Requirements for Coal Quality of Coke-making
Coking is a method of heating coal in an oxygen-deficient environment, which changes its chemical and physical properties so that it can be used for various industrial applications, including steel making. The quality of coal used in coking process is very important to the coking performance. Quality requirements for coke-making coal include proximate analysis, ash analysis and sulfur analysis, as well as the properties obtained from the test methods of CSR, CRI and the corresponding hardness properties.
Proximate analysis. First of all, the proximate analysis of coke-making coal should be done. The items mainly tested by the proximate analysis are moisture, volatile matter, fixed carbon and ash. According to the different use of coking coal, a variety of standard values corresponding to the proximate analysis are set. The volatile matter content should generally be (7.0~15.0) %, and the ash content should generally be(2.5~13.0)%, the fixed carbon should mainly stay in the range of (35. 0~90.0)%, while the moisture content should be controlled below (8.0)%.
Ash analysis. The ash analysis of coke-making coal should include factors such as stability, fluxing capacity and melting, thermal expansion, and etc. The levels of ash analysis are related to the quality requirements of the produced cokes, which affect the size and structure of the cokes. Generally the ash analysis of coking coal should include MgO, CaO, Al2O3, SiO2, Fe2O3, S, and etc. The MgO content of coke-making coal should be (1.0~3.0) %, the CaO content should be (1.0~3.0)%, and the Al2O3 content should be (2.0~9.0)%.
Sulfur analysis. The variation of sulfur content in coke-making coal is an important indi-cator to evaluate the environmental performance of the produced cokes. Generally speaking, the sulfur content of the coke-making coal should be (0.7~3.5)%. If the sulfur content of the coke-making coal is too high, the amount of sulfur dioxide emitted during the burning of cokes should be reduced accordingly.
CSR and CRI test method. CSR (Coking Strength of Raw Coal) and CRI (Coke Reactivity Index) are important evaluation indexes for predicting the coking performance of coking coal. The former mainly tests the combinations between macromolecular organic structures in coal and determines the structure of cokes. The latter mainly measures the electrical resistivity, pressure-intensification index and thermal decomposition properties of cokes produced from coking coal after calcination. Generally speaking, the coking strength of coke-making coal should be in the range of (60~75) CSR, and the coke reactivity index should be in the range of (60~78). Similarly, the hardness test should also be done to evaluate the consistency of the cokes produced by the coking coal.
In conclusion, the quality of coal used in coking process directly affects the coking performance of cokes. Therefore, the quality requirements for coke-making coal should be strictly observed, so as to ensure the production of safe and high quality cokes.
