Process Water from the Hydrothermal Carbonization of Biomass: A Waste or a Valuable Product?
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Hydrothermal carbonization (HTC) is a promising method for the production of energy dense coal-like material from low quality lignocellulosic biomass. The process takes place in the presence of water and therefore is unaffected by feedstocks containing a high moisture content. However, the substantial water requirement and disposal concerns for a large scale HTC plant may outweigh its advantages from an economical and environmental point of view. The work presented in this study proposes a solution to the aforementioned problem. Miscanthus feedstock was treated hydrothermally at three different reaction temperatures (190, 225, and 260 °C) for 5 min with a solid load ratio of 1:6. The liquid by-product from each experiment was characterized for chemical composition. The results show that the HTC process water was rich in organic acids (acetic, formic, levulinic, and glycolic acid), Hydroxy-methyl-furfural (HMF), and total organic carbon (TOC). The acidity and the concentration of intermediate products in the HTC process water increased with an increase in reaction temperature. The HTC process water produced at 260 °C was examined for the recirculation of process water. The results show that, during successive recirculation of HTC process water, the mass yield of the hydrochar samples increases by 5–10% and the energy yield of the hydrochar samples increased up to 15% compared to the HTC-reference sample (hydrochar sample produced at initial run). Most importantly, the HHV of hydrochars increased from 18.9 (raw biomass) to 26.6 MJ/kg (maximal value) during recirculation of process water. As a result, the recirculation of process water can increase the overall system’s efficiency and reduce both the operating costs and environmental impact of a commercial HTC plant.
KeywordsHydrothermal carbonization Organic acids Recirculation Process water
The authors would like to gratefully acknowledge research grants from Natural Sciences and Engineering Research Council of Canada (NSERC, Grant No. 400495), and Ministry of the Environment for Best in Science program (Project #1314010).
- 5.Libra, J.A., Ro, K.S., Kammann, C., Funke, A., Berge, N.D., Neubauer, Y., Titirici, M.-M., Fühner, C., Bens, O., Kern, J.: Hydrothermal carbonization of biomass residuals: a comparative review of the chemistry, processes and applications of wet and dry pyrolysis. Biofuels 2(1), 71–106 (2011)CrossRefGoogle Scholar
- 12.Kambo, H., Dutta, A.: Hydrothermal carbonization (HTC): An innovative process for the conversion of low quality lignocellulosic biomass to hydrochar for replacing coal. In: Proceedings of the 9th Annual Green Energy Conference (IGEC-IX) Tianjin, China May 25–28 (2014)Google Scholar
- 14.Wirth, B., Mumme, J.: Anaerobic digestion of waste water from hydrothermal carbonization of corn silage. Appl. Bioenerg. 1, 1–10 (2013)Google Scholar
- 19.Uddin, M.H., Reza, M.T., Lynam, J.G., Coronella, C.J.: Effects of water recycling in hydrothermal carbonization of loblolly pine. Environ. Prog. Sustain. Energy. 33(4), 1309–1315 (2014)Google Scholar
- 27.Kambo, H.: Energy densification of lignocellulosic biomass via hydrothermal carbonization and torrefaction. MASc. Thesis, University of Guelph, Ontario (2014)Google Scholar
- 28.Uddin, M.H., Reza, M.T., Lynam, J.G., Coronella, C.J.: Effects of water recycling in hydrothermal carbonization of loblolly pine. Environ. Prog. Sustain. Energy (2013)Google Scholar
- 31.van der Stelt, M.J.C., Gerhauser, H., Kiel, J.H.A., Ptasinski, K.J.: Biomass upgrading by torrefaction for the production of biofuels: a review. Biomass Bioenerg. 35(9), 3748–3762 (2011)Google Scholar