Air and steam gasification of almond residues

Authors: McCaffrey, Zachariah - Zach; THY, PETER - University Of California, Davis; LONG, MICHAEL - University Of California, Davis; OLIVEIRA, MELINA - Universidade Estadual Paulista (UNESP); WANG, LI - University Of California, Davis; Torres, Lennard; AKTAS, TURKAN - Namik Kemal University; Chiou, Bor-Sen; Orts, William; JENKINS, BRYAN - University Of California, Davis

Submitted to: Fuel Processing Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2019
Publication Date: 8/21/2019
Citation: McCaffrey, Z., Thy, P., Long, M., Oliveira, M., Wang, L., Torres, L.F., Aktas, T., Chiou, B., Orts, W.J., Jenkins, B. 2019. Air and steam gasification of almond residues. Fuel Processing Technology. 7(21):84. https://doi.org/10.3389/fenrg.2019.00084.
DOI: https://doi.org/10.3389/fenrg.2019.00084

Interpretive Summary: California produces 80 % of the world’s almonds which results in 1 billion pounds of shells per year as an agricultural waste. At present, almond shells have limited applications and are often landfilled. Gasification of almond shells is one technology that can generate biomass power and reduce lifecycle carbon impacts of almond production. Labscale experiments were performed to characterize the products from almond shell gasification. The results of these findings could extend the commercial value of almond shells and increase the diversity of biomass sources for renewable electricity generation.

Technical Abstract: Gasification experiments were performed to characterize the gasification products of almond residues including hulls, shells, and woody sticks removed in nut processing operations and to determine the effect of gasifying media on bed agglomeration. Agglomeration in the reactor bed due to reactions between the flue gas and the bed medium was significantly worse under air gasification than under steam gasification. The higher heating value during air gasification of almond biomass ranged from 4–6 MJ kg-3, whereas gas concentrations ranged from 14%–18% H2, 3–4% CH4, 43– 50% N2, 16 – 19% CO, and 16 –17% CO2. For steam gasification, higher heating value was 10–12 MJ kg-3 and gas concentrations were 35–40% H2, 5 – 7% CH4, 17 – 21% N2, 18 – 21% CO, and 16 – 18% CO2. The high level of potassium in the almond shells led to strong corrosion of the bed material due to flue gas transport of potassium compounds. As a result of long duration and elevated temperature approaching 1000 oC, potassium together with silica are mainly transported as aerosol melt particles that form an adhesive resulting in enhanced agglomeration.