METHOD OF CALCINING A CLAY MATERIAL

Abstract

A method of calcining a clay material for use as a supplementary cementitious material, includes providing a raw clay material, optionally drying the raw clay material, granulating the raw clay material in order to obtain raw clay granules, calcining the raw clay granules to obtain calcined clay granules, and grinding the calcined clay granules to obtain a pulverulent supplementary cementitious material.

Claims

1. A method of calcining a clay material for use as a supplementary cementitious material, comprising: providing a raw clay material, optionally drying the raw clay material, granulating the raw clay material in order to obtain raw clay granules, calcining the raw clay granules to obtain calcined clay granules, and grinding the calcined clay granules to obtain a pulverulent supplementary cementitious material, wherein the granulating is carried out to obtain raw clay granules having a volume based particle size of 3 mm to 80 mm.

2. The method according to claim 1, wherein the raw clay material contains at least 30%, of kaolinite, based on the weight of the dry raw clay material.

3. The method according to claim 1, wherein the raw clay material is provided in the form of a powder and wherein the granulating comprises introducing the raw clay powder into a rotating granulator, sprinkling the raw clay powder with water and forming the raw clay granules.

4. The method according to claim 1, wherein the raw clay material is provided in the form of a paste having a water content of 10-40 wt.-% of the raw clay material, and wherein the granulating comprises introducing the paste into a rotating granulator and forming the raw clay granules.

5. The method according to claim 1, wherein the raw clay material is provided clay material with a water content of above 40 wt.-% of the raw clay material, and wherein the granulating comprises introducing the material into a rotating granulator and forming the raw clay granules.

6. The method according to claim 3, wherein a vertical or semi-vertical rotating pan granulator is used for granulating the raw clay material.

7. The method according to claim 1, wherein the drying is carried out in a cement raw material preheater of a cement manufacturing plant and/or the calcinating is carried out in a calcination kiln of a cement manufacturing plant.

8. The method according to claim 1, wherein the drying comprises introducing the raw clay granules into a heat exchanger and heating the raw clay granules in heat exchange with an exhaust gas coming from a calcination kiln of a cement manufacturing plant.

9. The method according to claim 1, wherein the drying comprises forming a material bed of the raw clay granules on slotted grate plates of a moving grate preheater and directing a flow of hot gas through the slotted grate plates and the material bed.

10. The method according to claim 1, wherein the calcining is carried out in a rotary kiln.

11. The method according to claim 1, wherein the step calcining is carried out at a temperature of 600-800? C.

12. The method according to claim 1, wherein a residence time of the raw clay granules in the calcination kiln is selected to be 1.5-3 hours.

13. (canceled)

14. (canceled)

15. The method according to claim 2, wherein the raw clay material contains at least 40% of kaolinite, based on the weight of the dry raw clay material.

16. The method according to claim 9, wherein the flow of hot gas is exhaust gas coming from a calcination kiln.

17. The method according to claim 10, wherein the rotary kiln is heated by burning fuel.

18. The method according to claim 17, wherein the burning fuel is petcoke, fuel oil, biomass waste, or hot gas recovered in the calcined clay cooler.

19. The method according to claim 10, wherein the rotary kiln is operated with an oxygen content of <8 vol.-%.

Description

EXAMPLE

[0054] In the following example, the following two components were blended: [0055] 60 dry.-% of a clay extracted from the quarry of Bellegarde (France). This clay initially contained 15 to 18 wt.-% of water, was dried and ground in a vertical mill at a fineness of 7,500 to 12,000 cm2/g. This product was then then mixed with [0056] 40 dry.-% of a dry product, in powder form, containing 64% of kaolinite, supplied by Sibelco.

[0057] Granules were produced and subjected to a stability test, wherein the granules were dropped from a height of 5 meters, and remained intact. This easy test confirms that the granules are suitable for handling and storage in a cement plant.

[0058] Further, the raw material powders were analyzed by X-ray diffraction to quantify the main components and assess the impact of the calcination temperature (1 h) on the content of the individual components. In particular, it was analyzed, whether the material transformations obtained as a consequence of the calcination process are influenced by whether the clay material is calcined in granulated form or in its original powder form. Particular attention was paid to the decarbonation of the calcium carbonate component of the clay. As mentioned before, decarbonation of the calcium carbonate component of the clay is to be avoided as much as possible due to the undesired formation of CO.sub.2.

[0059] The results are summarized in the table below.

TABLE-US-00001 TABLE 1 Calcination of clay without prior granulation: Clay powder Temperature of calcination before 500? 600? 700? 750? 800? calcination C. C. C. C. C. Kaolinite 23 18 <2 <1 <1 <1 (wt.-%) Lime <1 <1 <1 2 3 4 (wt.-%) Calcium 14 12 11 7 2 <1 carbonate (wt.-%) Calculated 0 14 22 50 86 98 decarbonation wt.-%

TABLE-US-00002 TABLE 2 Calcination of clay after having been transformed into granules 750? C.* Kaolinite (wt.-%) 23 0.595 Lime (wt.-%) <1 0.06 Calcium carbonate (wt.-%) 14 9.48 Calculated decarbonation wt.-% 32% *estimated based on cooler heat balance

[0060] Industrial test shows that the calcination process with granulation is more efficient than powder in lab: For full kaolinite conversion into metakaolin (<1% remaining kaolinite), decarbonation is reduced to 32%, vs 50% in lab test.

[0061] For the same temperature (750? C.), decarbonation is reduced to 32% vs 86% in lab test. This higher temperature enables to reach 850? C. for 2 s in order to process waste.

[0062] The effect of granulation to decrease the decarbonation level despite of higher calcination temperature is essential to reduce carbon footprint (CO.sub.2 from decarbonation+CO.sub.2 from fuel).