METHOD FOR MANUFACTURING CEMENT CLINKER AND CEMENT PLANT

Abstract

A method for manufacturing cement clinker includes the steps: preheating a raw meal in a first preheater using kiln off-gas to provide a partially preheated raw meal, preheating the partially preheated raw meal in a second preheater to provide preheated raw meal, precalcination of the pre-heated raw meal in a calciner being a circulating fluidized bed reactor by burning fuel with oxygen and recirculated calciner exhaust gas instead of air to provide a precalcined raw meal wherein at least 2 mbar overpressure are adjusted in the calciner, transferring the precalcined raw meal to a rotary kiln for sintering to provide the cement clinker, cooling the cement clinker, and capturing carbon dioxide from a calciner exhaust gas in a carbon dioxide purification unit.

Claims

1: A method for manufacturing cement clinker comprising the steps: preheating a raw meal in a first preheater using kiln off-gas to provide a partially preheated raw meal; preheating the partially preheated raw meal in a second preheater to provide a preheated raw meal; precalcination of the pre-heated raw meal in a calciner being a circulating fluidized bed reactor by burning fuel with oxygen and recirculated calciner exhaust gas instead of air to provide a precalcined raw meal by partially recirculating the preheated raw meal to the calciner wherein at least 2 mbar overpressure are adjusted in the calciner; transferring the precalcined raw meal to a rotary kiln for sintering to provide the cement clinker; cooling the cement clinker; and capturing carbon dioxide from a calciner exhaust gas in a carbon dioxide purification unit.

2: The method according to claim 1, wherein an oxygen concentration from 1 to 3 Vol.-% dry is adjusted in the calciner.

3: The method according to claim 1, wherein the calciner exhaust gas is purified in a calciner exhaust gas cleaning unit and/or a carbon dioxide purification unit.

4: The method according to claim 3, wherein the calciner exhaust gas is subjected to compression in the carbon dioxide purification unit.

5: The method according to claim 3, wherein the calciner exhaust gas is subjected to one or more of the following steps in the calciner exhaust gas cleaning unit: dedusting at high temperatures, reducing of a temperature level by heat extraction, reduction of NO and NO.sub.2 in the presence of NH.sub.3 or a compound releasing NH.sub.3 in a catalytic or non-catalytic reactor at 300 to 400 C., burning down carbon monoxide and hydrocarbons to CO.sub.2 at an oxidation catalyst, additional heat recovery, purification from acid components in a scrubber, and/or cleaning in a direct contact cooler by adding an absorbent.

6: The method according to claim 1, wherein kiln off-gas is cleaned by passing through a mill for grinding raw materials to provide the raw meal and/or a raw material feed.

7: The method according to claim 6, wherein kiln off-gas is dedusted and/or NO and NO.sub.2 contained are reduced in the presence of NH.sub.3 or a compound releasing NH.sub.3 in a catalytic or non-catalytic reactor, and/or volatile organic compounds contained are burned down to CO.sub.2 and/or SO.sub.x contained is adsorbed on the raw meal during preheating, adsorbed on a raw material when drying it and/or scrubbed from the gas with a scrubbing device.

8: The method according to claim 1, wherein the oxygen fed to the calciner is preheated to a temperature of 100 C.

9: The method according to claim 1, wherein oxygen fed to the calciner has an O.sub.2 concentration 80 Vol.-%.

10: A cement manufacturing plant comprising a first cyclone preheater having a raw meal feed and adapted to receive off-gas from a rotary kiln, a second cyclone preheater adapted to receive partially preheated raw meal from the first preheater and recirculated exhaust gas as well as precalcined raw meal from a calciner, wherein the calciner is a circulating fluidized bed reactor and the calciner is arranged to receive preheated raw meal and a recirculated part of the precalcined raw meal from the cyclone preheater and adapted to precalcine the preheated raw meal, a rotary kiln adapted to receive precalcined raw meal via the second cyclone preheater from the calciner for converting the precalcined raw meal into cement clinker by sintering and to pass the cement clinker to a clinker cooler, and an oxygen supply arranged to provide oxygen to the calciner, wherein a combustion atmosphere inside the calciner is made up of oxygen from an oxygen supply and recirculated exhaust gas from the calciner, and wherein the plant comprises a carbon dioxide purification unit adapted to capture carbon dioxide from the exhaust gas from the calciner.

