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Re: [microhydro] Digest Number 351 Gas supersaturation

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  • Celso Penche
    I read the James D. Szura s message concerning superasaturation. Supersaturacion occurs behind a spillway but never at the outlet of a hydro turbine. Actually,
    Message 1 of 1 , Sep 1, 2001
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      I read the James D. Szura's message concerning superasaturation.
      Supersaturacion occurs behind a spillway but never at the outlet of a hydro
      turbine. Actually, modern turbines for small hydro plants start to be
      designed to aereate the water and increase the oxygen content in the water,
      but never attaining nitrogen supersaturation, origin of bend in fish.
      There is an interesting publication on gas saturation, made for the D.O.E,
      by Battelle, available at http://hydropower.inel.gov/turbine/DOEID-18553.pdf
      tha deals with the problem and the new turbine design (4 Mb).
      Advices to mitigate the river health include always an increase in the
      oxygen content in the river water, and new Francis designs include
      modifications to achiebe this target. In the Szura case the nitrogen
      introduced in the rapids are one thousand bigger than any oxygen in the
      turbine tail water.
      Celso Penche

      ----- Original Message -----
      From: <microhydro@yahoogroups.com>
      To: <microhydro@yahoogroups.com>
      Sent: Tuesday, August 28, 2001 12:37 PM
      Subject: [microhydro] Digest Number 351



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      There are 5 messages in this issue.

      Topics in this digest:

      1. Re: gas saturation in tailrace water
      From: "James D. Szura" <orca@...>
      2. Re: asking about quotation steel pipe
      From: "EDDY CASARES" <gulfatlan@...>
      3. Re: gas saturation in tailrace water
      From: Lancie1@...
      4. Re: gas saturation in tailrace water
      From: "JTurk" <jturk@...>
      5. conduit excemptions/ FERC license
      From: bradsan@...


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      Message: 1
      Date: Mon, 27 Aug 2001 08:25:42 -0500
      From: "James D. Szura" <orca@...>
      Subject: Re: gas saturation in tailrace water

      Rolf:

      I believe the Francis turbine will reduce the amount of nitrogen in your
      discharge water versus the turgo.

      I do not believe water can become supersaturated with nitrogen unless
      the air in contact with the water is above atmospheric pressure for some
      time. You may pick up slight metal contamination from the metals in the
      system, especially if you have much cavitation. Give up a little draft
      head and you will reduce cavitation. A well designed runner and guide
      vane system is important also.

      James D. Szura
      Ozark Industries
      Microhydro design, fabrication, maintenence.



      rolf.widmer@... wrote:
      >
      > On a project we have, we are looking to put in a turgo turbine on a
      > river just above a salmon fish farm. The discharge from the turbine
      > will go back into the river just above the fish farm's intake.
      > The fish farm are saying that their insurers aren't happy with the
      > scheme because the turbine will cause the water to become
      > supersaturated with gas (nitrogen) which can affect the fish. They
      > already have a gas desaturator (a tower full of pall rings) to remove
      > gas that has been absorbed by the water flowing down the rapids in
      > the river.
      > I was wondering if you had ever come across this, or had experience
      > of hydro schemes above fish farms in similar situations? It seems to
      > me that the turgo would certainly saturate the water with air, but
      > provided the air is not entrained into a deep pool, then it shouldn't
      > become supersaturated.
      > One solution that has just occurred is to use a francis machine (the
      > head is about 80m), such that there is no air entrained?
      > If you have any ideas or pointers for people to consult, I would much
      > appreciate the advice.
      >
      >
      > NOTE: The advertisements in this email are added by Yahoogroups who
      provides us with free email group services. The microhydro-group does not
      endorse products or support the advertisements in any way.
      >
      > More information on micro hydropower at http://microhydropower.net
      >
      > To unsubscribe: send empty message to microhydro-unsubscribe@...
      >
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      --

      Thank you; and good night, from Mountain Grove, Missouri.



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      Message: 2
      Date: Mon, 27 Aug 2001 13:41:06 -0400
      From: "EDDY CASARES" <gulfatlan@...>
      Subject: Re: asking about quotation steel pipe

      Depending on the amount I would recommend Ductile Iron Pipe as we have been
      using for minihydros in Central America.

      I would like to work with you since this has been my expertise for the past
      27 years.

      Reply to:
      Gulf Atlantic International Corp.
      Eddy J. Casares
      E-Mail: gulfatlan@...
      Tel: 305-229-5222
      Fax: 305-229-9004
      Miami, Florida

      ----- Original Message -----
      From: "JOSE HERMES LANDAVERDE" <hlandaverde@...>
      To: <microhydro@yahoogroups.com>
      Sent: Sunday, August 26, 2001 11:13 PM
      Subject: [microhydro] asking about quotation steel pipe


      Dear friends:


      Can you tell me somebody where I can find a very good quotation for steel
      pipe. Rigth now I am working in two feasibility studies of the two small
      hydroelectric projects in central america and I am too in the optimization
      of the install capacity of each one. I normally use a rate of US$ 2/kg but I
      would like to confirm it. The diameters that I am considering for the firts
      project are between 36 and 48 inches and for the second one are between 26
      and 34 inches


      thanks a lot for your help


      José Hermes Landaverde



      [Non-text portions of this message have been removed]




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      Message: 3
      Date: Mon, 27 Aug 2001 21:36:34 EDT
      From: Lancie1@...
      Subject: Re: gas saturation in tailrace water

      Rolf, regarding the turbine causing problems at the fish farm: Here in the
      Tennessee Valley, the Tennessee Valley Authority (local power producer) has
      added special blades on many of its hydropower (Francis) turbines for
      exactly
      the opposite reason: to add OXYGEN to the water so that the fish will grow
      better. So if it is true that the turgo will add nitrogen, then it will
      also
      add oxygen, which should be good for the fish. Is there some special
      situation with salmon eggs that requires exact control of the mixture of air
      and water? Could you run your discharge in a flume or ditch past the fish
      farm intake?


