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To investigate the pressure-relief and permeability enhancement mechanisms of hydraulic flushing (HF), this study conducted the triaxialseepage experiments on raw coal; the permeability changes during the loading process were analyzed, and the coal permeability evolution model was derived considering the damage effect. Given the boundary conditions of gas seepage and stress fields, a multifield coupling model was developed to reflect coal seam methane (CBM) extracted by the HF borehole. Based on the actual geological conditions of Yi'an Coalmine, the three-dimensional (3D) numerical simulation was implemented to investigate the effects of coal discharge amount on the relief range, coal permeability, and effective extraction radius of the HF borehole. Moreover, the validity of the coupling model was confirmed through field tests on hydraulic flushing. Then, the interactions of various factors, including coal discharge amount, borehole spacing, initial CBM pressure, and coal permeability, were investigated using the response surface methodology (RSM). Through the results obtained, it was found that the interactions between the factors involved were very significant and caused an obvious time effect on CBM extraction. The interaction between coal discharge amount and borehole spacing increasingly affected the extraction effect of HF boreholes, whereas the interaction between initial CBM pressure and coal permeability gradually weakened. Then, the RSM regression model was established to optimize the borehole placement parameters using predicted extraction time and coal discharge amount as variables. The regression prediction data were consistent with the simulation results and mutually validated. Therefore, based on the elimination of gas outbursts and reduced construction costs, the modeling approach and the RSM model introduced in this study can be used to optimize the precise placement parameters of HF boreholes for enhancing CBM recovery within the expected extraction period. [ABSTRACT FROM AUTHOR]

In order to solve the problems such as small influence range, fast decay rate, difficulty in gas disaster control and long treatment period of gas extraction drilling in Hebi Mining Area, a technological process of coordinated stamping operation was put forward, and the technical mode of drilling and stamping coordinated operation with automatic drilling rig group drilling - temporary sealing hole pre-pumping - stamping joint operation after pre-pumping is formed, and industrial test is carried out in Hebi No.6 Coal Mine for industrial trials, the field application results show that: the technology mode gives full play to the advantages of automatic drilling rig continuous drilling, fast operation, reducing staff and improving efficiency, realizes the specialization, continuity and scale of gas extraction drilling construction operation and hydraulic stamping coordinated penetration operation, and makes the construction work efficiency of construction of penetration drilling in the bottom rock tunnel for gas treatment increase by 48% under the same geological conditions; meanwhile, the at the same time, after the construction of extraction holes by automatic drilling rig is completed, the temporary sealing of the extraction holes is carried out, so that the free gas in the holes is greatly reduced after extraction, which greatly reduces the frequency of gas overrunning accidents in the roadway during the construction of hydraulic measures and effectively guarantees the safety of construction; the average gas extraction concentration of the test borehole is 1.31 times of that of the conventional hydraulic ramming measure, and the average daily pure extraction volume of the test unit borehole is 1.79 times of that of the conventional hydraulic ramming measure.

This article provides a comprehensive review and best practices for numerically simulating hydraulic flushing for reservoir sediment management. Three sediment flushing types are discussed: drawdown flushing, pressure flushing, and turbidity current venting. The need for reservoir sediment management and the current practices are reviewed. Different hydraulic drawdown types are described in terms of the basic physical processes involved as well as the empirical/analytical assessment tools that may be used. The primary focus has been on the numerical modeling of various hydraulic flushing options. Three model categories are reviewed: one-dimensional (1D), two-dimensional (2D) depth-averaged or layer-averaged, and three-dimensional (3D) computational fluid dynamics (CFD) models. General guidelines are provided on how to select a proper model given the characteristics of the reservoir and the flushing method, as well as specific guidelines for modeling. Case studies are also presented to illustrate the guidelines. [ABSTRACT FROM AUTHOR]

In order to explore the influence of environmental media on the characteristics of water jet coal breaking, ALE algorithm and LS-Dyna software are used to carry out numerical simulation of continuous water jet impact coal breaking and the characteristics of water jet propagation, coal breaking characteristics and time-varying characteristics of the relationship between the two coal breaking depths under the submerged and non-submerged environments are analyzed. The results show that because of the large loss of water jet, the jet velocity in submerged environment is much lower than that in non-submerged state. Under the obstruction of environmental medium, the submerged jet diverges and increases the area of broken coal, resulting in the increase of the area of broken coal and the decrease of the depth, but the damage element does not change much. It is necessary to prolong the impact time reasonably or reduce the spacing of boreholes when coal caving is carried out in submerged environment.

To enhance gas drainage in the soft and hard interbedded (SHI) coal seam, it’s necessary to unload the in-situ stress and improve its gas migration performance. In this research, a directional hydraulic flushing (DHF) technology was carried out. The stress-unloading and gas migration improvement mechanism was analyzed through numerical simulation, and systematic engineering tests were conducted to verify the gas drainage effect. The results show that the improvement of gas migration performance in the SHI coal seam is caused by a combined effect of seepage-improving and diffusion-improving. After DHF, stress-unloading and plastic failure could be achieved both in the soft coal (SC) sublayer and in the hard coal (HC) sublayer. However, the gas diffusion capacity improves significantly in the SC sublayer, while the gas seepage capacity improves notably in the HC sublayer. Meanwhile, the stress-unloading and gas migration improvement effect improves with the flushing radius and the thickness of the SC sublayer. Besides, after adopting the DHF technology, the gas drainage effect improved markedly. The borehole number dropped by 49%, the gas drainage ratio increased from 26.0% to 48.2%, and the average coal roadway excavation speed increased from 2.4 to 5.6 m/d.

At present, in drilling design and evaluation, the shape of hydraulic flushing hole is usually equivalent to cylinder, which is one of the important bases to determine the effective extraction radius. However, the shape of hole is subject to the joint action of many factors, so the scientific nature of the equivalent shape to cylinder remains to be discussed. By adopting the factors of gravity, friction, water force and in-situ stress of coal and rock mass, and introducing the parallel Bergmark-Roos equation and PKN model, the BR-PKN equation describing the pore shape is established, and the pore shape is reconstructed by MATLAB. In order to verify its accuracy, data are collected and analyzed by using YZD18.5 logging tool in the field, and the hole section is drawn. The equivalent ellipsoidal and cylindrical holes are simulated by COMSOL. The results show that the shape of the holes drawn by MATLAB is ellipsoid with different three axes. The shape of the drawn hole is basically consistent with that in MATLAB. Compared with cylindrical holes, the extraction radius, desorption surface area and effective extraction volume of quasi-ellipsoid holes are 93%, 80% and 117% respectively, which provides a basis for drilling layout.

To realize the precise stress relief and permeability enhancement of the coal seam with non-uniformly distributed gas, the criterion and optimization method of key construction parameters of hydraulic flushing was studied by modeling, numerical simulation and field tests. First, the multiphysics coupling model for stress-relieved coal seam was developed and index of optimal coal discharged was analyzed. Then the criterion and determination method of optimal coal discharged was put forward. Finally, the determination map of key construction parameters of hydraulic flushing was drawn, and a precise permeability enhancement technique for coal seam with non-uniformly distributed gas was proposed. The main conclusions are shown as follows: ① for a given gas extraction time, the residual gas content decreases while the residual gas pressure reduces followed by an increase with a rise of coal discharged; ② the criterion of optimal coal discharged includes the constraints of gas extraction reaching standard and minimization of roadway instability risk and construction cost. When the residual gas content and pressure are less than the critical values, it is considered that the gas extraction reaches the standard. On the premise of meeting the standard of extraction, the coal discharged should be reduced as far as possible to ensure the stability of coal roadway and reduce the project cost; ③ The optimal coal discharged decreases with the increase of ground stress, and increases with the increase of cohesion, gas pressure and borehole spacing. For a given coal seam, there is a maximum value of coal discharged and a minimum value of extraction time reaching standard; ④ comprehensively considering the correlation between coal seam gas pressure, coal yield, borehole spacing and extraction time reaching standard, the optimization map of key parameters of hydraulic flushing is drawn. Based on the map, a precise pressure relief and permeability enhancement technology for coal seams with non-uniformly distributed gas is put forward. In this technique, the construction parameters of hydraulic flushing corresponding to various gas occurrence areas can be determined, with the combination of gas occurrence and optimization map of key parameters, realizing the precise permeability enhancement of the coal seams with non-uniformly distributed gas.

This article provides a comprehensive review and best practices for numerically simulating hydraulic flushing for reservoir sediment management. Three sediment flushing types are discussed: drawdown flushing, pressure flushing, and turbidity current venting. The need for reservoir sediment management and the current practices are reviewed. Different hydraulic drawdown types are described in terms of the basic physical processes involved as well as the empirical/analytical assessment tools that may be used. The primary focus has been on the numerical modeling of various hydraulic flushing options. Three model categories are reviewed: one-dimensional (1D), two-dimensional (2D) depth-averaged or layer-averaged, and three-dimensional (3D) computational fluid dynamics (CFD) models. General guidelines are provided on how to select a proper model given the characteristics of the reservoir and the flushing method, as well as specific guidelines for modeling. Case studies are also presented to illustrate the guidelines.

Reservoirs are a crucial part of the human water supply system. The effectiveness and service life of a reservoir is decided mainly by its storage capacity, and as such, preventing reservoir capacity loss is of high interest worldwide. Due to climate change in recent years, precipitation types have changed, and heavy rainfall events have become more severe and frequent. Rainfall causes soil erosion in slope lands and transports large amounts of sediment downstream, forming deposition. This causes reservoir storage capacity to fall rapidly and decreases reservoir service life. The Sediment–Sluice Tunnel can reduce rapid deposition in reservoirs and is, thus, widely employed. By simulating sediment transportation in reservoirs, deposition reduction after building the Sediment–Sluice Tunnel can be evaluated. This study used the Physiographic Soil Erosion–Deposition (PSED) model to simulate the flow discharge and suspended sediment discharge flowing into the Zengwen reservoir then used the depth-averaged two-dimensional bed evolution model to simulate the sediment transportation and deposition in a hydrological process. Simulation results showed that the Sediment–Sluice Tunnel effectively reduced deposition and transported sediment closer to the spillway and Sediment–Sluice Tunnel gate. The deposition distribution with the Sediment–Sluice Tunnel built is more beneficial to the deployment of other dredging works. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to solve the problem of the high risk of coal and gas outburst in deep coal working face, taking 12090 working face of Shoushan No.1 Coal Mine as the engineering background, the paper analyzes the deformation and stress variation law of coal body after hydraulic flushing in coal working face under deep-buried and high-stress environment by numerical simulation method. The conclusions are listed as follows. The coal body around the hydraulic flushing hole deforms towards the hole, which is conducive to the development and conduction of cracks in the coal body, thus improving the permeability of the coal body. The horizontal stress of the coal body in the flushing area is effectively reduced. The pressure relief areas formed by each punching hole are interconnected to form a pressure relief strip, which is conducive to gas migration and extraction. According to the numerical simulation results and the actual project, the hydraulic flushing project scheme of 12090 working face in Shoushan No. 1 Coal Mine is determined. The upper side drilling angle is 5-6°, and the lower side drilling angle is −5-−4°. The drilling spacing is 4 m, and the length of each punching hole is 1 m. The spacing of flushing holes in each borehole is 7 m, and no flushing operation is carried out within 30 m from the roadway side. The flushing water pressure is 5-6 MPa, and the flow rate is 120-160 L/min. The practice shows that after adopting this scheme, the number of holes completed per month reaches 40 and the completion rate reaches 80%. The gas extraction concentration in the flushing hole is high and the gas attenuation is slow. After 50 days of extraction, the gas volume fraction in the flushing hole is 40%-60%, which is 2-3 times of that in the ordinary hole. After 120 days of extraction, the gas volume fraction in the flushing hole is still 20%. Hydraulic flushing effectively improves the gas extraction effect and reduces the gas content in coal seams. The average gas volume fraction of return air flow decreases to below 0.5%. The average daily footage of the working face increases from 2.4 m to 3.2 m, which improves productivity.

Structural coal has low permeability and high gas content. The increase of mining depth seriously restricts the safe mining of deep mines. Hydraulic flushing is the main means of gas extraction. The shape of the hydraulic flushing hole is an important basis to determine the pumping radius, which is widely regarded as a cylinder. However, due to the differences in the stress level, water force, friction and external moisture, the pore morphology, and permeability evolution need to be further studied. At present, the hole shape for hydraulic punching is equivalent to a cylinder in drilling design and evaluation, which is one of the important bases to determine the effective extraction radius. However, the hole shape is affected by many factors, so the scientific equivalent to a cylinder remains to be discussed. The BR-PKN equation describing the hole shape is established by introducing and combining the Bergmark–Roos equation and PKN model, and the hole’s shape is shown by MATLAB. To verify its accuracy, YZD18.5 is used as an onsite logging tool for data acquisition and analysis, and the hole section is drawn. The BR-PKN equation and permeability evolution model are simulated by COMSOL Multiphysics, and the permeability evolution law of conventional cylinder with hydraulic flushing is compared and analyzed. The results show that 1) the shape of the hydraulic punch hole is ellipsoid with three different axes, and its horizontal section is approximately an ellipse; 2) within the influence range of quasi-ellipsoid holes, the permeability changes in the long and short axis of quasi-ellipsoid holes are similar. The permeability evolution curve of the coal first increases, then decreases, and finally, flattens with the increase of distance from borehole, and the permeability of the coal body increases with the extension of extraction time); 3) the permeability of the equivalent ellipsoid pore decreases with the increase in coal water content. The effective radius in the long and short axes of the minimum cross section of the quasi-ellipsoid hole is 0.89 and 0.95 times the effective extraction radius of the equivalent cylinder, which provides a basis for a drilling layout.

