I have a friend who in the past few months has gotten heavily (and I mean heavily) into alternate fuels, in particular biodiesel. He’s in the process of converting one of his trucks to use it.
He’s also been telling me about this process where you 1)bubble the CO2 output from a power plant through a tank of algae, 2) turn the algae into biodiesel and 3) burn the biodiesel to run the power plant. After trying to explain the second law of thermodynamics to him, I handed him Cecil’s column on Ethanol. His response was “Well, yeah, ethanol is completely inefficient but you can make biodiesel for almost nothing, so that article doesn’t apply”.
OK, so help fight either my or his ignorance. How different are ethanol production and biodiesel production? Is biodiesel that much more efficient to make? And is biodiesel so efficient that power companies could convert to using it and save “billions of dollars per year” and the only reason they aren’t is because “the big oil and coal companies control their boards” (his argument). Google searches give me nothing but raging supporter sites or raging opponent sites so I turn to the Dope for something resembling the correct answer. I’d like to know so I can talk to him before he invests a major portion of his family’s savings in an algae biodiesel firm. Thanks.
I’ve never read anything about the algae/power plant scenario, and I don’t think we’re yet at the point where anyone can say for sure that fuel from algae will be cheap and plentiful. There was a recent breakthrough on a promising process for converting algae to fuel, but even that hasn’t been proven out as a large scale solution. It’s caused a stir because people are hopeful it will prove out:
The only reason biodiesel would be cheap to produce would be if the cost of the feedstock is cheap enough.
Right now you can make biodiesel from an oilseed like soybeans, or from used grease. However, the price of soybeans has gone up and there just isn’t that much used grease to go around (and believe it or not, there is a market for used grease.) Here are some figures.
The allure of algae-based biodiesel is that algae will be cheap and plentiful. Maybe it will, but algae biodiesel production is still in the early research stage. Recently PetroSun announced they would commercially produce algae biodiesel. But if you read the news releases carefully, you’ll see that a) the company never says how much the product is selling for; b) they seem to have trouble keeping partners in their venture; and c) their only “customer” so far seems to be PetroSun itself – supplying itself with product for future research.
Tell your friend to be sure and read the prospectus very closely, and not to invest any more than he can afford to lose. Right now it’s still in the speculative stage.
Sorry to let this drop off without thanking everyone for their input. I finally got up with my friend again and talked to him. It turns out that the PetroSun company that kunilou mentions is the company he is talking to. According to him, they have signed distribution agreements with at least one oil company.
The actual investment he is looking at is setting himself up as a distributor for them. I’m still not sure how good of an idea this is, but he’s started his own business before and I haven’t so I’ll assume he knows more of what he is doing than I do. He also says that the money he is putting up is all something he can afford to lose, so I guess he is safe there.
Who knows, maybe a few years from now I’ll be kicking myself for not going in with him. Anyway, thanks for everyone’s input.
In order to make ethanol (let’s say from corn) you must:
Mash corn and convert starch to sugar using enzymes. This takes heat and chemicals and time
Add yeast to convert sugar to alcohol. This takes time
Boil off the alcohol in a distiller. More heat
Collect alcohol
To make biodiesel, lets say from soy beans or rapeseed (canola)
Press beans / seeds
Purify oil
It always seemed to me that going through all the cooking and processing and boiling that it takes to make alcohol was terribly wasteful in comparison to just pressing and perhaps chemically stripping seeds/beans for oil.
True biodiesel is more complex than that. It requires going through a process called transesterification to convert the oils into something that is more compatible with petroleum diesel. You could certainly burn the oils directly (which is what you’re describing here), but that isn’t biodiesel.
With regard to the idea of bubbling up the CO2 through a bed of algae, you have to keep in mind the significant mismatch in rates between chemical processes (combustion) and biological processes (photosynthesis). A 300 MW coal plant will use about 300,000 lb of coal per hour (it’s roughly a 1 lb of coal per kilowatt-hr), or about 240,000 lb of carbon per hour. Algae currently grow at rates around 50 grams per day per square meter water surface area. Assuming that the algae is about 50% carbon, then you have a carbon uptake of 25 grams per day per square meter. Equate the carbon output (in the form of CO2) to the carbon uptake, convert all the units, and you’ll need an algae bed of about 40 square miles to use all the carbon emitted from the plant. There is likely to be a bit of difficulty getting a permit for that.
I haven’t run any numbers, but my guess is that it’s a lot more efficient to simply convert the coal to fuel using thermochemical processes like the Fischer-Tropsch process. You certainly get some boost from the solar energy input, but the amount of energy needed to push the flue gases through the algae beds will be significant, and could well overcome the solar input. And I have not seen anyone discuss the fact that the flue gases also contain a lot of stuff other than CO2, water, and nitrogen - sulfur, metals, and other inorganics - that don’t usually make for great growing conditions.
