JPH1133349A - Flue gas treatment method and flue gas treatment installation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to clean a flue gas without injecting ammonia by guiding the flue gas to an absorption tower after scattering powder into the flue gas, then bringing the flue gas into contact with an absorption liquid to absorb/remove SO2 contained in the flue gas and capturing the powder. SOLUTION: This flue gas treatment method uses a desulfurization device 10 comprising an air heater 1 for heating a combustion air, an electric precipitator 3 for removing dust B and liquid column absorption towers 12, 13 installed side by side on the top of a tank 11 to which an absorbent slurry is supplied. In addition, a powder loading means for scattering powder into a flue gas is provided right before the precipitator 3. That is, a step to scatter the dust (coal ash) contained in the combustion exhaust gas of coal as the powder is provided right before a step for capturing the dust by the precipitator 3. Further, the flue gas is guided to the precipitator 3 to capture at least, the powder contained in the flue gas, and the flue gas is guided to absorption towers 12, 13 so that the flue gas is brought into contact with an absorbent. Thus it is possible to absorb and remove at least, SO2 contained in the flue gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for purifying flue gas containing SO ₂ and SO ₃ as sulfur oxides (for example, flue gas from a heavy oil-fired boiler). The present invention relates to a flue gas treatment technology that can realize measures against SO ₃ in flue gas that becomes harmful sulfuric acid fume by low cost and simple operation or device configuration.

[0002]

2. Description of the Related Art Generally, for example, in a flue gas of a heavy oil fired boiler in a thermal power plant or the like, sulfur oxide is used as a sulfur oxide.
SO ₃ (sulfur trioxide) is contained in addition to SO ₂ (sulfurous acid gas). Then, the total sulfur oxide amount (for example, 1500 pp
The amount of SO ₃ with respect to m) varies depending on the combustion temperature in the boiler, the type of burner, the type of combustion catalyst, and the like, but in any case is a ratio of about several percent, for example, a relatively small amount of about 30 ppm. Therefore, in this type of flue gas desulfurization treatment, the basic performance is S
O ₂ absorption performance is important.

[0003] However, SO _{3 in} flue gas is harmful to H ₂ , which is highly corrosive and causes scale generation when fumes are formed.
It becomes mist of SO ₄ , and becomes submicron particles that can hardly be collected by simple gas-liquid contact with the absorbing solution.
For this reason, from the viewpoint of preventing corrosion and scale of the apparatus, or from the viewpoint of further purifying the smoke exhaust, some removal treatment is required for this SO ₃ .

Therefore, conventionally, for example, in a flue gas treatment facility for a heavy oil fired boiler, ammonia is injected into the flue gas upstream of the facility to convert SO ₃ in the flue gas into ammonium sulfate ((NH ₄ ) ₂ SO ₄ ).
It is common to collect as. Hereinafter, an example of such a conventional smoke exhaust treatment method and equipment will be described with reference to FIG.

In FIG. 4, reference numeral 1 denotes an air heater for recovering heat of flue gas and heating combustion air supplied to a boiler (not shown). Untreated smoke exhausted from the air heater 1 (usually about 160 ° C.) first comes into contact with ammonia (NH ₃ ) blown from a spray nozzle 2 a in an introduction duct 2, and SO _{3 in the} exhausted smoke is converted into ammonia. Reacts with moisture in flue gas and smoke to form ammonium sulfate.

Next, the flue gas A is introduced into the dry electric precipitator 3 to remove dust B such as fly ash (dust collecting step). The dust B is mainly composed of unburned carbon. For example, in the case of a heavy oil fired boiler, impurities such as vanadium and magnesium are also contained. Most of the ammonium sulfate is also collected by the electric precipitator 3, contained in the dust B and discharged, and is disposed of, for example, as industrial waste.

After that, the flue gas A is removed at least in the absorption towers 12 and 13 of the desulfurization unit 10 at least SO ₂ and a part of the slightly remaining dust (absorption step). And is discharged into the atmosphere from a chimney (not shown) as exhaust smoke C after treatment. The heating unit 5 may be constituted by, for example, a heat exchanger that heats the post-treatment flue gas C by using a part of the heat recovered by the air heater 1 described above. Can be omitted.

[0008] In this case, the desulfurization device 10 is provided above one tank 11 to which the absorbent slurry D (absorbing liquid) is supplied.
Two liquid column type absorption towers 12 and 13 (co-current type and counter-current type) are installed side by side, and the flue gas is sequentially guided to each absorption tower, and the flue gas and the slurry in the tank 11 are separated by each absorption tower. In this configuration, gas-liquid contact is performed. Each of the absorption towers 12 and 13 is provided with a plurality of spray pipes 15 and 16, respectively, from which the slurry sucked by the circulation pumps 17 and 18 is jetted upward in a liquid column shape. In this case, a mist eliminator 20 for collecting and removing entrained mist is provided on the downstream side of the absorption tower. The mist collected by the mist eliminator 20 is collected in a lower hopper (not shown) and returns to the inside of the tank 11 through a drain pipe at a lower part of the hopper.

