Algae live on a high concentration of carbon dioxide and nitrogen dioxide.  These pollutants are released by automobiles, cement plants, breweries, fertilizer plants, steel plants. These pollutants can serve as nutrients for the algae.

Using algae for reducing the CO₂ concentration in the atmosphere is known as algae-based Carbon Capture technology. The algae production facilities can thus be fed with the exhaust gases from these plants to significantly increase the algal productivity and clean up the air.  An additional benefit from this technology is that the oil found in algae can be processed into a biodiesel. Remaining components of the algae can be used to make other products, including Ethanol and livestock feed. About 1.8 tons of CO₂ are required for producing one ton of algae. A coal power plant produces about 1 ton of CO₂ for every MWh of energy produced i.e. 1 ton of CO₂ per MW per hour. Yield of algal biomass per hectare is about 0.3 to 1 ton per day. This technology offers a safe and sustainable solution to the problems associated with global warming.

Characteristics of Algae-based CO₂ Capture

• High purity CO₂ gas is not required for algae culture. It is possible that flue gas containing 2~5% CO₂ can be fed directly to the photobioreactor. This will simplify CO₂ separation from flue gas significantly.
• Some combustion products such as NOx or SOx can be effectively used as nutrients for microalgae. This could simplify flue gas scrubbing for the combustion system.
• Microalgae culturing yields high value commercial products that could offset the capital and the operation costs of the process. Products of the proposed process are: (a) Mineralized carbon for stable sequestration, and (b) Compounds of high commercial value. By selecting algae species, either one or combination or two can be produced.
• The proposed process is a renewable cycle with minimal negative impacts on environment.

Key advantages of the process of CO₂ sequestration using algae

• Owing to the fact that high purity CO₂ gas is not required for algae cultivation, flue gas containing CO₂ and water can be fed directly to the photobioreactor.
• Power plants that are powered by natural gas or syngas have virtually no SO₂ in the flue gas. The other polluting products such as NOx can be effectively used as nutrients for micro algae.
• Micro algae culturing yields high value commercial products that will offset the capital and the operation costs of the process. In addition to biofuels, algae are also as the starting point for high-protein animal feeds, agricultural fertilizers, biopolymers / bioplastics, glycerin and more.
• Algae can grow in temperatures ranging from below freezing to 158^oF.
• The entire process is a renewable cycle.

 

Algae Cultivation Coupled with CO₂ from Power Plants – Q&A

1)      Is there a possibility of heavy metal contamination in algae due to their presence in the flue gases?

Yes. The possibility exists because most of the absorption of toxic metals by algae is of the passive type.

2)      How do the constituents other than CO₂ in flue gas from power plants affect algal growth?

Sulfur oxides, particularly SO₂, can have a significant effect on the growth rates and health of the microalgae. Of greatest concern is the effect SO₂ has on the pH of the microalgal growth medium. When the SO₂ concentration reaches 400 ppm, the pH of the medium can become lower than 4 in less than a day, which significantly affects the productivity of the microalgae. However, if the pH is maintained at 8 using NaOH, the productivity does not decrease (Matsumoto et al., 1997). Other researchers have demonstrated tolerances to sulfur oxides at approximately half of what Matsumoto and coworkers (1997) demonstrated (Brown, 1996; Zeiler et al., 1995). Nannochloris sp. (NANNO02) was found to be resistant to 50 ppm SO₂, but without pH control, 300 ppm SO₂ inhibited growth within 20 hours (Negoro et al., 1991).

Nitrogen oxides also comprise a significant portion of power plant flue gas. As with the sulfur oxides, nitrogen oxides can affect the pH of the algal medium, but to a lesser degree. Microalgae have been shown to tolerate and grow in a medium containing 240 ppm NOx, with pH adjustment. Brown (1996) and Zeiler and coworkers (1995) also demonstrated that microalgae are not growth inhibited by the presence of 150 ppm NO. Negoro and coworkers (1991) found that NANNO02 grew in the presence of 300 ppm NO after a considerable lag time. A point of interest is that the nitrogen oxides can serve as a nitrogen source for the microalgae. NO is absorbed into the medium and oxidized into NO₂ in the presence of oxygen (Negoro et al., 1991). The greater the oxygen contents of the medium, the greater the NO₂ production and microalgal productivity rates (Matsumoto et al., 1997; Brown, 1996). However, the presence of elevated concentrations of oxygen results in algal photorespiration, which inhibits microalgal growth.

