Numerical comparative investigation of a flexible lignite-fired boiler using pre-dried lignite or biomass as supporting fuel

This work presents a numerical parametric investigation of an indirect firing scheme for a lignite-fired boiler during its operation at a thermal load of 35% of the nominal one, lower than the current technical minimum. The parametric investigation is important in order to evaluate different configurations of the firing concept and the impact of two different types of supporting fuels: pre-dried lignite and exhausted olive cake. Numerical results indicate that both types of supporting fuel can ensure the stable operation of the boiler at the reduced operating load. Moreover, it can be remarked, that the injection of biomass as supporting fuel improves the thermal efficiency of the boiler. Furthermore, the firing system setup especially for the injection of pre-dried lignite affects significantly the NOx emissions due to the developed temperature field. Finally, simulation results indicate that the injection of biomass particles through all vapour burners induces high thermal loading on boiler surfaces. Therefore, it is proved that the firing strategy plays a key role to the operation of a boiler using these fuel blends. (c) 2019 Elsevier Ltd. All rights reserved.