BFW Contamination with HC material 4

[processrj]

Greetings,

We experienced an oily contamination (*) in the high grade condensate used for four 550 psig pressure boilers. During two days the ph of the boilers' blowdown were detected by portable analyzers getting reduced from an average of 10 to about 6.5 - 8.0. Any ideas what might have caused this reduction in the ph? Why the presence of hydrocarbon (the oily material) may cause a pH reduction?

Contributors to this high grade condensate are 7 different plants, but no check was immediately made on their condensate until it was observed in the tanks (where this condensate is stored before being sent for deaeration) after two days. None revealed to show oily floating layers, nor traces of oil and grease. We are curretly developing hypotheses to find the cause, so any insights/clues from this forum will be of great help.

Thanks in advance.

(*) Evidenced by an oily layer floating on samples taken.

 

[mk3223]

IMO, the oily contamination and low pH in BFW are two different issues.
The pH control in BFW is a specialized and continuous process, and normally handled by the water treatment specialist, such as Nalco. The BFW may be continuously monitored and treated at the the condensate collection tank before the BFW feed pump.
In order to find out the source oft he oily contamination in BFW from 7 different plants, it is a big task and take some time and effort.

 

[processrj]

Thanks mk3223 for your feedback...Yes indeed it's been hard to find out the source of the HC/oily contamination. We are not quite sure if the reduction of boilers ph and the presence of oily material are separate issues or not, since this pH reduction took place whilst we experienced this condensate contamination....Is it possible that this foreign oily material could have inhited the performance / action of the chemicals influencing the pH of the BFW? If so, what might this mechanism be?

Thanks again for any feedback on this trial!

 

[EdStainless]

If you have condensate returning from multiple uses you need to have continuous monitoring on each of them. At some point it is more economical to dump 'bad' condensate than try to treat it. After all ion exchange is likely your only treatment option since you have strict TDS limits to stick to, you can't always 'just add more chemicals'.
The first thing that I would look for is a process that isn't continuous, either intermittent or in batches. Those are the most likely to have upsets.
Look at a good water analysis and figure out what caused the pH drop (which ions), then you might be able pinpoint the source easier.

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P.E. Metallurgy, consulting work welcomed

 

[springrise]

Hi,
I think there are several mechanisms how the oily contamination could lower the pH.
I assume you use NaOH to adjust the pH.
Maybe there was an interaction of NaOH with organics - emulgation.
Maybe the organics fouled the pH probe that controls the dosing.
Organics negatively affecting the deaeration process.
Have you checked if your dosing system is somehow disturbed? A contamination in your NaOH? (IBC containers?)
Just some wild ideas.

 

[hacksaw]

If the steam return is eventually used in process heat exchanges, you may be dealing with heat exchanger leakage.

 

[processrj]

Thanks for your kind feedback hacksaw, springrise & EdStainless.
We used a corrosion inhibitor based on 5 to 10 % NaOH among other components. When we noticed the pH reduction, we increased the dosing of this chemical to overcome the situation.

Question; under what mechanism could organics affect the deaeration process and this in turn get translated into a pH reduction in the boilers BFW?

The organic/oily material observed in the condensate was dark in color. Since there are some 5 turbine running with 500 & 170 psig steam that are contributors to this system. How wild an idea would be to think on a potential oil ingress from the bearings lubrication system into the turbine steam exhaust?

Thanks in advance for kind feedbacks.

 

[hacksaw]

As a rule lube oils are not acidic. High sulfur petroleum products do and release various acids.
Get a chemical assay of the dearator liquids, or take samples from the heat exchanger returns.

 

[processrj]

The high grade condensateis involved in the contamination is made up mainly from the steam exhaust of 500 # steam turbines ( 7 in total). This is why we wonder how likely is for the lub oil employed in these turbine to be the source of the contamination. Unfortunately when this event ocurred no samples were kept for further analysis. We do have some DCS data that can be track back to see trends during the core period of the incident.

 

[hacksaw]

lube oils have an acid number that advise of it protective benefit

https://www.machinerylubrication.com/Read/30007/acid-number-limits