Direct Coal Liquefaction Residue Research Articles

Utilization of direct coal liquefaction residue (DCLR) in recycled emulsified asphalt mixtures: A solution as geopolymer binder and filler materials

The study evaluates the feasibility of using coal liquefaction residue (DCLR) as a substitute for mineral powder and DCLR-based polymers as a substitute for cement in emulsified asphalt mixtures containing 100 % recycled asphalt pavement (RAP). This research examines the impact of various curing regimes on the functional attributes of the modified emulsified asphalt mixtures by evaluating road performance, compressive strength, and elastic modulus. The findings indicate that DCLR can effectively substitute mineral powder, maintaining the mixture’s stability and durability. The "three-stage double compaction" curing technique significantly enhances mechanical properties. Furthermore, the incorporation of DCLR-based geopolymers augments the dynamic stability of the mixture, albeit slightly affecting bending strain and residual stability. The integration of DCLR-based geopolymers substantially boosts the shear resistance of cold-recycled mixtures. During the enhancement of mixture performance, DCLR primarily serves a physical filling role, whereas DCLR-based geopolymers contribute to performance improvement through physicochemical interactions. This study validates the practicality of employing DCLR in emulsified asphalt mixtures for high-temperature applications, suggesting a sustainable pathway for asphalt mixture design.

Influence of compatibilization methods on the compatibility between asphalt and DCLR components with molecular dynamics (MD) method

This study aims to investigate the effect of compatibilization methods on the compatibility between asphalt and direct coal liquefaction residue (DCLR) components to identify the key components in DCLR and asphalt that affect their compatibility. In this article, three types of compatibilizers, including benzyl alcohol (BA), dioctyl phthalate (DOP), and BA/DOP, were selected and acted on asphalt's components and DCLR's components, respectively. The molecular models of asphalt components, asphalt components with compatibilizers, DCLR components, and DCLR components with compatibilizers were established. The compatibility between DCLR and asphalt's four components, as well as between asphalt and DCLR's three components, were evaluated by solubility parameter difference (SPD) and interaction energy (IE). The compatibility between DCLR and asphalt was analyzed by Segregation test and Scanning Electron Microscope. Results indicate that the SPD and IE values between DCLR and asphalt components declined after adding compatibilizers, which implies that the repulsion decreased and the attraction increased between asphalt components and DCLR and the compatibility between asphalt components and DCLR improved. The IE values between DCLR components and asphalt increased after adding compatibilizers, which indicates that the compatibility was reduced between DCLR components and asphalt. The SPD values between DCLR components and asphalt increased after adding the BA/DOP. The SPD values between pre-asphaltene and asphalt decreased after adding the BA and DOP. The SPD value between asphaltene in DCLR and asphalt increased after adding the BA and decreased after adding the DOP. Moreover, the storage stability and homogeneity of DCLR-modified asphalt improved after adding compatibilizers, indicating that the compatibilizers enhanced compatibility between DCLR and asphalt. Finally, comparing the results of the tests, it could be found that compatibilizers preferentially acted on the asphalt components and mainly affected the aromatics in asphalt, thereby improving the compatibility between asphalt and DCLR. The effect of BA/DOP on improving the compatibility between asphalt and DCLR was better than that of BA and DOP.

Evaluation of benzaldehyd and dioctyl phthalate modified direct coal liquefaction residue asphalt binder based on rheology and microscopic mechanisms

This study intends to investigate the influence of benzaldehyde and dioctyl phthalate (DOP) on the rheological properties and microstructure of direct coal liquefaction residue (DCLR) modified asphalt binder. The high and low temperature rheological properties and fatigue properties were obtained by dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests. The scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR) tests were conducted to evaluate the mechanism of property improvement in the DCLR modified asphalt binder. The results showed that the addition of DCLR increased the complex shear modulus G*, rutting factor G*/sin δ and fatigue life Nf of base asphalt binder, significantly improving the high temperature deformation resistance and fatigue resistance of base asphalt binder. This was attributed to the hardening effect resulting from the addition of DCLR, which enhanced the elastic properties, weakened the viscous properties and fluidity of asphalt binder. Additionally, the use of benzaldehyde and DOP reduced the creep stiffness S and lower continuous grading temperature Tc of DCLR modified asphalt binder, which compensated for the shortcomings of low temperature rheological properties of asphalt binder. The SEM images indicated that benzaldehyde and DOP significantly increased the compatibility of DCLR with the base asphalt binder. The FTIR tests showed that the addition of benzaldehyde and DOP introduced the aldehyde and ester groups, which were interacted with more polar functional groups in the asphalt to reduce the resistance to movement between the heavy components in the DCLR modified asphalt binder, which promoted the flow of asphalt and the dispersion of DCLR, and as a result, the benzaldehyde and DOP modified DCLR asphalt binder exhibited satisfied rheological properties.

