Results 1 to 2 of 2

Thread: STP recycled water reuse and discharge - system curve - excess flow

  1. #1

    Join Date
    May 2016
    Posts
    1

    STP recycled water reuse and discharge - system curve - excess flow

    Hi Patrick,

    Just want to ask for some advice in general regarding my infowater model.

    Scenario wherein the STP treats water and stores it in a 10ML tank which is then used for recycled water and/or excess is discharged to the lagoon at the end of the network.
    so the flows are from the STP ->10ML treated storage tank->pumped system->customer demand->remainder is discharged to lagoons.

    How i set it up.

    - I set up a reservoir (representing the STP) then a valve (where I loaded the diurnal flows pattern of STP production) then this discharges to the 10ML tank then a pump to provide the network supply. The 10ML tank is set to run the pump within levels (50-80% active level) and to discharge in the lagoon at the end of the network to release the excess from the STP and prevent the 10ML tank to overflow.

    - I turned the overflow volume on from the 10ML. converted this to flow and loaded this in the last node which I thought will represent the lagoon. (is this the way to go????) because it looks like the node is still pressurized after I run the simulation which does not seem to represent what I need. The flows balance out, there is no overflow in the 10ML tank but the pressures doesn't seem correct because if i release to a lagoon, it means that the pressure at that last node should be zero or atmospheric? Your advice is much appreciated.

    - So i thought of adding a tank after the last node that represents a lagoon. kept the "overflow rates" as demand to represent the excess overflow volume in the last node. The pressures dropped as expected but I am not sure if this is the correct. Do I remove the excess "overflow rates"? and keep the tank at the end? What's the best way to model for this with the excess flow and correct pressures?

    - The system curve does not seem to work when I did not have the tank at the end(lagoon) but when I added that in, it worked but not sure of the results.

    I hope the query makes sense and your advice is much much appreciated. Thanks!

    Rick

  2. #2
    Forum Moderator

    Innovyze Employee



    Innovyze Employee



    Join Date
    May 2015
    Posts
    421
    Rick,

    How you chose to model anything definitely requires a lot of engineering judgement but ultimately will be the call of each modeler.

    Here are some quick thoughts:

    1) OverFlow Usage - While this is always an option, the downside of this is that it leaves part of the "demand" as open ended. As most systems should not overflow (if designed and operated correctly as this is loss of supply and waste) many modelers try to avoid using this in the model and one can create something similar and still clearly see how much water is lost as well using like a pressure sustaining valve discharging to a Reservoir, with the PSV setting associated with a hydraulic grade line equal to the tank overflow, but its really user preference. I'd also put a flow totalizer on the supply pipe to the PSV so you could see the total flow sent to the overflow easily. I often prefer this over a specific model report as one can easily see what is occurring directly in a model element, but both would work.

    If you make "overflow" a demand the model will calculate flow to it as if it is under pressure. They key is generally knowing what the real system does and then testing what you do to account for an unusual factor like this to make sure the model setup will adequately represent what actually is occurring for all pressures, tank levels, and flows in the system. Often this is why you calibrate the model so you can verify if how you set it up is going to adequately do what the real system does. If things don't reflect reality, generally you will need to alter how you are modeling the unusual situation until it does adequately represent the real system.

    If you have a weir that sends water to a lagoon one could set up a PSV (pressure sustaining) valve that would reflect flow to the weir and this would keep the HGL near the flow to the lagoon as realistic as possible. If they just open a pipe to atmosphere then you may need to model a reservoir with the HGL set at what atmosphere pressure would be and then restrict flow to it so that you can represent the real conditions. THis could be modeling a smaller pipe or modeling an emitter (An emitter is essentially a flow to atmosphere and is represented in EPANET as a virtual reservoir at the elevation of the junction so this is why a reservoir can act like an emitter. The larger the emitter coef, the more the flow, the less the emitter coef the more resistance. to flow. You can play with an emitter coef to adjust the flow or just use a smaller pipe with headloss to restrict the flow somewhat when going to the lagoons. But find out what the real system actually does first so you can be best equipped and then verify it works after.

    For a system curve it is very critical the HGLs in the system are accurate. see here for a link to the system curve presentation: https://forums.innovyze.com/threads/...Considerations

    Knowing how system curves are calculated helps know what might cause issues as well. What controls the Hydraulic Grade Line (HGL) on both sides of the pump will completely impact the system curve calculations in the software.

    Let me know if you have additional questions.

    Patrick Moore




    Quote Originally Posted by Rick View Post
    Hi Patrick,

    Just want to ask for some advice in general regarding my infowater model.

    Scenario wherein the STP treats water and stores it in a 10ML tank which is then used for recycled water and/or excess is discharged to the lagoon at the end of the network.
    so the flows are from the STP ->10ML treated storage tank->pumped system->customer demand->remainder is discharged to lagoons.

    How i set it up.

    - I set up a reservoir (representing the STP) then a valve (where I loaded the diurnal flows pattern of STP production) then this discharges to the 10ML tank then a pump to provide the network supply. The 10ML tank is set to run the pump within levels (50-80% active level) and to discharge in the lagoon at the end of the network to release the excess from the STP and prevent the 10ML tank to overflow.

    - I turned the overflow volume on from the 10ML. converted this to flow and loaded this in the last node which I thought will represent the lagoon. (is this the way to go????) because it looks like the node is still pressurized after I run the simulation which does not seem to represent what I need. The flows balance out, there is no overflow in the 10ML tank but the pressures doesn't seem correct because if i release to a lagoon, it means that the pressure at that last node should be zero or atmospheric? Your advice is much appreciated.

    - So i thought of adding a tank after the last node that represents a lagoon. kept the "overflow rates" as demand to represent the excess overflow volume in the last node. The pressures dropped as expected but I am not sure if this is the correct. Do I remove the excess "overflow rates"? and keep the tank at the end? What's the best way to model for this with the excess flow and correct pressures?

    - The system curve does not seem to work when I did not have the tank at the end(lagoon) but when I added that in, it worked but not sure of the results.

    I hope the query makes sense and your advice is much much appreciated. Thanks!

    Rick

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •