JPH0693971B2 - Simultaneous desulfurization denitration method in furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to sulfur oxides (SO) in combustion exhaust gas discharged from various boilers, various heating furnaces, and refuse incinerators.
x) and nitrogen oxides (NOx) at the same time.

[Prior Art and Problems to be Solved] A general desulfurization and denitration method currently adopted in Japan is a method in which ammonia is used as a reducing agent for denitration and NOx is selectively catalytically reduced in the presence of a catalyst. Is the mainstream, and a wet method such as a wet lime gypsum method is used for desulfurization.

However, in these methods, the equipment installation occupied area is large, and the initial cost and running cost are high, so that a method that is more compact and can be implemented at low cost is desired.

On the other hand, the so-called in-furnace direct desulfurization method of directly introducing a desulfurizing agent such as limestone into the furnace, although the initial cost and running cost are considerably reduced, the effective use of the agent is less than half of the wet method, Unreacted agents such as CaO are excreted. For example, when a direct desulfurization method in a furnace is adopted for a coal-fired boiler, a large amount of Ca is discharged in the exhaust fly ash.
Since SO ₄ and CaO will be contained, it is necessary to establish a treatment method for discharged ash.

The present invention has been achieved to meet such a demand, and an object thereof is to provide a simultaneous in-furnace desulfurization denitration method that can be implemented at low cost and that can exhibit excellent desulfurization denitration performance. .

[Means for Solving the Problems] The present invention has been devised to achieve the above-mentioned object, and is a) ammonia gas or an aqueous solution thereof as a treatment agent in a range of temperature of 900 ° C or lower and 500 ° C or higher in a furnace. ,
b) an aqueous solution of ammonium sulfate and / or acidic ammonium sulfate, c) a powder or aqueous solution of urea and / or a urea compound, and i) the above-mentioned agents a), b) and c) alone, respectively, in the upstream and middle regions of the furnace. It is sprayed in the furnace in three stages of the basin and the downstream region, or ii) In the furnace in two stages with one of the agents a), b) and c) alone and the other two in a mixed state. Iii) or 1) in a mixed state with the agents a), b) and c) above.
The chemical is supplied by any one of the spraying forms in the furnace at the stage, and in the case of the spraying form of i) or ii), mainly the denitration reaction is performed in the upstream region and the desulfurization is mainly performed in the middle and downstream regions. Reaction and the second stage denitration reaction, and in the case of the spraying form of iii), the desulfurization reaction and denitration reaction occur simultaneously, and the exhaust gas treatment process and the exhaust gas cleaning device installed in the downstream flue of the furnace The method for simultaneous simultaneous desulfurization and denitration in a furnace comprises a chemical recovery step for trapping and recovering unreacted ammonia or ammonium sulfate or acidic ammonium sulfate generated from the exhaust gas treatment step.

In-furnace simultaneous desulfurization denitration method according to the present invention, preferably, the ammonia or ammonium sulfate or acidic ammonium sulfate aqueous solution recovered in the chemical recovery step is reacted with quick lime or slaked lime in a slurry or powder in a reaction crystallization tank, It is equipped with an ammonia recovery / gypsum crystallization step of recovering an ammonia component as a steam-containing gas and reacting a sulfate group or an acidic sulfate group with calcium ions to precipitate gypsum.

Further, the in-furnace simultaneous desulfurization denitration method according to the present invention preferably comprises an ammonia water production step of forming ammonia water by compressing and cooling the water vapor-containing ammonia gas recovered in the ammonia recovery / gypsum crystallization step. There is.

Furthermore, the in-furnace simultaneous desulfurization and denitration method according to the present invention preferably solid-liquid separates the gypsum slurry recovered in the ammonia recovery / gypsum crystallization step, recovers gypsum as a solid content, and uses ammonia water as a liquid content. Alternatively, a solid-liquid separation step of collecting an unreacted ammonium sulfate aqueous solution or an acidic ammonium sulfate aqueous solution is provided.

[Preferred Embodiment of the Invention] The in-furnace simultaneous desulfurization and denitration method according to the present invention includes the following four steps.

Step I ... In-furnace denitrification desulfurization step In a furnace, in a temperature range of 1100 ° C. or higher and 700 ° C. or higher, a) ammonia gas or its aqueous solution, b) ammonium sulfate and / or aqueous solution of ammonium sulfate alone or in a mixed state And the step of causing a first-stage denitration reaction and a slight desulfurization reaction.

Temperature in the furnace downstream of the above spraying area 900 ℃ or less 500 ℃
In the above range, a) ammonia gas or an aqueous solution thereof, b) an aqueous solution of ammonium sulfate and / or acidic ammonium sulfate, c) a powder or aqueous solution of urea and / or a urea compound, alone or in a mixed state, is sprinkled into the furnace. , A step of causing a desulfurization reaction and a second-stage denitration reaction.

In the region where the temperature is 500 ° C or lower downstream from the furnace outlet, a) ammonia gas or its aqueous solution
b) A step of spraying an aqueous solution of ammonium sulfate and / or an acidic ammonium sulfate alone or in a mixed state to cause the desulfurization reaction in the second step.

Step II: Recovery step of unreacted ammonia gas or steam and generated ammonium sulfate or acidic ammonium sulfate. Downstream flue of dust collector attached to boiler etc. (For those without a dust collector, smoke immediately before the chimney inlet road)
A step of capturing and recovering the ammonia gas discharged from the above step I or the vapor or ammonium sulfate or acidic ammonium sulfate gas or fumes containing the same, which is discharged from the above step I, by using a so-called wet smoke washing device or other suitable absorbing device when water is used as an absorption medium.

Step III: A step of reacting the recovered material in Step II with quicklime or slaked lime to recover ammonia and ship gypsum. Ammonia water and ammonium sulfate or acidic ammonium sulfate aqueous solution recovered in Step II are introduced into the reaction crystallization apparatus. Then, powder of calcium hydroxide or slaked lime or water slurry is added to this, and the sulfate radical or acidic sulfate constituting ammonium sulfate or acidic ammonium sulfate is reacted with calcium ions to precipitate gypsum, and further ammonia generated by this reaction is converted into gas or gas. Reactive crystallization process that expels as vapor.

