Numerical investigation Greek lignite/cardoon co-firing in a tangentially fired furnace

The present study presents a three-dimensional numerical model for co-firing lignite and biomass in large-scale utility boilers. The model takes into account the non-spherical form of the biomass particle, which influences the drag coefficient and its devolatilization and combustion mechanisms. Simulations under different co-firing rations and biomass particle sizes are performed for a 300 MWe pulverized-fuel, tangentially fired boiler located in Northern Greece, operating with low quality lignite. Validation of the simulations is performed using plant data for the reference case of lignite combustion. The results obtained, which include temperature and species fields, particle tracks and burnout per burner level and NOx calculations, provide useful conclusions regarding the maximum allowable biomass particle size and substitution ratio for an efficient boiler operation. In particular, the combustion behavior of particles from different burner levels suggests the optimum positions for dedicated biomass burners.

► Cardoon/lignite co-firing CFD model for tangentially-fired pulverized-fuel boiler.
► Co-firing up to 10% thermal basis has no negative effect on operation.
► Reduction of NOx emissions by up to 10% was found for co-firing cases.
► Very good burnout for 1 mm biomass particles; lignite burners sufficient.
► 5 mm Particles: low burnout. Direct injection near low main/oil burner suggested.