Method of operating a furnace
A method of firing a burner into a furnace process chamber supplies the burner with fuel and combustion air at a ratio that provides a level of excess air. The method includes the steps of reducing the flow rate of combustion air, and maintaining the level of excess air when the flow rate of combustion air is being reduced. Other steps include withdrawing exhaust gas from the process chamber, and supplying the burner with the exhaust gas at an increasing flow rate when the flow rate of combustion air is being reduced.
1. A method of firing a burner into a furnace process chamber, comprising:
supplying the burner with fuel and combustion air at a ratio that provides a level of excess air;
reducing the flow rate of combustion air to the burner;
maintaining the level of excess air when the flow rate of combustion air is being reduced;
withdrawing exhaust gas from the process chamber; and
supplying the burner with the exhaust gas at an increasing flow rate when the flow rate of combustion air is being reduced.
2. A method as defined in claim 1 wherein the level of excess air is maintained at or about 10%.
3. A method as defined in claim 1 wherein the level of excess air is maintained within the range of about 8% to about 12%.
4. A method as defined in claim 1 wherein the level of excess air is maintained within the range of about 5% to about 20%.
5. A method as defined in claim 1 wherein the level of excess air is maintained within the range of about 2% to about 50%.
6. A method as defined in claim 1 wherein the sum of the flow rates of combustion air and exhaust gas to the burner is maintained when the flow rate of exhaust gas is increasing.
7. A method as defined in claim 1 wherein the flow rate of combustion air is reduced throughout a range, and the burner is supplied with the exhaust gas at an increasing flow rate throughout the range.
8. A method as defined in claim 1 wherein the exhaust gas is withheld from the burner before the flow rate of combustion air is reduced.
9. A method as defined in claim 1 wherein the exhaust gas is supplied to the burner from a regenerative bed.
10. A method of firing a burner into a furnace process chamber, comprising:
supplying the burner with a flow rate of fuel and a flow rate of combustion air at a ratio that provides a level of excess air;
firing the burner throughout a range of firing rates by varying the flow rate of fuel and the flow rate of combustion air;
maintaining the level of excess air when the flow rates of fuel and combustion air are being varied;
withdrawing exhaust gas from the process chamber; and
supplying the burner with the exhaust gas at a flow rate that varies inversely relative to the flow rate of combustion air when the flow rate of combustion air is being varied.
11. A method as defined in claim 10 wherein the level of excess air is maintained at or about 10%.
12. A method as defined in claim 10 wherein the level of excess air is maintained within the range of about 8% to about 12%.
13. A method as defined in claim 10 wherein the level of excess air is maintained within the range of about 5% to about 20%.
14. A method as defined in claim 10 wherein the level of excess air is maintained within the range of about 2% to about 50%.
15. A method as defined in claim 10 wherein the sum of the flow rates of combustion air and exhaust gas to the burner is maintained when the flow rate of exhaust gas is being varied.
16. A method as defined in claim 10 wherein the flow rate of combustion air is varied continuously throughout the range of firing rates.
17. A method as defined in claim 16 wherein the flow rate of fuel is varied continuously through the range of firing rates.
18. A method as defined in claim 17 wherein the flow rates of fuel and combustion air are reduced in response to an elevated temperature in the process chamber.
19. A method as defined in claim 10 wherein the exhaust gas is withheld from the burner before the flow rate of combustion air is reduced.
20. A method as defined in claim 10 wherein the exhaust gas is supplied to the burner from a regenerative bed.
21. A method of firing a burner into a furnace process chamber, comprising:
supplying the burner with fuel and combustion air at a ratio that provides a level of excess air;
reducing the flow rate of combustion air from a first flow rate to a second flow rate;
maintaining the level of excess air when the flow rate of combustion air is being reduced;
withdrawing exhaust gas from the process chamber; and
when supplying the burner with combustion air at the second flow rate, further supplying the burner with the exhaust gas at a third flow rate equal to the difference between the first and second flow rates.
22. A method as defined in claim 21 wherein the level of excess air is maintained at or about 10%.
23. A method as defined in claim 21 wherein the level of excess air is maintained within the range of about 8% to about 12%.
24. A method as defined in claim 21 wherein the level of excess air is maintained within the range of about 5% to about 20%.
25. A method as defined in claim 21 wherein the level of excess air is maintained within the range of about 2% to about 50%.
26. A method as defined in claim 21 wherein the flow rate of combustion air is reduced from the first flow rate to the second flow rate in response to a temperature increase in the process chamber.
27. A method as defined in claim 21 wherein the exhaust gas is withheld from the burner before the flow rate of combustion air is reduced.
28. A method as defined in claim 21 wherein the exhaust gas is supplied to the burner from a regenerative bed.
29. A method of firing a burner into a furnace process chamber, comprising:
supplying the burner with a flow rate of fuel and a flow rate of combustion air at a ratio that provides a level of excess air;
monitoring a temperature in the process chamber;
responding to an increase in the monitored temperature by reducing the flow rate of fuel and the flow rate of combustion air;
maintaining the level of excess air when the flow rate of fuel and the flow rate of combustion air are being reduced;
withdrawing exhaust gas from the process chamber; and
further responding to the temperature increase by supplying the burner with the exhaust gas at an increasing flow rate when the flow rate of combustion air is being reduced.
30. A method as defined in claim 29 wherein the level of excess air is maintained at or about 10%.
31. A method as defined in claim 29 wherein the level of excess air is maintained within the range of about 8% to about 12%.
32. A method as defined in claim 29 wherein the level of excess air is maintained within the range of about 5% to about 20%.
33. A method as defined in claim 29 wherein the level of excess air is maintained within the range of about 2% to about 50%.
34. A method as defined in claim 29 wherein the sum of the flow rates of combustion air and exhaust gas to the burner is maintained when the flow rate of exhaust gas is being varied.
35. A method as defined in claim 29 wherein responding to the temperature increase includes reducing the flow rates of fuel and combustion air throughout a range of increases in the monitored temperature, and further includes maintaining the sum of the flow rates of combustion air and exhaust gas to the burner throughout the range of increases in the monitored temperature.
36. A method as defined in claim 29 wherein the exhaust gas is withheld from the burner before the flow rate of combustion air is reduced.
37. A method as defined in claim 29 wherein the exhaust gas is supplied to the burner from a regenerative bed.