problem in ammonia thermosyphon system

[ghanghas85]

good after noon to all my refrigeration engineer frnds.Dear frnds i have 5 grasso screw comressors.one compresor -2 system ,1 for -10 ,1 for -30 system,2 for -38 system for their oil cooling i have given common header from ammonia thermosyphon reciever.all the compressor are running very well but in -10 system compressor the oil temp. goes suddenly high fron 45 degree celsius to 70 degree celsius and compressor goes trip.this problem takes place after 10 to 12 hour running.ammonia level in thermosyphon is sufficient,i also close all other oil cooler liquid supply valve shut off but i face same problem.please give yours valuable advise

[ghanghas85]

good after noon to all my refrigeration engineer frnds.Dear frnds i have 5 grasso screw comressors.one compresor -2 system ,1 for -10 ,1 for -30 system,2 for -38 system for their oil cooling i have given common header from ammonia thermosyphon reciever.all the compressor are running very well but in -10 system compressor the oil temp. goes suddenly high fron 45 degree celsius to 70 degree celsius and compressor goes trip.this problem takes place after 10 to 12 hour running.ammonia level in thermosyphon is sufficient,i also close all other oil cooler liquid supply valve shut off but i face same problem.please give yours valuable advise

[charlie n]

Is the -10 compressor at the end of the thermosyphon header? Does it happen at night when your condensing pressure is probably lower? Can you post the Piping diagram or piping plan & section?

[ref717]

yes, can you post your thermosyphon pipe route/diagrams specifically the sizes and elevations. The oil temp. goes high because there is insufficient heat exchange at your -10 comp. oil cooler.

[ghanghas85]

Dear sir thanks for your reply it has been also takes place in day time after evevery 4 to 5 hours.i have one common header for thermosyphon oil cooling. on header one end is -38 degree compressors and other end -10 degree compressor.the temp. rise from 45 degree c to 70 degree c take place with in two minutes. while all the compressors have same line diagram.kindly give your valuable advise

[ghanghas85]

Is the -10 compressor at the end of the thermosyphon header? Does it happen at night when your condensing pressure is probably lower? Can you post the Piping diagram or piping plan & section?

Dear sir thanks for your reply it has been also takes place in day time after evevery 4 to 5 hours.i have one common header for thermosyphon oil cooling. on header one end is -38 degree compressors and other end -10 degree compressor.the temp. rise from 45 degree c to 70 degree c take place with in two minutes. while all the compressors have same line diagram.kindly give your valuable advise

[ghanghas85]

yes, can you post your thermosyphon pipe route/diagrams specifically the sizes and elevations. The oil temp. goes high because there is insufficient heat exchange at your -10 comp. oil cooler.

Dear sir thanks for your reply it has been also takes place in day time after evevery 4 to 5 hours.i have one common header for thermosyphon oil cooling. on header one end is -38 degree compressors and other end -10 degree compressor.the temp. rise from 45 degree c to 70 degree c take place with in two minutes. while all the compressors have same line diagram.kindly give your valuable advise

[ghanghas85]

Dear sir thanks for your reply it has been also takes place in day time after evevery 4 to 5 hours.i have one common header for thermosyphon oil cooling. on header one end is -38 degree compressors and other end -10 degree compressor.the temp. rise from 45 degree c to 70 degree c take place with in two minutes. while all the compressors have same line diagram.kindly give your valuable advise

thermosyphon liquid supply header is 100 mm and return header is 125 mm, while oil cooler supply and return tappings are 50 mm and 65 mm respectively for 2 high stage compressor.

[charlie n]

Hard to analyze without installation drawings. It is sometimes possible to form a gas bubble in the supply header which can cause a backflow or at least a flow restriction. Supply header should rise at a slight angle in the direction of flow and the end of the header should be vented to the return header. (this is not always so simple to do. It depends on piping layout)

[Andy]

good after noon to all my refrigeration engineer frnds.Dear frnds i have 5 grasso screw comressors.one compresor -2 system ,1 for -10 ,1 for -30 system,2 for -38 system for their oil cooling i have given common header from ammonia thermosyphon reciever.all the compressor are running very well but in -10 system compressor the oil temp. goes suddenly high fron 45 degree celsius to 70 degree celsius and compressor goes trip.this problem takes place after 10 to 12 hour running.ammonia level in thermosyphon is sufficient,i also close all other oil cooler liquid supply valve shut off but i face same problem.please give yours valuable advise

You should be running your oil between 70degc and 90 degc. The oil cooling is fine, your expectations are not.

Kind Regards Andy

[lowtempman]

Something is happening very fast to cause oil temperature to shoot up so quickly. I assume you have a three way oil temperature regulating valve. I suggest you check action of the three way oil regulating valve to see if it functioning properly. Could it be bypassing the hot oil around the oil cooler when it should be putting the hot oil through the oil cooler.

