A dynamic model of coalbed methane emission from boreholes in front of excavation working face: numerical model and its application.

China's current energy consumption is primarily fueled by coal, increasing coal mining with growing energy demand. Coal and gas outburst accidents are common problems in coal mining, and prediction methods are fundamental for preventing such accidents. The gas emission characteristics of boreholes are a combination of comprehensive coal properties and coal seam gas occurrence status; thus, the accurate prediction of gas emissions from boreholes is crucial for preventing such hazards. This paper presents a method for measuring the gas flow rate in continuous boreholes, which is used to predict outburst danger in front of the working face. The model was compared with field measurement data and found suitable for research. The effects of different initial gas pressures, different borehole radius, and different burial depths on gas emissions from boreholes were studied. The results showed that (1) initial gas pressure is the main influencing factor of gas gushing. The amount of gas emission during drilling and the attenuation of gas pressure are more sensitive to pressure. An increase in gas pressure considerably increases the amount of gas gushing out of drilling holes. (2) The increase in the drilling radius increases the generation of coal cuttings, the area of the drilling hole wall, and the degree of damage to the drilling hole wall. Consequently, the amount of gas gushing out of the drilling hole increases. (3) In situ stress occurs mainly because of the increase in gas pressure with an increase in burial depth and the increase in gas desorption caused by the increase in damage to the borehole wall. This study provides a new outburst prediction method, which involves identifying outburst hazards through the gas gushing out of the borehole. The results are expected to aid the control of underground coal and gas outbursts and ensure the safe production of coal mines.

Effects of nano metal oxide particles on denitrifying phosphorus removal system: Potential stress mechanism and recovery strategy.

The accumulation of nano metal oxide particles (NMOPs) in municipal sewage treatment systems harms the microbial community and its metabolism in activated sludge system, resulting in the degradation of its pollutants removal performance. In this work, the stress effect of NMOPs on the denitrifying phosphorus removal system was systematically investigated in terms of pollutants removal performance, key enzyme activities, microbial community diversity and abundances, and intracellular metabolites. Among the ZnO NPs, TiO2 NPs, CeO2 NPs, and CuO NPs, the ZnO NPs showed the most significant impacts with the chemical oxygen demand, total phosphorus, and nitrate nitrogen removal ratio decreased from above 90 % to 66.50 %, 49.13 %, and 57.11 %, respectively. The addition of surfactants and chelating agents could relieve the toxic effect of NMOPs on the denitrifying phosphorus removal system, and the chelating agents were more effective than surfactants in performance recovery. After adding ethylene diamine tetra acetic acid, the removal ratio of chemical oxygen demand, total phosphorus, and nitrate nitrogen under ZnO NPs stress was restored to 87.31 %, 88.79 %, and 90.35 %, respectively. The study provides valuable knowledge to better understand the impacts and stress mechanism of NMOPs on activated sludge systems and provides a solution to recover the nutrients removal performance of denitrifying phosphorus removal system under NMOPs stress.

Blasting dust diffuse characteristics of spiral tunnel and dust distribution model: similar experiment and numerical modeling.

The special linear shape of spiral tunnel changes the air flow structure during tunnel construction and changes the diffuse and distribution of blasting dust. Mastering the blasting dust distribution and diffuse mechanisms can provide theoretical basis for ventilation layout and dust removal measures during spiral tunnel construction. To study the influence of spiral shape on dust diffusion and concentration distribution after tunnel blasting, a similar scale model of 1:20 and full-scale numerical model of spiral tunnel during construction were established. The similarity criterion and the similarity ratio of each physical quantity are derived from the dust motion equation. The dust distribution and diffuse characteristics in the spiral tunnel under different dust release quantity and release velocity were studied by model experiment. The dust distribution and diffuse characteristics in spiral tunnel with different curvature radius were studied by numerical simulation. The dust distribution model is refined based on the research results. The dust distribution model divides the tunnel into heavily polluted area and slightly polluted area, and the influence characteristics of the curvature radius on the dust export area are found. The layout of ventilation systems can be optimized according to the volume of heavily polluted areas. The heavily polluted area should be as small as possible; the dust in the heavily polluted area should be discharged to the slightly polluted area in an orderly manner to avoid the accumulation of dust. Dust removal measures can also be arranged according to the dust export location to improve dust removal efficiency.

Relationship between Shale Hydration and Shale Collapse.

Shale gas has become the major source of natural gas. However, shale is rich in clay and easily collapsed by water invasion. This not only causes collapse of the reservoir but also causes the loss of natural gas and can even cause local earthquakes and affect the safety of human beings. This paper describes an investigation of the relationship between hydration and collapse. Shale samples were obtained from a series of wells drilled in the lower Silurian Longmaxi Formation at a depth of 3500 m. The different hydrated shales were simulated to analyze the hydration-collapse relationship. Magnetic resonance analysis and mechanical analysis were combined to analyze the collapse of the hydrated shales. The collapse progression was found to follow an S-shaped growth curve that can be divided into three parts, namely, the potential period, the exciting period, and the mature period. The hydration state and degree of damage were determined from the magnetic resonance of water molecules. This paper proposes a mechanism for shale hydration collapse based on basal and numerical data that can be used to predict shale collapse as a function of hydration.

