JP3133272B2 - Method for estimating suspended solids concentration and evaporating and concentrating desulfurization wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for estimating the concentration of a suspended substance in a solution in which salts are dissolved in real time.

[0002]

BACKGROUND OF THE INVENTION Flue gas desulfurization effluent contains an inorganic salt such as calcium sulfate dissolved therein. As a method of treating the flue gas desulfurization effluent, a coagulant such as a two-stage coagulation sedimentation filtration method is added to carry out sedimentation filtration. There are a method and a method of evaporating water by evaporative concentration. The evaporative concentration method has advantages over the two-stage coagulation sedimentation filtration method in that the treatment efficiency is high, the amount of sludge generated is small due to the small amount of chemical used, and the installation area of the apparatus can be reduced. In recent years, it has attracted attention as a method for treating flue gas desulfurization wastewater.

However, in the evaporative concentration method, since the moisture in the flue gas desulfurization wastewater is evaporated and concentrated by the evaporative concentration device, the scale component contained in the flue gas desulfurization wastewater in the concentration step is transferred to a heat transfer tube or the like in the evaporative concentration device. There is a disadvantage that it is easily attached. Various techniques have been proposed as a method for preventing scale adhesion.However, a seed crystal is added to the solution to perform evaporation and concentration, and the scale component is attached to the seed crystal or precipitated in a concentrated solution to form a heat transfer tube. There is a method of preventing the scale from adhering to the surface.

[0004] In the method of adding seed crystals, it is necessary to maintain the concentration of the seed crystals in the concentrated liquid circulating in the evaporative concentration apparatus at about 5 to 25 wt%. If the concentration of the seed crystal in the concentrate is out of the above range, the scale prevention effect is reduced, so that the concentration of the seed crystal in the concentrate, that is, the concentration of the suspended substance in the concentrate is accurately measured, and the suspension is measured. It is necessary to control the concentration of the substance.

[0005] The concentration of the concentrated liquid circulated in the evaporative concentration apparatus is generally controlled in accordance with the method for measuring suspended solids and evaporation residues according to JIS K0102 ("Method of testing wastewater from factories"). In order to measure the concentration of the concentrated liquid, the correlation between the indicated value of the hydrometer and the suspended substance and the evaporation residue is determined in advance, and the concentration of the concentrated liquid is calculated from the specific gravity of the concentrated liquid.

[0006] However, the hydrometer does not allow the suspended substance to dissolve.
The combined concentration of the volatile residues is measured and the suspended solids concentration cannot be measured alone.

As a method for measuring the concentration of the suspended substance in the concentrated liquid, there is a method using a turbidity meter. In the case of using a turbidity meter, the upper limit is usually to measure a concentration of about 5 wt%. In order to measure a concentrated solution having a concentration exceeding 5 wt%, it is necessary to dilute the concentrated solution. Therefore, it was difficult to measure the concentration of the suspended substance in the concentrate in real time.

[0008]

The problem to be solved by the present invention is that the concentration of suspended solids in a solution containing soluble evaporation residues and suspended solids, in particular, the elimination of seeds to prevent scaling. Provided are a method for automatically and in real time estimating the concentration of seed crystals (suspended substances), which is important in the evaporative concentration method of smoke desulfurization wastewater, in real time, and a method for evaporating and desulfurizing wastewater without attaching scale. That is.

[0009]

Means for Solving the Problems The present inventors have noticed that the boiling point of a solution in which salts are dissolved rises due to the presence of salts, and have completed the present invention.