This apparatus is provided with a so-called arm-rotating air sparger 21 for blowing oxidizing air as fine bubbles while stirring the slurry in the tank 11, and an absorbent which absorbs sulfur dioxide in the tank 11. The slurry and the air are efficiently brought into contact with each other to oxidize the slurry to obtain gypsum. That is, in this apparatus, the slurry jetted from the header pipe 15 or 16 by the absorption tower 12 or 13 and coming down in gas-liquid contact with the smoke exhaust while absorbing the sulfurous acid gas and the dust flows down in the tank 11 in the air sparger 21
It is oxidized by contact with a number of air bubbles blown while being stirred, and further causes a neutralization reaction to form gypsum. The main reactions occurring during these processes are represented by the following reaction formulas (1) to (3).

[0010]

## STR1 ## (absorption搭排smoke inlet _{section) SO 2 + H 2 O →} H + + HSO 3 - (1) ( ^{_{Tank) H + + HSO 3 - +}} 1 / 2O 2 → 2H + + SO 4 2- (2) 2H + ^{_{+ SO 4 2- + CaCO 3 +}} H 2 O → CaSO 4 · 2H 2 O + CO 2 (3)

In this way, gypsum, a small amount of limestone as an absorbent and a small amount of dust are constantly suspended in the tank 11, and the slurry in the tank 11 is supplied by the slurry pump 22 in this case. Supplied to the solid-liquid separator 23,
The gypsum is filtered and extracted as a low-moisture gypsum E. On the other hand, a part F1 of the filtrate from the solid-liquid separator 23 is passed through the filtrate tank 24 and the filtrate pump 25 to the absorbent slurry D.
Is supplied to the slurry adjusting tank 26 as water constituting the water and is circulated and used.

The slurry adjusting tank 26 has a stirrer, and stirs and mixes limestone G (absorbent) supplied from a limestone silo (not shown) with water sent from the filtrate tank 24 to form an absorbent slurry D. The slurry S inside the absorbent is supplied to the tank 11 by the slurry pump 27 as appropriate. In addition, for example, in the tank 11,
Supplementary water (industrial water, etc.) is supplied as appropriate, and the absorption towers 12 and 1 are supplied.
The water that gradually decreases due to evaporation or the like in 3 is compensated for.
As the limestone G, limestone collected from Yamamoto is usually finely pulverized to a particle size of about 100 μm. Another part of the filtrate in the filtrate tank 24 is used to prevent accumulation of impurities in the circulating liquid in the desulfurization device 10.
It is sent to a wastewater treatment step (not shown) as so-called desulfurization wastewater F2.

According to the above-mentioned smoke exhaust treatment, SO ₃ hardly exists in the smoke exhaust after the electric precipitator 3, and the above-mentioned problem can be avoided. That is, if SO ₃ is left without injection of ammonia, this SO ₃
According to the characteristics of the sulfuric acid dew point, it condenses in the equipment and fumes as described above.

For this reason, problems such as blockage of the flue gas flow passage due to corrosion of equipment components and generation of scale become a problem.
This leads to higher equipment costs and higher maintenance costs.
Further, since the fumes of SO ₃ remain in the treated flue gas C discharged from the desulfurization device 10, in order to achieve a high degree of cleanness of the flue gas, for example, a wet type is provided on the downstream side of the absorption tower 13. The necessity of installing a dust collector arises, and this also leads to an increase in cost and an increase in the size of the device. However, if ammonia injection is performed as shown in FIG. 4, SO ₃ in the flue gas in the upstream of the electrostatic precipitator ₃ is changed to ammonium sulfate, as described above.
Since the dust is collected as dust B by the electric dust collector 3, the SO
₃ problems will be solved.

[0015]

However, the above-mentioned conventional exhaust gas treatment method or equipment has the following various problems due to the above-described injection of ammonia. That is, it is necessary to purchase and supply expensive ammonia first, which is inferior in operation cost. In addition, it is necessary to lengthen the introduction duct 2 in order to inject and diffuse ammonia, which is an obstacle to downsizing of the equipment. Further, since there is ammonia remaining in the downstream of the electrostatic precipitator 3, the N component is contained in the desulfurization wastewater F2,
In the wastewater treatment of the desulfurization wastewater F2, troublesome N treatment such as denitrification treatment by microorganisms is required, and this also leads to an increase in operating costs and an increase in the size of the equipment.

Further, ammonia is also contained in the exhaust gas C after the treatment and is released to the atmosphere. Although the emission of ammonia into the atmosphere is not necessarily regulated in Japan, it is not desirable from the viewpoint of further purifying smoke emissions, and if it is strictly regulated in the future, some measures to remove ammonia will be required. (Addition of equipment, etc.) is required, and this also poses a problem in terms of cost and the like.
Furthermore, since ammonia is also contained in the by-produced gypsum E, it is necessary to wash the gypsum to prevent bad smell and the like depending on the gypsum take-up standard.

