The earlier post Fast Pyrolyzers discussed an interesting paper, The Charcoal Vision: A Win–Win–Win Scenario for Simultaneously Producing Bioenergy, Permanently Sequestering Carbon, while Improving Soil and Water Quality, that advocated a superior method of generating bioenergy in more environmentally benign ways. The technologies involved were only briefly mentioned.

Fast pyrolyzers rapidly (~1 s) heat dry biomass (10% H2O) to ~500°C and thereby thermally transform biomass into bio-oil (~60% of mass), syngas (~20% of mass), and charcoal (~20% of mass). The energy required to operate a fast pyrolyzer is ~15% of the total energy that can be derived from the dry biomass. Modern systems are designed to use the syngas generated by the pyrolyzer to provide all the energy needs of the pyrolyzer. Bio-oil is an energy raw material (~17 MJ kg–1) that can be burned directly to generate heat energy or easily shipped to a refinery for processing into transportation fuels and various co-products (Bridgwater et al., 1999). Charcoal is also a potential energy product, however, I advocate returning the charcoal to the soils from which the biomass was harvested thereby closing the nutrient cycle in a way the mimics the soil building effects of natural prairie fires.

Consider this related technology and a different view of its significance.

Research at the University of Hawaii (UH) has led to the discovery of a new Flash Carbonization™ process that quickly and efficiently produces biocarbon (i.e., charcoal) from biomass. This process involves the ignition of a flash fire at elevated pressure in a packed bed of biomass. Because of the elevated pressure, the fire quickly spreads through the bed, triggering the transformation of biomass to biocarbon. Fixed-carbon yields of up to 100% of the theoretical limit can be achieved in as little as 20 or 30 minutes. (By contrast, conventional charcoal-making technologies typically produce charcoal with carbon yields of much less than 80% of the theoretical limit and take from 8 hours to several days.) Feedstocks have included woods (e.g., leucaena, eucalyptus, and oak), agricultural byproducts (e.g., macadamia nutshells, corncobs, and pineapple chop), wet green wastes (e.g., wood sawdust and Christmas tree chips), various invasive species (e.g., strawberry guava), and synthetic materials (e.g., shredded automobile tires). Results of many of these tests are described in a series of technical, peer-reviewed, archival journals paper that can be obtained by request to Prof. M.J. Antal.

We are now testing a commercial-scale, stand-alone (off-the-grid) Flash Carbonization™ Demonstration Reactor ("Demo Reactor") on campus (see photos below). The first successful test occurred on 24 November 2006. A canister full of corn cobs was carbonized in less than 30 min. This test proved that the Flash Carbonization™ process can be scaled-up to commercial size.

This is one of a number of ideas for using biocarbon, aka biochar, at the Hawaii Natural Energy Institute (HNEI). Another interesting bit of research deals with an aqueous carbonate/alkaline biocarbon fuel cell. Soon to be published research will interest those of us concerned about soil.

Recently we began Flash Carbonization™ studies of raw sewage sludge produced in Honolulu's Ewa sewage sludge treatment plant. We were surprised by the ease with which air-dry sewage sludge can be converted into charcoal. We obtained charcoal yields of about 30% (dry basis) from the sewage sludge. The charcoal contained 45-51% ash and 40% fixed-carbon. Studies of the use of sewage sludge charcoal as a soil amendment (i.e., terra preta application) with the side-benefit of carbon sequestration are now beginning at UH. Results of these studies will be reported at the forthcoming AIChE meeting in Philadelphia (November, 2008).

Their focus isn't on producing liquid fuels for transportation. They argue that biocarbons produced efficiently from biomass are better used as a replacement for coal than for oil and its distillates. Coal has a greater environmental impact so its replacement is a larger net gain. Coal is used in ways not often discussed.

Q10: Does charcoal have any uses besides fuel for barbeque and electric power generation?

A10: Yes! Iron, steel, and ferrosilicon alloys are all produced using a carbon reductant. Almost one pound of carbon is consumed to produce a pound of steel. In the USA coal ("coke") is used as the carbon reductant and this use of coal adds substantial amounts of CO2 to the atmosphere and is an important contributor to climate change. Brazil and Norway use charcoal instead of coal to produce iron, steel, and ferrosilicon alloys. As the steel industry moves to reduce its carbon footprint, the demand for charcoal as a substitute for reductant coal will explode. . .

Q12: What does this all mean for Carbon Diversion? (Carbon Diversion Corporation - licensee of UH Flash Carbonization™ technology)

A12: The markets for charcoal as a boiler fuel for the sustainable production of electricity, a reductant for the sustainable production of metals, and a soil amendment for sustainable agriculture and carbon sequestration are enormous. We believe that Carbon Diversion is destined to become one of the Exxons of the 21st century.

I like the idea of being able to quickly turn everything from dung to shredded automobile tires into biocarbon. One of the limitations of biochar systems has been their slowness, which means that more processing equipment is needed for larger volume outputs, increasing capital costs and lengthening equipment payback time. Higher productivity means lower costs to users.

I want one.