Integration of Air Classification and Hydrothermal Carbonization to Enhance Energy Recovery of Corn Stover

Abstract

Air classification (AC) is a cost-effective technology that separates the energy-dense light ash fraction (LAF) from the inorganic-rich high ash fraction (HAF) of corn stover. HAF could be upgraded into energy-dense solid fuel by hydrothermal carbonization (HTC). However, HTC is a high-temperature, high-pressure process, which requires additional energy to operate. In this study, three different scenarios (i.e., AC only, HTC only, and integrated AC–HTC) were investigated for the energy recovery of corn stover. AC was performed on corn stover at an 8 Hz fan speed, which yielded 84.4 wt. % LAF, 12.8 wt. % HAF, and 2.8 wt. % below screen particles. About 27 wt. % ash was reduced from LAF by the AC process. Furthermore, HTC was performed on raw corn stover and the HAF of corn stover at 200, 230, and 260 °C for 30 min. To evaluate energy recovery, solid products were characterized in terms of mass yield, ash yield, ultimate analysis, proximate analyses, and higher heating value (HHV). The results showed that the energy density was increased with the increase in HTC temperature, meanwhile the mass yield and ash yield were decreased with the increase in HTC temperature. Proximate analysis showed that fixed carbon increased 18 wt. % for original char and 27 wt. % for HAF char at 260 °C, compared to their respective feedstocks. Finally, the hydrochar resulting from HAF was mixed with LAF and pelletized at 180 bar and 90 °C to densify the energy content. An energy balance of the integrated AC–HTC process was performed, and the results shows that integrated AC with HTC performed at 230 °C resulted in an additional 800 MJ/ton of energy recovery compared to the AC-only scenario.

Pretreatment of Biomass by Selected Type-III Deep Eutectic Solvents and Evaluation of the Pretreatment Effects on Hydrothermal Carbonization

“…The experimental procedure was followed from previously published literature. 28 In short, 20 g of dry biomass was mixed with 200 mL of deionized (DI) water, and the slurry was poured into the reactor. The reactor was sealed, and the content was heated to the desired HTC temperature with constant stirring (∼150 rpm) and autogenous pressure.…”

“…HTC was carried out in a 300 mL Parr reactor (Moline, IL) for 30 min at 180, 220, and 260 °C for raw pine and DES pretreated pine. The experimental procedure was followed from previously published literature . In short, 20 g of dry biomass was mixed with 200 mL of deionized (DI) water, and the slurry was poured into the reactor.…”

“…The TGA was carried out under inert atmosphere using a constant flow rate (40 mL/min) of nitrogen to avoid any possible oxidation and continuously purge the VM. A detailed procedure can be found in our previous article . In short, the sample was first heated to 105 °C and kept isothermal for 5 min to determine the moisture content (MC).…”

“…A detailed procedure can be found in our previous article. 28 In short, the sample was first heated to 105 °C and kept isothermal for 5 min to determine the moisture content (MC). The sample was then heated to 900 °C at a ramp rate of 20 °C/min and kept isothermal for 5 min.…”

“…The experimental procedure can be found in our earlier publication. 28 2.4.6. Van Soest Fiber Analysis.…”