Strategies to improve swine manure hydrochar: HCl-assisted hydrothermal carbonization versus hydrochar washing

Abstract

The work focuses on the study of hydrochar upgrading from hydrothermal carbonization (HTC) of swine manure by HCl-assisted HTC or washing with HCl or acetone, as a post-treatment to conventional HTC. Conventional HTC of swine manure yields a low-quality hydrochar (C content ~ 38 wt.%, higher heating value (HHV) ~ 15 MJ kg−1, and ash content up to 32 wt.%). HCl-assisted HTC (0.5 M HCl at 230 ℃) substantially reduced the ash content up to ~10 wt.% in the hydrochar and increased the C content to 58 wt.%, reaching a HHV of 23 MJ kg−1. However, the N and S contents remained at values similar to those of the swine manure. Washing post-treatment of conventional hydrochars with HCl or acetone significantly improved the C content and the HHV in the range 47–58 wt.% and 19–25 MJ kg−1, respectively, as well as the ash removal with values 7-11 wt.%. Washing the hydrochar with acetone significantly reduced the N and S contents, obtaining a carbonaceous material with properties suitable for solid biofuel according to ISO/TS 17225–8, (N < 3 wt.%; S < 0.15 wt.%; HHV > 17 MJ kg−1; and ash < 10 wt.%). Hydrochars obtained by HCl-assisted HTC and HCl/acetone washing post-treatment yielded higher thermal stability, as well as better reactivity and low ash agglomeration indexes than compared to conventional hydrochars. Washing post-treatment with acetone proved to be the best strategy to obtain improved hydrochars from swine manure for industrial use as a solid biofuel.

Energy Recovery from Garden and Park Waste by Hydrothermal Carbonization with Process Water Recycling

“…On the contrary, recycling of process water favors higher ash, N, S, nutrients, and volatile matter (VM) contents of the hydrochar, , which could reduce its potential interest as biofuel. Well-known problems associated with those features are ash sintering, causing fouling and slagging in boilers, NO X and SO 2 formation during combustion, as well as corrosion problems . High VM content can lead to rapid consumption of the solid material, incomplete combustion, and explosion risks .…”