Hydraulic flushing is a crucial technology for enhancing deep coal seam gas extraction, while the gas desorption characteristic is a critical factor impacting efficient gas extraction. This paper first analyzed stress variation around borehole during flushing and subsequently conducted experimental research to explore the effect of stress evolution on gas desorption. The results indicated that stress variation had a relatively insignificant effect on gas desorption during the early stage. When stress variation peaked in coal samples, instability and damage occurred, leading to a surge in the gas desorption rate. The ultrasonic wave velocity and dynamic elastic modulus of coal under different stress paths exhibited significant changes. With an increase in desorption time, the coal dynamic elastic modulus decreased, and the damage coefficient gradually increased. When comparing gas desorption behavior during constant stress and stress relief, Pingdingshan Mine (PDS) and Jiaozishan Mine (JZS) coal samples exhibited desorption amounts 2.85 and 1.41 times higher after stress relief, respectively. Based on the influence of stress relief on gas desorption rate and structure, a theoretical matrix scale change model was deduced. The mechanism controlling the rate of gas desorption by stress relief was illustrated. These research results offer theoretical guidance for implementing stress relief techniques to optimize coal seam gas extraction in practical field applications. • Quantitatively evaluated the effect of stress evolution on wave velocity and gas desorption rate. • A theoretical matrix scale change model of stress relief coal was deduced. • The controlling mechanism responsible for the effect of stress relief on gas desorption rate was illustrated. [ABSTRACT FROM AUTHOR]

In coal mine gas extraction in China, the current hydraulic permeability enhancement measures generally have complex processes, low adaptability, long operation time, and high labor intensity. This makes it challenging to meet the requirements of coal mining enterprises for safe and efficient mining, and there is an urgent need to develop new technologies to enhance gas extraction and production. This paper proposed an integrated drilling and stamping technology to enhance gas extraction and production and integrates drilling, hydraulic jet fracturing, and hydraulic punching to enhance the permeability of coal seams. A field test was conducted using the specially-developed integrated drilling and stamping equipment to extract gas from the 16101 bottom pumping lane penetration hole in the Jiulishan Mine, Jiaozuo, Henan. The test results show that compared with the hydraulic punching technology previously used in the mine, the punching time of the soft coal seam was shortened by 66–75%, the coal output was increased by 1.7 times, and the punching hole aperture was increased by 1.3 times. Hydraulic injection fracturing was successfully performed to increase the permeability of the hard coal seams, and the fracturing formed a shot hole depth of 345–539 mm. After the integrated drilling and stamping of the drill holes, the coal output, gas extraction concentration, pure gas extraction volume, and coal seam permeability coefficient increased by 2.4, 2.2, 4, and 37.3 times, respectively. The gas flow decay coefficient of the drills holes was also further reduced, which significantly improved the extractionefficiency. Thus the integrated drilling and stamping technology can transform the process of gas extraction from regular extraction to quick, economic, pure, and clean extraction. Thus, this technology has large applicable value for underground gas management in coal mines. [ABSTRACT FROM AUTHOR]

Soft coal seams are characterized by high gas content, high tectonic stress, low strength, and low permeability; thus, gas extraction from soft coal seams is rather difficult, and outburst accidents commonly occur in their driving face. To enhance gas extraction and thus prevent outburst disasters, a novel in-seam borehole discontinuous hydraulic flushing (ISBDHF) technology was proposed in this work. By adopting a multiphysical coupling model and a new FLAC3D and COMSOL Multiphysics combined numerical solving method, we first analyzed the enhanced gas extraction mechanism of hydraulic flushing using the numerical simulation method. After that, this new technology was applied in the Xinjing coal mine, and its application results were systematically investigated. The numerical simulation results showed that the generation of new fractures in the plastic failure zone caused by hydraulic flushing could not only increase the coal permeability by 2–3 orders of magnitude, but also decrease its gas sorption time from 1 day to several minutes due to the decrease in matrix size. Therefore, hydraulic flushing enhances gas extraction by the combined effect of increasing permeability and increasing diffusion. Moreover, nearby flushing cavities may interact with each other under multicavity conditions, further improving the permeability-increasing and diffusion-increasing effects. After adopting ISBDHF technology in the Xinjing coal mine, the borehole number and gas extraction period in the driving face decreased by 73.5 and 77.8%, respectively, while the gas extraction rate increased from 28.20 to 34.35%, which improved the coal roadway excavation speed by 1.37 times. [ABSTRACT FROM AUTHOR]

Although the effect of pressure relief and permeability increasing achieved by the technology of traditional hydraulic flushing (enlarging hole by high-pressure water jet) is great significance, it has some shortcomings, such as low efficiency, large consumption of water resources, and being difficult to guarantee the sizes of holes. The limitations of water jet are known as the main factors that would restrict the effective pressure relief in soft and low-permeability coal seam. For the purpose of solving the problems existing in the traditional technology, a new technology of mechanical cutting assisted by waterjet has been developed. Then, a numerical simulation method was employed to illustrate the flow field and the force characteristics of equipment equipped with new technology. Finally, the new technology and its supporting system were tested in the Xinjing Coal Mine, Shanxi Province, China. The test results obtained are as follows: the efficiency of mechanical cutting is much higher than that of hydraulic flushing; the maximum equivalent to enlarge hole radius is increased by 83.3% (t = 30 min), and the efficiency of the new technology is 3 times more than that of the traditional hydraulic flushing; the time used for gas drainage is increased by 19.3%, and the drainage efficiency is increased by 28%; the cost spent on gas control in one working face decreases by more than 14.7%. It is concluded that the new technology can efficiently enlarge borehole so as to enhance gas drainage in coal seam and decrease the cost of coal mining. [ABSTRACT FROM AUTHOR]

Accurate prediction of reservoir sediment inflows (Min) and adaptation of feasible sediment management strategies pose challenges in water engineering. This study proposed a two-stage complementary modeling approach for comprehensive reservoir sediment management. In the first stage, artificial neural network-based models provide real-time Min predictions using water inflow, water head, and outflow as input parameters. In the second stage, the parameter estimation method of the RESCON model is applied to hydraulic flushing in a reservoir. This approach was applied to the Sangju Weir and Nakdong River Estuary Barrage (NREB) in South Korea. Results from the RESCON model revealed that hydraulic flushing was effective for sediment management at both the Sangju Weir reservoir and the NREB approach channel. Efficient flushing at the Sangju Weir required a flushing discharge of 100 m3/s for 6 days and 40 m of water head. Efficient flushing at the NREB required a flushing discharge of 25 m3/s for 6 days with 1.8 m of water-level drawdown. The proposed approach is expected to prove useful in reservoir sediment management. [ABSTRACT FROM AUTHOR]

Abstract In China, one or several ultrathin soft coal sublayers are widely developed in the coal seam. Therefore, a method of using hydraulic flushing in soft sublayer to enhance the gas extraction in these particular coal seams is developed in this work. We first established a new fully coupled gas extraction model by combing gas diffusion, gas flow, and a permeability model that considers the effect of stress change and plastic failure. By adopting this model, the gas extraction enhancement mechanism and its main influence factors were studied using the numerical simulation method based on the engineering and geological background in the Yangquan No.5 coalmine. Thereafter, a hydraulic flushing equipment, which could move freely in the underground coalmine, was developed to apply the hydraulic flushing method in soft coal sublayers used in the 8402 working face. Its gas extraction effect was systematically investigated. Our simulation results match well with the field results, suggesting that our model is feasible. Meanwhile, after adopting this method, the gas extraction condition in this coalmine improves significantly. The borehole number decreases by 66.7%, while the gas extraction rate and gas extraction concentration increase by 1.33 times and 3 times, respectively. Moreover, during the coal mining process, the gas adsorption index of drilling cuttings, the quantity of drilling cuttings, and the CH4 concentration also decrease dramatically.

Hydraulic flushing (HF), which uses water jet with high pressure to break coal, is widely used in the prevention and control of coal and gas (methane) outburst in coal mines. The key of HF technology is to determine the proper water pressure of water jet, otherwise, serious construction accidents will be induced during the period of water jet breaking coal. In this paper, coal, which is determined to be a typical piezoelectric material by the analysis the composition with X-ray diffraction method, can generate electromagnetic radiation (EMR) signal under external load because of the piezoelectric effect. Then, two mechanical stages of water jet breaking coal are analyzed theoretically to explore the relation between initial water pressure of water jet and EMR signal. Accordingly, a new method based on the analysis of EMR emitted from the deformation of coal under the action of water jet with different initial pressure is proposed to determine safe water pressure. The research results are as follows: (1) According to the field test, EMR has obvious regional characteristics. when the coal is impacted by water jet with safe pressure, maximum, average and frequency of EMR are more normal than that of invalid water pressure and dangerous water pressure;(2) From the perspective of coal rupture, the development of pores and fractures in the coal is fast and the macroscopic fracture scale, which is simulated in the same calculation steps, is large under the impact of water jet with safe pressure. Furthermore, the coal mass does not have a serious instability phenomenon, which means the suitability of safe water pressure;(3) The fractal characteristics of EMR frequency which can present nonlinear and self-similarity characteristics of coal fracture process vary with pressure of water jet. When the initial water pressure of the water jet is safe, the value of the Δ α is smaller than that in invalid water pressure, but bigger than that in dangerous water pressure. This method has certain guiding significance for determining the safe water pressure of HF. [ABSTRACT FROM AUTHOR]

The effectiveness of the use of accumulation basins ordinarily used for river sediment to reduce the rate of silting of the reservoirs of hydroelectric power plants situated on mountain rivers is considered. The investigation is performed by methods of numerical hydrodynamic simulation based on the two-dimensional Saint-Venant equations and a new model of sediment transport that takes into account the fractional composition of the sediment. Using as an example a concrete reservoir located on a mountain river, it is shown that it is extraordinarily important to take into account the heterogeneity of the soil in the process of solving these types of problems. A combination of the annual hydraulic flushing of reservoirs and mechanical removal of soil from the accumulation basins together assure the required useful volume throughout the entire service life of the hydroelectric plant, though it requires the annual removal of up to 40% of the sediment discharge of the river. [ABSTRACT FROM AUTHOR]

In China, one or several ultrathin soft coal sublayers are widely developed in the coal seam. Therefore, a method of using hydraulic flushing in soft sublayer to enhance the gas extraction in these particular coal seams is developed in this work. We first established a new fully coupled gas extraction model by combing gas diffusion, gas flow, and a permeability model that considers the effect of stress change and plastic failure. By adopting this model, the gas extraction enhancement mechanism and its main influence factors were studied using the numerical simulation method based on the engineering and geological background in the Yangquan No.5 coalmine. Thereafter, a hydraulic flushing equipment, which could move freely in the underground coalmine, was developed to apply the hydraulic flushing method in soft coal sublayers used in the 8402 working face. Its gas extraction effect was systematically investigated. Our simulation results match well with the field results, suggesting that our model is feasible. Meanwhile, after adopting this method, the gas extraction condition in this coalmine improves significantly. The borehole number decreases by 66.7%, while the gas extraction rate and gas extraction concentration increase by 1.33 times and 3 times, respectively. Moreover, during the coal mining process, the gas adsorption index of drilling cuttings, the quantity of drilling cuttings, and the CH4 concentration also decrease dramatically. [ABSTRACT FROM AUTHOR]

The concept of sustainable development is gaining popularity and hydroelectric projects designed and operated on this concept require sediment management as prime design criteria. Drawdown flushing is being practised in such projects for sediment management. Investigations using hydraulic models are required for the projects to address the site-specific design concerns. In the present study, simulations conducted using hydraulic model for sediment removal by drawdown flushing of the reservoir of Punatsangchhu hydroelectric project, Bhutan, is presented. The experiments on 1:100 geometrically similar scale model indicated that flushing is effective in maintaining the power intake area clear of sediment deposition. Deposition from the upstream reaches could not be flushed hydraulically. Furthermore, based on wide range of experimental data from hydraulic model studies, empirical equations have been developed for predicting the quantity of sediment that can be flushed from the reservoirs. The present equations have been developed including more parameters than those used in equations already available in literature. Two equations have been developed for different riverbed slope ranges with steep slope (0.005–0.04) and moderate slope (0.001–0.005). The equations developed were validated against different sets of data and it indicated that the predictions could be made within reasonable accuracy. These equations can be effectively used for hydraulic design of sediment removal from run-of-the-river hydropower reservoirs. [ABSTRACT FROM AUTHOR]

Hydropower projects located on rivers transporting heavy sediment loads require design and operation criteria based on sediment management as a means of sustaining the project life. Sediment management is achieved by designing projects as a run‐of‐the‐river scheme, with provision for drawdown flushing, noting hydraulic model simulations are essential for optimizing the design of these projects. Sediment deposition levels are generally predicted with long‐term simulations using 1‐D numerical models, as well as experiments with scaled physical models that simulate drawdown flushing. The present study presents experiments with scaled model and 3‐D numerical model simulations conducted for hydraulic flushing of a reservoir. Experiments were conducted for various durations and discharges to finalize the intake alignment and optimize the flushing. The results of the 3‐D numerical model simulations are in agreement with the results of the experimental study (4%–6% variation). The results also indicate a combination of a 1‐D numerical model for sedimentation and a 3‐D numerical model for flushing can be effectively used to simulate the sedimentation and flushing of reservoirs during the planning and design stages. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hydraulic flushing technology can rapidly and effectively eliminate coal and gas outbursts and improve the permeability of a coal seam. Its effect mainly depends on the technical parameters of hydraulic flushing. To solve the problems on technical parameters that exist in the application of hydraulic flushing technology, the outburst elimination mechanism of hydraulic flushing technology was expatiated, the hydraulic flushing process was introduced, and a field test was performed on the B1 coal seam in Yi’an Coal Mine by using the pressure drop method. Moreover, the effective influence radius of hydraulic flushing measure was determined, and the technical parameters were analyzed. Finally, a series of relationships was obtained, including the relationships between hydraulic pressure and coal output, critical breaking coal pressure and firmness coefficient, flushing time and coal output, drilling hole angle and coal output, and coal output and effective influence radius. Results showed that the effective influence radius of hydraulic flushing in B1 coal seam was 9 m, and the outburst risk of the coal within the influence region was eliminated. In addition, the time of outburst elimination was shortened and the production rate was improved. The research results could provide technical support for the optimization of the technical parameters and the test scheme of hydraulic flushing measures.

Hydraulic fracturing and waterjet slotting fracturing have been demonstrated to be effective in creating artificial fractures and stimulating gas production in hard coal seams. However, these methods are inefficient for soft-outburst coal seams because these created fractures are short and easy to close. To eliminate the outburst risk of soft coals, a novel enhanced coalbed *Corresponding authors' email: Jiangjingyu@cumt.edu.cn, chengypcumt@ 163.com methane under-panel cross-strata drainage technique via hydraulic flushing was proposed in this work. The hydraulic flushing effects of boreholes of different sizes in the coal seam were also pre-evaluated by a simulation approach. The modeling results indicate that as the radius of the borehole increases, the plastic and stressdecreasing zone expands. A field test was also conducted in the Minjin mine, China, that investigated the gas pressure variation between three monitoring boreholes at different distances from a hydraulic flushing borehole. Test results indicate that the effective influence radius of gas extraction is approximately 5.5 m. Based on the results of the field test and borehole camera observation, the unloaded coal quantity and the average diameter of the boreholes were estimated to be 8.0 t and 942 mm, respectively. The borehole diameter expanded up to 10 times larger than its original size. The average gas extraction concentration and gas flow rate increased by approximately 2 and 3.5 times, respectively, demonstrating the effectiveness of the proposed hydraulic flushing in improving the gas extraction efficiency. The hydraulic flushing technique therefore is proved to be efficient in eliminating the outburst risk of coal and reducing greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Sediment removal from reservoirs is the major challenge faced by developers of hydropower projects in the Himalayan region. Sediment removal can be achieved by drawdown flushing or sluicing. In drawdown flushing, the water level in the reservoir is lowered sufficiently to establish riverine flow conditions. A flushing channel will be developed and retrogressive erosion will take place. However in the case of sluicing, the water level is kept sufficiently high to maintain pressure flow conditions. During sluicing, the incoming sediment is passed through the sluices and since water level is not lowered, previously deposited sediment will not be removed. Only a scour cone will be developed in the vicinity of the low level sluice outlet. In the case of run-of-the-river hydropower projects, it is important to estimate the parameters of the scour cone such as length, width and depth. The projects are generally operated at MDDL during monsoon season, when sediment concentration is high. Power intakes are generally located very near to the dam and in the scour cone area. Hydraulic model studies carried out to investigate the development of scour cone under pressure flushing of a reservoir is presented in this paper. The experiments were carried out in a laboratory flume. A single spillway bay was reproduced in the model. Experiments were conducted by varying the sluicing discharge and water depth. The various parameters of the scour cone were measured. Dimensional analysis was carried out to establish the relationship of scour cone parameters and hydraulic parameters. The available relationships in the literature also were verified. [ABSTRACT FROM AUTHOR]

Chinese coal mines often apply hydraulic flushing technology for pressure relief and permeability increase of difficult-to-extract coal seams In order to study effective detection methods for the impact range of hydraulic flushing on coal seams, we first experimentally investigated the response characteristics of the apparent resistivity of small-scale coal mass to hydraulic flushing, then theoretically analyzed the characteristics of its temporal variation and spatial distribution, and lastly measured the changes in apparent resistivity in the Hydraulic flushing process at Nuodong Coal Mine, Guizhou Province, China, and the effective range of Hydraulic flushing in the coal bed. The experimental results showed that the spatial distribution and variation of coal and rock mass structure could be reflected by apparent resistivity. Under high-pressure water, coal structure was changed (loosen, broken, or out-washed), forming cavities and a network of cracks in the surroundings of the drilling borehole, which reduced the conductivity of coal and caused a significant increase in apparent resistivity. In both laboratory and field experiments, the coal/rock apparent resistivity was relatively consistent, and the apparent resistivity in the hydraulic flushing impact region significantly grew. The hydraulic flushing impact range was gradually increasing, and the response of apparent resistance was closely associated with the role of high-pressure water and the evolution of the fracture field. [ABSTRACT FROM AUTHOR]

