Process and a plant for the production of Portland cement clinker
A process is disclosed for producing cement clinker, comprising the steps of: a) providing a mixture of ground calcareous materials and ground argillaceous materials; b) heating the mixture of step a) to a temperature sufficient to calcine and fuse the ground materials to form the cement clinker, and thereby producing an exhaust gas containing CO 2 ; c) catalysing the hydration of at least a portion of the CO2 contained in the exhaust gas and producing a solution containing bicarbonate ions and hydrogen ions; and d) adding to the solution obtained in step c) metal ions, and adjusting the pH of the solution to precipitate a carbonate or said metal. Preferably, the metal ions are Ca ++ obtained from the dissolution of a material selected from the group consisting of CaCl 2 , cement kiln dust and sea salts and the carbonate is CaCO 3 which is advantageously recycled into the process by adding the CaCO 3 to the mixture of step a). A cement plant for performing this process is also disclosed.
1. A process for producing cement clinker, comprising the steps of:
a) providing a mixture of ground calcareous materials and ground argillaceous materials;
b) heating the mixture of step a) to a temperature sufficient to calcine and fuse the ground materials to form the cement clinker, and thereby producing an exhaust gas containing CO 2 ;
c) catalysing the hydration of at least a portion of the CO 2 contained in the exhaust gas and producing a solution containing bicarbonate ions and hydrogen ions; and
d) adding to the solution obtained in step c) metal ions, and adjusting the pH of the solution to precipitate a carbonate of said metal.
2. A process as claimed in claim 1 , wherein said hydration is performed in the presence of an enzyme capable of catalysing the hydration of dissolved CO 2 into hydrogen ions and bicarbonate ions.
3. A process as claimed in claim 1 wherein, the metal ions are Ca++ and the carbonate is CaCO 3 .
4. A process as claimed in claim 3 , comprising, after step d), the step of:
e) recycling the CaCO 3 obtained in step d) into the process by adding the CaCO 3 to the mixture of step a).
5. A process as claimed in claim 2 , wherein the enzyme used in step c) is carbonic anhydrase or an analogue thereof.
6. A process as claimed in claim 5 , wherein step c) comprises the steps of
feeding liquid H 2 O and at least a portion of the exhaust gas into a bioreactor containing therein a reaction chamber filled with said carbonic anhydrase immobilized on a support.
7. A process as defined in claim 3 , wherein the ions Ca++ are obtained from the dissolution of a material selected from the group consisting of CaCl 2 , cement kiln dust and sea salts.
8. A process as defined in claim 1 , wherein the calcareous materials are selected from the group consisting of limestone, marine shells and marl.
9. A process as defined in claim 1 wherein the argillaceous materials are selected from the group consisting of clay, slate, sand, shale, and blast-furnace slags.
10. A process as claimed in claim 1 , wherein the mixture of step a) further comprises one or more material selected form the group consisting of aluminium, iron and chemical admixture.
11. A process as claimed in claim 1 , wherein the metal ions is selected from the group consisting of Ca++, Mg++, Ba++, CaMg++ and Na+.
12. A process as claimed in claim 1 , comprising, prior to step c) of hydration, the step of:
cleansing the exhaust gas for removing waste particles.
13. A process as claimed in claim 1 , wherein said temperature sufficient to calcine and fuse the ground materials is at least 1400° C.
14. A plant for producing cement clinker, comprising:
a kiln for burning raw materials suitable for producing cement clinker, the kiln having an inlet for receiving the raw materials, an outlet for discharging the cement clinker and a gas outlet for discharging an exhaust gas containing CO 2 ;
means for catalysing the hydration of the CO2 contained in the exhaust gas into bicarbonate ions and hydrogen ions;
means for reacting the bicarbonate ions with metal ions to precipitate the carbonate of said metal.
15. A plant as claimed in claim 14 , wherein said metal ions are Ca++ and the carbonate is CaCO 3 and wherein the plant further comprises:
means for transferring the precipitate CaCO 3 into the inlet of the kiln.
16. A plant as claimed in claim 14 , wherein the means for catalysing the hydration of the CO 2 comprises a bioreactor comprising:
a gas inlet for receiving at least a portion of the exhaust gas from the kiln;
a liquid inlet for receiving an aqueous liquid,
a reaction chamber in fluid communication with the gas inlet and the liquid inlet, the reaction chamber containing therein immobilized enzymes capable of catalysing the hydration of dissolved CO 2 into bicarbonate ions and hydrogen ions; and
a liquid outlet in fluid communication with the reaction chamber for discharging a solution of bicarbonate ions and hydrogen ions.
17. A plant as claimed in claim 14 , wherein the means for reacting the bicarbonate ions with metal ions is a reaction tank.
18. A plant as claimed in claim 14 , comprising;
cleansing means for cleansing the exhaust gas;
means for transferring the exhaust gas from the kiln to the cleansing means; and
means for transferring the clean exhaust gas from the cleansing means to the catalysing means.