Since ammonium sulfate ash remaining in the downstream of the electrostatic precipitator 3 has a relatively small particle size, it is not sufficiently collected by the gas-liquid contact of the absorption towers 12 and 13, and the treated smoke fumes C Therefore, there is still a problem in that smoke is further cleaned. Therefore, as flue gas purifying technology, which is required to be more advanced in qualitative and quantitative aspects in recent years, there are also simpler and lower-cost technologies for small-scale power generation business and private power generation, which are becoming increasingly popular in recent years. As the flue gas treatment technology, the conventional technology is insufficient and improvement has been desired.

Therefore, the present invention firstly provides SO ₃ in flue gas.
To provide a flue gas treatment method and equipment capable of easily realizing a countermeasure without injecting ammonia, and having no adverse effect that the injected substance remains in the flue gas after treatment, and capable of further reducing flue gas. It is an object. Second, it is an object of the present invention to provide a flue gas treatment method and equipment capable of easily and highly sophisticated measures for SO ₃ during flue gas and cleaning of flue gas with a simpler operation or device configuration. Third, if the lime-gypsum method is used as the absorption process for SO _{2 and the} like in flue gas, the purity of gypsum as a by-product can be ensured to be high, or the amount of industrial waste discharged can be reduced. It is an object.

[0019]

Means for Solving the Problems In order to achieve the above-mentioned object, the intense research has been carried out. However, in the flue gas treatment equipment for a boiler that uses only coal, the above-mentioned problem of SO ₃ can be solved without injecting ammonia. It has been empirically found that this does not occur, and it is clear that this is because flue gas such as fly ash contains a large amount of dust (about 10 to 100 times that in the case of oil-fired fuel) in the flue gas of coal-fired combustion. Was.

That is, according to the study by the inventors, when powder such as fly ash is contained in flue gas, SO ₃ condensation in the flue gas occurs on the particle surface of the powder, SO ₃
It is considered that the H ₂ SO ₄ particles formed by coagulation exist together with the powder particles and do not become harmful fumes (sulfuric acid mist). The present invention has been made based on such knowledge, and has solved the above-mentioned problem by the following features.

The method for treating flue gas according to claim 1 is a method for treating flue gas containing at least SO ₂ and SO ₃ ,
A powder inputting step for spraying a powder into the flue gas, followed by gas-liquid contact with the absorbing liquid directing the flue gas into the absorber, and absorbing and removing at least SO ₂ present in the flue gas, and the And an absorption step of collecting powder.

According to a second aspect of the present invention, there is provided a method for treating flue gas containing at least SO ₂ and SO ₃ ,
A powder charging step of spraying powder into the flue gas; a dust collecting step of guiding the flue gas to a dust collector to capture at least the powder in the flue gas; And bringing the absorbing liquid into gas-liquid contact with the absorbing liquid to absorb and remove at least SO ₂ in the flue gas.

According to a third aspect of the present invention, in the method for treating flue gas, the temperature of the powder is set lower than the temperature of the flue gas in the powder charging step.

According to a fourth aspect of the present invention, in the powder discharging step, the powder is dispersed in the flue gas as a slurry in which the powder is suspended in a liquid.

[0025] According to a fifth aspect of the present invention, there is provided a method for treating flue gas, wherein dust contained in flue gas of coal is used as the powder.

According to a sixth aspect of the present invention, in the method for treating flue gas, at least a portion of the powder collected in the dust collecting step is reused as powder to be dispersed in the smoke in the powder charging step. It is characterized by.

According to a seventh aspect of the present invention, in the smoke exhaust treatment method, the absorption step is performed by a lime gypsum method in which gypsum is produced as a by-product using an absorbing solution in which limestone is suspended as an absorbent. At least a part of the collected powder is mixed into gypsum by-produced in the absorption step and discharged out of the system.

[0028] The method for treating flue gas according to claim 8 is characterized in that limestone is finely pulverized as the powder.

According to a ninth aspect of the present invention, in the smoke exhaust treatment method, the absorbing step is performed by a lime-gypsum method in which gypsum is produced as a by-product using an absorbing solution in which limestone is suspended as an absorbing agent. The entire amount of limestone required as above is sprayed into the flue gas as the powder, so that the absorbent is indirectly supplied into the absorbent.

According to a tenth aspect of the present invention, there is provided a flue gas treatment facility, which is a facility for treating flue gas containing at least SO ₂ and SO _3. It is characterized by comprising an absorption tower for absorbing and removing SO ₂ , and a powder feeding means for spraying powder into the flue gas before the absorption tower.

[0031] A flue gas treatment facility according to claim 11 is a facility for treating flue gas containing at least SO ₂ and SO ₃ , wherein the flue gas is brought into gas-liquid contact with an absorbing liquid so that at least an absorption tower for absorbing and removing SO _2, and a dust collector for collecting the powder present in the flue gas in the upstream side of the absorption tower, and the powder dosing means for spraying the powder in the upstream of the dust collector in the flue gas , Is provided.