Present coal seams in China are characterized by great gas pressure and content, low permeability features, and thus, the extraction of gas is difficult and gas disaster remains serious. To improve the permeability of coal seam, the hydraulic flushing is adopted, so the effect evaluation of stree relief and permeability enhancement will be necessary before gas extraction. In this paper, an electromagnetic radiation (EMR) experiment system of coal seam hydraulic flushing was established, and the EMR characteristics of coal during hydraulic flushing were studied. The EMR test of hydraulic flushing was carried out in the Liangbei coal mine, China, and the gas extraction flow and coal stress were measured simultaneously. And then, the variation laws of EMR and the effect evaluation of hydraulic flushing were analyzed. The results showed that coal deformation and fracture produced abundant EMR signals during hydraulic flushing. The variation of the EMR signals was synchronous with the variation of load, and the large the load variation was, the greater the EMR intensity and count were. Compared with before hydraulic flushing, the EMR signals changed significantly after hydraulic flushing, and the variation amplitude of the EMR intensity was consistent with the variation amplitude of the coal stress and gas extraction flow. So the EMR method achieved the objective of effect evaluation. It's feasible and dependable to evaluate the effect of coal seam hydraulic flushing by EMR. [ABSTRACT FROM AUTHOR]

Hydraulic flushing has the advantages of reducing coal stress and improving coal seam permeability, so it is widely used in high gas outburst coal seams in China. However, the effect evaluation of stress relief and permeability enhancement will be necessary before coal mining. In this paper, an acoustic emission (AE) experiment system of coal seam hydraulic flushing was established, and the AE characteristics of coal during hydraulic flushing were studied. The results show that the changes in AE signals are basically consistent with those in load and water pressure. In addition, the quantitative relationship between the signals and the damage of coal around the borehole is revealed by the theory of damage mechanics. The in-situ AE test of hydraulic flushing was performed in the Liangbei Coal Mine, by measuring gas flow and coal stress simultaneously. The variation of AE activities and the effect evaluation of hydraulic flushing were analyzed. The results reveal that the changes in coal seam stress are basically consistent with those of AE signals. After the flushing has been completed for 1−3 h, the coal seam stress decreases rapidly, and the AE counts and intensity reach the peak. Therefore, this study proposes a new method for evaluating the effect of coal seam hydraulic flushing by AE, which has a very important practical significance.

To study the variation of the pressure relief scope and the stress around hydraulic flushing borehole, the theory of coalrock damage was utilized to distinguish the interaction area of water-jet and coal-rock into the coal-rock crushing area, the water-jet pressure stagnation area, the transition area and the original stress recovery area of coal-rock. Based on the actual occurrence conditions of the coal seam, the pressure variation and relief scope around the hydraulic flushing borehole were analyzed and simulated by RFPA2D-Flow software. The results showed that a relief area with the radius of 5.0 ~ 6.0 m around the borehole formed due to the hydraulic flushing with the pressure relief of 0.038 ~ 6.545 MPa, and the maximum principal stress is 15.85 MPa with a distance of 6.8 m from the inspected hole where stress concentration appeared. After hydraulic flushing test, the diameter (441.8 ~ 1171.6 mm) of the hole which can be an expression of coal crushing area size, was calculated based on the examination of the coal amount through the trial process, and it can be drawn that the pressure relief area must be larger than that of the coal-rock crushing area. Meanwhile, the measured pressures relief range(5.96 ~ 6.62 m) is basically consistent with the numerical simulation result (5.0 ~ 6.0 m) which verified the accuracy of the simulation analysis, according to the distance from the inspection drilling to the hydraulic flushing borehole and the decreased degree of the gas content in the inspection hole by the way of Gas Content.

The heading face in soft and low-permeability coal seams is one of the most high-risk areas for Chinese coal and gas miners because of the number of outburst-related accidents. To prevent and control these disasters, the in-seam borehole gas extraction technology is widely used because of its low construction cost. Unfortunately, few studies consider its gas extraction efficiency. Thus, a new in-seam borehole hydraulic flushing (ISBHF) gas extraction technology is proposed in this paper, where the hydraulic flushing technology is used to enhance the gas extraction of in-seam boreholes. Based on the engineering background in the Xinjing coal mine, a detailed study of this new technology is conducted. First, we model the permeability-increasing mechanism of this technology and the gas flow characteristics of the hydraulic flushing boreholes using a finite-element method. During this process, the strain-softening behavior of the coal mass and the effect of the coal mass failure on the permeability evolution are considered. Second, a reasonable gas extraction scheme is designed, which considers the divergent characteristics of boreholes in the heading face and the interactions among multiple boreholes in the gas extraction process. Finally, the gas extraction scheme is implemented at the S5 intake airflow roadway to verify the simulation results and to evaluate the efficiency of this technology. The field test results are consistent with the simulation results, which validates our model. Moreover, using this new technology, the number of gas extraction boreholes in the heading face decreased by 50%. Conversely, the gas extraction-based concentration and flow increased 10- and 6-fold, respectively, which results in a 65% decrease in gas extraction time and a 100% increase in monthly excavation length of the coal mine roadway. These results indicate that this new technology is a promising method to achieve efficient gas extraction and rapid excavation in the heading face of soft and low-permeability coal seams. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Shallow coal resources are increasingly depleted, die mining has entered the deep stage. Due to "High stress, high gas, strong adsorption and low permeability" of coal seam, the gas drainage has become more difficult and the probability of coal and gas outburst accident increases. Based on the flow solid coupling theory of coal seam gas, the coupling model about stress and gas seepage of coal seam was set up by solid module and Darcy module in Comsol Multiphysics. The gas extraction effects were researched after applying hydraulic technology to increase penneability. The results showed that the effective influence radius increases with the expanded borehole radius and drainage time, decreases with initial gas pressure. The relationship between the effective influence radius and various factors presents in the form: y = a + b/(1+(x/x0)p). The effective influence radius with multiple boreholes is obviously larger than that of the single hole. According to the actual coal seam and gas geological conditions, appropriate layout way was selected to achieve the best effect. The field application results are consistent with the simulation results. It is found that the horizontal stress plays a very important role in coal seam drainage effect Tire stress distribution change around the drilling hole will lead to the changes in porosity of coal seam, fiirther resulting in permeability evolution and finally gas pressure distribution varies. [ABSTRACT FROM AUTHOR]

Storage capacity of hydropower reservoirs is lost due to sediment deposition. The problem is severe in projects located on rivers with high sediment concentration during the flood season. Removing the sediment deposition hydraulically by drawdown flushing is one of the most effective methods for restoring the storage capacity. Effectiveness of the flushing depends on various factors, as most of them are site specific. Physical/mathematical models can be effectively used to simulate the flushing operation, and based on the results of the simulation, the layout design and operation schedule of such projects can be modified for better sediment management. This paper presents the drawdown flushing studies of the reservoir of a Himalayan River Hydroelectric Project called Kotlibhel in Uttarakhand, India. For the hydraulic model studies, a 1:100 scale geometrically similar model was constructed. Simulation studies in the model indicated that drawdown flushing for duration of 12 h with a discharge of 500 m/s or more is effective in removing the annual sediment deposition in the reservoir. The model studies show that the sedimentation problem of the reservoir can be effectively managed through hydraulic flushing. [ABSTRACT FROM AUTHOR]