The effect of soot dust and ash containing heavy metals has received limited attention. Matsumoto and coworkers (1997) confirmed that when soot dust concentration is greater than 200,000 mg/m³ (0.2 g/L), algal productivity is influenced. It is rare for the soot dust concentration to reach such an elevated value since it is most commonly on the order of 50 mg/m3 (5 × 10!5 g/L). The same argument can be applied to the presence of trace heavy metals. Higher concentrations can affect algal productivity, but only in rare situations will the concentrations exceed those that will result in a significant impact.

3)      Will NOx present in the flue gas serve as a nutrient, in addition to the CO₂?

Flue gas supplies the carbon dioxide and has the ability to supply some of the nitrogen (from nitrogen oxide; it absorbs SO₂ as well). However, it has been demonstrated that the nitrogen contribution from the flue gas is insufficient to maintain stable growth rates (Weissman and Tillett, 1992). Therefore, nitrogen (along with phosphorus and trace nutrients) needs to be added and maintained as necessary with proper engineering.

4)      Can algae withstand the high temperatures in the flue gases?

In a commercial application, flue gas from the desulphurization scrubbers would be sent to the CO₂ sequestration ponds for treatment. Temperatures exiting the scrubbers at many coal power stations are 140°F (60°C) and above – this could reach even upwards of 100^oC. Although most organisms cannot survive at these higher temperatures, some cyanophycean algae have been shown to grow at 176°F (80°C).

Since the temperature of waste gas from thermal power stations is high, the use of thermophilic, or high temperature tolerant species are also being considered (Bayless et al., 2001). Themophiles can grow in temperature ranging from 42-100^oC. An obvious advantage of the use of thermophilies for CO₂ sequestration is reduced cooling costs. In addition, some thermophiles produce unique secondary metabolites (Edwards, 1990), which may reduce overall costs for CO₂ sequestration. A disadvantage is the increased loss of water due to evaporation. Cyanidium caldarium, which can grow under pure CO₂ is a thermophilic species (Seckbach et al., 1971). Miyairi (1995) examined the growth characteristics of Synechococcus elongatus under high CO₂ concentrations. The upper limit of CO₂, concentration and growth temperature for the species was 60% CO₂ and 60ºC (Miyairi, 1995). Currently, an unidentified thermophilic species isolated from Yellowstone National Park has been examined by the group of researchers supported by the U.S. Department of Energy. Although less tolerant than thermophiles, some mesophiles can still be productive under relatively high temperature (Edwards, 1990). Such species also can be candidate species for the direct use of flue injection.

5)   What is amount of CO₂ required for algae growth?

It is estimated that approximately 2 T of CO₂ will be required to produce one T of algal biomass.

6)      Can we grow macroalgae for power plant CO₂ sequestration?

Macroalgae cultivation in marine environments have been studied as a possible means of large scale CO₂ sequestration, and many experts think that this avenue has good potential. A study has even estimated that a combination of micro- and macroalgae grown in open oceans could sequester between 0.7 to 3 gigatons (billion tons) of carbon per year from the atmosphere, at an estimated cost of $5 to 300 per T of carbon.

However, limited research has been done on growing macroalgae next to power plants for CO₂ sequestration. These researches have suggested that there are some disadvantages in using macroalgae for CO₂ sequestration, specifically in the context of the ability of macroalgae to survive in power plant flue gas. For instance, a patent by Friedlander et al, Israel Oceanographic & Limnological Research, National Institute of Oceanography (Feb 1996), suggests that Gracilaria cultures (a genus of macroalgae) did not survive more than 2-8 weeks in the power plant effluents during the one-year-long repeated experiments. The major reason was the high accumulation of copper, iron, lead and chromium from the power plant effluents as compared to concentrations in Gracilaria cultured in ambient seawater.

