Reforma de glicerol em um reator de recuperação de calor de leito fixo e fluxo continuo: análise de exergia

Abstract

The ever growing energy demand and its consequent environmental burdens make the use of renewable energy strategic in terms of sustainability, such as biofuels in mobility applications within this scenario. These alternative fuels were received with enthusiasm, but a series of issues emerged with their widespread utilization. Biodiesel‟s main concerns are deforestation impulse caused by feedstock crop demand; food security issues, raised by the use of edible raw materials; and large yield of glycerol, a low value sub product whose treatment requires waste water management. Glycerol„s pyrolysis and reforming have received increasing attention as alternatives to its use in the production of hydrogen rich syngas. Most of the cited works have its focus in process parameters or catalysts upon hydrogen yeld. However the energy efficiency has low publications. This subject is accessed trough the energy and exergy analysis of a bench scale glycerol reforming reactor. Exhaust gases from a limited cooling diesel engine were directed trough 21 baffles mounted outside the reactor shell, providing the energy input necessary to the reforming reactions. Exergy efficiency of the reforming process was determined in function of the reaction bed temperature and glycerol/water concentration by means of thermodynamic balances. The outlet reaction bed temperature varied from 600 ºC to 800 ºC for each glycerol/water feed concentration taken into account (10% to 90%wt of glycerol). Physical and chemical exergies of each syngas component were considered in the course of the analysis, as well as heat and mass exergy flows. The irreversibilities associated with the heat transfer from hot gases to the reacting bed and internal reaction bed processes were calculated individually. Exergy losses were grouped into distinct outflow contributions: sub-products total exergies (water, char and tar), syngas thermomechanical exergy and outflow exhaust gases exergy. The highest syngas exergy efficiency attained was 61,6%, being achieved at 750°C with 70% glycerol feed rate. The reaction bed outlet temperature was the most important parameter for H2 exergy efficiency, which continuously increased from 1.6% at 600°C to 19.0% at 800°C. The glycerol feed concentration impacted on the exergy irreversibilities and losses distributions, which were dominated by tar production at 90% glycerol concentration; reactions irreversibilities from 70 to 30% glycerol, and water outflow at 10% glycerol.