Ping Dingshan Research Articles

Simulation of the effects of nanopores at different scales on the wettability of coal

The structural difference of nanopores at different scales in coal is one of the important factors that affect the wettability of coal. Therefore, it is necessary to determine influences of nanopores at different scales in coal on the wettability thereof from the perspective of molecular structure. Taking coal samples collected from Pingdingshan (PDS), Hebi (HB), Xiegou (XG), and Changping (CP) as research objects, the nanopore combination types of the interface were divided by using Materials Studio (MS) molecular simulation software and Image Pro Plus (IPP) image processing software, fractal theory and wettability dynamic simulation method, and the fractal characteristics of different nanopore combination types and the wetting angle change characteristics of active water were analyzed. The effects of total porosity and fractal dimension of pore structure on wettability of nanopores were discussed. The results show that the nanopore combinations in coal can be divided into three types according to the diameter of water molecules: those separately dominated by diffusion pores, adsorption-diffusion pores, and adsorption pores. As the diameter of dominant pores decreases, the fractal dimension decreases and the structure becomes increasingly simple. The wetting angle of active water in diffusion pores changes as follows: it rapidly decreases at first, then tends to stabilizes, before increasing slightly; that in adsorption-diffusion pores changes in this way: it rapidly decreases after transient fluctuations, then basically stabilizes, and finally slightly increases; that in adsorption pores changes as follows: it fluctuates for a long period, then decreases with fluctuations, and finally basically stabilizes. As the total porosity of nanopores increases, the wetting angle decreases linearly. If the porosity is similar, the negative influence of fractal dimension on the wettability of coal interfaces by active water increases as the scale of dominant pores in pore combinations decreases.

Stability analysis of Pingdingshan pear-shaped multi-mudstone interbedded salt cavern gas storage

In China, salt cavern gas storages are typically constructed in strata of complicated bedded salt rock, which are made up of numerous thin interlayers and salt rock that contains impurity. The long-term stability and safety assessment of underground caverns is crucial for the safe operation of gas storage in this type of complicated strata. In order to more accurately describe the long-term creep characteristics of salt rock and mudstone, the fractional derivative creep-damage (FDCD) constitutive model is used in this work. Earlier researches have also demonstrated the advantages of this model when it comes to long-term creep. Pingdingshan (PDS)'s shape and dimensions are developed in accordance with the formation conditions, and a three-dimensional geological model is built according to the designed gas storage. The long-term stability and safety of gas storage under various constant operating internal gas pressures (IGP), cyclic IGP, and gas extraction rates are investigated based on the comprehensive evaluation criteria including deformation, volume shrinkage rate, safety factor, and plastic zone. The results reveal that when the constant operating IGP is 13 MPa, and the cyclic IGP is 13–27 MPa PDS gas storage has good long-term stability and safety. While the plastic zone of mudstone interlayer is still presented at the top and bottom of the gas storage at IGP = 13–27 MPa, and the plastic zone is more pronounced at low constant and cyclic IGP levels. The safety factor of rock mass close to the sidewalls is always <1.5 throughout the long-term operation of gas storage, which makes it more vulnerable to dilatancy failure and requires attention. The deformation and volume shrinkage of gas storage are greatly impacted by the gas extraction rate, and the evolution characteristics of 4 indicators under various gas extraction rates are provided. This study provides a crucial reference for the design of gas storage in China's intricate salt rock regions with multiple interlayers in the PDS region.

Experimental Study on the Pore Structure of Middle- and Low-Rank Coal and Its Influence on Methane Adsorption

The pore characteristics of coal have an important influence on the coal adsorption of methane. The liquid nitrogen adsorption method was used to study the pore structure of low- and middle-rank coal samples from two aspects: pore specific surface area and pore shape. Low-field nuclear magnetic resonance (NMR) technology was used to study the difference in methane adsorption of coal samples under the same adsorption conditions. The influence and mechanism of the pore structure of middle- and low-rank coal samples on gas adsorption are discussed and analyzed. The results show the following: (1) There are differences in the adsorption capacity of medium- and low-rank coal samples. Within 1 h of methane inflation, the methane adsorption capacity of middle-rank coals such as Henan Pingdingshan (PDS) and Shanxi Wangzhuang (WZ) and Xinjiang low-rank coals (XJ) increases by 36.4%, 31.7%, and 35.8%, respectively, and as the inflation time is extended to the cumulative inflation of 10 h, the order of the increase in methane adsorption capacity is still PDS&gt;XJ&gt;WZ. (2) The pore types of the experimental coal samples are mostly wedge-shaped pores and ink bottle-shaped pores. The order of the BET specific surface area of the coal samples is in the order of WZ&gt;PDS&gt; XJ, which means that the WZ samples can provide more adsorption sites for gas molecule adsorption, but under the same adsorption conditions, the WZ sample has the least amount of gas adsorbed. Further analysis shows that the order of the tortuosity of the coal sample is WZ&gt;XJ&gt;PDS, which means that the WZ sample has a large pore tortuosity, a long channel for methane molecules to diffuse into the internal pores of the coal sample, and large diffusion resistance. It is the main reason why the methane adsorption capacity of WZ coal samples is less than that of PDS and XJ coal samples in the same adsorption conditions.