7)      What are the major problems faced by companies implementing algae based CO₂ sequestration techniques near power plants?

Some of the major problems with algae based CO₂ sequestration technology are:

• The high cost of implementing the sequestration infrastructure
• The limited availability of land space near power plants for building algae systems
• There are some specific operational problems as well, which could result in significant inefficiencies. For instance, high CO₂ concentrations could cause the algae suspension to become acidic, thereby stunting algae growth.

8)      Can power plants use waste water from their facilities for growing algae?

Power plants may not be able to use waste water from their facilities. In the power plant industry, large volumes of water are used by cooling systems. Water is also used in the FGD (flue gas desulfurization) plant, boiler cleaning, ash transport, demineraliser plant regeneration, and water also accumulates from coal stockpile run-offs. As a consequence, the effluent from power plant industry has higher temperature and also has heavy metals such as chlorine, copper, aluminum, mercury and phosphorus. It is difficult to grow algae in these effluents. However, some strains that have tolerance to heavy metal contamination and high temperature could possibly be grown.

9)      What are the methods by which flue gas can be cooled before passing it into algae systems?

Studies have found that direct cooling with no heat exchangers using cooling towers and mechanical chillers, is the most efficient and low cost cooling method of cooling the flue gas.

10)   Is it necessary that algae ponds need to be constructed right next to power plants?

Construction of algae systems near power plants is mostly preferred for the reduced capital costs, which will otherwise be required for putting up the pipelines for CO₂ transportation from the power plant to algae cultivation systems.

11)   What is the average area required for the construction of algae ponds for each power plant?

Efforts at putting up algae-based CO2 sequestration systems near power plants are in a nascent stage. Hence only preliminary data are available regarding areas required and their attendant costs. Some initial research done at universities and during pilot projects suggest that it could take an open pond of about 8 square miles (5120 acre pond) to produce enough algae to remove carbon dioxide from a midsized — 500 MW — power plant.

Algal Species Suited for CO₂ Capture of Power Plant Emissions 

Several species of algae have been tested under CO₂ concentrations of over 15%. For example, Chlorococcum littorale could grow under 60% CO₂ using the stepwise adaptation technique (Kodama et al., 1994). Another high CO₂ tolerant species is Euglena gracilis. Growth of Euglena gracilis was enhanced under 5-45 % concentration of CO₂. The best growth was observed with 5% CO₂ concentration. However, the species did not grow under greater than 45% CO₂ (Nakano et al., 1996). Hirata et al. (1996a; 1996b) reported that Chlorella sp. UK001 could grow successfully under 10% CO₂ conditions. It is also reported that Chlorella sp. can be grown under 40% CO₂ conditions (Hanagata et al., 1992). Furthermore, Maeda et al (1995) found a strain of Chlorella sp. T-1 which could grow under 100% CO₂, although the maximum growth rate occurred under a 10% concentration. Scenedesmus sp. could grow under 80% CO₂ conditions but the maximum cell mass was observed in 10-20% CO₂ concentrations (Hanagata et al., 1992). Cyanidium caldarium (Seckbach et al., 1971) and some other species of Cyanidium can grow in pure CO₂ (Graham and Wilcox, 2000). The table below summarizes the CO₂ tolerance of various species. Note that some species may tolerate even higher carbon dioxide concentrations than listed in the table. Overall, a number of high CO₂ tolerant species have been identified.

                                              CO₂ Tolerance of Various Species

Species	Known maximum CO2 concentration	References
Cyanidium celdanum	100%	Seckbach et al. 1971
Scenedesmus sp.	80%	Hanagta et al. 1992
Chlorococcum littorale	60%	Kodama et al. 1993
Synechococcus elongates	60%	Miyairi 1997
Euglena gracilis	45%	Nakano et al., 1996
Chlorella sp.	40%	Hanagta et al. 1992
Eudorine spp.	20%	Hanagta et al. 1992
Dunaliella tertiolecta	15%	Nagase et al., 1998
Nannochloris sp.	15%	Yoshihara et al., 1996
Chlamydomonas sp.	15%	Miura et al., 1993
Tetroselmis sp.	14%	Matsumoto et al., 1995

Source: Mark E. Huntley (University of Hawaii) and Donald G. Redalje (University of Southern Mississippi

 

Current carbon capture projects using Algae

 

1)      CEP & PGE, USA

 Oct. 2008

One of the most recent algae-inspired projects is being undertaken by Washington-based Columbia Energy Partners LLC (CEP), which hopes to convert carbon dioxide from a coal-fired electricity plant into algal oil.

