Green coal mining technique integrating mining-dressing-gas draining-backfilling-mining

Aiming to address the following major engineering issues faced by the Pingdingshan No. 12 mine:(1) difficulty in implementing auxiliary lifting because of its depth(i.e., beyond 1000 m);(2) highly gassy main coal seam with low permeability;(3) unstable overlying coal seam without suitable conditions for implementing conventional mining techniques for protective coal seam; and(4) predominant reliance on ‘‘under three" coal resources to ensure production output. This study proposes an integrated, closed-cycle mining-dressing-gas draining-backfilling-mining(MDGBM) technique. The proposed approach involves the mining of protective coal seam, underground dressing of coal and gangue(UDCG), pressure relief and gas drainage before extraction, and backfilling and mining of the protected coal seam. A system for draining gas and mining the protective seam in the rock stratum is designed and implemented based on the geological conditions. This system helps in realizing pressure relief and gas drainage from the protective seam before extraction. Accordingly, another system, which is connected to the existing production system, is established for the UDCG based on the dense medium-shallow trough process. The mixed mining workface is designed to accommodate both solid backfill and conventional fully mechanized coal mining, thereby facilitating coal mining, USCG, and backfilling. The results show that: The mixed mining workface length for the Ji15-31010 protected seam was 220 m with coal production capacity 1.2 million tons per year, while the backfill capacity of gangue was 0.5 million tons per year. The gas pressure decreased from 1.78 to 0.35 MPa, and the total amount of safely mined coal was 1.34 million tons. The process of simultaneously exploiting coal and draining gas was found to be safe, efficient, and green.This process also yielded significant economic benefits.

Minimum secure speed of fully mechanized coal face based on critical temperature of coal spontaneous combustion

The critical temperature theory of spontaneous combustion of coal and the numerical simulation method are used to explore the minimum secure speed of fully mechanized coal face to prevent the spontaneous combustion in goaf. Combined with the actual situation of workface 31005 in a coal mine, the highest temperatures in goal at different advancing speeds were obtained by the numerical simulation of spontaneous combustion in goal, and then a power function equation between the highest temperature and the advancing speed was achieved by regression analysis. The advancing speed corresponding to the critical temperature value was taken as the minimum safe speed of workface based on the equation. Finally, the accuracy and reliability of the speed were verified by the actual advancing process of workface 31005. The results of this research show that the new judgment method of the minimum safety speed has a higher value to be applied in the field.

Dimensionless model to determine spontaneous combustion danger zone in the longwall gob

According to spontaneous combustion propensity,the longwall gob is divided into three zones,including heat dissipation zone,self-heating zone and the choking zone.Only in the self-heating zone can temperature of coal rise due to oxidation.Studying the distribution of the "Three Zones" in gob is important for predicting and preventing spontaneous combustion in coalmine.In normal mining operations,temperature of coal is roughly constant.The process of mass transfer in the gob is considered to be steady.Based on mass conservation,gas species conservation,darcy's law,Ficks law of diffusion and coal oxidation 1-grade reaction rule,governing equation for air leakage intensity and species concentration are deduced.With critical value of coal spontaneous combustion and the size of longwall workface as basic dimension,a dimensionless steady coupled model of air flow diffusion and chemical reaction in loose coal of Fully Mechanized Top-Coal Caving Mining Workface(FMTCCMW) is setup.By solving the model numerically,regulation of three zones' distribution and spontaneous combustion in the gob can be obtained.The results can be easily popularized to prediction of spontaneous combustion in other coalmines' longwall gob.