Surface condenser

[ali2u]

Hi,

We have experiencing slightly higher vacuum in our surface condenser. Design 0.24 bar abs and at the moment 0.40 bar abs.
Is it because of higher inert concentrations in the HP steam. Can we reduce the vacuum to around 0.3 by opening SU ejectors!

Thanx

 

[KevinN]

ali2u,

Your questions appear to be related to Ammonia Plant Operations. I would urge to be more descriptive if you wish to make full use of the knowledge base in these forums.

Non condensable buildup in the surface condenser can lead to vacuum problems but from the little information you have given, it is not possible to say if it is caused by higher inert concentrations in the HP steam.

It may be a strong possibility if there is a leakage of syngas into the HP Boiler Feed Water (BFW) preheater. This you can check by taking samples of the BFW into and exit the exchanger to see if it contains Ammonia, and if the Ammonia concentration increases.

You can also check for the presence of hydrogen in the vent from the vent on the ejector after condenser.

It is also not possible for anyone to tell you how much improvement you would get in the vacuum if you put the Start Up ejector online.

If non condensable build up is the cause, putting the ejector online will help. How much it helps depends on the the ejector's capacity and whether or not it can cope with the leak.

The only way is to know for sure is to try it.

Have you eliminated other potential causes of vacuum problems e.g.

Fouling of the surface condenser?

Casing drain open on condensing turbine?

Mechanical damage of existing ejectors i.e. worn nozzle?

Leaks in the vacuum system?

Best of luck in your troubleshooting.



Kevin

 

[TD2K]

Some more details would be helpful. Is this a recent problem or has it existed from day 1? If you have more than one surface condensor in your plant, are you seeing a similar problem on the other units? If it's a recent problem, what other changes to the system have happened such as changes in your cooling water temperature, loads, etc. Have you checked for vacuum leaks? What have you eliminated as possible causes?

My understanding of the S/U ejectors is that they are designed typically for removing large amounts of non-condensibles down to 'reasonably' low vacuum levels but not to the levels that your operating ejectors are designed to get you down to (although at the cost of less non-condensible capacity). Check the data files on your equipment and see what it says. As Kevin points out, the final check is to try running them.

With the lack of details, it's not possible to conclude your problem is necessarily due to additional non-condensibles from your steam system.

 

[rmw]

Have the cooling water conditions changed??? Is the water at the design inlet temperature, and are you sure you are getting rated CW flow through the condenser??? Is there any appearant change in the CW pressure drop across the condenser???

TD2K is probably right about the start up ejectors. They don't normally get a condenser down to the deep vacuum that the running ejectors do.

Can you do an air flow test on the exhaust of the final ejector?? Lots of stuff to look for, but we need more details to be able to point you in the right direction.

rmw

 

[smckennz]

Hi ali2u
only you have the information to answer this question. It depends on the ejector characteristic and the required flow rate/vacuum; neither of which you have provided.
The obvious answer is try it and see.
Then find out what the problem is.
Cheers

Steve2U