Cupola Furnace Troubleshooting and Techniques

Table of Contents

1. Cupola Design
   1. What Is an Efficient Cupola Design?
   2. Operating at the Optimum Blast Air Rate
      1. Blast Air Rate per Unit Area
      2. Average Tuyere Velocity
   3. Oversized or Undersized Cupolas for Melt Demand
   4. Stack Gas Concentrations
2. Troubleshooting
   1. Out-of-Control Temperatures
      1. Immediate Checks
      2. Corrective Action
         1. Blast Air Rate/Pressure Change
         2. Temperature Reading Inaccurate
         3. Blast Air System Leaks
         4. Tuyere Leaks
         5. Charge Change/Heavy Metallics
         6. Cupola Full
         7. Uneven Charge Distribution
         8. Wet Coke
         9. Coke Size Change
         10. Tap Hole Obstruction
         11. Viscous Slag
         12. Bridging or Scaffolding
         13. High Humidity
      3. Determine Approximate Coke Bed Height
         1. How to Check the Approximate Coke Bed Height
            1. Increase the blast are rate by 10%
            2. Decrease the blast air rate by 10%
            3. Enrich the blast air with oxygen
            4. Observe the stack gas concentrations
         2. Steps to Resolve the Coke Bed Height: Too Low or Too High
            1. Too Low
            2. Too High
      4. Long-Term Action
      5. Specific Situation: Cold Iron after an Unscheduled Shutdown
   2. Chill Test Changes
      1. Chill Too High: Hard Iron
         1. Immediate Checks
         2. Corrective Action
            1. Low in C, Si, %CE/High in Cr, Mo, S, B
            2. Lower Si/C Ratio
            3. Wet Refractory/Tuyere Leak
            4. Coke Bed Low
            5. Charge Components Changed
            6. Incorrect Charging Scales
      2. Chill Too Low: Soft Iron
         1. Immediate Checks
         2. Corrective Action
            1. High in C, Si, %CE
            2. Higher Si/C Ratio
            3. Charge Components Changed
            4. Incorrect Charging Scales
   3. Cupola Bridging
      1. Immediate Checks
      2. Corrective Action
      3. Further Checks
      4. Further Action
         1. Oversized Charge Metallics
         2. Insufficient Flux
         3. Uneven Charge Distribution
         4. Charging System Working Improperly
         5. Poor Refractory Lining
         6. Improper Refractory Installation
         7. Front Slagging Iron Dam Too High
         8. Rear Slagging Slag Hole Too High
         9. Poor/Weak Coke
         10. Excessive Blast Air Rate
         11. Too Many Shutdowns
         12. Leaking Tuyeres
         13. No Blast Air Reduction at End
      5. Potential Situation: Frozen Cupola
         1. How to Identify a Frozen Cupola
         2. Immediate Action
   4. Excessive Windbox Pressure
      1. Common Excessive Windbox Pressure Indications
      2. Further Checks
      3. Further Action
         1. Bridging
         2. Tuyere Velocity Too High
         3. Slag Buildup on Tuyere ID
         4. Dirt/Sand in Charge
         5. Small Coke/ExcessiveFines
         6. Tuyeres Too Small for Blast Rate
         7. Mismatched Blower/Exhaust System
   5. Excessive Refractory Consumption
      1. How to Determine Excessive Refractory Consumption
      2. Further Checks
      3. Further Action
         1. Bridging
         2. Poor Refractory Material
         3. Poor Refractory Removal
         4. Uneven Charge Distribution
         5. Excessive Flux Use
         6. Unequal Blast Air Distribution
         7. Under Blown
         8. Water Leaks
         9. Large Charge Materials
         10. Incompatible Refractory/Slag
         11. Incorrect Cupola Design
         12. Inconsistent Charge Weights
         13. Dark Tuyeres
3. Changing the Cupola State
   1. Melt Rate Control
      1. Cupola Utilization
      2. Increasing the Melt Rate by 10% or Less
      3. Melt Rate Increase of 25% or More
      4. Decreasing the Melt Rate by 10% or Less
      5. Melt Rate Decrease of 20% or More
   2. Carbon Control
      1. Suggestions for Lowering Carbon
         1. Immediate Action: Quick Results
         2. Immediate Action: Delayed Results
      2. Suggestions for Increasing Carbon
         1. Immediate Action: Quick Results
         2. Immediate Action: Delayed Results