JPH03165815A - Method for processing combustion exhaust gas - Google Patents

Abstract

PURPOSE:To effectively remove sulfer oxides and nitrogen oxides from combustion exhaust gas by blowing an exhaust gas processing agent such as a slurry of urea solution of calcium carbonate or calcium hydroxide, or urea-impregnated calcium carbonate into the exhaust gas. CONSTITUTION:The processing agent for exhaust gas consists of fine powder of urea-impregnated calcium carbonate or calcium hydroxide, or of water slurry of these powder. This agent is prepared by mixing a urea solution with calcium carbonate or calcium hydroxide, drying the obtd. slurry into a cake, and pulverizing the cake into fine powder. By another method of preparing the processing agent for exhaust gas, urea solution slurry of calcium carbonate or calcium hydroxide is used. The processing agent for exhaust gas is blown into combustion exhaust gas to remove sulfer oxides and nitrogen oxides in the gas or to remove sulfer oxides, nitrogen oxides and hydrochloric acid in a batch from the gas.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to various boilers, various heating furnaces, municipal waste incinerators,
Nitrogen oxides (NOx) and sulfur oxides (SOx) in exhaust gas generated from industrial waste incinerators and other waste incinerators
), relates to a method for removing hydrochloric acid (HC/), in particular dry simultaneous removal of NOx and SOx, NOx
The present invention relates to a simple and effective exhaust gas treatment method that can achieve simultaneous dry removal of x, SOx, and HC.

[Prior Art and Problem 1 of the Invention In the past, much research and development has been conducted on methods for removing NOx, SSOx, and HC/individuals from this type of exhaust gas.
An effective method for simultaneous removal has not yet been developed. First, regarding simultaneous removal of NOx and SOx, NH. Absorption methods, acetic acid absorption methods, sulfuric acid/nitric acid methods, etc. are known. In addition, as dry methods, activated carbon method, electron beam irradiation method, etc. have been proposed, and research and development is being carried out in pilot plants. However, as is well known, both the wet and dry methods of simultaneous removal of NOx and SOx have their own problems, and these techniques have not yet been established and put into practical use. That is, NOx
Although a lot of research has been conducted on simultaneous wet removal methods for both NOx and SOx, it has not been put into practical use due to the low removal rate of NOx.

As mentioned above, the dry method for simultaneous removal of NOx and SOx has been tested in a pilot plant, but there are economical issues and no practical example has yet been seen.

On the other hand, a method for simultaneously removing NOx, SOx, and HCI is a technology required in waste incinerator exhaust gas treatment, but this technology has not been studied at all.

As described above, a technology for simultaneous removal of NOx and SOxSHCI has not yet been established. If a process capable of achieving this simultaneous removal could be established, it would bring immeasurable effects both in terms of equipment and economy, but as it has not been established at present, the removal of NOx, SOx, and H C / It is done in a process. However, S.O.
Since x and HC/ are the same type of acidic gas, they are necessarily removed at the same time in a wet process as described later. N
Since Ox has poor reactivity, it is not removed simultaneously with SOx and/or I1Cl even in a wet method.

As a NOx removal method, a selective catalytic reduction method using ammonia gas as a reducing agent and a titania vanadium catalyst is the mainstream, and there are many practical examples. In addition, there is a so-called non-catalytic denitrification method in which ammonia is blown into high-temperature exhaust gas of about 900° C. or higher to reduce and remove NOx non-catalytically. In this method, in addition to ammonia, compounds that generate ammonia upon thermal decomposition, such as ammonium carbonate, urea, ammonium formate, and ammonium oxalate, may be used. However, the required amount of these reducing agents is much higher than in the case of the above-mentioned catalytic reduction method, and the denitrification rate is nevertheless about 50
% or less. Therefore, there are few practical examples of this method in large boilers such as thermal power plants, and the only examples in which it has been used to date are special cases such as garbage incinerators. Although there are many practical examples of the selective catalytic reduction method, it requires a catalytic reactor in terms of equipment, requires advanced technology, and is economically expensive. Therefore, it is desired to put into practical use other simpler and more economical methods. Although the non-catalytic denitrification method has met this demand to some extent, its denitrification rate is low and it has not completely solved the problem.

