1.Process Flow
A -- C process definition: to achieve automated control, mechanized charging and discharging. It is a process for producing direct reduced iron (sponge iron) of cold briquetting iron through reduction in rapid reducing furnace and cooling. The technology contains five processes:
1.1 Material Preparation, Drying and Cracking
Pack devulcanizing agent and reducer into measuring hopper in a certain weight ratio, and then send into drying shed by conveyor for baking and mixing. The moisture of the material is less than 3% after baking, then the material is sent into reducing crusher for crushing that the granularity is under 1.5mm. After crushing, the material is raised to the overhead bin, then to storage bin by conveyor. The moisture of refined ore powder after drying in the warm gasdrier is less than 3%. After drying, the refined ore powder is sent through overhead bin to storage bin.
1.2 Automated Charging Process
This process can produce direct reduced iron (sponge iron) of globular type, columnar type or shoe type according to various requirements. In order to guarantee product quality, reduce the production processes and realize automatic charging and discharge, to produce shoe type is the best. This process produces shoe type direct reduced iron (sponge iron). Charging system is composed by bin, measuring tube and charging head. Refined ore powder and reducer is discharged to material bin from measuring bin, and then put into reducing crucible.
1.3 Reducing Roasting Process
This process is finished in the reducing furnace. The suitable temperature and reducing time is the key for the quality of direct reduced iron (sponge iron). It contains preheating, reducing and cooling. First, send the loaded car in the rapid reducing furnace to be preheat, at this time, the moisture in the material is totally evaporated, devulcanizing agent is resolved, the temperature increases to reducing temperature. Ferric oxide changes into simple substance iron through fully reduced. And then enter the cooling stage. It will be discharged when the temperature is below 200℃.
1.4 Automated Discharging Process
After the temperature of the furnace charge drops to 100—50℃ under the normal temperature, it is sent to the discharging system to discharge. Powdered ash is absorbed through the wind-force, direct reduced iron (sponge iron) is taken away from crucible by spanner. This achieves the automated discharging.
1.5 Products’ Disposal Process
Magnetic separation, crushing, passivation and compact are finished in this process. Direct reduced iron (sponge iron) enters into middle bin by discharging system, and then conveyed into crusher for crushing. After crushing and magnetic separation, the powder of direct reduced iron (sponge iron) is compacted, and then it is put in storage by actuator.
2 .Process characteristics:
2.1 Raw material, reducer and fuel are easy to use
The raw material of this method is refined ore powder or Grade≥60% haematite or limonite, it is more easy to use than enriched iron ore. It doesn’t need to change the refined ore powder into oxidation ball, and the cost is low. Reducers used in this method are anthracite powder or coal powder. Blast furnace gas, coke gas, rotary oven gas, mixed gas, petroleum gas, generator gas and heavy oil also can be used as pyrogen.
2.2 Steady Technology
This process absorbs advantages from other direct reduced iron (sponge iron) process. Through technological improvement and innovation, it has become a new steady and stable process. In the enclosed crucible, to use reducing method can increase concentration and pressure compression of the reducing ambience. This process use computer to control the temperature of the furnace. The difference in temperature is small and the reducing ambience is easy to be remained. So it is easy to guarantee the demand of the reducing process, and the products’ quality is steady.
2.3 Strong Practicality
There is few demand for refined ore powder and reducing coal. The practicability of A-C process is strong. This process is easy to control, and after training, workers can master the process.
2.4 Low Cost, Steady Quality.
Direct reduced iron (sponge iron) cost of each ton is among 1600-1900 Yuan by using A-C process. It is lower by about 50% than using rotary oven, so this process has advantage on cost.
There is less process of producing direct reduced iron (sponge iron) by using A-C process. Under the same ambience, same container, and the same time, each crucible is through preheating, heating reducing, cooling, so the quality of the products must be the same.