Preparation and Electrochemical Performance of Activated Composite Carbon Nanofibers Using Extraction Residue from Direct Coal Liquefaction Residue

Organic carbon extracted from direct coal liquefaction residue (DLCR) is an ideal precursor for the preparation of carbon materials. However, investigations into the utilization of the extraction residue (ER) are rarely reported. In this work, ER from DCLR was pretreated with H2O2 to afford oxidized extraction residue (OER). Then, the OER was mixed with polyacrylonitrile (PAN) in N,N-dimethylformamide for the preparation of composite carbon nanofibers by electrospinning. With adding 80 wt.% OER, the composite carbon nanofibers still demonstrate a clear fiber profile and smooth surface under a scanning electron microscope, indicating that the OER has good solubility with PAN in N,N-dimethylformamide. The electrochemical performance characterization of the activated composite carbon nanofiber shows that the P-OER60-AC (activated composite carbon nanofibers prepared with 60 wt.% of OER and 40 wt.% of PAN) has a better electrochemical performance with a specific capacitance of 97 F/g at 0.5 A/g, as compared to the others. Additionally, the P-OER80-AC (activated composite carbon nanofibers prepared with 80 wt.% of OER and 20 wt.% of PAN) is also considerable for the perspective of coal-based solid waste treatment and utilization.

Investigation of the mechanism of solvothermal extraction of direct coal liquefaction residue by macromolecular models

Direct coal liquefaction residue (DCLR) is an industrial by-product from the direct coal liquefaction process. It has the unique characteristics of high carbon, high sulfur and high ash content, strong cohesiveness and low softening point, which makes DLCR a potential raw material. However, direct discharge of untreated DCLR can cause severe damage to environment and human body. Thus it is of great importance to utilize DCLR properly. In this study, solvothermal extraction of direct coal liquefaction residue (DCLR)was treated with N-methyl-2-pyrrolidone (NMP) and 1-methyl naphthalene (1-MN). In addition, molecular models of DCLR and two hypercoals (HPC: NMP-HPC, MN-HPC) were built to clarify the extraction mechanism, aiming to provide a technically feasible route to utilize DCLR and investigate the adaptation between extractant and raw materials. The structural parameters were obtained by means of industrial and elemental analysis, 13C NMR, XPS and FTIR. Subsequently, macromolecular structure models were constructed, with simulated molecular formulas C153H108N2O10S, C206H168N6O7 and C278H202N2O13S, respectively. After modifying the macromolecular models by Materials Studio for geometric optimization, annealing dynamics calculation, density simulation and analysis of chemical bonds and charge layout, these models reflected the macromolecular structural characteristics precisely. On the other hand, DCLR model underwent significant changes in functional groups, branched chain length and quantity pre and post solvothermal extraction, indicating that the thermal extraction process was mainly affected by swelling behavior and pyrolysis. Meanwhile the principles of the two extractants were also different.1-MN extraction was a heat-induced relaxation, while NMP extraction was heat & solvent-induced relaxation process. This study will be helpful in expanding the utilization of DCLR and understanding of mechanism of solvothermal extraction on the macromolecular level based on modeling.

