2022 Annual Meeting
Concentrated Solar As Alternative Heating Source to Increase Carbon Negativity of Small-Scale Biochar Reactors
Biochar produced through pyrolysis is commonly used in agricultural settings and has recently gained popularity as a carbon sequestration method. Most small-scale pyrolysis reactors use the combustion of wood or propane as a heating source for biochar production. Pyrolyzing biomass can be carbon negative when using waste feedstocks by converting up to 50% of the carbon to solid biochar1. However, for small-scale, batch producers of biochar these values are harder to achieve with simpler, low-cost reactor designs. Further, these pyrolysis reactors have lower efficiencies and can require more combustion. This research explores the use of concentrated solar as an alternative heating source for small-scale pyrolysis. A parabolic dish solar collector was assembled and water heating and evaporation was measured to calculate the potential heat flux for the reactor. The concentrator was tested in 4 conditions, and the total wattage observed ranged from 0.056 to 0.429 kW. The heat flux ranged from 0.0319 to 0.243 kW/m2. Two experiments taken 10 minutes apart resulted in dramatically different results due to slight changes in the weather conditions. The best case condition was measured on a partially cloudy, 77â September morning, in northern New Jersey. The total heat collected by the apparatus in 8 minutes at this condition is equivalent to burning 27 g of propane. Given the reported enthalpy of biochar production at 500â2, it would take 129 minutes to pyrolyze 1 kg of biomass using the solar concentrator. By using a solar concentrator to make 1 kg of biochar, 432 g of propane can be saved. Given the tested weather conditions, and the prices of the collector and propane, the solar concentrator would need to be run approximately 200 times to break even. Despite the difficulties of working with a variable heating source, this research demonstrates that using a solar collector is a viable method for producing biochar, significantly reducing the emissions for a small-scale biochar producer.
1. Lehmann, J., Cowie, A., Masiello, C.A. et al. Biochar in climate change mitigation. Nat. Geosci. 14, 883â892 (2021). https://doi.org/10.1038/s41561-021-00852-8
2. Klinar, D. 2016. Universal model of slow pyrolysis technology producing biochar and heat from standard biomass needed for the techno-economic assessment. Bioresource Technology 206, 112-120. (2016). https://doi.org/10.1016/j.biortech.2016.01.053