JP3294046B2 - Flue gas treatment system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flue gas treatment system,
In particular, the present invention relates to a flue gas treatment system that can easily remove and detoxify selenium (Se) in flue gas.

[0002]

2. Description of the Related Art Conventionally, as a flue gas treatment system installed in a thermal power plant or the like, a dust collection device (usually an electric discharge device) for removing dust such as fly ash from flue gas introduced into this wet flue gas desulfurization device is known. Dust collector), and by contacting the flue gas with an absorbent slurry (eg, a slurry containing calcium compounds) in the absorber, absorbs sulfur dioxide in the flue gas, and removes gypsum from the slurry in the absorber as a by-product. Although a flue gas treatment system provided with a wet flue gas desulfurization device that separates and produces is widespread, handling of harmful impurities other than sulfur oxides contained in flue gas has recently become a problem. In particular, in a flue gas treatment system for a coal-fired boiler, the harmfulness of selenium (Se) contained in coal at a content of up to about 10 mg / kg has become a problem, and it is desirable to treat it harmlessly. It is rare.

[0003] Se is insoluble by a treating agent.
Easy tetravalent Se (main form: SeO2 selenite)_Three ^2-)
And hexavalent Se which is difficult to insolubilize (main form: selenic acid
SeO _Four ^2-), And hexavalent Se in particular has a solubility of
High (solubility at 20 ° C 95%) and easy to elute. Also,
This Se has toxicity similar to arsenic compound,
There are cases of obstacles and emission regulations.
Environmental standards (0.01 mg / lit.)
), Wastewater standard (0.1mg / liter), landfill disposal
Elution standard (0.3mg / l) has been established
I have.

FIG. 4 shows a conventional example of this type of flue gas treatment system (an example of a flue gas treatment system for a coal-fired boiler). In FIG. 4, smoke exhausted from a coal-fired boiler 1 is subjected to nitrogen oxide (N) by a denitration device 2 attached to the boiler 1.
Ox) is removed, and after passing through the air heater 3 and the heat recovery unit 4 of the gas gas heater (GGH), the electric dust collector 5
(EP) to remove dust such as fly ash. The flue gas is then led to a wet flue gas desulfurization unit 6,
After the sulfur dioxide gas is removed in the desulfurization device 6, the gas passes through a reheating unit 7 of a gas gas heater (GGH), and is guided to a chimney (not shown), and is discharged from the chimney to the atmosphere. . The dust such as fly ash removed by the electric precipitator 5 is subjected to ash treatment, and part of the dust is reused as a cement raw material or the like, and the rest is discharged to an ash dump 8.
Thrown away.

[0005]

In the above-mentioned conventional flue gas treatment system, Se in coal (Se in flue gas) is used.
Most of the ash is condensed on the downstream side such as the air heater 3 and is removed by the electric dust collector 5 while being contained in the dust in the flue gas, and is used as it is in the waste of the ash dump 8 or as a raw material for cement. Will be mixed in the ashes. Therefore, in order to detoxify Se by observing the elution standard and the like, it is necessary to perform a troublesome and costly post-treatment such as diluting the ash removed by the electrostatic precipitator 5 with, for example, a large amount of water. There was a problem of becoming.

The present invention has been made in view of the above-mentioned prior art, and has as its object to provide a flue gas treatment system capable of easily achieving harmless Se contained in flue gas.

[0007]

Means for Solving the Problems The present invention provides the following (1)-
It includes the invention of (6) .

(1) A flue gas treatment system for treating flue gas containing sulfur dioxide gas, dust and Se components, comprising a dust collector for removing dust from flue gas and an absorbent slurry for absorbing and removing sulfur dioxide gas. A desulfurization device having a circulating absorption tower, and heating means for heating the dust removed by the dust collection device to a temperature at which Se in the dust is gasified, wherein the heating means heats the dust. In a configuration in which the generated gas is introduced into the desulfurization device together with the flue gas, Se is dissolved and collected in a slurry in the desulfurization device, and a processing agent that insolubilizes tetravalent Se during the slurry processing step is mixed. A flue gas treatment system characterized in that it has a configuration to be performed.

(4) Oxidation for controlling an oxidation-reduction reaction in the desulfurization apparatus so that hexavalent Se mixed into the slurry in the desulfurization apparatus is reduced to sulfuric acid in the slurry to become tetravalent Se. The flue gas treatment system according to (1) , further comprising a reduction reaction control means.

(3) A flue gas treatment system for treating flue gas containing sulfurous acid gas, dust and Se components, a dust collector for removing dust from flue gas, and cooling provided upstream of the absorption tower A desulfurization apparatus having a dust removal tower and an absorption tower through which an absorbent slurry for absorbing and removing sulfurous acid gas circulates; and heating means for heating the dust removed by the dust collector to a temperature at which Se in the dust is gasified. And the gas generated by heating the dust by the heating means is introduced into the cooling dust removal tower of the desulfurization device together with the flue gas so that Se is dissolved and collected in the circulating liquid of the cooling dust removal tower. A treatment agent for insolubilizing tetravalent Se during the treatment of the circulating liquid.

(4) The dust collecting means is provided with a plurality of collecting sections for separating and collecting the dust from the inlet side of the smoke exhaust to the outlet side, and collecting from the collecting section on the inlet side of the smoke exhaust. (1) separately separating and collecting the dust collected from the outlet and the dust collected from the outlet, and introducing only the dust separated and collected from the collection unit on the outlet to the heating means. The smoke exhaust system according to any one of (1) to (3) .