CEP is a renewable energy company that primarily focuses on wind and solar energy. Two years back, the company approached one of Oregon’s electric utilities, Portland General Electric (PGE) to pitch the idea of converting carbon dioxide from the utility’s coal-fired plant in Boardman, Ore., into algal oil for the production of biodiesel.

CEP is currently conducting the first phase of what will potentially be a three-phase project. A feasibility study is underway at the 600 megawatt Boardman facility to determine if algae can feed on the carbon dioxide emitted from the plant and what amounts of carbon dioxide, and potentially other greenhouse gases, can be consumed by the algae. Seattle-based BioAlgene LLC is providing the algae strains for this portion of the project. The possibility of a larger build-out is also being researched at this time. He anticipates a full-scale operation to include 7,500 acres of open air algae ponds.

Results from the first phase should be available sometime in December 2008. At that point, if the results are positive, the company plans to move forward with engineering details and the construction of larger, in-ground algae tanks while continuing to research the process. PGE had requested the project be conducted in “baby steps” and one can expect a commercial-scale project to be three to five years away. Some of the challenges that are being faced by the team have to do with keeping open-air algae ponds free from contamination and the actual process of squeezing oil from the algae. CEP is financing the project. The company hopes to eventually sell the carbon credits it would gain from the process back to PGE or another buyer, as well as generate revenue from the algae oil and potential animal feed byproducts.

 

2)      Linc Energy & BioCleanCoal, Australia

 Nov 2007

Two Australian firms, Linc Energy and BioCleanCoal, have partnered together in a joint venture to sequester carbon dioxide emissions from Australian coal-fired power stations to use as fuel or fertiliser, even re-burning it to produce additional energy.

The companies will spend $1 million to build a prototype reactor in Chinchilla, which will use the carbon dioxide emissions from the power plant to grow algae, which can then be dried and turned into biofuels. A company director of BioCleanCoal says that the process can easily remove 90 percent of carbon dioxide from the plant’s emissions, with 100 per cent removal possible but unlikely due to the increased costs.

 

3)      Seambiotic, Israel

 The Israeli company Seambiotic has found a way to produce biofuel by channeling smokestack carbon dioxide emissions through pools of algae that clean it. The growing algae thrive on the added nutrients, and become a useful biofuel.

For the last two years, the company has tested their idea with an electric utility company - a coal-burning power plant in the southern city of Ashkelon operated by the Israel Electric Company (IEC).

The company's prototype algae farm in Ashkelon uses the tiny plants to suck up carbon dioxide emissions from power plants. Seambiotic's eight shallow algae pools, covering about a quarter-acre, are filled with the same seawater used to cool the power plant. A small percentage of gases are siphoned off from the power plant flue and are channeled directly into the algae ponds.Originally when the prototype started operating, a common algae called Nannochloropsis was culled from the sea and used in the ponds. Within months, the research team noticed an unusual strain of algae growing in the pools - skeletonema - a variety believed to be very useful for producing biofuel.

If all goes according to plan, Seambiotic plans to build its first large-scale biofuel reactor by next year and hopes to do so with a large international partner. Several potentials are already knocking on the door. Menczel reports that Seambiotic is meeting with electric plant operators from Hawaii, Singapore, Italy and India, all keen on hearing about Seambiotic's technology.  (Aug 2007)

 

4)      Trident Exploration, Canada

Trident Exploration Corp. is a natural gas exploration company. The company was looking at ways to reduce its CO₂ emissions.  Trident approached a number of companies looking for solutions, and ended up teaming up with Menova last year.

