Emissions of CO2, CO, NOx and N2O from dried lignite combustion in oxygen-enriched O2/CO2 atmospheres in a circulating fluidized bed boiler

The paper presents the idea of oxygen-enhanced dried lignite combustion in a circulating fluidized bed (CFB) boiler as it gives a possibility of reduction of gaseous pollutants emissions. Calculations were conducted using one-dimensional model, which describes crucial processes associated with combustion of solid fuels under circulating fluidized bed conditions, e.g., hydrodynamics of bed material, fuel devolatilization, volatiles and char combustion and heat transfer. The paper is focused on CO2, CO, NOx and N2O emissions from a 670 t/h CFB boiler during dried lignite combustion in O2/CO2 atmosphere. The dependence of the gaseous pollutants’ emissions on oxygen fraction in an inlet gas as well as moisture content in lignite were studied. The oxygen fraction was increased from 21 to 30% vol., whereas moisture content was decreased from 43.5 to 10% – simulating fuel pre-drying. A case study considers solution when process is run with recirculation of CO2. The obtained results was compared to the case where CO2 is not recycled.