JP2863820B2 - Method for treating sulfate-containing waste liquid and improved reaction tank - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reaction tank for producing and depositing sulfate ions as gypsum (calcium sulfate) when treating a sulfate-containing waste liquid discharged from a desulfurization apparatus for coal combustion flue gas. The present invention relates to a method for treating a sulfate ion-containing waste liquid capable of preventing the generation of gypsum scale, which is an obstacle to water, and an improved reaction tank used for the method.

[0002]

2. Description of the Related Art Conventionally, as a method of treating a waste liquid containing harmful substances such as sulfate ions and fluorine ions, a calcium compound such as calcium hydroxide or calcium chloride is added to the waste liquid in a reaction tank and stirred. A method for removing the fluorine ions as calcium fluoride is widely known. However, according to this known method, a large amount of calcium sulfate is generated in the reaction tank, and most of the calcium sulfate precipitates quickly, but the remainder remains in the solution with supersaturation, and the residue is then converted to gypsum scale. As a result, it is deposited on the inner wall of the reaction tank, the stirrer, and the like, and the operation is not possible as it is. Therefore, there is an inconvenience that the operation must be frequently interrupted and the scale removal operation must be performed manually.

As a countermeasure, it has been reported that the seeding method is effective as a means for preventing the formation of gypsum scale. According to this, the seeding effect is shown in FIG. It is also known that the concentration is greatly affected by the concentration of gypsum particles added as seed crystals, as can be seen from the graph showing the “suppression state of supersaturation degree”.

[0004] Therefore, based on this seed crystal addition method, conventionally, a reaction step of obtaining a suspension by adding a calcium compound to flue gas desulfurization or denitrification wastewater containing fluoride ions and sulfate ions, And a step of separating the treated water and calcium sulfate, a precipitate mainly composed of calcium fluoride, wherein a step of returning the precipitate to the reaction step is added, whereby the precipitate is contained in the precipitate. A wastewater treatment method has been proposed that prevents gypsum scale from being generated in the reaction step by circulating gypsum as a seed crystal (Japanese Patent Publication No. 1-26755).

[0005]

However, in the conventional wastewater treatment method as described above, it is necessary to circulate the sediment at least twice as much as the wastewater supply amount in order to increase the gypsum particle concentration so as to prevent scale. Therefore, in the actual processing apparatus, not only the capacity of the dissolution tank, the reaction tank, and the capacity of the sedimentation tank must each be doubled or more, but also the control for adjusting the sediment in the sedimentation tank to a predetermined concentration. Means, pumps, pipes, and the like for circulating sediment having abrasion and sedimentation are required, and together therewith, there is a drawback that equipment costs are greatly increased.

[0006] A method of adding gypsum particles to the reaction step from outside the above-mentioned treatment step is also conceivable.
In addition to the need for equipment such as a supply device for the reaction process, the amount of sludge generated in the treatment process increases, and the capacity of the sludge concentration and dewatering device discharged from the sedimentation tank must be increased accordingly. The disadvantages of equipment costs remain as well. It is an object of the present invention to achieve sufficient scale prevention while reducing equipment costs.

[0007]

As for the desulfurization effluent discharged from the desulfurization unit for coal-fired flue gas, the effluent contains a large amount of sulfate ions, fluorine ions, aluminum ions and iron ions. When calcium hydroxide is injected into the reaction tank to remove these,
As an example, gypsum is most often produced at 50 to 70%, and then calcium fluoride, aluminum hydroxide, and iron hydroxide are usually produced in this order. Therefore, when the sedimentation rate of these products alone was measured by an experiment, it was found that the effect of the particle concentration was large as shown in the graph of "Relationship between concentration of generated crystal particles and sedimentation rate" in FIG. It was confirmed that the precipitation speed (interface precipitation speed) was high. As an example, the precipitation rate of a gypsum slurry having a particle concentration of 5% is 0.5 m /
When iron hydroxide is around 0.06%, the cohesion is good and the sedimentation rate is fast. However, at 0.1%, the coagulation does not occur and the sedimentation property is extremely poor. .1% data not shown).

