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What's the best way for this to work?

  1. Jul 25, 2014 #1
    Picture explains much better than words can (see attachment)

    the idea is to monitor the level between the two phases. the problem with this is you need to be constantly pumping out of that tank, or it will overflow, and the person who designs it gets chewed out.

    The guy before me wanted to get sight glasses installed. But I suspect the site glasses would have a high rate of fouling, and maintenance around here is pretty tied up.

    would like to keep it as simple as possible. I was thinking maybe some pneumatic fail/close check valves at the outlet, since the pump is pneumatic. but I don't know if those exist. even then, it'll be hard to keep the level constant without some type of level control.. meaning everything needs to be enclosed

    so is sight glass the best option then?
     

    Attached Files:

    Last edited: Jul 25, 2014
  2. jcsd
  3. Jul 25, 2014 #2
    explain your process a bit better and what your issue is. Is the overflow issue with the little tank in the middle feeding the pump?

    Edit: Oh, is the left tank the clarifier you were talking about in another thread? So I suppose the right tank is just some random process collection or buffer tank?

    Is the little tank then a slurry tank? Taking the thick sludge and slurrying it so it can be sent back into process? (most processes I've seen send the sludge to tailings ponds or gangue piles, so I'm not sure what's going on here).

    Why does the little tank overflow?

    I suppose you are trying to do this while avoiding electrical methods of level sensing as in the other thread you noted that the plant is hesitant to run power out there.

    Controlling processes with air can be done, but pneumatics are sometimes finicky.

    A good method here would be some high and high-high level sensors in the little tank. High turns on the pump if it is off for some reason, and HH closes new pneumatic solenoid valves in the little tank fill lines and sends an alarm to your control room, ideally. You need some power though, 120 volt at a minimum, though typically 240 V.
     
    Last edited: Jul 25, 2014
  4. Jul 25, 2014 #3
    this is a separate system from the sludge recirculation and the blowdown. the blowdown is on a timer that goes off to a mud pit. the recirculation will be driven by that pump you see in the picture. this schematic has to do with sampling the sludge taps along the side walls of the lamella, which to me makes sense to tie in with the sludge recirculation, because they end up in the same place.

    My problem with the design is risking the tank overflowing due to the static head provided by the lamella water level, hence the need for level control to keep pumping that stuff out, and a fail safe system that shuts the nozzles when the pump loses air.

    we do have 240V power out there, as well as some digital tags in the junction box. But the reason I want to be conservative with our DCS loops is because I want to get multiple turbidity meters installed, as well as an automated chemical feed (which is manual right now).
     
  5. Jul 25, 2014 #4
    There are lots of pneumatic fail-closed valves on the market, which are pretty reliable. If air loss is your biggest concern, a regulated supply to a couple fail-closed knife gates supplied from the pump air supply line would be a pretty cheap option to ensure the tank doesn't over flow, but only if the flow out is greater than the flow in. I would go further though and suggest some level control in the tank.

    For this, you could have an actuated knife gate in the lamella line actuated by an air line with a pneumatically actuated solenoid shutoff valve (or by using a standard pneumatic controllor which modulates output pressure based on some form of electronic input, say 4-20). I would install a high level sensor to control the shutoff valve, shutting off air supply in the event that the water reaches a certain level and sending an alarm to your control room letting them know there's a problem. I'm a mechanical guy, so I don't know much about how you'd want to actually control it so that the valve opens back up when you want it too, though.

    Something like these: http://www.redvalve.com/rv/index.php/content/view/55/104/ [Broken]

    edit: btw, this is just my offhand thoughts based on your initial thoughts on how to control this. There may be better/cheaper/more simplistic options out there.
     
    Last edited by a moderator: May 6, 2017
  6. Jul 25, 2014 #5
    yea... an enclosed system with sight glass sounds much simpler. keep it dumb and stupid, as they say.
     
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