JPH10192838A - Process and device for evaporation concentration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover calcium sulfate at high recovery percentage by carrying out the continuous operation for a long period of time without separating scale by a horizontal pipe type evaporation concentration device, concentrating a wet flue gas desulfurization waste liquid into the high concentration. SOLUTION: An evaporation concentration device comprises a stock solution feed pipe 1, an evaporator 2, a circulating pump 3, a vapor compression type blower 5, a seed crystal injection piping 8, a slurry tank 9, a circulating fluid extraction pump 12, a cyclone type separator 13 for separating low concentration slurry from high concentration slurry, a pH adjuster feed piping 24 and the like. The initial injection of seed crystals is applied into a circulating liquid, and the low concentration slurry or the high concentration slurry is returned into a circulating liquid system, and the slurry concentration of seed crystals in the circulating liquid is maintained at 5-25wt., and pH is kept at 3.5-6.5 to prevent the adhesion of scale to a heat transfer pipe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for evaporating and concentrating water in a waste liquid containing a large amount of calcium sulfate such as an absorbent in a wet flue gas desulfurization method.

[0002]

2. Description of the Related Art In a wet flue gas desulfurization method, a scrubber is used to absorb sulfur oxides and the like in exhaust gas generated from a boiler or an incinerator with an alkaline aqueous solution such as slaked lime or calcium carbonate. This is a method of purifying the exhaust gas by removing it from the exhaust gas. In order to recover calcium sulfate, that is, gypsum from the waste liquid that has absorbed the sulfur oxides in this way, an operation of further concentrating the waste liquid is necessary.For example, a method of coagulating and sedimenting the waste liquid with a thickener to obtain a solid-liquid A separation technique has been proposed (see Japanese Patent Publication No. 6-15012).

As such a concentration operation, the above-mentioned coagulation-sedimentation method requires a number of stepwise processes, and the waste liquid cannot be treated simply and quickly. For this reason, an evaporative concentration method for evaporating the water in the waste liquid is often employed. However, when the calcium sulfate-containing aqueous solution is concentrated by the evaporation concentration method, the calcium sulfate concentration in the solution increases with the concentration, and when the solubility exceeds the saturation solubility, the calcium sulfate scale is deposited and fixed on the heat transfer surface. There's a problem.

[0004] As a method for evaporating and concentrating a solution containing a hardly soluble salt such as calcium sulfate while solving this problem, the following various methods have conventionally been adopted. (1) A method of operating so that the concentration ratio is within the limit of the saturation solubility (Japanese Patent Publication No. 7-75641) (2) A method of frequently cleaning chemicals at short intervals (3) A forced circulation such as flash evaporation (4) As a pretreatment of the waste liquid, a treatment to remove solids,
Method for performing water softening treatment for removing calcium ion as a hardness component

However, the above method is
In (1), efficient enrichment cannot be performed because the concentration ratio is low. In (2), stable long-term continuous operation cannot be performed to improve operating efficiency. In (3), evaporation efficiency is not good. The method (4) has various problems, such as the need for a pretreatment device and its operation, which complicates the device and the treatment method.

Although a method for preventing the scale from sticking to the heat transfer surface by adding a seed crystal has been frequently used, there are problems that a pretreatment is required and the effect of preventing the scale is insufficient. Was.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the prior art, has a simple structure, is easy to operate, has a good evaporation efficiency, and has a long-term stable continuous operation without scale deposition. An object of the present invention is to provide a method and an apparatus for evaporating and concentrating a wet flue gas desulfurization waste liquid containing calcium sulfate to a high concentration to recover calcium sulfate at a high recovery rate.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to an evaporative concentrator for evaporating water in a wet flue gas desulfurization waste liquid containing calcium sulfate to concentrate the waste liquid. In the method, an introduction operation for introducing the waste liquid, a circulation supply operation for circulating the waste liquid as a circulating liquid to an outer surface of an evaporator heat transfer tube disposed substantially horizontally, and flowing a heating fluid into the heat transfer tube A heating operation, a seed crystal adding operation of adding a seed crystal containing at least a calcium sulfate crystal to the circulating fluid as a main component, and the seeding operation is performed so that the concentration of the seed crystal in the circulating fluid is 5 to 25 wt%. Extracting a part of the circulating fluid to separate a high-concentration slurry having a high concentration of the seed crystals and a low-concentration slurry having a low concentration, and selectively adding these to the circulating fluid; PH of 3.5 It characterized by having a a pH adjusting agent added operations to maintain 6.5.

According to a second aspect of the present invention, there is provided an evaporative concentration apparatus for evaporating water in a wet flue gas desulfurization waste liquid containing calcium sulfate and concentrating the waste liquid, wherein the introduction means for introducing the waste liquid is disposed substantially horizontally. Evaporator provided with a heat transfer tube, circulating means for circulating the waste liquid as a circulating liquid to the outer surface of the heat transfer tube, heating means for flowing a heating fluid into the heat transfer tube, and calcium sulphate in the circulating liquid. A seed crystal adding means for adding a seed crystal containing at least a crystal as a main component, wherein the concentration of the seed crystal in the circulating liquid is 5 to 25 wt%.
A part of the circulating fluid is extracted so that a high-concentration slurry having a high concentration of the seed crystals and a low-concentration slurry having a low concentration are separated and selectively added to the circulating fluid. Maintaining means, and adjusting the pH of the circulating fluid to 3.5 to 3.5.
PH adjusting agent adding means for maintaining the pH at 6.5.

[0010]

FIG. 1 shows an example of the overall configuration of an evaporative concentration apparatus to which the present invention is applied. The evaporative concentrator of this example is
This is a device that uses a self-vapor compression horizontal tube evaporative concentrator, which evaporates the water in the waste liquid of a scrubber that performs wet flue gas desulfurization containing calcium sulfate and evaporates and condenses the waste liquid. A raw liquid supply line 1 as an introducing means for introducing the waste liquid as a raw liquid, a header 2
a, an evaporator 2 having a substantially horizontally arranged heat transfer tube 2c which constitutes a heater portion together with a circulation pump 3, and a circulation pump 3 as circulation means for circulating the undiluted solution as a circulating liquid to the outer surface of the heat transfer tube 2c. A steam compression blower 5 as a heating means for flowing steam as a heating fluid into the pipe 4 and the heat transfer pipe 2c;
A pipe 6 connecting the suction port to the top of the evaporator 2 and a pipe 7 connecting the discharge port to the header 2a of the evaporator 2
Etc.

As a part for adjusting the slurry concentration and recovering the concentrated liquid, a seed crystal injecting line 8, which constitutes a seed crystal adding means for adding a seed crystal containing calcium sulfate crystal as a main component to the circulating liquid, The slurry tank 9, the slurry supply line 10, and the circulating fluid constituting the seed crystal concentration maintaining means for maintaining the concentration of the seed crystals in the circulating fluid within a certain range of about 5 to 25 wt% (% by weight) An extraction pipe 11, an extraction pump 12 for extracting a part of the circulating liquid and pumping it, a cyclone separator 13 for introducing the circulating liquid and separating it into a low-concentration slurry and a high-concentration slurry, a low-concentration slurry outlet pipe 13a, High concentration slurry outlet pipe 13
b, line 14 and valve 15 for selectively returning part or all of the low-concentration slurry or high-concentration slurry to the circulating liquid
Or, it has a conduit 16 and a valve 17. Symbols 18 to 21
Are pipes and valves for discharging the low-concentration slurry and the high-concentration slurry to recover the high-concentration liquid, respectively.

The evaporator 2 is provided with a liquid reservoir 2d, and the stock solution supply line 1 is connected to this portion. The liquid in the liquid reservoir 2d is concentrated while being repeatedly circulated and supplied to the heat transfer tube 2c and contains seed crystals. Therefore, by putting the stock solution into the stock solution, the stock solution also contains seed crystals. It can be circulated as a concentrate. Also, it becomes possible to introduce a stock solution by negative pressure in the evaporator. In the upper part of the evaporator 2,
A spray nozzle 2e for spraying the circulating liquid is provided on the heat transfer tube 2c. Usually, a plurality of spray nozzles 2e are provided.
Further, instead of the nozzle, a perforated tube or perforated plate may be used.

[0013] A distilled water pump 2g is connected to a lower portion of the header 2b of the evaporator 2 via an extraction pipe 2f for extracting distilled water condensed by heating the circulating liquid.
On the other hand, a vacuum pump 2i is connected to an upper portion of the header 2b via a bleeding line 2h. The circulation line 4 is equipped with a hydrometer 22 for measuring the seed crystal concentration in the circulating liquid, and a dispersant supply line 23 and a pH adjusting agent supply line forming a part of the pH adjusting agent adding means. 24 are connected.
Although not shown, a drug supply device or the like for supplying a drug for pH adjustment is connected to the conduit 24.

As in the present embodiment, if a vapor compression type enrichment method is used by the horizontal tube type evaporator 2, the blower 5, the pipes 6, 7 and the like, a concentrating apparatus with reduced running cost can be obtained. However, when there is another available steam source or the like, this may be used for heating the evaporator heating unit. Further, a steam ejector may be provided in place of the blower 5 to extract the evaporation in the evaporator, and the circulating liquid may be heated by the extracted steam and the driving steam.

A detection end 25 for detecting the level of the slurry is attached to the slurry tank 9 and a control valve 26 is installed in the slurry supply line 10 so that the level of the slurry in the slurry tank 9 is kept constant between them. A control circuit 27 for maintaining is provided. Cyclone separator 13
May be a centrifugal solid-liquid separator driven by rotation, a specific gravity difference gravity type separator, or the like.

The above-described evaporative concentrator is operated as follows, and exhibits the following operational effects. First, as an introduction operation for introducing waste liquid, a stock solution is supplied from a stock solution supply pipe 1 to a liquid storage chamber 2d of the evaporator 2. Next, the circulating pump 3 is operated as a circulating supply operation for circulating and supplying the undiluted solution as a circulating liquid to the outer surface of the evaporator heat transfer tube. As a result, the undiluted liquid initially put in is sent to the spray nozzle 2e at the upper part of the evaporator 2 through the circulation line 4, and is then sprayed on the outer surface of the heat transfer tube 2c, falls into the liquid reservoir 2d, and is continuously discharged. It is circulated by the circulation pump 3 together with the undiluted solution supplied.

As a heating operation for flowing a heating fluid into the heat transfer tube 2c, a vapor compression type blower 5 is operated, and a part of the undiluted solution is evaporated by depressurization and sucked into the blower 5, and adiabatically compressed inside. The temperature is raised and the heat is sent from the header 2a into the heat transfer tube 2c. On the outer surface of the heat transfer tube 2c,
The sprayed circulating liquid is heated by the heating steam in the heat transfer tube 2c to evaporate a thin film. The generated steam is similarly compressed and heated by the steam compression blower 5, sent to the inside of the heat transfer tube 2c, and continuously evaporates the circulating liquid. On the other hand, such heated steam is condensed by heating the circulating liquid on the outer surface of the heat transfer tube 2c, and is discharged from the distilled water discharge pipe line 2f below the header 2b of the heated portion via the distilled water pump 2g to the outside of the system. Taken out.

The seed crystal adding operation is performed when the apparatus having a low concentration of calcium sulfate in the circulating liquid is started, for example, at an early stage after the operation of the circulating pump. In this operation, calcium sulfate or a crystal mainly composed of calcium sulfate is introduced as a seed crystal from the slurry supply line 8 into the slurry tank 9, and this is put into the liquid reservoir 2 d via the slurry supply line 10.
Add to the circulating fluid circulated by the circulation pump. The seed crystals are initially added so that the concentration of the seed crystals in the circulating liquid is in the range of 5 to 25 wt%. The seed crystal slurry in the slurry tank 9 is usually sucked by the negative pressure in the evaporator and put into the liquid reservoir 2d.

In the circulation line 4, an appropriate amount of a dispersant compatible with scale components other than calcium sulfate, such as a calcium-based or silica-based dispersant, is injected from the dispersant supply line 23. Further, an acid or an alkali is injected from the pH adjusting agent supply line 24, and the pH of the circulating liquid is adjusted to 3.5 to 6.5.

When the operation is continued in this state, the circulating liquid is gradually concentrated. For example, in the case of operating for the purpose of high concentration for increasing the concentration ratio of the circulating liquid to 5 times, the specific gravity of the circulating liquid is monitored by the hydrometer 22. At about 33, the operation is continued while removing a part of the concentrated high-concentration circulating liquid.

In this case, in this embodiment, the extraction pump 12 constituting the concentration maintaining means is operated, and the concentrated liquid is passed through the line 18, the valve 19, the pipe 20, and the valve 21 via the cyclone-type separator 13. It is discharged out of the system, and the line 14, the valve 1
A part of the concentrated liquid is returned to the circulating liquid side via 5, and the discharge amount of the concentrated liquid and the slurry concentration described later are adjusted. Such a concentrated liquid has a very high concentration of about 50% and contains a large amount of calcium sulfate precipitated by supersaturation. Therefore, calcium sulfate or gypsum contained in the stock solution can be easily recovered by the subsequent treatment.

By circulating and concentrating the stock solution, the circulating solution becomes a highly concentrated solution, and calcium sulfate and the like in the stock solution precipitate in the circulating solution and adhere to the seed crystals initially charged or become independent in the circulating solution. Seed crystals, and the concentration of crystals in the circulating fluid increases. The crystal concentration of the seed crystal that makes the circulating liquid into a slurry in this manner is hereinafter referred to as “slurry concentration”. Such a slurry concentration has a substantially constant relationship with the specific gravity of the circulating liquid unless the properties of the stock solution are significantly changed.
Can be monitored by

The circulating liquid slurry is supplied to a cyclone separator 13.
, A high-concentration slurry and a low-concentration slurry are separated by a specific gravity difference. By adjusting the discharge amount of the separated high-concentration slurry and low-concentration slurry to the outside and the return amount to the inside of the system, it is possible to perform the operation in which the concentration of the slurry and the concentration of the slurry are kept constant. The slurry concentration maintaining operation is performed as follows according to the level of the concentration of calcium sulfate in the stock solution.

When the slurry concentration of the circulating fluid becomes high, the opening of the valve 21 is increased to increase the amount of high-concentration slurry discharged out of the system, and the opening of the valve 15 is increased to reduce the concentration of the slurry. Increase the amount of slurry returned to the system.

When the slurry concentration of the circulating fluid becomes low, the opening of the valve 15 is made small to reduce the return amount of the low-concentration slurry to increase the discharge amount to the outside of the system. Increase the return of high-concentration slurry to reduce emissions. In this case, to increase the slurry concentration quickly,
1 may be closed to return the entire amount of the high-concentration slurry. When returning the high-concentration slurry to the slurry tank 9, the high-concentration slurry is returned to the liquid reservoir 2 d while the liquid level is held by the control circuit 26 while stirring the inside of the tank.
If the slurry concentration of the circulating fluid cannot be maintained even by such an operation, crystals mainly composed of calcium sulfate are charged into the slurry tank 9 from the slurry supply line 8 and seeded into the circulating fluid. Additional crystals are injected. Also, the circulating fluid p
When H changes, acid or alkali is injected from the pH adjusting agent supply line 24 to adjust the pH of the circulating liquid to 3.5 to 6.5.
Keep in the range.

According to the above-mentioned operation, the slurry concentration can be adjusted almost only by opening and closing the valve, so that the operation is extremely simple. By maintaining the concentration of the slurry in the circulating liquid within a certain range and by injecting the dispersant and adjusting the pH, it is possible to almost completely prevent the scale from adhering to the heat transfer tube 2c. Further, by such a good operation, the entire amount of calcium sulfate in the stock solution can be taken out in the form of a concentrated solution having a very high concentration.

In the above, it has been described that the devices and valves are manually operated. The evaporative concentrator according to the present invention may be of a type that is manually operated, but may be a device that is appropriately incorporated such as fully automated, partially automated, or remotely operated. Such automation and the like can be easily configured by applying the conventional technology to the present invention. For example, in a fully automated system, sensors such as temperature, pressure, pH, etc., control valves, control devices, etc. are provided, and while the operating conditions are detected by the sensors, valve opening and closing adjustment, pumps, blowers, etc. In addition to performing such operations, while controlling the concentration of the circulating liquid with the hydrometer 20, the operation control relating to the concentrated liquid concentration and the slurry concentration maintaining device is performed.

Next, the results of evaporative concentration experiments performed by the inventors using the evaporative concentration apparatus to which the present invention is applied will be described. The experiment was performed under the following various operating conditions using a scrubber waste solution having the properties shown in Table 1 after pH adjustment as a stock solution.

[0029]

[Table 1]

[Experiment-1] Experimental conditions: circulating fluid pH 6, calcium-based dispersant 10 pp
m injection Circulating fluid concentration 50%, circulating fluid slurry concentration 15% Experimental result: shown in FIG. As shown in the figure, the evaporation amount of water in the circulating fluid and the specific gravity of the concentrated circulating fluid are constant, indicating that the operation state was stable. The specific gravity of the concentrated liquid is an apparent specific gravity, and the specific gravity of 1.33 shown in the drawing corresponds to a liquid concentration of 50% and a slurry concentration of 15%. Therefore, it can be seen that a concentrated solution having a high concentration could be recovered.

Further, as shown in (b), no increase in the heat transfer temperature difference with the passage of time was observed, indicating that there was no scale adhesion to the heat transfer tube. In addition, the heat transfer temperature difference is a temperature difference between the temperature of the heating steam flowing in the heat transfer tube and the temperature of the circulating liquid flowing on the outer surface of the heat transfer tube. Further, the rise in the boiling point, which is the difference between the temperature of the circulating liquid and the temperature of the vapor that evaporates, is substantially constant, indicating that the concentration ratio is constant.

Further, according to FIG.
The electric conductivity of distilled water extracted in g is 10-20 μS
/ Cm range, and the water quality was high. Therefore, this water can be collected and reused. In this case, since the concentration rate is large, the recovery rate is also high.

From the above, it can be seen that the operating condition was good despite the high concentration. In addition, as a result of a visual inspection of the heat transfer tube after the end of this experimental operation, slight scale adhesion was observed at the end of the heat transfer tube that did not appear in the heat transfer temperature difference, but it was easily removed by chemical cleaning. I was able to.

[Experiment-2] Experimental conditions: circulating fluid pH 7, calcium-based dispersant 10 pp
m injection Circulating fluid concentration 50%, circulating fluid slurry concentration 15% Experimental result: shown in FIG. This experiment was an experiment in which the circulating fluid pH 6 was changed to pH 7 with respect to Experiment 1, but as shown in the drawing, almost the same results as in Experiment 1 were obtained. The heat transfer temperature difference and boiling point rise were more stable. In addition, a visual inspection of the heat transfer tubes after the end of the experiment confirmed that the scale was slightly more adhered than in Experiment-1. However, also in this case, it could be easily removed by chemical cleaning. From this experiment, it can be said that it is desirable to set the PH to about 6.5 or less. It should be noted that reducing the PH value is effective in preventing alkali scale,
Taking the material aspect of the evaporative concentration apparatus into consideration, it is desirable that the PH be not more than about 3.5.

