JP2003154377A - Desulfurization wastewater treatment method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a desulfurization wastewater treatment method and apparatus capable of reducing the amount of consumption of caustic soda for adjusting pH necessary for separating and removing heavy metals to eliminate waste and capable of reducing the sludge amount of magnesium hydroxide to also dispense with the treatment of the sludge of magnesium hydroxide. SOLUTION: The pH value of desulfurization wastewater is adjusted to 8.5 or less and heavy metals are separated and removed as a solid by sulfide.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a desulfurization wastewater treatment method and apparatus.

[0002]

2. Description of the Related Art Generally, coal-fired boilers are used in power plants.
SO from the exhaust gas emitted from the ₂(Sulfur oxides)
Calcium carbonate as an absorbent to absorb and remove
(CaCO₃Wet flue gas desulfurization equipment using
However, the wet flue gas desulfurization apparatus is generally shown in FIG.
At the bottom, a liquid reservoir 1a for the absorbing liquid 1 is formed and at the top
An absorption tower 3 provided with a large number of spray nozzles 2 and the absorption tower 3
The above-mentioned spray for drawing up the absorbing liquid 1 in the liquid reservoir 1a of the collecting tower 3
Multiple circulation pumps that circulate by spraying from the nozzle 2.
4, and oxidizing air is supplied to the liquid reservoir 1a of the absorption tower 3.
Remove from the oxidizing air blower 5 and the liquid reservoir 1a of the absorption tower 3
Gypsum recovery device that recovers gypsum 10 from the absorbent 1 that is discharged
Place 40 and the gypsum dispenser 40
Gypsum silo that stores the gypsum 10 dispensed by the bayer 50
And 60.

The gypsum recovery device 40 has the absorption liquid 1 extracted from the liquid storage portion 1a of the absorption tower 3 through the extraction line 6.
A gypsum separator supply tank 7 in which a neutralizing agent such as caustic soda (NaOH) is added, and an absorption liquid 8 neutralized in the gypsum separator supply tank 7 is introduced through a neutralization absorption liquid line 9, A belt filter type gypsum separator 11 for separating the gypsum 10 by dehydrating a slurry containing solids in the absorbing liquid 8 by operating a vacuum pump 12, a filtrate 14 separated from the gypsum 10 by the gypsum separator 11, and the like. And a gypsum separator filtrate tank 13 into which is introduced.

In the gypsum separator 11, an endless belt filter 21 is wound around guide rolls 20 which are rotatably arranged at required intervals, and the belt filters 21 are rotated in a desired direction by a rotational drive. To a desired position on the upstream side of the belt filter 21 from the gypsum separator supply tank 7 in a state in which the lower surface side of the belt filter 21 is held at a negative pressure via the vacuum tank 22 by the operation of the vacuum pump 12. The absorption liquid 8 of the above is dehydrated to separate it into the gypsum 10 and the filtrate 14, and the operation of the vacuum pump 12 causes the gypsum 10 to be separated.
The filtrate 14 thus separated has a high chlorine concentration, and therefore is introduced into the high chlorine concentration filtrate storage section 27 divided by the partition wall 26 of the gypsum separator filtrate tank 13 via the filtrate line 15. Further, the belt filter 2 of the gypsum separator 11
At a required position on the downstream side of 1, the washing water 16 such as industrial water is made to flow down from the washing water line 17, and the lower surface side of the belt filter 21 is made a negative pressure through the vacuum tank 23 by the operation of the vacuum pump 12. By holding the dehydrated gypsum 10 and washing the gypsum 10, the chlorine-diluted filtrate 18 is passed through the filtrate line 19 to the partition wall 26 of the gypsum separator filtrate tank 13 through the filtrate line 19. It is adapted to be introduced into the divided chlorine-diluted filtrate storage section 28.

It is necessary to supply sealing water 24 such as industrial water for holding vacuum to the vacuum pump 12, and the water used as the sealing water 24 of the vacuum pump 12 is supplied through the sealing water line 25 as described above. The gypsum separator is introduced into the chlorine-diluted filtrate storage section 28 of the filtrate tank 13.