Subsequently, gypsum 5%, calcium fluoride 1
%, Aluminum hydroxide 0.5% and iron hydroxide 0.06
%, The gypsum particles precipitate at a much higher rate than these products without co-aggregating with calcium fluoride, aluminum hydroxide or iron hydroxide, which have low precipitation rates. Was confirmed.

On the basis of these experiments, the first invention of the present application is to dispose a reaction mixture containing gypsum particles generated when a calcium compound is reacted with a sulfate ion-containing waste liquid upward in the reaction chamber and then to the upper end of the reaction chamber. And the intermediate zone continuous with the upward flow velocity in the reaction chamber upward at a flow rate higher than the upward flow rate, and then in the acceleration chamber continuous with the intermediate zone in the discharge direction at a flow velocity higher than the flow rate of the intermediate zone, the precipitated gypsum particles obtained in advance The relationship between the concentration and the settling rate of the gypsum particles at that concentration, and the settling rate of the gypsum particles at the set particle concentration based on a preset gypsum particle concentration capable of effectively exhibiting a seed crystal effect in the gypsum precipitation reaction And select
The flow rate of the intermediate zone is substantially equal to the settling speed of the gypsum particles, and the gypsum particles of the set particle concentration are settled and held in the reaction chamber, and the excess gypsum exceeding the set particle concentration in the acceleration chamber. Propose a method for treating sulfate-containing waste liquid that discharges particles,

According to the second invention of the present application, an intermediate zone is provided at an upper end of a reaction chamber, and an acceleration chamber is connected on the intermediate zone in a three-way communication state. A reaction mixture containing gypsum particles generated when the calcium compound is reacted with the sulfate ion-containing waste liquid; and a flow urging means for continuously flowing the reaction mixture upward in the reaction chamber, the intermediate zone, and then into the acceleration chamber. The cross-sectional area of the intermediate zone is made smaller than that of the reaction chamber so as to make the ascending flow velocity of the zone faster than that of the reaction chamber, an outlet is provided at the upper end of the acceleration chamber, and the ascending velocity of the accelerating chamber is made lower than that of the intermediate chamber. An improved reactor for the treatment of sulfate-containing waste effluent is proposed in which the cross-sectional area of the acceleration chamber is made smaller than that of the intermediate zone in order to make it faster.

Hereinafter, an embodiment of an improved reaction tank having a gypsum scale generation preventing structure in a step of removing sulfate ions and the like from a sulfate ion-containing waste liquid discharged from a coal flue gas desulfurization apparatus will be described.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a reaction tank is formed by forming an intermediate zone (P) on a reaction chamber (1), and then an acceleration chamber (2) on the reaction chamber (1). 1) is formed in a cylindrical shape with a bottom, and a waste liquid supply pipe (3) and a calcium compound supply pipe (4) are connected to the side walls thereof, respectively, and the tip of each supply pipe (3), (4) is connected to a reaction chamber. (1)
The supply ports (5) and (6) at the tip of the extension are suspended near the inner bottom surface of the reaction chamber (1). Each supply pipe (3),
(4) The rear end is connected to a desulfurization waste liquid tank and a calcium hydroxide slurry tank (both not shown), respectively. 1) and the reaction mixture of the waste liquid and calcium hydroxide is continuously flowed upward in the reaction chamber (1) and then upward in the intermediate zone (P) and the acceleration chamber (2). Pumps (7) and (8) are connected as flow urging means.

