KR20030097738A - Process for automatically controlling of raw water quality - Google Patents

Abstract

PURPOSE: Provided is a method for automatically controlling corrosiveness index CCCP of waterworks raw water. CONSTITUTION: The method comprises the steps of (a) detecting water flow rate and water quality (pH, temperature, alkalinity and calcium hardness) of waterworks raw water, (b) feeding chemicals to the raw water so as for the detected water quality to reach to a target quality (pH 8.5, calcium hardness 65mg CaCO3/L), (c) calculating difference between target alkalinity and actual alkalinity of water by an equation DEAlk1 = (Alk1-Ca1) + DECa1, (d) calculating lime dosage to be fed to the water by subtracting actual alkalinity Alk1 from target alkalinity TEAlk1, (e) performing coagulation and sedimentation, (f) detecting calcium hardness of the water after sedimentation, (g) feeding chemical to the water to compensate difference theoretical value and actual value of calcium hardness, (h) calculating carbon dioxide dosage to be fed to the water by subtracting actual calcium hardness C2 of the water from the target calcium hardness DC2, (i) detecting water quality after final purification and calculating corrosiveness index CCCP using water quality data of finally purified water, and (j) automatically adjusting water quality (pH, alkalinity and calcium hardness) of purified water by feeding chemicals to the purified water so as the corrosiveness index CCCP to be positive value.

Description

Process for Automatic Control of Raw Water Quality

The present invention relates to an automatic corrosion control process for controlling the corrosive water quality according to the change in the quality of the source water, more specifically, the pH, alkalinity, calcium hardness and the corrosive index, It is to provide an automatic corrosion control process for controlling the corrosive water quality according to the water quality change of the source water, which allows the automatic control of the CCCP value in a stable range.

Korean water source may have a water quality change with large seasonal variation, the number of water sources pH, alkalinity, low calcium hardness, Cl ^-, SO _4, and represents the ^2-corrosive containing, as coagulant and disinfectant use further move through the water treatment step It is corrosive.

However, in the case of domestic water purification plants, the process of controlling and mitigating these corrosive waters is not applied. If the pH rises, the pH is lowered by using strong acid (H ₂ SO ₄ ) in the pre-aggregation stage. When it is low, alkalinity [Ca (OH) ₂ ] is used to increase the alkalinity, and the drug injection method is not systematic and quantitative injection is not performed. However, this depends only on the amount and type of flocculant.

In addition, in order to control the corrosive water quality, the pH was increased by adding lime in some water purification plants, or by adjusting carbon, alkalinity and calcium hardness by adding carbon dioxide and slaked lime in the purified water after the treatment stage. However, it is not able to automatically adjust to seasonal changes in raw water.

The present invention aims to control the corrosive index CCPP value in a stable range by adjusting pH, alkalinity and calcium hardness in water during water treatment, and shows the possibility of automatic corrosion control according to changes in raw water quality. That is, the present invention has been completed with the technical problem of the present invention by providing a target water quality standard and providing an automatic corrosion control process for estimating the amount of chemical injection according to seasonal changes in raw water quality.

1 is a schematic diagram showing an automatic corrosion control process provided by the present invention.

Figure 2 is the initial pH control before aggregation in the automatic corrosion control process provided by the present invention

Turbidity change graph

Figure 3 is a flow chart showing a step 1 automatic corrosion control process provided by the present invention

4 is a flowchart showing two steps of an automatic corrosion control process provided by the present invention.

5 is a chemical injection amount calculation using the Excel program (automatic corrosion control system)

6 is calculated in step 1 of the automatic corrosion control of the present invention (target calcium hardness 60, 65 days

Chemical injection concentration

7 is calculated in step 2 of the automatic corrosion control of the present invention (target alkalinity 60mg / L,

In case of 65mg / L)

■ Explanation of symbols used in main part of drawing ■

Pre-O3: Pre-Ozone Tank Coag: Coagulation Tank

Sedi: settling tank S / F: sand filtration tank

Post-O3: Huzonzone BAC: Bioactive Complex

Clean Wa: Purifier Q1, Q2: Flowmeter

pH, pH2, pH3: on-line pH

Alk1, Alk2, Alk3: on-line alkaline measuring instrument (Alkalinity)

Ca1, Ca3: on-line calcium hardness tester

Turb1, Turb2, Turb3: Turbidity measuring instruments (measuring and analyzing)

The automatic corrosion control process for controlling the corrosive water quality according to the water quality change of the constant water provided by the present invention is divided into one and two stages.

In the first step, the pH, calcium hardness, and alkalinity are controlled by controlling the coagulation process, and the second step is controlled by adjusting the pH and alkalinity in the final resin.

Lime (Ca (OH) ₂ ) and CO ₂ (carbonic acid gas) are used to control the calcium hardness in water and to adjust the pH and alkalinity in the water to the optimum range to increase the coagulation efficiency.

That is, it provides an automatic corrosion control process for quantitatively injecting the injected drug to calculate the pH, alkalinity, calcium hardness.

The flocculation efficiency is greatly influenced by pH and alkalinity in the water, but the pH and alkalinity are consumed in the flocculation reaction, so the pH is not in the proper range. .

Increasing flocculant consumption increases the amount of SO ₄ ^2- in the water, adding to the corrosiveness. Controlling pH and alkalinity through chemical injection, such as slaked lime and carbon dioxide, can reduce coagulant injection through chemical injection while increasing coagulation efficiency and reduce corrosion in the tube.

Since seasonal raw water changes in Korea are very large, as shown in Table 1, it is very important to control the water quality factors that affect corrosion such as pH, alkalinity, and calcium hardness, depending on the properties of the incoming raw water.

2 is a result of the aggregation experiment by adjusting the initial pH. First, Ca (OH) ₂ and carbon dioxide were injected to adjust the pH to 7.0 ~ 9.0 range, and the turbidity change according to the concentration of coagulant (PSO-M) was examined. In the range of 30 ~ 60mg / L coagulant, the water quality with initial pH adjusted to 8.48 showed the lowest haze.

The use of CO ₂ before the flocculation process is to increase the solubility.

When only Ca (OH) ₂ is used to increase calcium and alkalinity in water, the solubility is very low due to the characteristics of the chemicals, causing severe turbidity when added to water. Have.

In the present invention, this problem was solved by injecting CO ₂ together before the flocculation process to increase the dissolution of Ca (OH) ₂ together with the acid action of the flocculant.

3 is a flowchart showing one step of the automatic corrosion control process of the present invention.

[1] wherein pH1. Temp1, Alk1 and Ca1 represent the pH and temperature of the incoming raw water (℃), alkalinity (mg / L as CaCO ₃ ), calcium hardness (mg / L as CaCO ₃ ), and Q1 represents the flow rate of the influent. .

Measure inflow pH, temperature, alkalinity and calcium hardness on a monitoring instrument.

As shown in Table 1, the seasonal variation of the raw water is large.

[2] DECa1, DEpH1, DEAlk1, DECt1, and Ct1 represent the target calcium hardness (mg / L as CaCO ₃ ), pH, alkalinity (mg / L as CaCO ₃ ), and total carbonic acid concentration, respectively. Concentration and factor are correction coefficients and PV = nRT are gas equations.

DECal: Target calcium hardness, 65mg CaCO ₃ / L

DEpHl: Set target pH to 8.5 (set value can be changed)

1) The calcium concentration of raw water changes significantly according to the season.

2) If the calcium concentration of raw water does not reach the target concentration, the drug is injected as much as the difference, and if the target concentration is exceeded, the medicine is not injected.

3) The target calcium concentration can be adjusted to the desired concentration (but the concentration range is 40 ~ 70 mg CaCO ₃ / L suitable)

4) The target pH can also be adjusted to the desired value, which is adjusted according to the optimal conditions of flocculation and coagulant concentration according to the characteristics of the raw water (but the range of value is 8.0 ~ 8.5).

[3] DEAlkl = (Alkl-Cal) + DECal: target alkalinity

(IF Cal <65, DEAlk1 = "positive value"

IF Cal ≥ 65, DEAlk1 = "zero or negative value"

1) Drug dosage is calculated by pH and alkalinity value.

2) The target alkalinity value was adjusted to be fluid as in the above equation. This raises the alkalinity within the range that the calculated drug Ca (OH) ₂ does not exceed the set target calcium concentration.

In other words, Ca (OH) ₂ is used to increase the alkalinity, but if the target alkalinity is fixed, the calcium concentration in the water may be excessively increased.

[4] Lime Dosage = DEAlk1-Alk1: Determination of Lime injection concentration

(Injection flow rate determined by Lime CONC .. Q1)

: The injection concentration of Lime is determined by the target alkalinity value calculated in 3 above and the difference between alkalinity of influent.

[5] Factor = DECal / Cal ': Initial setting value 1.0, semi-automatic correction

(Cal '= calcium concentration after aggregation)

: After the coagulation process, the calcium concentration is measured to correct the difference between the theoretical value and the actual measured value. Automatic and semi-automatic are possible.

[6] Lime CONC. = 10: Lime solution concentration (%)

: It is possible to adjust the concentration of medicine. However, considering solubility of Lime, less than 15% is suitable.

To inject Lime (lime lime), adjust the pump operation (ON) or stop the injection of Lime (lime lime) by pump stop (OFF).

[7] calculation of carbon dioxide injection

[Ct (Total Carbonate Carbon)] = [H ₂ CO ₃ *] + [HCO _3- ] [CO ₃ ^2- ]

DECt1: using DEpH1, DEAlk1

Ct1: pH1, using Alk1

here

⇒PV = nRT, Templ, Q1 to determine injection flow rate

: The concentration of CO ₂ gas is determined by the difference between the target Ct value and the inlet Ct value, which is calculated by the ideal gas equation, water temperature and flow rate.

[8] Factor = DEpH1 / pH1 ': Initial value 1.0, semi-automatic correction

(pH1 '= pH before aggregation = pH after injection)

: Measure pH value after chemical injection and correct the difference between theoretical value and actual measured value. Automatic and semi-automatic are possible.

[9] PV = nRT

1) Calculate the gas volume according to the temperature and pressure in unit conversion by gas equation.

2) Adjust CO2 gas injector's regulator ON or OFF for CO2 gas injection.

(10) Monitoring Turbidity of Sedimentation

1) Observation of turbidity in the sedimentation tank by adjusting pH before flocculation (water quality stability and optimal injection of chemicals)

2) Since the amount of chemical injection was calculated in consideration of the flocculation efficiency, it is judged that the accuracy of chemical control was observed by monitoring the turbidity of the settling tank.

4 is a flowchart showing two steps of the automatic corrosion control process of the present invention.

[1] Here, pH2, Temp2, and Alk2 represent the pH, temperature (° C.) and alkalinity (mg / L as CaCO ₃ ) of the BAC treated water, and Q2 represents the flow rate of the BAC treated water.

The water quality change of BAC treated water during the same period is shown in Table 2. This resulted in the decrease of pH and alkalinity after the coagulation process, even though the chemical injection was performed as a result of applying the semi-automatic corrosion process. In this case, only pH and alkalinity are controlled without the need to adjust calcium hardness.

Water Quality Changes of BAC Treated Water (02 ~ 03) division December to mid July pH (ave) 5.80-7.79 (6.85) Temp. (Ave) ℃ 2.10-24.2 (12.0) Alk. (Ave) mg CaCO3 / L 14.3-61.0 (38.4)

Ca2 + (ave) mg CaCO3 / L 32.8-90.9 (61.7)

[2] DEAlk 2: target alkalinity, 65 mg CaCO ₃ / L

DEpH2: target pH, 8.2

1) In step 2, the target alkalinity value is fixed and the aim is to increase pH and alkalinity. Since the medicine used is soda ash (Na ₂ CO ₃ ) and does not contain calcium components, there is no increase in calcium concentration due to the use of the medicine.

2) The target alkalinity can be adjusted to a desired value. (However, the concentration range is 40 ~ 60 mg CaCO ₃ / L suitable)

3) The target pH can also be adjusted to the desired value. (However, the value ranges from 7.8 to 8.3 according to the CCPP formation principle.)

[3] SodaAsh Dosage = DEAlk2-Alk2: SodaAsh injection concentration determination

(Infusion flow rate determination by SodaAsh CONC .. Q2

NaOH (caustic soda) and Ca (OH) ₂ (slaked lime) available

1) The soda ash injection concentration is determined by the difference in the alkalinity between the target alkalinity value and the BAC treated water.

2) The chemicals used are not only soda ash but also Lime and caustic soda (NaOH). However, when using Lime, the calcium concentration is increased, so it is required to properly adjust the target calcium concentration in the first stage, and caustic soda needs to be carefully considered because it is inexpensive in terms of cost.

[4] Factor = DEAlk2 / Alk3: Automatic correction as Alk3 measurement

: After chemical injection, alkalinity is measured to correct the difference between theoretical value and actual measured value. Automatic and semi-automatic are possible.

[5] Soda Ash CONC. = 5.0: SodaAsh solution concentration (%)

: It is possible to adjust the concentration of medicine. However, since soda ash and caustic soda have good solubility, there is no problem, but when Lime is used in step 2, it is appropriate to adjust the concentration to less than 1% in consideration of turbidity induced in the treated water.

[6] CO ₂ Dosage = DECt ₂ -Ct ₂ : Determination of CO ₂ injection concentration

[Ct (Total Carbonate Carbon)] = [H ₂ CO ₃ +] [HCO ₃ ^-] [CO ₃ ^2-]

DECt2: using DEpH2, DEAlk2

Ct2: pH2, using Alk2

here

⇒PV = nRT, Temp2, Q2 to determine injection flow rate

: The concentration of CO ₂ gas is determined by the difference between the target Ct value and the inlet Ct value, which is calculated by the ideal gas equation, water temperature and flow rate.

[7] Factor = DEpH2 / pH3: Automatic calibration as pH3 measurement

: Measure pH value after chemical injection and correct the difference between theoretical value and actual measured value. Automatic and semi-automatic are possible.

[8] PV = nRT

: Calculate the capacity of carbon dioxide gas according to temperature and pressure by converting unit by the ideal gas equation, and adjust the regulator of carbon dioxide injection device to turn on or off the regulator.

[9] Monitoring pH3, Temp3, Alk3, Ca3

1) Calculate the CCPP corrosion index value by measuring the final water quality according to pH, alkalinity, calcium hardness control. (The values set at the pre-corrosion control stage were adjusted to maintain the CCPP index at '+'.)

2) Used to calibrate pH3 and Alk3-Factor

The chemical injection amount for each step of automatic corrosion control was calculated using an Excel program, and is shown as an example in FIG. 5.

Next, based on the raw water and BAC treated water quality data shown in Tables 1 and 2, the chemical injection amount of each step was automatically calculated. (Figs. 6, 7 and 3)

In addition, when the target pH was fixed at 8.5 and the target calcium hardness was 60mg / L and 65mg / L in step _{1, the} amount of slaked lime and CO ₂ was examined.In the two-step adjustment, the target pH was set to 8.2 and the target alkalinity was 60mg. In the case of / L and 65mg / L, the concentration of Na ₂ CO ₃ and CO ₂ is shown, indicating that the amount of drug is adjusted according to the change of the target setting value.

As described in detail above, the present invention primarily controls quantitatively by calculating pH and calcium hardness in the pre-aggregation step so that the constant raw water can stably control the CCCP value changed by seasonal factors. The alkalinity can also be controlled by quantitatively by calculation to control the corrosive water quality according to the change of raw water quality.

Claims (1)

In order to control the pH in the range of 7.0 ~ 9.0 by injecting Lime [Ca (OH) ₂ ] and CO ₂ at the first stage of the coagulation process, the inflow water quality (pH1, Temp1, Alk1, Ca1) (Q1) and the monitoring and reading process, Injecting drugs with a target calcium concentration (DECal) of 65 mg CaCO ₃ / L and a concentration range of 40 to 70 mg CaCO ₃ / L for a target pH (DEpHl) 8.5; Adjusting the target pH to 8.0 to 8.5 according to the optimum conditions of flocculation and coagulant concentration according to the characteristics of raw water, Calculate the amount of drug injection by the formula: DEAlkl = (Alkl-Cal) + DECal, with IF Cal <65, DEAlk1 = "positive value", IF Cal ≥ 65, DEAlk1 = "zero or negative value" Process by processing. Lime injection concentration is determined by the difference between the target alkalinity (DEAlk1) value and alkalinity (Alk1), After the agglomeration process, the calcium concentration (Cal ') is measured to automatically or semi-automatically correct the difference between the theoretical and actual measured values; Controlling the concentration of the drug within 15% in consideration of the solubility of Lime, Calculating the amount of CO ₂ injection by the ideal gas equation, water temperature, and flow rate through the difference between the target Ct value and the Ct value of the influent; Measuring the pH value after chemical injection and automatically or semi-automatically correcting the difference between the theoretical value and the actual measured value; A unit conversion (PV = nRT) by an ideal gas equation, Monitoring the turbidity of the sedimentation tank according to pH adjustment before aggregation and verifying the adequacy of chemical injection, The process of monitoring and reading the water quality (pH2.Temp2, Alk2) of the influent (BAC) with the influent flow rate (Q2) by two-step adjustment, The target alkalinity (DEAlk2) is raised and fixed to 65mg CaCO ₃ / L, but the concentration range is 40 ~ 60 mg CaCO ₃ / L, and the target pH (DEpH2) is adjusted to 8.2, but the setting range is 7.8 ~ 8.3. Determining the injection concentration by selecting one of Soda Ash, Lime, and Caustic Sodium (NaOH) as a drug based on the difference between the target alkalinity (DEAlk2) value and the alkalinity of BAC treated water; After the chemical injection, the alkalinity is measured to automatically or semi-automatically correct the difference between the theoretical value and the actual measured value. Adjusting the concentration of the drug, when using Lime as a drug to adjust the concentration of less than 1%, Determining the CO ₂ gas injection concentration based on the difference between the target Ct value (DECt2) and the influent Ct value (Ct2) by calculating the injection amount based on the ideal gas equation, water temperature, and flow rate; Measuring the pH value after chemical injection and automatically or semi-automatically correcting the difference between the theoretical value and the actual measured value; Determining a gas capacity by an ideal gas equation; The CCPP corrosion index value is calculated by measuring the final water quality according to pH (pH3), alkalinity (Alk3), and calcium hardness (Ca3), and the set values are adjusted to maintain the CCPP index at '+'. Automatic corrosion control process for controlling corrosive water quality according to water quality change