Special Issue "Hydrothermal Technology in Biomass Utilization & Conversion"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Bio-Energy".

Deadline for manuscript submissions: closed (29 April 2019).

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A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. David Chiaramonti
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Guest Editor
ReCord – Renewable Energy Consortium for Research and Demonstration and Department of Industrial Engineering of the University of Florence, Viale Morgagni 40, Florence, Italy
Interests: hydrothermal carbonization and liquefaction; pyrolysis; biocrude upgrading; biochar and biochar-derived products chararacterization and use; bio and thermochemical process integration; biofuels and biopoducts
Special Issues and Collections in MDPI journals
Prof. Dr. Andrea Kruse
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Co-Guest Editor
Institute of Agricultural Engineering, Conversion Technologies of Biobased Resources, Universität Hohenheim / University of Hohenheim, Stuttgart, Germany
Interests: hydrothermal carbonization; carbon materials; platform-chemicals from biomass; nutrient recovery; hydrothermal conversion; hydrothermal liquefaction; hydrothermal gasification; hydrothermal pretreatment
Special Issues and Collections in MDPI journals
Dr. Ing. Marco Klemm
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Co-Guest Editor
DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH, Leipzig, Germany
Interests: hydrothermal processes for solid and liquid products for different applications (e.g. solid fuel, carbon materials, liquid fuels, chemicals); balance, technical assessment and optimization of hydrothermal process; implementation of hydrothermal processes in provision chains; assessment of feedstock concerning application in hydrothermal processes
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

The possibility of converting biomass into fuels and products through wet processes is becoming more and more attractive, as new feedstock and applications are appearing on the scene of bioeconomy and bioenergy. Hydrothermal processing of various type of biomass, waste and residues thus rised the interest of many researchers and companies around the world, together with downstream upgrading processes and technologies: solid products as biochar, for instance, or liquid ones as crude bioliquids, are finding new market opportunities in circular economy schemes. The Special Issue aims at collecting recent innovative research works in the field, from basic to applied research, as well as pilot industrial applications/demo. The outcome will constitute a valuable set of references for those investing time and effort in research in the field.

Prof. Ing. David Chiaramonti
Prof. Dr. Andrea Kruse
Dr. Ing. Marco Klemm
Guest Editors

Manuscript Submission Information

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Keywords

  • Hydrothermal Processing
  • Liquefaction
  • Carbonisation
  • Biochar
  • Biofuels
  • Bioproducts
  • Biochemicals

Published Papers (9 papers)

