Research On The Molding Of Semi-coke And Its Ash Fusion Characteristics

During the production process of semi-coke, plenty of powder less than 3mm is created. Due to their small particle size, the semi-coke powder can’t be used in subsequent production. It’s generally treated as low-level fuel or casually discarded, which not only cause a lot of energy wasted, but also cause serious environmental pollution. The dumped semi-coke powder insteaded of anthracite is used to make gasification briquette, to reduce the cost of producing semi-coke and improve the resource utilization rate. But the ash fusion temperature of semi-coke is about 1200℃. The gasifier with solid state slag-tapping technology is used by the small and medium-sized chemical fertilizer plants, which requires the ash softening temperature higher than 1250℃. Using semi-coke directly as coal gasification will cause slagging or poor ventilation in the gasifier. Therefore, the investigation on the molding technology of gasification birquette and the effective improvement of the melting point with semi-coke are important for the utilization of semi-coke in gasification, and enhance the application of semi-coke in chemical fertilizer field.The molding process with room temperature and high pressure was employed to investigate the falling shatter strength of briquette coal under different conditions. Besides, the falling shatter strength and thermal stability of briquette coal were tested according to the requierment of chemical fertilizer. The briquette coal was molded by different binders such as sodium humate, starch, MgO-MgCl2, clay 1 and clay 2. The results showed that, the optimum molding condition was as follows:size grading was 85% 0～1mm and 15% 1～3mm, molding pressure was 25MPa, water content was 18%, molding time was 1h. Sodium humate and starch are organic binder, their bond performance is good, the briquette coals with them have large falling shatter strength at room temperature, but their thermal stability are bad. The bond performance of starch is better than that of sodium humate, but its price is higher, so the amount of starch should not be added too much. MgO-MgCl2, clay 1 and clay 2 are inorganic binders, their thermal stability is good. MgO-MgCl2 or clay 2 has a poor bond performance, while clay 1 can’t bond at all.Additionally, the mechanism to improve the ash fusion point of semi-coke was discussed in this paper. The contents of FeaCl2 and CaO in semi-coke ash were high, which easily reacted with SiO2 to form a low temperature eutectic, resulting in the low ash fusion point of semi-coke. After adding 14% clay 1 and 15% clay 2, ash fusion point was raised to above 1250℃, meeting the requirements of gasifier. The contents of Al2O3 in clay 1 and clay 2 were high, which can increase the ash content of Al2O3. Al2O3 and SiO2 combined easily to generate mullite. Mullite is a refractory mineral, not only play a skeleton role in ash, but also delay the formation of low temperature eutectic, thus improving the softening temperature.According to the above results, clay 2 not only has certain degree of bond performance, but also can improve the thermal stability and ash fusion point of semi-coke. Mixing sodium humate, starch, clay 2 to develop composite binder, can mutually make up respective deficiency, make falling shatter strength, thermal stability and ash fusion point of semi-briquette meet the requirements of gasification briquette.