Algae fuel

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The microalga Pediastrum duplex
Macroalgae recovery in northern France

Algae fuel is a fuel that is obtained from algae . Algae are photosynthetic organisms that live in the water and do not have to be phylogenetically related. Most live in either fresh or salt water. Algae consist of many different compounds and can be used as biofuel through different processes . A distinction is usually made between four different algae fuels:

Algae culture

So far, the cultivation of algae has mainly served to provide raw materials for the chemical and pharmaceutical industry and to provide food additives or as food. Types of multicellular macroalgae (e.g. brown algae , Laminaria sp. , Palmaria sp. ) Or single to multicellular microalgae (e.g. Chlorella sp. , Spirulina sp. ) Are used. Carbohydrate-rich species such as Sargassum , Gracillaria , Prym Magnesium parvum or Euglena gracilis can be used for ethanol production . These can either come from natural stocks or from cultivation. In studies on the production of algae fuel, species of both classes are used. Different cultivation systems are used:

Cultivation in open tanks

The cultivation of algae can be done by aquaculture , e.g. B. in open basins, happen. A control of the conditions is only possible to a very limited extent with this method, so that the high growth potential of the algae can only be exploited to a limited extent.

Cultivation in algae reactors

Algae reactors are closed systems in the form of glass tubes, plates or columns. Only free-swimming microalgae can be used. The advantage of the system is that there is a significantly larger surface so that more light can enter. In addition, conditions such as nutrient, CO 2 and O 2 concentration, temperature, mixing, etc. can be better controlled. Compared to agricultural crops, a multiple of CO 2 can be bound per area . However, high investment and operating costs are necessary. The CO 2 required for cultivation can come from combustion processes, for example from coal-fired power plants. The use of air has the disadvantage that the CO 2 concentration is very low at 0.038% and the gas injection costs are high.

Fuel production

The algae must first be recovered when cultivating in open tanks. When culturing in bioreactors, the low-concentration algae are separated from the aqueous nutrient solution by centrifugation or filtering . The subsequent process steps are mostly still under development. For algae with a high oil content, for example, a may pressing or extraction by means of hexane carried out. The oil mainly contains terpenes , which can be processed into fuel. The processes for producing ethanol and biogas could be derived from existing plants that use other raw materials. In addition to unchanged algae mass, the press residues from oil extraction could also be used here. Biohydrogen could be obtained directly from the bioreactor as a gas mixture with oxygen (O 2 ).

Advantages and disadvantages

Intensive research is currently being carried out to make algae usable for the production of biofuels and for CO 2 separation. Various advantages and disadvantages of algae fuel are listed:

advantages

  • The yield per area is significantly higher with cultivation in algae reactors than with agricultural production of biomass. The productivity of microalgae is given 15 times better than rapeseed, and a factor of 10 is given compared to maize
  • When cultivating algae, CO 2 can be extracted from exhaust gases, e.g. B. from coal power plants , intercepted and fixed as biomass.
  • There is no need to use valuable arable land for growing algae.

disadvantage

  • The area required for the complete capture of the CO 2 from the exhaust gases of a coal-fired power plant is very high. In a coal-fired power plant with an output of 1100 MW and an annual 5.4 million t CO 2 emissions, it is estimated that between 21,500 and 64,500 ha (215 to 645 km 2 ) would have to be equipped with microalgae reactors. At costs of 100,000 to 150,000 € / ha, total investments in the billions would be necessary. A pilot plant commissioned by RWE Power at the end of 2008 has a size of 600 m 2 , which ideally corresponds to 1 / 300,000 of the required area.
  • Operating costs are another important factor. Estimates assume € 30,000 to € 40,000 per hectare and year. The Federal Environment Agency estimates the costs of algae cultivation for CO 2 fixation to be extremely high and currently sees no steps in the production process that would lead to significant cost savings.
  • The energy consumption for production is high. For example, pumping the algae suspension and separating the low-concentration biomass by centrifugation or filtration are very energy-intensive.
  • In winter, productivity is significantly lower because, on the one hand, the algae grow better at higher temperatures, and on the other hand, solar radiation and thus photosynthesis is significantly lower.

outlook

Many companies are currently investing in the development of algae fuels, especially in the fields of power generation and oil production. For example, Exxon is planning a $ 600 million project with Synthetic Genomics Incorporated to produce algae biofuel. RWE is researching power plant exhaust gas cleaning using algae in a pilot plant . The US aviation group Boeing has announced that it is already planning test flights with algae fuel. In Germany, an “ Algae Biotechnology ” working group was founded under the umbrella of DECHEMA . So far, however, no commercial plants for the production of biofuels have been operated. A company in Klötze (Saxony-Anhalt) that uses algae reactors economically is only able to do this because the algae mass obtained is processed into food supplements, which can be sold at comparatively high prices. Despite numerous pilot projects and high research investments, the Federal Environment Agency estimates the potential of microalgae for the production of biodiesel to be low and assumes liter prices of 50 euros even with further optimization. The production of bio-hydrogen is also seen as inefficient and significant progress is only expected in about 10 years. The CO 2 fixation by means of microalgae is assessed as too expensive and no major developments are expected in the foreseeable future.

Projects are currently underway in Great Britain with the aim of using algae to filter various heavy metals out of toxic mine waste water and to use them for the production of biofuel. First attempts to do this show success in the extraction of heavy metals from the water by the algae. However, it remains to be seen to what extent the cultured algae can be further processed.

Web links

Commons : Algae Fuel  - Collection of Images, Videos and Audio Files

Individual evidence

  1. ↑ Algae become fuel - Technology - Energy + Environment - Energy + Technology - Handelsblatt.com . www.handelsblatt.com. Retrieved October 25, 2009.
  2. ↑ Microalgae - the energy source of the future. ( Memento from March 10, 2011 in the Internet Archive ) www.bmbf.de. Retrieved November 16, 2009.
  3. ↑ Algae for health and wellbeing . www.biothemen.de. Retrieved November 16, 2009.
  4. ↑ Ethanol from Algae . www.oilgae.com. Retrieved November 14, 2011.
  5. ↑ a b c d Glibber from Neptune's garden . www.neueenergie.net. Retrieved November 16, 2009.
  6. ↑ a b c Water, drinking water and water protection. In: Umweltbundesamt.de. Federal Environment Agency, archived from the original on September 9, 2013 ; Retrieved February 20, 2016 .
  7. ↑ a b power plant filters exhaust gas through algae . www.handelsblatt.com. Retrieved November 17, 2009.
  8. ↑ Exxon Mobil wants to extract fuel from algae - Current . www.fazfinance.net. Retrieved on October 25, 2009.  ( Page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Dead Link / www.fazfinance.net  
  9. ↑ ExxonMobil starts biofuel program . www.exxonmobil.de. Retrieved November 17, 2009.
  10. ^ Gene scientist to create algae biofuel with Exxon Mobil . www.guardian.co.uk. Retrieved October 29, 2009.
  11. ↑ Dr. Dieter Sell: Theses of the working group "Algae Biotechnology" of DECHEMA. (PDF; 1.3MB) Discussion paper "Recycling and storage of CO 2 ". In: mstonline.de. DECHEMA, archived from the original on August 25, 2009 ; Retrieved February 20, 2016 .
  12. ↑ Researchers to use algae to clean up mine water