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SCADA-system the chemical water treatment line

Production of semiconductor silicon requires purified water with low content of suspended solids, metal and acid ions, gases, organic substances and microorganisms.

Tasks of water treatment for production are:

  • disinfection of water (purification from microorganisms);
  • mechanical impurities filteration;
  • clarification (removal of iron and manganese);
  • desalination;
  • degassing (oxygen removal).

Analysis of water used on semiconductor plants is generally done according to following criteria:

  • electrical resistivity (conductivity);
  • oxidation
  • silica content

The main treatment technologies methods are distillation and ion-exchange resin transmission. After one or two stages of distillation water electrical resistivity reaches 0.3-0.5 MO*sm, and on the output of ion exchange units – 1-20 MOm*sm.

  • Client JSC "Zaporizhstal"
  • Skills Automation
  • Website https://www.zaporizhstal.com
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Even a product water is a solution containing such contaminants as dissolved acid, base, salts, oxides the amount of which you can count by means of the resistivity. Measurement of the resistivity is carried out by using two electrodes placed in the vessel of regular geometric shape. Measurements are made on an alternating current in order to exclude the dissolution and deposition of impurities on these electrodes.

Oxidability of water is determined by the amount of oxygen required for complete dissolution of contained organic substances. After adding a strong oxidant into a product water, they determine the content of oxides in water or amount of spent oxidant. The oxidation of water is calculated according to the results..

Water contamination with silicic acid occurs in the process of its purification or during transportation. Evaluation of the content of silicic is made by means of the colorimetric method – transforming silicic acid to silicomolybdic acid and comparing the color intensity of the test solution with the standard.

Water purification technology

At the first stage of cleaning the raw water passes through the bacteriological cleaning with sodium hypochlorite. Sodium hypochlorite, forming sodium cations and anions of hypochlorous acid when dissolved in water, today is one of the best means of showing strong antibacterial activity.

Disinfected water is cleaned through the mechanical filters and the storage tank, and then by adding sodium metabisulfite removal of chloramine is made.

Then water is degassed and sent to the mixed bed filters containing ion exchange resins. Thus receiving the highest degree of purification. Cleanability of resins in the process of saturation with anions and cations is reduced, which leads to the periodic need to regenerate. Regeneration is carried out with weak solutions of acids (cation exchange resins) and alkali (anion exchange resin), and after it the resins column is rinsed with water.

Chemical water treatment is a complicated process that requires monitoring and control of technological parameters of the equipment. In addition, registration and storing of indicators of preparation process is required. Chemical treatment system is equipped with the following sensors with analog outputs:

  • flow sensors;
  • pressure sensors;
  • sensors for measuring the resistivity (conductivity) of water;
  • water temperature sensors;
  • level sensors in vessels.

Also, the system has the valve position sensors with analog and digital output signals.


Advantages of SCADA-system:

  • increasing the efficiency of management of line of chemical treatment of water in general;
  • displaying the progress of technological water treatment process;
  • displaying, recording and storage of process parameters;
  • control of indicator values and alarms in case of deviation from the values of specified limits;
  • possibility of remote control of water treatment process from the automated working station;
  • prompts to the operator in making decisions in different situations;
  • recording of operator’s actions.

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