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1

Thermal transfer performance of downhole electric heaters for in-situ pyrolysis in tar-rich coal

Tang Ying, Xiao Li, Yang Fan, Wu Xiaodan, Su Zhan, Zhang Yue, Jiang Shixin, Yang Peng

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2025

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Vol. 73, nr 3

art. no. e153839

EN

The paper investigates the performance of a large-size helical baffle heater in an in-situ operation using a numerical simulation method. The study reveals that the fluid in the shell retains a spiral flow, and the output flow velocity is higher than in the surrounding area. However, the pitch design is big, resulting in a low-velocity flow zone on the backwind side. At 100 kW and 500 m3 /h, the fluid flow is turbulent. At 50 kW and 200 m3 /h, the fluid remains laminar. As the flow rate rises, the pressure of tar-rich coal formation grows dramatically. The wall temperature exhibits a spiral plunger at the inlet, but the bottom temperature is symmetrically distributed. Under low power and flow, Reynolds number change has a greater impact on the combination of Nusselt and Prandtl numbers. The wellbore experiences higher thermal loads during downhole heating, dramatically increasing the possibility of thermal damage. An increase in the heater shell length improves the total heat transfer performance. Conventional heaters often only heat the bottom formation. Therefore, while optimizing the construction, it is vital to ensure that the weight of the heater itself does not exceed the tensile strength of the cable and consider shifting down the perforation outlet or lowering the outlet.

2

Experimental study on triaxial compression mechanical properties of grouting reinforcement of broken surrounding rock

Yang Peng, Pang Dongdong

Archives of Mining Sciences

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2025

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Vol. 70, no. 2

273--291

EN

Grouting is a widely used method of reinforcement for stabilising fractured surrounding rock. To investigate the triaxial compression behaviour of surrounding rock after grouting reinforcement, laboratory-prepared grouted specimens were subjected to triaxial compression tests using an RMT-150B testing system. The analysis focused on the effects of confining stress, particle size, and water-to-cement ratio on the stress-strain behaviour. The internal friction angle and cohesion were determined based on the Mohr-Coulomb criterion. The variations in strain at peak stress and the elastic modulus were clarified, and the failure modes of the grouted specimens were examined. Additionally, Kendall’s correlation analysis was employed to evaluate the relationship between confining stress and other parameters. The results indicate that increasing confining stress significantly enhances the load-bearing capacity of the surrounding rock. The optimal rock particle gradation was observed when the particle size ranged between 5-10 mm, yielding the highest compressive capacity. Conversely, increasing the water-to-cement ratio reduced the strength of the specimens. Among the analysed factors, confining stress exhibited the strongest correlation with peak stress.

3

Coupling effect of hole enlargement and diffusion in the grouting process in a weak stratum based on analytical research

Zhao Zenghui, Meng Zhe, Li Longfei, Li Canlin, Yang Peng

Journal of Theoretical and Applied Mechanics

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2024

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Vol. 62 nr 3

637--649

EN

According to the tail grouting of a double shield TBM tunnel in a soft stratum, the spherical hole model with small and large diﬀusion radius were established respectively considering the slurry diﬀusion and slurry displacement eﬀect in the grouting compaction stage. An- alytical solutions of the spherical hole expansion stress and displacement ﬁeld under the hole expansion-diﬀusion coupling eﬀect are deduced. The interaction among plastic zone radius, reaming radius, initial radius of the spherical hole, and the seepage radius were analyzed. The results show that the larger the seepage pressure of grouting, the smaller the plastic radius. The larger the reaming radius is, the larger the plastic zone radius is. When the reaming radius reaches a certain value, the plastic radius tends to be stable, and the smaller the grouting seepage pressure, the earlier it tends to be stable. The above conclusions have important guiding signiﬁcance for optimizing grouting parameters in weak strata.