[lowtempman]

Suddenly realized that your 70 C oil temperature is fairly common and normal. [I do not use Centigrade but that is not a valid excuse on my part.] I agree with Andy post. You are OK.

[RANGER1]

70-90 deg C oil temp is big news for me !
Discharge temp would be interesting at these oil temps .

If thats the case all his other machines -30C & -38C have a problem now with 45 C oil temp !

[charlie n]

I kind of agree with Ranger1. I like to see the oil between 50 and 65. (SCT+ 15 or 20) I think 45 is a little low but oil going to the compressor above 70 is going to give pretty high discharge temps.

[PaulZ]

The recommended oil temp is 45 - 50 oC and the max oil temp is 80 oC, this is out of the Grasso manual.

As Ranger1 said what happens to the discharge temp if your oil is 70 - 90oC.
Charlie n could be on the right track.
A piping layout would be helpful.

Paul

[Scott B]

Does this occur when evaporators are being defrosted ? If you have large evaporators such as in a spiral freezer, when it goes on defrost it can cause a rapid fall in head pressure which can effect the thermosipon almost instantly.
We had a plant that would do this when the production staff tried to defrost both spirals together, not enough evaporators in the rest of the system to supply enough hot gas and the machines would drop out on high oil temperature. If this is the case, reduce the amount of coil being defrosted at any one time.

[Sandro Baptista]

Does this occur when evaporators are being defrosted ? If you have large evaporators such as in a spiral freezer, when it goes on defrost it can cause a rapid fall in head pressure which can effect the thermosipon almost instantly.
We had a plant that would do this when the production staff tried to defrost both spirals together, not enough evaporators in the rest of the system to supply enough hot gas and the machines would drop out on high oil temperature. If this is the case, reduce the amount of coil being defrosted at any one time.

Yes Scott, I agree with you...but why doesn't happened the same with the -2ºC compressor system?

[sterl]

How large is the Min 10 Cmp compared to the Min 38 machine? Does the Thermosyphon Ht Exchanger sit higher on the Min 10 Machine?

How is your condensing capacity controlled? Is there any substantial diversions for discharge gas on some form of on off control? As indicated, a large coil going into defrost will cause this but so will any condition that prompts a large and rapid change in discharge pressure or flow....Like a big heat reclaimer.

[ghanghas85]

Hard to analyze without installation drawings. It is sometimes possible to form a gas bubble in the supply header which can cause a backflow or at least a flow restriction. Supply header should rise at a slight angle in the direction of flow and the end of the header should be vented to the return header. (this is not always so simple to do. It depends on piping layout)

Thanks for your suggestion actually i have connected both the supply and return line to the bottom of main thermosyphon supply and return header. My thermosyphon vessel bottom is just 620 mm below the condenser liquid outlet nozzle while in thermosyphon vessel 370 mm nozzle height for liquid outlet to high pressure .Todai i have observed that after some time there is no liquid ammonia flow through my oil cooler even i have closed all other oil cooler liquid supply valves closed.

[ghanghas85]

How large is the Min 10 Cmp compared to the Min 38 machine? Does the Thermosyphon Ht Exchanger sit higher on the Min 10 Machine?

How is your condensing capacity controlled? Is there any substantial diversions for discharge gas on some form of on off control? As indicated, a large coil going into defrost will cause this but so will any condition that prompts a large and rapid change in discharge pressure or flow....Like a big heat reclaimer.

Thanks for your suggestion actually i have connected both the supply and return line to the bottom of main thermosyphon supply and return header. My thermosyphon vessel bottom is just 620 mm below the condenser liquid outlet nozzle while in thermosyphon vessel 370 mm nozzle height for liquid outlet to high pressure .Todai i have observed that after some time there is no liquid ammonia flow through my oil cooler even i have closed all other oil cooler liquid supply valves closed.

[ghanghas85]

Yes Scott, I agree with you...but why doesn't happened the same with the -2ºC compressor system?

Thanks for your suggestion actually i have connected both the supply and return line to the bottom of main thermosyphon supply and return header. My thermosyphon vessel bottom is just 620 mm below the condenser liquid outlet nozzle while in thermosyphon vessel 370 mm nozzle height for liquid outlet to high pressure .Todai i have observed that after some time there is no liquid ammonia flow through my oil cooler even i have closed all other oil cooler liquid supply valves closed.

[ghanghas85]

Thanks for your suggestion actually i have connected both the supply and return line to the bottom of main thermosyphon supply and return header. My thermosyphon vessel bottom is just 620 mm below the condenser liquid outlet nozzle while in thermosyphon vessel 370 mm nozzle height for liquid outlet to high pressure .Todai i have observed that after some time there is no liquid ammonia flow through my oil cooler even i have closed all other oil cooler liquid supply valves closed.

[Magoo]

Your thermosyphon oil cooler should have around 2 metres liquid head to feed enough liquid for cooling. Can you raise the liquid level in the receiver, has system lost ammonia, the grassos from memory have small internal oil filters as well.