JPS60202741A - Treatment of denitration catalyst - Google Patents

Abstract

PURPOSE:To recover the function of a denitration catalyst without stopping the operation and to maintain the function for a long period by injecting an iron compd. into waste gas during the decomposing and removing operation of NOX components in the waste gas. CONSTITUTION:An iron compd. (e.g., FeCO3) is injected into the waste gas from a boiler, etc, wherein fossil fuel such as heavy oil is used, and the iron compd. is deposited on the surface of a denitration catalyst in decomposing and removing NOX in the waste gas by using said catalyst. The amt. of the iron compd. to be injected into the waste gas is controlled so that the weight ratio of the amt. of iron and vanadium present in the waste gas to the total amt. of alkali metal and alkaline earth metal contained in the waste gas may be regulated to <=3/1. Namely, when the function of the denitration catalyst which is provided for removing the NOX in the waste gas from a heavy oil-fired boiler, etc. is deteriorated during the operation of the boiler, the function of the catalyst is recovered without stopping the operation, and the function can be maintained for a long period.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method for decomposing and removing NOx in exhaust gas from a boiler using fossil fuel such as heavy oil using a denitrification catalyst. Maintain or recover catalytic ability
The present invention relates to a method for treating the catalyst to be regenerated.

[Background technology]

A boiler that uses fossil fuels such as petroleum 1 and coal.

Heat engines such as diesel engines and gas turbines contain various types of sulfur oxides (SOX), including dust mainly composed of unburned carbon and ash, contained in the exhaust gas.

Nitrogen oxides (N0x) cause environmental pollution.
Measures are being taken for each. For example, the generation of soot and 80X can be solved by using high-quality fuel such as LM(2) or LPG, but this is economically disadvantageous since fuel costs account for a high proportion of operating costs. Heavy oil containing sulfur, which has low fuel costs, residual oil from petrochemical plants with relatively low sulfur content, and heavy oil called by-product oil contain a lot of nitrogen compounds, so when they are burned, they produce a large amount of NOx.
occurs, and it is necessary to install a denitrification device along with desulfurization.
The efficiency of these exhaust gas treatment facilities has become a major environmental regulatory and economic issue.

[Conventional denitrification methods and their drawbacks]

Currently, this type of denitrification method involves injecting ammonia gas into the exhaust gas and using a denitrification catalyst (e.g. TiO3-vgo).
The most common method is to introduce the Box into N2, H, and O by introducing it above s-wo3). In this method, the superiority or inferiority of the catalytic action has a great effect on the denitrification efficiency, so maintaining the catalytic function is extremely important from a practical standpoint. ), these particles adhere to the catalyst surface and physically interfere with the contact between the combustion gas and the catalyst, reducing the denitrification efficiency.

For example, fuel ash components include Ha, V, Fe, Sl, and El.
, Mf, Oa.

It mainly consists of compounds such as ht, but also Ha, K.

Compounds such as 81, S, Mt, Oa, At, etc., in particular, seriously interfere with the catalytic action. - On the other hand, in heavy oil-fired boilers, MP is added to brass fuel in order to prevent external corrosion damage caused by V, Na, and S compounds.
Since the compounds (MfO, MP(OH)!) are injected, the reduction in catalytic activity is even more severe than in the case where these Mf compounds are not injected.

Currently, the countermeasure is to remove foreign substances by washing the catalyst with water after the boiler is shut down, but a method to restore its function during operation or maintain its function for a long period of time is still being developed. It has not been.

[Object of the present invention]

The purpose of the present invention is to reduce NO in exhaust gas from heavy oil-fired boilers, etc.
If the function of the denitrification catalyst installed to remove The present invention provides a processing method.

[Configuration of the present invention]

The present invention, as a means for achieving the above object, consists in injecting an iron compound into the exhaust gas during the operation for decomposing and removing NOx in the exhaust gas.

That is, the present invention is a method for decomposing and removing Box in exhaust gas from a boiler using fossil fuel such as heavy oil using a denitrification catalyst, in which an iron compound is injected into the exhaust gas and the iron compound is A method for treating a denitrification catalyst for decomposing and removing NOx in exhaust gas, which is characterized by attaching it to the surface of the catalyst. In a preferred embodiment, the amount of iron and vanadium present in the exhaust gas is controlled and injected so that the weight ratio is 3 or less with respect to the total amount of similar metals.

