In reply to Jones Beene's message of Sun, 06 Mar 2005 13:14:40 -0800: Hi, [snip] >The big cost in either case is drilling the well, right? OK >once that has been accomplished, methane starts to flow >based on its pressure at the source, but in the case of >hydrogen, energy would need to be added to the water being >sent down.
Since e.g. FeSi2 reacts exothermally with water to produce iron and silicon oxides and hydrogen, the only energy that would need to be added is that of the pumping. Unless I have blundered seriously, pressure is energy/volume, so a pressure of say 10000 psi is 69 kJ/L. The water, once converted to hydrogen and burnt again to produce water, yields 241.826 kJ/mol, or 13430 kJ/L. Which looks pretty good compared to the 69 kJ/L used to pump the water down. :) The H2 is going to come out at the same pressure, but, since it's a gas, the volume will be larger, so expansion energy of the H2 can be used to drive the water pump, with extra to spare. This excess is actually part of the exothermal energy of the reaction. (p x volume_out) - (p x volume_in) > 0. One problem may be that SiO2 (or silicates) may form a coating over the silicides, preventing further reaction. Also, the temperature will probably boil water converting it to steam, so one should probably count on a mixed H2/steam gas flow. Regards, Robin van Spaandonk All SPAM goes in the trash unread.