(5) Classifying means for classifying the dust separated by the dust collecting means into a large particle size and a small particle size is provided, and only the small particle size dust classified by the classifying device is provided. , one of the flue gas treatment system of (1) to (3), characterized by comprising a structure to be introduced into the heating means.

(6) The heating means removes dust from 100 to 1
The flue gas treatment system according to any one of (1) to (5) , wherein the system is heated to a temperature of 200 ° C.

[0014]

In the flue gas treatment system according to the invention (1), most of the Se in the flue gas is removed by the dust collecting device while being contained in dust such as fly ash, and heated by the heating means. Gasify. And gasified
Se is introduced into the desulfurization unit together with the flue gas from which dust has been removed.
It is dissolved and collected in the absorbent slurry. And this
Insoluble tetravalent Se during processing of absorbent slurry
Is mixed with the treating agent to be solubilized and insolubilized.

[0015] ie, at least tetravalent Se, it is insolubilized by treatment agent as it is in the desulfurization apparatus, or is discharged in a mixed solids produced separated from the slurry in the desulfurization apparatus (gypsum, etc.), or In a wastewater treatment device for discharging a circulating liquid from a desulfurization device, the wastewater is insolubilized by a treatment agent and can be easily solidified.

Therefore, when hexavalent Se is small in the absorbing solution in the desulfurization apparatus, if only the insoluble treatment of tetravalent Se is performed, Se is easily released to the atmosphere without releasing Se into the atmosphere.
The elution standard of can be cleared. In addition, Se is separated from the dust by the heating means and introduced into the desulfurizer, and the entire dust is not introduced into the desulfurizer. Therefore, the dust can be easily reused and the desulfurization performance of the desulfurizer can be improved. It is possible to avoid adverse effects such as reduction.

In the flue gas treatment system according to the invention (2), the hexavalent Se mixed into the slurry in the desulfurization unit is reduced almost completely by the sulfurous acid in the slurry to the tetravalent by the oxidation-reduction reaction control means. The oxidation-reduction reaction of the slurry in the desulfurization device is controlled so that Therefore, this hexavalent Se
Can be almost completely changed to tetravalent in the desulfurization apparatus, and the treatment for insolubilizing Se in the flue gas can be performed more easily and completely.

In the flue gas treatment system according to the invention (3) , most of Se in the flue gas is removed by the dust collecting device while being contained in the dust such as fly ash, and heated by the heating means. And gasify. Then, the gasified Se is introduced into the cooling and dust removing tower of the desulfurization device together with the flue gas from which the dust has been removed, and is dissolved and collected in the circulating liquid.
Then, during the processing step of the circulating liquid, the circulating liquid is mixed with a processing agent that insolubilizes the tetravalent Se and is insolubilized. That is, at least tetravalent Se is directly discharged to the solid phase side by a solid-liquid separation unit or the like connected to the cooling and dust removing tower of the desulfurization device, or in a wastewater treatment device that performs a discharge process of the circulating liquid of the desulfurization device. It is insolubilized by the treating agent and can be easily solidified. In addition, most of hexavalent Se reacts with sulfurous acid absorbed from flue gas in the liquid in the cooling dust tower, is reduced to tetravalent Se, is insolubilized by the treating agent, and is solidified by the separation means. It is detoxified by being discharged.

Therefore, even with this system, S
e can be easily cleared of the elution standard of Se without releasing into the atmosphere, and the cooling and dust removing tower of the desulfurization unit also functions as a hexavalent Se reduction reaction facility, so that the entire system The equipment configuration is simplified. Further, in this system, Slurry in the absorption tower of the desulfurization unit contains S
Since e or other dust is less mixed, the desulfurization performance in the desulfurization device can be maintained high, and high-quality gypsum can be recovered as a by-product.

In the flue gas treatment system according to the invention (4) , only the dust separated and recovered from a specific recovery portion on the outlet side of the flue gas in the dust collecting means is introduced into the heating means and Se.
Since the gasification separation is performed, the capacity of the heating means can be reduced. In addition, the amount of the treating agent required for performing the insolubilization treatment of Se in a subsequent desulfurization device or the like can be reduced, and the detoxification of Se can be made easier and at lower cost. In other words, according to the study of the inventors, it was found that the Se (dust) contained in the dust (ash) having a smaller particle diameter separated and recovered from the specific recovery portion on the outlet side contained a larger amount of (sediment). And
It is possible to detoxify Se as a whole simply by performing heat treatment only on the dust having a small particle diameter and performing insolubilization treatment on gasified Se.

In the flue gas treatment system according to the invention (5) , only the small-sized dust classified by the classification means is introduced into the heating means to perform gasification and separation of Se.
The capacity of the heating means can be reduced. In addition, the amount of the treating agent required for performing the insolubilization treatment of Se in a subsequent desulfurization device or the like can be reduced, and the detoxification of Se can be made easier and at lower cost. That is, according to the research of the inventors, it has been found that a larger amount of Se is contained (attached) to dust (ash) having a smaller particle size. It is possible to detoxify Se as a whole simply by performing heat treatment only on the substrate and performing insolubilization treatment on gasified Se.