Step IV ... Ammonia recovery and recirculation, gypsum separation recovery, ammonium sulphate aqueous solution recovery and its circulation step A step of compressing and cooling the steam-containing ammonia gas recovered in the above Step III to form ammonia water.

The gypsum crystal slurry after the reaction crystallization is subjected to solid-liquid separation with a solid-liquid separator such as a centrifuge, and gypsum crystals are recovered as a product, and the filtrate is mixed with the above ammonia solution as an ammonium sulfate aqueous solution to form a mixed solution. The step of recirculation and use as the desulfurization and denitration agent of step I.

The combination of the above respective steps in the present invention differs depending on the target performance of desulfurization and denitration, whether the by-product is gypsum or used as an ammonium sulphate aqueous solution for other purposes. [1] SO ₂ in exhaust gas is absorbed and recovered as gypsum In order to obtain a high desulfurization rate and a high denitrification rate, a combination of steps I to and steps II, III and IV, and a combination of step I and or and steps II, III and I
In the case of using the combination of V, [2] by-produced ammonium sulfate or acidic ammonium sulfate for other purposes, a combination of any one of step I ~, ~, ~ and a combination of step II (in this case, recovered from step II). Immediately recycle the ammonium sulfate or acidic ammonium sulfate aqueous solution to step I,
Some of them are discharged to the outside of the system for other purposes), and various combinations.

[Desulfurization and denitration test] The reaction in each step in the present invention was confirmed by a vertical combustion test apparatus and another glass test apparatus shown in FIG.

The apparatus used in this test mainly comprises a pulverized coal burning combustion chamber (6) and a desulfurization / denitration reaction chamber (1) connected to the downstream side of the combustion chamber. The maximum capacity of pulverized coal combustion is 10 kg / hour,
It is possible to control the combustion temperature by burning the combustion-assisting propane, control the NOx generation amount, and adjust the SO ₂ concentration in the flue gas by injecting SO ₂ gas. The test was carried out by propane mono-burning, propane-pulverized coal mixed firing, or pulverized coal mono-firing, and the combustion temperature was set to a predetermined temperature by controlling the supply amount of these and the air amount used for combustion.

The smoke emitted from the reaction chamber (1) is the air heater (4).
And, it is cooled by the gas cooler (5), dust is removed by the bag filter (3), and it is released to the atmosphere.

The reaction chamber (1) is composed of a stainless steel tube having an inner diameter of 330 mm and a height of 4 m. A cylindrical electric heater (2) is provided on the outer surface of the reaction chamber (1), and thereby the reaction chamber (1) is provided.
The internal combustion exhaust gas temperature can be controlled to a predetermined temperature. The desulfurization and denitration agent is injected into the reaction chamber (1) through an air flow from an inlet (11) at the top thereof.

The O ₂ , SO ₂ , and NOx concentrations in the flue gas were analyzed at the outlet of the reaction chamber (1) and the outlet of the bag filter (3) (7)
Each is measured in (8). That is, in these analyzers (7) and (8), the exhaust gas after dust removal by a metal sintered filter with a self-cleaning device is led to an infrared SO ₂ analysis type and a zirconia type oxygen analyzer, and
Perform SO ₂ and O ₂ analysis. Also bug filter (3)
At the exit of NOx, NOx analysis is further performed by a Chemilumi type NOx analyzer, and SOx is analyzed by wet exhaust gas analysis specified by JIS method.
The analysis and the total S content absorbed in this absorbing solution and the NH ₄ ⁺ concentration analysis are performed.

The temperature at each location shown in Fig. 1 is measured by a thermocouple thermometer (9), and the amount of fuel input is measured by the amount reduced by a metering device in the case of pulverized coal, and by a gas flow meter in the case of propane. The amount of air is measured by an orifice type flow meter, and the amount of exhaust gas is measured by a venturi type gas flow meter (10). In addition,
The theoretical exhaust gas amount calculated from the fuel amount and the input air amount and the measured exhaust gas amount agree well within a few percent, and it was confirmed that each meter was operating correctly.

It was added industrial SO ₂ gas as SO ₂ in the exhaust gas was adjusted amount such that the SO ₂ concentration in the exhaust gas becomes 500 ppm.

[1] Desulfurization and Denitration Reaction of Aqueous Urea Solution It is well known that urea exhibits a denitration reaction, but experiments by the present inventors have revealed that a desulfurization reaction also occurs at the same time.

It is considered that these reactions are based on the reaction formulas shown below.

(1) DeNOx reaction 2NO + (NH ₂ ) ₂ CO + 1 / 2O ₂ → 2N ₂ + CO ₂ + 2H ₂ O …… (2) Desulfurization reaction (NH ₂ ) ₂ CO + H ₂ O → NH ₃ + CO ₂ …… NH ₃ + SO ₂ +1 / 2O ₂ + H ₂ O → (NH ₄ ) HSO ₄ …… 2NH ₃ + SO ₂ ＋ 1 / 2O ₂ ＋ H ₂ O → (NH ₄ ) ₂ SO ₄ …… Here, the denitration reaction of the formula was clarified in the published literature. However, the reaction of the formulas is a reaction formula assumed by the present inventors. It is not clear at this stage whether ammonium sulphate or acidic ammonium sulphate is formed through this process, or whether urea and SO ₂ react directly, but it is certain that ammonium sulphate or acidic ammonium sulphate is formed as described below. Is.

Here, the desulfurization performance is shown in Fig. 2 when the test apparatus of Fig. 1 is used, and the urea aqueous solution is sprayed into the reaction chamber (1) of the apparatus through the inlet (11). The performance is shown in FIG. 3, respectively.

In FIG. 2, the horizontal axis represents the molar equivalent ratio of urea and SO ₂ , the vertical axis represents the desulfurization rate, and the combustion gas temperature at the blowing position is used as a parameter.

