In blast furnace tapping operations, the flame color at the taphole serves as a critical visual signal for furnace foremen to assess furnace conditions. The distinction between “white” and “red” flames not only reflects variations in furnace temperature and airtightness but also directly impacts the sintering quality of taphole clay and the effectiveness of taphole maintenance. This article systematically examines this issue from four perspectives—procurement needs, industry research, procurement guide, and supplier comparison—offering reference for ferroalloy enterprises in their selection of taphole clay.
Changes in taphole flame color essentially reflect variations in temperature field and atmosphere within the taphole channel, which are direct manifestations of taphole clay sintering performance.
When the taphole flame appears white or bright white, it typically indicates high hot metal temperature (approximately above 1450°C), with ample hearth heat and good permeability. For taphole clay, this means:
Ideal sintering conditions: The high-temperature environment enables silicon carbide, carbon, and other components in the clay to fully oxidize and sinter, forming a dense refractory layer;
Stable taphole depth: The clay rapidly cokes under high temperature, enhancing erosion resistance and facilitating maintenance of taphole depth;
Smooth tapping: Stable iron flow, with average flow rate ideally within the range of 3.0–4.5 tons/minute.
Procurement Implication: If the site consistently exhibits white flames, it indicates normal furnace conditions, requiring moderate sintering speed from the clay. Procurement should prioritize high-temperature flexural strength and erosion resistance to prevent “runout” under sustained high temperatures.
A red or dark red flame often indicates low furnace temperature or “chilled” tuyeres. Under such conditions:
Insufficient sintering drive: The clay cannot fully sinter at lower temperatures, prolonging coking time and leaving the taphole weak after opening;
Risk of taphole splashing: Insufficiently sintered clay has a loose structure, allowing gas channeling around the taphole, resulting in damp clay splashing during tapping and deteriorating the working environment;
Declining taphole depth: Poorly sintered clay offers weak erosion resistance, causing taphole depth to decrease from opening to the end of tapping, and in severe cases, eroding the taphole furnace wall.
Procurement Implication: For blast furnaces with fluctuating thermal conditions, choose clays with faster coking speed and appropriate Marsh value (plasticity index), capable of achieving adequate strength even at lower temperatures. Simply increasing binder content to lower the Marsh value is inadvisable, as it extends coking time and worsens splashing.
Industry research indicates that clay selection should not adopt a “one-size-fits-all” approach; rather, performance should be matched to the furnace’s specific campaign stage.
In the early campaign stage, blast temperature and pressure are relatively low, hearth activity around the taphole is limited, and refractory moisture needs gradual expulsion. Clay faces two conflicting demands: a lower Marsh value for ease of mud injection, and faster coking speed to avoid splashing.
Recommended Direction: Opt for splash-suppressing taphole clay, striking a balance between reducing Marsh value and accelerating coking speed, gradually eliminating gas channeling at the taphole.
Once the furnace enters stable production, smelting intensity is high and tapping is frequent, with accelerated erosion around the taphole area. Taphole depth qualification rate and full-blow plugging rate become core performance indicators.
Industry Trend: During the stable production stage, clay procurement should prioritize cost-effectiveness rather than lowest bid. Clay quality should not fluctuate significantly due to changes in raw material batches, seasons, or ambient temperature.
In the late campaign stage, hearth refractory erosion is severe, with the taphole area relying on clay pads and slag crusts for protection. If the clay’s erosion resistance is insufficient, the clay pad cannot form effectively, endangering cooling stave safety and, in extreme cases, leading to hearth breakouts.
Technical Frontier: For abnormal temperature rises in cooling staves around the taphole area, vanadium-titanium-bearing clays may be selected. Vanadium and titanium compounds in the clay form TiN and TiC near the taphole, providing enhanced hearth protection.
Integrating flame color assessment with furnace campaign stage considerations, the following technical indicators should be prioritized in clay procurement:
Based on common industry tender standards:
| Parameter | Reference Value |
|---|---|
| Al₂O₃ | ≥20% |
| SiO₂+Si | ≥28% |
| SiC+C | ≥20% |
Taphole depth: Typically ≥2400–2500mm depending on furnace volume, with qualification rate ≥90%;
Opening performance: Opening time <10 minutes, no layering, no splashing, smooth mud injection;
Tapping time and flow rate: Stable iron flow, instantaneous flow rate <5 tons/minute, average flow rate 3.0–4.5 tons/minute;
Storage stability: On-site storage of waterless clay should support ≥15 days of normal production; water-bearing clay should be in sealed small bags to ensure it remains usable for 20 days without hardening.
Modern steel plant clay procurement has shifted from simple product purchasing to turnkey service contracts. Suppliers should demonstrate:
Strong supply capacity and proven track record of stable delivery;
On-site technical guidance and follow-up service;
Comprehensive quality assurance systems (ISO9001, ISO14001, ISO45001 certifications);
Rapid response capability to varying furnace conditions.
Ferroalloy enterprises are advised to assess potential clay suppliers across the following dimensions:
Experience in formula adjustment for different furnace campaign stages;
Availability of specialty products such as vanadium-titanium clay or splash-suppressing clay;
Understanding of the client’s specific blast furnace operating parameters.
Fluctuation range of physical and chemical indicators across batches;
Establishment of full-process quality traceability from raw materials to finished products;
Availability of third-party test reports as verification.
Provision of on-site technical support;
Ability to adjust clay performance based on real-time signals such as taphole flame color;
Rapid response and supply assurance in emergency situations.
Proven supply cases for comparable blast furnaces;
Scale of partner steel plants and user feedback;
Successful prequalification through public tendering processes.
Beifang Alloy Co., Ltd. specializes in the R&D and production of ferroalloy furnace materials and refractories, offering a product range including waterless taphole clay, trough materials, and patching materials. We provide customized clay formulations tailored to clients’ furnace campaign stages and on-site flame conditions. For more technical information or sample testing support, please visit www.beifangalloy.com or contact us at info@hnxyie.com.
