Small-Scale Pyrolysis Reactor Modifications for Carbon Balance Measurements

As of 2023, the US produces 120 billion pounds of foodwaste that ends up in landfills each year, releasing greenhouse gasses that contribute to the ongoing climate crisis. Currently the atmospheric carbon dioxide has been growing over 2 ppm each year, with a global average of 417.06 ppm recorded in 2022. One method of preventing CO₂ from being released into the atmosphere is using pyrolysis to convert biowaste into biochar. Pyrolysis is a method of sequestering carbon by heating biomass to high temperatures (~300°C-800°C) in the absence of oxygen. This process creates a solid carbon material called biochar, which farmers have been producing for millenniums to improve their soil. Although farmers use biochar in a purely agricultural sense, this process has the potential to be carbon negative. This study attempts to quantify the carbon sequestered and released during pyrolysis in a laboratory setup under a chemical hood. Thus far, two semi-batch reactors (with recirculating syngas) have been built that are partially able to pyrolyze biomass. These prototypes used propane as the energy source and wood shavings as the biomass. The first reactor, which contained an average of 171.25 g of biomass, had inefficient heat transfer, with a biochar yield ranging from 4-11% of the initial mass (w/w%), and a max temperature of ~314°C. The second prototype was much smaller, with an initial mass of 31 g. A flow sensor was also attached to measure syngas. This reactor had improved the heat transfer and data collection due to the change in size and shape, with a biochar yield of 65% of the initial mass (w/w%), and a max temperature of 330°C. It was found that the carbon emitted outweighed the carbon mitigated, with results showing 926.9 g of CO₂ was emitted and 73.3 g of CO₂ was sequestered with a reaction time of ~51 minutes and no measurable syngas flow. The reactor is still inefficient, the chemical hood worsens the heat transfer that reaches the biomass. To optimize the CO₂ emitted:stored as well as increase the max temperature, the next prototype will be powered electrically.

References:

1) “Food Waste in America in 2023: Statistics & Facts: RTS.” Recycle Track Systems, www.rts.com/resources/guides/food-waste-america/. Accessed 28 Sept. 2023.

2) Lindsey, Rebecca. “Climate Change: Atmospheric Carbon Dioxide.” NOAA Climate.Gov, www.climate.gov/news-features/understanding-climate/climate-change-atmos.... Accessed 25 Sept. 2023.

3) “Biochar Then & Now.” Biochar Then & Now | US Biochar Initiative, biochar-us.org/biochar-then-now#:~:text=Biochar%20has%20also%20been%20created,in%20some%20places%2C%20toxic%20soils. Accessed 30 Sept. 2023.