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Saturday, September 6, 2008

Biodiesel From Algae - no way

The title of this blog is somewhat misleading. While this blog gives reasons why we will never manage to produce biodiesel from algae it could be thought of as a catalogue of the problems you would have to overcome to produce economic diesel from algae.

I would be the first to laud anyone who solved the huge series of problems and made us free from foreign sources of oil and while I think that pretty soon, we will be converting to electric cars for domestic transport, the powering of large transport trucks will be pretty close to impossible without concentrated liquid fuel. In-country production of biodiesel is something of a holy grail.

Producing bio diesel in, for instance, our deserts would be a fabulous thing to do and would stop a great deal of misery in the world. Look at the support of terrorism, using the discretionary spending of rich oil countries or the exploitation of their own citizens by leaders with obscene levels of richness at their command. How obscene is it that citizens of oil poor countries adjacent to Nigeria, for instance, are better of than citizens of oil rich Nigeria. Bio diesel from algae is a very worthwhile aim but virtually impossible. I hope I will be in the position in a few years of the sages that said heavier than air machines will never fly. I doubt it.

First lets look at what you have to compete with. The theoretical efficiency of photosynthesis from sunlight to chemical energy is about 6.6% although when the actual biomass is measured and compared with the energy which has fallen on a crop, you are lucky to come up with 3.5% as much chemical energy as fell on the crop as sunshine. Photosynthesis is a solar energy harvesting system, converting sun energy into chemical energy. Take a piece of desert, cover it with your algae ponds, tanks or whatever and the total chemical energy you can produce, in theory, is equal to 6.6% of the sun energy which falls on the site. Cover the same area with solar cells and you can collect about 20% of the energy even with existing solar panels. Put this energy into power lines and you can charge up your car batteries. I know that a practical electric car is not yet commercially available but I believe it is just around the corner. Batteries and electric motors are pretty efficient and from solar to wheel you can probably count on a 10% energy conversion. Lets look at our algae cultures again and remember solar-electric farms will be in competition with solar-algae farms for such sites. Of course, solar electric 'farms' need no water.

The chemical energy in the algae cell is not all oil. Some algae cells will store oil as a food reserve in vacuoles inside their cytoplasm but they also need to produce the protein, carbohydrates cytoplasm, nucleoplasm and outer coating of their cells. Lets be generous and say that half of the energy is in oil and half in the rest of the cell. We are down to 3.3%, even if we use the theoretical maximum energy conversion figure or about 1.5% if the more usual observed conversion figures are used. Actually this could be an advantage. After extracting the oil, a lot of "algae pulp" is left and could be a source of a range of valuable products. Perhaps bio diesel could be a by product of the production of some other more valuable product. Even more likely is that the algae could produce oil for massage, pharmaceuticals or specialty lubrication, all of which have a higher price than diesel oil. However, this is not giving us cost effective fuel.

Back to the bio diesel. To grow significant amounts of oil producing algae, your sun collecting area (pond, tank tubules etc will have to be measured in hectares or more likely in square kilometers. You can forget about growing pure algae cultures in such circumstances (there is a small possibility mentioned later that might render this statement incorrect). To sterilize the required quantities of water is simply too expensive and you only need a few cells of a wild algae to get into your culture to crash it. All is not lost though. There are a couple of possible techniques known and probably more that have yet to be discovered.

You can grow extremophyles. These are algae which grow in such harsh conditions that other algae die. Spirolina grows in high concentrations of bicarbonate, Dunaliella grows in high concentrations of salt and certain algae found in hot springs grows in temperatures too high for other algae. So if you can find or engineer an extremophyle that produces oil, you may be able to produce oil from hectares of algae culture. A slight glitch in this scenario is that extremophyles are at the limit of their growth conditions and are not the fastest growing amongst the algae. This further cuts down the total percentage of the incident radiation that can be harvested.

You now have the problem of temperature. Obviously you have to grow the alge with sunshine. That is the whole purpose of the exercise: namely to use sun energy and turn water and carbon dioxide into diesel oil. This virtually ensures that you will be growing your algae in a desert and probably close to the equator which receives the most sun energy per unit of area per year. If you are turning 6% of the incoming energy into biomass and reflecting a bit too, you will have around 90% of the incoming energy being absorbed by your culture and heating it up. Algae and most poikilothermic organisms grow best a little below their lethal high and for the best production it is best to keep the temperature of the culture up there. In an open culture, much of the cooling is taken care of by evaporation.

Sun energy is about 1kilowatt per square metre with about 5 peak hour equivalents per day in desert areas. This amounts to 5kWh per square metre per day and if 90% of this energy heats up the water rather than producing biomass you have a severe cooling problem. This amount of heat will evaporate about 10mm of water and this amount of make up water will have to be found. Closed cultures are impractical since you would have to refrigerate to keep the temperature below the lethal level and circulate the water rapidly past the cooling coils to avoid heat stress. Evaporation can be a great help in bleeding off this excess heat. Another help is to have deep, well mixed cultures. The deeper the culture, the less a certain amount of heat will warm up the culture. Then at night, the culture can radiate heat out into space, starting the next morning at a cooler temperature. The depth is not needed to grow the algae. After the algae achieves even a modest concentration, only the top few cm of the culture is photosynthesizing. The rest of the depth is for temperature control and you must pay the extra construction costs. Of course the algae is distributed throughout the depth of the culture so you must agitate to bring all the cells up to absorb sun energy. Another energy expense.

A further problem with temperature occurs at night. Areas suitable for algae culture will generally have clear skies at night. In the middle of the Sahara, a container of water will freeze at night due to radiative cooling. Cultures are likely to be well below their optimum growth temperatures in the morning. They will be close to their lethal temperature in the afternoon. Only a small part of the day is at the best growing temperature.

Now you have to separate the algae from the water medium. Filtration of independently living single cell algae is not practical except on a small scale. filters plug up much to quickly. An alternative is centrifuging. This works but uses a huge amount of energy in relation to the amount of product separated out. The energy use is from the acceleration of large amounts of water from zero speed to high speed. Once it is up to speed, not much energy is used and the algae separates out.

There is one bright spot in this scenario, though. Some single cell algae stay connected in chains and these can be separated from the water by reletively simple, inexpensive filters.

There is one filtering (or rather concentrating system) that might be practical. If you can persuade your algae to sink or float. Plate separators are very efficient in concentrating such materials with minimal energy inputs. Once separated, the algae must be processed to extract the oil and if you want diesel, it must be chemically converted. Diesel engines can run on pure oil with some modification so the conversion stage could be eliminated.

Once produced, the diesel enters the existing distribution system with already known energy costs.

As I said at the beginning, I would be chuffed beyond belief to see practical bio diesel from algae but the only possibility I can see is if some natural system such as a eutrophic lake is naturally producing a type of algae that washes up on the beach and only has to be processed. Even then, The energy costs vs the energy you obtain are likely to be uneconomic. For an algae system to be economic, you have to be collecting more energy than you are using and you have to out compete other potential users of the same piece of real estate that could produce more usable energy from the same location.