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 ID fan sits
- Melter
- End-port regenerator
- Reversing valve
- Dry scrubber
- ESP
- ID fan
- Chimney
The fan stands after the ESP, with a bypass damper to the original chimney so the furnace can run on natural draft during filter maintenance or a fan trip. Gas reaches the fan at 300 to 380°C with a hot ESP, or 180 to 230°C if a waste heat boiler cools it first. Total suction is typically 150 to 300 mmWC. Crown pressure is held slightly positive, and reversal every 20 to 30 minutes causes a short pressure swing that the fan control must absorb.
Gas at the ID fan
| Gas temperature, normal | 300 to 380°C after a hot ESP; 180 to 230°C after a waste heat boiler |
| Maximum or upset | Up to 500°C when gas cooling or the boiler is bypassed |
| Dust at the fan | Fine sodium sulphate and lime, below about 30 mg/Nm³ after the ESP |
| Moisture and dew point | About 10 to 15% water; dew point 50 to 55°C |
| Corrosive species | SO₂, SO₃, HCl and HF; acid dew point roughly 140 to 170°C |
| Density at the design temperature | About 0.58 kg/m³ at 340°C, 48% 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. |
ID Fan selection for container glass furnaces
| Blade form | Backward inclined, robust and tolerant of light deposits |
| Material of construction | Boiler quality plate up to about 380°C; heat-resisting steel impeller where the bypass upset exceeds that |
| Drive and arrangement | Direct coupled, arrangement 8, sliding supports |
| Bearings and cooling | Cooling disc, heat shield and oil or water cooled bearings |
| Flow control | Variable speed drive on crown pressure, coordinated with the chimney bypass |
| Also specified | Standby fan or bypass path, cleaning doors, full insulation and slow turning gear |
What this ID fan has to cope with
Deposits from cullet contamination
External cullet brings labels, food residues, plastics and metal. These add organics, chlorides and lead or other metals to the waste gas, producing finer and stickier dust than clean batch alone. When the ESP is upset, deposits build on the impeller quickly. Cleaning doors, a blade shape that sheds dust and monitoring vibration trend catch the build-up early.
Reversal pressure swings
End-port furnaces reverse every 20 to 30 minutes. The firing pauses and the gas path changes, and crown pressure jumps. If the ID fan control is slow or over-tuned, it hunts after each reversal. Feed-forward from the reversal signal and a fan with smooth response at the operating point keep the crown steady.
Acid attack during ESP outages
When the ESP is off and the furnace switches to chimney draft, the idle fan and ducts cool, and SO₃ condenses as sulphuric acid on the casing and impeller. Isolation dampers that seal well, a warm air purge or slow rotation, and full insulation protect the idle fan, and it should be dried out before restart.
Energy and control
Container glass furnaces change pull rate with job changes on the forming machines and with colour changes. An ID fan on a variable speed drive follows these changes and the gradual fouling of regenerators. Correct crown pressure also stops air infiltration through the port necks and doghouse, which saves fuel and helps foam and colour control.
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 Forced Draft (FD) Fan for container glass furnaces.
Questions buyers ask
Why does a container glass furnace need an ID fan if it has a chimney?
The chimney was sized for the regenerators alone. Adding a dry scrubber and ESP adds 100 mmWC or more of resistance that the chimney cannot provide on its own. The ID fan supplies this extra draft, while the chimney stays as the bypass path for filter maintenance and for emergencies if the fan trips.
What temperature should the ID fan on a container glass furnace operate at?
Typically 300 to 380°C after a hot ESP, or 180 to 230°C after a waste heat boiler. The gas should always stay above the acid dew point, roughly 140 to 170°C on a sulphate-fined furnace, so ducts and the fan casing must be fully insulated.
How does high cullet use affect the ID fan?
More cullet saves energy and lowers the gas volume per tonne of glass, but external cullet brings contaminants. The waste gas then carries more chlorides, organics and fine dust, which are sticky and corrosive. The fan needs cleaning access, robust blades and protection against acid condensation, and the ESP needs to stay efficient.
Information needed to quote an ID fan for container glass furnaces
- Duty point. Gas volume in m³/h or Am³/h at the fan inlet and the static pressure the fan must develop, with the margin you want on each.
- Gas condition. Normal and maximum gas temperature at the fan, dust loading after the collector, moisture and any acid gases such as SO₂ or HCl.
- System. Boiler or furnace capacity and fuel, collector type and its pressure drop, and the existing fan curve or nameplate if this is a replacement.
- Mechanical. Drive arrangement, flow control (damper, inlet vanes or variable speed drive), rotation and discharge orientation, and a layout drawing or site photograph.
- Furnace and pull. End-port, cross-fired or oxy-fuel, pull in tonnes per day and cullet ratio.
- Bypass arrangement. How the chimney bypass works and the gas temperature in bypass mode.
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.