In the smoke exhaust treatment system according to the invention (6) , the heating temperature of the dust in the heating means is set to 100 to 12
Since the temperature is set to 00 ° C., re-condensation of gasified Se into dust is prevented, Se can be easily removed from dust, and the Se elution standard of dust can be satisfied.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. The same reference numerals are used for the same components as those in the conventional example, and the description thereof will be omitted. Embodiment 1 FIG. 1 is a schematic configuration diagram showing an example of the smoke exhaust treatment system according to the inventions (1) , (2), and (4) to (6) . As shown in FIG. 1, in the smoke exhaust treatment system of this embodiment, the dust to which Se is attached is removed by an electric dust collector 70, and the dust (ash) removed by the electric dust collector 70 is heated by a heating unit 11. Then, Se in the dust is raised and gasified, and this gas is introduced into a wet flue gas desulfurization unit 20 (hereinafter, simply referred to as a desulfurization unit 20) together with the flue gas from which the dust has been removed for treatment. Within the desulfurization apparatus, the reaction formula (1), as shown in (2), tetravalent Se: (main form selenite SeO ₃ ^2-) 6-valent Se (main form: selenious acid SeO ₄ ^{2 -} ) Exists. This hexavalent Se is so-called ORP control (oxidation-reduction potential control) in the desulfurization unit 20.
, Is converted to tetravalent Se by reduction of almost all the amount.

## STR1 ## _{SeO 2 (g) + H 2} O → 2H + + SeO 3 2- (1) SeO 3 2- + 1 / 2O 2 → SeO 4 2- (2)

The heating means 11 is, for example, a kiln in this case, and heats the ashes B3, B4 introduced from the electric precipitator 70 to a temperature at which Se is raised and gasified by the supplied high-temperature air I. The product gas M is introduced into the absorption tower 21 of the desulfurization unit 20 together with the flue gas, and the remaining ash J is taken out for reuse as a raw material such as cement. In this case, as a means for supplying the high-temperature air I to the heating means 11, in this case, the heavy oil-fired boiler 1
2 is provided, and the heavy oil K is burned to heat the air L, so that high-temperature air I of, for example, about 1000 ° C. is supplied.

The processing temperature in the heating means 11 is as follows:
The temperature may be set to 100 to 1200 ° C., but in order to more completely and efficiently gasify the Se in the dust, the temperature is preferably set to 320 to 1
Preferably, the temperature is set to 000 ° C. Further, when the amount and temperature of the dust introduced from the electrostatic precipitator 70 to the heating means 11 are, for example, 15 t / h and 90 ° C. and the dust is heated to about 320 ° C., the flow rate and temperature of the hot air I or the heating means The specifications of the kiln that constitutes 11 may be set, for example, as follows. That is, the flow rate of the hot air I is 3
100 m ³ N / h, the temperature of the hot air I is 1000 ° C., the filling rate in the kiln is 8%, the ash density in the kiln is 0.5, and the residence time in the kiln is 0.5 hr.

The electric precipitator 70 has a plurality of hoppers 71 to 74 for separating and collecting the dust, and these hoppers 71 to 74 are arranged from the inlet (upstream) to the outlet (backstream) of the flue gas. With such a configuration, dust having a larger particle diameter is collected from the hopper on the inlet side, and dust having a smaller particle diameter is collected from the hopper on the outlet side. . In this case, the dusts B3, B separated and collected from the specific hoppers 73, 74 on the outlet side are used.
4 is introduced into the heating means 11 and the remaining dust B1, B
2 is reused or disposed of as a cement raw material. The electric precipitator 70 in the present embodiment functions as a dust collecting means and a classifying means of the present invention.

The desulfurization unit 20 is a desulfurization unit of a tank oxidation type in this case, and an absorption tower 2 in which an absorbent slurry (in this case, made of limestone) is supplied to a bottom tank 22.
1, a circulating pump 23 for sending the absorbent slurry in the tank 22 to the upper part 21a (smoke exhaust introduction section) of the absorption tower 21 to make contact with the exhaust gas, and a motor supported in the tank 22 and not shown. , The arm rotates an air sparger 24 that agitates the slurry in the tank 22 and efficiently blows the supplied air as fine bubbles into the tank 22, and air that feeds the air into the air sparger 24. The supply pipe 25 is provided, and the absorbent slurry having absorbed the sulfurous acid gas in the tank 22 is efficiently brought into contact with air to oxidize the entire amount to obtain gypsum.

A slurry pump 31 for sucking out the slurry in the tank 22 is connected to the tank 22, and the slurry sucked by the slurry pump 31 is supplied with the treating agent A by the mixing means 14 and then mixed. Solid-liquid separator 32
And the gypsum C in the slurry is extracted as a cake-like solid (usually, a water content of about 10%). On the other hand, the filtrate (mainly water) from the solid-liquid separator 32 is once sent to the filtrate tank 33, and after the replenishment water D and the return liquid E from the wastewater treatment device 50 are added as necessary, the pump A part of the absorbent slurry tank 35 due to 34
, Mixed with limestone F (CaCO ₃ ) supplied from a limestone silo (not shown), and supplied to the tank 22 again by the slurry pump 36 as an absorbent slurry. The mixing means 14 includes, for example, a mixing tank and a stirring mechanism for stirring the liquid in the mixing tank. Further, as the treatment agent A, a chemical which reacts with at least tetravalent Se (main form: SeO ₃ ^2- selenite) to be insolubilized is required. For example, FeCl ₃ or Fe ₂ (SO ₄ ) ₃ is used. Can be.

