Investigation On The Nonlinearity Of Self-Heating Process Of Sulfide Ore Heap And Numerical Simulation

Spontaneous combustion of sulfide ores can induce a series of safety and environment problems, and cause great economic loss in mining enterprises. Nowadays, the mechanism of spontaneous combustion, evaluation of spontaneous combustion tendency, prevention and control technology were carefully analyzed by many scholars over the world. However, the problem was not solved ultimately because of the high complexity and strong nonlinearity of self-heating process of sulfide ore heap. With the increasing scarcity of resources in shallow layer, metal mines in China enter the stage of deep mining gradually. The mining depth increasing can lead the high ground temperature problem during mining process to become more serious than before. Ground temperature rising will increase the possibility of spontaneous combustion of sulfide ores.Therefore, research on nonlinearity of the oxidation and self-heating process, and numerical simulation of seepage field and temperature field is a trend in spontaneous combustion prevention research of sulfide ores, which has great theoretical significance and practical value.On the basis of reviewing the previous papers at home and abroad, research methods combining the theoretical analysis, laboratory simulation and numerical simulation were used to systematically analyze the dynamic self-heating process and its nonlinear characteristics, and the variation of seepage field and temperature field. The main works and achievements of the thesis are as follows:(1) The dynamic self-heating process of sulfide ore heap was simulated in the laboratory. The relationship between temperature and time, relationship between temperature discrete degree and time, relationship between average temperature rise rate and depth, and spatial difference of the ore heap responding to ambient temperature changes were revealed. The temperature field was two dimensional reconstructed based on measured temperature, and the range of the self-heating layer in the ore heap was proved. (2) The wavelet technology and approximate entropy method were used to analyze the self-heating process of sulfide ore heap. The concept that low frequency component of measured temperature series in the laboratory reflects the effects of gradient increased temperature to the ore heap and the complicated information of self-heating process is embedded in the high frequency component was proposed. The approximate entropy distribution of the ore heap was analyzed and the self-heating process of different regions was detected based on approximate entropy method, which confirms the existence of self-heating layer from dynamics view.(3) The self-heating process was analyzed based on chaotic dynamics methods. The results indicate that gradient increased temperature weakens chaotic degree of self-heating process to some extent. The sulfide content, oxygen concentration, temperature, oxidation rate and heat liberation intensity of the ore heap were determined as the5variables to describe the self-heating process. Correlation dimension and maximum Lyapunov exponent positively correlated with self-heating effect were proved.(4) The concept that measured temperature series of the ore heap can be divided into three parts:trend item, chaos item and stochastic item was proposed. The trend model for temperature prediction was established according to the temperature rising characteristics of sulfide ore heap from field test. The chaos prediction model for difference series of trend prediction was established by means of the adding-weight one-rank local-region method through optimization after chaotic identification. Then, the trend and chaos prediction model was established by the superposition of these two models and it was tested based on measured temperature data in the laboratory. The results indicate that the trend and chaos prediction model is very precise. As a result, it can be used to predict spontaneous combustion of sulfide ore heap during early stage.(5) Coupled with digital image processing technology and finite element method, the air seepage field in pores of the ore heap was analyzed. The distribution of air velocity and pressure in pores was proved at different granularity, which explains the reason for self-heating layer existing in the ore heap qualitatively. The effective thermal conductivity method applied to the numerical simulation for temperature field of the ore heap was developed. The variation of temperature field was analyzed and the starting time of spontaneous combustion was calculated. The change characteristics of spontaneous combustion region varying with time, and the variation of temperature field affected by sectional area, air velocity and the height of the ore heap were proved.