JPS5951846B2 - Method for removing sulfur oxides and nitrogen oxides in waste gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves adding ammonia gas to waste gas containing sulfur oxides, nitrogen oxides, oxygen, and water vapor at a temperature of about 110°C to 180°C, and flowing the gas from above to below in a reactor. The present invention relates to an improvement in a method for removing sulfur oxides and nitrogen oxides in the presence of a catalyst or without using a catalyst by feeding them into a moving bed formed by a granular carbon-containing adsorbent that moves in the air.

Some waste gases discharged from combustion furnaces and the like contain sulfur oxides, initially in the form of sulfur dioxide gas, and nitrogen oxides, initially in the form of nitrogen monoxide.

Many methods are known for removing sulfur dioxide gas from waste gas or flue gas, but these all involve cleaning or catalytic adsorption under drying conditions.
(Davids,
Techn0Mitteilungen71 (197
8), pp. 131-135).

Nitrogen oxides can likewise be removed by washing or by a catalytic reduction reaction using ammonia as the reducing agent.

However, methods of cleaning the waste gas are significantly more expensive as they reduce the temperature of the waste gas and often require reheating the waste gas.

On the other hand, the method of reducing nitrogen oxides in the presence of a catalyst using ammonia as a reducing agent can be carried out without causing a decrease in temperature (Renz, Hempel
mann.

Huber, “Verfahren zur A.
Stickoxiden
und Schwefeldioxid aus A
bgasenindustrier Fe
Karlsr
uhe1978, Eigenverlag, No. 293
(See pages 295 to 295).

These known methods require the reaction to take place at a temperature of 250° C. or higher using a catalyst and a support material containing aluminum or silicon, and the catalytic ability of the catalyst is reduced by sulfur dioxide or sulfur trioxide. Ru.

Also: unreacted ammonia forms ammonium bisulfate or ammonium sulfate in the subsequent waste gas cooling step, resulting in undesirable precipitation (Renz et al., op.
cit, pp. 291 and 292).

Furthermore, some of the ammonia is oxidized by the oxygen contained in the waste gas to N2, NO, or NO2, which is contrary to the purpose of reducing nitrogen oxides in the waste gas (Renz et al., op. cit. p. 293).

Moreover, even though sulfur dioxide can be removed by known methods at relatively low temperatures, it is necessary to reheat the waste gas before nitrogen oxides can be reduced with ammonia.

However, it goes without saying that such reheating is inefficient in energy use, and even if energy is recovered by heat exchange, for example, only a small portion of the energy is recovered, resulting in high costs.

Furthermore, there is also known a method for simultaneously removing sulfur oxides and nitrogen oxides in a single step.

This method involves blowing ammonia into the waste gas, reducing nitrogen oxides by contacting them with a porous catalyst to produce nitrogen and water vapor, and separating sulfur oxides as ammonium hydrogen sulfate or ammonium sulfur. be.

In this case, if activated carbon is used as an adsorbent/catalyst, the reaction can be carried out at a temperature of 180°C to 230°C (German Published Patent Application No. 2433076), and if a metal oxide attached to an aluminum or silicon carrier material is used. ,
The temperature range can be 200 to 250°C (J
apan Textile News 1976, No. 84
(pages 87 to 87).

At temperatures below 250°C, both sulfur dioxide and nitrogen oxides react with ammonia.

That is, as long as NOx and SO2 exist at the same concentration, the reaction between NOx and NH3 will take precedence if the temperature is high, and the reaction with SO2 will take precedence if the temperature is low.

A disadvantage of these known processes is that the consumption of ammonia is considerably high due to the undesirable reactions that occur.

Furthermore, the loss of carbon in activated carbon is also large. In addition, in the method of simultaneously removing sulfur oxides and nitrogen oxides in a single step, the temperature of the waste gas generated from a coal-fired boiler or an oil-fired boiler is equal to the reaction temperature necessary for the above-mentioned simultaneous removal. The drawback is that the simultaneous removal can only be carried out after the waste gas has been heated by an air preheater or an electrofilter.