Molecular structure characterization of middle-high rank coal via 13C NMR, XPS and FTIR spectroscopy

Elemental analysis, 13C nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), combined with Grand Canonical ensemble Monte Carlo (GCMC) simulations and energy minimizations were used to establish the molecular structure model of middle-high coal rank accurately. The three-dimensional molecular structure models of middle-high coal rank (from the No. 6 Mine of Pingdingshan (PDS) Mining Area and the No. 4 Mine of Hebi (HB) Mining Area in Henan Province, Xiegou (XG) Mine, Changping (CP) Mine, and Sihe (SH) Mine in Shanxi Province, China) were optimized and constructed. The results showed that the structural arrangement is more orderly and compact with the increase of coal rank. The established molecular formulae for PDS, HB, XG, CP, and SH are respectively C69H43NO3, C166H93N3O8, C191H125N3O7, C169H105N3O7, and C221H123N3O7.

Characterization of structure of kaolinite in tectonically deformed coal: evidence of mechanochemistry

ABSTRACT Coal and gas outbursts are one of the most serious disasters in coal mines and are closely related to the distribution of tectonically deformed coal. To explore the environment of formation and the mechanochemical genetics of tectonically deformed coal and investigate the influence of tectonic stress on the crystal structure parameters of kaolinite in coal, this paper identifies whether the occurrence of the advanced evolutionary phenomenon of tectonically deformed coal is dominated by thermal metamorphic temperatures or mechanochemical stress. Three pairs of unaltered coal and tectonically deformed coal samples were collected from three different coal seams at the No. 8 coal mine in Ping Dingshan Henan Province in China. After low-temperature ashing treatment, SEM, XRD and FTIR were used to characterize the kaolinite crystal morphology, crystallinity parameter (Hinckley index, HI), structural defects, and other characteristics. The results show that compared with the unaltered coal, the crystal morphology of kaolinite in tectonically deformed coal is more disordered, the crystal plane spacings, d(020), d(1–10), and d(11–1), increase, the crystallinity parameter HI decrease from 1.018, 1.104, 1.001 (more than 1, ordered) to 0.882, 0.784, 0.978 (less than 1, disordered), and the strength of the characteristic absorption band decreases, the differences in morphology and structural defects are mainly caused by the destruction of bonds, such as -OH, Al-O-Si, Al-O-Al, and Si-O-Si. Tectonic stress promotes the mechanochemical evolution of kaolinite in coal, resulting in lattice dislocations, an increase in crystal plane spacing, an increase in crystal defects and a decrease in the ordering degree. The experimental phenomenon of kaolinite converting to montmorillonite (microcrystalline kaolinite) and the mechanochemical evolution result of the crystallinity parameter decrease reflect that the crystal structure of kaolinite in tectonically deformed coal has not evolved to be ordered with the aid of temperature, which confirms that stress plays a dominant role in the evolution of advanced phenomenon of tectonically deformed coal structures.

Behavior of mercury in chemical looping with oxygen uncoupling of coal

Mercury pollution is a critical point in chemical looping with oxygen uncoupling combustion (CLOU) of coal. This work aims to investigate the behavior of mercury and the role of oxygen carrier (OC, CuO@TiO2-Al2O3) in the CLOU of Pingdingshan (PDS) anthracite. The average CO2 yield was 93.9% during the 15 redox cycles. The mercury balance was 119.0% ± 0.49 in the CLOU test (8 min, 4 repeated redox cycles). The distribution of Hg0(g) and Hg2+(g) was 0.033 ± 0.9*10−5 μg and 0.054 μg within the reduction process, respectively. The removal efficiency of Hg0(g) by the OC was 60.71%. Moreover, the Hg(p) was adsorbed on the OC with an adsorption capacity of 0.281 μg/g and was composed of 23.48% and 76.52% for Hg0 and Hg2+. The decreasing removal efficiency of Hg0 was listed as: OC + the complicated atmosphere of CLOU > OC + 5 vol% O2 > the completely oxidized OC > the partially reduced OC. The oxidation of Hg0(g) was promoted by sufficient active sites, absorbed oxygen and lattice oxygen of the OC. A long reduction time in the fuel reactor reduced the mercury released in the air reactor.

