W-grate (BS) Mark 6 water-cooled - for high calorific refuse

The patented water-cooled (BS) Mark 6 w-grate has approx. 32,000 hours of prototype operation and approx. 16,000 hours of commercial operation (up to year 2004).

The (BS) Mark 6 is distinguished by its suitability for high calorific fuel. The Mark 6 also offers full integration with the air-cooled Mark 5, providing complete freedom within the grate area, be it air-cooled, water-cooled, or both.

Application:

Features:
  • Combustion of all types of waste
  • Steam, hot water and district heating
  • Capacity: 3 - 30 t/h
  • Can handle unsorted waste
  • High calorific waste up to 25 MJ/kg
  • Optimal primary air addition
  • Possibility of biomass co-firing
   

Process advantages of the water-cooled (BS) Mark 6

  • Grate surface cooling is independent of combustion; air can thus be added and adjusted for optimal combustion
  • Minimal corrosion due to low grate surface temperature
  • Energy from grate cooling used for air preheating
  • Constant high flow of cooling water through the grate bars, avoiding boiling
  • Low differential temperature over the grate results in low thermal stress
  • Simple control

Mechanical advantages of the (BS) Mark 6

  • Cooling water is led to and from the grate through the shaft ends and to the middle sections of the shafts through pipe connections
  • No sensitive hose connections inside the furnace. Damage due to grate siftings, molten tin, aluminium etc. is effectively prevented
  • No grate bar damage due to temporary cooling system failure
  • Separate cooling system for each grate section provides protection against total cooling water failure

Water cooling provides adequate grate durability for combustion of high calorific refuse which causes high thermal stresses in the grate. The amount of primary air or under-fire air does not provide enough cooling.

How does the grate work?

The water-cooled BS version of the w-grate is mechanically the same as the air-cooled version expect for the water-cooled BS grate surface. The movement pattern is also similar. The water-cooled BS version thus provides the same process and mechanical advantages as the air-cooled BS version.

The grate is built in sections, using the same principles as the air-cooled version. The grate may consist of a number of water-cooled and air-cooled sections and, air-cooled and water-cooled bars can be used within the same section. The first two or three grate sections are often water-cooled.

As the water-cooled grate has the same movement pattern, the grate bars have the same basic geometric design as the air-cooled versions, but the width is 400 mm compared with 100 mm for the air-cooled version.