NOx and SO2 emissions of coals, biomass and their blends under different oxy-fuel atmospheres

• We present research studies on NOx and SO2 emissions in the oxy-fuel atmosphere.
• We use four different fuels i. e. two coals and two biomasses.
• We use 3 atm i.e. air, dry RFG and wet RFG.
• Results indicate that a level of emission in oxy is lower as in the air.
• Use biomass in oxy combustion gives additional reduction in emissions.

Co–firing biomass and coal under oxy-fuel combustion holds the potential for negative CO2 emission into the atmosphere and is a promising technology to realized atmospheric CO2 reduction and NOx and SO2 emission. NOx and SO2 emission and control is a relevant element of combustion of fossil fuels and subject to strict supervision and monitoring. The implementation of combustion techniques in the oxygen-enriched atmosphere makes it necessary to get to know the oxy atmosphere, its impact and changes of combustion conditions onto the process of emissions of gaseous pollutants. NOx and SO2 emissions have been investigated for different atmosphere in Entrained Flow Reactor. Experiments co–firing hard and brown coals, wood and straw pellets, and selected mixtures of these under three different atmospheres: air, oxy with recirculation of dry and wet exhaust gases. The reactor set point temperature was held constant at 1000 °C, NOx and SO2 emission levels were measured as a function of air excess ratio. The effect of fuel mixing, fuel nitrogen and fuel sulphur content on the conversion of fuel nitrogen to NOx and fuel sulphur to SO2 is also reported and discussed. The results obtained under oxy-fuel atmospheres were compared with those attained in air. The replacement of CO2 by 10% of steam in the oxy-fuel combustion atmospheres was also evaluated in order to study the wet recirculation of flue gas. The emissions of NOx and SO2 during oxy-fuel combustion were lower than under air-firing. Fuel mixing has a positive influence on the NOx and SO2 emission level. Emissions of NOx and SO2 were significantly reduced by the addition of biomass to the coal, but the addition of biomass can also increase the NO emissions, it depends on the fuels nitrogen content.