Absorption Chiller Crystallization - Does it affect performance? 3

[UtilityLouie]

I'm working with some absorption units that have been crystallized and decrystallized A LOT. What are the long term effects of this? I know it's not good... I just need to know what to check on.

The operators can't operate the system.

Maintenance doesn't maintain the chillers.

My manager has a soft spot in his heart for keeping them and reusing them - even though they are operating poorly.

 

[imok2]

This sounds like a loosing proposition, you know beating a dead horse. Crystallization occurs when the machine
operates too close to the saturation temperature of the lithium bromide solution and the lithium bromide begins to precipitate out of the solution. While this will not damage the machine, it is a nuisance and usually requires application of external heat to get the lithium bromide back into the solution. Newer machines have electronic controls which prevent the chiller from operating at temperatures and concentrations which allow
crystallization to occur. If the unit is operated properly, and maintained, crystallization is nearly a thing of the past.
Vacuum leaks are a serious problem adversely affecting the
efficiency of the machine and causing corrosion in the unit.

A big advantage with absorption chillers are no CFCs, and
the lithium-bromide solution is non-toxic. Also, direct-fired,natural gas absorption chillers can cut sulfur dioxide emissions by 100%, nitrogen oxide by 68%, carbon dioxide by 57%, and particulates by 97% over oil-fired, peaking power plants and coal-fired, baseload power plants.

 

[Yorkman]

It won't necessarily hurt them but you need to make sure you have them fully decrystalized especially the heat exchanger before you put them back into service, or you won't get full capacity out of them. Sometimes that means getting the solution wicked hot and circulating, before returning them to service. These machines work well but are real fussy about condenser water, too cold and you can drive the solution to strong.
Air leaks on these machines seem a lot more critical to performance than on a low pressure centrifugal. They need to be at 5 to 6 MM. Hg absolute to get the proper refrigerating effect from the H2O. The chemisty in the machine has to be monitored also, these machines have the ability to produce ammonia and hydrogen. If the system gets out of balance (chemically), the ammonia will attack the copper tubes if gone unchecked. And the hydrogen?, well who needs extra hydrogen in your evaporator anyway.

I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int./JCI

 

[quark]

There is absolutely no problem with mechanical integrity of the machine with respect to no. of crystallization and decrystallization cycles.

You have to be careful with the concentrated solution side of the low temperature heat exchanger. Generally, the cooling water temperature should be higher than 22⁰C to minimize crystallization. Many times, I saw operators bypass the low water temperature switch for an easy startup of the chiller.

Inspite of all care, I used to face severe crystallization of the unit. I followed two crude solutions for quick remedy. One is to provide a steam condensate line to cooling tower basin and the other one is steam jacketing the LTHE (generally conc. sol. will be on shell side). These two things gave me relief but the final relief was when I replaced the VAMs with centrifugals.

There are some check points for early prediction.

1. The dilute solution line to generator should be hot.
2. Concentrated solution line to the absorber should be relatively cool.
3. Evaporator should not be flooded (beyond the sight glass).

When ever you pass by the machine, have a feel of the temperature at various parts so that you can judge any abnormality.

keep your cooling water low temperature switch in good working condition. Never allow it to be bypassed.

The system definitely requires good operators, atleast dedicated if not intelligent.

 

[UtilityLouie]

It seems like I'm fighting a losing battle with these machines...

The biggest hinderance is that I'm located in a corporate office and these machines are across the country from where I'm located. They were installed because of tax credits and the need to use more low pressure steam - all great reasons - by the way.

The issue - this mill didn't have any experience with absorbers - and had minimal experience with chillers outside of their pulp mill ClO2 plant - but those are all centrifugals.

All of their other AC units are water cooled unitary systems. I putting in another system and am being forced to put in at least one absorption unit. I am fighting to beat the band to put a centrifugal in parallel, just for ease of use.

Thanks for your input.

We're seeing reduced performance on these machines, but I'm guessing it's lack of purging.

By the way, these units are the were top of the line new units with all of the crystallization prevention controls and the operators still rocked them up really good a number of times.

 

[quark]

If the machines are new, the reduction in performance is due to air ingress. Try to maintain vacuum at 5 to 6 mm as suggested by Yorkman. This corresponds to about 5⁰C saturation temperature of water.

One more thing I missed to tell you is about dilution of the system. Before stopping the machine, you should go through the dilution cycle for 15 minutes. Though, this is automatically done, take care of any mishandling by a hurrying operator.

It may help you if you prepare standard operating procedure with the help of manufacturer and train the people.

 

[UtilityLouie]

Agreed Quark...

When these systems were started up - all this training was performed. I even followed up with the same training 6 mos. later. I thought I had people that would take ownership after that, but cut backs happened and with only enough staff to "fire fight", the chillers seem to be losing the battle.

I might be relocating out to this site for a while and can bring back the ownership, but it's still frustrating.