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Research

Open AccessArticle
Extraction Behavior of Different Conditioned S. Rubescens
Energies 2019, 12(7), 1336; https://doi.org/10.3390/en12071336 - 08 Apr 2019
Cited by 1
Abstract
Microalgae utilized for experiments are often not produced by the researchers that are doing experiments with them. The microalgae are made storable through thermal or freeze-drying by the producer. In an industrial scaled process, because of efficiency reasons, microalgae would not be dried, [...] Read more.
Microalgae utilized for experiments are often not produced by the researchers that are doing experiments with them. The microalgae are made storable through thermal or freeze-drying by the producer. In an industrial scaled process, because of efficiency reasons, microalgae would not be dried, but processed directly. With that, the question is, if drying already could change the composition or structure that much, that a process scaled up from laboratory to productive scale with fresh microalgae would be less efficient or even would not work at all. The effect of freeze drying on the extraction behavior for the species Scenedesmus rubescens was investigated. It was obtained in freeze-dried condition and again was delivered in fresh state. The utilized microalgae were extracted with n-hexane, without and with different pretreatments (acidic hydrolysis and hydrothermal carbonization) to examine the differences in the yields. In conclusion, it was demonstrated that freeze drying harms the cell wall and therefore this process already influences the quantity of extracted lipids. Depending on the harshness of the treatment process for cell wall disruption this might influence the extracted yield when the algae are not freeze-dried. The quality of the extracted lipids does not change when freeze-dried. Full article
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Open AccessArticle
Hydrothermal Carbonization of Various Paper Mill Sludges: An Observation of Solid Fuel Properties
Energies 2019, 12(5), 858; https://doi.org/10.3390/en12050858 - 05 Mar 2019
Cited by 1
Abstract
Each year the pulp and paper industries generate enormous amounts of effluent treatment sludge. The sludge is made up of various fractions including primary, secondary, deinked, fiber rejects sludge, etc. The goal of this study was to evaluate the fuel properties of the [...] Read more.
Each year the pulp and paper industries generate enormous amounts of effluent treatment sludge. The sludge is made up of various fractions including primary, secondary, deinked, fiber rejects sludge, etc. The goal of this study was to evaluate the fuel properties of the hydrochars produced from various types of paper mill sludges (PMS) at 180 °C, 220 °C, and 260 °C. The hydrochars, as well as the raw feedstocks, were characterized by means of ultimate analysis, proximate analysis, moisture, ash, lignin, sugar, and higher heating value (HHVdaf) measurements. Finally, combustion indices of selected hydrochars were evaluated and compared with bituminous coal. The results showed that HHVdaf of hydrochar produced at 260 °C varied between 11.4 MJ/kg and 31.5 MJ/kg depending on the feedstock. This implies that the fuel application of hydrochar produced from PMS depends on the quality of feedstocks rather than the hydrothermal carbonization (HTC) temperature. The combustion indices also showed that when hydrochars are co-combusted with coal, they have similar combustion indices to that of coal alone. However, based on the energy and ash contents in the produced hydrochars, Primary and Secondary Sludge (PPS2) could be a viable option for co-combustion with coal in an existing coal-fired power plant. Full article
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Open AccessArticle
Comparative Life Cycle Assessment of HTC Concepts Valorizing Sewage Sludge for Energetic and Agricultural Use
Energies 2019, 12(5), 786; https://doi.org/10.3390/en12050786 - 26 Feb 2019
Abstract
In many countries, sewage sludge is directly used for energy and agricultural purposes after dewatering or digestion and dewatering. In recent years, there has been a growing interest in additional upstream hydrothermal carbonization (HTC), which could lead to higher yields in the energetic [...] Read more.
In many countries, sewage sludge is directly used for energy and agricultural purposes after dewatering or digestion and dewatering. In recent years, there has been a growing interest in additional upstream hydrothermal carbonization (HTC), which could lead to higher yields in the energetic and agricultural use. Twelve energetic and agricultural valorization concepts of sewage sludge are defined and assessed for Germany to investigate whether the integration of HTC will have a positive effect on the greenhouse gas (GHG) emissions. The study shows that the higher expenses within the HTC process cannot be compensated by additional energy production and agricultural yields. However, the optimization of the HTC process chain through integrated sewage sludge digestion and process water recirculation leads to significant reductions in GHG emissions of the HTC concepts. Subsequently, nearly the same results can be achieved when compared to the direct energetic use of sewage sludge; in the agricultural valorization, the optimized HTC concept would be even the best concept if the direct use of sewage sludge will no longer be permitted in Germany from 2029/2032. Nevertheless, the agricultural valorization concepts are not generally advantageous when compared to the energetic valorization concepts, as it is shown for two concepts. Full article
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Open AccessArticle
Evaluating the Impacts of ACP Management on the Energy Performance of Hydrothermal Liquefaction via Nutrient Recovery
