain.

The test equipment and conditions at this time were as follows.

That is, eight Ti-based catalysts having a thickness of 1 cm, a length of 40 cm, and a length of 1,001 mm were packed in a 40+ am square glass sleeve reaction tube at intervals of -, and the tube was preheated to the width shown in Table 2. gl! Exhaust gas was passed through at 5 Nt/min. As shown in Figure 6, the simulated exhaust gas was heated to 500°C every hour in a preheater to simulate the startup of the gas turbine.Example 4 Preheated simulated exhaust gas was introduced into the catalyst layer. 11,000 pp of NH was diluted as shown by the solid line E in FIG.

was passed through the catalyst layer for 20 minutes at 6 Nj/min. After that, simulated exhaust gas is introduced into the catalyst layer and at the same time the N mountain is increased to 300p.
pm injected. At this time, the denitrification rate changes over time as shown by the solid line E in FIG. 9, and the denitrification rate increases from the 8th operation, and before startup, as shown by the solid line E in FIG.

It was concluded that injecting ants is also effective.

Example 5.6 At the same time as model III IP gas was introduced into the catalyst layer, 11,000 ppm and 2,000 ppm of NH were first injected for 20 minutes as shown by the one-dot chain line F and double-dot chain line G in Figure 8, and then 300 ppm of NHsl was injected once. (Equimole with NO)
KLJ, :. As a result, the denitrification rate is the single-dot chain-F in Is9 diagram.
As shown by the two-dot chain line G, it was found that the denitrification rate at startup was better than that of the comparative example 20 points 4H.

Comparative Example 2 300pp of NH is passed through the catalyst layer and at the same time
m (equimolar to NO). This result is shown in FIG. 9 by a broken @H.

As mentioned above, the denitrification rates A-C and E-F obtained in Examples 1 to 6 according to the present invention can obtain a higher denitrification rate immediately after starting compared to Comparative Example H, and this is because This is because the excess NHI injected before or at the time of startup was adsorbed onto the catalyst no, and this adhering Nt(1) promoted denitrification.

In the embodiments of the present invention, only the denitrification of gas turbines has been described, but the present invention is not limited to gas turbines only, but is also effective in denitrification devices that use a wide range of other fuels.

According to the present invention, a high denitrification rate can be obtained immediately after the denitrification equipment is started, and on the other hand, it is possible to obtain a high denitrification rate immediately after starting the denitrification equipment. Il! Since a large amount of NOx is generated at one time, the denitrification efficiency is more effective.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the denitration equipment, Figure 3 is NH, Figure 11 shows the correlation between the absorption cap and the denitrification rate, Figure 4 is [
Figures 6 and 7 show the exhaust gas temperature and inlet NO used in the example.
, FIG. 8 is a diagram showing the start timing and injection amount of reducing agent injection, and FIGS. 5 and 9 are characteristic charts 11 showing the relationship between the denitrification rate and time. . Figure 2 Figure 3 Figure 4 Figure 5-B! l lV'l ('I)

Claims (1)

[Claims] 1. Install a denitrification device with a built-in catalyst in the gas duct,
In a device in which an injection pipe for injecting a reducing agent is arranged upstream of the denitrification device and the reducing agent is injected into the exhaust gas duct, the time point at which the injection of the reducing agent is started is from before the exhaust gas ventilation to the denitrification device is stopped at the latest. A method for injecting a reducing agent, characterized in that an excess reducing agent is injected at the same time as startup, and the excess reducing agent is adsorbed onto a catalyst in advance.