Comprehensive Combustion Index Research Articles

Phosphorus extracted municipal sludge-derived hydrochar as a potential solid fuel: Effects of acidic leaching and combustion mechanism

Hydrochar from hydrothermal liquefaction (HTL) of municipal sludge is often seen as waste. Initially, acidic leaching has been performed on hydrochar to recover phosphorus. This study evaluated the resulting hydrochar as solid fuel, thus achieving zero waste for integrating HTL into wastewater treatment plants. The effects of various leaching conditions on acid-modified hydrochar properties were examined. Compared to raw hydrochar, acid-modified hydrochar had a significant ash reduction (up to 44%). The leaching conditions (10 mL of 0.6 N HNO3/g for 2 h) for near-complete phosphorus extraction also achieved the following most desirable properties of acid-modified hydrochar: Maximized fuel ratio (1.3), higher heating value (20.5 MJ/kg), carbon content (48%), and minimized ash content (34%) on a dry basis. By removing most alkali and alkaline earth metals, acid-modified hydrochar could carry a low slagging and fouling risk compared to a high/severe risk for raw hydrochar. Acidic leaching also enhanced ignition temperature from 317 to 351 °C for safer storage and transportation of hydrochar, with a higher comprehensive combustion index (up to 9.9 × 10−8 min−2 °C−3). Overall, hydrochar fuel property was improved by acid modification, comparable to bituminous coal. For the first time, it was identified that hydrochar combustion was controlled by a two-step nth-order reaction mechanism f(α) = (1 − α)n with the reaction order changing from 3 to 1 as progressed. The acid modification did not affect combustion mechanisms but reduced activation energy in the first stage. The results demonstrated a sustainable approach for closing the waste loop and provided a pathway for transforming hydrochar into biofuel.

Investigation of Co-Combustion Characteristics of Waste Biomasses and Anthracite by TG-DTG/DSC and Machine Learning Method

ABSTRACT The co-combustion characteristics and thermodynamics of waste biomasses, namely coconut shell and corncob, with anthracite were investigated using TG-DTG/DSC analysis and artificial neural networks. TG-DTG experiments were conducted at different ratios of CS-AN and CC-AN, and the samples were heated from 293 K to 1273 K at heating rates of 10, 15, 20, 25, and 30 K·min−1. The results indicated three main stages in the combustion process of the mixtures and the combustion profiles shifted to higher temperatures with increasing heating rates. As the mass fraction of biomass in the mixtures increased from 10 wt.% to 90 wt.%, the residual mass of the co-combustion mixture decreased by 19.50 wt.% and 21.78 wt.% for CS-AN and CC-AN, respectively. The comprehensive combustion index of CS-AN increased from 24.645%2·min−2·K−3 to 167.274%2·min−2·K−3, while that of CC-AN increased from 26.262%2·min−2·K−3 to 102.654%2·min−2·K−3. The DSC results showed a peak of heat absorption followed by an exotherm in the co-combustion process. As the mass fraction of anthracite in the mixtures increased, the curve shifted toward the high temperature region and the exothermic time increased. The apparent activation energies (E) for CS, CC, and AN were 75.36, 112.08, and 90.90 kJ·mol−1, respectively. Additionally, 50 wt.% CS and 50 wt.% CC were more conducive to CS-AN and CC-AN co-combustion processes. 63 ANN models were utilized to predict the post-combustion residual weight of CS5-AN5. ANN56 was identified as the best performer, with error results (RSME = 1.482, MBE = 1.120, R 2 = 0.9982) and a topology of (3 × 15 * 5 × 1), which proved to be the most suitable model for the co-combustion characteristics of this mixture. This study provides theoretical and practical guidance for solving engineering problems related to the energy utilization of waste biomasses (coconut shell and corncob) with anthracite.

