Ammonia plant running conditions
Just to see if there's something to learn from you guys.
Single Sabroe screw ammonia plant with HP receiver level control, pumped liquid to a tunnel, two evaporative condensers of different sizes, thermosiphon oil cooler.
Links to a few pictures, not very good but might help.
Original layout https://www.flickr.com/photos/s34n/5...ream/lightbox/
--New condenser layout https://www.flickr.com/photos/s34n/5...ream/lightbox/
--Liquid line pipework https://www.flickr.com/photos/s34n/5...ream/lightbox/
--Smaller cond https://www.flickr.com/photos/s34n/5...ream/lightbox/
--Larger cond trap https://www.flickr.com/photos/s34n/5...ream/lightbox/
--Larger cond https://www.flickr.com/photos/s34n/5...ream/lightbox/
--Level Control https://www.flickr.com/photos/s34n/5...ream/lightbox/
Reported that the suction pressure dropped low and tunnel temps went high. Been told sites way to fix it was to switch the compressor off and keep the two liquid pumps running in hand. Once the suction pressure had built back up they switched the compressor back on and its back to normal. I didn't get to see how it was in fault. In the past others have added gas as the fix.
How it was found running after site had restarted the comp,
-- Compressor seemed to be at full capacity. Discharge pressure between 9.5-10.5 bar.
-- Receiver level just under half full, marked up as the normal level being about 5/8 full or what looks to be slightly above the NH3 line on the Danfoss level controller. The liquid feed to the surge drum seems to be piped halfway into the receiver going by the drawing and the text in the manual.
-- Surge drum level, bottom sight glass full, second glass sometimes a bit of splashing at the bottom. Dont know their normal operating level.
-- Two liquid pumps running, think originally designed for one, pressure on the outlet gauge read 2.5bar. The gauge up by the compressor showed about -0.5bar suction and 0.5bar pumped liquid diff.
-- Both condensers running with fixed speed fans and water pumps running.
The smaller condenser if I'm remembering correctly has air leaks from large holes in the fan housings, didnt get to check the coil or spray nozzles. Its inlet pipe temp was at saturation temperature or lower, outlet about the same. Air on temp 18.5 DegC.
The larger condenser inlet temp was up at around 48 DegC, and outlet at saturation temp or lower.
-- Air purger, the foul gas line was open to the smaller condenser's liquid outlet purge point. No bubbles coming from the foul gas blow off. Got a little bit of air out manually purging from the purgers gauge connection, swapped over to the larger condenser purge point and got more from there but again not much. No real change in discharge pressure or condenser pipe temps.
-- The surge drum's level controller controlled fill valve was frosty on the outlet, the manual bypass was closed but sweating at the strainer, and the feed from the oil cooler to the surge drum was frosty after the hand valve.
--The temp display on the control panel showed -29 to -31 DegC, meant to be the tunnel air temp. Said to normally be -32 to -35 DegC.
Switched off the smaller condensers fan and the discharge went up by about 0.5bar and receiver level stayed the same. Switched off its water pump as well and the pressure went up to 12bar, the receiver level dropped to about a 1/4, and then built back up after switching the fan and pump back on. I don't know if the level changed due to the surge fill valve opening or lack of liquid draining from the condensers.
My questions are,
Is that liquid feed from the bottom of the oil cooler to the surge drum just there to stop oil from logging in the refrigerant side of the oil cooler, or is there another reason for it?
Is the low inlet and outlet pipe temp of the smaller condenser due to lack of gas flow through it, and is that lack of flow due to a low rate of condensation of the ammonia vapour?
With the different sized condensers, are both of the traps at appropriate size, height and locations from the outlets? The larger condensers trap is about 300mm below the gantry.
Does the bottom entry of the liquid line to the receiver now cause a problem with this two condenser setup, with each condenser having its own trap?
I thought the discharge pressure seemed a little high, suction a little low (if the gauge was reading correctly), maybe these running condition were just giving the plant low cooling capacity. If not, would you have expected the condenser liquid outlet temps to have been warmer, considering the smaller condenser seems to be operating poorly?
When the site engineers switched the compressor off, is it likely liquid had been building in the condensers and was then able to drain to the receiver?
Cheers
Re: Ammonia plant running conditions
Quote:
Originally Posted by
seanf
Just to see if there's something to learn from you guys.
Single Sabroe screw ammonia plant with HP receiver level control, pumped liquid to a tunnel, two evaporative condensers of different sizes, thermosiphon oil cooler.
Links to a few pictures, not very good but might help.