As is clear from the figure, lower temperature is more efficient for desulfurization, and at a temperature of 750 ° C, almost 100% desulfurization is possible with an equivalence ratio of about 1.1.

The combustion exhaust gas conditions at this time are as follows.

Fuel: Propane SO ₂ concentration: 500 ppm NOx concentration: 170 ppm to 60 ppm * Combustion exhaust gas amount: 90 to 100 Nm ³ / hour Urea aqueous solution concentration: 25 to 50 g / (Note) * NOx generation rate varies depending on combustion temperature.

In FIG. 3, the horizontal axis represents the temperature at the blowing position, and the vertical axis represents the denitration rate.

This figure plots data when the molar equivalent ratio of urea and NOx is fixed at 5. From FIG. 3, it can be said that the denitrification rate is about 80% when the temperature at the blowing position is 820 ° C. or higher, and at the temperature lower than that, the denitrification rate tends to gradually decrease with temperature decrease. Although the denitrification rate tends to decrease in the temperature range exceeding 1150 ° C, this relationship is not shown in this figure.

Next, the bag filter (3) shown in FIG.
The exhaust gas after passing through the sintered filter on the outlet side of the JIS
After washing with water according to the method specified in the Act, the amounts of sulfuric acid and total sulfur contained in the washing solution were determined by volumetric analysis using a 1/10 N caustic soda standard solution and gravimetric analysis by barium sulfate precipitation method, respectively. Further, the ammonia concentration in the same solution was determined by an ammonia ion electrode analyzer. Calculated from the total sulfur content from these analytical results
The amount of SO ₄ (B) calculated from the amount of SO ₄ (A) and the amount of sulfuric acid was obtained, and the amount of NH ₄ ⁺ that reacts with the amount of (AB) was calculated. Incidentally, SO ₃ in the absorbent solution at this ^- is not present, all SO ₄
^- that has become a has already been confirmed.

Figure 4 shows the correlation between the NH ₄ ⁺ amount obtained from this calculation NH ₄ ⁺ amount and ion electrode analyzer.

In the figure, points were distributed on a straight line with a slope of 1 when the reaction substance was converted assuming that it was ammonium sulfate, which confirmed that the reaction product was ammonium sulfate. In addition, the test in which the urea addition equivalence ratio is low shows the portion with a small NH ₄ ⁺ conversion value in Fig. ₄ , and in this case each point is on a straight line with a slope of 1/2 when it is converted assuming that it is acidic ammonium sulfate. It was confirmed that it was distributed, and that the reaction product at that time was acidic ammonium sulfate, and that the above reaction formulas (1) to (5) occurred.

This reaction product such as ammonium sulfate is contained in the exhaust gas that has passed through the bag filter and the sintered filter, and the product such as ammonium sulfate in this process is considered to exist in the form of fumes or gas. . If these are solids, one should be able to observe the deposition of these reactants on the surface of the bag filters or on the surface of the sintered filters, although the reactants on these surfaces should remain visible after extended operation of the test. No accumulation was observed. In addition, even if urea water was added during pulverized coal combustion as part of this test,
The amount of NH ₄ ⁺ contained in the fly ash captured by the bag filter was almost trace level in most cases.

From the above events, the substance produced by the desulfurization reaction when urea is added is ammonium sulfate or acidic ammonium sulfate.
Exists as gas or fume in the atmosphere above ℃,
It became clear that it was not captured by bug filters.

[2] desulfurization and denitrification performance ammonium sulfate ammonium sulfate is its composition on SO ₄ ^- in order to have a root, when used as furnace desulfurization and denitration agent, there is a risk of releasing decomposition when SO ₂ ammonium sulfate, common sense It was not used as a desulfurization denitration agent.

However, in the test results of the present inventors, as described below,
It was revealed that ammonium sulfate exerts a desulfurization and denitration reaction action.

(1) denitration reaction (i) high temperature _{range: 2NO + (NH 4) 2} SO 4 → 2N 2 + SO 2 + 4H 2 O ...... (ii) a medium temperature _{range: 2NO + (NH 4) 2} SO 4 + 1 / 2O 2 → 2N 2 + H ₂ SO ₄ + 3H ₂ O ...... The reaction in the above formula is a reaction that occurs in the high temperature range, and SO ₂ is obviously released under these conditions. The reaction of the formula is a reaction that occurs in the middle temperature range, and under this condition, denitration occurs but desulfurization is not observed.

(2) Desulfurization reaction (NH ₄ ) ₂ SO ₄ + SO ₂ + 1 / 2O ₂ + H ₂ O → 2 (NH ₄ ) HSO ₄ ...... In a relatively low temperature range, desulfurization reaction occurs even with ammonium sulfate. It is assumed that desulfurization occurs during the process in which ammonium sulfate absorbs SO ₂ and is then oxidized to form acidic ammonium sulfate as in the reaction of the equation.

It is considered that the sulfuric acid generated by the reaction of the formula becomes acidic ammonium sulfate by the reaction of the following formula.

(NH ₄ ) ₂ SO ₄ + H ₂ SO ₄ → 2 (NH ₄ ) HSO ₄ ...... To confirm these reactions, the ammonium sulfate concentration is 40 g / under the same conditions as the desulfurization and denitration test with urea described above. The aqueous solution is introduced into the reaction chamber (1) shown in FIG.
The desulfurization and denitration characteristics when spray-supplied from 1) were investigated.

FIG. 5 shows the relationship between the temperature and the desulfurization rate when the molar equivalent ratio of the aqueous solution of ammonium sulfate and SO _{2 in} the exhaust gas is set to about 1.

In this figure, the horizontal axis shows the exhaust gas temperature at the solution injection position,
The vertical axis is the desulfurization rate in the furnace. When the desulfurization rate shows-(minus), it is confirmed that SO ₂ is released by the decomposition reaction of ammonium sulfate.

From FIG. 5, even when an ammonium sulfate aqueous solution was used as the desulfurization denitration agent, some desulfurization reaction was observed at a temperature of 800 ° C. or lower
This is considered to be due to the reaction of the equation as described above.