Investigation of the Effects of Cohydrothermal Carbonization on the Physicochemical Characteristics and Combustion Behavior of Straw Hydrochars

The use of straw biomass for energy can reduce the use of fossil energy and alleviate air pollution. Herein, the cohydrothermal carbonization (Co‐HTC) of rice straw and wheat straw with corn straw is investigated, and synergistic effects of multistraw biomass are observed in the Co‐HTC process. When the corn straw ratio is 75%, the energetic recovery efficiency, C content, and heating value increase compared to the calculated values of the Co‐HTC products. At 260 °C, the energetic recovery efficiency increases by 8.96% and the heating value increases by 2.28 MJ kg−1, which is beneficial for its application. The positive synergistic effect is probably caused by the enhanced dehydration and decarboxylation reactions. For the combustion behavior analysis, the entire combustion process is divided into two stages. When the corn straw ratio is greater than 50%, compared to the calculated values of the Co‐HTC products, the comprehensive combustibility index and activation energy of stage I increase and the activation energy of stage II decreases at 180 °C, while the activation energy of stage I decreases and the activation energy of stage II increases at 260 °C. These findings demonstrate that the Co‐HTC of multistraw biomass is suitable for solid biofuel production.

Distinct property of biochar from pyrolysis of poplar wood, bark, and leaves of the same origin

The biochemical composition of wood, bark, and leaves is different, and this difference will inevitably project to products from the pyrolysis of different parts of a tree. In this study, different tissues of the same poplar tree (wood, bark, and leaves) were pyrolyzed to probe the characteristics of pyrolysis products of varied feedstock. The results indicated that wood tended to be pyrolyzed to form bio-oil with the highest yield (57.7% at 600 °C) while gases with the lowest yield (12.2% at 400 °C) among the three feedstocks. The high content of inorganic species in bark (5.8%) and especially leaves (10.3%) promoted the gasification of the aliphatic structures to produce a high yield of gases (18.9% of gas yield in leaves pyrolysis at 600 °C). In addition, unlike that in pyrolysis of wood, the pyrolysis of leaves produced little sugar derivatives like ketones (0%) /aldehydes (0%), but more hydrocarbons, N-containing organics, and phenolics with large fused ring structures. The organic components in leaves and bark were highly unstable, and their decomposition was further enhanced with the abundant inorganic species. This hindered the aromatization of the leaves/bark-derived biochar, resulting in their lower heating value, energy density, thermal stability, and their lower comprehensive combustion index than the biochar derived from wood. Additionally, as the pyrolysis temperature increases, the varied composition of feedstock also led to distinct patterns for the evolution of functionalities of biochar.

Experimental investigation on co-combustion characteristics of semi-coke and coal: Insight into synergy and blending method

Co-combustion of semi-coke and coal is a prospective technique for large-scale disposal or utilization of the solid waste. In this paper, the co-combustion behaviors and kinetics of semi-coke and coal were studied by thermogravimetric analysis with a focus on the influence of blending method and synergy. The results indicated that the semi-coke combustion was improved by blending with coal, and the interaction between fuels tended to promote the co-combustion. The ignition and burnout temperatures were positively correlated with the carbon content of the mixture, while the comprehensive combustion index and stability index were negatively correlated with it. The layer blending and partition blending method seemed to show stronger promotion than uniform blending method, and the layer blending method with coal in the upper layer was recommended due to the better combustion behavior. The promotion of coal on semi-coke combustion was less affected in devolatilization stage but weakened by the decrease of O2 concentration in char burnout stage. The apparent activation energy (Ea) of the mixture decreased with the increasing faction of coal. The layer blending method with coal in the upper layer had the lowest Ea in devolatilization stage and relatively high Ea in char burnout stage. The work can give some new insights into waste co-disposal strategy and carbon emission reduction in China.

Investigation of the synergetic regulation of O2/Ar preheating treatment and sodium salt addition on semichar combustion characteristics

Using Raman spectroscopy, temperature-programmed desorption (TPD) and laser-induced breakdown spectroscopy (LIBS), the relationship between microstructural characteristics and molecular emissions was determined. It can be concluded that the enhancement of C2 and CN emissions was related to the generation of small aromatic rings and C(O) groups. Compared with the Ar preheating treatment, the presence of additional amount of O2 and sodium salt accelerated the dissociation of the large aromatic ring skeleton, leading to the significant enhancement of small aromatic rings, C(O) and CONa groups. Subsequently, the combustion performance of preheated semichar was investigated by the TG-DTG method. The experimental results demonstrated that pretreatment under oxidizing atmospheres (without and with sodium salt addition) enhanced the comprehensive combustion index (S) and the combustion stability (Rw) of semichars. The corresponding combustion activation energy (E) was weakened. Furthermore, the DFT method was used to analyse the combustion behaviours of semichars. This result demonstrated that preheating treatment (with or without sodium participation) altered the distribution of the Hirshfeld atomic charge (ADCH) of preheated samples, and the combustion essence of semichar was the fracture and recombination of aromatic clusters. For the semichar preheated in the O2/Ar atmosphere, the energy gap of the most optimized pathway was 436.26 kJ/mol. When sodium participated in the oxidizing pretreatment, the energy gap of the most optimized pathway was 413.80 kJ/mol. The positive effect of sodium on the combustion performance of semichar was identified, which was in good agreement with the experimental results.

Co-combustion dynamics and products of textile dyeing sludge with waste rubber versus polyurethane tires of shared bikes

The co-combustions of major waste streams such as textile dyeing sludge (TDS) and waste tires of shared bikes may reduce the dependence on fossil fuels, as well as enhance their circular management and the recovery of their value-added products. In this study, the ash-to-gas products, interaction effects, and reaction mechanisms of the co-combustions of TDS and waste tires were characterized. The mono-combustions included the three stages of water evaporation, volatiles release, and mineral decomposition for TDS and the five stages for both rubber (RT) and polyurethane (PUT) tires. The three substages of the main stage of volatiles release for TDS had the activation energy of 124.5, 144.9, and 167.5 kJ/mol and were best explained by the reaction mechanism models of D3, D5, and F2, respectively. The (co-)combustion performance indices rose with the increased heating rate. The blend of 25% TDS with 75% RT (TR) and 75% PUT (TP) led to the best co-combustion performance according to comprehensive combustion index, with TP outperforming TR. The co-combustions of TP and TR reduced the activation energy required for the main devolatilization stage reaction. There was no significant difference in the main reaction mechanisms between the co-combustions. The interaction between TDS and waste tires reduced the applied energy required for the main devolatilization stage. The co-combustions at the low temperature produced O-H, CH4, CO2, CO, SO2, NO, carbonyl products, olefin products, and ketones. The co-combustions increased the production of C-H, reduced SO2 release and the viscosity of their ashes, promoted the complete combustion of substances, and alleviated the scale and sintering issues regardless of TP versus TR and caused the early release of NO from TP. According to the thermodynamic equilibrium simulations, the TR co-combustion promoted the retentions of Ca, S, Si, and Fe, in particular, the fixation of S. The addition of PUT enhanced the combination of Ca and Si into CaSiO3. The optimization based on the artificial neural networks pointed to the temperature range of 400–800 oC and the TR co-combustion as the optimal operational conditions.

Thermal reactivity and flowability of pulverized coal blending with iron-bearing dust injection in blast furnace process

Pulverized coal (PC) blending with iron-bearing dust (IBD) injection technology in blast furnace (BF) iron-making process was proposed to valorize the IBD. Three aspects containing the co-flow property of PC and IBD, thermal reactivity and corresponding kinetics during the PC combustion process, as well as thermal variation and unburned PC distribution in BF were the main focuses of the present work. It has found that the Carr-flowability indexes of PC and IBD appear little difference. Their blends can be smoothly transported when adding portion of the IBD is less than 6%. In addition, comprehensive combustibility index (S), ignition index (Ci), and burnout index (Db) of the PC are improved when the mass fraction of the IBD enhances from 0% to 3%, and 6%, which proves that blending with the IBD can accelerate the PC combustion process. Moreover, the combustion activation energy (E) decreases after adding the IBD, which supports the improved thermal reactivity. Also, the accumulation of unburned PC in BF presents a decline tendency, which may promote the permeability of BF and help enhancing the pulverized coal injection dosage.

