Pyrolysis Of Low-rank Coal Research Articles

Behaviors and mechanism of volatiles producing during coal pyrolysis with calcium oxide loading: Insights from model compounds analysis

Calcium is a highly effective catalyst for controlling the tar compounds produced during the pyrolysis of low-rank coal, forming valuable end products. However, the exact catalytic mechanism of calcium in coal pyrolysis remains unclear due to the complex nature of coal. In this study, the pyrolysis process and tar composition of lignite, both with and without the addition of calcium, were investigated across three distinct temperature intervals. The addition of calcium oxide increased the hydrocarbon content of tar by 16.39 % in the low-temperature range and 26.53 % in the intermediate-temperature range. Four model compounds containing different coal-related functional groups were selected to investigate the effects of calcium on pyrolysis performance and tar composition using thermogravimetric analysis, fixed bed reactor experiments, gas chromatography/mass spectrometry, in situ Fourier transform infrared spectroscopy, X-ray diffractometer, and X-ray photoelectron spectroscopy. The addition of calcium did not affect the thermal decomposition of polystyrene or polyethylene terephthalate; however, the primary pyrolysates underwent secondary reactions on the surface of calcium, which affected the composition of the liquid pyrolysis product. Meanwhile, calcium interacted with the carboxyl and phenolic hydroxyl groups in trimeric acid and phenolic resin to form carboxylates and phenates, which affected the thermal reaction and distribution of liquid products. The influence of calcium on the transformation mechanism of coal-related functional groups provides a theoretical basis for understanding the mechanism of calcium-catalyzed coal pyrolysis.

Comparative study of the composition and microstructural properties of semi-coke from microwave and conventional pyrolysis of low rank coal

Microwave pyrolysis technology can effectively realize the clean and quality improvement of coal. In order to study the changes of each component of coal in the process of microwave pyrolysis, the d002, La, Lc, combustion reactivity and conductivity of semi-coke after pyrolysis were analyzed by using XRD, TG, conductivity meter and other testing instruments, and the infrared spectra of semi-coke after pyrolysis were finely resolved by using Origin peak-splitting technique, and the composition of the coal gas in the process of pyrolysis and its percentage content were analyzed. The composition and percentage content of gas in the pyrolysis process were analyzed and compared with conventional pyrolysis. The results showed that compared with conventional pyrolysis, microwave pyrolysis can be completed at a lower temperature and microwave pyrolysis is more favorable to the release of volatile components, in which the content of CO and H2 in the gas fraction increased significantly compared with conventional pyrolysis. At the same pyrolysis temperature, the microwave semi-coke has a higher maximum combustion rate temperature than the conventional semi-coke, which is conducive to improving the thermal stability of semi-coke. The orderliness of the semi-coke increased with the increase of pyrolysis final temperature, resulting in the phenomenon of "similar graphitization". The increase in the number of carbon microcrystalline structures generates off-domain electrons, leading to a significant increase in conductivity. Meanwhile, FT-IR peak fitting analysis revealed that the R value inflection point temperature of microwave semi-coke was much lower than that of conventional semi-coke, which further proved that microwave pyrolysis could be accomplished at lower temperatures, and the C value showed a decreasing tendency with the increase of the final temperature of pyrolysis, which indicated that pyrolysis was an effective method to improve the quality of coal. The above analysis shows that compared with conventional pyrolysis, microwave can prepare high stability and high conductivity semi-coke at lower temperature.

Carbon nanotubes growth in modified bluecoke powders: Preparation and characterization, formation mechanism of CNTs, and potential application

Bluecoke powders pose challenges in large-scale industrial utilization due to their small particle size and low added value that become one of primary constraints on the coking industry. In this work, Fe catalyst-assisted microwave pyrolysis of low-rank coal to prepare the modified bluecoke powders containing carbon nanotubes (CNTs) was investigated, and their potential applications were discussed. The results showed that when the addition ratios of Fe(NO3)3 and Fe(C5H5)2 were 0.05 and 0.15 respectively, the yields of CNTs in the modified bluecoke powders were 4.77 wt% and 4.15 wt%, with diameters primarily range of 50–135 nm and 30–80 nm. Additionally, the specific surface area reached 1306.29 m2/g and 643.76 m2/g. Fe(C5H5)2 significantly influenced the MBPs, and Fe and Fe3C played pivotal roles in the growth of CNTs. The excellent adsorption property and good electrochemical activity of the MBPs exhibited their considerable potential applications.