Original layout https://www.flickr.com/photos/s34n/5...ream/lightbox/
--New condenser layout https://www.flickr.com/photos/s34n/5...ream/lightbox/
--Liquid line pipework https://www.flickr.com/photos/s34n/5...ream/lightbox/
--Smaller cond https://www.flickr.com/photos/s34n/5...ream/lightbox/
--Larger cond trap https://www.flickr.com/photos/s34n/5...ream/lightbox/
--Larger cond https://www.flickr.com/photos/s34n/5...ream/lightbox/
--Level Control https://www.flickr.com/photos/s34n/5...ream/lightbox/
Reported that the suction pressure dropped low and tunnel temps went high. Been told sites way to fix it was to switch the compressor off and keep the two liquid pumps running in hand. Once the suction pressure had built back up they switched the compressor back on and its back to normal. I didn't get to see how it was in fault. In the past others have added gas as the fix.
How it was found running after site had restarted the comp,
-- Compressor seemed to be at full capacity. Discharge pressure between 9.5-10.5 bar.
-- Receiver level just under half full, marked up as the normal level being about 5/8 full or what looks to be slightly above the NH3 line on the Danfoss level controller. The liquid feed to the surge drum seems to be piped halfway into the receiver going by the drawing and the text in the manual.
-- Surge drum level, bottom sight glass full, second glass sometimes a bit of splashing at the bottom. Dont know their normal operating level.
-- Two liquid pumps running, think originally designed for one, pressure on the outlet gauge read 2.5bar. The gauge up by the compressor showed about -0.5bar suction and 0.5bar pumped liquid diff.
-- Both condensers running with fixed speed fans and water pumps running.
The smaller condenser if I'm remembering correctly has air leaks from large holes in the fan housings, didnt get to check the coil or spray nozzles. Its inlet pipe temp was at saturation temperature or lower, outlet about the same. Air on temp 18.5 DegC.
The larger condenser inlet temp was up at around 48 DegC, and outlet at saturation temp or lower.
-- Air purger, the foul gas line was open to the smaller condenser's liquid outlet purge point. No bubbles coming from the foul gas blow off. Got a little bit of air out manually purging from the purgers gauge connection, swapped over to the larger condenser purge point and got more from there but again not much. No real change in discharge pressure or condenser pipe temps.
-- The surge drum's level controller controlled fill valve was frosty on the outlet, the manual bypass was closed but sweating at the strainer, and the feed from the oil cooler to the surge drum was frosty after the hand valve.
--The temp display on the control panel showed -29 to -31 DegC, meant to be the tunnel air temp. Said to normally be -32 to -35 DegC.
Switched off the smaller condensers fan and the discharge went up by about 0.5bar and receiver level stayed the same. Switched off its water pump as well and the pressure went up to 12bar, the receiver level dropped to about a 1/4, and then built back up after switching the fan and pump back on. I don't know if the level changed due to the surge fill valve opening or lack of liquid draining from the condensers.
My questions are,
Is that liquid feed from the bottom of the oil cooler to the surge drum just there to stop oil from logging in the refrigerant side of the oil cooler, or is there another reason for it?
[QUOTE I think so, probably on a timer, or every time it shuts down opens for a short period
Is the low inlet and outlet pipe temp of the smaller condenser due to lack of gas flow through it, and is that lack of flow due to a low rate of condensation of the ammonia vapour?
Quote:
More than likely, but from you tests it is doing something. Could have been better piping
With the different sized condensers, are both of the traps at appropriate size, height and locations from the outlets? The larger condensers trap is about 300mm below the gantry.
[QUOI would say it was okay with original condenser, but with two liquid drain off new one probably could have been piped down to inlet area on liquid receiver inlet where original is piped[/QUOTE]
Does the bottom entry of the liquid line to the receiver now cause a problem with this two condenser setup, with each condenser having its own trap?
I thought the discharge pressure seemed a little high, suction a little low (if the gauge was reading correctly), maybe these running condition were just giving the plant low cooling capacity. If not, would you have expected the condenser liquid outlet temps to have been warmer, considering the smaller condenser seems to be operating poorly?
When the site engineers switched the compressor off, is it likely liquid had been building in the condensers and was then able to drain to the receiver?
Cheers[/QUOTE]
[QUAdd 50kg of ammonia, level in surge vessel probably a bit low [/QUOTE]
Re: Ammonia plant running conditions
The solenoid valve for the oil cooler to surge drum liquid line was warm with the plant running, and a layer of frost on the pipe.
