Surface condenser Mechanical design 2

[deepu78]

Hi All,

Surface condenser mechanical design using HEI
Does any one has information regarding Surface condenser mechanical design and fabrication?

 

[MJCronin]

deep ...

As is typical, you offer almost zero information because this would require another minute of your time, so...

LET THE GUESSING GAMES BEGIN !!!

First, is this a "Steam Surface Condenser" operating as part of a Rankine cycle power plant or in a process chemical steam application ? ... perhaps something else ?... Who the hell knows ?

- What are the design/operating temperatures and pressures ?
- What are your desired materials of construction for the shell ?
- What are your desired materials of construction for the tubesheets ?
- What is YOUR SELECTION for condenser tube materials ? (you have many choices, budget and availabilty is key )
- Will the SCC accept "steam dumps" common among steam plant upset operations ?

...... and on and on and on ....

Eng-tips has many threads about SCC design... suggest that you read up a bit and ask more specific design questions

Oh, ... and never, never use "please" or "thank you" ... these are common terms of respect we use here in the west

.., and we do not like to see these terms used by newbies .... Just bark out your demands !!

MJCronin
Sr. Process Engineer

 

[Latexman]

Goodness gracious, MJ! You've outdone yourself. I'm surprised you didn't tell them "and keep off my grass" too.

deepu78 - my advice is learn to use Search. Top left, between Forum and FAQs. You will may learn a lot!

Good Luck,
Latexman

 

[EdStainless]

First, You need to own one of these;

https://www.heatexchange.org/products/standards-for-steam-surface-condensers-12th-edition

Then come back when you have some specific questions.
There are a lot of issues involved and the standard covers most of them fairly well.

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P.E. Metallurgy, consulting work welcomed

 

[deepu78]

Hi All,
1. What is the difference in design between steam surface condenser and other process condensers for Eg. Ammonia condenser
2.HEI-2629 is used for thermal design of surface condenser. Why it is not used for ammonia condenser thermal design?
3.To increase the size of surface condenser(number of tubes increased 50%), what all needs to be considered with regards to turbine steam out let and ejector performance?
4.Why baffle design is critical to the surface condenser performance?
5.Is mechanical design proprietary for different surface condenser manufacturer.

 

[EdStainless]

The HEI steam surface condenser standard is based off of 7/8" OD brass tubing (at a fixed flow rate, enthalpy, and so on) and everything else uses correction factors.
There are very definite limits in how far you can push this approach.
Changing the condensing fluid is well outside of what this model was intended for.
You have to think about the size of the condenser and how it is mounted.
Is small and hung from the turbine? Is it larger and mounted on spring packs? Is it huge and firmly anchored with flex joints above?
If you are intending to move more steam you will need to look at the turbine outlet design because of flow velocities and pressure drop. The turbine will handle that much more steam? Or is the steam from another source?
Your ability to extract non-condensables is a function of the condenser size. Bigger means that you will need more.
The support plates are the only structural part of a condenser. Their spacing is critical for controlling tube vibration and how they are braced supports the entire shell.
In theory you could either go wider or longer. These options have very different cooling water demands (wither more flow or more head).
Either way the thermal design becomes a real issue.
Model the existing one and get a baseline. I presume that you have all of the needed details (materials, sized, temps and flow for both sides, and so on).
I usually use the HEI default values and then add a correction factor to match the current actual performance.

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P.E. Metallurgy, consulting work welcomed

 

[deepu78]

Thanks.
Can steam surface condenser can be designed to any other standard other than HEI-2629?

 

[MJCronin]

EdStainless offers good and practical advice based on years of experience ... He is a seasoned professional engineer.

Wisely, he points to the crux of the engineering issues ...

In my opinion, Steam Surface Condenser design for a BRAND NEW application by a BRAND NEW employee has special and unique challenges

1) There must be a balance between the limitations of the mechanical design and the desired thermal design
2) SSC design is particularly sensitive to selection of tube materials, gauge and baffle spacing
3) Inlike most other STHXs, SCCs are very sensitive to tube vibration for some materials
4) Subtle issues such as internal vapor flow, non-condensible removal and steam dump can often control overall design
5) SSC casing thermal expanasion and support issues are non-trivial and complex (unlike most smaller STHXs)
6) You can design your silly ammonia condenser to any damn standard you want to .... there are no codes and standards i

Please tell us nothing about your particular problem ... by all means, dribble information out, bit by bit ...,

What are your thermal and flowrate design conditions ?

What materials have you selected for use ?







MJCronin
Sr. Process Engineer

 

[MJCronin]

These Steam Surface Condenser postings might help:

https://www.eng-tips.com/viewthread.cfm?qid=455296

https://www.eng-tips.com/viewthread.cfm?qid=284853

https://www.eng-tips.com/viewthread.cfm?qid=377707

MJCronin
Sr. Process Engineer

 

[deepu78]

https://www.eng-tips.com/viewthread.cfm?qid=455296

in the thread above davefitz (Mechanical) mentioned
"...The US designers did not consider the fact that the steam to be condensed during 100% MCR steam discharge leads to 140% MCR steam flow after attemporation..."
What is MCR? Can anyone explain above statement?

