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In this work, a heating stage microscope and a thermogravimetric analyzer were adopted to explore behaviors of char-slag/ash transition during CO 2 gasification of rice straw (RS) and Neimeng lignite (NM). Effects of demineralized treatment and various gasification temperatures on the char-slag/ash evolution process were studied. Both RS and NM particles exhibited shrinkage particle form at a moderate reaction temperature (1000 °C). The variation of the existential state of K with char-slag/ash transition could well explain the reactivity differences between RS raw char and demineralized char. Compared to RS raw char, NM raw char showed a more significant flow of molten slag at 1350 °C, which accounted for the high inhibitory effects at the late stage of NM raw char gasification. There is a threshold conversion (x = 0.9) during the evolution processes of NM char samples to NM slag/ash at 1200 °C and 1350 °C, while this threshold value is only existing at 1000 °C for RS char gasification. [ABSTRACT FROM AUTHOR]

The effects of water on the pyrolysis and gasification characteristics of coal water slurry (CWS) and pulverized coals with different ranks have been studied in the present work. Rapid pyrolysis characteristics (i.e. char yield, char structure evolution) of raw carbonaceous materials with varied water contents were investigated by using a high frequency furnace at 800–1200 °C. Moreover, gasification characteristics of the pyrolysis char were studied by using a thermogravimetric analyzer (TGA). The results indicate that at the pyrolysis temperature of 800 °C, the char yield of Wu-ran-cha-bu (WRCB) lignite slightly decreased with increasing the water content from 2.1 wt.% to 13.98 wt.%, while that of Yun-nan (YN) lignite showed a more significant decrease with increasing water content from 2.2 wt.% to 11.54 wt.%. This could be attributed to a higher coal reactivity of YN lignite than that of WRCB lignite. When the pyrolysis temperature was at or above 1000 °C, due to more significant in-situ coal-steam interactions, a lower char yield of both the pulverized lignites were observed with increasing water content from 2 wt.% to above 10 wt.%. CWS char presented a higher graphitization degree than pulverized coal char. The carbon microcrystalline structure factors (i.e. L 002 /d 002 value) of pyrolysis char increased with coal rank, which might reflect the variation trend of the graphitization degree from low rank coal to high rank coal. During the rapid heat treatment processes, the water evaporation and the in-situ steam-char gasification were favorable for void formation for both pulverized coals with high water contents and CWS. Notably, during the gasification processes of three different rank coals at 1200 °C, a more significant inhibition effect of residual ash on CWS char was observed compared to the pulverized parent coal char with high carbon conversion (x > 0.9). [ABSTRACT FROM AUTHOR]

Pyrolysis behaviors of two lignite coals with different drying conditions were determined by a thermogravimetric analyzer coupled with mass spectrometer (TG-MS) and a high-frequency furnace. An in-situ heating stage microscope was adopted to observe the morphological changes during char-CO 2 gasification process. It is concluded that the effects of moisture contents in coals on the gaseous release process during coal pyrolysis mainly depend on coal type, final pyrolysis temperature and heating method. The in-situ heating stage experiments indicate that the shrinking particle mode is suitable to illustrate the gasification reaction mechanism in the initial and midterm reaction stages of all the lignite char samples. Although drying conditions have significant effects on coal pyrolysis process under rapid heating, these dewatering conditions result in little noticeable reactivity loss of the char during the subsequent char-CO 2 gasification reaction. The measuring results of catalytic active sites can well explain the similar reactivity of lignite coals with different drying conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of HTC on coconut shell fuel properties were quantitatively studied. • The composition of hydrochar is similar in condition of 200 °C–0 h and 180 °C–3 h. • The migration behavior of different forms potassium was studied after HTC process. • Kinetic models were adopted to predict products yield during HTC. Hydrothermal carbonization is a promising renewable technology to produce high quality solid biofuel with characters of sterilization, micronization, and homogeneous. In this work, coconut shell was used as feedstock to investigate the products distribution, reaction kinetics and the migration of potassium during HTC process. Experiments were carried out in 180–240 °C with residence time of 0–5 h. The results showed that the content of fixed carbon increased from 20.76 wt% to 49.80 wt%, and HHV increased from 20.75 MJ/kg to 31.77 MJ/kg at 240 °C with the holding time of 3 h. The ratio of H/C dropped from 1.78 to 0.86 and O/C dropped from 0.68 to 0.16 which all indicated the improvement of fuel performance. The effects of increasing temperature and prolonging residence time on the products were in the same direction but different in severity. The properties of the products changed little after the residence time was more than 1 h. In addition, chemical fractionation method was used to investigate migration behavior of potassium. The best removal temperature of potassium was 200 °C which decreased potassium concentration from 2.7 mg/g to 0.6 mg/g specifically. Due to the increase of specific surface and porosity caused by high temperature, the content of potassium rose slightly at 220 and 240 °C. A kinetic model was adopted to predict the products distribution and yield of solid phase and gas phase. The activation energies (Ea) of different reaction paths were calculated and the results showed that Ea of gas formation is greater than that of solid. Migration behavior of potassium and modeling of HTC process is of great significance for design, optimization of industrial HTC reactor and selecting the best time for discharging and feeding to achieve better performance. [ABSTRACT FROM AUTHOR]

In this work, the influences of the gasification temperatures (1000–1150 °C) and blended ratios (3:1, 1:1, 1:3) on the co-gasification reactivity and synergy of petroleum coke (PC) and municipal solid waste (MSW)-derived hydrochar (HTC) were studied using a thermogravimetric analyzer (TGA). Chemical fractionation analysis (CFA) coupled with an inductively coupled plasma optical emission spectrometer (ICP-OES) was adopted for quantitatively investigating the active alkali/alkaline earth metal (AAEM) transformation (i.e., active AAEM content variation) during co-gasification in order to correlate the synergy mechanism of co-gasification. The results indicated that the co-gasification reactivity of the blended chars was enhanced with increasing gasification temperatures and HTC char proportions. The variations of the synergy behaviour on co-gasification reactivity at different conversions showed continuously enhanced synergistic effect at early co-gasification stage and decreased synergistic effect with further co-gasification. Moreover, higher gasification temperatures and HTC char proportions were more favourable for the continuous enhancement of the synergistic effect as co-gasification conversions increased. The overall synergistic effect on co-gasification reactivity was more obvious at higher HTC char proportions and lower gasification temperatures. The relative transformation ratio ( P ) was proposed to characterize the active AAEM content variation during co-gasification. P was negative when more active AAEM remained in blended chars, meaning that there was inhibition effect on the active AAEM transformation. It was found that the inhibition effect on the active Ca/K transformation was first enhanced and then weakened whereas the promotion effect on the active Na transformation showed an opposite trend with increasing conversion of co-gasification, which well correlated the synergy behaviour variations during PC-HTC blended char co-gasification. This work not only revealed synergy mechanism of petroleum coke and MSW-based hydrochar co-gasification but also provided reference data for the design and operation of industrial gasification units consuming mixture of petroleum coke and waste biomasses. [ABSTRACT FROM AUTHOR]

• CCD-RSM was used to determine the effects of parameters during HTC process. • A thorough evaluation of the optimize process was based on overall desirability. • 200 ℃-0 min was determined to be the optimal processing condition in HTC of CS. • Improved hydrochar properties showed high potential of HTC for upgrading biomass. The utilization of biomass energy is desirable to achieve carbon neutrality in the world. Hydrothermal carbonization of coconut shell was performed using center composite design with an aid of response surface methodology to determine the individual effects and combined effects of parameters on responses. The experimental design incorporates two variables and three responses. More specifically, the effects of temperature (180–220 °C) and hold time (0–60 min) on hydrochar yield, higher heating value (HHV) and energy yield were investigated. According to the results, hydrochar yield varies monotonically with temperature and hold time. With increasing temperature and hold time, hydrochar yield was dropped gradually. The highest hydrochar yield of 75.67 % was obtained at 180 °C-0 min and the lowest hydrochar yield of 63.13 % was achieved at 220 °C-60 min. HHV showed opposite trend to hydrochar yield, reaching a maximum value of 29.39 MJ/kg at 220 °C-60 min. The change in energy yield was influenced by the variation of hydrochar yield and HHV and does not change monotonically with temperature or time. It reaches the maximum value 90.83 % at 200 °C-0 min. Furthermore, to select best operating conditions, a comprehensive evaluation of the experiments was conducted based on the overall desirability. A series of characterization experiments were conducted on selected hydrochar samples. The results of functional group and pore structure changes showed that raw biomass has converted into value-added products with stable structure properties. In conclusion, hydrothermal carbonization as a pretreatment for upgrading coconut shells is a feasible process and can be used for biofuels production. [ABSTRACT FROM AUTHOR]

• Wet and dry carbonization of food wastes were detailed compared for bio-fuel production. • Dry carbonization showed superior fuel properties while led to N-relating issue. • Key factors for evaluating the solid biofuel qualities were provided. In this research, three categories of food waste (dried cabbage, chicken, and rice) were separately subjected to hydrothermal carbonization (HTC) under 180 °C, 200 °C, and 220 °C and pyrolytic carbonization (PC) under 200 °C, 250 °C, 300 °C, 350 °C, and 400 °C for solid biofuel production, respectively. Carbonization pathways, solid yield, high heating value (HHV), the transformation of nitrogen and ash, and char reactivity were detailly compared. After both pre-treatments, the ratio of fixed carbon (FC) to volatile matter (VM) of solid increased with the increase of the temperature, except for HTC of chicken. HTC of chicken led to more VM in solid product with very low solid yield and significantly lower N content. HTC-chars showed higher VM even at the same temperature as PC despite more severe carbonization (higher C content). Even though the N content can be reduced by both HTC and PC, HTC showed superiority than PC in regards to reducing the N content, indicating the potential to mitigate the N-related emission. Even though the HHV of HTC char was higher than that of PC char at the same pretreatment temperature, the product yield of the former one was much lower, resulting in lower energy yield in HTC char. The alkaline index (AI) can be used as the main factor for comparisons of gasification reactivity between (1) HTC and PC-chars and (2) Among HTC-chars from different temperatures. PC-chars presented higher reactivity than HTC-chars for all types of feedstock when considering at the same pre-treatment temperature at 200 °C. In conclusion, the key parameters including VM, the solid yield, HHV, the N content reduction, and char reactivity can be adopted to well evaluate the solid biofuel qualities production from different processes of HTC and PC, respectively. [ABSTRACT FROM AUTHOR]

• Effect of biomass hydrothermal treatment on co-gasification reactivity and synergy was studied. • Co-gasification synergistic effect was weakened at higher hydrothermal treatment temperature. • Chemical structure evolution of coal char in co-gasification well correlated with co-gasification synergy. This work investigated the influence of biomass hydrothermal treatment (HT) on co-gasification reactivity and synergy of anthracite coal and banana residue hydrochar (HTC) prepared at varying HT temperatures (180 °C, 200 °C and 220 °C). In addition, the effect of HTC char on chemical structure evolution of coal char in co-gasification process was studied to correlate the co-gasification synergy. The results revealed that the co-gasification reactivity of the blended chars was enhanced with decreasing HT temperature. Moreover, the differences in synergistic effect on co-gasification reactivity was greatly influenced by HT temperature, and a more pronounced synergistic effect was achieved at the lowest HT temperature (180 °C). This phenomenon could be well explained by the chemical structure variations of coal char during co-gasification. Active AAEM contained in HTC char showed positive effect on the chemical structure evolution of coal char, specifically on the decrease in the order degree of carbon structure as well as increase in the amount of amorphous carbon structure of coal char; furthermore, this positive effect was weakened as HT temperature increased, being more evident for HT temperature of 180 °C than 200 °C and 220 °C. The findings in this work would be useful in revealing the co-gasification synergy mechanism of biomass hydrochar and coal blends, and may provide valuable information on the relevance of HT to industrial-scale gasification systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • An integration of pilot-scale HTC, gasification, and anaerobic digestion for EFB conversion was investigated. • Inherent AAEMs have significant effects on gasification products. • CO and H 2 were enhanced under CO 2 /O 2 gasification. • Liquid products from HTC can be utilized for methane production via anaerobic digestion. • The mass and energy balance revealed that the whole process could be feasible. In the context of evolving a circular economy for the palm-oil industry, this article presents a study of oil-palm empty fruit bunch (EFB) conversion and utilization within a palm-oil mill. Pilot-scale hydrothermal carbonization (HTC), washing and gasification processes, as well as anaerobic digestion of the HTC liquid product were investigated. Results showed that the fuel properties of hydrochars had improved. In terms of air gasification, char and tar products accounted for 22.7–33.8 % and 17.3–28.8 %, respectively while CO 2 /O 2 gasification resulted in 31.3–36.6 % for char and 8.5–30.8 % for tar. In general, hydrochar (HT-EFB) gave the lower tar content compared to washed hydrochar (HTW-EFB) due to the catalytic effects of alkali and alkaline earth metals. Major tar components from HT-EFB and HTW-EFB were aliphatic and monoaromatic hydrocarbons, respectively. Syngas products from air gasification of hydrochars were 39.9–56.5 %, 11.4–21.4 %, and 9.0–14.4 % for CO, H 2 and CH 4 , respectively while CO 2 /O 2 gasification products yielded 45.1–56.6 %, 11.6–24.3 %, and 9.4–14.0 % for CO, H 2 and CH 4 , respectively. The lower heating value of syngas was in the range of 4.7–6.6 MJ/Nm3 and cold gas efficiency was approximately 39.1–55.1 %. The cumulative methane from the liquid products amounted to 213.8 and 154.5 L/kg COD for food/microorganism ratios of 1:2 and 1:3, respectively. The mass and energy balance showed that the whole process is promising for future commercialization. [ABSTRACT FROM AUTHOR]