Menova's Power-Spar system uses solar concentrators to focus the sun on photovoltaic solar cells, which produce electricity, and fluid-filled channels that capture the sun's heat. But the system goes one step further, capturing the sunlight and redirecting it where necessary through fibre-optic cables.

What this means is that an algae farm – Menova’s photobioreactor – can be designed in a way where heat and light are concentrated in a relatively more confined area, allowing for the high-density growth of algae without the need for acres and acres of land.

On top of this, any algae system using Menova's collectors can produce electricity that can be sold into the grid or, in the case of Trident, used for their own power needs. Suddenly the economics, compared to other models on the market, begin looking attractive – even in Canada. Companies that purchase such a system can earn revenues generating electricity, producing raw material for making fuels and other bioproducts, and selling carbon credits into cap-and-trade markets.

In fact, Trident and Menova expect the system will reduce by half the amount of carbon emissions resulting from petroleum processing. The pilot project is expected to begin shortly, and a working commercial system is being targeted for 2010. (July 2007)

 

5)      EniTecnologie, Italy

The objective of the EniTecnologie R&D project on microalgae biofixation of CO₂ was to evaluate on pilot scale the feasibility of using fossil CO₂ emitted from a NGCC power plant to produce algal biomass. The biomass would be harvested and then fermented by anaerobic digestion to methane to replace a fraction of the natural gas, with the residual sludge, containing most of the N, P and other nutrients, recycled back to the cultivation ponds. In a preliminary mass balance calculation, assuming near-theoretical productivities, a 700 ha system was projected to be able to mitigate 15% of the annual CO₂ emissions from a 500 MWe NGCC power plant. The R&D focuses on how to increase the productivities of algal mass cultures under outdoor operating conditions. The target is to double biomass productivities from the currently projected 30 g (dry weight)/m2/day to 60 g (dry weight)/m2/day for peak monthly productivities, corresponding to a solar energy conversion efficiency of about 5%. This would reduce land area requirements (footprint of the process) and costs of algal biomass production. As a first step towards this goal the team set out to demonstrate the currently achievable algal biomass productivity under outdoor conditions using a simulated NGCC-flue gas for CO₂ supply and two different mass cultivation systems

Researchers at EniTecnologie in Italy conducted a field experiment of CO₂ uptake by algae in a raceway pond. The tetraselmis suecica algae were supplied with CO₂ from natural gas turbine flue gas. The experiment was conducted between the months of April to November and it measured the rates of production correlated to ambient temperature and available light. EniTecnologie reported growth rates as mass of dry algae produced each day per square meter of raceway. During the April to November time period, productivity ranged between 10 and 30 g/m²/day. The CO₂ uptake represents roughly half the weight of the dry algae, or ~5 to 15 g CO₂/m²/day.

 

6)      Kolaghat Thermal Power Plant, West Bengal, India

Aug 2009

A Kolkata, India-based organization is conducting a pilot project at the Kolaghat thermal power plant and is expected to start production next.

The 1,260-MW kolaghat thermal power plant emits 15,000 T of CO₂ every day. It is proposed that this gas be trapped and channelized into a pond where algae will be farmed.

The company is attempting to use the CO₂ from the power plant as follows: Fifty percent of the CO₂ emitted is planned to be used for algal farming, 25% for farming of Spirulina, and the rest to be compressed in its uncontaminated form to produce dry ice. The oilcakes (left over after the oil is extracted) are could be burnt to generate power to run this entire process. Thus, the company plans to design this into a self-sustaining technology. The power plant will be assisted by Sun Plant Agro, and plans to start commercial production of algae bio-fuel by 2010.

Both West Bengal Power Development Corporation (WBPDCL) (which owns the power plant) and Sun Plant Agro will earn carbon credit for the algae project. The power plant plans to use the wastelands near the plant for algal farming.

 

7)      MBD Energy, Australia

Aug 2009

Melbourne company MBD Energy is about to introduce technology that allows algae to capture half or more of the greenhouse gases emitted by a power station, at virtually no cost to the utility.  Managing director Andrew Lawson says testing at James Cook University in Townsville suggests for every two tonnes of carbon captured, the MBD technology can produce almost 1 tonne of algae, of which one-third can be made into oil products and two-thirds into meal. With meal sales about $400/tonne (rival soymeal product sells at about $780/tonne) and oil selling at $800/tonne, that equates to about $570 of revenue from each tonne of algae, or more than $250 for each tonne of CO₂ captured.

