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The work evaluates the energy recovery from hydrothermal carbonization (HTC) of cow manure through the thermal analysis of hydrochar and the anaerobic digestion (AD) of the process water (PW). The increase of the HTC temperature in the range of 170–230 °C improved solid-fuel properties (higher heating value (16.4–20.1 MJ kg−1), fuel ratio (0.19–0.33)) of dairy manure, but less energy can be recovered by its combustion ascribing to reduction of hydrochar yield (65.0–54.0%). Fixed carbon content (12.5–18.7%), and ignition (263–278 °C) and burnout (581–619 °C) temperatures increased with carbonization temperature, thereby reducing risks of fire and explosion. However, the highest value of the comprehensive combustion index, related with good fuel characteristics, was obtained for the hydrochar carbonized at 170 °C. The high organic matter content of the PW allows energy recovery by AD, obtaining the highest methane yield for the PW generated at 170 °C (294 ± 2 mL STP CH4 g−1 VS added). HTC led to higher energy recovery than conventional AD of dairy manure (4.1 MJ kg−1). The energy recovery by AD combined with the energy content of the hydrochar (13.7 MJ kg−1 feedstock for HTC conditions below 200 °C) accounted around 85% of the total energy content of feedstock, allowing a potential valorization route for dairy manure.

This work evaluates the nutrient (phosphorus and nitrogen) recovery from cow manure by hydrothermal carbonization (HTC). A series of experiments were conducted to evaluate the effects of reaction t...

Torrefaction is a promising technology to improve fuel properties of biomass. However, torrefied char does not show densified energy content compared with coal and typically requires densification such as pelletization. Several key parameters including pelletization and torrefaction conditions were investigated in order to determine the effects on energy density of torrefied char pellets. In this study, multivariate analyses were performed using three independent variables, torrefaction temperature, pelletization temperature, and pelletization pressure; and five dependent variables: mass density, durability, volume expansion, higher heating value (HHV), and energy density (ED). The variation and correlation of the dependent variables were evaluated using principal component analysis (PCA). Additionally, multivariate linear regression was performed to correlate independent variables and dependent variable responses using an adjusted sum of squares method and a two-sided, 90% confidence interval for the mean response; the model was fitted with statistically significant linear, quadratic, and interaction terms. The statistical analysis showed that all independent parameters are statistically significant for ED with the largest model variation from experimental data being 1.44%. Response curve of the regression analysis showed that mass density, HHV, and energy density model have the highest output predictability with higher R2 values of 95.3%, 98.1%, and 74.1%, respectively.

Water hyacinth hydrothermal carbonization was studied under different temperature (160–250 C), time (30–120 min) and biomass/water ratio (10–50%) conditions. The research was designed following response surface methodology, which was very useful to infer interactions between variables and to develop models predicting the system behaviour with good accuracy. Output functions were solid yield, hydrochar C and N content, as well as their captures, and heating value. It was found that while temperature was the most influential variable promoting HTC reactions, time and even biomass load were decisive to provide particular C and N captures; based on these results, reaction mechanisms were discussed. On the other hand, 2D graphs allowed to build different scenarios in which target properties might be achieved under a wide range of dissimilar conditions, leading to process optimization. The study was complemented by exploring hydrochar surface properties by N2 adsorption at 77 K, SEM micrography and XPS analyses.

Grindelia squarrosa biocrude is a promising feedstock for producing high-density cycloalkane fuels for high-performance aircraft due to the branched tricyclic nature of its primary diterpenoid component, grindelic acid. Herein we designed a novel biphasic tandem catalytic process (biTCP) for the conversion of Grindelia squarrosa biocrude into high-density aviation fuels with a superior carbon atom efficiency. The systematic experimental studies provided valuable insights into the effects of process conditions. The detailed speciation was carried out with the complementary chemical analysis techniques. Under the optimum conditions, a ∼90% carbon yield of aviation fuel components was produced from the Grindelia squarrosa biocrude. Multistep tandem reactions, including cyclic ether ring opening, dehydration, hydrogenation, and decarboxylation were carried out in the “one-pot” biTCP. The detailed catalytic reaction mechanism is discussed. A continuous process was designed integrating the extraction of biocrud...

