Thermosiphon Issues

[freezerman11]

Hi Guys,

We have a plant that runs on NH3, single stage approx 10MW Refrigeration Capacity,

However we have a new Thermosiphon system (approx 3 years old) and every now and then, (more so in the summer) it is causing the compressors to trip on high discharge temp/high oil temp,

There is usually no problem when all 7 Compressors are running ''UNITL'' one compressor cycles off on temperature and then we have 2-3 compressors alarming on high oil temp, sometimes if left it will sort itself out (after approx 15-20mins) and the oil temperatures will go back to normal 52 degree's,

Other days there are no issues at all,

The thermosiphon system is a closed loop circuit, and has a dedicated condensor which controls @10.5BARg,
The liquid level is 3/4 full, so plenty of liquid present, its like the other oil cooler(s) are being starved once 'a' compressor is turns off.
To hand I don't have any info on the oil coolers but will get access to this tommoro.
There are no valves on the liquid inlet to the oil cooler or outlet ,only isolation valves.

Any ideas?

Regards

[US Iceman]

What you are describing sounds like some other systems I have seen. These are usually piping related issues that cause liquid to not be available where it is needed. This can be the result of vapor locking or flow issues.

[Frank Day]

What about oil logging and can you give us a piping layout showing traps?

[Segei]

Hi Guys,

We have a plant that runs on NH3, single stage approx 10MW Refrigeration Capacity,

However we have a new Thermosiphon system (approx 3 years old) and every now and then, (more so in the summer) it is causing the compressors to trip on high discharge temp/high oil temp,

There is usually no problem when all 7 Compressors are running ''UNITL'' one compressor cycles off on temperature and then we have 2-3 compressors alarming on high oil temp, sometimes if left it will sort itself out (after approx 15-20mins) and the oil temperatures will go back to normal 52 degree's,

Other days there are no issues at all,

The thermosiphon system is a closed loop circuit, and has a dedicated condensor which controls @10.5BARg,
The liquid level is 3/4 full, so plenty of liquid present, its like the other oil cooler(s) are being starved once 'a' compressor is turns off.
To hand I don't have any info on the oil coolers but will get access to this tommoro.
There are no valves on the liquid inlet to the oil cooler or outlet ,only isolation valves.

Any ideas?

Regards

Can you give us more information about condenser, receiver? How do you control 10.5 bars(pumps, fans sequence)?

[benji]

US iceman is right, what type of receivers and condensers are being used? If it occurs more in summer then one thing to look at would be the condensers.

[US Iceman]

If it occurs more in summer then one thing to look at would be the condensers.

It depends on what the problem is. I have seen some that operated fine in the cool months and later find out the summer problems were due to the oil cooler itself.

These are just like gravity flooded evaporators. When they do not work it is a pain to fix.

[pavilion]

I've seen one of these systems where the thermosiphon oil coolers are totally seperate from the main plant, the thermosiphon phx is mounted above a liquid receiver and uses the pond water from the evaporative condensers. The pressure is controlled by inverter driven pumps to 10 Bar. Is the liquid line common to all oil coolers & has the system been balanced?

Pavilion

[shanmug71]

Hi FM11
First isolate individual compr by stopping them.Then close the isolation valve for Liquid in and out of oil cooler. Drain the trapped Nh3 liquid safely to outside. while doing so if there any oil trapped in the oil cooler refrigerant area it will get drained out. After that flush it with Nitrogen to remove all the trapped oil if any.Then put back this compressor in operation.Similarly carry out the same for balance 6 comprs and observce. This this plant is working for 3 years with Thermosyphon, it could be one of the problem. Best of luck

[nh3wizard]

Ask a question and never respond... Oh Well

[subb-zero]

Have you got an auto-purger on your system? if not also check for non-condensables as this would cause a difference in pressure in the oil cooler restricting the liquid seal.

[freezerman11]

hey guys,
sorry I haven't replied, have not been on for sometime now to respond,

the problem was a heavily fouled condenser.
Checked the sump water temperature and found that there was a 4C-5C split from the condensing temperature.
Purged air from condensor and seems to be ok so far.
Thanks for all the help!!