Coal -based direct reduction refers to the process of directly using coal as a reducing agent, and is directly related to the gas-based process (using natural gas or other reducing gas as a reducing agent). The history of coal-based may be earlier than that of gas-based, but the gas-based development is very fast, and both the technical level and the scale of production far exceed the coal-based. In the 30 years from 1975 to 2005, the annual production of direct reduced iron (DRI) worldwide increased from 800,000 tons to 56 million tons, or 70 times. Among them, the gas base accounts for 85%, while the coal base accounts for only 15%. However, mainly due to resource factors and related economic benefits, the development of gas-based is constrained. The industry has turned its attention to coal-based, and coal-based direct reduction without coking coal is friendly to the environment, and thus it is subject to industrial policies in China. stand by. There are many coal-based direct reduction processes in the world, but there are two main types of production scale: one is a rotary kiln; the other is a rotary hearth furnace. The rotary kiln process has a long history. It has previously produced 'granular iron' and later converted to produce DRI. Its main advantage is that the product quality is good and can be directly used as electric steelmaking raw material. The kiln product has been magnetically selected to enhance the taste of the kiln. At present, the production process has matured and reached a certain scale, and its products have become one of the clean iron sources for electric furnace smelting high-quality steel. However, the rotary kiln process also has its inherent disadvantages: 1. The material is rolled in the kiln with the rotation of the kiln body, and is easily crushed. The generated powder and the coal ash stick together to form a 'ring ring', thereby damaging the lining and forming an operation accident, thereby reducing the operation rate. 2. Subject to the 'ring ring', the reduction temperature is low, generally about 11000C, affecting the reduction rate. 3. Therefore, the efficiency is not good. 4. Unit investment is relatively large. 5. There are specific requirements for the coal used. For example, the ash melting point must be at 12800C, otherwise it will be 'knotted'. In the past, why did the coal go wrong and suffered a lot! For these reasons, the domestic industry has been optimistic about the kiln process after a while in the past ten years. In fact, it is not entirely true. The production of the existing minority rotary kiln in China has also made progress and accumulated a lot of experience. Of particular note is India's experience in developing rotary kiln processes. The Indian rotary kiln has an annual output of several million tons of DRI, and Jindal, which has the largest output of the world's rotary kiln, has an annual output of 1.47 million tons. Moreover, it is developing a new technology for producing high-quality DRI in rotary kiln using the domestically produced lean iron ore and ash coal. The rotary hearth furnace technology that has emerged in recent years has attracted the attention of the domestic industry. Not only have they developed themselves, but some have also tried to introduce them from abroad. What are the characteristics of the game to the bottom of the furnace? Well there? What is the problem? Please comment one or two. The rotary hearth furnace process is to mix fine iron ore powder and coal powder into a pellet (ball or ball) in a certain ratio, and then add it to the rotary hearth furnace. The layer is evenly laid on the bottom of the furnace, with the bottom of the furnace. After one rotation, the furnace is discharged, during which it undergoes preheating (drying), heating and reduction, soaking and deep reduction, and finally cooling. The high temperature zone reaches about 13500C. The most basic feature of the process is that the fine-grained coal is tightly combined and rapidly reduced at the temperature. Therefore, the whole process only takes 10-20 minutes, the production cycle is very short, which is the first advantage of the rotary hearth furnace; the second is that after the material is added to the bottom of the furnace, it no longer moves, and quietly follows the bottom of the furnace, so It does not break, so the strength of the ball is not high. The third advantage is that the energy utilization rate is é«™, and the reduction product CO emits a large amount of heat energy through secondary combustion, which is about half of the total heat supply (two-thirds reported abroad). The fourth is that the raw materials contain harmful impurities ( zinc , lead , arsenic, etc.), which can be partially or largely volatilized in the rotary hearth furnace and can be recovered from the flue gas. The fifth is environmentally friendly, because the furnace is a micro-negative pressure system, smokeless gas is discharged, and there is no process sewage. The sulfur dioxide emissions in the flue gas are also much lower than sintering. The sixth is that the investment is not too big, and it is lower than the equivalent size of the kiln. The rotary hearth furnace process has only been around 30 years old and is still in the development stage and still not perfect. There are mainly the following problems: 1. Only one layer of ball can be laid on the bottom of the furnace, otherwise the temperature of the lower layer will not go up, because the furnace mainly relies on radiation heat transfer, which greatly affects the output. As a result, the effect of rapid reduction is offset, so that the bottom is turned. The scale of the furnace is difficult to expand. At present, the largest one is the rotary hearth furnace with an annual output of 600,000 tons of DRI built by American Power Steel Company. Its diameter has reached 50 meters, which is amazing! 2. As the coal of the reducing agent, the ash content enters the product with the gangue in the ore, which makes the grade drop, and it is difficult to use it as the DRI for the electric furnace. 3, the rotary hearth furnace must be supplied with gas fuel for heating, and foreign countries use natural gas or other high calorific value gas. If you introduce a foreign rotary hearth furnace and ignore this article, it will have serious consequences. Domestic use of thermal storage combustion technology to burn low calorific value gas can be said to be innovative. Rotary hearth furnace developed in recent years, mainly in the United States and Japan, the earliest American INMETCO the rotary hearth furnace, electric stove with matching production with nickel, chromium iron, stainless steel hook using the smelting wastes and other ferrous scrap, to become the eastern United States and consumptive steel mill waste center of. The furnace has an outer diameter of 16.7 meters and a width of 4.3 meters. The cost per ton of iron is 144-177 dollars, and the unit investment is 160-180 dollars/ton-year. At present, the largest rotary hearth furnace is also in the United States. As mentioned above, the furnace has an outer diameter of 50 meters and a width of 7 meters. It is matched with a submerged arc furnace, with an annual output of 500,000 tons of molten iron, a cost of 150 US dollars per ton, and a unit investment of 120 US dollars. Tons - year. The raw materials used are iron concentrates, and the molten iron is supplied to the steelmaking electric furnace for hot charging. The most active development in Japan is Kobe Steel, and the larger one is Nippon Steel. The Junjin Plant was built in 2000 and 2002 to treat steel mill dust and products for blast furnaces. From the practice of these rotary hearth furnaces, different development modes have emerged. As far as the process flow is concerned, it can be roughly divided into the following three types: The first type is a single rotary hearth furnace, the so-called FASTMET, which directly feeds the furnace steel or blast furnace iron. It should be pointed out that, as mentioned above, due to the iron ore grade and the ash content in the coal, the product of the rotary hearth furnace is difficult to be used as the raw material of the electric furnace, so the current trend is to supply the blast furnace, which is extremely effective for reducing the coke ratio of the blast furnace, the above-mentioned Japanese Junjin This is the case with the factory. The second type is the combination of a rotary hearth furnace and a melting furnace (a submerged arc electric furnace, that is, a submerged arc furnace in foreign countries), the so-called FASTMELT. The large-scale rotary hearth furnace of the above-mentioned American Power Steel Company is a typical example, and its product is molten iron. Shipped to electric furnace steelmaking (of course, it can also be exported to cast iron blocks). In fact, this series process has been involved in the scope of smelting reduction. The rotary hearth furnace became the "pre-reduction" of the two-step smelting reduction. The third type is a high-temperature rotary hearth furnace for producing iron nuggets. The carbon-containing pellets should be quenched in the rotary hearth furnace to separate the slag iron (no need to be melted after being baked) to form iron nuggets (Nuggets or Pebbles). Japan's Kobe Steel called this method Itmk-3 (meaning the third generation of ironmaking), and Japan's other (JFE) Hi-QIP method is similar. This type of rotary hearth furnace is under development, and both have conducted pilot tests. Kobe cooperates with relevant companies in the United States to build a large-scale equipment with an annual output of 500,000 tons in the United States. However, many major technical problems still appear to be unresolved. It is worthy of attention. As far as the current level and scale of rotary hearth process development is concerned, it is still difficult to enter the mainstream of steel, but there are still a lot of room for development. 1. Using a single rotary hearth furnace, namely the FASTMET method, to treat the dust and related waste generated in steel production, to produce DRI for the furnace, and to use ordinary iron concentrate under conditions, only when the raw material conditions are excellent. Direct power supply furnace DRI. DRI is not necessarily used for a metal ratio Gao Gao furnace, generally around 70%, which can provide a rotary hearth furnace productivity Gao. 2. The rotary hearth furnace is matched with the melting furnace, that is, the FASTMELT method to produce molten iron, which is matched for the hot charging of the electric furnace. Generally, the electric furnace is far away from the furnace, and it is difficult to obtain molten iron. The construction of this process is combined with it, and it can be said that the charcoal is sent in the snow. 3, using a rotary hearth furnace to treat some special antimony ore, such as or containing zinc, lead, arsenic and other harmful impurities, or containing nickel, vanadium , titanium and other useful elements, can use the process advantages of the rotary hearth furnace, or volatilization, Or selective reduction, combined with subsequent processes to achieve comprehensive utilization of resources. TPU Vacuum Casting,Custom Plastic Vacuum Casting Parts,Vacuum Casting Service,Custom Vacuum Casting Ningbo Jiongke Technology Co., Ltd , https://www.precisioncncmachiningparts.com