Subbituminous Coal Research Articles

Cohesive components in coal and their cohesive mechanism during pyrolysis

The cohesive components in coals and their detailed structure were investigated. The results show that the caking index of Linfen fat coal after extracting by benzene and tetrahydrofuran (THF) decreases from 89 to 43. Through analyzes of FT-IR and synchronous fluorescence spectrometry, anthanthrene is considered as the primary cohesive component to determine the cohesiveness of coal, and it is 42.4 wt% in the extract by THF from fat coal. Meanwhile, 1-naphthol, the secondary cohesive component to influence the cohesiveness of coal, is 22.8 wt% in the extract by benzene from fat coal. The cohesive phenomenon of coal has a positive correlation with the maximum aromaticity index (fa), and the cohesive phenomenon cannot be found during pyrolysis when the maximum fa of samples is smaller than 0.640, which are found from SEM images and XRD spectra of the carbonized samples. Moreover, the addition of anthanthrene makes Shenfu sub-bituminous coal produce cohesive phenomenon that coal particles connect together through the formation of a uniform surface. Based on these findings, a possible cohesive mechanism of coal was proposed.

Occurrence Relationship between Sodium and Maceral Groups in Subbituminous Coal: A Case Study on Zhundong Coal and Shenfu Coal

The occurrence characteristics of sodium and its potential relationship with macerals in Zhundong coal, as well as in Shenfu coal with average sodium levels, are investigated in this study. A new five-step sequential extraction method was first conducted for determination. The occurrence status of sodium and its related macerals in samples was determined by microscope and SEM–EDS (scanning electron microscope–energy dispersive X-ray spectroscopy). Soluble sodium salts (H2O-Na) make up the primary proportion of sodium in Zhundong coal, at approximately 50%, while various sodium species are distributed in Shenfu coal with nonobvious differences. Inertinite contains more sodium than vitrinite does in both coals, and the highest enrichment degree of sodium was discovered in inertinite from Zhundong coal, which presented primarily as NaCl crystals (H2O-Na) in fusinite cells, with a local weight percentage of over 15%. More specifically, H2O-Na and insoluble Na both tend to enrich in fusinite. Additionally, it is found that maceral-rich products can be gathered using triboelectrostatic separation, and a portion of sodium can thus be removed from the coal by removing inertinite. This study may provide new insights and references regarding sodium removal from Zhundong coal.

Thermodynamic Irreversibility Analysis of Thermal Radiation in Coal-Fired Furnace: Effect of Coal Ash Deposits.

In this paper, a three-dimensional (3-D) high-temperature furnace filled with a gas-solid medium was investigated, and the radiative transfer equation and the radiative entropy transfer equation in the chamber were applied in order to analyze the effect of coal deposits on thermal radiation. The heat flux on the walls of the furnace and the entropy generation rate were determined due to the irreversibility of the radiative heat transfer process in the furnace. Furthermore, the effect of ash deposits on the wall surface on the irreversibility of the radiation heat transfer process was investigated. The numerical results show that when burning bituminous and sub-bituminous coal, ash deposits in the furnace led to a 48.2% and 63.2% decrease in wall radiative heat flux and a 9.1% and 12.4% decrease in the radiative entropy rate, respectively. The ash deposits also led to an increase in the entropy generation number and a decrease in the thermodynamic efficiency of the radiative heat transfer process in the furnace.

Mesoporous zeolite Beta supported Ni nanoparticles for the catalytic hydroconversion of extraction portion from Jinjitan subbituminous coal to cycloalkanes

The catalytic hydroconversion (CHC) of heavy carbon organic species (HCOSs) to cycloalkanes represents an importantly used chemical industry process due to the wide applicability of the resulting products in energy and fine chemistry. Despite the existing conventional catalysts applied to the CHC of HCOSs, the development of highly active bifunctional Ni-based heterogeneous catalysts for this process is still a challenge. Therefore, we show that the modified deposition–precipitation of nickel (II) nitrate on hydrothermally synthesized mesoporous zeolite Beta (MZB) prepares a Ni/MZB catalyst with a through-crosslinking mesopore structure and uniformly disperse Ni nanoparticles (NPs) at rough MZB crystal surface. The 10%Ni/MZB (10% Ni loading), in the presence of exposing on amount of accessible Lewis acid sites (LASs) and attaching Ni NPs by chemical bonding from the silica matrix of MZB skeleton, exhibits excellent activity to promote the CHC of all kind of aromatic rings and heteroatom-containing species, including chain alkanes, arenes, oxygen-containing organic compounds (OCOCs), nitrogen-containing organic compounds (NCOCs), and sulfur-containing organic compounds (SCOCs), to produce cycloalkanes and hydroarenes under mild conditions. Interestingly, density functional theory (DFT) calculations indicate that the transfer of biatomic active hydrogen (H…H) and heterogenous H+ from 10%Ni/MZB plays important roles during the CHC of diphenoxybenzene (DPOB). After being recycled 4 times, 10%Ni/MZB is still maintains high activity for CHC of DPOB under mild conditions.

