demin water plant turndown

[767]

I have to purchase a demin water package with rated flow 100 mc/h and min flow 10 mc/h.
Unfortunately The minimum flow for the resins beds is 40 mc/h.
Should have I recycle 30 mc/h at the inlet of the package or to the untreated water storage tank?
Thanks

 

[bimr]

It is hard to say with the information that you presented. You will probably maintain a higher water quality if you keep the water moving in your piping system. However, you do not indicate whether the piping distance is 2' or 2000' nor if you have an elevation difference for pumping. Note also that for this option, all of the piping as well as the untreated water storage tank would have to be constructed of materials that can withstand demin. water.

Recirculation around the demin system is probably the least expensive option.

 

[767]

Thanks for your answear.
The piping distance is 300 meters, SS, 4". The minimum flow rate to be recirculated is 60 mc/h.All the untreated water line is SS.

 

[767]

I forgot that the plant is specified for 0-100 mc/h.I think that at low flow rate temperature may increase

 

[GarySCWSVI]

You need to recirculate the water from the outlet of the unit back to the inlet at times when the flow is too low. You can do that by installing a recirculation pump from a tee on the outlet line to a tee on the inlet line. The pump is activated by a flow switch that will send an electrical signal to the pump to run when the flow is less than the minimum for the resin. You will need a flow control after the pump so that the water flows at a flow rate just above the minimum flow rate for the resin. You will also have to install a check valve on the inlet line before that tee to prevent backflow and a check valve on the recirculation line to the inlet line to prevent backflow from the inlet back to the outlet line.

Distance and size of the line is not important.

Gary Schreiber, CWS VI
The Purolite Co.

 

[bimr]

Still lacking some information, but could make some general comments.

If you are just making demin. water for a boiler and are not that concerned about organic material, recirculation around the demin. plant will probably suffice.

If you are trying to make a higher grade of water such as that used in a semi-conductor plant. You probably want to recirculate the water back to the storage tank.

 

[cub3bead]

The semiconductor guys learned along time ago that they couldn't leave their mixed beds in recycle mode over the weekend and then come in and get them rinsed down to quality. The resins reached equilibrium with the recirculating water and had to be regenerated.

Would it not be better to fill your demin storage tank and then shut down the demin until you could bring it back up to refill the tank. You would have to rinse to quality again which could hurt your plant's water balance but you save all the kWhs burned recirculating water.