Flash vessel control valves 1

[Abhijeet242]

Hello community,

I am working on a selection of control valve, which will regulate the inlet to the Flash vessel. The sizes of the inlet and outlet of the valve are DN600 and DN1800.
Is it realistic? Are there any flash vessels with the inlet flanges more than DN1000 or so?

Also one more question, what are the typical control valves ( I mean which type: Globe straight passage valves or Angle valves) used at the inlet to the flash vessel?
This question I ask specifically, because I assume the flashing is common inside these valves? is it right?

Thank you community for the help.

 

[shvet]

what fluid is this flash vessel going flashing?

 

[LittleInch]

Far too vague.

But a 70 inch flange??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

From memory, for solids free non corrosive flashing, baseline selection would be stellite hardened trim.

 

[Abhijeet242]

Thank you for the comments community! The fluid here is Deaerated water/ steam.

 

[NovaStark]

@Abhijeet242

These are quite large pipe sizes.

What flow rate and DP are you looking at? Depening on these, you will need stellit trims as georgeverghese suggested but also you can possibly run into steam erosion problems in the piping itself. Noise can also be a factor as well (maybe you might need special trims for noise e.g. whisper type from Fisher).

 

[MJCronin]

Najeeb,

If you are trying to size and design a flash steam system and your valve is part of a boiler blowdown tank/vessel, I suggest that you specify and purchase the entire system, including valves, tanks and controls ...

Otherwise, we will have another 317 questions from you as you slowly come to realize what you are trying to do ...

Q1 ......Is this task related to a boiler blowdown/blowoff tank ?
Q2.......What are the massflows, temperatures, pressures and duty cycles ?
Q3 ......Why do you insist on designing your own system, valve by valve ... instead of purchasing a system from those with experience who know the Codes and boiler opeations ?
Q4...... What else can you tell us ?.... Spill ...

https://www.pennseparator.com/prod.htm

https://cleaverbrooks.com/Product/blowdown-systems

Anxiously awaiting your response

MJCronin
Sr. Process Engineer

 

[georgeverghese]

Will placing the entire duty on a single large control valve pose flow turndown issues ? What is min operating flow and what is max operating flow ? Note that control valve turndown on Cv is usually 25:1, and specially engineered control valve may do 50:1( not recommended). So do you have the sizing spec sheet for this valve? What is the required Cv in both min flow and max flow cases? Can we see it? Also post a PID so we get some background.
If min Cv to max Cv exceed 25:1, it is better to use 2 control valves arranged in parallel - one smaller Cv, and the other with larger Cv, and operate them on split range.

 

[shvet]

DN600 means ~1'500 tones of water per hour. What is a process that produces 1.5k t/h of deaerated [and I assume demineralized] water? Community definetly should know more about this megafactory! Where does this DN600 water pipe come from?

 

[Abhijeet242]

@MJCronin
Thanks for the cool link about steam system.I am not designing a complete flash system and so no reason to expect any further questions. At this point, I also dont have much information or lets say, not much information which I could share, from my client. But what I understood is that, the client is also in Design phase. As pointed out by @shvet correctly, the flows are really that high about 2400 tonnes/hr of dearated water. And thats the reason why, it completely blown my mind, to imagine how big the Deaerator tank/ Vessel will be and how big the Flash vessel will be.
Hence I just wanted to know from community, if something like this is expected in steam applications. Because I have never seen Flash steam valves so big. I will try to find out from my client, if what they are designing/ calculating is really worthwhile or is it just a mistake somewhere in the calculations. Thank you guys!

 

[shvet]

Seems like a mistype from Client side - 2400 kg/h, not 2400 t/h.

what are the typical control valves ( I mean which type: Globe straight passage valves or Angle valves) used at the inlet to the flash vessel?

See chap. 6

https://www.emerson.com/documents/a...sourcebook-power-severe-service-en-137754.pdf

as mentioned above Cv rangebility will be a main issue

 

[KevinNZ]

Seems similar to geothermal power stations flash systems. I have seen systems for up to 4000t/h of water. But not with one control valve. These systems often use ball sector valves and bespoke globe valves.

 

[FacEngrPE]

Geothermal power stations are NOT flashing demineralized water. That water will contain saturated levels of dissolved solids, and may also contain large amounts of just precipitated solids. This sticky material significantly complicates design.

A Guide for Blowoff Vessels - 2012 Edition - NB-27 is the best reference I am aware of for blowoff vessel design. The design of flashtanks is very similar. These vessels must be considered pressure vessels unless the venting is unrestricted, and large enough that pressure will not rise above the criteria requiring a code tank (usually 15 psig).

https://www.nationalboard.org/index.aspx?pageID=357

[highlight #FCE94F]NB-27,Guide for Blowoff Vessels 2024 Edition, Rev. 0[/highlight]

The 2012 edition discussed below contains design information not included in the 2024 edition.

https://www.campbell-sevey.com/nb-27-a-guide-for-blowoff-or-blowdown-vessels/

https://www.maddenep.com/a-simplified-walk-through-of-the-nb-27-guide-for-blowoff-vessels/