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In the study, Amit Suri, Masayuki Horio and colleagues note that about 67 percent of Japan is covered with forests, with that biomass the nation's most abundant renewable energy source. Wider use of biomass could tap that sustainable source of fuel and by their calculations cut annual carbon dioxide emissions by 4.46 million tons.

Using waste biomass charcoal, their heater recorded a thermal efficiency of 60-81 percent, compared to an efficiency of 46-54 percent of current biomass stoves in Turkey and the US.

"The charcoal combustion heater developed in the present work, with its fast startup, high efficiency, and possible automated control, would open a new era of massive but small-scale biomass utilization for a sustainable society." the authors said.

The problem with biomass
Biomass in its raw form with its low calorific value (15 MJ/kg - MegaJoules per kilogram) is very ineffective in its storage, transportation, and combustion and cannot compete with kerosene or gasoline (~45 MJ/kg) combustion.

To overcome the inefficiencies of using raw biomass, like logs, wood pellets have become a popular alternative.  However, even these have drawbacks because they need additional energy to dry, mill and to mould, which ultimately makes them less than ideal.

Using charcol
Once carbonised, wood biomass becomes a stable, clean, and high-caloric fuel (25-30 MJ/kg). Charcoal can be easily to powder a powder which makes it easy to store and easy to transport, and ideal for the kind of system being proposed.

To burn quickly and at a high temperature, charcol needs plenty of oxygen.  The designers of this system designed it with an internal rotating drum which allos the charcol to for a thin uniform bed fixed to the drum's wall.