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New role -for farmers in "green" fuel production

   
 
PictureTop of the CFB (circulating fluidised bed) pyrolyser.
Fuel derived from plants could have a big impact in both cutting carbon dioxide emissions and supporting the agricultural economy. Now, researchers have developed a reactor to produce "bio-fuel" from widely available renewable resources such as wood and cereal crops. The fuel can be burned in gas turbines, diesel engines, and Stirling engines, as well as in conventional, oil-fired boilers. The objective is to develop a small-scale, bio-fuel electricity generator for farms and small communities. Above:

 

As governments seek ways of reducing their dependence on fossil fuels, researchers are investigating new sources of renewable energy. One of these is "bio-fuel", a term used to describe any kind of fuel derived from cultivated crops. Not only are bio-fuels infinitely renewable, but they can be burned without increasing the amount of carbon dioxide in the atmosphere - the CO2 released in burning is balanced by an equal amount removed from the air via the photosynthesis process when the crop is growing. This energy resource thus reduces the problem of global warming.

Pasquali Macchine Agricole, an Italian manufacturer of farm machinery, is leading a JOULE project to develop a small electricity generator which runs on fuel made from various kinds of crops. The project was helped by Italian state subsidies for electricity generation from renewables, explains Henk de Lange, the project's technical co-ordinator. "There was a lot of tension in the agricultural community because the European Commission obliged farmers to set aside a significant part of the land they used to use for food production - often as much as 15 or 20%. But if the land could be used to grow energy crops, you would have a new important source of green fuel while maintaining farm employment. Currently, this problem is reduced because the Commission is thinking of abolishing the set-aside policy. Still, growing energy crops on unused land will contribute to employment in the agricultural community."

One way to use cultivated material - known as biomass - is to simply to burn it like coal, using the heat to generate electricity in conventional power stations. But this is not very efficient, and a better way is to turn the biomass into gas first, and then use it to drive a gas turbine generator. "But these schemes are only useful for electricity production for base load," Mr de Lange says. "You have a continuous cycle and you just go on producing electricity." They are not suitable for small-scale generation schemes.

From biomass to bio-
fuel The process chosen in this JOULE project is called pyrolysis, in which the biomass is heated to around 500°C. A limited amount of oxygen is allowed to enter the reactor to provide the heat to sustain the pyrolysis process. The biomass does not burn; instead, it produces bio-fuel vapours, which condense to a dark-brown, mobile liquid that can substitute for fuel oil. The gasification process takes place at a higher temperature and longer residence times, and involves the partial combustion of the fuel to obtain a fuel-gas whose combustible compounds are carbon monoxide, hydrogen, and a small fraction of very light hydrocarbons. Pyrolysis has the advantage over gasification that bio-fuel has a much higher energy density. Moreover, it can be stored for long periods and easily pumped and transported. "This is one of the first attempts to go from biomass to electricity production using this route," says Mr de Lange. "No other systems are widely available on the market yet. The objective of this project was to develop a commercial application for this process."

The design and construction of the pyrolysis reactor (the pyrolyser) and power plant were the responsibility of project leader Pasquali. The Umbrian Region (Italy) offered its support for investigating the development, harvesting, transport, and storage of the fuel crops. Stadtwerke Saarbrücken (Germany) carried out a market survey in their area to find out how this technology could be implemented there. They also investigated the use of this bio-fuel in Stirling engines.

The prototype power plant consists of a pyrolyser coupled to a 100-150 kWe generator. Early tests showed that 55-65% of the biomass was being converted into fuel.

Picture
Control room

Sorghum performs best
In principle any kind of biomass can be used to make bio-fuel by this process, but the quality depends on crop used. "So far the best results have been obtained with wood, but from a strategic point of view wood is not the best energy crop," explains Mr de Lange. "Wood typically gives 15 dry tonnes per hectare per year, whereas sorghum could give you as much as 40. So sorghum and certain other types of cereal grasses would be more interesting, but it is more difficult to pyrolyse them."

Sorghum is especially useful because the juice extracted from it can be fermented to make ethanol, while the solid residue is processed by pyrolysis. The mixture of these two fuels performs even better than bio-fuel alone, especially in existing engines. One part of the project was the design of a harvesting tool to harvest, cut, and dry the sorghum directly in the field.

Mr de Lange is cautiously optimistic about the future for bio-fuel. "It was a very useful project. We have developed a pyrolyser which works. We have looked into using it in gas turbines, diesel engines, and also conventional boilers. It's not really commercial yet, because a number of problems remain to be solved and a number of issues have to be looked at further."

Although Pasquali is concentrating on small-scale applications of up to a few hundred kilowatts - specifically for farms and agricultural co-operatives - there is also a lot of interest in Europe in generating electricity from bio-fuel at the megawatt scale. Similar projects are underway elsewhere, especially in Britain, Sweden and Finland. "In Sweden they don't have their own oil resources, but they have large forests and also stringent objectives in reducing carbon dioxide emissions. On a European level there is quite some interest in this technology."

 

 

Project Title:  
Advanced small electricity farm generator (100-150 kWe) optimised for herbaceous crops.

Programmes:
JOULE 2

Contract Reference: JOU2-CT93-0442

CORDIS databaseFor more information on this project,
go to the Cordis database Record

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