Probing the interaction between coal particle and collector using atomic force microscope and density functional theory calculation

Revealing the interaction mechanism between coal and collector is essential for coal flotation. However, direct determination of the interaction force between coal and collector has rarely been reported. In this work, an atomic force microscope (AFM) was used to directly measure the interaction between collectors, i.e., n-dodecane, nonyl benzene and sub-bituminous coal (SC), bituminous coal (BC) and anthracite coal (BC) with different metamorphic degrees, and density functional theory calculation (DFT) was used to simulate the interaction mechanism of coal and collectors at the molecular level. The results indicate that the interaction force between coal and collector improves with the increase of coal metamorphic degrees for the same type of collector. Extended DLVO fitting reveals that the hydrophobic interaction decays exponentially. Consistent with the AFM force measurement results, the adsorption energy between the coal and the collector calculated by DFT all show that the interaction between n-dodecane and the three types of coals is weaker than that of nonyl benzene. This work provides quantitative information on the molecular interaction mechanism underlying the adsorption of collectors on the coal of varying surface chemistry at the nanoscale, with valuable implications for developing influential collectors for coal preparation and many other engineering processes.

Characteristics of Co-firing Solid Recovered Fuel with sub-bituminous Coal on Pulverized Coal Boiler Power Plant 300 MWe

The biomass co-firing test was conducted at a pulverized coal power plant with a capacity of 300 MWe to determine the effect of cofiring on the operating parameters, such as Mill Outlet Temperature (MOT), Furnace Exit Gas Temperature (FEGT), Specific Fuel Consumption (SFC) and environment. Biomass Solid Recovered Fuel (SRF) and coal was mixed in a stockpile with a composition of 5 % SRF and 95 % coal. Fuel mix was fed into the four operating bunker mills. The load stabilization process duration is 1 h after the biomass is fed to the boiler by keeping the loading constant at the maximum capacity rate. The data was recorded for 2 h with a retrieval interval of every 15 min. The results showed that the FEGT value during co-firing was 0.7 % lower than during coal firing. The mill outlet temperature ranges from 58 °C to 60 °C in both test conditions. NOx emissions increase by 10.1 %, and SO2 emissions increase by 5.5 % during co-firing than coal-firing conditions. There is no significant change in SFC where the value equals 0.54 kg kWh-1 on both tests.

The role of biocatalysts in the synthesis of graphene nanosheets from sub-bituminous coal

The synthesis of graphene nanosheets (GNs) from sub-bituminous coal aims to increase the added value of coal in a cheap, easy and proclaimed this method on an industrial scale. The addition of biocatalyst (BFS) in the pyrolysis process can reduce the reactive temperature of the pyrolysis process so that the combustion reaction runs better at low temperatures of 200-300℃. Followed by hydrothermal carbonization of coal at 180℃ for 6 h with the addition of pyrolysis liquid smoke. Filter the results and exfoliate using 24 kHz ultrasonication for 30 min. Then centrifuge at 10,000 rm for 10 min to separate the solids. Wash the solids with deionized water to obtain a neutral pH. Using FESEM and TEM to obtain the morphological characteristics of GNs, structural characterization was studied using XPS, FTIR, and XRD. The GNs produced using BFS yielded 7–8 layers of Graphene, and a crystal size of 2.7 nm showing promising efficiency from the methodology used.

Prospect evaluation of CO2 sequestration in coal beds of Anambra Basin, Nigeria

Sequestrating carbon dioxide (CO2) for enhancing methane production from coal beds is one of the approaches being advanced to reduce the concentration of CO2 in the Earth's atmosphere. Some aspects of CO2 sequestration and coalbed methane (CBM) exploration within three coal seams (seam I-III) in the Anambra Basin, Nigeria was investigated in this study. The rank, grade and type of coals were determined using proximate/ultimate and petrographic analyses, fourier transform infrared reflectance (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results from these analyses were used to determine the suitability of the coal for CO2 storage and CBM/CO2-ECBM production. Physicochemical properties including volatile matter (27.03, 72.74 and 15.14%), fixed carbon (48.60, 30.10 and 54.30%), and the calorific values (13,103, 11,517 and 14,263 Btu/lb), were used to determine the coal rank based on the ASTM standard for coal ranking. This revealed that all the coal samples fell within the subbituminous low-rank coals to high volatile C bituminous coals. Petrographic analysis revealed that the main lithotypes in the coal seams are fusain, durain with few vitrains. The effective storage capacity estimated using the Carbon Sequestration Leadership Forum (CSLF) methodology, indicated that Seam III is the most promising coal seam with the largest CO2 storage capacity of 5.77 × 109 tons around the Enugu area. Finally, this study has provided insights into the coal beds in the Anambra Basin for the implementation of CBM, CO2-ECBM production, and the potential for CO2 storage projects.

Efficient coal concentration using a short-chain amine-type compound as collector reagent: Flotation and optimization studies

This work presents the flotation of a sub-bituminous coal using 1-butylamine as a short-chain amine collector. The flotation results have been obtained with 1-butylamine (coal yield: 100%) and compared with those achieved with a quaternary amine (coal yield: 95.4%), kerosene (coal yield: 100%) and diesel (coal yield: 95.7%). The best results have been obtained with 1-butylamine. Less depressant effect has been observed with 1-butylamine. The FTIR signals have been attenuated when the coal is conditioned with 1-butylamine. Zeta potential measurements have also been changed after conditioning. The contact angle of water and graphite has decreased from 82.3° to 32.2°. An optimization has been performed using a Box-Behnken experimental design. Flotation has significantly affected by time and collector dosage. The pH is not a significant factor. The optimal conditions for the best efficiency using 1-butylamine as a collector are 2.0 min of flotation and 10-3 mol/L of collector.

Characterization of Porosity and Pore Accessibility of Vitrinite-Rich Bituminous and Subbituminous Coals by Small-Angle Neutron Scattering, Mercury Intrusion Porosimetry, and Low-Pressure N2Adsorption

Three bituminous and one subbituminous vitrinite-rich coals were characterized using small-angle neutron scattering with contrast matching, mercury intrusion porosimetry, and low-pressure N2 adsorption techniques to quantify their porosity and pore accessibility in an effort to assess their solvent extractabilities, as a first approximation, for manufacturing useful end-products. The techniques revealed consistent results while complimenting one another. The total porosity was found to follow the coal rank with the lowest rank having the highest porosity within the studied coals. The amount of inaccessible pores was found to increase with rank for the bituminous coals studied here. The increase in the ease of accessibility and total porosity with decreasing rank suggested easier penetration of chemical reagents for solvent extraction, for example.

Hydrothermal Conversion of Food Waste to Carbonaceous Solid Fuel-A Review of Recent Developments.

This review critically discussed recent developments in hydrothermal carbonization (HTC) of food waste and its valorization to solid fuel. Food waste properties and fundamentals of the HTC reactor were also covered. The review further discussed the effect of temperature, contact time, pressure, water-biomass ratio, and heating rate on the HTC of food waste on the physiochemical properties of hydrochar. Literature review of the properties of the hydrochar produced from food waste in different studies shows that it possesses elemental, proximate, and energy properties that are comparable to sub-bituminous coal and may be used directly as fuel or co-combusted with coal. This work conclusively identified the existing research gaps and provided recommendation for future investigations.

