Moving step grate firing system UTSW

Operating medium: water / hot water / steam
Grate cooling: water
Operating range: 300 - 4200 kW
Capacity regulation: modulating
Water content: M 8 - 44
Fuel types: scrap wood / residual wood / pellets / alternative fuels

Fuels with an extremely high calorific value or low ash melting point, such as particleboard waste, old timber, corn, rice husks.


  • Furnaces for special fuels such as grains/corn, etc. 
  • Crushed wood 
  • Pellets and industrial pellets 
  • Particleboard furnaces in the wood processing industry
  1. Fuel supply with stoker screw
  2. Combustion chamber with water cooling
  3. Water-cooled step grate
  4. Burnout zone
  5. Under-grate de-ashing – automatic or manual
  6. Automatic grate ash discharge
  7. Access door to under-grate
  8. Radiation vault
  9. Refractory concrete with defined heat passage
  10. Secondary combustion chamber – in accordance with low NOx process
    by means of air stages
  11. 3-pass steam boiler
  12. Boiler door with automatic pulse-jet cleaning system of the boiler tubes
  13. Flue gas cleaning by multi-cyclone with automatic fly ash discharge
  14. Flue gas fan – can be positioned either on the right, left or at the rear
  15. Grate door with safety lock

The UTSW boiler unit is equipped with a step moving grate and also suitable for fuel with a high ash content. The fuel is fed on to the sloping feed grate from the rear of the furnace. The grate consists of water-cooled grate girders; the rods overlap on both sides, so that the minimum fuel slips through the grate. Furthermore, the grate is designed to enable a clear, uniform distribution of the primary air supplied to the various zones, thereby creating a steady, undisturbed gasification zone. The grate carriage has a hydraulic drive, so that the movement intervals can be automatically adjusted to the capacity. The entire combustion chamber is water-cooled and lined with fireproof material, thereby ensuring the required cooling even in the case of fuel that generate a high temperature in the combustion chamber.

Combustion chamber design

  • Insulation of the combustion chamber (100 mm) with external cladding plate
  • Water cooling inside double-walled steel plate structure connected with tension bolts
  • Fireproof ceramic fibre mat coated with aluminium foil
  • Heat resistant wall anchors
  • Fireproof cast concrete (100 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 protects the steel plate structure against overheating.

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