Pyrolysis of shenmu coal to prepare blue-coke used as reductant

Blue-coke is a form of granular char prepared by medium-low temperature pyrolysis of low-rank coal. As a reductant, it has been widely used in calcium carbide production, ferroalloy, copper pyro refining, and ferrosilicon production in China due to the abundant reserves of raw coal and its excellent performance. However, there is little research on the pyrolysis process of granular coal to produce blue-coke and its characteristics as a reductant. Thus, the effects of pyrolysis temperature, heating rate, particle size and holding time at the final temperature on blue-coke preparation were investigated in a rotary kiln reactor. The quality index of blue-coke as a reductant and its properties, including the element composition, surface function groups, carbon forms, reactivity and lower heating value under different pyrolysis temperatures, were analyzed in detail. It is demonstrated that the pyrolysis temperature had a more significant impact on the quality of blue-coke compared to other pyrolysis conditions. With the rise of pyrolysis temperature, the blue-coke’s C/O and C/H increased. With the particle size and heating rate increased, the temperature gradients developed within the granular coal during the pyrolysis process led to the volatile release shifting to higher temperature zone and more secondary reaction occurrence. Nevertheless, the secondary reaction was restrained in the rotary kiln with good heat and mass transfer. The indexes of blue-cokes as reductants were met by the chars produced at temperatures from 550 oC to 750 oC with a holding time 60 min at this temperature and a heating rate of 10 oC/min. As the key index of blue-coke, the electrical resistivity decreased with the increase of pyrolysis temperature. It was found to be closely related to the removal of H and O heteroatom at the pyrolysis temperature below 700 °C. While at the higher temperature, the development of graphitized carbon structure took a major role on it. Nonetheless, the crystallite sizes of the blue-coke obtained under this low temperature pyrolysis were small and the carbon forms were turbostratic. These resulted in the blue-coke's high combustion reactivity, which would gradually decline with the rise of pyrolysis temperature.

Analysis of Structural Heterogeneity in Low-Rank Coal and Its Pyrolyzed Char Using Multi-Point Scanning Micro-Raman Spectroscopy.

Understanding the changes in carbon structure during the mid-low-temperature pyrolysis of low-rank coal is important for efficient utilization. Raman spectroscopy is commonly used to analyze the structural order of carbonaceous materials, but traditional methods may overlook the heterogeneity of coal/char. This research explores the heterogeneity of char structure derived from low-rank coal at 700 °C through multi-point micro-Raman analysis. The analysis of parameters such as area (A), intensity (I), full width at half maximum (FWHM/W), and peak position (P) reveals that the carbon structure becomes less ordered as coal transforms into char due to the deposition of small molecules on the surface. The study emphasizes the benefits of multi-point detection for gaining in-depth insights into the structural evolution of carbonaceous materials. The increased standard deviation of Raman parameters indicates diverse structural characteristics resulting from pyrolysis at this temperature, which traditional methods may not capture effectively. The mapping method used in this research visually illustrates the distribution of carbon structures in the region.

Catalytic Pyrolysis of Naomaohu Coal Using Combined CaO and Ni/Olivine Catalysts for Simultaneously Improving the Tar and Gas Quality