Effect of Replacement of Limestone Mineral Powder with Fly Ash and Direct Coal Liquefaction Residue on the Rheological Properties of Asphalt Mastic

Fly ash (FA) and direct coal liquefaction residue (DCLR) are coal-based industrial solid waste. Their unreasonable disposal has brought enormous economic, resource and environmental pressures. An effective treatment method is urgently needed. This study used FA and DCLR as fillers to replace limestone mineral powder (LP). The rheological properties of their corresponding asphalt mastics were evaluated by conventional performance tests and DSR tests. The effect of different properties of fillers on the rheological properties of mastic was revealed through finite element simulation. The test results show that FA and DCLR improve the viscosity, rutting resistance, elasticity and permanent deformation resistance of asphalt mastic, and reduce the temperature sensitivity. The improvement effect of FA is the most significant. The simulation results show that particle size and shape of filler affect the rheological properties and temperature sensitivity of asphalt mastic to different degrees respectively, and the filler particle size is the dominant factor.

Thermal extraction of coal and derivatives to prepare hot-pressed coal briquette for COREX application

In this study, the thermal extraction of various coal and derivatives by N-methylpyrrolidone was systematically compared and the extract was used as binder to prepare hot-pressed coal briquettes (HPCBs). The results demonstrate the effectiveness of thermal extraction in converting coal to HyperCoal, and the conversion yields varied from 12 to 71%. While the extraction tends to have a linear relationship with hydrogen-carbon ratio of raw coals, this relationship was not directly observed for derivatives due to inherent changes occurring during production. Proximate analysis of the extract reveals a reduction in ash content to below 1% while an increase in volatile matter by more than 8%. XPS and FTIR spectra demonstrate the high efficiency of thermal extraction in extracting hydrocarbons, but poor for compounds such as alcohols, phenols, ethers, and carboxylic acids. The extracts, rich in hydrocarbons, exhibited excellent thermoplasticity, making them suitable binders for HPCBs preparation. Among the extracts, coal derivatives exhibited higher compressive strength compared to coals. Consequently, the extract derived from direct coal liquefaction residue with the highest compressive strength was selected for preparing HPCB. Furthermore, we investigated the application characteristics of the HPCB and identified its great potential for use in COREX melting-reduction ironmaking. The preparation of HPCB is vital for expanding the utilization of bituminous coals while reducing dependence on lump coal and coking coal resources.

Char structure evolution and behaviors of sodium species during catalytic gasification of sodium-rich direct coal liquefaction residue under CO2 atmosphere

In this work, to better understand catalytic gasification process of direct coal liquefaction residue rich in sodium species, char structure evolution and behaviors of sodium species during gasification under CO2 atmosphere were investigated in detail by N2 adsorption and desorption, FT-IR, XRD, SEM, and Raman analyses. The results show that sodium species developed pore structure of direct coal liquefaction residue during gasification, especially expanded mesoporous structures which increased from 0.05 to 0.16 cm3/g at maximum. With the increase of gasification time, different crystalline compounds were formed in chars. Most of the mineral matters identified by XRD were calcium-containing ones, whereas no obvious sodium-containing crystalline compounds were found. This was because that most of sodium species volatilized at high temperature and the crystalline forms of sodium-containing compounds had defects. Compared with sodium species, calcium species were more prone to react with aluminosilicates, which happened to make sodium species remain active during gasification process. The ratio of (GR + VL + VR)/D rose initially and then decreased, which could be explained as the dissociation of the large aromatic and the rearrangement of small aromatic rings into large aromatic structures. Moreover, release ratio of sodium species was closely related with gasification time and 49.8% of them released in the initial stage of gasification process (within 15 min). Compared with that of direct coal liquefaction residue reloaded with water-soluble sodium species, the release ratio of sodium species in the original direct coal liquefaction residue was on a lower level (85.2% versus 89.7%).

