Abstract: Co-gasification of agroforestry waste biomass and coal realizes energy-saving, low-carbon emission, clean and efficient raw material conversion by taking advantage of their similarities and complementarities. The physicochemical properties of ash slag for raw materials are one of the key factors affecting the stable operation of co-gasification. It is the focus of co-gasification research. This paper reviews the research status of physicochemical properties of ash slag from co-gasification of agroforestry waste biomass and coal. It mainly includes the similarity and difference between agroforestry waste biomass ash and coal ash, the fusion and viscosity-temperature characteristics of mixed ash, the effect of alkali/alkaline earth metals in mixed ash on co-gasification reactivity, and sintering behavior during the slagging process. The influence mechanism of adding agroforestry waste biomass on the melting flow and sintering behavior of mixed ash is discussed. The prediction models and methods of fusion characteristics, viscosity-temperature, and slagging characteristics of mixed ash are also summarized. Finally, the future research directions of ash slag from co-gasification of agroforestry waste biomass and coal are proposed.
Abstract: With consumption of high quality coal resources, clean and efficient conversion of high sulfur coal has attracted much attention, and especially the regulation of organic sulfur in high sulfur coking coal is very important. During pyrolysis transformation of organic sulfur in coal begins with cleavage of C-S bonds in the macromolecular structure of coal and stabilization of sulfur-containing free radicals, and active hydrogen/oxygen is an important factor affecting the transformation behavior of organic sulfur. It is found that, during coal pyrolysis under hydrogen-enriched or oxygen-enriched atmosphere or co-pyrolysis with biomass or oxygen-containing organic matter, the active hydrogen/oxygen in the system can weaken C−S bonds of organic sulfur, and promote their cleavage, timely combination with the generated sulfur-containing free radicals. This can promote sulfur in coal transform to the gas phase and reduce the secondary reaction of sulfur-containing free radicals with coal matrix. At the same time, during co-pyrolysis of high volatile and high sulfur coals, the relatively abundant active hydrogen/oxygen in volatile will also affect the organic sulfur transformation behavior in high sulfur coal, and reduce the sulfur content in coke, which provides a theoretical basis for directional regulation of sulfur in coal.
Abstract: The co-thermochemical conversion of coal and biomass can contribute to the low carbonization of current fossil energy system. In this work, the bituminous and lignocellulosic biomass were selected to study the co-pyrolysis and co-gasification of coal and biomass, with the consideration of different hydrothermal carbonization (HTC) temperature and biomass blending ratio. The synergistic effect of co-pyrolysis and co-gasification was analyzed by using the thermogravimetric analyzer, and the H2 release property was investigated by the online mass spectrometer. The model-fitting method was adopted to analyze the overall kinetics during pyrolysis and gasification stage, respectively. The results showed that the synergistic effect of coal and biomass in co-gasification stage was much stronger than that in co-pyrolysis stage. The gasification synergy was enhanced with the biomass blending ratio, while the HTC pretreatment could weaken the synergy. The H2 production was inhibited during co-pyrolysis. The first-order reaction model could well describe the co-gasification process, while the n-order reaction model was suitable for the co-pyrolysis process. For the blends of raw or the slight HTC biomass and coal, the overall pyrolysis activation energy (Ea) was greater than that calculated by the weighted average, whereas the overall gasification Ea showed the opposite trend. For the blends of the severe HTC biomass and coal, the Ea of co-pyrolysis and co-gasification were both close to the weighted average value.
Abstract: The distributions of Hongshaquan coal's alkaline (earth) metals and their influence on coal char gasification reaction activity under different gasification conditions were investigated in a high-temperature gasification fixed-bed experimental system. The results showed that the Na discretely distributed on the char surface at low temperature, while it showed a slight aggregation phenomenon when the gasification temperature was higher than ash fusion temperature. During the gasification process, the K was evenly distributed on the char surface. The enrichment of Ca and Mg elements on the surface of coal char was relatively obvious. The migration clusters of calcium-containing and magnesium-containing minerals formed large-sized ash sphere in the depressions on the surface of coal char. There was a certain dependence on the distribution of the above two elements. As the carbon conversion increased, the apparent activation energy and pre-exponential factor all increased, and the reactivity of coal char became worse.