Characterization of PM2.5-Bound Polycyclic Aromatic Hydrocarbons at Two Central China Cities: Seasonal Variation, Sources, and Health Risk Assessment.

In this study, ambient PM2.5 samples were collected from October 2014 to August 2015 in urban area of Luoyang (LY) and Pingdingshan (PDS), two medium-size industrial cities in central China. Sixteen priority polycyclic aromatic hydrocarbons (PAHs) were analyzed to investigate the seasonal variation, potential pollution sources, and health risk of PAHs bound to PM2.5 (PM2.5-bound PAHs). The diagnostic ratios analysis and positive matrix fraction (PMF) model were used to identify potential sources of PM2.5-bound PAHs. The annual average concentrations of PM2.5 and PM2.5-bound PAHs were 128μgm-3 and 73ngm-3 for LY, and 119μgm-3 and 182ngm-3 for PDS, respectively, both displaying seasonal trends with higher concentrations in winter and autumn than in spring and summer. BaP equivalent concentrations were 14.4 and 16.5ngm-3 in LY and PDS, respectively. The predominant PAHs were 4-6 ring PAHs, with contribution of more than 80% at both sampling sites. PMF analysis revealed that coal combustion was the most important source of PM2.5-bound PAHs in LY and PDS, accounting for 37% and 39%, respectively, followed by traffic emissions (34% and 33% in LY and PDS, respectively). The average inhalation cancer risk (ICR) for a lifetime of 70years were 12.5 × 10-4 and 14.3 × 10-4 in LY and PDS, respectively, which were much higher than US EPA guideline limit of 10-6. The traffic source and coal combustion source contributed the highest ICR values in LY and PDS, respectively.

A Novel in Situ Stress Monitoring Technique for Fracture Rock Mass and Its Application in Deep Coal Mines

A novel in situ stress monitoring method, based on rheological stress recovery (RSR) theory, was proposed to monitor the stress of rock mass in deep underground engineering. The RSR theory indicates that the tiny hole in the rock can close gradually after it was drilled due to the rheology characteristic, during which process the stress that existed in the rock can be monitored in real-time. Then, a three-dimensional stress monitoring sensor, based on the vibrating wire technique, was developed for in field measurement. Furthermore, the in-field monitoring procedures for the proposed technique are introduced, including hole drilling, sensor installation, grouting, and data acquisition. Finally, two in situ tests were carried out on deep roadways at the Pingdingshan (PDS) No. 1 and No. 11 coal mines to verify the feasibility and reliability of the proposed technique. The relationship between the recovery stress and the time for the six sensor faces are discussed and the final stable values are calculated. The in situ stress components of rock masses under geodetic coordinates were calculated via the coordinate transformation equation and the results are consistent with the in situ stress data by different methods, which verified the effectiveness of the proposed method.

Numerical simulation research of coal and gas outburst near tectonic region in Ping ding shan mining area

The complicated process of coal and gas outburst hinders the exploration of gas outburst mechanism. In order to better quantitatively evaluate gas outburst instability of reverse fault and normal fault combination using the RFPA2D numerical simulation software to study the coal face through fault from downthrown side to uplifted side and from uplifted side to downthrown side, the results showed that the outburst process can be divided into four stages, namely, stress concentration stage, coal-rock fracturing and splitting induced by the combinations of gas pressure and in situ stress, cracks propagation driven by gas pressure and the abrupt ejection of coal and gas; Wu 9-10-20090 belt transporter tunnel outburst occurs near the fault by the tensile failure, coal seam pressure shear failure occur, due to the fault sealing formation pressure gradient, under the influence of ground stress and gas pressure, fault and broken coal outburst risk; − 320 east outstanding is due to the fault sealing effect in coal roadway, gas pressure, coal shear failure occurs, breakage of coal is relatively serious, to highlight the accident when exposed fault; face from fault plate to increase plate driving is more likely to happen to highlight the phenomenon is determined by the conditions of gas release.