The first  1ha display plant of its "fuel synthesiser" is to be installed at the Loy Yang A coal-fired power station in the next six months. If the concept is proved over six to 12 months, MBD will move ahead to build a commercial pilot plant over 80ha.

That will require a $25 million investment, but Lawson estimates it will produce earnings before interest, taxes, depreciation and amortisation of $15 million. If that project succeeds, the facility can quickly be scaled up to a $300m demonstration facility.

Australia's largest power station, NSW's Eraring Energy, and a large-scale emitter in Queensland have signed agreements with MBD to install display plants over the next 12 months.

The company says a privately funded, $1.2 billion facility could capture half of Loy Yang's carbon emissions and generate $740m of meal income a year and $660m of oil income, as well as carbon credits of about $225m, while using just 10MW of energy. It also recycles water.

The process can currently capture only half a utility's emissions because it relies on sunlight to cause photosynthesis, but Lawson says more can be captured if future testing with LED lighting proves successful.

$1.2 billion for a massive algae farm may sound costly, but Lawson says this is likely to be funded as a separate infrastructure project, with the utilities having the option to co-invest. Each project of that scale would create 2000 regional jobs.

MBD Energy is in the process of raising about $10 million from three cornerstone investors, including an international energy company and a local carbon fund.

 

8)      Arizona Public Service Co., USA

Sep 2009

Arizona Public Service Co. has landed a $70.5 million US Department of Energy grant to try to feed algae with the carbon dioxide coming from its coal-fired electricity plants.

The grant will support the utility's carbon sequestration project at its Cholla Generating Station in northeastern Arizona. The project calls for the plant feed its carbon emissions to an algae pond, and that algae will be converted to biofuel. The grant comes from the DOE's roughly $1.4 billion Clean Coal Power Initiative, which has also seen applications from Duke Energy, NRG, Southern Co. and American Electric Power Co., among other utilities.

At least one other project of its kind is seeking DOE funding. Algae-to-biofuel company Origin Oil said last month that it was seeking grants for a project that would see captured carbon fed into algae ponds.

 

9)      RWE, Germany

RWE has studied in detail various options for climate-beneficial recycling and trapping CO₂ in order to identify potentials and obtain recommendations for action. One result of these investigations is the project launched by RWE for binding CO₂ using micro-algae. RWE – together with partners – has launched a project:  flue gases from the Niederaussem power station are fed into an algae production plant in the vicinity of the station to convert the CO₂ from the flue gas into algae biomass. On the basis of the algae biomass thus produced, a further aim is to investigate different conversion routes for the algae involving energetic and material use, e.g. for construction materials or fuels.  Flue gas is withdrawn from a power plant unit and transported through pipes to the micro-algae production plant. The CO₂ contained in the flue gas is dissolved in the algae suspension and absorbed by the algae for growth. The algae are removed (harvested) and further explored for conversion into fuel and chemicals.

Source link: http://www.rwe.com/web/cms/mediablob/en/247480/data/235578/34391/rwe-power-ag/media-center/lignite/blob.pdf

 

10)   E-On Hansa, Germany

In Nov 2007, German energy group E-On Hansa said it would build a $3.2 million pilot algae farm at its Hamburg power plant with support from the city government.

From October 2005 to October 2006 Thomsen, in collaboration with Eon Ruhrgas, Essen, and Bluebio-Tech, Kollmar, carried out a feasibility study of the capture of greenhouse gases by algae. It used marine microalgae as a natural carbon dioxide sink for the flue gases of a 350-MW coal-fired power station in the Bremen precinct of Farge. The aim was to capture 1% of the total emissions of this power station in a closed reactor system within five years. Two strains of algae used as animal feed and to produce oil were used.