Control of harmful algae in the coves or bays of larger water bodies could be accomplished by hydraulic flushing with algae-free water. This suggestion is examined with a mathematical model of a harmful algal population, parameterized to represent the toxic haptophyte Prymnesium parvum , and its limiting nutrient. A small cove with a hydraulic storage zone and longitudinal advection and dispersion is coupled to a larger lake where ongoing or transient blooms serve as a source for the algal population. This population is transported upstream by dispersion and flushed downstream by advection. Morphometry and hydraulics represent a lake in Texas where blooms of P. parvum have been problematic. When dispersion and hydraulic storage are low to moderate, available pumping technology is predicted to be capable of suppressing the algal population within a variable portion of the cove, under both steady state and transient conditions. This suppression occurs when temperature-dependent algal growth is low. At temperatures high enough to support more rapid growth, flow augmentation carries a risk of stimulating a bloom under some hydraulic conditions. The model presented here complements similar models without population sources, and contributes to theoretical understanding of population persistence in reservoirs and other flowing-water habitats. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

By analyzing the stress characteristics around boreholes，the visco-elastic plastic model of coal around hydraulic flushing considering plastic softening and dilatancy was established，the pressure-relief and permeability improvement effect of hydraulic flushing and aperture variation were analyzed，thus the anti-blocking technology and the measures for gas drainage improvement were formulated. The results show that：① Hydraulic punching measures can greatly improve the coal permeability around boreholes，the more punching coal amount，the greater relief range of hydraulic flushing，the higher the permeability of coal is increased；② Shrinkage phenomenon of borehole occurs over time because of rheological properties，the greater the stress，the lower the coal strength，the more intense the creep deformation of coal，once drainage channels are blocked，gas extraction effect will be greatly reduced；③ Anti-blocking technology by installing casting pipe reserves a drainage channel，thus high concentrations gas can be extracted for a long time，the effect of gas drainage increase by 2.7 times；④ By gas injection combined with hydraulic flushing technique，the gas drainage amount of single hole increases by 8.1 times，which can effectively improve gas drainage effect. [ABSTRACT FROM AUTHOR]

Run-of-the-river hydropower projects are developed based on the concept of sustaining reservoir life by sediment management. Sediment management is achieved by sluicing or drawdown flushing through low-level spillways. Simulations with numerical and physical models are essential for optimizing the design and operation of such projects. In this paper, numerical and physical model simulations carried out for sediment management of a run-of-the-river hydropower project are presented. For Devsari Hydroelectric Project, Uttarakhand, India, a physical model was constructed to a geometrically similar scale of 1: 60. Experiments were carried out for sediment management for various scenarios. One-dimensional model Hydrologic Engineering Center's –River Analysis System was used to simulate the longitudinal sedimentation and velocity profiles in the physical model. The numerical model was further applied to the prototype for predicting the long-term sediment deposition along the reservoir stretch. Results of the simulation indicated deltaic sediment deposition in the upstream reaches of the main Pinder and Kailganga rivers. The delta advanced towards downstream for lower reservoir operation levels. The flow velocities in the entire reservoir stretch were observed to be very low, thus confirming the design concept of reservoir functioning as a desilting basin. Experiments were carried out on the physical model for simulating sediment removal by drawdown flushing. It was observed that reservoir capacity can be restored by annual flushing during peak flows. Flushing with discharge of 300 m3/s for 12 h duration can remove about 0.0086 Mm3 of sediment and hence may be adopted for reservoir operation. [ABSTRACT FROM AUTHOR]

Current coal seams in China are characterized by great depth, low permeability, and strong adsorption features, and thus, the extraction of methane is relatively difficult and gas disaster remains serious. To overcome this limitation, the hydraulic flushing and hydraulic slotting are adopted to improve the permeability of coal seams. A 2D model of gas seepage was established by using the solid mechanics and darcy module in Comsol Multiphysics, version 4.3b. The factors influencing pressure relief, such as the radius of borehole after hydraulic flushing, the initial gas pressure, and the permeability of coal seam, were studied. The coupling effects of these three factors on the effective influence radius were studied through the response surface methodology, and a quadratic polynomial equation between effective influence radius and three factors was derived. The results showed that Gas pressure distribution (e.g. gas full emission region, gas pressure transition region and original gas region) near the borehole, corresponded well with stress distribution (stress relief zone, stress concentrating range and original stress zone). The plastic zone formed around the borehole leaded to stress reduction, and the increasing porosity and permeability resulted in pressure decline. The effective influence radius increased with the borehole radius and the initial permeability, but decreased with original gas pressure. Besides, it was found that an increase in one factor would restrict the role of other two factors on the effective influence radius. This study is helpful to choose the most suitable parameters to achieve high extraction efficiency and lower gas content/pressure. [ABSTRACT FROM AUTHOR]

Fouling is an inevitable phenomenon with most of the water treatment systems. Similar to RO, NF and other membrane-based systems, fouling also seriously affects the performance of low-cost forward-osmosis (FO) systems and disturbs the overall efficiency of these systems, and various cleaning practices have been evaluated to restore their designed performances. This study evaluates the performance of various physical and chemical cleaning techniques for hollow fibre forward-osmosis (HFFO) membrane. HFFO membrane was subjected to various fouling conditions using different brackish groundwater qualities and model organic foulants such as alginate, humic acid and bovine serum albumin. Results indicated that physical cleaning affects differently the flux restoration according to the type of foulants (i.e. inorganic or organic) and the crossflow rates play an important role in membrane cleaning in both membrane orientation. The higher cross flow Re values at any particular area seem important for the cleaning. With hydraulic flushing, the flux performances of HFFO were recovered fully when operated in AL-FS orientation, as high shear force helps to detach all scaling layers from the surface; however, the lower shear force did not fully restore the flux for the FS membrane in AL-DS orientation. Chemical cleaning was planned for the fouled HFFO membrane, and HCl and NaOH were used in various combination sequences. It was found that HCl did not clean the membrane used for AL-DS orientation for combined fouling. HCl cleaning (at pH 2) was found to be more effective for removing inorganic scale, whereas NaOH cleaning (at pH 11) for a similar period successfully restored the flux for all the membranes used for FS with inorganic and/or organic foulants. ethylenediamine tetra acetic acid (EDTA) was also evaluated for its cleaning performances and it was found that compared to NaOH, EDTA cleaning (1 mM concentration at pH 11) showed superior results in terms of membrane cleaning, as it helped to successfully restore the membrane flux in a very short time. [ABSTRACT FROM PUBLISHER]

