Fluidized Bed after Super Saturator
Procedure
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h1. Current Research h2. Procedure {float:left|border=2px solid black} [!SandFilterSetup5.png|width=1000px!|Sand Filter Diagram] h5. Current experimental setup {float} \\ \\ {anchor:Table 1} Figure 1. Experimental setup showing the super saturator, fluidized bed, and bubble collector. {float} |
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h5. Table 1: Filter media types and sizes
||Filter Media||Sieve Size||Diameter (mm)||
|Glass Beads|50|0.297-.42|
|Sand|40|0.42-.59|
|Sand|30|0.84-1.18|
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The
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...
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consists
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of
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a
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vertical
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clear
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PVC
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pipe
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that
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is
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125
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cm
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long
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with
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a
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2.5
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cm
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diameter.
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This
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is
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the
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filter
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column,
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and
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it
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is
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partially
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filled
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with
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the
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filter
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media.
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The
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filter
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media
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used
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were
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size
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50
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glass
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beads
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and
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sands
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with
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sieve
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sizes
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30
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and
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40.
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These
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are
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summarized
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in
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...
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at
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the
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right.
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Tap
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water
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is
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sent
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upward
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through
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the
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filter
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column.
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The
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tap
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water
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cannot
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be
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guaranteed
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to
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be
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super-saturated
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with
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gases
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already,
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so
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the
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...
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previously
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used
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in
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the
...
...
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has
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been
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implemented
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to
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supersaturate
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the
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cold
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water
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before
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it
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is
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fed
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through
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the
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filter
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column.
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The
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aeration
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chamber
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is
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kept
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under
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1
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atmosphere
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of
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pressure
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while
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the
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water
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is
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bubbled
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by
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an
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aeration
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stone.
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Air
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is
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allowed
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to
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leave
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the
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aeration
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apparatus
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through
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a
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valve
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controlled
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by ProCoDA Software and a rotameter,
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which
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restricts
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the
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air
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flow
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to
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maintain
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pressure
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inside
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the
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chamber.
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From
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the
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bubbling
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chamber,
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the
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super-saturated
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cold
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water
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joins
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hot
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tap
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water
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and
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flows
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through
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1/4"
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tubing
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into
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the
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flow
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accumulator,
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which
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uses
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a
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pressure
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sensor,
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temperature
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probe,
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and
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two
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valves
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(one
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for
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hot
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water,
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one
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for
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cold
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water)
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controlled
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by ProCoDA Software to regulate the water's
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flow
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rate
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(which
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is
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altered
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to
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achieve
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the
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desired
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level
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of
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suspension
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of
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the
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filter
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media
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in
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the
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vertical
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column)
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and
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the
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water's
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temperature
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(which
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is
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set
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to
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20°C,
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and
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can
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be
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changed
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to
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mimic
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water
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temperatures
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in
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Honduras).
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The
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mixed
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water
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passes
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from
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the
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flow
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accumulator
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and
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into
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the
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filter
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column
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through
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1/4"
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tubing,
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suspending
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the
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filter
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media
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in
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the
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column.
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After
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flowing
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through
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the
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suspended
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filter
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media,
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the
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water
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and
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any
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bubbles
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that
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formed
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in
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the
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process
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pass
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through
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3/8"
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tubing
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into
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the
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bubble
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collector.
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A
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pressure
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sensor
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is
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located
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in
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the
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3/8"
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tubing
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between
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the
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filter
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column
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and
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the
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bubble
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collector.
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This
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sensor
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measures
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the
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pressure
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inside
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the
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system
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as
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cm
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of
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head.
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For
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the
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setup
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to
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truly
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mimic
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the
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open-to-atmosphere
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conditions
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of
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a
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grit
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chamber,
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the
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height
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of
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the
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final
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outlet
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of
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water
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from
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the
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system
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must
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be
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adjusted
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until
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this
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pressure
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sensor
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reads
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zero.
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The
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bubble
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collector
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is
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made
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of
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a
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3.8
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cm
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-
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diameter
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PVC
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pipe
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that
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is
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sealed
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at
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both
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ends.
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Water
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and
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bubbles
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from
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the
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glass
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filter
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column
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enter
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the
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chamber
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through
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3/8"
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tubing
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that
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connects
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the
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top
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of
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the
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glass
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filter
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column
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to
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the
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bottom
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of
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the
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bubble
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collector.
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Inside
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the
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chamber
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(which
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is
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initially
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filled
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with
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water
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before
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each
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experiment),
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bubbles
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float
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to
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the
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surface
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while
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the
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water
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flows
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out
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through
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3/8"
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tubing
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attached
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the
...
bottom
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of
...
the
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bubble
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collector.
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A
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1/4"
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tube
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attached
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to
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the
...
top
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of
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the
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bubble
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collector
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allows
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air
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to
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enter
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and
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leave.
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This
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tube
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as
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well
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as
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the
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water
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outflow
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tube
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at
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the
...
bottom
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are
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both
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controlled
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by
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valves
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that
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are
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opened
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and
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closed by ProCoDA Software, which uses a pressure sensor to monitor the water level inside the chamber. The water level inside the chamber can be visually monitored through an additional 1/4" clear plastic tube that is attached to the top and bottom of the bubble collector.
