Chemical compositions and technological properties of low-rank coals in the south Shenfu mining area: Characteristics, relationship and practice

Coal grading utilization is an essential way to fit its high-efficiency, clean and green development trends. Understanding the basic chemical composition and key technological properties of coal is the basis for achieving grading and qualitative utilization of coal resources. The South Shenfu mining area in Shaanxi Province is rich in coal reserves and it is an important low-rank coal production base in West China. However, it has not been able to achieve the qualitative utilization of coal practically completely for a long time, which restricts the full play of the value of coal resources and the further improvement of coal economic and social benefits. Based on this background, the low-rank coal samples were collected from the South Shenfu mining area to carry out coal chemical composition and technological property tests. The chemical composition tests include industrial components, major elements, total sulfur and form sulfur, harmful element P and coal ash composition. Technological property tests include calorific value, low-temperature carbonization, thermal stability and coal ash melting temperature. Quantitative analysis method was used to reveal the chemical compositions and technological properties of coal and their internal relationships. A mathematical model for predicting technological properties based on chemical compositions is constructed to provide a foundation for the grading and qualitative utilization of coal. The results show that:1) The low-rank coal resources in the study area are characterized by ultra-low ash, ultra-low sulfur, ultra-low phosphorus, high-very high calorific value, oil-rich, high thermal stability, and weak-non-adhesion characteristics, presenting a significant advantages in grading and qualitative utilization, especially the widely distributed oil-rich coal should be highly valued; 2) There is a close genetic relationship between the technological properties and chemical compositions of coal. The calorific value is positively correlated with the fixed carbon content, and the low-temperature carbonization tar yield is positively correlated with the volatile yield and hydrogen content. The moisture content determines the total moisture yield of low-temperature carbonization, and under specific coal type conditions, ash yield is a key factor controlling many technological properties of coal, including calorific value, cohesiveness, tar yield, etc., all presenting negative correlations; 3) Based on stepwise regression analysis and saliency test, a series of mathematical models for predicting the key technological properties of coal based on chemical compositions were built. Taking Zhangjiamao Mine as an example, the model was used to predict the tar yield of low-temperature carbonization and the distribution of oil-rich coal. The prediction results were consistent with the actual situation, verifying the reliability of the model. The mathematical models permit the further investigation on the coal technological properties and oil-rich coal distribution based on the geological data obtained during the previous coal exploration period. The research results have enriched the basic understanding of the material compositions and chemical properties of low-rank coals in terretrial basin, and described their intrinsic relationship and quantitative models, which can provide a theoretical foundation for the scientific evaluation and optimal utilization of high-quality coal resources(oil-rich coal) in the south Shenfu mining area and other similar areas.