Catalytic pyrolysis of low-rank coal is currently an effective method for producing high-quality tar and gas. In this study, catalytic upgrading of volatiles from Naomaohu (NMH) coal pyrolysis has been conducted in a two-stage fixed-bed reactor using combined CaO and Ni/olivine (Ni-loaded olivine) catalysts. The effect of catalyst distribution modes and catalytic temperature on the tar and gas quality has been investigated. Simulated distillation and GC-MS analysis have been used to investigate the distribution of tar components. The results indicated that the light oil fraction in tar dramatically increased due to the combination of CaO and Ni/olivine. The CaO-Ni/olivine mode is especially better compared to the layouts of the Ni/olivine-CaO mode and the mixed mode. The CaO-Ni/olivine mode ensures a higher light fraction in tar at 69.3% and a light oil fraction at 29.8% at a catalytic temperature of 450 °C, while the heavy tar fraction decreased to 30.7%. Meanwhile, the contents of benzene (heteroatomic substituents) in tar significantly increased from 2.55% to 6.45% compared with the blank test. In this scenario, CaO breaks down macromolecular compounds in tar and cleaves long-chain esters to produce aliphatic hydrocarbons. These hydrocarbons are then dehydrogenated to produce lighter aromatic hydrocarbons over the CaO surface. Subsequently, the volatiles pass through the Ni/olivine catalysis, where ether compounds are produced by means of dehydration reactions. In addition, the CaO absorbs the CO2 in the pyrolysis gas, leading to an elevation of CH4 and H2 concentration. Particularly, the concentration of H2 significantly increased from 16.2% to 30.37%, while the concentration of CO2 significantly decreased from 37.9% to 10.57%. These findings suggest that the usage of combined CaO and Ni/olivine catalysts is beneficial for improving both the tar and gas quality.

Effect of pretreatment synergistics on Shenfu low-rank coal pyrolysis in molten metal

The two key factors that significantly impact coal pyrolysis are its structural composition and the medium in which it is carried out. In this study, effects of acid pretreatment (AP), hydrothermal pretreatment (HTP), and acid-hydrothermal synergistic pretreatment (AP-HTP) on Shenfu Low-rank coal (SF) structure were investigated. In molten metals (MM), the distribution and composition of coal pyrolysis products were investigated to evaluate the impact of pretreatment synergistics. The results showed that changing the structure of the coal had a significant effect on the pyrolysis behavior. The molten metal stimulated the pyrolytic conversion of the coal. Pyrolysis in molten metal with AP-HTP synergistic pretreatment coal (SF-AH/MM) increased the tar yield and reduced the water yield. The tar of SF-AH/MM increased aromatic and phenolic compounds, while decreased the aliphatic and oxygen compounds. The H2 increased by 19.48 % and carbon oxides decreased for the gas of SF-AH/MM. Moreover, the char of SF-AH/MM enriched the aromatic structure and the content of the perfect graphite crystal structure, while reduced the degree of graphite lattice defects. The pretreatment synergistics affected the structure of coal and the molten metals enhanced the pyrolysis process, the distribution of products was optimized. Pyrolysis of synergistic pretreatment coal in molten metals is promising to enhance the tar yield, the H2 yield and improved the quality of the char.

Analysis of tar and pyrolysis gas from low-rank coal pyrolysis assisted by apple branch

Analysis of tar and pyrolysis gas from low-rank coal pyrolysis assisted by apple branch

Effects of pyrolysis temperature and atmosphere on grinding properties of semicoke prepared from Shenmu low-rank coal

This study investigated the effect of temperature and atmosphere on the grindability of the semicoke prepared via a mid–low temperature pyrolysis of low-rank Shenmu coal, analyzed the variation in its grinding characteristics with the increase of ball grinding duration, and explored the influence mechanism of the pyrolysis conditions on the grindability of semicoke based on the pyrolysis process and semicoke structure evolution. The results show that as the pyrolysis temperature increases (400–700 °C), grindability and grinding mechanism of the semicoke change significantly; the grindability first increases and then decreases with the increase of the pyrolysis temperature. As the grinding duration increased, high-Hardgrove grindability index (HGI) semicoke underwent intensive bulk grinding at a specific grinding time. Additionally, the varying contents of the proximate analysis during devolatilization are not the main cause of the varying HGI during pyrolysis. Using thermogravimetric and thermomechanical analyses, the optimal grindability of the semicoke was found to occur at the transition stage of the pyrolysis to pyrocondensation reactions (approximately 600 °C). During the transition, the intense pyrolysis reaction led the semicoke to have abundant pores and cracks, a highly disordered chemical structure, and low matrix hardness. The porous semicoke which has high grindability first underwent surface grinding; subsequently, the loose cores were more prone to bulk grinding, whereby the optimal grindability was obtained. HGIs of the semicoke prepared in the reductive atmospheres such as H2, CO and CH4 are lower than that of the semicoke prepared in N2 atmosphere at the same pyrolysis temperature. Moreover, the reductive atmospheres inhibited pore development in the semicoke and made its carbon structure more ordered, which densified the structure and decreased the grindability of the semicoke.