At the open upper end of the reaction chamber (1), a hollow truncated cone having a large diameter portion having the same diameter as that of the reaction chamber (1) is connected at the large diameter portion. Is formed in an intermediate zone (P) having a smaller diameter than the reaction chamber (1), and the entire upper portion thereof is formed in an acceleration chamber (2) having a smaller diameter than the intermediate zone (P). .
An overflow discharge port (9) is provided at the upper end of the acceleration chamber (2), and a discharge pipe (10) connected to the discharge port (9).
Is connected to a sedimentation tank (not shown) in the next step, and a gear motor (11) is installed on the upper surface of the acceleration chamber (2), and a stirring shaft (12) connected to the output shaft of the motor (11). Are suspended on the center lines in the acceleration chamber (2) and the reaction chamber (1), and stirring blades (13) are attached to the lower end of the reaction chamber.

A method for treating a sulfate ion-containing waste liquid using the above-described reaction tank will be described below. For convenience, sulfate ion 15000 mg / l, fluorine ion 1900 mg / l
, 680 mg / l of calcium ion, 460 mg / l of aluminum ion, 460 mg / l of iron ion, and 3000 mg / l of sodium ion, and a simulated waste liquid of PH = 1 (adjusted by adding hydrochloric acid) was prepared and pumped (7). ) Is driven through the supply pipe (3) through the supply port (5).
At the same time, the calcium hydroxide slurry is supplied into the reaction chamber (1) while the pump (8) is driven by the supply pipe (4).
Is supplied into the reaction chamber (1) through the supply port (6), and when the reaction chamber is stirred by rotating the stirring shaft (12) by starting the motor (11), each ion in the waste liquid and calcium hydroxide Reacts to produce and precipitate calcium sulfate, calcium fluoride, aluminum hydroxide, and iron hydroxide and flow upward.

Here, by supplying the waste liquid and the calcium hydroxide slurry at a predetermined flow rate from the supply ports (5) and (6), the ascending linear flow rate in the intermediate zone (P) of the above-mentioned reaction tank can be set to, for example, a seed crystal. It is equal to the gypsum precipitation speed of 0.5 m / h (see FIG. 4) at the set particle concentration of 5% that can sufficiently exert the effect. Accordingly, the ascending linear flow rate in the reaction chamber (1) is lower than the gypsum settling velocity of 0.5 m / h, and the ascending linear flow rate in the accelerating chamber (2) is faster than that. Gypsum particles settle down by a concentration equivalent to 5%,
Excess gypsum particles exceeding 5% rise from the inside of the reaction chamber (1) to the inside of the acceleration chamber (2) along with an ascending flow together with aggregates of calcium fluoride, calcium hydroxide and iron hydroxide having a low sedimentation rate. , And is discharged from the discharge port (9). That is, the concentration of gypsum particles in the intermediate zone (P) increases with the gypsum particles continuously generated by the reaction between the supplied waste liquid and calcium hydroxide, and the sedimentation speed becomes slower than 0.5 m / h. Excess gypsum particles exceeding the above are sent upward from the intermediate zone (P) by a fast ascending flow, and are discharged from the discharge port (9). As a result, the reaction chamber (1) has high purity, is active and has a seed crystal effect. The gypsum having a sufficiently exertable particle concentration is maintained, thereby exhibiting a seed crystal effect in the reaction chamber (1) and preventing the formation of gypsum scale.

As shown in FIG. 3, the set particle concentration of gypsum that can effectively exhibit the seed crystal effect is about 2 to 7 as shown in FIG.
% Is appropriate.

Incidentally, the outlet (9) in the steady state
The solids contained in the effluent from
When the calcium ion concentration of the filtrate was measured,
The value was 580 mg / l, indicating that the supersaturated state of gypsum was sufficiently avoided. The filtrate was allowed to stand for 3 days, but no crystallization was observed.

Further, the slurry in the reaction chamber (1) was taken and its gypsum particle concentration was measured to be 5.5%.
In FIG. 4, the particle concentration almost coincided with the particle concentration of 5.0% at the sedimentation speed of 0.5 m / h, and it was confirmed that a gypsum particle concentration sufficient to exhibit the seed crystal effect was formed.