The filtrate 32 containing the filtrate 18 introduced into the chlorine-diluted filtrate storage portion 28 of the gypsum separator filtrate tank 13 and the water used as the sealing water 24 of the vacuum pump 12 is
The liquid level is returned to the absorption tower 3 through a recovery line 31 provided with a flow rate adjusting valve 33 on the way, and the liquid level is stored in the chlorine content diluted filtrate storage section 28 of the gypsum separator filtrate tank 13. A level indicating controller 29 is provided which outputs an opening degree command 30 for holding the set value to the flow rate adjusting valve 33.

In FIG. 2, 34 is the filtrate 14 introduced into the high chlorine concentration filtrate storage section 27 of the gypsum separator filtrate tank 13.
A discharge line for discharging the wastewater to the wastewater treatment device 35, 36
Is an absorbent slurry supply line for supplying a required amount of absorbent slurry to the absorption tower 3 as needed.

In the case of the wet flue gas desulfurization apparatus as described above, the absorbing liquid 1 is circulated while being sprayed from the spray nozzle 2 by the operation of the circulation pump 4, and a gas gas heater heat recovery unit and an electrostatic precipitator are supplied from a boiler (not shown). The exhaust gas sent to the absorption tower 3 through the operation of the induced draft blower comes into contact with the absorbing liquid 1 sprayed from the spray nozzle 2 to absorb and remove SO ₂ (sulfur oxide), The gas is discharged to the flue 70 on the outlet side of the absorption tower 3, and discharged from the chimney to the atmosphere via a gas gas heater reheater (not shown).

On the other hand, the absorbing liquid 1 which has absorbed SO ₂ from the exhaust gas is dropped into the liquid reservoir 1a and is forcibly oxidized by the oxidizing air supplied into the liquid reservoir 1a by the operation of the oxidizing air blower 5. , Gypsum (calcium sulfate (CaS
O ₄ )) is generated, and a part of the absorbing liquid 1 in the liquid reservoir 1 a containing the gypsum is withdrawn to the gypsum separator supply tank 7 through the extraction line 6, and the gypsum separator supply tank In 7, the absorption liquid 8 neutralized with a neutralizing agent such as caustic soda (NaOH) and neutralized in the gypsum separator supply tank 7 is introduced into the gypsum separator 11 via the neutralization absorption liquid line 9. The gypsum separator 11 is dehydrated by the operation of the vacuum pump 12 to be separated into the gypsum 10 and the filtrate 14, and the vacuum pump 1
The filtrate 14 separated from the gypsum 10 by the operation of 2 is introduced into the high chlorine concentration filtrate storage portion 27 of the gypsum separator filtrate tank 13 through the filtrate line 15, and the gypsum 10 dehydrated by the gypsum separator 11 is also used. Is washed with wash water 16 such as industrial water that has flowed down from the wash water line 17, and the gypsum 10
The filtrate 18 in which the chlorine content is diluted after being washed is introduced into the chlorine content diluted filtrate storage section 28 of the gypsum separator filtrate tank 13 through the filtrate line 19.

Further, the vacuum pump 12 is supplied with sealing water 24 such as industrial water for holding vacuum, and the water used as the sealing water 24 of the vacuum pump 12 is passed through the sealing water line 25 to It is introduced into the chlorine-diluted filtrate storage section 28 of the gypsum separator filtrate tank 13.

The liquid level of the chlorine-diluted filtrate storage section 28 of the gypsum separator filtrate tank 13 is detected by a level indicating controller 29, and the level command 30 output from the level indicating controller 29 determines the liquid level. The opening degree of the flow rate adjusting valve 33 is adjusted to include the filtrate 18 introduced into the chlorine-diluted filtrate storage section 28 of the gypsum separator filtrate tank 13 and the water used as the sealing water 24 of the vacuum pump 12. The filtrate 32
The liquid level is appropriately returned to the absorption tower 3 via the recovery line 31, whereby the liquid level of the chlorine-diluted filtrate storage section 28 of the gypsum separator filtrate tank 13 is maintained at the set value.

