Fuel-staged co-combustion of sunflower shells (as a base fuel) and coconut coir dust/moisturized' rice husk (as a secondary fuel) was studied on a 205 kW(th) fluidized:bed combustor with bottom air injection. During the experiments, the energy fraction ofiboth secondary fuels in the total heat input to the reactor was varied from 0 to 0.22, while the amount of excess air ranged from similar to 20% to similar to 80% for each co-firing option. Temperature and gas concentrations (O-2, CO, CxHy, and NO) were measured along the reactor centerline,. as welLas at stack, to evaluate the emissions and combustion efficiency of the combustor for the specified operating parameters. The experimental results revealed significant effects of excess air on the combustion and emission characteristics of the reactor, whereas the influence of fuel staging on these characteristics was moderate. An optimization method minimizing "external" costs of the co-firing was used to quantify the optimal energy fractions of the co-fired fuels and optimal amount of excess air. When operated optimally, the combustor can exhibit high (similar to 99%) combustion efficiency at minimal "external" costs and reduced NO emission (by 25% as compared to burning sunflower shells on its own), because of the fuel staging.