More importantly, although these two methods are effective in removing NOx, they are completely ineffective in removing SOx and HCl.

The mainstream method for removing SOx is the wet lime gypsum method, which is an established technology that has been put into practice in many countries including Japan. However, since this method uses lime slurry, the temperature 5 of the exhaust gas drops to around 60°C. This temperature drop is considered a problem because it restricts the diffusion of exhaust gas into the atmosphere and leads to the generation of white smoke. Furthermore, since the wet method requires treatment water and wastewater treatment, there is a strong desire to develop and put into practical use a dry method that does not use water. In order to meet the demand for practical application of this dry method, we have developed a lime blowing method in which fine calcium carbonate, limestone, etc. are directly injected into the exhaust gas, and a lime slurry is injected into the exhaust gas to evaporate the moisture in the slurry using the sensible heat of the exhaust gas. A semi-dry method is being considered in which the lime acts as solid particles. However, the former method requires a reaction temperature of about 1000° C. or higher, the SOx removal rate is less than 50%, and there is no example of it being put into practical use. On the other hand, the latter method operates in a relatively low temperature range and achieves an SOx removal rate of 60 to 80%, so it has been put into practical use mainly in West Germany and the United States.

HCI! Regarding the removal of waste from waste incinerators, a dry method using limestone injection is also being considered6. HC/ is more reactive than SOx, and HCjl
Due to the physical properties of CaCl2 produced by the reaction between ' and limestone (due to its relatively low melting point, the reaction is less likely to form a shell on the surface of limestone particles and stop the reaction, as in the case of CaSO4), The HCI removal rate becomes relatively high. However, the limestone blowing method does not remove NOx.

Therefore, when simultaneous removal of NOx and SOx or simultaneous removal of NOx, SOx, and HCA is required, NOxSSOx and HCI are removed by a combination of denitrification, desulfurization, and desalination processes. .

Many methods have been proposed for combining denitrification and desulfurization, and there are many practical examples. The most common method is a combination of selective catalytic reduction and wet lime gypsum. This combination is excellent in that a high denitrification rate and a high desulfurization rate can be obtained. However, since this method is a combination of two processes, it is not necessarily a satisfactory method because the process is complicated and desulfurization is a wet method. As mentioned above, there is no practical example of a method for simultaneously removing the three components of denitrification, desulfurization, and desalination, and many combination methods have not been studied. In the treatment of exhaust gas from municipal waste incinerators, there are examples in which a combination of a non-catalytic denitrification method (NH3 blowing method) and a wet alkali absorption method (which allows simultaneous absorption and removal of SOx and HCI) is implemented. However, this also has the same problems as the above-mentioned denitrification and desulfurization.

Looking at the above situation, this type of NOx, Sox, HCA
For example, a dry method such as the lime blowing method has a lower reaction temperature than the current method, and if the exhaust gas contains NOx, SOx, and even HCl, it also removes HCl at the same time. Needless to say, a process that allows this is ideal. However, at present, such a process has not been put into practical use.

[Means for solving the problem] The combustion exhaust gas treatment method according to the present invention is a dry method, and N
It is a very simple and effective method in which simultaneous removal of Ox and SOx, simultaneous removal of NOX and SOX and HCA' is achieved.

That is, this method involves mixing calcium carbonate or potassium hydroxide with an aqueous urea solution, drying the resulting slurry, and pulverizing the resulting solid. An exhaust gas treatment agent made of fine powder or a water slurry of the same fine powder, or an exhaust gas treatment agent consisting of a urea aqueous solution slurry of calcium carbonate or calcium hydroxide is injected into the combustion exhaust gas to remove sulfur oxides and nitrogen oxides in the exhaust gas. This is a combustion exhaust gas treatment method characterized by simultaneously removing sulfur oxides, nitrogen oxides, and hydrochloric acid.

In this method, an exhaust gas treatment agent is usually blown into the combustion exhaust gas at a temperature range of 600°C to 900°C.

