Method and apparatus for producing cement clinker

Abstract

In methods of and/or plants for manufacturing cement clinker, the amount of chloride bypass exhaust gas 79 can be substantially decreased, when using previously cooled chloride bypass exhaust gas 81 and/or cooled kiln exhaust gas as coolant for the chloride bypass exhaust gas 39 prior to deducting the chloride bypass exhaust gas 39.

Claims

1. Method for chloride bypass gas treatment, comprising: providing a chloride bypass gas flow by drawing at least a fraction of a main exhaust gas flow from a kiln, a first cooling step of cooling the chloride bypass gas flow by mixing it with a cooling gas to form a mixed chloride bypass gas flow, dedusting the mixed chloride bypass gas flow, and a second cooling step of cooling the dedusted-and-mixed chloride bypass gas flow by bringing the dedusted mixed chloride bypass gas flow into thermal communication with at least one heat carrier fluid which is heated as a result of the thermal communication with the dedusted mixed chloride bypass gas flow, wherein at least a part of the cooled dedusted-and-mixed chloride bypass gas flow obtained after the second cooling step is used as cooling gas in the first cooling step.

2. A method of claim 1, further comprising: providing a reductant to the chloride bypass gas flow before the second cooling step.

3. A method of claim 2, where the reductant is provided to the chloride bypass gas flow before beginning the dedusting.

4. A method of claim 2, further comprising: after providing the reductant and before the second cooling step, contacting the chloride bypass gas flow with at least one catalyst for selective catalytic reduction of nitrogen oxide.

5. A method of claim 4, wherein the dedusting step comprises providing at least a part of the chloride bypass gas flow to a filter into which at least one catalyst for selective catalytic reduction of nitrogen oxide (NOx) is incorporated and/or embedded.

6. A method of claim 1, wherein the chloride bypass gas is cooled to a temperature T.sub.1 between 350 C. and 450 C. in the first cooling step.

7. A method of claim 1, wherein the chloride bypass gas is cooled to a temperature T.sub.2 between 70 C. and 170 C. in the second cooling step.

8. A method of claim 1, wherein the thermal communication of the second cooling step is performed in at least one heat exchanger, the dedusted-and-mixed chloride bypass gas flow is provided to a warm inlet of the heat exchanger and drawn off at a cold outlet of the heat exchanger, and the heat carrier fluid is provided to a cold inlet of the heat exchanger and drawn off at a warm outlet of the heat exchanger.

9. A method of claim 1, wherein at least a part of the heat provided to the heat carrier fluid is used as process heat in the clinker process and/or converted into electric energy.

10. A method of claim 1, wherein, after the second cooling step, the at least a part of the cooled dedusted-and-mixed chloride bypass gas flow is drawn off from an outlet of a heat exchanger associated the second cooling step and recirculated via a conduit to at least one mixing chamber associated with the first cooling step to thereby provide the cooling gas in the first cooling step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment and with reference to the drawings.

(2) FIG. 1 shows a schematic sketch of a cement clinker line.

(3) FIG. 2 shows a schematic flow diagram of a chloride bypass system.

(4) While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) The cement clinker line in FIG. 1 comprises as usual a preheater 2, a kiln 30 and a clinker cooler 4. Raw meal 8 is preheated in the preheater 2 and provided to the kiln inlet 31. In the kiln 30 the raw meal 8 is calcined and sintered to clinker. The clinker 9 is discharged on the clinker cooler 4 and can be further processed after being cooled down (indicated by an arrow, symbolizing the clinker 9), e.g. by milling. Hot air from the clinker cooler 4 is provided to the kiln 30 as secondary air and leaves the kiln 30 at its inlet 31 as flue or exhaust gas. Said kiln exhaust gas is dust loaden and hot (typically 1500 C. to 2000 C.). The main amount of the kiln exhaust gas is provided to the preheater 2 for pre-warming the raw meal 8. Optionally a calciner 5 may be installed between the preheater 2 and the kiln 30. In that case the raw meal 8 is provided from the preheater 2 to the calciner 5 and from the calciner 5 to the kiln 30. At least a part of the kiln exhaust gas may be provided to the preheater via the calciner 5. Further, tertiary air may be provided from the clinker cooler 4 to the calciner 5.

