Advantages and Disadvantages of RHF
Advantage
1. Good adaptability to raw materials and fuels
Iron-containing raw materials: The rotary hearth furnace can directly produce high-quality sponge iron by reducing hematite, magnetite, iron sand and other high-quality iron concentrates or lumps for use in steelmaking furnaces; it can process ordinary-quality iron ore powder, or even vanadium-titanium magnetite and ferroalloy composite ore raw materials containing manganese, chromium and other metals. After high-temperature reduction and mechanical separation, they can be used in power furnaces or converters. If necessary, other valuable metals can also be recovered; in addition, the rotary hearth furnace process It originated from the treatment of dust, mud and solid waste containing harmful elements such as zinc, potassium, and sodium. The raw materials have strong applicability. Reducing agent: The rotary hearth furnace can use various carbonaceous fuels such as coal, coke or charcoal as reducing agents to reduce metal iron and other oxides, and use various types of gases such as coal gas, shale gas, natural gas, liquefied gas, fuel oil and Pulverized coal and other fuels provide heat, which can fully adapt to the global energy structure according to time and place, without local limitations, and can be widely used.
2. Low operating costs
The applicable types and particle size ranges of raw materials are wide, eliminating the traditional pelletizing process, thereby minimizing the production cost of pelletizing from iron-containing raw materials. Using carbonaceous fuel directly as the reducing agent eliminates the traditional coking process and can replace part of the fuel. The sensible heat recovery rate of exhaust gas is high, which greatly reduces energy consumption.
3. Low fixed investment
Compared with other coal-based direct reduction (such as rotary kiln) technologies, the equipment level of the rotary hearth furnace has achieved a high degree of mechanization and automation. The storage and transportation of raw materials and fuels in the whole process, the finished product processing system and the structure of the rotary hearth furnace body are all It is relatively simple. By integrating existing mature technologies and equipment in each process, the technological maturity is greatly improved, the operational risks are controllable, and the one-time investment is reduced by about 25 to 30%.
4. Equipment operation is stable and reliable
The core equipment of the rotary hearth furnace, the annular heating furnace, has been successfully used in the steel rolling process and direct reduction field for many years. The charge is quickly reduced at high temperature because it is relatively stationary with the rotation of the hearth. Therefore, the rotary hearth furnace process has low requirements for the mechanical strength of raw material pellets. , the control and maintenance of the equipment are therefore relatively simple.
5. Environmentally friendly
During production, the rotary hearth furnace operates under a slight negative pressure and has good air tightness. The reducing gas is controlled to be fully burned in the furnace under high temperature and low pressure. The flue gas recovers heat through a special waste heat recovery device, ensuring that CO and other gases are in the furnace. Eliminates itself in the furnace without overflowing. The secondary dust generated in the workshop can be returned to the raw material system for use, thereby reducing the occurrence of harmful solid waste and avoiding secondary pollution to the environment.
Disadvantage
1. Product quality needs to be improved
Since pulverized reduced coal is added to iron-containing materials, high melting point substances such as ash and solid binders brought by the reduced coal will remain in the metallized pellets of the product, increasing the gangue content in the pellets; another On the other hand, because the sulfur in the raw fuel cannot be effectively removed in the rotary hearth furnace, the sulfur content in the products produced is generally high. These unfavorable factors force the current rotary hearth furnace reduction production to use high-grade iron ore and low-sulfur, low-ash coal to meet electric furnace production. But even so, the finished product of the rotary hearth furnace still cannot reach the quality of high-quality direct reduced iron, which also makes the subsequent processing of the rotary hearth furnace process tend to increase the melting process.
2. The atmosphere in the furnace is highly volatile
Due to the open-flame heat supply in the rotary hearth furnace, the reduction atmosphere in the furnace is adjusted through the combustion system, that is, while the combustion air is mixed with heat sources such as gas and burned to release heat, the actual adjustment of the flue gas atmosphere generated is relatively difficult. Large, the pellets are more likely to undergo secondary oxidation during the reduction process, which reduces the quality of the product, that is, the metallization rate.
3. Thermal efficiency is low and waste heat recovery needs to be fully considered.
Radiation heat transfer is the main method between the high-temperature flue gas generated by the rotary hearth furnace combustion system and the furnace charge, and the heat transfer efficiency is low. A large amount of high-temperature flue gas enters the flue from the discharge outlet of the rotary hearth furnace, causing the heat of the rotary hearth furnace itself to The utilization efficiency is low. Usually, the flue gas of the rotary hearth furnace takes away more than 40% of the input heat. In various current rotary hearth furnace processes, after the high-temperature flue gas passes through the subsequent use of waste heat recovery facilities, the recovery rate is about 40%, but the heat utilization rate of the entire process is still low. In summary, the rotary hearth furnace process still has many shortcomings and room for improvement, which needs continuous improvement and perfection, leaving a large space for innovation in the rotary hearth furnace process. It is also very important for the development of the technology of using the rotary hearth furnace to prepare granular iron. Good opportunity, this technology deserves further in-depth research until development and application.
