Let's talk about the role of coke in the domain process. We consider in detail the essence of this metallurgical production.
Nowadays, in the manufacture of cast iron and steel, a blast furnace process is used, in which the furnace is an important component.
Unit Specifics
Consider the features of the device, its purpose. The main processes of the blast furnace are associated with the melting of coke. It is a porous material that is sintered from a mass of carbon obtained by calcining coal without the presence of atmospheric oxygen.
A blast furnace is a powerful and high-performance unit where a significant amount of blast and charge is consumed.
Raw material loading
A modern blast furnace involves finding materials in it for 4-6 hours, gaseous substances - 3-12 seconds. If the gases are completely distributed over the cross section of the furnace, one can count on high melting indices, and pig iron is being produced. The blast furnace process involves accounting for the movement of gases through zones with lower charge resistance. Therefore, when it is loaded into the furnace, the coke and sinter are redistributed over the furnace cross section so that they differ in gas permeability. Otherwise, a larger percentage of gases will leave the furnace with a significant temperature, which will negatively affect the use of thermal energy, the blast furnace process will not be fully effective.
In those areas that have high resistance, the gas mixture will pass slightly heated, additional heat consumption will be required in the lower part of the furnace, as a result, the consumption of raw materials will increase significantly.
What other features are important to consider when downloading? The blast furnace process for producing pig iron is energy-intensive production. That is why a layer of less gas-permeable agglomerate is used at the furnace walls, in the center - a layer of coke is increased, due to which the gas flow to the center is redistributed. The materials are arranged evenly around the circumference.
The charge is loaded in separate portions - feeds. One portion consists of several skips, ore part (agglomerate), coke. The ratio of the starting ingredients is determined by specialists.
The blast furnace process allows the joint supply of raw materials, in which the skips of coke and sinter are collected on a large cone, and then it is loaded into the furnace.
Charge distribution adjustment
Management of the distribution of coke and agglomerate over the top section is carried out by the following methods:
- the arrangement of raw materials on a large cone changes;
- split and separate feeds are used;
- movable plates are installed near the top walls.
The domain process involves taking into account certain laws of making bulk materials:
- laying of raw materials falling from a large cone on a top with an elevation - a crest;
- fines accumulate near the ridge (at the place of incidence) of the charge, large pieces roll down to the foot of the ridge, therefore, in this zone the gas permeability of the mixture is greater;
- the crest is affected by the level of backfill on the top, as well as the distance with a large cone;
- the large cone is not completely lowered, so small pieces of coke fall on the periphery.
For the most part, material from feed skips that are the last to be loaded into a large cone enters the center of the furnace. If you change the boot order, then you can achieve a redistribution of materials along the cross section of the top.
To regulate the distribution process over the furnace volume of the used charge, two conical apparatuses are used. Recently, some blast furnaces have been equipped with movable plates at the top walls, allowing you to change the angle of inclination, move them horizontally.
The pieces of the charge that fall on the plates are reflected from them, which allows you to send raw materials to certain zones of the top.
Coneless furnace options
In a furnace that does not have a cone loading device, the loading of raw materials is carried out through two lock silos that are opened in turn. Raw materials are delivered to them by inclined belt conveyors, on which coke and agglomerate are located at clear intervals. One portion arrives from the belt in one hopper, then is discharged to the furnace top through a rotating inclined tray. During the unloading period, they complete about ten full revolutions around a fixed central axis.
Loading cycle
Under it is called the repeating number of batches of charge materials. The maximum portion is determined by the volume of the lock hopper of the filling mechanism. The number of servings in one cycle can be from 5 to 14. How to get the full value of the domain process products? In order to answer this question, we will take a closer look at the essence of the process. With an increased content of carbon dioxide in the mixture, low temperature contributes to the completeness of heat exchange and chemical processes in the blast furnace. In order for the apparatus to work economically and intensively, the quantitative content of carbon dioxide along the axis and on the periphery of the furnace should be lowered, and at a height of one or two meters from the walls - high.
Temperature control in new furnaces is carried out by introducing probes through openings in the casing. Mandatory for all processes is to control the level of backfill on the top.
Among the innovations is the use of non-contact level measurement methods based on the readings of microwave and infrared sensors.
Features of temperature distribution
In addition to the heat that is introduced by the heated blast, as the main source of heat for heating the gases and the mixture, the recovery and compensation of heat loss, you can compensate for the loss of heat that is released during the combustion of fuel in the upper part of the hearth. As gaseous products move upward from the hearth, the heat sinks to the charge cold materials, and heat exchange occurs. A similar process explains the decrease from 1400 to 200 degrees of temperature at the outlet of the furnace top.
Removal of excess moisture
Consider the basic physical and chemical processes in a blast furnace. In the charge, which is loaded into the blast furnace, there is hygroscopic moisture. For example, in coke, its content can be up to five percent. Moisture quickly evaporates at the top, therefore, additional heat is required to eliminate it.
Hydrated moisture appears when brown iron ore and kaolin are loaded into a blast furnace. To solve the problem in modern pig iron production, these ores are practically not used as raw materials.
Carbonate decomposition processes
Carbonic acid salts may enter the blast furnace. As they heat up, they decompose into calcium and carbon oxides, and the process is accompanied by the release of a sufficient amount of energy.
Recently, almost no ore is loaded into blast furnaces. What is the role of fluxes in a domain process? They increase its efficiency and reduce production costs. Thanks to the use of fluxed agglomerate, complete removal of limestone from the blast furnace charge, significant coke savings can be achieved. The process of decomposition of limestone during agglomeration is ensured by the combustion of low-grade fuel.
Iron recovery
Iron is introduced into the blast furnace in the form of oxides. The main objective of the process is the maximum recovery of iron from oxides by reduction. The essence of the process is to remove oxygen, carbon, carbon monoxide, and hydrogen are used for this. Reduction with carbon is called a direct process, and the reaction with gaseous substances is called an indirect interaction. What are their distinguishing features? In a direct reaction, carbon is consumed, as a result of which its amount is significantly reduced. The second type of reduction of iron from oxides requires an excess of hydrogen.
During the process, solid iron is formed. The degree of recovery in cast iron is 99.8%. Thus, only 0.2 -1% is converted to slag.
Smelting of manganese cast irons
In the process of smelting converted cast iron, manganese enters into a blast furnace in the form of agglomerate. In some quantities, manganese ores in the form of manganese silicates contribute to the production of manganese cast iron.
Recovery from manganese oxides occurs in steps. In order to fully carry out the process, high temperatures must be set in the hearth. The process of smelting pig iron is accompanied by the restoration of manganese only in the ratio of 55-65%. Currently, due to the deficiency of manganese ores and manganese, a small amount of manganese cast irons has been used in the technological chain. When switching to low-manganese cast irons, it is possible to save not only manganese itself, but also coke, since its consumption for direct metal reduction will be reduced.
Conclusion
The blast furnace process is one of the main methods of smelting cast iron and steel. Depending on what components are introduced into the initial charge, various types of the finished product are currently being prepared. Among the areas of application of the resulting cast iron and steel, we single out: mechanical engineering, chemical industry, medicine, instrument making.