6 replies to this topic

[chemical_jojo]

all,

 

I am new to heat exchanger design. I have to cool down Natural Gas using Sea Water as below :

 

Hot Fluid :

 

Natural Gas  Inlet : 65 barg @ 60 DegC

                   

Natural Gas  Outlet : @ 40 Deg C

flow rate @ 130 kg/s

 

 

 

Cooling Fluid :

 

Sea Water Inlet : 2.5 barg @ 36 Deg C

Sea Water Outlet : @  45 Deg C

 

 

Which side shall I consider for Natural Gas?

If I place NG towards shell side then is there a possibilty of Gas leaking into water ?

 

Regards,

 

jojo

 

 

 

[ColinR33]

Rule of thumb is to put HP side on the tube side wherever practically possible in order to minimize cost, eg. bulk of the shell will be lower design pressure, just the channel ends are high pressure.   This is important with sea water cooling as you usually need costly alloy materials for the sea water side.  If you are new to exchanger design I would suggest going to some exchanger vendors and letting them handle the design, you just provide the process data for the process and sea water side (operating and design T&P, composition, flow, allowable pressure drop, fouling factor if known, preferred nozzle sizes and ratings if known).  Don't limit yourself to shell and tube style either, there are plate and shell exchangers that can be used for this and in my experience have come in much cheaper than shell and  tube when using seawater (due to titanium material spec for sea water side).

 

Cheers,

Colin

[chemical_jojo]

Thanks Colin!

 

I am on client side. And my contractor is suggesting the Shell side - Gas flow. Hope this will clarify the issue.

 

would you still suggest for Plate & Frame HE ( PFHE ) as the Gas side pressure is 65 barg?? As I think that they use gaskets in PFHE.

 

Rather as you hinted its good to have :

       Tube Side :  Natural Gas

       Shell Side : Sea water 

But I am not clear about the cost advantage as now whole Shell side has to be made up of  " Alloy material " as well as it requires coating on Tube -Outer side.

 

Kindly review, and suggest what you used previous designs in similar conditions???

 

 

Any senior member  , plz review and comment .

[gegio1960]

jojo,

for this applications (and a lot of others), sea water is always in tube side.

carefully read what colin has written.

good luck

[Raj Mehta]

Natural gas on shell side & Sea water on tube side.

 

Sea water is corrosive and contains high amount of salts which will deposit and cause corrosion and fouling. If placed at shell side it will eat away the shell in due course of time also some of the the salts would deposit on the tube thus reducing the heat transfer area.

 

as gegio mentioned, sea water or even cooling water for general cooling purpose, it is given in tube side.

[Art Montemayor]

My experience shows Gegio1960 and Colin are correct and Raj hasn't focused on the details that comprise a complete and working heat exchanger.

 

Before making a general statement apply to your case, one must be careful of the details involved.  For example, the facts in this case are:

• The high pressure fluid is obviously the natural gas; this is a presumption I have to make since seawater is the coolant and therefore an offshore application is obvious;
• The tube side involves less mass of expensive alloy material.  Anyone who has built a heat exchanger will recognize this.  Only the tubes are high alloy and the internal, shell-side face of the tube sheet is laminated with alloy with welding or explosives;
• The shell side is the low pressure side and the shell is normally 3/8" thick approx..  If the tube bundle is a U type (as I have done in the past offshore applications), then the internal shell side can either be coated or alloyed.
• By personal experience, this is the least cost option.

[Arpit_Jain]

This file (http://www.oilasia.c...IORS/PDF/20.pdf ) on "Guideline on Selection and Design of Cooling Options for Offshore Application" might be of some use to you. Though it does not discuss about fluid allocation, it discusses about various cooling options in offshore application.

 

Regards,

Arpit