CEMENT MANUFACTURING PLANT AND METHOD OF OPERATING A CEMENT MANUFACTURING PLANT

Abstract

A cement manufacturing plant includes a raw meal mill, at least one preheater string, a clinker furnace and a clinker cooler including a first section and a second section, wherein a preheater exhaust gas recirculation device is provided for recirculating exhaust gas leaving the at least one preheater string into the first section of the clinker cooler, and wherein the cement plant is configured for switching between an air operation mode and an oxyfuel operation mode, includes a first switching device for connecting either a source of air or a source of oxygen rich gas to a burning zone of the clinker furnace burner, and a second switching device for either establishing or separating a connection of the preheater exhaust gas recirculation means to the first section of the clinker cooler.

Claims

1. A cement manufacturing plant comprising: a raw meal mill for grinding raw meal to obtain ground raw meal, at least one preheater string comprising cyclone suspension-type preheaters for preheating the ground raw meal in counter current flow to hot exhaust gas coming from a clinker furnace, optionally a pre-calciner for pre-calcining the preheated raw meal, a clinker furnace for calcining the preheated and optionally pre-calcined raw meal in counter current flow to combustion gas of a clinker furnace burner to obtain cement clinker, a clinker cooler for cooling the cement clinker, wherein the clinker cooler comprises a first section and a second section, the first section being adjacent a clinker discharge end of the clinker furnace and the second section being remote from the clinker discharge end of the clinker furnace, optionally cooler vent-air recirculation means for recirculating clinker cooler vent-air from the raw meal mill to the second section of the clinker cooler, optionally bypass gas recirculation means for recirculating bypass gas, which is taken from between an exhaust gas end of the clinker furnace and the at least one preheater string, to the first section of the clinker cooler, preheater exhaust gas recirculation means for recirculating exhaust gas leaving the at least one preheater string into the first section of the clinker cooler, the cement plant being configured for switching between an air operation mode and an oxyfuel operation mode and comprising: first switching means for connecting either a source of air or a source of oxygen rich gas to a burning zone of the clinker furnace burner, and second switching means for either establishing or separating a connection of the preheater exhaust gas recirculation means to the first section of the clinker cooler.

2. The cement manufacturing plant according to claim 1, wherein an air separation unit is used as the source of oxygen.

3. The cement manufacturing plant according to claim 1, wherein the optional bypass gas recirculation means comprises cooling means for cooling the bypass gas that is recirculated to the first section of the clinker cooler.

4. The cement manufacturing plant according to claim 20, wherein the preheater exhaust gas recirculation means comprises a diverter for diverting a partial flow of the preheater exhaust gas to the mixing chamber, wherein third switching means are provided for either using air, or the preheater exhaust gas that is diverted from the preheater exhaust gas recirculation means, as the cooling gas.

5. The cement manufacturing plant according to claim 1, wherein the preheater exhaust gas recirculation means comprises a thermal oxidizer, for thermally decomposing volatile compounds in the preheater exhaust gas.

6. The cement manufacturing plant according to claim 5, wherein the preheater exhaust gas recirculation means comprises a first and a second heat exchanger, the first heat exchanger being arranged upstream of the thermal oxidizer and second heat exchanger being arranged downstream of the thermal oxidizer, wherein the first and second heat exchangers are integrated into a working fluid cycle of a heat-to-power unit and arranged to transfer heat from the preheater exhaust gas to a working fluid of the working fluid cycle, wherein, in the working fluid cycle, the first heat exchanger is arranged downstream of the second heat exchanger.

7. The cement manufacturing plant according to claim 1, wherein the preheater exhaust gas recirculation means comprises a cooling and condensing unit for cooling the preheater exhaust gas in the oxyfuel operation mode so as to condense and separate water from the preheater exhaust gas.

8. The cement manufacturing plant according to claim 1, wherein the preheater exhaust gas recirculation means comprises a diverter for diverting a partial flow of the preheater exhaust gas to the clinker furnace burner, wherein fourth switching means are provided for either using air, or the preheater exhaust gas that is diverted from the preheater exhaust gas recirculation means, as a transport gas for a fuel of the clinker furnace burner.

9. The cement manufacturing plant according to claim 1, wherein the preheater exhaust gas recirculation means comprises a diverter for diverting a partial flow of the preheater exhaust gas to a CO.sub.2 purification unit.

10. A method of operating a cement manufacturing plant according to claim 1, comprising: grinding raw meal in the raw meal mill to obtain ground raw meal, preheating the ground raw mill in the preheater string in counter current flow to hot exhaust gas coming from the clinker furnace, optionally pre-calcining the preheated raw meal in the pre-calciner, calcining the preheated and optionally pre-calcined raw meal in the clinker furnace in counter current flow to combustion gas of the clinker furnace burner to obtain cement clinker, cooling the cement clinker in the clinker cooler, optionally recirculating bypass gas, which is taken from between an exhaust gas end of the clinker furnace and the at least one preheater string, to the first section of the clinker cooler, recirculating exhaust gas leaving the at least one preheater string into the first section of the clinker cooler, switching between an air operation mode and an oxyfuel operation mode, comprising: actuating first switching means for feeding either air or oxygen rich gas to a burning zone of the clinker furnace burner, and actuating second switching means for either recirculating preheater exhaust gas to the first section of the clinker cooler or releasing preheater exhaust gas through an exhaust stack.

11. The method according to claim 10, wherein the bypass gas is cooled before being recirculated into the first section of the clinker cooler.

12. The method according to claim 11, wherein said switching between an air operation mode and an oxyfuel operation mode comprises actuating third switching means for either using a partial flow of the preheater exhaust gas as a cooling gas or using air as the cooling gas.

13. The method according to claim 10, wherein said switching between an air operation mode and an oxyfuel operation mode comprises actuating fourth switching means for either using air or a partial flow of the preheater exhaust gas as a transport gas for a fuel of the clinker furnace burner and/or as a transport gas for a fuel of the burner of the pre-calciner.

14. The method according to claim 10, wherein the preheater exhaust gas is subjected to a thermal oxidation at a temperature of 750-900 C. in a thermal oxidizer for thermally decomposing volatile compounds in the preheater exhaust gas.

15. The method according to claim 14, wherein the preheater exhaust gas is cooled in a first heat exchanger arranged upstream of the thermal oxidizer and subsequently cooled in a second heat exchanger arranged downstream of the thermal oxidizer, wherein heat transfer is effected from the preheater exhaust gas to a working fluid of a working fluid cycle comprising the first and second heat exchangers, the working fluid circulating such that working fluid coming from a heat-to-power unit is first directed through the second heat exchanger and subsequently directed through the first heat exchanger.

16. The method according to claim 10, wherein the preheater exhaust gas in the oxyfuel operation mode is directed through a cooling and condensing unit to condense and separate water from the preheater exhaust gas.

17. The method according to claim 10, wherein in the oxyfuel operation mode a partial flow of the preheater exhaust gas is directed to a CO.sub.2 purification unit.

18. The cement manufacturing plant according to claim 1, wherein the clinker cooler is connected to the raw meal mill for feeding clinker cooler vent-air to the raw meal mill.

19. The cement manufacturing plant according to claim 1, wherein the first switching means is for connecting either the source of air or the source of oxygen rich gas to the burning zone of the clinker furnace burner via the first section of the clinker cooler.

20. The cement manufacturing plant according to claim 3, wherein the cooling means comprises at least one mixing chamber for mixing the bypass gas with a cooling gas.

Description

[0076] The invention will now be described in more detail with reference to the attached drawings. Therein, FIG. 1 shows a schematic illustration of a cement manufacturing plant according to the invention, FIG. 2 shows the cement manufacturing plant of FIG. 1 when operated in an air operation mode, and FIG. 3 shows the cement manufacturing plant of FIG. 1 when operated in an oxyfuel operation mode.