• The combustion reaction of char was promoted by injecting electrons into air. • Carbon oxidation to CO and CO 2 was promoted by injecting electrons into air. • There is a synergy effect on the thermal decomposition for the mixture. • The thermal decomposition of the mixture enhanced by injecting electrons into air. • The CH 4 production rate increased for the pyrolysis reaction when using electrons. In this research, the thermal decomposition characteristics of cellulose, polyethylene, and their mixture with electron injected air were investigated using a laboratory-scale reactor. An electron generator with a voltage of 12 V was adopted as the key part to inject the electrons into the air in order to accelerate the thermal decomposition of the carbonaceous materials in the reactor. In addition, a modified fixed bed reactor was adopted to investigate the effects of the different parameters including the ON/OFF of the electrons injection into air, the thermal decomposition temperatures (400 °C and 500 °C) and the feedstock (cellulose, polyethylene and their mixture) on the syngas generation as well as the weight reduction rate. The results showed that the combustion reaction of char was more accelerated in the electron-ON case than that in the electron-OFF case. For example, in the case of cellulose, the amount of CO 2 generation differs about 2 times between the electron ON and OFF cases. Also under the same conditions, the amount of CO generated can be suppressed to about 2/3 by the electron injection. In the case of polyethylene, the electron injection effect was confirmed only for enhancing the CH 4 generation. However, there was a significant synergy effect in the electron-ON case for the cellulose and polyethylene mixture. These results showed that the electron injected air can accelerate the combustion reaction of char. The results suggest a potential advantage of electron injection to improve conventional waste incinerators. [ABSTRACT FROM AUTHOR]

• A high quality fuel could be obtained from EFB through HTW and pelletization. • HTW was effective in miniaturizing the particle size of EFB. • 100 °C is sufficient in producing durable pellet. • Energy recovery from HTW and pelletization of EFB is 89.90%. Empty fruit bunch (EFB) has a high potential to be utilized as energy source. This study investigated the effects of the hydrothermal treatment and pelletizing temperature on the physical properties of the EFB pellets. EFB was hydrothermally treated using 10 m3 batch-type reactor and water washed using a centrifugal machine. Single pellet making device was used for pelletization of both treated and untreated EFB. The pellets were densified at a pressure of 60 MPa and a temperature of 100, 150 and 200 °C by using a single pelletizer. The pellet density, the compressive strength, the hydrophobicity and the durability of the produced pellets were evaluated. In addition, scanning electron microscope (SEM) was also utilized to examine the binding mechanism and its quality. The results showed that combination of hydrothermal treatment and water washing significantly improved the physical properties of EFB pellets especially, at the pelletizing temperature of 100 °C. At the pelletizing temperature of 100 °C, the pellet durability index (PDI) and compressive strength of untreated EFB pellet increased from 78.1% and 5.6 MPa to 98.72% and 15.6 MPa, respectively when compared to the treated pellet. Notable increase in pellet properties of untreated EFB were also observed as pelletizing temperature increase. At pelleting temperature of 200 °C, PDI and maximum load to 92.83% and 14.2 MPa respectively. However, only slight improvement in characteristics of the washed hydrochar pellets were observed as the pelletizing temperature increased. Finally, the energy balance in the process of EFB-to-Pellet was roughly calculated for the commercialized system, and the output energy in pellet products could reach 89.90%. [ABSTRACT FROM AUTHOR]