Wei Lu

Carbon-rich organic solid wastes should be introduced to students not only as pollutants to be disposed of, but also as secondary carbon resources that can be converted into energy carriers and useful products. To connect waste valorization, low-carbon energy conversion, and experimental engineering education, this study reports a comprehensive teaching experiment based on the fixed-bed pyrolysis and CO₂-assisted gasification of polypropylene-rich waste, together with the complete reference dataset and calculation workflow that accompany it. Waste face masks are used as a representative and familiar feedstock: the melt-blown filtration layer is polypropylene, whereas the spun-bonded outer layers may be polypropylene or polyethylene terephthalate, so the material is deliberately treated as a heterogeneous real waste. Every indicator reported here is defined so that it can be computed from the measured gas-phase data and the weighed feed mass alone, without elemental analysis or calorimetry of the feedstock. Students complete feedstock pretreatment, reactor operation, online micro-gas chromatography, tracer-based quantification, gas-phase mass and energy balances, uncertainty propagation, a stoichiometric oxygen balance for CO₂ conversion, and a documented risk assessment. Two inert pyrolysis and two CO₂-assisted gasification cases at 850 and 900 °C were implemented with 35 g of feedstock. CO₂-assisted gasification raised the combustible-gas yield by about one order of magnitude: at 850 °C, the total combustible gas was 24.40 ± 0.86 g, of which strictly defined syngas (H₂ + CO) was 17.87 ± 0.83 g, the combustible-gas energy 536.8 ± 12.9 kJ, and the specific energy recovery 15.34 ± 0.37 kJ g⁻¹ feed. Evaluated over the identical 21 min window used for pyrolysis, gasification still delivered 21.87 g against 1.89 g, so the improvement is not an artefact of the longer run. Release profiles are described quantitatively by an exponentially modified Gaussian model (R² = 0.983–0.999) with peak positions of 1.3–2.4 min and widths of 1.3–1.9 min. Using the inert run at the same temperature as a baseline. An assumption-dependent estimate indicates a CO₂ conversion of 13.0 ± 0.7 g per 35 g of feedstock at both temperatures, with a possible upper estimate of approximately 26 g if the reverse water–gas shift reaction contributes. The stated uncertainty reflects the propagation of the measured gas-phase quantities but does not include the potential systematic bias associated with the unmeasured PET fraction or atmosphere-dependent behavior of oxygen-containing constituents. This estimate assumes that the CO formed from oxygen-containing minor constituents such as PET is largely removed by the baseline subtraction. The dataset comprises one run per condition; no replicate experiments were performed, so the reported uncertainties are single-run combined standard uncertainties and no claim of run-to-run reproducibility is made. The paper contributes a documented platform, a four-case reference dataset, and a fully documented calculation workflow for teaching thermochemical conversion, gas analysis, element balances, energy recovery, measurement uncertainty, and process safety.

To elucidate the influence of mineral composition on CO₂ mineralization and mechanical reinforcement, three synthetic tailing systems representing felsic, high-calcium silicate, and magnesium-carbonate compositions were prepared using a full-component reconstitution approach. Their carbonation kinetics, phase evolution, pore structure, and mechanical response were systematically investigated. The alkaline buffering duration increased in the order of felsic < high-calcium silicate < magnesium-carbonate types, with plateau durations of approximately 300, 650, and 2000 s, respectively. TG-DTG, XRD, and FTIR analyses collectively indicated composition-dependent formation of carbonate-bearing products, with the magnesium-carbonate type showing the strongest carbonate-related signals. SEM observations further revealed precipitation on particle surfaces and within interparticle regions, suggesting precipitation-induced particle bonding. Nitrogen adsorption–desorption measurements showed pronounced pore-structure reorganization after mineralization; the average pore size converged to approximately 7.5–7.9 nm, whereas the specific surface area decreased in all systems. The failure loads of the felsic and high-calcium silicate types increased by factors of 2.97 and 3.81, respectively. The mineralized magnesium-carbonate type exhibited the highest apparent compressive strength (53.69 kPa). These results demonstrate clear composition-dependent relationships among carbonation, pore evolution, and mechanical response in the synthetic systems. Because the materials were prepared from analytical-grade reagents and no complete carbon balance was established, the results should be regarded as mechanistic model-system evidence rather than quantitative estimates of CO₂ sequestration in natural tailings.

