Operation Test of Pilot-Scale Low-Emission Multi-Fuel Boiler with Plasma-Chemical Hybrid NOx Reduction System

A pilot-scale low emission boiler plant which consists of a multi-fuel boiler and a plasma-chemical hybrid NOx removal system was investigated. This plant can achieve carbon neutrality because the multi-fuel boiler uses waste vegetable oil as one of fuels. The plasma-chemical hybrid NOx removal system has two processes; one is NO oxidation by ozone produced from plasma ozonizers, and the other is NO₂ removal using a Na₂SO₃ chemical scrubber. The operation tests of the plant were carried out for mixed oils (mixture of heavy oil and waste vegetable oil). Stable combustion was achieved for the mixed oil (20% ~50% vegetable oil). The flue gas properties, such as O₂, CO₂ and NOx in firing mixed oils, were nearly the same as those in firing heavy oil when the flue gas flow rate was 1000 Nm³/h on average. NOx concentrations at boiler outlet were 90~95 ppm. Furthermore, it is confirmed that during a 300 min continuous operation in firing 20% mixed oil NOx removal efficiency was attained more than 90%, equivalent to less than 10 ppm at scrubber outlet when the flue gas flow rate was 870 Nm³/h. In addition, the effect of replacing heavy oil by waste vegetable oil on CO₂ reduction was estimated.