(602ba) Verification of Biochar Pyrolysis

Lucas J. Rice and Tom R. Marrero

Department of Chemical Engineering

University of Missouri

Columbia, MO 65211

Abstract

This study attempts to verify the ability to generate a carbon-negative cycle from the pyrolysis of biomass materials to supplement soil nutrients. 

The pyrolysis process is simulated with ChemCAD software with inputs from new of field and bench scale data. 

Field data correspond to a kiln approximately 100 feet long with a nominal cross-sectional area of 100 ft². The kiln maintains a nitrogen atmosphere to pyrolysis the biomass to biochar. A series of operating characteristics are measured; temperatures in the chamber, moisture of raw materials and biochar, and process residence time.  Furthermore, biochar characteristics such as porosity, elements, and carbon content were determined.

Results indicate the maximum and minimum temperatures required for the process.  The maximum temperature of the kiln allows for pyrolysis energy balances to determine other factors required such as the residence time.  Furthermore, an ideal temperature is calculated in order to create the most efficient.

Biomass materials are used for the biochar include: corn stover, milo stover, and hay.

Recent publication describes the carbon life cycle of normal energy production.  There are three potential cycle types mapped out in this process: carbon positive, carbon neutral, and carbon negative.  

Carbon positive represents the burning of fossils and release carbon dioxide into the atmosphere.  This process results in a net gain of carbon dioxide in the atmosphere, which is why it’s called carbon positive.

The burning of biomass in a similar process as fossil fuels also can produce the same carbon dioxide in the atmosphere.  During photosynthesis, plant life takes up the produced carbon dioxide facilitating more green growth, which in turn can be used as biofuels.  This process is called carbon neutral since the net gain of carbon in the cycle is zero.  However, the half-life of carbon dioxide in the atmosphere is significantly longer than 100 years which results in a loss of carbon.

The third type of process discussed is the focus of this presentation, the carbon negative cycle.  Biomass is subjected to slow burning pyrolysis which results in two usable products.  Similarly to the previous two cycles, carbon dioxide is generated as a bi-product and can be used as energy or recycled back through green life.  The biomass is converted to biochar and can be used as soil amendments thereby a portion is sequestered or captured into the soil due to its refractory properties.  This sustainable process is called the carbon negative cycle.

To obtain the nutrient rich qualities of biochar for soil enhancement, the biomass is subjected to slow pyrolysis.  During pyrolysis, nitrogen and/or nitrogen containing compounds are adsorbed by biochar.

The amount of soil amendment obtained from the biomass is quantified by measurements of the dry weight and the burn-down of the biomass to biochar.

The production of biochar provides fertilizers with a variety of benefits for the environment.  The use of biochar instead of traditional fertilizers (ex. ammonia) can potentially provide a more efficient alternative to soil supplements in theory and in practice.  By returning the biomass materials to the soil in this manner, the nutrients are recycled and already in a form useable by vegetation.  Furthermore, the biochar in the soil helps the ground to maintain its strength preventing the fast erosion due to wind or rain.  Water has a higher rate of retention in soil which contains biochar.  Biochar is also able to revitalize grounds that have had all the nutrients drained by over cultivation or other methods.  This would allow for a larger area base for farmable land.  This also leads to the ability forgo such strategies as crop rotations.   Lastly, as the carbon negative cycle utilizes more energy from the pyrolysis of the biomass, the efficiency helps to convert energy.

The final results of the study are a new simulation of a sustainable biomass pyrolysis using the ChemCAD software.  This simulation is verified and calibrated by field and bench scale data.