5 replies to this topic

[Mazfar]

We are operating several centrifugal chillers.These machines are of size of 2000 Ton refrigeration.
Sometimes we get into contamination problems like oil , moisture and dirts.This causes reliablity problems with the machines as low performance , tripping etc The tripping occurs mostly the due to level transmitters getting plugged up and affects the level controls.The inventory into the evaporators goes to zero and machines trips on low suction pressure.
I have seen through the internet several operators doing online freon cleaning.But its not available in the middle east.
Freon R 134 A is costly and worth to clean up contaminants.
Anybody has experience in it ?

[Art Montemayor]

Mazfar:

I've never had to clean out a mechanical refrigeration system. And I've operated a lot of refrigeration systems through the years. The reason I never have had to clean one out is that I never accept dirt, moisture, or foreign substances in my refrigerant inventory prior to startup. The obvious result is that my refrigerant has never been contaminated. And the remarkable thing about this is that the majority of my compressors have been oil-lubricated reciprocating machines. I would never accept what you are experiencing with centrifugal machines. Where is the oil coming from? Where is the mositure coming from?

First, tell us the manufacturer of your machines and the type of machine. Then tell us the process characteristics, such as the refrigerant, the number of compression stages, the normal compressor suction pressure, the evaporator normal pressure. Also tell us the type and make of the refrigerant levels that are causing trouble - and where they are located. A process sketch would be a big help.

Basically, something is wrong with the way your process is operating - and it isn't the refrigerant. If your system is contaminated, the fault lies with the operator and/or the operation. Once the refrigeration system is started up, it is virtually impossible (short of sabotage) to contaminate the refrigerant. Therefore, I would critically look at the startup procedures and its preparation. Something was not done right. Contaminants just don't "appear" all of a sudden. They are put there or left there by humans.

[srtools1980y]

hi!
may be due to TAMPERING.
investigate.

goodday
srt.

[Mazfar]

There is no way the system can generate the moisture.It always comes from outside.Several reasons are poor drying/tube leak / during freon-loading offloading.
The system is a Hitachi make centrifugal chiller.
System do have a online side stream dessicant dryer but capacity is too small.
Also it do have a oil cleaner which is basically heating the evaporator liquid refrigerant by compressor discharge.The oil is drained.

Once the moisture entered into the system it causes corrossion problem.It cannot be shutdown as it has to complete the run of two years.

There are no design issues as other machines do not have these problems.Some machines have it.
The machine is a three stage centrfugal compressor from hitachi , suction pressures are 300 KPAG producing chilled water at 10 C.

Offcourse its best to take care at the first place with good drying procedures.The question is once its happened then what are the options.

[Ali66]

Hello Mazfar,

I think the first thing is to quantify the contaminants, how much particulates, water and oil are we talking about? Where are the solids/particulates that plug up the instruments coming from?

Would the contaminants re-surrect again, meaning are you certain now that you are not dealing with a re-occuring problem which means you need to investigate root cause prior to the clean up?

Are you not able to use a refrigerant reclamation machine on a side stream (or on batch mode) and gradually clean up your refrigerant? Such machines do a thorough job and enable obtaining the ARI spec but you don't need to go that far as you are not reselling to other users. However, the basics should work for you. You'd remove oil, free water and non-condensables. You can remove residual low content moisture with molecular sieves.

Ali

[Art Montemayor]

Mazfar:

You are simply repeating what I already stated when you say “There is no way the system can generate the moisture”. I said: “Contaminants just don't “appear” all of a sudden. They are put there or left there by humans”. And, if your operations do not take the care and precaution to correctly prepare the units for initial startup, then you will have moisture in the system. This is easily avoided by careful and prudent pre-commissioning and startup procedures. You must pull an efficient and effective vacuum in your system before introducing the initial charge of refrigerant.

With 300 kPag pressure in your compressors suction, you will not be sucking in air from the atmosphere. If you have leaks, your valuable R-134a is leaking OUT to the atmosphere; air can’t get in because of the positive pressure you maintain in your suction. This is a good process design.

The 300 kPag compressor suction pressure you report is equal to a saturated temperature of 8.9 ^oC. That means that your evaporator is at a temperature of approximately 9.5 – 10 ^oC due to the higher pressure there. With this evaporator temperature, I don’t think you can produce chilled water at 10 ^oC, so you must have a lower evaporator – and compressor suction - pressure. As long as it is not in the partial vacuum range, this is OK.

Is your Hitachi centrifugal compressor oil-lubricated? Centrifugal compressors need no lubrication in their process end – just in their driver end. How is oil getting into the refrigerant? Are your shaft seals defective or not holding up? This is usually considered abnormal. Please explain. This oil contamination must be identified and resolved before this is all over. One of the reasons for using centrifugals is because they don't contaminate the refrigerant with oil. Now, you have lost this advantage and caused a potential fouling of your evaporator.

Although you don’t admit it, I get the picture that you have had a very badly organized and commissioned startup of some of your compressors and now you are stuck with water, oil, and air in your system that you must tolerate for at least a 2-year operational run. This is a very bad situation and hopefully whoever caused it is no longer around. As I have stated, the startup of a mechanical refrigeration system should be done very religiously clean and in great detail because once you charge the refrigerant, there is no turning back. As you say, R-134a is very expensive. Obviously someone screwed up and ruined the 2-year operation expected of these machines. There are options that you can use to allow the machines to a clean-up and removal of the oil and water as they operate – but you are going to have to warm-up the system in order to melt the frozen water that already exists within the closed system. The way you do this is as follows.

Fabricate or purchase custom activated carbon and activated alumina adsorber vessels. Install the both the carbon and alumina vessels in key positions within your refrigerant piping such that the carbon is used preferentially to adsorb (& retain) the oil contaminant. The alumina is used to adsorb and retain the liquid water that is in the system as well. These vessels should be installed in a parallel, by-pass loop that allows you to manually block them in service and out of service. The adsorbent is sacrificial; it will not be regenerated. That is why you must have the piping done in such a manner that you can block off the adsorber vessels for a duration. The selective removal of both the oil and water will take time and may require several adsorbent changes. It all depends on the amount of contamination you have and the size of the adsorbers you use.

I have been brief because I think you know what you have to do. This is the only way that you can salvage the refrigerant charge you have in the system and stay on line for the maximum amount of time. You have no other option that I know of, except a complete shutdown and removal of all present refrigerant with a subsequent total clean out and strict pre-commissioning procedure.

I hope this experience is of some help.