The sintering process is the first step of the iron-making process and plays an important role in creating iron ore that can be used in a blast furnace. Raw iron ore, on its own, is like dirty coal in that it burns unevenly and doesn’t allow for efficient airflow. Sintering transforms it into a more usable raw material for the next stage.
We will discuss the sinter plant design and special specifications, including the physical and chemical principles of the sinter plant process.
What Is A Sinter Plant And How Does A Sinter Plant Design Work?
A sinter plant is a facility where fine particles of iron ore and other materials, such as coke and limestone, are agglomerated into larger, porous clumps called sinter. The sintering plant process comprises several key components.
First, we have the raw material handling component, which stores and discharges the materials transferred from the material yard. Second, the sinter machine that produces the actual sinter ore. The third part is the crushing facility that crushes and screens the iron ore and conveys it.
The sintering machine is a large, continuous belt conveyor that carries the raw materials through the sintering process. The raw materials are mixed and fed onto the sinter machine, where they are formed into a bed and ignited.
As the bed moves through the sinter machine, it is heated to a high temperature, causing the particles to bond and form a sinter.
Other components in a sinter plant include the Exhaust ESP, which collects the dust generated from the sintering process; the De-Dusting ESP, which collects the dust generated in the screening and crushing equipment; and the bag filter, which collects the dust generated in the fuel crushing equipment.
In some cases, additional bag filters may be installed to collect the dust generated in the fuel and material storage bins.
In addition to these components, the sinter plant may also have a special cooling bed. The cooling bed is a long, sloping conveyor that carries the sinter away from the sinter machine and allows it to cool slowly. This helps to improve the strength and quality of the sinter.
In addition to these key components, a sinter plant may also include other equipment, such as screens and crushers, to prepare the raw materials for sintering and dust collection systems to control emissions. The specific sinter plant design and configuration may vary depending on the specific requirements of the facility and the type of sinter being produced.
Physical and Chemical Processes of Sintering
The sintering process involves compacting or fusing together small particles to create a larger mass without actually melting the particles.
In the context of an iron ore sinter plant or steel production, this process is used to agglomerate iron ore fines with flux fines (such as limestone, dolomite, and pyroxenite) and coke fines as a solid fuel.
When heated to high temperatures (between 1200°C and 1300°C), these particles fuse to form a heterogeneous, lumpy mass.
The raw materials are thoroughly mixed and then delivered to the sinter machine as a bed. The top layers of this bed are ignited in the ignition furnace, and the bed then moves toward the cooler.
At this point, there is precision in temperature, pressure, and time.
Afterward, an artificial downward draft is created, causing the red-hot combustion layer to travel downward, igniting and sintering the lower layers of the raw mix bed.
When the entire cross-section of the bed has been sintered, it reaches the machine’s discharge side or cooler side, where it is cooled before being conveyed to the blast furnace or storage area.
In the process of sintering, one chemical bond is broken to allow for the formation of a new, more stable bond. When a system is given a certain amount of energy, it naturally tries to move to a minimum energy state.
In sintering, the excess energy required for this process comes from the particles’ surfaces. By supplying external energy, the bonds between atoms on the particle surfaces are broken, allowing new bonds to be formed with neighboring atoms. This elimination of the surface between particles results in a decrease in the system’s overall energy.
However, this process cannot occur at normal temperatures due to insufficient energy for the atoms to break their initial bonds and form new ones with their neighbors. During sintering, pressure is also applied to reduce the distance between particles and facilitate the formation of new bonds.
How Long Will This Process Take?
The sintering process can take anywhere from a few milliseconds to 24–30 hours, depending on the material and the technique used.
Here are some factors that determine the speed of the process:
- The properties of the material being sintered, such as atomic mobility, self-diffusion coefficients, melting temperature, and thermal conductivity, are all important considerations.
- The specific sintering technique employed also affects the duration of the process. For example, field-assisted sintering techniques are known to significantly reduce sintering times. In contrast, selective laser sintering (or SLS, a type of 3D printing for metals) tends to be slower due to heat dissipation and distortion control.
- The desired microstructure of the final product can also impact sintering time. For example, add a liquid phase with sintering aids such as phosphorus in iron-based powders. You can drastically reduce sintering time by increasing matter flow at the particle necks. However, reducing sintering time can also result in lower density and residual porosity, which may be acceptable in certain structural applications where sintered components are used to reduce production costs.
Conclusion
In a sinter plant design, iron ore, coke, and limestone are transformed into “sinter” clumps, making raw iron ore usable for iron production. This process involves mixing and heating the materials to create a homogeneous mixture, which is then cooled to form a sinter.
Sintering enhances the properties of raw iron ore, making it suitable for use in blast furnaces. And while the sintering process timeline can be reduced, manufacturers must consider the quality of the iron ore, ensuring that the final product has acceptable porosity.
FAQ
How long does sintering take?
The sintering process can take a few milliseconds to more than a day. Factors that determine the speed include the sintering technique, materials used, and the desired microstructure of the final product.
Should I always be concerned about reducing sintering time?
It depends on your product’s eventual application. Sintering in steel plants is crucial, so reducing sintering time can lead to lower density and residual porosity; however, if the product is acceptable and cuts production costs, you should not be worried.
Author:
Robert C. Green
This Article is written by Robert C. Green, and he is a metallurgy expert with a wealth of industry knowledge. With a passion for helping businesses optimize their processes and achieve excellence in metallurgical practices, they share valuable insights in their articles on metallurgy consulting.
