TWI752711B - Monitoring method for alkalinity of bicarbonate ions in waste water from steelmaking process - Google Patents

Abstract

The present invention relates to a monitoring method for an alkalinity of bicarbonate ions in waste water from a steelmaking process. In the monitoring method, judgment indexes are established by standard solutions with known alkalinities of bicarbonate ions and standard pH values corresponding thereto. According to the judgment index corresponding to a measured pH value of waste water from the steelmaking process, an alkalinity of bicarbonate ions in waste water from the steelmaking process is obtained correspondingly. The monitoring method can obtain rapidly the alkalinity of bicarbonate ions in waste water from the steelmaking process, thereby taking response measures into practice.

Description

Method for monitoring bicarbonate ion alkalinity in wastewater from steelmaking process

The present invention relates to a method for monitoring the alkalinity of bicarbonate ions, and in particular to a method for monitoring the alkalinity of bicarbonate ions in waste water from steelmaking processes.

In the steelmaking process, when blowing molten steel, lime is added to the steelmaking furnace as a flux to remove impurities in molten iron. Lime in powder form is easily dissipated into the converter chimney, so the converter dust washing water is used to wash the lime and other dust dissipated in the converter chimney and converter gas. The lime will react with the water in the converter dust washing water to form calcium hydroxide, which is one of the sources of calcium hardening in the converter dust washing water. The aforementioned reaction is shown in the following formula (I): CaO+H ₂ O→Ca(OH ) ₂ (I)

Because the converter gas contains carbon monoxide and carbon dioxide, during the washing process, the carbon dioxide will react with the sodium hydroxide in the converter dust washing water to generate sodium carbonate and sodium bicarbonate, and the reactions are shown in the following formulas (II) and (III): 2NaOH+ CO _2(g) →Na ₂ CO ₃ +H ₂ O (II) Na ₂ CO ₃ +CO _2(g) +H ₂ O→2NaHCO ₃ (III)

Secondly, the calcium hydroxide in the converter dust washing water can further react with sodium carbonate and/or sodium bicarbonate to generate calcium carbonate (as shown in the following formulas (IV) and (V)). By removing the calcium carbonate, the hardness of the converter dust washing water can be reduced, thereby avoiding the fouling of equipment such as converter chimneys and induced windmills. Ca(OH) ₂ +2Na ₂ CO ₃ →CaCO _3(s) +2NaOH (IV) Ca(OH) ₂ +2NaHCO ₃ →CaCO _3(s) +Na ₂ CO ₃ +2H ₂ O (V)

Accordingly, hydroxide ions, carbonate ions and/or bicarbonate ions in the converter dust washing water will affect the generation of calcium carbonate. When carbonate ions and bicarbonate ions coexist in the converter dust washing water, it is beneficial to the formation of calcium carbonate and helps to reduce the hardness of the converter dust washing water. When the concentration of bicarbonate ions decreases, the converter dust washing water tends to have too many hydroxide ions, which is not conducive to the production of calcium carbonate. Accordingly, by monitoring the alkalinity of bicarbonate ions in the converter dust washing water, the rate and amount of carbonate added to the converter dust washing water can be adjusted, thereby facilitating the generation of calcium carbonate and reducing the hardness of the converter dust washing water.

Generally, acid-base titration is used to monitor the alkalinity of bicarbonate ions. Wherein, titration to the end point of phenolphthalein indicator by sulfuric acid standard solution, can utilize the usage quantity of sulfuric acid to calculate the equivalent number, then through the conversion of calcium carbonate molecular weight, and obtain the P alkalinity (phenolphthalein alkalinity (phenolphthalein alkalinity) represented _{by mgCaCO 3 /L unit} ).

Then, continue the titration to the end point of the methyl red mixed indicator, and through the same conversion method, the total alkalinity or M alkalinity can be obtained. As shown in Table 1 below, the alkalinity of bicarbonate ions can be calculated from the P alkalinity and M alkalinity.

