Introduction to Hydrothermal Carbonization (HTC)
2. Utilization of the HTC Biocokes
Waste to Energy: A Community Based Resource Production
HTC can convert a wet biomass mix into biocokes (for energy) or biochar (for soil conditioning, activated char and filters, carbon sequestration) pending on the feedstock material and how the plant is tuned. The output material should be produced in a way to meet local project objectives for specific calorie ranges or safety for use in agricultural soil. Conventional sources such as wood waste and bark can certainly be used for the reduction of biocokes, as well as methane fermentation and sewerage sludge and manure, making HTC excel in “turning waste into resources”. Without pre-drying or pressing, a biomass mix with a water content of between 50-70% can be converted into biocokes and progress water.
The energy content of the biocokes relates directly to the input material. For example, in Japan a 10 tons per day input of dairy cow manure (80-90% water) for 360 days will only yield about 4.6 million yens of feed in tariff income at current (2015) rates, correlating with the energy content. With additional input such as chicken manure and wood waste, far more energy can be produced, easily surpassing 5 times or more such energy output and income. Abandoned tree parts and bark are part of the same “unused wood” and with proper collection and utilization, it can fetch the same FIT income as wood chips per KWh. Instead of designing a project that is too large and eventually relies on imported feedstock, local resource utilization would maximize benefits not only for the project developers, but also for the stakeholders in the community.
Current operation and energy losses should also be included in the financial planning. For example, local governments in Japan used to spend a lot of money to get rid of sewerage sludge. In many cases, the sludge is pressed into dried sludge cakes and buried in landfills. Sewerage sludge dumping has now become illegal and local governments must look for solutions. Moreover, a mid-sized municipality may have been spending several 10s of million yens just to bury such waste, in addition to the mechanical process management and energy input. To process such waste in a way that eliminates harmful materials without worry of dioxins can create the double benefit of reducing environmental impact and creating a fuel that is readily useable with high calories. It can also become a community effort by combining other local feedstocks. Such initiatives are now gaining interest outside of Japan in Germany and Brazil as well.
From Soil Conditioning to Carbon Sequestration
Biochar has been receiving international interest over the last decade and in Japan, there are already commercial initiatives to convert local waste biomass into biochar to condition soil and sequester carbon in measurable, solid form to create branded vegetables in a carbon negative farming method. The modern-day “Tera Preta” can be a community effort that connects the kitchen to the farmlands and the city with the rural areas. (About Carbon Negative Farming)
Details at: The Japan Biochar Association (JBA)
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