Gasification behavior and kinetics of chars derived from coal pyrolysis in a CO-containing atmosphere

Char gasification enables clean and efficient utilization of low-rank coal resources. The CO2 gasification behavior and kinetics of char samples produced via low-rank coal pyrolysis under the N2 and CO-containing atmospheres (char-N2 and char-CO) were investigated based on a series of thermogravimetric experiments, and the physicochemical structure of chars were characterized via Raman diffraction, X-ray diffraction, and CO2 adsorption methods, respectively. The apparent activation energies (Ea) of char-N2 and char-CO were obtained using the Flynn–Wall–Ozawa method and the reaction mechanism was determined via the Malek method. The results indicate that the graphitization and order degrees of the carbon chemical structure of char-CO are higher than those of char-N2 below gasification temperature (approximately 850 °C), whereas the specific surface area of char-CO is higher than that of char-N2 before gasification. Char-CO gasifies faster than char-N2 owing to its developed pore structure, and the gasification activation energy is lower than that of char-N2 (from 450 °C to 650 °C, the activation energy of char-N2 is 186.3 kJ mol−1, 192.4 kJ mol−1, and 203.6 kJ mol−1, and that of char-CO is 175.8 kJ mol−1, 187.5 kJ mol−1, and 199.1 kJ mol−1, respectively). The CO2 gasification reaction process of char-N2 and char-CO can be explained using a three-dimensional diffusion model. Moreover, the ash content in coal char affects the diffusion of reaction carrier gas and gas products during the gasification process, indicating that diffusion is the primary limiting factor in coal char CO2 gasification.

Insight into product characteristics from microwave co-pyrolysis of low-rank coal and corncob: Unraveling the effects of metal catalysts

Microwave pyrolysis of low-rank coal can provide high yield and quality of valuable products. Coupling with hydrogenated and catalytic pyrolysis is considered to achieve the selective or targeted generation of pyrolysis products. In this study, three metal catalysts KCl, Fe2O3, and CaO were used in the microwave catalytic co-pyrolysis of low-rank coal and corncob to investigate their effects on the temperature rise, product distribution, and product structure characteristics. The results showed that the maximum and final temperatures of microwave co-pyrolysis with the addition of a metal catalyst increased, and the corresponding yield and quality of tar were considerably improved. The porous structure of the char with the added metal catalyst was significantly enhanced, and the carbon microcrystal structure became significantly strong, but the change in thickness was minimal. The formation of aliphatic hydrocarbons and CO functional groups in both char and tar was inhibited when Fe2O3 and CaO were added. Among the three metal catalysts, CaO had the most obvious effect on the pyrolysis products, resulting in a maximum tar yield of 10.89 % and the highest light oil of 17.20 %. The char had a more regular and integrated porous structure; its Aar/Aal ratio reached a maximum of 12.603, showing the highest aromaticity. In addition, the total of valuable gas component and heat value of the pyrolysis gas arrived at 84.81 vol% and 14.93 MJ/m3, which showed excellent yield and performance. This work provides sufficient evidences for clean and efficient utilization of low-rank coal using catalytic microwave pyrolysis technology.

Directional Conversion of Volatiles from Low-Rank Coal to BTX-Rich Tar by Combined In Situ and Ex Situ Catalytic Pyrolyses.