Therefore, either the boiler must be modified to produce hot waste gases at the expense of its thermal efficiency, or the waste gases must be heated before being fed to the reactor.

On the other hand, in the first step, activated carbon is used as an adsorption medium to adsorb and remove NOx from the exhaust gas containing a mixture of NOx and SOx, and then in the second step, the above-mentioned N
An industrial exhaust gas treatment method (Japanese Unexamined Patent Publication No. 4164570) is already known, which consists of adsorbing and removing SOx from the exhaust gas after Ox removal.

The two-stage waste gas treatment technology disclosed in Japanese Patent Application Laid-Open No. 49-64570 has been found to have the following serious drawbacks, based on the experimental findings of the inventor of the present application.

That is, in the case of a mixed gas in which S02 (SOx) and NOx are present simultaneously in the waste gas, the NOx adsorption power of activated carbon is severely limited by the 802 (SOx) in the waste gas.

In general, SO2 (SOx) has the characteristic that it is adsorbed on activated carbon preferentially than NOx, and therefore, in the previously disclosed method, experimental results show that even in the first step adsorber for NOx separation, SO2 (SOx) is adsorbed more preferentially than NOx. Mainly SO2 (SOx) has been separated in the form of sulfuric acid.

In fact, based on the experimental knowledge of the inventor of the present application, for example, in a gas that requires purification, 50 ppm of NOx and 700 pp of NOx
If 5O2 (SOX) of 0pp or more is present, NOx
The adsorptivity in the adsorber in the first step for separation is (200℃
There is a problem in that the NOx removal rate was only 5-10% (under the following temperature conditions).

Therefore, even if an attempt is made to separate NOx and SOx and capture them separately using the previously disclosed technology, the end result is SOx (SOx
2) can be sufficiently adsorbed and removed in the first step for NOx separation and the second step for SOx separation, but NOx cannot be sufficiently adsorbed even in the first step for NOx separation, and only a very small proportion of NOx is removed. It cannot be removed by adsorption.

Therefore, the NOx-SOx mixed exhaust gas disclosed in JP-A-49-64570 was used in the first stage NOx, -second stage NOx
The above-mentioned West German Patent Publication No. 2433 is used in the first stage NOx removal step of the method in which SOx is adsorbed and removed in two stages.
No. 076 (1975), the technique of adding ammonia to increase the denitrification effect can be combined with N.
There was also a proposal that suggested that both NOx and SOx gases could be successfully adsorbed and removed from the Ox-SOx mixed exhaust gas.

However, it has become clear through experience by the inventor of the present application that this draft example also has the following drawbacks.

That is, NOx disclosed in Japanese Patent Application Laid-Open No. 49-64570
Adding NH3 gas to the first step for removal is not a problem, as disclosed in the above-mentioned West German patent application (i.e., nitrogen oxide removal and sulfur oxide removal). (simultaneous) unit reactions were to occur.

In this draft example, NOx and SOx are
(SO2) was also unsatisfactorily adsorbed and removed at the same time, resulting in an unnecessary second step.

More importantly, there was a bigger problem with this draft example than the drawback that this second step was unnecessary.

That is, the biggest drawback of this draft example is the same as the drawback of the technology disclosed in the above-mentioned West German Publication (the drawbacks of this technology have already been described). (A) A significantly large amount of ammonia is required to be added. (B) The carbon consumption of activated carbon is large.
(C) The waste gas must be reheated to approximately 50°C to the temperature required for simultaneous NOx and SOx removal;
This is a drawback.

To explain in more detail, the temperature of the waste gas supplied from the flue to the exhaust gas treatment device is usually 110-180°C, and S
O2 is removed as ammonia salt much faster than NOx in this low temperature range of 110-180°C.

Therefore, in this temperature range, NOx can be effectively reduced unless much more ammonia is added than is necessary for NOx reduction alone.
x cannot be removed.

This is because the formation of SOx (SO2) as an ammonia salt has priority over the reduction of NOx.

