A big part of my shtick is that through a combination of conservation gains and offsetting load to electricity that it would be practical to produce and consume biofuels as our portable fuel of choice. Still I have to say to myself, "do the math stupid." Too many ideas attractive paper concepts don't stand up to rigorous analysis. As such I would like to do a systems analysis for an integrated biofuel farm setup. It would be run as a co-operative by many farmers who grow not just biodiesel but food and other cash crops.
An abstract diagram of the concept is below (click to enlarge):
Integrated Farm Biofuel Layout
For the moment I will use rapeseed (aka Canola) as my oil source, wheat as food, and clover as a nitrogen fixing rotation. Rapeseed appears to be the best crop for biodiesel production in Northern climates (ignoring algae schemes for now). Its yields are significantly below that of tropical palm kernel oil although that does not necessarily mean anything on an energy return basis.
By integrating the production locally I hope to realize higher well-to-tank efficiency for the farm machinery. A local biodiesel plant will reduce the cost of distribution for the farm tractors. Similarly the trucks that transship the farm producst to to a pipeline or train depot could fuel up literally at the well. The transesterification of biodiesel will require either ethanol (derived from seedcake) or methanol (derived from the biogas).
The seedcake and other farm waste goes into a set of solar ponds (not the salt gradient variety). Filled with methane farting bateria they mangent away on pretty much any organic material thrown their way. The biomass is slowly converted to methane gas which is then captured, compressed to a high pressure and stored on-site in tanks. The biogas can fill a number of local uses. It can be burned to provide energy inputs for biodiesel production. It can be used locally for home heating, irrigation pumps, etc. Or it can be shipped off in compressed natural gas tanker trucks. By being a net producer of natural gas the farm co-op should be insulated from variations in the price of fertilizer production. Ammonia and potash production are particularly dependant on natural gas.
Electricity is produced locally as well. Wind turbines are sited when viable, and linked to a local substation that does voltage regulation. A electricity storage system may be located on site to make the electricity production more reliable. A solid oxide fuel cell or steam turbine operates as a combined heat and power plant for the biodiesel production facility.
Writing the entire analysis in one sitting is totally infeasible. I have too much material to explore and learn. I would like to take a blog-style approach to the problem and break it up into its constituents and post them in turn.
"Filled with methane farting bateria they mangent away on pretty much any organic material thrown their way."
What is mangent?
"No entry found for mangent."
Try a french-english dictionary.
Moving a low-density fuel like CNG via tankers seems to be a bad idea.
The issue of biogas production from the non-oil component of canola is interesting, but perhaps problematic. A lot of the cake is protein, which is loaded with nitrogen; in an anaerobic environment, it looks like this will wind up as ammonia. Dumping or burning ammonia just to have to fix more nitrogen for the next crop is rather inefficient.
If the goal is to make food, why not feed protein meal to chickens, turkeys or arthropods like shrimp or crayfish? Poultry manure digests well, effluent is fertilizer.
Last, a large fraction of the off-gas from any digester is going to be CO2. You may deride the idea of hydrogen-producing solar panels but after you've captured a load of carbon and have it highly concentrated it makes little sense to dilute it with oxygen and nitrogen again. Hydrogen plus CO2 fed to a Sabatier reactor can make methane, and other catalysts can produce a wide variety of products including methanol and ethylene. These last have a further advantage of travelling much better by truck than methane.
I suspect that your best energy capture system for the area stretching across Saksatchewan and Manitoba may be a high-productivity grass (usable for either fuel or forage) grown on land covered with wind turbines.
For all I know it may make more sense to produce large volumes of methanol and export that in place of methane.
The CO2 in biogas has a couple of applications. First, it's necessary for the production of pure methanol that is used to transesterfy vegetable oil into biodiesel. CO2 is also used to separate oil from the crop. It can give you a few extra percent yield from over mechanical methods.
Back to the direct hydrogen photovoltaic panels, I'm panning them for good reason. They are trying to match photovoltaic band gaps to water's redox potential. Nature simply hasn't been kind to the solid state physics for this concept. Moreover the production of hydrogen on the surface is going to damage the material. Since all they are really doing is cutting out the electrolyzer I remain very skeptical. They can outdo the electrolyzer step for efficiency. Can they outdo PV cells for producing electrons? No.
Oh yeah, on the nitrogen. It gets fixed into ammonium, not ammonia, and will settle into the sluge. This is why I chose this route instead of burning the stuff -- you can preserve the nitrogen and phosphorous. Excessive use of liquid sludge for fertilizer does have issues mind you. Namely the organic content of the soil rises too high.
Hydrogen Sulfide does bubble off but it can be captured.
Ammonium is just the ionic (NH4+) form of ammonia; they exist in chemical equilibrium while in solution.
A quick search for biogas composition found a cite for landfill gas which claims 50-60% methane and 38-48% CO2. Ergo, venting the CO2 after use means throwing away between 2/5 and 1/2 of the carbon in the meal. This seems doubly silly after you've gone to the trouble of separating it to use for solvent separation of oil from meal; fixed carbon is your product.
I'm not sure what your insolation is there, but if you get 700 kWh/m^2/yr and the photolytic hydrogen folks get a panel that is 10% efficient, that's 1.7 kg of hydrogen per square meter per year. Converting hydrogen and CO2 to methanol via
CO2 + 3 H2 -> CH3OH + H2O
consumes 12.5 kg/m^2/yr of CO2 and produces 9.1 kg of methanol. Alternatively, the Sabatier reaction could be used to make methane:
CO2 + 4 H2 -> CH4 + 2 H2O
In this case, the 1.7 kg of hydrogen would convert 9.4 kg of CO2 into 3.4 kg of CH4 and 7.7 kg of water. That's what, about 4.9 cubic meters (175 ft^3) of methane or 1.75 therms? At $10/mmBTU that's about $1.75 of product per square meter of shaded ground (even more per square meter of properly-oriented panel) per year. That's not shabby at all.
The hydrogen could also replace methane as a fuel for process heat around the farm.
I'm trying to minimize cost here, not maximize efficiency. Capital costs matter.
Post a Comment