How match splint dryers work
Match splints are cut from peeled veneer of soft woods such as poplar, aspen or local softwoods, then soaked in an ammonium phosphate solution so the stick does not glow after the flame goes out. The wet splints, at 50% moisture or more, are dried to about 6 to 10% in rotary drum dryers. Hot air at typically 80 to 130°C comes from a wood-waste or husk-fired furnace through an indirect heat exchanger, or from steam coils. The drum tumbles the splints in the air, and the exhaust leaves at 45 to 70°C, humid and carrying wood fines and phosphate dust, through a cyclone to atmosphere. Dried splints are polished in drums before the match machine. Many small units still sun dry.
Where the FD fan sits
- Inlet
- FD fan
- Heat exchanger or steam coil
- Hot air duct
- Spark screen
- Rotary drum
The blower sits before the heat exchanger, handling cool ambient air and keeping the exchanger air side under pressure. A tube leak then sends clean air into the furnace gas rather than sparks and smoke into the drum. The blower overcomes the exchanger, ducting and the drum, typically 60 to 150 mmWC. In shared systems one blower supplies several drums through dampers.
Air at the FD fan
| Air temperature at the fan | Ambient, 25 to 45°C |
| Air after the heater | 80 to 130°C, downstream of the fan |
| Dust | Workshop air with wood dust; inlet screened |
| Pressure at the fan outlet | Typically 60 to 150 mmWC |
| Humidity | Ambient humidity affects drying time, not fan duty |
| 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 match splint dryers
| Blade form | Backward curved for efficiency on clean air |
| Material of construction | Mild steel |
| Drive and arrangement | Belt driven or direct coupled |
| Bearings and cooling | Standard bearings |
| Flow control | Inlet damper, or variable speed drive on larger systems |
| Also specified | Inlet screen and an intake from outside the dusty work area |
What this FD fan has to cope with
Sparks in the drying air
Direct-fired or leaking indirect heaters can carry sparks into a drum full of dry splints. Placing the blower before the exchanger so the air side is pressurised, and fitting a spark screen in the hot air duct, prevent dryer fires. Inspect the exchanger each season.
Wood dust at the inlet
Match units are dusty, and a blower drawing from inside the shed collects fibre on its blades. A screened intake from a clean area keeps the impeller clean and balanced. The screen is cleaned regularly so that it does not choke and starve the drums of drying air without any visible sign.
Uneven drying between drums
Where one blower serves several drums, the drum nearest the fan gets more air. Balancing dampers and a fan with enough pressure margin give even drying. Each drum branch has its own damper, set once at commissioning and checked when drum loading changes, so the drying time stays even.
Energy and control
Splint drying follows production and weather. A blower with a damper set for the wettest batch wastes power later in the batch and on dry days. Speed control, or simply correct pulley selection for the real duty, cuts power. Matching air flow to moisture removal also saves wood fuel in the furnace, which usually matters more to the plant than the fan electricity.
ID fan and FD fan in match splint dryers
| ID fan | FD fan | |
|---|---|---|
| Position | After the cyclone, before the exhaust stack | Before the heat exchanger, feeding the drum |
| What it handles | Humid air with wood and phosphate dust | Clean ambient air |
| Temperature at the fan | 45 to 70°C | Ambient |
| Main design concern | Build-up, corrosion and fire | Spark-free air and even flow |
| Control | Drum suction | Drying air flow |
See also the Induced Draft (ID) Fan for match splint dryers.
Questions buyers ask
What blower is used for hot air in a match splint dryer?
A backward curved centrifugal blower is usual. It pushes ambient air through a heat exchanger or steam coil, and the hot air then enters the rotary drum. It handles only clean air. A screened intake from outside the dusty shed keeps fibre off the impeller and protects the balance.
Should the splint dryer blower be before or after the heater?
Before. The forced draft fan then handles cool air and pressurises the exchanger, so a tube leak sends air into the furnace rather than sparks into the drum of dry splints. It also keeps the blower cool, so it needs only mild steel and standard bearings.
What temperature is used to dry match splints?
Typically 80 to 130°C hot air, drying the splints from about 50% moisture to 6 to 10%. Higher temperature dries faster but raises fire risk and can crack the splints. Drum speed and air flow are set together with temperature for each splint size and wood species.
Information needed to quote an FD fan for match splint dryers
- 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.
- Drum arrangement. Number of drums served and the air flow each needs.
- Heater. Heat exchanger type and its air side pressure drop.
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.