PDA

View Full Version : Oil, ammonia and flooded shell and tube chiller







jellef
26-07-2013, 06:35 PM
We are having issues with oil possibly getting trapped between the finned tubes in a flooded evaporator where seawater goes on the inside of the tubes and ammonia on the outside. The oil is preventing heat exchange to happen. The oil we have been using is mineral oil type Cappella 68. We have in the past manufactured and installed many similar systems with R-22 and finned tubes but never seen this problem, is there something with ammonia and the oil mix that causes the oil to get stuck on the tubes and therefore preventing heat exchange?

Has anybody had any similar prob/ems and if so how did you rectify it?

RANGER1
26-07-2013, 08:39 PM
Jelled, seems unusual can you warm h/e up &drain oil to see quantity, if any? Is there a possibility of sea water freeze up insulating tube. Different regions have different freezing point, also check flow & evaporating temp. You may also check how much oil you have to add to compressor to determine how much oil is being thrown into system. Because of no oil return oil has to be drained from evap regularly.

jellef
27-07-2013, 01:08 AM
Ranger1,

We have oil pots on this chiller and they get drained regulary, everything is normal except of course suction pressure gets low, compressor unloads etc. but nothing is happening. We know it is not the seawater freezing. We think it might be that the wrong oil has been added?

RANGER1
27-07-2013, 07:39 AM
Ranger1,

We have oil pots on this chiller and they get drained regulary, everything is normal except of course suction pressure gets low, compressor unloads etc. but nothing is happening. We know it is not the seawater freezing. We think it might be that the wrong oil has been added?

Have you tested sea water freezing point?
What suction pressure/temp are you normally running before suction pressure drops off?
Does suction drop suddenly, or does it look like it works for awhile before suction suddenly drop off?
Tell us in detail lead up to problem, then what happens.
How is liquid level on ammonia side & how is it controlled, can you physically see a level?

Tycho
29-07-2013, 06:28 PM
Does the liquid injection from the pilot/condenser enter the RSW chiller from the bottom, side, or top?

As I see it, since it's a flooded chiller, the boiling of the liquid ammonia is "lifting" the oil up into the tubes, where it sticks on the tubes and prevents heat transfer.

We are using the gargoyle Arctic 300, reflo 68 and icematic 300 oil with no problems.

I'd also like to ask what Ranger1 asked, and add a twist of my own:

What is the temperature of the water leaving the chiller when it unloads, and what is the suction pressure/temp when it happens?

and to follow up with what Ranger1 asked, is the suction pressure stable as it unloads and then suddenly it drops?

And again, how much oil are you getting out and at which intervals?


Depending on the amount you drain, could it be that there is a high oil carryover from the compressor, which causes too much oil to get into the chiller?

---------------------------
On another note

On R-22 systems, the oil mixes with the ***** and you have oil rectifiers to remove excess oil from the chiller and send it back to the compressor.

On ammonia systems, the oil does not mix with the ammonia, but is supposed to "sink to the bottom" where as you said, it get's drained.

Depending on the layout of the oil draining pipes on the chiller down to the collector, and how the liquid is injected into the chiller from the pilot/condenser, this could agitate the oil and move it up into the tubes.

let's say there is a layer of oil on the bottom of the shell, if the ammonia level is low, and the LP is getting close to the cutout, the excessive boiling in the liquid that is not in contact with the tubes could cause the oil to be lifted along with the boiling ammonia up into the tubes and then cause an even worse heat transfer, and then of course it cuts out on LP.


A suggestion is, if it's possible, to stop the system for a day, keep circulating "warm" water through the chiller, and then drain the oil.

or get a spray chiller ;)

Josip
30-07-2013, 09:48 AM
Hi, jellef :)

welcome to RE forums ...


Ranger1,

We have oil pots on this chiller and they get drained regulary, everything is normal except of course suction pressure gets low, compressor unloads etc. but nothing is happening. We know it is not the seawater freezing. We think it might be that the wrong oil has been added?

You know the best ... but above statement can be a problem too mixing mineral with synthetic oil ... someone made a mistake, maybe ... then some obstruction in the liquid feed line into chiller ... maybe lack of the refrigerant .... but you have low suction either without heat exchange thus no flow of seawater ... clogged strainers ... problem with water pump ...

... definitely we need some more info as per request of RANGER1 and Tycho ...

Best regards, Josip :)

Magoo
31-07-2013, 03:29 AM
With shell and tube HX there will be high turbulence and difficult for oil to separate and be drainable. Leaving HX ideal for several hours will allow oil to settle on bottom of vessel and then drained out. The oil will go like glue at chiller evaporating conditions and stick to tubes reducing heat transfer. Are you using Capella P68 ammonia grade oil

shaaf
01-08-2013, 01:53 PM
Please try to drain oil from liquid receiver from bottom side if there is point. some time system run at high discharge pressure that`s why compressor consume more oil than normal. We having problem also but every week we draining oil from freezers and daily twice time in the day from liquid receiver.

shaaf
02-08-2013, 06:39 PM
A suggestion is, if it's possible, to stop the system for a day, keep circulating "warm" water through the chiller, and then drain the oil.

or get a spray chiller ;)

EXACTLY..................................................