Chemical dosing for cooling tower water

[u/Trigathoras69]

Hello guys, junior engineer here. I was given the task to install a control panel to inject chemicals for cooling tower water and design the suitable piping pathway and where should the chemicals be injected into the cooling tower system. I was thinking of just directly inject the chemicals into the cooling tower basin, but since the cooled water in the basin is stagnant, im afraid the chemicals will not mix well inside the basin. My supervisor suggested do the piping to that the chemicals are injected into the header at recirculation pump discharge side. The constraint with this idea is that the header is made of stainless steel, and the chemical piping is PVC. I would like to ask for any ideas or comment from you guys, especially for those who are working with cooling tower. Is there any industry standard on how to inject the chemicals into the cooling tower system?

[u/Expertnovice77]

Feel free to PM me, I’ve just upgraded all of our CWT chemical controllers.

We use Walchem controllers with Pyxis probes. We use conductivity to control blowdown, and a free chlorine probe (which also takes pH) to control bleach addition via a class 1 div 2 pneumatic peristaltic pump. We also inject 2 separate Gengard (Veolia) chemicals via diaphragm pumps on a percent-time basis.

We have a lot of agitation/mixing in our ponds, so we dump the chemical directly into the pond. I have heard some say that you can route the chemicals directly back into the return header (right prior to entering CWT) to increase mixing if you don’t already get enough in your pond. Just obviously take your sample/controller feed location upstream of your chemical discharge location. Fyi, these peristaltic/diaphragm pumps have very high discharge pressure abilities, so no problem getting them into the return header

[u/Expertnovice77 → u/Expertnovice77]

Also- seeing the constraint- just have your pipefitters redo the chemical pump discharge lines into stainless tubing- it’s not difficult and will last forever. If you have the ability to temporarily bypass the return header injection location (eg dump directly into the pond instead of tower), consider putting in some injection quills + more threadolets for additional injection locations. The chemicals we use cannot be mixed prior to injection.

[u/Trigathoras69 → u/Expertnovice77]

we don't have bypass for discharge header..if we decided to do the piping on the header, we have to do it during plant hold

[u/Expertnovice77 → u/Trigathoras69]

Then just run tubing over to where the water discharges out of the CWT into the pond. Just use plastic tubing lines for now. Consider using a back pressure valve so your chemical pumps don’t siphon. You’ll get similar mixing/agitation there. Next TAR consider having a spoolpiece ready for the return header with several threadolets on it for an injection quill+ball valve + stainless tubing.