The desulfurizer 20 has an absorption tower 2
An oxidation-reduction reaction control means 40 for controlling the oxidation-reduction reaction in 1 is provided. Redox reaction control means 40
In this case, the sensor 41 provided on the discharge side pipe of the circulation pump 23 to detect the oxidation-reduction potential of the slurry in the tank 22 and the air supply amount to the air sparger 24 provided on the air supply pipe 25 A flow control valve 42 to be adjusted;
The controller 43 controls the operation of the flow control valve 42 based on the detection output of the sensor 41. here,
The sensor 41 is, for example, an electrode made of platinum immersed in a slurry. The controller 43 also controls the opening of the flow control valve 42 so that the amount of air supplied to the air sparger 24 becomes the minimum amount necessary for sulfurous acid dissolved in the slurry from the exhaust gas to be oxidized and disappear. The degree is controlled continuously. For example, specifically, based on the correlation between the sulfurous acid concentration and the oxidation-reduction potential, the oxidation-reduction potential when the sulfurous acid concentration is substantially zero is set in advance as a reference potential, and the oxidation-reduction potential detected by the sensor 41 is When the potential becomes lower than the reference potential, the air supply amount is increased in accordance with the deviation, and when the oxidation-reduction potential detected by the sensor 41 becomes higher than the reference potential, the air supply amount is decreased in accordance with the deviation. Performs proportional control.

Since the oxidation-reduction reaction control means 40 supplies the minimum necessary air for oxidizing the sulfurous acid in its entirety, the other acids contained in the slurry are substantially reduced by sulfurous acid as a result. It has the function of causing a reaction to be performed. That is, the vaporized S coming out of the heating means 11
The gas M containing e is introduced into the absorption tower 21 together with the flue gas, and tetravalent Se (main form: SeO ₃ ^2- selenite) and 6
Under the control of the controller 43, the hexavalent Se reacts with the sulfurous acid absorbed from the flue gas to form tetravalent Se (principal form: SeO ₄ ^2- selenate). A reduction reaction to be selenate SeO ₃ ^2- ) occurs in the absorption tower 21. This reaction is represented by the following reaction formula (3).

## STR2 ## _{^{SeO 4 2- + SO 3 2- →}} SeO 3 2- + SO 4 2- (3)

In this case, the wastewater treatment device 50 is a so-called non-drainage treatment device, and has a well-known configuration including a pretreatment device 51, an electrodialysis device 52, a secondary concentration device 53, and a solidification device 54. It is the subject. In the wastewater treatment device 50, a part of the liquid in the filtrate tank 33 is supplied by the pump 34 of the desulfurization device 20, and impurities (for example, Cl ) Is removed, and the residue after the removal is returned to the filtrate tank 33 or the absorbent slurry tank 35 of the desulfurization device 20. Then, the removed impurities are finally solidified by the solidification equipment 54. In this case, at least at a stage before the solidification step (for example, at a position upstream of the secondary concentration equipment 53), 4
The treating agent A, which reacts with monovalent Se (main form: SeO ₃ ^2- selenite) to be insolubilized, is mixed therein.

In the flue gas treatment system configured as described above, the flue gas is sufficiently cooled before the electric precipitator 70, and most of the Se in the flue gas is condensed to generate dust (particularly particle size) such as fly ash. Most of the Se in the flue gas is once collected by the electric dust collector 70 together with the dust. In this case, of the collected dust B1 to B4,
No. 2 has a low Se content, so it is reused or discarded as it is as a raw material for cement, etc.
Only 3 to B4 are subjected to heat treatment in the heating means 11, and Se in the dusts B3 to B4 is gasified, and together with the flue gas discharged from the electrostatic precipitator 70, the absorption tower 21 of the desulfurization device 20.
Will be introduced.

Then, the flue gas introduced into the absorption tower 21 (including the gas sent from the heating means 11 and the like).
The gas comes into contact with the absorbent slurry injected from the spray pipe 26 by the circulation pump 23 to absorb and remove the sulfurous acid gas and gasified Se, and is discharged from the flue gas discharge section 21b as treated smoke. The sulfurous acid gas injected from the spray pipe 26 and absorbed in the absorbent slurry flowing down through the filler 27 is oxidized by contacting with a number of bubbles blown while being stirred by the air sparger 24 in the tank 22, Further, a neutralization reaction occurs to form gypsum.
In addition, in the absorption tower 21, hexavalent Se (main form: SeO ₄ ^2- selenate) is obtained by the reaction of the above-mentioned reaction formula (3).
Is substantially tetravalent Se (main form: selenite Se)
O ₃ ^2- ). The main reactions (other than the above-mentioned reaction formula (3)) occurring during these processes are the following reaction formulas (4) to (6).

[0034]

Embedded image (absorption tower flue gas inlet _{section) SO 2 + H 2 O →} H + + HSO 3 - (4) ( ^{_{Tank) H + + HSO 3 - +}} 1 / 2O 2 → 2H + + SO 4 2- _{^{(5) 2H + + SO 4}} 2- + CaCO 3 + H 2 O → CaSO 4 · 2H 2 O + CO 2 (6)

Thus, gypsum (CaS
O ₄ · 2H ₂ O) and a small amount of limestone is absorbent (CaC
O ₃ ) and mainly tetravalent Se (main form: SeO 2 selenite)
₃ ^2- ) are suspended, and these are sucked out by the slurry pump 31, mixed with the treating agent A in the mixing means 14, then supplied to the solid-liquid separator 32, and filtered to obtain a cake-like gypsum having a low water content. Extracted as C (usually, a water content of about 10%). At this time, most of the tetravalent Se (main form: SeO ₃ ^2- selenite) undergoes a reaction represented by the following reaction formulas (7) and (8) or (9) and (10) to form a sublimate. It becomes iron selenate (Fe ₂ (SeO ₃ ) ₃ ), is insolubilized, and is mixed in the separated gypsum C.

