SO3 reduction in the 210 MW oil-fired Power Plant Sisak

Various impacts of the combustion process parameters and burner design characteristics on the SO3 generation in the steam generator furnace of the 210 MW oil-fired Power Plant Sisak have been studied by using 3-D mathematical modelling. Problems of the Power Plant Sisak, which burns heavy-oil fuel with 2-3% sulphur and exhibits flue gas temperatures of 135-140 degreesC at the exit of the regenerative Ljungstrom air-heater, are related to severe low temperature corrosion and environmental pollution. Different parameters were varied: combustion air excess ratio, spray angle of fuel injection, number of openings on the steam-pressure atomiser nozzle and fuel droplet size. By using the FLUENT (TM) software package for simulation of the oil combustion process in the furnace, relatively reliable results have been obtained which favourably could be compared with scarce existing experimental data. This means that trends of influential parameters have been well predicted rather than absolute values of the same parameters. The results of the simulation showed that the excess combustion air of 1.07-1.10 could not be decreased without a reconstruction of combustors because of soot appearance and increased CO concentration. By increasing the number of nozzle openings and the fuel atomising steam pressure i.e. by decreasing the fuel droplet size, the excess air has been decreased to 1.035, which represents the upper limit of desired result. Thereby the average SO3 concentration in flue gases was about 25-30 ppm. The variation of fuel spray angle has been found not to have any significant influence on SO3 and CO concentrations. By major reconstruction at the air inlet and air swirl generator and by modification of the combustion control better results could be expected which would maximally reduce problems with low temperature corrosion and environment pollution.