Development of Low-Emission Bio-Fuel Boiler System With Plasma-Chemical Hybrid $\hbox{NO}_{\rm x}$ Reduction

A pilot-scale low-emission boiler system consisting of a bio-fuel boiler and a plasma-chemical hybrid NO
_x
removal system is investigated. This system can achieve carbon neutrality because the bio-fuel boiler uses waste vegetable oil (WVO) as one of the fuels. The plasma-chemical hybrid NO
_x
removal system has two processes: NO oxidation by ozone produced from plasma ozonizers and NO
₂
removal using a Na
₂
SO
₃
chemical scrubber. Test demonstrations of the system were carried out for mixed oils (mixture of heavy oil and WVO). A stable combustion was achieved for the mixed oil (20%-50% WVO). The properties of flue gas-e.g., O
₂
, CO
₂
, and NO
_x
-when firing mixed oils were nearly the same as those when firing heavy oil for an average flue gas flow rate of 1000 Nm
³
/h. The NO
_x
concentrations at the boiler outlet were 90-95 ppm. Furthermore, during a 300-min continuous operation when firing 20% mixed oil, a NO
_x
removal efficiency of more than 90% was confirmed. This is equivalent to less than 10 ppm at the scrubber outlet when the flue gas flow rate was 870 Nm
³
/h. In addition, CO
₂
reduction when heavy oil was replaced with WVO was estimated. The system comparison is described between the plasma-chemical hybrid NO
_x
removal and the conventional NO
_x
removal.