Sewage is power
29 Apr 2002
Researchers at the University of Warwick's Warwick Process Technology Group have devised a process that turns wet waste from sewage farms and paper mills into a source of power.
University of Warwick researcher Dr Ashok Bhattacharya and his team are part of a Europe wide consortium that have cracked the problem of how to extract very pure levels of hydrogen from wet bio-matter, such as sewage or paper mill waste.
This very pure hydrogen can then be used in 'fuel cells' to power homes, factories and cars. The research consortium have now received £2.5million in European funding to work up their lab based solution into larger prototypes.
Eventually the research team's 'plated membrane reactors' could be built as small industrial units, no bigger than a large room in some cases, and added directly to the sites of sewage plants or paper mills.
Previous attempts to extract pure hydrogen from bio-matter to power fuel cells have only met with limited success, even with dry material. The new process extracts very pure hydrogen from the more difficult but exceedingly abundant wet bio-matter and even makes a virtue of the water content of the material to generate even more pure hydrogen.
First the waste biomass is gasified breaking it down into its Methane CH4, water H2O, Carbonmonoxide CO, and carbondioxide CO2 and some hydrogen. All these gases are then fed into a reactor which uses them in a chemical reaction which extracts the hydrogen from both the methane and the water.
In normal circumstances this reaction would reach an equilibrium and simply stop once a certain amount of hydrogen had been generated. However the research team uses a palladium coated ceramic semi-permeable membrane as part of the reactor which only lets hydrogen pass through.
This allows the researchers to both harvest very pure hydrogen from the system (it can be over 95% pure) and to keep the reaction going as long as it is fed with the waste biomass as the hydrogen never builds up to the point where a chemical equilibrium would be reached thus stopping the reaction.
The hydrogen produced by this method can then be used to power hydrogen fuel cells. This process is also much cleaner than traditional production of H2 as it does not use up fossil fuels, thus it produces no more CO2 than would be produced naturally from the material biodegrading and it produces no other emissions such as nitrous oxides.
Other novel engineering in the process includes the use of a coated nanocrystaline catalyst to accelerate the reaction, and particular methods to manage heat transfer and pressure.
The research project brings together the University of Warwick's Warwick Process Technology Group team with Dutch, German and UK firms. In particular the Dutch firm BTG and the University of Twente have contributed to the gasification process and the Sheffield firm Dytech have contributed to the highly engineered porous ceramics used in the reactor.