Effects of oxygen concentration on devolatilization and combustion behavior of coal particles: A multi-parameter study

The devolatilization and volatile combustion of lignite coal (LC), sub-bituminous coal (SBC) and bituminous coal (BC) with different O2 concentrations (21%-50%) were investigated on a concentrating photothermal experiment platform. The characteristics and mechanism of different coal particle combustion were analyzed by using multiple diagnostics, including Planar Laser Induced Fluorescence (PLIF) of OH radicals and polycyclic aromatic hydrocarbons (PAHs), high-speed cinematography and FT-IR. The results showed that, with increasing O2 concentration, the ignition delay time (tign) of different ranks of coal decreased, which was associated with the increase of OH concentrations during the ignition stage. The good correlation between tign and OH concentration was observed. For the volatile combustion, the OH concentration, volatile release amount and volatile flame duration time (tvol) significantly increased with the increasing of O2 concentration at low O2 concentrations. In the higher O2 concentrations, coals with different PAHs generation amount responded differently on the increasing of O2 concentration. On one hand, for the coals with lower PAHs generation amount, the OH concentration increased with the increasing of O2 concentration, while the tvol was not sensitive to changes of the O2 concentration. On the other hand, for the coals with higher PAHs generation amount, the OH concentration decreased with the increasing of O2 concentration while the tvol increased with the increasing of O2 concentration. It can be concluded that PAHs inhibited the OH generation, and the generation characteristics of OH and PAHs affected the sustained state of volatile combustion. The higher PAHs concentration consumed higher amount of OH during the volatile combustion. Meanwhile, with the increasing of PAHs concentration, the reaction rate of H + O2+M→HO2+M in which PAHs participate was increased, inhibiting the reaction H + O2→OH+O, and the increasing of polymer soot of PAHs will reduce the flame temperature through thermal radiation, which further inhibited the OH formation.

Combustion reactivity of chars pyrolyzed from low-rank coal using a fixed bed reactor installed with internals

Pyrolysis of low-rank coal could contribute toward the goal of upgrading coal quality, chemical feedstock and fuel production. This research investigated the combustion reactivity of char pyrolyzed from a low-rank sub-bituminous coal using a conventional fixed bed reactor and a novel reactor with internals at 0 kPa and − 40 kPa gauge pressures. Proximate and ultimate analyses showed that the novel reactor reduced char’s fuel ratio by 46% and 54% at 0 kPa and − 40 kPa respectively. The chars derived from the novel reactor also had a higher order of carbonaceous structure and active sites, as supported by the increment in both IG/IALL and ID3/(IG+ID2+ID3) area ratios obtained from a Raman spectrometry analysis. From a non-isothermal combustion analysis, it was found that the ignition temperature of char derived from the novel reactor was 24–40 °C and 30–45 °C lower at 0 kPa and − 40 kPa respectively. A micro fluidized bed reactor analyzer was used for an isothermal differential analysis and it showed that chars produced from the novel reactor had an average combustion activation energy of around 77.3 kJ·mol−1, which was 23% and 10% lower than chars obtained from the conventional reactor at 0 kPa and − 40 kPa respectively. Overall, the novel reactor produces chars with more desirable combustion quality and, therefore, provides the opportunity for more low-rank coal to be upgraded and utilized more effectively as a fuel source for energy sustainability.

FTIR-based study on the effect of deashing on the molecular structure of Hefeng sub-bituminous coal and its liquefaction residue

ABSTRACT Mineral presents an important effect on the structure and reactivity of coal, and deashing pretreatment is one of the most effective ways to remove mineral from coal. However, deashing pretreatment can change the molecular structure of coal, thus affecting its clean and efficient utilization. To understand the effect of deashing on the molecular structure of Hefeng coal (HF) and its liquefaction residue (LR), HF, LR, Hefeng deashed coal (HFAC), and its liquefaction residue (LRAC) were investigated by Fourier transform infrared spectroscopy (FTIR). Results showed that the deashing treatment could destroy the chemical structure of the coal, while the removal of mineral is not conducive to the liquefaction process of HF. After deashing treatment, the relative content of OH–π hydrogen bonds and self-associated –OH hydrogen bonds declined by 22.40% and 32.10%, respectively. For the aliphatic structure, the content of aliphatic –CH2 changed obviously, among which the asymmetric –CH2 reduced by 12.23%, while the symmetric –CH2 added by 15.27%. For the oxygen-containing functional groups, the carboxyl group increased by 118.95%, and the relative content of C–O group reduced by 49.35%. The 5-substitutions of benzene ring almost disappeared after the deashing process, and the 2-substitutions of benzene ring remarkably increased by 148%, which are predominant in the aromatic structure. After liquefaction, compared to HF, the characteristic peaks ascribed to hydroxyl structure, aliphatic structure, and C=O in LR almost vanished, while the intensity of these peaks in LRAC was stronger than that in LR. The relative content of 5- and 4-substitutions of benzene rings dropped by 33.9%, while the content of 2- and 3-substitutions of benzene rings were increased by 45.47% in LRAC. Structural parameters from functional groups indicated that the length of aliphatic chain was shortened in HFAC and LRAC, and the aromaticity and the condensation degree of aromatic ring were decreased.

Degradative solvent extraction of subbituminous coal with deep eutectic solvent and effect of reaction conditions on products

A degradative solvent extraction method for upgrading low-rank coal was performed at 200–350 °C for 90 min to obtain a substance dissolved in the solvent at room temperature (Soluble). Because the resulting mixture exhibited a high carbon content without ash, it could be readily used as a fuel. Furthermore, deep eutectic solvents (DESs) have attracted attention for improving the Soluble yield and decreasing the oxygen content in Soluble. DES is known to cleave oxygen-containing functional groups in biomass and is considered effective for deoxidizing low-rank coal. Herein, DES was prepared by mixing choline chloride, FeCl3·6H2O, and Adaro subbituminous coal (AD) and then added to 1-methylnaphthalene (1-MN) in a non-polar solvent, followed by degradative solvent extraction in the range of 200–350 °C. The effects of reaction temperature and added DES amount on the product yield and the composition were evaluated. As the reaction temperature and amount of DES added increased, the Soluble yield and carbon content increased. It was also found that the thermal decomposition temperature and oxygen content decreased with the increasing DES amounts. This decrease indicates that DES promotes the deoxygenation and decomposition of AD and increases the soluble yield of the fuel source.

Copyrolysis and Cocombustion Performance of Karamay Oily Sludge and Zhundong Subbituminous Coal.

Karamay oily sludge (KOS), Zhundong subbituminous coal (ZSBC), and their equal mass mixture (M KOS/ZSBC) were selected as the research samples, and composition characteristics and pyrolysis performance of KOS, ZSBC, and its mixture were investigated by means of various analytical methods. Results showed that yields of fixed carbon and volatile matter from ZSBC are higher than those from KOS, and the content of moisture in ZSBC is also higher; most of the components in KOS are inorganic minerals, with the ash yield of 71.4%, and the fixed carbon yield of nearly 0. According to Fourier transform infrared spectrometer (FTIR) analysis, the types of functional groups in KOS and ZSBC are basically the same, while the contents of which are different. Thermogravimetry-differential thermogravimetry (TG-DTG) analysis indicated that the mass loss of ZSBC, KOS, and M KOS/ZSBC are 41.1%, 25.7%, and 32.8% with a heating temperature up to 990 °C, respectively. By analyzing the theoretical pyrolysis and combustion TG-DTG profiles of M KOS/ZSBC and the measured composition of the flue gas produced during the tested processes, it is found that the mixture of oily sludge and coal helps generate remarkable combustible gases with significantly reduced CO2, indicating that there is an effective "synergistic effect" between KOS and ZSBC. Based on the Coats-Redfern (CR) model, in the main pyrolysis temperature range, when the reaction order is selected as 1, the kinetic fitting effect of pyrolysis and combustion profiles for ZSBC is better, with the correlation coefficient R 2 > 0.98. While for KOS and M KOS/ZSBC, in N2 atmosphere, the fitting effect is satisfactory as the reaction order is set to 5, in air atmosphere, the better fitting effect is considered that reaction order is selected as 1.

Numerical modeling of the co-firing process of an in situ steam-torrefied biomass with coal in a 230 MW industrial-scale boiler

This paper presents the CFD modeling results of the torrefied maize straw co-firing with sub-bituminous coal in various mass ratios in the industrial scale boiler, to recognize possible application issues of the coal substitution with upgraded biomass. The steam torrefaction of biomass took place in a pilot in a counter-flow torrefaction reactor fed with superheated steam from the OP-230 (Rafako, Poland) boiler. Using a TGA, it was possible to analyze the combustion indexes and synergy effects after burning the torrefied biomass-coal mixtures. Additionally, a kinetic model of pyrolysis devolatilization was established and used in the modeling along with Ansys Fluent kinetics of the coal and gas-phase combustion models. Due to the numerical modeling, it was possible to determine the temperature distribution in the boiler's furnace chamber, the heat flux densities, the simulated distribution of carbon monoxides and carbon dioxide concentration, and the decomposition of nitrogen oxides resulting from co-combustion. Steam torrefied biomass indicates higher combustion activity compared to coal, ignites easier, and burns more intensely with better combustion stability. A synergistic effect between the coal-torrefied blend was observed. According to numerical analysis, it was found that with the increase of the share of torrefaction in the fuel mixture, the share of unburned fuel in fly ash increases. Additionally, an increased share of the torrefied biomass in the fuel blend from 30% to 40% results in a slight increase in the molar NO concentration in the furnace chamber. The authors strongly recommend the continuation of work on further investigation of the co-firing of the coal with torrefied biomass in the pre-mixed blends injected through all burners.