Emission reduction of particulate matter from the combustion of biochar via thermal pre-treatment of torrefaction, slow pyrolysis or hydrothermal carbonisation and its co-combustion with pulverized coal

Emission reduction of PM10 (of an aerodynamic diameter of 10 μm or less) was investigated via the combustion of biochar pre-treated from straw by torrefaction at 300 °C (T-300), slow pyrolysis at 500 °C (S-500), or hydrothermal carbonisation at 240 °C (H-240), and their co-combustion with Ping Ding Shan (PDS) bituminous coal in a drop tube furnace at 1400 °C. The generated PM10 was collected by a Dekati low pressure impactor (DLPI) sample system, and its mass/chemical composition was characterised. During single combustion of the straw and its pre-treated biochar, the emission amount of PM0.3 (aerodynamic diameter of ≤0.3 μm) from the biochar was linearly affected by the release of Cl during various pre-treatments and the formed KCl release into the gas phase during combustion. The emission of PM1-10 still changed linearly, mainly because of the increased ash content after pre-treatment. Co-combustion of biomass fuels and PDS coal presents an obvious reduction in PM10 emission, particularly PM0.3. The higher Cl content in biomass fuels is also linearly correlated with a greater reduction in PM0.3 emission. Aluminosilicates in coal, e.g. kaolinite, are responsible for the capture of gaseous species from biofuels and the subsequent coalescence of sticky minerals, reducing PM0.3 and PM1-10 emissions following co-combustion.

A case study of mining-induced impacts on the stability of multi-tunnels with the backfill mining method and controlling strategies

Deep mining practices are jeopardized by the recurrent instability and failure of roadways/multi-tunnels. This paper describes a case study of the mining-induced impacts on the stability and control strategy of overlying multi-tunnels with backfill mining in the Ping Dingshan No. 10 Coal Mine in Henan Province, China. To reveal the dynamic impacts of coal mining on the stability of overlying multi-tunnels, particularly in the process of mining cycle and after the overlying strata long-term stability period, a 3D finite element model was applied to explore the effect of longwall panel width, advancing distance, and backfill material’s compaction ratio (BMCR) on the multi-tunnels’ deformation characteristics. The results obtained demonstrate that failure and deformation of the overlying multi-tunnels become more pronounced with the increased longwall panel width and advancing distance, as well as with BMCR reduction. The ranking of deformation degree in the overlying multi-tunnels is as follows: main haulage roadway > auxiliary haulage roadway > main inclined shaft > rock crosscut > auxiliary inclined shaft. Using a 2D physical simulation experiment, a comprehensive analysis method and engineering design concept for the stability control of overlying multi-tunnels with backfill mining are put forward based on further research of the deformation characteristics of multi-tunnels using caving and backfilling method. The results obtained are instrumental to the stability control of overlying tunnels in deep mining practices with similar conditions.

Strata behavior at fully-mechanized coal mining and solid backfilling face.

Taking Ping Dingshan Coal Mine Group 12 as an example, this paper explains the system layout, key equipment and backfilling technology in detail. It probes into the characteristic of rock strata movement behavior and surface deformation above the gob area through in-site measurement method. The results show that as the overburden strata are effectively supported by the backfill body in mined out areas, there were no evident phenomena as first weighting or periodic weighting during mining process. Besides, influencing scope of advanced support pressure and the strata behavior degree were much smaller than that of the traditional methods of caving mining. Since overburden strata had been well supported by backfill body, it shows the posture of sinking slowly, only resulting in bending zone and minor fracture zone.

Influence of water-insoluble content on the short-term strength of bedded rock salt from three locations in China

Unlike the presence of thick domes and thick layers of rock salt deposits in Europe and the USA, rock salt in China is mainly composed of thin layers (80–300 m), characterized by a high content of water-insoluble impurities. Thus, the influence of these impurities on the strength of rock salt is barely known and has become an important topic for basic research in the construction of underground salt caverns for energy storage in China. In this paper, the influence of water-insoluble content on the short-term strength of bedded rock salt, based on a series of combined laboratory tests including solubility, uniaxial and triaxial compression tests, on bedded rock salt samples from three locations in China, namely the Huai’an (HA) site in Jiangsu Province, the Pingdingshan (PDS) site in Henan Province and the Anning (AN) site in Yunnan Province, is presented. Samples in which the water-insoluble content was less than 50 % were defined as “rock salt” and the remainder as “impure rocks with salt”. Analysis of the experimental results for rock salt samples leads to the conclusion that the uniaxial strength, including the error in its measurement, increases with increase in the water-insoluble content in the sample. Meanwhile, the triaxial strength of rock salt will hardly vary with changes in the water-insoluble content. It can also be concluded that application of confining pressure will suppress the impact of the water-insoluble content on the short-term strength of rock salt, i.e. the inhibition will increase with increasing confining pressure. Application of Hou’s strength model to bedded rock salt from the three regions yields comparable results with the measured data, nevertheless with a bearable small degree of uncertainty. The modified Hou’s strength model has been proved to be more suitable for the determination of strength of bedded rock salt from the three study locations in China.