Would you have concerns liquid could be backing up in the condenser(s)? I know the fix wouldnt be a cheap one, and its more than likely more ammonia will be added instead.
Thanks Ranger.
Re: Ammonia plant running conditions
Hi Shaun.
Was the solenoid Valve being called for ? I.e current to the coil. If powered up does coil magnetise/ energise? also what controller do you have? I assume a Unisab?
What are your level control settings in your EKC controller?
I would check out your suction control settings as I would not expect that system to be running in negative Pressure on Ammonia. Someone may have tweaked the suction control settings?
Yet to study your drawings but I would be looking at the oil temp control settings.But do you have an oil temp problem.
It seems more like refrigerant flow issues.
Which could well be caused by the Comp suction being so low that the Liquid level in the surge drum Hangs up (Stalls at a High Level) thereby loosing control of the liquid control levels and loss of temps.
try raising the Suction pressure / temp to just above Zero and lower your working level control on the ekc controller. what you call Liquid controller is actually the level sensor which is calibrated to the EKC.
I would not add more liquid as of yet.
Good luck Grizzly
Re: Ammonia plant running conditions
Sorry Shaun. Just reread your issues listed.
It would seem you are not getting enough liquid into the surge drum? And that its restricted somewhere am I correct?
I however am still concerned by the low suction operating pressures ( Set points?)
let us know how you get on. Grizzly
Re: Ammonia plant running conditions
How is the liquid pumps arranged? Normally only one pump should be running. I have also seen a problem with check valve with twin pumps where the liquid just recirculates thru the pump not running.
Also -0,5 barg suction seems abnormal low.
Also this system design is old type with just float in liquid receiver that opens at fixed level and sends power to surge drum liquid supply line
I have had problems with the switch contacts in the level float switch wont close and make a circut. danfooss aks 38
Maybe add pressure gauge at evaporator liquid supply, have you drained oil from the evaporator?
Is there any valves at the suction line from evaporator? ICLX or PM valve only opening partially?
Re: Ammonia plant running conditions
Quote:
Originally Posted by
Grizzly
Hi Shaun.
Was the solenoid Valve being called for ? I.e current to the coil. If powered up does coil magnetise/ energise?
Didnt get to check the surge fill valve electrically. The pipework and valve were frosty and sticky to touch, the pilot valve solenoid was warm. Assumed to be working due to surge drum level being reasonably steady looking at the sight glasses. Would have liked to check the oil cooler to surge liquid hand valve setting, to make sure the level wasnt somehow being maintained via the oil cooler.
also what controller do you have? I assume a Unisab?
Seemed to be on an old Siemens, didnt get to check it over. Probably could have got better pressure readings off it though, the drawing shows suction, discharge and pumped liquid transducers.
What are your level control settings in your EKC controller?
Receiver level setting assumed to be around 5/8 of the receiver column where normal level had been marked. The NH3 line on the level switch sitting about 1.5-2" below the mark on the column.
I would check out your suction control settings as I would not expect that system to be running in negative Pressure on Ammonia. Someone may have tweaked the suction control settings?
I was expecting it to be just in a vacuum, the pressure was read off a gauge and I only checked the discharge gauge calibration. It was off by 0.5 bar.
Yet to study your drawings but I would be looking at the oil temp control settings.But do you have an oil temp problem?
Oil temp seemed ok, thermosiphon oil cooler seeming to work well enough, with preferential feed from the receiver.
It seems more like refrigerant flow issues.
Seems to be a flow issue in the smaller condenser, and maybe not enough liquid being drained to the receiver.
Which could well be caused by the Comp suction being so low that the Liquid level in the surge drum Hangs up (Stalls at a High Level) thereby loosing control of the liquid control levels and loss of temps.
No surge drum level control from what I can see, only reciever (if thats what you mean?). The high temp may have been from surge drum level being too low, and then no pump pressure, and then pressure being able to go too low.
try raising the Suction pressure / temp to just above Zero and lower your working level control on the ekc controller. what you call Liquid controller is actually the level sensor which is calibrated to the EKC.
I cant say Ive looked at these receiver switch/controllers before (I was assuming its more like a float switch), Ill need to look into it. The Surge drum liquid feed pipe in the receiver looks to have an inlet about half way into the vessel, going by the drawings and what was in the manuals description.
I would not add more liquid as of yet.
My concern was trying to get the receiver level back up, and the pipe temps on the condensers made me think there could be liquid being held up there. But the pipework seems a bit bodged together, definitely atleast second hand with a second condenser added.
Good luck Grizzly
Cheers Grizzly.
