Thermodynamics of hydrogen production from urea by steam reforming with and without in situ carbon dioxide sorption

The thermodynamic effects of molar steam to carbon ratio (S:C), of pressure, and of having CaO present on the H-2 yield and enthalpy balance of urea steam reforming were investigated. At a S:C of 3 the presence of CaO increased the H-2 yield from 2.6 mol H-2/mol urea feed at 940 K to 2.9 at 890 K, and decreased the enthalpy of bringing the system to equilibrium. A minimum enthalpy of 180.4 kJ was required to produce 1 mol of H-2 at 880 K. This decreased to 94.0 kj at 660 K with CaO-based CO2 sorption and, when including a regeneration step of the CaCO3 at 1170 K, to 173 kJ at 720 K. The presence of CaO allowed widening the range of viable operation at lower temperature and significantly inhibited carbon formation. The feasibility of producing H-2 from renewable urea in a low carbon future is discussed. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.