JP2009095699A - Method for treating unreacted slurry in flue gas desulfurizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form high-purity gypsum by restoration to a normal slurry state within a short time when an unreacted slurry is formed. <P>SOLUTION: In forming gypsum by forming calcium sulfite from sulfur oxides contained in a flue gas discharged from a boiler 1 in, e.g., a thermal power station by treatment with a limestone slurry and oxidizing the calcium sulfite formed in an absorption tower 3 in an oxidation tower 4, a normal slurry state is restored by preventing the formation of an unreacted slurry by charging a limestone slurry into the absorption tower 3 while controlling the pH in the absorption tower 3, feeding oxygen into the oxidation tower 4 so as to optimize the gypsum slurry concentration in the oxidation tower 4, and altering the starting conditions of a gypsum concentration tank 5 and of a centrifuge 13. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a technology for removing sulfur oxides contained in exhaust gas discharged from a thermal power plant or the like, and in particular, exhaust gas that is restored to a normal slurry state when unreacted slurry is generated during the desulfurization treatment process. The present invention relates to a method for treating unreacted slurry in a desulfurization apparatus.

Sulfur oxides (SO _x ) are contained in the combustion exhaust gas of thermal power plants, particularly coal-fired power plants. Usually, the desulfurization unit in the equipment is provided, are discharged through a stack is treated to reduce the SO _x concentration.

  For example, as shown in the system diagram of FIG. 5, the main facilities of the exhaust gas desulfurization apparatus are a cooling tower 2 for cooling the exhaust gas discharged from the boiler 1 in a thermal power plant or the like, and sulfur contained in the cooled exhaust gas. It comprises an absorption tower 3 storing limestone slurry for removing oxides, an oxidation tower 4 for oxidizing calcium sulfite produced in the absorption tower 3, and a gypsum concentration tank 5 for treating the produced gypsum.

  In such an exhaust gas desulfurization apparatus, the exhaust gas discharged from the boiler 1 is sent to the cooling tower 2 through the exhaust gas passage. In this exhaust gas flow path, an induction fan and a desulfurization fan are provided downstream of the boiler 1. A gas reheater (GGH) for exchanging heat of the exhaust gas is provided between the desulfurization ventilator and the cooling tower 2.

  Also, a mist eliminator that removes steam is disposed between the exhaust gas flow path connected to the absorption tower 3 and the gas reheater (GGH), and the exhaust gas after heat recovery is discharged from the chimney 6 to the atmosphere. ing.

Next, the sulfur component in the exhaust gas is removed from the exhaust gas flowing into the absorption tower 3 in the absorption tower 3. The absorption tower 3 is provided with a limestone supply equipment 7 for supplying a slurry of the absorption agent calcium carbonate (CaCO ₃₎ were mixed in water. At this time, in the absorption tower 3, a chemical reaction represented by the chemical formula of Chemical Formula 1 occurs between calcium carbonate supplied by the limestone supply facility 7 and sulfur dioxide (SO ₂ ) in the exhaust gas, and calcium sulfite ( CaSO ₃ .1 / 2H ₂ O) is produced.

  The calcium sulfite produced in the absorption tower 3 flows into the reaction tank 10 through the absorption tower circulation tank 8 and the cooling tower circulation tank 9. In the reaction tank 10, sulfuric acid corresponding to the unreacted limestone extracted from the absorption tower 3 is added to produce sulfite gypsum.

Further, calcium sulfite flows into the oxidation tower 4, and the chemical formula of Chemical Formula 2 is established between oxygen in the air supplied into the oxidation tower 4 by the atomizer 11 and calcium sulfite flowed into the oxidation tower 4. A chemical reaction occurs, and calcium sulfate, that is, gypsum (CaSO ₄ .2H ₂ O) is produced.

  A gypsum concentration tank 5, a centrifuge 13 connected to a gypsum slurry tank 12, and a centrifuge drainage tank 14 are provided downstream of the oxidation tower 4. In this centrifugal separator 13, it separates into gypsum and separated waste water. This separated wastewater is stored in the centrifugal separator drainage tank 14 and then sent to the absorption tower circulation tank 8.