Biorefinery-oriented full utilization of food waste and sewage sludge by integrating anaerobic digestion and combustion: Synergistic enhancement and energy evaluation

Biorefinery-oriented full utilization of organic wastes by integrating anaerobic digestion and combustion is a promising approach. The objectives of this study were to investigate the effect of the co-treatment of food waste and sewage sludge on the performance of the combined system in terms of methane production, combustion characteristics and total energy output. The anaerobic co-digestion of food waste with sewage sludge showed a clear synergistic enhancement at the optimal food waste/sewage sludge ratio of 2:2, where the methane yield increased by 99 mL/g VSadded compared with the theoretical value. The analysis of aqueous products suggested that the synergistic effect was attributed to reduced volatile fatty acids accumulation and ammonia inhibition. Furthermore, the digestate at a ratio of 2:2 showed the best combustion characteristics with the highest comprehensive combustion index and combustion stability index of 4.87 × 10−7%2 min−2 °C−3 and 4.80 × 103%2 min−2 °C−3, respectively, which could be resulted from the more stable organic components and the catalytic effects of inorganic minerals. Finally, the energy evaluation showed that the co-treatment would increase the daily energy output and specific energy output of 100 t/d full-scale plant by 14.3 GJ/day-33.7 GJ/day and 0.3 GJ/t-0.6 GJ/t, respectively. These findings could provide some valuable information for anaerobic digestion-combustion-based biorefinery of organic wastes.

Thermal behavior and kinetics analysis of co-combustion of petroleum coke and paper sludge-derived hydrochar

The co-combustion reactivity and kinetics of petroleum coke (PC) and paper sludge-derived hydrochar (PS) were investigated via thermogravimetric analysis. The physical and chemical structure features were also systematically tested. The results show that the combustion process of PS could be divided into three stages, while for PC only one stage could be clarified. Due to high volatile content, developed pore structure and low carbon-order degree, the combustion reactivity of PS was higher than that of PC. Although the ignition property of the blends could be significantly improved by addition of PS, it changed little for the burnout temperature and as a result the combustion intensity was deteriorated. For the samples with addition of PS from 20 % to 80 %, the comprehensive combustion index decreased from 3.69 × 10-15 to 2.12 × 10-15. The Kissinger AkahiraSunose model-free method was used in the co-combustion reaction of PC and PS, and good fitting results were obtained. For different samples with varying addition of PS, the activation energies were in the range of 107.51–198.44 kJ/mol, with the lowest value obtained at 20 % of PS, which was also the optimum proportion for co-combustion of PC and PS.

Acid-promoted hydrothermal on Chinese herbal residue toward upgradation and denitrogenation capabilities

Chinese herbal residue (CHR) is an association of renewable resource and hazardous waste, and high nitrogen content and low energy density are two primary obstacles to its efficient and clean thermal utilization. In this paper, acid-promoted hydrothermal was employed to probe the feasibility on CHR toward enhanced solid biofuel concerning upgradation and denitrogenation. A more excellent hydrothermal promoter (H2SO4) was demonstrated to upgrade and denitrogenate CHR with better energy (1.125) and nitrogen densities (0.586) at optimal conditions (160 °C, 0.5 N H2SO4), which could be attributed to the improved removal of oxygen, amino and ash during acid-promoted hydrothermal. Compared to raw feedstock or the conventional hydrochar, the acid-promoted hydrochar had enhanced compositional characteristics with higher heating value (21.00 kJ·mol−1), lower nitrogen (1.44 wt%) and ash (11.03 wt%) contents, thus showing more stable combustion flame with a higher comprehensive combustion index of 4.861 × 10−8, a higher combustion stability index of 4979.342, lower combustion alkali index of 0.026, and less nitrogen gaseous pollutant emission. Thus, acid-promoted hydrothermal would be a promising way to convert CHR into much cleaner and higher-grade solid biofuel.

