Closed Circuit Cooling System

[SAYYED]

Dear Sir,
I would like to ask about our Closed Circuit Cooling System.
since long time, we are facing gas traping into the Cooling exchangers, While we have checked all of them for Gas leak.
Now a days, we are venting gas from each and every exchangers during once a shift.But this smell not kind of our process gas.we have shell and tube type heat exchanger. in which, tube side we are using process gas and shell side temper water, which is being cooled by sea Water.
If you have any idea to find this problems then I shell remain thankful you. If you want to do any quey/data about our process then let me know.
Your co-operation will be highly appreciated.

 

[smckennz]

Hi Sayyed
I encountered a similar problem last year which I traced to the dissolution of dissolved gas as the pressure decreased.
The same thing can happen as the temperature increases.
If your closed circuit water is stored in the cooled state in a reservoir where it contacts a gas, then some of the gas may be forced out of solution as the liquid warms up while passing through the heat exchanger.
Of course, the most obvious thought is that you have a leak which is letting gas in but you should be able to check this out.

Cheers

Steve

 

[jherbert]

If I understand correctly:

- S&T heat exchangers
- sea water (shell) cooling process gas (tube)

is the gas is being trapped in the shell?
If yes, and assuming no leakage, probably
air acculumating at highest point in the
shell from the sea water.

cheers,

 

[25362]

The tendency for gas release upon heating of the circulating tempered water is generally cancelled out by the system's prevailing back-pressure.

A once-per-shift actual gas venting for every HE shell seems too much to blame air dissolution in the storage tank.

Anyway, I'd suggest you repeat your checking and verify whether a leak has developed at the tubesheet expansions, and whether the water quality has deteriorated and become corrosive may be because sea water has entered the (otherwise soft) tempered water circuit.

If the range of temperatures for the tempered water allows it, try to use an air cooler rather than sea water as a heat sink.

 

[rmw]

If his sea water cooling system is a "syphon" type, or even if the pressure is constantly declining once it leaves the the supply pump, but still remaining slightly positive, then the backside of the loop could be at a low enough pressure, or even under vacuum at times, and the air would off gas easily due to the temperature rise across the exchanger(s).

rmw

 

[unclesyd]

What does the gas smell like?
You could have SRB'S in the tempered water system. Under certain circumstances they can generate large amounts of gases with the smell of H2S.
I don't see them generating as much gas as you state but any amount of gas will have the characteristic odor.

Another area to check is your pump seals and see if you are leaking air in.

Also we had system of cold/hot water where the piping was configured to where we were aspirating air at the top flange in a vertical run of pipe.

 

[tkdhwjd]

Instead of guessing what the gas could be... why don't you sample it for component analysis? Having composition data should narraow down the possible sources of leak, I believe.

 

[sshep]

Questions:
1. Is your tempered water surge tank a pressurized tank? If a pressurized tank what pressure and what gas is used as a pad?
2. What is the source of your tempered water make-up? Are you having to frequently add (or remove) tempered water from the system to keep level, or add treatment chemicals frequently?
3. What is the tempered water supply temp (after the sea water coolers) and return temp?
4. What is the pressure at the tempered water pump discharge and elevation of these vapor locked exchangers relative to the tempered water surge tank? If you are already sure that all parts of the system are at positive pressure, have you considered using automatic float type vent traps on the high points? These are most often installed to facilitate start-up but will also keep the system from accumulating vapor as in your case.
5. Have you tested the gas to see if it is hydrocarbon or inert (odor alone is not a good test)? You probably have a LEL detector which operations and/or safety uses for vessel entry- if so this is an easy in plant check.