SUSTAINABLE process down under

Sustainable development is proving to be the Holy Grail of industry - everyone is searching for it, few have seen it, and even fewer will ever get their hands on it. Politicians meet (as most recently at Kyoto), pronounce, and immediately expect industry to turn away from processes based on dwindling natural resources to ones that meet the new goal of sustainability.

All of which is fine in principle, but more problematical in practice. Take the attempts to develop sustainable methods of power generation, for example. Windfarms are indeed fine (to some eyes at least), but not many people want them in their backyards. Wavepower again works in theory, but has been washed ashore by some unfortunate engineering failures.

Wood, which after all is just a precursor to fossil fuels give or take a few million years, should also have a lot going for it as a renewable energy feedstock. There have been many wood-based bioenergy plants built around the world, but again few have proved commercially successful.

Now, however, a wood-based process developed initially by the CSIRO (formerly the Commonwealth Scientific and Indusrial Research Organisation)in Australia could bring sustainable power generation along with a commercial process producing high quality activated carbon.

Fluidised bed process

Licensed in 1998 to the process engineering consultancy Enecon for commercialisation, the process uses specially designed fluidised beds to carbonise wood to charcoal, which is then further treated in another plant for conversion to activated carbon.

According to Enecon's managing director Colin Stucley, the fluidised bed combustion (FBC) system is quite versatile. Operating at atmospheric pressure, it can burn green wood of varying sizes - chips and sawdust, for example - and it can be controlled to allow either complete combustion for maximum thermal and electrical energy recovery, or partial combustion for lower direct energy recovery but increased charcoal production.

The charcoal itself has a potentially large international market for cooking and metallurgical uses and Enecon is also promoting its use as the feedstock for the second stage of the CSIRO process, the production of activated carbon (AC). Activated carbon has an established use worldwide as an adsorbent to remove contaminants from water and gases, but CSIRO's interest in the material originally developed from the fact that the Australian gold mining industry had to import all its activated carbon for its gold recovery process.

Activated carbon traditionally produced from timber sources is not hard enough to withstand the abrasive processing of the gold industry, so CSIRO developed its technology to process the charcoal prior to activation and increase its hardness.

The energy-generating potential of the process stems from both stages. The FBC plant produces heat from wood combustion which could be used for steam and power generation. This heat is recovered by conventional heat transfer, whereas the AC plant recovers energy via the production of water gas during the activation step. This gas can then be burnt cleanly to generate heat for cogeneration of steam and power.

Exclusive rights

Enecon now has the exclusive worldwide rights to the technology for the production of charcoal and activated carbon from wood, lignocellulose and other carbonaceous materials. Building on the success of the CSIRO pilot plants in Melbourne, Enecon is taking the technology to market by: carrying out feasibility studies on a variety of wood feedstocks; helping bring together companies with wood feedstocks and those interested in the production or purchase of charcoal and carbon; carrying out design and project management for full scale plants; and optimising project economics of the energy aspects of the process.

To this end, Stucley recently visited Europe and, in addition to picking up an environmental technology award for the process from the IChemE, found `considerable interest from UK carbon companies'. Back home in Australia the potential for the process is closely associated with a government-sponsored `Land Care' project. In Western Australia deforestation over many years is leading to severe salt degradation of large agricultural areas, a threat to wheat-growing areas which is being combated by the extensive coppice planting of mallee eucalyptus trees. Such planting will be greatly increased if the trees themselves also have a commercial return. An integrated approach to whole tree utilisation is being developed, with leaves as a feed for eucalyptus oil via distillation and wood as a feed for charcoal and activated carbon. All residues are used for energy generation.

On this basis, the CSIRO/Enecon process has the potential to drive an industry that could use more than 1million tonnes of sustainable green biomass per year, generating renewable energy and selling activated carbon, charcoal and oil.

Power generated by such an industry could range from 50MW to more than 100MW - not to mention the boost to Australia's tourist trade from all those well-nourished koala bears. PE