JPH04271893A - Treatment of sulfuric acid ion-containing waste liquid and improved reaction chamber - Google Patents

Abstract

PURPOSE:To sufficiently prevent the generation of gypsum scale in a reaction chamber, intermediate zone and acceleration chamber and to drastically reduce the cost of equipment by settling and holding the gypsum particles of the set particle concn. at which a seed crystal effect can effectively be exhibited into the reaction chamber, and discharging the excess gypsum particles exceeding the set particle concn. CONSTITUTION:A reactive liquid mixture contg. the gypsum particles generated when a Ca compd. is brought into reaction with a sulfuric acid ion-contg. waste liquid are made to flow upward in the reaction chamber 1, then flow upward the intermediate zone P connecting to the top end of the reaction chamber 1 at the flow velocity higher than the rising flow velocity in the reaction chamber 1, and then toward a discharge direction in the acceleration chamber 2 connecting to the zone P at the flow velocity higher than the flow velocity of the zone P. The settling rate of the gypsum particles at the above-mentioned set particle concn. is then selected in accordance with the relation between the precipitated gypsum particle concn. and the settling rate of the gypsum particles at this concn. and the preset gypsum particle concn. at which the seed crystal effect in the gypsum precipitation reaction can be exhibited, by which the flow velocity of the zone P is set nearly equal to the selected settling rate of the gypsum particles.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to a reaction tank in which sulfate ions are generated and precipitated as gypsum (calcium sulfate) when treating sulfate ion-containing waste liquid discharged from coal combustion flue gas desulfurization equipment, etc. The present invention relates to a method for treating sulfate ion-containing waste liquid that can prevent the formation of gypsum scale, which is a hindrance to the production of gypsum scale, and an improved reaction tank used therein.

0002

[Prior Art] Conventionally, as a method for treating waste liquid containing harmful substances such as sulfate ions and fluoride ions, calcium compounds such as calcium hydroxide and calcium chloride are added to the waste liquid in a reaction tank and the mixture is stirred. A widely known method is to remove the fluorine ions as calcium fluoride. However, in this well-known method, a large amount of calcium sulfate is produced in the reaction tank, and although most of it is quickly precipitated, the remainder remains in the solution as a supersaturated state, and this residue subsequently becomes gypsum scale. It deposits on the inner walls of the reaction tank, the stirrer, etc., and if left untreated, it becomes impossible to operate, resulting in the inconvenience of having to frequently interrupt operation and perform scale removal work manually.

[0003] As a countermeasure against this problem, the excellent effectiveness of the seed crystal addition method as a means of preventing the formation of gypsum scale has already been reported, and the seed crystal effect is shown in Figure 3. It is also known that the concentration of gypsum particles added as seed crystals has a large effect, as shown in the graph showing "Suppression of supersaturation".

[0004] Based on this seed crystal addition method, conventional methods include a reaction step in which a calcium compound is added to flue gas desulfurization or denitrification wastewater containing fluoride ions and sulfate ions to obtain a suspension, and The treated water and calcium sulfate,
and a step of separating calcium fluoride into a precipitate and a precipitate, in which a step of returning the precipitate to the reaction step is added, thereby recycling and using the gypsum contained in the precipitate as a seed crystal. A wastewater treatment method was proposed that prevents the generation of gypsum scale in the reaction process by doing so (Japanese Patent Publication No. 1-26755).

[0005]

[Problems to be Solved by the Invention] However, in the conventional wastewater treatment method as described above, it is necessary to circulate more than twice the amount of wastewater supplied in order to increase the concentration of gypsum particles so that the scale prevention effect is achieved. Therefore, in the actual processing equipment, not only do the capacities of the dissolution tank, reaction tank, and precipitation tank each have to be more than doubled, but also controls are required to adjust the precipitate in the precipitation tank to a predetermined concentration. This method requires pumps, piping, and the like to circulate the abrasive and sedimentary precipitate, which has the drawback of significantly increasing equipment costs.

