Cooling Tower Pressure Transmitter - Freeze Protection 1

[xnetfly]

We have a situation at one of our plants where the cooling pressure transmitter sensing unit seems to be freezing. This has been an on going problem. The pressure transmitter is located on the cooling tower condenser header to the spray nozzles where it controls a valve to provided the needed pressure at the top of the cooling tower for water delivery into the nozzles. The cooling tower is not run in the winter but the line to the pressure transmitter is freezing. Is there an automated solution. Anyone have any experience with this?

 

[imok2]

You might want to consider a heat trace cable systems which are used to counteract the effects of heat dissipation from process pipe and equipment through its insulation. This heat loss allows drop in temperature, bringing about unacceptable consequences such as frozen pipes, reduced fluid viscosity, etc.
check it out at

http://www.oemheaters.com/heat_trace_cable.html

 

[gepman]

Another alternative is to have a flush mount pressure transmitter (like a sanitary pressure transmitter used in food applications) so that there is no water left in the process connection. I think that imok2's solution would be less expensive though if you can get insulation and heat tracing in the location that you described. They also make flush mount isolation diaphrams so that you could use it in between the process connection and the existing pressure transmitter. You then fill the tubing between the isolation diaphram and the pressure transmitter with antifreezer such as propylene glycol. Here is a link to a well known brand of seal. (no endorsement of the product)

http://ashcroft.com/products.cfm?doc_id=666

 

[danw2]

The Ashcroft diaphragm seal referenced in the link above - installation requires pulling a vacuum on the assembled components (seal and transmitter) and backfilling the volume under vacuum with the fill fluid, then sealing it off. Typically done by a service that specializes in the process. The seal isn't something you fill with fluid and screw together on the bench and expect to get any performance out of it.

Electric heat trace tape is intended to function inside insulation, as imok2 mentions. When I see it wrapped around the transmitter or impulse line with no insulation and people ask why it froze, I ask, "Why wouldn't it?"
Heat trace and insulate.

Heat tracing is used for head pressure transmitters in industrial and municipal water towers, where a dead-headed impulse line needs freeze protection. Of course, it needs power.

I'm don't know how a sanitary diaphragm would fare in a freeze situation. Usually the transmitters are designed so that the wetted diaphragm can be fully depressed at full pressure against a back stop without damage, but I've never actually encountered freeze up situation involving a sanitary seal where ice would push against the diaphragm. I don't even know how much deflection typical diaphragm head offers. Maybe someone else does.

Dan

 

[xnetfly]

Any more solutions??? Does not look like there is much experience here with this...

 

[tommy75]

Ok, genius... Install a heated instrument enclosure for your particular PT and trace then insulate the lines. All of the responses to the OP are all good suggestions, I don't think bagging on ones level of experience is the correct way to gain any help!!

 

[DrRTU]

Place the tap at the 2:00 position and 45 to vertical. Install the TP on the sample line and make sure the spray header auto drains when layed up.

 

[gepman]

Actually having the tap at the 2 o'clock position is not a good idea since it can trap compressible gasses between the water and the pressure diaphragm of the pressure transmitter. This is the same reason that it is slightly difficult (as danw2 states) to fill the diaphragm seals since you cannot have any compressible gasses trapped in the seal (and no dissolved gasses in the fill fluid, which the vacuum helps eliminate). You could install the tap at the 3 or 9 o'clock positions very carefully and they should be self draining and hopefully not trap any gasses for long (especially if the tap is short). Since for some reason xnetfly does not like any of the solutions given previously I will propose I few outlandish solutions (none of which I think is as good as heat racing or a diaphragm seal):

a) Use a vented standpipe on the water supply header with a capacitance, RF, or magnetorestrictive type level transmitter and covert height to pressure.
b) Use a bubbler type level transmitter (I only use bubblers if all else fails)
c) Put a drain solenoid on the line to the pressure transmitter and open it automatically when the system is shut down during the winter.

 

[ChrisConley]

I think that we have discovered another problem with the electronic age.

It amazes me that someone can show up, ask a very specific question, receive three educated measured responses and then complain about the free advice without clarifying what issues they have with the free advice...

Imagine this in the workplace.

 

[TXiceman]

If this is an electronic transmitter, why not buy it with the cold weather heater package to keep it warm. Also, use a chemical seal to keep the water diredtly off the intrument.

In extreme cold applications, we have bult heated panle boxes to mount the instruments and heat trace any sensing lines that could be a problem.

Remember that free advice is worth exactly what you paid for it....nothing!

Ken

Ken
KE5DFR

 

[xnetfly]

WOW... Sorry I did not respond earlier... Believe me I really did not mean to "bag" on anyones experience. From the threads it seems this has not been done on a cooling tower spray header application. The tone of my comment was not derogatory at all. I apologize if that was the way it was taken... I just wondering if anyone has actually done this and had experience with it. If so are there any down falls...
Again, I apologize if this seemed to be a smack. This was not the intent of the last post. SORRY!