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A coke blast furnace is a vertical, cylindrical container, usually made of iron or steel, which is used to convert raw materials into metallic iron. There are generally two types of blast furnaces used to produce coke for ironmaking.
Traditional blast furnace
The traditional blast furnace is a huge vertical vessel. The size of the furnace is gigantic, reaching about 30-40m in height and 7-10m in diameter. The whole furnace is divided into several distinct parts, including the throats, stoves, bosh, hearth, belly, and tuyere. In general, the furnace is narrow at the top and wider at the middle and bottom. Raw materials are added from the top, such as coke, iron ore called taconite, and limestone. Air is injected through the tuyeres located at the bottom part of the furnace. The temperature inside the furnace varies a lot, from 1,000 degrees Celsius in the upper part to about 1,500-2,000 degrees Celsius in the lower part. Iron and slag are extracted from the furnace through the open hearths. The traditional blast furnace is still widely used. In fact, a report published in 2021 stated that nearly 80% of the steel produced came from countries that mainly use the blast furnace method to make steel from iron.
Continuous blast furnace
The continuous blast furnace is somewhat similar to a traditional or vertical blast furnace. In this setup, raw materials are continuously fed into the furnace, and molten iron and slag are simultaneously extracted from it. The temperature in the continuous blast furnace is also very high. However, what’s remarkable about the continuous blast furnace is that even though coke is needed to fuel the furnace and make iron from iron ore, the continuous blast furnace needs much less coke compared to the traditional blast furnace. Continuous blast furnaces are also known as electric furnaces. Reports say that about 20% of steel worldwide is produced by electric blast furnaces, mainly in the Middle East and North America.
Specifications are vital parameters to consider when looking to invest in a coke blast furnace. The following are some critical specifications whose values users should know:
Capacity
The task of the capacity of a blast furnace is to show how much iron ore it can process in a given timeframe, usually a month or year. For blast furnaces, the capacity is usually in tons per month or per year. Typical capacities of large industrial blast furnaces range from 1,000,000 tons/year to 2,000,000 tons/year.
Height
The height of a blast furnace is a key influencing factor in its ability to produce pig iron and other metallic products from iron ore. An ideal height dimension for a blast furnace is 20 to 30 meters (66 to 98 feet).
Diameter
The diameter of a blast furnace plays a vital role in determining the volume of raw materials that can be charged into the furnace, as well as the rate at which pig iron and slag are produced. Large industrial blast furnaces have a tap diameter that typically ranges from 10 to 15 meters (33 to 49 feet).
Material
The material used to build a blast furnace affects its ability to produce pig iron efficiently and sustainably. The key components of a blast furnace are the lining, the shaft, and the hearth. The lining of a blast furnace is built using refractories. The shaft and hearth are constructed using steel plates. The steel plates are then bonded with cemento, which is a calcium-based substance, also known as slag.
Tapping System
Modern blast furnaces use advanced tapping systems to control the flow of molten iron and slag in a precise and safe manner. These systems employ hydraulic or mechanical techniques to open and close tappings, regulating the volume of materials extracted.
Gas Collection System
The gas collection system of a blast furnace collects the byproduct gases generated during the iron-making process. This includes carbon monoxide, carbon dioxide, hydrogen, and other gases. These gases are then routed to cleaning and recovery facilities for further processing.
The maintenance of a blast furnace is critical for ensuring its efficient operation and longevity. Regular maintenance helps prevent breakdowns, optimise performance, and extend the life of critical components. The following is a brief outline of routine maintenance tasks for a blast furnace:
Pre-Maintenance Inspection
Before the start of maintenance activities, operator and technician teams should carry out detailed inspections of the entire furnace body. They should look at the lining, gas ducts, feeding systems, tappings, and slag removal systems. The goal of the inspection is to detect any early signs of damage or abnormality. Once they notice irregularities, they should promptly take corrective actions. The pre-maintenance inspection helps improve the reliability of blast furnaces and cut down on unscheduled maintenance needs.