That is, the present invention provides: (1) A method for estimating the concentration of suspended solids in a solution containing soluble evaporated residues and suspended substances, the method comprising: ) Total evaporation residue (wt%) = f (specific gravity) (1) is obtained, and the correlation equation between the soluble evaporation residue and the boiling point rise temperature (2) Soluble evaporation residue (wt%) = f (Boiling point rise temperature) …… (2) is determined, the specific gravity and the boiling point rise temperature of the solution containing the soluble evaporation residue and the suspended substance are measured, and the measured specific gravity and the boiling point rise temperature are expressed by the formula (3) (wt%) = f (specific gravity) -f (boiling temperature increase) .... of the solution containing the soluble evaporation residue <br/> and suspended matter, characterized in that assignment to calculating the (3) suspension Estimation method of suspended matter concentration, (2) Measure boiling point temperature, solution temperature and generated steam temperature (4) The method for estimating the concentration of suspended solids according to the above item (1), wherein the temperature is determined by the following equation: , (3) a solution containing a soluble evaporation residue and suspended solids, suspended solids concentration as described in (1) or (2) of a desulfurization waste water containing soluble evaporation residue and suspended solids (4) a method of evaporating and concentrating by circulating desulfurization wastewater containing a soluble evaporation residue and a suspended substance, wherein the concentration of the suspended substance in the evaporative concentrate is estimated by the method described in (1) above. ,
The present invention relates to a method for evaporating and condensing desulfurized wastewater, wherein the concentration of suspended solids is maintained at 5 wt% to 25 wt%.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention has been made focusing on the fact that the boiling point of a solution in which salts are dissolved increases. First, the total amount of the soluble evaporation residue and the suspended substance in the solution containing the suspended evaporation residue and the suspended substance to be measured in advance, that is, the correlation between the total evaporation residue and the specific gravity of the solution The relationship is determined, and the correlation equation (1) using specific gravity as an independent variable, total evaporation residue (wt%) = f (specific gravity) (1) is determined in advance.

On the other hand, the boiling point of the solution rises due to the presence of the soluble evaporation residue .
The boiling point of the solution containing evaporation residues and suspended solids
The correlation with the concentration of the soluble evaporation residue is determined, and the correlation equation (2) using the boiling point rising temperature as an independent variable is determined. Soluble evaporation residue (wt%) = f (boiling point rising temperature) (2) deep.

Next, the specific gravity of the solution whose boiling point concentration is to be actually estimated and the boiling point rise temperature are measured and substituted into the above-mentioned correlation equation to determine the concentrations of the total evaporation residue and the soluble evaporation residue. Since the value obtained by subtracting the concentration of the soluble evaporation residue from the total evaporation residue is the concentration of the suspended substance, the concentration of the suspended substance can be calculated by the following equation (3).

Suspended substance (wt%) = f (specific gravity) −f (boiling point rising temperature) (3) In this way, specific gravity and boiling point rising temperature of a solution containing a soluble evaporation residue and a suspended substance Is measured, the concentration of the suspended substance in the solution can be estimated in real time.

[0015] In the method of the present invention, to measure the boiling temperature increase the solubility evaporation residue and measuring the boiling point of the solution containing the suspended matter, the boiling point of the solution containing no soluble evaporation residue and suspended solids May be determined, but the solubility evaporation
The temperature of the solution containing the residue and the suspended substance and the generated steam temperature of the solution are measured, and the equation (4): Boiling point rise temperature (° C.) = Solution temperature (° C.) − Generated steam temperature (° C.) (4) Is more preferable in that the boiling temperature can be measured in real time.

In the method of the present invention, the method for measuring the specific gravity is not particularly limited, but a Coriolis type or differential pressure type specific gravity meter is preferable because it can perform a measurement process using an electric signal.

[0017] The method of claim 1, soluble evaporation residue
If a solution containing mono- and suspended matter, soluble evaporation residue
This method is capable of estimating the concentration of suspended solids regardless of the type of solids , suspended solids, and solutions. Particularly, when desulfurization wastewater is evaporated and concentrated, the solubility of magnesium, calcium, chloride ions, sulfate ions, etc. This is particularly effective because the concentration of the suspended substance (seed crystal) in the concentrated liquid containing the evaporation residue and the suspended substance (seed crystal) such as gypsum (gypsum) can be controlled in real time.

The method for estimating the concentration of suspended solids according to the present invention comprises:
The measurement and the calculation may be performed manually, but the equations (1), (2), and (3) of the correlation equation obtained in advance and the equation (4) for obtaining the boiling point rise temperature from the solution temperature and the generated steam temperature are used. Automatically estimated by a storage substance concentration estimating device having a storage section for storing and a calculation section for estimating the concentration of the suspended substance from the measured specific gravity, solution temperature, and generated steam temperature by the equations (3) and (4). May be.

Hereinafter, a method for evaporating and condensing desulfurization wastewater will be described with reference to the flowchart of FIG. The invention according to claim 4 is a method for evaporating and condensing desulfurization wastewater, but the means for evaporating and condensing is not particularly limited. For example, the evaporating concentrator may be a horizontal heat transfer tube system or a vertical thin film system. May be. The heating may be of an external heating type or a self-vapor compression type.

The desulfurization effluent is supplied from the effluent supply line aa
P which stores acid or alkali for adjustment tank 1
A pH-adjusting chemical is injected from the H-adjusting chemical tank 5 via an injection pump 8 to adjust the pH of the desulfurization effluent from weakly acidic to neutral.

The desulfurized wastewater whose pH has been adjusted is supplied to the evaporative concentrator 2 via a supply pump 9. The evaporating concentrator 2 is supplied with a vacuum pump 11 through the condenser 3 to about -500 mmHg.
, And the steam supplied from the heating steam line bb is supplied to a heat transfer tube (not shown) to serve as a heat source, and the operating temperature is set to about 70 ° C.

The vapor evaporated by the evaporator 2 is sent to a thermometer 7
The condensed water pump 12 discharges the generated steam to the outside of the system. Line cc, dd
Is a line for cooling water flowing into and out of the condenser 3.

On the other hand, the concentrated liquid concentrated in the evaporative concentrator 2 is circulated to the evaporative concentrator 2 by the concentrated liquid circulating pump 10 and the switching valve 15.
The specific gravity and the temperature of the concentrate are measured by 4 and a thermometer 6. When the concentrated liquid concentrated while circulating reaches a certain concentration, the flow path is switched by the switching valve 15 and discharged to the concentrated liquid tank 4. The drain of the heated steam is discharged by the steam drain pump 13.

For the desulfurization wastewater, the correlation between the total evaporation residue and the specific gravity and the correlation between the soluble evaporation residue and the boiling point rise temperature are determined in advance.

From the temperature of the concentrate and the temperature of the generated steam during the concentration circulation, the boiling point rise temperature is determined by the above equation (4), and the suspension in the concentrate is calculated by the above equation (3) from the measured specific gravity of the concentrate and the boiling point rise temperature. Estimate the concentration of suspended matter.

If the concentration of the suspended solids becomes less than 5 wt%, a solid-liquid separation facility typified by a cyclone separator is provided in the concentrated liquid discharge line to collect and return the suspended solids. If the concentration of the suspended solids exceeds 25 wt%, there is a concern that the suspended solids may be clogged in the pipes, so that the operation is performed to reduce the concentration ratio. By adjusting the concentration of the seed crystal (suspension substance) by such a method, generation of scale in the evaporator 2 can be prevented.

FIG. 2 is a flow chart in the case of automatically estimating the concentration of the suspended substance in the concentrated liquid. In the figure, the same devices are denoted by the same reference numerals and description thereof is omitted. The electric signals (dotted lines) measured by the specific gravity meter 14, the concentrated liquid thermometer 6, and the generated steam thermometer 7 are used as input signals, and the correlation formulas (1), (2), (3) and (4) obtained and stored in advance are used. The values of the specific gravity, the temperature of the concentrated solution, and the temperature of the generated steam are substituted in the above), and the suspended substance concentration estimating device 16 calculates the suspended substance concentration in the concentrated liquid in real time. By maintaining the estimated suspended solid concentration in the range of 5 wt% to 25 wt%, the occurrence of scaling can be prevented.

[0028]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 In the evaporative concentration test in the examples, the desulfurization effluent shown in Table 1 was evaporated and concentrated under the conditions of -500 mmHg and about 70 ° C., and the concentration operation was performed to about 12 times.

[0030]

[Table 1]

In the process of concentrating the desulfurized effluent of Table 1 to about 12 times, the total evaporation residue and specific gravity of the concentrated liquid were determined according to JIS K
Appropriately determined on the basis of 0102, it was determined both correlation relationships were as follows. The specific gravity meter used was a Coriolis type densitometer (Sakura Endless, model number 63FS25).

Total evaporation residue (wt%) = 160 × (specific gravity-1) Similarly, in the concentration process, the boiling point increase temperature and the soluble evaporation residue were appropriately measured based on JIS K0102, and the relationship between the two was determined. The correlation equation was as follows.

Soluble evaporation residue (wt%) = 8 × boiling point temperature (° C.) Accordingly, the concentration of the suspended substance is represented by the following equation.

Suspended substance concentration (wt%) = 160 × (specific gravity−1) −8 × boiling point rise temperature (° C.) = 160 × (specific gravity−1) −8 × (solution temperature (° C.) − Evolved steam temperature ( ° C)) According to the above equation, the concentration of the suspended substance was estimated from the measured values of the specific gravity of the concentrated solution during the evaporation concentration, the concentrated solution temperature, and the generated steam temperature. Further, the concentrated liquid at that time was analyzed based on JIS K0102, and the concentration of the suspended substance was analyzed. FIG. 3 shows the results of the estimated value (horizontal axis, calculated value) and the analytical value (vertical axis, analytical value) of the concentration of the suspended solids.

As is clear from the results shown in FIG. 3, the estimated value of the concentration of the suspended substance according to the method of the present invention correlated well with the analytical value of the suspended substance.

[0036]

According to the method of the present invention, the concentration of a suspended substance in a solution containing a soluble evaporation residue and a suspended substance can be estimated accurately and in real time.

According to the method of the present invention, when evaporating and concentrating desulfurization effluent containing soluble evaporation residues and suspended solids, seed crystals (suspended solids) which are important factors for preventing scaling are removed . The concentration can be measured in real time, and scaling can be easily prevented.

Further, the method of the present invention is easy to automate, and enables automatic operation of evaporative concentration of desulfurization wastewater.

[Brief description of the drawings]

FIG. 1 is a flow chart for estimating the concentration of suspended solids in a concentrated liquid when evaporating and condensing desulfurization wastewater.

FIG. 2 is a flowchart for automatically estimating the concentration of suspended solids in a concentrated liquid when evaporating and condensing desulfurization wastewater.

FIG. 3 is a graph showing a relationship between an estimated value according to the present invention and an analytical value of the concentration of a suspended substance in a concentrated solution in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 pH adjustment tank 2 Evaporation concentrator 3 Condenser 4 Concentrated liquid tank 5 pH adjusted chemical tank 6 Circulating fluid temperature 7 Generated steam thermometer 8 pH adjusted chemical injection pump 9 Drainage supply pump 10 Concentrated liquid circulation pump 11 Vacuum pump 12 Condensed water pump 13 Steam drain pump 14 Densitometer 15 Switching valve 16 Suspended substance concentration estimating device aa Wastewater supply line bb Heating steam line cc Cooling water inlet line dd Cooling water outlet line

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C02F 1/04 (72) Inventor Hideki Takahashi 5-5-1-16 Hongo, Bunkyo-ku, Tokyo Organo Corporation (72) Inventor Tomoaki Ito 5-5-16 Hongo, Bunkyo-ku, Tokyo Organo Corporation (56) References JP-A-51-51997 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 25/10 B01D 1/00 B01D 53/34 ZAB B01D 53/50 B01D 53/77 C02F 1/04

Claims (4)

(57) [Claims] In a method for estimating the concentration of a suspended substance in a solution containing a soluble evaporation residue and a suspended substance, a correlation equation between the total evaporation residue and the specific gravity of the solution (1) %) = F (specific gravity) (1) is obtained, and a correlation equation between the soluble evaporation residue and the boiling point rise temperature (2) Soluble evaporation residue (wt%) = f (boiling point rise temperature) (2) is determined, the specific gravity and the boiling point rise temperature of the solution containing the soluble evaporation residue and the suspended substance are measured, and the measured specific gravity and the boiling point rise temperature are expressed by the following equation (3): suspended substance (wt%) = f ( Specific gravity) -f (boiling point rise temperature) A method for estimating the concentration of a suspended substance in a solution containing a soluble evaporation residue and a suspended substance, which is calculated by substituting into (3). 2. The boiling point rise temperature, the solution temperature and the generated steam temperature are measured, and the following equation (4): Boiling point rise temperature (° C.) = Solution temperature (° C.) − Generated steam temperature (° C.) (4) The method for estimating the concentration of a suspended substance according to claim 1, wherein the estimation is performed. 3. A solution comprising a soluble evaporation residue and suspended solids, soluble evaporation residue and suspended matter estimation of suspended matter concentration according to claim 1 or claim 2 is desulfurized effluent containing Method. 4. A method of circulating desulfurization wastewater containing a soluble evaporation residue and a suspended substance and evaporating and concentrating the suspension, estimating the concentration of the suspended substance in the evaporative concentrated liquid by the method according to claim 1, A method for evaporating and condensing desulfurization wastewater, wherein the substance concentration is maintained at 5 wt% to 25 wt%.