High pressure condensate temperature

Hi, I was very confused about the condensate temperature from the high pressure steam. For example, if the condensate is from a high pressure steam of 125psig, is it going to be 353F or is it going to be 212F same as the 0psig condensate?

 

[Goorah]

Beginner:

Remember saturation temps, subcooling and superheat?

Look at a steam table to find the "saturation temp" associated with the fluid (water) pressure. Then if the actual water temperature is above the sat'd temp (for that P) you have "superheated" condensate: [Tsh = Tact-Tsat]

If the Tact is below the Tsat, then you have subcooled condensate: [Tsat-Tact = Tsc]

Why is this important? Ideally you want to minimize heat input @ boiler to change the condensate back to steam; so you shouldn't subcool the water ... it should be sat's so the entire Hfg is not needed to change phase (1,000BTU/lb-F).

This mixed condensate [part sat'd, part superheated and maybe part subcooled (a really small par; hopefully)]has a certain "quality" depending on the % of the total mass that is fully sat'd. Fully sat'd condensate requires the least amount of heat to change back to the steam phase. Let's say that 50% "quality" requires only 500 BTUH/lb-F...... See what I mean???

Any "Steam Experts" out there are welcome to comment as well. Buddha's advice 2,500 yrs ago (I'm Christian!!???!!): "After deep, careful observation/analysis; and it agrees with reason, is conducive to the common good: accept it and live up to it."

 

[ChasBean1]

Beginner - Goorah is right, but to simplify, it will be at or just below the saturation temperature for that pressure. Condensate lines could have some pressure above atmospheric, but the condensate will be at a temperature that correlates with the pressure in the condensate line after traps. The condensate will not be at the saturation (or slight subcooling) temperature correlating to the steam main pressure.

 

[quark]

Beginner!

As far as steam is concerned 125 psi is not high pressure and is called medium pressure. (pardon me from being irrelevant at this moment) When heat transfer takes from steam to some other mass, latent heat is being transfered to the mass and x deg.C steam becomes x deg.C water(condensate).

Some traps (thermostatic)restrict condensate flow to a certain offset so that you can utilise high sensible heat also. As long as your condensate flows in a pipeline you can consider it's pressure equal to that of steam pressure (unless you didn't install a pressure gauge) and the temperature is saturated temperature. The moment condensate enters atmosphere part of condensate flashes because of the pressure drop by taking heat from the remaining condensate. So remaining condensate temperature drops down.

As for Goorah I disagree with superheated condensate as that case is hypothetical only. There will be a mix of condensate and steam but not superheated condensate.

One Kg of water at 100 deg.C takes 550Kcal/Kg of heat to evaporate. You require only 1 Kcal/Kg of heat to heat up water by 1deg.C. That is why Saturation and total heat capacity are not directly proportional by multiples.

Regards,

 

Thanks guys... Actually I would like to calculate the expansion of the high pressure (or medium pressure as quark mentioned) condensate line at 125psig. So if the condensate temperature of about 350F (for 125psig steam) vs. 210F (for 0psig steam make a lot of difference. Besides, when I select the steam trap (inverted bucket), am I going to use the full differential pressure (which is about 125psig) or only partial of it? Thanks again.

 

[TBP]

I would disagree with quark on the classification of 125 PSIG steam as "medium" pressure. That's a relative term. I worked in a central station where the 450 PSIG steam system was referred to as "low pressure". And compared to the 2,600 PSIG main steam supply, it was. As far as the ASME piping codes are concerned, if the safety vavles lift at anything over 15 PSIG, it's a pressure piping system.

The differential pressure across the orifice in the trap will determine the flow. If there no temperature control valve that will throttle the upstream steam pressure, then the only time you'll have pressure lower than 125 is on a start up. If your trap discharges directly to a vented receiver, then the downstream pressure is "0". If it discharges to a condensate header with traps from other points also feeding into it, the pressure across the trap in question can (and likely will) vary.

Select the trap size based on the operational requirements. However, make sure the BODY of the trap you select is rated for the safety valve setting, which is very likely 150 PSIG. There are a huge number of systems like this (operating at 125 PSIG) that are just full of under-rated components like valve, strainer & trap bodies.

 

[Goorah]

TBP:

Well said!! I read of a service man who was knocked unconscious in a valve pit and then literall cooked to death by "low pressure" steam at 15 psig. :-(

No pun intended, but at a saturation temp of 212F the poor guy was "well done" when they found him. (Yuck :-( )

In any case, a vapor that "hot" for humans is nothing to be played with; which is why ASME has the codes it does.

As for "superheated condensate", the problem of flash gas in the return line is present if the pressure drops too low in the return.

AT least that's what I was told when sizing traps for absorption chillers; or did I hear incorrectly?

Does anyone know of a good web site to get a "primer" on steam? This is sort of a lost art these days.

Thanks, guys. Buddha's advice 2,500 yrs ago (I'm Christian!!???!!): "After deep, careful observation/analysis; and it agrees with reason, is conducive to the common good: accept it and live up to it."

