Method and apparatus for reducing the NOx emissions in a rotary kiln

Abstract

In a method for reducing the NOx emissions of a rotary kiln of a clinker production plant, fuel supplied through a burner of the rotary kiln is burned along with primary air fed through the burner, wherein the primary air has a lower oxygen content and the primary air has an oxygen content reduced relative to that of the ambient air and a temperature increased relative to that of the ambient air, and the primary air is obtained by mixing ambient air with exhaust gas from the rotary kiln or from a heat exchanger connected to the rotary kiln and used for preheating raw meal. The primary air is further obtained by mixing with hot air, in particular waste air from a clinker cooler.

Claims

1. A method for reducing the NOx emissions of a rotary kiln of a clinker production plant, in which fuel supplied through a burner of the rotary kiln is burned along with primary air fed through the burner and the primary air has an oxygen content reduced relative to that of ambient air and a temperature increased relative to that of the ambient air, the primary air being obtained by mixing the ambient air with exhaust gas from the rotary kiln or from a heat exchanger connected to the rotary kiln and used for preheating raw meal, wherein the primary air is further obtained by mixing with hot air, wherein the ambient air, the exhaust gas and the hot air are separately supplied to a mixing chamber to mix them and form the primary air, and wherein said primary air formed by a mixture of the ambient air, the exhaust gas and the hot air is fed to the burner.

2. The method according to claim 1, wherein the mixing ratio of ambient air, exhaust gas and hot air is controlled such that the primary gas is fed to the burner at a temperature of 50-250 C. and an oxygen content of 8-18% by vol.

3. The method according to claim 1, wherein the mixing of ambient air, exhaust gas and hot air is controlled to maintain a volume flow of primary gas adapted to the process.

4. The method according to claim 1, wherein hot air is used at a temperature of 80-150 C.

5. The method according to claim 1, wherein exhaust gas is used at a temperature of 100-200 C.

6. The method according to claim 1, wherein exhaust gas with an oxygen content of 6-10% by vol. is used.

7. The method according to claim 1, wherein 5-20% by vol. of primary gas, and 80-95% by vol. of secondary gas, are fed to the rotary kiln.

8. The method according to claim 1, wherein a portion of the primary gas is used as transport gas for fuels.

9. A device for reducing NOx emissions of a clinker production plant, the device comprising a rotary kiln with a burner, a heat exchanger connected to the rotary kiln on the exhaust-gas side, and a clinker cooler, wherein a primary gas supply for supplying primary gas to the burner with a main fan is provided, wherein fuel supplied through the burner of the rotary kiln is burned along with the primary gas fed through the burner and the primary gas has an oxygen content reduced relative to that of the ambient air and a temperature increased relative to that of the ambient air, wherein a mixing device including an ambient air supply, an exhaust gas supply fed with the exhaust gas from the heat exchanger, and a hot air supply fed with the waste air from the clinker cooler are disposed upstream of the main fan, wherein the ambient air supply, the exhaust gas supply and the hot air supply are each equipped with a control element for controlling the respective volume flow, wherein the control elements are connected to a control device to which measurements of a temperature sensor and oxygen-content sensor disposed downstream of the main fan are fed, wherein the control device is arranged to adjust the control elements such that a specified temperature and a specified oxygen content of the primary gas supplied to the burner are maintained.

10. The device according to claim 9, wherein the control device is arranged to adjust each control element such that a specified volume flow of the primary gas supplied to the burner is maintained.

11. The method according to claim 1, wherein the hot air is waste air from a clinker cooler.

12. The method according to claim 2, wherein the mixing ratio of ambient air, exhaust gas and hot air is controlled such that the primary gas is fed to the burner at a temperature of 100-150 C.

13. The method according to claim 2, wherein the oxygen content is of 13-16% by vol.

14. The method according to claim 4, wherein hot air is used at a temperature of 90-100 C.

15. The method according to claim 5, wherein exhaust gas is used at a temperature of 145-185 C.

16. The method according to claim 6, wherein exhaust gas with an oxygen content of 6-8% by vol. is used.

17. The device according to claim 9, wherein the specified temperature is 50-250 C. and the specified oxygen content is 8-18% by vol.

18. The device according to claim 17, wherein the specified temperature is 100-150 C.

19. The device according to claim 17, wherein the specified oxygen content is 13-16% by vol.

Description

(1) In the following, the invention will be explained in more detail by way of an exemplary embodiment schematically illustrated in the drawing. FIG. 1 depicts a stack 1 for discharging exhaust gas from a heat exchanger of a preheater for raw meal. Exhaust gas is branched off from the stack 1 via a duct 2, the branched-off volume flow being adjustable via a control element 3. The fan for withdrawing the exhaust gas is denoted by 4. The exhaust gas is preferably conducted through a condenser 5, in which water is removed from the exhaust gas, which water can subsequently be recycled. The oxygen content, the temperature, and optionally the pressure, of the exhaust gas are measured by sensors 6, a further control element for adjusting the volume flow being denoted by 7. The exhaust gas is subsequently fed to a mixing chamber 8. To the mixing chamber 8 is further supplied waste air from the stack 9, said waste air being waste air from the clinker cooler. The waste air is conducted via a duct 10 and a fan 12. The temperature, and optionally the pressure, of the waste air are determined by sensors 11. The volume flow of the waste air can be adjusted by means of a control element 13.

(2) Furthermore, ambient air 14 is supplied to the mixing chamber 8 via a duct 15.

(3) The mixture of ambient air, exhaust gas and waste air is supplied to the burner 19 of the rotary kiln as primary gas via a fan 17 and a duct 18. A portion of the primary gas can be fed as transport gas to respective fuel metering units via a duct 21 and a fan 22. A control element 16 is provided for adjusting the volume flow of the primary gas. At the measuring point 20, the temperature, the oxygen content, the pressure and the volume flow of the primary gas are measured and compared to set points in a control device not illustrated. In the event of a deviation from the set points, the control device cooperates with the control elements 3, 7, 13 and a control element (not illustrated) for adjusting the amount of ambient air in order to effect a correction.