Torrefaction

Technology Strengths, Weaknesses and Critical Indicators

Torrefaction:

  • 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

Overall Summary

Primary Application

  • 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.

Industry Update

  • 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.

Technology Maturity

  • Used for lignocellulosic feedstocks such as woody biomass at small scale. Not yet used for processing dairy manure.

Primary Benefits

  • 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.

Secondary Benefits

  • 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.

Limitations

  • 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.

Other considerations

  • 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.

Technology Providers in order of 9-Point Scoring System

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