Friday, June 01, 2012

Interesting New 57% Efficient Solid Oxide Fuel Cell

Fuel cells can burn a wide range of fuels: from hydrogen to biomass to methane to diesel. They are also more efficient than internal combustion engines. This makes them practical for both stationary power generation facilities, and for mobile power generation in electric-powered vehicles. Below we have republished two excerpts from stories reporting on important developments in solid oxide fuel cell (SOFC) design and development, which makes SOFCs more efficient and practical.

Researchers at the Pacific Northwest National Laboratory report on a highly efficient, small-scale solid oxide fuel cell system featuring PNNL-developed microchannel technology in combination with adiabatic, external steam reforming and anode gas recirculation. The heat and water required for the endothermic reforming reaction are provided by the recirculated anode gas emerging from the SOFC stack. They refer to this as adiabatic steam reforming because external heat sources, such as a combustor or an electric-resistance heater, are not necessary to support the reaction.

The new fuel cell system achieves up to 57% efficiency—significantly higher than the 30 to 50% efficiencies previously reported for other solid oxide fuel cell systems of its size—according to a study published in this month’s issue of the Journal of Power Sources. The pilot system generates about 2 kW of electricity; the PNNL team designed it to be scaleable to produce between 100 and 250 kW. _GCC

The PNNL SOFC system has been streamlined to make it more efficient and scalable by using PNNL-developed microchannel technology in combination with processes called external steam reforming and fuel recycling. PNNL’s system includes fuel cell stacks developed earlier with the support of Department of Energy’s Solid State Energy Conversion Alliance.

The big numbers for the efficiency of this small SOFC system is the use of a PNNL-developed microchannel technology in the system’s multiple heat exchangers. Instead of having just one wall that separates the two gases, PNNL’s microchannel heat exchangers have multiple walls created by a series of tiny looping channels that are narrower than a paper clip. This increases the surface area, allowing more heat to be transferred and making the system more efficient. PNNL’s microchannel heat exchanger was designed so that very little additional pressure is needed to move the gas through the turns and curves of the looping channels. Even more interesting is the second unique aspect of the system – it recycles the heat. _NewEnergyandFuel
SOFCs using heat recycling fuel reformers, should eventually be able to use a wide range of carbonaceous fuels -- including biomass. So much for the collapse of civilisation when crude oil is abandoned as a primary fuel.

More on biomass fuel cells (PDF)

Here is a "kinder, gentler" way of turning biomass into energy. As we have predicted, the conversion of cellulose to energy and fuels is likely to follow a rough trajectory over various processes. The "brute force" thermal and thermochemical approaches are more practical initially. As better organisms and enzymes are engineered, the biological approach is likely to grow more efficient. Finally, as nanotechnological bio-mimics improve, the greater robustness of inorganic nanotech-catalysts should facilitate their use in place of more fragile bio-based catalysts. In the background, the movement of more advanced societies to safe, clean, reliable, and affordable gen III and gen IV nuclear reactors at various scales, is likely to increase the energy and fuel production choices of societies almost exponentially.

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