Methods of Discharging Slag from Blast Furnaces
Introduction
A blast furnace is a smelting machine primarily used in ironmaking since the 18th century. This furnace is heated to extreme temperatures, enabling the melting and purification of iron ore and other metals. During the process of smelting, slag is formed, which is a glassy material that contains impurities and is left behind when the metal is removed. This slag must then be discharged from the furnace and safely stored for future disposal. There are several methods for this process, each with their own advantages and disadvantages. This paper will discuss the methods for discharging slag from blast furnaces.
Basics of Slag Discharge from Blast Furnaces
The burning of coke within a blast furnace produces a range of by-products, including a liquid slag that is formed from the combination of flux and impurities in the ore. This slag is composed of calcium silicates, calcium aluminate and magnesium silicate, and is collected at the bottom of the furnace.
In order to both improve the metallurgical efficiency of the furnace and manage the slag produced, it must be discharged. Slag discharge is typically performed every five to ten minutes, although the timing can vary depending on the type of ore being used and the desired result.
Types of Slag Discharge Methods
There are several methods for discharging slag from a blast furnace. This section will discuss the most commonly used methods, their advantages and disadvantages, and the conditions under which they are best used.
Bottom Opening Door
The bottom opening door is the simplest and most common method of discharging slag. This method involves the installation of a fire-resistant door at the base of the furnace that can be opened to allow the molten slag to escape.
Advantages
This method is quick and easy to operationalise as it does not require extensive modifications to the furnace or complex equipment. The process is also relatively safe as the door can be opened quickly and without endangering any workers.
Disadvantages
Unfortunately, this method is not suitable for all furnaces due to the intense heat. The success of this method is largely dependent on the ability of the door to withstand the furnace temperatures, which can be difficult and expensive to do. Furthermore, the door is subject to wear and tear over time, leading to a short shelf life of the process.
Side Opening Door
This method is used when a bottom opening door is not sufficient or feasible. This method involves the use of a door installed at the side of the furnace that is opened part way to allow the slag to escape.
Advantages
Using a side opening door allows for the discharge of slag in narrower furnaces or when the door cannot be installed at the bottom. This can be a more efficient way to manage the slag as it prevents the need for the extended discharge time of an open-bottomed furnace.
Disadvantages
As with a bottom opening door, a side opening door can be difficult and expensive to ensure it is heat resistant; a factor that can make this method unfeasible and limit its adoption.
Slag Lifting Crane
Another common method for slag discharge is using a slag lifting crane. This apparatus is comprised of a hoist attached to an overhead crane. The crane is situated above the furnace and lowered to the base when a slag ladle is needed.
Advantages
This method is highly safe and efficient for slag discharge as it eliminates the need for a bottom door or side opening door. Furthermore, it is also a much faster process compared to the bottom door, meaning that it can be operationalised with shorter durations between slag displacement.
Disadvantages
This method requires a significant amount of capital investment as it involves the installation of a crane, as well as other safety requirements and modifications. It is also limited to a certain type of furnace.
Conclusion
Slag discharge is an important part of the ironmaking process and there are several methods for achieving it, each with its own set of advantages and disadvantages. The most common methods include the use of a bottom opening door, side opening door or slag lifting crane. Careful consideration should be given to which method is most suitable given the operating environment, requirements and budget.