[Experiment-3] Experimental conditions: circulating fluid pH 5, calcium-based dispersant 10 pp
m injection Circulating fluid concentration 60%, circulating fluid slurry concentration 30% Experimental result: shown in FIG. This experiment was performed to confirm the limit concentration of the circulating liquid slurry, but the experiment was interrupted as shown in the figure because an abnormality such as blockage of a pipe line occurred. At this time, the concentration of the concentrate was 60%. Although the interruption of the experiment is a problem in the experimental apparatus, it is presumed that continuous operation under these conditions is somewhat difficult. Therefore, the circulating fluid concentration is reduced to about 50%,
It is desirable that the slurry concentration be up to about 25%.

[Experiment-4] Experimental conditions: circulating fluid pH 5, calcium-based dispersant 10 pp
m injection, circulating fluid concentration 50%, circulating fluid slurry concentration 15% Experimental results: shown in FIG. This experiment was performed to confirm long-term continuous operation performance. In this experiment, results similar to those in Experiments 1 and 2 were obtained. The analysis results of the concentrated liquid (circulating liquid) and distilled water obtained in this experiment are shown in Table 1. Although the heat transfer temperature difference slightly changed, there was no increase in the heat transfer temperature difference due to the adhesion of the scale. In addition, a visual inspection of the heat transfer tubes after the one-month continuous experiment showed that the scaling was slightly smaller than in Experiment-1. Of course, this scale could be easily removed by chemical cleaning.

[Experiment-5] Experiment conditions: circulating fluid pH 5, calcium-based dispersant 10 pp
m injection, circulating fluid concentration 10%, circulating fluid slurry concentration 9% after 3% Experimental result: shown in FIG. This experiment was a continuous operation test performed to confirm the operation state when the circulating fluid was reduced in concentration. As shown in the experimental conditions and experimental results, the experiment was started with the circulating fluid concentration set to 3%, but after about 50 hours, the heat transfer temperature difference began to increase due to scale adhesion, so the operation was temporarily stopped in 120 hours. The heat transfer tube was chemically cleaned, and then sludge of the concentrated solution was additionally added as seed crystals, and the operation was performed while maintaining the slurry concentration at about 9%. As a result, thereafter, the increase in the heat transfer temperature difference was suppressed, and stable operation could be continued. From this experiment, the circulating fluid slurry concentration was reduced to 5% to prevent the scale containing calcium sulfate as the main component from adhering to the heat transfer tube.
It has been found that it is desirable to make it more than the degree.

As shown in the above experiments, in concentrating the liquid containing calcium sulfate, the concentration of the circulating liquid slurry is maintained at about 5 to 25% by the apparatus to which the present invention is applied, so that the heat transfer tube Calcium sulfate can be completely prevented from adhering to the scale.
By adding a modifier and a soft scale dispersant,
Long-term stable continuous operation without scale adhesion can be performed.

[0039]

As described above, according to the present invention, in the first aspect of the present invention, the wet flue gas desulfurization waste liquid containing calcium sulfate is introduced by the introduction operation, and the waste liquid is circulated as the circulating liquid by the circulation supply operation. Is circulated and supplied to the outer surface of the evaporator heat transfer tube disposed in the heater, and the heating fluid flows through the heat transfer tube by the heating operation. Thus, the waste liquid can be used as the circulating liquid to evaporate the water therein and concentrate it.

In this case, since the heat transfer tube of the evaporator is a horizontal tube, water can be efficiently evaporated. Further, a vapor compression method can be used as a heating operation. In this method, steam generated at the time of concentration can be used as a heat source for heating, and the operating cost for concentration can be significantly reduced by combining with a horizontal tube evaporator.

Next, the seed crystal containing calcium sulfate as a main component is added at an appropriate time, such as immediately after the start of the operation, by the seed crystal addition operation. Even if calcium sulfate crystals, that is, new scales, are deposited, the seed crystals prevent adhesion to the heat transfer tube, and the scales adhere to the surface of the seed crystals or precipitate in the circulating fluid. As a result, it is possible to prevent the scale from being attached to the horizontal tube type heat transfer tube having good evaporation efficiency. In this case, since no preprocessing is performed, the operation is simple.