In an atmosphere at a temperature of 900 ° C or higher, SO ₂ release, which is considered to be caused by the reaction of the formula, is observed, and the desulfurization rate becomes negative. In the intermediate temperature range between the desulfurization reaction and the NOx releasing reaction, the reactions of ~ occur intricately intertwined with each other, and it is considered that the variability of the data is caused by this entanglement. In addition to the above desulfurization reaction phenomenon, denitration reaction was also observed.

FIG. 6 shows the denitration characteristics at this time.

The configuration of the figure is the same as that of FIG. 5, but the vertical axis shows the denitration rate in the furnace.

From Fig. 6, the denitrification reaction has a higher denitrification rate when the temperature is higher.
It can be seen that the percentage tends to be constant.

Also, since SO ₂ is released at 800 ° C and above,
The reaction is believed to follow the equation and at temperatures below this the equation reaction is assumed.

The denitration rate shown in the figure is based on the NOx generated by propane combustion without addition of ammonium sulfate. For example, when the temperature at the blowing position is 1100 ° C, the generated NOx value is 170
In the case of 700 ° C, the ppm is 60ppm, and the generated NOx reference value differs depending on the temperature.

Next, in order to confirm the products associated with the desulfurization and denitration reaction at the time of injecting an aqueous solution of ammonium sulfate, in the same manner as the above-mentioned urea addition,
As shown in FIG. ₄ , the relative relationship between the converted NH ₄ ⁺ concentration value and the NH ₄ ⁺ concentration obtained from the ion electrode analysis is shown in FIG. 7.
From the figure, it was revealed that the product was ammonium sulfate or acidic ammonium sulfate, and it was revealed that the acidic ammonium sulfate was produced in a larger amount by the formula and the reaction described in the formula than when urea was added.

From the above events, it is clear that the ammonium sulfate aqueous solution causes desulfurization and denitration reaction depending on the reaction conditions, and the reaction product is acidic ammonium sulfate.

The ammonium sulphate shown in FIG. 7 is considered to be the ammonium sulphate that has not participated in the reaction of the formula (1) to be taken out of the system without being reacted and trapped.

[3] Desulfurization and denitration performance of ammonia It is a well-known fact that ammonia has a reducing effect on NOx, and when used as a denitration agent, it is generally common to use a catalyst together in order to improve reaction efficiency.

It is generally well known that when SO ₂ gas is passed through ammonia water and then excess air is introduced, ammonia easily reacts with SO ₂ and O ₂ to generate ammonium sulfate.

The reaction at this time is based on the following equation.

(1) DeNOx reaction 6NO ＋ 4NH ₃ → 5N ₂ ＋ 6H ₂ O …… (2) Desulfurization reaction 2NH ₃ + SO ₂ ＋ 1 / 2O ₂ ＋ H ₂ O → (NH ₄ ) ₂ SO ₄ …… (NH ₄ ) ₂ SO ₄ + SO ₂ + 1 / 2O ₂ + H ₂ O → 2 (NH ₄ ) HSO ₄ …… When ammonia is injected into the furnace as a desulfurization denitration agent, a considerable effect can be expected with regard to denitration, although the reaction efficiency is lower than when using a catalyst.

FIG. 8 shows the desulfurization performance when ammonia gas is added from the inlet (11) into the reaction chamber (1) shown in FIG.

The horizontal axis of the figure shows the concentration of ammonia gas added to the exhaust gas, and the vertical axis shows the denitration rate and desulfurization rate at that time.

The exhaust gas conditions during this test were: fuel: mixed combustion of propane and pulverized coal, combustion exhaust gas amount: 105 Nm ³ / hour, addition position temperature: 800 ° C SO ₂ concentration: 800 ppm NOx concentration: 200 ppm.

As is clear from Fig. 8, the denitration performance of ammonia shows a denitration rate of 70% in the region where the addition amount is 600 ppm (NH ₃ / NO equivalent ratio = 3) or more, and even if the addition amount is increased beyond this The rate did not increase and remained constant.

However, at this time, the desulfurization reaction in the furnace did not occur at all as shown in FIG. 8, and the desulfurization effect could not be obtained by the method of adding dry ammonia gas to the high temperature range. It is considered that this is because the reaction does not proceed because the water necessary for the equation to be established does not exist and the reaction temperature is too high.

It is clear that the reaction of the formula in the presence of sufficient water readily proceeds as explained above. Therefore, ammonia gas was used as the ammonia gas, and the desulfurization reaction was investigated at a low temperature portion of 500 ° C or less and in a sufficiently wet state, that is, a semi-wet state. The test results at this time are additionally shown in FIG.

As is clear from the figure, it was confirmed that the desulfurization reaction with ammonia easily occurs by adding sufficient water necessary for the reaction of the formula.

[4] Absorption of Ammonium Sulfate or Acidic Ammonium Sulfate in Water As described above, the by-product after the desulfurization and denitration reaction is caused by using urea, ammonium sulfate and ammonia water as desulfurization denitration agents is ammonium sulfate or acid ammonium sulfate, and The morphology was found to be fume-like or gaseous in exhaust gas at 100 ° C.

Also, since these are extremely soluble substances in water,
It can be easily absorbed and captured by a simple wet exhaust gas cleaning device using water as a medium.

For example, as a result of a confirmation test using a simple exhaust gas cleaning device such as the absorption bottle used in the above-mentioned wet analysis, NH ₄ ⁺ is the first
The total amount is captured in the absorption bottle, and NH ₄ ⁺ is extracted from the second absorption bottle.
The absorptivity was so good that it could hardly be detected.

[5] Gypsum Reactive Crystallization from Ammonium Sulfate or Acidic Ammonium Sulfate The present inventors produce gypsum from ammonium sulfate or acidic ammonium sulfate as a by-product,
A method for recovering ammonia was examined.

Quick lime or slaked lime was added to an aqueous solution of ammonium sulfate or acidic ammonium sulfate, and the reaction was investigated.

These reactions are assumed to be due to the following equations.

(1) When quicklime is added to water, slaked lime is produced.