Further, the filtrate 14 introduced into the high chlorine concentration filtrate storage section 27 of the gypsum separator filtrate tank 13 is drained,
It is discharged to the wastewater treatment equipment 35 through the discharge line 34,
In the wastewater treatment device 35, harmful nitrogen compounds are decomposed by the action of nitrifying bacteria, and reducing substances represented by COD (chemical oxygen demand) are adsorbed and removed by an adsorption resin made of a polymer material, and then externally Is released to.

Incidentally, manganese (Mn) and cadmium (C) contained in the wastewater sent to the wastewater treatment equipment 35.
Heavy metals such as d) and lead (Pb) are caustic soda (NaO).
H) raises the pH value to about 9 to 11 to generate hydroxide as a solid content, which is then removed by solid-liquid separation. Here, when an n-valent metal ion is represented by M ^{n +} , the reaction in which the heavy metal becomes a hydroxide is

[Chemical 1] It is represented by the reaction formula.

On the other hand, the absorber 3 is supplied with a required amount of the absorber slurry from the absorber slurry supply line 36 as needed.

[0015]

However, as described above, in the waste water treatment equipment 35 in which the heavy metal contained in the waste water is solid-liquid separated as a solid content by adjusting the pH value with caustic soda (NaOH), When the purity of calcium carbonate (CaCO ₃ ) as the absorbent is not so high and magnesium (Mg) is contained as an impurity, the magnesium concentration in the waste water becomes high (several thousands to 30,000 [mg / l]), and caustic soda for pH adjustment

As shown by the reaction formula such as 2NaOH + Mg ²⁺ → Mg (OH) ₂ (↓ white solid), it is consumed to produce solid magnesium hydroxide (Mg (OH) ₂ ), As a result, the consumption of caustic soda increases and waste increases, and the amount of sludge of magnesium hydroxide increases, which necessitates treatment. The reaction represented by the reaction formula [Chemical Formula 2] has been confirmed by a test actually conducted by the inventors of the present invention to rapidly progress at a pH value of around 8.5.

In view of such circumstances, the present invention can reduce the consumption of caustic soda for pH adjustment required for separating and removing heavy metals to eliminate waste, and reduce the amount of magnesium hydroxide sludge. An object of the present invention is to provide a desulfurization wastewater treatment method and apparatus that can eliminate the need for such treatment.

[0017]

SUMMARY OF THE INVENTION The present invention is designed to remove the p
The present invention relates to a desulfurization wastewater treatment method characterized in that the H value is suppressed to 8.5 or less and the heavy metal is separated and removed as a solid content by a sulfide.

Further, according to the present invention, the pH value of the desulfurization wastewater is 8.5.
By supplying a sulfide to the pH adjusting means to be suppressed below and to the desulfurization wastewater having a pH value suppressed to 8.5 or less by the pH adjusting means, a reaction in which the heavy metal contained in the desulfurization wastewater becomes a solid content is performed. The present invention relates to a desulfurization wastewater treatment apparatus comprising: .

According to the above means, the following effects can be obtained.

When the pH value of the desulfurization effluent is suppressed to 8.5 or less, the purity of calcium carbonate (CaCO ₃ ) as an absorbent is not so high, magnesium (Mg) is contained as an impurity, and the magnesium in the effluent is Even if the concentration is high, the caustic soda for pH adjustment is no longer consumed because it produces solid magnesium hydroxide (Mg (OH) ₂ ), and the consumption of caustic soda does not increase and waste is eliminated. The sludge amount does not increase and the treatment is not necessary. Even if the pH value of desulfurization wastewater is suppressed to 8.5 or less, heavy metals are separated and removed as solids by sulfides, so the concentration of heavy metals in wastewater is regulated. There is no worry of exceeding the density value.