 

[ChasBean1]

Beginner, yes, use the full DP. Elsewise, stick a gauge on the condensate line. You'll generally only find that condensate drains are pressurized if you have one or more faulty traps. You'll also find that condensate lines are gravity-drain systems, although they can usually still work with some incline in the piping because the upstream pressure is so much greater than downstream pressure. Otherwise, how would you size a condensate system so that it remains at a pressure equal to the steam side? If you are a refrigerant kind of guy, why is there a high side and a low side? The trap sort of acts as the expansion valve in that it changes the phase of the throttled medium while greatly reducing pressure. Assume atmospheric/saturated or slightly subcooled at atmospheric pressure for your calcs. Good luck, CB

 

[TBP]

goorah - Check out

http://www.bellgossett.com

for online info on steam equipment. Spirax Sarco's "Hook-Ups" is an excellent publication. Beginners should look at their "Steam Utilization" book first. People should remember that these publications are coming at this topic from a function standpoint, as opposed to any codes that may apply. And conversly, that the code folks don't really care if your system functions as intended, only that it's safe. These are two separate, but related, issues that the designer must address.

There's also "The Lost Art Of Steam Heating" by Dan Holohan -

http://www.heatinghelp.com

. It's on residential & small commercial systems, but these all work the same way. It covers steam heating from the 1850's to the 1940's. Things like considering differential pressures become even more important when you're only dealing with 1 or 2 PSIG for supply pressure, and sometimes, just ounces.

 

[Goorah]

TBP:

Thanks much, TBP. The web and info highwayis truly a wonderful place!

Now I just need a good antivirus package. :-0 Buddha's advice 2,500 yrs ago (I'm Christian!!???!!): "After deep, careful observation/analysis; and it agrees with reason, is conducive to the common good: accept it and live up to it."

 

[quark]

Only fascination I have of cannibals is Ursula Endress (sorry if I sound ironically). But that is quite high a temperature to cook anything. 121 deg. C is called wet sterilization temperature for heat at this temperature can kill any living organism.

Once a wise guy was asked to make a line shorter but he was not supposed to erase it. The wise guy drew a longer line beside that and made it short.

The broad classification of low, medium and high pressure steam is 0 to 10, 10 to 30 and 30 to 60 Kg/Sq.Cm respectively as per boiler manufacturers. ( as per bobcock and wilcox)

For rest of the things I agree with TBP.

For superheated condensate, at any point of time and pressure there does exist some flash steam which reduces the temperature of the condensate, and nothing like superheated condensate.

Regards,

 

[Goorah]

Quark:

Thanks for wrapping up this nice little discussion. I really learned a lot. Thanks to everyone else who kicked in their 10 cents. The only dumb ? are one not ??

Even though "i've worked with steam" for awhile, it appears I always have something to learn; which makes life not dull! ;-)

What is you're area of "specialty" Quark?

Me: I'm sort of a "generalist" and so I know less and less about more and more until I seem to know nothing about everything.

Of course you all know the flip side of that... !!

Yes!! .............. Generalists ans Specialists are one and the same.

As Quark said: It's all relative!

Now if you want.................. Let's talk about steam at "vacuum" pressure levels.

Why? Because single stage absorption chillers can turn even that waste into chillec water. Preactically speaking, commercial large chillers work (with a derate) to about 20" Hg vacuum. The limit right now is economics; but it does pose an interesting possibility of extracting all we can out of our environment... if $ were not a concern.

Actually on second thought: let's stay focused on "practical" engineering matters!!

Ciau!

Buddha's advice 2,500 yrs ago (I'm Christian!!???!!): "After deep, careful observation/analysis; and it agrees with reason, is conducive to the common good: accept it and live up to it."

 

[TBP]

quark - We'll have to agree to disagree on the "low-medium-high" pressure designation. I do a lot of piping work (mostly steam & compressed air) in various plants, and the confusion about the applicable piping codes is just about total. I've found it's best to stick with the ASME threshold of "if the safety valve lifts at anything over 15 PSIG, it's a pressure piping system". I was in a little place a couple of weeks ago, trying to tell the maintenance supervisor that just because he RAN his boiler at 10 PSIG that didn't make it (and his piping system) "low pressure", because the boiler safety valve was set for 65 PSIG. As far as the code is concerned, his plant (boiler and piping) are under it. I doubt he believes what I'm telling him. He really thinks that because he operates at 10 PSIG, he's "low pressure", and is out from under all of the code requirements.

 

[Goorah]

Hello All:

This conversation gets better and better!!

And I thought it was "wrapped"!

As someone in this thread said: "All things are relative."

About all I can say to the last message is: RIGHT ON!!!

Perhaps this too: "The existence of a code does not a safe installation make."

Maybe Buddah was right: to paraphrase him: "dig below the surface"

Heck even old Sherlock Holmes hasn't let us down: "Once you have eliminated the obvious, whatever remains however improbable has got to be the truth!"



Buddha's advice 2,500 yrs ago (I'm Christian!!???!!): "After deep, careful observation/analysis; and it agrees with reason, is conducive to the common good: accept it and live up to it."