Hydrothermal carbonization: Fate of inorganics
TL;DR: In this article, a pretreatment process for making a homogenized, carbon rich, and energy-dense solid fuel, called biochar, from lignocellulosic biomass is described.
Abstract: Hydrothermal carbonization (HTC) is a pretreatment process for making a homogenized, carbon rich, and energy-dense solid fuel, called biochar, from lignocellulosic biomass. Corn stover, miscanthus, switch grass, and rice hulls were treated with hot compressed water at 200, 230, and 260 °C for 5 min. Mass yield is as low as 41% of the raw biomass, and decreases with increasing HTC temperature. Higher heating values (HHV) increase up to 55% with HTC pretreatment temperature. Up to 90% of calcium, magnesium, sulfur, phosphorus, and potassium were removed with HTC treatment possibly due to hemicellulose removal. At a HTC temperature of 260 °C, some structural Si was removed. All heavy metals were reduced by HTC treatment. The slagging and fouling indices are reduced with HTC treatment relative to that of untreated biomass. Chlorine content, a concern only for raw and HTC 200 switch grass, was reduced to a low slagging range at 230 °C, and 260 °C. Alkali index was medium for raw biomass but decreased by HTC.
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TL;DR: An overview of biochar production technologies, biochar properties, and recent advances in the removal of heavy metals, organic pollutants and other inorganic pollutants using biochar is provided.
1,301 citations
Cites background from "Hydrothermal carbonization: Fate of..."
...Most studies about HTC were concerned with its use for making energy-dense solid fuel from lignocellulosic biomass (Liu et al., 2013; Reza et al., 2013; Yan et al., 2014)....
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TL;DR: In this paper, an updated review on the fundamentals and reaction mechanisms of the slow-pyrolysis and hydrothermal carbonization (HTC) processes, identifies research gaps, and summarizes the physicochemical characteristics of chars for different applications in the industry.
Abstract: Slow-pyrolysis of biomass for the production of biochar, a stable carbon-rich solid by-product, has gained considerable interest due to its proven role and application in the multidisciplinary areas of science and engineering. An alternative to slow-pyrolysis is a relatively new process called hydrothermal carbonization (HTC) of biomass, where the biomass is treated with hot compressed water instead of drying, has shown promising results. The HTC process offers several advantages over conventional dry-thermal pre-treatments like slow-pyrolysis in terms of improvements in the process performances and economic efficiency, especially its ability to process wet feedstock without pre-drying requirement. Char produced from both the processes exhibits significantly different physiochemical properties that affect their potential applications, which includes but is not limited to carbon sequestration, soil amelioration, bioenergy production, and wastewater pollution remediation. This paper provides an updated review on the fundamentals and reaction mechanisms of the slow-pyrolysis and HTC processes, identifies research gaps, and summarizes the physicochemical characteristics of chars for different applications in the industry. The literature reviewed in this study suggests that hydrochar (HTC char) is a valuable resource and is superior to biochar in certain ways. For example, it contains a reduced alkali and alkaline earth and heavy metal content, and an increased higher heating value compared to the biochar produced at the same operating process temperature. However, its effective utilization would require further experimental research and investigations in terms of feeding of biomass against pressure; effects and relationships among feedstocks compositions, hydrochar characteristics and process conditions; advancement in the production technique(s) for improvement in the physicochemical behavior of hydrochar; and development of a diverse range of processing options to produce hydrochar with characteristics required for various industry applications.
1,061 citations
TL;DR: In this article, mild hydrothermal (HT) conversion processes are used to produce clean solid biofuel from high moisture content waste biomass (bio-waste) with high nitrogen (N)/chlorine (Cl) content.
315 citations
TL;DR: In this article, the feasibility of two different thermal pre-treatments, torrefaction and hydrothermal carbonization (HTC), followed by densification, was evaluated in terms of the strength, storage, and combustion properties for energy applications.
299 citations
TL;DR: In this article, a comprehensive overview of recent research and development activities in the field with focus on improvements in the chemical, physical and fuel properties of the solid product after wet torrefaction is provided.
Abstract: Biomass pretreatment is an essential step prior to several thermochemical conversion processes. Wet torrefaction, a biomass pretreatment method in hydrothermal media or hot compressed water at temperatures within 180–260 °C, has been receiving a lot of attention because it possesses some advantages over other pretreatment methods. Apart from the undoubted benefits of upgrading biomass fuels to closer to coal properties, wet torrefaction has the capacity to work with wet or even extremely wet biomasses and enhance the ash removal from the biomass. The technology has recently attracted great interest from both academic groups and industrial companies. This review aims at providing a comprehensive overview of recent research and development activities in the field with focus on improvements in the chemical, physical and fuel properties of the solid product after wet torrefaction. Moreover, a brief introduction to dry torrefaction, a more conventional thermal pretreatment of biomass in the absence of oxygen under atmospheric pressure and in a temperature range of 200–300 °C, is also given and compared with wet torrefaction. Main differences in the properties of the solid products from the two torrefaction methods are also discussed.
