DISSOLVED OXYGEN IN BOILER FEEDWATER

[tobman]

We have been obtaining higher than desired readings of dissolved oxygen within our boiler feedwater recently. Tests of the level of dissolved O2 in the suction of the boiler feedwater pump is currently 5 parts per billion and at the discharge it is 10 parts per billion. The question is: What can cause an increase in the level of dissolved oxygen within the boiler feedwater as it works its way through the pump?

 

[jproj]

Your pump either has an air or water leak (I thought I read in your other post that the pump is cooled by raw water). If the pump is operating above atmospheric pressure then an air leak is really not likely.

jproj

 

[nambi]

My Question is,

How are u measuring the Do2 in suction and discharge?

If there are no leaks then the possibility of increase in O2 content at the discharge may be due to the following reason.

1. If you are measuring continously using a sampling system then take care that the sample pressure inside the flow through chamber (for the discharge sample) is same as the pressure that of the suction sample (i.e from the deareator).

2. Based on my experience i can tell you that there would be drastic difference if you use two types of measurement (i.e inline instrument for one measurement and measurement by sample conditioning for the other)

3. Check for any leaks in the sample tubing.

 

[TBP]

I have seen installations where the pump suction can fall just slightly below atmospheric pressure. Not far enough to cause any particular operating problems, but just enough that a small amount of air is drawn in around the seal or packing.

 

[chicopee]

PUMP SEALS ARE A COMMON PROBLEM TO AIR GETTING INTO THE CONDENSATE RETURN.