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OrganoEnergy

Does the future of Algae for Biodiesel look good?

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I think it's a much more feasible option than using plant crops, since it doesn't destroy food crops and doesn't consume space in poorer nations where subsistence farming is a way of life. It needs a lot of work though. Currently, algal bioreactor crops produce the highest yield of feedstock out of any other biofuel per hectare per year, but they are also one of the most expensive to process and extract oils from. If the people working in the area can find a cheaper way around that, then I'm sure that it has a pretty bright future, but who knows when and if that will happen.

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There are two types of algae-agriculture: One is the open pond systems that have slow moving water. The other are closed systems made of tubes in which a highly turbulent suspension of algae is transported at high velocity, with CO2 addition (using compressors) and O2 removal.

 

I don't believe in the latter. Too complicated. Too many parameters. And it simply costs too much energy to operate. I've noticed that the production of such algae biofuel reactors are often overestimated in commercial publications (if you read something about it, calculate back the production based on insolation - there's a lot of BS in this business).

 

The former (the open ponds) is more realistic. The algae in this type of reactor aren't much more efficient than ordinary plants... but the process also requires little energy. Harvesting and drying are the main problems.

 

Both systems are often land-based, and therefore in direct competition with other agriculture and nature. In the end, all bio-based energy systems will become a problem because the world population just keeps growing exponentially, and meat production keeps growing fast as well. The earth's surface area will become a bottleneck at some point, and other systems (wind power and to some extent solar power) are much less in competition with food.

 

Algae are nice, but if the research cannot provide a system that is profitable within 5-10 years from now, the algae have missed their opportunity. Food should always go before energy.

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There's a much greater risk of contamination with open pond systems. Secondly, the bioreactor models have the advantage in that you don't require as much space to achieve the same yields. The set up is more expensive, yes, but the yields are greater per hectare per year and it's easier to control.

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Profitability (or lack thereof) is still one of the biggest issues. The yield per dollar is still too low and quite some funding has been pulled out of that area because of this (and other issues).

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There's a much greater risk of contamination with open pond systems. Secondly, the bioreactor models have the advantage in that you don't require as much space to achieve the same yields. The set up is more expensive, yes, but the yields are greater per hectare per year and it's easier to control.

Let me start by saying that I agree with you - all you say is correct. But you ignore the energy input into the system, which in the case of the bioreactors is substantial. IMHO, the two main problems are:

 

- Compressors for CO2 addition and O2 removal

- Cooling systems (there is no evaporation)

 

Compressors

I postulate that the closed bioreactors require more energy to operate than they generate in the form of biomass (based on the lower heating value of the algae after drying). I'm not in the mood to do the detailed calculations, they are not complicated, but might require two or three backs of envelopes rather than just one.

 

The calculation must for a large part be based on the gas systems (CO2 addition and O2 removal). A smart design can overcome a lot of problems, but some things cannot be solved. You will always require a certain pressure difference to get the gas into your tubing. If the CO2 is not coming from a power plant which offers pressurized stack gas, then the CO2 also will have to be compressed.

 

But especially oxygen removal is troublesome because the oxygen can inhibit oil production (or growth in general?) at concentrations lower than the solubility (i.e. oxygen must be stripped out with a carrier gas, and it is unadvisable to wait until it comes out by itself in the form of bubbles).

 

Cooling

The tubes of the bioreactor heat up.

The tubes will obviously be made from a transparant material, rather than a reflective material.

Since the algae only absorb (in a best case scenario) 15% of the sunlight (1-5% is probably more likely on large scale), a lot of heat will be created. Since the system is by definition closed, the only possible cooling is an external cooling system!

 

A refrigeration system is out of the question because efficient refrigeration systems might have a Coefficient of Performance (COP) of 5-6 but that is not enough. Since the heat input by the sun will be about 5 times higher than the energy of the sun that is actually converted into algae, the refrigeration system alone will likely require the same energy as the total output in the form of algae.

 

Summary

You end up with a massive length of tubes full of highly turbulent water with about 1% wt algae. At several intervals you have sterilized gas bubbling through the liquid phase to remove oxygen, requiring a secondary gas pipe network. And you need cooling, requiring a tertiary cooling network. Obviously, you can also build many decentralized oxygen/cooling stations... which will ruin your economy of scale.

 

I haven't done any calculations, but my chemical engineers' gut feeling tells me that such a system is an economic disaster.

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I think we'll move toward bacteria rather than algae.

 

But if you want to read more about algae, you may want to read into the "Aquatic Species Program."

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Algae in this context is usually used as a catch-all phrase which includes cyanobacteria.

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I have heard of farms using manure as a source of methane fuel then the left over basic manure in algae producing ponds. They skim the ponds, dry and pelletize the algae for food to feed the animals, but add minerals to the algae for extra nutrients. I imagine you could use the dried pellets in a gasifier and produce some combustible fuel and the net C02 output to environment would be zero as the algae takes in C02 as it grows like a plant or tree does. Is algae food the same as manna, like in the bible, just wondering? I have heard you can eat just algae and be totally fine as far as nutrition is concerned without adding anything. An algae bar a day keeps the doctor away. YUM!

 

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