We have a 360 MW CCPP. For boiler make up & other usage we have a 20 m3/hr (20hr) capacity (400m3 before exhausted) Demi water train (2B3T) comprised of One SAC column(2200L), one mixed Anion column (30% WBA+70%SBA;1400L) and one Mixed bed polisher(300L SAC+300L SBA).

The outlet conductivity of MBP is 0.3~0.4 micro siemens/cm and the water from MBP directly goes to storage tank. There are two Demi water transfer pumps which supply to condenser as make up. There is a conductivity meter at common discharge of Demi water transfer pumps.

This conductivity meter shows 1.74 micro siemens/cm almost always. The storage tank has a top vent to atmosphere. We had experience the conductivity at storage tank 0.9 ~ 1.0 micro siemens/cm. But this time we are experiencing a higher conductivity. The outlet water pH & conductivity of Anion & MBP are 7.0 & 6.56 and .3 micro siemens/cm & 0.3 micro siemens/cm respectively. Can anyone help me to find the real cause of the problem?

 

Could be lots of things.

Is your tank isolated from the rest of the plant or do you recycle back to it?

Is it possible you have a lining failure in your tank?

Or some corrosion in your piping?

Does your tank use a nitrogen blanket? or is it just vented to atmosphere.

I can't think well in uS but 0.3 uS is only 3 MegOhm water and that is not all that pure. I am kind of surprised your mixed bed can't produce better quality then that. perhaps the resin is not separating properly or is not being mixed after regeneration.

The ph does not mean all that much.

Have you tried to talk with the equipment supplier? You might want to get a grab sample coming out of the tank and have it analyzed to see if there is some kind of contaminant in it. It might just be CO2 from the atmosphere though. The only way to deal with that is a nitrogen blanket.

--
Bob

 

For your kind information...

1. The tank is isolated from rest of the plant. The water from the tank supplies to users by two transfer pumps. There is no option for recycling.

2. There is no line failure.

3. There is no nitrogen blanketing system. It is just vented to atmosphere.

With the same equipment we had experienced 0.9 micro-siemens/cm conductivity at storage tank. But this time it is 1.74 micro-siemens/cm.

Can a contaminant resin continuously contribute to increase the conductivity?

 

>The tank is isolated from rest of the plant. The water from the tank supplies to users by two transfer pumps. There is no option for recycling.<

Have you done a water sample recently? You really need to compare a recent water sample with one done before you had the problem. Might be something growing in the tank. Not real likely, but if you had a small amount of resin leakage out of your mixed bed... Do you have resin traps downstream of your mixed bed? Have you noticed that your MB resin level has dropped over the last year or so?

>There is no line failure.<

How do you know this? Has it been spark tested lately? That's really the only way to know. And if it is an FRP or other kind of plastic tank is it possible that it has degraded over time? Possibly due to being out in the sun and exposed to UV?

>There is no nitrogen blanketing system. It is just vented to atmosphere.<

You could be getting contaminants in through the vent. Anything from CO2 to birds. Have you inspected the venting system recently? Do you tightly control the level so it is as high as possible in this makeup tank so that you don't get as much air in though the vent? Or do you have wide and regular swings in level?

>With the same equipment we had experienced 0.9 micro-siemens/cm conductivity at storage tank. But this time it is 1.74 micro-siemens/cm.<

You might be able to clean it up by rigging a recycle line from the pump discharge back to the mixed bed inlet.

>Can a contaminant resin continuously contribute to increase the
conductivity?<

If the water quality going into the tank has not changed, it is likely something to do with the tank itself. Perhaps a dead bird is floating on top of the water.

 

Thanks for your reply. Will come back after doing the tests those you suggested.

 

What is the pH at the Demi Tank Outlet? If it is above 7, CO2 absorption from atmosphere is possible.