Embedded image FeCl ₃ → Fe ³⁺ + 3Cl ⁻ (7) 2Fe ³⁺ + 3SeO ₃ ^2- → Fe ₂ (SeO ₃ ) ₃ ↓ (8) or Fe ₂ (SO ₄ ) ₃ → 2Fe ³⁺ + 3SO ₄ ^2- (9) 2Fe ³⁺ + 3SeO ₃ ^2- → Fe ₂ (SeO ₃ ) ₃ ↓ (10)

However, when it is not desired to mix iron selenite (Fe ₂ (SeO ₃ ) ₃ ) into the separated and recovered gypsum C, the slurry from the slurry pump 31 is supplied to the line 3.
7 (shown in FIG. 1), and directly supplied to the solid-liquid separator 32 to recover high-purity gypsum C. At this time, the Se treatment is insolubilized by the wastewater treatment device 50 described below.

Next, the operation of the waste water treatment device 50 in the above-described smoke exhaust treatment system will be described. As mentioned above,
In the slurry of the desulfurization unit 20, the vaporized Se is absorbed together with the sulfur dioxide in the flue gas, and the hexavalent S
In the absorption tower 21, almost all of e becomes tetravalent Se by the above-mentioned reaction (reaction formula (3)). And this tetravalent Se
In the wastewater treatment device 50, other impurities (for example, C
1), and Se and other impurities are removed so as not to be excessively accumulated in the slurry solution circulating in the desulfurization device 20.

That is, in the wastewater treatment device 50, the filtrate in the filtrate tank 33 is partially extracted from the discharge side of the pump 34 in the desulfurization device 20, and the impurities in this solution are mainly used by the function of the electrodialysis equipment 52. (Cl and the like) are removed and returned to the filtrate tank 33 of the desulfurization device 20. Then, after the treatment agent A is added to the liquid that has exited the electrodialysis facility 52 and mixed, and the like, the solution is concentrated in the secondary concentration facility 53 and solidified by the solidification facility 54, and is conveyed as an impurity chip H to an ash dumping site or the like. Discarded. At this time, the tetravalent Se in the impurities is the treating agent A
(7), (8) or (9), (1
0)), the iron selenite (Fe ₂ (SeO ₃ ) ₃ )
And exists in the impurity chip H in an insoluble state.

As described above, according to the flue gas treatment system of this embodiment, in addition to the conventional flue gas purification (removal of dust and removal of sulfur dioxide), Se in the flue gas is removed together with the dust. Finally, the gypsum cake G or the impurity chips H can be made to exist in an insolubilized state so as not to be eluted upon reuse or disposal.
Moreover, hexavalent Se, which is difficult to treat (insolubilize), is supplied to the oxidation-reduction reaction control means 40 in the absorption tower 21 of the desulfurization unit 20.
Of tetravalent S that can be easily disposed of with a treating agent
e, it is possible to remove and detoxify Se in the flue gas with a simple and inexpensive facility as compared with, for example, providing a separate reaction tower for converting hexavalent Se into tetravalent Se. Becomes

Further, according to the above-mentioned smoke exhaust treatment system,
By the action of the oxidation-reduction reaction control means 40, almost all of the hexavalent Se eventually becomes tetravalent Se in the absorption tower 21 and is finally insolubilized and discarded, so that the gypsum cake C or the impurity chips H The concentration of hexavalent Se (not insolubilized) remaining in the solution is extremely low, and the elution standard and the like can be satisfied with a large margin. Further, in this case, if only the dust B3 and B4 separated and recovered from the specific hoppers 73 and 74 on the outlet side of the flue gas in the electrostatic precipitator 70 are subjected to the Se insolubilization treatment, the necessary amount of the treatment agent A and the heating means 11 can reduce the capacity and the like, and has an inherent effect that the detoxification of Se can be made easier and at lower cost. In other words, as described above, according to the study of the inventors, Se (Dr) (ash) is contained in a larger amount in dust (ash) having a smaller particle diameter separated and recovered from a specific recovery part on the outlet side, and thus adheres (adheres). It has been found that simply performing the insolubilization treatment only on the dust having a small particle diameter makes it possible to detoxify Se as a whole, and has an effect of contributing to reduction of equipment cost and operation cost.

Hereinafter, an apparatus similar to that of the above embodiment will be described.
The results of a dust heating experiment and a dust collection and elution experiment will be described. A dust containing 84 mg / kg of Se was heated at a heating temperature (200 to 1200 ° C.) and a heating time (5 to 30 ° C.).
Min) was changed to perform a heating experiment. In addition, a Se dissolution test of the dust before the heating device and after the heating experiment was notified by the Environment Agency.
No. 3 and the Se in the eluate
The concentration was analyzed by an atomic absorption method using a hydrogen compound generation method. The results are shown in FIG. 5 for the effect of the heating temperature and in FIG. 6 for the effect of the heating time. Temperature 320 ° C
When heating is performed for 10 to 30 minutes as described above, the elution of Se in the dust is 0.3 mg / liter or less, which is the elution standard for landfill disposal, and it can be seen that most Se is gasified.
It can be seen that by increasing the heating time to 30 minutes even at a temperature of 200 ° C., the elution of Se from the dust satisfies the elution standard for landfill disposal. Therefore, S in the dust
When gasifying e by heating, the temperature of the dust is set to 100 to 1200 ° C. as a temperature at which the gasified Se does not recondense,
Preferably, Se in the dust can be removed by heating to 320 to 1000 ° C. That is, in the above example, it was demonstrated that the dust J heated by the heating means 11 can be reused or discarded as it is.

