| Lunar Blast Furnace Reactions Revisited Hematite and magnesite do not exist on the Moon. Lunar "ores" will be fayalite-Fe2SiO4 and ferrosilite-Fe2Si2O6. Hypothetically, these will react: Fe2SiO4 + 2CO ===> 2Fe + SiO2 + 2CO2 Fe2Si2O6 + 2CO ===> 2Fe + 2SiO2 + 2CO2 FeO + CO ==> Fe + CO2 (FeO ==> Fe + O +267 kj/mol) (CO + O ==> CO2 -283 kj/mol) Since CO combustion will release 283 kj and FeO decomposition will absorb 267 kj, only 16 kj or 3.8 kcals CaO + SiO2 ==> CaSiO3 -89 kj/mol or 21.2 kcals Of great importance, at 800 C. to 1300 C. some CO reacts: CO + CO ==> CO2 + C This is where the carbon comes from that dissolves into the iron to form pig iron or steel if we are really lucky. Some heat will be released from these reactions, the rest will come from electric heating with graphite resistors energized by solar panels and/or direct solar heat. How much energy to make these reactions happen? Direct reduction is done at 1200 C. Titanium pipes lined with ceramic, perhaps rutile (TiO2), might suffice. One thing is certain, iron bearing silicates can be reduced with CO. See:http://www.lpi.usra.edu/meetings/leag2005/presentations/wed_am/04_berggren.pdf The researchers at Pioneer Astronautics were striving to get oxygen. At low temperatures carbon was deposited and then at higher temps the carbon reduced SiO2. To get iron with some carbon in it, I want to use higher temperatures. I am not aware of any research in this direction, but somebody might do it. Keeping it simple, let's say we want 100 tons of iron in 12 hours and the charge is all ferrosilite. From: http://www.iem.ac.rv/staff/aranovich/berman96.pdf we find the std. state heat cap. value for Fe2Si2O6 is 174.2 J/K-mol To get 100 tons of iron we will need 235.7 tons of ferrosilite or 235.7 megagrams = 892,803 mols Q = 892,803 mols * 174.2 * 1200 = 186,631.5 megajoules or 51.84 MWhrs. G = H -T(S) H of 2FeO + 2SiO2 = Fe2Si2O6 -1,193,000 j/mol H of Fe2Si2O6 = 2FeO + 2SiO2 +1,193,000 j/mol 1,193,000 j/mol – [(1470 deg. K)(96.47 j/K mol)] =1,051,189 j/mol ans * 892803 = 9.385E11 megajoules 260.7 MWhrs to drive the decomposition ferrosilite FeSiO3 = 892,803 mols FeO and 892,803 mols SiO2 thus the FeO + CO releases 14,300 megajoules the CaO + SiO2 releases 79,450 megajoules total, just 22 MWhrs 51.84 + 260.7 = 312.54 MWhrs. ans.-22 = 290.54 MWhrs. Calculations also show that 116 MW hrs. will be needed to electrolyze the water formed when recycling the CO used to make 100 tons of iron. . Since there will be losses into the structure of the furnace unless the stack is well insulated, heat lost in the off gas that could be recovered with a heat exchanger to heat CO input, resistance heater inefficiencies, power conditioning losses, heat absorbed to induce the reactions, energy req. to electrolyze water formed by the RWGS reaction used to recycle CO from CO2, electricity required to run compressors, etc. we will make a wild estimate. 700 MWhrs required. That's 7MWhrs/ton iron, about half as much as required for producing aluminum! Since the run will take 12 hours, 58 MWe constant power is req. With 10% efficient solar panels (135 watts/m^2) 430,000 square meters are needed or 655m by 655m (2150 ft by 2150 ft) Perhaps we should use one square kilometer of solar panels on the Moon to run the "electric blast furnace" that produces 100 tons of iron in 12 hours. If we make one run every 24 hours we can make 1400 tons during the lunar day and 16,800 tons per year from one big furnace. With ten furnaces 168,000 tons per year and in ten years 1.68 million tons, but we need about 125 million tons of material to build 1000 solar power satellites. More and bigger furnaces on the Moon running constantly even at night with nuclear power would be needed to produce enough steel for the tube steel structures of 1000 SPS in a reasonable number of decades. Silicon, boron and phosphorus dopants, for the thin film solar panels of the SPS is another story altogether. It seems lesser amounts of steel to build fleets of helium 3 mining machines is more reasonable! |
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| To make the lunar DRI system efficient, heat as well as reductant gas must be recovered. |
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| Hi temp steam electrolysis requires less electricity by adding thermal energy to split water. |
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| Carbon monoxide can be stored in gaseous form in hi pressure storage tanks such as the one to the left. CO at 147 psi and 0 C. has a volume of 3120 cubic meters, or a spherical tank 18 meters (59 ft) in diameter. Thus, it is not necessary to liquefy CO gas. That would just be a waste of energy to cool it and reheat it for injection into the DRI furnace. |