Print

CO2 and Algae Projects

An opportunity to sequester carbon and foster algae production
By Sam A. Rushing | April 19, 2011

The Japanese nuclear disaster makes it clear the world is in dire need of clean, safe, reliable (renewable) energy alternatives. Biofuels are a major component of this need; more specifically, algae is feedstock for tomorrow’s fuel, and the high-energy crop far exceeds other biofuel options. A mix of biofuels is necessary, however, to bridge tomorrow’s energy demands, and reduce and sequester the ever problematic carbon dioxide (CO2) emissions glut.

CO2 is one of the essential components required to grow algae, along with sunlight, water and nutrients. The technology is in relatively early stages, used in smaller settings such as breweries, but global power projects are also interested. It may be a while before it’s brought to full-scale commercialization, however, all components exist—particularly a need for high-energy biofuels. Carbon capture and storage (CCS), or carbon sequestration, is a growing science. This involves geologic sequestration in oil production and coal recovery projects—replacing recovered methane gas with CO2, natural aquifer sinks for CO2—such as those in the North Sea.

Of the gross total daily CO2 emissions on a global basis, China is the highest emitter, followed by the U.S. and the EU. CO2 is by far the greatest greenhouse gas by volume, but others (methane) are much worse. Sequestration means are constantly being evaluated by those major emitters such as chemical and power generation plants, and oil and ethanol refineries.

Some estimates indicate at least 75 million metric tons of CO2 are emitted daily from a wide variety of sources. Natural processes such as photosynthesis and natural oceanic activity are major carbon sinks. The ocean has traditionally absorbed about 25 million metric tons of carbon but it’s becoming more difficult for the oceans to absorb CO2 naturally. Many think the oceans are becoming saturated because atmospheric CO2 is also elevated, and the oceans’ pH is dropping toward an acidic state, where “oceanic acidification” may become a major problem. Acidification will damage and kill marine life such as coral reefs, perhaps indefinitely.

Algae produced for biofuels markets will become a major component of the advanced biofuels sector. Algae is an extraordinarily energy-rich crop, exceeding the energy value of soy by 30-fold. A small amount of physical space is required to produce sufficient algae to replace all domestic petroleum needs.

Requirements

Studies suggest two pounds of CO2 on average is utilized per each pound of algae grown. This can be as low as one pound per pound, and as high as three pounds of CO2 per pound of algae. Growth settings include raceway configurations, vertical thin sunlit bioreactors, open ponds and coastal sea operations. Best suited algae operations for CO2 are a function of strain selection, project size and geography, and the presence of adverse temperatures and other conditions. If the CO2 were delivered via pipeline, and because of the gas’ corrosiveness, the delivery system should be constructed of a high-density polyethylene (HDPE) versus the standard, more costly stainless steel. The CO2 would probably be introduced into the pond, bioreactor or raceway as a gas, and the commodity is stored, piped and transported as a liquid. Small operations might start with so-called microbulk storage tanks, which can hold from 400 to 600 pounds. Larger operations would use on site, vacuum-insulated liquid storage vessels or refrigeration systems to maintain pressures under 300 psig, and temperatures near 0 degrees Fahrenheit. Delivery to the algae system might be a series of diffusers, similar to those used in water treatment applications for CO2, and the piping from the storage to the application site could be composed of stainless steel, or type “K” copper tubing. The systems could be operating on timers, with or without a flow meter, however set to inject a given sum of CO2 into the growth medium. The storage, deployment and hardware for CO2 use is rather simple, but CO2 is essential for algae growth.

