How tyre pyrolysis plants work
Tyre pyrolysis plants heat whole or shredded end-of-life tyres in a closed reactor at about 400 to 500°C without air. The rubber breaks down into oil vapour, a non-condensable gas, carbon black and steel wire. Batch rotating drum reactors are common; continuous plants use shredded feed. The reactor is heated externally by a furnace burning the non-condensable gas and pyrolysis oil. Tyres contain about 1.5 to 2% sulphur, so the gas and oil carry hydrogen sulphide and sulphur compounds, and their combustion gives SO₂ in the furnace flue gas. Most plants pass this flue gas through a cyclone and an alkaline water scrubber, or desulphurisation tower, before the ID fan and stack. A combustion air fan supplies the heating burners.
Where the FD fan sits
- Inlet screen
- FD fan
- Burner
- Heating furnace
- Reactor jacket
The fan sits beside the heating furnace and delivers ambient air to the burners that fire the non-condensable gas and pyrolysis oil around the reactor. It works against burner and duct resistance, typically 150 to 400 mmWC. Its inlet should be well away from the carbon black discharge and the wire handling area, where fine black dust and rubber particles are in the air.
Air at the FD fan
| Air temperature at the fan | Ambient, 25 to 45°C |
| Air at the burner | Ambient on most plants |
| Dust | Carbon black and rubber dust near the plant; inlet screen needed |
| Pressure at the fan outlet | Typically 150 to 400 mmWC |
| Load profile | Changes through each batch |
| 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 tyre pyrolysis plants
| Blade form | Backward curved for efficiency |
| Material of construction | Mild steel throughout |
| Drive and arrangement | Direct mounted on the motor shaft |
| Bearings and cooling | Motor bearings |
| Flow control | Variable speed drive or damper with oxygen trim |
| Also specified | Inlet screen, air pressure interlock |
What this FD fan has to cope with
H₂S from incomplete combustion
Too little air leaves H₂S and unburnt hydrocarbons in the flue gas, causing odour complaints and extra corrosion in the scrubber and ID fan. Enough air throughout the batch, confirmed by oxygen measurement at the furnace outlet, avoids this.
Carbon black at the fan inlet
Fine carbon black from the reactor discharge and screening is easily drawn into the fan. It coats the impeller, causing unbalance, and blocks inlet screens. Taking the air intake from a clean area away from these operations prevents it.
Variable gas flow
Gas production changes through the batch, peaking during the main reaction. Fixed air settings produce smoke at the peak or waste fuel at the end. Air control linked to burner firing or oxygen keeps combustion right across the cycle.
Energy and control
The combustion air fan is small, and its effect on fuel use and on the gas volume through the scrubber and ID fan matters more than its own power. Oxygen-trimmed air control and a variable speed drive through the batch cycle cut both. Excess air also dilutes SO₂ and raises the gas flow the scrubber must treat, so it is worth keeping low.
ID fan and FD fan in tyre pyrolysis plants
| ID fan | FD fan | |
|---|---|---|
| Position | After the desulphurisation scrubber | Beside the heating furnace |
| What it handles | Wet flue gas with SO₂ | Ambient combustion air |
| Temperature at the fan | 55 to 75°C | Ambient, 25 to 45°C |
| Main design concern | Sulphurous acid corrosion | Complete burning of sulphurous gas |
| Control | Furnace pressure | Oxygen and firing rate |
See also the Induced Draft (ID) Fan for tyre pyrolysis plants.
Questions buyers ask
Does the FD fan supply air to the tyre pyrolysis reactor?
No. The reactor operates without air, since air would burn the tyres rather than pyrolyse them. The FD fan supplies combustion air only to the burners in the heating furnace around the reactor.
Why is good combustion air control important on a tyre pyrolysis plant?
The non-condensable gas from tyre pyrolysis contains sulphur compounds. With too little air, H₂S and hydrocarbons pass unburnt, causing odour and corrosion. With too much, fuel use and the gas load on the scrubber rise.
Where should the combustion air fan take its air from?
From a clean area, away from the carbon black discharge, screening and bagging, so that fine dust does not build up on the impeller or block the screen. On many plants this means a short inlet duct taken from the outside wall.
Information needed to quote an FD fan for tyre pyrolysis plants
- 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.
- Burners. Number of burners, fuels and firing range.
- Air intake. Location of the intake relative to carbon black handling.
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.