Abstract: A serial of Fe modified Zr-based montmorillonites were prepared by mechanical ball milling and their characteristics were depicted by X-ray diffractometer (XRD), N2 adsorption-desorption instrument (BET), temperature-programmed desorption of ammonia (NH3-TPD, H2-TPD), X-ray photoelectron spectrometer (XPS). The results show that compared with 24ZrAM, when FeCl3·6H2O and FeCl2·4H2O are used as iron sources, Fe–O–Zr structure appears on the 3Cl−-24ZrAM and 2Cl−-24ZrAM catalysts. In the presence of Fe sulfate, the specific surface area of the catalysts decreases markedly. With the introducing of Fe, the total acid content of catalysts reduces. Wherein, 3Cl−-24ZrAM has the highest acid content and strongest acid strength. H2-TPR shows that the temperature for Fe2O3 reduced to Fe3O4 in 3Cl−-24ZrAM, 2Cl−-24ZrAM and $3{\rm{NO}}_3^ - $-24ZrAM is lower than 500 ℃. Then, the effect of catalysts on the pyrolysis behavior of Xinjiang Hefeng coal and the bridge bond cleavage mechanism of different model compounds were investigated in a fixed bed reactor. It is noted that compared with 24ZrAM, the fraction of coal tar pitch all declines under the action of Fe species. Among them, 3Cl−-24ZrAM has the highest cracking activity with the light tar fraction of 63%, which is 18.9% higher than that of 24ZrAM. Meanwhile, the content of light oil and phenol oil are 1.3 times and 1.4 times higher than that of 24ZrAM, respectively. As for long-chain hydrocarbons, a further decline by 0.7% is observed. In addition, the conversion rates of benzyl phenyl ether (BPE), dibenzyl and biphenyl increase by 5%, 1.6% and 43.9%, respectively.
Abstract: Pyrolytic desulfurization of two Shanxi high-sulfur anthracites was investigated experimentally under hydrogen atmospheres using a micro fluidized bed reaction analyzer (MFBRA), the dynamic release behavior of sulfur-containing gas during pyrolysis was characterized by a rapid online gas analyzer, and the transformation between sulfur-containing components in the resultant char was analyzed based on morphological and XPS characterizations. The results show that the dynamic release of sulfur-containing gas features two intensity peaks at 530−560 ℃ and 812−830 ℃, respectively, indicating that the sulfur release proceeds by two subsequent processes: the reduction reaction of pyrite and the organic sulfur decomposition. The migration from inorganic to organic sulfur occurs predominately at lower temperatures, while the transformation between different forms of organic sulfur components is dominant at higher temperatures. Overall, the anthracite coal with a higher organic sulfur content has a higher sulfur removal efficiency in the hydrogen atmosphere. The research results provide the essential data supporting the development of highly efficient pyrolysis desulfurization technology for clean and efficient utilization of high sulfur anthracite coal resources.
Abstract: To address the slagging problem during coal entrained-flow bed (EFB) gasification, the influences of textile dyeing sludge (TDS) addition on the fusing characteristics of high ash fusion temperature (AFT) coal were explored under a reducing atmosphere. And the change mechanisms were investigated by X-ray diffraction, Fourier Transform Infrared Spectroscopy (FT-IR) and FactSage calculation. The results showed that the flow temperature of high ash fusion temperature (AFT) coal decreased below 1380 °C when the TDS addition reached 20%−25%, which met the requirements of liquid-slag removal for EFB gasification. With the content of TDS increasing, the formations of low-melting minerals (e.g., hercynite, anorthite, and albite) decreased AFT. The bridging oxygen bonds of the network structure were destroyed by metal ions (e.g., Fe2+, Ca2+, Na+), formation of much non-bridged oxygen (NBO) bonds relaxed the silicate network, thus decreasing the AFT. The formations of NBO bonds were confirmed by gradual decreases in the peak strengths of Si−O−Si and Si−O−Al bonds and intensified the vibration of Fe−O and Si−O−M ( M: Ca2+ or Na+) bonds. FactSage calculation results were in good agreement with the experimental ash fusion behavior.