Numerical simulations of gas–solid fluidized beds based on the kinetic theory of granular flow exhibit a significant dependence on domain discretization. Bubble formation, bubble size and shape all vary greatly with the discretization, and the use of an inappropriate scale resolution leads to inaccurate predictions of fluidization hydrodynamics. In this study, grid-independent solutions of the two fluid model were examined by comparing the bed expansions obtained from numerical simulations with experimental results and empirical predictions, based on bubbling fluidized beds of Geldart B particles. Grid independence was achieved with a grid resolution equal to 18 times the particle diameter. The simulation results were compared with previously published data for verification purposes. The results of this work should provide a guideline for choosing the appropriate grid size and thereby minimize the time and expense associated with large simulations.

The transient behavior of rising bubbles plays a critical role on the performance of fluidized bed reactors, but predicting bubble dynamics is difficult. CFD has been shown to be capable of reproducing bubbling phenomena, but data interpretation and visualization is challenging. In this study, a 3-D detection and tracking algorithm, called face-masking, is developed and validated by numerical simulations of lab-scale and pilot-scale gas–solid fluidized beds. This algorithm identifies discrete bubbles using the instantaneous whole-field void fraction data. Individual bubbles are characterized in detail, including size, shape and location. The algorithm tracks bubbles across successive time frames and computes axial and lateral bubble velocities. Bubble dynamics predicted by the face-masking algorithm are validated against four different published experimental measurements. The face-masking algorithm provides a new tool for post-processing large-scale three-dimensional fluidizedbed simulation data. The bubble surfaces found by this algorithm will enable computation of normal fluxes through the surface. This algorithm can also be applicable in other areas of multiphase flows where characterization of bubbles, droplets, and clusters is necessary.

Gumweed (Grindelia squarrosa) has potential as a biofuel/biomaterial crop in arid lands. Two years of biomass production data at University of Nevada, Reno (UNR) field plots varied from 6700 kg/ha up to 14 900 kg/ha with an average of 9950 kg/ha. Gumweed was planted in 4 m × 4 m plots at spacings of 15, 20, 25, 30, and 37 cm with three replications each. Acetone extraction of the ground, dried biomass yielded about 12.5% extractable hydrocarbons, called biocrude or crude resin. Approximately 52% of the biocrude extract consists of the C20 diterpene acid grindelic acid, which is also approximately 6.5% of the dried plant biomass. Additional carboxylic acids bring the total carboxylic acid fraction to approximately 68% of the biocrude. Also found in the biocrude is approximately 4.7% monoterpenes, including pinene, limonene, germacrene, elemene, and camphene. Acid-catalyzed methylation of the biocrude followed by hexane extraction and removal of the hexane and remaining methanol produced an approximately 72...

In this study, the autoclaved organic fraction of municipal solid waste pulp (OFMSW) and the digestate from OFMSW pulp after anaerobic digestion (AD) were processed by hydrothermal carbonization (HTC) at 200, 250, and 300 °C for 30 min and 2 h. The focus of this work was to evaluate the potential for producing an energy-dense solid hydrochar from either OFMSW or digestate by HTC. The fate of inorganics, especially the heavy metals in hydrochar is discussed. In addition, the aqueous products were analyzed to identify the chemicals produced and the chemical changes during HTC. A carbon balance was performed from the solid and liquid phase analyses. Moreover, two conceptual MSW treatments consisting of autoclaving with or without AD, but including HTC, were proposed and mass and energy balances were performed. From the proximate, ultimate, FTIR, and fiber analyses, the hydrochar becomes increasingly energy and inorganic dense with the increase of HTC temperature.

As a green, low-pressure pretreatment for biomass, ionic liquids (ILs) have great potential, but their high cost has limited commercial application to date. Glycerol, a safe byproduct of the growing biodiesel industry, was investigated as an IL cosolvent. In this study, the ILs 1-ethyl-3-methylimidazolium formate ([C2mim][O2CH]) and 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) were diluted with up to 75% glycerol and used to pretreat corn stover (CS) at 145 °C and ambient pressure. The pretreated CS residues were enzymatically hydrolyzed, yielding over 90% of the cellulose in the raw CS as glucose and 80% of the xylan as xylose. These mixture pretreatments gave yields 40% higher than the pure IL pretreatments. Fourier transform infrared spectroscopy indicated that lignin had been removed by the glycerol–IL pretreatments. Compared to the ILs used, glycerol’s viscosity was an order of magnitude higher at ambient temperature, but at the processing temperature used the viscosities of the ILs and their m...

