Next generation of pelletizing plants for the transition to green steel

However, reducing the carbon footprint of mining and pelletizing will be equally important to achieve globally agreed targets, while the shift towards direct reduced iron (DRI) production requires more highly beneficiated ores and higher-quality pellets than the traditional blast furnace (BF) route. To support this transition of the industry, Metso Outotec has launched the NextGen™ Pelletizing concept, following a clear product vision: The pellet plant of the future is carbon neutral and fully autonomous.

Metso Outotec’s NextGen^TM Pelletizing

The concept follows a modular approach that will see more modules in future and is available for new greenfield installations, but also as upgrade for existing travelling grate pelletizing plants.

Focusing on the carbon-neutral production of pellets there are three main sources of CO₂ in the pelletizing process:

• Solid fuel addition in the concentrate mix

• Burner fuels

• Electricity, mainly for the process gas fans

While removing solid fuel from the raw mix for hematites requires finding “green” substitutes, looking at ways to increase fuel and energy efficiency and to burn suitable alternatives to fossil fuels has been the main driver for our developments.

Only recently Metso Outotec launched its own FerroFlame burner family for travelling grate pelletizing plants, for standard and low NOx applications and we are actively developing a hydrogen burner utilizing the same patented LowNOx technology. At the same time, the Advanced Cooling concept is providing more fuel efficiency and gentle cooling of pellets by further recuperating parts of the off-gas.

The NextGen™ Pelletizing plant also provides the option for advanced burner configurations in a re-designed indurating hood, which improves the temperature distribution across the width of the bed, providing more pellets with the same temperature history throughout the process and hence more consistent quality.

At the same time, the increasing quality demands of DR-grade pellets require more stable operations in a narrower operating window and thus higher-level process control where the need for human intervention is minimized.

Here, advanced process control (APC) is of paramount importance. The already available Metso Outotec Optimus advance process control system optimizes the processes in the induration furnace by means of pressure, temperature, and fan-speed control.

To enable holistic optimization of the performance of the pelletizing process, all relevant factors for energy efficiency, plant production, and pellet quality throughout the entire process need to be taken into account. The main factors are the concentrate quality, the quality of the mixing step and the green pelletizing, the bed distribution on the pallet car, and the induration process in the furnace. The final aim is to control the entire process based on online measurement of the quality (strength and metallurgical composition) of the burned pellets.

Portfolio of online digital tools covering the important steps of the pelletizing process

For the particle size measurement Metso Outotec has its technologies like the online sampling and analysis system PSI 500 R, which measures the particle size distribution (PSD) of ground concentrate, with a target of maintaining the concentrate feed quality in the optimum window. In case of deviations to the targeted PSD in the ground product the process can be adjusted either automatically or via information to the operator.

For the online quality measurement of the pellet feed mix quality our MixGuard™ is close to market launch. This system predicts the plasticity of green pellets already at the mixing stage by measuring the green mix material’s plasticity and moisture. As pellet plasticity is one determining factor for bed permeability and hence the electrical energy efficiency of the plant, the system provides valuable insight and helps with the holistic optimization of the induration furnace’s performance.

The second main parameter to determine the bed permeability is known to be the green pellet size distribution. Metso Outotec’s green pellet size measurement and control system VisioPellet is in use for many years in pellet plants all over the world. It is a pellet size-control system that measures the size of green pellets using proven camera technology installed at a pelletizing disc or drum. Based on the measurement data the plant’s process control system can optimize the rotation speed of pelletizing discs/drums, the feed rate and the water addition in real time.

The pallet cars of the travelling grate machine have paramount significance to the performance of the induration process with regard to product quality, plant availability and thus production, but also to the operational costs due to maintenance, spare part and repair requirements.

Our advanced Pallet Car Conditioning Monitoring System does acquisition, processing visualization and storage of data coming from a new designed hardware system that measures the deflection of the pallet cars, identifies missing or blocking wheels, and detects bent or missing sidewalls and grate bars.

A further step to an advanced and condition-based maintenance system for the pallet cars is the combination of the pallet car condition monitoring as described above with an automatic pallet car changing device, which is integrated in the drive station of the travelling grate.

With the conventional solution, production must be stopped for about 10 minutes to remove and replace the pallet cars. An automated pallet car changer provides a simpler, more reliable, safe and cost-effective way of extracting and inserting pallet cars in the traveling grate at only slightly reduced speed of operation.

Summary

There is no denying the fact that pelletizing will remain crucial in future for steelmaking in general and it can support the transition to green, carbon-neutral steel production.
For this, the pelletizing process needs to reduce its CO₂ footprint, this can be achieved using Metso Outotec’s NextGen Pelletizing vision, which recommends

• Further improved gas schemes

• Advanced combustion and burner technology (LowNOX, Hydrogen, alternative fuels)

• Increased plant stability and performance by advanced process control

It can be implemented either fully or in parts, depending on the customer needs, and when the need arises, it can easily upgrade also the existing plants. Our experts have shed more light on this concept in a webinar. Click this link to watch.