Interaction, rheological and physicochemical properties of emulsified asphalt binders with direct coal liquefaction residue based geopolymers

The use of solid waste and low-cost gel materials to replace or reduce the use of ordinary Portl and cement (OPC) in emulsified asphalt (EA) binder has positive significance for the comprehensive energy consumption and economic cost of cold mix asphalt (CMA) pavement. The proposed study investigates the interaction, rheological and physicochemical properties of emulsified asphalt (EA) with direct coal liquefaction residue based geopolymers (DG) by fluorescence microscopy tests, the pH test, asphalt conventional tests, dynamic shear rheological test (DSR), and Fourier transform infrared spectroscopy test (FTIR). The test results show that the reaction between DG mortar and EA particles was faster and more violent than that of OPC mortar, resulting in faster demulsification of EA. The added DG mortar increased the pH of the EA binder. Similar to OPC, DG decreased the penetration and ductility of EA evaporation residues, but increased its softening point. The addition of DG to EA changed the rheological properties of its evaporation residue, including complex modulus (G*) and phase angle (δ). Temperature sweep and frequency sweep test results show that DG was comparable to OPC in efficacy against EA residues, improving rutting resistance at the expense of fatigue performance. Complex modulus coefficient (ΔG∗) and complex viscosity coefficient (Δη∗) indicate that the interaction of EA-DG is stronger than that of EA-OPC. FTIR analysis showed that the interaction between DG and EA is linked as a chemical bond.

Energy utilization of direct coal liquefaction residue via co-slurry with lignite: Slurryability, combustion characteristics, and their typical pollutant emissions

Direct coal liquefaction residue (DCLR) as an auxiliary feed material with lignite to prepare coal water slurry (CWS), which is then used as combustion fuels, enables recycle resources of DCLR and diminishes its impact on the surrounding environment. This paper aims to study the slurryability, combustion characteristics, and typical pollutant emissions of the lignite water slurry (LWS), DCLR water slurry (DCLRWS), and lignite-DCLR water slurry (L-DWS). Results showed that the DCLR and lignite were complementary in physicochemical properties for preparing the L-DWSs. The maximum solid concentration (ωmax) of the DCLR was 73.19 wt% with poor static stability, whereas that of the LWS was 41.70 wt% with high pseudoplasticity. By contrast, the ωmax of the L-DWS-5 prepared from the lignite and DCLR at mass ratio of 5:5 was 53.91 wt% with lower pseudoplasticity and static stability. Meanwhile, combustion experiments confirmed that the introduced DCLR was effective in improving the ignition, burnout, and comprehensive combustion performance of the L-DWS. The Qnet, p of the slurrying samples increased from 6.70 MJ/Kg for the LWS to 14.41 MJ/Kg for the L-DWS-5. And the addition of the DCLR exhibited slight influences on the emissions of NOx and SO2, but significantly increased HCN and other organic compounds such as CnHm, CO, and NH3 emissions. Furthermore, except for Pb and Zn, more than 85% Cr, Cu, and Ni were intercepted in solid residues.

High-Temperature Reaction Mechanism of Molybdenum Metal in Direct Coal Liquefaction Residue

In this paper, the extraction residue of direct coal liquefaction residue-DCLR(ER) was used as raw material. The high-temperature reaction mechanism of Mo compound in DCLR(ER) was investigated using a synchronous thermal analyzer and the Factsage database. The high temperature reaction of DCLR(ER)-MoO3 in an oxygen atmosphere consists of pyrolysis of organic components at 400–600 °C, molybdenum trioxide sublimation at 747–1200 °C, and a stable stage at 600–747 °C. The thermal reaction process of the DCLR(ER)-MoS2 system in the oxygen atmosphere involves the pyrolysis of unreacted coal and asphaltene, the oxidation of molybdenum sulfide at 349–606/666 °C, the diffusion of MoO3 at 606/666–85 °C, and the sublimation reaction process of MoO3 at 854–1200 °C. The results show that the lower heating rate can promote the oxidation of the Mo compound and the sublimation of molybdenum trioxide. On the other hand, the oxides of aluminum, calcium, and iron in DCLR(ER) can inhibit the oxidative pyrolysis efficiency of the DCLR(ER)-MoS2 system.