CaO + H ₂ O → Ca (OH) ₂ (2) Slaked lime reacts with ammonium sulfate or acidic ammonium sulfate to precipitate gypsum.

(NH ₄ ) HSO ₄ + Ca (OH) ₂ + H ₂ O → CaSO ₄・ 2H ₂ O + NH ₄ OH… (NH ₄ ) ₂ SO ₄ + Ca (OH) ₂ + 2H ₂ O → CaSO ₄・ 2H ₂ O + 2NH ₄ OH… ( 3) Ammonia water is released as ammonia gas in the form of steam or gas by heating.

Heating NH ₄ OHNH ₃ + H ₂ O… Cooling This is restored to ammonia water when cooled.

Here, the formula and the formula are known reaction formulas, but the formula and the formula need to be confirmed.

To confirm the formula and the reaction of the formula, we
The reaction test was carried out with a simple glass tester. In this test, 500 ml of ammonium sulfate aqueous solution was placed in a flask of 1000 ml capacity, slaked lime was added to this, the solution was heated to evaporate by boiling, and the generated vapor was cooled and condensed in a Liebig cooling tube, and this condensate was further condensed. Was added to a dilute sulfuric acid solution, and the NH ₄ ⁺ component was absorbed and reacted in the same solution. At this time, this absorption liquid was replaced with a new diluted sulfuric acid liquid every 10 minutes, and this was repeated 6 times
It lasted for 60 minutes. The absorption liquid thus obtained was subjected to NH ₄ ⁺ amount analysis by the ammonia ion electrode method, and the reaction course thereof was examined.

FIG. 9 shows the relationship between the elapsed time of the amount of NH ₄ ⁺ released by this reaction and the integrated amount thereof.

The test conditions of () and (B) shown in the figure are as follows.

Reaction test conditions The only difference between the conditions (A) and (B) is that the amount of slaked lime added is different, and the other conditions were the same.

As is clear from FIG. 9, slaked lime and ammonium sulfate react fairly easily, and in the case of (A), about 80% of the NH ₄ ⁺ amount of the ammonium sulfate input is about 80%.
After reacting for 60 minutes, it was confirmed that 90% of the case (B) was completed.

Note that sum of NH ₄ ⁺ amount of NH ₄ ⁺ amount of residual liquid side and discharge side is approximately equal to the NH ₄ ⁺ amount of initial charge in ammonium sulfate, account balance was not match well.

From this result, it was confirmed that the reaction represented by the formula proceeded easily. This reaction seems to be related to the amount of slaked lime added, that is, the alkali concentration in the solution, and the reaction rate tended to be higher in (B) when 22 g was added than when (15 g) was added (A).

Although the reaction of the formula has not been confirmed, it is theoretically estimated that the reaction rate is higher than that of the formula.

[6] Recovery of gypsum and ammonia The gypsum slurry liquid after the above-mentioned reaction could be easily solid-liquid separated by a suction filtration test with filter paper. The filtrate was clear and no solid was seen to pass through.

Although a large amount of unreacted slaked lime remains in the separated gypsum, further reduction of the residual amount of slaked lime and gypsum conversion of the residual slaked lime need to be further examined when using this as a product in the future.

Regarding the recovery of ammonia gas, ammonia can be easily recovered only by cooling and condensing the reaction vapor as described above, and the recovery loss can be made zero without using a special device.

Although unreacted ammonium sulfate remains in the filtrate, it can be reused as the desulfurization and denitration agent described in item [1] by mixing this with ammonia water again.

[7] Summary of test results The above research results are summarized as follows.

(1) In-furnace desulfurization denitration reaction in step I i) Urea aqueous solution has excellent desulfurization denitration performance, and urea / SO ₂
100% desulfurization can be expected at an equivalence ratio of 1.1. Its performance is affected by the temperature at the injection position, and for denitration, a denitration rate of about 80% is obtained in the temperature range of 800 ° C or higher. As the reaction formula at that time, ~ is assumed.

ii) Ammonium sulfate aqueous solution also has a desulfurization and denitration effect. This greatly influenced by the temperature, re-releasing reaction of SO ₂ occurs at 800 ° C. or higher. In addition, desulfurization and denitration show opposite behaviors, and SO ₂ is released when the denitration effect is increased. As the reaction formulas at that time, ~ formulas are assumed, and these are involved in a complicated manner. From this phenomenon, it was found that ammonium sulfate has a denitration effect of 60% or more.

iii) Ammonia gas has excellent denitration performance, for example, 8
A denitration rate of 70% is obtained at an ammonia / NOx equivalent ratio of 3 at 00 ° C. The reaction at that time depends on the formula.

Ammonia has no desulfurization effect when dry. However, in the wet state, a great desulfurization effect is obtained, and the reaction depends on the formula and the formula.

iv) The reaction by-products of the above i) to iii) are ammonium sulfate or acidic ammonium sulfate, which are present in the combustion exhaust gas in the form of fumes or gases after reaction in the furnace, and have an atmosphere of gas temperature of 100 ° C. or higher. Since it does not exist as particles, it cannot be captured by a dust collector such as a bag filter.

Further, these are adsorbed only to a trace level even in fly ash during combustion of pulverized coal and pass through the dust collector.

(2) Absorption of ammonium sulphate or acidic ammonium sulphate in step II Ammonium sulphate or acidic ammonium sulphate, which is the product of step I, has a high solubility in water and is a substance that can be completely recovered with a simple washing device.

(3) Gypsum Reactive Crystallization and Ammonia Recovery in Step III Ammonium sulfate or acidic ammonium sulfate easily reacts with slaked lime to cause precipitation of gypsum and release of ammonia gas. For this reaction
Expression is assumed.

At this time, the precipitated gypsum crystals have good filterability and can be easily solid-liquid separated. In addition, the filtrate is clear without inclusion of gypsum.

Further, the released ammonia gas can be easily recovered by a cooling condensation operation.