The smoke exhaust treatment equipment according to claim 12, wherein at least a part of the powder collected by the dust collector is reused as powder dispersed in the smoke by the powder input means. It is characterized by having done.

[0033]

Embodiments of the present invention will be described below with reference to the drawings. The same elements as those in the conventional example shown in FIG. First Example First, a first example of the present invention will be described with reference to FIG. In this example, in the conventional flue gas treatment shown in FIG. 4, the ammonia injection step was deleted, and a powder input means (not shown) for spraying powder during the flue gas was installed immediately before the electric precipitator 3. The step of dispersing the dust (so-called coal ash H) contained in the combustion exhaust gas of the coal as powder into the flue gas A by the powder input means (powder input step) is performed immediately before the dust collecting step by the electric dust collector 3. It is provided in.

As the above-mentioned coal ash H, for example, the one collected by an electric dust collector of a flue gas treatment facility in a coal-fired power plant can be used. Such coal ash is
Since it is usually treated as industrial waste, it can be obtained at very low cost with almost no transportation cost.

Further, as the above-mentioned powder feeding means, for example, a means by air flow transfer or a means by slurry transfer can be used. As a method by airflow transport, for example, a blower or air compressed air or a transport pipe for airflow transport of powder, and a fixed nozzle for dispersing the airflow transported powder into a flue gas duct and jetting it Can be used.
In addition, as a method by slurry transport, for example, a stirring tank in which powder is mixed into a liquid to form a slurry, a slurry pump for pressure-feeding the slurry generated in this stirring tank, and a pump for discharging the pressure-fed slurry are discharged. A fixed nozzle that disperses and sprays in a smoke duct can be used.

When the powder is sprayed as a slurry, the liquid constituting the slurry is instantaneously heated by the heat of the flue gas so that the effect of trapping SO ₃ on the surface of the powder particles is enhanced. It is preferable that the liquid evaporate, but as this liquid, for example, water such as general industrial water is sufficient. This is because the temperature of the flue gas A is as high as about 160 ° C., and the water in the sprayed slurry evaporates immediately. Also, the powder concentration of the slurry may be about the same as the solid concentration of the absorbent slurry in the desulfurization apparatus 10 (for example, about 20 to 30% by weight).

The input amount of coal ash H as powder is as follows:
Even when the slurry is sprayed, the weight ratio (D / S) of the amount of powder (D) in the smoke exhaust per unit volume to the amount of SO ₃ (S) in the smoke exhaust per unit volume is described in FIG. What is necessary is just to set so that the relationship as shown in FIG. For example, SO
When it is necessary to achieve the removal rate of ₃ about 70%,
What is necessary is just to spray so that D / S ≧ 25 (for example, when the SO ₃ concentration is 50 mg / m ³ N, the amount of the powder including the dust in the flue gas is 1250 mg / m ³ N or more. , Coal ash H).

In this way, the above-mentioned action of the powder is reliably and sufficiently realized, and the measures against SO ₃ during flue gas can be realized with low cost and simple operation and apparatus configuration without injecting ammonia. . That is, even if SO ₃ in the flue gas condenses, almost all of the coagulation occurs on the particle surface of the powder in the flue gas such as the coal ash, and H ₂ S formed by condensing the SO _3.
O ₄ particles are present integrally with the powder particles, and harmful fumes (sulfuric acid mist) hardly occur.

Moreover, the charged coal ash has a particle size of 10
Because of the relatively large diameter of about μm, most of the dust is collected in the electrostatic precipitator 3 at a relatively high collection rate, as compared with conventional sulfuric acid mist as well as conventional ammonium ash,
Even a small residue that is not collected by the electric dust collector 3 is almost completely collected in the absorption towers 12 and 13 of the subsequent desulfurization apparatus 10, and hardly remains in the exhaust gas C after the subsequent processing. The small amount of coal ash collected in the absorption towers 12 and 13 is dissolved or suspended in the circulating slurry and is finally contained in the by-produced gypsum E. no problem. On the other hand, sulfuric acid composed of SO ₃ condensed on the surface of coal ash and the like and collected along with the coal ash and the like in the absorption towers 12 and 13 finally reaches the limestone and the above-described neutralization reaction in the tank 11 of the absorption tower. (3) is caused and becomes a part of by-produced gypsum.

In this example, a part B1 of the dust collected in the dust collecting step by the electric dust collector 3 (including the powder scattered in the smoke and the dust in the smoke) is replaced with the smoke It is configured to be reused as the powder of the present invention which is dispersed therein.
That is, a part B1 of the dust collected by the electric dust collector 3
In this case, is once supplied to the powder silo 30, where new coal ash H is added, and is again scattered to the upstream of the electric dust collector 3 by the above-described powder charging means, and is circulated and used. For this reason, in the case of this example, in addition to the coal ash H supplied from the outside, the powder to be sprayed in the flue gas is originally contained in the untreated flue gas A derived from the air heater 1. Dust such as fly ash is also included.

In the present embodiment, the remaining part B2 of the dust collected by the dry electric dust collector 3 is uniformly mixed into the gypsum E by-produced in the desulfurizer 10, and discharged out of the system. ing. Here, the total amount of powder to be sprayed is preferably set to the minimum necessary amount within a range satisfying the above-mentioned D / S condition, and the amount of dust B1 to be circulated is determined by the amount of powder to be sprayed. It is preferable to increase the amount of the coal ash H to be newly added and the amount of dust B2 to be discharged to a necessary minimum by increasing the body to the limit at which the body has the ability to capture SO ₃ . In this way, the amount of the dust B2 mixed in the gypsum E can be made small, the purity of the gypsum E can be kept high, and the amount of coal ash H to be newly added is reduced to reduce the amount of coal ash. H can be handled easily.

Therefore, according to this embodiment, the generation of scale and corrosion due to SO ₃ can be prevented with high reliability, and the following various effects excellent in practical use can be obtained. (1) The consumption amount of ammonia becomes zero, and the operating cost can be remarkably reduced. (2) A facility for injecting ammonia is not required, and a duct does not need to be particularly long for ammonia diffusion, so that facility cost can be reduced and the facility can be downsized. (3) Since the N component is not contained in the desulfurization effluent F2, troublesome N treatment is not required in the wastewater treatment of the desulfurization effluent F2. In this respect, the operation cost can be reduced and the equipment can be downsized.

(4) The amount of ammonia contained in the exhaust gas C after treatment and released to the atmosphere is reduced to zero, which can greatly contribute to further purification of the smoke exhaust gas and can easily cope with future regulations on the release of atmospheric ammonia. . (5) Since the ammonia contained in the gypsum E by-produced is also eliminated, it is not necessary to wash the gypsum to prevent bad smell. (6) As in the past, the dust consisting of sulfuric acid mist and ammonium sulfate remaining in the flue gas C after treatment is eliminated, and the entire facility can be installed without taking measures such as installing a wet type electric dust collector downstream of the absorption tower. As a result, the dust removal performance is improved, and in this respect, it is also possible to contribute to further purification of the smoke exhaust.

(7) In the case where coal ash H as powder is sprayed as a slurry, a stirring tank or a slurry pump for generating a slurry which has been conventionally used in a desulfurization apparatus or the like, and further a slurry for spraying the slurry. Equipment such as nozzles can be used as is, which is advantageous in terms of equipment costs and operability of the equipment.
It becomes easier to diffuse uniformly in the flue gas than in the case of airflow conveyance, and the problem caused by SO ₃ can be prevented more efficiently. Further, in this case, the temperature of the particles of the coal ash H is kept lower due to the cooling effect when the slurry liquid evaporates into the flue gas (or the cooling effect due to the presence of the slurry liquid). The condensation of SO _{3 on} the surface of the H particles is promoted, and the function of collecting SO ₃ by the coal ash H, which is a powder, is more enhanced.

(8) In the case of this example, since the coal ash H or the like as the powder for collecting SO ₃ is circulated, the amount of coal ash H to be newly supplied is reduced. And an inherent effect that the purity of the gypsum E can be kept high by minimizing the amount of dust B2 mixed in the gypsum E.

(9) Since the dust B2 is mixed into the gypsum E, the amount of dust discharged as industrial waste is eliminated, and this also contributes to a reduction in operating costs. When higher gypsum purity is required, it goes without saying that part or all of the dust B2 may not be mixed into the gypsum E.

Second Example Next, a second example of the present invention will be described with reference to FIG. In this example, a powder feeding means for spraying powder is installed immediately before the absorption towers 12 and 13, and limestone (C
aCO ₃ ) is finely pulverized (that is, for example, the above-mentioned limestone G) is sprayed into the flue gas A as the powder of the present invention. In this case as well, limestone finely pulverized may be sprayed into the flue gas by air current transport, or may be slurried and sprayed.

In this embodiment, the slurry adjusting tank 26 and the slurry pump 27 shown in FIG. 1 are deleted, and the filtrate F1 is directly returned to the tank 11 of the absorption tower. By introducing the entire amount of limestone required as an absorbent for the flue gas into the flue gas,
The absorbent is indirectly supplied into the slurry in the tank 11 of the desulfurization device 10. In this case, limestone G required as an absorbent
Is basically stoichiometrically proportional to the amount of sulfur oxides in the flue gas, so that the flue gas A is a normal flue gas (for example, flue gas of an oil-based fuel such as heavy oil). If so, the weight ratio (D / S) of the amount of powder (D) in the flue gas per unit volume to the amount of SO ₃ (S) in the flue gas per unit volume is calculated according to the inventors' calculations. D / S = about 28.

For this reason, in this embodiment, the above-mentioned action of the powder is reliably and sufficiently realized, and the countermeasure against SO ₃ during flue gas can be realized with low cost and simple operation and apparatus configuration without injecting ammonia. . That is, even if SO ₃ in the flue gas condenses, almost all of the coagulation occurs on the particle surface of the powder in the flue gas such as the limestone, and H ₂ S formed by condensing SO _3.
O ₄ particles are present integrally with the powder particles, and harmful fumes (sulfuric acid mist) hardly occur.