Study on interaction and mechanisms of direct coal liquefaction residue and gas coal in coal blending during coking

Crucible cokes were prepared by blending direct coal liquefaction residue (DCLR) with five bituminous coals (JM, FM, 1/3JM, QM, SM). The cold strength and thermal strength of cokes were analyzed. Coal petrology was used to guide and optimize coal blending for coking which was aimed at finding out the mechanism of DCLR and QM partially replacing coking coal (FM or JM) during coking. Results showed that QM and DCLR could partially replace FM or JM when the ratio of high caking coal was under 70%, and the DCLR ratio cannot exceed 6% to guarantee the coke strength. Based on blending scheme JT20, partially replacing JM with DCLR and QM (termed as DCLR-QM-JM system), the optimal DCLR ratio was 3% as M13 increased by 1.20%, M3 declined by 1.21% and CSR* increased by 0.79%. Partially replacing FM with DCLR and QM (termed as DCLR-QM-FM system), the optimal DCLR ratio was 2% as M13 increased by 2.14%, M3 declined by 2.13% and CSR* increased by 1.97%. There existed obvious interactions between raw materials in coal blending and the function mechanism of DCLR and QM could be concluded as follows: With the addition of DCLR, temperature range of the interaction between metaplast and gas in coking system extended to the low temperature region by 50 °C. The continuous gas driving force provided by QM drove much metaplast into the pores of coal particles and bound them to more inert components, which led to decreasing reaction surface and increasing thermal strength of coke.

Improve the slurry ability of lignite through co-slurrying and microwave co-pyrolysis with direct coal liquefaction residue

This study is devoted to demonstrating experimentally the advantages of direct coal liquefaction residue (DCLR) on improving the slurry ability of lignite through co-slurry and microwave co-pyrolysis. The results show that: as the lignite/DCLR mass ratio decreased from 10:0–5:5 the maximum solid concentration (MSC) of the mixed slurry increased from 42.14 wt% to 54.25 wt%, simultaneously, the pseudoplasticity and static stability gradually decreased. This is because the organic matter and abundant minerals in DCLR remarkably changed the slurry ability of mixed slurry. And during microwave pyrolysis with the assist of 12 wt% DCLR the slow drying stage of lignite pyrolysis was shortened, and the constant temperature stage was extended, thus, the coal quality was improved, the oxygen-containing functional groups was removed significantly and the BET specific surface area increased. These changes caused the MSC of upgraded lignite water slurry (ULWS) increased to 64.54 wt%; but the “shear-thinning” characteristic became inconspicuous, and the static stability became slightly worse. In general, DCLR could effectively improve the slurry ability of lignite through co-slurry with lignite at a mass ratio of 5:5 and co-pyrolysis with lignite at a microwave power of 1000 W.

Properties of direct coal liquefaction residue water slurry: Effect of mineral matters by acid‐leaching demineralization

AbstractThe effects of demineralization treatment by acid leaching on the properties of direct coal liquefaction residue water slurry (DCLRWS) were investigated. The demineralized direct coal liquefaction residue (DCLR) with different mineral matter content and composition was prepared by leaching with the solution of HCl/HF, HCl, and HF, designated as DEM‐1, DEM‐2, and DEM‐3, respectively. After demineralization, the slurryability of DCLR decreases but their effective solid loading (ash‐free basis) increases. The results indicate that metallic minerals are the principal factor improving the slurryability of DCLRWS, mainly by increasing the dispersant adsorption capacity of DCLR. In addition, the decreasing density of DCLR after demineralization is not advantageous to its slurryability. DCLRWSs prepared by DCLR, DEM‐1, and DEM‐2 all have the same stabilization time (2 days), indicating that removal of metallic minerals could not deteriorate the stability. However, after removal of clay minerals, the slurries prepared by DEM‐3 tend to form sediment after stopping high‐speed stirring, attributed to its lowest zeta potential and loss of stability due to clay minerals. Except for DEM‐3, the slurries prepared by other three samples all have a shear‐thinning behavior, with the strongest behavior observed for DEM‐1 slurry.

Effect of direct coal liquefaction residue on the properties of fine blue-coke-based activated coke

Abstract Activated coke was obtained by CO2 activation with disused fine blue-coke serving as the main raw material and direct coal liquefaction residue (DCLR) as binder. The effect of the dosage and activation temperature of DCLR on the compressive strength of active coke and desulfurization were mainly investigated. The experimental results showed that the compressive strength of the activated coke increased first and then decreased with the increase in the amount of D-DCLR (DCLR after ash removal). When the amount of D-DCLR was 40%, the compressive strength of the activated coke was 492.55 N and the specific surface area was the highest (189.78 m2·g−1) among other samples. The results show that the activated coke has a high removal rate for low concentrations of sulfur dioxide. This work provides a way for efficient utilization of DCLR, which avoids waste of resources and environmental pollution. In addition, it is important for finding green and efficient blue-coke powder processing and utilization technology for the sustainable development of the blue-coke industry.