The above-mentioned exhaust gas treatment agent that is more effective than fine powder of urea-containing calcium carbonate or calcium hydroxide can be produced by, for example, mixing calcium carbonate or potassium hydroxide with an aqueous urea solution, drying the resulting slurry, and converting the resulting solid matter into fine powder. It is manufactured by converting into The exhaust gas treatment agent may be used in the form of the above-mentioned fine powder, but this fine powder can also be made into a water slurry and sprayed into the exhaust gas. That is, it uses the same principle as the above-mentioned semi-dry desulfurization method and operates as a dry method.

[Function] According to the method of the present invention, SOx in exhaust gas is removed with high efficiency despite the low temperature range.

In other words, the conventional method of injecting calcium carbonate into exhaust gas requires a reaction temperature range of 1000°C or higher,
Since a shell of calcium sulfate is formed as a reaction product on the surface of the lime particles, the utilization rate of lime is low, the amount of calcium carbonate blown into the method is large, and the removal rate of SOx is low. On the other hand, this method provides extremely high desulfurization at a low temperature range of 10,600°C to 900°C. The lower limit of this temperature range is, of course, a necessary value because below this value, it is difficult to achieve the desired SOx removal rate due to a decrease in the reaction rate. Further, the upper limit value should be determined in relation to the NOx removal rate, that is, the denitrification rate; in a temperature range higher than this, not only is NOx removal not achieved, but the NOx temperature tends to increase. If only the desulfurization reaction is considered, there is no problem even if the reaction temperature is higher than 900°C.

In the method of this invention, it is also possible to effectively reduce NOx and S by mixing fine powders of calcium carbonate or calcium hydroxide and urea and dispersing the mixture into the exhaust gas.
Although simultaneous removal of Ox is achieved, higher desulfurization rates are obtained with urea-impregnated calcium carbonate or calcium hydroxide fines by this method. In the conventional lime blowing method, the desulfurization rate was not high even in the temperature range exceeding 1000℃11.The reason why the desulfurization rate was not high even in the temperature range exceeding 1000℃11 is because calcium sulfate is formed on the surface of the calcium oxide fine particles generated by decomposition of calcium carbonate due to the reaction with SOx. This is said to be because a film, or shell, becomes viable and prevents the subsequent diffusion of SOx into the interior, thereby suppressing the reaction. On the other hand, in the case of calcium carbonate or calcium hydroxide impregnated with urea, a low melting point substance is generated by reaction with urea during the decomposition process of the calcium carbonate or calcium hydroxide, and the surface of the calcium oxide is activated. It seems that there are. This means that it is better to blow fine particles of calcium carbonate or calcium hydroxide impregnated with urea into the exhaust gas than to blow a mixture of particles of calcium carbonate or calcium hydroxide and urea. This is consistent with the fact that it was effective as stated earlier. Here, the fine powder of calcium carbonate or calcium hydroxide impregnated with urea is slurried again, or calcium carbonate or calcium hydroxide is slurried with an aqueous solution containing urea, and the resulting slurry is used as an exhaust gas treatment agent. Even when blown into the exhaust gas, the same effect as when using urea-impregnated calcium carbonate or calcium hydroxide fine powder as is can be obtained. In other words, the slurry blown into the exhaust gas evaporates moisture almost instantly, becomes particles of urea-containing calcium carbonate or calcium hydroxide, and changes to calcium oxide, so it is different from the fine particles of urea-containing calcium carbonate or calcium hydroxide. It will have the same effect.

The product of the SOx removal reaction in this method is calcium sulfate, and there is no production of calcium sulfite or ammonium sulfate.

On the other hand, according to this method, NOx in the exhaust gas is removed at the same time. In this method, NOx is removed not by a reaction that produces solid biomaterials as in the case of SOx removal, but by a reduction reaction using a urea component, which decomposes it into hydrogen and nitrogen. Although it has been known that NOx can be removed non-catalytically using a compound containing a certain amount of ammonia,13 the temperature range of this non-catalytic denitrification method is below 900°C as in the method of the present invention. It was not a temperature range like this, but rather a higher temperature range. And the denitrification rate is also 50
It was so low that it was said to be less than %. On the other hand, in the method of the present invention, the reaction temperature range is 900°C or less,
In the temperature range above that, NOx shows an increasing tendency,
Substantial NOx removal is not achieved.