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      Message: 4
      Date: Mon, 27 Aug 2001 21:45:44 -0700
      From: "JTurk" <jturk@...>
      Subject: Re: gas saturation in tailrace water

      I design the electronics for one the dissolved gas saturation
      pioneers in the US, Brian d'Aoust, Common Sensing, Inc.
      Granted, I do the electronic part, but I have spent several
      years doing station maintenance on the Columbia and Snake rivers
      and have had a chance to learn just a bit about the physics of
      gas saturation..

      In a nutshell, surface water contains atmospheric gasses
      (nitrogen, oxygen, argon, etc.) dissolved in the water at the
      same pressure as the atmospheric pressure. (This would be about
      760mm HG at sea level.) Supersaturation is the term used when
      the amount of gasses dissolved in water exceed atmospheric
      pressure. This phenomenon seldom exists to any extent in nature
      and is generally caused by mixing air and water at significant
      depths. Saturation levels in excess of 110% are generally
      considered dangerous to fish because it causes the equivalent of
      the "bends" when they come to the surface.

      Anyway, such mixing often happens at man-made dams. Excess flow
      is generally allowed past the dam through some type of spillway.
      The most common spillway design releases water from near the top
      of the dam and allows it to drop to the down-stream level below.
      Depending on the dam, this can be as much as several hundred
      feet.

      When large volumes of dropping water fall into the downstream
      water, air is also sucked in as this dropping water plunges
      below the surface. Depending on spillway design, the falling
      water can plunge 50 or 100 feet below the surface. During this
      condition the pressure of the air bubbles is elevated to the
      hydrostatic pressure created by the weight of the water. When
      this happens some of the air bubbles to be dissolved into the
      water creating the supersaturation condition.

      Now to specifically address the concern that the turbine will
      cause gas supersaturation. As explained above, creating
      supersaturation requires air from the atmosphere in addition to
      the water. In most cases the turbine part of a dam does not
      produce much gas saturation. This is because water from a head
      source is routed to the turbine through a penstock. After
      passing through the turbine the water has had most of it's
      energy extracted, if the system is efficient, and actually falls
      only a very short distance into the tailrace.

      Supersaturation does not happen in the turbine because there is
      no source of outside air and no water free-falling long
      distances. While there is some variation in turbine designs, I
      do not think you would need to be concerned with gas saturation
      in microhydro. The turgo turbine does mix air and water, but
      this is done at very close to atmospheric pressure, which can
      not cause supersaturation. You may, however, need to have
      concern if you are going to have a spillway with a large volume
      of water dropping a great distance.

      I hope this has been a help. If you should have further
      questions, please visit Common Sensing at www.commonsensing.com
      . Their site can probably do a better job of explaining things
      than I have.

      Jay Turkovsky



      ----- Original Message -----
      From: <rolf.widmer@...>
      To: <microhydro@yahoogroups.com>
      Sent: Monday, August 27, 2001 12:09 AM
      Subject: [microhydro] gas saturation in tailrace water


      On a project we have, we are looking to put in a turgo turbine
      on a
      river just above a salmon fish farm. The discharge from the
      turbine
      will go back into the river just above the fish farm's intake.
      The fish farm are saying that their insurers aren't happy with
      the
      scheme because the turbine will cause the water to become
      supersaturated with gas (nitrogen) which can affect the fish.
      They
      already have a gas desaturator (a tower full of pall rings) to
      remove
      gas that has been absorbed by the water flowing down the rapids
      in
      the river.
      I was wondering if you had ever come across this, or had
      experience
      of hydro schemes above fish farms in similar situations? It
      seems to
      me that the turgo would certainly saturate the water with air,
      but
      provided the air is not entrained into a deep pool, then it
      shouldn't
      become supersaturated.
      One solution that has just occurred is to use a francis machine
      (the
      head is about 80m), such that there is no air entrained?
      If you have any ideas or pointers for people to consult, I would
      much
      appreciate the advice.




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      http://microhydropower.net

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      ________________________________________________________________________
      ________________________________________________________________________

      Message: 5
      Date: Tue, 28 Aug 2001 02:06:10 -0000
      From: bradsan@...
      Subject: conduit excemptions/ FERC license

      I recently joined the group although I've been reading messages for
      soom time.I'm located in Washington State near the Snake River hydro
      system the extremists want to remove. I'm wondering how small of a
      system must be licensed? For years I've looked at a sight on my farm
      that has 5m head and 3m3 flow. The process for licensing looks very
      time consuming and difficult. I'm thinking about filing for a conduit
      excemption but figure it may also take alot of time. I desire
      communication with others that have experience with this process.
      Can copies of other small licenses be obtained to be used as examples
      for the application? Any help would be appriciated.




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