absorption chillers simplified

[marc5180]

Hi all, i am going down south on Friday to look at an absorption chiller that isn't working properly.
I will be going down with my boss but eventually he wants me to take over the maintenance of it. I don't know much about them and was wondering if anyone could try and help me understand how they work.
I've looked on the internet but still dont fully understand.
What i do know about the absorption chiller we will be working on is that it uses lithium bromide and steam as the heat source..... but thats about it.

Any help would be appreciated.

[frank]

I'll take a bet that it has had poor weekly maintenance and it needs Purging.

See if you can carry out a purge and dilution routine, after you have checked the vacuum level.

Confused? They take some getting used to mate.

If you haven't got an on site maintenance manual that spells the routines out for you, I would tell your boss that he ought to get someone more experienced to look after it.

Some of the things to look for and note

Generator firing temperature
Vacuum level
Cooling water circuit temperature
Water Quality records
Fault History

Does your boss have any experience with these machines?

Good luck.

[marc5180]

Yes my boss knows his stuff on them. Only problem is he isn't the best teacher, which is why i want to learn a bit about them before i go down.

[icecube51]

an absorption chiller is like an absorption refrigerator.the cind you find in RV's , only bigger and they might use a different heat source like steam.take your time to observe and learn.see wat is going were and is used for wat. don't let your boss take control of you,hey is only interested in $$$.

Ice

[absrbrtek]

Get a model number.

[marc5180]

From what i have read i understand it to work like this:
(please correct me if i am wrong)

Lithium Broide solution (60%) along with refrigerant (water) (40%) is in the bottom of the absorber.

This is then comes out of the bottom of the absorber and is pumped up to a concentrator (generator) where it picks up heat from the heat source ( either steam or hot water).

This concentrates the soloution ( gets rid of some of the water) and the concentrated soloution (liquid) flows back down to the absorber, whilst the vapour passes over to the condenser. Here it is condensed into a liquid and this flows out of the bottom of the condensor and into an orrifice at the top of the evaporator as a warm liquid.

Once the water passes through the orifice it drops the pressure and the temperature as it is in a vacuum. This then falls to the bottom of the evaporator where it is then pumped up through a tube with holes across it and sprayed onto the chilled water pipework.

The liquid that falls to the bottom of the evaporator keeps getting pumped from the bottom of the evaporator around and up to the tube with holes to spray on the chilled water pipework, whilst the vapor is attracted by the lithium bromide so this caused the vapourto cross over to the absorber....and then they cycle starts again.

I have a couple of questions also.
1) is the whole of the system under a vacuum or just the evaporator?

2) What is the purpose of the lithium bromide? Is it just to attract the water from the evaporator?

I read that the water and the lithium bromide causes a pressure difference ( like a compressor) but why would i need a pressure difference when a)its under a vac and b) pumps are being used to pump the soloution around.

Sorry to ramble on but i would really appreciate some help on this, is my thinking right or am i way off?

[absrbrtek]

Answer to 1. Single stage machines run about 5 to 6 mm hg abs (mm of mercury absolute) on the low side (evaporator/absorber) and 60 mm Hg abs on the high side (Generator/condenser)

Two stage machines run about 600 mm HG abs on the high temp generator, 60 mm Hg abs on the low temp generator and 5 to 6 mm HG abs on the low side. Some 2 stage machines may run a 1 to 2 PSI pressure on the high temp generator.

Answer to 2. Lithium bromide is an absorbent, It wants to absorb the refrigerant (IE R718/water)

As far as the simple circuits go there are normally 3 concentrations on a single stage absorber. Strong solution leaving the generator 63% to 64% concentration. Intermediate solution spraying over the absorber tubes 60% to 61% concentration, this is a combination of concentrated and dilute solution. Dilute solution leaving the absorber, 58% to 59% concentration.

Most single stage machines run a 5% solution spread between the dilute and concentrated solutions.

