Toplarna Siska (TOS) uses almost exclusively natural gas as energetic fuel. When Slovenia and thus Ljubljana connected to the European networkof natural gas, wewere in 1979 among the first Slovene consumers of gas. "Ecological" parameters of natural gas are very favourable, pollution of air with toxic substances is low especially due to optimal burning quality in large boiler units. The average structure of natural gas is as follows:
Methane (CH4) - 98,2% of vol.
Ethane (C2 H6) - 0,6% of vol.
Other Carbohydrates (Cx Hx) - 0,2% of vol.
Carbon Dioxide (CO2) - 0,1% vol.
Nitrogen (N2) - 0,9% of vol.
Sulphur (S) - 0,0% of vol.
Toplarna Siska uses as substitute fuel middle weight fuel oil (mazout). Four tanks are built to store this fuel. Their joint capacity is 36,000 m3 (20,000 m3 + 10,000 m3 + 5,000 m3 + 1,000 m3). The appropriate distribution of quantities of medium weight fuel oil to individual tanks according to sulphur contents enables us to reach the highest quality level of fuel in critical days when Ljubljana faces temperature inversion.
The following diagram shows average year values of supplied quantities of medium weight fuel oil. It can be determined that the quality of fuel is on the increase in the last years. Peak load heating station in Termoelektrarna-toplarna Ljubljana (LPB - low pressure boiler station) uses medium weight fuel oil. The capacity of tanks is 3,000 m3 (2 x 1,500 m3).