11: The cement manufacturing plant according to claim 10, wherein the plant comprises means for preheating the oxygen to a temperature of 100 C.

12: The cement manufacturing plant according to claim 10, wherein the oxygen supply is adapted to feed the oxygen to a calciner burner without dilution by recirculated exhaust gas.

13: The cement manufacturing plant according to claim 10, wherein the plant additionally comprises a calciner exhaust gas cleaning unit which comprises on or more of a dust filter for dedusting at high temperatures, a heat exchanger adapted for reducing the temperature level by heat extraction, a catalytic or non-catalytic reactor for reduction of NO and NO.sub.2 at 300 to 400 C. in the presence of NH.sub.3 or a compound releasing NH.sub.3, an oxidation catalyst adapted for burning down carbon monoxide and hydrocarbons to CO.sub.2, a scrubber adapted for purification from acid components, and/or a direct contact cooler adapted for cleaning by adding an absorbent.

14: The cement manufacturing plant according to claim 10, wherein the plant additionally comprises a kiln off-gas cleaning unit and/or a carbon dioxide capture system.

15: The cement manufacturing plant according to claim 11, wherein the oxygen fed to the calciner is preheated by heat exchange with recirculated calciner exhaust gas in a heat exchanger to a temperature from 300 to 400 C.

16: The method according to claim 4, wherein the calciner exhaust gas is subjected to one or more of the following steps in the carbon dioxide purification unit: cooling, drying, filtration, and/or cryogenic distillation.

17: The method according to claim 8, wherein the oxygen fed to the calciner is preheated by heat exchange with recirculated calciner exhaust gas in a heat exchanger to a temperature from 300 to 400 C.

18: The method according to claim 9, wherein the oxygen fed to the calciner has an O.sub.2 concentration of 90 Vol.-%.

19: The method according to claim 9, wherein the oxygen fed to the calciner has an O.sub.2 concentration of 99 Vol.-%.

20: The method according to claim 16, wherein the calciner exhaust gas is subjected to one or more of the following steps in the calciner exhaust gas cleaning unit: dedusting at high temperatures, reducing of the temperature level by heat extraction, reduction of NO and NO.sub.2 in the presence of NH.sub.3 or a compound releasing NH.sub.3 in a catalytic or non-catalytic reactor at 300 to 400 C., burning down carbon monoxide and hydrocarbons to CO.sub.2 at an oxidation catalyst, additional heat recovery, purification from acid components in a scrubber, and/or cleaning in a direct contact cooler by adding an absorbent.

Description

[0054] In the figures

[0055] FIG. 1 shows a first embodiment of a plant according to the invention and

[0056] FIG. 2 shows a second embodiment.

[0057] In the figures, the same reference numbers are used for analogous parts. Gas streams are depicted in broken lines and solid streams in solid lines. To enhance clarity of the figures not all units of the plants as well as gas streams and solid streams are shown.

[0058] In FIG. 1 a cement production plant with a circulating fluidized bed calciner operated in oxyfuel combustion and a carbon capture is depicted. A cyclone preheater 1 with two cyclones preheats the raw meal feed rm using the gas originating from combustion of fuels f in the rotary kiln 3. The partially preheated material enters a second cyclone preheater 2 with three cyclones that uses hot gases originating from the combustion of fuels f in the calciner 4 for further preheating. The preheated material is then introduced in the calciner 4, which is a circulating fluidized bed reactor operated in slight overpressure. Precalcined raw meal is fed to the rotary kiln 3 and the cement clinker c obtained is cooled in clinker cooler 9, which is operated with air a.

[0059] The exhaust gas from the calciner 4 is used in the second preheater 2 to further preheat the partially preheated raw meal from the first preheater 1 and also to preheat an oxygen stream o inside a heat exchanger 10. A portion of the exhaust gas is recirculated to the calciner 4 and together with the oxygen stream o is used to burn fuel f in the calciner 4, while the rest is passed to an exhaust gas cleaning system 5. The gas flow in the calciner 4 and in the second preheater 2 is controlled by adjusting the duty balance of the two fans 12 and 12 which are located inside the calciner exhaust gas circulation loop and after the calciner exhaust gas cleaning system 5, respectively. The solids exiting the calciner 4 at the top pass into the lowest cyclone of the second cyclone preheater 2. From there they are partially fed to the rotary kiln 3 and partially recirculated to the calciner 4. Thereby, the calciner 4 is a recirculating fluidized bed reactor with regard to the gas and the solids. This ensures sufficient calcination of the preheated raw meal in the calciner 4.

