Measurements were carried out to investigate the emissions of SO2, NOx, fly ash, heavy metals, radioactive elements and polycyclic aromatic hydrocarbons (PAH) from one oil-fired, two coal-fired, five peat-fired and four natural gas-fired power plants or district heating plants.
The emissions of sulphur dioxide depended mainly on the sulphur content of the fuel. In the combustion of oil, practically all the sulphur in the fuel reached the atmosphere as sulphur dioxide. When coal and peat were used as fuel, the amounts of sulphur retained in the ash were about 15 and 20%, of the original sulphur content, respectively. The SO2 emissions from oil, coal, peat and natural gas were typically 1000, 600, 120, and < 10 mg MJ−1, respectively.
The emissions of oxides of nitrogen depended on the nitrogen content of the fuel and also on the combustion temperature. The NOx emissions from plants burning oil, coal peat and natural gas were typically 100, 300, 160 and 100 mg MJ−1, respectively. The lowest emissions were measured in the small natural gas-fired district heating plants (20–30 mg NOx MJ−1).
The emissions of fly ash and various elements depended mainly on the ash content of the fuel and on the efficiency of the dust collectors, which decreases sharply when the power plant output exceeds its nominal value. When the dust separation efficiency is 99% for coal- and peat-fueled power plants, and when there are no dust collectors in oil-fueled power plants, the typical fly ash emissions are 45, 20 and 25 mg MJ−1, respectively. Characteristic emissions of heavy metals and natural radioactive elements were greatest in the combustion of coal, with the exception of vanadium and nickel, of which the greatest emissions were from oil; the greatest emissions of 210Po were from peat.
The PAH emissions of the different fuel-fired power plants were, with one exception, similar (2–10 μg MJ−1). Emissions from the circulating fluidized bed combustion of peat were about 10 times (40 μg MJ−1) those of the other methods of combustion.