JPS61150708A - Method for treating roll-cooling water by using ozone - Google Patents

Abstract

PURPOSE:To reduce the injecting amount of gaseous O3 and the operation cost by adjusting the pH concentration of cooling water a little lower to lengthen the half life of O3, when the gaseous O3 is injected into roll-cooling water. CONSTITUTION:A gaseous O3 injecting pipe 20 is parallelly connected to a water-supplying piping 10 at the outlet side of a cooling tower 7. A gaseous O3 generating and supplying device 15 is connected to the pipe 20 to supply gaseous O3 to the pipe 20 by an ejector 16, and high-pressure cooling water is supplied to the ejector 16 by an ejector pump 21. An acid injection pump 17 interlocked with the pump 21, is actuated together with the pump 21, i.e. the ejector 16. By this construction, a sulfuric acid, for instance, supplied from an acid tank 19 through a control valve 18, is injected into the cooling water of piping 10 at the suction side of a water supplying pump 9. Accordingly, the pH concentration of cooling water is lowered. This pH concentration is measured by a pH meter 22, and the valve 18 of pump 17 is adjusted to control the amount of acid to be injected, so that the actual pH concentration coincides with the aimed one.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to the treatment of roll cooling water in a cold rolling mill, and relates to the treatment of roll cooling water in a cold rolling mill, and in cold rolling, between the rolling roll surface and the surface of an EEffl material during rolling. This invention relates to treatment for preventing slime formation in roll cooling water for maintaining friction at an appropriate value and cooling rolls and rolled materials below a predetermined temperature.

(Prior art) Conventionally, there are two types of roll cooling methods for cold rolling mills: recirculation method and direct method. In the former method, a large amount of emulsion liquid made by adding rolling oil to cooling water is used. It circulates and supplies the rolling rolls and the material to be rolled to simultaneously lubricate and cool them. On the other hand, in the latter direct method, I! As shown in 61W, rolling oil is injected from the rolling oil header 2 to the metal strip 1, which is the rolling material of W1, through the /' nozzle to lubricate the space between the work roll a and the metal strip l. [Water is injected onto the work roll 8 by the nozzle of the roll cooling water header 4 to cool it. The cooling water and rolling oil after injection are collected in a drainage tank 5, and after oil and impurities such as iron powder are removed by a water purification device 6, they are cooled by a cooling tower 7, and fresh water is supplied from a water supply pipe 8. The coolant is replenished and supplied to the cooling water header 4 via a pipe 10 by a pump 9 for circulation. On the other hand, the oil separated by the water purification device 6 is regenerated in the regeneration device 11, temporarily stored in a tank 12, where it is replenished with new oil as needed, and is rolled by a pump 13 through a pressure ff1m supply pipe 14t. The oil is supplied to the oil header 2 and used for circulation.

However, in the conventional direct roll cooling method as described above, microorganisms multiply in the water supply pipe 10 and form slime, resulting in the water supply pipe 10 being blocked or slime peeling off from the inner wall of the water supply pipe. There was a problem in that the roll cooling water was sprayed from the nozzle of the roller along with the cooling water, causing scratches on the surfaces of the rolls and metal strips.

Conventionally, as a countermeasure to such problems caused by slime,
The following methods are used to suppress slime generation.

(1) By replenishing 40 to 60% of the water supply with fresh water, the cooling water is kept clean and the growth of microorganisms is suppressed.

(2) Add chlorine or sodium hypochlorite to the cooling water,
Its bactericidal effect suppresses the generation of slime. (Problem that the invention aims to solve) However, method (1) has the problem of large water consumption, and method (2) The concentration of chlorine increases during circulation, which not only adversely affects the surface quality of the metal strip but also increases the cost of chemicals.

(Means for Solving the Problems) An object of the present invention is to provide a roll cooling water treatment method that solves the above problems.

The present inventor has discovered that when performing roll cooling using the direct method,
What is the ozone concentration in the cooling water at the cooling water injection part to the roll by injecting ozone into the cooling water? Ozone, which has been shown to be able to suppress slime formation at concentrations above 0.1 ppm, not only has a higher bactericidal effect than conventionally used chlorine, but also decomposes into oxygen in a relatively short period of time and removes metals. Although ozone has the advantage of having no effect on the strip, its tendency to decompose into oxygen in a relatively short period of time, ie, ozone has a lifetime (half-life), creates new problems.

That is, while the cold rolling mill is located indoors, the water purifier 6. Water treatment equipment such as cooling tower 7 is located outdoors.
Therefore, the water supply pipe 10 is often very long, and in such cases, even if the Ozone cooling water is supplied upstream of the water supply pipe 10, the roll cooling water header 4 at the end The ozone concentration decreases significantly due to the long residence time, and therefore the ozone concentration in the cooling water injected from the nozzles of the end roll cooling water header reaches a predetermined value.

In order to secure 0.1 ppm or more, a large amount of ozone is required to be supplied, and therefore a large-capacity ozone generation and supply device is required.

The inventor has discovered that the half-life of ozone is greatly affected by the pH of cooling water (6 degrees), and as shown in Figures 2 and 3, the pH
As the llI degree increases, the ozone half-life becomes shorter; at pH 7.3, the half-life is 100 seconds;
The present invention was made based on the recognition of the fact that in H7.8-8.0, the half-life is shortened to 25 seconds and 14 seconds.

Therefore, according to the present invention, in order to cool the rolls of a cold rolling mill, ozone is generated and supplied to the cooling water supplied to the roll cooling water header 4 through the water supply pipe 10 as shown in FIG. When injecting acid into the cooling water in the water supply pipe 10 by the ejector 16, the acid is injected into the cooling water in the water supply pipe 10 from the acid liquid tank 19 via the control valve 18 by the acid injection pump 17 which is linked to the ozone injection operation by the ejector 16. Adjust the pH concentration of the cooling water.

It is desirable that the pH concentration of the cooling water is set to pH 6 or higher in consideration of the influence on the rolled material and equipment.

(Function) As described above, according to the present invention, by adjusting the pH concentration of the cooling water to be low, the ozone half-life is lengthened, and the amount of ozone injection can be reduced. For example, FIG. Cooling water is supplied to a water supply pipe with a diameter (lQQm, length 951 JOm) at a flow rate of 1800 m'/Hr, and ozone is injected into the cooling water at the end of the water supply pipe so that the ozone concentration at the end of the water supply pipe reaches the target value t1. .25pp
Figure 4 shows the relationship between the pH value of the cooling water and the amount of ozone injected when ozonating the water so that the pH value is 6.5. In this case, the injection amount can be reduced to about 1/70 compared to the case of I)) 17.5.

(Example) Figure 1 shows a water treatment system configured to adjust the pH concentration of cooling water according to the present invention. A pipe 20 is provided, and the water supply pipe 1 is connected by an ejector pump 21.
configured to pass cooling water from 0 to the ejector 16 at high pressure,
Water is supplied from an acid liquid tank 19 containing sulfuric acid, for example, to the suction side of the water supply pump 9 on the outlet side of the cooling tower 7 via the control valve 18 by the acid injection pump 17 which is linked to the operation of the ejector 16, that is, the operation of the ejector pump 21. Sulfuric acid is injected into the cooling water in the pipe 10 to reduce the I)H concentration in the cooling water.

The pH concentration of the cooling water in the water supply pipe 10 is measured by a pH meter 22 on the discharge side of the water supply pump 9.

The control valve 1 of the acid injection pump 17 is adjusted to meet the target pHm degree.
The injection amount is controlled by adjusting the opening degree of 8.

As shown in FIG. 5, the ozone generation and supply device 15 boosts the pressure of oxygen supplied from the oxygen supply station 28 using the circulation proa 24 and sends it to the ozone generator 25 to convert a part of the supplied oxygen into ozone. to produce ozone-containing gas.

In the ozone generator 25, for example, a dielectric material such as a glass plate is sandwiched between the electrodes and an alternating current, high voltage is applied between the electrodes to generate a silent discharge. By flowing oxygen between the electrodes, ozone-containing gas is generated.

Oxygen supply device! The oxygen supplied from 23 has a purity of 99.9%.
In the above, the dew point converted to atmospheric pressure is -5o'C or less.

The ozone concentration in the ozone-containing gas generated by the ozone generator 25 is around 4% Ik%, and the remaining 96% is oxygen and the ozone concentration is low. therefore.

If the ozone-containing gas generated by the ozone generator 25 is used as it is, the amount of oxygen consumed will increase, so an ozone adsorption tower 26 for temporarily accumulating ozone is connected to the ozone generator 25 via a valve 27.

The ozone adsorption tower 26 preferentially absorbs ozone in the ozone-containing gas fed from the ozone generator 25.
A cooling fin 29 through which cold gas from a refrigerator 28 passes for the purpose of cooling the ozone adsorption tower 26 during ozone adsorption in order to increase the ozone adsorption capacity for a given volume of the adsorbent, and Temperature raising fins 80 are provided to partially desorb the adsorbed ozone.

Inside the temperature increasing fin 30, a temperature increasing medium is introduced from a prine tank 31 through a pipe 33 by a pump 32 and is circulated, and a heater (not shown) is installed in the brine WJal. The temperature increasing medium is controlled to be kept constant at a predetermined temperature.

Next, the operation of the apparatus configured as described above will be explained.

First, in order to generate ozone by the ozone generation supply Ht15, oxygen from the oxygen supply electric generator 23 shown in ig4 is boosted in pressure by the circulation proa 24 and sent to the ozone generator 25. of ozone is converted into ozone, and the generated ozone-containing gas is sent to the ozone adsorption tower 26 via the control valve 27. During this ozone adsorption, the adsorbent in the ozone adsorption tower 26 is cooled by the refrigerator 28, so that the ozone in the ozone-containing gas is adsorbed by the adsorbent. Oxygen released from the ozone adsorption tower 29 is circulated through the proa 24.
The ozone is sent to the ozone generator 'a25 again. The above-described ozone adsorption operation is repeated, and when the required amount of ozone has been adsorbed, the circulation prower 24, ozone generator 25, and refrigerator 28 are stopped, and the control valve 27 is closed. Next, in order to desorb the ozone adsorbed by the g&3 adhesive in the ozone adsorption tower 26, the temperature raising brine pump 82 is operated to move the temperature raising medium in the prine tank 81 to the ozone adsorption tower 26. It is sent into the warming fin 30. As a result, when the temperature inside the tower reaches around 0°C, ozone desorption (synonymous with ozone injection) begins.

Next, the ejector pump 21 is started, and after the ejector 17 enters normal operation, the control valve 85 in the ozone delivery pipe 34 from the ozone adsorption tower 26 to the ejector 17 is opened.

The ejector 17 reacts and mixes the ozone-containing gas and the treated water. The ozone concentration in the ozone-containing gas at the point injected into the ejector 17 is about 85% by weight or more. By repeating the above operations, ozone can be intermittently injected into the treated water at a required ozone concentration.

The ozone injection concentration is controlled by controlling the ozone adsorption time mentioned above, and generally the ozone adsorption time is about 2 hours to 48 hours, and the ozone injection time is completed in 1 minute to several minutes. All of this is done by setting a timer appropriately, and the injection cycle and injection time naturally depend on the properties of the target treated water.The treated water containing ozone flows through the cooling water supply pipe 1o,
Clean with 4 tons of roll cooling water header to prevent slime formation. It is necessary that the ozone concentration in the roll cooling water header 4 is at least 0.1/cm or more, and it has been confirmed that the residual ozone has no effect on the metal strip.

(Effects of the Invention) According to the present invention, the half-life of ozone injected into the cooling water is lengthened, so that the target ozone concentration of the cooling water supplied through a long water supply pipe can be ensured at the end of the water supply pipe. This reduces the amount of ozone injection required for the process, thus reducing the amount of oxygen used as a raw material, requiring only a small ozone generation and supply device, and reducing power consumption and other running costs. can get.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a water treatment system in which roll cooling water for directly cooling rolls of a cold rolling mill is subjected to ozone treatment according to the present invention. Figure 2 is a graph showing the change in ozone concentration in cooling water over time using the I) Hi1 degree of cooling water as a parameter, and Figure 3 is a graph showing the relationship between pH concentration of cooling water and half-life of ozone in cooling water. , Figure 4 is a graph showing the relationship between the amount of ozone injection required to ensure the required target ozone concentration at the end of the water supply pipe and the pH concentration of cooling water, and Figure 5 is a block diagram showing an example of an ozone generation and supply device. Figure 6 is a circulation system diagram of roll cooling water that cools the rolls of a conventional cold rolling mill by a direct method. 1... Metal strip 2... Rolling oil header 8.
... Work roll 4 ... Roll cooling water header 5
... Drainage tank 6 ... Water purification device 7 ... Cooling tower 8 ... Water cutoff supply pipe 9 ... Water supply pump 10 ... Water supply pipe 11 ... Regeneration device
12...Rolling oil tank 18...Pump
14... Rolling oil supply pipe 15... Ozone generator 16... Ejector 17... Acid injection pump 18
... Acid injection amount control valve 19 ... Pickling tank 2
0...Ozone injection pipe 21...Ejector pump 2
2...PH measuring device 28...Oxygen supply device 24.
...Circulation proa 25...Ozone generator 26...
・Ozone adsorption tower 2nd floor...Control valve 28...
- Refrigerator 29...Cooling fins 80...Temperature raising agent fins 81...Pline tank 32...Temperature raising pline pump a3...Temperature raising agent pline circulation pipe 34
゛...Ozone delivery pipe 35...Control valve

Claims (1)

[Claims] 1. A method for ozone treatment of roll cooling water of a cold rolling mill, which comprises adjusting the pH concentration of the cooling water at the time of ozone injection.