How container glass furnaces work
Container glass furnaces melt soda-lime glass for bottles and jars, usually in end-port regenerative furnaces of 150 to 400 tonnes per day, with recuperative and oxy-fuel furnaces on some lines. Batch is sand, soda ash, limestone, dolomite and a high share of cullet, often 40 to 80%, with sodium sulphate as fining agent. Melting runs at about 1,500 to 1,550°C, firing alternating between the two ports every 20 to 30 minutes. Waste gas leaves the regenerators at 450 to 550°C carrying sodium sulphate, SO₂ and traces of HCl and HF. Modern lines add dry or semi-dry scrubbing with hydrated lime and an ESP, sometimes a waste heat boiler, with the ID fan after the ESP.
Where the FD fan sits
- Inlet filter
- FD fan
- Air flow measurement
- Reversing valve
- Regenerator
- Port and melter
The fan stands near the reversing valve at the regenerator base. It blows ambient air into whichever regenerator is on air at the time, where the hot checkers heat it to 1,100 to 1,250°C before it reaches the port. The fan pressure is moderate, typically 150 to 300 mmWC, because the checkers are large and open. Flow is measured in the cold duct after the fan and ratioed to the fuel.
Air at the FD fan
| Air temperature at the fan | Ambient, 25 to 45°C |
| Air after the regenerator | 1,100 to 1,250°C, downstream of the fan |
| Dust | Batch dust in the furnace hall; filtered intake |
| Pressure at the fan outlet | Typically 150 to 300 mmWC |
| Duty pattern | Continuous, switching sides every 20 to 30 minutes |
| Density at the design temperature | About 1.13 kg/m³ at 40°C, 94% of standard air. Pressure developed and power drawn scale with density, so the fan is selected at this condition and the motor is checked at the coldest operating or start-up condition. |
FD Fan selection for container glass furnaces
| Blade form | Backward curved, with a stable curve for accurate flow |
| Material of construction | Mild steel |
| Drive and arrangement | Direct coupled, with a standby fan |
| Bearings and cooling | Standard bearings with vibration and temperature monitoring |
| Flow control | Variable speed drive on measured air flow, ratioed to fuel |
| Also specified | Inlet filter, silencer, automatic changeover and emergency power |
What this FD fan has to cope with
Redox and colour shifts
In container glass the oxygen available in the flame affects redox state and colour, particularly in amber and green glass. Uneven air delivery after each reversal or slow drift of the fan output changes the ratio. Accurate flow measurement and closed loop speed control keep the air steady.
Regenerator leakage
Cracks in the regenerator walls let combustion air leak to the waste gas side, so the measured air does not all reach the flame. The fan then has to supply more, and the furnace runs short of air. Checking fan output against flue gas oxygen identifies leakage.
Standby fan not ready
A standby fan that is never run tends to be found with a seized or brinelled bearing on the day it is needed. Scheduled changeover runs, a vibration check on each and keeping the changeover damper free make sure the standby can take over without disturbing the furnace.
Energy and control
The combustion air fan runs throughout the campaign. Variable speed control on measured air flow cuts power during reduced pull, job changes on the forming machines and colour changes. Holding excess air to the minimum that keeps combustion complete saves fuel in the melter and limits NOx, which matters far more than the fan's own electricity.
ID fan and FD fan in container glass furnaces
| ID fan | FD fan | |
|---|---|---|
| Position | After the ESP, with a chimney bypass | Before the reversing valve and regenerator |
| What it handles | Waste gas with sulphate dust and acids | Ambient filtered air |
| Temperature at the fan | 180 to 380°C | Ambient |
| Main design concern | Deposits and acid dew point | Accurate, steady air flow |
| Control | Crown pressure | Air flow ratioed to fuel |
See also the Induced Draft (ID) Fan for container glass furnaces.
Questions buyers ask
What is the combustion air fan on a container glass furnace?
It is the forced draft fan that supplies all the air for combustion. On an end-port container glass furnace it blows ambient air through a reversing valve into the regenerator that is on the air cycle, where the hot checkers preheat the air before it reaches the burner port and meets the fuel.
How is combustion air controlled on a regenerative glass furnace?
Air flow is measured in the cold duct after the fan and controlled by fan speed or a damper, in ratio to the fuel flow. Flue gas oxygen at the port or regenerator top is used to trim the ratio and to check for air leakage in the regenerators.
Why does the container glass furnace FD fan need a standby?
The furnace runs continuously for years and cannot tolerate a long loss of combustion air. A standby fan with automatic changeover keeps the furnace firing if the duty fan trips, and allows maintenance of either fan without putting the melter on a hot hold that costs production and stresses the refractory.
Information needed to quote an FD fan for container glass furnaces
- Duty point. Combustion air quantity in m³/h or kg/h and the static pressure at the fan outlet, with the margins you want.
- Air condition. Site ambient temperature range and altitude, and whether the fan takes ambient air or air already heated.
- System. Boiler or furnace capacity and fuel, resistance of the air heater, windbox, grate or burner, and the existing fan curve or nameplate if this is a replacement.
- Mechanical. Drive arrangement, flow control (damper, inlet vanes or variable speed drive), noise limit, rotation and discharge orientation.
- Air flow range. Combustion air flow at maximum and minimum pull.
- Standby requirement. Whether duty and standby fans with automatic changeover are needed.
Built and tested in Chennai
Adroit Fantech Engineers has designed and manufactured industrial fans at Ayanambakkam, Chennai since 2004. Each impeller, casing and shaft is built for the gas and temperature it will see, performance tested as per IS 4894 or BS 848 Part I, and balanced to grade G 6.3 or G 2.5 as per ISO 21940-11, with the records supplied with the fan. We also replace rotors and retrofit existing fans of any make.