Influence of flotation reagents on separation mechanism of macerals: A multi-scale study

The precise separation of macerals is the premise and foundation for the efficient utilization of coal resources, and flotation is the separation method with the greatest industrial potential. The differences in the surface hydrophobicity of macerals provide the basis for flotation, but the complexity of their surface properties makes separation challenging. In this study, sub-bituminous coal was used to obtain vitrinite and inertinite, and a detailed analysis was carried out on the samples. The surface morphologies of vitrinite and inertinite were observed in the QITM (quantitative imaging) mode of AFM (atomic force microscope) to explore the adsorption of the reagents. The effect of the reagents on the interaction forces between the coal particles and bubbles was measured to reveal the change in hydrophobicity. The attachment performance of macerals under different reagent treatments was investigated using a laboratory-built apparatus. Overall, the results demonstrated that the difference in zeta potential between vitrinite and inertinite was a viable approach for separating the macerals. CTAB adsorption on coal samples changed the surface morphology and the interaction force between particles and bubbles. Interestingly, CTAB adsorption on the gas–liquid interface decreased the interaction force. Vitrinite and inertinite attachment performances were enhanced when Al3+ and SDS were used simultaneously.

Evolution of PAHs in the mobile phase of low-rank coal during medium–low-temperature pyrolysis

The generation and release of polycyclic aromatic hydrocarbons (PAHs) during coal pyrolysis have been extensively studied, yet the evolution process of PAHs in the mobile phase is poorly understood. In this study, Yulin (YL) subbituminous coal and its solid products (YL350–700) obtained by pyrolysis at ∼350–700 °C were treated with dichloromethane, and the extracted PAHs were analyzed by gas chromatography and mass spectrometry. The total PAH concentration in the YL350–700 mobile phase was found to increase and then decrease with increasing pyrolysis temperature, and peak in the YL380 sample. The concentrations of alkylated PAHs were found to be the main contributors to the total PAH concentrations among the YL350–700 samples. YL coal was dominated by 4-ring PAHs, while YL350–700 samples were all dominated by 2-ring PAHs (naphthalene and alkylated naphthalenes). Variations in the proportion of 2-ring PAHs and the degree of naphthalene alkylation in YL350–700 indicated that alkylated naphthalenes were the main component of PAHs generated during YL coal pyrolysis at medium–low temperatures. This may suggest that the condensed aromatic units in the macromolecular structure of YL coal mainly consist of low-ring PAHs. Finally, an evolutionary process for PAHs in the mobile phase of YL subbituminous coal during pyrolysis at medium–low temperatures was proposed.

Simultaneous production of nutritional compounds and hydrochar from Chlorella pyrenoidosa via hydrothermal process

Hydrothermal process is an eco-friendly method for simultaneously extracting antioxidant compounds and producing hydrochar. This study examined the simultaneous production of nutritional compounds and hydrochar from Chlorella pyrenoidosa via a hydrothermal process. The experiments were conducted using a batch reactor at varying temperatures (160, 180, and 200 °C) and holding times (10, 20, and 30 min). The results revealed that phenolic contents, antioxidant activity, and hydrochar production were strongly affected by both temperature and time. The highest total phenolic content (1.70 ± 0.16 mg/g) and antioxidant activity (94.2 ± 1.8 %) were found in process water at 200 °C with a holding time of 20 min. Under these conditions, a hydrochar yield of 30.79 % was obtained. Intriguingly, the hydrochar obtained at 200 °C exhibited higher heating values (24.93–28.32 MJ kg−1) than typical sub-bituminous coals, giving it potential for use as a solid fuel.