JPS60129186A - Device for controlling injection of alkaline agent - Google Patents

Abstract

PURPOSE:To compensate correctly the deviation of a pH value by providing an arithmetic means I for calculating the total concn. of carbonic acid, an arithmetic means II for calculating a buffering capacity from the calculated result of the arithmetic means I , and an arithmetic means III for calculating the deviation of alkalinity. CONSTITUTION:The output signals ph, Alk, and Rc from a pH meter 16, an alkalinity meter 17, and a residual chlorine concn. meter 18 are transmitted to a means 19 for calculating the total concn. of carbonic acid Ct, and the calculated result is transmitted to a means 20 for calculating a buffering capacity. The calculated buffering capacity beta and an output signal ph from the pH meter 16 are transmitted to a means 22 having a contact 21 for inputting the desired value SV which is used for calculating the deviation of alkalinity EAlK. The deviation of alkalinity EAlK is sent to a means 23 for carrying out a proportional-plus-integral calculation wherein the injection ratio MVn of sodium hydroxide is calculated. The injection ratio MVn is outputted to a setting device 24, and the injection of the alkaline agent is controlled.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides an alkaline agent for a water purification plant that corrects input deviation by buffering capacity in feedback control based on the pH value after injection of an alkaline agent in the water purification plant. The present invention relates to an injection control device.

[Technical background of the invention and its problems]

Figure 1 shows the flocculants P, AC(
FIG. 2 is a flow diagram showing a water purification process by injecting polyaluminum chloride), chlorine as a disinfectant, and aqueous soda as an alkaline agent. The raw water taken (from a water intake source (not shown) flows into the receiving well 11C from the water supply pipe 1, where chlorine and caustic soda are injected into the pre-chlorine injection device 2 and the alkali injection device 3. Further, in the rapid mixing pond 4, PAO is injected from the flocculant injection device 5 and rapidly mixed by the flash mixer 6. In the next floc formation pond 7, the raw water is gently stirred, and the turbid substances in the raw water coagulate to form flocs. The formed flocs are sent to the sedimentation tank 8.
will be removed.

Furthermore, the micro flocs that were not precipitated and removed in the sedimentation tank 8 and carried over with the sedimentation tank outflow water were injected with chlorine and caustic soda from the medium chlorine injection device 9 and the medium alkali injection device 0 in the water conduit B. After that, the raw water that has passed through the filtration basin 11 receives injection of chlorine and caustic soda by a post-chlorine injection device 12 and a post-alkali injection device 13 through a water conduit C.
The water is stored in the water purification pond 14. In this way, turbidity substances in the raw water are completely removed, and the water is thoroughly disinfected and safe P.
H value water is supplied to consumers from the water purification pond 14.

In the water purification process using chemical injection, the purpose of coagulant injection is to remove turbid substances, and the purpose of chlorine injection is to oxidize and sterilize microorganisms including pathogenic organisms. On the other hand, the purpose of injecting caustic soda, which is an alkaline agent, is to 1) neutralize the flocculant and chlorine, which are acidic substances, and 2) favor the flocculation reaction in the rapid mixing tank 4 and the floc growth reaction in the floc formation tank 7. P is effective for maintaining pH value, 3) preventing scale and corrosion in the pipes of supplied purified water, and 4) sterilizing residual chlorine.
It is important and has multiple purposes, such as maintaining the H value.

However, sub-control of pH using an alkaline agent such as caustic soda is extremely difficult due to the extreme non-linearity of the pH value. In other words, as shown by the solid curve a in the PH titration curve in Figure 2, the PH value does not have a linear relationship with the amount of alkaline agent injected, but usually rapidly nears neutrality (PH = 7). NaP
H change occurs.

Furthermore, the gradient of the rapid pH change varies greatly depending on the water quality, especially the buffering capacity. For this reason, conventional feedback control using PH values cannot prevent vibration phenomena such as limit cycles and oat coating.

Therefore, in order to realize feedback control of alkaline agent injection using PH1ifK, it is necessary to measure the momentary buffering capacity against the ever-changing water quality fluctuations, that is, the amount of caustic acid that should be injected to produce a unit amount of pH change. It can be understood that the input deviation in the foot-knock control can be corrected by the amount of "(gradient of the dotted lines S and C in FIG. 2)".

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an alkali injection control device for a water purification plant that accurately calculates the buffering capacity that changes from moment to moment and uses this to accurately compensate for deviations in pH values.

[Summary of the invention]

The present invention relates to an alkaline agent injection control device for treating raw water by injecting chemicals such as a coagulant, a disinfectant, and an alkaline agent. a residual chlorine concentration meter, and a calculation means I for calculating the total carbon dioxide concentration from the PH value, alkalinity, and residual chlorine concentration measured by each of the above-mentioned measuring instruments, and the IjII value measured by the above-mentioned measuring instruments. and calculation means (3) for calculating the buffer capacity from the residual chlorine concentration and the total carbon dioxide concentration determined by the calculation means I, and means for inputting a target value of PH, and the input target value of PH and the above-mentioned P A calculation means (■) that calculates the alkalinity deviation from the measured value of the H meter and the buffer capacity determined by the above calculation means (■), and a calculation means that performs PI calculation by using the alkalinity deviation determined by the above calculation means (■) as an input deviation. (1), and by controlling the injection of the alkali agent based on the calculation result of the calculation means (2), the pH value can be controlled to a target value. The invention will be described in detail with reference to an embodiment shown in FIG.

In this embodiment, pre-alkali injection control Yc is applied. In the figure, raw water from pipe A flows into Kerr reservoir well 1,
Here, as in the conventional case, after receiving pre-chlorine injection and injection of caustic soda, the water flows down to the rapid mixing basin 4 where PAO injection is performed. The water that has passed through the floc formation pond 7 is then collected as water sample sZ.
PHHI sample water with pump 15 and measure the pH value ph
It is sent to an alkaline needle 17 that measures the O2 alkaline degree Alk and a residual chlorine concentration meter 18 that measures the residual chlorine concentration Rc. Note that since each injection device is similar to the conventional one, illustration thereof is omitted.

Output signals Pi from each of the measuring instruments 16, 17, 18
].

Alk and Rc are transmitted to means 19 for calculating the total carbon dioxide concentration Of. Here, the total carbon dioxide concentration 0t is the solution of the following simultaneous equations (1) to (8), and the equation (8) is obtained! 7 obtained.

Kw = (H) −(0H−) −= (1) To A7 == 2 ・(003” 'J+[HOOs)+(O
H) − [H”] − (5) 1 also c = (L(Oeo) +
[060) −(G)Ph =−log((H)) m
River (7)Of = (003”)-1-[HOO3
) + (I-T2C!03) -0-1 (8) Here, K
w, Ka 1. ,'Ka2,K,c
is an equilibrium constant that depends only on the temperature t and can be determined by the following equation.

-JogKw=4.5-10"・t'+1.1
・10-t-6,1-(9)-logJ(al=
8.1-0.006 t...IJ01] (a2=4
．． 7 ・ 10-” ・ (0,02t-5) Old ・
Q10gC ni (200.06・to 100.00036・t
2)・10-"...a The total carbon dioxide concentration at, which is the above calculation result, the output signal Ph of the PI-1Ri 16, and the output signal RC of the residual chlorine concentration meter 18 are the means 20 for calculating the buffering capacity. Here, the buffer capacity β is calculated according to the following equation.

up=10 911. (13), Ho =lI)-
"""-Ph)-(14)Ph The buffer capacity β, which is the above calculation result, and the output signal Ph of the PH meter 16 have a contact point 21 for inputting the target value sV of the PH value, and are calculated by the following formula. It is transmitted to means 22 for calculating the alkalinity deviation EAik.

EAJ, k-β・(SV-Ph)・eye・o6)
Formula (m IC = total gu, P 14 value)% -M
(SV-Ph) multiplied by the buffer capacity β-, aA7k, and therefore ΔPh ΔA11lc, that is, the alkalinity deviation EAfk is obtained. This alkalinity deviation EAJ- is:
This is sent as a control input to means 23, which is a PI (proportional integral) calculation unit 2, where the injection rate MVn of caustic soda is calculated using the following formula 〇η, α barrel. Then, this Q) injection rate MVnl is outputted to the setting device 24, and the injection of the alkali agent is controlled.

△5=Kp・(1l-s for bAl kll-bAJ-)
+ ” ・bAJ-kn ・・・・・・ For α, where △S is the alkalinity output deviation, Kp is the proportional gain, h is the control period, TI is the integration time, n and nt are the current and current values, respectively. In the previous control cycle, 1g NaoH is the alkalinity of caustic soda.

The alkaline agent injection control device of the above embodiment is a water treatment plant 1'i
l: :i, - pre-alkali injection side &l (Pre-PH sub-control is performed, but the present invention is pre-alkali injection 1)] In addition to the pre-alkali injection side &l, in addition to the pre-alkali injection side downstream of the It can also be used for post-alkaline injection control.

〔Effect of the invention〕

As described above, according to the present invention, in feedback control based on the PH value after injection of an alkali agent, by setting the control input deviation (SV-Ph) to the alkalinity deviation with the buffering capacity β, Pl-, [ In order to approximate the nonlinearity of the linearity, vibration phenomena such as limit vehicles can be prevented,
Adjust the pH value of the water treatment process after injection of alkaline agent to the target value V
This can be controlled. As a result, the flocculant coagulates and forms flocs well, resulting in flocs with good sedimentation properties.Settling and filtration are also performed successfully, exhibiting a sufficient turbidity removal effect, and retaining the sterilizing power of residual chlorine. Since the PH with good Hia properties is maintained, it is possible to supply high quality and safe purified water.

[Brief explanation of drawings]

Fig. 1 is a flow diagram showing a general water purification process, Fig. 2 is a PH titration curve, and Fig. 3 is an embodiment of the alkaline agent injection control device according to the present invention. It is a control block diagram showing. l...Irrigation well 4...Rapid mixing basin 7...70Tsuku formation pond 8...Settlement basin 11...P Passing pond 16...p ■(Total 17...Alkalinity 18...Residual chlorine concentration Total

Claims (1)

[Claims] In an alkaline agent injection control device for treating raw water by injecting chemicals such as coagulants, disinfectants, and alkaline agents, a PH meter, alkaline needle, and residual chlorine concentration meter are installed at the downstream point after injection of the above chemicals. , P measured by each of the above measuring instruments
calculation means I for calculating the total carbon dioxide concentration from the H value, alkalinity, and residual chlorine concentration; and P measured by the measuring device.
A calculation means for calculating the buffering capacity from the H value, the residual chlorine concentration, and the total carbon dioxide degree calculated by the calculation means I above, and a means for inputting the target value of PH. a calculation means (■) for calculating the deviation of alkalinity from the measured value of the PH meter and the buffer capacity determined by the calculation means;
It is characterized by comprising a calculation means 1V for performing PI calculation using the deviation of the alkalinity determined by the calculation means (■) as an input deviation, and controlling the injection of the alkaline agent based on the calculation result 11f'i of the calculation means (■). Alkaline injection control device.