Re: Ammonia plant running conditions
Quote:
Originally Posted by
Grizzly
Sorry Shaun. Just reread your issues listed.
It would seem you are not getting enough liquid into the surge drum?
From what site is saying it sounds like they loose surge drum level, but its the usual thing of not all the pressures and levels were checked when it faulted.
And that its restricted somewhere am I correct?
Going by the level marked on the receiver the HP liquid level seems to be low, and from how it seems to feed the surge drum with a pipe fitted well into the receiver it may then not be feeding the surge as well as it should.
I however am still concerned by the low suction operating pressures ( Set points?)
That was the thing to be looked at next, another ammonia plant on the site was also being run very low at -0.55bar set point.
let us know how you get on. Grizzly
Will do, hopefully get to go back, its a more interesting fault to figure out.
Cheers Grizzly
Re: Ammonia plant running conditions
Quote:
Originally Posted by
HwT
How is the liquid pumps arranged? Normally only one pump should be running. I have also seen a problem with check valve with twin pumps where the liquid just recirculates thru the pump not running.
Also -0,5 barg suction seems abnormal low.
From the drawing it looks like it was originally only one pump. The two pumps looked to take their inlets off the same drop leg off the surge drum. First time looking at this plant, but Im going to assume the site engineers stick the other pump on as well when they loose pressure. The suction pressure reading might not be correct, it was taken off an old gauge.
Also this system design is old type with just float in liquid receiver that opens at fixed level and sends power to surge drum liquid supply line.
I have had problems with the switch contacts in the level float switch wont close and make a circut. danfooss aks 38
Maybe add pressure gauge at evaporator liquid supply, have you drained oil from the evaporator?
Didnt get to check the evaporator for oil. The surge drum oil pot had no frost on it, but I didnt get to check it properly. They may have just closed off the inlet like was found on one of the other ammonia plants on site.
Is there any valves at the suction line from evaporator? ICLX or PM valve only opening partially?
Not sure, didnt get to check the full pipe run.
Cheers HwT
.....
Re: Ammonia plant running conditions
seanf,
Missed the bit where you mention others have added ammonia as the fix.
I suggested it as well because sounds like liquid pumps may have lost their prime for a bit causing low suction, high tunnel temps.
You are right to suggest fixing small condenser issue, looks like it has been there for awhile.
To change pipework you need to work with design engineer, not wing it with what we say.
The "P' or "S" traps currently there do nothing really, it relies on liquid seal at bottom of high pressure liquid receiver, that's why original design okay.
You can check manually for air, close discharge stop & thermosyphon valve on inlet while plant running, monitoring discharge pressure (hopefully can handle it), purge carefully of top of discharge inlet between stop valve & inlet of condenser coil, if there is a valve to atmosphere, When liquid comes out, no air, in your case may not take long.
Alternatively isolate condenser when plant off & purge into water off top, monitoring any air bubbles coming to top of fresh water.
As far as 2 pumps running, this place may have history, talk to a few people on site, as is unusual.
Pretty average plant with no economizer for efficiency, built to a price no doubt.
Liquid drain off oil cooler may open on each start or stop of plant, that's why ice on downstream.
Any manual on site to shed light on it?
Re: Ammonia plant running conditions
Quote:
Originally Posted by
RANGER1
seanf,
Missed the bit where you mention others have added ammonia as the fix.
I suggested it as well because sounds like liquid pumps may have lost their prime for a bit causing low suction, high tunnel temps.
You are right to suggest fixing small condenser issue, looks like it has been there for awhile.
The plants second hand, atleast. think its dated on the drawing 1991.
To change pipework you need to work with design engineer, not wing it with what we say.
The "P' or "S" traps currently there do nothing really, it relies on liquid seal at bottom of high pressure liquid receiver, that's why original design okay.
You can check manually for air, close discharge stop & thermosyphon valve on inlet while plant running, monitoring discharge pressure (hopefully can handle it), purge carefully of top of discharge inlet between stop valve & inlet of condenser coil, if there is a valve to atmosphere, When liquid comes out, no air, in your case may not take long.
Alternatively isolate condenser when plant off & purge into water off top, monitoring any air bubbles coming to top of fresh water.
As far as 2 pumps running, this place may have history, talk to a few people on site, as is unusual.
Pretty average plant with no economizer for efficiency, built to a price no doubt.
Liquid drain off oil cooler may open on each start or stop of plant, that's why ice on downstream.
Any manual on site to shed light on it.
There is a manual, but couldnt find anything on the drain operation.
Cheers Ranger.