Crack Evolution and Failure Modes of Shale Containing a Pre-Existing Fissure under Compression.

To investigate the crack evolution of Longmaxi shales with a single prefabricated fissure, a CCD (charge coupled device) camera and AE (acoustic emission) monitoring equipment were employed. On the basis of real-time CCD photographs and AE events, a real-time crack evolution process in fissured shale specimens under uniaxial compression was investigated. The crack initiation angle and extension angle were calculated, the relationship between the crack initiation stress, strength, and crack angle was compared, and the proportion of tensile and shear cracks at different stages of the whole compression process was briefly analyzed. The results demonstrate that, with the increase in fissure angle (α), the weakening ability of the prefabricated fissure to uniaxial compressive strength and crack initiation stress was reduced. The initial cracks and secondary cracks always appeared at the tip of the pre-existing fissure in the form of tensile cracks for α = 30-90°. The crack initiation angle and expansion angle increased first and then decreased rapidly with α increasing. Furthermore, the ultimate failure modes were mixed tensile and shear failure when α = 0-90°. The crack evolution of the fissured shale was progressive, but the final failure of the fissured specimen occurred rapidly. Furthermore, the appearance of the cracks, stress drops, and AE counts had good consistency in time.

Draft Genome Sequence of Bifidobacterium longum subsp. infantis BI-G201, a Commercialization Strain.

Bifidobacterium longum subsp. infantis has been widely used in many food products such as solid beverages and dietary supplements. Here, a draft genome sequence of a commercialization strain, Bifidobacterium longum subsp. infantis BI-G201, is reported.

Microscopic investigations on the healing and softening of damaged salt by uniaxial deformation from CT, SEM and NMR: effect of fluids (brine and oil).

Nowadays, a salt cavern, used as underground energy storage (e.g. natural gas, crude oil, hydrogen), is becoming more and more popular in China due to its many advantages, such as low permeability (≤10-21 m2), good water-soluble mining and the damage-healing characteristic of salt rocks. It not only solves the problem of energy resource supply-demand imbalance in China, but also provides a better, more secure and cost-effective way to store energy compared to aboveground energy storage systems. As for salt cavern storage, permeability is our primary concern in engineering, which is mainly influenced by damage and healing. In this work, some damaged salt specimens were prepared by uniaxial compression tests (the loading rate was 0.033 mm s-1). Then those specimens were immersed in either a saturated brine solution or oil at 50 °C for a few days. Microscopic investigations were carried out by X-ray Computed Tomography (CT), Scanning Electron Microscope (SEM) and Nuclear Magnetic Resonance (NMR) to investigate the change of salt microstructures after healing. Possible micro-healing mechanisms were discussed. It was found that fluids played an important role in the healing process of damaged salt. Healing effectiveness of micro-pores and -cracks with the brine solution was higher than that with oil mainly because of crystal recrystallization. The surface of the grains was smooth and had no visible microcracks after healing in brine, while there were many pits and micro-tunnels with oil. Oil could hinder the healing process by impeding the diffusion effect and restraining grain recrystallization. Meanwhile, intragranular and intergranular water could also work as a lubricant resulting in softening which made salt rock more deformable. NMR results confirmed that damaged salt had a better recovery with brine, displaying lower porosity and lower permeability compared to that with oil. This work provides preliminary microscopic investigations on the healing of damaged salt in order to reveal the salt healing mechanism.

Self-Healing Characteristics of Damaged Rock Salt under Different Healing Conditions.

Salt deposits are commonly regarded as ideal hosts for geologic energy reservoirs. Underground cavern construction-induced damage in salt is reduced by self-healing. Thus, studying the influencing factors on such healing processes is important. This research uses ultrasonic technology to monitor the longitudinal wave velocity variations of stress-damaged rock salts during self-recovery experiments under different recovery conditions. The influences of stress-induced initial damage, temperature, humidity, and oil on the self-recovery of damaged rock salts are analyzed. The wave velocity values of the damaged rock salts increase rapidly during the first 200 h of recovery, and the values gradually increase toward stabilization after 600 h. The recovery of damaged rock salts is subjected to higher initial damage stress. Water is important in damage recovery. The increase in temperature improves damage recovery when water is abundant, but hinders recovery when water evaporates. The presence of residual hydraulic oil blocks the inter-granular role of water and restrains the recovery under triaxial compression. The results indicate that rock salt damage recovery is related to the damage degree, pore pressure, temperature, humidity, and presence of oil due to the sealing integrity of the jacket material.