Low-Temperature Consolidation Briquetts Research

  At present, the raw materials used in ironmaking blast furnaces mainly include sinter, pellets, natural lump ore, and a small amount of cold consolidated pellets. In general, Cold-consolidated pelletizing is mix iron-containing wastes (such as ironmaking dust, steelmaking converter sludge, blast furnace slag, iron scale, etc.) and concentrate powder produced in metallurgical process with special binders. After being pressed into balls by a rolling ball press and cured for 2-3 weeks in a natural environment at normal temperature and pressure, a chemical reaction occurs in the pellets, thus slowly consolidating to reach the required strength. Cold-consolidated pellets effectively solve the problem of comprehensive utilization of metallurgical iron-containing wastes such as ironmaking dust, steelmaking converter sludge, blast furnace slag, iron scale, etc. However, due to long solidification time, low curing efficiency, and large occupied area, it is very difficult to realize high-efficiency mass industrial production, thus restricting the development and industrial application of this technology. 

Experimental method 
1. Raw Material Formula 
   In the experiment, the rolling ball is used for forming, so the moisture content of raw materials is required to be higher. According to the experience of rolling balls, the moisture content of raw materials entering the ball pressing machine needs to be controlled at 5.5-6%, so as to obtain the better pelletizing effect. Because the liquid binder has a certain amount of moisture, it is necessary to dry the raw materials to reduce the moisture to less than 3%. 

2. Orthogonal test of key technologies 
   The key factors affecting the compression resistance of briquetts include: binder dosage, roller pressure, drying temperature and drying time, etc. 
   Under normal circumstances, the more binder is added, the better the pellet strength index will be. However, increasing the amount of binder will reduce the total iron content of pellets and reduce the economy. Therefore, the amount of binder added only needs to meet the compression index of briquetts above 2000N/P. 
    In a certain range, the greater the pressure of the ball press, the higher the strength of the briquetts. However, due to the limited pressure that the materials can bear, when the pressure exceeds a certain limit, the pellets will be separated from the middle to form hemispheres, and the liquid binder will be extruded from the inside of the pellets, thus affecting the strength of the briquetts. 
    Drying temperature and drying time also have a great influence on pellet strength. If the drying temperature is too high and the drying time is too long, the production cost will increase. If the temperature is too low, the time is too short, and the drying is not thorough, the residual moisture will greatly affect the strength of the briquette. After comparing the experimental results and analyzing the experimental data, it is found that the primary and secondary order of factors affecting the compression index of pellets is: binder addition > drying time > ball press pressure > drying temperature. 

3. Conclusion 
(1) Low-temperature consolidated briquetts use iron-containing metallurgical wastes such as ironmaking dust, steelmaking converter sludge, blast furnace slag, scale, and the like as raw materials, which can effectively solve the problem of comprehensive utilization of these materials. 
(2) Compared with the roasting temperature of traditional oxidized briquetts at about 1150 ℃, the drying temperature of low-temperature consolidated briquetts at 500 ℃ is relatively low, and the energy-saving effect is very obvious. 
(3) Compared with cold-consolidated pellets, the drying and curing of low-temperature consolidated briquetts only takes about 40 minutes and does not need long-term curing. From the production line, it can be directly transported to the finished product silo by belt, which is convenient for loading and transportation, saves the occupied area of the production line, can realize high-efficiency mass industrial production, and has a good application prospect.