Abstract
Hydrothermal carbonization (HTC) is a promising thermochemical pre-treatment to convert waste biomass into solid biofuels. However, the process yields large amounts of organic process water (PW), which must be properly disposed of or reused. In this study, the PW produced from the hydrothermal carbonization of lemon peel waste (LP) was recycled into HTC process of LP with the aim of maximize energy recovery from the aqueous phase while saving water resources and mitigating the overall environmental impact of the process. The effects of HTC temperature on the properties of solid and liquid products were investigated during PW recirculation. Experiments were carried out at three different operating temperatures (180, 220, 250 °C), fixed residence times of 60 min, and solid to liquid load of 20 wt%, on a dry basis. Hydrochars were characterized in terms of proximate analysis and higher heating values while liquid phases were analyzed in terms of pH and total organic carbon content (TOC). PW recirculation led to a solid mass yield increase and the effect was more pronounced at lower HTC temperature. The increase of solid mass yield, after recirculation steps (maximum increase of about 6% at 180 °C), also led to a significant energy yield enhancement. Results showed that PW recirculation is a viable strategy for a reduction of water consumption and further carbon recovery; moreover preliminary results encourage for an in-depth analysis of the effects of the PW recirculation for different biomasses and at various operating conditions.
Highlights
Published: 3 March 2021The rising world energy demand together with the decrease in the fossil fuels reservoirs threaten environmental sustainability and push the research for reliable and renewable resources.Biomass exploitation represents one of the most common form producing renewable energy
As reported in literature, only a small amount of cellulose has been degraded at 220 ◦ C [52], the increase in gas yield was due to decarboxylation of organic acids derived from hemicellulose hydrolysis and dehydration
This work described the effects of process water recirculation on solid and liquid products obtained after Hydrothermal carbonization (HTC) tests carried out at temperatures of 180, 220, and 250 ◦ C using dried lemon peel waste as starting material
Summary
Biomass exploitation represents one of the most common form producing renewable energy. Waste biomass in particular is widely available in large amounts at low cost and represents a carbon-neutral and programmable resource for the production of energy dense biofuels and valuable carbonaceous materials for several other applications [1]. In the last decades thermochemical upgrading of waste biomass has been largely investigated to yield high energy dense biofuels. Dry thermochemical treatments like torrefaction [3,4,5], pyrolysis [6,7], and gasification [8,9,10] have been used to produce solid, liquid, and gaseous bio-fuels, respectively. The high moisture content (typically higher than 50%), commonly found in waste biomass, deeply affects energy efficiency of dry thermochemical technologies conversion.
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