JP2012020216A - Wet-type apparatus for desulfurizing flue gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wet-type apparatus and a wet-type method for desulfurizing a flue gas, capable of preventing the deterioration of the dehydration capability thereof caused by low-quality limestone.SOLUTION: A flue gas and a liquid absorbent containing an alkaline desulfurization agent are made to contact with each other to allow the liquid absorbent to absorb a sulfur oxide present in the flue gas to remove a harmful substance composed of the sulfur oxide present in the flue gas discharged from a combustion apparatus. Air is fed into the liquid absorbent containing a sulfite ion resulting from absorbing the sulfur oxide present in the flue gas, to produce gypsum therefrom. The pH of the liquid absorbent containing gypsum is controlled lower than 5 to dissolve aluminum sludge or Al(OH)and iron sludge or Fe(OH)present therein, whereby gypsum is easily dehydrated. The pH of solid gypsum can be controlled by washing the gypsum with alkaline cleaning water during its dehydration treatment.

Description

The present invention relates to an exhaust gas treatment apparatus that removes sulfur dioxide (SO ₂ ) in exhaust gas discharged from a combustion apparatus such as a boiler.

In a thermal power plant and the like, a limestone-gypsum method wet method is mainly used as a desulfurization system for removing sulfur oxides in flue gas generated by combustion of fossil fuel.
FIG. 4 shows a side view of an absorption tower constituting the desulfurization apparatus as a known example of the wet flue gas desulfurization apparatus adopting the spray system of the prior art (see Japanese Patent Application Laid-Open No. 2005-152745). This wet flue gas desulfurization apparatus mainly includes an absorption tower body 1, an inlet duct 2, an outlet duct 3, an absorbing liquid circulation pump 4, a circulating tank 6, a stirrer 7, an air supply pipe 8, a mist eliminator 9, and an absorbing liquid extraction pipe 10. , A circulation pipe 11, a spray header 12, a spray nozzle 13, and the like.

  The desulfurization apparatus has an absorption tower main body provided with an inlet duct 2 for introducing exhaust gas from a combustion apparatus (not shown) in a substantially horizontal direction and an outlet duct 3 for discharging exhaust gas in a substantially horizontal direction on the opposite side walls above the circulation tank 6. 1 There is an exhaust gas passage in the space inside the absorption tower body 1 between the inlet duct 2 and the outlet duct 3, and the exhaust gas flowing in from the inlet duct 2 is a plurality of spray nozzles of the spray header 12 in the process of ascending the exhaust passage. Desulfurized in contact with the absorbent sprayed from 13, removed by mist eliminator 9 disposed in outlet duct 3, and then discharged into the atmosphere.

Sulfur oxide in the exhaust gas is absorbed by the absorbent and falls into the circulation tank 6. Sulfurous acid generated in the absorbing solution that has absorbed SO ₂ in the exhaust gas in the circulation tank 6 is oxidized by the air supplied from the air supply pipe 8 and is discharged from the desulfurization apparatus as gypsum. At this time, the air supplied from the air supply pipe 8 into the absorption liquid is stirred by the stirrer 7 to promote air oxidation of sulfurous acid.

A part of the absorption liquid in the circulation tank 6 is supplied to the spray header 12 by the pump 4 via the circulation pipe 11.
A part of the absorption liquid in the circulation tank 6 is extracted by the pump 18 from the extraction pipe 10, sent to a gypsum dehydrator (belt filter) 14, and dehydrated, and the gypsum in the absorption liquid is recovered as solid gypsum. .

JP 2005-152745 A JP 2003-236333 A

The conditions required in recent wet flue gas desulfurization equipment projects are equipment that can flexibly cope with various coal types, operating conditions, and design conditions. In particular, in recent years, the quality of limestone used as a desulfurizing agent has to be low, and due to the influence of Al (aluminum) salts and iron salts mixed in as impurities, there is a problem that the gypsum dewaterability is reduced. is there.
The subject of this invention is providing the waste gas processing apparatus and method which prevent the dehydration performance fall resulting from using low grade limestone.