Coalbed methane (CBM) reservoirs in southwestern China are characterized by thick, multi-layered coal sequences partitioned into several independent pressure systems by impermeable strata. Commingled production from multiple coal seams in such multi-superposed CBM systems often suffers from severe inter-layer interference, leading to suboptimal gas recovery. To address this challenge, we developed a systematic four-step optimization workflow integrating geological data screening, pressure compartmentalization analysis, and numerical reservoir simulation. The workflow identifies the key “main” coal seams and evaluates various co-production layer combinations to maximize gas recovery while minimizing negative interference. We applied this method to a CBM well (LC-C2) in the Western Guizhou–Eastern Yunnan region, which penetrates three discrete CBM pressure systems. In the case study, single-layer simulations first revealed that one seam (No. 7 + 8) contributed over 30% of the total gas potential, with a few other seams (e.g., No. 18, 13, 4, 16) providing moderate contributions and many seams yielding negligible gas. Guided by these results, we simulated five commingling scenarios of increasing complexity. The optimal scenario was to co-produce the seams from the two higher-pressure systems (a total of six seams) while excluding the low-pressure shallow seams. This optimal six-seam configuration achieved a 10-year cumulative gas production of approximately 2.53 × 10⁶ m³ (about 700 m³/day average)—roughly 75% higher than producing the main seam alone, and even about 15% greater than a scenario involving all available seams. In contrast, including all three pressure systems (ten seams) led to interference effects where the high-pressure seams dominated flow and the low-pressure seams contributed little, resulting in lower overall recovery. The findings demonstrate that more is not always better in multi-seam CBM production. By intelligently selecting a moderate number of compatible seams for co-production, the reservoir’s gas can be extracted more efficiently. The proposed quantitative optimization approach provides a practical tool for designing multi-seam CBM wells and can be broadly applied to similar geologically compartmentalized reservoirs.

The dynamic process of water depletion plays a critical role in both surface coalbed methane (CBM) development and underground gas extraction, reshaping water–rock interactions and inducing complex permeability responses. Addressing the limited understanding of the coupling mechanism between heterogeneous pore water evolution and permeability during dynamic processes, this study simulates reservoir transitions across four zones (prospective planning, production preparation, active production, and mining-affected zones) via centrifugal experiments. The results reveal a pronounced scale dependence in pore water distribution. During low-pressure stages (0–0.54 MPa), rapid drainage from fractures and seepage pores leads to a ~12% reduction in total water content. In contrast, high-pressure stages (0.54–3.83 MPa) promote water retention in adsorption pores, with their relative contribution rising to 95.8%, forming a dual-structure of macropore drainage and micropore retention. Multifractal analysis indicates a dual-mode evolution of movable pore space. Under low centrifugal pressure, D₋₁₀ and Δα decrease by approximately 34% and 36%, respectively, reflecting improved connectivity within large-pore networks. At high centrifugal pressure, an ~8% increase in D₀−D₂ suggests that pore-scale heterogeneity in adsorption pores inhibits further seepage. A quantitative coupling model establishes a quadratic relationship between fractal parameters and permeability, illustrating that permeability enhancement results from the combined effects of pore volume expansion and structural homogenization. As water saturation decreases from 1.0 to 0.64, permeability increases by more than 3.5 times. These findings offer theoretical insights into optimizing seepage pathways and improving gas recovery efficiency in dynamically evolving reservoirs.

This study presents a comprehensive multifractal characterization of full-scale pore structures in middle- to high-rank coal reservoirs from the Western Guizhou–Eastern Yunnan Basin and establishes a permeability prediction model integrating fractal heterogeneity and pore throat parameters. Eight coal samples were analyzed using mercury intrusion porosimetry (MIP), low-pressure gas adsorption (N₂/CO₂), and multifractal theory to quantify multiscale pore heterogeneity and its implications for fluid transport. Results reveal weak correlations (R² < 0.39) between conventional petrophysical parameters (ash yield, volatile matter, porosity) and permeability, underscoring the inadequacy of bulk properties in predicting flow behavior. Full-scale pore characterization identified distinct pore architecture regimes: Laochang block coals exhibit microporous dominance (0.45–0.55 nm) with CO₂ adsorption capacities 78% higher than Tucheng samples, while Tucheng coals display enhanced seepage pore development (100–5000 nm), yielding 2.5× greater stage pore volumes. Multifractal analysis demonstrated significant heterogeneity (Δα = 0.98–1.82), with Laochang samples showing superior pore uniformity (D₁ = 0.86 vs. 0.82) but inferior connectivity (D₂ = 0.69 vs. 0.71). A novel permeability model was developed through multivariate regression, integrating the heterogeneity index (Δα) and effective pore throat diameter (D₁₀), achieving exceptional predictive accuracy. The strong negative correlation between Δα and permeability (R = −0.93) highlights how pore complexity governs flow resistance, while D₁₀’s positive influence (R = 0.72) emphasizes throat size control on fluid migration. This work provides a paradigm shift in coal reservoir evaluation, demonstrating that multiscale fractal heterogeneity, rather than conventional bulk properties, dictates permeability in anisotropic coal systems. The model offers critical insights for optimizing hydraulic fracturing and enhanced coalbed methane recovery in structurally heterogeneous basins.