Boiler Feed Water Deaerator Method and Apparatus

Abstract

A nitrogen sweep stream for use in a deaerator during deaerator operations to disperse and remove oxygen and carbon dioxide from boiler feed water prior to being fed to a boiler. The nitrogen sweep stream substantially reduces the amount of oxygen and carbon dioxide in the water supply system. The water supply system can be sent to a deaerator stripper or can be heated using a heat exchanger. A heat water supply stream can also be sent directly to the deaerator water tank. The nitrogen sweep stream reduces the amount of oxygen contained with the boiler feed water stream to less than 7 ppb and reduces the amount of carbon dioxide to nondetectable levels. The nitrogen sweep may be provided to an existing deaerator, not having been previously provided with a nitrogen sweep, while the deaerator is running without shutting down the deaerator.

1 . A method of removing oxygen from a boiler feed water stream, comprising the steps of:
 supplying a water supply stream to a deaerator stripper;   heating the water supply stream and removing at least a portion of oxygen and carbon dioxide contained within the water supply stream to produce a reduced oxygen containing water stream, the reduced oxygen containing water stream descending down the stripper to a deaerator water tank;   supplying a nitrogen sweep to the deaerator water tank during deaerator operations thereby diffusing remaining oxygen in the reduced oxygen containing water stream resulting in a substantial portion of the remaining oxygen being removed from the reduced oxygen containing water stream; and   supplying the reduced oxygen containing water stream to a boiler as a feed water stream having substantially reduced oxygen contained therein.   
   
   
       2 . The method of  claim 1 , wherein the step of supplying the reduced oxygen containing water stream to a boiler includes supplying the reduced oxygen containing water stream having an oxygen concentration of less than about 7 ppb. 
   
   
       3 . The method of  claim 1 , wherein the step of supplying the reduced oxygen containing water stream to a boiler includes supplying the reduced oxygen containing water stream having essentially no oxygen contained therein. 
   
   
       4 . The method of  claim 1 , wherein the step of supplying a water supply stream to a deaerator stripper includes the step of supplying the water supply to a deaerator stripper being selected from the group consisting of an atomizer tower, a tray tower, and a packed tower. 
   
   
       5 . The method of  claim 1 , wherein the step of supplying a water supply stream includes supplying a water supply stream selected from the group consisting of a demineralized water supply stream, a condensate return stream, an external stream, and combinations thereof. 
   
   
       6 . The method of  claim 1 , further including a step of maintaining a water level within the deaerator water tank in a range of about 40% to about 70%. 
   
   
       7 . The method of  claim 6 , wherein the step of supplying a continuous nitrogen sweep to the deaerator water tank includes supplying the continuous nitrogen sweep to a vapor space located above the reduced oxygen containing water stream contained within the deaerator water tank. 
   
   
       8 . The method of  claim 1 , further including a step of supplying a low pressure steam stream to the deaerator stripper to assist in the step of removing at least a portion of oxygen and carbon dioxide contained within the water supply stream, the low pressure steam stream providing at least a portion of stripping vapors to remove the at least a portion of oxygen and carbon dioxide contained within the water supply stream. 
   
   
       9 . A method of removing oxygen from a boiler feed water stream, comprising the steps of:
 heating a water supply stream to produce a heated water supply stream;   supplying the heated water supply stream to a deaerator water tank;   supplying a nitrogen sweep to the deaerator water tank during deaerator operations thereby diffusing oxygen contained in the heated water supply stream resulting in a substantial portion of the oxygen being removed from the heated water supply stream; and   supplying the heated water supply stream to a boiler as a feed water stream having substantially reduced oxygen contained therein.   
   
   
       10 . The method of  claim 9 , wherein the step of supplying a water supply stream includes supplying a water supply stream selected from the group consisting of a demineralized water supply stream, a condensate return stream, an external stream, and combinations thereof. 
   
   
       11 . The method of  claim 9 , wherein the step of heating a water supply stream includes heating the water supply stream by heat exchange contact with a heat transfer stream selected from the group consisting of a condensate return stream, a low pressure steam stream, an external stream, and combinations thereof. 
   
   
       12 . A method of removing oxygen from a boiler feed water stream, comprising the steps of:
 supplying a heated water supply stream to a deaerator water tank;   supplying a nitrogen sweep to the deaerator water tank during deaerator operations thereby diffusing oxygen contained in the heated water supply stream resulting in a substantial portion of the oxygen being removed from the heated water supply stream; and   supplying the heated water supply stream to a boiler as a feed water stream having substantially reduced oxygen contained therein.   
   
   
       13 . The method of  claim 12 , wherein the step of supplying a heated water supply stream includes supplying a heated water supply stream selected from the group consisting of a heated demineralized water supply stream, a condensate return stream, an external heated stream, and combinations thereof. 
   
   
       14 . A deaerator apparatus for removing oxygen from boiler feed water comprising:
 a deaerator stripper to mechanically remove at least a portion of oxygen and at least a portion of carbon dioxide from a water supply stream supplied to the deaerator stripper, the deaerator stripper producing a reduced oxygen containing water stream that descends down the deaerator stripper to a deaerator water tank; and   a deaerator water tank for storing the reduced oxygen containing water stream, the deaerator water tank including a nitrogen supply connection and nitrogen return connection for providing a nitrogen sweep stream to diffuse remaining oxygen in the reduced oxygen containing water stream contained within the deaerator water tank resulting in a substantial portion of the remaining oxygen being removed from the reduced oxygen containing water stream.   
   
   
       15 . The deaerator apparatus of  claim 14 , wherein the deaerator stripper is selected from the group consisting of an atomizer tower, a tray tower, and a packed tower. 
   
   
       16 . The deaerator apparatus of  claim 14 , wherein the nitrogen supply connection and the nitrogen return connection are located within a vapor space located above the reduced oxygen containing water stream contained within the deaerator water tank.