Influence Of Process Conditions On Reduction Reaction System Of Pidgeon Process And The Research On Mechanism

At present the main method of smelting magnesium is Pidgeon process in China. Because of the unique advantages, Pidgeon process is particularly suitable for the areas(Shaanxi, Shanxi, Xinjiang etc.) in our country where the coal resources are rich, so Pidgeon process gets great development in these areas. But the Pidgeon process also has many problems, such as low reduction efficiency, long reduction cycle, high energy consumption, serious environmental pollution etc. The state is restricting the development of Pidgeon process. So improving the existing Pidgeon process or to seek new thermal reduction method has become very urgent. Based on the silicon thermal method,it is put forward to add additives into the raw materials of Pidgeon process to improve the existing Pidgeon process and optimize the reduction reaction system of Pidgeon process, aiming at improving the reduction efficiency, shortening the reduction period, and saving energy.The thermodynamic and dynamic principle of silicothermic reduction process were studied. Through calculation, it showed that the vacuum conditions and slagging reaction could greatly reduce the critical temperature of reduction reaction. The functional mechanism of calcium fluoride was studied in the reaction system. The factors affecting the reduction efficiency of magnesium which included reduction temperature, reduction time, the pressure of briquettes, the amout of Ca F2 and the adding silicon ratio were analyzed in the actual production. After the reaction briquettes are added 5%(mass fraction) Ca C2, the vacuum reduction experiments were processed in laboratory. The influence of adding Ca C2 into the reduction system was discussed. Considering that if Si O2 participated in the reduction process of Ca C2-Mg O system,and reacted with Ca O generating stable chemical compound(2Ca O·Si O2 or 3Ca O·Si O2), or considering that the Ca C2-2Mg O·Si O2 reaction system was formed,the critical reduction reaction temperature of the Ca C2-Mg O system would be reduced greatly. The calcium carbide as a reducing agent was compared with ferrosilicon. By adding the 5%(mass fraction) powder based on graphite into raw materials of Pidgeon process and analyzed the thermodynamics conditions of C-Mg O reaction system. Further adding different ingredients of composite additives including the powder based on graphite and calcium carbide into the reaction briquettes of Pidgeon process was put forward based on the silicon thermal method and the industry experiments were simulated in laboratory. The experiments showed that optimal ingredient(mass fraction: 6% the powder based on graphite, 2% calcium carbide) of the composite additive could improve the reduction rate 26% in 2 hours. The influence rule was proposed based on the experimental result, and the "?-shaped" reduction efficiency curve was discovered. The character of curve was analyzed, and the influence of composite additives on thermodynamic and dynamic mechanism of Pidgeon reduction process was discussed. Considering that the point of M was due to the reduction of Ca C2, while the emergence of Q point was due to the powder based on graphite combustion exothermic effect dominates in the system. The thermodynamics conditions of the reaction system incuding C-Si O2 system, C-Ca O system, and CO-Mg O system were analyzed. In the end, by not only adding the composite additive but also changing process conditions which included reduction time, reduction temperature, and the pressure of briquettes, the influence on the reduction efficiency of magnesium was researched.