In addition, precipitation of ammonia salts onto activated carbon reduces NO.
In addition to the deterioration of the properties of the activated carbon for x reduction (this is also stated in the West German Publication), ammonium sulfate on the activated carbon precipitates between particles, causing the pressure inside the adsorption tower to become abnormally high. However, there was a drawback that it was necessary to regenerate the activated carbon at an early stage.

Furthermore, as mentioned above, in order to improve the above-mentioned drawbacks and improve the selective reaction between NOx and NH3, it is necessary to increase the exhaust gas temperature to 180 degrees or higher, which increases the energy efficiency of exhaust gas reheating. There were also drawbacks to the above.

Furthermore, JP-A-55-11020 discloses a method for removing combustion waste gas containing nitrogen oxides and sulfur oxides, but in the specification attached at the time of filing of this already disclosed method, In the first stage removal process, a granular adsorbent layer was used at room temperature to 300°C (200°C to 300°C in the examples and text) and a space velocity of 5000 h-1 (25 in the examples).
00 to 10000h-1), and the S in SOx
However, in the previously disclosed method disclosed in Example 1, the removal rate of S03 is 0%, and the invention described in the claims is not an example. Although it is not supported and the validity of the invention is questionable)
Theoretically, there is a two-stage waste gas removal method in which ammonia gas is supplied to the waste gas from which SO3 has been selectively removed, and NOx is reduced through a reduction reaction using a catalyst different from the granular adsorbent in the first stage. has been disclosed.

However, this disclosed method lacks specificity in its disclosed content, and its theoretical method also has problems.

Of course, this already disclosed method had not been disclosed before the application of the claimed invention, and the claimed invention itself was not disclosed in the specification or drawings attached at the time of filing, but this is provided for reference. We will discuss the issues as a pre-filing technology.

In this disclosed method, theoretically, most of the SO3 in the sulfur oxides must be removed in the first step, so the apparatus is cumbersome.

According to the experimental knowledge of the inventor of the present application, 80% of sulfur oxides
The sulfur oxide removal rate is 90% compared to the case where the removal rate is about 90%.
In order to increase the amount by more than 10%, the amount of adsorbent should be increased by 2.
Therefore, the previously disclosed apparatus had the disadvantage that the first stage apparatus became a very large apparatus.

In addition, the method disclosed above is actually the second method of the disclosed specification.
As shown in the figure, from the viewpoint of SO3 removal efficiency, it is necessary to treat the waste gas at a temperature of approximately 200°C or higher, so once the temperature has dropped, the waste gas must be reheated. Ta.

Furthermore, in the previously disclosed method, different adsorbents are used in the first stage and second stage treatment, so the treatment tower must be separated into two, and the regenerator must be separated into two parts. Required for each of the 1st and 2nd stages,
There was a drawback that the entire device became a nuisance.

In particular, since SOx cannot be completely removed in the first step, the adsorbed residue of sulfur oxides remains on the adsorbent in the second step and must be regenerated.

In addition, in the previously disclosed method, the space velocity of waste gas is 5000 h-1
Although it is large (2,500 to 10,000 h-' in the examples) and can be processed at high speed, it requires a large amount of adsorbent that can be processed at this flow rate, which has the disadvantage that the apparatus becomes cumbersome.

The present invention was made in order to eliminate all of these conventional drawbacks, and without reheating the waste gas whose temperature has decreased,
The first moving bed removes 20 to 80% of the sulfur oxides and reduces the space velocity of the waste gas to about 4%.
00 to 1800=', thus reducing the size of the device, and using the same carbon-containing adsorbent in the first and second moving beds to perform both steps in a single device. In addition, the regeneration process can be simplified by using the same adsorbent regeneration device, and a method has been completed in which ammonia gas is added to the waste gas from which only a certain amount of SOx has been removed, and NOx and SOx can be completely removed in the second moving bed. This is what I did.

An object of the present invention is to minimize the drawbacks of conventional methods for removing sulfur oxides and nitrogen oxides, to efficiently remove the above oxides at relatively low temperatures, and to reduce the consumption of ammonia. The aim is to provide a method that allows for

The above object is achieved by the method of the present invention, namely, removing most of the sulfur dioxide in the waste gas using an adsorbent in the first moving bed, and then converting the nitrogen oxides into nitrogen gas by a catalytic reaction in the second moving bed. This can be achieved by reducing the amount and adding a predetermined amount of ammonia gas to remove remaining sulfur oxides.

The method of the present invention opens the door to a dry method for efficiently removing sulfur oxides and nitrogen oxides at relatively low temperatures.

The method of the invention allows the use of the same adsorbent in both the first and second mobile beds.

The method of the present invention removes 20 to 80% of sulfur oxides in the first moving bed, and removes about 0% of sulfur oxides per mo1 of nitrogen oxides, calculated as NO contained in the waste gas, in the second moving bed.
．． Nitrogen oxides are reduced using 4 to 1.5 mol of ammonia gas.

Copper, iron, lithium, nal in elemental form on carbon-containing adsorbents
- If 0.05 to 5% by weight of 1 type or a combination of 1 type or a combination of 1 type, aluminum, barium, or vanadium is used, the SO2 removal rate and NOx reduction rate can be further increased.

It is better to separate a part of the sulfur oxide in the first moving layer.
Compared to methods that remove all sulfur oxides in a single step, the process can be completed in a much shorter time.

Therefore, in the present invention, the waste gas is brought into contact with the adsorbent at a space velocity of 400 to 1800 h-1.

The ammonia gas is dosed at the stage where the sulfur oxides have been partially removed, i.e. before being fed into the second moving bed.

Therefore, the amount of ammonia consumed can be reduced compared to the simultaneous removal method using a single step, and the reaction between NOx and NH3 in the second moving bed can be carried out efficiently.

The amount of adsorbent in the first and second moving beds can be varied, and there can be a difference in the flow rate of the adsorbent in the first moving bed and the second moving bed.

The adsorbent in the first moving bed is preferably removed after about 20 to 100 hours and the adsorbent in the second moving bed is removed after about 20 to 200 hours.

The final regeneration of the adsorbent packed into both moving beds can be carried out by combining the adsorbent of the first moving bed with the adsorbent of the second moving bed, for example by washing or heating.

Also, both moving beds may be incorporated into a single reactor,
Alternatively, two separate reactors each provided with one moving bed may be connected.

Furthermore, the adsorbent may be supplied to each moving bed separately or may be supplied using a single supply pipe.

Ammonia gas can be added directly to the waste gas just before it enters the second moving bed, or if each moving bed is provided in separate reactors, these reactors can be connected. It can be directly fed into the conduit.

Further, it is not necessary that the ammonia gas be added uniformly to the entire moving layer, and even if it is added non-uniformly, there will be no particular problem.

Hereinafter, a reactor for carrying out the present invention will be explained based on the accompanying drawings.

First, the case where a single reactor shown in FIG. 1 is used will be explained.

This single reactor consists of a first chute 1 for sulfur oxide removal;
and a second chute 2 for reducing nitrogen oxides are incorporated into a single reactor.

Both chutes 1, 2 have opposing porous walls 3.4 and 5, respectively.
, 6.

A chamber 11.15 is formed adjacent to each of the outer porous walls 3,6.

The chamber 11 is provided with a gas inflow lower, and the chamber 15 is provided with a gas outlet 8.

Further, a chamber 9 is formed by the inner porous wall 4°5.

The powder adsorbent may be fed into the chutes 1 and 2 by providing a common supply pipe as shown in FIG. 1 and 2 may be sent separately.

The waste gas is fed from the gas inlet lower, passes through the porous wall 3, passes across the adsorbent bed moving in the first chute 1, then passes through the porous wall 4 and enters the chamber 9. .

In this chamber 9, ammonia is administered to the waste gas by means of an ammonia supply device 10.

'The ammonia-containing waste gas thus obtained passes through the porous wall 5, across the granular adsorbent bed moving in the second chute 2, and then, after passing through the porous wall 6, the gas stream It flows out from outlet 8.