(4) Recovery and Recycle of Ammonium and Ammonium Sulfate Aqueous Solution in Step IV The ammonia obtained from the use step III is mixed with the ammonium sulfate aqueous solution in the filtrate as ammonia water, and then again in step I.
It can be used as a desulfurization and denitration agent.

[Examples] Next, examples of the present invention will be described with reference to the drawings.

Example 1 From the various tests described above, urea, ammonium sulfate, acidic ammonium sulfate, and ammonia were sprayed uniformly or individually in a mixed state in a furnace to perform desulfurization and denitration reaction in the furnace, and then contained in combustion exhaust gas. The gas or fume of ammonium sulfate or acidic ammonium sulfate as a by-product to be collected is collected with a cleaning device,
Furthermore, quick lime or slaked lime was added to the above obtained by-product aqueous solution to carry out a gypsum crystallization reaction, gypsum was recovered, and ammonium sulfate contained in the filtrate at this time and ammonia generated by the reaction were desulfurized and denitrified again. To use as.

According to this method, the amount of desulfurization and denitration agent consumed is considerably small, and SO ₂ can be finally recovered as gypsum.

As an example of the process having the above characteristics, a process example created by the present inventors is shown in FIG.

Explaining the flow sheet of FIG. 10 in detail, pulverized coal is supplied as fuel to the combustion device (22) of the boiler body (21). The combustion exhaust gas generated here is used in the boiler tube group (23).
Heat is sufficiently absorbed while passing through the economizer (24), and after collecting ash by the dust collector (25), it is passed through the exhaust gas cleaning device (26), that is, the absorption tower, and then the chimney (28) is drawn by the induced exhaust fan (27). ) To the outside of the system.

In the above exhaust gas flow, in the present process, an aqueous solution of ammonia or ammonium sulfate or acidic ammonium sulfate is mixed and dispersed uniformly in the furnace through the nozzle (40) installed at a relatively high temperature part of the boiler body (21). The first-stage in-furnace denitration reaction and some desulfurization reaction are caused. Next, the urea aqueous solution is uniformly dispersed in the furnace through the nozzle (41) installed in the relatively low temperature part of the boiler body (21) to mainly cause desulfurization in the furnace and the second-stage denitration reaction. This urea aqueous solution is adjusted in the solution adjusting tank (42) and pressurized by the pump (43), or the urea single aqueous solution is mixed with the urea single aqueous solution from the nozzle (40) into the furnace. It was done. Since ammonium sulfate or acidic ammonium sulfate produced as a by-product from these in-furnace desulfurization and denitration reactions exists in the form of fumes or gases in high-temperature combustion exhaust gas, the boiler tube group (23), economizer (24) and dust collector (twenty five)
And is recovered as an aqueous solution by the exhaust gas cleaning device (26).

If white smoke in the exhaust gas becomes a problem, a heating device is installed downstream of the exhaust gas cleaning device (26).

Process water is supplied to the exhaust gas cleaning device (26) as cooling water for replenishment accompanying evaporation, and this water is sprinkled into the tower by a water sprinkling device installed in the upper stage to suppress mist of the absorbing liquid. Circulating pumps for fumes or gases from ammonium sulfate towers (29)
The absorption liquid circulated and used in step 1 is sprayed from the lower nozzle into the tower to be absorbed by the absorption liquid. A part of this absorbing solution, that is, ammonium sulfate or acidic ammonium sulfate aqueous solution, is then introduced into the reaction crystallization tank (30). Quick lime or slaked lime is further charged into the same tank, and well mixed with the above solution by the impeller (32) of the stirrer (31). In the reaction crystallization tank (30), a reaction between ammonium sulfate or acidic ammonium sulfate and slaked lime occurs,
Deposition of gypsum begins. At this time, in order to promote the reaction inside the reaction crystallization tank (30), a heated state is desirable, and it is necessary to blow steam or attach a heating device to raise the temperature.

The gypsum deposited by this reaction is then subjected to solid-liquid separation in the solid-liquid separator (33) and discharged out of the system. The filtrate discharged from the solid-liquid separator (33) is pressurized by the pump (34) and then circulated for use.

On the other hand, the water vapor-containing ammonia gas generated by the reaction is pressurized by the compressor (35), further made into ammonia water through the cooling condenser (36), and stored in the reservoir (37). This is further pressurized by the pump (38) and then mixed with the filtrate discharged from the solid-liquid separator (33), and this mixed liquid is uniformly dispersed and supplied from the nozzle (40) or nozzle (41) into the furnace. And is reused as a desulfurization and denitration agent. Further, this mixed solution is uniformly dispersed and supplied into the furnace from the nozzle (44) downstream of the economizer (24) as required, and is used for the second-stage desulfurization reaction.

On the other hand, urea, which is mainly used for desulfurization, uses a stirrer (3
In the solution preparation tank (42) equipped with 9), it is dissolved in process water, further pressurized by the booster pump (43), then uniformly dispersed in the furnace by the nozzle (41), and the desulfurization reaction in the furnace And the second stage denitration reaction is performed.

At this time, recirculated ammonia water to be sent to the nozzle (40)-
A part of the mixed solution of ammonium sulfate water is mixed with this urea solution to reduce the consumption of urea. Since the degree of desulfurization and denitration varies depending on the distribution amount of the recirculated mixed liquid to the nozzles (40) and (41), it is necessary to set the distribution amount to an optimum value.

As an example of a specific application, the desulfurization and denitration performance and the consumption amount of chemicals will be described with reference to FIG.

The <> mark in Fig. 10 indicates the material balance at that location. From the example described below, the desulfurization rate was 97.5%, the denitrification rate was 70%, and gypsum was 1297 kg in this process.
/ It was obtained and it became clear that in-furnace desulfurization and denitration were effectively performed.

