de-Chlorination of water

[ukengineer58]

Hi we have a project where we are looking into automatic dosing of chemical into a chamber to dechlorinate water from a water treatment site. Does anyone have a design reference or the kind of thing that needs to be considered? Note I am not doing final detailed design I would just like to understand what info is key and how it is done before the 'real' designers get a handle on it. Just so I understand the constraints etc. I'm thinking based on previous experience with dechlor tablets to automatically dose into the chamber we would need to consider;

flow rate, total volume, PPM of chlorine. Also would it matter the distance to the receptor or sampling chamber? Contact time?

Any help or links to design guides etc much appreciated.

Thanks

 

[Compositepro]

I would think that dechlorination in any sort of significant volume would be done by steam stripping. Basically just boiling the water to remove any dissolved gases. A heat exchanger is used between the feed and exit flows so that very little energy is used.

 

[ashtree]

There are many techniques to de-chlorinate water but the two which would probably be used most often is activated carbon or dosing with sodium metabisulfite (SMBS). Unless the size of the plant is small or the amount of chlorine to remove is low granular activated carbon would not be the usual choice. Activated carbon will work fine but it can be expensive.

Theoretically 1.34grams of SMBS will remove one gram of chlorine. It is common practice in de-chlorination applications to slightly overdose and with everything else actual dose rates are normally about 3:1.
The reaction is quite rapid but mixing should be thorough. These reactions will normally be completed with in a few seconds and its not unusual to dose the SMBS into a pipe ahead of a mixer, rather than having a dedicated chamber.

The Dow Filmtec RO Membranes Technical Manual page 60 refers to this.

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

 

[ukengineer58]

Thanks for your assistance guys. Yes ashtree we are looking into whether a chamber is required. This is for de chlorinating water before putting back into the environment as part of a treatment process.

 

[bimr]

A chamber is generally specified. Sodium bisulfite is added in the dechlorination chamber which is typically located at the end of each chlorine contact tank.