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We have ongoing issues with our Dissolved Oxygen levels (as measured at Condensate Pump discharge) which average well above the target 10 ppb, even upwards of 300 ppb. As expected, the high DO spikes are typical after saturated Demin makeup is delivered to the DA. The DA is supposedly designed to remove DO levels to <10ppb even with saturated makeup water. Regardless, I think a performance check on the Deaerator is warranted.
I have reviewed the HEI standard for tray type Deaerators, specifically section 7.4 (Testing). It is clear that the sample should be taken from a point as close the Condensate Storage tank as possible to eliminate the potential for air in-leakages causing false readings of the DA performance. The HEI standard also recommends running the sample for 2 hours prior to taking readings. Because the DA is operated at vacuum (~2.5 psia) it poses the obvious challenge of pulling a sample stream between the Condensate Storage tank and the Cond Pump suction nozzle. I am considering using a grab sample chamber with appropriate isolation and vent valving and a small vacuum pump to evacuate the air. My concern is that with this method the sample could be contaminated with air as the grab sample chamber would need to be opened to atmosphere before draining down the sample for testing with a colorimetric test (CHEMets kit).
I contacted the DA manufacturer for support and they had no experience with testing a Vacuum Deaerator. Has anyone completed an online performance test of their Vacuum DA? If so, I would appreciate any information related to your test setup, equipment, and methodology. Thanks.
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Hi Noah.
Maybe a little late but here goes. I’m not a specialist in the area myself but I have a colleague or two and I ask them since it’s quite an interesting problem.
We don’t know if the problem is with the DA. Here’s why…
We have tray types DA’s at an old station of ours (wet cooled) – 1960s. These particular trays have a lot of vibration and are on fairly small brackets and mostly break out later. As the trays failed in one of the units we simply took them out. At the end there were only one or two trays left (probably 6 months back), but the DA still worked as he should do with DO’s in spec. We believe the saturated conditions in the DA with condensate falling from the top with a reasonable spread (1 tray) are sufficient…
Having said that no one really knows exactly what’s going on in the DA. This specific DAs had two tanks, each 50m^3 each. You have condensates and distillates that come in, feed water suction that goes off, RFT filling in, balancing lines between the two tanks above and below, the vents that go out and then you try to control the level quite accurately by adding more water in the condenser or dumping condensate to the RFT i.e. many things going on!
To answer the question, we’ve noted ASME PTC 12.3: Performance Test Code on Deaerators. We’ll start there.
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