Combustion Behavior Of Hydrochars Research Articles

Hydro thermal carbonization (HTC) of sewage sludge: process optimization through RSM and assessing its energy potential

Sewage sludge is a by-product of municipal wastewater treatment, and its production is increasing with population growth and urbanization. Hydrothermal carbonization (HTC) is a promising method for managing sewage sludge due to its applicability and cost-effectiveness. The HTC process produces hydrochar, a stabilized carbon material derived from sewage sludge. In this study, sewage sludge was subjected to HTC at optimized conditions of 200 °C and 6 h using the response surface methodology (RSM) statistical tool. The structural morphology of the hydrochar was analyzed using Scanning Electron Microscopy and Transmission Electron Microscopy, which revealed a fluffy and coarse surface with deeper fragments, indicating the presence of carbon microspheres. Fourier Transform Infrared (FTIR) spectra showed that the hydrochar retained similar functional groups as the original sewage sludge, such as hydroxyl, aliphatic methyl, amino, ketonic, amide, and ether groups, with minimal shifts and reductions in vibrational peaks. The higher heating value (HHV) of the sewage sludge increased from 16.24 to 19.41 MJ kg−1 after HTC, indicating energy densification with a factor of 1.07. However, when hydrochar was blended with coal, the HHV gradually decreased. Thermo-gravimetric analysis was performed to assess the co-combustion effectiveness, and it showed that a blend of 50% coal and 50% sewage sludge-derived hydrochar exhibited extended heat generation with minimal reduction in HHV compared to other blends, reaching a value of 23.16 MJ kg−1. These findings suggest that hydrochar produced from sewage sludge through HTC could serve as an alternative energy source in industries, reducing the reliance on coal. Furthermore, the combustion behavior of hydrochar was significantly altered after the HTC process, highlighting its potential for energy generation. By utilizing hydrochar, the industry can contribute to the sustainable management of sewage sludge while reducing greenhouse gas (GHG) emissions associated with coal combustion.

Fuel properties and combustion kinetics of hydrochar derived from co-hydrothermal carbonization of tobacco residues and graphene oxide

Tobacco residues produced from domestic cigarette industry are an abundant biomass resource which have the potential to be exploited and utilized as solid fuel. In the present study, a comprehensive investigation was performed on the fuel properties of hydrochars which were derived from hydrothermal carbonization (HTC) of tobacco residues in the presence of minute amount of graphene oxide (GO). The effect of HTC temperature and residence time on the chemical compositions, structure, and combustion performance of the resultant GO-assisted hydrochars was evaluated. The carbon content and energy densification increased with the hydrothermal treatment intensity accompanying with the decline in hydrogen and oxygen contents. Meanwhile, the combustion behavior of hydrochars was analyzed based on the thermogravimetric curves and isoconversional Kissinger-Akahira-Sunose method. The activation energy varied with conversion degrees for the tested samples, indicating the complexity of hydrochar combustion. Notably, the decreased activation energies for GO-assisted hydrochars may indicate the catalytic role of GO during the combustion process of components in hydrochars.

Comparison study on fuel properties of hydrochars produced from corn stalk and corn stalk digestate

In this study, hydrothermal carbonization (HTC) was employed to upgrade the fuel quality of corn stalk digestate (CSD) ranged from 190 to 240 °C. Meanwhile, a comparison of corn stalk (CS) was investigated to explore the effects of anaerobic digestion (AD) on the fuel property and combustion behavior of hydrochars. The results showed that the HTC increased the carbon content and heating value of hydrochars while decreased the alkali and alkaline earth metals (AAEMs) content and hydrophilicity. Compared to CS, the CSD showed higher low-temperature HTC activity, but lower sensitivity to temperature changes. The improvement of fuel properties on CSD was limited with the HTC temperature increasing. The thermogravimetric analysis displayed the relative low temperature HTC (190 and 215 °C) improved the combustion of CSD, while 240 °C was appropriate for CS. FTIR and SEM analyses confirmed the aromatization and formations of spherical particles in CS hydrochars obtained at 240 °C, respectively, but was not observed in CSD hydrochars. The AD process weakened the pyrolysis-like reaction of cellulose in HTC. Considering the energy balance and engineering, 190 °C was recommend for the preparation of solid fuels from CSD and seemed to be more viable for the combination of AD and HTC.

Co-hydrothermal carbonization of corn stalk and swine manure: Combustion behavior of hydrochar by thermogravimetric analysis

The combustion behavior of the hydrochar from co-hydrothermal carbonization (HTC) of corn stalk (CS) and swine manure (SM) was thermogravimetrically investigated. Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) were used for kinetic analysis, and the thermodynamic parameters were determined. Results showed that HTC decreased the combustion property and stability of SM, while co-HTC with CS significantly improved the combustion performance of the hydrochar including the increased ignition temperature and decreased burnout temperature. HTC of SM decreased the average activation energy (Ea) value from 140.40 and 137.31 KJ/mol to 124.40 and 120.17 KJ/mol by FWO and KAS, respectively, and increasing proportion of CS during co-HTC increased the Ea value of the hydrochar to 141.53–171.23 and 138.35–169.66 KJ/mol, respectively. The thermodynamic parameters confirmed the enhanced combustion reactivity of the hydrochar from co-HTC of CS and SM. These findings demonstrated that co-HTC with CS benefited the hydrochar production from SM with improved combustion performance.

The influence of combined pretreatment with surfactant/ultrasonic and hydrothermal carbonization on fuel properties, pyrolysis and combustion behavior of corn stalk

The surfactant/ultrasonic combined with hydrothermal carbonization (HTC) were performed to investigate the effect on fuel properties, pyrolysis and combustion behavior of hydrochar under different condition. The results showed that the C/H and O/C ratio of corn stalk (CS) + H2SO4 + tween was 1.1 and 0.29, which were close to coal, and the heat value reached 28.89 MJ/kg. HTC combined with ultrasonic/surfactant realized the complete separation of lignin with cellulose and hemicellulose in CS. Ultrasonic restricted the hydrolysis of lignin under alkaline condition and pseudo-lignin formation under acidic condition. Tween inhibited the formation and deposition of “pseudo-lignin”. The thermogravimetric (TG) experiments displayed the tween combined with HTC improved the pyrolysis temperature and decreased activation energy as well as the combustion ignition temperature which showed better pyrolysis and combustion characteristics. The nth-order kinetic mode was fit with the TG datas. The mechanism of tween combined with HTC was also analyzed.

Hydrothermal carbonization of holocellulose into hydrochar: Structural, chemical characteristics, and combustion behavior

The main aim of this work was to systematically investigate the effects of time on hydrothermal carbonization of holocellulose coming from the forestry residues. Based on the results, reaction time has a significant impact on the structural, chemical, fuel characteristics and combustion behavior of hydrochars. With increasing reaction time, holocellulose is gradually converted into the amorphous hydrochars with aromatic structure and abundant oxygen-containing functional groups; the O/C and H/C decrease from 0.85 and 1.60 to 0.23 and 0.71, respectively. The HHVs of some hydrochars have reached the quality grade of medium-high quantity calorific coal. The combustion stage and characteristic parameters of holocellulose are predominantly modified after HTC, and HC-14 could be regarded as a good fuel. Additionally, the structural and chemical formation processes of holocellulose-derived hydrochar are proposed. These results revealed that HTC is an effective and simple strategy for converting holocellulose into functional, value-added, and energy-dense hydrophobic solid fuels.

Persulfate oxidation assisted hydrochar production from Platanus Orientalis Leaves: Physiochemical and combustion characteristics

Platanus Orientalis Leaves (POL), a widely planted tree in parks and along streets, was employed by sequential persulfate oxidation (Fe2+and persulfate) and hydrothermal treatment (HTC) to improve the thermal stability, energy yield and combustion behavior of hydrochars (HCs). Higher heating values (HHVs) of HCs derived from persulfate pretreated POL was increased by 30.5% at mild HTC temperature (i.e., 210°C) as compared to char without pretreatment. Elevating Fe2+/persulfate ratio to 0.2 enables HCs with high fractions of lignin, thus promoting the energy yield going up to 64.4%. The ultimate and proximate analysis, N2 adsorption-desorption isotherms, FT–IR spectroscopy and thermogravimetric analysis were conducted to probe into chars’ physiochemical and combustion characteristics. Results indicated that persulfate pretreatment on POL strengthened efficient HTC conversion from volatile matter to fixed carbon, increasing the ignition temperature of HCs from 261.5 to 404.3°C as compared to the char obtained with only HTC.