Preparation of hot-pressed coal briquette with the extract from direct coal liquefaction residue

Direct coal liquefaction residue (DCLR) is an industrial by-product from the direct coal liquefaction process. It is harmful to the environment and the human body when directly charged or used due to the high content of sulfur, ash, and polycyclic aromatic hydrocarbons (PAHs). Therefore, it is of great importance to treat and utilize DCLR. In this paper, the thermal extraction method was applied to extract DCLR with N-methylpyrrolidone (NMP), and the hot-pressed coal briquette (HPCB) was prepared with DCLR extract and anthracite powder. DCLR and its extract and residue were characterized by TG, FTIR, and GC-MS. The ash content was decreased from 11.72% to 0.72% and the sulfur content was decreased from 1.72% to 0.09% after thermal extraction. TG analysis shows that the weight loss of the extract was about 30.4% higher than that of the residue during the pyrolysis process, indicating that the extract contained more light components. FTIR analysis shows that the thermal extraction process had strong extraction capacity for aliphatic hydrocarbons and aromatic hydrocarbons, but weak extraction capacity for carboxyl, phenol, or alcohol groups. GCMS shows that 60.6% of the volatile substances in the extract were PAHs, while the residue had only 6.8% of PAHS. It is proven that the residue has been rendered harmless to humans and the environment. Moreover, the HPCB with a compressive strength exceeding 2.5 MPa was prepared by using the DCLR extract as a binder and anthracite powder as a raw material. It has the potential and advantages of being used as a metallurgical raw material.

In-situ catalytic gasification of sodium-rich direct coal liquefaction residue under CO2 atmosphere and kinetic analysis of gasification reaction process

Due to attractive features, such as low mineral matter content and strong reactivity, sodium-rich coals are viewed as suitable raw materials for direct coal liquefaction technology. After direct coal liquefaction process, the inherent sodium species in sodium-rich coals will be enriched in direct coal liquefaction residue. In this work, to provide potential guidance for better utilization of sodium-rich direct coal liquefaction residue, catalytic effects of the inherent sodium species on gasification reactivity of sodium-rich direct coal liquefaction residue and kinetic analysis of gasification reaction process were investigated in detail. The results show that inherent sodium species has obvious catalytic effects on gasification of sodium-rich direct coal liquefaction residue. Compared with that for demineralized direct coal liquefaction residue, the time for sodium-rich direct coal liquefaction residue to be completely gasified at 1000 °C and 1100 °C was shortened by 82% and 70%, respectively. With the increase of gasification temperature, CO2 gasification reactivity of all types of direct coal liquefaction residue was enhanced. For instance, gasification reactivity indexes (R0.5) of sodium-rich direct coal liquefaction residue are 0.06 min−1, 0.15 min−1, and 0.23 min−1 at 900 °C, 1000 °C, and 1100 °C, respectively. Kinetic analyses indicate that linear correlation coefficients obtained by homogeneous model and shrinking core model are on high levels and they are closely related with gasification temperature and residue type. According to calculation of homogeneous model and shrinking core model, activation energies of demineralized direct coal liquefaction residue are 78.60 kJ/mol and 73.73 kJ/mol, respectively. In contrast, the corresponding activation energies of sodium-rich direct coal liquefaction residue are 75.42 kJ/mol and 71.55 kJ/mol, which proves that activation energy required for gasification of direct coal liquefaction residue can be reduced by the inherent sodium species. To conclude, catalytic coal gasification may be potentially efficient to process sodium-rich direct coal liquefaction residue.

