Mass balance of a demineralisation unit.

[padovano]

Hi all, we have just received FEED documents from a new demineralization unit we intend to buy. The demineralization chain is made up of a Carbon filter, Cationic drum, CO2 degasser, Anionic Drum and a mix bed drum to complete the demineralizing process. In the documents, it is stated that, the flow rate of water entering the unit is 80m3/h and flow rate of water out of the chain is 68m3/h. I would like to understand the origin of the losses of about 12m3/h of water during the production process. I would like somebody to explain to me the causes of these losses. I personally think it`s too much.

 

[ashtree]

padovano

First of all the degasser will have a couple of different loss pathways.(In saying this i am assuming its a packed tower type). These losses include evaporation and spray/mist. Given that you break the water down into thin films that pass over the packing and then blow large volumes of air over it to get the mass transfer from liquid to gas evaporation is likely and not insignificant. Losses from spray or mist in a well designed system should be small but you do see it sometimes.

The Cationic , anionic and mixed bed drums will require regeneration , backwashing and rinsing all of which will use water. The frequency of these functions are a factor of the type of resins and the chemical, and physical quality of the water that you are treating.

Some carbon filters are also designed to be backwashed to remove accumulated particulates, but you have not given enough information to know.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

The typical wastewater volume produced from a demineralizer is approximately 10% of the influent treated, not flow. The actual wastewater volume will depend on the amount of salts present in the raw water.

The mass balance sounds like it is a little on the high side.

Most demineralizer systems are preceded by a membrane process.

 

[dfmorvan]

Hi

There will be negligible water loss thru the degasser (the water/air flows are not comparable to a cooling tower plus the water is not hot (normally)). There may be some small losses with mist generation but really not a lot, 1% would be a max.

However as other have pointed out, there is the need to backwash the filters and regenerate the resins. The higher the salinity to remove, the shorter the cycles between regeneration will be for the same volume of resin. 15% water loss is in the range but maybe a bit high. There are ways to reduce the final rinsing water volume which can be easily implemented.

Do you have only one line? If you want to produce all the time you need to have a duplex unit (one line in production & the other regenerating or on stand by).

Look at the regeneration principle (I expect counter current for the primary here) to save on chemicals and water.

Sometimes it is also advisable, depending on the water analysis to use a combination of weak anionic and strong anionic resins to reduce caustic use. As your application is not that small it could be worth looking into.

 

[padovano]

Thanks all for your various contributions. They will help me to prepare the meeting with the engineering company. I thought about the losses from the degasser as well but I think the estimation is far on the high side.
: 1) The degasser is packed tower bed.
2) There are 3 demineralization chains. 2 on production and 1 on regeneration or stand-by
3) There is a silex filter for suspended materials, a carbon filter for organic materials before the cationic, degasser, anionic and mix bed.