Hydrothermal carbonization (HTC) is a promising thermochemical treatment of wet biomass. The byproduct HTC process liquid often contains a very high total organic carbon (TOC). Various toxic organic compounds (e.g., phenol, furfural, 5-HMF, etc.) can be found in HTC process liquid. As a result, the HTC process liquid often requires further treatment prior to discharge into the environment. In this study, wet air oxidation (WAO) is applied to process liquid produced from HTC of dairy manure and wastewater biosolids. Different oxygen loadings (25 and 50 atm partial pressure) were charged for WAO at 260 °C for 30 min. Furthermore, the oxidation capability of copper oxide (CuO) was evaluated at the same temperature and time. In all cases, the resulting liquid product was clear and has reduced TOC. With an increase in oxygen partial pressure, TOC is reduced up to 60% compared to the control run and 74% compared to the original HTC process liquid. The primary products in the WAO liquid product are short chain o...

In this study, cow manure was hydrothermally carbonized (HTC) at 180°C–260°C for 5 and 30 min. Mass and elemental (carbon and nitrogen) balances were performed for each HTC reaction condition. Fuel, fertilizer, and nutrient recovery potential of HTC products are evaluated and discussed. In terms of mass loss, dehydration, and energy densification, cow manure is shown to be relatively less reactive than lignocellulosic biomass in HTC. Ash-free HHV for hydrochar increased up to a maximum of 22.1 MJ/kg from 19.1 MJ/kg. NPK values of the hydrochar are approximately 20:20:3. Significant amounts of phosphorous and other minerals were absorbed by the solid char from the liquid phase during reaction between 5 and 30 min reaction time. HTC process liquid pH was slightly acidic to neutral, and contains organic acids, sugars, and some amino acids. About half of the nitrogen and most of the potassium are dissolved in the liquid product. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1002–1011, 2016

In this study, feasibility of selected nutrient sequestration during hydrothermal carbonization (HTC) was tested for three different HTC temperatures (180, 230, and 300 °C). To study the nutrient sequestration in solid from liquid solution, sugar and salt solutions were chosen as HTC feedstock. Glucose was used as carbohydrate source and various salts e.g., ammonium hydrophosphate, potassium chloride, potassium sulfate, and anhydrous ferric chloride were used as source of nitrogen and phosphorus, potassium, and iron, respectively. Solid hydrochar was extensively characterized by means of elemental, ICP-OES, SEM-EDX, surface area, pore volume and size, and ATR-FTIR to determine nutrients’ sequestration as well as hydrochar quality variation with HTC temperatures. The spherical mesoporous hydrochars produced during HTC have low surface area in the range of 1.0–3.5 m2 g−1. Hydrochar yield was increased about 10% with the increase of temperature from 180 °C to 300 °C. Nutrient sequestration was also increased with HTC temperature. In fact, around 71, 31, and 23 wt% nitrogen, iron, and phosphorus were sequestered at 300 °C, respectively. Potassium sequestration was very low throughout the HTC and maximum 5.2% was observed in solid during HTC.

In this study, bagasse from two arid land plants, grindelia and rabbitbrush, were hydrothermally carbonized (HTC) along with their raw biomass at 200–260 °C for 5 min. Prior to HTC, biocrude was extracted from grindelia (Grindelia squarrosa), whereas rubber was extracted from rabbitbrush (Ericameria nauseosa). Solid hydrochars and HTC process liquids of extracted feedstocks were characterized by ultimate, proximate, fiber, FTIR, higher heating value (HHV), and GC–MS analyses and the results were compared with their corresponding unextracted conditions. Hydrochars were pelletized in a single-press pelletizer and mass and energy densities of the pellets were measured. From the proximate, ultimate, FTIR, and fiber analyses, the bagasse show similar properties of the raw biomass, although the HHV was slightly increased with crude extraction from grindelia and decreased with rubber extraction from rabbitbrush. With the increase of HTC temperature, solid mass yield was decreased up to 44% for grindelia bagasse ...

Glycerol was used as a cosolvent with the two ionic liquids 1-ethyl-3-methylimidazolium formate ([C2mim][O2CH]) and 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) to pretreat loblolly pine at 140 °C. Enzymatic hydrolysis was then performed on raw and pretreated pines to establish pretreatment efficacy. With pretreatment, glucose yield from enzymatic hydrolysis was improved from 2 % for raw pine up to 43 %, while yields of mannose/xylose combined improved from 4 % up to 77 %. Pine pretreated with a 50 % [C2mim][O2CH]-50 % glycerol mixture exhibited a pulp-like structure, likely formed from removal of the lignin that binds cell walls together. Using this 50 % mixture of [C2mim][O2CH] and glycerol for pretreatment gave a slightly lower glucose yield than a 75 % mixture of [C2mim][O2CH] and glycerol but gave a mannose/xylose yield twice as high. Klason lignin and Fourier transform infrared spectroscopy (FTIR) analysis indicated that [C2mim][O2CH]-glycerol pretreatment preferentially dissolves lignin. FTIR analysis also suggested increased amorphous cellulose content with this pretreatment. Using the anti-solvent ethanol, a lignin-rich substance was precipitated from the solvent mixtures.

