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Lean improvement case to improve the quality rate of steelmaking lime – to steel

In recent years, the average pass rate for raw stone has been only 67.84%, with the lowest being 37.04%. These raw stone quality issues directly lead to fluctuations in the quality of steelmaking lime, which not only makes dephosphorization in the converter difficult but also increases flux consumption for slagging and dephosphorization.

To address this challenge, a research team was established in the raw materials area. With the core goal of “improving the pass rate of steelmaking lime quality,” they achieved a quality breakthrough through systematic analysis and targeted policy implementation.

Problem Analysis

1. Low calcium oxide content in raw stone: A comparison of the quality pass rates of raw stone and steelmaking lime revealed a correlation coefficient of 0.96 (highly correlated). Substandard raw stone directly leads to substandard finished product quality, and this cannot be completely corrected by later measures such as increasing coal gas.2. Lack of standardized calcination parameters: Minor differences exist in the belt weighing, pusher hydraulics, and dust removal systems of the four rotary kilns in the plant. Actual kiln conditions vary greatly, but the process only provides basic parameters, requiring adjustments based on the experience of the main firing operators. Furthermore, the main firing experience of the four shifts is inconsistent, resulting in frequent parameter changes after shift handovers, leading to quality fluctuations.3. Inadequate quality supervision and traceability: The rotary kiln’s quality management is extensive, with a low percentage of quality performance and weak quality awareness among personnel. A lack of professional personnel on the day shift to track quality issues has left recurring issues unresolved, preventing a closed-loop improvement process.

Improvement measures

1. Improve the qualified calcium oxide content of raw stone from 70.46% to 80.00%. Clarify raw stone quality requirements, promptly report quality objections to unqualified raw stone, promote targeted improvements at the mine, revise the raw stone quality deduction rules, reduce quality losses, supplement the procurement of high-quality Benxi limestone, and optimize the overall quality structure of raw stone.2. Establish a universal and efficient calcination parameter system to achieve unified and standardized management of calcination parameters for four rotary kilns. Focusing on the five core parameters of “push rod frequency, gas volume, air volume, kiln speed, and environmental protection indicators,” multiple sets of comprehensive experiments were conducted to identify the optimal control indicators for different kiln conditions. This “Rotary Kiln Calcination Parameter Setting Table” clarified the parameter adjustment ranges for different kiln conditions, replacing “reliance on experience” and avoiding frequent parameter changes between shifts.3. Improve the quality supervision and traceability system, establishing a closed-loop quality tracking and rectification process. Add “raw material quality management” personnel to be responsible for the quality supervision of rotary kiln lime, problem tracking and improvement promotion; establish a “weekly inspection” mechanism to conduct special inspections on the quality operation of the rotary kiln every week, and immediately urge rectification when problems are found; establish a record of unqualified steelmaking lime quality, record the cause, treatment measures and rectification effect of each quality problem, so that problems can be traced and improvements can be verified.

Achieve results

By August 2025, all corrective measures had been fully implemented, significantly improving the quality of steelmaking lime: the qualified rate increased from an average of 67.84% in 2023-2024 to 81.82%, successfully achieving the research target. This research not only solved the dephosphorization problem in the converter and reduced flux consumption, but its “raw material control + parameter standardization + closed-loop quality” model was also replicable, providing a scalable quality improvement solution for similar rotary kiln lime production and providing strong support for cost reduction and efficiency improvement.#steelmaking#tosteelprocess

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Lean improvement case to improve the quality rate of steelmaking lime – to steel

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