In the desulfurization wastewater treatment method and apparatus, the sulfide may be trimercapto-S-triazine.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an embodiment of the present invention, in which a wastewater treatment device 35 is constructed so that the pH value of desulfurization wastewater is suppressed to 8.5 or less, and heavy metals are separated and removed as solids by sulfides. It was done.

In the case of this illustrated example, the wastewater treatment device 35
The desulfurization wastewater is introduced, and the pH value of the desulfurization wastewater is adjusted to 8 by adjusting the opening degree of the valve 82 based on the pH value 81 of the desulfurization wastewater detected by the pH meter 80 to adjust the supply amount of caustic soda. A pH adjusting tank 83 for suppressing the pH value to 5 or less, and desulfurization wastewater having a pH value 81 suppressed to 8.5 or less by the pH adjusting tank 83 are introduced, and required based on the flow rate 85 of the desulfurization wastewater detected by the flow meter 84. A reaction tank 86 for supplying a quantity of sulfide to carry out a reaction in which the heavy metal contained in the desulfurization wastewater is used as a solid content, and a desulfurization wastewater made into a solid content by reacting with the sulfide in the reaction tank 86. Of the heavy metal of FIG. There is introduced desulfurization effluent of supernatant that is sedimentation, pH meter 89 based on the pH value 90 of the desulfurization effluent to be detected by performing the opening degree adjustment of the valve 91 sulfuric acid (H
₂ SO ₄ ) is adjusted to adjust the p
A pH adjusting discharge tank 92 for setting the H value 90 to 7 and discharging is provided.

In the waste water treatment device 35, a device for performing a step of decomposing harmful nitrogen compounds by the action of nitrifying bacteria and a reducing substance represented by COD (chemical oxygen demand) are made of a polymer material. Equipment and the like for performing the step of adsorbing and removing with the adsorbent resin are omitted in FIG. 1.

On the other hand, as the sulfide,

[Chemical 3] The trimercapto-S-triazine (trimercapto-s-triazine, trisodium salt) represented by the following chemical formula can be adopted, and as a specific example, the portion of X in the chemical formula of [Chemical Formula 3] is, for example,

[Chemical 4] Sodium (Na) as shown by the chemical formula, or the portion of X in the chemical formula of [Chemical Formula 3] is, for example,

[Chemical 5] Hydrogen (H) as shown by the chemical formula can be used.

Next, the operation of the illustrated example will be described.

When desulfurization wastewater is introduced into the pH adjusting tank 83 of the wastewater treatment device 35, the opening degree of the valve 82 is adjusted based on the pH value 81 of the desulfurization wastewater detected by the pH meter 80 to supply caustic soda. The amount is adjusted, whereby the pH value of the desulfurization wastewater in the pH adjusting tank 83 is suppressed to 8.5 or less.

The pH value 81 in the pH adjusting tank 83 is 8.5.
The desulfurization wastewater suppressed below is introduced into the reaction tank 86,
In the reaction tank 86, by supplying a required amount of sulfide based on the flow rate 85 of the desulfurization wastewater detected by the flowmeter 84, a reaction in which the heavy metal contained in the desulfurization wastewater is made into a solid content is performed.

Here, the heavy metal is due to sulfide.

[Chemical 6] Reacts as shown by the reaction formula to form a solid content. It has been confirmed in an actually conducted test that the supply amount of sulfide should be set to about 50 mg with respect to 1 [l] of desulfurization wastewater.

The heavy metal in the desulfurization effluent made solid by reacting with sulfide in the reaction tank 86 is thickener 8
The solid content (sulfide containing heavy metal) separated by sedimentation in 7 and separated by the thickener 87 is collected by squeezing out water in the filter press 88.

On the other hand, the supernatant desulfurization wastewater from which heavy metals have been settled and separated by the thickener 87 is introduced into the pH adjusting discharge tank 92, and in the pH adjusting discharge tank 92, the pH of the desulfurization wastewater detected by the pH meter 89. By adjusting the opening of the valve 91 based on the value 90 and adjusting the supply amount of sulfuric acid (H ₂ SO ₄ ), the pH value 90 of the desulfurization effluent was set to 7, neutralized and cleaned. Desulfurization wastewater is discharged.

