Study of syngas co-firing and reburning in a coal fired boiler

Combustion simulations were conducted to evaluate the technical feasibility of using a waste-based syngas as a supplemental fuel in a 70,000 kg/h-steam coal-fired boiler. The syngas was either co-fired with coal at the burners or injected downstream as a reburning fuel under both fuel lean and conventional (fuel rich) reburning configurations. Sensitivity of syngas heat input and furnace stoichiometry were examined. Results indicated that the syngas was an effective reburning fuel although it contained less than 6% hydrocarbons. NOx reductions from 12–46% were predicted for different reburning configurations; the highest NOx reduction of 46% was achieved with 23% heat input under a conventional reburning configuration. Furnace LOI increased over baseline values for all but one reburning configuration. The highest LOI came from the top burner row in all cases. Results suggested the LOI increase due to reburning might be mitigated by biasing more air to the upper burners to enhance particle burnout. Predictions indicated co-firing syngas at the burner centerline was not beneficial as it resulted in poor combustion of the coal particles and high LOI and CO emissions. Simulation results also indicated that minor changes to the syngas composition do not significantly affect the performance of syngas reburning.