The adsorbent is discharged from the lower ends of the chutes 1 and 2 and sent to an appropriate regenerator either separately or combined.

Next, the case of using the multiple reactor shown in FIG. 2 will be explained.

This multiple reactor has a first reactor (1) provided with a first chute 1 and a second reactor II (2) provided with a second chute 2.

In reactor I there are two opposing porous walls 3, 4, each of which forms a chamber 11, 12.

The chamber 11 is provided with a gas inflow lower, and the chamber 12 is provided with a conduit 13, respectively.

Conduit 13 is for connecting first reactor I and second reactor II.

Like the first reactor, this second reactor is also provided with two opposing porous walls 5, 6, each having a chamber 14,15.

The chamber 14 is connected to the conduit 13, and the chamber 15 is provided with a gas outlet 8.

The particulate adsorbent may be supplied to chutes 1 and 2 separately from two independent supply pipes as shown in FIG. 2, or through one common supply pipe as shown in FIG. Alternatively, the water may be supplied to the chutes 1 and 2 from the chutes 1 and 2, respectively.

The waste gas is fed from the gas inlet lower, passes through the porous wall 3, passes across the adsorbent layer moving in the first chute 1, and further passes through the porous wall 4 and flows into the chamber 12. .

This waste gas is then passed through conduit 13 into chamber 14, in which it or alternatively in chamber 14 is dosed with ammonia.

The thus obtained waste gas containing ammonia is passed through the porous wall 5.
, traverses the bed of adsorbent moving in the second chute 2 and then flows through the porous wall 6 into the chamber 15 .

This waste gas is finally transferred from the gas outlet 8 to the second reactor I.
It is expelled outside.

Hereinafter, the method of the present invention will be specifically explained based on Examples.

Example 1 Activated carbon (Brunauer), Emmett (Brunauer) with a specific surface area of 500 m2/g was used as a carbon-containing adsorbent.
Emmet and Teller et al.

1.0 in the first moving layer formed in the first chute 1
m3 activated carbon is used.

This first moving layer is perpendicular to the flow direction of the waste gas and has a cross-sectional area of 1 m2 and a depth of 1 m.

The second moving layer formed in the second chute 2 has a length of 0.9 m.
Activated carbon No. 3 is used, and its cross-sectional area is 1.0 m2 and the depth is 0.9 m.

In the first moving layer, NO: 0.072% by volume, SO2:
0.1% by volume, 02:6, 4% by volume and H2O: 10
．． Waste gas containing % O by volume at 720 m/h at a temperature of 120°C
3 supply, space velocity 720h-' (calculated value at room temperature)
Let it pass.

As a result, the average concentration of SO2 is reduced to about 0.03% by volume (reduction rate of 70%).

The activated carbon is then used in the first moving bed for about 70 hours.

Before the waste gas is supplied to the second moving bed, a sufficient amount of ammonia gas is added to the waste gas until the NH3 concentration becomes 0.079% by volume.

Next, this was adjusted to a space velocity of 800h-1 (calculated value at room temperature)
If the activated carbon residence time is about 90 hours, about 62% of NO will be removed.

The total removal rate of sulfur oxides after passing through this second moving bed is 95%.

Comparative Example 1 A single moving bed with a cross-sectional area of 1.0 m2 and a depth of 1.90 m is charged with 1.9 m'' of the same activated carbon as used in Example 1 above.

After adding a sufficient amount of ammonia gas to the waste gas to make the NH3 concentration 0.079% by volume, the waste gas is made to pass through the single moving bed at a temperature of 120° C. and a space velocity of 340 h −1 (calculated value at room temperature).

Activated carbon is used for about 25 hours.

As a result, only about 10% of NO is removed.

In this case, the pressure in the moving bed increases so that the device is
It is impossible to run it for more than an hour.

The sulfur removal rate is over 98%. Example 2 Activated carbon used as an adsorbent was immersed in a copper sulfate solution, dried, and then fired at a temperature of about 500°C to obtain a specific surface area of 470 m2 coated with about 0.063 g of copper per 1 g of activated carbon. /g (specified by Plutzier, Emmett, and Tele) is used.

