Method and plant for denitrifying bypass gases in a multi-stage system of mixing chambers in a plant for producing cement clinker

Abstract

A method and a corresponding plant for denitrifying bypass exhaust gases in a cement clinker production plant. Raw meal is sintered in a rotary kiln and deacidified in a calciner. A rotary kiln inlet chamber is connected to the calciner directly or by a riser duct. Bypass exhaust gas is drawn off near the inlet chamber. This exhaust gas is guided into a first mixing chamber, in which the exhaust gas is cooled to between 800 and 950° C., then the exhaust gas is guided through a reaction pipeline segment, wherein the dwell time is between 0.5 and 3 seconds and ammonia, aqueous ammonia solution, or ammonia-releasing substances are injected for denitrification. Then the exhaust gas is guided into a second mixing chamber, in which the exhaust gas is cooled to between 150 to 250° C. Then the exhaust gas is guided to a filter for dust removal.

Claimed is: 
     
         1 . A plant for the denitrification of bypass exhaust gases in the production of cement clinker, comprising:
 a rotary kiln for the sintering of raw meal to cement clinker, the rotary kiln having a rotary kiln inlet chamber,   a calciner for the deacidification of the raw meal, the rotary kiln inlet chamber being connected directly or via a kiln riser duct to the calciner, and   a takeoff device for drawing off the bypass exhaust gases from the region of the rotary kiln inlet chamber,   wherein a first mixing chamber is provided for the cooling of the bypass exhaust gas, drawn off from the region of the rotary kiln inlet chamber, to a temperature of between 800° C. and 950° C. so that chloride compounds remain in a gaseous phase after the bypass exhaust gas is cooled,   wherein downstream of the first mixing chamber in the gas flow direction, a reaction section is provided which is disposed in a conduit,   wherein the conduit has dimensioning such that the residence time of the bypass exhaust gas in the reaction section is between 0.5 s and 3 s, and   wherein in the region of the conduit, at least one device is provided for the injection of ammonia, aqueous ammonia solution or ammonia-releasing substances into the reaction section for the denitrification of the bypass exhaust gas by the process of selective non-catalytic reduction (SNCR),   wherein downstream of the reaction section, a second mixing chamber is disposed, for the cooling of the bypass exhaust gas to a temperature of between 150° C. and 250° C. to remove chloride compounds from the gaseous phase by deposition, and   wherein downstream of the second mixing chamber at least one filter is disposed for the dedusting of the bypass exhaust gas.   
     
     
         2 . The plant as claimed in  claim 1 , wherein the conduit is dimensioned such that the residence time of the bypass exhaust gas in the reaction section is between 1 s and 2 s. 
     
     
         3 . The plant as claimed in  claim 1 , wherein downstream of the at least one filter in the gas flow direction there is disposed a fan. 
     
     
         4 . The plant as claimed in  claim 1 , wherein in the region of the conduit, at least one device is provided for feeding at least one sorbent into the reaction section for additional, pollutant-removing purification of the bypass exhaust gas. 
     
     
         5 . An apparatus for the denitrification of bypass exhaust gases in the production of cement clinker, comprising:
 a rotary kiln configured to sinter raw meal and provide cement clinker, the rotary kiln having a rotary kiln inlet chamber;   a calciner configured to deacidify raw meal, the rotary kiln inlet chamber being connected directly or via a kiln riser duct to the calciner;   a first mixing chamber configured to receive bypass exhaust gas from the rotary kiln inlet chamber and cool the bypass exhaust gas to a temperature of between 800° C. and 950° C. so that chloride compounds remain in a gaseous phase after the bypass exhaust gas is cooled;   a reactor, configured to receive the bypass exhaust gas after the bypass exhaust gas is cooled in the first mixing chamber, the reactor disposed in a conduit and dimensioned such that the residence time of the bypass exhaust gas in the conduit is between 0.5 s and 3 s,   at least one device configured to inject ammonia, aqueous ammonia solution or ammonia-releasing substances into the reactor for the denitrification of the bypass exhaust gas by the process of selective non-catalytic reduction (SNCR),   a second mixing chamber configured to receive the bypass exhaust gas and ammonia, aqueous ammonia solution or ammonia-releasing substances from the reactor and to cool the bypass exhaust gas to a temperature of between 150° C. and 250° C. to remove chloride compounds by deposition, and   at least one filter, downstream of the second mixing chamber in the gas flow direction, for dedusting the bypass exhaust gas after it has been cooled in the second mixing chamber.