1、Prerequisites for Blast Furnace Slag Injection
The catalytic effect of converter slag is suitable for coal with low volatile content. At present, the domestic coal for blast furnace injection in China is basically mixed coal, with a volatile content of about 15%. At the same time, the oxygen enrichment rate and air temperature of the blast furnace are higher than the previous ones. In recent years, there has been a substantial increase, so the combustion of injected coal is no longer a problem. Under these conditions, the use of catalysts has little effect. In fact, the benefits of injecting converter slag into the blast furnace are far from the benefits of injecting converter ash. In addition to catalytic combustion and improving the gas permeability of the blast furnace, the converter ash contains about 60% iron, which can effectively increase production and reduce coke.
2、Suitability of Converter Slag Injection Method
The pulverized coal catalyst must be mixed with the pulverized coal as much as possible, otherwise its catalytic effect will not be fully exerted. Therefore, it is required that the converter slag and coal powder are mixed to make powder to achieve the purpose of fully mixing.
The bulk density of converter slag is about three times that of pulverized coal. Most of the converter slag fine powder will "precipitate" at the bottom of the pulverized coal silo. Therefore, the mixed injection will cause the converter slag to be too concentrated and the catalytic effect will be greatly reduced.
At the same time, the calcium oxide, iron oxide and other substances in the converter slag mainly exist in the form of calcium ferrite. After being injected into the blast furnace, it will hinder the negative effect of free calcium oxide from catalyzing the combustion of pulverized coal. In other words, the effect is very small; at the same time, the decomposition of calcium ferrite needs to absorb a lot of heat. Under the current domestic raw fuel conditions, blast furnace injection of converter slag from the mechanism analysis is not feasible.
3、Phosphorus Content of Converter Slag
The converter slag has a high phosphorus content, and the blast furnace slag does not have the ability to dephosphorize. If the converter slag is injected into the blast furnace, most of the phosphorus brought in will return to the molten steel, except for a small amount of phosphorus that is removed with the blast furnace gas, which will increase the cost of molten steel dephosphorization.
4、Damage to Equipment
Before the blast furnace was shut down, the coke oven dust ash was injected, and the injection ratio was about 10%. This caused a large area of the injection pipe to wear. It once caused the coal to be stopped for emergency repairs. The converter slag hardness is higher, and the pipe wear will be more severe. The converter slag contains a small amount of particulate iron, which will cause damage to the mill when making powder. In addition, the converter slag has high hardness, poor grindability, and high processing costs.
At present, China's domestic blast furnace injection coal has good combustibility, blast furnace oxygen enrichment rate, and blast furnace air temperature. The catalytic effect of using converter slag is of little significance. At the same time, calcium ferrite will also greatly reduce the catalytic effect of free calcium oxide. At present, China's domestic blast furnace injection process equipment is difficult to achieve uniform mixing of converter slag and coal powder, and the catalytic combustion effect is weakened. The phosphorus content in the converter slag is too high. If blast furnace injection is performed, phosphorus will be cyclically enriched between the blast furnace and the converter, which will increase the cost of molten steel dephosphorization. The particulate iron in the converter slag causes damage to the coal injection pulverizer, and the injection pipe cannot support the injection of the converter slag.
Based on the above analysis, it is believed that blast furnace injection of converter slag can reduce its blast furnace coke ratio and achieve better economic benefits, which should be directly related to the raw fuel conditions. At present, it is of little significance to catalyze the improvement of the pulverized coal combustion rate by blast furnace slag injection in China. The converter slag injection is not economically cost-effective, and the equipment does not meet the injection requirements. The blast furnace slag injection technology is not suitable for promotion in China.
Post time: Oct-11-2021