Axial Fans for Steel Plants: Ventilation, Heat Removal and Cooling Duties

Steel plants are among the hottest and dustiest industrial buildings, and their ventilation is a heat problem first. Melt shops, reheating furnaces, and hot rolling mills release large amounts of sensible heat into tall, open bays, and workers, electrical equipment, and structures all suffer if that heat is not removed. Axial fans are the right tool for much of this: high-volume ventilation, heat removal, and equipment cooling at low to moderate resistance. They are not the right tool for the furnace and dedusting gas streams, and being clear about that boundary is the first step to a sound specification.

Where Axial Fans Fit in a Steel Plant

Area	Typical duty	Fan type
Melt shop and rolling mill bays	Roof and wall extraction, heat removal, make-up air	Axial
Reheating furnace and hot-strip areas	Bay ventilation, worker cooling	Axial
Electrical and hydraulic rooms	Cooling and pressurisation with clean air	Axial
Motor, gearbox, and equipment cooling	Local air supply	Axial
Cooling towers and water-cooling systems	Forced or induced draught, small towers	Axial
Dust-collector houses and transfer stations	Building ventilation	Axial
Furnace fume extraction and dedusting	Hot, dust-laden gas through filters	Centrifugal
Combustion and process gas	High-pressure, hot gas	Centrifugal

The last two rows are important. Furnace and dedusting fans move hot, abrasive, dust-laden gas through high-resistance filter systems, and centrifugal fans with wear protection are the standard answer. Our axial versus centrifugal guide explains why.

Heat Removal in a Rolling Mill Bay: A Worked Example

The airflow needed to carry away a given sensible heat load is:

Airflow = heat load ÷ (air density × specific heat × allowed temperature rise)

Example. A rolling mill bay gains 1,200 kW of sensible heat. You allow an 8 K temperature rise between supply and exhaust air, and use 1.15 kg/m³ and 1.006 kJ/kg·K.

Airflow = 1,200 ÷ (1.15 × 1.006 × 8) = 129.7 m³/s, or about 466,800 m³/h.

That is well beyond one fan. Our axial fans reach 185,000 m³/h each, so this duty is naturally split across several roof or wall fans, for example three fans of about 155,600 m³/h each, or four fans of about 116,700 m³/h each to allow one to be out of service without losing the bay. Splitting the duty adds redundancy, allows staged control, and puts the extraction where the heat is. See how to size an axial fan.

Ambient Heat Changes the Numbers

Steel plants in hot regions may see outdoor air at 45 to 50 °C. Air density then falls, and so does the pressure a fan develops at a given speed. At sea level and 45 °C, density is about 92% of standard, so a fan selected from a standard-air catalogue develops 8% less pressure than rated. Heat removal by air is also less effective, since the air entering the bay is already hot, which limits the temperature rise you can allow. Always select from density-corrected curves and state the design ambient temperature. See fan laws and air density.

Roof Extraction and Natural Ventilation

Hot bays create strong buoyancy, so many steel plants use roof ventilators and natural ventilation, supplemented by fans. Fans help when natural forces are weak, in still air or when heat loads are highest. When designing:

• Provide low-level make-up air. Extraction needs an inlet. Without enough openings, fans cannot achieve their duty and may draw air backward through unintended paths.
• Place extraction near the heat. Removing hot air at the roof above the source works better than diluting the whole bay.
• Account for wind. Wind pressure on roof fans can oppose flow. Use suitable cowls and check performance in wind.
• Use backdraught shutters so idle fans do not let outside air, or hot air, flow back.

Dust and Deposits

Steel plants generate scale, iron oxide dust, and fume. Axial fans handling building air should have suitable guards, cleanable impellers, and, where dust is heavy, pre-filtration or a location away from the worst dust. Dust builds up on blades unevenly, causing unbalance and vibration. Plan for cleaning access and monitor vibration. See axial fan vibration, balancing and maintenance.

Cooling Electrical and Hydraulic Rooms

Electrical rooms and control rooms need clean, cool air, and often positive pressure to keep dust out. Axial fans with filtered inlets, sized with the filter resistance in the system curve, serve this well. Filters raise resistance as they load, so check the fan at fouled resistance and stay clear of stall.

High-Temperature Duty

Some steel plant duties involve hot air near furnaces. A standard fan is not automatically suited: motor, bearings, materials, and coatings all have temperature limits. If the gas is hot, consider a motor outside the airstream and high-temperature materials. Our guide to high-temperature axial fans sets out the options. Smoke-extraction duty is different again and needs a certified class.

Noise

Roof fans over large numbers of workers, and fans near plant boundaries, may need noise limits. Larger fans running slower reduce noise and energy. See axial fan noise.

Where Our Range Fits

NextAir Systems manufactures axial fans with impeller diameters up to 1,600 mm, static pressure up to 2,400 Pa, and air volume up to 185,000 m³/h. That covers bay and roof ventilation, electrical and hydraulic room supply, equipment cooling, and small cooling systems in a steel plant. It does not cover furnace fume extraction, dedusting, or process gas fans, which are centrifugal fans outside what we build.

What to Specify

1. Heat load and allowed temperature rise, or air changes required.
2. Design ambient temperature and altitude, for density correction.
3. Dust load and whether filters or pre-filters are needed.
4. Number of fans, redundancy requirement, and control approach.
5. Mounting: roof, wall, or duct.
6. Noise limits.
7. Any high-temperature or corrosive conditions.

Get a Fan Selection for Your Steel Plant

Send your bay dimensions, heat load, and site conditions, and we’ll size the fans and confirm the arrangement. Contact us for a free quote.

Frequently Asked Questions