As a non-food, renewable energy resource, lignocellulosic biomass can be used for reducing greenhouse gas emissions. Hydrothermal carbonization (HTC) is a process to prepare the lignocellulosic biomass for subsequent thermochemical conversion. Biomass is reacted in hot compressed water at temperatures between 200 and 275 °C and at pressures sufficient to maintain liquid water. HTC was performed on corn stover, rice hulls, Tahoe mix (Jeffrey pine and white fir), switch grass, and Loblolly pine. These biomass sources encompass a variety of types, including a primary agricultural residue, a secondary agricultural residue, a forest product removed to reduce wildfires, a primary energy crop, and a primary forest crop. HTC reaction temperature was found to be the process variable with the greatest effect. For the five biomass studied, hydrochar mass yields were found to decrease with increasing reaction temperature, while higher heating values increased with increasing reaction temperature. Differences in these results among biomass sources were found to correlate with their original hemicellulose, lignin, aqueous soluble, and ash contents. These components appeared to be observable in scanning electron microscope images of hydrochar.

Dry torrefaction and hydrothermal carbonization (HTC) are two thermal pretreatment processes for making homogenized, carbon rich, hydrophobic, and energy dense solid fuel from lignocellulosic biomass. Pellets made from torrefied biochar have poor durability compared to pellets of raw biomass. Durability, mass density, and energy density of torrefied biochar pellets decrease with increasing dry torrefaction temperature. Durable pellets of torrefied biochar may be engineered for high durability using HTC biochar as a binder. In this study, biomass dry torrefied for 1 h at 250, 275, 300, and 350 °C was pelletized with various proportions of biomass HTC treated at 260 °C for 5 min. During the pelletization of biochar blends, HTC biochar fills the void spaces and makes solid bridges between torrefied biochar particles, thus increasing the durability of the blended pellets. The engineered pellets' durability is increased with increasing HTC biochar fraction. For instance, engineered pellets of 90% Dry 300 and 10% HTC 260 are 82.5% durable, which is 33% more durable than 100% Dry 300 biochar pellets, and also have 7% higher energy density than 100% Dry 300 biochar pellets.

Hydrothermal carbonization (HTC) is a promising upgrading process to convert various low energy-density lignocellulosic biomass materials to homogeneous, energy-dense HTC biochar, known as hydrochar. A novel two-chamber reactor was designed and built to investigate the effects of HTC reaction parameters on the resulting hydrochar produced from woody biomass. Reaction parameters investigated included temperature (200–230°C), feedstock particle size (0.60–2.38 mm), and reaction time (1–5 min). Mass yield and higher heating value (HHV) of the hydrochar products were determined as two important measures. Reaction temperature was found to have a much stronger influence on mass yield and HHV than particle size or reaction time. Hydrochar can be formed readily into robust, dense pellets, without requiring any additional binding agent. Pellet density ranged from 1260 to 1320 kg m−3, while volumetric energy density ranged from 27.3 to 29.5 GJ m−3. Several analyses were performed on hydrochar pellets, including ultimate analysis, proximate analysis, and water immersion tests. Results are presented and discussed to illustrate the chemical composition, energy density, and water resistance of hydrochar pellets. This study confirmed that the HTC process can transform lignocellulosic biomass into a solid fuel with favorable properties, and provides insightful guidance regarding optimum reaction parameters for producing hydrochar and pellets in a continuous, industrial process. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 676–680, 2014

Hydrothermal carbonization (HTC) is a thermochemical process to convert lignocellulosic biomass into lignite-like HTC biochar. In this study, chemical reactions occurring during a relatively short HTC reaction time are discussed (5–30 min), and reaction mechanisms are examined at temperatures between 200 and 260 °C. Solid HTC biochar products were analyzed by attenuated total reflectance (ATR)/Fourier transform infrared spectroscopy (FTIR), elemental analysis, and gas chromatography-mass spectrometry (GC-MS), while liquid products were analyzed with GC-MS and ion chromatography (IC) to predict the reaction schemes. HTC reactions for whole biomass (loblolly pine) were proposed in the context of HTC reactions for individual biomass fractions. Hydrolysis, dehydration, and decarboxylation reactions are the major reactions of HTC, though condensation, polymerization, and aromatization also occur. An experimental procedure was developed to determine the net water production, a balance between consumption by hydrolysis reactions and production by dehydration reactions. Net production of water is evaluated. At lower HTC temperature (200 °C), water was consumed. However, at higher HTC temperatures, water was produced and the production increases with increasing reaction time.

