Vertical coal milling for blast furnace pulverized coal injection

The integration of pulverized coal injection (PCI) technology in blast furnace operations has significantly enhanced the efficiency and productivity of steel manufacturing. Central to this process is the use of vertical coal mills for the precise and efficient processing of coal into fine powder suitable for injection into the blast furnace.

The Significance of Pulverized Coal Injection in Blast Furnace Operations:

Pulverized coal injection is a method used to inject fine coal particles into the blast furnace to replace or supplement the use of coke as a reducing agent and fuel. The benefits of PCI include:

- Reduced Coke Consumption: By using coal as an alternative fuel, the demand for coke, which is produced from costly and environmentally damaging processes, is decreased.

- Lower Fuel Costs: Coal is generally less expensive than coke, leading to cost savings in steel production.

- Enhanced Energy Efficiency: The high reactivity of pulverized coal improves the efficiency of the blast furnace, reducing specific energy consumption.

- Decreased Emissions: PCI can lower greenhouse gas emissions and reduce the environmental impact of steel production.

The Role of Vertical Coal Mills in PCI Processing:

Vertical coal mills are preferred for the production of pulverized coal due to their unique design and operational capabilities:

1. Grinding Efficiency: Vertical mills utilize a grinding table and rollers to achieve a high efficiency of coal grinding. The vertical arrangement allows for a more direct and efficient transfer of energy to the coal particles.

2. Particle Size Control: The mill's classifier ensures that the coal is ground to the precise particle size required for effective injection into the blast furnace, typically around 70-80% passing through a 200 mesh screen.

3. Drying Capability: Vertical coal mills can simultaneously dry and grind wet coal, which is essential for maintaining the quality and flowability of the pulverized coal.

4. Low Wear and Maintenance: The design of vertical mills reduces wear on grinding parts, leading to lower maintenance requirements and longer equipment life.

Operation of Vertical Coal Mills for PCI:

The process of vertical coal milling for PCI involves the following steps:

- Feeding: Raw coal is fed into the mill from the top, where it is gravity-fed onto the rotating grinding table.

- Grinding: The coal is ground between the table and the rollers, which rotate at different speeds to achieve the desired particle size.

- Drying: Hot air, often heated by the mill's exhaust gases, is passed through the mill to dry the coal as it is ground.

- Classification: The ground coal and air mixture is then passed through a classifier, which separates the coal particles based on size, with oversized particles returning for further grinding.

- Collection: The properly sized coal particles are collected and conveyed to a storage silo before being injected into the blast furnace.

Vertical coal mills are a critical component in the production of pulverized coal for blast furnace injection. Their ability to efficiently grind and dry coal to the exact specifications required for PCI makes them an indispensable part of modern steel manufacturing. As the steel industry continues to seek ways to reduce costs and minimize environmental impact, the role of vertical coal mills in the PCI process will likely grow in importance, driving innovation and technological advancements in coal processing equipment.