Method and plant for preheating particulate or pulverulent material
Described is a method as well as a plant for preheating particulate or pulverulent material such as cement raw meal or similar material in a cyclone preheater ( 1 ), comprising at least two cyclone stages, each comprising a riser duct ( 2 a , 2 b , 2 c , 2 d ) and a cyclone ( 1 a , 1 b , 1 c , 1 d ). The method is peculiar in that a portion of the material which is fed to at least one cyclone stage is introduced to the first part of the riser duct, viewed in the direction of travel of the exhaust gases, and is heated from a temperature of maximum 450° C. to a temperature of at least 550° C., and in that the remaining material which is fed to the same cyclone stage is introduced into the last part of the said riser duct. As a result, there will be a reduction in the amount of SO 2 which is discharged from the cement plant preheater as emission, without a simultaneous increase in energy consumption.
1. A method for preheating particulate or pulverulent material in a cyclone preheater comprising at least two cyclone stages, each cyclone stage comprising an associated riser duct and a cyclone, the method comprising:
feeding a first portion of the material to a first cyclone stage, wherein the material is introduced to a first part of a riser duct of the first cyclone stage in the direction of travel of the exhaust gases;
heating the first portion of material from a temperature of maximum 450° C. to a temperature of at least 550° C.; and
feeding remaining material to a last part of the riser duct of the first cyclone stage.
2. The method according to claim 1 , wherein the first portion of the material is heated from a temperature between 300 and 450° C. to a temperature between 550 and 700° C., before the remaining material is introduced into the last part of the riser duct.
3. The method according to claim 1 , wherein the material that is discharged from the first cyclone stage is split into at least two sub-streams, of which a first sub-stream via a duct is directed to and introduced into a riser duct immediately above the exhaust gas outlet in a third cyclone stage and a second sub-stream is introduced via a duct into a riser duct at a location immediately ahead of a gas inlet in a second cyclone stage.
4. The method according to claim 1 , wherein the material which is fed to the cyclone preheater is split into at least two sub-streams, of which one sub-stream via a duct is introduced into and preheated in a first riser duct and then via the first cyclone is directed to and introduced into a riser duct immediately above an exhaust gas outlet in a third cyclone stage, whereas a second sub-stream via a duct is bypassed around the first cyclone stage and introduced into a second riser duct immediately ahead of a gas inlet in a second cyclone stage.
5. The method according to claim 1 , wherein the material comprises cement raw meal.
6. A plant for preheating particulate or pulverulent material comprising:
a cyclone preheater having at least two cyclone stages, each cyclone stage comprising an associated riser duct and a cyclone, wherein the cyclone preheater comprises means for heating a portion of the material from a temperature of maximum 450° C. to a temperature of at least 550° C. within one cyclone stage.
7. The plant according to claim 6 , wherein the means for heating comprises splitter gates.
8. The plant according to claim 6 , wherein a duct is configured as a swan neck comprising an upwardly directed first section, a bend and a downwardly directed second section which is connected to an associated cyclone.
9. The plant according to claim 6 , characterized in that a duct is configured with increased diameter over at least a part of its extent.