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能源互联网时代，用户参与能源消费与生产的互动将变得容易。在此背景下，区别于传统意义上用户用能成本的概念，提出了用户用能三重价值概念—空间价值、时间价值、柔性价值，来反映用户参与能源消费与生产互动中的用能价值。分析了用户用能的柔性价值挖掘对系统优化运行的影响，构建了考虑用户用能柔性价值的电力系统优化运行模型。该模型计及了柔性价值挖掘对系统功率平衡和备用容量约束的影响。多个场景下的算例研究表明，通过挖掘用户用能的柔性价值，不仅能有效增加风电消纳能力，还可以明显降低系统运行成本和碳排放。

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Biomass-based porous activated carbon is a carbon-based material with well-developed pore structure, good adsorption, and capacitive properties. To achieve the goals of peak carbon dioxide emission and carbon neutrality, biomass-based porous activated carbon is widely used in the fields of electrochemical energy storage, capacitive deionization, and wastewater treatment owing to its low cost, environmental friendliness, and cleanness. Biomass-based porous activated carbon is one of the commonly used electrode materials for supercapacitors, whose electrochemical performance is mainly influenced by its physicochemical structure. To address the problems of high energy consumption and difficult regulation of the performance of porous activated carbon electrode materials, some research has proposed the activation and oxidation gradient heat treatment technology. This technology adopts a chemical-physical co-activation synergistic control process and utilizes the waste heat of pyrolysis activation, which can reduce the consumption of chemical activator and reaction energy and alleviate environmental pollution. This technology can attain the dual objectives of efficient and clean conversion of agricultural and forestry waste and high-value utilization of porous activated carbon. In this study, porous activated carbon was prepared by using waste bamboo as the carbon source and KHCO3 as the activator for medium- to high-temperature (500-800 ℃) activation and low-temperature (200-350 ℃) air oxidation using air for synergistic regulation. The study also investigated the physicochemical structure and electrochemical properties of porous activated carbon under the synergistic effect of different activation and oxidation temperatures. The results showed that porous activated carbon activated at 600 ℃ was oxidized by low-temperature air at 350 ℃ (PAC-600-350), and the specific surface area was increased from 154.361 m²·g−1 to 264.235 m²·g−1, indicating that O2 in the air activates the expansion of pores. An increase of oxidation temperature from 200 ℃ to 350 ℃ elevated the elemental oxygen content in the porous activated carbon and the content of surface oxygen-containing groups (such as -C=O-O and -C-OH), enhanced the wettability, and improved the defect structure and pore structure. Moreover, the porous activated carbon after activation at medium to low temperatures (600 ℃ and 700 ℃) is more sensitive and susceptible to oxidation by low temperature air. Among different activation temperatures from 500 to 800 ℃, the PAC-600-350 porous activated carbon had the highest oxygen content (25.54%) and degree of defects (2.53) at the activation temperature of 600 ℃; while the pore structure of PAC-800-350 is the most developed at the activation temperature of 800 ℃, with a specific surface area as high as 1096.18 m²·g−1. In addition, PAC-800-350 is less affected by the oxidation of low temperature air and its surface oxygen-containing groups change to a lesser extent. In the three-electrode test, the specific capacitance of PAC-600-350 at a current density of 1 A·g−1 was 215.29 F·g−1, which is 1.47 times that of non-air oxidized porous activated carbon. At the current density of 5 A·g−1, PAC-600-350 exhibited higher cycling stability with a capacitance retention rate of 93.51% after 5000 cycles of charging and discharging. In the two-electrode test, the symmetrical supercapacitor with PAC-600-350 as the working electrode showed good electrochemical performance, with an energy density of 9.06 Wh·kg−1 at a power density of 215 W·kg−1. Overall, PAC-600-350 porous activated carbon is considered to have potential for practical application, this study can provide a reference for high value utilization of agroforestry wastes. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Functional Materials / Gongneng Cailiao is the property of Chongqing Functional Materials Periodical Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A large amount of crop straw waste has been generated every year in China at present. The crop straw needs to be treated in an environmentally friendly way for the sustainable development of agricultural production. Fortunately, the porous carbon materials can be fabricated from the biomass crop straw as a carbon source in recent years. Among them, the porous biochar has been one of the most important electrode materials in the field of the electrochemical energy systems, due to the developed pore structure with a large specific surface area, abundant surface functional groups, and excellent electrochemical performance. But, there are only a few surface-active locations, non-developed pore structures, and low electrochemical performance of crop straw porous biochar prepared by one-step pyrolysis activation technology. In this study, a new preparation test of porous biochar was conducted at different activation temperatures ranging from 500-900 ℃. A microwave hydrothermal pretreatment was also used to prepare the precursor, i.e., the phosphoric acid hydrothermal carbon of rice straw. Meanwhile, a systematic investigation was made on the chemical composition, surface groups and defects, as well as the pore structures and electrochemical properties of porous biochar at different activation temperatures. The results showed that the yield of porous biochar from the rice straw hydrothermal carbon was reduced from 50.31% to 33.47%, with the increase of activation temperature, where the yield of gas increased, and no tar was formed after 800°C. The highest carbon content of porous biochar (74.09%) was achieved at 800 ℃ during treatment. The H/C and (N+O)/C values decreased in the porous biochar, as the activation temperature increased, indicating that the increasing temperature strengthened the aromatization structure of the porous biochar. Hydrothermal carbonization and KHCO3 activation introduced a large amount of O element and some active oxygen-containing functional groups into the porous biochar. Specifically, the surface of porous biochar presented some oxygen-containing groups, such as -OH and C-O-C coupling, and the nitrogen-containing groups, such as pyridine N-6, pyrrolin N-5, graphite nitrogen N-Q, and nitrogen oxide N-O. These functional groups were beneficial to the wettability of the porous biochar, further reducing the ion transfer resistance in the electrolyte solution. The disorder degree and the carbon defects first increased and then decreased in the pore biochar, as the activation temperature increased. The largest surface defect of pore structure in the porous biochar was obtained after the full reaction of KHCO3 with the carbon atoms at 800 ℃. An optimal condition was achieved for the adsorption, transport, and storage of electrolyte ions, with a specific surface area of 1 002.20 m2 /g, a maximum total pore volume of 0.79 cm³ /g, and a mesopore volume ratio of 45.57%. Correspondingly, the best porous biochar was obtained under the three-electrode and KOH electrolyte system at 800 ℃, indicating the largest specific capacitance, the best rate performance, and the lowest resistance. The specific capacitance at 1 A/g current density of porous biochar was 312.81 F/g. The energy density of the symmetrical capacitor was up to 10.73 W·h/kg at the power density of 228 W/kg. Meanwhile, the specific capacitance retention of the symmetrical capacitor was 95.82% at the current density of 10 A/g after the 5 000 cycles of charge-discharge, showing excellent circulating stability in the prepared porous biochar. [ABSTRACT FROM AUTHOR]

It is of great significance to comprehensively study the physicochemical properties of microwave-assisted hydrochar Hydrochars (carbon-rich solids) from biomass can be converted to activated carbons via hydrothermal carbonization. This offers a promising way for the disposal of the lignocellulosic wastes in modern agriculture. In this study, a systematic investigation was made to explore the physicochemical and electrochemical properties of microwave-assisted hydrochar and alkali-activated carbon from straws. A microwave hydrothermal experiment was carried out using straws with different mass fractions of citric acid for the preparation of hydrochar and alkali-activated carbon. The physicochemical behaviors of the hydrochars and alkali-activated carbon were also investigated using various characterization techniques. The results showed that the yield, volatile matter and H content of the hydrochar from straws decreased, whereas, the ash, fixed carbon, C, S and higher heating value increased, as the mass fraction of citric acid increased. These parameters tended to be stable, when the acid mass fraction reached 10%. In the hydrochar, the conversion rate of oxygen, carbon, and