http://bioenergy.msu.edu/feedstocks/algae_feasibility_alabama.pdfThis is specific to the climate of Alabama, but as a general, realistic overview of one process that is available now it is very informative. Well worth reading in its entirety - but especially the discussion on carbonation.
Algae as a Biodiesel Feedstock:
A Feasibility Assessment
DRAFT
Submitted by:
Center for Microfibrous Materials Manufacturing (CM3)
Department of Chemical Engineering
Auburn University, Alabama 36849-5127
Ron Putt
Principal Investigator
ronputt@auburn.edu
November 20, 2007
Executive Summary
Alabama has an immediate opportunity to lead the nation in becoming self sufficient with
respect to liquid fuels for transportation. Mass cultivation of micro-algae in the state,
using less than 3% of our land area, could produce the 3 B gallons of fuel we need every
year. Through careful design and efficient operation of algae farms, the payback on the
initial investment would be within a few years, which makes algaculture an attractive
investment opportunity on its own. Factoring in the geo-political benefits of energy self-
sufficiency and closing the loop on the carbon cycle makes the proposition of statewide
algaculture compelling. With the potential for production rates exceeding 4,000 gallons
of biodiesel per acre annually, algae-to-biodiesel is unique among the alternative fuels
concepts in having the potential to be a 100% solution for our transportation fuel needs.
The seminal work on algae-to-biodiesel within the U.S. was the U.S Department of
Energy Aquatic Species Program performed by the National Renewable Energy
Laboratory (NREL) from the mid 1970’s through the mid 1990’s in response to the
nation’s first energy crisis. The original goal of the ASP was carbon dioxide mitigation,
but early on they realized the biodiesel feedstock potential of micro-algae, and therefore
redirected the program. Two key technology development needs were identified during
the ASP, namely the cost and energy efficient means of (1) providing sufficient carbon
dioxide to the ponds to support the high growth rates inherent to micro-algae, and (2)
harvesting dilute (200-300 ppm) micro-algae from the pond water. The program was shut
down by DOE in the mid-90’s when gasoline returned to $1 per gallon.
The present assessment, performed under contracts to the Choctawhatchee, Pea, and
Yellow Rivers Watershed Management Authority and the Alabama Departments of
Economic and Community Affairs and Agriculture and Industry, with cost sharing by the
Alternative Energy Committee of Auburn University, was for technical and economic
feasibility of statewide algaculture in Alabama for the production of biodiesel feedstocks
from algal oil, and nutritional and animal feedstocks from algae meal. It consisted of
experimental investigations, technology development, interviews with government
agencies and private enterprises, and an engineering design and cost analysis. The
assessment, as discussed herein, developed solutions for the challenges of providing
sufficient carbon dioxide to the ponds and harvesting micro-algae using commercially
available technology.
There were several important innovations during the course of the program, namely (1)
integration of animal litter digesters to provide nutrients and energy for the algae farms,
(2) integration of carbonation pits and their pumps with a novel linear pond design, (3) a
low-cost harvesting system, and (4) a scheme for integration of algaculture with catfish
aquaculture to improve the competitiveness of this industry within the state.
The economic analysis estimated an installed cost for 100 acre algae farms of less than $1
million, and annual nets of $200,000. The analysis identified key cost and price variables
which are likely to have the biggest impact on the economic performance of the algae
farms, including those for petroleum crude, algal oil and meal, carbon from carbon
dioxide capture, and commercial fertilizer.
The assessment resolved three phases to algaculture within Alabama, two near term and
another somewhat longer term. The near term phases employ animal litter as the nutrient
source for the algae ponds.
One phase would involve digesting poultry litter and cattle manure in an anaerobic
digester which would produce methane, and carbon dioxide, to power a diesel generator
that would provide electrical and thermal power to run the farm. The exhaust of the diesel
generator would provide the heat for a drum dryer at the end of the algae harvesting
system, and the cooled, carbon-dioxide rich exhaust would then feed the algae pond
water via gas-liquid exchange in a carbonation pit. All the poultry litter and cattle manure
in Alabama would provide about 2% of the nutrients for the state’s liquid transportation
fuels via algae-to-biodiesel.
The other near-term phase would integrate algae ponds with catfish ponds. Using algae
ponds to remove catfish litter from the catfish ponds at an accelerated rate would improve
the yields of the catfish ponds dramatically. The algae ponds would also hyper-oxygenate
the catfish pond water and reduce, or eliminate, unwanted algae blooms in the catfish
ponds. Productivity from the catfish ponds could easily triple, and the revenues from the
algae ponds would match those of the catfish ponds. While the production of algae from
the catfish farms would be only a small fraction of that from the poultry and cattle farms,
it could have a significant beneficial impact on cost and quality for Alabama’s catfish
industry.
The longer term phase of algae farming would require capturing carbon dioxide from
fixed and vehicle point sources in the state. An international movement is underway to
scrub carbon dioxide from stack gases and then compress it for underground storage. A
better solution would be to feed them to algae ponds. The carbon dioxide from Alabama
Power’s fossil-fuel fired power plants would provide 50% of the state’s transportation
fuels via algae-to-biodiesel. And a Welsh company, Maes Anturio Ltd, has a “greenbox”
technology that can capture up to 90% of the carbon dioxide produced by vehicle
engines; their original purpose in developing this technology was to feed algae farms.
While these means of providing carbon dioxide are several years away, it would likely
take the intervening years to perfect and implement algaculture on animal litter.
A credible scenario therefore exists in which algaculture can provide all the liquid fuels
required for transportation within the state of Alabama. This scenario is financially
attractive on its own, and the added benefits of sustainable energy self-sufficiency and
closing the loop on the carbon cycle compel us to give it serious consideration.