When the unreacted slurry is generated, the desulfurization efficiency is lowered, so that it is necessary to prevent it. The cause of generation of unreacted slurry in each facility in the exhaust gas desulfurization apparatus described above is as follows.
In the absorption tower 3, efficiency decreases due to high concentration SO ₂ and an increase in gypsum / sulfite gypsum concentration (reduction in makeup water) in the absorption tower circulation tank 8. Although the normal excess of limestone is about 11, in order to maintain efficiency, as a result of excessively adding limestone slurry to the absorption tower circulation tank 8, the PH value also rises, and a large amount of limestone and sulfite gypsum are extracted.

  In the reaction tank 10, sulfuric acid corresponding to the unreacted limestone extracted from the absorption tower 3 is added to produce sulfite gypsum. If sulfuric acid does not follow due to excessive extraction amount and insufficient sulfuric acid injection, unreacted limestone slurry will be extracted to the oxidation tower 4. The sulfite gypsum does not react in the reaction vessel 10.

  In the oxidation tower 4, in order to oxidize the sulfite gypsum to gypsum, the atomizer 11 generates fine bubbles to increase the gas-liquid contact surface area and increase the reaction efficiency. Moreover, the proper oxidation rate is maintained by passing the specified level in the oxidation tower 4. The more reaction of sulfite gypsum, the higher the temperature of the oxidation tower 4. Atomizer 11 failure, air shortage. When the oxidation time is insufficient, sulfite gypsum is extracted.

  In the gypsum concentration tank 5 and the gypsum slurry tank 12, since the unreacted slurry has small particles and specific gravity, it floats without settling, and the unreacted slurry gradually accumulates in the gypsum concentration tank 5 and overflows. It is difficult to settle in the gypsum slurry tank 12, and even if it settles, since the specific gravity is smaller than that of gypsum, the specific gravity rises slowly. When the sample is collected, it is small particles, the sedimentation rate is slow, and the solid ratio is large and it is easy to float.

  In the centrifuge 13 and the gypsum conveyor 15, the starting interval of the centrifuge 13 becomes long. When the unreacted slurry flows into the centrifugal separator 13, liquid drainage failure occurs, part of the cake comes off, and abnormal vibration occurs. Since the discharged cake is poor in drainage, it causes meandering of the gypsum conveyor 15, clogging of the chute, and blockage of the strainer. Since the fine particle unreacted slurry is not trapped, it remains in the system.

On the other hand, various techniques for removing sulfur oxides contained in exhaust gas and treating the slurry generated there have been proposed. For example, as shown in Japanese Patent Application Laid-Open No. 10-128055 of "Patent Document 1", "Exhaust flue gas desulfurization apparatus and gypsum slurry treatment method", the exhaust gas is brought into contact with an absorption liquid containing a Ca component that is circulated and the above absorption In the flue gas desulfurization apparatus, in which air is introduced into the liquid to remove sulfurous acid gas from the exhaust gas as gypsum slurry, the generated gypsum slurry is extracted and solid-liquid separated in a gypsum separator and recovered as gypsum, the gypsum separation The machine is configured such that an endless filter cloth is supported on a belt having air permeability stretched between drums, and the gypsum slurry supplied from a supply tank is placed on the filter cloth below the belt. Is a belt-type vacuum dehydrator that is sucked from a dehydration chamber that is held at a negative pressure and separated into filtrate and the gypsum, and the supply tank of the belt-type vacuum dehydrator Above the filter cloth located in the flow side, flue desulfurization apparatus has been proposed which is formed by disposing a steam cleaning and drying apparatus for dewatering the water from the gypsum slurry being conveyed.
JP-A-10-128055

  However, if unreacted slurry is generated, desulfurization efficiency decreases, so it is necessary to investigate, confirm, and operate each system. However, there has been a problem that there is no fixed operation method, and it becomes a response from time to time, and it takes a lot of labor and time to identify the cause.

  Further, when this unreacted slurry is generated, the commercial value as gypsum is lowered, and there is a problem that resources cannot be efficiently reused.

  Patent Document 1 discloses a method for treating flue gas desulfurization apparatus and gypsum slurry. When gypsum is separated from gypsum slurry produced by desulfurization of exhaust gas, chlorine concentration and water content are not increased without increasing washing water of gypsum slurry. The purpose is to obtain a high-quality gypsum by reducing the rate, and no technology for preventing the generation of unreacted slurry or restoring to a normal slurry state has been disclosed.

  The present invention has been developed to solve such problems. That is, the object of the present invention is to restore the normal slurry state in a short time when unreacted slurry is generated by taking the cause of unreacted slurry in each treatment step of the desulfurization apparatus and the countermeasures. Therefore, it is providing the processing method of the unreacted slurry in the exhaust gas desulfurization apparatus which can produce | generate a highly pure gypsum.

According to the present invention, the exhaust gas discharged from the boiler (1) of a thermal power plant or the like is cooled by the cooling tower (2) and contained in the exhaust gas cooled by the cooling tower (2) in the absorption tower (3). When the calcium sulfite is produced from the sulfur oxide to be produced in the limestone slurry and the calcium sulfite produced in the absorption tower (3) is oxidized in the oxidation tower (4) to produce gypsum, the absorption tower (3) The limestone slurry was put into the absorption tower (3) while adjusting the PH value in the inside, and oxygen was supplied to the oxidation tower (4) so that the concentration of the gypsum slurry in the oxidation tower (4) was optimized, The unreacted slurry in the exhaust gas desulfurization apparatus is characterized by suppressing the generation of unreacted slurry by changing the starting conditions of the concentration tank (5) and the centrifuge (13), and recovering to a normal slurry state. Processing method provided It is.
For example, the limestone slurry is put in while maintaining the PH value in the absorption tower (3) so as not to exceed 6.0.
Further, oxygen is supplied while maintaining the temperature of the oxidation tower (4) so as not to exceed 60 ° C.

Regarding the generation state of the unreacted slurry, a state where the PH value of the absorption tower (3) becomes 6.0 or more and the temperature of the oxidation tower (4) starts to rise is referred to as an “initial state”. The state in which the increase in specific gravity in 12) becomes slow, the start-up interval of the centrifuge (13) becomes long, and the transparency of the gypsum concentration tank (5) decreases is referred to as “medium state”, and the gypsum concentration tank (5) From this, the unreacted portion overflows, flows into the filtrate water tank (16), abnormal vibration occurs in the centrifuge (13), and the tripping state is set as the “terminal state”, and the determination criteria are set in three stages. It is preferable to take measures to suppress the generation of unreacted slurry and restore the normal slurry state according to each state.
For example, when the unreacted slurry is generated in the “initial state”, the limestone slurry is stopped from being put into the absorption tower (3), and the extraction flow rates of the absorption tower (3) and the cooling tower (2) are stopped. Is reduced to 1/2, the PH set value of the reaction tank (10) is reduced to -0.1, the air amount of the atomizer (11) of the oxidation tower (4) is adjusted to +70 Nm ³ , and the drainage of filtered water By changing the set value of the flow rate to 0 T / H, generation of unreacted slurry is suppressed and the normal slurry state is restored.
By changing the starting condition of the centrifuge (13), adjusting the seed crystal supply flow rate, and adjusting the gypsum slurry flow rate when the unreacted slurry is in the “medium state”. Suppresses the generation of slurry and restores to a normal slurry state.
When the unreacted slurry is generated in the “terminal state”, the start condition of the centrifugal separator (13) is changed, the gypsum conveyor (15) is stopped, and the agitator of the blow tank (22) is started. Then, the filtered water drainage flow rate control valve rear valve (19) is fully closed, the filtered water tank blow valve (21) is adjusted open, the gypsum slurry pump circulation line blow valve (23) is adjusted open, and the gypsum slurry specific gravity control valve (24) is manually opened fully, and the filtered water tank replenishment water valve is adjusted open to suppress the generation of unreacted slurry and restore the normal slurry state.

  In invention of the said structure, when oxidizing calcium sulfite produced | generated in the absorption tower (3) and producing | generating gypsum, a limestone slurry is stuck in an absorption tower (3), adjusting PH value in an absorption tower (3). The generation of unreacted slurry can be suppressed and restored to a normal slurry state by a process of supplying oxygen to the oxidation tower (4) so that the gypsum slurry concentration in the oxidation tower (4) is optimized. . Therefore, a decrease in the desulfurization efficiency can be prevented by accurately conducting investigation, confirmation and operation of each system.

  With regard to the state of unreacted slurry generation, the state in which unreacted slurry begins to be generated is set in three stages from "initial state" to "medium state" and "end state", and measures are taken according to each state. As a result, generation of unreacted slurry can be suppressed, and a normal slurry state can be restored in a short time.

  The method for treating unreacted slurry in the exhaust gas desulfurization apparatus of the present invention is to squeeze limestone slurry into the absorption tower while adjusting the PH value in the absorption tower when oxidizing calcium sulfite produced in the absorption tower to produce gypsum. In this method, the generation of unreacted slurry is suppressed by a process of supplying oxygen to the oxidation tower so that the gypsum slurry concentration in the oxidation tower is optimized, and the normal slurry state is restored.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a system diagram for carrying out the method for treating unreacted slurry according to the present invention. FIG. 2 is a system diagram around the gypsum concentration tank.
As shown in FIG. 5 described above, the exhaust gas desulfurization apparatus that performs the method for treating unreacted slurry of the present invention includes a cooling tower 2 that cools exhaust gas discharged from a boiler 1 in a thermal power plant and the like, An absorption tower 3 storing limestone slurry to remove sulfur oxides contained therein, an oxidation tower 4 that oxidizes calcium sulfite produced in the absorption tower 3 to produce gypsum, and the produced gypsum are treated. This is a facility equipped with a gypsum concentration tank 5.

The exhaust gas flowing into the absorption tower 3 is supplied by the limestone supply facility 7, and calcium sulfite (CaSO ₃ · 1 / 2H ₂ O) is generated between calcium carbonate and sulfur dioxide (SO ₂ ) in the exhaust gas. . Calcium sulfite produced in the absorption tower 3 flows into the reaction tank 10 through the absorption tower circulation tank 8 and the cooling tower circulation tank 9. In the reaction tank 10, sulfuric acid corresponding to the unreacted limestone extracted from the absorption tower 3 is added to produce sulfite gypsum.

Further, as shown in FIG. 2, calcium sulfite flows into the oxidation tower 4, and in this oxidation tower 4, the oxygen in the air supplied by the atomizer 11 and the calcium sulfite flowed into the oxidation tower 4. In the meantime, calcium sulfate, that is, gypsum (CaSO ₄ .2H ₂ O) is produced.

  A gypsum concentration tank 5, a centrifuge 13 connected to a gypsum slurry tank 12, and a centrifuge drainage tank 14 are provided downstream of the oxidation tower 4. In this centrifugal separator 13, it separates into gypsum and separated waste water. This separated wastewater is stored in the centrifugal separator drainage tank 14 and then sent to the absorption tower circulation tank 8.

  A filtered water tank 16 for storing the filtered water is provided downstream of the gypsum concentration tank 5. Downstream of the filtrate water tank 16, a desulfurization drainage raw water receiving tank 20 is provided via a filtrate water pump 17, a filtrate water drain flow rate control valve 18, and a rear valve 19. Further, the filtrate tank 16 is provided with a filtrate tank blow valve 21.