Next, dust collection and elution experiments were performed at 3 mg /
coal containing Se in kg is supplied to the combustion furnace at 25 kg / h, the flue gas of 200m ³ N / h discharged from the combustion furnace 1
It cooled to 50 degreeC and introduced into the electric precipitator and performed. In this case, 99% or more of the dust is collected by the electric dust collector,
The total amount recovered from all hoppers was 3.4 kg / h. The dust B1 and B2 (collected ash) collected by the hoppers 71 and 72 on the upstream side and the hoppers 73 and 74 on the downstream side are collected.
The discharge amount, the average particle size, and the eluted Se concentration of the dusts B3 and B4 collected in the above were measured as shown in Table 1, respectively.

[0043]

[Table 1]

That is, the hoppers 73 and 7 on the outlet side of the smoke exhaust
Of the dusts B3 and B4 separated and recovered from the sample No. 4 is 1.
It is as low as 14 kg / h, but the eluted Se concentration is 0.49 mg.
Per liter, which was much higher than the standard. However, the dust B separated and recovered from the hoppers 71 and 72 on the inlet side of the flue gas
1, B2 had a large carry-out amount of 2.27 kg / h, but the eluted Se concentration was as low as 0.20 mg / liter, lower than the standard. Therefore, it can be seen that the dusts B1 and B2 separated and collected from the hoppers 71 and 72 on the smoke exhaust inlet side can be directly discarded. In other words, the Se insolubilization treatment of the dust on the inlet side of the flue gas, which is about twice as large, is not required.
It is clear that the required amount of the treatment agent A and the capacity of the heating means 11 can be remarkably reduced.

The difference in the concentration of the eluted Se is as follows.
It is thought to be due to the particle size of the dust (ash). That is, when gaseous Se (SeO ₂ ) is condensed and adheres to the surface of ash constituting dust, the ash having a small particle diameter has a large specific surface area per unit weight, so that more Se adheres. become. On the other hand, in a dust removing device such as an electric dust collector as described above, coarse ash is easily collected on the smoke exhaust inlet side and fine ash is easily collected on the smoke exhaust outlet side, and has a so-called classification function. It is considered that the concentration of eluted Se in the dust collected on the outlet side is increased.

In the case of the above embodiment, there is a possibility that it is difficult to realize high quality (purity, etc.) of the gypsum C due to the influence of Se mixed in the absorption tower. As described above, the Se treatment is insolubilized only by the wastewater treatment device 50. The mixing of the treating agent A may be carried out at a position other than the position shown in FIG. 1 as long as it is a slurry system of the desulfurization device 20, or it may be directly introduced into the absorption tower 21. In addition, the mixing of the treating agent A is
1 is performed only in the wastewater treatment apparatus 50 of FIG.
May be omitted. In this case, in the desulfurization apparatus 20, all Se (mainly tetravalent Se) circulates in a state of being dissolved in the slurry solution, and a part of these Se is sequentially guided to the wastewater treatment apparatus 50, where it is insolubilized. The gypsum is not mixed into the gypsum C, so that it is advantageous when it is desired to ensure high gypsum purity. Further, if it is not necessary to reduce the input amount of the treatment agent A, the capacity of the heating means 11, etc., all the dusts B1 to B4 collected by the electric dust collector 70 may be introduced into the heating means 11 for processing. It goes without saying that it is good.

(Embodiment 2) FIG. 2 is a schematic configuration diagram showing an example of the smoke exhaust treatment system according to the invention (3) . Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. As shown in FIG. 2, the flue gas treatment system of this embodiment includes a desulfurization device 60 provided with a cooling / dust removing tower 61 for cooling and removing dust from the upstream side of the absorption tower 21. After the gas containing Se generated by the heating means 11 is introduced together with the flue gas into the cooling / dusting tower 61 of 60, and after the treatment agent A is introduced into the slurry extracted from the cooling / dusting tower 61 by the mixing means 14, It is characterized in that the solid-liquid separation is performed by the separation means 15. Here, in the cooling and dust removing tower 61, the liquid in the filtrate tank 33 is supplied by the pump 34, and this liquid is injected from the upper header pipe 63 by the circulation pump 62. Note that a mist eliminator (not shown) is provided between the cooling and dust removing tower 61 and the absorption tower 21.

In this case, Se separated from the dust by heating once enters the cooling and dust removing tower 61. In the cooling and dust removing tower 61, the above-mentioned reaction (reaction formula (3)) takes place, and the hexavalent is removed. Substantially the total amount of Se becomes tetravalent Se, and this tetravalent Se is insolubilized by the treating agent A,
In the dust cake G separated by 5 or wastewater treatment device 5
0 will be mixed into the impurity chip H. In this case, unlike the case of the first embodiment, fine dust that could not be collected by the electrostatic precipitator is not mixed into the absorption tower 21, so that a high desulfurization rate can be secured, and high quality (purity, etc.) can be secured. There is an effect that gypsum C can be easily obtained. In FIG. 2, the separated water from the separation means 15 is directly introduced into the wastewater treatment apparatus 50, but the hexavalent Se is converted to the tetravalent S
In order to further complete the conversion reaction to e, this separated water is introduced into, for example, an absorbent slurry tank 35 and the absorption tower 21
May be led. Further, the treatment agent A can be directly charged into the cooling and dust removing tower 61, and similarly to the first embodiment, the treatment agent A is charged only in the wastewater treatment device 50,
The mixing means 14 and the separation means 15 can be omitted.