註：「P」表示P鹼度；「M」表示M鹼度 Table 1

Note: "P" means P alkalinity; "M" means M alkalinity

However, the aforementioned monitoring method needs to send the sample to another place for inspection, and cannot provide real-time measurement results, so it is difficult to adjust the addition rate and amount of carbonate in real time, and it is impossible to take immediate countermeasures.

Therefore, there is an urgent need for a new method for monitoring the alkalinity of bicarbonate ions in wastewater from steelmaking processes to improve the aforementioned shortcomings.

In view of this, one aspect of the present invention provides a method for monitoring the alkalinity of bicarbonate ions in wastewater from a steelmaking process. This monitoring method is based on the standard solution of known bicarbonate ion alkalinity and its corresponding standard pH value to establish the judgment index. Then measure the pH value of the wastewater in the steelmaking process, and according to its corresponding judgment index, to quickly obtain the alkalinity of bicarbonate ions of the wastewater, and then take immediate measures.

According to an aspect of the present invention, a method for monitoring the alkalinity of bicarbonate ions in wastewater from a steelmaking process is provided. The monitoring method includes a modeling step and a measurement step. In the modeling step, a pH meter is used to determine the standard pH value of each of a plurality of standard solutions, each of which has a known bicarbonate ion alkalinity.

Next, a database is established, wherein the database includes the known basicity of bicarbonate ions and the corresponding standard pH value of each standard solution. Then, the standard pH values in the database are sorted to establish a plurality of judgment indexes, wherein each judgment index corresponds to a bicarbonate ion alkalinity range according to the aforementioned database.

In the measuring step, a pH meter is used to measure the pH value of the wastewater from the steelmaking process. Next, the measured pH value and these judgment indicators are compared to obtain the bicarbonate ion alkalinity of the aforementioned steelmaking process wastewater correspondingly.

According to an embodiment of the present invention, the standard solutions include a plurality of converter dust washing waters.

According to yet another embodiment of the present invention, the known basicities of bicarbonate ions are measured by acid-base titration.

According to another embodiment of the present invention, the aforementioned judgment index includes a first judgment index, a second judgment index and a third judgment index, wherein the first judgment index represents that the pH value is greater than or equal to 9.4 and less than 10, and the second judgment index It represents that the pH value is greater than or equal to 10 and less than or equal to 10.5, and the third judgment index represents that the pH value is greater than 10.5 and less than or equal to 11.0.

According to yet another embodiment of the present invention, when the measured pH value of the steelmaking process wastewater corresponds to the first judgment index, the bicarbonate ion alkalinity of the steelmaking process wastewater is judged to be less than or equal to 1600 and greater than 300. mgCaCO ₃ /L.

According to yet another embodiment of the present invention, the aforementioned monitoring method further includes performing a first countermeasure, wherein the first countermeasure is not to add carbonate to the waste water of the steelmaking process.

According to another embodiment of the present invention, when the measured pH value of the steelmaking process wastewater corresponds to the second judgment index, the bicarbonate ion alkalinity of the steelmaking process wastewater is judged to be less than or equal to 300 and greater than or Equal to 1 mgCaCO ₃ /L.

According to yet another embodiment of the present invention, the aforementioned monitoring method further includes a second response measure, wherein the second response measure is to monitor the pH value of the steelmaking process wastewater.

According to yet another embodiment of the present invention, when the measured pH value of the steelmaking process wastewater corresponds to the third judgment index, the bicarbonate ion alkalinity of the steelmaking process wastewater is judged to be less than 1 and equal to or greater than 0 mgCaCO ₃ /L.

According to another embodiment of the present invention, the aforementioned monitoring method further includes performing a third countermeasure, wherein the third countermeasure is to add carbonate to the waste water of the steelmaking process.

The method for monitoring the alkalinity of bicarbonate ions in the waste water of the steelmaking process of the present invention is to measure the alkalinity of bicarbonate ions and the pH value of the standard solution by acid-base titration and acid-base measurement, respectively, to establish By determining the index, the alkalinity of bicarbonate ions can be obtained according to the acid-base value of the wastewater in the steelmaking process, and contingency measures can be taken.