After the treatment in the reaction tank has been carried out for 5 consecutive days, the inner surface of the reaction tank, the stirring shaft (12) and the blades (13) ...
Was observed, but almost no gypsum scale was deposited.

FIG. 2 shows another embodiment of the reaction reaction tank, in which the acceleration chamber (2a) is formed in a cylindrical shape having a smaller diameter than the reaction chamber (1a), and is connected to the arc-shaped inclined connection portion with the reaction chamber (1a). An intermediate zone (Pa) is formed, and other structures are substantially the same as those in FIG.

[0021]

According to the method for treating a sulfate ion-containing waste liquid of the first invention of the present application, gypsum particles having a set particle concentration capable of effectively exhibiting a seed crystal effect are precipitated and held in the reaction chamber, and the set particle concentration is reduced. Excess gypsum particles can be discharged, thereby sufficiently preventing the formation of gypsum scale in the reaction chamber, the intermediate zone, and the acceleration chamber. In comparison with this, the equipment can be greatly simplified and the equipment cost can be significantly reduced.

According to the improved reaction tank for treating sulfate ion-containing waste liquid of the second invention of the present application, the method for treating sulfate ion-containing waste liquid of the first invention can be effectively carried out. As compared with the conventional processing apparatus, the equipment can be greatly simplified and the equipment cost can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view of a reaction tank for a sulfate ion-containing waste liquid.

FIG. 2 is a front view of another embodiment of the reaction tank.

FIG. 3 is a graph showing how the supersaturation of calcium sulfate is suppressed by the seed crystal effect.

FIG. 4 is a graph showing the relationship between the concentration of produced crystal particles and the precipitation rate.

[Explanation of symbols]

 1 Reaction chamber P Intermediate zone 2 Acceleration chamber 7, 8 Pump 9 Overflow outlet

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-225691 (JP, A) JP-B Hei 1-26755 (JP, B2) JP-B Hei 3-15512 (JP, B2) (58) Field (Int.Cl. ⁶ , DB name) C02F 1/58 B01D 53/50 B01D 53/77 C02F 5/00 B01D 9/02

Claims (2)

(57) [Claims] A reaction mixture containing gypsum particles produced when a calcium compound is reacted with a sulfate ion-containing waste liquid,
The reaction chamber is discharged upward, then the intermediate zone connected to the upper end of the reaction chamber is discharged upward at a flow rate higher than the rising flow rate in the reaction chamber, and then the acceleration chamber connected to the intermediate zone is discharged at a flow rate higher than the flow rate of the intermediate zone. Flow in the direction, based on the relationship between the previously determined gypsum particle concentration and the precipitation rate of the gypsum particles at that concentration, and a preset gypsum particle concentration capable of effectively exhibiting a seed crystal effect in the gypsum precipitation reaction. The sedimentation speed of the gypsum particles at the set particle concentration is selected, and the flow rate of the intermediate zone is made substantially equal to the selected sedimentation speed of the gypsum particles, and the gypsum particles of the set particle concentration are maintained in the reaction chamber. A method for treating a sulfate ion-containing waste liquid, wherein excess gypsum particles exceeding the set particle concentration are discharged in the acceleration chamber. 2. An intermediate zone is provided at the upper end of the reaction chamber, and an acceleration chamber is connected to the intermediate zone in a three-way communication state. The gypsum particles produced when the calcium compound is reacted with the sulfate ion-containing waste liquid. A flow urging means for continuously flowing the reaction mixture containing the reaction mixture upward in the reaction chamber, the intermediate zone, and then into the acceleration chamber, and a cross-sectional area of the intermediate zone in order to make the rising flow rate of the intermediate zone faster than that of the reaction chamber. Was made smaller than that of the reaction chamber, a discharge port was provided at the upper end of the acceleration chamber, and the cross-sectional area of the acceleration chamber was made smaller than that of the intermediate zone so that the ascending flow velocity of the acceleration chamber was faster than that of the intermediate zone. , An improved reaction tank in the treatment of sulfate ion-containing waste liquid.