Condenser manufacturer qualification/certification 1

[audentesfj]

Does the manufacturer of a steam condenser, always less than 50C (122F), need to be ASME certified?

The condenser for our engine will be 12 feet long and 2 feet in diameter. It will be water cooled and protected from pressures above 120 inch water gauge by a check valve and lute.

 

[TJOrlowski]

Are you installing this condenser in the United States? If so, what state?

-TJ Orlowski

 

[audentesfj]

Yes it will be installed in the USA in California. I am an Australian PE, hence the uncertainty.

 

[TJOrlowski]

The proper thing to do would be the contact California, give them the volume of the vessel, and the design pressure. They'll be able to tell you whether the vessel needs to be ASME Stamped or not. The National Board of Pressure Vessel Inspectors (

http://www.nationalboard.org)

may be useful as well.


As an aside, if I were the owner of such a condenser, I would want it to be at least designed and constructed in accordance with ASME VIII, Div1, even if it weren't stamped.

-TJ Orlowski

 

[audentesfj]

Thanks TJ. It is designed to ASME Section VIII, Div1. I rang DOSH California. My contact there was unsure but is checking for me. Great advice thanks.

 

[MJCronin]

Could you explain how the lute protects the shell against overpressure ?

http://www.thefreedictionary.com/lute.

I agree with TJ regarding an ASME basis for the design, even if your pressures are low.

What this post reveals (yet again and again in the USA) is that there are no clear rules for design of industrial equipment at modest pressures ( say 5-14 psig).

HX shells are NOT and ASME design, nor an API design.

The Europeans have a Pressure Vessel Code that covers this range of equipment.

Perhaps the lute emits soothing sounds to the stressed condenser ???

 

[audentesfj]

A lute is a delightful shape and that is why the name is applied to the pressure limiting device. It has a bulbous vessel at the bottom with a space above a liquid surface that connects with the vessel or system that is to be protected. A vertical pipe extends into the vessel to end well below the liquid level. The pipe extends vertically out the top of the vessel. It can look just like the neck of a lute.

I envisaged a check valve between the lute and the condenser. The check valve connection might be submerged so that the condenser sucks water, if it leaks. If the condenser pressure rises, due to cooling water failure or overload, the pressure will open the check valve and push water up the vertical pipe. In Australia I have recommended making the pipe 4.9 metres tall. That keeps the pressure below the level defined in our code as "not a pressure vessel, if it is smaller than ...". The code pressure limit is 50 kPa gauge or about 7.35 psig.

Here in the USA the code seems fixated on 212 F (100C) rather than the major risk factor, the pressure. To me that seems very strange.

The top of the lute can have another bulbous vessel to avoid losing the water. This also lets the system reset itself without a float valve or some other way to fill it with water again.

The check valve can be eliminated if the lute can be 9.8 metres above the lute. Then the lute will work both ways to limit pressure and keep the system simple.

 

[MJCronin]

auden,

Here in the good old US of A, we are concerned with overpressure of the condenser shell, .....

In fact we are so concerned that we stay away from lutes, banjos, guitars and all string instruments and use a sentinel relief valves.

Will you have a full-vacuum design for your shell ?

Many steam surface condensers are built to HEI standards. These standards specify requirements for minimum thermal loadings, mechanical strength and required safety features.

http://www.heatexchange.org/

Tell us more about your design.....

 

[rmw]

Most vacuum condensers are NOT ASME certified. Many are designed and built according to the standards of ASME, however (to the extent possible with some of the shapes encountered.) ASME is not required on vessels operating at less than 15 PSIG.

Graham-Mfg.com makes small round condensers to ASME and stamps them and theirs typically have more metal than a similar version built only to HEI.

rmw

 

[audentesfj]

We have designed an all steel condenser with five passes of water cooling. It is 600 mm diameter and 3 metres between tube plates with 300 tubes. The total area for heat exchange is 49 square metres.

The first pass ensures that the extraction region for un-condensibles is the coolest part. The pass that is warmest is at the bottom so that condensate undercooling is kept to a minimum, hopefully less than 4K.

The pass where steam first enters at about 20 metres per second has sparse tubes. That will limit the velocity where steam passes between the tubes and accelerates to about 32 metres per second.

Some, very limited, sources of information suggest that droplet erosion increases rapidly as the steam velocity rises above 35 metres per second. Any harder evidence of that would be great to have.

Given the relatively small steam rate of our system, about 1600 pound per hour, the condensate extraction is a challenge. We have opted for a unique system. Pumps are available for larger system but consume too much power for our system. As yet I cannot say more about the trap.

This week we found a supplier that can supply condensers, off the shelf. About 50% cheaper than building a one-off condenser to our design. Later we may find our design is cheaper, for volume manufacture. It seems to me that 300 tubes, 16 mm diameter, to expand into two tube plates with one shell must be cheaper than a total of 1392 tubes 9.5 mm in diameter expanded into six tube plates. The key here is volume production.

 

[rmw]

Have you ever designed a condenser before?

Is this condenser for your use or is it to sell to others?

Why all steel? Why not tube metallurgies that have higher heat transfer coefficients?

Do you have a completely separate air removal (non-condensables) removal section?

Prevention of subcooling is best done by designing the condenser so that steam flows under the tube bundle and penetrates from the bottom so that the condensate droplets have to fall through the steam entering the bundle.

The comparison that you make in your last paragraph is not completely obvious (to me at least.)

rmw

 

[audentesfj]

I have only designed condensers recently. Most of my design work has been with heat exchangers, boilers, vacuum vessels, flash vessels, superheaters, boilers and engines. I have only studied and worked with condensers in the past. They are a very interesting challenge.

In the future we may have our condensers made by others to a design similar the the one I described. Currently, we intend to buy condensers of a design very different from ours.

Our initial selection of steel was based on three factors as follows:
lower material cost than titanium that has been used widely in recent years,
avoiding the possible problem copper may have on the chemistry of boiler water treatment and
the adequate conductivity of steel.

We chose to disregard the very limited life that may result from using an all steel design.

I have found that the temperature differences associated with the water side fluid film is more than five times the temperature difference across our steel tube wall. Also the steam side fluid film appears to add a similar temperature difference to that across the tube wall. The steel conductivity is a minor factor.

Furthermore, we may not be able to prevent fouling of the steam side and deposits on the water side. Our preliminary check suggests that fouling may require condensers with almost double the surface area. The steel walls of tubing is the least of our problem.

We do have separate air removal arrangements. Many of our design approaches are significantly constrained by the small capacity of our system.

I do like your suggestion of using the incoming steam to heat the droplets as they fall to the bottom. Our design does do that but the flow may be too limited to provide best effect. We could adjust the design to increase that effect. Is there a report or text that provides design guidance for that approach?

My last paragraph conveys my surprise that a design with 1392 0.375" tubes in six small condensers is a fraction of the cost of our design. The cost difference is about three to one cf our condenser with only 300 tubes 0.625" diameter. The total amount of material is similar but the labour involved in drilling tube plates and installing tubes would appear to be much greater.

 

[MJCronin]

Yup.....condensers using smaller tubes will result in smaller tubesheets, smaller boxes, less drilling costs etc. etc.

But your 0.375 inch tubes means that you better have some type of particle size control. .... and 0.375 inch also means that the slightest amount of fouling may be a significant problem for your design

Most large industrial steam surface condensers and power plant use 0.75 and 1.0 inch tubes for these reasons. Some use 1.25 inch tubes

Nothing is for free.....