JP3110251B2 - Low-grade gypsum separation and recovery method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention separates low-grade gypsum by mixing a part of gypsum slurry produced as a by-product in a wet lime gypsum method flue gas desulfurization apparatus and sludge slurry generated from a wastewater treatment apparatus attached to the apparatus. It relates to improvement of the method of collecting.

[0002]

2. Description of the Related Art When SOx in flue gas containing a large amount of dust, such as flue gas from a coal-fired boiler, is treated by a wet lime-gypsum method flue gas desulfurization device, fly ash is supplied from a wastewater treatment device that treats wastewater from the desulfurization device. , CaF ₂ , Al (O
Sludge components such as H) ₃ , Mg (OH) ₂ , and Fe (OH) ₃ are generated. When this sludge component is treated by burying it, the treatment cost is high and handling is difficult. Therefore, one of the gypsum (purity of gypsum: 95 to 98 wt%) produced as a by-product in the wet lime-gypsum method flue gas desulfurization apparatus is used. Sludge generated from a wastewater treatment device attached to the device is mixed in the section and collected as low-grade gypsum (purity of gypsum: 80 to 90 wt%), and is effectively used as a cement mixture. The quality of the low-grade gypsum as a cement admixture was determined by a take-off maker to prevent salt damage to the cement material by 100-150 mg / kg (dry base) as the Cl ^- concentration in the low-grade gypsum and 20 wt. % Or less quality is required.

Conventionally, a centrifugal separator has been used as a device for separating and recovering this low-grade gypsum. Hereinafter, a conventional low-grade gypsum separation and recovery method will be described with reference to FIG. A gypsum slurry 1 produced as a by-product in a wet lime-gypsum method flue gas desulfurization apparatus and a sludge slurry 2 from a wastewater treatment apparatus are mixed in a separator supply tank 3 and supplied to a centrifugal separator 6 via a path 5 by a pump 4. This centrifuge 6 is operated at high speed to separate solid and liquid,
Low-grade gypsum which is solid is washed with washing water 10 Cl ^- After lowering the concentration is further discharged from dehydrated by path 7.
The recovered cake is transferred to a predetermined place by a belt conveyor 8 and recovered as low-grade gypsum 9. On the other hand, the filtrate and the overflow liquid are sent from the path 11 to the filtrate tank 12. Since this filtrate tank 12 contains a slurry of several weight%, it is sent from a path 14 to a filtrate thickener 15 by a pump 13 to settle and separate solids. The concentrated slurry 16 from the lower part of the filtrate thickener 15 is returned to the separator supply tank 3 via the path 18 by the pump 17. On the other hand, the supernatant liquid flows from the drainage tank 20 through the path 19.
Is once returned to the integrated wastewater treatment device via the path 22 by the pump 21.

[0004]

In the conventional method using a centrifugal separator as a low-grade gypsum separation and recovery device, the dewatering property is good, the water content of the cake can be reduced to 10% by weight, and the average particle size can be reduced. It is effective for separating and recovering by-product gypsum of 30 to 50 μm (gypsum purity of 95 to 98 wt%). However, when separating low-grade gypsum containing fine-particle sludge slurry having an average particle size of 2 to 10 μm. In the case, the cake layer is compacted by centrifugal force and the filterability deteriorates. Therefore, it is necessary to reduce the slurry supply speed and the washing water supply speed, and it is necessary to increase the number of centrifuges in order to process a predetermined amount of slurry. In addition, since it is a batch type, the control thereof is complicated, maintenance is complicated, and a filtrate thickener is required, so that there are drawbacks in that equipment becomes expensive.
In addition, because of poor filtration properties, there is a drawback that the efficiency is low and a long time is required for cleaning Cl ⁻ . In view of the above prior art, is inexpensive to equipment specific and Cl ^- is intended to propose a method cleaning efficiency of good low-grade gypsum separation.