As described above, when the pH value of desulfurization wastewater is suppressed to 8.5 or less, calcium carbonate (CaC) as an absorbent is obtained.
The purity of O ₃ ) is not so high that magnesium (Mg)
Is contained as an impurity, and even if the magnesium concentration in the waste water is high, the reaction as shown in the reaction formula of [Chemical Formula 2] becomes difficult to occur, and caustic soda for pH adjustment is solid magnesium hydroxide (Mg (OH) ₂ ) is not consumed to generate it, the consumption of caustic soda does not increase and waste is eliminated, and the amount of sludge of magnesium hydroxide does not increase and its treatment becomes unnecessary.

Further, as described above, the pH value of the desulfurization wastewater is set to 8.
Even if it is suppressed to 5 or less, the heavy metal reacts with the sulfide as shown in the reaction formula of [Chemical formula 6], and is separated and removed as a solid content, so there is a concern that the concentration of heavy metal in the wastewater may exceed the regulated concentration value. Nor.

In an actual test, it was confirmed that heavy metals such as manganese (Mn), cadmium (Cd) and lead (Pb) can be separated and removed as solids by trimercapto-S-triazine even in the vicinity of pH = 7. Has been done.

Thus, the pH required for separation and removal of heavy metals is
The amount of caustic soda used for adjustment can be reduced to eliminate waste, and the amount of sludge of magnesium hydroxide can be reduced to eliminate the treatment.

The desulfurization wastewater treatment method and apparatus of the present invention are not limited to the above-described illustrated examples, and it goes without saying that various modifications can be made without departing from the scope of the present invention.

[0038]

As described above, according to the desulfurization wastewater treatment method and apparatus of the present invention, the consumption of caustic soda for pH adjustment necessary for separating and removing heavy metals can be reduced and waste can be eliminated. The excellent effect that the amount of sludge of magnesium hydroxide can be reduced and the treatment thereof can be omitted can be achieved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an embodiment of the present invention.

FIG. 2 is an overall schematic configuration diagram of a general wet flue gas desulfurization apparatus.

[Explanation of symbols]

35 Wastewater treatment equipment 80 pH meter 81 pH value 82 valve 83 pH adjusting tank (pH adjusting means) 84 Flowmeter 85 flow rate 86 Reaction tank (reaction means) 87 thickener (separation and removal means) 88 Filter press (separation and removal means) 89 pH meter 90 pH value 91 valve 92 pH adjusting discharge tank

Continued front page    (72) Inventor Eisuke Miyamatsu             3-2-16 Toyosu, Koto-ku, Tokyo Ishikawajima             Harima Heavy Industries Tokyo Engineering Co., Ltd.             In the center F-term (reference) 4D002 AA02 AC01 BA02 CA01 DA05                       DA16 EA07 FA03 GA01 GA02                       GB09 HA10                 4D038 AA08 AB66 AB71 AB74 AB81                       BA04 BB13 BB17 BB18

Claims (4)

[Claims] 1. The pH value of desulfurization effluent is suppressed to 8.5 or less,
A desulfurization wastewater treatment method, characterized in that heavy metals are separated and removed as solids by sulfides. 2. The desulfurization wastewater treatment method according to claim 1, wherein the sulfide is trimercapto-S-triazine. 3. Desulfurization by supplying a sulfide to the desulfurization effluent whose pH value is suppressed to 8.5 or less by the pH adjusting means for suppressing the pH value of the desulfurization effluent to 8.5 or less. The reactor was provided with a reaction means for carrying out a reaction of solidifying heavy metals contained in the wastewater, and a separating and removing means for separating and removing the heavy metals in the desulfurization wastewater made solid by reacting with the sulfide by the reaction means. A desulfurization wastewater treatment device characterized by the above. 4. The desulfurization wastewater treatment device according to claim 3, wherein the sulfide is trimercapto-S-triazine.