[0006]Also, a method of adding gypsum particles to the reaction process from outside the treatment process can be considered, but a gypsum particle storage tank,
Not only will equipment such as supply equipment to the reaction process be required, but the amount of sludge generated in the treatment process will increase, and as a result, the capacity of the sludge concentration and dehydration equipment discharged from the settling tank must be increased. The problem of equipment costs remains as well. An object of the present invention is to sufficiently prevent scale generation while reducing equipment costs.

[0007]

[Means for Solving the Problem] By the way, when we look at the desulfurization waste liquid discharged from a coal combustion flue gas desulfurization device, we find that the waste liquid contains a large amount of sulfate ions, as well as fluorine ions, aluminum ions, and iron ions. If calcium hydroxide is injected into the reaction tank to remove these substances,
As an example, gypsum is usually produced in the largest amount at 50 to 70%, followed by calcium fluoride, aluminum hydroxide, and iron hydroxide in that order. Therefore, when we experimentally measured the sedimentation rate of these products alone, we found that the influence of the particle concentration was large, as shown in the graph of "Relationship between the concentration of crystal particles produced and the sedimentation rate" in Figure 4. It was confirmed that the precipitation rate (interfacial precipitation rate) was high. As an example, the sedimentation velocity of gypsum slurry with a particle concentration of 5% is 0.5 m/
At around 0.06%, iron hydroxide has good flocculation and a fast precipitation rate, but at 0.1%, no flocculation occurs and the sedimentation rate is extremely poor (however, since the precipitation rate is extremely slow, .1% data not shown) was also observed.

Next, 5% gypsum, 11% calcium fluoride
%, aluminum hydroxide 0.5% and iron hydroxide 0.06
% of the mixed product, it was found that the gypsum particles did not coagulate with calcium fluoride, aluminum hydroxide, or iron hydroxide, which have a slow precipitation rate, but precipitated at a much faster rate than these products. was confirmed.

Based on these experiments, the first invention of the present application aims to move a reaction mixture containing gypsum particles generated when a calcium compound is reacted with a waste liquid containing sulfate ions upwardly into the reaction chamber, and then to the upper end of the reaction chamber. The precipitated gypsum particles obtained in advance are made to flow upward through the intermediate zone which is continuous with the intermediate zone at a flow rate higher than the upward flow rate in the reaction chamber, and then in the discharge direction through the acceleration chamber which is continuous with the intermediate zone at a flow rate higher than the flow rate in the intermediate zone. Based on the relationship between the concentration and the sedimentation rate of gypsum particles at that concentration, and a preset gypsum particle concentration that can effectively exhibit the seed crystal effect in the gypsum precipitation reaction, the sedimentation rate of gypsum particles at the above-determined particle concentration is determined. is selected, and the flow rate in the intermediate zone is made approximately equal to the selected sedimentation rate of the gypsum particles, so that the gypsum particles at approximately the set particle concentration are precipitated and held in the reaction chamber, and the set particle concentration is maintained in the acceleration chamber. We proposed a treatment method for wastewater containing sulfate ions, which discharges excess gypsum particles exceeding

[0010] The second invention of the present application, which is effectively used for carrying out the first invention, provides an intermediate zone at the upper end of the reaction chamber, and an acceleration chamber above the intermediate zone in a three-way communication state. and a flow urging means for continuously flowing a reaction mixture containing gypsum particles produced when a calcium compound is reacted with a sulfate ion-containing waste liquid upward into the reaction chamber, the intermediate zone, and then into the acceleration chamber; In order to make the upward flow rate of the zone faster than that of the reaction chamber, the cross-sectional area of the intermediate zone is made smaller than that of the reaction chamber, and a discharge port is provided at the upper end of the acceleration chamber. We propose an improved reaction tank for the treatment of sulfate ion-containing waste liquid, in which the cross-sectional area of the acceleration chamber is smaller than that of the intermediate zone in order to achieve faster speed.

[0011] Hereinafter, an embodiment of an improved reaction tank equipped with a gypsum scale prevention structure in the process of removing sulfate ions, etc. from a sulfate ion-containing waste liquid discharged from a coal flue gas desulfurization device will be described.

0012

[Example] In Fig. 1, the reaction tank has an intermediate zone (P) above the reaction chamber (1), and an acceleration chamber (2) formed above it in a three-way communication state, of which the reaction chamber ( 1) is formed into a cylindrical shape with a bottom, and a waste liquid supply pipe (3) and a calcium compound supply pipe (4) are connected to its side wall, and the tips of each supply pipe (3) and (4) are connected to the reaction chamber. (1)
The supply ports (5) and (6) at the ends of the extension are suspended near the inner bottom surface of the reaction chamber (1). each supply pipe (3),
The rear end of (4) is connected to a desulfurization waste liquid tank and a calcium hydroxide slurry tank (both not shown), and the waste liquid and calcium hydroxide slurry in each tank are transferred to the reaction chamber ( 1), and the reaction mixture of the waste liquid and calcium hydroxide is supplied to the reaction chamber (
1) Inside upwards, then the middle zone (P), the acceleration chamber (2
Pumps (7) and (8) are respectively connected as flow urging means for continuously causing the fluid to flow upwardly through the fluid.

[0013] A hollow truncated cone whose large diameter part has the same diameter as the reaction chamber (1) is connected to the open upper end of the reaction chamber (1), and this hollow truncated cone Inside the large diameter part of the reaction chamber (1), there is an intermediate zone (P
), the entire upper part of which is formed into an acceleration chamber (2) whose diameter is gradually smaller than that of 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).
A geared motor (11) is installed on the top surface of the acceleration chamber (2), and a stirring shaft (12) is connected to the output shaft of the motor (11). is suspended on the center line of the acceleration chamber (2) and the reaction chamber (1), and stirring blades (13) are attached to the lower end of the reaction chamber.

[0014] Next, a method for treating sulfate ion-containing waste liquid using the reaction tank of the above example will be explained. For convenience, sulfate ion 15000mg/l, fluorine ion 1900mg/l
A simulated waste liquid with a pH of 1 (adjusted by adding hydrochloric acid) was prepared with a component ratio of 680 mg/l of calcium ions, 460 mg/l of aluminum ions, 460 mg/l of iron ions, and 3000 mg/l of sodium ions, and this was pumped (
At the same time, calcium hydroxide slurry is supplied into the reaction chamber (1) from the supply port (5) through the supply pipe (3) by driving the pump (8) through the supply pipe (4). ) into the reaction chamber (1), and when the stirring shaft (12) is rotated by starting the motor (11) to stir the inside of the reaction chamber, each ion in the waste liquid reacts with calcium hydroxide, and sulfuric acid It flows upward while producing and precipitating calcium, calcium fluoride, aluminum hydroxide, and iron hydroxide.

[0015] By supplying the waste liquid and calcium hydroxide slurry at a predetermined flow rate from the supply ports (5) and (6), the ascending linear flow velocity in the intermediate zone (P) of the reaction tank can be adjusted to, for example, the seed crystal. The gypsum sedimentation rate is set to be equal to 0.5 m/h (see FIG. 4) at a set particle concentration of 5%, which can fully exhibit the effect. As a result, the upward linear flow velocity in the reaction chamber (1) is slower than the gypsum precipitation rate of 0.5 m/h, and the upward linear flow velocity in the acceleration chamber (2) becomes faster than that, and as a result, the upward linear flow velocity in the reaction chamber (1) becomes faster than that. Gypsum particles precipitate at a concentration equivalent to 5%,
Excess gypsum particles exceeding 5% rise from the reaction chamber (1) to the acceleration chamber (2) along with the aggregates of calcium fluoride, calcium hydroxide, and iron hydroxide, which have a slow settling rate. , is discharged from the discharge port (9). In other words, the concentration of gypsum particles in the intermediate zone (P) increases due to the gypsum particles that continue to be generated by the reaction between the supplied waste liquid and calcium hydroxide, but the sedimentation speed becomes slower than 0.5 m/h, so the 5% The excess gypsum particles are sent upward from the intermediate zone (P) by a fast upward flow, and are sent to the discharge port (
9), and as a result, gypsum with high purity and activity remains in the reaction chamber (1) at a particle concentration that can sufficiently exert the seed crystal effect. and prevents the formation of gypsum scale.

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

By the way, the discharge port (9) in steady state
Filters the solids contained in the discharged liquid in an extremely short time,
When the calcium ion concentration of the filtrate was measured,
The value was 580 mg/l, indicating that the supersaturation of gypsum was sufficiently avoided. Further, this filtrate was allowed to stand for 3 days, but no crystal precipitation was observed.

Furthermore, when the slurry in the reaction chamber (1) was taken and the gypsum particle concentration was measured, it was 5.5%, and in FIG. 4, the particle concentration at a sedimentation rate of 0.5 m/h was 5.5%.
It was found that a sufficient concentration of gypsum particles was formed to exhibit a seed crystal effect.

After carrying out the treatment in the reaction tank for 5 consecutive days, the inner surface of the reaction tank, the stirring shaft (12) and the blade (13)...
When the surface of the specimen was observed, almost no gypsum scale precipitation was observed.

FIG. 2 shows another embodiment of the reaction tank, in which the acceleration chamber (2a) is formed in a cylindrical shape with a smaller diameter than the reaction chamber (1a), and an arcuate inclined connection part with the reaction chamber (1a) is formed. An intermediate zone (Pa) is formed, and the other structures are substantially the same as in FIG.

[0021]

Effects of the Invention According to the method for treating sulfate ion-containing waste liquid of the first invention of the present application, gypsum particles with a predetermined particle concentration that can effectively exert a seed crystal effect are precipitated and retained in the reaction chamber, and the predetermined particle concentration can be maintained. Excess gypsum particles can be discharged, thereby sufficiently preventing the formation of gypsum scale in the reaction chamber, intermediate zone, and acceleration chamber, and without using the conventional sediment circulation method or external gypsum particle addition method. In comparison, the equipment can be significantly simplified and equipment costs 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, and as in the first invention, Compared to conventional processing equipment, the equipment can be significantly simplified and a significant reduction in equipment costs can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional front view of a reaction tank for waste liquid containing sulfate ions.

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

FIG. 3 is a graph showing how calcium sulfate supersaturation 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 room 7, 8 Pump 9 Overflow outlet

Claims (2)

[Claims] Claim 1: A reaction mixture containing gypsum particles produced when a calcium compound is reacted with a waste liquid containing sulfate ions is moved upwardly within the reaction chamber, and then an intermediate zone continuous with the upper end of the reaction chamber is moved upwardly within the reaction chamber. Flowing upward at a flow rate higher than the flow rate, and then flowing in the discharge direction at a flow rate higher than the flow rate of the intermediate zone in an acceleration chamber continuous with the intermediate zone,
Based on the relationship between the precipitated gypsum particle concentration determined in advance and the sedimentation rate of the gypsum particles at that concentration, and the preset gypsum particle concentration that can effectively exert the seed crystal effect in the gypsum precipitation reaction, the above-mentioned set particle concentration is determined. Select the sedimentation rate of the gypsum particles in the intermediate zone, make the flow rate in the intermediate zone approximately equal to the selected sedimentation rate of the gypsum particles, and maintain the gypsum particles at approximately the predetermined particle concentration in the reaction chamber, and at the same time A method for treating wastewater containing sulfate ions, which indoors discharges excess gypsum particles that exceed the set particle concentration above. 2. An intermediate zone is provided at the upper end of the reaction chamber, and an acceleration chamber is provided above the intermediate zone in a three-way communication state,
A flow urging means is provided for causing a reaction mixture containing gypsum particles produced when a calcium compound is reacted with a sulfate ion-containing waste liquid to flow continuously upward into the reaction chamber, the intermediate zone, and then into the acceleration chamber. In order to make the upward flow rate faster than that of the reaction chamber, the cross-sectional area of the intermediate zone is made smaller than that of the reaction chamber, and a discharge port is provided at the upper end of the acceleration chamber, and the upward flow rate of the acceleration chamber is made faster than that of the intermediate zone. An improved reaction tank for the treatment of sulfate ion-containing waste liquid, in which the cross-sectional area of the acceleration chamber is smaller than that of the intermediate zone in order to speed up the treatment.