With the seed crystal added in an appropriate amount, the liquid to be treated is circulated and concentrated while supplying the liquid to be treated, and the concentrated liquid concentrate is discharged from the circulation system. The concentrated and precipitated high concentration liquid can be recovered. However, the concentration of the seed crystal in the circulating liquid depends on the concentration of calcium sulfate in the liquid to be treated and the concentration ratio, and thus changes when these conditions change. When the value is out of the predetermined range, problems such as a reduction in the scale prevention effect occur. Therefore, an operation for maintaining the concentration of the seed crystal in the circulating fluid to be within a certain range of about 5 to 25 wt% is performed by the seed crystal concentration maintaining operation. In this case, a new seed crystal can be added by a seed crystal adding operation as needed.

As described above, the seed crystal concentration maintaining operation is to select a high-concentration slurry or a low-concentration slurry according to the situation, return an appropriate amount thereof to the circulating liquid, and adjust the slurry concentration in the circulating liquid to a certain range. Operation to keep By this operation,
Regardless of the concentration of calcium sulfate in the liquid to be treated and the concentration ratio, the calcium sulfate is completely prevented from adhering to the scale and stable long-term continuous concentration operation is performed. It can be concentrated. As a result, calcium sulfate can be recovered from the liquid to be treated at a high recovery rate, and the recovery rate of the distilled water that is evaporated and condensed increases, which can be reused.

The various operations described above are performed while maintaining the pH of the circulating liquid at a low value of 3.5 to 6.5 under the operation of adding a pH adjuster. Precipitation and adhesion of the alkali scale to the heat transfer surface are prevented. Also, by lowering the pH, an effect of changing the surface potential of the fine particles (seed crystals) contained in the slurry liquid is generated, and the precipitation of various scale components on the seed crystals is promoted by combination with an appropriate slurry concentration. And deposition and adhesion on the heat transfer surface are prevented. As a result, the wet flue gas desulfurization waste liquid can be treated in a scale-free state for a long period of time.

Further, since the above-mentioned operation is constituted by an evaporating concentration operation, a seed crystal adding operation, a seed crystal concentration maintaining operation, and a pH adjusting agent adding operation, many stepwise processes including pretreatment and the like are performed. Do not need. Therefore, the operation is simple. That is, the evaporative concentrating operation is, for example, an operation for operating a vapor compression type concentrator, and if the operation becomes a steady operation, almost no operation is required thereafter. And both are simple operations. Furthermore, since the operation of maintaining the seed crystal concentration can be performed only by operating a few valves, for example, this is also simple. or,
The pH adjusting agent addition operation is a normal operation that can be easily performed by the drug supply device.

According to the second aspect of the present invention, the evaporating and concentrating apparatus includes an introducing means for introducing a waste liquid, an evaporator having a heat transfer tube arranged substantially horizontally, and a circulating means for circulating and supplying the liquid to be treated. Since the apparatus is mainly composed of a heating means for heating this, a seed crystal adding means, a seed crystal concentration maintaining means, and a pH adjusting agent adding means, a small and simple apparatus can be obtained. That is, the evaporator, the circulation means, the heating means, and the like are configured as, for example, a vapor compression type concentrator. The seed crystal adding means is constituted by, for example, a tank for converting the seed crystal into a slurry and a pipe for sucking the seed crystal into an evaporator. The seed crystal concentration maintaining means includes a pump for extracting the circulating liquid, a cyclone-type separator for separating the circulating liquid slurry according to the concentration, a pipe, a valve, and the like. The pH adjusting agent adding means is constituted by, for example, a simple drug supply device and piping. Therefore, an apparatus combining these is a small and simple apparatus that can be almost unitized. In addition, the operation cost is low.

With such a small, simple structure and low operating cost, the apparatus prevents calcium sulfate from adhering to the heat transfer tube, performs stable continuous operation for a long period of time, and efficiently increases the concentration to a high concentration. The concentrated concentrate can be recovered.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of the overall configuration of a concentration and evaporation device to which the present invention has been applied.

2 (a) and 2 (b) are curve diagrams showing the results of an operation experiment using the above-mentioned concentrating and evaporating apparatus.

FIGS. 3A and 3B are curve diagrams showing the results of another driving experiment.

FIGS. 4A and 4B are curve diagrams showing the results of still another driving experiment.

FIGS. 5A and 5B are curve diagrams showing the results of still another driving experiment.

FIGS. 6A and 6B are curve diagrams showing the results of still another driving experiment.

[Explanation of symbols]

Reference Signs List 1 stock solution supply pipe (introduction means) 2 evaporator 2c heat transfer pipe 3 circulation pump (circulation means) 4 circulation pipe (circulation means) 5 vapor compression blower (heating means) 8 seed crystal injection pipe (seed crystal addition means) 9) Slurry tank (seed crystal adding means) 10 Slurry supply line (seed crystal adding means) 11 Circulating liquid extraction line (seed crystal concentration maintaining means) 12 Extraction pump (seed crystal concentration maintaining means) 13 Cyclone separator ( Seed crystal concentration maintaining means) 14 Pipe line (seed crystal concentration maintaining means) 15 Valve (seed crystal concentration maintaining means) 16 Pipe line (seed crystal concentration maintaining means) 17 Valve (seed crystal concentration maintaining means) 24 pH adjusting agent supply pipe Road (pH adjusting agent addition means)

Continued on the front page (72) Inventor Hiroshi Shiomi 4-73-2 Takeshima, Nishiyodogawa-ku, Osaka-shi, Osaka Inside Sasakura Inc. (72) Inventor Kazumi Tahara 4-732, Takeshima, Nishiyodogawa-ku, Osaka-shi, Inc. Inside Sasakura (72) Inventor Hideki Takahashi Organo Co., Ltd. 5-5-16-1 Hongo, Bunkyo-ku, Tokyo (72) Inventor Koichi Hosoda 1-4-9 Kawakishi, Toda City, Saitama Prefecture Organo Research Institute (72) Inventor Takumi Nanami 1-4-9 Kawagishi, Toda City, Saitama Prefecture Inside Organo Research Institute

Claims (2)

[Claims] 1. An evaporative concentration method for evaporating water in a wet flue gas desulfurization waste liquid containing calcium sulfate and concentrating the waste liquid, wherein an introduction operation for introducing the waste liquid and the waste liquid are disposed substantially horizontally as a circulating liquid. A circulating supply operation for circulating and supplying the outer surface of the evaporator heat transfer tube, a heating operation for flowing a heating fluid into the heat transfer tube, and a seed crystal containing at least a calcium sulfate crystal as a main component in the circulating liquid. The seed crystal adding operation to be added, and the concentration of the seed crystal in the circulating liquid is 5 to 25 wt%
A part of the circulating liquid is extracted so as to separate a high-concentration slurry having a high concentration of the seed crystals and a low-concentration slurry having a low concentration of the seed crystals, and selectively add these to the circulating liquid. And an operation of adding a pH adjuster for maintaining the pH of the circulating liquid at 3.5 to 6.5. 2. An evaporating and concentrating apparatus for evaporating water in a wet flue gas desulfurization waste liquid containing calcium sulfate and concentrating the waste liquid, comprising: an introduction means for introducing the waste liquid; and a heat transfer tube disposed substantially horizontally. Evaporator, circulating means for circulating the waste liquid as a circulating liquid to the outer surface of the heat transfer tube, heating means for flowing a heating fluid into the heat transfer tube, and at least calcium sulfate crystals in the circulating liquid. A seed crystal adding means for adding a seed crystal contained as a component, and extracting a part of the circulating fluid so that the concentration of the seed crystal in the circulating fluid is 5 to 25 wt%, and A high-concentration slurry having a high concentration and a low-concentration slurry having a low concentration and selectively adding these to the circulating liquid; and adjusting the pH of the circulating liquid to 3.5 to 6.5. Add pH adjuster to maintain Evaporative concentration apparatus, comprising: the means.