[0005]

SUMMARY OF THE INVENTION The present invention relates to (1) mixing a part of gypsum slurry by-produced in a wet lime-gypsum method flue gas desulfurization apparatus and a sludge slurry generated from a wastewater treatment apparatus attached to the apparatus. A method for separating and recovering low-grade gypsum by treating the mixed slurry with a horizontal belt vacuum dehydrator. (2) The method for separating and recovering low-grade gypsum according to the above (1), wherein a precoat layer is previously formed on the belt of the horizontal belt type vacuum dehydrator with gypsum slurry. It is.

That is, the present invention employs a horizontal belt type vacuum dehydrator in place of the conventional centrifugal separator, so that it is not compacted by a strong force unlike the centrifugal separator and has good filterability. The present invention provides a simple, simple and inexpensive and economical method in terms of equipment because continuous separation and recovery can be performed and a filtrate thickener is not required. Furthermore, the processing step of the horizontal belt type vacuum dehydrator is performed by forming a pre-coat layer with gypsum slurry, and then supplying and processing a mixture of the gypsum slurry and the sludge slurry without clogging of the filter cloth of the horizontal belt type vacuum dehydrator. , And can maintain stable filterability for a long time. It is a good filterability is Cl ^- is a also increases that cleaning effect, Cl low-grade gypsum ^- 10 as the concentration
0-150mg / kg (dry base) and water content 2
The quality of 0 wt% or less can be ensured and the demand value of the take-off maker can be satisfied.

[0007]

The concentration of gypsum slurry by-produced in the wet lime-gypsum method flue gas desulfurization apparatus is about 20% by weight and the average particle size is as large as 30 to 50 μm. Is suitable for centrifugal separator, but the average particle size is 2 ~
Fly ash such as 10 μm, CaF ₂ , Al (O
To separate low-grade gypsum containing sludge slurry which is fine particles such as H) ₃ , Mg (OH) ₂ , Fe (OH) ₃ ,
The centrifugal separator rotates at high speed, so the centrifugal effect ｛Z = rω ² /
g, Z: centrifugal effect (-), r: radius of gyration (m), ω: angular velocity (red / sec), g: acceleration of gravity (m / sec)
c ² ) is as large as 300 to 800. This results to be consolidated will take the pressure of several kg / cm ² ~ several tens of kg / cm ² to cake. For this reason, the filtration specific resistance (α) (m / kg) which affects the filtration characteristics is increased, and the filtration speed is reduced. Therefore, in order to process the same amount of slurry, it takes time to process the reduced filtration speed, and it is necessary to increase the number of centrifuges. Also, because it is a batch type,
The control is complicated and the maintenance is complicated. That point,
The horizontal belt type vacuum dehydrator can be operated continuously, and the operation pressure is low, such as 300 to 600 mmHg.

Further, since the centrifugal separator contains several percent by weight of solids in the overcharged liquid at the time of filtration, it must be once sent to a filtrate thickener to separate the solids by sedimentation. And a drain tank is required, but the solid content in the recovered filtrate of the horizontal belt type vacuum dehydrator is 1000 mg.
Per liter, and can be returned directly to the integrated wastewater treatment equipment, reducing equipment costs and providing a great economic advantage.

[0009] Even though it is a horizontal belt type vacuum dehydrator,
When treating a slurry containing fine particles of 10 μm, if used for a long period of time, the filter cloth will be clogged, and the filtration speed will be reduced, resulting in poor efficiency. In order to solve such a drawback, in the present invention, after a pre-coat layer is first formed with a gypsum slurry having a large particle diameter, a mixture of a gypsum slurry and a sludge slurry having a small particle diameter is supplied, and then washing and dewatering are performed. . By forming a constant pre-coat layer in this way, a stable filtration rate can be obtained for a long time without causing clogging of the filter cloth even when a slurry having a small particle size is supplied. Alternatively, the cleaning interval can be lengthened, which is very effective. In addition, since the filterability is good, Cl
^-Easy to clean.