Hydrothermal carbonization (HTC) is a pretreatment process to convert diverse feedstocks to homogeneous energy-dense solid fuels. Understanding of reaction kinetics is necessary for reactor design and optimization. In this study, the reaction kinetics and effects of particle size on HTC were investigated. Experiments were conducted in a novel two-chamber reactor maintaining isothermal conditions for 15s to 30 min reaction times. Loblolly pine was treated at 200, 230, and 260°C. During the first few minutes of reaction, the solid-product mass yield decreases rapidly while the calorific value increases rapidly. A simple reaction mechanism is proposed and validated, in which both hemicellulose and cellulose degrade in parallel first-order reactions. Activation energy of hemicellulose and cellulose degradation were determined to be 30 and 73 kJ/mol, respectively. For short HTC times, both reaction and diffusion effects were observed.

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.

As a highly available waste product, rice hulls could be a starting block in replacing liquid fossil fuels. However, their silica covering can make further use difficult. This preliminary study investigates effects of dissolving rice hulls in the ionic liquids 1-ethyl-3-methylimidazolium acetate (EMIM Ac), 1-hexyl-3-methylimidazolium chloride, (HMIM Cl), and 1-allyl-3-methylimidazolium chloride (AMIM Cl), and what lignocellulosic components can be precipitated from the used ionic liquid with water and ethanol. EMIM Ac dissolution at 110 °C for 8 h was found to completely remove lignin from rice hulls, while ethanol was capable of precipitating lignin out of the used EMIM Ac. With 8 h dissolution at 110 °C using HMIM Cl, approximately 20% of the cellulose in the rice hull sample can be precipitated out using water as co-solvent, while more than 60% of the hemicellulose can be precipitated with ethanol.

Hydrothermal carbonization (HTC) is a pretreatment process for making a homogenized, carbon rich, and energy dense solid fuel, called biochar, from underutilized lignocellulosic biomass. Compared to raw biomass, HTC biochar is both more hydrophobic for better storage and more friable for better processing. In this pretreatment method, the biomass is treated with hot compressed water in the temperature range of 200–260°C. Hemicelluloses and water extractives react very quickly compared to cellulose. Lignin is relatively inert, resulting in a biochar with increased lignin content. Lignin acts as a binder for pelletization of pretreated lignocellulosic biomass. A hydraulic press with a controllable heated die was used for pelletization studies. The materials used to make pellets were raw loblolly pine and pine pretreated at different temperatures. The presence of solid bridges was observed in both raw pine pellets and HTC biochar pellets. Pellets made from HTC biochar exhibit favorable properties, including increased hydrophobicity, abrasion resistance, energy density, and mass density compared to pellets produced from raw pine or from dry torrefied pine. Pellets produced from biomass pretreated at 260°C have a volumetric fuel value 70% greater than pellets produced from untreated pine (38.8 MJ/m3 vs. 22.8 GJ/m3), a mass density of 1468 kg/m3, and a higher heating value of 26.4 MJ/kg. © 2012 American Institute of Chemical Engineers Environ Prog, 2012

The equilibrium moisture content (EMC) of raw lignocellulosic biomass, along with four samples subjected to thermal pretreatment, was measured at relative humidities ranging from 11% to 97% at a constant temperature of 30 °C. Three samples were prepared by treatment in hot compressed water by a process known as wet torrefaction, at temperatures of 200, 230, and 260 °C. An additional sample was prepared by dry torrefaction at 300 °C. Pretreated biomass shows EMC below that of raw biomass. This indicates that pretreated biomass, both dry and wet torrefied, is more hydrophobic than raw biomass. The EMC results were correlated with a recent model that takes into account additional non-adsorption interactions of water, such as mixing and swelling. The model offers physical insight into the water activity in lignocellulosic biomass.

