fuel-system-power-33.html
Procedings
34 / 88
32 e n e r g y + p r o c e e d i n g s paired with cogeneration applications the
sofc
tech- nology is capable of producing total heat and power efficiencies of more than 80% which is above that of traditional coal and natural gas power plants. the typical hydrogen production source which is also the most economical has been natural gas, according to the steam reforming and shift equation (1) and (2) given above. coal is also indirectly a future alternative. however, both of these processes release co 2 into the atmosphere. hydrogen can be made from electrolysis of water ac- cording to the equation: (4) h 2 o h 2 + 1 / 2 o 2 e 0 = 1.229 v a significant amount of heat and electricity is re- quired for driving this water electrolysis reaction which currently makes this technology more than two times as expensive as natural gas steam reforming. alternative technologies such as solar, wind, geother- mic or hydro are potential ways to produce hydrogen based on electrolysis via electricity without the release of co 2 , but they are not likely to be economically feasible for the foreseeable future. electrolysis of water based on high-temperature electrolysers – so-called solid oxide electrolyser cells (
soec
) – possess the largest future potential because the high-temperature heat loss from these cells helps to balance the energy economy in the heat consum- ing water splitting and water heating process, and thus completes the electrolysis with less electricity con- sumption. low-temperature water electrolysers run at a practical efficiency of about 45-60%, whereas the high-temperature electrolysers promise efficiencies above 70%. in principle, a
soec
is a
sofc
operated in the reversed mode. therefore, a system principally con- sisting of a heat exchanger and a reversible
sofc
/
soec
has a lot of potential advantages compared to other conversion techniques.
soec
also has the potential of splitting co 2 into co and oxygen. this means that the electrolysis of a mixture of steam and co 2 results in a mixture of hydrogen and co (syngas). the
soec
materials for the cells and stacks are very similar to those for the
sofc
as described above, but further challenges regarding material stabil- ity and durability are obvious. hence,
soec
may be considered an interesting future spin of the current
sofc
development. figure 11 shows the diversity of known energy sources, energy carriers and the poten- tial to use these with high efficiency and co 2 neutral- ity based on future
sofc
and
soec
technology. page 42 of 122 coal natural gas renewables nuclear syngas liquid
fuel
electricity biomass
sofc
electricity
soec
hydrogen figure 11. diversity of energy sources, carriers and high efficiency power systems. references 1. christiansen, n., j. b. hansen, h. holm-larsen, m. j. jørgensen, l. theil kuhn and p. v. hendriksen, a. hagen and s. linderoth, solid oxide
fuel
cell research and development at topsoe
fuel
cell a/s and risø/dtu. european
sofc
symposium, lucerne, 2008. 2. larmine, j., and a. dicks,
fuel
cell systems explained . john-wiley & sons ltd, reprint 2001, isbn 0471490261. 3. pålsson, j., j. b. hansen, n. christiansen, j. u. nielsen and s. kristensen, solid oxide
fuel
cells – assessment of the technology from an industrial perspective . risø energy conference, risø 2003. 4. hansen, j. b., and n. christiansen, solid oxide
fuel
cell development at topsoe
fuel
cell a/s . world hydrogen technology convention 2007, montecatini, 2007. 5. christiansen, n., s. kristensen, h. holm-larsen, p. h. larsen, m. mogensen, p. v. hendriksen and s. linderoth, status of stack development at haldor topsøe/risø. to be presented at the 8 th international symposium on solid oxide
fuel
cells (
sofc
-viii), paris, april 2003. 6. wandel, m., j. r. bowen and m. mogensen, performance, degradation and microstructure of lscf/cgo composite cathodes . european
sofc
symposium, lucerne, 2008. 7. søgaard, m., t. z. sholklapper, m. wandel, l. c. de jonghe and m. mogensen, european
sofc
symposium . lucerne, 2008. figure.11..diversity.of.energy.sources,.carriers.and.high.efficiency. power.systems.
fuel-cell-oxide-35.html