[0010]

FIG. 1 illustrates an embodiment of the present invention.
A gypsum slurry 1 produced as a by-product in a wet lime-gypsum flue gas desulfurization apparatus and a sludge slurry 2 from a wastewater treatment apparatus are mixed in a separator supply tank 3, and are mixed as a slurry of 10 to 15% by weight through a path 5 by a pump 4 via a path 5. The liquid is sent to the belt-type vacuum dehydrator 6. The horizontal belt type vacuum dehydrator 6 holds the filter cloth 16 by a perforated endless belt 19 installed horizontally via drums 17 and 18, supplies the slurry to a slurry supply chamber 13, and then supplies the slurry to a cleaning chamber 14. Cleaning water 10 sprayed from above with C
l ^- washed and dehydrated to a predetermined moisture content in the dehydration chamber 15, the cake is transferred to a predetermined location from the path 7 is peeled off from the filter cloth 16 by the belt conveyor 8 low-grade gypsum 9
Will be collected as

Slurry supply chamber 13, washing chamber 14, dehydration chamber 1
5 has a structure in which a vacuum of 300 to 600 mmHg is maintained, and the filtered liquid is sent to a gas-liquid separator 20 via a path 11, and the filtrate is passed from a path 25 to a filtrate tank 1.
After being collected by the pump 2, it is returned to the integrated wastewater treatment device via the path 22 by the pump 21. On the other hand, the gas-liquid separator 20 is supplied to the vacuum pump 24 via
A vacuum of mmHg is maintained. Since the filter cloth 16 is clogged by filtering the slurry, the filter cloth 16 is backwashed with washing water or compressed air from 26 to prevent clogging. The discharged liquid is returned to the filtrate tank 12 via a path 27. As in the present invention, by employing the horizontal belt vacuum dehydrator instead of a centrifuge, it can be continuously operated, and because the cake also have good filterability without being compacted, Cl ^- cleaning effect is large, Cl low-grade gypsum is separated and recovered ^-
The quality of a pickup manufacturer with a concentration of 100 to 150 mg / kg (dry base) and a water content of 20 wt% or less is satisfied. In addition, it is possible to omit a filtrate thickener or the like, thereby reducing equipment costs.

Referring to FIG. 2, a method for performing long-term stable operation without clogging of a filter cloth when a horizontal belt type dewatering machine is applied in the separation and recovery of low-grade gypsum will be described. This method provides a more effective separation and recovery method by improving the processing steps of the horizontal belt dehydrator. That is, even though it is a horizontal belt type dehydrator,
When a filter cloth is repeatedly used for separating low-grade gypsum containing sludge slurry of 10 μm fine particles, the filter cloth is clogged, and the filtration speed decreases with time. To prevent this, the filter cloth is washed, but it cannot be completely removed and the filterability deteriorates when used for a long time.

In order to eliminate such a drawback, the processing steps of the horizontal belt type dehydrator have been improved. The gypsum slurry 1 by-produced in the wet lime-gypsum method flue gas desulfurization apparatus is passed through a valve 30 from a path 28 to a gypsum slurry supply chamber 3 of a horizontal belt dehydrator 6.
4 to form a pre-coated layer of high quality gypsum of 5 to 20 mm. In addition, since high-grade gypsum has good filterability, it is not necessary to increase the length of the gypsum slurry supply chamber 34, and one or two chambers are sufficient. Once the precoat layer is formed,
It moves to the slurry supply chamber 13 in the next step. On the other hand, the gypsum slurry 1 and the sludge slurry 2 are supplied and mixed to the separator supply tank 3 via the valves 32 and 33, respectively, and supplied to the slurry supply chamber 13 via the valve 35 and the path 5 by the pump 4.
Filter cloth 16 on which a precoat layer is formed with gypsum slurry 1
Since the low-grade gypsum slurry including the sludge slurry 2 is supplied thereon, the filter cloth 16 is not directly clogged. Thereafter, the cleaning water 10 sprayed from above in the cleaning chamber 14 is used to remove Cl ^−.
Is washed and dehydrated in the dehydration chamber 15 so as to have a predetermined water content, and then separated and collected as low-grade gypsum 9. Other operations are as described in FIG. Therefore, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description of the other reference numerals is omitted.

