[Gasification] algae as a fuel generator

[Zietsman, Rex]

Art wrote:
"Peter,
I like your focus on anaerobic digestion (AD) because it works in all
sizes, a wide range of feedstocks and scales of production.
BUT, here is a more symbiotic idea.  Algae can produce between 5000 and
20000 gallons of bio-oil per acre when optimized.  The algae are between
30 - 50% lipid oils by weight and the rest of the body is starch.  They
live on CO2, nutrients from dirty water and use sunlight for
photosynthesis to produce the plant matter.  Details of the system can
be located at http://www.oilgae.com/
Here is the great combination.  An AD produces on the order of 35 - 40%
CO2 and 60 - 65% methane.  The CO2 is easily removed from the gas and
could be recycled back to the algae bioreactors as feedstock for the
photosynthesis. The crude purified methane could be used as compressed
gas for mobile fuel.
The oil is removed from the algae via several solvent or centrifugal
systems already made.  The oil goes to bio-oil collection and the starch
goes back to the AD system to produce more methane and CO2.
The only thing missing is sunlight and direct sunlight has 10 times the
energy per unit area necessary for the photosynthesis.
This is not perpetual motion but it is an interesting symbiotic
reaction. It works in small scale as well but suffers from economy of
scale issues as do most energy processes
Good luck with that one!
Art Krenzel"

Art,
In principle you are right about algae. There are some challenges
however. The challenge in this case is the type of algae reactor used.
To get really big installations to produce oil in quantity requires the
use of open ponds. The difficulty with this is that wild species of
algae can then enter the pond and before you know it, they have taken
over. Generally wild species do not have a great oil/lipid content. So,
to protect the high oil species algae requires a photobioreactor (PBR)
which bumps up the cost enormously but guarantees that you will get the
yield. The forerunners of this technology are building their plants next
to power stations so that they feed the algae with CO2. That speeds up
the process even more. Algae also has the wonderful benefit of absorbing
NOx as well. So it is a good thing.
There is still hope for open ponds. You can harvest open pond or wild
algae and feed it directly to an AD. That will generate the methane you
are talking about that can be fed into the power station as fuel.
Alternatively, you can use the power station off gas to dry the algae.
The dry algae can then be fed into a coal fired power station to
displace some of the coal. Some of the offgas heat can be used to keep
the ponds warm to improve the performance of the algae, particularly in
winter. So large scale open ponds do have some payback though not to the
extent of generating a biofuel that can be used by vehicles.
Rex