Max condenser cooling water velocity

[lmirjana]

What is recommendation for the maximum cooling water velocity for the large steam condensers, havig on mind tube erosion? (I want to increase condenser heat capacity by increasing the cooling water flow rate. Designed cooling water velocity is 1.95 m/s)

 

[metengr]

Cooling water velocity for large turbine steam condensers is based on tube material. What is the condenser tube material?

 

[panduru]

Thanks lmirjana, for raising an important issue.

As metengr pointed out, the cooling water velocity is a function of the tube material properties.

I am keen to know the specific tube material properties that influence the limits on water velocity, and the relationship.

 

[lmirjana]

The condenser tube material is lead bronze (70% Zu, 29% Cu, 1% Pb).

 

[metengr]

We typically range from 5 (1.5 m/sec) to 8 feet/sec (2.4 m/sec) flow rates in our large steam turbine condensers containing brass tubes. I would not go above 9 feet/sec especially if you have any sediment or sand in your cooling water. Increased flow will result in higher wastage rates.

 

[lmirjana]

Thank you, metengr.
I am aware of increased wastage rates, but we have problems in acheiving designed power, and it is, in my opinion, due to inadequate condenser cooling surface.

 

[metengr]

Are you sure about the heat transfer surface area? We have had silting problems with several of our condensers that required periodic mechanical cleaning to increase heat transfer during summer months, especially when the river water temperatures typically increase.

What is your design inlet water temperature? Could this be a source of your turbine back pressure problems?

 

[lmirjana]

I am quite sure that heat transfer surface is too small. Turbine is type 18 K 348, and condenser heat transfer surface area is around 8500 m2.In my calculation, that area should be at least around 11000 m2. I think that it was some mistake during plant design, 10 years ago.
Designed temperature inlet water temperature is 12 degC, and it is also problem during summer months. Currently I am working on calculating dependance of the plant heat rate (wastage rate)againts cooling water inlet temperature.
And, of course, I beg you a pardon if my english is not correct!

 

[rmw]

Your english is just fine.

I agree with Metengr about the upper limit on tube velocity. Even if you don't have a silt problem, you will accelerate the wear at the vena contracta at the tube inlet with too high of a velocity.

What gage is your tube material? You might consider retubing with a thinner wall tube recognizing that you won't get the life out of it, but you will have more flow area, and can get more water through the condenser, and get a better heat rate.

In my opinion, if you are that short of surface, there is not really much you can do except to do a modular changeout of your tube bank. With a modular change out, you can change the tube diameter which allows more of a smaller diameter tube, and your tube surface ratio goes up. Plus, you can change metallurgy and if other considerations like water chemistry permit, you can choose a high heat transfer coefficient stainless or super stainless material that has high strength and can use a very thin tube wall. Modular change outs include the tubesheets, tube supports, and of course, the tubes. The support plate spacing can be decreased to accommodate the very thin wall tubes.

I have seen condenser surface areas increased up to 42% by dropping a tube size and using a 25 ga super ferritic tube.

Major condenser manufacturers offer this design.

rmw

PS: strange topic for a ASME Standards thread.

 

[EdStainless]

Yes, this should be in heat transfer, but we took care jsut fine.

lmirjana, Don't push velocity on your current tubes. I'll wager that if you measure your tubes carefully you will find that you have some wall loss already.
You will probably need to rebuild the condenser to get the capacity that you need.
One option is to retube with light gage superferritic stainless tubes. These tubes will handle any flow velocity that you can give them. I know of plants running 15fps. It is just a matter of your pumping capacity, other cooling system flow restrictions, and the trade off in pumping power and cooling capacity.
The second option is more expensive, but it is technically better. Do a modular re-build. This is where you replace the entire guts of your condenser, in the existing shell. This lets you change tube diameter and pitch, support spacing and everything.
rmw has seen more of these than I have. They really work.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[rmw]

Ed Stainless,

Without knowing all about Imirjana's condenser, I would make the guess that if he has lead bronze tubing, he has Muntz metal (or similar) tube sheets. Are you proposing rolling light gage superferritics into Muntz metal or similar metallurgy tubesheets?

rmw

 

[lmirjana]

Thanks to you all for valuable suggestions.
I am aware that this question is more for Heat transfer Forum, but at first I needed to know standard for cooling water velocity.
However, if you are still interested in 'my condenser', I will certainly give you more details.

 

[rmw]

Imirjana,

Since the thread is started, put them in here. We are all friends here. Maybe there are some other details that you might give that would allow us to make other suggestions.

rmw

 

[EdStainless]

rwm, Well, it could be done, and it has been done, but I don't like it either. One route would be to coat the Muntz tubesheets. While this is better than nothing I would rather see them replaced. At that point a modular rebuild is probably not much more money and will yield real performance improvements.

Imirjana, Go ahead and post some design details. We will give it a look.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[MJCronin]

Imir...

The answer to your qestion about acceptable velocity ranges is contained in the HEI standard on Steam Surface Condenser Design (9th edition)....availbale for purchase

http://www.heatexchange.org/pub/HEI.pdf

(No, I will not send a .pdf copy to your "hotmail" website)


_MJC