Hydrothermal carbonization of sawdust with the bio-oil of same origin impacts evolution of structures of hydrochar

The high tendency towards polymerization is a bottle-neck issue in upgrading of bio-oil, which, however, is highly desirable in co-hydrothermal carbonization (HTC) of biomass with bio-oil for enhancing production of hydrochar. In this study, co-HTC of bio-oil of the same origin with poplar sawdust was conducted at 180 to 260 °C. The results showed that the HTC in a water medium containing 10% bio-oil could enhanced the yield of hydrochar by ca. 36% at 220 or 260 °C through the cross-polymerization of the sugar-derived furans and ketones/aldehydes as well as the phenolics in bio-oil with the sawdust-derived organics. Furans/sugars in bio-oil showed much more contribution to the increase of hydrochar yield than the phenolics like guaiacol. The highly reactive organics in bio-oil even could react with the crystal region of cellulose at 180 °C, and affected property of hydrochar at especially the higher temperatures by promoting deoxygenation, enhancing carbonization, eliminating polar functionalities like -OH, retaining C=O for continued polymerization, etc. The co-existence of aliphatic organics and phenolics in bio-oil renders the simultaneous formation of highly volatile fraction and aromatic structures in the hydrochar. These created the carbon-rich hydrochar with higher crystallinity, lower hydrophilicity and improved comprehensive combustion index.

Interactive effects of NOx synergistic and hydrothermal aging on soot catalytic combustion in Ce-based catalysts

The Thermal gravimetric analysis (TGA) with In-situ Fourier transform infrared Spectrometer (In-FTIR) of fresh/hydrothermal aging Ce-based catalysts was carried out for the soot oxidation at different transition metal Mn, alkali metals K, precious metals Ag and rare earth metal Zr doping which used to extend the hydrothermal aging resistance of CeO2 catalysts. The comprehensive combustion index S, combustion stability index Rw and peak temperature Tp from TG-DTG curves were extracted to evaluate the soot catalytic combustion performance, and the NO2/NO ratio during the combustion process was also measured to analyze the NOx synergistic oxidation performance. The effect of metal oxide doping type, doping ratio and hydrothermal aging time on S, Rw, Tp and NO2/NO ratio was evaluated to reveal the change in soot catalytic combustion performance. The result shows that, compared with PU, the NOx synergistic oxidation performance of various metal oxides modified Ce-based catalysts ranked as K > Ag > Mn > Zr. With the metal oxide doping ratio increased, the soot catalytic combustion performance of K and Zr metal oxides modified Ce-based catalysts decreased, Mn and Ag metal oxides modified catalyst increased. After hydrothermal aging treatment, the NOx synergistic oxidation performance of various metal oxides modified Ce-based catalysts ranked as K > Ag > Mn > Zr. This work is helpful to reveal the basic mechanism of hydrothermal aging metal oxide modified Ce-based catalyst and NOx during soot catalytic combustion process.

Combined acid pretreatment and co-hydrothermal carbonization to enhance energy recovery from food waste digestate

To achieve clean and efficient utilization of food waste digestate (FWD), a novel strategy of combining acid pretreatment and co-hydrothermal carbonization was developed to prepare value-added hydrochar from food waste digestate. The acid pretreatment of FWD was carried out with 1 M HCl for 8 h at a solid-to-liquid ratio of 1:5. In addition to the characterization of physicochemical properties including proximate analysis, elemental content, heating value, and thermal stability of the hydrochar, TG-FTIR-MS and TG-DSC were used to evaluate the pyrolysis gaseous products and combustion performance of hydrochar. The results showed that the combination strategy enhanced the fuel properties of the hydrochar. In particular, the ash content of hydrochar was reduced to a minimum of 6.3%, thereby increasing the heating value by nearly two folds. The acid pretreatment and the addition of wood waste increased the H/C and O/C ratios of hydrochar while enhancing the thermal stability of hydrochar. The peak types of the infrared spectrum and mass spectrum of the pyrolysis gaseous products remained largely unchanged. Based on the comprehensive combustion index and combustion stability index, blending with wood waste could obtain a comparable combustion performance of the hydrochar with multiple cycles of acid pretreatment. The apparent activation energy of hydrochar was 102.0 and 90.4 kJ mol−1 by FWO and KAS methods, respectively. The strategy advocated here presents a new ‘green’ perspective for the large-scale energy recovery from food waste digestate that is currently under-utilized.