(Embodiment 3) FIG. 3 is a schematic configuration diagram showing an example of the smoke exhaust treatment system according to the invention (5) . Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. As shown in FIG. 3, the smoke exhaust treatment system of this embodiment converts dust B1 to B4 collected by the electrostatic precipitator 70 and conveyed in a lump into a large particle (hereinafter referred to as coarse ash) B5. And a small particle size (hereinafter referred to as fine ash) B6 are provided with a classification device 81 (classification means), and only the fine ash B6 classified by the classification device 81 is collected by the fine particle collection device 82. It is configured to be introduced into the heating means 11. In this case, the dusts B1 to B4 are transported by the air N and introduced into the classification device 81. Further, the classification device 81 can be constituted by, for example, a cyclone, and is of any type that can adjust the degree of classification. Further, a bag filter is used as the fine particle collecting device 82 in this case.

In this case, only Se in the fine ash B6 is gasified and introduced into the desulfurizer 20 to be insolubilized, so that the required amount of the treating agent A and the heating means 11 This has the effect that the capacity and the like can be reduced, and the detoxification of Se can be made easier and at lower cost. Further, in the case of the system of this embodiment, a modification is made by adding a heating means, a classifying device, and the like to a conventional flue gas treatment system (a system in which dust from the electric dust collector is conveyed collectively). This system can be configured without changing the configuration of the conveyor that conveys the dust from the electrostatic precipitator.
This makes it possible to easily modify existing flue gas treatment systems and to use existing designs or equipment as they are even when newly installing this system.

Hereinafter, an apparatus similar to that of the above embodiment will be described.
The results of a dust heating experiment and a dust collection and elution experiment will be described. In the experiment, coal containing 3 mg / kg of Se was supplied to the combustion furnace at 25 kg / h, and 200 m ³ N / h of flue gas discharged from the combustion furnace was cooled to 150 ° C. and introduced into the electric dust collector. Was. In this case, 99% or more of the dust is collected by the electric dust collector, and the amount of dust collected by the conveyor (total amount collected from each hopper) is 3.4 kg /.
h. The amounts of coarse ash B5 and fine ash B6 collected, the average particle size, and the eluted Se concentration were measured as shown in Table 2, respectively.

[0052]

[Table 2]

That is, the fine ash B6 has an average particle size of 5.
4 μm and the collection amount is as small as 1.30 kg / h.
The eluted Se concentration was 0.36 mg / liter, exceeding the standard. However, coarse-grained ash B5 had an average particle size of 13 μm and a large collection amount of 2.0 kg / h, but the eluted Se concentration was as low as 0.26 mg / l, which was lower than the standard.
For this reason, it turns out that coarse ash B5 can be discarded as it is. That is, since the Se insolubilization treatment of the coarse ash B5, which has a significantly large carry-out amount, becomes unnecessary, it is apparent that the required amount of the treatment agent A, the capacity of the heating means 11, and the like can be significantly reduced.

The present invention is not limited to the embodiments described above, but may have various aspects. For example, when hexavalent Se does not exist in the absorbing solution of the desulfurization apparatus and only Se other than hexavalent exists, a step of reducing hexavalent Se to tetravalent Se or an apparatus configuration therefor Is unnecessary. Further, the configuration of the desulfurization apparatus is not necessarily limited to the tank oxidation type as shown in the above embodiment.For example, an oxidation tower into which the slurry extracted from the absorption tower is introduced is separately provided, and air is blown into the oxidation tower. Thus, a configuration in which a final oxidation-reduction reaction is performed may be employed. Even in this case, hexavalent Se is converted into tetravalent Se in the absorption tower or the oxidation tower. In addition, as described above, in each of the above embodiments, the place where the treating agent A is charged may be one place of the wastewater treatment device 50.
This is because the slurry in the absorption tower or the cooling / dust removing tower of the desulfurization apparatus circulates to the wastewater treatment apparatus 50. Therefore, even if the treating agent A is supplied only in this wastewater treatment apparatus, the entire Se is insolubilized and treated. it can. Further, as a treating agent for insolubilizing Se, in addition to FeCl ₃ or Fe ₂ (SO ₄ ) ₃ , a chelating agent (for example, Miyoshi resin EPORAS MX-7)
Alternatively, a polymer heavy metal collector (for example, Miyoshi resin Epofloc L-1) or the like can be used.

[0055]

According to the flue gas treatment system according to the invention (1), Se removed from the flue gas together with dust can be heated.
Gas into the desulfurization unit and eventually convert all hexavalent to tetravalent
It can be treated as Se, and is insolubilized by a treating agent.
If only the process is performed, the Se elution standard can be easily cleared,
The absorption tower of the desulfurization unit can be used as a hexavalent Se reduction reaction facility
Since it functions, a separate reaction tower for reducing Se is provided.
Equipment configuration of the entire system is simpler than the above configuration
become.

[0056] Also, by separating Se from dust by the heating means so as to introduce into the desulfurization apparatus, since the entire dust has a configuration which is not introduced into the desulfurization apparatus, it becomes easier to reuse dust, desulfurizer In this case, adverse effects such as a decrease in desulfurization performance can be avoided.

According to the flue gas treatment system according to the invention (2) , the oxidation-reduction reaction control means reduces the total amount of hexavalent Se mixed in the slurry in the desulfurization unit with the sulfurous acid in the slurry to obtain tetravalent Se. The oxidation-reduction reaction of the slurry in the desulfurization device is controlled so that Therefore, hexavalent Se can be almost completely changed to tetravalent in the desulfurization apparatus, and the insolubilization treatment of Se in the flue gas can be performed more easily and completely.

According to the smoke exhaust treatment system of the invention (3) , the Se elution standard and the like can be easily cleared.
Since the desulfurization device also functions as a hexavalent Se reduction reaction facility, the equipment configuration of the entire system is simplified as compared with a configuration in which a reaction tower or the like for reducing Se is separately provided. Further, in this case, the gasified Se and the flue gas are introduced into the cooling and dust removing tower of the desulfurization unit and processed, and a large amount of impurities such as Se as well as dust are mixed in the slurry in the absorption tower of the desulfurization unit. Therefore, the desulfurization rate in the desulfurization device can be maintained high, and high-quality gypsum can be obtained.

