The design of the VSBK is a method of continuous brick firing that resembles a vertical shaft lime kiln or an intermittent updraft kiln. The VSBK kiln has a building-like structure with a lifespan of more than 15 years.

Elements of a VSBK

• A roofed and buttressed rectangular support building of 9-11m high and 6-8m wide, made of reinforced bricks walls.
  
  
• The 6.5-8m high rectangular vertical shafts (1m/2m), is constructed with refractory bricks in the middle of the building.
  
  
• The shafts are open at top and bottom but can be covered by a lid cover which can be removed during loading.
  
  
• The space between shafts and outside walls are filled with insulating materials (broken brickbats, brick dust, ashes).
  
  
• At the shafts’ top level, a roofed loading platform allows storage of a buffer quantity of green bricks for night operation.
  
  
• Bricks are transported to the platform via a ramp, a bridge (if the topography allows it), staircases, lifts or conveyors.
  
  
• At the base of each shaft is an arched transversal tunnel that links the unloading zone to the two cooling chambers.
  
  
• The unloading zone is equipped with a screw jack, or a hydraulic cylinder, that allows slow lowering of the loaded bricks.
  
  
• Unloading rail trolleys allow the unloaded bricks to be shifted the cooling chamber.
  
  
• The cooling chambers are made of bricks (or other material) and act as thermal buffer zone, for wind protection and storage.
  
  
• Provisions for peep holes for thermocouples are provided along the shaft height to monitor the position of the fire as well as the temperature profile of the kiln.
  
  
• Chimneys (1-2 per shaft) allow controlled air and exhaust gas flow and protect the firing crew from toxic gases.

VSBK working principle

The VSBK is a vertical kiln with stationary fire and moving brick arrangement. The kiln operates like a counter current heat exchanger, with heat transfer taking place between the air moving upwards and the bricks moving downwards. The shaft is loaded from the top in batches of green bricks. Each batch typically contains four layers of bricks set in two distinct predetermined patterns. The fired bricks are unloaded from the bottom of the shaft. The shaft itself can be divided into a top section where bricks are pre heated with the exhaust heat from the firing zone, the middle section where actual firing takes place and the lower section where fired bricks cool down.

VSBK is a natural draft kiln and requires no electricity for the supply of combustion air. The air required for combustion enters from the bottom of the kiln. It extracts the heat from the cooling bricks before reaching the firing zone. The flue gases leaving the firing zone exchange heat with dry unfired bricks thereby preheating them. For evacuation of exhaust gases, typically, two chimneys are provided.

The stack of bricks rest on ‘I’ shaped support bars (which can be removed or inserted) and supported in turn by a pair of horizontal beams across the arches in the unloading tunnel. A single screw jack system is used to unload fired bricks.