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Flow Control Valves Applications of Walking Beam Furnaces

 

Walking beam furnaces are continuous, reheat furnaces commonly used in steel milling applications. They use a walking beam mechanism to transport steel bars, billets or slabs from the charge to the discharge end of the furnace. The advantage of this mechanism is that the steel slab can be “walked” through different heating zones and at different speeds to obtain desired rolling temperatures. The walking beams also eliminate furnace wear from heavy steel slabs sliding along the surface of the beams. In general, flow control valves are used to maintain constant flow, independent of pressure and temperature, by throttling an orifice from inlet to outlet of the valve. They are used within walking beam furnaces for the control of three separate furnace functions:

¨        Walking Beam Movement Control

¨        Burner Fuel Flow Control

¨        Beam Structure Cooling Control

 

Walking Beam Movement Control

 

Walking beam furnaces transport steel slabs through the furnace for processes such as, sintering, brazing, calcining, carbon & ceramic firing, and metallizing. The transport or conveying mechanism is a walking beam assembly that consists of both stationary and moveable beams that are lifted and lowered (vertical movement) as well as pushed and retracted (lateral movement) to convey the slab through the furnace. The movement of the walking beams can be accomplished through a variety of electro-mechanical devices such as screw jacks, eccentric drives, or rack and pinion assemblies, to name of few. But due to cost and maintenance concerns, these devices have been replaced by hydraulic power and control. Flow control valves control the movement of electro-hydraulic actuators or cylinders that control both the up/down (vertical) and horizontal (lateral) movement of the walking beams.

 

Burner Fuel Flow Control

 

Flow control valves also provide a means to control fuel oil flow to furnace’s burner. In addition, flow control valves can also function as safety cut-off valves (although the safety function is generally accomplished with a separate valve.) A typical walking beam furnace burner is fitted with solenoid valves for both gas and air combustion. The burner control enables the gas- and air-flow control valve actuators to generate a spark and create a flame. The fuel and air volumes are then adjusted or throttled by the valves. Correct flow is determined relative to a set-point temperature. Burners are pulsed on and off via these valves until the furnace reaches its target operating temperature.

Beam Structure Cooling Control

Walking beam furnaces are operated at very high temperatures, which potentially can have adverse effects on the walking beam structure. To both protect the structure as well as increase the maximum temperature that the beams can be safely operated at, a cooling system is integrated along the length of the beams. In the past, alloy steel walking beams were used in walking beam furnaces and were exposed to the total heat of the furnace. This design caused heat corrosion. To circumvent this problem, the current design of walking beam furnaces includes a steel beam cooling system, consisting of water-cooled tubular sections that run the length of the walking beam structure. Flow control valves provide control of the beam cooling pump system that forces coolant along the cooling tube section.