[0077] FIG. 1 shows a schematic illustration of a cement manufacturing plant according to the invention that can be selectively operated in an oxyfuel operation mode and in an air operation mode. The cement manufacturing plant comprises a raw meal mill 1 for grinding raw meal to obtain ground raw meal. The ground raw meal is introduced into the preheater string 2 that comprises a number of cyclone suspension-type preheaters for preheating the ground raw meal in counter current flow to hot exhaust gas coming from the clinker furnace 3, In the lower part of the preheater string 2, a pre-calciner is arranged for pre-calcining the preheated raw meal. As schematically indicated by arrow 4, a fuel is introduced into the pre-calciner for pre-calcining the preheated raw meal. The clinker furnace 3 is provided for calcining the preheated and pre-calcined raw meal in counter current flow to combustion gas of a clinker furnace burner to obtain cement clinker. The clinker furnace burner is arranged at the clinker discharge end of the clinker furnace 3 and the feeding of fuel to the clinker furnace burner is schematically indicated by arrow 5.

[0078] Further, a clinker cooler 6 is arranged for cooling the cement clinker coming from the clinker furnace 3. The clinker cooler 6 comprises a first section 7 that is adjacent the clinker discharge end of the clinker furnace 3 and a second section 8 that is remote from the clinker discharge end of the clinker furnace 3. A separation means for separating the first section 7 from the second section 8 is denoted by reference numeral 9. Cooler vent-air leaving the second section 8 of the clinker cooler 6 is directed to the raw meal mill 1 for drying the raw meal, after having been separated from dust particles in a cyclone separator. If the raw meal mill 1 is not in operation, the clinker cooler vent-air may bypass the raw meal mill 1 by being guided through an air-to-air heat exchanger 11, in order to cool the cooler vent-air for protecting the downstream bag filter 12 from high temperature. The cooler vent-air is recirculated into the second section 8 of the clinker cooler 6. A partial flow of the cooler vent-air may also be released into the environment through the exhaust stack 13. Further, an air introduction 48 is provided for adding fresh ambient air into the cooler vent-air circulation.

[0079] The preheater exhaust gas is leaving the preheater string 2 at 14 and is directed to a waste heat recovery system that comprises a first heat exchanger 15 and a second heat exchanger 16. The preheater exhaust gas flows through the first heat exchanger 15, is then cleaned from dust particles in the dust filter 17, is led through the regenerative thermal oxidizer 18 and finally flows through the second heat exchanger 16. Upstream of the regenerative thermal oxidizer 18, oxygen 10 may be injected into the preheater exhaust gas, if needed. The first heat exchanger 15 and the second heat exchanger 16 are integrated into a working fluid cycle 19 of a heat-to-power unit 20 and arranged to transfer heat from the preheater exhaust gas to a working fluid of the working fluid cycle 19. In the working fluid cycle 19 the first heat exchanger 15 is arranged downstream of the second heat exchanger 16. The preheater exhaust gas coming from the second heat exchanger 16 is subjected to further purification and cooling in the wet scrubber 21.

[0080] The purified preheater exhaust gas coming from the wet scrubber 21 can either be directed to an exhaust stack 13 or can be recirculated into the clinker furnace 3 via the clinker cooler 6. Before being recirculated, the preheater exhaust gas introduced into a cooling and condensing unit 25, in which the exhaust gas is further cooled and water is removed. The preheater exhaust gas coming from the cooling and condensing unit 25 is directed to the first section 7 of the clinker cooler 6 via the line 26. A partial flow of the gas may be branched off and led through the CO.sub.2 purification unit 27.

[0081] Bypass gas is extracted from the inlet chamber of the clinker furnace 3 and via the line 28 and directed through a first mixing chamber 29 and a second mixing chamber 30, in which cooling gas is added to the bypass gas, in order to decrease the temperature of the bypass gas. Volatile components contained in the bypass gas are removed by means of a filter 31 and the purified bypass gas is recirculated into the clinker furnace 3 via the first section 7 of the clinker cooler 6. The recirculation is performed by a connection (not shown in FIG. 1) between the line 32 and the inlet 33 of the clinker cooler 6, whereby additional oxygen 23 may be introduced here, if needed.

[0082] The combustion gas resulting from the combustion in the clinker furnace 3 and the pre-calciner is subjected to a selective non-catalytic reduction (SNCR) of NO by injection of NH.sub.3 at 47 at around 900 C. The reagent is typically injected at the exit of the pre-calciner and results in a reaction of NO with NH.sub.3 to N.sub.2 and eventually also CO.sub.2.

[0083] The cement plant shown in FIG. 1 is configured for switching between an air operation mode and an oxyfuel operation mode. In the air operation mode, air is used as the combustion gas for burning fuel 5 in the clinker furnace 3 and for burning fuel 4 in the pre-calciner. Air is introduced into the first section 7 of the clinker cooler 6 at 34 and is led into the burning zone of the clinker furnace burner. Further, air 35 is used as a transport gas for conveying fuel 5 to the clinker furnace burner and air 36 is used as a transport gas for conveying fuel 4 to the burner of the pre-calciner. In the air operation mode, air is also used as cooling gas for cooling the bypass gas in the first mixing chamber 29 and in the second mixing chamber 30 and optionally further downstream in the bypass recirculation line 32, the respective air introduction being denoted by reference numeral 37. In the air operation mode, the preheater exhaust gas coming from the wet scrubber 21 is led to the exhaust stack 23 via line 24.

[0084] In the oxyfuel operation mode, an oxygen rich gas is used as the combustion gas instead of air. Therefore, instead of introducing air into the clinker cooler 6 at 34, oxygen coming from an air separation unit via line 39 is introduced into the clinker furnace 3 via the first section 7 of the clinker cooler 6 and oxygen is also introduced into the pre-calciner via line 40. In the oxyfuel operation mode, the preheater exhaust gas that is rich in CO.sub.2, instead of being directed to the exhaust stack 23 via the line 24, is fed to the cooling and condensing unit 25, in order to increase the concentration of CO.sub.2 in the exhaust gas. The preheater exhaust gas is recirculated into the clinker cooler via line 26. A partial flow of the preheater exhaust gas is diverted via line 41 and used as cooling gas in the first mixing chamber 29 and in the second mixing chamber 30 and optionally further downstream in the recirculation line 32, by being introduced at 42. Another partial flow of the preheater exhaust gas is branched off at 43 and used as transport gas 44 and 45 for conveying fuel 4 and 5 to the clinker furnace burner and the burner of the pre-calciner, respectively. Additional oxygen 38 may be introduce here, if needed. Further, a partial flow of the CO.sub.2 rich preheater exhaust gas is branched off from the recirculation line and introduced in the CO.sub.2 purification unit 27, where all undesired components (e.g. N.sub.2, H.sub.2O, CO, SO.sub.x, NOx, HF, Ar) are removed, in order to achieve a CO.sub.2 concentration of >96.5% to >99.5%. CO.sub.2 is extracted from the CO.sub.2 purification unit at 46, while the remaining components are released via the exhaust stack 23.

[0085] For switching between the air operation mode and the oxyfuel operation mode, the cement manufacturing plant comprises first switching means for connecting either air 34 or source of oxygen rich gas to the burning zone of the clinker furnace burner. Further, second switching means 22 are provided for either establishing or separating a connection of the preheater exhaust gas to the first section 7 of the clinker cooler 6. Third switching means are provided for either using air 37, or the preheater exhaust gas 42 that is diverted from the preheater exhaust gas recirculation at 41, as the cooling gas in the mixing chambers 29 and 30. Finally, fourth switching means are provided for either using air 35 and 36, or the preheater exhaust gas 44 and 45 that is diverted from the preheater exhaust gas recirculation at 43, as a transport gas for the fuel 4 and 5, respectively, of the clinker furnace burner and the burner of the pre-calciner.

[0086] For better illustration of the air operation mode, FIG. 2 shows only the parts of the cement manufacturing plant from FIG. 1 that are used in the air operation mode.

[0087] For better illustration of the oxyfuel operation mode, FIG. 3 shows only the parts of the cement manufacturing plant from FIG. 1 that are used in the oxyfuel operation mode.