Air and Steam Gasification of Almond Biomass

Zach Mccaffrey,William Orts,Bryan M Jenkins,Lennard Torres,Li Wang,Turkan Aktas,Peter Thy,Melina Oliveira,Bor-Sen Chiou,Michael Long

doi:10.3389/fenrg.2019.00084

Abstract

Experiments were performed to characterize the gasification products of almond shells 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.

Highlights

Almond processing residues constitute a significant resource for small to medium scale integrated power generation systems in California and elsewhere around the world
The results showed that for smaller particle sizes, differences in product yield, and gas composition practically disappeared at the higher temperature trials
Gasification experiments were conducted with four almond byproduct samples from four different geographic locations in California (S2, S4, S5, and S7) using two gasifying agents of air and steam

Summary

Introduction

Almond processing residues constitute a significant resource for small to medium scale integrated power generation systems in California and elsewhere around the world. These systems can help meet process energy needs and reduce lifecycle carbon impacts of almond production. The Central Valley of California is one of the most productive agricultural regions in the world with an almond production in 2018 of 5.6 billion dollars in value (Almond Board of California, 2018). With ∼6,800 growers, California produces 80% of the world’s almonds and effectively all the U.S commercial supply (Almond Board of California, 2018). In 2013, almond hull and hull and shell blends were sold for 311 million dollars, primarily as animal feed (Almond Hullers and Processors Association (AHPA), 2014). Interest has increased in using almond by-products at higher efficiency or in more local cogeneration energy facilities (e.g., at huller and/or sheller facilities) to support state level renewable portfolio standards

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