Energies 2019, 12(4), 729; https://doi.org/10.3390/en12040729 - 22 Feb 2019
Cited by 2
Abstract
Hydrothermal liquefaction (HTL) is of interest in producing liquid fuels from organic waste, but the process also creates appreciable quantities of aqueous co-product (ACP) containing high concentrations of regulated wastewater pollutants (e.g., organic carbon, nitrogen (N), and phosphorus (P)). Previous literature has not [...] Read more.
Hydrothermal liquefaction (HTL) is of interest in producing liquid fuels from organic waste, but the process also creates appreciable quantities of aqueous co-product (ACP) containing high concentrations of regulated wastewater pollutants (e.g., organic carbon, nitrogen (N), and phosphorus (P)). Previous literature has not emphasized characterization, management, or possible valorization of ACP wastewaters. This study aims to evaluate one possible approach to ACP management via recovery of valuable scarce materials. Equilibrium modeling was performed to estimate theoretical yields of struvite (MgNH4PO4·6H2O) from ACP samples arising from HTL processing of selected waste feedstocks. Experimental analyses were conducted to evaluate the accuracy of theoretical yield estimates. Adjusted yields were then incorporated into a life-cycle energy modeling framework to compute energy return on investment (EROI) for the struvite precipitation process as part of the overall HTL life-cycle. Observed struvite yields and residual P concentrations were consistent with theoretical modeling results; however, residual N concentrations were lower than model estimates because of the volatilization of ammonia gas. EROI calculations reveal that struvite recovery is a net-energy producing process, but that this benefit offers little to no improvement in EROI performance for the overall HTL life-cycle. In contrast, corresponding economic analysis suggests that struvite precipitation may be economically appealing. Full article
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Open AccessArticle
Lignocellulosic Ethanol Biorefinery: Valorization of Lignin-Rich Stream through Hydrothermal Liquefaction
Energies 2019, 12(4), 723; https://doi.org/10.3390/en12040723 - 22 Feb 2019
Cited by 5
Abstract
Hydrothermal liquefaction of lignin-rich stream from lignocellulosic ethanol production at an industrial scale was carried out in a custom-made batch test bench. Light and heavy fractions of the HTL biocrude were collected following an ad-hoc developed two-steps solvent extraction method. A full factorial [...] Read more.
Hydrothermal liquefaction of lignin-rich stream from lignocellulosic ethanol production at an industrial scale was carried out in a custom-made batch test bench. Light and heavy fractions of the HTL biocrude were collected following an ad-hoc developed two-steps solvent extraction method. A full factorial design of experiment was performed, investigating the influence of temperature, time and biomass-to-water mass ratio (B/W) on product yields, biocrude elemental composition, molecular weight and carbon balance. Total biocrude yields ranged from 39.8% to 65.7% w/w. The Temperature was the main influencing parameter as regards the distribution between the light and heavy fractions of the produced biocrude: the highest amount of heavy biocrude was recovered at 300 °C, while at 350 and 370 °C the yield of the light fraction increased, reaching 41.7% w/w at 370 °C. Instead, the B/W ratio did not have a significant effect on light and heavy biocrude yields. Feedstock carbon content was mainly recovered in the biocrude (up to 77.6% w/w). The distribution between the light and heavy fractions followed the same trend as the yields. The typical aromatic structure of the lignin-rich stream was also observed in the biocrudes, indicating that mainly hydrolysis depolymerization occurred. The weight-average molecular weight of the total biocrude was strictly related to the process temperature, decreasing from 1146 at 300 °C to 565 g mol−1 at 370 °C. Full article
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Open AccessFeature PaperArticle
Techno-Economic Assessment of Co-Hydrothermal Carbonization of a Coal-Miscanthus Blend
Energies 2019, 12(4), 630; https://doi.org/10.3390/en12040630 - 15 Feb 2019
Cited by 3
Abstract
Co-Hydrothermal Carbonization (Co-HTC) is a thermochemical process, where coal and biomass were treated simultaneously in subcritical water, resulting in bulk-homogenous hydrochar that is carbon-rich and a hydrophobic solid fuel with combustion characteristics like coal. In this study, technoeconomic analysis of Co-HTC was performed [...] Read more.
Co-Hydrothermal Carbonization (Co-HTC) is a thermochemical process, where coal and biomass were treated simultaneously in subcritical water, resulting in bulk-homogenous hydrochar that is carbon-rich and a hydrophobic solid fuel with combustion characteristics like coal. In this study, technoeconomic analysis of Co-HTC was performed for a scaled-up Co-HTC plant that produces fuel for 110 MWe coal-fired power plant using Clarion coal #4a and miscanthus as starting feedstocks. With precise mass and energy balance of the Co-HTC process, sizing of individual equipment was conducted based on various systems equations. Cost of electricity was calculated from estimated capital, manufacturing, and operating and maintenance costs. The breakeven selling price of Co-HTC hydrochar was $117 per ton for a 110 MWe. Sensitivity analysis indicates that this breakeven selling price could be as low as $106 per ton for a higher capacity plant. Besides plant size, the price of solid fuel is sensitive to the feedstock costs and hydrochar yield. Full article
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Open AccessArticle