calorific value first decreased, and then increased during the test. Hydrochar with the citric acid mass fraction of 10% exhibited the most abundant carbon microsphere structure, as well as the largest specific surface area and pore volume, with the mesopore volume of 0.06-0.10 cm³/g. After the 10% citric acid, the hydrochar was activated by KOH solution at 900 . The ℃ yield of activated carbon was about 8%-11%, while, that of activated gas was about 32%-35%, mainly including CO and H2. The total output of combustible gases was 450-530 L/kg. The abundant pore structure was formed for the activated carbon at 900℃, where the specific surface area, total pore volume, and diameter of pores were 1 250-1 570 m²/g, 1.00-1.20 cm³/g, and 3.55-4.10 nm, respectively. The majority of pores were the mesopores of 0.69-0.81 cm³/g and micropores of 0.35-0.38 cm³/g. Compared with hydrochars, the activated carbon showed the lower strength of O-H, aliphatic C-H, C=O, C=C and C-C, while, the higher intensity of peak energy in C-O-C bond. Similar to the hydrochars, the graphitization degree of activated carbon decreased, due to the increasing disorder and defects in carbon, indicating suitable for the energy storage of electrode materials. At low scanning rates, the cyclic voltammetric curves of activated carbon behaved symmetrical rectangular shapes, indicating that the characteristic of a typical double electric layer capacitance occurred in the activated carbon. Nevertheless, the cyclic voltammetric curve was gradually deformed, as the scanning rate increased. When the current density was 1 A/g, the specific capacitances of activated carbon at 900°C based on hydrochars from rice straw, maize stover and rape stalk were 160.54, 150.12 and 155.17 F/g, respectively. The capacitance retention rates of activated carbon from rice straw, maize stover and rape stalk after 5000 cycles were 91.04%, 88.12% and 89.06%, respectively, showing a good cycle stability. Among different straws, the rice straw showed the highest yield, ash content, carbon conversion rate and energy conversion rate of hydrochar and activated carbon. The maize stover represented the highest fixed carbon, C and higher heating value of hydrochar and activated carbon, whereas, the rape stalk displayed the lowest carbon conversion rate of hydrochar and activated carbon. The hydrochar and activated carbon from rice straw indicated the largest specific surface area, total pore volume, mesopore volume and micropore volume, whereas, those from rape stalk showed the largest pore size. The activated carbon from rice straw demonstrated the strongest vibration absorption peak of oxygen-containing functional groups, the lowest graphitization degree, as well as the largest specific capacitance, and highest capacitance retention rate. The findings can be benefit to improving the quality of hydrochar, and the utilization of activated carbon as electrode materials in intelligent industry. [ABSTRACT FROM AUTHOR]

The development of slow pyrolysis technology has great significances for using crop residue resources and relieving energy and environment crisis. In China, sunflower is an important oil crop, which is widely planted. The yield of sunflower straw is about 120 million tons. In this study, Sunflower straw was used as the raw material, the biochars derived from sunflower straw was used as additives, and TG-FTIR was used to analyze the pyrolysis process, and to study the effects of different preparation temperatures (500, 700, 900 ℃) and proportions (10%, 20%,30%,40%) of biochar on the pyrolysis characteristics of sunflower straw and gas products，which mainly include furans, acids, carbonyl compounds, aromatic aldehydes, CO, CH4, etc. The results showed that the activation energy of sunflower straw pyrolysis decreased from 60.21 kJ/mol to 38.07-50.35 kJ/mol at different proportions of biochar. With increasing proportion of biochar, the activation energy for the pyrolysis of mixed samples decreased, With the increase of biochar prepared at 500 ℃, the pyrolysis final temperature of sunflower straw increases from 367 to 380 ℃, the maximum weight loss rate of sunflower straw decreased from 15.68%/min to 9.83% /min, and the maximum weight loss temperature increased from 328 to 334 ℃. When biochar prepared at 500 ℃ with 10% addition, aromatic aldehydes showed the maximum release, and the release amounts of aromatic aldehydes and carbonyl compounds in the pyrolysis gas products decreased, while those of CO and CH4 decreased，furans and acids