View Full Version : Lithium Bromide

24-10-2005, 04:15 PM
Hi Johnny

The question relates to the chemist's analysis of the absorbant in the machine we are now looking after http://www.refrigeration-engineer.com/forums/showpost.php?p=23373&postcount=1

The report reads:
Rob has analysed the two samples supplied for alkalinity and lithium content, two of the main analyses mentioned in the instruction document.
The pure water is modified by the addition of an inhibitor lithium molybdate and a salt to lower the freezing point of the water. The salt is lithium bromide as required as lithium hydroxide and hydrogen bromide to give an alkalinity of approximately 0.1N. The salt and inhibitor levels are convieniently monitored by analysing the water for lithium which should be approximately 150ppm (mg/litre).

The water is also analysed for copper and iron most probably to monitor corrosion.


Analysis of metals by ICP
The water samples supplied had to be diluted 10,000 times for the lithium analysis and were much more concentrated than anticipated.

Refrigerant - Lithium content 6170 ppm, alkalinity 0.009N
Absorbant - Lithium content 28020 ppm, alkalinity 0.08N

The lithium content is clearly too high indicating a gross error in monitoring the water and calculating the lithium hydroxide and bromide content.
The alkalinity values are almost correct indicating that the Li and Br content are similar.
No significant iron or copper were observed.

When repairing the leak on the machine we decanted 125 litres of absorbant.

Given the figures above are you able to advise the amount of inhibitor that should be added to return the concentration to normal?

24-10-2005, 11:14 PM
Frank, I assume the machine was running at full load when the sample was pulled because that's when the spread between the dilute and the strong solution is the widest, which results in the capacity of the machine to lower the pressure to absorb the water from the evaporator. Other wise the results could indicate a high concentration of Li-Br in the water. Now full load has to be at the currect hot water flow and temperature or steam pressureto the concentrator. I'm curious as to why they didn't check the trim with a Hydrometer:) Some manufacturers furnish a trim chart for for a partial load

Johnny Rod
25-10-2005, 03:55 PM

It's Greek to me I have to admit, can you tell me something about the system? Got the instructions that are referred to? The numbers certainly look a long way from what you were expecting.

25-10-2005, 07:23 PM
I'll pick them up next time I'm on site.