Sunday, May 4, 2008

biomass to hydrogen

Today a significant market for hydrogen exists. It is used widely as a chemical feedstock and for processing fossil fuels. The current avenues for hydrogen production include steam reforming or gasification of fossil fuels, water electrolysis and biomass to hydrogen processes. We will continue to use fossil fuels for hydrogen production, but we may find that this feedstock is not economical because of rapidly increasing prices for fossil fuels and because fossil fuels contribute to climate change. Unless a virtually infinite source of energy is found, water electrolysis will remain infeasible as it is very energy intensive. Biomass to hydrogen processes are effective, but rely on catalysts, which have some associated problems and are not optimum for all applications.

I am researching a novel, non-catalytic method of producing hydrogen from biomass. This method, partial oxidation fuel reforming, relies on heat recirculation in a bed of inert porous media. The heat recirculation from the hot exhaust gases to the cold reactant gases through the porous media is used to react extremely oxygen starved mixtures, which produce hydrogen and carbon monoxide as well as normal combustion products, water and carbon dioxide. In order to study this process, my group performs physical experiments and numerical experiments. We run three different sets of codes for numerical experiments including a code that models the porous media reactor, a code that models a free, premixed flame and a code that finds the equilibrium mixture of the reactants at constant pressure and without heat loss.

This project focused on equilibrium computations as a means to select the fuels with the best potential for conversion to hydrogen. Equilibrium calculation is not best for this application (see Smith and Missen 1982 for a discussion on the applicability of equilibrium calculations), but its weakness in this regard is also its strength. Equilibrium is general and applies to all processes that occur with the same thermodynamic conditions, so the results of this study not only pertain to my experiment, but all processes that occur under the same thermodynamic conditions.

I selected fuels for equilibrium study based on the following criteria:

1. What thermodynamic data are available?

2. What fuels have the strongest potential for production?

3. What fuels can be made from waste streams?

4. A strength of our reactor is that it can accept unprocessed fuels and impurities. What fuels take advantage of this strength?

5. Another strength of our reactor is that it can accept a variety of feedstock and mixtures of feedstock. What fuels take advantage of this strength?

6. Are there fuels that offer significant benchmarking opportunities?

Based on the answers to these initial questions, I chose to investigate cottonseed oil, rapeseed oil, soybean oil, sunflower oil, pyrolysis oil, algae oil, ethanol and methanol.

Equilibrium analysis showed that there is little difference in hydrogen production potential between the set of fuels I chose to study. This is important for my research because it means I should decide on fuels to study based on economic and practical considerations. Because the results show that each of the fuels produce hydrogen with similar efficiency, I will focus my efforts on algae oil. Algae has the greatest potential for production does not need to be grown on arable land. As mentioned above, these results are general, so claims that any of these sources of biomass should be preferentially used for hydrogen production should not be heeded.

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