Effect of CaO and hydrothermal carbonization conditions on the fuel characteristics of rice husk hydrochars.

The effects of hydrothermal temperature and catalyst concentration on the basic elements and combustion characteristics and kinetic parameters of hydrochars were investigated using ultimate analyzer and thermogravimetric method with rice husk as the research object and CaO as the additives. The results showed that: (1) the fixed carbon content of hydrochars gradually increased with the increase of hydrothermal temperature, whereas the volatile content gradually decreased. When CaO was added, the changes of fixed carbon and volatile fraction gradually decreased with the increase of hydrothermal temperature, and H/C atomic ratio increased to different degrees, which had a certain inhibitory effect on the degree of hydrothermal carbonization of rice husk. (2) The peak of the volatile fraction combustion section of hydrochars combustion derivative thermogravimetric curve was higher than that of the fixed carbon combustion section. CaO concentration has less effect on the volatile combustion section, and the combustion peak of the fixed carbon section is significantly reduced. (3) When the heating rate of the combustion test is accelerated, the ignition and burnout temperatures of the sample increase and the overall combustion curve shifts to the high temperature region. (4) The comprehensive combustion index SN decreases with the increase in hydrothermal temperature. When the hydrothermal temperature is certain, the CaO concentration causes the SN to increase and then decrease, which finally reduces the combustion performance of hydrochars. (5) The activation energy of the fixed carbon combustion section of hydrochars is lower than that of the volatile combustion section, and the activation energy of both volatile and fixed carbon combustion sections gradually decreases after adding CaO. The primary reaction kinetic model was used to describe the combustion kinetics of hydrochars, and the correlation coefficients (R2) were all above 0.92, and the results were reliable.

Evaluating the impact of wood sawdust and peanut shell mixing ratio on co-combustion performance

Mixed combustion of different biomass fuels often occurs in household stoves and biomass boilers, depending on the economy and availability. It has been verified that the co-combustion of agricultural and forestry residues with coal and plastics can significantly improve combustion efficiency and reduce carbon emissions. This study focused on the long-neglected co-combustion of agricultural and forestry residues. Kinetic and thermodynamic analyses of five types of pellets made of wood sawdust (WS) and peanut shell (PS) with different mixing ratios were conducted based on data from a thermogravimetric analyzer. Real combustion experiments in a force-draft biomass stove were conducted, and the nitrogen oxides (NOx) and carbon monoxide (CO) emissions of the five pellets were discussed. Our study showed that the combustion performance of mixed fuel (including the flammability index, burnout index and comprehensive combustion index) is improved to varying degrees compared to that of WS. The combustion mechanism, activation energy, and other thermodynamic parameters can vary with the mixing ratio. All three mixed fuels significantly reduced CO emissions while increasing NOx emissions. Our study revealed the dynamics, thermodynamics, emission performance and other parameters of the co-combustion of WS and PS.

Assessment of micro‐scale thermal behaviors and combustion performance of organic fireproof plugging material in air atmosphere

AbstractOrganic fireproof plugging material (OFPM) has excellent flame retardance and is widely used in construction cable holes. In order to study the micro‐scale thermal behaviors and combustion performance of OFPM, thermogravimetric experiments were performed at five heating rates of 5, 10, 20, 40 and 60 K/min in air atmosphere. The results showed that polychloroprene, China clay and carbonate in OFPM were involved in the whole degradation process, which included four stages. In the first stage, polychloroprene was decomposed into the intermediate and HCl. Subsequently, the intermediate participated in the nonoxidative pyrolysis and combustion process in the second stage. The char generated from pyrolysis continued to burn completely, which can explain the complex process involving multiple peaks in this stage. The decomposition of China clay into metakaolin and H2O was responsible for third stage. The fourth stage was assigned to the thermal decomposition of carbonate. In addition, Shuffled Complex Evolution algorithm was used to optimize the kinetic parameters for the simplified four‐stage reaction scheme. The accuracy of the optimized kinetic parameters was verified by the comparison of experimental data at the extra heating rates. Finally, the combustion performance indices including ignition index, flammability index and comprehensive combustion index for the major components were calculated to evaluate the flame retardance of OFPM.