Study on the corrosion of refractory materials by coal blended with the extraction residue of direct coal liquefaction in a simulated gasification atmosphere

Abstract Utilizing the extraction residue (ER) of direct coal liquefaction residue as a gasification feedstock has significant economic value. But the characteristic of high ash and iron in the ER would increase the risk of corrosion of the refractory materials and affect the long-term operation of the gasifier. In this work, corrosion experiments of molten slag derived from a mixture of 20 wt% ER and 80 wt% coal on a high-chromia refractory brick and SiC brick were carried out using a rotary-drum furnace in a simulated gasification atmosphere. The experimental results show that the viscosity of the poured slag is larger as compared to the initial ash sample at the same temperature, which suggests that the viscosity–temperature relationship of the poured slag should be used as the reference for the operation temperature of the gasifier to ensure that the slag can flow during operation. For a high-chromia refractory brick, iron oxides in molten slag could react with Cr2O3 in the refractory matrix but, because the aggregate was not found to be damaged, the damage to the matrix structure was the key factor for causing the corrosion of the high-chromia refractory brick. Metallic iron was observed in the exposed SiC brick, which indicated that the reaction between the iron oxides in the slag and SiC occurred, forming metallic iron and SiO2. The corrosion of a SiC brick by molten slag depended mainly on the dissolution of Al2O3 particles and the reaction between iron oxides in the molten slag and SiC particles. Therefore, the high iron content in coal ash had a serious influence on the corrosion of refractory materials. More efforts need to be made on coal blended with ER as a gasification feedstock in the future.

Microwave co-pyrolysis of lignite with direct coal liquefaction residue: Synergistic effects and product combustion characteristics

To effectively and cleanly handle the direct coal liquefaction residue (DCLR), a two-phase microwave reaction system was designed based on poly-generation lignite technology, that performed both individual pyrolysis and co-pyrolysis, to investigate the effect of microwave co-pyrolysis of lignite with different addition of DCLR on the pyrolysis products characteristics. The experimental results demonstrated the presence of synergism during microwave co-pyrolysis, which enhanced the condensation reaction of different free radicals, and thus increased the char (upgraded lignite, UL) yield by 6.14–10.42%. The DCLR showed excellent catalytic effects as consumable absorbents in terms of heating rate, and char and gas yields, and it eventually converted into high value-added combustible gases (CO, CH4, and H2). Furthermore, when compared to the individual pyrolysis sample and lignite, the co-pyrolysis samples’ chemical structures were progressively aromatized, and exhibited significantly lower O/C ratios, re-adsorption moisture content, and reactive groups and available sites. Moreover, the pore structures on the surface for the co-pyrolysis samples were dominated by cracks, blowholes, and open-ended fissures, which gradually decreased as DCLR contents increased. Combustion behavior and kinetic analysis confirmed that microwave co-pyrolysis changed activation energy (Ea) distribution of ULs and thus improving their combustion performance. Therefore, microwave co-pyrolysis of lignite with DCLR was an effective and economical approach for clean utilization DCLR and obtaining high-quality lignite fuel.

In situ FT-IR analysis of coke formation mechanism during Co-pyrolysis of low-rank coal and direct coal liquefaction residue

In situ Fourier transform infrared spectroscopy and thermogravimetric analysis were conducted to characterise the co-pyrolysis of low-rank coal (SJC) and direct coal liquefaction residue (DCLR) as well as the evolution of the main functional groups of the pyrolysis products. This research is expected to further elucidate the reaction mechanism of co-pyrolysis. It was found that the co-pyrolysis of SJC and DCLR has synergistic effects and increases the hydrogen supply during co-pyrolysis. The chain breakage and thermal decomposition of functional groups during co-pyrolysis lead to the formation of solid, liquid, and gaseous products. The presence of DCLR promotes deep pyrolysis to produce numerous aromatic and aliphatic groups; many of these free-radical fragments rearrange and condense with hydrogen free radicals ([H]) to produce tar with a high molecular weight. When the [H] content is low, the free-radical fragments combine with each other to form solid coke. During co-pyrolysis, SJC and DCLR serve as both, hydrogen transmitters and donors. The catalysed hydrocraking of aromatic hydrocarbons and phenols in the tar product in the presence of hydrogen increases the content of the light component in the tar and produces alkanes, decreasing the aromatics and phenol contents.