Air preheater and method for preventing corrosion and blockage of the same

Abstract

An air preheater, including a flue; an air channel; a first segment for producing secondary air; a second segment for producing primary air; a third segment for anti-condensation of ammonium bisulfate; and a fourth segment for curing of ammonium bisulfate. The flue and the air channel are disposed on the downstream of a denitration device. The first segment, the second segment, the third segment and the fourth segment are disposed in that order along the gas flow direction. The first segment, the second segment, the third segment and the fourth segment each include a phase-change heat exchanger. The phase-change heat exchanger includes a heat absorption segment disposed in the flue, a heat release segment disposed in the air channel, an ascending tube and a downcomer which are configured to connect the heat absorption segment and the heat release segment.

The invention claimed is: 
     
         1 . An air preheater, comprising:
 a flue;   an air channel;   a first segment for producing secondary air;   a second segment for producing primary air;   a third segment for anti-condensation of ammonium bisulfate; and   a fourth segment for curing of ammonium bisulfate;   
       wherein
 the flue and the air channel are disposed on a downstream of a denitration device; 
 the first segment for producing secondary air, the second segment for producing primary air, the third segment for anti-condensation of ammonium bisulfate and the fourth segment for curing of ammonium bisulfate are disposed in that order along a gas flow direction; 
 the second segment for producing primary air, the third segment for anti-condensation of ammonium bisulfate, and the fourth segment for curing of ammonium bisulfate each comprise a phase-change heat exchanger; the phase-change heat exchanger comprises a heat absorption segment disposed in the flue, a heat release segment disposed in the air channel, an ascending tube and a downcomer which are configured to connect the heat absorption segment and the heat release segment; the heat release segment is disposed higher than the heat absorption segment, and the phase-change heat exchanger is provided with a cycling medium; and 
 a wall surface temperature of the third segment for anti-condensation of ammonium bisulfate is higher than a dew temperature of the ammonium bisulfate; 
 a wall surface temperature of the fourth segment for curing of ammonium bisulfate is lower than a solidification point temperature of the ammonium bisulfate. 
 
     
     
         2 . The air preheater of  claim 1 , wherein the air preheater further comprises an acid-dew resistant segment disposed on a downstream of the fourth segment; the acid-dew resistant segment also comprises the phase-change heat exchanger, and a wall surface temperature of the acid-dew resistant segment is higher than an acid dew point temperature. 
     
     
         3 . The air preheater of  claim 2 , wherein the heat absorption segment in the second segment for producing primary air, the heat absorption segment in the third segment for anti-condensation of ammonium bisulfate, the heat absorption segment in the fourth segment for curing of ammonium bisulfate, the heat absorption segment in the acid-dew resistant segment each are provided with a temperature sensor. 
     
     
         4 . The air preheater of  claim 2 , wherein the cycling medium in the second segment, in the third segment, in the fourth segment, and in the acid-dew resistant segment is water, Freon, or heat transfer oil. 
     
     
         5 . The air preheater of  claim 1 , wherein the first segment for producing secondary air is a segment of a regenerative air preheater. 
     
     
         6 . The air preheater of  claim 1 , wherein the first segment for producing secondary air comprises the phase-change heat exchanger, and the cycling medium in the second segment for producing primary air is water, Freon, or heat transfer oil. 
     
     
         7 . A method for preventing corrosion and blockage of an air preheater, the air preheater being disposed on a downstream of a denitration device, the method comprising:
 1) introducing flue gas in a flue to an upstream of the air preheater, and allowing the flue gas to pass a first segment for producing secondary air, a second segment for producing primary air, a third segment for anti-condensation of ammonium bisulfate and a fourth segment for curing of ammonium bisulfate in that order; introducing air in an air channel to a downstream of the air preheater, and allowing the air to pass the fourth segment for curing of ammonium bisulfate, the third segment for anti-condensation of ammonium bisulfate, the second segment for producing primary air, and the first segment for producing secondary air;   2) adjusting a wall surface temperature of the third segment for anti-condensation of ammonium bisulfate to be higher than a dew temperature of the ammonium bisulfate, and adjusting a wall surface temperature of the fourth segment for curing of ammonium bisulfate to be lower than a solidification point temperature of the ammonium bisulfate;   3) gasifying the ammonium bisulfate in the flue prior to and in the third segment for anti-condensation of ammonium bisulfate; curing the ammonium bisulfate in and after the fourth segment for curing of ammonium bisulfate, the ammonium bisulfate being cured on a wall surface of a pipe of the fourth segment and a wall surface of a downstream pipe of the fourth segment; and   4) eliminating solid ammonium bisulfate on the wall surface of the pipe of the fourth segment and on the wall surface of the downstream pipe of the fourth segment.