The catalyst to which the present invention can be applied is ATO3 or T I O2
is used as a carrier, and appropriately selected oxides of vanadium, iron, tungsten, chromium, and molybdenum are mixed with this and coated on the surface of the carrier. For example, a mixed oxide of 30% vanadium oxide, 55% iron oxide, and 15% tungsten oxide coated on a TlO2 support, or 15% vanadium oxide, 70% iron oxide, and molybdenum oxide. 10%.

An example is one in which a mixed oxide consisting of five layers of chromium oxide is coated on an Al2O2 carrier.

The present invention uses, for example, a soot blower upstream of a denitrification catalyst provided in a rear flue of a boiler to inject an iron compound into combustion gas and deposit it on the surface of the catalyst. The specific structure of the present invention and its effects are listed as follows.

(1) When an iron compound is attached to the catalyst surface, it exhibits the same function as the iron compound ψ-engineering catalyst.

(2) Therefore, even if solid foreign matter such as fuel ash adheres to the surface of the catalyst and loses its function, it appears that the function of the catalyst has been restored by adhering thereon.

(3) By using a soot blower or the like, it is possible to inject iron compounds into the furnace even while the boiler is operating, without stopping the operation.

(4) Iron compounds are safe and easy to handle in terms of hygiene.

(5) Continuous injection is effective, but injection is also effective when the catalyst function is reduced and discontinued after the function is restored.

(6) Although the fuel ash also contains iron compounds, the amount thereof is generally small (about 2 to 5 iron in the fuel ash), but this alone does not have the ability to restore the catalytic action.

(7) Iron compounds include Fe1O1, Fe104,
Fe(OH%.

Any material that changes into an oxide (FJO3, partially F6304) in the boiler exhaust gas, such as Fe(on), FeCO3, etc., may be used, and these are non-polluting and inexpensive.

(8) Injection of large amounts of iron compounds leads to an increase in the amount of SO2 in the exhaust gas, but by appropriately controlling the injection amount,
It is possible to suppress an increase in the amount of S03 while maintaining the detouching function.

The present invention will be explained in detail below based on FIG. FIG. 1 shows a cross section of a heavy oil combustion boiler used to carry out the present invention, in which fuel is combusted by a burner 2 provided in a combustion chamber 1 and becomes high-temperature combustion gas, which is heated to a superheater 3.
, 5', the reheater 4, the low-temperature superheater 5, the low-temperature reheater 6, the economizer 7, and the excess air preheater 8 before being discharged to the outside.

(Actually, it is purified by a dust collector, desulfurization device, etc. and then discharged to the outside.) Ammonia (MHz) is preheated through the ammonia injection nozzle 9 installed at the rear (swaft side) of the economizer 7. The ammonia is injected in the direction of the ammonia injection nozzle 8 and passes through the denitrification catalyst layer 10 provided downstream of the ammonia injection nozzle 9 while being mixed with various components in the combustion gas. The iron compound injection nozzle 11.11' of the present invention is installed on the downstream side of the economizer 7 and the ammonia injection nozzle 9, and on the upstream side of the economizer 7, respectively, and both nozzles 11.11' can be used simultaneously as necessary. However, only one of them may be used as long as the injection effect is sufficient.

On the catalyst surface, Mo is removed by ammonia gas as shown below.
The amount of NOx is reduced by promoting the reduction reaction of x.

200-450℃ 2 Noz +4 NHB 102 5H1+6 H1
The present invention restores this catalytic reaction and maintains the function of the catalyst over a long period of time, which will be described later. In the figure, 13 indicates the flow of combustion gas, and 12 indicates the flow of combustion air.

The combustion gas of heavy oil fuel contains unburned carbon I'i,
Although in trace amounts, Ha, V, Fe, Sl, B, Mf
, Ca.

