Sodium Hypochlorite Process Help

[JSchule]

Good Evening. Im a Production Technician at a small power plant in Texas. My background is in I&E but due to staffing, we are required to operate the plant as well. We bring in raw water through a 36” pipeline to be used as cooling water, service water and demineralized water for steam. We have to inject 12.5% sodium hypochlorite at multiple points for algae and condenser protection. Our vessel that stores the bleach is approximately 6500 gallons. From that vessel, a discharge line is attached to 3 manifolds which is then routed to the chemical injection pumps. One of the pumps is used to inject the bleach into a 3.9 million gallon raw water tank. That tank level stats at about 96% full. There’s about 2700 GPM of raw water going in and out of the tank for days at a time. Our set point for the bleach pump is about .60 ppm FAC. So we are constantly pumping bleach to that tank. Now, here’s the problem... that pump constantly air locks, looses prime. The head pressure of the bleach vessel should always keep the pump primed because it is below the level in the tank. The injection point is through a quill with mounted on the discharge line of the recirculating pump for the 3.9 million gallon tank. Some people believe the sodium hypochlorite is gassing off causing the pump to loose prime... that’s impossible because the tank is vented and it looses prime during winter months.. this is an issue that is driving me crazy and I am hoping that someone can help me. I can take pictures of the manifold etc and can provide more information.

 

[georgeverghese]

Correction to my previous post: The vapor bleed at the pump immediate suction should work, but not the bleed suggested at the high point at the bleach tank exit - this will break the syphon and stop flow to the pumps. For this location, I dont see any solution other than relocating the tank exit to the tank bottom.

 

[Compositepro]

You could use a recirculation line back to the supply tank from the pump suction manifold. That would require an additional small centrifugal pump.

 

[Latexman]

Correct me if I'm wrong.

I see 6 identical pumps. 5 do not vapor lock; 1 does.

The problem pump seems to be the only one with a 45^o riser in the suction header right before it's suction take-off. After the suction take-off, the suction header appears to me to slope down, thus creating a high point pocket.

What is it 3/4" or 1" CPVC? It also seems like the easiest and cheapest thing to change that has been mentioned so far. But, JSchule, you are the only one with the real world perspective. I'm just SGOTI.

Good Luck,
Latexman
Pats' Pub's Proprietor

 

[JSchule]

We are going to get an engineer to come out and look at it, give us some quotes to replace all of the manifolds etc... Latexman, yeah I don’t know why they put that 45 to the suction of the problem pump.. There’s really a lot of bastard issues here with the entire process... I appreciate the feedback... I’ll let keep y’all in the loop.