exnavynuke
Industrial
- Jan 3, 2005
- 13
Steam cycle chemistry question.
Background: This is a 2x1 550 MW merchant power plant with 7FA gas turbines, two IHI heat recovery steam generators (HRSGs), and a D-11 steam turbine, with auxialiaries. Heat removal is by forced draft cooling tower.
We have been using an excessive amount of amine to keep condensate pH within spec (9.0-9.6). We had been using about 200 gal/week of Nalco 352, which is %(w/w) 40-70% morpholine.
We have recently begun testing Nalco Tri-Act 1800, which is %(w/w): (according to the vendor, this is stronger stuff, so we will require less of it)
5-10% Cyclohexylamine
10-30% Monoethanolamine
10-30% Methoxypropylamine
This quick fix does not resolve the real problem however of too much acidity in the system that requires excessive amounts of chemical to neutralize.
Here's where we are: Three year old plant that has had the HRSGs chemically cleaned during start-up. Previously experienced major condenser tube failure, that went on for a long time before it was identified.
The condenser tube failure was corrected several months ago and currently the HP drum blowdowns are shut to about 8%, IP shut to about 30%, with silica well under control. Surveys have been performed on the main condenser to check for air leakage (oxygen demand), and several leaks were corrected. Air leakage falls within the design limits of the condenser.
There has *never* been a sample in which dissolved oxygen was detected in either the condensate or boiler feedwater(we test down to 2ppb).
The make-up water is quite clean with no detectable chloride and average of 2-4 ppb silica. In any event we don't make up much of it with the blowdowns shut so far.
So... I'm humbly requesting some help from people with other experiences in this subject: Why are we using so much chemical to maintain pH? Is the DA scrubbing it all out because it's much more volatile than water? The DA vents don't seem to be blasting more than any other plants I've worked at...
Background: This is a 2x1 550 MW merchant power plant with 7FA gas turbines, two IHI heat recovery steam generators (HRSGs), and a D-11 steam turbine, with auxialiaries. Heat removal is by forced draft cooling tower.
We have been using an excessive amount of amine to keep condensate pH within spec (9.0-9.6). We had been using about 200 gal/week of Nalco 352, which is %(w/w) 40-70% morpholine.
We have recently begun testing Nalco Tri-Act 1800, which is %(w/w): (according to the vendor, this is stronger stuff, so we will require less of it)
5-10% Cyclohexylamine
10-30% Monoethanolamine
10-30% Methoxypropylamine
This quick fix does not resolve the real problem however of too much acidity in the system that requires excessive amounts of chemical to neutralize.
Here's where we are: Three year old plant that has had the HRSGs chemically cleaned during start-up. Previously experienced major condenser tube failure, that went on for a long time before it was identified.
The condenser tube failure was corrected several months ago and currently the HP drum blowdowns are shut to about 8%, IP shut to about 30%, with silica well under control. Surveys have been performed on the main condenser to check for air leakage (oxygen demand), and several leaks were corrected. Air leakage falls within the design limits of the condenser.
There has *never* been a sample in which dissolved oxygen was detected in either the condensate or boiler feedwater(we test down to 2ppb).
The make-up water is quite clean with no detectable chloride and average of 2-4 ppb silica. In any event we don't make up much of it with the blowdowns shut so far.
So... I'm humbly requesting some help from people with other experiences in this subject: Why are we using so much chemical to maintain pH? Is the DA scrubbing it all out because it's much more volatile than water? The DA vents don't seem to be blasting more than any other plants I've worked at...