Moreover, the limestone charged has a particle size of 10
Since the diameter is as large as about 0 μm, it is collected in the absorption towers 12 and 13 of the desulfurization apparatus 10 at a remarkably high collection rate as compared with the conventional sulfuric acid mist as well as the conventional ammonium ash,
Almost no residue remains in the flue gas C after the subsequent treatment. In addition,
The limestone collected in the absorption towers 12 and 13 is dissolved or suspended in the circulating slurry and acts as the above-mentioned absorbent (alkali agent) for neutralizing the slurry and producing gypsum as a by-product. On the other hand, the sulfuric acid composed of SO ₃ which is condensed on the surface of limestone or the like and collected together with the limestone or the like finally causes the above-described neutralization reaction (3) with limestone in the tank 11 of the absorption tower or the like, thereby producing by-products. Will be part of the gypsum.

Therefore, according to this embodiment, the generation of scale and corrosion due to SO ₃ can be prevented with high reliability, and the same effects as (1) to (7) described in the first embodiment can be obtained. In addition, in this example, the entire amount of limestone required in the absorption step of the desulfurization device 10 is supplied as the powder, and the conventional slurry adjustment tank 26 and slurry pump 27 are omitted. The unique effect of reducing the cost of the device and reducing the size of the device can be obtained.

FIG. 3 shows actually measured data supporting the principle of the present invention. This data indicates that SO ₃ is between 3.7 and 11.5.
When the slurry consisting of limestone powder and water (having a concentration of about 20 to 30% by weight) is simply sprayed into the flue gas containing about ppm, and the heat is not recovered by the heat exchanger from the subsequent flue gas. Of limestone and the ratio of SO ₃ gas condensed and removed on the surface of limestone particles. From this data, it can be seen that SO ₃ can be effectively removed simply by spraying limestone as a slurry on the flue, and D / S
It can be seen that SO ₃ can be removed at a considerable removal rate according to the setting of. The mist removal effect of such finely ground limestone is a physical one that causes SO ₃ to condense on the surface of the particles during flue gas. Therefore, powder (eg, coal ash) other than finely ground limestone is used. This also occurs in the case.

The present invention is not limited to the embodiments described above, but may have various other embodiments. For example, the powder of the present invention
Not limited to limestone and coal ash, any powder can be used as long as SO ₃ can condense on the particle surface and can be collected in an absorption tower of a usual electric dust collector or desulfurization device. However, the above-mentioned limestone and coal ash are conventionally used in the treatment of flue gas treatment equipment, and the equipment and the handling technology for that purpose are already existing, so it is easy to obtain and handle. Not only is there no adverse effect on the operation of the entire facility, but also there is an advantage that, as described above, the labor for supplying limestone to the absorption tower tank can be omitted.

In the first example shown in FIG. 1, for example, limestone may be used instead of coal ash. Further, as the powder of the present invention, for example, both limestone and coal ash may be mixed or separately charged. Further, even when limestone is charged, only the amount necessary for trapping SO ₃ may be sprayed into the flue gas, and the rest may be supplied directly to the tank of the absorption tower of the desulfurization device as in the past. Further, in the above-described first example, the dust containing the powder collected by the electric dust collector 3 is reused as the powder of the present invention.
As before, all of the waste may be discarded as industrial waste.

Further, in order to promote the condensation of SO ₃ on the surface of the powder particles, a powder (or a slurry thereof) having a temperature lower than the temperature of the flue gas, for example, a powder which is forcibly cooled as required ( Alternatively, the slurry may be sprayed during the flue gas. In this way, SO ₃ can be more effectively condensed on the surface of the powder particles, and the generation of harmful SO ₃ mist can be more advanced and easily prevented.

Further, it goes without saying that the structure of the absorption step or absorption tower of the present invention is not limited to the embodiments described above. For example, the structure of the absorption tower may be a single tower type, or various types of absorption towers (gas-liquid contacting device) such as a filling type, a spray type, and a bubbling type may be employed. Also,
The absorbent is not limited to one using a calcium compound such as limestone, and a desulfurization method using, for example, sodium hydroxide or magnesium hydroxide may be employed.

The present invention is particularly effective when used for exhausting smoke from boilers using various oil-based fuels such as heavy oil, orimulsion, VR-fired, and CWM / heavy oil. The same effect can be obtained even when used in a co-firing boiler. Further, even in the case of a coal-fired boiler, an oil-based fuel may be burned at the time of start-up, test operation, or the like, and in such a case, it is effective to apply the present invention.

[0058]

According to the present invention, the powder charging step of dispersing the powder that can be collected in the absorption tower or the dust collector into the flue gas is performed before the absorption step by the absorption tower or in the dust collection step by the dust collector. Provided upstream. For this reason, even if the SO ₃ in the flue gas condenses after the powder charging step, the coagulation occurs on the particle surface of the powder, and the H ₂ SO ₄ particles formed by the condensation of the SO ₃ It is integrated with the powder particles and reduces the generation of harmful fumes (sulfuric acid mist).

