Learn details of belt roaster pelletizing new technology

In recent years, due to the inferior, poor, miscellaneous and refractory iron ore resources in my country, fine grinding must be carried out in order to improve the utilization efficiency of iron ore, which can result in the majority of domestic iron concentrates with fine particle size. And half of the iron concentrates are suitable for the production of pellets. In addition, the pelletizing process is cleaner and more environmentally friendly than the sintering process, and meets the requirements of clean production and ultra-low emissions in the steel industry. Therefore, increasing the amount of pellets in the blast furnace charge has been included in the development plan of major iron and steel enterprises.

Necessity and development of large proportion of flux pellets in blast furnace

In 2017, the blast furnace charge structure of China Iron and Steel Association member units is roughly 78% sinter, 13% pellet, and 9% lump. Appropriate charge structure is the guarantee of optimization and cost reduction of blast furnace production. Increasing the ratio of blast furnace charge pellets can improve the iron content of the ore into the furnace, reduce the amount of iron ore per ton, reduce the fuel ratio, increase the output, and also reduce pollutant emissions, promote energy saving and emission reduction in the ironmaking system, and reduce agglomeration. Process flue gas treatment costs.

Blast furnace slag comes from sinter, pellet, lump ore, coke and pulverized coal, and the basicity of slag is generally required to be 1.0-1.2. The basicity of sinter is generally 1.8-2.2. When the ratio of pellets is about 50%, the basicity of pellets needs to be about 1.0 to meet the basicity requirements of slag. Therefore, the blast furnace adopts a large proportion of pelletized charge structure and needs to use flux pellets.

From December 2015 to September 2017, Shougang Jingtang conducted several industrial tests of blast furnace large proportion pellets (up to 55%) + limestone/steel slag, which verified the feasibility of Shougang Jingtang blast furnace large pellet ratio smelting. From October 2018 to January 2019, two industrial tests were carried out using the charge structure of alkaline pellets + acid pellets + sinter + raw ore, and the blast furnace charge structure was determined, and the quality control of alkaline pellets was found. Since the No. 3 blast furnace was put into operation on April 26, 2019, the proportion of pellets has gradually increased, reaching a maximum of 59.1%. During this process, the relationship between blast furnace pressure and volume is stable and furnace conditions continue to be stable. At present, the three blast furnaces of Shougang Jingtang all adopt the charge structure of about 53% pellets. The utilization coefficient of No. 3 blast furnace is 2.34 t/(m³·d), the fuel ratio is 481kg/t, and the comprehensive ore grade is 61.3%. , the amount of slag is reduced to 225kg/t. Practice has proved that the ratio of pellets can be increased by 10%, and the fuel ratio can be reduced by about 5kg per ton of iron.

New Technology of belt type sinterer pelletizing process

1. Flux pellet technology

1) Limestone or slaked lime is used as the flux to meet the basicity requirements of the blast furnace for pellets. 2) When slaked lime is used as flux, the amount of binder can be reduced.

3) The suitable roasting temperature is lower than that of acid pellets, which reduces the generation of NOx.

2. Magnesium pellet technology

1) Dolomite, magnesite, olivine, magnesia powder, etc. are used as magnesia fluxes to meet the requirements of blast furnace for MgO content of pellets.

2) Adding MgO to the pellets can effectively improve the metallurgical properties of the pellets, reduce the reduction expansion index, and improve the low-temperature reduction pulverization index; it can also reduce the MgO content of the sinter, and improve the utilization factor of the sinter and the strength of the sinter.

3. Titanium-containing pellet technology

1) Add raw materials containing TiO2 to meet the requirements of the blast furnace for the TiO2 content of pellets.

2) TiN (TiC) layer will be formed on the hearth and sidewall of the blast furnace due to the titanium-containing pellets. Since the melting point of TiN (TiC) is as high as 2950°C (3140°C), the effect of protecting the furnace is achieved and the furnace age of the blast furnace is increased.

