Steam generator and various auxiliary systems
The boiler consists of a steam generator and various auxiliary systems built into the boiler or around it, participating in the process of steam production. The manufacturer of the steam generator is the company “Duro Dakovic” from the town of Slavonski Brod, Croatia, under Sulzer company license. Pulverized coal is used as the main fuel. The coal is transported from the depot by belt conveyors to six coal bunkers placed between the power house and the boiler. From the coal bunkers coal is continuously transported to mills where it is ground and dried. The pulverized coal dust is introduced into the boiler furnace through the fuel nozzles by a current of air. Extra light fuel oil is used for the starting and supplementary firing of the coal fuelling. The specific criteria for reduction of nitrogen oxides (NOx) have been applied to the construction of the furnace, thereby keeping the emission values of NOx significantly below the prescribed limits. Hot flue gases stream towards the top of the boiler and deliver heat to the evaporating system, the steam superheater system, the economizer and the air preheater. The further process comprises cleansing the flue gases of incombustible ingredients and ashes in the electrostatic precipitator and decrease the sulphur dioxide content in the flue gas desulphurization equipment. The process ends with the release of flue gases into the atmosphere through a chimney 340 metres high.
The pressurized water-steam system consists of the evaporating system with a water-steam separator, the economizer, the steam superheater and the reheater. In respect of the circulation principle, the steam generator is once-through, type Sulzer. The main feature of this circulation principle is that all feedwater that flows freely through the feeding head evaporates during one flow in the spiral evaporator. Feedwater is supplied by three feeding pumps driven by squirrel cage induction motors, 4100 kW (two of them are necessary for the rated power, while the third one is a stand-by). Raw water, supplied from the local spring “Bubic jama”, is processed in the chemical water treatment plant into demi-water. The capacity of demi-water production for TPP 2 is 2x 25 t/h and for TPP1 2x 20 t/h. The main technical data of the boiler: live steam generation 670 t/h live steam pressure 14.8 Mpa live steam temperature 535°C coal consumption Hd = 24 MJ/kg 80 t/h steam generator efficiency 92.9%.