A 250-ton-class gas-fired aluminum melting furnace typically ships as a 7000 (L) × 5000 (W) × 3500 (H) mm cell with 8 high-speed auto-control burners on compressed natural gas (CNG), refractory-fiber shell insulation over a refractory-brick hearth, and a PLC plus instrument-meter control loop, per manufacturer datasheet [S1].
Inside dimensions of 7000 × 5000 × 3500 mm and a 1200°C rated temperature define the envelope engineers must clear during foundation, gas-train, and chimney layout, while the 250 t max charge and CNG fuel source set the supply, exhaust, and safety-relief sizing [S1]. For background on the equipment family, see the aluminum melting furnace encyclopedia entry and the gas-fired aluminum melting furnace types and classifications reference.
Cell Footprint, Foundation, and Steel Frame
The 7000 × 5000 × 3500 mm inside dimensions of a 250-ton-class gas-fired aluminum melting furnace correspond to a foundation pad roughly 8500–9000 mm long and 6500–7000 mm wide once burner quarl projections, door swing, and a 600–900 mm service aisle are added, and the steel-bar-and-plate frame is designed to carry the refractory plus a 250 t hydrodynamic load on the hearth [S1].
Foundation concrete should be a minimum 3000 mm-deep mat with rebar at 150–200 mm centers, finished flat to within ±3 mm over the hearth footprint; a 50 mm isolating cork or ceramic-fiber expansion joint separates the frame base from the concrete so thermal growth of the shell does not load the foundation. Embed 12 mm anchor plates at 400 mm centers on a 600 mm grid before the pour so the frame can be grouted and shimmed after the concrete reaches 28-day cure. Field engineers routinely allow 600–900 mm of clearance on the loading side for ladle swing, and 1200 mm on the burner side for tube withdrawal, based on standard industrial furnace cell practice.
Refractory Stack-Up: Fiber Lining Over Brick Hearth
The reference build uses a refractory-fiber lining on walls and roof with a refractory-brick hearth, paired to a 1200°C rated set point so that the hot face sees ceramic-fiber blanket or board rated for at least 1260°C and the hearth carries 250 t of molten aluminum through a high-alumina or magnesia brick course [S1]. The general fired-brick properties reference applies when sizing hearth courses.
The hearth is normally 300 mm of high-alumina (70–80% Al₂O₃) brick on a 50 mm calcium-silicate board, with a 20 mm ceramic-paper expansion allowance at the perimeter. After installation, the lining must be brought up on a controlled cure ramp: room temperature → 200°C at 30°C/h hold 4 h to drive moisture, → 600°C at 40°C/h hold 4 h, → 1200°C at 50°C/h hold 8 h before the first metal charge. Skipping the 200°C moisture hold is the single most common cause of steam-driven spalling on a new hearth.
Burner Layout, Gas Train, and Combustion Air
Eight high-speed auto-control burners on CNG are arranged in opposed pairs along the long axis, four per side wall, fed through a single manifold with individual motorized ball valves and ratio-controlled combustion-air blowers, per the reference spec sheet [S1].
The gas train upstream of each burner must carry a manual ball valve, a solenoid valve, a high-/low-pressure regulator set 20–50 kPa, a leak-test cock, a flame-rod igniter, and a UV or ionization flame scanner, in that order. CNG supply is normally regulated down from 0.4–0.8 MPa district pressure to 10–20 kPa at the burner throat; a venturi zero governor holds a stable gas-to-air ratio across the 1:10 turndown that high-speed burners typically need. Combustion-air preheat to 300–450°C from the flue gas raises thermal efficiency by roughly 8–12 percentage points and lowers flame temperature peaks that otherwise damage the fiber lining.
Control Architecture: PLC Plus Instrument Loop
The reference unit uses a computer control system plus instrument-and-meter layer with a PLC supervising the bath thermocouples, furnace pressure transmitter, oxygen probe, and the eight burner modulation loops, allowing automatic ratio control and recipe-based charge/hold cycles [S1].
At minimum, the I/O list should cover: 8 zone thermocouples (S-type for the bath, K-type for flue and preheat), 1 furnace pressure transmitter (–50 to +50 Pa range), 1 flue O₂/CO lambda probe, 8 burner enable and 8 flame-status discretes, 8 fuel valve position feedbacks, plus a hardwired safety chain (gas-pressure switch, air-pressure switch, door interlock, emergency stop, and UV scanner loss-of-flame) wired through a safety relay that drops the gas train within 1 s of a fault. The PLC and HMI should log 1-Hz trends for bath temperature, O₂, and pressure for at least 30 days, and the door interlock must be proven closed before any burner is allowed to fire. For comparison with the gas-fired aluminum melting furnace types and classifications reference, this control package sits in the high-end PLC tier, not the simple PID-only tier.
Door, Trolley, and Loading Interface
Loading and unloading convenience plus air-tight performance are listed as the unit's key advantages, and the design pairs a heavy-roller car-bottom trolley with a guillotine-type door that seats against a refractory-fiber gasket to limit infiltration at the 1200°C set point [S1].
Acceptance criteria at cold start: door drop time ≤8 s, gasket compression 8–12 mm, and furnace pressure held within ±10 Pa of –20 Pa set point under natural-draft conditions. Infiltration air above 100 Nm³/h per square meter of door opening pulls flame toward the door, increases NOx, and cools the bath — the most common field problem on this furnace type. Trolley rails should be set to 1435 or 1524 mm gauge on 60 kg/m rail with welded joints ground flush, and the car-bottom refractory should be a single hot-face course of 70% alumina brick to match hearth thermal mass.
Commissioning, Acceptance, and First-Metal Protocol
Commissioning must verify flame stability on each of the 8 burners, bath-temperature uniformity within ±15°C across all 8 zones, furnace pressure at –20 Pa, and O₂ at 2–4% in the flue, before the first aluminum charge is admitted to a hearth that has completed the 1200°C hold from the refractory cure ramp [S1].
If bath uniformity exceeds ±20°C, ratio or burner-staging tuning is required before the next charge. Refractory life on this build typically runs 18–36 months on the wall fiber and 5–10 years on the hearth brick, depending on flux chemistry and bath turnover. Track the next two signals: burner-tuning baseline against 8-hour hold temperature spread, and lining hot-face temperature after the first 100 hours of operation, both of which predict refractory service life and burner-nozzle maintenance intervals.
Component reference pages worth checking: gas aluminum melting furnace.