289 citations
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TL;DR: A molecular-level assessment of the physical organization and chemical complexity of biomass-derived chars and, specifically, that of aromatic carbon in char structures suggests the existence of four distinct categories of char consisting of a unique mixture of chemical phases and physical states.
Abstract: Char black carbon (BC), the solid residue of incomplete combustion, is continuously being added to soils and sediments due to natural vegetation fires, anthropogenic pollution, and new strategies for carbon sequestration (“biochar”). Here we present a molecular-level assessment of the physical organization and chemical complexity of biomass-derived chars and, specifically, that of aromatic carbon in char structures. Brunauer−Emmett−Teller (BET)−N2 surface area (SA), X-ray diffraction (XRD), synchrotron-based near-edge X-ray absorption fine structure (NEXAFS), and Fourier transform infrared (FT-IR) spectroscopy are used to show how two plant materials (wood and grass) undergo analogous but quantitatively different physical−chemical transitions as charring temperature increases from 100 to 700 °C. These changes suggest the existence of four distinct categories of char consisting of a unique mixture of chemical phases and physical states: (i) in transition chars, the crystalline character of the precursor ma...
2,283 citations
TL;DR: Several biomass hydrothermal conversion processes are in development or demonstration as mentioned in this paper, which are generally lower temperature (200-400 °C) reactions which produce liquid products, often called bio-oil or bio-crude.
Abstract: Hydrothermal technologies are broadly defined as chemical and physical transformations in high-temperature (200–600 °C), high-pressure (5–40 MPa) liquid or supercritical water. This thermochemical means of reforming biomass may have energetic advantages, since, when water is heated at high pressures a phase change to steam is avoided which avoids large enthalpic energy penalties. Biological chemicals undergo a range of reactions, including dehydration and decarboxylation reactions, which are influenced by the temperature, pressure, concentration, and presence of homogeneous or heterogeneous catalysts. Several biomass hydrothermal conversion processes are in development or demonstration. Liquefaction processes are generally lower temperature (200–400 °C) reactions which produce liquid products, often called “bio-oil” or “bio-crude”. Gasification processes generally take place at higher temperatures (400–700 °C) and can produce methane or hydrogen gases in high yields.
1,822 citations
TL;DR: In this paper, a review of the properties of biomass relevant to combustion is briefly reviewed and the compositions of biomass among fuel types are variable, especially with respect to inorganic constituents important to the critical problems of fouling and slagging.
1,764 citations
TL;DR: In this article, a review summarizes knowledge about the chemical nature of this process from a process design point of view, including reaction mechanisms of hydrolysis, dehydration, decarboxylation, aromatization, and condensation polymerization.
Abstract: Hydrothermal carbonization can be defined as combined dehydration and decarboxy lation of a fuel to raise its carbon content with the aim of achieving a higher calorific value. It is realized by applying elevated temperatures (180–220°C) to biomass in a suspension with water under saturated pressure for several hours. With this conversion process, a lignite-like, easy to handle fuel with well-defined properties can be created from biomass residues, even with high moisture content. Thus it may contribute to a wider application of biomass for energetic purposes. Although hydrothermal carbonization has been known for nearly a century, it has received little attention in current biomass conversion research. This review summarizes knowledge about the chemical nature of this process from a process design point of view. Reaction mechanisms of hydrolysis, dehydration, decarboxylation, aromatization, and condensation polymerization are discussed and evaluated to describe important operational parameters qualitatively. The results are used to derive fundamental process design improvements. Copyright © 2010 Society of Chemical Industry and John Wiley & Sons, Ltd
1,428 citations
01 Jan 2011
TL;DR: The wet pyrolysis process, also known as hydrothermal carbonization, opens up the field of potential feedstocks for char production to a range of nontraditional renewable and plentiful wet agricultural residues and municipal wastes as discussed by the authors.
Abstract: The carbonization of biomass residuals to char has strong potential to become an environmentally sound conversion process for the production of a wide variety of products. In addition to its traditional use for the production of charcoal and other energy vectors, pyrolysis can produce products for environmental, catalytic, electronic and agricultural applications. As an alternative to dry pyrolysis, the wet pyrolysis process, also known as hydrothermal carbonization, opens up the field of potential feedstocks for char production to a range of nontraditional renewable and plentiful wet agricultural residues and municipal wastes. Its chemistry offers huge potential to influence product characteristics on demand, and produce designer carbon materials. Future uses of these hydrochars may range from innovative materials to soil amelioration, nutrient conservation via intelligent waste stream management and the increase of carbon stock in degraded soils.
1,360 citations