Lining Maintenance
The refractory lining of a blast furnace provides thermal insulation and protection against corrosive slags and molten metals. Regular lining maintenance is crucial to extending the lining's life and preventing overheating of the furnace shell. During scheduled maintenance intervals, the operators should inspect the condition of the lining. They should look for signs of wear, damage, or erosion. Upon noticing any abnormality, they should quickly replace the damaged sections of the lining.
Coke blast furnaces are critical components of the steel industry. Their primary use is in the production of pig iron, which is the primary ingredient in the manufacture of steel.
Worldwide, about 70% of steel produced uses the blast furnace method. The furnace combines iron ore, coke, and limestone at extremely high temperatures. The coke is created by pyrolyzing coal in the absence of air. While serving as a fuel, it also acts as a reducing agent for the ore, which is made up of iron oxide.
Once the chemical reaction takes place, pig iron is formed. It contains a very high level of carbon, between 3.5 and 4.5 percent. Other alloys are then added to create various grades of steel that can be used in construction, automobile, shipbuilding, and other industries. Apart from being the primary ingredient in steel production, one of the greatest advantages of using coke in a blast furnace is the high quantity of carbon it contains, which contributes to the furnace's energy.
Industries that use blast furnaces include construction, shipbuilding, automobile, machinery, and container manufacturing. About 2,500 kg of raw materials are used to manufacture 1,000 kg of hot metal in a blast furnace.
The scheme shows the end products that come from a blast furnace aside from pig iron. They include steel, slag, and carbon dioxide. The slag is the impurity of sand, clay, and other minerals that were part of the iron ore used. It settles on top of the pig iron and is usually removed and processed to form aalite, which is a crystalline mineral used in the manufacture of cement.
Quality:
The quality of the cokes produced by the blast furnace furnace has a major impact on the performance of the blast furnace itself and other downstream industries. When shopping for furnaces, business buyers should consider their raw materials and end-use requirements to find out what kind of cokes their blast furnace will be producing. Also, buyers should try to find out if the product supplier or manufacturer offers customisation options to tailor the machine's output to their specific requirements.
Coke specification:
Not all cokes are the same, neither are all blast furnaces. Business buyers need to consider coke specifications, such as size, strength, and porosity, to see if they are compatible with their current or planned processes. If a blast furnace is not suited to certain types of coke, productivity may suffer or even damage the entire system.
Production capacity:
The optimal size of a blast furnace is proportional to the scale of industrial operations. Buyers should calculate the expected annual production of molten iron and steel to help them determine the optimal working capacity and choose a furnace that meets their production requirements.
Technology and Equipment:
Numerous advancements have been made in the technology and equipment used in blast furnaces, including tuyere design, burden distribution systems, and gas cleaning technologies. Such technological advancements have resulted in increased efficiency and reduced environmental impacts.
Cost and Budget:
Business buyers need to carefully consider the costs associated with operating and maintaining a blast furnace. To help them do this, buyers should assess installation expenses, energy consumption, maintenance costs, and any environmental fines that may arise from non-compliance with industry standards or regulations.
Q1: What is the chemical composition of coke produced in a blast furnace?
A1: The primary product of the blast furnace is pig iron. It has a chemical composition of about 3.5 percent carbon, 0.5 percent silicon, 0.2 percent manganese, and traces of other elements.
Q2: What are the byproducts of a blast furnace?
A2: A blast furnace produces several byproducts. The main ones are slag and gases. Blast furnace slag is a byproduct formed when impurities like silica, alumina, and lime exit the iron ore during the smelting process. The slag has many uses. For example, it can be ground into a fine powder and used as a cement additive. On the other hand, blast furnace gases consist mostly of carbon monoxide and nitrogen. They may be trapped and refined into useful chemicals.
Q3: How long does it take to build a blast furnace?
A3: Modern blast furnaces are huge and complex. It takes around 2-3 years to build one. The cost is high, often in the billions. These furnaces are built to last 10-20 years without major repairs.
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