According to the smoke exhaust treatment system of the invention (4) , only the dust separated and collected from the specific collection section on the smoke exhaust outlet side in the dust collecting means is heated, and only the gasified Se is thereby heated. By being introduced into the desulfurization apparatus and subjected to the insolubilization treatment, the required amount of the treatment agent, the capacity of the heating means, and the like can be reduced, and the detoxification of Se can be performed more easily and economically.

According to the flue gas treatment system according to the invention (5) , only the small particle size dust classified by the classification means is heated, and only the gasified Se is introduced into the desulfurization device and insolubilized. This makes it possible to reduce the required amount of the treatment agent, the capacity of the heating means, and the like, and it is possible to make Se harmless more easily and economically.

According to the exhaust gas treatment system of the invention (6), the heating temperature of the dust in the heating means is set to 100 to 120.
Since the temperature is set to 0 ° C., the gasified Se does not re-aggregate in the dust, so that Se can be efficiently removed from the dust, and the Se elution standard of the dust can be easily cleared.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a smoke exhaust treatment system according to a first embodiment.

FIG. 2 is a schematic configuration diagram of a flue gas treatment system according to a second embodiment.

FIG. 3 is a schematic configuration diagram of a smoke exhaust treatment system according to a third embodiment.

FIG. 4 is a schematic configuration diagram showing an example of a conventional flue gas treatment system.

FIG. 5 is a graph showing the relationship between the dust heating temperature and the Se concentration in the eluate in the dissolution test of Example 1.

FIG. 6 is a graph showing the relationship between the dust heating time and the Se concentration in the eluate in the dissolution test of Example 1.

[Explanation of symbols]

 5,70 Electric dust collector (dust collector) 11 Heating means 6,20,60 Desulfurizer 21 Absorption tower 40 Oxidation-reduction reaction control means 50 Wastewater treatment equipment 61 Cooling / dust removing tower 71-74 Hopper 81 Classifier 82 Fine ash collector A treatment agent

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsushi Atani 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd. Headquarters (72) Inventor Naohiko Ugawa 4-6-kannonshinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture No. 22 Mitsubishi Heavy Industries, Ltd.Hiroshima Research Center (72) Inventor Masao Hino 4--22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd.Hiroshima Research Center (72) Inventor Susumu Okino Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Hiroshima Research Institute, Mitsubishi Heavy Industries, Ltd. (Chapter 7) Inventor Takashi Haruki 4-62, Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd.Hiroshima Research Center (72) Inventor Toru Takashina Hiroshima Mitsubishi Heavy Industries, Ltd.Hiroshima Research Laboratory 4-62 Kanon Shinmachi, Nishi-ku, Hiroshima City (56) References JP-A-6-86966 (JP, A) JP-A-63-72340 (JP, A) JP-A-53-28596 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/34 B09B 3 / 00

Claims (6)

(57) [Claims] 1. Exhaust gas containing sulfur dioxide, dust and Se
A flue gas treatment system that treats
Dust collector to remove and absorbent to absorb and remove sulfurous acid gas
A desulfurization device having an absorption tower through which a slurry circulates, and
The dust removed by the device is converted into Se in the dust.
Heating means for heating to a temperature at which the heating means
The gas generated by heating the dust by the
Se was introduced into the desulfurization unit as Se.
Dissolve and collect in the slurry in the desulfurizer to treat the slurry
During the process, a treatment agent for insolubilizing tetravalent Se is mixed.
A flue gas treatment system characterized by the fact that: 2. Mixing into the slurry in the desulfurization unit
Hexavalent Se is reduced by sulfurous acid in the slurry to form 4
Oxidation-reduction reaction in the desulfurization unit so that
And a redox reaction control means for controlling the
The flue gas treatment system according to claim 1, wherein: 3. A flue gas containing sulfur dioxide, dust and Se.
A flue gas treatment system that treats
Dust collection device for removal and cooling and removal provided in the upstream of the absorption tower
Dust tower and absorbent slurry that absorbs and removes sulfur dioxide gas circulates
A desulfurization device having an absorbing tower that performs
The removed dust is heated to a temperature at which Se in the dust is gasified.
Heating means for heating, the heating means
The gas generated by heating the dust is discharged together with the smoke
Se is used as a component introduced into the cooling and dust removing tower of the sulfurizing device.
Dissolve and collect in the circulating fluid of the cooling and dust removing tower.
A treatment agent that insolubilizes tetravalent Se is mixed during the treatment process
A flue gas treatment system characterized by having a configuration as described above. 4. A dust collecting means for separating and collecting dust.
Multiple collections from the inlet to the outlet of the flue gas
That is collected from the collecting section on the inlet side of the flue gas
Dust and dust collected from the outlet side are separately separated and collected,
Only the dust separated and collected from the collection section on the exit side is
Claims characterized in that it is configured to be introduced into heating means
Item 4. The exhaust gas treatment system according to any one of Items 1 to 3. 5. The dust separated by the dust collecting means,
Set up a classification means to classify large and small particle sizes.
Only the small particle size dust classified by this classification means
Is introduced into the heating means.
The flue gas treatment system according to any one of claims 1 to 3,
Tem. 6. The heating means removes dust from 100 to 120.
Heating to a temperature of 0 ° C.
Item 6. The smoke exhaust treatment system according to any one of Items 1 to 5.