4

Study on upper and lower gas drainage and prevention and control technologies in deep high-gas mines

Pang Dongdong, Wang Xi, Yin Zhiqiang, Niu Xiangang, Yang Peng, Ni Zongyu

Archives of Mining Sciences

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2024

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Vol. 69, no. 4

633--654

EN

In response to the “three highs” problem in the mining of deep high-gas mines, the rapid increase in the coal seam permeability coefficient and gradual increase in coal and gas outburst problems have made gas control more difficult. This study considered the occurrence of remote outburst coal seams in the Zhujixi Mine as the research background and performed theoretical analysis, calculations, numerical simulations, and other technical methods to analyze the gas occurrence characteristics of the 11-2 coal seam and the feasibility of using this seam as a lower protective layer for mining. The pressure relief protection range for the overlying 13-1 coal seam, to the recovery of the 11-2 coal seam, was determined. A regional antioutburst technology was proposed for underground through-layer and parallel-layer drilling, focusing on pre-gas extraction for the protective layer. In addition, a pre-gas extraction regional anti-outburst technology combining the surface and underground mining of the protected layer is also proposed. Gas occurrence in the 11-2 coal seam is uneven and has poor regularity, presenting high gas areas. It is significantly affected by the geological structures and shale properties of the coal seam roof and floor. The 11-2 coal seam is a stress-dominated and gas-outburst coal seam. The Zhujixi Mine presents a joint underground extraction and regional outburst prevention mode; that is, the 11-2 coal seam with a lower outburst risk is selected as the protective layer for mining first, whereas the 13-1 coal seam is protected while the gas in the protected layer is extracted. The 11-2 coal is characterized by the gas control mode of “one side, three lanes+ground drillings” to achieve multi-purpose, joint treatment, and continuous mining of one lane. The excavation face exhibits comprehensive anti-outburst measures, such as through-layer drilling pre-extraction and a coal mining face over the layer drilling pre-extraction area. During the mining period, surface drilling and a top extraction roadway are used to extract 13-1 coal-depressurized gas. By adopting joint extraction technology in the upper and lower mining areas, the residual gas content and pressure were measured at the underground excavation and mining working face. The predicted indicators did not exceed the standard levels, and no dynamic phenomena occurred. As a result of the application of the anti-outburst technology in the joint extraction area of the Zhujixi Mine, the proportion of extraction in the upper and lower mining areas was 56.7%, and the proportion of extraction in the underground mining area was 43.3%. These factors are interdependent and indispensable. The maximum height of the caving zone after mining the 11-2 coal face was 11.6 m, whereas the height of the fracture zone was 34.4‒52.2 m. The 13‒1 protective-layer working face is arranged on the upper part of the fracture zone or lower part of the curved subsidence zone, which can effectively increase the permeability of the 13‒1 coal seam. Engineering practice has shown that the joint regional anti-outburst technology and engineering application in Zhujixi mine have achieved good results, forming a regional anti-outburst technology system for joint extraction of mines and providing a reference for the safety production of similar conditions in outburst mines.

5

The Behaviour of Low Arsenic Copper Anodes at High Current Density in Electrorefining

Zhang Xuyong, Chen Silei, Li Lu, Yang Peng

Archives of Metallurgy and Materials

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2023

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Vol. 68, iss. 4

1377--1382

EN

Arsenic is the only beneficial impurity for copper electrorefining through inhibiting anode passivation and the formation of floating slimes. The behaviour of copper anodes with different content of arsenic were studied at high current density (>280 A/m2). It showed that low arsenic anodes (As < 300 ppm) easily generated anode passivation, floating slimes and cathode nodules during the electrorefining proccess. The floating slimes, electrolyte, cathode and anode were observed and analyzed. As result, low arsenic anodes were more likely to be passivated due to their microstructure defects and irregular microstructure. Increasing electrolyte temperature and addition of glycerol were propitious to reduce low arsenic anodes’ passivation. The floating slimes occured when the concentration of As(III) in electrolyte decreased to 1 g/L, and they would be precipitated by polyacrylamide. All measures greatly improved the cathode quality at current density of 300 A/m2.