Next, the cause of the generation of unreacted slurry, the phenomenon before the occurrence and the treatment for each phenomenon will be described for each apparatus.
[Causes and phenomena before the absorption tower]
The cause of unreacted slurry in the absorption tower 3, a high concentration SO ₂ and absorption tower circulating slurry concentration increase of tank 8 reduced efficiency due to the (up water decreases), PH meter malfunction due to absorption tower circulation tank 8 F limestone There is an excessive input.
As a phenomenon before such a state occurs, the PH value of the absorption tower circulation tank 8 increases. Care must be taken when the PH value is 6.2 or higher. Bubbles are generated in the absorption tower circulation tank 8 and the like by a large amount of CO ₂ being degassed by an abrupt absorption reaction.

[Measures for the phenomenon]
When such unreacted slurry is generated in the absorption tower 3, the limestone slurry is reduced from being put into the absorption tower circulation tank 8 to prevent an increase in PH. When the gypsum / sulfite gypsum slurry concentration in the absorption tower circulation tank 8 is increased (cooking phenomenon), a thinning operation is performed so that the concentration becomes 94 wt% and the specific gravity is 1.06, and the extraction is slightly increased. On the other hand, when the gypsum slurry concentration is normal and the limestone content is large, the extraction is reduced to about 1/2.
Further, the PH meter, PH pot of the absorption tower circulation tank 8, the specific gravity meter of the limestone slurry tank 12, etc. are inspected. Moreover, the PH set value of the reaction tank 10 is lowered to 0.1.

[Other causes and pre-occurrence phenomena in the absorption tower]
Other causes of generation of the reaction slurry in the absorption tower 3 include excessive reaction (amount / concentration), sulfuric acid pump malfunction, reaction failure of the reaction tank 10 due to pH meter malfunction.
As a phenomenon before such a state occurs, the injection opening of the sulfuric acid pump increases, the PH value of the reaction tank 10 increases, and the state becomes unstable.

[Measures for the phenomenon]
When such unreacted slurry is generated, the amount extracted to the reaction vessel 10 is reduced. In addition, check the sulfuric acid pump, the PH meter of the reaction tank 10, and the PH pot.

[Causes and phenomena before the occurrence in the oxidation tower]
The cause of the generation of the reaction slurry in the oxidation tower 4 includes an atomizer trip of the oxidation tower 4 and oxidation failure due to the shortage of oxidized air.
As a phenomenon before such a state occurs, the amount of oxidation decreases with respect to the concentration of the sulfite gypsum slurry flowing into the oxidation tower 4, and the temperature of the oxidation tower 4 decreases. A temperature increase at the lower part of the gypsum concentration tank 5 is observed.

[Measures for the phenomenon]
When such an unreacted slurry is generated in the oxidation tower 4, if the atomizer 11 cannot be started, the amount extracted to the reaction vessel 10 is reduced. The number of startable atomizers 11 is multiplied by the standard extraction amount to determine the extraction amount to the reaction tank 10. For example, the amount of oxidized air per one atomizer 11 is increased by, for example, +70 Nm ³ .

[Causes and phenomena before other oxidation towers]
The cause of the generation of the reaction slurry in the other oxidation tower 4 is that when the amount of slurry flowing into the oxidation tower 4 is excessive, the oxidation rate due to the reduction in the level of the oxidation tower 4 is insufficient.
As a phenomenon before such a state occurs, the amount of oxidation increases with respect to the concentration of the sulfite gypsum slurry flowing into the oxidation tower 4, and the temperature of the oxidation tower 4 rises.

[Measures for the phenomenon]
When such unreacted slurry is generated in the oxidation tower 4, the amount extracted to the reaction vessel 10 is decreased and the amount of oxidized air in the atomizer 11 is increased. If the oxidation tower level drops, check the oxidation tower level. That is, check the oxidation tower level meter and flush water.

FIG. 3 is an explanatory view showing the generation stage of the unreacted slurry in the initial stage, the middle stage, and the final stage and the treatment method thereof. FIG. 4 is an explanatory cross-sectional view in the graduated cylinder showing the state of the unreacted slurry sample.
Regarding the generation state of the unreacted slurry, determination criteria are set in three stages of “initial state”, “medium state”, and “end state”, and measures corresponding to each state are taken.
Because unreacted reactions often occur due to multiple factors, instrument monitoring and periodic sampling are taken, and a sample of slurry is placed in a graduated cylinder as shown in FIG. Monitoring and management is performed. Liquid composition chemical analysis is also conducted to understand the properties of each tank. It is important to make a comprehensive judgment in order to remove the cause from the root.
Because it is a chemical reaction, symptoms appear with a time lag, so the course should be followed over a 2-3 day span. Even if the symptoms relieve somewhat, do not carry out extreme operations easily (excessive overloading of limestone, increased withdrawal, etc.).
When there is a large amount of unreacted matter, it is not discharged from the gypsum concentration system.

  The normal values of the liquid PH value, solid concentration, specific gravity, and temperature of each part are as shown in Table 1. Therefore, the possibility of generating unreacted slurry increases as the distance from the values in this table increases.

"initial state"
In the “initial state” of the unreacted slurry generation determination criterion, as a phenomenon, PH 6.0 or more of the absorption tower 3 continues for several hours. Be especially careful when PH is 6.2 or higher. Next, the opening degree of the sulfuric acid pump is increased, and the PH tracking is deteriorated. Finally, the temperature of the oxidation tower 4 rises. Care must be taken especially when the temperature exceeds 65 ° C.

  In the “initial state” of the absorption tower circulation tank 8, in a normal state, the solid concentration is about 93 wt%, and the ratio is, for example, 85%: 1%: 15% for gypsum: sulfite gypsum: limestone, or It is about 28%: 65%: 7%. As the PH value increases, the amount of gypsum decreases and the proportion of sulfite gypsum and limestone increases.

As shown in FIG. 4, when the slurry is focused on the graduated cylinder, the substance with a higher specific gravity settles earlier. Layer in order of limestone (upper layer), sulfite gypsum (middle layer), gypsum (lower layer).
As a processing method for this “initial state”, the absorption / reaction system is adjusted.
For example, the limestone slurry flow rate is adjusted.
The extraction flow rate from the absorption tower 3 and the cooling tower 2 is set to “1/2 closed”. At this time, the PH pot around the absorption tower 3 is confirmed.
The PH set value of the reaction tank 10 is changed to -0.1. At this time, the PH pot around the reaction tank 10 is checked.
The amount of air in the atomizer 11 of the oxidation tower 4 ^is adjusted to +70 Nm ³ . At this time, attention is paid to the internal pressure of the oxidation tower 4.
Change the set value of the filtrate drainage flow rate to 0 T / H. At this time, pay attention to the filtered water tank level.

"Mid-term condition"
In the “medium state” of the unreacted slurry generation determination criterion, as a phenomenon, an increase in the specific gravity of the gypsum slurry tank 12 becomes slow, and the startup interval of the centrifuge 13 becomes long. Next, the transparency of the gypsum concentration tank 5 decreases.
In addition, since it is thought that the hydrometer of the gypsum slurry tank 12 is unsatisfactory, this hydrometer is washed and inspected, and compared with the manually analyzed value.

In the “medium state” gypsum slurry tank 12, the solid content settles and separates into three layers. Since the gypsum content has smaller particles than usual, it takes about 5 minutes to settle. Since sulfite gypsum and limestone are mixed, it takes 10 minutes or more to completely settle. When the water is discharged after standing for about 1 hour, about 1/3 of the fixed portion flows out.
In a normal state, the solid content is only the lower-layer gypsum, and settles and separates within 3 minutes. If the water is discharged after standing for about 1 hour, it will not stick out.
Further, in the “mid-term state” centrifuge 13, a soul (dama) containing moisture is generated in the plaster.

As a processing method for this “mid-term state”, a return / discharge operation to the absorption tower 3 is performed.
For example, the hydrometer of the gypsum slurry tank 12 is washed with water and replaced. At this time, the instrument value is compared with the manual analysis value.
The starting condition for the centrifuge 13 is changed to 30% and 1075.
Adjust the seed crystal supply flow rate.
Adjust the gypsum slurry flow rate. At this time, the level of the centrifuge drainage tank 14 is confirmed.

"Terminal state"
In the “end state” of the unreacted slurry generation determination criterion, as a phenomenon, the unreacted portion overflows from the gypsum concentration tank 5 and flows into the filtrate water tank. Abnormal vibration occurs in the centrifuge 13 and trips. The chute strainer of the gypsum conveyor 15 is clogged and trips.
In a normal state, the solid content is only the lower-layer gypsum, and settles and separates within 3 minutes. If the water is discharged after standing for about 1 hour, it will not stick out.

In the “late stage state” gypsum slurry tank 12, the solid component is mainly sulfite gypsum and limestone, so it takes 20 minutes or more to settle. Since it is always fluffy, the solid content appears to increase. When the moisture is discharged after standing for about 1 hour, the entire fixed part flows out.
In a normal state, the solid content is only the lower-layer gypsum, and settles and separates within 3 minutes. If the water is discharged after standing for about 1 hour, it will not stick out.
Moreover, in the centrifuge 13 in the “end stage state”, the gypsum adhering moisture increases and the centrifuge 13 is not dehydrated.

As a processing method for this “terminal state”, a gypsum concentration system blow operation is performed.
For example, the centrifuge start condition is changed to a normal value. The gypsum conveyor 15 is stopped. This is a case where the centrifuge 13 causes abnormal vibration or a trouble occurs due to a large amount of water adhering to the gypsum.
The agitator of the blow tank 22 is started. At this time, the blow tank 22 is checked.
The filtered water drainage flow control valve 18 and the rear valve 19 are fully closed.
The filtered water tank blow valve 21 is opened. At this time, pay attention to the level of the filtered water tank 16.
Reiki of the gypsum concentration tank 5 is stopped.
The gypsum slurry pump circulation line blow valve 23 is adjusted to open. At this time, pay attention to the level of the blow tank 22 and check the line.
The gypsum slurry specific gravity adjusting valve 24 is fully opened manually. At this time, pay attention to the level of the gypsum slurry tank 12.
Adjust the filtrate water tank replenishment water valve.

  When implementing the method for treating an unreacted slurry of the present invention, attention should be paid to water balance in the system, that is, overflow, level reduction, and the like. Blowing is performed directly to the blow tank 22, and side groove blow is avoided as much as possible. This is because there is a risk of overflow due to clogging of the side grooves, and the side grooves need to be cleaned later. The slurry collection in the blow tank 22 is performed after the composition in the system is stabilized, and an interval of about 3 days is opened. Avoid collecting large quantities at once.

  In the present invention, by taking the generation factor of the unreacted slurry in each treatment step of the desulfurization apparatus and the countermeasures thereof, when the unreacted slurry is generated, it is restored to the normal slurry state in a short time, Of course, as long as high-purity gypsum can be produced, the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the scope of the present invention.

  The method for treating unreacted slurry in the exhaust gas desulfurization apparatus of the present invention can be used for exhaust gas discharged from facilities other than thermal power plants, and can also be used for combustion exhaust gas of heavy oil other than coal.

It is a systematic diagram which implements the processing method of the unreacted slurry of this invention. It is a systematic diagram around a gypsum concentration tank. It is explanatory drawing which shows the generation | occurrence | production stage of the unreacted slurry of an initial stage, a middle period, and the last stage, and its processing method. It is explanatory sectional drawing in the measuring cylinder which shows the state of the sample of an unreacted slurry. 1 is an overall system diagram of an exhaust gas desulfurization apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Boiler 2 Cooling tower 3 Absorption tower 4 Oxidation tower 5 Gypsum concentration tank 12 Limestone slurry tank 13 Centrifugal machine 16 Filtrated water tank 10 Reaction tank 11 Atomizer 19 Filtrated water drainage flow control valve rear valve 21 Filtrated water tank blow valve 22 Blow tank 23 Gypsum slurry pump circulation line blow valve 24 Gypsum slurry specific gravity control valve