It is logical to evaluate more enriched forms of CO2 from industry, such as ethanol plants. The power industry is the worst offender by volume of CO2, and the unique nature of hot flue gas from them could apply well to certain blue-green algae that endure heat from the Yellowstone Park geysers. Power plant CO2 is lean in content compared to ethanol refining effluent or anhydrous ammonia production, with raw gas, water saturated basis of 98 to 99 percent volume or greater. These “clean sources” generally don’t include sulfur, heavy metals or heavy hydrocarbons. The flue gas from combustion of coal and natural gas can range from 14 percent volume in the raw gas with coal fired plants to 3 percent from a turbine exhaust source. If concentrating CO2, costs become significant but concentration has not yet been considered in the algae project tests and pilot ops within the power sector. 

One such power plant algae project is in Southeast Queensland, Australia, owned and operated by MBD Energy and a research cooperative. It is moving forward with an algae synthesis system, whereby the Tarong Power Station flue gas will be injected into wastewater, which contains nutrients, along with sunshine, for production of select algae in a (membrane-based) closed system structured to be a large raceway project. The algae mass is expected to double every 24 hours and be harvested daily and crushed to produce algae oil suitable for biodiesel, meal for cattle feed and clean water. The crude mass for cattle feed contains from 50 to 70 percent crude protein, and feeding trials are being conducted at James Cook University. The ultimate operating project is planning an 80-hectare site sequestering more than 70,000 metric tons of CO2 from the flue gas, and producing 11 million liters (2.9 million gallons) of oil plus 25,000 metric tons of algae meal. This form of bio-CCS algae sequestration is similar to the earth’s natural carbon cycle, however, it is accelerated exponentially, taking only a day. Other applications for the oil beyond biodiesel include jet fuel production and bioplastic materials. Beyond feed the meal can be used in plastics and fertilizers. The algae product yields 35 percent oil and 65 percent meal. The project has Australian government funding and will lead the way throughout Australia for similar projects.

U.S. power plant algae endeavors are underway, some are feasibility and pilot studies, many funded by U.S. DOE’s $1.4 billion Clean Coal Power Initiative. Applications for federal and state funding and initiatives for algae-based sequestration have taken place with Arizona Public Service Company, Duke Energy, NRG, Southern Company, and American Electric Power Co.,  to name a few. The power industry has been the major component of CO2 emitters to evaluate, test and work on developments toward sequestering CO2 via algae growth. The methodology surrounds a rather methodical selection of the best-suited strains of algae, usually capable of enduring SOx, NOx and other compounds, including heavy metals from the power plant flue gas, as well as being tolerant to high temperatures. Other criteria for selection of algae strains are driven by those that yield high amounts of oils and starches. The point of application has been tested in bags, vertical bioreactors, raceways and ponds.  Conceptually, the algae are harvested daily in a large or commercial-scale facility.

The Future’s Choice

Many forms of sequestration will be needed beyond a cap-and-trade system. Some estimates consider at least 50 million metric tons of CO2 are emitted to the atmosphere daily, beyond what the oceans, photosynthesis and other natural means can absorb. This number is likely to grow, with the so-called BRIC countries, growing rapidly. As they grow, so do carbon emissions. Further, the battle against deforestation places added stress on the whole CO2 emissions equation, which removes a significant natural carbon sink: photosynthesis.

Many strains of algae are being investigated to fit niche markets, such as those which retard extreme heat or cold, or grow during the nighttime with minimal light. Specific algae strains will eventually meet extreme or unique physical conditions for growth. The end result will be extracting the oils for fuels, plastics and other products, and the use of the algae meal for numerous markets. The strains of algae may be derived from far-flung African swamps to frozen, high-altitude snowfields in South America. The strains selected to endure the harshest of temperatures and other physical conditions are vast, and commercialization to fit many conditions is one of the most viable concepts ever developed to meet tomorrow’s renewable energy needs.

Author: Sam A. Rushing
CEO, Advanced Cryogenics Ltd.
(305) 852-2597
rushing@terranova.net

 

0 Responses

     

    Leave a Reply

    Biomass Magazine encourages civil conversation and debate. However, comments containing personal attacks, profanity, business solicitations or other advertising will be deleted.

    Comments are closed