Abstract: Gasification fine slag is a kind of solid waste with high carbon content produced in coal gasification process. The residual carbon obtained by carbon ash separation is a potential carbon source for preparing high quality carbon materials. In this study, the carbon residue after flotation of fine gasification slag was used as the precursor to prepare N-doped carbon-based electrocatalysts through high temperature activation. Combined with the characterization of Raman spectroscopy, XPS and SEM, the influence of activator ratio and nitrogen source on the physical and chemical structure of the catalyst was explored. The intrinsic relationship between activation formula and oxygen reduction performance of catalyst was revealed. The feasibility of preparing carbon-based electrocatalysts with gasification fine slag as raw material was verified. The results demonstrate that the oxygen reduction catalytic performance of carbon materials increases first and then decreases with the increase of the proportion of KOH. The optimal catalytic performance was achieved when the mass ratio of carbon residue to KOH was 1:4. In addition, melamine has stronger nitrogen doping effect as a nitrogen source than NH4Cl, making the initial potential of CKN6-143 up to 0.87 V (vs. RHE), the limiting current density is 4.95 mA/cm2, and the average electron transfer number is 3.82, indicating that CKN6-143 has good electrocatalytic performance. The results provide a possibility for preparing oxygen reduction catalyst with gasification fine slag.
Abstract: The low permeability of plastic layer of coking coal causes the formation of coking pressure, and the evolution of permeability is closely related to the release behavior of volatiles. In this paper, a low-volatile bituminous coal C1 and a high-volatile bituminous coal C2 were selected as research objectives, and a lignite L1 and two semi-cokes produced from the pyrolysis of C2 at two temperatures were used as the contrast. The permeability tests of single coal, binary coal or semi-coke and separated combination were conducted. The influence of volatiles release behaviors on the evolution of permeability of plastic layer was revealed by thermogravimetric and fluidity analyses. The results showed that there was a low permeability plateau stage of plastic layer of C1, while the permeability of plastic layer of C2 was rapidly improved after reaching the lowest. This was related to the difference in the mass transfer conditions of volatiles from two coals. C2 could enhance the mass transfer driving force of volatiles and bring both inert components (semi-coke after pyrolysis) and transferable hydrogen, thus the permeability of plastic layer could be improved without destroying the stability of plastic layer. The hydrogen-rich volatiles released from C2 before its initial softening temperature helped the low permeability of the plastic layer of C1 be formed and reach the maximum. The volatiles released during the plastic stage of C2 helped maintain the low permeability plateau of plastic layer of C1. It was plausible to further improve the permeability of plastic layer of C1 by consuming part of hydrogen-rich volatiles from C2 with prolonging the volatiles’ reaction. This paper provided a new insight in selecting high-volatile coals for improving permeability of the plastic layer from the aspect of volatiles’ release behaviors.
Abstract: Corn straw was torrefied under at different temperatures and the torrefied products were characterized by proximate analysis, ultimate analysis, FT-IR, TGA and pyrolysis experiments; the effect of gas-pressurized torrefaction on the upgrading and pyrolysis characteristics of corn stalk was investigated. The results indicate that the deoxidation efficiency and energy density of torrefied products under both atmospheric pressure (AP) and gas pressured (GP) conditions increase with the increase of torrefaction temperature. The temperature required for GP torrefaction is almost 40 °C lower than that for AP torrefaction to obtain the same mass yield. The energy yield, carbon yield, deoxidation efficiency and the energy density of GP-torrefied corn straw are 1.125, 1.142, 1.539 and 1.131 times higher than those of AP-torrefied one, respectively. The GP-torrefied corn straw shows better hydrophobicity and is easier to dehydrate. In addition, the pyrolysis of GP-torrefied corn straw produces significantly higher fractions of CH4 and H2 in the gaseous product than the pyrolysis of AP-torrefied one; meanwhile, the relative content of phenols in the liquid products for the pyrolysis of GP-torrefied samples also increases up to 51.11%, whereas the contents of furans and acids decrease considerably. All these suggest that GP torrefaction performs better in biofuel upgrading than AP torrefaction under the same temperature.