By forming the precoat layer with the high-grade gypsum slurry in this manner, clogging of the filter cloth 16 can be prevented, and it is not necessary to perform backwashing of the filter cloth, or the number of times of backwashing can be reduced. As a result, a stable filtration rate was obtained for a long time, and the Cl ^- cleaning effect was able to be enhanced. In addition, even if the precoat layer is formed with high-grade gypsum, the filtration speed is ten and several times higher than that of low-grade gypsum, so that no problem is caused.

(Example 1) A gypsum slurry having a gypsum purity of 98% by weight (average particle diameter: 32 μm) produced as a by-product in a wet lime-gypsum method flue gas desulfurization apparatus and a sludge slurry generated in a wastewater treatment apparatus were mixed. 80% by weight of low-grade gypsum was prepared, and the relationship between filtration pressure and filtration specific resistance was measured with a pressurized leaf tester. The properties of the above sludge slurry were as follows: average particle size: 4.3
μm, the composition of which is expressed in weight% as CaSO ₄ .2H ₂ O: 1
4.6, CaCO ₃ : 6.1, Al (OH) ₃ : 28.
0, Fe (OH) ₃ : 11.3, Mg (OH) ₂ : 1.
4, CaF ₂ : 3.8, SiO ₂ : 31.6.
The result is shown in FIG. Here, the filtration specific resistance was calculated by the following equation. _{dV / dθ = g c · ΔP} · A / μ (R c + R m) ··· (1) R c = α · W / A ··· (2) V: filtrate volume [m ^3] theta: Filtration Time [sec] A: Filtration area [m ² ] ΔP: Filtration pressure [kg / m ² ] μ: Filtrate viscosity [kg / m · s] R _c : Cake resistance coefficient [1 / m] R _m : Filter Resistance coefficient [1 / m] g _c : Gravity conversion coefficient α: Filtration specific resistance [m / kg] W: Cake weight [dry-kg]

As is clear from FIG. 3, compared with high-grade gypsum having a gypsum purity of 98% by weight, the sludge component is mixed and the gypsum purity is 8%.
The filtration specific resistance of low-grade gypsum prepared to 0% by weight is 50 to 1
00 times larger. The filtration specific resistance is inversely proportional to the filtration speed as shown in the equations (1) and (2), and the filtration speed decreases as the filtration specific resistance increases. In addition, low-grade gypsum with low gypsum purity has higher filtration specific resistance and consolidation as the filtration pressure (ΔP) increases. Therefore, if a centrifugal separator is used for the separation of low-grade gypsum, the centrifugal effect is large as described above, and the cake is several kg / cm ² to several tens of kg / cm.
The pressure of ² is applied, which increases the filtration specific resistance and makes filtration difficult. Therefore, it takes a long time to separate and collect low-grade gypsum, and it is necessary to increase the number of centrifuges in order to treat the same amount of slurry. On the other hand, since the horizontal belt type vacuum dehydrator operates at a low pressure of 300 to 600 mmHg, a sufficient filtration speed can be secured by selecting an appropriate cake thickness without consolidation.

(Example 2) Using a low-grade gypsum slurry having a gypsum purity of 90% by weight prepared in the separator supply tank 3 using the method of the present invention shown in FIG. 1 and the conventional method shown in FIG. separation and recovery and Cl low-grade gypsum ^- washing tests were carried out. The results are shown in Table 1. When the horizontal belt type dehydrator of the present invention was used, the Cl ^- cleaning effect was 95% or more and the Cl ^- concentration in low-grade gypsum was 100 mg / kg (dry base) or less. Also, the water content was 15 wt%, which was a result satisfying the quality of the collection manufacturer. The centrifugal separator used as a comparative example has a Cl ^- cleaning effect of 95% or more, which is the same as that of the horizontal belt dehydrator, but requires a large amount of water with a cleaning water ratio of 1.7 and requires a long cleaning time. . However, the water content is 1
At 0 wt% or less, the dewaterability was good, and the horizontal belt dehydrator was slightly inferior in dewaterability. Therefore, by adopting a horizontal belt type dewatering machine in the separation and recovery of low-grade gypsum, the performance is not inferior to that of a conventional centrifugal separator. It can be cheaper and has a great economic advantage.

