Reduction of Greenhouse gases

Bioethanol is produced from plants and is a renewable resource. This means that as much carbon dioxide is taken up by the growing plants as is produced when the bioethanol is burnt. Theoretically the net contribution to greenhouse gas emissions (GHG) is thus zero. In reality this cycle is never to 100% closed since we are not able to utilize the energy content of the crops to 100 %.

During the processing and transport from the field and to the tank of the car we also have losses and need to put in energy. Just as we have to invest energy as we extract and process raw-oil to the petrol we fill in our cars.

Different feedstocks and different plants vary in energy content and efficiency. Thus the GHG savings vary depending on how the bioethanol is produced.

Well to Wheel analysis of bioethanol production

Savings in Greenhouse Gas Emissions and Fossil Energy (Source Concawe 2007)

Savings in GHG emissions (right box) and fossil energy (left box) for different feedstocks, production methods and different use of rest products compared to petrol (the bar at the bottom of the diagram) according to Convawe.

The above example shows how important it is to study the greenhouse gas reduction potential in the perspective from well to wheel (WTW), i e from the very origin of the crops that are used to produce the fuel and all they way through production and distribution to having used the fuel to drive your car. This is sometimes also called LCA, Life Cycle Analysis.

WTW–analysis of bioethanol shows that the reduction of green house gas emissions varies widely depending on how the bioethanol has been produced. Especially how the energy for the ethanolplant was generated is important. The extent of fossil energy input of course influences the GHG-reduction potential to a high extent.

Advanced processes (from wood or straw) can give very high savings of greenhouse gas emissions, mostly because these processes use part of the biomass intake as fuel and therefore involve little fossil energy.

For bioethanol produced from sugar cane the "bagasse", the leftover after extraction of the sugar, is a convenient and abundant fuel for which there is no alternative use and which can meet all the needs of the processing plant. In the best cases surplus heat or electricity can be produced, further boosting the energy balance. Thus driving on Brazilian bioethanol can reduce GHG emissions with around 90%.

Using the by-products from the bioethanol production for energy production rather than animal feed (which is the most common use today) has a very large impact on the greenhouse gas emissions in the WTW-perspective. If the sugarbeet pulp is used for heat production, the sugar beet pathway can deliver high savings of energy and GHG emissions. Similar reduction can be achieved with wheat when the distiller’s dried grain with solubles” (DDGS) rests from the from.conventional production of ethanol are used for heat.

kids infront of an ethanol bus

Bioethanol from sugar beet and wheat, as until now practiced in Europe (a simple, usually (fossile-)gas-fired, boiler provides the steam while electricity is taken from the grid) gives however modest fossil energy/GHG savings compared with gasoline.

With conventional energy production scheme and the currently most economic way of using by-products (as cattle fodder) the schemes save about 20% of the fossil energy required for gasoline and just over 30% of the GHG emissions. Use of co-generation particularly in combination with a gas-fired gas turbine can significantly improve these figures to over 40% for energy and GHG emissions.

 

Combined heat and power production, CHP, also improve the environmental profile of the produced ethanol. BUT the wrong choice of energy for the production plant, like brown coal, wipes out most of these gains and can even in worst case result in increased GHG emissions.

Figures and data above are taken mainly from the very extensive work on fuels WTW analysis have been conducted jointly by Concave (Oil companies European organisation for Environment, Health and Safety), JRC (Joint Research Center of the European Commission) and EUCAR (European council for automotive research and development). They published their first results in 2004 and a second adjusted version in may 2006. Their process involved stakeholders mainly from automotive and petro-industry whereas agriculture and environmental sector was not involved.

Similar studies was also conducted by the Viewls project that compared around 600 LCA studies giving the following overall picture: Bioethanol from starch crops as produced today can be both better and worse than petrol when it comes to GHG emissions from a WTW perspective, where as bioethanol from sugar crops gave less or much less GHG emissions and bioethanol from lignocellulose residuals looks even more promising. The viewls project actively invited any stakeholder to participate in the process, and the response came mainly from stakeholders already involved in biofuel or biomass sector.

For more info please contact:Jeremy Woods

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