Further, since this powder is collected in the absorption step or the dust collection step, the H ₂ SO ₄ particles are also collected together with this powder in any of these steps. This powder and H ₂ SO ₄ particles do not remain therein. Therefore, according to the present invention, S
O ₃ measures can be easily realized without injection of ammonia,
In addition, there is no adverse effect that the injected substance remains in the smoke after the treatment, and the smoke can be further cleaned.

Accordingly, various practically excellent effects as described below can be obtained. (1) ammonia is not required operating costs for the SO ₃ measures can be significantly reduced. (2) A facility for injecting ammonia is not required, and a duct does not need to be particularly long for ammonia diffusion, so that facility cost can be reduced and the facility can be downsized.

(3) Since the N component is not contained in the desulfurization wastewater, troublesome N treatment is not required in the wastewater treatment of the desulfurization wastewater. In this respect, the operation cost can be reduced and the equipment can be downsized. (4) The amount of ammonia contained in the exhaust gas after treatment and released to the atmosphere is reduced to zero, which can greatly contribute to further purification of the exhaust gas and can easily comply with future regulations on the release of atmospheric ammonia.

(5) When the lime-gypsum method is adopted, ammonia contained in the gypsum by-produced is also eliminated, so that it is not necessary to wash the gypsum to prevent an odor. (6) There is no dust such as sulfuric acid mist or ammonium ash remaining in the flue gas after the treatment as in the past, and the entire facility can be cleaned without taking measures such as installing a wet dust collector on the downstream side of the absorption tower. The performance is improved, and this also contributes to the further purification of the smoke exhaust.

Further, when the temperature of the powder sprayed during the flue gas is set to be lower than the temperature of the flue gas, S
O ₃ is condensed on the surface of the powder particles, and the generation of harmful SO ₃ mist can be more advanced and easily prevented.

In the case where the powder is dispersed as a slurry in which the powder is suspended in a liquid, the slurry may be stirred in a desulfurization apparatus or the like, or a slurry pump or a slurry pump. Nozzles and other equipment can be used as is,
This is advantageous in terms of equipment cost and operability of the apparatus, and also makes it easier to diffuse uniformly in smoke exhaustion than in the case of airflow conveyance, thereby preventing problems caused by SO ₃ more efficiently. Further, in this case, the temperature of the particles of the coal ash H is kept lower due to the cooling effect when the slurry liquid evaporates into the flue gas (or the cooling effect due to the presence of the slurry liquid). The condensation of SO _{3 on} the surface of the H particles is promoted, and the function of collecting SO ₃ by the coal ash H, which is a powder, is more enhanced.

Further, even when dust (coal ash) contained in the combustion exhaust gas of coal is used as the above-mentioned powder, a high degree of cleansing of smoke exhaust is realized. In other words, coal ash has a relatively large particle diameter of about several tens of μm, so that it has a relatively high collection rate compared to conventional ammonium sulfate as well as conventional sulfuric acid mist and dust collectors and absorbents. Collected in the tower and hardly remains in the fumes after further processing. In addition, coal ash, like limestone, has been used and handled in flue gas treatment equipment, and the equipment and handling technology for that purpose need only be existing, making it easy to obtain and handle. Operating costs and equipment costs can be further reduced. In particular, coal ash is generally discarded as industrial waste in coal-fired power plants and the like, and is therefore available almost free of charge and is advantageous.

When at least a part of the powder collected in the dust collection step is reused as powder to be scattered in the flue gas, in addition to the above-described basic effects, Further, there are the following specific effects.

That is, in this case, since coal ash and the like as powder for collecting SO ₃ are circulated and used, the amount of coal ash and the like to be newly supplied can be reduced.
The amount of dust such as coal ash to be discharged out of the system can be reduced. Therefore, as described later, even when dust such as coal ash to be discharged out of the system is mixed into the gypsum in the case of the lime-gypsum method, the amount of this dust is minimized to increase the purity of the gypsum. It has an inherent effect that it can be secured.

Further, at least a part of the powder collected in the dust collecting step (that is, dust such as coal ash to be discharged outside the system) is mixed into gypsum which is a by-product in the case of the lime-gypsum method. In this case, the amount of dust discharged as industrial waste is eliminated, and this also contributes to a reduction in operating costs.

In the case where limestone finely pulverized is used as the powder, the limestone introduced has a large particle diameter of about 100 μm, so that not only conventional sulfuric acid mist but also conventional mist is used. Compared to ammonium sulfate, it is collected in a dust collector (dust collection step) or absorption tower (absorption step) at a remarkably high collection rate, and hardly remains in the flue gas after the subsequent treatment. For this reason, the cleanness of the smoke exhaust is realized to a particularly high degree.