<1> Specification of exhaust gas generated by combustion of coal Type of coal: Australian coal Coal combustion amount: 21.57 tons / hour Combustion exhaust gas amount: 212,000Nm ³ / hour Exhaust gas composition CO ₂ 14.5vol% O ₂ 3.3vol% H ₂ O 8.4vol% SO ₂ 800ppm NOx 200ppm (after Nox suppression combustion) <2> Exhaust gas specifications after furnace desulfurization and denitration (chimney inlet) SO ₂ 20ppm NOx 60ppm <3> First stage desulfurization and denitration agent specifications (nozzle (40) More solution specifications for dispersion in furnace) Amount of supplied solution: 1.2m ³ / hr Solution composition Ammonium sulfate: 3.5wt% Ammonia water: 14.8wt% Water: 81.7wt% <4> Second stage denitration agent specification (nozzle ( 41) Solution specification for dispersion in furnace) Supply amount: 2.5m ³ / hr Solution composition Urea: 7.0wt% (192kg / hr) Ammonium sulfate: 2.8wt% Ammonia water: 11.6wt% Water: 81.7wt% <5> Quick lime supply: 434kg / hour <6> Steam supply: About 1000kg / hour <7> Supply of absorption liquid to reaction crystallization tank Supply solution amount: 5.2m ³ / hour Solution composition Ammonium sulfate: 30.8wt% Water: 69.3 wt% 8> gypsum byproduct weight: (as a reference example) 1297Kg / hr (where slaked lime 2.2% contamination) Example 2 FIG. 11 illustrates another process instances according to the invention. Explaining in detail the flow sheet of the same figure, pulverized coal is supplied as fuel to the combustion device (52) of the boiler body (51). The flue gas generated here is the boiler tube group (5
Heat is sufficiently absorbed while passing through 3) and economizer (54), and ash is collected by dust collector (55), and then exhaust blower (56), that is, suction blower (57) through absorption tower.
It is then discharged to the outside of the system after being attracted to the chimney (58). The ash collected by the economizer (54) and the dust collector (55) is fly ash containing anhydrous gypsum.

In the above exhaust gas flow, the storage tank (6
Nozzle (60) which installed calcium carbonate powder in 4) at relatively high temperature part of boiler body (51) by air for air delivery
To uniformly spray and disperse in the furnace, and mainly cause the first-stage in-furnace denitration reaction and some desulfurization reaction. Next, the nozzle (61) installed in the relatively low temperature part of the boiler body (51)
The urea aqueous solution is uniformly dispersed in the furnace to mainly cause desulfurization in the furnace and the second-stage denitration reaction. This urea aqueous solution is a urea single aqueous solution which is adjusted by a solution adjusting tank (62) equipped with a stirrer (69) and pressurized by a pump (63). Since ammonium sulfate or acidic ammonium sulfate produced as a by-product from these in-furnace desulfurization and denitration reactions exists in the form of fumes or gases in high-temperature combustion exhaust gas, the boiler tube group (53), economizer (54) and dust collector After passing through (55), it is recovered as an aqueous solution by the exhaust gas cleaning device (56).

If white smoke in the exhaust gas becomes a problem, a heating device is installed downstream of the exhaust gas cleaning device (56).

Process water is supplied to the exhaust gas cleaning device (56) as replenishing cooling water accompanying evaporation, and this water is sprayed into the tower by a sprinkler installed in the upper stage to suppress absorption mist of the absorbing liquid. Circulating pumps for fumes or gases such as ammonium sulfate (59)
The absorption liquid circulated and used in step 1 is sprayed from the lower nozzle into the tower to be absorbed by the absorption liquid. A part of this absorption liquid, that is, ammonium sulfate or acidic ammonium sulfate solution, is pumped (65).
Then, it is sent to the nozzle (60) or a nozzle (66) provided above the nozzle (60), and from there is uniformly dispersed in the furnace. In addition, this absorbing liquid is uniformly dispersed and supplied into the furnace from the nozzle (74) downstream of the economizer (54) as necessary, and is used for the second-stage desulfurization reaction.

Embodiment 3 FIG. 12 shows another process example according to the present invention. Explaining in detail the flow sheet of the same figure, pulverized coal is supplied as fuel to the fuel device (82) of the boiler body (81). The combustion exhaust gas generated here absorbs heat sufficiently while passing through the boiler tube group (83) and the economizer (84), and after collecting ash by the dust collector (85), the exhaust gas cleaning device (56) After being guided to the chimney (88) by the induced draft fan (87) through the absorption tower, it is discharged to the outside of the system.
The fly ash collected by the economizer (84) and the dust collector (85) is used in the gypsum reaction tank (95) described later.
Sent to.

In the above exhaust gas flow, the storage tank (9
Nozzle (90) installed in relatively high temperature part of boiler body (81) by calcium carbonate powder in 4) by air for air delivery.
To uniformly spray and disperse in the furnace, and mainly cause the first-stage in-furnace denitration reaction and some desulfurization reaction. Next, the nozzle (91) installed in the relatively low temperature part of the boiler body (81).
The urea aqueous solution is uniformly dispersed in the furnace to mainly cause desulfurization in the furnace and the second-stage denitration reaction. This urea aqueous solution is adjusted in a solution adjusting tank (92) equipped with a stirrer (99) and pressurized by a pump (93), or the urea single aqueous solution is supplied to the inside of a furnace from a nozzle (116) described later. It is a mixture of aqueous solutions to be dispersed. Since ammonium sulfate or acidic ammonium sulfate produced as a by-product from these in-furnace desulfurization and denitration reactions exists in the form of fumes or gases in the combustion exhaust gas at high temperature, it is a boiler tube group (83), economizer (84) and dust collector. After passing through (85), it is recovered as an aqueous solution by the exhaust gas cleaning device (86).

If white smoke in the exhaust gas becomes a problem, a heating device is installed downstream of the exhaust gas cleaning device (86).

Process water is supplied to the exhaust gas cleaning device (86) as replenishing cooling water accompanying evaporation, and this water is sprayed into the tower by a sprinkler installed in the upper stage to suppress absorption mist of the absorbing liquid. Circulating pumps for fumes or gases such as ammonium sulfate (89)
The absorption liquid circulated and used in step 1 is sprayed from the lower nozzle into the tower to be absorbed by the absorption liquid. A part of this absorption liquid, that is, ammonium sulfate or acidic ammonium sulfate solution, is stirred (101).
It is sent to a gypsum reaction tank (95) equipped with, where it is reacted with the collected fly ash. The fly ash containing gypsum dihydrate deposited by this reaction is then subjected to solid-liquid separation in the solid-liquid separator (103) and discharged to the outside of the system. The filtrate discharged from the solid-liquid separation device (103) is stored in a storage tank (96), then pressurized by a pump (104) and then circulated.

