Some considerations about bioethanol combustion in oil-fired boilers

Abstract

The combustion of bioethanol in boilers has been analyzed and compared with conventional liquid fuels. The study includes an experimental evaluation of combustion performance as well as the estimation of the impact of replacing gasoil by ethanol on the thermal efficiency of an industrial boiler. Several works have been dedicated to the study of fuel substitution in internal combustion engines, being the use of gasoil–bioethanol blends in engines a common practice. However, very few studies have addressed the characterization of switching of conventional liquid fuels by bioethanol in boilers. Combustion tests demonstrate significant differences between bioethanol and gasoil flames. Soot, NO x and SO 2 emissions are significantly lower with ethanol, whereas this fuel can produce higher amounts of CO than gasoil if the burner is not properly adapted. The experimental tests have demonstrated that both the burner and boiler operation should be readjusted or modified as a result of the change of fuel in industrial boilers. If thermal input is to be kept constant, nozzles of larger capacities must be used and the air feeding rate needs to be significantly modified. Also, the flame detector may have to be replaced and the fuel feeding system should be revised due to the enhanced tendency of ethanol to cavitation. Using the same thermal input may not guarantee keeping the same steam production, but some parameters of boiler operation should be modified in order to avoid reductions in the capacity of the boiler when switching from gasoil to bioethanol, such as gas recirculation fraction, steam cooling systems and percentage of oxygen in the exhaust gases. The feasibility of burning bioethanol in gasoil boilers has been analyzed, and the results confirm that fuel switching is technically possible and offers some advantages in terms of pollutants reduction.