In the case of limestone, it has been conventionally used in smoke exhaust treatment equipment, and the equipment and handling technology for that purpose need only be existing, so it is easy to obtain and handle, and the operating cost is low. And equipment costs can be further reduced.
Limestone also has the advantage that it does not adversely affect the operation of the entire facility even if it is put into smoke. That is, in this case, the limestone collected in the absorption tower is dissolved or suspended in the absorbing solution, acts as an absorbing agent (alkali agent) for neutralizing the absorbing solution, and reverses the sulfur oxide absorption reaction. Facilitate. In addition, when the lime gypsum method of producing gypsum from the absorbed sulfur oxide using limestone as an absorbent is adopted, if the limestone is put into flue gas as a powder, the entire limestone If the input amount is controlled as before, there is no adverse effect on the gypsum purity, and the input limestone becomes a useful gypsum, so that there is no increase in industrial waste.

In the case where the absorption process of SO ₂ or the like in the flue gas is performed by the lime gypsum method, the entire amount of limestone required as an absorbent in the absorption process is dispersed as the powder in the flue gas. In the past, equipment that had conventionally been used to convert limestone to slurry and supply it to the absorption tower tank became completely unnecessary,
In this respect, the equipment cost can be further reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a flue gas treatment facility as a first example of the present invention.

FIG. 2 is a diagram showing a configuration of a flue gas treatment facility which is a second example of the present invention.

FIG. 3 is a diagram showing data supporting the operation of the present invention.

FIG. 4 is a diagram showing a configuration example of a conventional smoke exhaust treatment facility.

[Explanation of symbols]

 2 Introductory duct 3 Dust collector 10 Desulfurizer 12,13 Absorption tower A Untreated flue gas B, B1, B2 Dust (powder) C Treated flue gas E Gypsum G Fine limestone (powder) H Coal ash (powder)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naohiko Ugawa 4--22 Kannonshinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Inside the Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Inventor Susumu Okino 4-chome Kannonshinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture No. 6-22 Mitsubishi Heavy Industries, Ltd. Hiroshima Laboratory

Claims (12)

[Claims] 1. A method for treating flue gas containing at least SO ₂ and SO ₃ , comprising a step of introducing powder into the flue gas, and then guiding the flue gas to an absorption tower to absorb the flue gas. by gas-liquid contact with the liquid, the flue gas treatment method characterized by having an absorption step at least a SO ₂ removed by absorption, and collecting the powder in the flue gas. 2. A method for treating flue gas containing at least SO ₂ and SO ₃ , comprising a step of introducing powder into the flue gas, and then guiding the flue gas to a dust collector to remove the flue gas. A dust collecting step of collecting at least the powder in the air; and an absorption step of absorbing and removing at least SO ₂ in the smoke by introducing the smoke into an absorption tower and bringing the smoke into gas-liquid contact with an absorbing liquid. A flue gas treatment method comprising: 3. The flue gas treatment method according to claim 1, wherein the temperature of the powder is set lower than the temperature of the flue gas in the powder charging step. 4. The flue gas treatment method according to claim 1, wherein, in the powder charging step, the powder is dispersed in a flue gas as a slurry in which the powder is suspended in a liquid. 5. The flue gas treatment method according to claim 1, wherein dust contained in combustion exhaust gas of coal is used as the powder. 6. The method according to claim 2, wherein at least a part of the powder collected in the dust collecting step is reused as powder to be scattered in the flue gas in the powder charging step. Exhaust gas treatment method. 7. The absorption step is performed by a lime gypsum method in which gypsum is produced as a by-product using an absorption liquid in which limestone is suspended as an absorbent, and at least a part of the powder collected in the dust collection step is used. 3. The method according to claim 2, wherein said gypsum is mixed into gypsum by-produced in said absorption step and discharged out of the system. 8. The method according to claim 1, wherein limestone is finely pulverized as the powder. 9. The absorption step is performed by a lime gypsum method in which gypsum is produced as a by-product using an absorption solution in which limestone is suspended as an absorbent, and the total amount of limestone required as the absorbent in the absorption step is determined by 9. The smoke exhaust treatment method according to claim 8, wherein the absorbent is indirectly supplied into the absorbent by dispersing the powder in the smoke. 10. A flue gas treatment facility containing at least SO ₂ and SO ₃ , wherein the flue gas is brought into gas-liquid contact with an absorbing liquid to absorb and remove at least SO ₂ in the flue gas. Powder input means for spraying powder into the flue gas upstream of the absorption tower,
A flue gas treatment facility comprising: 11. A flue gas treatment facility containing at least SO ₂ and SO ₃ , wherein the flue gas is brought into gas-liquid contact with an absorbing liquid to absorb and remove at least SO ₂ in the flue gas. A dust collector that collects powder in the flue gas in front of the absorption tower, and a powder input unit that sprays powder in the flue gas in front of the dust collector. Exhaust gas treatment equipment. 12. The apparatus according to claim 11, wherein at least a part of the powder collected by said dust collector is reused as powder to be scattered during flue gas by said powder charging means. The flue gas treatment equipment described.