Absorption Chiller troubleshooting 1

[C4Reactor]

Having problem with absorption chiller which is delivering only 60% of the design load. Vendor recommends that we clean the Evaporation CW tubes. We opened up the tubes and guess what? It was as clean as new!. Second recommendation from vendor is to add a small amount of alcohol to improve the heat transfer (wetting agent). Still waiting the opportunity to do this. Appreciate any help or suggestion.
Our absorption chiller uses LiBr+Water.
Regards

 

[gkandy]

Some of the things you could check :


Assuming the design was correct , the heat exchange could be affected if there is a mechanical problem ( tube choke,vacuum,air ingress etc ) or a delta T problem across the different heat exchangers in the loop.

1. is the vacuum pump functioning normally
2.Is the vacuum being maintained at the design conditions
3.Has your CW inlet temperature altered? This can alter the delta T?
4.You might be using this chilled water in a process environment. Have the temperatures changed across this heat exchanger.

Hope this is of some help to you.

 

[quark]

When did you filter LiBr previously? It is always better to filter it yearly. Check for system leaks.How old is your machine? As far as my experience with vapor absorption systems are concerned 60% is a good figure

Regards,


Repetition is the foundation of technology

 

[6748]

Cleaning of CW tubes and adding alcohol is the standard remedy which any vender will say without even seeing your machine. The problem could be Partial or full crystallisation of LiBr. This will happen a) If the CW temp goes below certain temp. say 22 Deg C. b) If the CW valves were kept open ( even if the water temp is above 25 deg C)when the machine is kept ON without load. c) When the machine is without load, passing of steam valve which will increase the temp of generator. d) Switching off the machine immediately without a dilution cycle to reduce the generator temp ie if the machine supply is switched off before bringing down the generator temp.
Decrytallization is an expert job. Ask the vender to do it. Pl ensure one of your technician/engr gets trained.
Best of luck

 

[C4Reactor]

My update based on the above replies:
-The vacuum pump is working well. It gives the negative pressure as per design specification.
-The chiller is very sensitive towards CW temperature. Even if the temp increases by 1 degC, we will lose the Solution level in the evaporation drums.
-Temperature of the circuit do change when we increase the plant load. But when the chilling requirement hit 60% of the chiller design, we'll start to lose the solution level in the Generator.
-We have never filtered the LiBr. Only did once during pre-comm. I will slot this into our Turnaround plan.
-We do maintain the CW valve open all the time, but based on 6784 comment, this practice need to be reviewed.
-During start up of shutdown, the chiller goes thru an auto dilution mode to stabilise the temperature, nevertheless, I'll consult the vendor for decrystallization

Thank you to all! I plan to get the vendor in by next week. I'll give an update in two weeks time.
Regards

 

[quark]

There is always a cooling water temperature control supplied with a standard machine. Make sure that it is working.

Have checked up the quantity of LiBr and refrigerant(water)?
Crystallization(of strong solution) generally starts at low temperature heat exchanger because of high concentration and low temperatures. Two symptoms are increasing evaporator level and cool generator to high temp. heat exchanger pipeline.

Decrystallization is not very hard to do. But as you say the machine is working upto 60% load I think crystallization is not the problem. But better to shut the cooling water valve after completion of dilution cycle.
It is always better to filter LiBr once a year. (some machines have online filters also) How about the condition of pressure parts?

By the way how old is your machine? (I still feel 60% is a good figure for VAS)

Regards,
Repetition is the foundation of technology

 

[C4Reactor]

As we have two chiller units (one standby), my options are:
A. Run the chiller in series or,
B. Run the chiller in parallel or,
C. Install a rental unit downstream of the exisitng.

Option A requires extensive piping modification, Option B may cause insufficient flow (i.e. laminar) thru the tubes. I'm looking into option C as an interim measure.

Appreciate any comment

 

[6748]

Reply to hfzmm dt Dec 02,2002.
Why rent it when you have it?
We can run the chillers in parallel. The reduction in fluid flow can make the both the units to run with partial load. The inbuilt control systems will automatically reduce the generator temp or in other words the steam flow to the system.
Before putting both machines on line, pl ensure that all the low temp safety switches are working. The machine has to trip if the chilled water(Is it what is being chilled ?) temp goes below your set point.
The machine may trip due to low chilled water flow, since we are splitting the flow. This will call for resetting the differential pressure switch settings.
Keep the vendor informed of what you intend to do. They will suggest the set points for all safety controls.
Pl keep the low temp alarm settings for one machine slightly above that of the other machine so that you can be prewarned of the fluid reaching a very very low temp.
I have worked with 2 machines in parallel. By keeping the low temp set point differently, one machine will run at higher load and the other machine will come ON and OFF.