Torrefaction is a process to convert diverse lignocellulosic biomass feedstocks into an energy dense homogeneous solid, a pretreatment for subsequent thermochemical conversion. Loblolly pine was treated by wet torrefaction (hot compressed water, 200–260°C) and dry torrefaction (nitrogen, 250–300°C), with mass yield of solid product ranging between 57 and 89%, and energy densification to 108–136% of the original feedstock. The solid product has been characterized, including proximate analysis, fiber analysis, ultimate analysis, and equilibrium moisture. In both dry and wet torrefaction, increasing temperature results in decreased mass yield and increased energy densification, and results in a solid with increased carbon content, decreased oxygen content, and decreased volatiles. The biomass is transformed into a fuel similar to a low-rank coal. Generally, the wet torrefaction process produces a solid with greater energy density than dry torrefaction, with the same mass yield. The fiber analysis indicates that hemicellulose is quickly removed during wet torrefaction, and the solid product contains substantial quantities of aqueous soluble compounds. The equilibrium moisture content of solids produced by both processes is somewhat decreased from that of the biomass feedstock, indicating a hydrophobic solid suitable for storage and transportation. © 2009 American Institute of Chemical Engineers Environ Prog, 2009

Provided that moisture is well managed, biosolids, or digested wastewater sludge, can be converted from an expense to a resource of renewable energy. Toward this goal, the equilibrium moisture content (EMC) for biosolids was determined experimentally in the ranges of 10–84% relative humidity and 30–60°C. Several well-known models were used to fit the EMC data, including a new one that considers mixing and swelling effects on water activity. The rate of drying was measured as a function of temperature and gas velocity in a 3-inch fluidized bed. The drying rate increased with temperature and was independent of gas velocity. In all cases, the drying rate continuously decreased; no period of constant rate was observed. This indicates that the dominant resistance to drying was internal diffusion. © 2009 American Institute of Chemical Engineers Environ Prog, 2009

Equilibrium moisture content (EMC) plays a fundamental role on the properties of bioderived solids such as food, waste biomass, seeds, and many others. For foods, the moisture content affects flavor, texture, and the way the food is stored. In other applications, moisture affects drying conditions and energy requirements for biomass processing. Adequate modeling of EMC in biomass as a function of the water activity is very important in many engineering applications. Most models used to correlate EMC with water activity are based on traditional adsorption models which take into account the adsorption energy of water with the substrate only and do not consider other nonadsorption interactions of water within the substrate such as mixing and swelling effects. Many other models are empirical, which are commonly used for interpolation. Although a detailed description of this type of substrate is very complex, we present a simple model based on standard molecular-thermodynamic models and standard statistical mechanics formulations to correlate the EMC with water activity that attempts to consider both adsorption and nonadsorption interactions of the water with the substrate. Although the model is basic, it captures the behavior of water in this type of systems fairly well and it can be used to fit experimental data with parameters that provide better physical insight on the nature of system. We suggest how to improve the model fundamentally if better knowledge of the water interactions in the substrate are available. © 2009 American Institute of Chemical Engineers AIChE J, 2009

It has long been known that fluidization of dissimilar materials can result in either a well-mixed bed or a segregated bed. In a fluidized bed, particle mixing and segregation phenomena are dominated by bubble activity. Depending on operating conditions, lighter or smaller particles (“flotsam”) tend to rise to the bed, and larger, heavier particles (“jetsam”) tend to sink to the bottom of the bed. A series of unsteady, three-fluid CFD simulations were performed using FLUENT™ 6.0. The solids consist of two dissimilar materials, coke and rutile, with different diameters and densities. Simulation parameters (solution technique, grid, maximum packing fraction, drag law) and operating conditions (gas velocity, bed makeup, nozzle location) were each investigated for the relative effects on bubbling and hence on particle mixing and segregation. From the simulations, it is possible to identify the solids wake trailing a rising gas bubble by looking at the vertical solids flux. The mixing mechanisms (particle exchange and circulation) are readily identified, also from the solids flux. A segregation mechanism is observed by watching the difference in the particle velocities (particle slip velocity) caused by a passing bubble. The simulations predict for all conditions investigated a well-mixed fluidized bed with modest localized segregation. However, a collapsed bed simulated by turning off the gas did predict a discernible segregation profile, similar to that measured in laboratory experiments.

As a renewable non-food resource, lignocellulosic biomass has great potential as an energy source. When pretreated by hydrothermal carbonization, the resulting biochar (or hydrochar) is hydrophobic and of higher energy density. Addition of ionic salts to this high pressure aqueous pretreatment reduces reaction pressure. Ca propionate, Ca acetate, Mg acetate, Ca lactate, Li chloride, Ca chloride, and Ca formate were tested in hydrothermal carbonizations at 260 °C for 5 min. Ca chloride and Ca lactate were found to be Ca salts whose addition increases HHV and which decrease the pretreatment pressure. Biomass pretreated with chemical addition of selected salts may have desirable properties when co-fired in existing coal boilers.

Lignocellulosic biomass such as corn stover can contain high ash content, which may act as an inhibitor in downstream conversion processes. Most of the structural ash in biomass is located in the cross-linked structure of lignin, which is mildly reactive in basic solutions. Four organic acids (formic, oxalic, tartaric, and citric) were evaluated for effectiveness in ash reduction, with limited success. Because of sodium citrate’s chelating and basic characteristics, it is effective in ash removal. More than 75 % of structural and 85 % of whole ash was removed from the biomass by treatment with 0.1 g of sodium citrate per gram of biomass at 130 °C and 2.7 bar. FTIR, fiber analysis, and chemical analyses show that cellulose and hemicellulose were unaffected by the treatment. ICP–AES showed that all inorganics measured were reduced within the biomass feedstock, except sodium due to the addition of Na through the treatment. Sodium citrate addition to the preconversion process of corn stover is an effective way to reduced physiological ash content of the feedstock without negatively impacting carbohydrate and lignin content.

Rice hulls, a widely-available secondary agricultural residue, can be pretreated with ionic liquids (IL) prior to enzymatic hydrolysis to enhance glucose and xylose yields. The high cost of ILs is a deterrent to commercial deployment at present. ILs 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium formate, 1,3-dimethylimidazolium dimethylphosphate, and 1-ethyl-3-methylimidazolium diethylphosphate were investigated for rice hull pretreatment. Effects of diluting ILs with glycerol were investigated for biomass pretreatment efficacy, and for solvent recovery. When diluted with 50% glycerol, rice hulls treated in 1-ethyl-3-methylimidazolium formate was found to give glucose and xylose yields after enzymatic hydrolysis better than rice hulls treated in pure 1-ethyl-3-methylimidazolium formate. Dilution in glycerol resulted in an increased rate of solvent recovery after pretreatment, as much as six times that when pure 1-ethyl-3-methylimidazolium formate was used. Diluting 1-ethyl-3-methylimidazolium formate with 50% glycerol was found to decrease solvent viscosity at the pretreatment temperature (110 °C) helping explain improved biomass pretreatment.

Previous workers have shown that the net particle flux within the riser of a circulating fluidized bed (CFB) may be measured by a simple technique with a suction probe facing upwards and then downwards. However, this technique does not give accurate measurements of the upward and downward particle fluxes independently. A probe similar to that of previous workers is used here to measure the flux of the upflow. However, the flux of the downflow is measured with a probe through which no external air flow is imposed. The method presented here uses an 8-mm tubular probe, penetrating the riser wall and rising at a sharp angle. The probe is constructed of sections of steel tube and 400 mesh screen. Particles fall into the probe and then into a sealed reservoir for subsequent analysis. The gas flow in the riser passes through the screen sections of the tube, so that the gas flow at the tip of the probe is virtually undisturbed by the presence of the probe. The method is verified in a CFB riser of diameter 115 mm, fluidizing sand of average size 209 μm, with a solids circulation rate in the range of 10–30 (m2s) and air velocity in the range of 3.4–5.4 m/s, corresponding to a nominal solids concentration (based on pressure-drop measurements) of 0.5–2.5%. The technique presented here allows for accurate and independent measurements of both the upward flux and the downward flux, and thus represents an improvement on previous methods. Previous workers have specified that a critical surface where the time-averaged net flux is zero demarcates the dilute core from the dense annulus. However, the total particle flux, defined as the sum of the upward and downward fluxes, is proportional to the time-averaged local particle concentration, and so is indicative of physical phenomena in the riser. Trends for the total flux are presented.

Hydrothermal carbonization (HTC) of lignocellulosic biomass is a pretreatment process to homogenize and densify diverse biomass feedstocks. The solid product is hydrophobic and friable with ultimate analysis similar to that of lignite, and is easily made into durable, dense pellets. Byproducts include aqueous sugars, acids, carbon dioxide, and water. The process consists of treatment in hot (180–280 °C) compressed water for short contact times, and has been demonstrated on woody biomass, agricultural residues, and grasses. HTC reactions include hydrolysis, dehydration, decarboxylation, condensation, polymerization, and aromatization. Nearly all hemicellulose is removed and converted to simple sugars and furfural. Cellulose begins to react at 200 °C, and produces oligosaccharides, glucose, 5-HMF, and organic acids. Lignin is relatively inert. HTC reactions are relatively fast, with reaction times measured in minutes. Both hemicellulose and cellulose degrade by apparent first-order reaction kinetics, where hemicellulose exhibits an activation energy of 30 kJ mol−1, and that of cellulose is 73 kJ mol−1. There has been a flurry of research on HTC published recently, but little commercial activity. Innovative design is required for commercialization, and costs may be high, due to high pressure operation. However, as demand for biomass increases, HTC will surely play a role in enhancing supply chain logistics.

