Regenerative air preheater design to reduce cold end fouling

Abstract

An air preheater 100 is described having an air damper assembly 162 that partially restricts an air inlet 130 and a flue gas damper assembly 152 that partially restricts flue gas inlet 124 during periods of reduced boiler load. Restricting the flue gas inlet 124 reduces the effective surface area of the preheater causing more heat to pass to the cold end of the air preheater 100 , reducing acid condensation and fouling. Restricting the gas inlet 124 , increases gas velocity, thereby eroding accumulations in the air preheater 100 , also reducing fouling. Restricting the air inlet 130 reduces the effective heat transfer surface area of the air preheater, which raises the gas temperature in the cold end of the air preheater and thereby reduces acid condensation and fouling.

1 . An air preheater having a flue gas inlet for receiving flue gases from a boiler, a flue gas outlet for exhausting flue gases, an air inlet for receiving air to preheat and an air outlet for providing preheated air to the boiler, the air preheater exhibiting reduced fouling under varying boiler operation levels, comprising:
 a. an air damper assembly adapted to adjust an opening of said air inlet, the air damper assembly fitting tightly against the air inlet to minimize and air leakage between the damper assembly and the air inlet;   b. a flue gas damper assembly adapted to adjust an opening of said flue gas inlet, the flue gas damper assembly fitting tightly said against flue gas inlet to minimize and air leakage between the flue gas damper assembly and the flue gas inlet;   c. a controller coupled to the air damper assembly adapted to operate the air damper and the flue gas damper assembly during varying boiler operation levels to maintain desired air and gas flow velocities to reduce fouling.   
     
     
         2 . The air preheater of  claim 1 , wherein controller is adapted to receive input regarding the boiler operation level and interactively control at least one of the flue gas damper assembly and the air damper assembly based upon the received input. 
     
     
         3 . The air preheater of  claim 1 , wherein controller is adapted to receive input regarding temperature of flue gases exiting flue gas outlet and interactively control at least one of the flue gas damper assembly and the air damper assembly based upon the received input. 
     
     
         4 . The air preheater of  claim 1 , wherein controller is adapted to receive input regarding a velocity of flue gases exiting the flue gas outlet and interactively control at least one of the flue gas damper assembly and the air damper assembly based upon the received input. 
     
     
         5 . The air preheater of  claim 1 , wherein controller is adapted to:
 a. receive input regarding a maximum allowable flue gas outlet temperature;   b. measure a temperature of a flue gas outlet stream; and   c. control at least one of the flue gas damper assembly and the air damper assembly to maximize a velocity of air flowing into the air inlet while keeping the measure temperature of the flue gas outlet stream below the maximum allowable flue gas temperature.   
     
     
         6 . The air preheater of  claim 1 , wherein controller is adapted to receive input regarding the flue gas outlet velocity and interactively control at least one of the flue gas damper assembly or the air damper assembly based upon the received input. 
     
     
         7 . The air preheater of  claim 1 , wherein the controller is further adapted to adjust the flue gas damper assembly and the air damper assembly to reduce the amount of acid condensation within the air preheater. 
     
     
         8 . The air preheater of  claim 1 , wherein the air damper assembly comprises:
 a plurality of dampers adapted to adjustably close at least a portion of the air inlet.   
     
     
         9 . The air preheater of  claim 1 , wherein the flue gas damper assembly comprises:
 a plurality of dampers adapted to adjustably close at least a portion of the flue gas inlet.   
     
     
         10 . The air preheater of  claim 1 , wherein the dampers are pivotable and are pivoted by a drive bar attached to the dampers. 
     
     
         11 . The air preheater of  claim 10 , wherein an actuator moves the drive bar to cause the dampers to pivot. 
     
     
         12 . A method of reducing fouling in an air preheater having an air inlet and a flue gas inlet during periods of reduced boiler operation comprising the steps of:
 a. measuring a temperature of flue gas outlet stream exiting the preheater;   b. determining if the measured gas outlet temperature is lower than a predetermined threshold;   c. calculating an amount to close at least one of the flue gas inlet and the air inlet to increase the flue gas outlet stream temperature to be above the threshold temperature, when the measured temperature is below the predetermined threshold; and   d. closing the flue gas inlet and the air inlet by the calculated amount when the measured gas outlet temperature is below the predetermined threshold to result in increased flue gas outlet stream temperature, thereby reducing acid condensation and fouling.   
     
     
         13 . The method of reducing fouling of  claim 12  wherein the predetermined threshold temperature is the condensation temperature of an acid present in the flue gases plus a safety margin. 
     
     
         14 . A method of reducing fouling in an air preheater having an air inlet and a flue gas inlet, during periods of reduced boiler operation comprising the steps of:
 a. measuring velocity of at least one of the flue gases and air passing through the preheater;   b. determining a difference between the measured velocity and a desired velocity;   c. calculating an amount to adjust at least one of a flue gas inlet opening and an air inlet opening to minimize the difference between the measured velocity and the desired velocity; and   d. adjusting at least one of the flue gas inlet and the air inlet opening by the calculated amount to result in adjusted outlet velocity, thereby increasing erosion of any accumulations and fouling.   
     
     
         15 . The method of reducing fouling of  claim 14  further comprising the steps of:
 a. receiving maximum flue gas outlet stream temperature; 
 b. measuring flue gas outlet stream temperature, and 
 c. limiting the step of adjusting to insure that the measured flue gas outlet stream temperature is below the maximum flue gas outlet stream temperature.