2.5 High Degree of Mechanization
This process uses mechanized charging and discharging system instead of traditional artificial charging and discharging system, so it lightens workers' labor intensity, improves the working environment, improves the quality of the products, reduces the products cost and amount of labor used. There are 100 staff in the factory with annual output 50,000 tons of producing direct reduced iron (sponge iron). There are 130 staff of the whole factory with annual output 100,000 tons of producing direct reduced iron (sponge iron).
2.6 High Degree of Automatization, High Production Efficiency
This process adopts computer control system to regulate the furnace’s temperature automatically. Automatically control of charging system, discharging system and compacting system improves working efficiency and accuracy of equipment operation.
2.7 Mechanized combustion system, Temperature apt to control
Use coal gas or coal powder as fuel. The automated degree is high. It is convenient for temperature control, and it is help to guarantee the quality of the products.
2.8 Good environmental protection condition, easy to achieve environmental protection standard
This process adopts advanced desulfurizing ash separator, high-efficiency blowback flat ash separator, and advanced energy-conserving low-noise equipments. By using these equipments, the dust content is less than or equal to 60mg/m3,S02 content is less than or equal to 480mg/m3, and noise is less than or equal to 65db. Every environmental protection index can up to the national requirement for environment protection. This process dose not have sewages and the working environment is clean and sanitary.
2.9Use carborundum reducing crucible or metal crucible, because they have long performance life.
This kind of crucible has good heat conductivity, so the reducing time is shortened, the quality and output of the products are also improved. Its service life is above 120 times and it can be recycled. After recovery, it can make crucibles again or used as fireproof aggregate after crashing, so the cost is lower. The metal crucible can be used 150 times or. Because this kind of crucible has characteristics of high intensity and invariant, it helps to realize automatic discharging.
2.10 Passivating treatment of direct reduced iron (sponge iron)—cold briquetting
This process adopts passivating treatment of cold briquetting in order to prevent formation of oxides. Press direct reduced iron (sponge iron) with the density of 1.9g/cm3 into cold briquetting with the density of 4.5g/cm3. Producing cold briquetting improves the antioxygenic property of direct reduced iron (sponge iron), and reduces the hygroscopicity of direct reduced iron (sponge iron). It is help to long term storage and long - distance transportation of direct reduced iron (sponge iron) by lessened volume. It also improves the output of the molten steel, so this process is popularized in steel making enterprises, and it has strong life force and competitive power in the market.
2.11 Adopt fuel gas’ remaining heat recovery system to improve the thermal efficiency
Absorb the remaining heat of flue gas into raw material’s drying machinery to dry the raw material. It avoids investing on other heat sources, and saves the consumption of the heat energy. The energy that be saved can convert into 5,544 tons of standard coal (that is the scale for producing direct reduced iron (sponge iron) with annual output 50,000 tons). In addition, preheat gas by remaining heat of flue gas (using heat exchanger) to support combustion in the furnace. It can bring a large amount of physical heat, improve the heating environment in the furnace, and reduce the consumption. The energy that be saved in a year can convert into 2,880 tons of standard coal. So it just uses 350 kg of standard coal to producing one ton of direct reduced iron (sponge iron).
2.12 This process adopts automated enclosed charging and discharging system, so the pollution can be controlled, the working environment is improved. It meets the requirement of the national environment protection.
Arrangement of A—C process is flexible according to the different landform and output. Because the packing methods of crucible is various and flexible, so the process can produce direct reduced iron (sponge iron) of globular type, columnar type or shoe type.
2.13 Little investment on fixed asset
Tianjin seamless steel tube company has two rotaries, and the annual output of direct reduced iron (sponge iron) is 300,000 tons. Its total investment is more than dozens of hundred million RMB; it means the investment of per ton of direct reduced iron (sponge iron) is more than 4,000 Yuan. Tangshan steel company has a blast furnace, supporting sintering equipment and coking equipment. Direct reduced iron (sponge iron) investment of per ton in Tangshan steel company is higher by 10% than in Tianjin seamless steel tube company. Direct reduced iron (sponge iron) investment of per ton which uses A-C process with annual output of 50,000 tons is about 600 Yuan. The larger the scale is, the less investment is
2.14 Little demand of raw material, high quality of products
Demand of refined ore powder:TFe≥67% Si02≤3% S≤0.02% P≤0.05%
Demand of reducer: ash content≤15% volatile content≤10% fixed carbon≥75%
Demand of devulcanizing agent:Ca0=53% Si02+AL2O3≤3% P205≤0.22% S03≤0.5%
all the raw materials are easy to be purchased, the products' quality by using this process is TFe≥92% MFe≥89% M≥94% S≤0.02% P≤0.05% C≥0.04%
2.15 A wide range of application scope
Direct reduced iron (sponge iron) produced by this process can be used as the raw material of producing high-quality steel and the raw material of powder metallurgical factory. Its metalized rate can be up to 99%, but the content of S, P and other elements is very low.
2.16 Metalized degree of products can be controlled
It is flexible for adjusting proportion of raw material, furnace temperature and reducing time, so it can produce different metalized rate of direct reduced iron (sponge iron) according to different usage or requirement.
2.17 It is difficult for products to be secondary oxidized
The whole reduction reaction is carrying on in a closed crucible. After reduction reaction, the furnace charge within the crucible is out of the oven, and be cooled under the normal temperature that can isolate the contact of direct reduced iron and the air. In addition, there are excessive reducer in the crucible, so the reduction reaction is still carried on at the initial cooling stage. The reducing ambience can be remained. It also prevent the outside gas from entering into the pot, so it can guarantee the quality of the products. It is difficult for products to be secondary oxidized
2.18 Fill factor is high (generally above 35%)
3.main equipments
Main equipments: rapid reducing furnace, thruster, charging system, discharging system, chimney, conveyor, crusher, drying machinery, hoist, magnetic separation machinery, air-compressor, ash separator, compacting machinery, instrument.
Direct reduced iron (sponge iron) production line with annual output 50,000 tons occupies an area that the length is 174M and width is 42M. The main workshop adopts the light colored steel structure.
4. Electric Power:
Installed capacity of direct reduced iron (sponge iron) production line with annual output 50000 tons is 900KW, it mainly used for power distribution, workshop lighting, lighting distribution and other power distribution system. The water is mainly used for environmental protection and fire prevention
5. Investment Estimation
The investment of this process is 10% less than rotary oven (including cost of all equipment). The fixed investment of producing direct reduced iron (sponge iron) with annual output of 50,000 tons is 30 million Yuan, the construction period is 3 months, and it can go into operation and become effective in the same year. The fixed investment of producing direct reduced iron (sponge iron) with annual output of 100,000 tons is 55 million Yuan (the price can be adjusted according to the price of raw material in the local place), the construction period is 5 months. The cost per ton of direct reduced iron (sponge iron) of this process is 1,600-1,900 Yuan, the lowest price of cold briquetting is 2,500 Yuan/ton. The total payback period is 1-2 years (not including construction period). Inside earning ratio is 39—45% (after-tax income). Investment profit margin is 35-50%. Break-even point is about 25%.
6.Cost Estimation
A—C Process of direct reduced iron (sponge iron) with annual output 50.000 tons needs 120 staff (including all the workers and administrative staff). The cost of direct reduced iron (sponge iron) of per ton is 1,600-1.900 Yuan according to the general price.
The cost may vary according to different raw materials’ price in different areas, it should be adjusted by local actual price.
7.Economy Evaluation and Explanation:
Construction period of direct reduced iron (sponge iron) with 50,000 tons annual output is 4 months. The products are cold briquetting, the price in the market is 2,500 Yuan/ton. Based on tax rate 6%, tax is 75.0 million yuan. And yearly profit is 20 million yuan.
To calculate by above-mentioned, if the production rate is 85%, it can regain all investment within 2.5 years.
Under the normal situation, if calculate on the date of production, it can regain all investment in 2.2 years.
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