Towards ideal NOx control technology for bio-oils and a gas multi-fuel boiler system using a plasma-chemical hybrid process

A super-clean boiler system comprising a multi-fuel boiler and a reactor for plasma-chemical hybrid NOx aftertreatment is developed, and its industrial applications are examined. The purpose of this research is to optimally reduce NOx emission and utilize waste bio-oil as a renewable energy source. First, NO oxidation using indirect plasma at elevated flue gas temperatures is investigated. It is clarified that more than 98% of NO is oxidized when the temperature of the flue gas is less than 130 °C. Three types of waste bio-oils (waste vegetable oil, rice bran oil, and fish oil) are burned in the boiler as fuels with a rotary-type burner for CO2 reduction considering carbon neutrality. NOx in the flue gases of these bio-oils is effectively reduced by the indirect plasma-chemical hybrid treatment. Ultralow NOx emission less than 2 ppm is achieved for 450 min in the firing of city natural gas fuel. The boiler system can be successfully operated automatically according to unsteady steam demand and using an empirical equation for Na2SO3 supply rate, and can be used in industries as an ideal NOx control technology.