The manufacture and use of embodiments of the present invention are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are provided for illustration only, and are not intended to limit the scope of the invention.

Please refer to FIG. 1 , which is a schematic flowchart of a method for monitoring the alkalinity of bicarbonate ions in wastewater from a steelmaking process according to an embodiment of the present invention. In the monitoring method 100, the modeling step 110 is performed first. In the modeling step 110 , a pH meter is used to measure the standard pH value of each standard solution, wherein these standard solutions all have a known alkalinity of bicarbonate ions, as shown in operation 111 .

In some embodiments, such standard solutions may include salts of hydroxide, carbonate, and bicarbonate with Group IA and Group IIA metals. In the foregoing embodiments, such standard solutions may optionally contain oxides of Group IIA metals. Specific examples of the standard solution may be an aqueous solution prepared from salts such as sodium hydroxide, sodium carbonate, sodium bicarbonate, calcium hydroxide, calcium carbonate, calcium bicarbonate, and calcium oxide.

In other embodiments, the converter dust washing water can be used as the standard solution, and the converter dust washing water can be verified to prove that the alkalinity of the bicarbonate ions measured is not disturbed by the matrix (ie other composition) in the converter dust washing water. In the verification step, a known amount of calcium bicarbonate was added to the converter dust washing water, and the bicarbonate ions of the converter dust washing water without and after addition were measured by the following acid-base titration method of P alkalinity and M alkalinity of alkalinity. According to the difference between the bicarbonate ion alkalinity of the aforementioned two and the alkalinity measured by the aforementioned known amount of calcium bicarbonate alone, the same two values represent that the matrix in the converter dust washing water does not interfere with the bicarbonate ion alkalinity. .

The bicarbonate ion alkalinity of the standard solution was determined by acid-base titration. In some embodiments, the acid-base titration is performed using a calibrated standard acid solution, wherein the standard acid solution may be a standard hydrochloric acid solution or a standard sulfuric acid solution, and the concentration of the standard acid solution may be 0.02 N or 0.1 N. The calibration of the standard acid solution can be carried out using a potentiometric titrator and a sodium carbonate solution of the primary standard.

When the first end point of the titration is reached (ie, the pH value is 8.3), the hydroxide ions are completely neutralized, and half of the carbonate ions are converted to bicarbonate ions. Therefore, the equivalent number of the titrated standard acid solution (called P alkalinity) is equal to 1/2 the sum of the alkalinity of carbonate ions and hydroxide ions.

Then, the titration is continued, and when the second titration end point (that is, the pH value is 4.3) is reached, the carbonate ions and bicarbonate ions are all neutralized. Therefore, the number of equivalents of the total titrated standard acid solution (called M alkalinity) is the sum of the alkalinities of hydroxide ions, carbonate ions and bicarbonate ions.

In some embodiments, the aforementioned first titration end point or second titration end point can also be determined by using an indicator or a pH meter. For example, the indicator for the first titration endpoint may include phenolphthalein or m-cresol violet, and the indicator for the second titration endpoint may include methyl red, methyl orange, or bromocresol green.

For example, in the calibration process, a standard sulfuric acid solution of a known volume (V2, in mL) is calibrated with a sodium carbonate solution of known normality (N1, in N), and according to the volume of sodium carbonate solution (V1 , the unit is mL) to calculate the normal concentration (N2, the unit is N) of the standard sulfuric acid solution, and its calculation formula is shown in the following formula (VI).

Then, the determination of P alkalinity and M alkalinity is carried out, wherein 2 to 3 drops of phenolphthalein indicator solution are added dropwise to each standard solution of known volume (V3, in mL). Titrate the standard sulfuric acid solution whose normal concentration (N2) is known through calibration until the standard solution changes from red to colorless, record the volume (V4, in mL) of the titrated standard sulfuric acid solution, and calculate according to the following formula (VII) P alkalinity (in mgCaCO ₃ /L).

Next, drop 2 to 3 drops of bromocresol green-methyl red mixed indicator solution into the aforementioned standard solution, continue to titrate with standard sulfuric acid solution until the standard solution changes from red to blue, and record the volume of the titrated standard sulfuric acid solution (V5, in units of mL), and M is an alkali度calculated by the following formula (VIII) in accordance with (in mgCaCO ₃ / L).

In this way, according to Table 1, the alkalinity of the bicarbonate ion of the standard solution can be obtained by using the P alkalinity and the M alkalinity. Further, the alkalinity of bicarbonate ions of the remaining standard solutions was obtained in the same manner.

After the aforementioned operation 111 , a database is established, wherein the database includes the basicity of bicarbonate ions and the corresponding standard pH value of each standard solution, as shown in operation 112 . In some embodiments, the bicarbonate ion alkalinity of each standard solution and its corresponding standard pH value are collected in a database.

After the aforementioned operation 112 , the standard pH values in the database are sorted to establish a plurality of judgment indicators, as shown in the operation 113 . Wherein, each judgment index corresponds to a pH value range, and the basicity range of bicarbonate ions can be correspondingly obtained according to the pH value range.

The aforementioned sorting can be performed according to the size of the measured standard pH value. For example, sort from small standard pH to large standard pH. In some specific examples, these standard solutions are divided into three categories to establish three judgment indicators. For example, the judgment index may be a first judgment index, a second judgment index, and a third judgment index, wherein the first judgment index represents that the pH value is greater than or equal to 9.4 and less than 10, and the second judgment index represents that the pH value is greater than or equal to 10 and less than or equal to 10.5, and the third judgment index represents that the pH value is greater than 10.5 and less than or equal to 11.0.

It is understandable that the number of the aforementioned judgment indicators is only an illustration. In other embodiments, those with ordinary knowledge can set the number of judgment indicators according to requirements according to the content disclosed in the present invention. For example, four judgment indexes may be established, wherein the first judgment index, the second judgment index, and the third judgment index are as defined above, and the fourth judgment index represents that the pH value is greater than 11.0.

Please continue to refer to Figure 1. After the modeling step 110, a measurement step 120 is performed. In the measuring step 120 , a pH meter is used to measure the measured pH value of the wastewater from the steelmaking process, as shown in operation 121 . After operation 121 , the measured pH value and the aforementioned judgment index are compared to obtain the bicarbonate ion alkalinity of the wastewater in the steelmaking process, as shown in operation 122 . According to the obtained bicarbonate ion alkalinity of the wastewater from the steelmaking process, on-site operators can immediately take contingency measures to control the hardness of the converter dust-washing water, which can avoid the converter chimneys and induced windmills from fouling.

For example, after three judgment indexes are established in the database, the measured pH value of the steelmaking process wastewater is measured to be 9.8, which corresponds to the first judgment index. According to the established database, the bicarbonate ion alkalinity of the wastewater from the steelmaking process can be obtained correspondingly to be less than or equal to 1600 and greater than 300 mgCaCO ₃ /L. At this time, the concentrations of bicarbonate ions and carbonate ions are favorable for the formation of calcium carbonate, so the first countermeasure is taken, that is, no carbonate is added to the waste water of the steelmaking process.

When the measured pH value of the steelmaking process wastewater is 10.2, it corresponds to the second judgment index, and the bicarbonate ion alkalinity of the steelmaking process wastewater correspondingly obtained is less than or equal to 300 and greater than or equal to 1 mgCaCO ₃ / L. At this time, it is necessary to pay attention to whether the alkalinity of bicarbonate ions in the wastewater from the steelmaking process has decreased (that is, the pH value has increased). If the above situation occurs, carbonate or its solution should be added to the steelmaking process wastewater appropriately to maintain the bicarbonate ion alkalinity of the steelmaking process wastewater by regulating carbonate ions within the range that is conducive to the production of calcium carbonate.

When the measured pH (10.8) of the steelmaking process wastewater corresponds to the third judgment index, the bicarbonate ion alkalinity corresponding to the steelmaking process wastewater is less than 1 and equal to or greater than 0 mgCaCO ₃ /L. This bicarbonate ion alkalinity indicates that there are almost no bicarbonate ions in the wastewater from the steelmaking process, which is not conducive to removing hardness. Therefore, carbonate or its solution is added to react with carbon dioxide to generate bicarbonate ions, which is beneficial to remove the hardness of the wastewater from the steelmaking process. The aforementioned carbonates may include salts such as sodium carbonate or potassium carbonate, and such salts can regulate the pH value of the wastewater from the steelmaking process.

The following examples are used to illustrate the application of the present invention, but it is not intended to limit the present invention. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention.

Create a database

1. Determination of bicarbonate ion alkalinity and standard pH value of standard solution

Example 1

Using converter dust washing water as the standard solution, take 10 mL of converter dust washing water into a conical flask, drop 2 to 3 drops of phenolphthalein indicator solution, and stir evenly. The acid-base titration was performed using a calibrated 0.02 N standard sulfuric acid solution. When the color of the converter dust washing water changes from colorless to pink, it means that the first titration end point is reached, and the P basicity of the converter dust washing water is calculated by the above formula (VII).

Then, add 2 to 3 drops of bromocresol green-methyl red mixed indicator solution dropwise and stir uniformly. Continue with the titration. When the color of the converter dust washing water changes from red to blue, it means that the second titration end point is reached, and the M alkalinity of the converter dust washing water is calculated by the above formula (VIII). Then, according to the above Table 1, the basicity of bicarbonate ions in the converter dust washing water of Example 1 was calculated by using the P basicity and the M basicity. In addition, the standard pH value of the converter dust washing water of Example 1 was measured using a pH meter.

Examples 2 to 213

Examples 2 to 213 In the same manner as in Example 1, the basicity and the standard pH value of the bicarbonate ion of the standard solution were measured. The measurement results of the aforementioned Examples 1 to 213 are shown in Table 2 below, and a database is established therefrom.

Table 2

2. Establish judgment indicators

Please refer to Table 2, after sorting the standard pH values, classify these standard solutions into three categories, and establish three judgment indicators, wherein the first judgment index represents that the pH value is greater than or equal to 9.4 and less than 10, the second The judgment index represents that the pH value is greater than or equal to 10 and less than or equal to 10.5, and the third judgment index represents that the pH value is greater than 10.5 and less than or equal to 11.0.

Further, corresponding to the first determination index equal to or less than 1600 and greater than 300 mgCaCO3 / L of bicarbonate ions alkalinity, corresponding to the second determination index is less than or equal to 300 and greater than or equal to 1 mgCaCO ₃ / L of bicarbonate ions base degree, and the third judgment index corresponds to the bicarbonate ion alkalinity less than 1 and equal to or greater than 0 mgCaCO _{3 /L.}

Determination of acid-base value of wastewater from steelmaking process

Application Example 1 to Application Example 89

89 converter dust washing waters were obtained and used as the waste water in the steelmaking process of Application Example 1 to Application Example 89. Use a pH meter to measure the converter dust washing water of these application examples to obtain the measured pH value of each application example. The above-mentioned measured pH value is compared with the three judgment indicators to obtain the bicarbonate ion alkalinity of the converter dust washing water corresponding to these application examples.

Further, the measurement results of these application examples are verified by the traditional acid-base titration method, and the measurement results and verification results are shown in Table 3 below:

table 3

The correct rate (unit is 100%) of the monitoring method of bicarbonate ion alkalinity in the waste water of the steelmaking process of the present invention is calculated by dividing the number of the application examples that the measurement result is correct in the above table 3 by the total number of the application examples. , its value is 88.8%.

To sum up, the method for monitoring the alkalinity of bicarbonate ions in the wastewater of the steelmaking process of the present invention includes a modeling step and a measuring step. In the modeling step, the bicarbonate ion alkalinity and the standard pH value of the standard solution are measured by the acid-base titration method and the acid-base meter measurement method respectively, so as to establish the judgment index. In the measuring step, the measured pH value of the steelmaking process wastewater is measured, and after comparing the measured pH value with these judgment indicators, the corresponding bicarbonate ion alkalinity of the wastewater is obtained. Compared with the traditional acid-base titration method, the method for monitoring the alkalinity of bicarbonate ions in the waste water of the steelmaking process of the present invention can reduce the time for manual sampling and traditional testing, so that contingency measures can be taken immediately.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field to which the present invention pertains can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the appended patent application.

100: Method 110, 120: Steps 111, 112, 113, 121, 122: Operation

In order to have a more complete understanding of the embodiments of the present invention and their advantages, please refer to the following description together with the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are for illustrative purposes only. The relevant diagrams are described as follows:

FIG. 1 is a schematic flow chart illustrating a method for monitoring the alkalinity of bicarbonate ions in wastewater from a steelmaking process according to an embodiment of the present invention.

100: Method

110, 120: Steps

111, 112, 113, 121, 122: Operation

Claims (10)

A method for monitoring the alkalinity of bicarbonate ions in wastewater from a steelmaking process, comprising: performing a modeling step, wherein the modeling step includes: using a pH meter to measure a standard acid-base of each of a plurality of standard solutions value, wherein each of the standard solutions has a known bicarbonate ion alkalinity; creating a database, wherein the database includes the known bicarbonate ion alkalinity and the known bicarbonate ion alkalinity of each of the standard solutions The corresponding standard pH value; and sorting the standard pH values in the database to establish a plurality of judgment indexes, wherein according to the database, each of the judgment indexes corresponds to a bicarbonate ion alkalinity and performing a measuring step, wherein the measuring step includes: using the pH meter to measure a measured pH value of the steelmaking process wastewater; and comparing the measured pH value with the judgment indicators to correspond to Obtain the bicarbonate ion alkalinity range of the steelmaking process wastewater. The monitoring method according to claim 1, wherein the standard solutions comprise a plurality of converter dust washing waters. The monitoring method as claimed in claim 1, wherein the known The bicarbonate ion alkalinity was determined by an acid-base titration. The monitoring method according to claim 1, wherein the judgment indexes include a first judgment index, a second judgment index and a third judgment index, wherein the first judgment index represents a pH value greater than or equal to 9.4 and less than 10, the second judgment index represents a pH value greater than or equal to 10 and less than or equal to 10.5, and the third judgment index represents a pH value greater than 10.5 and less than or equal to 11.0. The monitoring method according to claim 4, wherein when the measured pH value of the steelmaking process wastewater corresponds to the first judgment index, then interpreting the bicarbonate ion alkalinity range of the steelmaking process wastewater is less than or equal to 1600 and greater than 300 mgCaCO ₃ /L. The monitoring method of claim 5, further comprising performing a first response measure, wherein the first response measure is not to add carbonate to the steelmaking process wastewater. The monitoring method according to claim 4, wherein when the measured pH value of the steelmaking process wastewater corresponds to the second judgment index, then interpreting the bicarbonate ion alkalinity range of the steelmaking process wastewater is less than or equal to 300 and greater than or equal to 1 mgCaCO ₃ /L. The monitoring method of claim 7, further comprising performing a second response measure, wherein the second response measure is to monitor a pH value of the steelmaking process wastewater. The monitoring method according to claim 4, wherein when the measured pH value of the steelmaking process wastewater corresponds to the third judgment index, then interpreting the bicarbonate ion alkalinity range of the steelmaking process wastewater is less than 1 and equal to or greater than 0 mgCaCO ₃ /L. The monitoring method of claim 9, further comprising performing a third response measure, wherein the third response measure is to add carbonate to the steelmaking process wastewater.

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