Realizing the directional conversion of volatile matter (especially tar) from catalytic pyrolysis of low-rank coal (LRC) and reducing the consumption of catalysts have been considered great challenges for the classified utilization of LRC. In order to realize this aim, in this work, combined in situ and ex situ catalytic pyrolyses (IECPs) were first applied to the conversion of low-rank coal. A small amount of in situ ZSM-5 (5 wt %) was mixed with LRC to regulate the pyrolysis reaction, and then a large amount of ex situ ZSM-5 (100 wt %) was used to control the volatiles produced by pyrolysis. The IECPs (550 °C) of LRCs were investigated in a fixed-bed reactor. For three LRCs with different coalification degrees, IECPs could obviously reduce the complexity of the tar components. When ZSM-5 dosage was 5 wt % and the reaction temperature was 550 °C, the relative content of BTX in ZT, BS, and JY tar increased from 20.23, 15.86, and 14.59% to 84.79, 77.26, and 50.11 area %, respectively. The relative contents of aliphatic hydrocarbons with a complex composition and a low price decreased from 67.84, 34.47, and 33.89 area % to 3.02, 1.81, and 7.60 area %, respectively. The catalysis mechanism was explored by TG-FTIR spectroscopy, which revealed that ZSM-5 had a great influence on the migration of aliphatic hydrocarbon intermediates in IECP, such that large amounts of aliphatic hydrocarbons of complex composition produced by IECP tended to be converted to small molecular substances (gas) or aromatic hydrocarbons (tar). It will provide a new theoretical support for the staged utilization of LRC.

Effects of CO2 atmosphere on low-rank coal pyrolysis based on ReaxFF molecular dynamics.

Pyrolysis of low-rank coal in CO2 atmosphere can reduce carbon emissions while comprehensively utilizing coal resources. Based on ReaxFF molecular dynamics (ReaxFF-MD), the pyrolysis processes of low-rank coal in inert and CO2 atmosphere are simulated. By comparing the evolution of pyrolysis products, the influences of CO2 on the pyrolysis characteristic and product distribution are analyzed. It is found that CO2 slightly inhibits the conversion of char to tar in the early stage of pyrolysis. In the later stage, CO2 significantly promotes the decomposition of char and increases the yield of tar and pyrolysis gas. According to the different bond breaking behaviors of coal molecules, the pyrolysis process can be divided into pyrolysis activation stage, initial pyrolysis stage, accelerated pyrolysis stage and secondary pyrolysis stage. The reforming reaction of CO2 with alkanes generates free hydrogen radicals, which promotes the cleavage of ether bond, Car-Car bridge bond and aliphatic C-C bond. Compared with in inert atmosphere, final yield of light tar in CO2 atmosphere increases from 17.98% to 20.68%. In general, the CO2 atmosphere helps to improve the tar yield and tar quality of low-rank coal pyrolysis.

Catalytic effect of industrial waste carbide slag on pyrolysis of low-rank coal

Calcium-catalyzed coal pyrolysis to light tar is an attractive technology in coal clean conversion. The pyrolysis behavior and product distribution of low-rank coal over carbide slag (CS) were investigated by a thermogravimetric analyzer, fixed-bed reactor, and in-situ pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry (in-situ Py-VUVPI-MS). The results indicated that CS impregnation has a more significant effect on coal pyrolysis products than mechanical mixing and layered packing. The addition of CS makes coal pyrolysis tar significantly lighter, and the pitch content decreases from 33.5 wt.% without CS to 8.0 wt.% with CS impregnation but also makes benzenes and phenols content reduced by 16.4% and 55.5%, respectively. In-situ Py-VUVPI-MS analysis revealed that the decrease of benzenes content is mainly due to the secondary reaction of primary products catalyzed by calcium in CS, while the decrease of phenols content is mainly from the changed reaction path of oxygen-containing structure in coal caused by calcium catalysis. This work provides a theoretical basis for experimental research and practical application of coal pyrolysis catalyzed by CS, and the high catalytic activity, low cost, and abundant storage make the waste CS a promising Ca-based catalyst in coal pyrolysis.

Combustion reactivity of chars pyrolyzed from low-rank coal using a fixed bed reactor installed with internals

