Study on process optimization of nitrogen injection in low gas spontaneous combustion goaf
In order to analyse the impact of nitrogen injection port depth and flow rate on the range of the oxidation zone in the goaf,and to optimize the nitrogen injection fire prevention process in low gas spontaneous combustion goafs,a method combining numerical simulation with on-site measurement is adopted.Simulations are conducted for various scenarios:without nitrogen injection,with nitrogen injection at the designed flow rate and nitrogen injection port depths of 15 m,30 m,45 m,60 m,and 75 m;with nitrogen injection port at a depth of 45 m and nitrogen injection flow rates of 0.50,0.75,1.00,1.25,1.50,and 1.75 times the designed nitrogen injection flow rate.On-site measurements are taken with nitrogen injection port at a depth of 45 m and the designed flow rate.The results show that as the nitrogen injection port depth increases,the area of the oxidation zone gradually decreases.With nitrogen injection port depths of 15 m,30 m,45 m,60 m,and 75 m,the area of the oxidation zone is 100.8%,96.1%,90.5%,95.0%,and 79.1%of the area without nitrogen injection,respectively.As the nitrogen injection flow rate increases,the area of the oxidation zone also decreases,with flow rates at 0.50,0.75,1.00,1.25,1.50,and 1.75 times the designed flow rate,the area of the oxidation zone is 95.8%,93.4%,90.5%,87.1%,83.3%,and 79.2%of the area without nitrogen injection,respectively.An increase of 50%in nitrogen injection flow rate reduces the area of the oxidation zone by 7.9%,while a reduction of 50%increases it by 5.9%.The on-site measurement results are generally consistent with the numerical simulation results.For the 9202 working face,a reasonable nitrogen injection port depth is between 30 m and 60 m,with the optimal depth being 45 m,and a suitable nitrogen injection flow rate is between 1.00 and 1.50 times the designed flow rate,with the optimal flow rate being 1.25 times the designed flow rate.
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