Approximately 0.7 m 3 of active copper impregnated with the above described copper is used for the first transfer layer.

This first moving layer had a cross-sectional area of 1 m2 and a depth of 0.7 m.

On the other hand, the amount of the copper-impregnated activated carbon used in the second moving layer is 0.9 m3.

Further, this second moving layer has a cross-sectional area of 1.0 m2 and a depth of 0.9 m.

When waste gas having the same composition as in the first embodiment was passed through the first moving bed at the same temperature, space velocity of 1030h-'' (calculated value at room temperature), and activated carbon residence time of 70 hours, the waste gas It was possible to reduce the average concentration of SO2 in the sample to about 0.03% by volume (reduction rate of 70%).

Before sending this waste gas to the second moving bed, a sufficient amount of ammonia gas is added to make the NH3 concentration 0.079% by volume, and this is converted into a spatial measure soo'-" (calculated value at room temperature). When the activated carbon was allowed to pass through the second moving bed for a residence time of 90 hours, the No removal rate was 66%.

The sulfur removal rate after passing through the second moving bed was about 97%.

Comparative Example 2 Activated carbon 1 was prepared by using waste gas having the same composition as in the first example and impregnated with the same copper as used in the second example.
．． At the same temperature and with the required amount of ammonia added to a single moving bed containing 6 m3, a space velocity of 460 h-1 (
When activated carbon was passed through the activated carbon for a residence time of 35 hours (calculated value at room temperature), the removal rate of No was only 12%.

Reaction times of more than about 35 hours were not possible due to the increased pressure.

The desulfurization rate was 99% or more. From the above, the gist of the present invention should have been sufficiently clarified, and those skilled in the art should be able to readily apply the technical idea of the present invention in various forms by applying current technical knowledge.

[Brief explanation of the drawing]

The drawings show a reactor that can be used when carrying out the method of the present invention, and FIG. 1 is a vertical sectional view showing an outline of a single reactor incorporating two chutes in which a moving bed is formed, and FIG.
The figure shows two reactors each having one moving bed forming chute.
FIG. 2 is a vertical cross-sectional view schematically showing a multiple reactor in which individual reactors are connected. 1.2... Shoot 3, 4, 5, 6...
... Porous wall, 7... Gas inlet, 8...
・Gas outlet, 9°11, 12. 14. 15...
... Chamber, 10 ... Ammonia supply device, 1
3... Conduit.

Claims (1)

[Claims] 1. A granular carbon-containing adsorbent in which ammonia gas is added to waste gas containing sulfur oxides, nitrogen oxides, oxygen, and water vapor, and the ammonia gas is flowed from the top to the bottom in a reactor. In a method for removing sulfur oxides and nitrogen oxides from waste gas by passing it through a moving bed formed by
Using waste gas at a temperature of 10 to 180°C, the first moving bed and the second moving bed are filled with the same carbon-containing adsorbent, and the waste gas is first introduced into the first moving bed at a space velocity of about 400 to 1800 h-
1, 20 to 80% of the sulfur oxides are adsorbed on the adsorbent and removed, and then ammonia gas is added to this waste gas, which is then sent to the second moving bed, where nitrogen oxides are removed by a catalytic reaction. is reduced to nitrogen and the remaining sulfur oxides are removed, and the carbon-containing adsorbent packed in the first moving bed is heated for 20 to 100 hours, and the carbon-containing adsorbent packed in the second moving bed is heated for 20 to 100 hours. A method for removing sulfur oxides and nitrogen oxides from waste gas, which comprises taking out and regenerating in the same regenerator after 200 hours, and filling the first moving bed and the second moving bed again. 2 Nitrogen oxidation calculated as NO contained in waste gas*
Approximately 0.4 to 1.5 Mol per 'lMo1 (7) 7
The method according to claim 1, wherein ammonia gas is added. 3 Copper, iron, lithium,
The method according to claim 1, wherein one or more of sodium, aluminum, barium, or vanadium is deposited in an amount of about 0.05 to 5% by weight.