The Scam of Scum
ALGA (Photo credit: La maldición de Sísifo)
Algae, the green stuff suspended in and floating on the surface of over-fertilized (polluted) water, AKA scum, is supposed to save America’s dependence on foreign crude oil. The President has said so. He stated that “up to 17% of the oil we import for transportation” could be replaced with this fuel [1].
The Chemistry
To begin with, a mass of algae is not the same as a container of crude oil. Algae are small plant-like organisms living in water. Like all plants, they use the energy of sunlight to convert carbon dioxide (CO2, i.e., one carbon and two oxygen atoms per molecule) to plant matter. In chemical terms, crude oil is a pure hydrocarbon of the approximate composition CH2 (i.e., one carbon and two hydrogen atoms per molecule). The composition of algae is more like CH2O, sort of half way in between CO2 and CH2. Because of the remaining oxygen atom in the plant matter (CH2O), its energy content is substantially lower than that of a pure hydrocarbon. You might say that it is already half burnt (the end product of which, of course, is CO2).
Fuel from Plants
Technologically, it is quite feasible to convert any plant matter (CH2O) to pure hydrocarbons (CH2). That process requires a reducing agent, such as elemental hydrogen (H2), dry plant matter, heat, and technology. We can make any amount of hydrogen we wish, by electrolysis from abundant water (H2O), but this process consumes a lot of energy. Then you need more energy for the reducing process itself. Overall, in energy terms, the entire process would consume more energy than the product would likely deliver to your car. So, really no energy savings accrues whatsoever.
The Technology
Growing algae in a pond is quite simple. All you need is some fertilizer (phosphate and other mineral salts) and sunlight. Mother Nature does the rest. It may take a few weeks, but then you have a pond of green water, with mostly suspended algae and some floating on the surface. While the pond may look like “green pea soup” to you then, all that green stuff represents a rather small amount of solid material, the actual algal biomass which you need for the next step.
The next step is to separate the algae from the water. That is not as easy as it may sound. Most of the algae are very small particles; so attempting to filter them out will quickly lead to clogged filters, with hardly any water making it through the filter after a short while. Keeping the filtration going will be a major headache. That problem is well known from sewage treatment systems, which are essentially such artificial ponds for bacteria and algae production.
Filtration problems can be avoided if using methods to agglomerate the small particulates to larger ones, which then settle out and accumulate at the bottom as sludge. Still, that sludge contains much water, which is even more difficult to separate from the solids. In any event, the dewatering process requires substantial time and/or energy. The US Environmental Protection Agency (EPA) has a 200+ page document on Dewatering Municipal Wastewater Sludges describing the various methods and processes [2].
Fuel from Carbon
If we really would wish to convert a readily available carbon source to hydrocarbons, the well known Fischer-Tropsch synthesis of oil from coal and water would be a much better way. That process was used on a large scale in Germany for many years. The reason is easy to understand. First and foremost, you start out with more or less pure and dry carbon (coal). You don’t need a large pond, fertilizer, time, a filtration or sludge settling and dewatering system, or any exorbitant amount energy to mine it. Second, you don’t need expensive hydrogen to reduce it to CH2. In fact, water (hot steam) will do.
Fuel from Limestone
The same process which turns coal into fuel (Fischer-Tropsch process) can be used to make fuel from limestone. I have described it in more detail before [3, 4]. In fact, it would be much easier and more straightforward to make diesel or gasoline from limestone than from algae.
Conclusion
The current administration’s concept to replace a large part of imported crude oil with “homegrown” stuff from algae is akin to superstition. It bears no semblance to any reasonable cost/benefit analysis in either energy or cost terms.
In simple terms, it’s just another “green” scam.
[1] http://www.washingtontimes.com/news/2012/feb/29/kelp-is-on-the-way-to-help-with-high-gas-prices/
[2] EPA-625/1-82/014
[4] http://ezinearticles.com/?Wind-+-Limestone-=-Gasoline&;id=6157604
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