Fuel-Lean Gas Reburning(TM) (FLGR) is a method of controlling NO x emissions produced during coal combustion in utility boilers by injecting natural gas into the boiler downstream of the primary combustion zone. Whereas traditional reburning requires 10%--20% of the total energy input from the reburn fuel followed by over-fire air to complete combustion of fuel fragments, FLGR uses only 5%--10% of the total energy input from the reburn fuel. Because less fuel is used, the overall environment in the boiler remains fuel-lean, with only localized eddies that are fuel-rich, where the NOx reduction takes place. FLGR does not require over-fire air to complete the combustion of fuel fragments. Fuel-lean biomass reburning is a variation of FLGR that uses biomass instead of natural gas as the reburn fuel.;The goal of this work was to simulate a coal-fired utility boiler in an experimental down-flow reactor, and evaluate the influence of several variables, including the initial oxygen concentration, the type of biomass used, the % energy input from biomass, and the type of carrier gas used for injecting the biomass into the reactor.