Pyrolysis of low-rank coal could contribute toward the goal of upgrading coal quality, chemical feedstock and fuel production. This research investigated the combustion reactivity of char pyrolyzed from a low-rank sub-bituminous coal using a conventional fixed bed reactor and a novel reactor with internals at 0 kPa and − 40 kPa gauge pressures. Proximate and ultimate analyses showed that the novel reactor reduced char’s fuel ratio by 46% and 54% at 0 kPa and − 40 kPa respectively. The chars derived from the novel reactor also had a higher order of carbonaceous structure and active sites, as supported by the increment in both IG/IALL and ID3/(IG+ID2+ID3) area ratios obtained from a Raman spectrometry analysis. From a non-isothermal combustion analysis, it was found that the ignition temperature of char derived from the novel reactor was 24–40 °C and 30–45 °C lower at 0 kPa and − 40 kPa respectively. A micro fluidized bed reactor analyzer was used for an isothermal differential analysis and it showed that chars produced from the novel reactor had an average combustion activation energy of around 77.3 kJ·mol−1, which was 23% and 10% lower than chars obtained from the conventional reactor at 0 kPa and − 40 kPa respectively. Overall, the novel reactor produces chars with more desirable combustion quality and, therefore, provides the opportunity for more low-rank coal to be upgraded and utilized more effectively as a fuel source for energy sustainability.

Analysis and distribution of volatile gases from catalytic pyrolysis of Sulcis low-rank coal

Catalytic pyrolysis of Sulcis low-rank coal over naturally occurring olivine, and home-made 15 wt%Ni/γ-Al2O3 catalyst was conducted for the upgrading of coal pyrolysis volatile gases in the temperature range ambient-900 °C under atmospheric pressure. Raw coal and mixtures of coal-additive (90:10 wt%) were slowly heated in temperature programmed mode using a laboratory-scale quartz furnace coupled in parallel to Fourier transform infrared (FTIR) spectrometer and GC chromatograph for quantitative analysis of flue gas. Coal pyrolysis with and without additives was also conducted by TG/DTG/DSC analysis at different heating rate (β = 15, 20, 30 °Cmin−1). DSC results clearly indicated some extra exothermic events during catalytic coal pyrolysis. Quantitative gaseous products distribution with temperature showed yields significantly and selectively improved with additives. Generally, more CO and CO2 were emitted under catalytic coal pyrolysis. Meanwhile, nickel catalyst exerted a marked positive effect on H2 yield overall in the temperature range 400–500 °C. The light hydrocarbons such as methane, ethane, propane and n-hexane substantially remaining unchanged, whereas a remarkable increase of emitted ethene was originated from catalytic pyrolysis. A deeper SO2 evolution was observed over olivine, whereas the N-containing compounds (NH3, NOx) were also modified in catalytic pyrolysis. Formaldehyde was also monitored, which represents a fragment originating from polycyclic aromatic side chains. Reaction kinetic study by a model-free isoconversional method indicated a complex multiple-step mechanism of coal pyrolysis, exception made for conversion values between 5% and 50% where a single-step reaction path was operating. The calculated average Ea and the pre-exponential factor were markedly reduced by the presence of additives. Meanwhile the compensation effect was also existing.

Effects of variable amounts of volatiles in corncob on microwave co-pyrolysis of low-rank coal and corncob

Crop waste-assisted microwave pyrolysis of low-rank coal (LRC) can provide sufficient hydrogen for thermal decomposition reactions of LRC, which can change the pyrolysis reactions and product characteristics. To reveal the effect of crop waste as a hydrogen supply on the microwave pyrolysis of LRC, the temperature-rise characteristics, product distribution, and product characteristics of microwave co-pyrolysis of LRC and corncob (CR) with different amounts of volatiles were investigated in detail, and the crystal and chemical structures of char and tar were analyzed. The results showed that the volatiles in CR promoted the production of tar and inhibited the generation of pyrolysis gas within a certain range during microwave co-pyrolysis; however, the volatiles had the opposite effect beyond this range. With an increase in volatiles in CR, the yields of char and pyrolysis water gradually decreased and increased, respectively. CR with low amounts of volatiles at high final pyrolysis temperatures increased the specific surface area and total pore volume of the char obtained by microwave co-pyrolysis and improved the aromaticity and graphitization of char and the ordered structure of the crystal structure in char. Additionally, the formation of aromatic structures in the tar was promoted, and the contents of oxygen-containing functional groups and aliphatic hydrocarbons in the tar were reduced. The fraction of light oil in the tar increased by 18.49%, indicating that the lightness and stability of the tar significantly increased. These findings have provided a theoretical basis for microwave co-pyrolysis of LRC and crop wastes, as well as experimental evidence for regulating its product characteristics.

Superfine comminution characteristics of low-rank coal pyrolysis semicokes and evolution of fragmentation fractal dimension

• The millimeter size comminution process conforms to the Steacy model. • The scale-depended fractal model could describe the superfine comminution process. • Pore structure and micro-defects have a significant impact on the comminution process. • With size decrease, the comminution mechanism shifts from shattering to abrasion. Based on the real demand of co-combustion of low-rank coal and its semicokes in pulverized coal furnace, Shenhua sub-bituminous coal (SH) and Ximeng lignite (XM) and their 700 °C semi-coke were selected to study their superfine comminution characteristics. With the increase of input energy, the comminution result of SH semi-coke is better than that of SH raw coal. And the comminution result of XM semicokes is always better than its raw coal. The fragmentation fractal analysis showed that as the input energy increases, the fragmentation fractal dimension (Df) of the two coals increased, approaching the limit fractal dimension of its material, similar to the Steacy model's 2.565. With excessive comminution energy input, both SH and XM samples showed that the higher the semicokes content, the better the comminution result. The size-dependent fractal model analysis showed that as the size of the breakage product gradually decreases, its Df decreases from about 3 to about 2 and the dominant comminution mechanism changes from overall shattering to surface abrasion. For semicokes with larger particle size contain more micro-cracks, these defects inside are easier to expand when excessive energy is input. Thus, semicokes samples would exhibit brittleness. When the size is reduced to a few microns, the raw coal and semicokes particles contain fewer defects and higher strength, resulting in a change in the comminution mechanism from overall shattering to surface abrasion.

Pilot test of low-rank coal pyrolysis coupled with gasification to hydrogen-rich gas for direct reduced iron: Process modeling, simulation and thermodynamic analysis

A Coal-Coke-Hydrogen-Iron (CCHI) system, low-rank coal pyrolysis coupled with gasification based on pilot test to hydrogen-rich gas for direct reduced iron (DRI), was proposed. The new process creatively proposes to blend the pyrolysis gas produced by pyrolysis of non-coking coal with the gasification gas produced by gasified coke to obtain the reducing gas that can meet the requirements of the DRI technology, addressing the problems of overcapacity in the coking industry and high carbon emissions in the steel industry. A strategy of partial cycle of top gas (rich in H2 and CO) from the shaft furnace is adopted to improve gas utilization and reduce carbon emissions, which is named as CCHI system with top gas cycle (CCHI-WTC) system. The key operation parameters and conditions such as steam/coke ratio, oxygen/coke ratio, reforming ratio and circulation ratio are optimized at 0.98, 0.43, 1.00 and 12.33 %, under which the energy consumption per unit product, exergy loss per unit product and greenhouse gas unit product emission of CCHI-WTC system can reach 15.13 GJ/t, 7.85 GJ/t and 761.50 kg/t, being reduced by 24.16 %, 20.14 % and 50.01 % compared to the traditional Coking-Blast furnace ironmaking process, respectively. This work provides a new low-rank coal application approach and breaks down the industry barriers of coal chemical industry and metallurgy.

Effect of coal grade and heating rate on the thermal degradation behavior, kinetics, and thermodynamics of pyrolysis of low-rank coal

ABSTRACT The work investigates the thermal degradation characteristics, kinetics, and thermodynamics of low-rank coals of three different grades selected from coal mines of Odisha, India by thermogravimetric analysis in temperatures ranging from 30°C to 1000°C under a nitrogen atmosphere at five heating rates of 5, 10, 15, 20, and 25°C min−1. The kinetic parameters are computed using model-fitting methods assuming first-order kinetics in the 250–635°C temperature range of major weight loss. The average activation energy of the reaction at different heating rates is found to be in the range of 55–65 kJ/mol. The average entropy change is found to vary from −180.03 to −165.887 J/K/mol1, the average enthalpy change varies from 51.1758 to 57.574 kJ/mol and that of free energy change varies from 189.718 to 177.9 kJ/mol. In addition, the composition of the oil obtained by pyrolysis of the coal in a semi-batch reactor at different temperatures is analyzed by FTIR and GC-MS techniques. The composition of the oil is found to be affected by the pyrolysis temperature.