Technology Type - Torrefaction
Technology Strengths,Weaknesses and Critical Indicators
- May produce a soil amendment in the form of biochar or ash
- Biochar does not yet have an established, stable commercial market
- There is significant variation in energy use and recovery depending on feedstock
- There is significant variation of operational intensity by site and by technology, many technologies require pairing with other technologies to offer a comprehensive manure management solution
- There is significant variation of cost depending on site and by technology
- Proven technology for phosphorous recovery, storage reduction, GHG reduction, odor control and pathogen reduction
- This technology loses nitrogen to the atmosphere
- Primary application is for treatment of separated manure solids or open-lot solids, packed beds.
- While no scale limits theoretically exist, practical economics potentially limit application to large dairies.
- No climate condition limitations exist with this technology.
Economic/Return on Investment Considerations
- Torrefaction has not yet been applied to dairy manure as feedstock, with economic considerations a strong reason for its non-application.
- Technology in combination with produce pelletization has begun to be commercially available due to increase in demand for biomass-derived fuels however as noted, no application to manure solids.
- Co-fired power generation industry is considering torrified biomass as coal replacement.
- Used for lignocellulosic feedstocks such as woody biomass at small scale. Not yet used for processing dairy manure.
- Reduces moisture in biomass feedstock.
- Increases heating/calorific value by increasing energy density.
- Hydrophobicity is increased in biomass, this increases storage/shelf life.
- Improves the handling characteristics of biomass (particle size, shape, and distribution).
- Increases its combustion efficiency.
- Reduces biomass weight by more than 30%.
- Some nitrogen content of biomass can be lost.
- Phosphorus is retained with solid product (biochar).
- Odor could be reduced due to decomposition of volatile organic compounds during torrefaction.
- Pathogens do not survive at temperature of 200-300 0C.
How it works?
- Torrefaction is a non-combustive thermo-chemical process in which biomass is heated in oxygen free environment with temperature range 200-300 0C at low heating rates (less than 50 0C/min) and less than 1 hour holding time at maximum temperature.
- Torrefaction is divided into several steps including heating, drying, and cooling.
- Removes oxygen and lowers O/C ratio of biomass by decomposing hemicellulose and not affecting cellulose and lignin content.
- Produces three products: biochar, (a charcoal like solid), torrified gas (a mixture of hydrogen, carbon dioxide, carbon monoxide, and hydrocarbons), and condensate (water, organic compounds, and lipids).
- Biochar accounts for 70% of mass and 90% energy of the original raw biomass.
- Torrified gas mixture accounts 30% mass and 10% energy.
Pretreatment and/or Post-treatment Required
- Torrefaction does not require any pretreatment of feedstock. It is itself a pre-treatment technology for lignocellulosic feedstocks for combustive technologies.
- Torrefaction requires pelletization as post-treatment to improve the energy density.
- Torrified and pelletized biomass is more convenient for transport and handling to use as feedstock for biofuel production.
- Torrefaction has not been utilized for processing dairy manure either pilot or large scale.
- There is a lack of standardization and consistency for torrefaction protocols and qualitative assessment of their products.
- The cost of torrefied products could be higher than coal if utilized as coal replacement.
- Biomass feedstock’s characteristics (both physical and chemical) influence the distribution of torrified outputs including gas, liquid, and solid.
- Moisture content of biomass feedstock is critical to determinant for energy footprint of torrefaction.
- Torrefaction needs to be accompanied with pelletization to improve the economic, transport and handling viability of torrified products.
- Torrefaction is one of the thermo chemical technologies that has tremendous potential to advance the biomass-based energy industry if optimal policy and financial opportunities are created.
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