Desal Conductivity Issue

Mechanical Vapour Recompression desalinators are, by their very nature, troublesome.

10 bar absolute saturated steam has a temperature of 180degC; 10 bar gauge is 184degC. If there is a high temperature difference across the heat exchange surfaces, as there might be if each and any of the effects are being operated at sub-atmospheric pressure, then boiling is going to be violent and this condition could cause carry-over of droplets from the boiling pool into the condenser side, carrying conductive species from the pool over with them, giving the higher conductivity mentioned.

Has the original equipment manufacturer, or its maintenance service provider, been contacted for advice?

It sounds initially as though the equipment is being pushed beyond its design operating conditions. If so, then adjust the equipment to perform at its as-commissioned conditions and see if the problem goes away.

If the problem persists, reduce the throughput of the unit until the problem goes away. It may indicate scaling of the heat exchange surfaces, which may entail dismantling the unit for cleaning.

If nothing works, then consider replacing the equipment with reverse osmosis technology instead.

_{<subscribes to discussion>}

Oooooh, ooooh! One more thought -

Should the unit be dismantled for descaling the heat exchange surfaces, take a good look at the mist eliminators and either clean or replace them.

Do report back with the findings.

the normal working pressure is around 15-17 bar at which auxilliary steam comes and its temp is around 300 Celsius .

i dont know much about reverse osmosis as far as i know, reverse osmosis is much more troublesome than reheat type desal plants because of their diaphram or so....

this machine of mine is working for about 15 years without any problem and this is the first time this sort of problem has occured.heat tranfer surfaces are clean and in good condition

regards,

hasnain

Check the demisters:

• Are they dirty?
• Are they still there?

Check that the unit is not operating at too high an auxiliary steam temperature.

• Over the past 15 years, what operating parameters differ now from the commissioning records that might cause carry-over of droplets into the condensate?

What does the original equipment manufacturer have to say on the problem?

Under what arrangements is maintenance carried out and how do these differ from the as-commissioned condition?

<...reverse osmosis is much more troublesome than reheat type desal plants because of their diaphram or so....>

Complete bollocks.

I would suggest contacting the supplier if possible or their agent foe advice. As is usually the case in these situations people always tell you change to a RO unit and if you were having problems with the RO unit then they would tell you to change to a compression type. Like many other things in the world there are advantages and disadvantages to RO units.

I have work with SASAKURA desalination plant 15 years ago and conductivity problem exist if the vacuum pump is not working propertly. Check also for possible leak and the compression system effeciency for possible defects.

Please check orignal STU/commissioning records/parameters and compare with the current parameters.

FYI

Nelson