Hydrothermal carbonization (HTC) is a process to densify, homogenize, and stabilize diverse biomass feedstocks. The water requirements of HTC need to be assessed to determine commercial feasibility. This current research work focuses on the effects on HTC of using recycled process water for multiple process cycles. Loblolly pine was treated in hot, compressed water at 200, 230, and 260°C for 5 min with a 5:1 water:biomass mass ratio. Liquid product was separated and recycled for reuse in HTC, nine cycles at 200 and 230°C and five cycles at 260°C. The solid products (biocarbon) were characterized by their mass yields, higher heating values (HHVs), and equilibrium moisture content (EMC), whereas in the liquid samples, total organic carbon (TOC) content and pH were determined. With successive recycling, biocarbon mass yield increases by 5–10% above the yield recorded for the initial cycle at each temperature investigated, whereas biocarbon HHV is essentially unchanged. The aqueous TOC is increasingly concentrated with the number of cycles and reaches an equilibrium. The EMC results suggest that the effects of recycling process water on hydrophobicity of the biocarbon are negligible. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 1309–1315, 2014

A new method for determining the onset of slugging in fluidized beds is presented. Pressure-drop fluctuations, measured from below the distributor to the gas exit line, are transformed to the frequency domain by the power spectral density function (PSDF). The dominant frequency of the PSDF corresponds to the eruption frequency of bubbles or slugs. A fluidized bed is in the slugging regime when this dominant frequency, fd, remains constant with changing gas velocity. This method is an improvement over previous methods because of the simple nature of the apparatus required, and because it is possible to locate the pressure probes so that they do not interfere with the fluidization or undergo rapid wear from the constant particle movement. This method was used to determine the gas velocity corresponding to the transition from the bubbling to the slugging regime for a 10 cm diameter bed of sand fluidized with air and containing three 1.9-cm diameter vertical rods at 5.2 cm centre-to-centre triangular spacing and extending the length of the bed, and to compare the results with those from the same bed without any internal rods. The presence of the vertical rods inhibited the onset of the slugging regime, and significantly extended the bubbling regime to higher gas velocities.

As a renewable non-food resource, lignocellulosic biomass has great potential as an energy source or feedstock for further conversion. However, challenges exist with supply logistics of this geographically scattered and perishable resource. Hydrothermal carbonization treats any kind of biomass in 200 to 260°C compressed water under an inert atmosphere to produce a hydrophobic solid of reduced mass and increased fuel value. A maximum in higher heating value (HHV) was found when 0.4 g of acetic acid was added per g of biomass. If 1g of LiCl and 0.4 g of acetic acid were added per g of biomass to the initial reaction solution, a 30% increase in HHV was found compared to the pretreatment with no additives, along with greater mass reduction. LiCl addition also reduces reaction pressure. Addition of acetic acid and/or LiCl to hydrothermal carbonization each contribute to increased HHV and reduced mass yield of the solid product.

An advanced multiple-stage fluidized bed reactor system has been devised for the energy-efficient extraction and conversion, from tar sand, of bitumen into synthetic crude oil. The reactor consists of four fluidized beds arranged as stages in series with respect to flow of sand. In the first stage, tar sands are heated, causing the bitumen to pyrolyse into coke, which is deposited on the sand, and gas, which is mostly condensed into oil. The coke is partially combusted with air or enriched oxygen in the second stage, which is thermally coupled to the first stage by multiple vertical heat pipes. Combustion is completed adiabatically in the third stage and heat recovery from the sand is carried out in the fourth stage. By conducting the coke combustion in two stages in this manner, the overall reactor residence time to produce clean sand is greatly reduced from that for a single combustion stage. Laboratory experimental studies have confirmed the ability to operate and control the two thermally coupled stages. The two-phase bubbling bed model of Grace, amended to account for bubble growth in the axial direction, has been adopted to model the mass transfer and fluid mechanics of the fluidized beds. The model for the first and second combustion stages is complete. Predictions for exit reactor conditions at various operating conditions are in reasonable agreement with experimental observations. The operating parameters have been found to exert a much greater influence on the predictions of the model than do the values of the physical parameters, indicating a desirable degree of reactor stability. Extension of the model to the pyrolysis and heat recovery stages will permit the optimization of the reactor configuration and operating conditions.