Compounds such as At exist in the form of fine powder at temperatures after the low-temperature superheater 5 in FIG. 1 (below 850° C.), and adhere not only to the surface of the boiler tube but also to the surface of the denitrification catalyst. Even if V or Fe compounds adhere to the catalyst surface, they do not often interfere with the catalytic action, but if Mf or Ca compounds adhere to lJa, the catalytic function will be severely degraded. In particular, in boilers in which Mf and Oa compounds are mixed in the fuel to promote combustion reactions and prevent the corrosive effects of combustion gas, MY, (a compounds) adhere to the catalyst surface and cause the interaction between the catalyst and the combustion gas. Direct contact is obstructed.The effect of interference is an increase in the amount of NOx in the exhaust gas, so when this tendency begins to occur, inject iron compounds from iron compound injection nozzle 11.N' in Figure 1. The injected iron compound turns into fine powder and adheres to the catalyst surface, restoring the catalytic function.In other words, ammonia is adsorbed on the surface of the injected iron compound, and NOx reacts with it to form N2, H, and O. Decompose. Figure 2 is a schematic illustration of this. As shown in Figure 2, for a catalyst with an iron compound attached,
NHI addition → NH, adsorption → reaction with NOx → Nl, H,
NOx decomposes into N, H, and O through the O removal process.

Hereinafter, the present invention will be explained in more detail by giving experimental examples of the present invention.

[Experimental Example 1] The catalyst used in this experimental example was a mixed oxide containing 30% vanadium oxide, 55% iron oxide, and 15% tungsten oxide coated on a TlO2 carrier. and fuel properties are as follows.

(1) Combustion conditions: Combustion was performed at an excess air ratio of 0.1%.

(2) Fuel used: S: 2.13% residual carbon 11.28
%.

Ash content Q, 05% V: 86 ppmNa:
23 ppm (3) Whether or not a fuel additive is used: 1) Mr(oH)1 was injected into the fuel at wt/=t o (weight ratio).

2) MSI(OH)2 was not injected.

The boiler was operated under the above conditions, and ammonia was injected (MH34°8, molar ratio 1.0 to 1.5) from the ammonia injection nozzle 9 in Fig. 1 to perform denitrification, and then to the air preheater 8.
The denitrification effect was investigated at the inlet of the system over the course of operation time. (Comparative Example 1 with fuel additive injected, Comparative Example 2 without injection).

On the other hand, the method of the present invention was carried out as follows.

To the boiler operating under the above conditions, iron oxide powder (IRE304) of about 0.1 μm suspended in water was injected together with water vapor using the iron compound injection nozzle 11.11' shown in Fig. 1. It was injected into the boiler furnace. The injection amount was set to correspond to 50 g of Mf(oH) injected into the fuel.

In addition, the original F! There are two methods for injecting iron compounds into the AK: one is to inject the boiler at the beginning of operation (invention 1), and the other is to operate without injecting iron compounds and inject only when the denitrification effect has decreased (invention 2). method was adopted. Table 1 shows the results.

Table 1 As is clear from Table 1 above, when operating under the conditions of Comparative Example 1, the denitrification performance of the catalyst significantly deteriorates after 2 to 4 months. If the iron compound injection of the present invention is omitted during this period, the denitrification efficiency will be at its peak. Also, as in Comparative Example 2, M in the fuel
In the case where r(on) is not injected, there is relatively little decrease in denitrification efficiency, but if the method of the present invention 1 is adopted, the decrease in efficiency is even smaller and is better.

However, FezO was used as an iron compound by the method of the present invention 2.
3. When FeCO3, I'e(OH%, Fe(on)s, etc.) were injected, effects were observed for all iron compounds.These iron compounds decomposed in the boiler and reacted to produce F. ＠20g (part of which is Fe2O2), so any iron compound that forms this type of oxide in the boiler furnace can be used in the present invention.Therefore, in the present invention, the above-mentioned It is not limited to iron compounds only.

[Experimental Example 2] By injecting a Fe compound into the exhaust gas, the function of the denitrification catalyst could be maintained using the same catalyst as in Experimental Example 1. However, injection of a large amount of Fe compounds will reduce the amount of SO contained in the exhaust gas.

