Underfeed stoker furnace UTSK

Operating medium: Water / Hot Water / Steam
Grate cooling: Air
Operating range: 180 - 900 kW
Capacity regulation: modulating
Water content: M 10-50
Fuel types: woodchips / residual wood


  • Wood chips furnaces for private and public installations 
  • Chips and sawdust furnaces in the wood processing industry
  1. Fuel supply with stoker screw
  2. Combustion tray with cast ribs and primary air supply
  3. Combustion chamber
  4. Refractory concrete for heat storage
  5. Secondary air inlet
  6. Radiation vault
  7. 3-pass steam boiler
  8. Boiler door with automatic pulse-jet cleaning system of the boiler tubes
  9. Flue gas cleaning by multi-cyclone with automatic ash particle discharge
  10. Flue gas fan – can be positioned either on the right, left or at the rear
  11. Grate door with safety lock
  12. Burnout grate
  13. Automatic grate ash discharge
  14. Ash container for grate ash

Fuel is passed from below into the high-alloy casting combustion retort of the UTSK underfeed stoker furnace. The complete combustion chamber is lined with fireproof material, thereby producing a high furnace temperature even in case of wet fuel. A radiation roof, which varies according to the material, is placed over the combustion chamber. The primary air is passed into the combustion retort through the cast-iron bars, where a steady gasification of the combustion material commences. The secondary air that is passed into the combustion chamber leads to optimum combustion and therefore low emission. The ash is removed over a full-combustion grate. Under the full-combustion grate, there is a screw conveyor that conveys the ash directly into an ash collection box or container. The furnace is fully flushed with primary and secondary air and combined with the highly effective insulation, there is minimum radiation. A suitably dimensioned 3-pass flue boiler is installed above the furnace. The multiple dry cyclone is installed directly behind the heat exchanger and therefore receives an optimum flow.

Combustion chamber design

  • Insulation of the combustion chamber (100 mm) with external cladding plate
  • Air cooling inside double-wall steel plate construction (5-5 or 6-6 mm)
  • High temperature resistant heat insulation board (60 mm)
  • Fireproof ceramic fibre mat coated with aluminium foil (13/25 mm)
  • Fireproof cast concrete (115-150 mm)

The refractory concrete is secured to the steel structure of the combustion chamber with heat resistant wall anchors. The refractory concrete has a high density as well as a high temperature resistance and is cast in sections. Dilation seams between the sections compensate for expansion of the refractory concrete when the temperature fluctuates. The ceramic fibre mat behind the refractory concrete and the high temperature resistant heat insulation board protect the steel plate structure against overheating.

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