Alternate Energy Resources “Sunshine moonshine”…


Question Description:

20.50

Alternate Energy Resources “Sunshine moonshine” The ever-resourceful scientists at the Lenfest Energy Center discover a photo/catalytic (PC) process to produce ethanol from CO2 and H2O, powered only by sunshine. The reaction {2CO2 + 3H2O a C2H5OH + 3O2} occurs when water on the Lenfest proprietary catalytic substrate at the base of the reactor is illuminated by sunlight in the presence of gaseous CO2. The process is quite insensitive to temperature, and because it is largely driven by the UV in sunlight, can operate even on partly cloudy days. The limited photon energy range within sunlight that is suitable for powering the catalysis, and the less than perfect rate at which suitable photons cause the reaction to occur, mean that at peak efficiency the process only transfers 5% of the sunlight’s energy into chemical energy. One application of Lenfest PC reactors is that they may be used to synthesize transport fuels from the exhaust products of central electricity generating power stations. It is your job to evaluate this development by answering the following questions. 1. What advantages/disadvantages would the Lenfest PC reactor have compared to photovoltaic (PV) energy schemes? Comment upon the appropriateness of the comparison. What advantages/disadvantages would the Lenfest process have for making ethanol compared to the current biomass fermentation route? 2. How large an area would a Lenfest PC reactor need to cover to be able to accommodate 2 days worth of the exhaust stream of a GWe coal power plant? [The reactor is inflatable as exhaust gases collect. Assume that a Lenfest reactor is usefully limited to a meter in thickness when full of feedstock exhaust, because gas must be no more than 1 meter from the substrate in order to react rapidly enough to make ethanol in average sunlight.] Why 2 days? 3. How large an area would a Lenfest PC reactor need to cover to receive sufficient solar energy to effect the catalysis of the exhaust of a GWe coal power plant, assuming some average sunlight? Compare to your answer in 2/, perhaps with comments. 4. What is the water requirement for a Lenfest PC reactor for coal, biomass, and natural gas fuels in the power plant? What would you do with the O2 by-product? 5. Suggest and discuss a transition strategy in the framework of Socolow’s wedges, plateaus, and ramps-down for evading our fossil carbon problems. Make good use of the Lenfest PC reactor.

Answer

20.50