There are two cases: when urea is impregnated with calcium carbonate or calcium hydroxide and injected into the exhaust gas, and when urea fine powder is mixed with calcium carbonate or calcium hydroxide fine powder and injected into the exhaust gas in the form of a mixture. There is a clear difference in the denitrification rate, with the former having a higher denitrification rate. In other words, calcium carbonate or calcium hydroxide is not just an absorbent for SOx, but also has the function of effectively promoting the reaction between NOx and urea.

Above, for convenience, the method for simultaneous removal of SOx and NOx in exhaust gas has been explained separately into SOx removal and No14
The simultaneous removal of urea is achieved at a much lower temperature than conventional dry methods (lime blow desulfurization, non-catalytic denitrification), and the chemicals used are calcium carbonate or calcium hydroxide impregnated with urea. It is a fine powder or a slurry of the same fine powder, and it is recognized that this calcium carbonate or calcium hydroxide and urea exhibit a strong interaction in the removal of SOx and NOx. especially,
It is revolutionary that desulfurization and denitrification can be achieved in the low temperature range of 600 to 900°C using the dry method. In addition, H(
, / can also be effectively removed, and in this case is more easily accomplished than the removal of SOx.

The embodiment of the present invention in a real device is simple.

That is, in various boilers, heating furnaces, municipal waste incinerators, and waste incinerators, when the combustion exhaust gas reaches a temperature range of 600 to 900°C after passing through a group of heat exchangers, urea is Cium fine powder or water slurry of the same fine powder,
Furthermore, a urea aqueous solution slurry of calcium carbonate or calcium hydroxide may be dispersed and injected into the exhaust gas in the above temperature range. Thereafter, the exhaust gas is cooled to a temperature range where a cyclone or a bag filter can be used, and calcium sulfate or calcium chloride, which is a raw material, is collected and removed there. NOx is reductively decomposed by urea in the aforementioned reaction zone, becomes water and nitrogen, and becomes harmless.
It is independent of the raw material recovery rate in the wake.

Various boilers, heating furnaces, garbage incinerators, etc. are originally equipped with a group of heat exchangers, and are also equipped with dust collectors such as cyclones. Therefore, to put it in a slightly extreme way, it is possible to desulfurize, denitrify, and/or desalinate using a dry method by installing a device that blows fine powder of urea-impregnated supported calcium carbonate or calcium hydroxide, or a device that sprays and injects slurry. Become.

16 [Effects of the Invention] According to the dry simultaneous removal method of NOx and SOxSHCI of the present invention, these removals can be achieved with a high efficiency that could not be achieved by any conventional simultaneous removal method. In order to achieve highly efficient removal of NOx, SOx, and HCI with conventional technology, selective catalytic reduction method and wet lime-gypsum method (more precisely, S
This is a method for removing Ox, but if HC/ coexists, HC
7 can be removed at the same time as SOx), but according to the present invention, white smoke is generated because it is a dry method that does not involve a wet method and is performed in one step, which is much simpler than this conventional method. It also does not cause a decrease in exhaust gas (, NOx
, SOx, and HCI can be removed, thereby contributing to the improvement of atmospheric environmental pollution.

[Examples] Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

The attached FIG. 1 is a flow sheet showing an outline of the apparatus for carrying out the tests in the following comparative examples and examples. This device is a pulverized coal-fired combustion chamber (6,
) and the reaction chamber (11) on the downstream side of this. The amount of pulverized coal combustion is 10 kg/hour, the combustion temperature is controlled by combustion of auxiliary propane, the NOx generation amount is controlled, and SO2
By injecting gas and HC/gas, it is possible to adjust the concentration of each in the exhaust gas. The reaction chamber (1) for denitrification, desulfurization and desalination is 350A (inner diameter 330
It is constructed of stainless steel tubes with a height of 4 m. The reaction chamber (1) can be controlled to a predetermined temperature by an electric heater (2) provided on its outer surface. When the exhaust gas treatment agent, that is, the denitrification, desulfurization, and desalination agent is in the form of fine powder, it is injected into the reaction chamber (1) along with the air flow. Note that in the case of slurry, it is similarly injected into the exhaust gas from this position. 02, NOx and SOx in exhaust gas
Each concentration is measured at the outlet of the reaction chamber (1) and the bag filter (3).
Measurements were made with an analyzer (7) (Ill) installed at the outlet of the NOX and SOx analyzer (7) (
It has been confirmed that the measured values in 8) are the same, and that no reaction regarding either substance occurred in 18 during this time. On the other hand, the amount of HCI was measured by wet chemical analysis, but the values analyzed by analyzers (7) and (8) were considerably different, and the value analyzed by analyzer 8) was lower. That is, HCl was capable of reacting with CaO in a low temperature range, and the salt removal rate showed a tendency to improve as a whole. The exhaust gas is cooled by an air heater (4) and a gas cooler (5), removed by a bag filter (3), and then released into the atmosphere. In this figure, (9) indicates a thermometer, and (10) indicates a flowmeter.

