(7d) Separation Efficiencies of Hydrogen From Steam Gasification Products – Thermodynamic Evaluation

The paper presents a procedure for the comparison of various technologies for the production of hydrogen from carbon based materials based on First and Second Law Analysis. All known technologies in publicly available literature are analyzed based on calculations of the energetic and exergetic analysis of the whole process as well as the sub processes. Special emphasis has been given to chemical separations. The thermodynamic limits to the separation efficiencies for any given hydrogen concentration has been identified. Methane was chosen as a model compound for evaluating single stage separation. The incremental changes in efficiencies as a function of process parameters such as temperature, steam amount, chemical type and amount were estimated. Energy and exergy losses associated with generation of syngas, separation of hydrogen from COx as well as exergetic loss associated with emissions are presented. The optimal conditions for each process by minimizing these losses are presented. Based on the results, the most energy efficient process for a given hydrogen purity is suggested along with the optimal conditions for operation. The primary chemical processes that were considered were simple steam gasification, steam gasification with CO2 capture using chemical looping of a reactive carbon dioxide removal agent, steam gasification with oxygen carrier, steam gasification with Boudouard reaction catalyst and steam gasification with Boudouard reaction catalyst and reactive carbon dioxide removal agent in a chemical looping system. The information presented will clearly demonstrate the differences in efficiencies between the various chemical looping processes for hydrogen generation. The data obtained from the theoretical studies will be compared with data from experimental research available in literature and in our laboratories to establish the degree of inefficiency during practical applications. Finally, the protocol will be used for other hydrogen production systems such as membrane separations, pressure swqing absorption etc.