Claims (7)

The exhaust gas discharged from the boiler (1) of the thermal power plant etc. is cooled by the cooling tower (2),
In the absorption tower (3), calcium sulfite is produced from the sulfur oxide contained in the exhaust gas cooled in the cooling tower (2) with a limestone slurry.
In the oxidation tower (4), when the calcium sulfite produced in the absorption tower (3) is oxidized to produce gypsum,
While adjusting the PH value in the absorption tower (3), the limestone slurry was put into the absorption tower (3),
Oxygen is supplied to the oxidation tower (4) so that the gypsum slurry concentration in the oxidation tower (4) is optimized,
By changing the starting conditions of the gypsum concentration tank (5) and the centrifugal separator (13), the generation of unreacted slurry is suppressed, and the unreacted state in the exhaust gas desulfurization apparatus is restored. Slurry processing method. The method for treating unreacted slurry in an exhaust gas desulfurization apparatus according to claim 1, wherein the limestone slurry is placed while maintaining the PH value in the absorption tower (3) so as not to exceed 6.0. The method for treating unreacted slurry in an exhaust gas desulfurization apparatus according to claim 1 or 2, wherein oxygen is supplied while maintaining the temperature of the oxidation tower (4) so as not to exceed 60 ° C. About the generation state of the unreacted slurry,
A state where the PH value of the absorption tower (3) is 6.0 or more and the temperature of the oxidation tower (4) starts to rise is referred to as an “initial state”.
The state in which the increase in specific gravity of the gypsum slurry tank (12) becomes slow, the startup interval of the centrifuge (13) becomes long, and the transparency of the gypsum concentration tank (5) decreases is referred to as “medium state”.
The unreacted portion overflows from the gypsum concentration tank (5), flows into the filtrate water tank (16), abnormal vibration occurs in the centrifuge (13), and the tripping state is defined as the “end state”. The exhaust gas desulfurization apparatus according to claim 1, 2 or 3, wherein a judgment criterion is provided at each stage, and countermeasures for suppressing the generation of unreacted slurry according to each state and for restoring to a normal slurry state are taken. Method of treating unreacted slurry in When the initial state of the unreacted slurry generation state,
Stop the limestone slurry from being put into the absorption tower (3), reduce the extraction flow rate of the absorption tower (3) and the cooling tower (2) to 1/2, and set the PH set value of the reaction tank (10) to- Reduce to 0.1, adjust the amount of air in the atomizer (11) of the oxidation tower (4) to +70 Nm ³ and change the set value of the filtrate drainage flow rate to 0 T / H to generate unreacted slurry The method for treating unreacted slurry in the exhaust gas desulfurization apparatus according to claim 4, wherein the process is restored to a normal slurry state. When it is a “medium state” of the unreacted slurry generation state,
The start condition of the centrifuge (13) is changed, the seed crystal supply flow rate is adjusted, and the gypsum slurry flow rate is adjusted to suppress the generation of unreacted slurry and to restore the normal slurry state. The processing method of the unreacted slurry in the exhaust gas desulfurization apparatus of Claim 4 characterized by the above-mentioned. When it is the “terminal state” of the unreacted slurry generation state,
Change the starting condition of the centrifuge (13) and stop the gypsum conveyor (15), start the blower (22) stirrer, fully close the filtered water drainage flow control valve rear valve (19), Open the filtered water tank blow valve (21), open the gypsum slurry pump circulation line blow valve (23), manually open the gypsum slurry specific gravity control valve (24), and open the filtered water tank replenishment water valve. The method for treating unreacted slurry in the exhaust gas desulfurization apparatus according to claim 4, wherein the generation of unreacted slurry is suppressed to restore a normal slurry state.

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