Hydrogen Production from Sewage Sludge by Steam Gasification

L. Aye and P. Klinkajorn (Australia)


Hydrogen; Steam gasification; Sewage sludge; Gibbs free energy; RAND algorithm. Nomenclature iµ = chemical potential, kJ/kmol * iµ = standard chemical potential, kJ/kmol kψ = RT kλ ω = step size parameter ζ = Lagrangian λ = vector of M unknown Lagrange multipliers ijδ = Kronecker delta kia = the subscript to the th k element in the molecular formula of species i kb = the number of moles of the th k element G = Gibbs free energy of the system, kJ H = enthalpy of components, kJ


Hydrogen from biomass steam gasification (SG) is a net zero green house gas emission fuel. Sewage sludge (SS) has a potential to produce hydrogen-rich gaseous fuel. Therefore, hydrogen production from sewage sludge may be a solution for cleaner fuel and the sewage sludge disposal problem. This paper aims to develop a computer model for SSSG by using Gibbs free energy minimization (GFEM) method. The computer model developed was used to determine the hydrogen production limits for various steam to biomass ratios (S/Bs). Results from the model showed that for equivalent ratios (ERs) 0 to 0.5 hydrogen yield ranges from 135 to 70 g/kg of dry ash free (daf) SS. It was found that the higher the S/B, the higher the hydrogen yield is, however, heat energy requirement increases with S/B. Results from the simulations showed that above ER 0.48, the SSSG can operate without external heat input and the hydrogen production is about 75 g/kg of daf SS. It should be noted that this optimum ER would change depending on the amount of heat loss and other operating parameters.

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