Das, Keshav C. (University of Georgia, Dept of Biological and Agricultural Engineering,
Athens, GA, 30602, Phone: 706-542-8842; Fax: 706-542-8806; Email: kdas@uga.edu)

Long-term sequestration of carbon in soils using Charcoal from renewable energy production

D. Day, J. Lehmann, C. Steiner, Bayreuth, Keshav C. Das*

Pyrolysis is the thermal treatment of biomass (e.g. peanut shells) in the absence of oxygen, which produces Charcoal, hydrocarbon vapors (BioOil), and gases (CO₂, CO, H₂) as primary products. It is known that Charcoal and BioOil can have beneficial properties that assist plant growth and nutrient retention in soils. The carbon in charcoal is highly recalcitrant, which allows it to persist in the environment for centuries. This makes Charcoal an easily quantifiable carbon sink. Although several biomass pyrolysis systems have been developed in the past, a complete carbon and energy balance, and related economics of this approach to carbon sequestration has not been analyzed and presented. This paper presents the energy and carbon balances in one biomass pyrolysis system for producing Charcoal and converting it to a carbon based nitrogen fertilizer (ECOSS) through an ammonia carbonation process.

Physical and chemical properties of pyrolysis Charcoal from different processes will be presented, such as charcoal carbon, volatile fraction, surface area, pore size distribution, cation exchange capacity, pH, available nutrients and total nutrients. These properties are discussed with respect to their importance to plant growth response and crop yields.

Based on the energy balance, a model is developed for computing and evaluating the potential for carbon sequestration through use of carbon-based fertilizers in commercial agriculture. The model is based on studies reported in the literature on the long-term carbon sequestration potential of Charcoal in soils.

We present here a first generation model of the energy and carbon flows in the thermochemical conversion of biomass to Charcoal and its use in agriculture. The ultimate goal is to provide a basis for comparing different Charcoal production and use technologies for agriculture and estimate the cost of sequestered carbon ($/kg-C) and the land-base required for carbon sequestration (ha/tonne-C) through this approach.