[0060] The exhaust gas cleaning system 5 for the CO.sub.2-rich exhaust gas from the calciner 4 includes one or more of the following units: dust collection, NOx reduction, dry/wet desulfurization, and water removal. A heat exchanger 11 cools the withdrawn calciner. A CO.sub.2 purification unit 6 eliminates the remaining impurities through a vent stream v, while the purified CO.sub.2 stream is obtained ready for transport or storage.

[0061] Kiln off-gas is split as usual into by-pass gas bp and gas used to preheat raw meal rm in the first preheater 1. For this, it is passed into the lowest preheater cyclone via a riser duct 13. By-pass bp gas can be used as known and could also be zero. The exhaust gas cleaning system 7 for the off-gas from the kiln 3 includes one or more of the following units: dust collection, NOx reduction, dry/wet desulfurization, and water removal. The CO.sub.2 capture system 8 is an amine-based system or a similar capture method. Part or all the heat h needed for the regeneration of the solvent is extracted from the exhaust gas stream of the calciner 4 in heat exchanger 11.

[0062] FIG. 2 shows another embodiment of a cement production plant with a circulating fluidized bed reactor as calciner 4 operated in oxyfuel mode. Therein the preheater and calciner section is arranged different from that in FIG. 1, the other parts are unchanged. A cyclone preheater 1 preheats a first portion of the raw meal rm using the gases originating from combustion of fuels f in the rotary kiln 3. A second raw meal feed introduces additional raw meal rm to the second preheater 2 where exhaust gas from the calciner 4 is used for preheating. The preheated material from the first preheater 1 and the second preheater 2 is introduced into the calciner 4, which is a circulating fluidized bed reactor operated in overpressure. The gases of the kiln line do not mix with the gases of the calciner line. Precalcined raw meal is fed to the rotary kiln 3 and the cement clinker c obtained is cooled in clinker cooler 9 operating with air a. Like in FIG. 1 a part of the precalcined raw meal exiting the calciner 4 at the top is recirculated into the calciner 4 by the lowest cyclone of the second preheater 2 to adjust the desired degree of calcination of the raw meal.

[0063] The exhaust gas from the calciner 4 is used in the second preheater 2 to preheat the rest of the raw meal rm and also to preheat an oxygen stream o in a heat exchanger 10. A portion of the calciner exhaust gases is recirculated to the calciner 4 using a fan 12 and together with the preheated oxygen stream o is used to burn fuels f in the calciner 4, while the rest is passed to an exhaust gas cleaning system 5 with the help of fan 12.

[0064] The exhaust gas cleaning system 5 for the CO.sub.2-rich exhaust gas from the calciner 4 includes one or more of the following units: dust collection, NOx reduction, dry/wet desulfurization, and water removal. A CO.sub.2 purification unit 6 eliminates the remaining impurities through a vent stream v, while the purified CO.sub.2 stream is obtained ready for transport or storage.

[0065] The exhaust gas cleaning system 7 for the off-gas from the kiln 3 includes one or more of the following units: dust collection, NOx reduction, dry/wet desulfurization, and water removal. The CO.sub.2 capture system 8 is an amine-based system or a similar capture method. Part or all the heat needed for the regeneration of the solvent is extracted from the exhaust gas stream of the calciner 4 in a heat exchanger 11.

LIST OF REFERENCE NUMBERS

[0066] 1 cyclone preheater [0067] 2 second cyclone preheater [0068] 3 rotary kiln [0069] 4 calciner [0070] 5 calciner exhaust gas cleaning unit [0071] 6 carbon dioxide purification unit [0072] 7 kiln exhaust gas cleaning unit [0073] 8 carbon dioxide capture system [0074] 9 clinker cooler [0075] 10 heat exchanger [0076] 11 heat exchanger [0077] 12, 12 induced draft fans [0078] 13 riser duct [0079] a air [0080] bp by-pass gas [0081] c cement clinker [0082] f fuel [0083] h heat [0084] o oxygen [0085] mm raw meal feed [0086] V vent stream