Power Plant Dearator (feed water) Pressure tranmitter 2

[sjjata]

Dear all,
At our power plant we measure the dearator pressure from the top of the tank and the transmitters are located above the tank. We have been having problems with the inpulse lines being blocked with ammonia crystals. It has been suggested that we relocate the transmitters to be below the tank so that we have a head of water above the transmitters which will stop the ammonia from crystallising and leave the tapping point at the same place.Could you suggest better solution to this or is this solution the best.

Regards
Sjjata

 

[roydm]

That should work but you will be effected by changes in level. You could subtract the level from pressure.

Regards
Roy

 

[roydm]

On reading the post again you say " leave the tapping point at the same place"
Where in the impulse tube do the crystals form? I suspect the steam is condensing in the line depositing the ammonia.
Here are a few ideas
Put a condensate pot right at the isolation valve and connect to the transmitter as you would for steam drum level.
Add a small water purge at the present location.
Connect the pressure transmitter to a tap below the liquid level and subtract the level value to get pressure
Use a remote diaphragm seal coupled directly to the root valve.
Use a 1:1 isolator coupled directly to the root valve and run the transmitter on air.

How do you get rid of the crystals at the moment?

I/m sure someone else has had this same problem
Good Luck
Roy

 

[sjjata]

The crystals form in the impulse tube close to the transmitter up to the diaphram of the transmitter.

 

[roydm]

"The crystals form in the impulse tube close to the transmitter up to the diaphram of the transmitter"

Then the steam must be condensing at that point and condensate running back down. Touch the tube, see if it's hot. Perhaps all you need to do is put a loop down near the root valve i.e. like the pigtail syphon on a gauge.
Bear in mind if the transmitter is mounted above the root valve it will shift the zero equivalent to the head of water that forms between loop and transmitter.
Regards
Roy

 

[sjjata]

The tube is not that hot just warm. Thankyou Roy I will try and your ideas in our next shut down but I am still open to new ideas.

Jason

 

[rmw]

The fact of the tube being cool enough to make that determination verifies that condensation is occuring in the tube. If it weren't the tube would be at the saturation temperature for he deaerator and for anything atmospheric pressure or above, that would be too touch.

rmw

 

[danw2]

Roy,

What's a "1:1 isolator"?

Dan

 

[roydm]

Danw2,
I can't recall the manufacturer. They have an elastomer diaphragm with process on one side, air on the other. In the center of the air side is a small bleed port to atmosphere. A tiny flow pressurizes the air side to a point where the diaphragm uncovers the air bleed.
I have seen these used to replace a bubble tube where you don't want to introduce gas into the process. I have also used them for the upper tap on a DP level application to avoid condensation in the LP connection.
I thought it was Moore Products but I can't find it on the Siemens site.
Regards
Roy

 

[danw2]

Is the constant flow regulator part of the mechanical package that contains the diaphragm isolator?

Or is it two pieces: isolating diaphragm and regulator/vent

 

[danw2]

I was so curious, I called Siemens and actually got an answer.

They call it a 1:1 repeater. It was a Moore product, a model 19L, manfactured in Canada. Siemens has discontinued the item and has only a few remaining on the shelf.

The body is 316SS, with a teflon coated fiberglas diaphragm. The connection is 1" NPT, with a separate 1/8" or 1/4" NPT port for the air supply.

A purge relay 62 series would be used to maintain constant flow.

I never knew that . . .

Dan

 

[roydm]

Nice one Danw2, I guess they weren't selling enough to keep the machine shop busy. The isolator could be made by anyone with a lathe.
I hate to see a fine company like Moore Products, Milltronics and others gets swallowed by a giant like Siemens.
Roy