Basic Question Looking for member experiences

[adirondackweldor]

We have a small Electric boiler at our facility. It is used to produce "clean" steam for sterilization of some piping and a couple small production machines. It is fed with RODI water with conductivities less than 1.00 microS/cm. We have always cleaned it with a citric acid based cleaner. This boiler is cold flushed daily before start-up. We test the steam condensate regularly for a number of things including total organic carbon. Despite hours of flushing, the citric acid causes a major upset in the TOC readings, and results in all sorts of hair pulling and teeth gnashing after every regular cleaning. Being responsible for this equipment, my department has increased the cleaning interval a couple times already, and are about to propose an even greater interval(we have never seen a trace of scale in 3 years). We have also discussed cleaning with a mineral acid. I am just curious if others here have dealt with a similar situation, and if so how you have handled it.

 

[puigi]

Using RO/DI water as your feed-water source should all but eliminate any chemical cleaning requirement. Are you chemically cleaning based on a predetermined frequency or a condition assessment (the presence of mineral scale)? I would not recommend perfoming a cleaning procedure unless there are deposits to remove.

 

[GenB]

I suggest after you flush with acid. To flush with another mild of chemical soap based. Non foaming.. consult a chemical company specialist in cleaning p. v.s. if

 

[Compositepro]

Why are you intentionally contaminating ("cleaning") your boiler every day? To remove mineral build-up in the boiler you should simply blow-down some water periodically. Acid washing should be infrequent and only when scale actually accumulates. Scale should not be a problem if you are feeding DI water and do periodic blow-down.

 

[GenB]

compositepro, generating clean or pure or even ultra pure steam is critical of some processes. some processes will not need the generator to be cleaned or even blown down ever but some processes require constant monitoring and I believe this is the case of this Company,
the suggestion to them is to find a mild soap or chemical based comparable with the acid as to clear the rems after "polishing it with acid"
and only a suitable knowledgeable chemical person or company can probably help them.
one question is to them to post the problem: just going crazy about the after chem cleaning is not a question. it got to be a water level system problem; pump overfilling or not filling; power disconnecting or not. what type of water level are they using noow.
that can help troubleshooting the problem.
genblr

 

[Compositepro]

According to the OP: "my department has increased the cleaning interval a couple times already, and are about to propose an even greater interval(we have never seen a trace of scale in 3 years".

It seems pretty clear that in this case they are unnecessarily creating a problem.

 

[zdas04]

It really does sound like you are creating more problems than you are solving with the acid flush. I can't tell how often you are doing this flush, but it sounds like it is based on a calendar instead of a need. If I had a requirement for ultra pure steam, I'd approach it with sampling (like you're doing) and watching for trends. If the TOC is creeping up, then I would set a condition-based PM to clean it out as the TOC approaches some point like 75% of the limit.

Then I would probably clean it with dense phase CO2 instead of acid. This stuff is starting to be used in all sorts of applications from dry cleaning clothing to replacing carbon tetra chloride for decreasing. It requires some skill to use, but seems to be incredibly effective.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[adirondackweldor]

Thanks for all the replies. When I first came to this job the cleaning interval was 60 days, I got it pushed to 90, then 120. I kept arguing that our makeup water is essentially mineral free, and the boiler is self sanitizing, therefore no scale, and no bio load. I argued for a couple of different cleaning chemicals, but got shot down. I finally convinced the powers that be that a regular inspection of internal surfaces is better than what we are doing. The boiler manufacturer sticks by their guns to clean with acid (HCL for non-food applications, citric otherwise) no less than once a year, but they are in CYA mode I think in this case, regardless of feed water quality. In any case I just performed a visual inspection and wonder of wonders, zero scale after 6 months. To answer one last question, we do blow down daily. We do a cold flush of makeup water before each boiler run. Basically open the drain, and start filling. The operators do this cold flush for 2 minutes each day at start-up.