Because it has the effect of oxidizing oxidation to Sos, it is necessary to maintain the function of the denitrification catalyst. It is preferable to determine an appropriate implantation amount to suppress the oxidation effect on the oxidation effect.

In other words, when a large amount of S03 is generated, it combines with moisture in the exhaust gas and forms sulfuric acid (EI03-4-H, O → H, S
O4) Causes corrosion of pipes, air preheaters, flues, chimneys, etc. (This is also called sulfuric acid dew point corrosion.) Therefore, in the present invention, it is preferable to determine an appropriate amount of iron compound injection to suppress the oxidation effect on 80. In Experimental Example 2 of this 1, an experiment was conducted to select an appropriate injection amount of an iron compound.

The boiler combustion conditions and fuel properties in this experimental example are as follows.

(1) Boiler combustion conditions: Same conditions as Experiment 1 (2) Use
(3) Use of fuel additive: My (on) was added appropriately to the fuel. (4) Ammonia injection amount: Same conditions as Experimental Example 1. A dust collector is inserted into the exhaust gas between the denitrification catalyst layer 1o and the ammonia injection nozzle 9 in the figure to collect solid matter in the exhaust gas, and the chemical analysis results show that components that interfere with the action of the denitrification catalyst ( By changing the ratio of alkali metals (alkaline earth metals) to components that improve the catalytic function (iron and vanadium) and components that do not interfere with the catalytic function (iron and vanadium), NOx in the exhaust gas at the outlet of the denitrification catalyst is reduced by 80%. This was done by measuring the amount.

The amount of alkaline earth metals can be increased or decreased by changing the injection amount of the fuel additive, and the amount of iron can be changed by F f3z
04 Fine powder with water vapor through iron compound injection nozzle 11.1
This was done by changing the amount injected into the exhaust gas from 1'.

The results are shown in Table 2. Here, the NOx amount and the sog amount at 4 o'clock in the hot summer season are set as 100, and the ratio is shown.

Table 2 As is clear from the results, the more iron component is injected, the more effective it is in reducing NOx, but if it is too much, the amount of SO increases. Therefore, an appropriate amount of injection is based on the assumption that the rate of increase in SO3 is within 10 degrees.As the amount of Os increases, it reacts with ammonia to produce ammonium sulfate or acidic ammonium sulfate.

Of these, the latter is extremely corrosive, but the presence of iron components has been recognized to have the effect of suppressing the corrosivity, and is effective not only for denitrification, but also for denitrification.
It was also effective against this type of corrosive action.

[Effects of the present invention]

As described in detail above, the present invention injects an iron compound into the exhaust gas so that when the function of the denitration catalyst decreases during the operation of the exhaust gas treatment operation, the catalyst can be removed without stopping the operation. It has the effect of restoring function and maintaining that function for a long period of time.

[Brief explanation of drawings]

FIG. 1 shows a cross section of a heavy oil-fired boiler used to carry out the present invention. FIG. 2 schematically shows the process of decomposing Box into N2, E, and O. 1... Combustion chamber 11.11'... Iron compound injection nozzle 2... Burner 12... Air flow 5.3'...
・Superheater 13... Combustion gas flow 4... Reheater 5... Low temperature superheater 7 (... IAF reheater 7... Energy saver 8... Air preheater 9... Ammonia injection nozzle 10... Denitrification catalyst layer agent 1) Meifu agent Ryo Hagiwara −

Claims (2)

[Claims] (1) In a method of decomposing and removing NOx in exhaust gas from boilers that use fossil fuels such as heavy oil using a denitrification catalyst, an iron compound is injected into the exhaust gas and the iron compound is applied to the surface of the catalyst. A method for treating a denitrification catalyst for decomposing and removing NOX in exhaust gas, the method comprising making it adhere to the denitrification catalyst. (2) The amount of iron compounds injected into the exhaust gas is determined so that the amount of iron and vanadium present in the exhaust gas is 3 or more by weight relative to the total amount of alkali metals and alkaline earth metals contained in the exhaust gas. A method for treating a denitrification catalyst for decomposing and removing NOx in exhaust gas according to claim 1, wherein the method is controlled so that the following is achieved.