Energy and exergy analysis as tools for optimization of hydrogen production by glycerol autothermal reforming

Investigating the chemical reactions of autothermal reforming (ATR) of glycerol reveals that the optimal conditions, based on maximizing the hydrogen production, minimizing the methane and carbon monoxide contents and eliminating coke formation at thermoneutral conditions, can be achieved at a water-glycerol feed ratio (WGFR), reforming temperature (T) and oxygen-glycerol feed ratio (OGFR) of 9, 900 K and 0.35, respectively. The energetic study of the resulting process indicates that approximately two-thirds of the energy fed to the process is recovered in the useful product (H2) and that the remaining incoming process energy is exhausted in the off-gas. The exergetic investigation reveals that the exergetic efficiency of the ATR process is 57% and that 152 kJ are destroyed to generate 1 mol of hydrogen. The process operating conditions recommended by the chemical reaction investigation suffers from low performance because energetic and exergetic efficiencies are comparatively lower than values previously reported in literature for other reformates. The parametric investigation indicates that more accurate conditions are needed to convert glycerol-hydrogen. These conditions ensure the lowest consumption of energy to generate a given amount of hydrogen. This paper recommends WGFR = 5.5, T = 900 K and OGFR = 0.96 as the optimum conditions for the entire glycerol-to-hydrogen process. For this configuration, the thermal and exergetic efficiencies are 78.7% and 67.8%, respectively.