have no obvious change. With the addition of biochar at different preparation temperatures, the main pyrolysis range of sunflower straw was extended and shifted to different degrees, which migrated to high temperature zone when adding biochar prepared at 500 ℃, and migrated to low temperature zone when adding biochar prepared at 700 and 900 ℃. Maximum weightlessness temperature of sunflower straw pyrolysis rise from 319 to 334 ℃, then decreased to 309 ℃, and maximum weight loss rate has decreased, which indicates that biochar prepared at 500 ℃ shows strongest inhibitory effect of sunflower straw pyrolysis; The pyrolysis of biochar prepared at 700 ℃ and 900 ℃ promoted at the initial stage and inhibited at the whole process of pyrolysis. As the preparation temperature of added biochar increased, the pyrolysis activation energy of sunflower straw decreased from 60.21 kJ/mol to 45.05-50.35 kJ/mol. The release of furan, acid and carbonyl compounds from sunflower straw pyrolysis added with biochar prepared at three different temperatures was reduced. Upon the addition of biochar prepared at 500 and 700 ℃, the aromatic aldehydes in sunflower pyrolysis gas products were increased; upon the addition of biochar prepared at 900 ℃, the CO production in sunflower pyrolysis gas products increased. Compared with biochar prepared at the medium-and low-temperature，biochar prepared at 900 ℃, the furan, carbonyl compounds and CH4 in the pyrolysis products of sunflower straw decreased more obviously and the CO increased more obviously, which was related to the loose structure of biochar prepared at 900 ℃，which fully contact with sunflower straw. It is concluded that when the proportion of biochar prepared by 500 ℃ is 40%, the furans, acids and carbonyl compounds in the gas products are all decreased the effect of reduction is the best. And when the addition ratio is 10%, the low-temperature preparation of biochar (500 ℃) is conducive to the production of combustible gas, while the high-temperature preparation of biochar (900 ℃) is conducive to reducing the emissions of furans, acids and carbonyl compounds in the gas products. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

It is important to fully understand the formation mechanism and the physicochemical characteristics evolution of the microwave-assisted hydrothermal products from crop residues, which is also of great significance for high added value utilization of crop residues and quality control of hydrothermal products. The control variable method was used to design the single factor experiment. The effects of hydrothermal temperature, retention time, catalyst and crop residue types on the compositions and structural characteristics of the microwave-assisted hydrothermal products from rice straw, corn stover, rape stalk and cotton stalk were studied. The results showed that with the increase of hydrothermal temperature and retention time, the pH value of the liquid products decreased first and then increased, reaching the lowest value of 3.13, while the electrical conductivity and PO43+-P concentration of the liquid products increased first and then decreased, and the NH4+–N concentration of the liquid products increased and reached the highest concentration of 155 mg/L at 260 °C. With the increase of hydrothermal temperature and retention time, the yields, H/C and O/C of hydrothermal cokes decreased, while the fixed carbon, C and higher heating value (HHV) of hydrothermal cokes increased. The addition of alkaline catalyst of K2CO3 decreased the C content, HHV value, carbon conversion rate and energy conversion rate of hydrothermal cokes from crop residues, while increased the O/C content of hydrothermal cokes. The carbon conversion rates and energy conversion rates of hydrothermal cokes from crop residue can reach 56.65%-98.13% and 58.22%-92.19%, respectively. With the increase of hydrothermal temperature and retention time, the fragmentation degree in the surface and interior of hydrothermal cokes of the four crop residues were getting more seriously, and the surface and interior of hydrothermal cokes exhibited more nano carbon microsphere structures, while the O–H bond of the hydrothermal cokes of the four crop residues increased first and then decreased. Higher hydrothermal temperature increased the aromatic hydrocarbon structures of C=C, C–H, C–C and active oxygen functional groups of C=O and C–O of hydrothermal cokes, while the aromatic hydrocarbon structures and active oxygen functional groups of hydrothermal cokes increased