 

[EdStainless]

Not sure what he means by MCR, but I have seen this in combined cycle plants when they run in steam bypass.
The steam is attemperated and the volumes are larger than when the plant is running at full output.
The vibration and erosion effects on the tubes can be serious.
Saw a plant where they destroyed the top 5 rows of Ti tubes in under 4 hours.

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P.E. Metallurgy, consulting work welcomed

 

[MJCronin]

Thank you for that caution,EdStainles ... you refer to operation under "Steam Bypass", I called it "Steam Dump" ...

I mentioned this extreme and IMHO, DANGEROUS condition in my above post !!

Frequently, Steam Dump will control the surface condenser design volume AND bracing scheme for the condenser tubes most likely to be affected.

--- IT IS THE SOLE/MAJOR FACTOR IN COMPLEX STEAM SURFACE CONDENSER DESIGN!! ----

.... and...for the record ...

Maximum Continuous Rating (MCR)

"Maximum continuous rating (MCR) is the capability of steam boiler to produce and provide the stated quantity of steam continually and easily without unwanted effects (for example overloading, slagging, or overheating) upon the principal steam boiler and its components. Maximum continuous rating specifies the maximum output of the boiler at the specified operating pressure. I.e. if the rating specifies 2TPH at 10 kg/sq.cm it would deliver 2TPH at 10 kg/sq.cm."

https://www.aatralengineering.com/2021/07/boiler-rating.html

KneeDeep seems to be in deep trouble ... he has never designed, specified nor (probably) ever seen a steam condesnser


MJCronin
Sr. Process Engineer

 

[davefitz]

MCR= maximum continuous rating. Often steam cycles are expected to operate at 5% overpressure so there could be a steady load above 100% MCR.

During steam turbine bypass operation the steam flow entering the condenser is about 140% MCR steam flow and it could be vented into the condenser thru a pipe that does not correctly distribute the steam to all rows of tubes. Therefore the design of the tube supports to prevent vibratory failure must consider the turbine bypass operation mode. The HEI rules apparently only consider typical US central station steam turbine exhaust ( equally distributed) which normally does not have a turbine bypass. If one neglects to design for bypass operation then the top 3 rows of tubes will fail from vibration within the first 4 hrs.

Another peculiarity is the common practice of adding 20% extra tubing indirectly thru an 80% cleanliness factor. In real practice the 20% margin will enable a 1-2 yr achievement of design plant heat rate if an undersized mechanical draft cooling tower is used; it is common for the designers of these cooling towers to undersize them by 20% to achieve lowest bid cost as they know the 20% margin on condenser tubes will lead to an acceptable heat rate for the first 2 yrs. The better practice is to keep the cooling tower vendor honest by requiring that they provide certified design data on the type of fill they are using and not allow them to hide behind " proprietary" data insults.

NH3 ammonia is poisonous and will kill an operator within seconds if it leaks from the casing, and this is not an issue for steam surface condensers. Also NH3 will damage copper alloy componetns quickly. For these reasons one cannot rely soley on a steam surface condenser standard to design a HX to condense ammonia or hydrogen cyanide or a thousand other chemicals.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[EdStainless]

The last that I heard from friends at the Cooling Tower Inst is that of towers that are actually tested about half fail to meet the operating point. And this is the better ones.
Overbuilt condensers cause many issues. It leads to oversized pumps, piping, condensers, and more control issues since you will often not heed the full capacity.

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P.E. Metallurgy, consulting work welcomed

 

[deepu78]

I was reading the attached Graham surface condenser installation manual where it mentioned that the function of a surface condenser is to create the lowest possible turbine or process operating back pressure while condensing steam.How critical is that for a steam turbine? Any insights/ experience?

 

[MJCronin]

"I was reading the attached Graham surface condenser installation manual where it mentioned that the function of a surface condenser is to create the lowest possible turbine or process operating back pressure while condensing steam.How critical is that for a steam turbine? Any insights/ experience?"

OMG !!!

https://www.youtube.com/watch?v=e6IpOcztJ50

https://www.youtube.com/watch?v=SPg7hOxFItI

MJCronin
Sr. Process Engineer

 

[EdStainless]

Look at the turbine operating curves.
The turbine was designed with a specific terminal pressure in mind.
And this is way below 1 atm.
If you want to extract as much power as possible from your costly steam and use the turbine as designed you need to reach these low pressures.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[davefitz]

It may sound elementary, but the HEI design methods for steam surface condensers assume the use of water, so the condensing heat trasnfer coeficient and temperature correlations only work for H2O and are not useful for NH3.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick