Drier cores in ammonia systems

[garyb]

Hi All

I'm interested in feedback from anyone who has used standard drier cores to clean up or at least assist cleaning ammonia in a system. Both Danfoss and Sporlan state that their cores can be used in ammonia and maybe others also.

The driver for this is two plants in particular that are giving erratic problems with their level controls sticking and pumping out their suction pots. Both plants are in very good condition and are only a couple of years old and both have PMFL+SV1 set-ups and both having been giving us grief but with no particular pattern. We are confident that the selection and pipe work is correct and one of them has had the complete PMFL and SV1 replaced. They run with no problem for a period of time and then one day, for no reason we can see, they pump out and the plant drops out on LP.

The only thing we are still looking at is that when the valves or strainers are manually pumped out for inspection, there is a slight stickyness or tacky feel to the internal surfaces rather than the dry or slightly oily finish you would expect. Fitting a purifier is not really an option hence the question regarding the drier cores.

Any thoughts, comments?

[gregd1401]

Hi Garyb
Are you thinking that your plant has moisture in the ammonia. Liquid line driers will not remove water from ammonia systems. The only way I can suggest to do this is to install a heated perculator and separate the water from the ammonia. We have done this on a plant over here. PM me if you want more details.

[gregd1401]

Hi Gary.Have a read of this. http://www.nhtres.com/differs.php

[cricri]

hello garyb,
I don't believe that the problem is the ammonia but I had some bad experiences with PMFL and SV1 level control. Any change in subcooling and/or pressure différential can cause opening difficulties. You need then to adjust the settings on the SV1. To day its better to use AKS + ICM for LP level control witch is much more reliable. PMFH + SV is still a good way for HP level control.

[Sandro Baptista]

Do you have experienced any problems with the oil regarding the damage of components on the compressors or in other places of the plant?

[charlie n]

I've used filter driers to clean up an old system that had been poorly maintained and poorly modified (rust, carbon etc from oil breakdown, welding slag). Results were reasonable good but, as others have said, the filter cores act only as a filter & won't remove water.
Sandro is asking the question that needs answering, Is this an oil problem? Has the plant recently changed oil types?

[Sandro Baptista]

For instead MO oil directly to PAO oil it's not a good idea.

[lowtempman]

Can't comment on type of controls you have since not familiar with the acronym. I do not think your problem is with water since ammonia systems can operate with a lot of water and controls will still work.[ The suction pressure will go a lot lower for the same evaportaor temerature though!]. I would check further into the oil you are using. You don't say how cold the system runs. Inferior oil may have wax and/or parrafins that will become sticky at cold temperatures. A good mineral oil should be used.

[garyb]

Thanks for your comments.

Oil being used is Petro-Canada Reflo 68. We have used this product extensivley over the last 8 years or so with no problems or failures observed. The systems are clean and one is less than a year old. Both systems are thermosiphon PHE chillers on glycol at -5/30oC R717.

PMFL + SV1 is a Danfoss low side float system with a main valve and a pilot level float valve - not my favourite system and they are not a true modulating control as Danfoss claim, more on/off or open/closed no mater how you adjust the spring tension. However there are literally thousands of them around the world and they are generally reliable - replaceing them is not an option (yet).

Danfoss claim some moisture recovery properties when the DM cores are used in ammonia but I don't beleive we have significant amounts of water in the systems. (Having said that we have not actually checked for water as the systems are quite new - we might do that anyway). I am more hoping to remove the sticky residue that we can see/feel.

[lowtempman]

Now that I know the type of liquid make up system you have, my comment is that the orifice in the liquid feed valve may be very very small, esp with ammonia which has very low lbs/min flow rate per TR to begin with. With a very small orifice, obviously, as you well know, any small amoint of dirt. grit, what have you, will clog the opening and starve your vessel. Your idea of a filter drier thus has real merit, not to take out water but to remove any grit or dirt that may be in the liquid feed line upstream of the liquid make up system.

[RANGER1]

garyb ,
How have you got the SV1 piped series or parallel ?

SV1 sounds like parallel with adjusting orifice on float housing .


How long & what size is vent line from PMFL to SV float ?

[RANGER1]

We would only use PMFL with SV3 needle & seat in series.
SEE MANUAL FOR DETAILS AS WELL AS CHANGING POSITION OF PORTS/ PLUGS

Having said that sometimes tip if needle can get damaged if not handled carefully , have you checked ?
SV3 makes possitive opening & closing every time & is not influenced by different pressure drop across valve etc .

Float adjusting orifice would be fully open & use a gauge in pilot line to watch it cycle open & closed .

Needle & seat has to be set very accurate with a square off housing .
You want maximum opening of float without ot hitting housing , so I measure off where edge of gasket seals .

[D.D.KORANNE]

Water mix up with nh3 results in acqua ammonia which has a far lower freezing temp & free water can be trcked in an accumulator ......... If large qty exists in system .

[Magoo]

garyb.
Does the PMFL vav have the heavy spring set fitted, this will tend to slow down the vav action and give a softer control. Ihave got many similar systems but slight mod from Danfoss configuration and they continually modulate for soft control.
I had a similar problem with the sticky effect with PetroCanada oil, they advised that an additive was reacting with some O/ring materials etc., I have change oil to CPI and no problems since.

[lowtempman]

I agree with Magoo that CPI is good oil. They are very much respected in the USA refrigeration industry and really know their stuff.