CRISP Technology: Revolutionary Continuous Steelmaking Process

Introduction to CRISP Technology

Numerous advancements have transformed DRI-based steelmaking processes over the past decade. The practice of charging hot DRI directly from a Direct Reduction (DR) module to the electric arc furnace represents arguably the most significant improvement in this field. This hot charge practice delivers energy savings estimated between 20 to 30% compared to conventional cold-fed EAFs. However, the continuous discharge of hot DRI to EAF faces complications due to the batch operation nature of traditional EAFs.

The Continuous Reduced Iron Steelmaking Process (CRISP) emerges as a novel steelmaking technology developed by Hatch. This innovative system utilizes a stationary electric arc furnace to continuously melt and decarburize DRI and other metallic materials for steel production. The key distinguishing feature of CRISP technology lies in its significant modification of conventional EAF process parameters, extending refractory life beyond one year while maintaining continuous operation.

CRISP Process Flow and Design

Figure 1: Flow diagram of a CRISP plant

The CRISP flowsheet demonstrates an integrated approach where DRI production occurs in the DR or reduction furnace before feeding to the main furnace alongside scrap and iron oxide. The charge materials feed continuously into the CRISP furnace, which functions as a six in-line electrode stationary EAF. This continuously operated CRISP EAF creates a direct link between two critical processes: DRI production in the reduction furnace and continuous casting operations.

Figure 2: Schematic diagram of CRISP furnace

The decarburization of DRI occurs without gaseous oxygen, instead utilizing oxidation by slag supplied with iron oxide in the form of ore lumps, pellets, or mill scale. Since charge materials enter the furnace continuously, precise adjustment of specific material feeding rates becomes critical to ensure sufficient decarburization within the furnace. Steel and slag undergo periodic tapping through slag and metal tap-holes using an approach similar to blast furnace operations. Following steel tapping, the remaining process steps align with conventional steelmaking practices, including ladle refining and casting.

Unique Features of CRISP Technology

The essence of CRISP technology's unique characteristics encompasses several revolutionary aspects. The process enables continuous melting without downtime for charging, tapping, or fettling operations. It maintains a large liquid heel with attendant long residence time of metal within the furnace. The power density operates within the range of 300 to 500 kW/m² of hearth, representing a fraction of conventional EAF levels that typically range from 2,500 to 3,000 kW/m². Additionally, the system demonstrates the ability to decarburize to low carbon levels (> 0.04 wt% C) without requiring gaseous oxygen.

Operational Benefits and Advantages

These technological differences translate into significant operational benefits that revolutionize steelmaking efficiency. Decarburization occurs at slag FeO levels closer to equilibrium conditions, while the related improved yield provides meaningful savings in metallics costs. Furnace refractory life extends to years rather than the weeks or months typical of conventional systems.

The high furnace availability approaches 8,000 hours annually, leading to improved plant logistics and better matching with upstream and downstream facilities. Arc shielding utilizes the foaming slag inherent to continuous DRI melting, while low gas velocity in the furnace freeboard significantly reduces dust carryover from the furnace. This reduction not only decreases dust disposal costs but also enables the charging of fine materials to the furnace as a cost-effective measure.

Energy Efficiency and Environmental Impact

The total specific energy requirement encompassing power, oxygen, natural gas, and carbon remains lower than conventional EAF operations. In comparative analysis, CRISP achieves 610 kWh/tonne liquid steel versus 756 kWh/tonne liquid steel for conventional systems. The continuous nature of CRISP operation, combined with furnace design, allows capture and utilization of furnace off-gas as fuel gas.

The steady, even furnace power load characteristic of continuous CRISP operation reduces demands on electrical utility grids while enhancing the feasibility of connecting to captive power plants. Furthermore, the process demonstrates a significantly lower greenhouse gas (GHG) footprint and particularly reduced NOx emissions compared to conventional steelmaking methods.

This revolutionary approach to steelmaking represents a significant advancement in the industry, offering enhanced efficiency, reduced environmental impact, and improved economic performance through continuous operation and optimized energy utilization.