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Biochar from Biomass Gasification (Pyrolysis)

In developing strategies and incentives to address climate change, Policymakers have placed very little emphasis on greenhouse gas emissions from the agriculture and land use sectors. However as the below chart reflects, this market segment is clearly just as important as (1) electricity generation and (2) transportation fuels (e.g., ethanol).

Biochar may be a key commponent in achieving a comprehensive carbon management strategy by integrating:

  • Biomass renewable energy (gasification),
  • Terrestrial carbon sequestration and reductions in
        other greenhouse gases like nitrous oxide
        emissions from soils,
  • Agriculture (improved soils for higher crop yields
        requiring less fertilizer),
  • Water resources (e.g., wetland creation and
        enhancements, water pollution from nutrient runoff
        -- P, K, N.

    • What is Biochar? Simply stated, Biochar is a solid by-product/waste stream (~90% of highly stable fixed carbon) resulting from the gasification of biomass feedstock (pyrolysis technology where biomass is heated with a minimum or absence of oxygen).

    Enhanced Biomass Energy Carbon Cycle With Biochar

    Below is the chemical composition of biochar from biomass gasification:

    Composition & Analysis:
    Biochar by Weight %
    Proximate Analysis:
     
    Volatile Matter
    7.6
    Fixed Carbon
    90.2
    Ash
    2.2
    Ultimate Analysis (daf)
     
    Carbon
    98.58
    Hydrogen
    0.4
    Oxygen
    0
    Nitrogen
    1.0
    Sulfur
    0.02

    Understanding Biochar A key in understanding biochar is the dynamic of soil organic matter (SOM) and soil organic carbon (SOC), discussed on our webpage on soils.

    For simplicity, SOM can be divided into two major groups: (1) particulate organic matter (active fraction) and (2) humus (stable fraction) -- which would include biochar. Compared to the short half-life of particulate organic matter, highly stable humus can last in soils for centuries.

    The functions of SOM can be broadly classified into the following three groups -- where these groups are not static entities and dynamic interactions occur between these three major components.

    Two Aspects of Interests: There are several theories and numerous possible interactions (biological, physical, and chemical) as to why biochar increases soil productivity. Building on our knowledge base of SOM/SOC (including work performed with the U.S. Department of Energy's Oak Ridge National Lab) -- two aspects have especially caught our attention:

  • One is that biochar creates a base for micro-organisms
        that produce substances that hold soil particles and
        nutrients together.
  • Two, biochar may adsorb and slowly release nutirents to
        plants over time (note the word adsorb, not absorb) -- by
        increasing the cation exchange capacity (CEC) and also
        anions of soils.

    • Engineering for Biochar Creation: From an engineering perspective, the most critical aspect in creating biochar is to maximize surface area (pore space) with an objective of trying to create surface areas approaching activated charcoal to maximize the capture/sequester of Greenhouse gases in soils (CO2, methane, nitrous oxide).

    In order to achieve high surface areas the key engineering parameter of oxygen starved biomass gasification is temperature formation, where the optimal range is approximately 500 to 700 degrees C (~900 to 1,300 F).

    While quite a bit of research is with small scale gasifiers (e.g., laboratory, stove, etc.), our research and demonstration effort is focused on large-scale, commercial up-draft gasifiers where the biochar is a waste product in creating biogas (for end-use applications such as product drying/heating, electricity, steam).

    In our approach, we extract biochar (just above the incandescent zone) on a semi-continuous basis using nitrogen to “quench and cool” the biochar removed/recovered from the bed cooled to room-temperature for storage and eventual soils application. The recovery of biochar from the gasifier will not significantly impact the gasifier continuous operation of biogas generation for power/heat/steam. It is also important to note that our approach to "quench and cool" in a nitrogen environment is also attempting to address the extremely high carbon/nitrogen ratio of biochar.