Risk Assessment on Coal and Gas Outburst Based on TOPSIS Model

Risk assessment on coal and gas outburst was necessary to Coal mine safety management. The model of TOPSIS(Technique for Order Preference by Similarity to Ideal Solution), which is based on entropy weight, was constructed to evaluate outburst risk. The subjectivity which lies in ascertaining factors’ weights was avoided in this model. So the evaluation result is more objective than other evaluation methods. The model was applied in the safety assessment of coal and gas outburst for four mining faces from east area of Ping Dingshan mining area. The order preference of outburst risk was gained. At the same time, the risk differences among four faces were attained. The evaluation results indicate that TOPSIS method be more reasonable and objective. It is easier to use in Coal mines.

Study on two operating conditions of a full-scale oxidation ditch for optimization of energy consumption and effluent quality by using CFD model

The operating condition of an oxidation ditch (OD) has significant impact on energy consumption and effluent quality of wastewater treatment plants (WWTPs). An experimentally validated numerical tool, based on computational fluid dynamics (CFD) model, was proposed to optimize the operating condition by considering two important factors: flow field and dissolved oxygen (DO) concentration profiles. The model is capable of predicting flow pattern and oxygen mass transfer characteristics in ODs equipped with surface aerators and submerged impellers. Performance demonstration and comparison of two operating conditions (existing and improved) were carried out in two full-scale Carrousel ODs at the Ping Dingshan WWTP in Henan, China. A moving wall model and a fan model were designed to simulate surface aerators and submerged impellers, respectively. Oxygen mass transfer in the ditch was predicted by using a unit analysis method. In aeration zones, the mass inlets representing the surface aerators were set as one source of DO. In the whole straight channel, the oxygen consumption was modeled by using modified BOD-DO model. The following results were obtained: (1) the CFD model characterized flow pattern and DO concentration profiles in the full-scale OD. The predicted flow field values were within 1.98 ± 4.28% difference from the actual measured values while the predicted DO concentration values were within −4.71 ± 4.15% of the measured ones, (2) a surface aerator should be relocated to around 15 m from the curve bend entrance to reduce energy loss caused by fierce collisions at the wall of the curve bend, and (3) DO concentration gradients in the OD under the improved operating condition were more favorable for occurrence of simultaneous nitrification and denitrification (SND).

Study and Application of the Technology of Progressive and Large Diameter Buried Drainage Pipe by Crossing-Hole

The purpose of the paper is to solve gas limitation of the upper corner of working face of the protective seam. According to the actual situation of the 12nd Mine of the Ping Dingshan Mining Group Corporation (hereinafter referred to 12nd Mine), the technology of progressive and large diameter buried drainage pipe by crossing-hole was put forward, by the way of numerical simulation and field tests. The best reasonable distance and drainage hole diameter of the buried drainage pipe was obtained through the FLUENT simulation, and in accordance with the actual site, the protective seam Ji 14-31010 and Ji 15-31010 have implemented the buried drainage pipe in the site layout, and effective analysis was carried out. It's known by the actual performance that the technology can solve the problem of the gas limitation in the upper corner effectively.

Flow field prediction in full-scale Carrousel oxidation ditch by using computational fluid dynamics

In order to optimize the flow field in a full-scale Carrousel oxidation ditch with many sets of disc aerators operating simultaneously, an experimentally validated numerical tool, based on computational fluid dynamics (CFD), was proposed. A full-scale, closed-loop bioreactor (Carrousel oxidation ditch) in Ping Dingshan Sewage Treatment Plant in Ping Dingshan City, a medium-sized city in Henan Province of China, was evaluated using CFD. Moving wall model was created to simulate many sets of disc aerators which created fluid motion in the ditch. The simulated results were acceptable compared with the experimental data and the following results were obtained: (1) a new method called moving wall model could simulate the flow field in Carrousel oxidation ditch with many sets of disc aerators operating simultaneously. The whole number of cells of grids decreased significantly, thus the calculation amount decreased, and (2) CFD modeling generally characterized the flow pattern in the full-scale tank. 3D simulation could be a good supplement for improving the hydrodynamic performance in oxidation ditch designs.