Outcomes of the pilot experiment:

• Per ton of dry matter, the algae captured about two tons of CO₂
• Concurrently, the production fluctuated between 0.6 and 10 tons of dry algae mass per hectare and month, the highest yields achieved in summer
• Parallel to this the Bremen state government has installed a glass photo-bioreactor in a greenhouse of the university’s ocean laboratory
• It’s to be used for experiments in the use of marine microalgae for renewable primary products
• The Eon project is ongoing with the aim to cut production costs from one euro per Kg of dry algae mass to 60 cents.

 

11)    GreenFuel Technology, USA

Note: Greenfuel Technology officially reported that it was closing down operations in May 2009. The details provided below are based on the data during the company’s operations prior to its closure announcement

GreenFuel Technologies (www.greenfuelonline.com) - Its technology converts CO₂-containing emissions from power plants into valuable biofuels using proprietary algal photobioreactors (PBRs). The company develops systems for recycling CO₂ streams from power and manufacturing plant flue gases to produce biofuels and feed. It grows and harvests algae to produce byproducts, such as dry whole algae and algae oil for recycling CO₂ emissions. The company has installations in gas, coal, and oil burning facilities in Arizona, Kansas, Louisiana, Massachusetts, New Mexico, and New York. GreenFuel Technologies Corporation was founded in 2001 and is headquartered in Cambridge, Massachusetts.

In Nov 2008, GreenFuel Technologies and Aurantia announced the second phase of their joint project to develop and scale algae farming technologies in the Iberian Peninsula. Initiated in December 2007 at the Holcim cement plant near Jerez, Spain, the project's goal is to demonstrate that industrial CO₂ emissions can be economically recycled to grow algae for use in high-value feeds, foods and fuels. The Aurantia-GreenFuel project at Holcim consists of a series of development stages that could eventually scale to 100 hectares of algae greenhouses producing 25,000 tons of algae biomass per year. Aurantia anticipates the project will be eligible for subsidies from both regional authorities and the central government which will partially offset its development costs.

Technology Description

Greenfuel is a Massachusetts based start-up company that designed a biological CO₂ capture system using algae in photobioreactors. The company created a new photobioreactor designed specifically to capture CO₂ from flue gases and industrial processes, namely ethanol fermenters. The algae used in the bioreactors are selected specifically for the needs of each installation. The engineering principals used to design the system were based on maximizing the value of algae production. The company calls their capture process “emissions-to-biofuels.” The process begins with flue gas entering the system downstream of all other environmental controls. It is cooled and then distributed through manifolds to a series of individual inclined clear tube bioreactors that are filled with water and suspended algae. The bioreactors are oriented to receive maximum exposure to the sun. A blower is used to pull the flue gas through the reactor columns creating gas bubbles that physically mix the reactor liquid. The nature of the mixing is important to the rate of the photosynthesis reaction. In photobioreactors, the density of algae in water is significantly higher than what is found in nature. This high density makes for very poor light transmittance through the reactor tubes. By mixing the rector fluid in an ideal manner, the algae are cycled from areas of low light to areas of strong light. The company also claims that physical motion of the bubbles moving along and up the inside surface of the columns help keep the inside surface clean. As the algae mix with flue gas, they scavenge CO₂ to use in their photosynthesis reaction. As the algae reproduce, the surplus is collected and removed from the bioreactor in order to maintain a relatively constant concentration of algae to water in the bioreactor. The harvested algae are passed through a two-stage dewatering process with recovered water returned to the reactors, leaving dewatered algae cake. Greenfuel refers to the process to this point as the “front end” of their system. after passing through the photobioreactor, the flue gas is exhausted to the atmosphere. Results from a prototype unit operated on flue gas during 2004 and 2005 demonstrated that the carbon dioxide in the flue gas slip stream was reduced by 82.3% ±12.5% on sunny days and 50.1% ±6.5% on cloudy days. NOx emissions dropped 85.9% ±2.1% on both sunny and cloudy days.

According to the company, the rate of algal production for their design is 100 g/m2 per day, about five times that of a raceway.  The primary application for greenfuel’s design is biofuel production. By using algae which  produce high amounts of oil, the capture system can produce significant amounts of oil that can  be converted to biofuels. Alternatively, different algae can be used which maximize the amount of calorific energy production. These algae can be harvested, dried and then co-fired as a renewable crop. 

Greenfuel began development of their CO₂ capture concept in 2001 with seed money provided through the Massachusetts Institute of Technology (MIT) entrepreneurship competition. The first demonstration of the bioreactor design took place in 2002 with a 30 cell reactor operating on a slip stream from a 20-mw natural gas fired cogeneration plant at MIT. The company describes this unit as their first-generation design. The MIT pilot-plant featured a triangular reactor geometry.

In their second generation design, Greenfuel changed the photobioreactor geometry to a simple inclined tube reactor. In 2006, Greenfuel and Arizona Public Service (APS), tested a pilot unit at APS’s 1040 MW Redhawk power plant in Arlington, Arizona, west of Phoenix. The pilot plant scrubbed CO₂ using algae that were selected for their high production of oils and starch. These oils were separated and converted into biofuels. A transportable demonstration unit was used which allows Greenfuel to conduct a primary site assessment of potential commercial plant sites more easily. During the summer of 2006, Greenfuel demonstrated their process using the small-scale transportable bioreactor at NRG's Dunkirk coal plant. In these tests, partially sponsored by New York State Energy Research and Development Authority (NYSERDA), Greenfuel characterized performance of their system on unscrubbed PRB coal. Greenfuel is also planning a small-scale demonstration and field assessment at the Kelvin power station in Johannesburg, South Africa. These tests will provide performance information to global renewable energy efficiency network who recent acquired a license to build large-scale installations of the Greenfuel technology in South Africa.

 

12)   NRG Energy, USA

April, 2007

NRG Energy and GreenFuel Technologies have started testing GreenFuel’s algae-to-biofuels technology at a 1,489 megawatt coal power plant in Louisiana. GreenFuel’s Emissions-to-Biofuels™ process uses engineered algae to capture and reduce flue gas carbon dioxide (CO₂) emissions into the atmosphere. The algae can be harvested daily and converted into a broad range of biofuels or high-value animal feed supplements, according to the company.

In the initial field testing, which is to last approximately four months, algae species will be selected to optimize biofuel production based on the site’s flue gas composition, local climate and geography.  The ultimate goal is construction of a commercial-scale facility. A full scale commercial deployment could recycle enough CO₂ to yield as much as 8,000 gallons of biodiesel per acre annually under optimum conditions, GreenFuel claimed. NRG owns a diverse portfolio of power-generating facilities, primarily in Texas and the Northeast, South Central and West regions of the United States.

 

Challenges while Using Algae for CO₂ Capture

• There are no comprehensive and authoritative estimates of cost of sequestering CO₂ from power plants using algae. Some initial estimates question the economics of having algae sequestration of CO₂, with current cultivation technologies and bioreactors.
• Many power stations might not have the requisite area nearby. This would increase the capital costs for the pipes and the power used to move the gas through them by around twenty-fold. To cope with this change, the piping costs of instead of  are used to approximate a more realistic situation, along with additional piping for distribution to the individual algae farm ‘modules’ and increase pumping requirements for the gas.
• High land costs near power plants
• A quote from an algae-based power plant sequestration effort in Canada (Jan 2009) – “In view of the interest and potential utility of algae culture for carbon capture, a preliminary calculation of the costs was conducted using a base model scenario, running for 6 months. The current cost of producing algae for carbon sequestration in BC (British Columbia) is $793 per tonne of CO₂. Note that this calculation only considers the carbon fixed in the algae biomass; full lifecycle carbon losses due to electricity and fertilizer use, etc. and other costs such as transportation and deep burial would have to be included, which will increase the cost per tonne. This cost is prohibitively high, about twenty times higher than the estimated cost of burying CO₂ underground, and at least one order of magnitude higher than the cost of the fuel, indicating that at this point carbon capture using algae is not cost effective in BC.”-http://www.bcic.ca/images/stories/publications/lifesciences/microalgae_report.pdf
• Sub-optimal Location of Power Plants - The ASP Program by NREL report concluded that flue gas sources would be a poor source for CO₂ for the microalgae ponds, as power plants were not generally located in a suitable area for microalgae cultivation.