Study on gas transport characteristics of positive pressure beam tube system and its application to coal spontaneous combustion early warning

Abstract

Coal spontaneous combustion (CSC) beam tube monitoring and early warning is one of the most important ways of mine fire prevention and achieve cleaning production. Aiming at solving the problem of distortion of gas leakage data collected by the CSC beam tube monitoring and warning system, a one-dimensional steady flow rate model of compressible gas was constructed based on the theory of hydrodynamics; and the calculation formula of gas transport flow is deduced. Besides, through laboratory research, the law of gas transmission caused by pipeline diameter, output pressure and pipeline length is revealed, and the gas transmission lag time is calculated. The theoretically calculated time is compared with the experimental data to verify the accuracy of the model. Research shows that when the pipeline diameter and pipeline length are constant, the gas steady flow rate is proportional to the output pressure; when the output pressure and pipeline length are constant, the gas steady flow rate is proportional to the fourth power of the pipeline diameter. The theoretically calculated gas transmission time is in good agreement with the experimental transmission time. Furthermore, the developed positive pressure beam tube monitoring system was used for early warning. CO, C2H4 and C2H6 are determined as the index gases for predicting CSC, the CH4, O2, CO and C2H4 concentrations under manual sampling and beam tube sampling were compared. The system would not lead to distorted composition and concentration of downhole gas after running for a long time and can timely and accurately reflect the real downhole situation. Finally, the concentrations of CO, O2, CH4 and C2H4 after fire extinguishing during the sealing period and test error is analyzed. The research presented in this paper has important practical value for promoting the accuracy of on-site CSC beam tube monitoring.