How edible oil refinery thermal oil heaters work
Edible oil refineries and vanaspati plants need heat at temperatures steam cannot easily reach: deodorisers run at 240 to 270°C under vacuum, and physical refining of palm and rice bran oil needs the upper end. Most plants use a thermal oil heater supplying fluid at 280 to 320°C, alongside a steam boiler for the lower temperature duties. The heater is a coil-type unit fired by furnace oil or gas through a forced draft burner, or by coal, wood or briquettes on a fixed or reciprocating grate. Because the fluid returns hot, the flue gas leaves the coil at 350 to 400°C and passes an air preheater or economiser to about 180 to 230°C, then a multicyclone and bag filter on solid fuel, before the ID fan and chimney.
Where the ID fan sits
- Furnace and grate or burner
- Radiant and convection coils
- Air preheater
- Multicyclone
- Bag filter
- ID fan
- Chimney
On solid fuel heaters the fan sits after the bag filter, so it handles little dust. It works against the furnace draft, the coil bank, air preheater and collectors, typically 150 to 300 mmWC. On oil or gas fired heaters with a forced draft burner, an ID fan is often not needed at all, and the chimney handles the draft unless a heat recovery unit adds resistance.
Gas at the ID fan
| Gas temperature, normal | 180 to 230°C after the air preheater |
| Maximum or upset | Up to 350 to 400°C if the air preheater is bypassed or fouled |
| Dust at the fan | Low after a bag filter; fly ash and unburnt char on briquette and wood firing |
| Moisture and dew point | Moderate; wood and briquettes give higher moisture |
| Corrosive species | SO₂ with furnace oil or coal; acid dew point about 120 to 150°C |
| Density at the design temperature | About 0.73 kg/m³ at 210°C, 61% 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 edible oil refinery thermal oil heaters
| Blade form | Backward curved on clean gas after a bag filter; backward inclined flat blades where only a multicyclone is fitted |
| Material of construction | Mild steel, with wear liners on the blade inlet for multicyclone-only plants |
| Drive and arrangement | Direct coupled or belt driven, arrangement 8 or 9 |
| Bearings and cooling | Cooling disc for the upset temperature; standard bearings |
| Flow control | Variable speed drive on furnace draft |
| Also specified | Inlet damper for start-up, insulated casing and inspection door |
What this ID fan has to cope with
Draft swings with deodoriser cycles
Batch and semi-continuous deodorisers draw heat in pulses, so firing changes quickly. A slow fan control lets the furnace go positive and smoke at the doors, which is not acceptable in a food plant. Speed control on furnace draft with a fast loop keeps it steady.
Overheating of fan and fluid
If the air preheater fouls and is bypassed, the gas at the fan rises towards 400°C. The fan must be designed for this, and the heater interlocks must protect the thermal oil from overheating if the ID fan trips.
Acid corrosion at low load
During nights or weekends the heater idles at low fire, and the gas at the fan cools. With sulphur-bearing fuel, acid condenses and corrodes the casing. Holding a minimum fan inlet temperature through the air preheater bypass prevents it.
Energy and control
Refinery heaters run long hours but at a load that follows the refining schedule, with frequent changes between products and idle periods at low fire. A variable speed drive on draft saves much more than a damper at these partial loads. Keeping excess air low also matters, because the flue gas leaves hot and every extra cubic metre of air carries heat out of the chimney.
ID fan and FD fan in edible oil refinery thermal oil heaters
| ID fan | FD fan | |
|---|---|---|
| Position | After the bag filter, before the chimney | Before the air preheater |
| What it handles | Flue gas at moderate temperature | Ambient air |
| Temperature at the fan | 180 to 230°C | Ambient |
| Main design concern | Stable draft through load swings | Clean combustion at low fire |
| Control | Furnace draft | Firing rate |
See also the Forced Draft (FD) Fan for edible oil refinery thermal oil heaters.
Questions buyers ask
Does a thermal oil heater in an edible oil refinery need an ID fan?
On solid fuel heaters with an air preheater and bag filter, yes. Oil or gas fired heaters with a forced draft burner often run on chimney draft alone, unless heat recovery equipment adds resistance.
What temperature does a thermic fluid heater ID fan handle?
With fluid at 280 to 320°C, the flue gas leaves the coil at 350 to 400°C. After an air preheater it reaches the fan at about 180 to 230°C, which allows a mild steel fan with a cooling disc.
Why does the ID fan need fast control on a refinery heater?
Deodoriser batches draw heat in pulses, so firing changes quickly. A fan that responds slowly lets the furnace go positive, and smoke or flue gas escaping in a food plant is not acceptable.
Information needed to quote an ID fan for edible oil refinery thermal oil heaters
- 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.
- Heater and fluid. Heater rating, thermal oil outlet and return temperatures, and whether an air preheater is fitted.
- Load pattern. How the refinery load varies across a day and the minimum firing rate.
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.