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.