1. Equipment Overview
The Blast Furnace (BF) molten slag modification furnace,
categorized as submerged-arc modification furnace, directly
receives hot liquid blast furnace slag at over 1,350°C. Modifying
agents with silica-alumina composition are fed online to adjust
slag basicity, chemical composition, temperature and viscosity of
molten slag. The homogenized melt is further processed into rock
wool, slag wool, glass-ceramic or recycled aggregate, realizing
waste recycling and full utilization of high-temperature residual
heat from molten blast furnace slag. Two mainstream types are
available: three-phase AC submerged-arc furnace and DC modification
furnace, structurally divided into integrated single-chamber type
and dual-chamber type (charging compartment + homogenizing
compartment).
2. Complete Equipment Composition (5 Core Systems)
2.1 Main Furnace Body System
- Furnace Shell: Welded cylindrical or square steel structure
equipped with external water-cooling coil or spray cooling. Outer
diameter ranges Φ3,600～Φ5,200 mm with overall height 2,200～3,200
mm.
- Refractory Lining: Multi-layer masonry structure: light
high-alumina castable for thermal insulation layer,
corundum/chrome-corundum ramming mix for working layer against
corrosion from blast furnace slag. Furnace chamber is partitioned
into feed modification zone and molten pool homogenization zone by
partition wall with liquid through-hole and water-cooled sliding
gate.
- Material Inlet & Outlet
- Hot Slag Inlet: Water-sealed chute on furnace top/sidewall
connecting BF slag runner for gravity feeding of liquid hot slag;
- Modifier Feeding Port: Sealed feed opening on furnace top coupled
with dust containment;
- Main Tapping Hole (water-cooled copper fitting): Lower sidewall for
continuous controlled melt feeding to fiber forming line;
- Iron Discharge Outlet: Bottom drain for periodic removal of
precipitated iron granules and iron-bearing residues.
2.2 Electrode Power Supply System (Core Heating Unit)
- Electrodes: Φ350～Φ500 mm graphite electrodes (3pcs for 3-phase AC,
2pcs for DC type) with servo hydraulic lifting control;
- Special furnace transformer: On-load tap-changing transformer with
electrically regulated grading voltage, power rated per furnace
capacity;
- Short-net copper busbar, water-cooled electrode clamps and full set
of hydraulic lifting cylinders.
2.3 Automatic Modifier Batching System
Consists of sealed storage silos, variable-frequency belt/spiral
loss-in-weight feeders and negative-pressure dust-proof enclosure.
Modifiers (quartz sand, fly ash, bauxite, waste refractory) are
dosed precisely with blending ratio: hot slag 85～95% : modifier
5～15% by mass.
2.4 Molten Bath Homogenizing System
- Arc self-stirring: Molten pool agitated by electric arc
disturbance;
- Bottom nitrogen bubbling system: Pre-buried permeable bricks inside
furnace bottom + high-pressure nitrogen pipeline, nitrogen pressure
0.2～0.4 MPa for forced homogenization of slag and additives;
- Optional carbon mechanical stirring impeller for large-capacity
furnaces.
2.5 Auxiliary Supporting Systems
Circulating water cooling system, top baghouse dust collection
system, PLC full-automatic control system for temperature, liquid
level and power, water-cooled tapping chute, infrared +
thermocouple dual on-line liquid level monitoring.
3. Standard Technical Parameters by Production Capacity
| Item | Small Unit (1.5t/h) | Medium Unit (5～8t/h, mainstream for rock wool line) | Large Unit (12～15t/h) |
|---|
| Effective Furnace Volume | 1.8m³ | 5.5～7.5m³ | 12m³ |
| Rated Transformer Capacity | 1250kVA | 3150～5000kVA | 8000kVA |
| Graphite Electrode Dia. | Φ350mm | Φ450mm | Φ500mm |
| Inner Furnace Diameter | Φ2800mm | Φ3800～4200mm | Φ4800～5200mm |
| Molten Pool Depth | 1200mm | 1600～1800mm | 2000mm |
| Outer Furnace Shell Dia. | Φ3600mm | Φ4400mm | Φ5300mm |
| Power Consumption | 420～500kWh/t slag | 330～400kWh/t slag | 300～360kWh/t slag |
4. Core Process Control Parameters
4.1 Temperature Parameters
- Incoming BF hot slag temp.: 1,320～1,380°C;
- Target tapping temp. after modification: 1,360～1,420°C (optimal
1,380±20°C for rock wool production);
- Furnace holding temperature range: 1,350～1,450°C; electrodes supply
supplementary heat to offset temperature drop caused by cold
modifiers.
4.2 Chemical Composition & Acidity Coefficient (Mk)
- Raw BF slag basicity (CaO/SiO₂): 0.9～1.0;
- Target acidity coefficient Mk=(SiO₂+Al₂O₃)/(CaO+MgO): 1.25～1.55
(1.4～1.5 preferred for mineral wool);
- Modifier chemical index: SiO₂=45%～75%, Al₂O₃=8%～35%, feed particle
size ＜0.1 mm.
4.3 Physical Properties of Molten Slag
- Tapping viscosity: 1.2～4.0 Pa·s (optimal 1.5～2.5 Pa·s for
fiberization);
- Allowable liquid level fluctuation: ≤±80 mm to guarantee stable
continuous tapping;
- Nitrogen bubbling pressure: 0.25～0.35 MPa, homogenization duration
≥35 min for uniform composition.
4.4 Material Proportion Index
- Modifier adding ratio: 5%～15% by mass, max blending rate up to 30%;
- Raw slag iron content: ＜3%, accumulated bottom iron discharged per
shift intermittently.
5. Equipment Operational Advantages
- Waste Heat Recovery: Rely on inherent high sensible heat above
1300°C of BF slag; electrodes only supply supplementary power,
saving over 50% power vs cold-feed cupola furnace;
- Continuous Feeding: Direct hot slag feeding without ladle transfer,
minimizing heat loss and raising incoming slag temperature by
around 30°C compared with tank transportation process;
- Full Automation: PLC interlocked control for batching, power
regulation, temperature and tapping flow, one-click formula
modification available;
- Eco-friendly Design: Fully enclosed feeding + top dust collection,
zero unorganized flue gas emission, 100% solid waste resource
utilization.
6. Selection Suggestions
- On-line tapping matched with blast furnace: adopt continuous
single-chamber modification furnace; intermittent ladle-delivered
hot slag: dual-chamber furnace with dedicated molten storage tank;
- High-grade rock wool production: DC modification furnace for
superior uniform bath temperature and stable chemical composition;
ordinary slag wool: 3-phase AC furnace for lower investment cost.
