Coating direct reduced iron (DRI) with lime slurry is a key step in the steelmaking process, playing an important role in preserving material quality and ensuring safety. Due to its high porosity and high metallic iron content, DRI is prone to re-oxidation, self-heating, and even spontaneous combustion during storage and transport. A thin lime coating on the surface of DRI granules forms a protective layer that prevents direct contact between oxygen/moisture and the metallic surface, slowing the oxidation rate and significantly reducing the risk of fire in silos and during shipping. In addition, lime helps reduce inter-particle stickiness and improves material flowability within conveying systems.

The lime supply process begins at a lime storage silo, which holds the raw material in bulk. To prevent bridging and flow interruption at the silo's discharge outlet, a bin activator is installed at the bottom of the silo, using controlled vibration of its conical chamber to ensure a uniform, continuous discharge of lime. Along the outlet path, a manual slide gate is provided for line isolation during maintenance operations, and a pneumatic slide gate enables automatic, controlled charging of the downstream weighing system; whenever the material level in the weighing hopper drops to a set threshold, the pneumatic gate automatically receives an open command and refills the hopper.

Lime discharged from the silo enters a loss-in-weight feeder system, responsible for the precise, controlled dosing of lime based on the actual consumption rate. By continuously monitoring the weight loss of its hopper, this system regulates the lime discharge mass flow rate with high accuracy. Critically, this dosing is coordinated with data received from the belt scale installed on the conveyor carrying the DRI. The belt scale continuously measures the mass flow rate of DRI passing through and transmits this data to the central control system (PLC), which calculates the required lime-to-DRI ratio and issues a command to adjust the loss-in-weight feeder's speed accordingly. This continuous communication between the two weighing systems ensures that the lime-to-DRI ratio remains constant and optimal under all operating conditions and production rate variations, preventing both excess and insufficient lime dosing.

Lime, dosed at the precisely regulated rate from the loss-in-weight feeder, enters the mixing tank to be combined with water and form the lime slurry. At this stage, a flow meter installed on the water inlet line measures the water flow rate entering the tank and reports it to the control system; by combining the lime input rate data (from the loss-in-weight feeder) with the water input rate data (from the flow meter), the precise lime-to-water ratio is maintained according to the defined formulation. The mixing tank's internal agitator homogenizes the slurry, which is then discharged evenly through a multi-channel outlet trough onto the DRI moving along the conveyor belt below. This precise coordination between the lime weighing, DRI weighing, and water control systems ensures that the lime coating is applied with uniform concentration and thickness across the entire material surface, achieving the desired protective quality for subsequent storage and transport processes.