The above problem is solved by the following means.
The invention according to claim 1 is an exhaust gas treatment apparatus for removing harmful substances including sulfur oxides in exhaust gas discharged from a combustion apparatus such as a boiler, and makes an absorption liquid containing an alkali desulfurizing agent and the exhaust gas come into gas-liquid contact. By absorbing the sulfur oxide in the exhaust gas into the absorption liquid and supplying the air to the absorption liquid containing sulfite ions arranged in the lower part of the absorption tower, the absorption liquid is stored while generating gypsum A circulation tank, a gypsum dehydrator that dehydrates and separates gypsum in the absorption liquid discharged from the circulation tank, and a pH adjustment tank that adjusts the pH of the gypsum-containing absorption liquid supplied to the gypsum dehydrator are provided. This is an exhaust gas treatment apparatus.

  A second aspect of the present invention is the exhaust gas treatment apparatus according to the first aspect, wherein an alkaline cleaning liquid tank is provided for spraying the alkaline cleaning liquid onto the gypsum of the gypsum dehydrator.

  According to a third aspect of the present invention, there is provided an exhaust gas treatment method for removing harmful substances including sulfur oxides in exhaust gas discharged from a combustion apparatus such as a boiler, wherein an absorption liquid containing an alkali desulfurizing agent and the exhaust gas are brought into gas-liquid contact. By absorbing the sulfur oxide in the exhaust gas into the absorption liquid, absorbing the sulfur oxide in the exhaust gas and supplying air to the absorption liquid containing sulfite ions to generate gypsum, the absorption liquid containing gypsum The exhaust gas treatment method is characterized in that the pH is adjusted and the gypsum is dehydrated and separated from the absorbing solution containing the gypsum whose pH is adjusted.

  The invention according to claim 4 is the exhaust gas treatment method according to claim 3, wherein the pH of the absorbent containing gypsum is adjusted to less than 5 by adjusting the pH.

The invention according to claim 5 is characterized in that the pH of the absorbent is adjusted so as to dissolve aluminum sludge Al (OH) ₃ and iron sludge Fe (OH) ₃ in the absorbent containing gypsum. 3. The exhaust gas treatment method according to 3.

  The invention according to claim 6 is the exhaust gas treatment method according to claim 3, wherein the gypsum is washed with an alkaline washing water when the gypsum is separated from the absorption liquid containing the gypsum whose pH is adjusted and dehydrated. is there.

  According to the first and third aspects of the present invention, the dehydration performance of gypsum derived from limestone, which is a desulfurization agent, is deteriorated, and the gypsum is separated from the absorption liquid even if the aluminum salt and iron salt are contained in the absorption liquid. Processing performance does not deteriorate.

  According to the invention described in claim 4, by making the pH of the absorbent containing gypsum less than 5, the dehydration performance of gypsum becomes equivalent to the case where the absorbent does not contain aluminum salt and iron salt.

The invention according to claim 5 is a dehydration treatment of gypsum by adjusting the pH of the absorbent so as to dissolve aluminum sludge Al (OH) ₃ and iron sludge Fe (OH) ₃ in the absorbent containing gypsum. The performance is equivalent to the case where aluminum salt and iron salt are not contained in the absorbing solution.

  According to the second and sixth aspects of the invention, the pH of the solid gypsum dehydrated by alkali washing can be adjusted.

