Mother Nature invented a process called photosynthesis, where plants recycle CO2 (carbon dioxide) into energy in the presence of sunlight. One type of plant that is particularly adept at this process is algae. Algae grow naturally almost anywhere from fresh & brackish water to desert sands, and from hot boiling springs to snow and ice. Algae growth is significantly accelerated when exposed to large quantities of concentrated CO2. What better source for this CO2 than from the stack gases of electric power plants?
The use of algae bioreactors (see video & transcript) to scrub smoke stacks is a relatively new development. Most of these bioreactors consist of tubes containing algae suspended in water. Stack gases are bubbled through the tubes. The tubes are made of clear plastic so sun light can shine through. Some of the algae is often harvested on a continuous basis by de-watering and drying. Dried algae biomass contains: lipid oils that can be processed into bio-diesel; carbohydrates that can be fermented into ethanol; and, protein.
One of the early bioreactor researchers was Dr. Berzin at MIT, a founder of GreenFuel Technologies. GreenFuel's technology has received a large amount of media attention in the USA and around the world. Several other start-up companies and researchers are involved in algae bioreactors, such as: Aurora Biofuels; Imperium Renewables refining algae oil supplied by Solazyme; a joint venture between Royal Dutch Shell and HR BioPetroleum; Vertigro Energy, a joint venture between Global Green and Valcent; Solix BioFuels working with Colorado State; Diversified Energy; PetroSun; Inventure; and, a European biodiesel company - BioKing's AlgaeLink.
Several of these companies have made claims based on small, short-term tests that may not prove to be accurate or profitable on larger, full-scale projects running for a period of several years, when all income and expenses are considered. For example: Valcent, El Paso, TX, recently announced they are harvesting algae with their bioreactor that could deliver approximately 33,000 gallons of algae oil per acre per year. Valcent says a food crop such as soybeans will typically produce some 48 gallons oil per acre per year and palm will produce approximately 630 gallons oil per acre per year. Of course Valcent's costs per acre are significantly higher than those to raise soybeans also!
Some of these companies talk about removing up to 80% of the CO2 from stack gases on bright, sunny days. But the efficiency goes way down on cloudy days and basically stops altogether at night without artificial light. If carbon credits can be sold at a future date, it could make the technology more profitable. Research is being conducted to increase profitability by genetically modifying algae to increase hydrogen and bio-fuel production. It is likely to be several years before any modified algae will be placed into large-scale production.
Eprida has an unique method of scrubbing smoke-stacks that does not involve growing algae. They burn waste biomass in a pyrolysis process. Oil from the pyrolysis process is converted into bio-diesel and the hydrogen is used in a Haber-Bosch process to produce ammonia. The ammonia along with charcoal from the pyrolysis process and CO2 flue gases from a smoke stack are combined to create an unique fertilizer. This unique "biochar" fertilizer (somewhat similar to terra preta) "substantially improves soil fertility, water holding and plant yield far beyond what is possible with nitrogen fertilizers alone." It is quite possible that the Eprida system could be used with algae bioreactor systems for complete smoke stack scrubbing.
Note: See this article online, with
hyperlinked references, at: http://www.friendlyinnovators.com/mn/20080215.htm
Next time:
How Thermal Electric Power Plants Work (Fueled by: coal, natural gas, biomass, nuclear or geothermal
energy.)
Al Leedahl
Engineering Design Concepts
www.leedahl.com/engineering/design/concepts.htm