On the other hand, the steam-containing ammonia gas generated by the reaction is made into ammonia water through the cooling condenser (106) and stored in the reservoir (107). This is a further pump (10
After being pressurized in 8), it is mixed with the filtrate discharged from the solid-liquid separation device (103), and this mixed liquid is sent to the nozzle (116) provided above the nozzle (90), and from there, inside the furnace. It is uniformly dispersed and supplied to and reused as a desulfurization and denitration agent. Also,
This mixed liquid is uniformly dispersed and supplied from the nozzle (114) downstream of the economizer (84) into the furnace as needed, and is used for the second-stage desulfurization reaction.

[Effects of the Invention] Since the in-furnace simultaneous desulfurization denitration method according to the present invention is configured as described above, desulfurization denitration can be carried out at low cost and excellent desulfurization denitration performance can be exhibited. Further, unreacted ammonia or ammonium sulfate or acidic ammonium sulfate produced from the exhaust gas treatment step can be captured and recovered for reuse.

[Brief description of drawings]

Figure 1 is a flow sheet showing the combustion test, and Figure 2 is urea / S.
A graph showing the relationship between the O ₂ equivalent ratio and the desulfurization rate, FIG. 3 is a graph showing the relationship between the temperature and the denitration rate, and FIG. 4 is the NH ₄ ⁺ conversion value and NH ₄ ⁺
Fig. 5 is a graph showing the relationship between analytical values, Fig. 5 is a graph showing the relationship between temperature and desulfurization rate, Fig. 6 is a graph showing the relationship between temperature and denitrification rate, and Fig. 7 is NH ₄ ⁺ conversion value and NH ₄ ⁺ analysis. Fig. 8 is a graph showing the relationship between the values, Fig. 8 is a graph showing the relationship between the amount of added ammonia gas and the desulfurization rate and the denitration rate, Fig. 9 is a graph showing the relationship between time and the reaction rate, and Figs. It is a flow sheet which shows a denitration method. (21) (51) (81) …… Boiler body, (22) (52) (8
2) …… Combustor, (23) (53) (83) …… Boiler tube group, (24) (54) (84) …… Economizer, (25)
(55) (85) …… Dust collector, (26) (56) (86) …… Exhaust gas cleaning device, (27) (57) (87) …… Induced exhaust fan,
(28) (58) (88) …… Chimney, (29) (59) (89) ……
Circulation pump, (30) ... Reactive crystallization tank, (31) (101) ...
… Agitator, (32) …… impeller, (33) (103) ……
Solid-liquid separator, (34) …… pump, (35) …… compressor,
(36) (106) …… cooling condenser, (37) (107) …… reservoir, (38) (108) …… pump, (39) (69) ……
Stirrer, (40) (60) (90) …… Nozzle, (41) (61)
(91) …… Nozzle, (42) (62) (92) …… Solution adjusting tank, (43) (63) (93) …… Boost pump, (64) (94)
…… Storage tank, (65) …… Pump, (66) …… Nozzle, (9
5) ... gypsum reaction tank, (96) ... storage tank, (44) (74) (1
14) …… Nozzle.

Front page continuation (72) Inventor Michio Ishida 5-3-28 Nishikujo, Konohana-ku, Osaka City, Osaka Prefecture Hitachi Shipbuilding Co., Ltd. Issue Hitachi Shipbuilding Co., Ltd.

Claims (4)

[Claims] 1. A furnace gas having a temperature in the range of 900 ° C. or higher and 500 ° C. or higher in the range of a) ammonia gas or an aqueous solution thereof as a treating agent,
b) an aqueous solution of ammonium sulfate and / or acidic ammonium sulfate, c) a powder or aqueous solution of urea and / or a urea compound, and i) the above-mentioned agents a), b) and c) alone, respectively, in the upstream and middle regions of the furnace. It is sprayed in the furnace in three stages of the basin and the downstream region, or ii) In the furnace in two stages with one of the agents a), b) and c) alone and the other two in a mixed state. Iii) or 1) in a mixed state with the agents a), b) and c) above.
The chemical is supplied by any one of the spraying forms in the furnace at the stage, and in the case of the spraying form of i) or ii), mainly the denitration reaction is performed in the upstream region and the desulfurization is mainly performed in the middle and downstream regions. Reaction and the second stage denitration reaction, and in the case of the spraying form of iii), the desulfurization reaction and denitration reaction are simultaneously caused by the exhaust gas treatment process and the exhaust gas cleaning device installed in the downstream flue of the furnace. A method for simultaneous desulfurization and denitration in a furnace, which comprises a chemical recovery step for capturing and recovering unreacted ammonia or ammonium sulfate or acidic ammonium sulfate produced in the exhaust gas treatment step. 2. Ammonia or ammonium sulphate or acidic ammonium sulphate aqueous solution recovered in the chemical recovery step is reacted with quick lime or slaked lime in the form of slurry or powder in a reaction crystallization tank to recover the ammonia content as water vapor containing gas, The method according to claim 1, further comprising an ammonia recovery / gypsum crystallization step of reacting silver sulfate or acidic sulfate with calcium ions to precipitate gypsum. 3. The method according to claim 2, further comprising an ammonia water production step of forming ammonia water by compressing and cooling the steam-containing ammonia gas recovered in the ammonia recovery / gypsum crystallization step. 4. A gypsum slurry recovered in the ammonia recovery / gypsum crystallization step is subjected to solid-liquid separation to recover gypsum as a solid component, and ammonia water or an unreacted ammonium sulfate aqueous solution or an acidic ammonium sulfate aqueous solution is recovered as a liquid component. The method according to claim 2, further comprising a solid-liquid separation step of: