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Preparation of industrial water

Water of various quality is required for the operation of the devices in the power plant (boilers, turbines, machine cooling devices, devices for carrying away slug and for the purification of flue gases). Water is prepared in several facilities which were built simultaneously with the construction of the production blocks. The quality of the obtained water is measured during the production process with controls carried out by the Department for Water, Fuel and Lubricant Technology.

Water of the best quality is used for supplying boilers with industrial water from which working vapour for driving turbines is obtained. This water has to be chemically pure, without minerals, metal elements, different salts or silicon. Such chemically pure water is obtained by purifying potable water in the facility referred to as total demineralisation facility (abbreviation DEMI). The purified water is referred to as deionised water. The purification quality is controlled by measuring water conductivity and the content of silicon.

The conductivity of our natural waters is >250 S/cm, whereas the conductivity of industrial water  for boilers can range up to 0.2 S/cm. Three desalting tracks with production capacities of 40 m3/h are used for obtaining deionised water.

Chemical purification of water is based on artificial substances (masses) which can bind ions. Natural water contains various dissolved substances forming positive and negative ions. These masses bind ions to them, thus removing them from the water. Each purification track consists of a sand filter for mechanical purification and a cationic filter followed by the CO2-degasifier and then anionic and mixed filters.

The obtained ionised water is collected in two reservoirs located on blocks 4 and 5 with volumes of 600 m3. The water-vapour systems and reverse cooling systems are filled with deionised water. The reverse cooling systems are used for cooling various engines, cooling air for motors and work and lubricating oils.

Other industrial water is chemically less pure and is referred to as decarbonised water. Raw water for obtaining decarbonised water is collected by means of mechanical purification in raw water tanks from the Paka River and Lake Družmir. Water from here is pumped to consumers with pressure pumps, which are the reactors for preparing decarbonised water and device for carrying away slug.  This water is purified in facilities referred to as decarbonisation facilities (abbreviation DEKA). It consists of a water catchment, pump room, a slow reactor followed by sand filters and tanks with pure water.

Carbonates are removed through a chemical procedure in the reactor, where conditions for coagulation and settlement of substances in water are created, and water is finally purified by means of filtration in sand filters. Water quality is assessed by measuring ,p’and ,m’ values. These are measures for assessing the presence of liquors, carbonates and bicarbonates in water and are used in the decarbonisation process as a measure for the dosage of chemicals. There are two decarbonisations, namely DEKA 1 for the supply of blocks 3 and 4 and DEKA 2 for the supply of block 5. The maximum capacity of the DEKA 1 reactor which contains closed sand filters of 10 x 150 m3/h is 850 m3/h. The designed capacity of the DEKA 2 reactor which has open sand filters of 6 x 250 m3/h is 1250 m3/h.

Decarbonised water is used for filling the main cooling systems for individual blocks or for obtaining deionised water in case of a shortage of potable water.

Raw water is used to partially and temporary carry away slug and, if necessary, also ash.  Due to the new system for carrying away slug mixed with the stabilised side-product, the existing closed water circuit system is used only occasionally.

The devices for the desulphurisation of flue gases of blocks 4 and 5 require water for preparing the washing suspension. Fresh decarbonised water is used for this purpose or collected from the pressure conduit of the main cooling system. This collection is also used for the blow-down of the cooling system.