The coal seam condition of test coal mines is low permeability, large dip angle, soft coal, and low gas drainage rate. This text researches hydraulic flushing as pressure relief and increased permeability measures. It adopts theory analysis, numerical simulation, and field testing to research key technology for hydraulic flushing. It combines previous studies of ?three-steps drainage method?, propose to gas comprehensive treatment measures. First, it studies coal breaking mechanisms of high-pressure water jets and confirms the water pressure of hydraulic flushing. Next, it adopts numerical simulation and field testing to study the scope of influence. Finally, it studies the gas treatment effect of gas comprehensive measures after the measures have been carried out. Studies show that the result of influence scope between numerical simulation and field tests are close. The final influence scope confirms at 4.5m. Adopting the inspection of the weight of washed coal, residual gas pressure, residual gas content verified the effectiveness of measures. These measures achieve the aim that gas drainage rate increases, quantity measures are reduced, engineering time is reduced, and safety and quickly eliminate the outburst danger of working face, The study guarantees safety production of similar coal seam condition as the test coal mine. [ABSTRACT FROM AUTHOR]

Composite coal seam is a kind of special coal seam that is formed after complex geological structure action, including a tectonic coal sublayer. Gas can't be drained easily from this coal seam, which cause coal and gas outburst accidents (CGOA) occur frequently. A new hydraulic flushing technology was proposed in this paper to improve gas drainage. Accordingly, a new set of mechanical equipment, technology process, roadway layout system and gas extraction monitoring system are provided by drawing lessons from the Guhanshan coal mine. The stress variation and damage failure were investigated by numerical simulation on the basis of flushed-out coal and borehole geometry. The gas drainage effect, coal seam permeability and outburst risk-sensitive indexes of the special coal seam were obtained by field measurements. According to the results, hydraulic flushing can enlarge the stress unloading and plastic damaged zone around boreholes dramatically, and the coal seam permeability can be increased largely. • A new technology was proposed to enhance gas drainage in the special low-permeability composite coal seam with a tectonic coal sublayer. • The stress damage and permeability increase mechanism of hydraulic flushing were revealed by theoretical analysis and numerical modeling. • Abundant field experiments were carried to investigate and verify the gas drainage effect in the coal seam after hydraulic flushing. [ABSTRACT FROM AUTHOR]

Abstract: Micellar-enhanced ultrafiltration (MEUF) is a promising technology developed for treating the wastewater containing metal ions or organic pollutants. One of the greatest problems in MEUF is membrane fouling which is mainly caused by concentration polarization, gel layer or cake formation caused by the deposition of surfactant micelles on the membrane surface and surfactant adsorption in the membrane interior. In this study, surfactant sodium dodecyl sulfate (SDS), which was used in membrane separation as colloidal particles, caused the flux decline. The transmembrane pressure (TMP) and feed concentration of SDS had significant influences on the flux. This paper presented that the lower TMP had a smaller effect on membrane fouling, and when SDS concentration was around the critical micelle concentration (CMC), lower permeate flux and higher additional membrane fouling resistance were obtained. The effects of three kinds of hydraulic flushing methods on membrane permeate flux were investigated, including periodic forward flushing, periodic backwashing and forward flushing followed by backwashing. It was found that when the periodic combined flushing interval was 10min, forward flushing and backwashing phase times were 150s and 90s, respectively, and that combined flushing was more conductive to permeate flux recovery in this study. [Copyright &y& Elsevier]

• Hydraulic flushing integrated with gas injection displacement was proposed. • Gas injection displacement can weaken the adverse effects of concentrated stress. • A coupled gas flow model was established to optimize the engineering parameters. • The gas drainage and outburst elimination efficiency are significantly improved. With a continuous increase in mining depth, high gassy coal seams with low permeability increasingly appear. Although hydraulic flushing (HF) is an efficient technology applied widely for enhanced coalbed methane (ECBM) in low permeability coal seams (LPCS), the methods utilized to eliminate the adverse effects of stress concentration (SC) zones generated by HF on gas drainage have not been proposed. Therefore, a synergistic ECBM extraction technology based on HF integrating with gas injection displacement (GD) has been put forward in this paper. The primary role of HF is to provide ample migration space for gases so that the gas injection resistance can be reduced in the following GD process. Accordingly, the GD is implemented to eliminate the negative effect of the SC zones on gas drainage by increasing the pressure gradient, and the permeability enhancement and pressure holding function of nitrogen-rich gas also take effect. Additionally, a coupled gas flow model was developed and validated to describe the synergistic process. The optimal engineering parameters that can provide theoretical reference for engineering application were determined systematically according to the modeling results. The on-site boreholes should be all flushed, and the actual drilling diameter should still be determined according to the geological and technical conditions in the field. Furthermore, low pressure (LP) is the best choice before the effects of HP being further investigated on fracturing coal and inducing outbursts. Meanwhile, the analysis results of the field experiment in the Chensilou coal mine indicate that the proposed technology can effectively promote the adsorbed methane remaining in the SC zones to desorb adequately and then migrate to the gas drainage boreholes. Especially for LPCS, this synergistic ECBM extraction technology integrating HF with GD possesses a great application prospect. [ABSTRACT FROM AUTHOR]

To study the variation of the pressure relief scope and the stress around hydraulic flushing borehole, the theory of coalrock damage was utilized to distinguish the interaction area of water-jet and coal-rock into the coal-rock crushing area, the water-jet pressure stagnation area, the transition area and the original stress recovery area of coal-rock. Based on the actual occurrence conditions of the coal seam, the pressure variation and relief scope around the hydraulic flushing borehole were analyzed and simulated by RFPA2D-Flow software. The results showed that a relief area with the radius of 50 ~ 6.0 m around the borehole formed due to the hydraulic flushing with the pressure relief of 0.038 ~ 6.545 MPa, and the maximum principal stress is 15.85 MPa with a distance of 6.8 m from the inspected hole where stress concentration appeared. After hydraulic flushing test, the diameter (441.8 ~ 1171.6 mm) of the hole which can be an expression of coal crushing area size, was calculated based on the examination of the coal amount through the trial process, and it can be drawn that the pressure relief area must be larger than that of the coal-rock crushing area. Meanwhile, the measured pressures relief range(5.96 ~ 6.62 m) is basically consistent with the numerical simulation result (5.0 ~ 6.0 m) which verified the accuracy of the simulation analysis, according to the distance from the inspection drilling to the hydraulic flushing borehole and the decreased degree of the gas content in the inspection hole by the way of Gas Content. [ABSTRACT FROM AUTHOR]