Deaerator Blowdown Pipe Sizing 2

[dogbertcountry2]

I have a deaerator with a surge tank below to serve as Boiler Feedwater to gas fired boilers. We use a sulfite for oxygen scavenging. The deaerator has a continuous blowdown line for further non-condensables removal.

Somewhere along the line, someone advised the plant population that a 18-inch plume should be visible to confirm proper oxygen removal. I am guessing that this was a rul-of-thumb that just confirms that there is a bleed off point, but I would like to know anyone else's experiences with this.

Furthermore, I am wondering what sizing criteria should be used for this removal line. We were planning on creating a gravity separation of the condensate and non-condensables using a vertically aligned Tee. I am unsure of the guidelines for sizing this line and if there is some plume length required.

 

[rmw]

Where is this "blowdown" line? Blowdown usually connotes a liquid line at a low point in a process or vessel. Might you mean a "blow off" line located at the top of the deaerator?

If so, it was common in the old days to have a gate valve in this line with a hole drilled in the gate so that it would continuously vent while the valve was closed. The valve could be opened during start up conditions when there was lots of non condensables to vent and closed when in operation. The size of the hole was determined by the deaerator manufacturer. The piping size wasn't very large, normally 1/2" or 3/4".

I like the 18" rule of thumb although I never hear it before.

rmw

 

[mbeychok]

dogbertcountry2:

With all due respect, your use of the words "blowdown" and "non-condensibles" is confusing. As pointed out by rmw, there is no "blowdown" from a typical deaerator. Instead there is a vent on top of the deaerator.

The function of a deaerator is to use steam to strip dissolved air from the incoming boiler feedwater (so as to lower the the oxygen content of the boiler feedwater). The stripped-out air exits via the vent. We don't usually refer to that stripped-out air as "non-condensibles" in this context.

Perhaps the very simplified diagram of a typical deaerator shown below will help:

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[dogbertcountry2]

rmw, thank you for your response and demonstrated ability to understand a problem and answer the question, despite the phrasing. I did indeed mean "blow-off" from the top of the deaerator. I was unaware of the history progression that you offered. Again, many thanks.

mbeychok, thanks for the lesson, but an answer would have been more helpful. You misspelled and misquoted "non-condensables" by the way. Furthermore, air, in a typical manufacturing plant, is considered a non-condensable. I recognize the use of the term "blowdown" is inappropriate - as noted by rmw by correcting to "blow off". Perhaps you are unfamiliar with un-exact plant jargon. Neverthelless, thanks for the response. I asked for what other people thought.

 

[sailoday28]

dogbertcountry2 (Chemical)
I have no comments on size/length of plume.
Other than rule of thumb or recommendation of DA vendor, the sizing of vent line should be based on max expected flow rate of air in a line with 100 %RH. Of course upstream and downstream pressures/temp and friction effects will also guide.

Regards

 

[mbeychok]

dogbertcountry2:

I did not misspell condensibles. My Webster's dictionary has both spellings ... condensible and condensable.

When a condenser is involved (as on the overhead of a distillation column, for one example), we speak of condensibles and non-condensibles. A deareator is not a condenser, it is a stripper and it is removing air from the incoming boiler feedwater... and, therefore, I found your use of the word non-condensibles (or non-condensables) to be somewhat inappropriate. Hence, I decided to include a sketch. I regret that my response seems to have offended you for some reason.

You may be right, perhaps after 50 years of designing and operating oil refineries and other plants, I may not be familiar with industry jargon.

I really appreciated your gracious thanks.




Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[toothless]

Wow Dogbert,

Based on your original question including the apparent misunderstanding of a blowdown vs. blowoff, I thought MBeychok's first response was completely appropriate providing you with the most basic information required.

You ask for help, he attempts to provide it, and in return he receives an insult. Good luck getting advice from this site in the future.

 

[BenThayer]

ditto toothless's comments!

 

[dogbertcountry2]

Dear mbeychok,

I am humbly writing in response to my inappropriate response from a few days ago. Please accept my sincerest apologies. I am sure that given your wealth of years within both industry and in life, that you too have.... reached a breaking point. Indeed, I have met mine. I have prided myself in rising above such hurdles in years past, but alas, I have fell victim to...... stress. And my reply was given during this breakdown.

Regardless, this does not excuse nor justify my behavior. I only hope that you will to coninue to help those who request help and do not let my demonstrated foul spirit keep others from benefitting from your experience and wisdom.

Again, I offer my apologies.

 

[rmw]

I'll give you a star for that. A really professional post.

rmw

 

[mbeychok]

dogbertcountry2:

Apology accepted.

Milt Beychok