Hydrothermal carbonization of waste ginkgo leaf residues for solid biofuel production: Hydrochar characterization and its pelletization

This study explored the potential of hydrothermal carbonization (HTC) for the production of a carbon-rich solid fuel from Ginkgo leaf residues (GLRs). Density, durability, hardness, hydrophobicity, and energy input estimates for HTC treated and untreated GLRs pellets were determined. Results showed that hydrothermal treatment significantly improved the physical properties of pellets made from GLRs, especially, at the temperature treatment of 220 °C. Pellet durability and hardness from samples treated at 220 °C (HT220) increased from 70.1% and 0.8 N/mm2 to 96.8% and 2.1 N/mm2 when compared to those made from untreated GLR (control). Hydrochar pellets had higher fixed carbon contents, elevated heating values, and enhanced energy densification ratio in comparison to the control pellets. The equilibrium moisture content decreased from 13.9% to 4.8% for HT220 pellets. The activation energy of HT220 pellets decreased from 44.6 to 26.8 kJ/mol in the first order reaction model and from 93.9 to 61.2 kJ/mol in the 3D diffusion model compared to the control pellets. The comprehensive combustibility index S was enhanced twice for HT220 pellets. The high durability, low moisture uptake, and improved pyrolysis property indicated that combining hydrothermal carbonization with pelletization is an efficient way for GLRs utilization as solid biofuel.

Catalytic activity and influence factors of Mn-Ce mixed oxides by hydrothermal method on diesel soot combustion

To solve the soot elimination and optimize catalyst diesel particulate filter (CDPF) regeneration strategies, a series of Mn-Ce catalysts with different Mn/(Mn+Ce) molar ratios are successfully synthetized by hydrothermal method and the complete catalytic oxidation of diesel engine soot are investigated. Compare to CeO2 and MnO2, the catalytic promotion on soot combustion of Mn-Ce catalysts is more excellent by thermogravimetric experiments due to their better ability to activate oxygen species, which is consistent with results in characterization analysis. Among as-prepared catalysts, MC-0.40 has the best catalytic activity with the lowest starting temperature (Ts), peak temperature (Tp) and largest comprehensive combustion index (S) both in O2/N2 and NO/O2/N2 atmosphere. Influence factors on catalytic performance are studied. Weight ratios of soot/MC-0.40 catalyst are suitable at the range of 1:9–1:13, which makes soot combustion more easily. Ashes in the reaction process show adverse effects due to their ability to increase ignition point by inhibit heat and oxygen transfer. Mn-Ce catalysts are more sensitive and show better catalytic activity in NO atmosphere because of generations of abundant adsorbed species and NO adsorption/desorption. The three consecutive cycles of MC-0.40 catalyst are performed to study the catalytic stability, and thermogravimetric curves show that the potential reusability of MC-0.40 catalyst can be relatively accepted in soot combustion.

Integration of hydrothermal carbonization and aqueous phase reforming for energy recovery from sewage sludge

This study investigates the energy recovery from sewage sludge by combining hydrothermal carbonization and aqueous phase reforming of the generated process water. The hydrothermal treatment was carried out at 170 °C and 230 °C for 1 h, and produced a hydrochar with adequate physicochemical properties, such as a higher heating value (20–24 MJ kg−1) than sludge, improved fuel ratio (0.2–0.5) and a broad comprehensive combustion index (5.8 × 10−7 to 10.0 × 10−7 min−2 °C−3). Aqueous phase reforming of the process water was carried out at 220 °C and 25–29 bar for 4 h. A maximum H2 yield of 98.7 mmol H2 gTOC−1 was achieved using a bimetallic Pt/Rh catalyst supported on carbon black and for the process water obtained at the lowest carbonization temperature. The integration of hydrothermal carbonization and aqueous phase reforming processes is an interesting alternative for the management and energy recovery of sewage sludge, which allows reaching a potential energy recovery of 17.3 MJ per kg of dry sewage sludge, equivalent to 93.5 % gross energy recovery, under optimized conditions.