Abstract: In order to study the pyrolysis and combustion characteristics of different fibers, the kinetics of six kinds of plant fibers (coniferous, broadleaf, bamboo, flax, grass and cotton) in N2 and air atmosphere were studied by non-isothermal thermogravimetric (TG) method using Friedman method. The results showed that the fibers had different pyrolysis and combustion characteristic parameters, which were related to their own structural compositions. In the process of pyrolysis and combustion of fibers, the initial volatilization temperature (Ts), terminal decomposition temperature (Th), DTG peak temperature (Tmax), fixed carbon combustion peak temperature, maximum mass loss rate, pyrolysis character index (P) and combustion character index (S) increased with the increase of heating rates; In N2 atmosphere, the flax fiber Tmax and bamboo fiber Tmax were shown to be the highest and lowest among all fibers, respectively, and Ts of cotton fiber was the largest; Grass fiber had the smallest maximum pyrolysis mass loss rate (−(dm/dt)max), pyrolysis index (P), and combustion index (S); Between the conversion of 0.05−0.85, the average apparent activation energies (E) of broadleaf fiber and bamboo fiber were the smallest (173.30 kJ/mol) and highest (201.10 kJ/mol), respectively. In air atmosphere, Tmax of all fibers in the pyrolysis process was lower than that in N2. The apparent activation energy (Eα) of fiber pyrolysis in air atmosphere was shown to be lower than that in N2 when the conversion was between 5% and 65%.
Abstract: As the most abundant and renewable aromatic source on the earth, lignin is a good alternative to fossil fuel on producing versatile petrochemicals and biofuel. However, current techniques for lignin conversion generally suffer from some key problems of harsh reaction condition and low selectivity of products. In this study, an efficient process was provided for selective depolymerization of herbaceous lignin to a fine chemical of methyl p-coumarate (MPC) by using cost-effective catalysts of metal oxides. The influences of different metal oxides, reaction temperature, time and solvent on the yield and selectivity of MPC were systematically investigated. The results showed that ZnO exhibited the best catalytic activity, where the yield and selectivity of MPC reached 9.80% and 61.6%, respectively, at the optimized reaction conditions. Furthermore, the results of products distribution and comparative investigation on the raw and unreacted lignin using FT-IR and 2D HSQC NMR spectra demonstrated that the efficient cleavage of the ester linkage in lignin was responsible for this good MPC yield and selectivity. Therefore, this work provides a new insight on producing fine chemicals from the renewable lignin.
Abstract: Cellulose is one of the most abundant renewable organic carbon resources in the world. Levoglucosenone (LGO) is a high value-added platform chemical derived from cellulose pyrolysis. In this study, the influence of ionic liquid catalyst on the production of LGO by catalytic pyrolysis of cellulose was revealed. The results showed that 1-butyl-2,3-dimethylimidazolium triflate performed best for the LGO formation. The reason was that the decrease in the length of the side chain weakened the interaction between the cation and anion of the ionic liquid, which increased the diffusion of the ionic liquid. LGO reached a yield of 15.6%-C at pyrolysis temperature of 300 ℃, and the recovery rate of ionic liquid attained to 95.9%. Besides, LGO yield only slightly decreased after 3 times re-utilization of the ionic liquid. The formation path of LGO was calculated by density functional theory. The result showed the lowest activation energy was 176.2 kJ/mol. Moreover, this method was effective to obtain porous char at the same time, and the highest specific surface area and pore volume were 389.4 m2/g and 0.689 cm3/g, respectively.
Supervisor：Chinese Academy of Sciences
Sponsors by：Shanxi Institute of Coal Chemistry, Chinese Academy of Sciences Chinese Chemical Society