first and then decreased with the increase of retention time. With the increase of hydrothermal temperature and retention time, the specific surface area, pore volume and pore diameter of hydrothermal cokes from crop residue increased first and then decreased. The addition of alkaline catalyst of K2CO3 increased the aromatic hydrocarbon structures, active oxygen functional groups, specific surface area, pore volume and pore diameter of hydrothermal cokes from crop residue. Comparing the four types of hydrothermal cokes from crop residues, the yields of hydrothermal cokes from cotton stalk and rice straw were higher, and the contents of C, H, volatile matter and the higher heating value of hydrothermal coke from rape stalk were the highest. The nano carbon microsphere structures of hydrothermal cokes from corn stover, rice straw and rape stalk were relatively obvious. Comparing the hydrothermal cokes from the other three types of crop residues, the specific surface area and pore volume of hydrothermal coke from cotton stalk were the largest, while the pore diameter was the smallest. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agricultural Science & Technology (1008-0864) is the property of Journal of Agricultural Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Biochars are solid products from the pyrolysis of crop residues, and their physicochemical properties vary with the pyrolysis conditions and crop residue types. It is of great significance to optimize the pyrolysis process and to regulate the physicochemical properties for high-value utilization of biochars. In this study, rice straw, wheat straw, corn stover, rape stalk and cotton stalk were taken as raw materials. And the orthogonal experiment was designed for considering the carbonization temperature, holding time and heating rate. Then the comprehensive scoring method was used to optimize the pyrolysis process. At last, the physicochemical properties of biochar under optimal technological conditions were analyzed. The results showed that the main order of the quality factors affecting physiochemical properties was carbonization temperature, holding time and heating rate. The optimum combination of the five kinds of straw carbonization process parameters was that the carbonization temperature was 500℃, the holding time was 30 min, and the heating rate was 10℃·min-1. The yields of biochars under the optimal conditions were 37.38% for rice straw, 34.42% for wheat straw, 34.39% for corn stover, 32.74% for rape stalk and 37.87% for cotton stalk, respectively. Thermal analysis showed that most of cellulose, hemicellulose and lignin in the straws were decomposed when the carbonization temperature exceeding 500℃ and the biochars showed the higher stability under optimal conditions. Due to the difference of straw compositions, the residue content of five kinds of straw had the significant differences. Under the optimal conditions, the mass fraction of fixed carbon was more than 40% and the C element was greater than 53%. The mass fractions of the N and K were 0.7% - 2.5% and 3.41% - 6.81%, respectively. The H/C and O/C ratios of the biochars were lower than those of crop residues. The ratio of H/C was lower than 0.6 in the corn stover, rape stalk and cotton stalk biochar. Therefore the biochars can be used as soil additives or carbon sequestration materials. The mass fraction of P, K, Na, Ca and Mg of the biochars were more than those of original feedstocks. Especially, the mass fraction of K was from 3.41% to 6.81%. Therefore, the biochars could be used to improve soil nutrient levels and promote plant growth, particularly in potassium-deficient soil. Furthermore, oxygenic functional groups such as —COOH and —OH are found on the surface of biochars obtained under the optimal conditions by Fourier transform infrared spectra analysis, and the species of groups were similar. The BET surface area of rice straw biochar obtained under optimal conditions was 10.35 m2/g. The N2 adsorption and desorption isotherms of the rice biochar belong to the type Ⅳ of isotherms. The average diameter of pores in rice straw biochar was calculated by the Barrett—Joyner— Halenda model. It showed that some meso-pores and macro-pores with diameters were greater than 3 nm. The biochar surface had oxygen-containing functional groups and mesoporous structures, which had the potential of fertilizer utilization. The results could provide some theoretical basis for the efficient utilization of crop residue biochars. [ABSTRACT FROM AUTHOR]