Comparative Example 1 This comparative example shows the measurement results of the desulfurization rate and the denitrification rate in the conventional lime blowing method, so that the characteristics of the examples described below will become clear.

Using the apparatus shown in FIG. 1, finely ground calcium carbonate was added to the exhaust gas as an exhaust gas treatment agent. The test conditions at this time are shown in Table 1, and the test results are shown in Table 2.

↑ 9 Table 1 Test conditions Fuel: Propane/pulverized coal mixed combustion (propane = 0.64
Nm3/hour, coal: 3.24 kg/hour) Air ratio +1.81 (02 concentration in exhaust gas: 9.4%) Exhaust gas amount: 70Nm3/hour NOx concentration: 30011I1m SO2 concentration: 900I111m Reaction time: 4 to 5 Table 2 Test results Reaction temperature Reaction time Ca/S molar ratio Desulfurization rate Denitrification rate 1100℃ 4 seconds 2.1 62% 0%8
00°C 5 seconds 2,1 15% 0% At a reaction temperature of 800°C, the desulfurization rate is 15%, and the lime blowing method in such a low temperature range cannot obtain a practical desulfurization rate.

Of course, the denitrification rate is 0%, and NOx is not removed at all.

Example 1 20 An exhaust gas treatment agent according to the present invention was prepared as follows. 10k of commercially available calcium carbonate (average particle size 12μm)
It was weighed and placed in a large stainless steel vat. On the other hand, 1 kg of reagent grade 1 urea was weighed and dissolved in 4 liters of water. Then, pour this urea aqueous solution into the stainless steel vat,
Mix well with calcium carbonate. As a result, this mixture became a slurry. Next, the slurry together with the stainless steel vat was placed in a dryer and left at a temperature of 110° C. overnight to evaporate and remove moisture. The slurry becomes a solid substance by removing water, but it is relatively easy to crush, and after crushing it in a mortar, it was passed through a sieve with an opening of 0.3 mm. The fine powder thus prepared is calcium carbonate fine powder containing about 10% of urea, and is used as an exhaust gas treatment agent.

Using the apparatus shown in Figure 1, the above exhaust gas treatment agent is blown into the exhaust gas, and SOx and NOx are removed by the same operation as in the comparative example.
A simultaneous removal test was conducted.

The test conditions at this time are as shown in Table 3. This 21 The test results are shown in Figures 2 and 3, respectively.

Table 3 Test conditions Fuel: Propane/pulverized coal mixed combustion (Propane: 0.65
Nm3/hour, coal: 2.12 kg/hour) Air ratio: 1.86 (02 concentration in exhaust gas: 11.0%) Exhaust gas amount: 56Nm3/hour NOx concentration: 200 ppm SO2 concentration: 900 ppm Reaction time : 6 seconds reaction temperature = 800° C. FIG. 2 is a graph showing the relationship between the Ca/S ratio and the denitrification rate, and FIG. 3 is a graph showing the relationship between the Ca/S ratio and the desulfurization rate. In these drawings, curve (A) is the test result when using the exhaust gas treatment agent of the present invention, and curve (A) is the test result when using the exhaust gas treatment agent of the present invention.
B) is calcium carbonate and urea fine powder with an average particle size of 12 μm (
These are the test results when a mixture (calcium carbonate: urea = 4:1) of 1st grade reagent (particle size of approximately 10 to 30 μm) was injected. In the case of curve (B), desulfurization and denitrification reactions, which were not achieved at all by blowing cassylium carbonate at a temperature of 800°C, are achieved, but in the case of curve (A), the desulfurization and denitrification reactions are achieved even more. Significant denitrification and desulfurization have been achieved. In particular, the dramatic increase in desulfurization rate is noteworthy, suggesting that this denitrification reaction is different from conventional non-catalytic denitrification and is more effective in interacting with calcium carbonate.

