What is coke? This is a strategically important product obtained by thermal oxygen-free decomposition. It is divided into many types. So, oil and pitch, peat and coal coke are isolated. But the main one is the latter. It is coal coke that acts as the basic component of blast furnace production.
Important product
What does the word “coke” mean? The morphology of this concept tells us that it is a combustible solid residue formed during the thermal oxygen-free heating of some organic substances, including coal (brown or stone), oil, and peat. The word itself has English roots. Coke means nothing but the product obtained by thermal decomposition.
Coke production in Russia is an important component of the industrial complex. According to statistics, this strategically important product is annually produced in the amount of 27 million tons. In such quantities, it is vital to foundry and the metallurgical industry. The largest Russian producer of coke is Severstal. This corporation owns its own production of this type of fuel and uses it for the needs of its own metallurgical plants. The largest blast furnaces owned by Severstal are located in Cherepovets. They produce the highest quality coke.
Charge
To maintain the burning of blast furnaces requires a large amount of coal coke. This product is a porous, but at the same time, solid sintered mass. It is obtained by removing volatiles from coal.
Coke chemical production is based on a hydrolysis process. In addition, dry distillation of coal is also possible. But in any case, the production of coke is associated with the heating of the initial product without the slightest air access. The purpose of hydrolysis is to separate carbon from all other substances that make up coal. What is the raw material for the production of coke? This is coal of various grades, including fat and coke, gas and lean. Such raw materials are called a charge. The basis of this product is the most expensive variety - coking coal. The charge is delivered to Russian metallurgical plants from the Kuzbass and Pechora deposits. Yakutia can be proud of the rich deposits of coking coal. Here they are mined on the territory of Neryungri, to which a railway line was specially drawn.
Due to its scale, the production of coke requires a large amount of raw materials. It is delivered to production shops in bulk wagons. Here, the charge is loaded into huge towers, in which special mechanisms, like pumps, pump incoming coal into coke columns. In winter, the charge arrives, as a rule, in a frozen state. And therefore, before unloading it is heated directly in the cars, driving them into special huge hangars.
Charge preparation
Coke production itself begins with the sorting of the charge. All coal that has come to the plant is divided by its property and composition into the necessary groups. After this, the mixture is crushed and mixed. What follows is its dosage. It is made on automatic scales. After such preparation, the mixture is enriched using dust removal, screening, washing, flotation and other methods. All this allows you to eliminate impurities from raw materials. After the charge is to be dried and fed to the final stage of crushing, which results in grains whose radius does not exceed 3 mm.
Raw materials prepared in this way are ready to begin production of blast furnace coke. It is reloaded into the mixing units, and then enters the storage bins located in the coal tower.
Coke oven batteries
The finished raw material, which is necessary in order to carry out the production of coke, is poured from the coal mine into the hopper of the loading car. After that, it is delivered to coke oven batteries. This is a system consisting of several chambers in which the process of production of the final product takes place.
The coke oven is a structure, the walls of which are lined with refractory bricks. Its length is 13-15 m, its width is 0.4-0.5 m, its height is 5-5.5 m. Such chamber dimensions allow the coke production process to be carried out at a fairly fast pace.
In the arches of such chambers there are three or four hatches with tightly closing covers. They are designed to load raw materials. The end walls of the chambers also have sealed metal doors. In the process of how coke is formed, production requires the removal of gaseous products arising from this. This is also provided in the design of the cameras. In their upper part, they have special risers along which volatile substances enter the gas collector.
At a time when coke production is in progress, process technology requires significant heating of the chambers. For this, special piers are constructed between them. They represent a whole system of heating channels through which hot gases move. As a result, the walls of the chambers are heated. At the bottom of the facilities for the production of coke, regenerators are located. They are necessary for heating the chambers with gases supplied through gas pipelines, as well as those that leave the air.
Charge heating
There is a rail track above the coke oven chambers. A loading car moves along it. From it, the mixture through the hatches enters the chamber. This is due to special mechanisms located on the car, which can unscrew and then close the sealed covers.
A special coke-ejector machine moves along a rail located along one of the sides of the chamber. It is she who comes to the side doors and opens them. Further, this device pushes the resulting coke. On the other hand, a quenching car approaches the camera. He takes the hot product and transports it to the area under the extinguishing tower, then unloading it on a ramp.
End product education
All production of metallurgical coke strictly adhere to technological processes that require to prevent air from entering the chamber. How does this happen? The coke production process begins immediately after the loading car delivers a measured dose of the charge into the chamber. At the same time, its hatches are closed and heating devices are turned on.
What happens at the initial stage when coke production is carried out? The process technology at its first stage provides for the release of gases and water from the finished raw materials. After this, the mixture melts and settles. A further increase in temperature leads to the expansion of this intermediate product. This is due to the further evolution of gases and vapors. Further, the charge gradually solidifies. What is the last stage of the process that results in coke? The production of this product is carried out during cracking and shrinkage of cake. As a result, the formation of the so-called coke cake occurs. All fractions having a vapor-gas form are discharged along risers to the gas collector.
The process of heating the charge in the chambers goes from its heated walls to the center. Due to the low thermal conductivity of raw materials in various places, coking stages are at different stages.
The whole process of coke formation lasts from 14 to 17 hours.Its duration depends on the combustion temperature of the charge, its composition and size of the chamber.
After completion of the coke production process, the heating devices turn off and the risers overlap. An ejector is suitable for the coke oven doors, with the help of which the resulting product is unloaded into a quencher. Thus, the furnace is released. After that, the ejector hangs the airtight doors and goes on rails to the next chamber. There also follows a loading car. He opens the hatches and loads a new dose of recycled charge.
Product delivery to the tower
The coke obtained in the chambers must be extinguished. After all, after its contact with air, spontaneous combustion occurs. In the extinguishing car, coke is delivered to the tower, where it is finally extinguished by water. The product then pours out of the car onto an inclined concrete surface called a ramp. Here, within twenty minutes, it cools down. After this, coke is conveyed by conveyors to sort.
Associated Products
Coke production is not possible without the release of volatile substances. They are a mixture of gases and vapors. Such components are collectively referred to as direct coke oven gas. After processing one ton of the mixture, the moisture content of which reaches 6%, 270 kg of direct coke oven gas are obtained. In volume terms, this figure is 330 cubic meters.
In direct coke oven gas obtained from one ton of the charge contains:
- about thirty kilograms of coal tar;
- 10 kg of crude benzene;
- 3 kg of ammonia;
- 5 kg of hydrogen sulfide;
- 80 kg of water;
- 140 kg of return gas.
Until recently, coke production was the only supplier offering benzene hydrocarbons. However, after the development of the oil refining sector, it became possible to obtain these products with less investment. This led to the fact that the share of coke production in the supply of benzene hydrocarbons fell to forty percent. This product is used as raw material in the process of organic synthesis. Its light fraction is processed with crude benzene.
Other types of by-products after their rectification and processing with chemical reagents, as well as after freezing and subsequent crystallization, make it possible to obtain about three hundred high-quality chemical compounds.
Oil use
This natural substance, like coal, is strategically important for our country. Their production of coke and petroleum products, which are:
- fuel;
- ceresins and paraffins;
- lubricating oils;
- bitumen;
- grease;
- raw materials intended for the main organic and petrochemical complex;
- other products.
Petroleum coke
This phrase is collective in nature. Petroleum coke is understood as deep processing products of “black gold”. The raw materials for its production are the components obtained in the primary processing of oil. These are tar and semi-tar, asphalt and extract.
The production of petroleum coke occurs in one of two ways:
- delayed coking, which is carried out in unheated reactors;
- in distillation plants using horizontal heated reactors.
The first of these two methods is the most popular. With its help, almost eighty percent of this type of product is produced.
Petroleum coke is subsequently used in the manufacture of electrodes, as well as anode masses and anodes for aluminum smelting. It finds application in the technological processes of manufacturing ferroalloys, abrasives, silicon. Petroleum coke is widely used in the chemical industry.
Obtaining this product occurs at low pressure. At the same time, the temperature is maintained from 480 to 560 degrees.This allows the production of petroleum coke and gasoline, hydrocarbon gases, as well as kerosene-gas oil fractions.
The coking process is the splitting of all the components that make up the raw material. In this case, liquid distillate fractions and hydrocarbon gases are formed.
The industrial process for producing petroleum coke is carried out using three types of plants. In addition to periodic coking in special cubes and a slowed-down process in the chambers, it can occur continuously in the fluidized mass of the coke carrier. Consider one of them, which is used most often, in more detail.
Slow coking
This process is also called semi-continuous. This method of producing petroleum coke is most common in world practice. It implies such a technological process in which the raw material preheated to 350-380 degrees is continuously fed to special plates located in distillation columns. Such installations operate at atmospheric pressure. Raw materials for the production of petroleum coke flows down the plates and is in contact with the vapors rising from the reaction apparatus. The result of this mass and heat transfer is condensation. It is he who forms, together with the initial product, secondary raw materials to be further heated to 490-510 degrees in tube furnaces.
Next, the mixture enters the coke oven chambers. These are vertically located hollow cylinders, the height of which reaches 22-30 meters and a diameter of 3-7 m.
The reaction mass enters the coke oven chambers continuously. Moreover, this process lasts from 24 to 36 hours. During this time, the mass, thanks to the heat it holds, gradually cokes. When the chamber is 70-90 percent filled with the final product, it is removed using a normal jet of water under high pressure.
Next, coke is placed in a crusher, in which it is crushed into pieces whose size does not exceed 150 mm. After that, the product is fed to the screen using an elevator, sorting it into fractions of different sizes. The chamber in which the coke was obtained is subject to heating with water vapor and those vapors that are supplied from working devices. Next, the tank is again filled with raw materials.
After passing through the process, volatile products arise. This is a vapor-liquid mixture, which is continuously removed from the existing chambers and sequentially separated into gases, first in a distillation column, and then in a water separator and gas block, as well as in a stripping column.