(6) At least fraction, typically about 3% to 10% of the kiln exhaust gas is drawn of via a chloride bypass intake 35. From said chloride bypass intake 35, bypass gas 39 flows to a first inlet 41 of a mixing chamber 40 for mixing the bypass gas 39 with a cooling gas in a first cooling step. The cooling gas may be provided to the mixing chamber by a second inlet 42. The cooled bypass gas 49 leaves the mixing chamber 40 via its outlet 43 and flows to a dust removal means 60 for filtering the cooled bypass gas 49. The filtered bypass gas 69 exits the dust removal means 60 via outlet 62 and is provided to the warm inlet 71 of a heat exchanger 70. In the heat exchanger 70 the filtered bypass gas 69 is subjected to a second cooling step by thermally contacting the bypass gas with a heat carrier fluid as coolant being provided to the heat exchanger 70 via a cold inlet 73. Warmed heat carrier fluid is drawn off the heat exchanger 70 via a warm outlet 74. The heat carrier fluid may be water, in particular if the heat shall be converted into mechanical energy by expanding steam in a turbine. Other heat carrier fluids may be used as well, e.g. thermal oils as set out above. The cooled bypass gas 79 is referred to as bypass exhaust gas 79, but only to clearly distinguish the bypass gas after the second cooling step from the cooled bypass gas obtained after the first cooling step. Said bypass exhaust gas 79 may be split in two portions, for example by two ventilation means as indicated by reference numeral 20 and 26: a first portion 81 of the bypass exhaust gas 79 is provided via a conduit 80 to the second inlet 42 of the mixing chamber 40. Alternatively or additionally, the first portion 81 (or at least a part it) may be drawn off by the ventilation means 20 downstream of the ventilation means 26, as indicated by a dashed line. A further alternative is to draw of a fraction of the main kiln exhaust gas flow, e.g. downstream the preheater; preferably, downstream of a dedusting step. Said fraction may as well be provided to the mixing chamber.

(7) The remaining second portion 82 of the bypass exhaust gas 79 is drawn off and may be provided to an exhaust 100 as depicted. Alternatively the second portion 82 may be provided to a clinker cooler as cooling agent or to raw meal pre-warming means. The second portion may be provided to an exhaust 100, to a raw meal mill for drying the raw meal, to the clinker cooler 4 or any other suited place. As apparent from FIG. 2, no oxygen rich air is introduced into the chloride bypass. Thus, the amount of bypass exhaust gas is significantly reduced. Further, as the bypass exhaust gas 79 has the same low oxygen concentration as the kiln exhaust gas it may be released in the same way, compliant with the governmental emission limits. Fresh air is only required for emergency cooling. The fresh air may be provided via a fresh air intake 90 of the conduit 80.

(8) Optionally a reductant injector 50 (shown with dashed lines) may be provided, e.g. between the mixing chamber and the dust removal means 60. A catalyst for catalytic denitrification may be positioned in the flow path as well, e.g. directly downstream the reductant injector 50. The catalyst may be embedded in at least one filter element of the dust removal means 60. For example, the dust removal means 60 may comprise at least one ceramic or sintered filter element into which said at least one catalyst is embedded.

(9) In particular in case no catalyst is embedded in the in the dust removal means, a catalyst unit 65 (shown with dashed lines) may be positioned preferably in the flow path of the dedusted bypass gas 69, as the temperature T.sub.1 of the bypass gas prior to the second cooling step is typically in the range required for a SCR-process. As well the reductant injector 50 may be positioned in the flow path of the dedusted bypass gas 69 (different from the depicted position). Further, the bypass gas is less abrasive after dust removal and accordingly the life span of the catalyst unit is augmented.

(10) A further option is a further catalyst unit 95, a so called oxi-cat for oxidizing hydrocarbons. Said further catalyst 95 may arranged between the deducting means 60 and the heat exchanger 70. Particularly preferred the further catalyst 95 may be positioned downstream the SCR catalyst unit 65.

(11) It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide an improved chloride bypass process for a cement clinker line and as well an accordingly improved cement clinker line. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.

LIST OF REFERENCE NUMERALS

(12) 2 preheater 3 kiln 4 clinker cooler 5 calciner 6 tertiary air duct 7 to waste gas processing 8 raw meal 9 clinker 20 ventilation means 26 ventilation means 30 kiln 31 kiln inlet (raw meal inlet and flue gas outlet) 32 cement clinker 35 chloride bypass intake 39 chloride bypass gas 40 mixing chamber 41 first inlet of mixing chamber 42 second inlet of mixing chamber 43 outlet of mixing chamber 49 cooled bypass gas/bypass gas after first cooling step 50 reductant injector 51 bypass gas inlet of reductant injector 53 reductant inlet of reductant injector 52 outlet of reductant injector 59 bypass gas with reductant 60 dust removal means 61 inlet of dust removal means 62 outlet of dust removal means 65 catalyst unit 66 inlet of catalyst unit 67 outlet of catalyst unit 69 deducted bypass gas 70 heat exchanger 71 warm inlet of heat exchanger 72 cold outlet of heat exchanger 73 cold inlet of heat exchanger 74 warm outlet of heat exchanger 79 bypass gas after second cooling step/chloride bypass exhaust gas 80 conduit 81 fraction of bypass gas provided to second inlet of mixing chamber 82 fraction of bypass gas provided to exhaust 90 fresh air intake 95 further catalyst unit/oxi-cat 96 inlet of further catalyst unit 97 outlet of further catalyst unit 100 exhaust