Key Development Factors of Hydrothermal Processes in Germany by 2030: A Fuzzy Logic Analysis
Energies 2018, 11(12), 3532; https://doi.org/10.3390/en11123532 - 19 Dec 2018
Cited by 3
Abstract
To increase resource efficiency, it is necessary to use biogenic residues in the most efficient and value-enhancing manner. For high water-containing biomass, hydrothermal processes (HTP) are particularly promising as they require wet conditions for optimal processing anyway. In Germany, however, HTP have not [...] Read more.
To increase resource efficiency, it is necessary to use biogenic residues in the most efficient and value-enhancing manner. For high water-containing biomass, hydrothermal processes (HTP) are particularly promising as they require wet conditions for optimal processing anyway. In Germany, however, HTP have not yet reached the industrial level, although suitable substrates are available and technological progress has been made in previous years. This study aims to determine why this is by identifying key factors that need to occur HTP development in Germany until 2030. By using results of previous analyses within this context (i.e., literature review, SWOT analysis, expert survey, and focus group workshop) and combining them with the results of an expert workshop and Delphi-survey executed during this analysis, a comprehensive information basis on important development factors is created. Fuzzy logic is used to analyze these factors in terms of interconnections, relevance, and probability of occurrence by 2030. The results show that technological factors, such as a cost-efficient process water treatment and increased system integration of HTP into bio-waste and wastewater treatment plants, are given high relevance and probability of occurrence. The adaptation of the legal framework, for example, the approval of end products from HTP as standard fuels, has very high relevance but such adaptions are considered relatively unlikely. Full article
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Open AccessArticle
Catalytic Hydrotreatment of Microalgae Biocrude from Continuous Hydrothermal Liquefaction: Heteroatom Removal and Their Distribution in Distillation Cuts
Energies 2018, 11(12), 3360; https://doi.org/10.3390/en11123360 - 01 Dec 2018
Cited by 8
Abstract
To obtain drop-in fuel properties from 3rd generation biomass, we herein report the catalytic hydrotreatment of microalgae biocrude, produced from hydrothermal liquefaction (HTL) of Spirulina. Our contribution focuses on the effect of temperature, initial H2 pressure, and residence time on the [...] Read more.
To obtain drop-in fuel properties from 3rd generation biomass, we herein report the catalytic hydrotreatment of microalgae biocrude, produced from hydrothermal liquefaction (HTL) of Spirulina. Our contribution focuses on the effect of temperature, initial H2 pressure, and residence time on the removal of heteroatoms (O and N) in a batch hydrotreating setup. In contrast to common experimental protocols for hydrotreating at batch scale, we devised a set of two-level factorial experiments and studied the most influential parameters affecting the removal of heteroatoms. It was found that up to 350 °C, the degree of deoxygenation (de-O) is mainly driven by temperature, whereas the degree of denitrogenation (de-N) also relies on initial H2 pressure and temperature-pressure interaction. Based on this, complete deoxygenation was obtained at mild operating conditions (350 °C), reaching a concurrent 47% denitrogenation. Moreover, three optimized experiments are reported with 100% removal of oxygen. In addition, the analysis by GC-MS and Sim-Dis gives insight to the fuel quality. The distribution of heteroatom N in lower (<340 °C) and higher (>340 °C) fractional cuts is studied by a fractional distillation unit following ASTM D-1160. Final results show that 63–68% of nitrogen is concentrated in higher fractional cuts. Full article
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Open AccessArticle
Hydrothermal Carbonization Brewer’s Spent Grains with the Focus on Improving the Degradation of the Feedstock
Energies 2018, 11(11), 3226; https://doi.org/10.3390/en11113226 - 21 Nov 2018
Cited by 13
Abstract
Hydrochar is a very interesting product from agricultural and food production residues. Unfortunately, severe conditions for complete conversion of lignocellulosic biomass is necessary, especially compared to the conversion of sugar compounds. The goal of this work is to improve the conversion of internal [...] Read more.
Hydrochar is a very interesting product from agricultural and food production residues. Unfortunately, severe conditions for complete conversion of lignocellulosic biomass is necessary, especially compared to the conversion of sugar compounds. The goal of this work is to improve the conversion of internal carbohydrates by application of a two-steps process, by acid addition and slightly higher water content. A set of experiments at different temperatures (180, 200, and 220 °C), reaction times (2 and 4 h), and moisture contents (80% and 90%) was performed to characterize the solid (high heating value (HHV), elemental) and liquid product phase. Afterwards, acid addition for a catalyzed hydrolysis reaction during hydrothermal carbonization (HTC) and a two-steps reaction (180 and 220 °C) were tested. As expected, a higher temperature leads to higher C content of the hydrochar and a higher fixed carbon (FC) content. The same effect was found with the addition of acids at lower temperatures. In the two-steps reaction, a primary hydrolysis step increases the conversion of internal carbohydrates. Higher water content has no significant effect, except for increasing the solubility of ash components. Full article
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