Concentrations vary by manufacturer so these are just some figures you need to be close to at full load with design water flows. It is kid of a balancing act, you need to absorb as much refrigerant as you are generating and visa versa. If all is well your levels will remain stable at which point you have achieved equilibrium. JMHO

I have a couple of questions also.
1) is the whole of the system under a vacuum or just the evaporator?

2) What is the purpose of the lithium bromide? Is it just to attract the water from the evaporator?

I read that the water and the lithium bromide causes a pressure difference ( like a compressor) but why would i need a pressure difference when a)its under a vac and b) pumps are being used to pump the soloution around.

Sorry to ramble on but i would really appreciate some help on this, is my thinking right or am i way off?

[Grizzly]

Mark.
Coupled with what the guys have already told you.
You may like to refer to the very good schematic that I had posted on Vikings Website! www.the-viking.eu

Homepage, Engineers please enter, useful downloads, and about 1/2 way down the page principles of an absorbsion chiller, enter and enjoy!

He very kindly hosts it or me as it was to big to post on the forum.
It may help assimilate what's being said here?
Grizzly

[chabby]

Never knew that There is a 1-2 psi in the generator. I know that there are equalization lines to allow flow , as in the Trane and Broad chillers I work on Chillers

[marc5180]

Thanks for the help everyone, i couldn't reply back as i travelled down to the job last night. By the way the model number of the unit was a LG LWM K027 Absorption chiller.

Went to the site this morning and the customer was complaining of no chilled water and a problem with the liquid filter drier on the purge side.

We started by checking for a vacuum and found positive pressure. We had a look around the system and found that a plug had been left out of the liquid drier so the system wouldn't pull a vac, we screwed the plug back in and tried to run the purge pump. We found this seized and upon furthur inspection, found that the soloution had travelled into the purge tank and filled the purge tank and the purge pump up, which caused it to seize.
We drained out all of the oil/soloution from the pump and changed for new oil. We managed to free the purge pump which was seized then went about getting the air out of the whole of the chiller, this took 4 hours but eventually it got down to the reccommended 4mm Hg.
We restarted the chiller up and waited to see the chilled water temp come down.


Again though i have a few questions;

1) Is the purpose of the purge system to vac out the air from the absorber and the evaporator? Also from what i saw today this has to be done manually by switching on the purge pump but how often does this need to be done? Surely once it is down to an acceptable level then it shouldnt need to be vacced out/purged again unless the is a leak?

2) i read last night that when the Lithium Bromide and the refrigerant (water) are attracted to each other that this also creates an extreme vacuum, is this true? and if so then why the need for a purge system?

Sorry for the long winded post.

[marc5180]

Anyone?.......

[absrbrtek]

OK, first off there is no liquid ''drier'' in an absorption system. Could be a strainer or filter, but no driers.

Yes the purge pump is to remove non condensables. There could be air, hydrogen or a host of other gasses brewing in your machine. The air is introduced into the machine normally by leaks. THe other gasses are generated by the lithium bromide attacking the steel due to a lack of inhibiters.

LiBr only creates the proper vacuum if there are not any non condensables present. The reason it creates the vacuum is after the LiBr is pumped into the absorber it needs to absorb refrigerant. The refrigerant is metered through an orifice(s), this is what seperates the high side.

Unlike vapor compression where your non condensables are in your condensor, an absorber collects them at the lowest pressre point. This is just under the absorber tubes. Non condensables equal higher absorber pressure. Higher absorber pressure creates crystalization ans/or lack of performance.

Again though i have a few questions;

1) Is the purpose of the purge system to vac out the air from the absorber and the evaporator? Also from what i saw today this has to be done manually by switching on the purge pump but how often does this need to be done? Surely once it is down to an acceptable level then it shouldnt need to be vacced out/purged again unless the is a leak?

2) i read last night that when the Lithium Bromide and the refrigerant (water) are attracted to each other that this also creates an extreme vacuum, is this true? and if so then why the need for a purge system?

Sorry for the long winded post.