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From agricultural waste to green energy

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By far the most heated debate surrounding biofuels is the use of food crops to produce fuel, as the practice increases the competition for land and drives up the price of food . With a decade of research behind it, the European Union (EU)-funded project KACELLE has proven that crops such as wheat and maize do not necessarily need to be used in the increasing demand for energy.

Coinciding with the 2009 United Nations (UN) climate summit, Conference of the Parties (COP) 15, the Kalundborg plant was built by Denmark’s largest energy provider, DONG Energy, using their patented Inbicon biomass technology. KACELLE project was integral in bringing this technology out of the research and development phase and into a near-commercial level, which culminated in July 2013.

The input for the Kalundborg plant is a by-product of agriculture – straw. Some 1.5-2 billion tonnes of it are leftover  from farming in Europe and unlike first generation biomass, such as soy or rapeseed, straw does not require extra land to grow. The Institute for European Environmental Policy has established that there is enough straw available to account for 40% of the EU’s ethanol demand by 2020 , with enough for its usual usage as fodder and compost.

“DONG Energy only uses leftover (waste) straw from agriculture,” explains Henrik Maimann, Vice President of DONG Energy in Kalundborg, Denmark and responsible for Inbicon technology. Some countries outside the EU have already capitalised on waste as a fuel source. In Malaysia, for example, the palm shells and branches from palm oil production are burnt to generate energy.

Straw consists of three parts: cellulose, lignin and hemicellulose. Cellulose is the most abundant renewable carbon source on Earth, after which is lignin, and both are the main components of plant cell walls, giving wood its strength and binding cells, fibres and vessels.  The patented Inbicon technology converts this biomass to sugars using a process called enzymatic hydrolysis – essentially liquidising the biomass using enzymes.

First, the straw is pressure cooked to open the protective lignin structure and expose the cellulose to the enzymes. As the straw is naturally very dry the consumption of water, and therefore energy, is minimised. Enzymes added to the fibre mass liquefy the straw so that it can be pumped into traditional fermenters, breaking down the biomass into less complex carbohydrates such as sugar.

Yeast then converts the sugar to ethanol and carbon dioxide. After 140 hours of fermentation, the CO₂ is captured,  purified and used in carbonated beverages and flash freeze applications. The ethanol is distilled and then used as an additive in gasoline to replace toxic lead compounds that have significant adverse effects on the environment.

Four tonnes of biomass can be converted in this way per hour. That is 5.4 million litres of ethanol annually. The Kalundborg plant handles 30,000 tonnes of straw per year and produces ethanol, lignin pellets and C5 molasses as outputs.

“The industry needs to prioritise second generation ethanol,” says Maimann. “The EU is acknowledging this importance, but we still need to see a real market like we see in China and Brazil. Our Kalundborg plant made it possible to test the design and the research is expected to benefit three or four other projects in Europe,” he adds.

The next step for the KACELLE research team is to optimise the inputs – follow-up projects will look at a modified type of yeast that can increase the yield of ethanol. Biofuels are projected to produce half of the country (Denmark)’s energy needs by 2050, above and beyond the EC target of 10% by 2020 .
 

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