How to Balance Flows between two Claricones

[Rover886]

Hey there guys. Got a situation where I have two claricones. I need to balance the flow between the two. Each feed pipe flowing into a claricone has a control valve and a magmeter to read back flow. I know I need a PID for each of the valve controllers but I think I need a third PID' output to act as a valve position controller. I am trying to maximize flow through each cone while balancing the flow to each one at the same time. Anyone ever run across this. This is my first time with this problem.

Thanks

Rover886

 

[semo]

Do you have room to install a flow splitting structure? You could fabricate such a structure with two wiers each set at the same level so flow is split evenly. One pipe into the center, flow over the weirs, and two pipes out, one to each cone. The structure will have to be higher than the cones so it may take some piping up the side of the head tank and then back down to the cone inlet piping.

 

[brennanpe]

How are you determining this maximum flow? Dependent upon the answer, it could be as simple as three lines of PLC logic. Based upon my exposure to CBI's claricone clarifier's build weir structures doesn't seem to be the answer. This would have to be accomplished through PI control using the FIT's and the CV's as mentioned and is most likely not that complicated.

brennans7

 

[semo]

I'm assuming you have variable flow in this plant. Let me say it may sound easy to split with the valves; but pay attention to what you are doing. The reason I recommended a structure is to eliminate some of the potential problems. It costs for piping and structure; but, is a no brainer for equal flow. I don't know your piping layout and that will affect the split using valves and controllers.

You already know this; but, you have two splits to make. One splitting the flow to each cone, then one splitting the flow to keep the rotational speed in the cone. This doesn't sound hard; but, if split one is not made evenly at 1/2 of the incoming flow, you can overflow something, drain something, or depending on your piping layouts, you can increase/decrease head on these pipes causing unequal flow distribution which can then bouce the valves open/close. All of your flow measuring systems need to be equal in performance and/or could require additional meters or replacements.

Split two will work out because you are only restricting flow in the large inlet pipe. The excess/deficient flow will run through the smaller inlet pipe increasing/slowing the rotation.

 

[Rover886]

Thanks for the help guys. Unfortunately the structure is already built. The municipality Im dealing with does not have any kind of hydraulic profile for the plant. None were ever given to the plant for archival purposes. Brennans7, in answer to your question, there is a central wetwell that feeds both claricones through 30" diameter pipes which are then necked down to 18". On each feed pipe to the claricones are a magmeter and a control valve. The requirement is to maximize flow while balancing the flow betweeen the the two cones. I have one idea to work this. In the wetwell that feeds both pipes, we are measuring the level using a pressure sensor to measure head. I plan on scaling the head height in to flow. Then its simply dividing th e flow equally between the two cones. The wetwell will act as a psuedo anemometer. The higher the the flow rate from the raw water pumps, the higher the wetwell height. In turn I increase the flow rate through each claricone. For example, if I have 10 MGD coming from the raw water pumps, I will achieve a head height of about 17 ft, hypothetically. Then I just have my PID controller on each cone flow at 5 MGD which is equal to the plant flow from raw water. Qin=Qout. I use a scale with parameters block to convert the height to flow. If the water gets too high in the wetwell, I just rescale the flow to height. What do you guys think?

Eric

 

[semo]

Based on my understanding of what you are trying to do:

That solution sounds plausible but complex to me.

Another option that seems easier is to maintain a constant level in the wetwell (headtank?). If you calc your hydraulics between the cone and wetwell, set the "level to maintain" above your max flow level, you just have to open/close the valves to keep a constant level and double check to see the flows are even.