JPS59116537A - Measuring method of residual chlorine - Google Patents

Abstract

PURPOSE:To omit acquisition of a reagent such as sodium sulfate and periodic preparation and replenishment of a solution and to make it possible to perform continuous measurement, by adding raw material sea water or intermediate fresh water turned from the sea water into sample water, and measuring residual chlorine. CONSTITUTION:At a place where sea water can be obtained conveniently, measurement is accurately performed by the following way: the sea water is added to sample water at a rate of about 1/100; and the sample is guided to a residual chlorine meter. This method is conducted without procurement of sodium sulfate and the preparation and replenishment of a solution. In some cases, a material, which consumes chlorine, is included in the sea water. Since the amount of addition is as small as about 1/200 of the sample, the effect can be usually neglected. If the amount cannot be neglected, intermediate fresh water turned from the sea water is taken and added to the sample water. In this case, the concentration of the residual chlorine in the added sea water is low and the rate of addition is small. Therefore there is no problem. It is appropriate that a flow ratio of the sample water 3 and the sea water 4 from a sample feeding pump 1 and a sea water feeding pump 2 is about 200:1 or less.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for directly quantitatively measuring p, using product water produced by seawater desalination as a test liquid, by polarographic method using a fully rotating metal electrode for chlorine remaining in the test liquid.

Chlorine is widely used in various industrial fields, such as by adding it to drinking water, sewage water, pool water, etc. for sterilization, and injecting it into waste liquid to decompose hydrazine used to prevent corrosion in boilers. There is.

In order to effectively achieve the purpose of chlorine injection, such as sterilizing drinking water and maintaining cleanliness all the way to the end of the water supply, the residual chlorine concentration in the sample after chlorine injection must be constantly measured to ensure that the concentration is appropriate. It is necessary to control it so that it is kept within a range.

Methods for measuring residual chlorine concentration include (1) a method in which the color is developed by 0-) lysine and is used for absorbance measurement; (2)
A solution containing potassium iodide or potassium bromide is added to the sample water, and the liberated iodine or bromine is collected using the polarographic method using a rotating metal electrode.(3) Direct rotation of the sample water without adding any reagent to the sample water. There are polarographic methods using metal electrodes, etc. Of these, (1) 0-tolidine is gradually no longer used because it is a triggering substance, and methods (2) and (3) are now widely used, partly because continuous measurements are easy. There is. Especially (3
) method does not require the regular preparation and replenishment of reagents, and
Since the price of the measuring instrument is also lower than that in (2), it is likely to be widely used.

However, in order to be able to accurately measure the total residual chlorine using method (3), it is necessary that the sample water has a certain level of electrical conductivity. Therefore, the present inventors found that the electrical conductivity of the sample water in the method (3) was not as high as the residual chlorine concentration measurement, and the results of the influence sound investigation were obtained as shown in FIG.

As you will see, the sample water conductivity is approximately 200μS/
There is almost no measurement error over lyn, but when the sample water conductivity is about 150μS/σ, errors start to appear.3
It can be seen that an extremely large error occurs when the value becomes 0 μS/Cm.

Therefore, when measuring the residual chlorine concentration of sample water with such a low conductivity, a method has been adopted in which, for example, a sodium sulfate solution is added to the sample water in small amounts at a time while increasing the conductivity. This method has an advantage over method (2), which uses potassium iodide solution, because sodium sulfate has a very low density compared to potassium iodide, but it does not require regular preparation and replenishment of the reagent solution. The uniqueness will not be resolved.

Drinking water has traditionally been produced by completely purifying river water, but as water resources tend to become scarce and in order to secure drinking water in places such as the Middle East where river water and precipitation are low, seawater desalination is gradually becoming more and more popular. In this case, chlorine is injected into the product water (drinking water) produced in a seawater desalination plant to disinfect and disinfect it.
Sterilization is being carried out, and measuring the residual chlorine concentration is equally important.

The conductivity of the product water obtained by this seawater desalination is 50
It is less than μS/cm, and in many cases it is around 25 μS/z, and residual chlorine can be measured using method (3).
It is not possible to perform a constant measurement, and it is necessary to perform measurements while adding all the sodium sulfate solution, etc. However, many of these plants are constructed in the Middle East, where rainfall is low, such as in Arab countries. Most of the countries in these regions are developing countries, where chemicals are extremely valuable, and it is not necessarily realistic to expect them to be regularly prepared and replenished to a predetermined concentration. .

The present invention proposes that if seawater, which exists inexhaustibly around seawater desalination plants, is used to increase the conductivity of sample water, operations such as obtaining reagents such as sodium sulfate and periodic preparation and replenishment of solutions will become unnecessary. This was realized because it offers a great advantage in continuous measurement.

Now, the conductivity of seawater is about 40,000μS/cm,
If 17200 or more is added to the sample water, the electrical conductivity of the sample water will be as high as about 200 μS 7 cm or more, and in terms of electrical conductivity, no error will occur in the measurement of residual chlorine by method (3).

On the other hand, seawater contains small amounts of rum ions and calcium ions generated from sodium chloride. Therefore, these coexisting substances have a negative impact on the measurement of residual chlorine concentration. I don't care if it doesn't affect the water, but seawater is actually added to sample water with low conductivity. /100 and checked the presence or absence of a lead error kA on a residual chlorine meter. The results are shown in Figure 2, and the meter readings were in excellent agreement with the true concentrations.

From this result, in places where seawater is easily obtained, such as when residual chlorine is determined in freshwater production by seawater desalination, all seawater sample water can be used without purchasing, dissolving, and replenishing sodium sulfate. 1/10 against
By introducing the residual chlorine into a residual chlorine meter while adding the residual chlorine with a moving table of about 0, it is possible to measure with high accuracy, which is very effective for practical use.

Note that seawater may contain substances that consume all of the chlorine, but since the amount added is as small as about 1/200 of the sample, it can usually be ignored. If the level is not negligible, there is a step in the seawater desalination plant to add all chlorine to eliminate chlorine-consuming substances, so all of the intermediate desalination water is taken from the pipe after that, and this is used as sample water. What is necessary is to add it to

In this case, the residual chlorine concentration in the added seawater is low and the addition rate is also small, so there is no problem.

FIG. 3 shows an embodiment of the invention. The part marked ■ above the one-dot chain line is a known reagentless residual chlorine meter, and the part marked ■ below the one-dot chain line is a part added to carry out the entire invention. Sample water feed pump (1) and seawater feed pump (
According to 2), it is appropriate to select the flow rate ratio of sample water (3) and seawater (4) to 200 or less: process level.

In addition, it is not used for constant flow pumps (1), (2), and each head tank is connected to all phases, and the flow rate ratio is 20% by appropriate throttling.
0 or less: It is possible to reduce the process level and introduce it into the measuring tank (5).

In the figure, (6) is the rotating metal electrode, (7) is its detection electrode, (8) is the counter electrode, (9) is the motor that rotates the electrode (6), and (10) is the residual chlorine concentration indicator. show.

FIG. 4 shows an example of the present invention, in which desalination intermediate water is separated from a pipe after salt addition in a seawater desalination plant (CI) through a pipe (1, 1,)ffi,
It is added to the residual chlorine concentration. (12) is a chlorine injection machine,
(13) is a pump, (14) is a seawater desalination plan) (
(15) is a seawater sampling tube for adding sample water. Further, (16) is a product water line, and (17) is its supply line.

[Brief explanation of the drawing]

Figure 1 is a chart showing the relationship between the conductivity of sample water and the residual chlorine concentration, and Figure 2 is the error A when using the method of the present invention.
......Additive-free residual chlorine meter B...Seawater addition device C...Seawater desalination plant 1.2...
Metering pump 6...Rotating metal electrode 11...Piping for adding seawater to sample water after chlorine injection

Claims (1)

[Claims] (1) When measuring the residual chlorine in product water from seawater desalination as sample water by the polarographic method using a direct rotating metal electrode, raw seawater or its desalination intermediate water is added to the sample water and the residual chlorine is measured. A residual chlorine measurement method characterized by measuring total chlorine.