Example 2 The exhaust gas treatment agent used in Example 1 was made into a 20% water slurry, and this slurry was added to the reaction chamber (
1) Sprayed inside. As a result, the denitrification rate was 55%, and the desulfurization rate was 6%.
Obtained 0%. Note that the C a /S ratio at this time is approximately 1.
It was 5.

Example 3 The test conditions were almost the same as in Example 1, and HCI was contained in the exhaust gas.
Denitrification, desulfurization, and desalination tests were carried out by adding 1. The exhaust gas treatment agent used in this test was the fine powder used in Example 1. Table 4 shows only the test conditions that were different from those in Example 1. As a result of this test, a denitrification rate of 50%, a desulfurization rate of 75%, and a desalination rate of 98% were obtained. Regarding the desalination rate, when sampling analysis was performed on the piping upstream of the bag filter (3) of this device, the desalination rate was 65%. This shows that HCl can be removed even at a fairly low temperature range, for example about 120°C.

Table 4 Test conditions HCI concentration: 80011pm SOx concentration: 2001111+11 NOx concentration: 200ppm Ca/(S+2C/) ratio: 4 Comparative example 2 In this comparative example, finely ground calcium hydroxide was used instead of calcium carbonate as an exhaust gas treatment agent. The test conditions were the same as those of Comparative Example 1, and the test of Comparative Example 1 was repeated. The test results are shown in Table 5.

24 Table 5 Test results Reaction temperature Reaction time Ca/S molar ratio Desulfurization rate Denitration rate 1100°C 4 seconds 2.1 58% 0%80
0°C 5 seconds 2.1 10% 0% At a reaction temperature of 800°C, the desulfurization rate is 10%, and the lime blowing method in such a low temperature range cannot obtain a practical desulfurization rate.

Of course, the denitrification rate is 0%, and NOx is not removed at all.

Example 4 In this example, an exhaust gas treatment agent was prepared in the same manner as in Example 1, using commercially available calcium hydroxide (average particle size 20 μm) instead of calcium carbonate. Using this exhaust gas treatment agent, the test conditions were the same as those of Example 1, and Example 1
The test was repeated. The test results are shown in Figure 3 as a curve (A').
Indicated by

As can be seen from the figure, the exhaust gas treatment agent according to this example exhibited great denitrification and desulfurization effects as the exhaust gas treatment agent according to Example 1.

25 Example 5 20 kg of calcium hydroxide and 5 kg of urea were dissolved in 75 kg of water to form a slurry. This slurry-like exhaust gas treatment agent was sprayed into the reaction chamber (1), the test conditions were the same as those of Example 1, and the test of Example 1 was repeated.

As a result, a denitrification rate of 70% and a desulfurization rate of 83% were obtained. In addition,
The Ca/S ratio at this time was about 2.1.

[Brief Description of the Drawings] Fig. 1 is a flow sheet showing an example of the present invention, Fig. 2 is a graph showing the relationship between the Ca/S ratio and the denitrification rate, and Fig. 3 is a graph showing the relationship between the Ca/S ratio and the denitrification rate. It is a graph showing the relationship between desulfurization rates. that's all

Claims (2)

[Claims] (1) Fine powder of urea-impregnated calcium carbonate or calcium hydroxide produced by mixing an aqueous urea solution with calcium carbonate or calcium hydroxide, drying the resulting slurry, and pulverizing the resulting solid matter. Sulfur oxides and nitrogen oxides, or sulfur oxides and A combustion exhaust gas treatment method characterized by simultaneously removing nitrogen oxides and hydrochloric acid. (2) The exhaust gas treatment according to claim 1, which is produced by mixing calcium carbonate or potassium hydroxide with an aqueous urea solution, drying the resulting slurry, and pulverizing the resulting solid matter. agent.