Process of Cold-solid Briquetting
Cold-solidified briquetting is the main method for steelmaking sludge treatment in metallurgical enterprises at present.
The process is as follows:
1. First, the filter-pressed converter dust and mud with about 30%-40% water content is added with 20-30% rolled iron scale, and then dried in a rotary drum dryer, and the moisture content of dried materials is generally below 5%.
2. The second step is to filter out large impurities, especially iron blocks, from the dried materials with a screen, and then enter a mixer for fully mixing, 8% ~ 10% binder will be added at this stage.
3. The third step is to directly convey the mixed material into a high-pressure briquette machine for cold solidification into briquettes.
4. Finally, the molded cold-solid briquettes pass through a fixed screen, the materials under the screen return to a high-pressure briquette machine, the materials on the screen enter a flap dryer for dehydration and drying, and the dried finished briquettes, whose moisture content is generally below 3%, are transported to the finished product stockyard for later use.
Production process:
1) All kinds of materials are mixed with forklifts, and then transferred to the raw material warehouse.
2) The materials are conveyed to the rotary drum dryer through the belt for drying, and the dried materials are conveyed to the belt.
3) Quicklime is also quantitatively transported to a belt by a dry powder feeder after artificial digestion, and finally conveyed to a buffer silo by the belt.
4) The material is quantitatively sent to the feeding belt through the metering belt at the lower part of the silo, and the feeding belt enters the mixing section.
5) The binder can be purchased directly or prepared from the reactor site. Starch is used, and this organic formula has no damage to the converter lining.
6) The binder is also quantitatively added into the mixer, the material and the binder are fully mixed at this section and then enter the silo. The silo is uniformly and quantitatively added into the briquette machine.
7) A fixed screen is arranged at the discharging place of the briquette machine, the materials on the screen enter the flap dryer for drying, the dried materials will be conveyed to the finished product storage, while the materials under the screen will be returned and conveyed to the feeding belt, and then they will be re-formed by the briquetting machine.
8) The slaked lime in the technological process is mainly used to reduce the amount of binder, to reduce the cost of the consumption. However, more slaked lime is easy to be pulverized due to damp when piled up for too long, and the quality of steel will be affected because of too much water content in pellets when piled up for a short period. Excessive calcium ions will also cause pressure on sewage treatment in the plant. Therefore, slaked lime can not be added if the production cost is not strictly controlled. Generally speaking, steel mills require that the strength of finished briquettes should not be less than 800N to meet the needs of steelmaking. However, it should be considered that the pellets will be damaged during transportation, resulting in more small particles and ash in briquettes, which is not conducive to steelmaking environment. Therefore, the strength of finished pellets should be ensured to be above 1000N as much as possible. The finished pellets just out of the flap dryer can be stacked for 48-72 hours, which can not only reduce the moisture, but also naturally increase the strength of the finished products.
If the flap dryer is not used in the steelmaking sludge treatment process, and the moisture content of the finished briquette is above 10%, it is better to stack it for 7 days or even longer before using it. Cold-solidified pellets have good water and weathering resistance when treated with steelmaking sludge, but do not weathering them when placed in air for a long time.
