Best way of Steam condensate system 2

[brainstorming]

I have got a question regarding the best system of steam condensate generated by distillation column reboilers.
From my experience, centrifugal pump is used to pump the condensate by every reboilerto a collection drum of condensate then to utility for recovery. I heard that a common sump is used to collect all condensate generated from various distillation column reboilers using steam as heating medium and the condensate is being transferred by gravity to the sump.
By this condensate pumps can be eliminated and a common sump with pumps (one spare) can be used instead.
Has any one have such application in which the condensate generated by various reboilers is sent to a sump and to recovery unit via a pump?

Cheers

 

[katmar]

Yes, what you describe is very common. The condensate recovery system must be considered from the very beginning of the design of the structure, and the columns and their reboilers not mounted too low. You will want a bit of height on the column bases anyway because you want enough NPSH on the pumps that will pump the column's bottom product.

Unless the steam pressure on the reboilers is very low, you should be able to take the condensate after the steam trap (or control valve) to a central collection tank. This tank will often be designed as a flash tank, with the vapor generated being fed into the next lower pressure steam range.

Using centrifuagal pumps for condensate is common, but the NPSH requirement must be carefully considered. I have seen condensate pumps installed in a pit alongside the condensate tank, to generate sufficient suction pressure.

 

[brainstorming]

Thank you for your contribution
but what I am looking for is the best way of handing the condensate either by pumps or gravity to a sump.

Any advice and previous experience in such service is appreciated.

Cheers

 

[EGT01]

As Katmar indicates, condensate collection systems are very common. In some cases, a condensate collection system used to collect condensate from one steam source can be used to produce steam of a lower pressure value. For example, condensate generated from 200 psig steam can be used to produce 60 psig steam. Here are a couple of links that have excellent information about steam and condensate systems.

http://www.spiraxsarco.com/learn/

http://www.armstrong-intl.com/prodlit.php3

Look for the handbook N-101 on the Armstrong website.

 

[katmar]

Hi Brainstorming,

On re-reading what I wrote I see that I didn't relate my comments exactly to your question, so let me try again.

It is unusual to have a pump on every reboiler. There is usually sufficient pressure in the reboiler to drive the condensate to a central sump. The steam traps or control valves would be specified knowing the pressure available in the reboiler and the friction pressure drop in the line to the sump.

So it is the steam pressure rather than gravity that causes the flow of condensate from the reboiler to the sump.

When people talk of sumps and gravity flows I think of open systems. If you were to do this you would have clouds of flash steam in your plant. This is wasteful, unpleasant for operating staff and results in corrosion. The usual practice is to collect the condensate in a closed tank as I described before.

The condensate is usually close to boiling point and is difficult to pump because of NPSH problems. A sump in the usual sense of a pit in the ground would make pumping very difficult. The condensate tank needs to sufficiently high above the pumps to give the required NPSH.

I hope this is clearer?

 

[brainstorming]

Thank you guys for your inputs
Can I understand from both of you that a common sump can be used instead of installing pump for each reboiler?
By the way the last project I worked at we used pumps for all condensate generated from reboliers in the plant about total of 2 reboilers. In the current project we have the same service but the idea of using a common sump is of interest from cost and operation as well as maintenance.

Cheers

 

[roker]

hello,

in our last project we are collecting the low pressure condensate into one common flash tank with an air cooled heat exchanger above it for condensing the vapors, centrifugal pumps (one op the second stand by) are transfering the condensate.
there are plants that are using tansfer pumps operated with steam or air (no electrical motors).

regards