4. Advanced automatic ball making technology

The special image analysis software is used to analyze the green pellet images captured by the camera in real time, and automatically adjust the relevant parameters of pelletizing to realize automatic pelletizing, ensure the quality of the green pellets, and reduce the labor force.

5. Advanced reciprocating distributor

1) The head retraction adopts a mobile trolley, which is driven by a hydraulic cylinder.

2) The speed of the moving trolley matches the speed of the conveyor belt to realize one-way feeding and ensure the smoothness of the material surface.

3) Reduce the number of transfers and drop of green balls, avoid damage to green balls, and improve the pass rate of green balls.

6. Advanced grading cloth system

1) The 4m trolley only uses φ85mm rollers, the grooves between the rollers are shallow, and the screening effect is good;

2) The roller adopts centrifugal casting, which has small deflection, is not easy to deform, and has a high pass rate of green balls;

3) The surface of the roller is provided with a coating, which is not easy to stick to the material and has a long service life;

4) The use of a new type of side baffle will not produce grooves on the surface of the roller, and the roller has a long service life.

advantage:

1) Grading and screening and larger screening area to improve the screening efficiency of powder;

2) Improve the air permeability of the material layer;

3) Increase the air volume of the roaster per unit area;

4) Shorten the reaction time;

5) Reduce fuel consumption;

6) Improve the production capacity of the roasting machine;

7) Improve the physical properties of pellets.

7. Advanced thick layer roasting technology

1) Reduce the proportion of pellets with low strength at the bottom of the material layer.

2) Reduce the speed of the belt roaster.

3) Better drying, preheating, roasting and cooling.

4) Increase production.

8. Advanced combustion system

1) Automatic ignition to realize online start and stop of online burner.

2) Flame monitoring, realize automatic identification and automatic purging of flameout, and ensure production safety.

3) The excess air coefficient is lower than 15%, reducing the production of NOx.

4) Advanced valve group and control system to realize automatic temperature control of single or single group of burners.

9. Advanced internal fuel distribution technology

The internal fuel distribution process is adopted to increase the porosity and reducibility of the finished pellets, reduce the total fuel consumption, the temperature of the trolley grate and the power consumption of the fan, and improve the production capacity of the system. This high porosity, high reducibility pellets are used in blast furnace production to increase productivity and reduce heat consumption.

10. Advanced trolley, star wheel and curved track technology

The material with high cost performance is selected to meet the requirements of high temperature, heat exchange and other working conditions of the roasting machine, and a reasonable trolley structure is designed to effectively improve the service life of the trolley. Only a few trolleys are needed for online grate changing. The cost of spare parts for the trolley is greatly saved, and the operation rate of the belt roaster is greatly improved. The solution to the problem of the life of the trolley has set off the pelletizing fever of the belt roaster in the pelletizing industry in China. The star wheels and curved rails at the head and tail adopt a structure that conforms to the operating characteristics of the belt roaster, with stable operation and no collision and abnormal noise. The tooth surface adopts a replaceable design, which is convenient for production and maintenance.

11. Advanced non-water-cooled structural beams and partitions

The side sealing beam adopts advanced non-water-cooled beam technology, and the partition wall cancels the support of the water-cooled beam and adopts a hanging structure to achieve zero cooling water consumption of the belt roaster, and avoid the damage of the equipment and refractory materials due to corrosion and leakage of the water beam.

12. Advanced sealing technology

Advanced bellows end and partition sealing technology, simple structure, adaptable to thermal conditions, stable operation, convenient maintenance, effectively solve the follow-up problem of the sealing device in the horizontal and vertical directions, and can effectively eliminate the phenomenon of dust accumulation.

The sealing technology of the new furnace hood and the bench workshop: the sealing plate forms a seal with the friction plate of the trolley by its own weight, and the sealing performance is good; the structure is optimized, the service life is long, and the maintenance is convenient.

13. Advanced automatic control technology

1) Automatic speed regulation of belt roaster;

2) The process fan automatically adjusts the speed;

3) The valve of the air system automatically adjusts the opening;

4) The bottom material screen automatically adjusts the feeding amount;

5) The entire belt roasting machine is automatically controlled by computer.