It is an Example by this invention, and shows the system which provided the pH adjustment tank between the circulation tank and the gypsum dehydrator in the wet desulfurization apparatus. The example by this invention is applied and the change of the gypsum moisture concentration when changing absorption liquid pH is represented. FIG. 4 shows another embodiment of the present invention, and shows a system in which an alkaline cleaning liquid spray is installed in a gypsum dehydrator in the embodiment shown in FIG. 1 shows a wet flue gas desulfurization system employing a spray system of the prior art.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing a wet desulfurization system of this embodiment, and shows a system in which a pH adjusting tank is provided on the upstream side of a gypsum dewatering machine.
The wet flue gas desulfurization apparatus shown in FIG. 1 is mainly similar to the apparatus shown in FIG. 4, mainly an absorption tower main body 1, an inlet duct 2, an outlet duct 3, an absorbing liquid circulation pump 4, a circulation tank 6, a stirrer 7, an air supply. The pipe 8, the mist eliminator 9, the absorption liquid extraction pipe 10, the circulation pipe 11, the spray header 12, the spray nozzle 13, and the like.

  An absorption tower body 1 having an inlet duct 2 for introducing exhaust gas from a combustion apparatus (not shown) in a substantially horizontal direction and an outlet duct 3 for discharging the exhaust gas in a substantially horizontal direction on opposite side walls is provided above the circulation tank 6. There is an exhaust gas passage in the space inside the absorption tower main body 1 between the inlet duct 2 and the outlet duct 3, and the exhaust gas flowing in from the inlet duct 2 is provided in the spray header 12 in the process of ascending the exhaust gas passage. It is desulfurized in contact with the absorbent 5 sprayed from the plurality of spray nozzles 13, and is discharged into the atmosphere after the mist is removed by the mist eliminator 9 disposed in the outlet duct 3.

Sulfur oxide in the exhaust gas is absorbed by the absorbent and falls into the circulation tank 6. Sulfurous acid generated in the absorbing solution that has absorbed SO ₂ in the exhaust gas in the circulation tank 6 is oxidized by the air supplied from the air supply pipe 8 and is discharged from the desulfurization apparatus as gypsum. At this time, the air supplied from the air supply pipe 8 into the absorption liquid is stirred by the stirrer 7 to promote air oxidation of sulfurous acid.

A part of the absorption liquid in the circulation tank 6 is supplied to the spray header 12 by the pump 4 via the circulation pipe 11.
A part of the absorption liquid in the circulation tank 6 is extracted from the extraction pipe 10 by a pump 18 and sent to a gypsum dehydrator (belt filter) 14 for dehydration. The gypsum in the absorption liquid is recovered as solid gypsum 15. The

After the absorption liquid 5 is sprayed from the spray nozzle 13, it falls into the circulation tank 6, is again sucked into the circulation pump 4, is supplied to the spray header 12 via the circulation pipe 11, and is sprayed again into the absorption tower. The absorbent 5 is circulated in the desulfurization system.
At this time, aluminum salt and iron salt may be mixed in the desulfurization system due to dust contained in the exhaust gas in a trace amount. The mixed aluminum salt and iron salt are concentrated in the absorbent 5 circulating in the system. Although the salt in the absorbent 5 is once dissolved as Al ³⁺ and Fe ³⁺ , it is precipitated as Al (OH) ₃ and Fe (OH) ₃ in the pH range (about 5 to 6) in the absorbent 5. To do. These precipitated aluminum and iron sludge are sent to the gypsum dewatering machine 14 from the absorption liquid extraction pipe 10 along with gypsum generated by air oxidation of the sulfite in the absorption liquid.

In the gypsum dewatering machine 14, aluminum and iron sludge are also dehydrated and collected together with the solid gypsum 15. However, since the aluminum and iron sludge contains a large amount of moisture even in the dewatering, the resulting solid is obtained. Gypsum also contains a lot of moisture. In order to reduce the moisture, a pH adjusting tank 16 is installed in the embodiment shown in FIG. The absorbing solution 5 extracted from the circulation tank 6 is sent to a pH adjusting tank 16 and an acid such as dilute sulfuric acid is added to adjust the pH of the absorbing solution. When the absorbing solution is acidified in the pH adjusting tank 16, the aluminum sludge Al (OH) ₃ and Fe (OH) ₃ are dissolved again in the absorbing solution to become Al ³⁺ and Fe ³⁺ , and the dewatering performance is improved.

  FIG. 2 shows the absorption liquid pH and the water content in the obtained gypsum, and it can be seen that the dehydration performance is restored by adjusting the pH to less than 5 in the pH adjustment tank 16.

  FIG. 3 is a schematic diagram showing the wet desulfurization system of the second embodiment, and is an embodiment in which the alkaline cleaning liquid from the alkaline tank 17 is sprayed in the gypsum dehydrator 14. The configuration other than the configuration for supplying the alkaline cleaning liquid from the alkaline tank 17 to the gypsum dewatering machine 14 is the same as that described in the first embodiment, and the same reference numerals as those in FIG. .

  When the absorption liquid acidified in the pH adjustment tank 16 shown in FIG. 3 is dehydrated by the gypsum dehydrator 14, the resulting solid gypsum 15 is also acidic. Reusing this acidic solid gypsum may be harmful. Therefore, it is possible to adjust the pH of the solid gypsum by spraying the alkaline washing liquid from the alkali tank 17 onto the solid gypsum in the gypsum dehydrator 14.

  When limestone contains a large amount of aluminum and iron, the problem of reduced dehydration performance of the gypsum-containing absorbent solution is solved, and thus the industrial applicability is high.

DESCRIPTION OF SYMBOLS 1 Absorption tower body 2 Inlet duct 3 Outlet duct 4 Absorption liquid circulation pump 5 Absorption liquid 6 Circulation tank 7 Stirrer 8 Air supply pipe 9 Mist eliminator 10 Absorption liquid extraction pipe 11 Circulation pipe 12 Spray header 13 Spray nozzle 14 Gypsum dehydrator 15 Gypsum 16 pH Adjustment tank 17 Alkali tank 18 Pump

Claims (6)

In exhaust gas treatment equipment that removes harmful substances including sulfur oxides in exhaust gas discharged from combustion equipment such as boilers,
An absorption tower for absorbing the sulfur oxide in the exhaust gas into the absorption liquid by gas-liquid contact between the absorption liquid containing the alkali desulfurization agent and the exhaust gas; and
A circulation tank for storing the absorption liquid while supplying air to the absorption liquid containing sulfite ions disposed in the lower part of the absorption tower and generating gypsum;
A gypsum dewatering machine that separates and dehydrates gypsum in the absorbent discharged from the circulation tank;
An exhaust gas treatment apparatus provided with a pH adjustment tank for adjusting the pH of the gypsum-containing absorbent supplied to the gypsum dehydrator.   2. The exhaust gas treatment apparatus according to claim 1, further comprising an alkaline cleaning liquid tank for spraying the alkaline cleaning liquid on the gypsum of the gypsum dehydrator. In an exhaust gas treatment method for removing harmful substances including sulfur oxides in exhaust gas discharged from a combustion device such as a boiler,
By making gas-liquid contact between the absorption liquid containing an alkali desulfurizing agent and the exhaust gas, the sulfur oxide in the exhaust gas is absorbed in the absorption liquid,
Absorbs sulfur oxides in the exhaust gas and supplies air to the absorbent containing sulfite ions to produce gypsum,
Adjust the pH of the absorbent containing gypsum,
An exhaust gas treatment method, wherein gypsum is separated from an absorption liquid containing gypsum whose pH is adjusted and dehydrated.   The exhaust gas treatment method according to claim 3, wherein the pH of the absorbent containing gypsum is adjusted to less than 5 by adjusting the pH. 4. The exhaust gas treatment method according to claim 3, wherein the pH of the absorbent is adjusted so as to dissolve aluminum sludge Al (OH) ₃ and iron sludge Fe (OH) ₃ in the absorbent containing gypsum.   4. The exhaust gas treatment method according to claim 3, wherein the gypsum is washed with an alkaline washing water when the gypsum is separated from the absorption liquid containing the gypsum whose pH is adjusted and dehydrated.

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