[0018]

[Table 1] Cl ^- cleaning efficiency = {1- (Cl in cake after washing ^- Cl in cake without concentration / washing ^- concentration)} × 100
(%) Wash water amount ratio = Wash water amount (kg / h) / Low-grade gypsum cake amount (kg / h)

The specifications and operating conditions of the dehydrator used here are as follows. (1) Horizontal belt type dehydrator (a) Filtration area: 0.3 m ² (b) Vacuum pressure: -500 mmHg (c) Dehydration time: 120 sec (d) Filter cloth used: N-0091 (manufactured by Daiki Rubber Industry Co., Ltd.) : Product name) (e) Cake thickness: 20mm (2) Centrifuge (a) Basket specification: φ485 × 200H × φ3
85 mm (b) Basket capacity: MAX 13.7 liters (c) Rotational speed: 1415 rpm (d) Centrifugal effect: 544 G (e) Cake thickness: 50 mm (f) Average filtration area: 0.273 m ² (g) Dewatering time : 120 sec

Example 3 Using the method of the present invention shown in FIG. 1, a low-grade gypsum slurry (gypsum purity 8
(5% by weight) was supplied so as to form a cake layer having a thickness of 20 mm, and washing, dehydration, and separation of the cake were successively performed, and the filter cloth was washed for a long time, and the rate of decrease in filtration speed was examined. On the other hand, a high-grade gypsum slurry (gypsum purity: 98% by weight) is used to first form a precoat layer with a thickness of 5 mm using the method of the present invention shown in FIG. 2, and then a low-grade gypsum slurry (gypsum) from a separator supply tank is formed. (Purity: 85% by weight), and the total cake thickness was adjusted to 25 mm. After that, washing, dehydration, and separation of the cake were sequentially performed, and the reduction rate of the filtration rate was compared and examined.

FIG. 4 shows the result. Table 2 shows the specifications and operating conditions of the horizontal belt dehydrator. As is clear from FIG. 4, in the method of forming the precoat layer with high-grade gypsum, the filtration speed hardly decreases even when used for a long time, and clogging of the filter cloth hardly occurs. Became possible.

[0022]

[Table 2]

[0023]

As described above, the present invention is more effective than the conventional method.
Since the cake layer is not compacted, a sufficient filtration rate can be ensured, and continuous operation is possible, and the equipment is simple and inexpensive. Furthermore, Cl ^- cleaning effect conventional apparatus equivalent performance is obtained with a small amount of wash water as compared with the conventional method. In addition, even when used for a long time, the filter cloth of the horizontal belt type dehydrator can be stably operated with less clogging. Accordingly, the present invention provides a method for separating and recovering low-grade gypsum by mixing a part of gypsum slurry produced as a by-product in a wet lime gypsum method flue gas desulfurization apparatus and sludge slurry generated from a wastewater treatment apparatus attached to the apparatus. Inexpensive and high-performance separation and recovery are possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a system flow according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a system flow according to a second embodiment of the present invention.

FIG. 3 is a chart showing the relationship between filtration pressure and filtration specific resistance depending on gypsum purity.

FIG. 4 is a table showing the operation time and the reduction rate of the filtration speed in the first embodiment and the second embodiment.

FIG. 5 is an explanatory diagram of a system flow of a conventional low-grade gypsum separation and recovery method.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 11/26 B01D 53/50 B01D 53/77

Claims (2)

(57) [Claims] 1. A method for separating and recovering low-grade gypsum by mixing a part of gypsum slurry by-produced in a wet lime-gypsum method flue gas desulfurization apparatus and a sludge slurry generated from a wastewater treatment apparatus attached to the apparatus. And treating the mixed slurry with a horizontal belt vacuum dehydrator. 2. The method for separating and recovering low-grade gypsum according to claim 1, wherein a precoat layer is previously formed on the belt of the horizontal belt type vacuum dehydrator with gypsum slurry.