At the start of an experimental run, the bubble collector chamber is nearly filled with water, the air valve at the top of bubble collector is shut, and the water outflow valve at the bottom of the bubble collector is open. As bubbles enter the bubble chamber and gather at the top, the water level in the chamber slowly sinks. When enough bubbles have entered the chamber to lower the water level as far as possible, the outflowing water valve is shut and the air valve is opened, allowing the chamber to refill. When the water level in the chamber reaches the maximum level again, the air valve shuts and the water valve opens, and the process begins again. The chamber can be drained by opening both valves at the same time. The system continues running during all of these processes in order to keep conditions as constant as possible.
The Process Controller Method we are using to run this setup can be downloaded here.
The rate at which the water depth changes during a run is the same as the rate that air is being added to the collector, and so this is proportional to the rate that dissolved gases are being removed from the super-saturated water. Our data can be used to find the volume of dissolved gases removed per liter of water that flows through the system, allowing us to compare the relative effectiveness of each sand size, flow rate, and bed depth combination.
Results and Discussion
For each sand grain size, the change in water level was recorded over a period of time. Usually, the experiment was left to run for several hours. Water level vs. time was plotted for each of these runs. #Figure 2 serves as an example, showing the raw data for a run using glass beads in the filter column. Runs with the other filter media share the same patterns. Where the graph is slanted downward, the water level inside the bubble collector is sinking due to bubbles of gas leaving the water inside it. The steep upward climbs in the graph occur when the bubble collector has been completely filled with air and has to refill with water in order to continue the run. The data behaves fairly linearly, so after each run, a linear trendline is fitted to the data in Excel, as shown by the red line in #Figure 2.
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by [Process Controller], which uses a pressure sensor to monitor the water level inside the chamber. The water level inside the chamber can be visually monitored through an additional 1/4" clear plastic tube that is attached to the top and bottom of the bubble collector. At the start of an experimental run, the bubble collector chamber is nearly filled with water, the air valve at the top of bubble collector is shut, and the water outflow valve at the bottom of the bubble collector is open. As bubbles enter the bubble chamber and gather at the top, the water level in the chamber slowly sinks. When enough bubbles have entered the chamber to lower the water level as far as possible, the outflowing water valve is shut and the air valve is opened, allowing the chamber to refill. When the water level in the chamber reaches the maximum level again, the air valve shuts and the water valve opens, and the process begins again. The chamber can be drained by opening both valves at the same time. The system continues running during all of these processes in order to keep conditions as constant as possible. The Process Controller Method we are using to run this setup can be downloaded [here|Current Experiments^SandFilterConfiguration.pcm]. The rate at which the water depth changes during a run is the same as the rate that air is being added to the collector, and so this is proportional to the rate that dissolved gases are being removed from the super-saturated water. Our data can be used to find the volume of dissolved gases removed per liter of water that flows through the system, allowing us to compare the relative effectiveness of each sand size, flow rate, and bed depth combination. h2. Results and Discussion For each sand grain size, the change in water level was recorded over a period of time. Usually, the experiment was left to run for several hours. Water level vs. time was plotted for each of these runs. [#Figure 1] serves as an example, showing the raw data for a run using glass beads in the filter column. Runs with the other filter media share the same patterns. Where the graph is slanted downward, the water level inside the bubble collector is sinking due to bubbles of gas leaving the water inside it. The steep upward climbs in the graph occur when the bubble collector has been completely filled with air and has to refill with water in order to continue the run. The data behaves fairly linearly, so after each run, a linear trendline is fitted to the data in Excel, as shown by the red line in [#Figure 1]. {anchor:Figure 1} {float:left|border=2px solid black|width=700px1000px} !Water level vs. Time, GB, raw data.png|width=700px1000px! h5. Figure 12: Water level in bubble collector vs. time, using Glass Beads as filter media. Flow rate: 180 mL/min, Bed Expansion: 50% {float} \\ \\ |
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h5. Table 2: Properties of trendlines fitted to water level vs. time data. Bed Depth: 60cm, Expansion: 50%.
||Filter Media||Flow Rate (mL/min)||Slope (cm/min)||R ^2^ value||
|Glass Beads|185|.1426|.999|
|Sand 40|345|.1541|.9992|
|Sand 30|500|.1423|.9915|
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The
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slope
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of
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this
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trendline
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represents
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the
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rate
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of
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change
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of
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the
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water
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level
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inside
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the
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bubble
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collector
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as
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water
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runs
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through
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the
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filter.
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The
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slopes
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found
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for
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the
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filter
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media
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tested
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are
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summarized
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in
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...
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,
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along
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with
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the
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R
...
2 value
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of
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the
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linear
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fit.
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All
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of
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the
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R
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2 values
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are
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very
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close
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to
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one,
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which
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means
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that
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the
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data
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is
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in
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fact
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nearly
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linear
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and
...
can
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be
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accurately
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represented
...
by
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the
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equations
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given
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by
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Excel.
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For
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each
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run
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shown
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in
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the
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table,
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the
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filter
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bed
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was
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60
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cm
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deep
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and
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expanded
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by
...
50%.
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The
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the
...
rate
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of
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change
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of
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the
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water
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level
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can
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be
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converted
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to
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an
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equivalent
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rate
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of
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change
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in
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gas
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volume
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by
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multiplying
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the
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trendline's
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slope
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by
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the
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cross-sectional
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area
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of
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the
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bubble
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collector:
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} $$ \frac{\Delta Volume}{\Delta Time} = slope * \pi * r _{collector} ^2 $$ \\ {latex} To determine how much gas is removed per liter of water sent through the filter column, that volume rate of change is then divided by the flow rate of water in L/min. {latex} |
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!Gas removal, mL-L. GB, 40, 30.png|width=300px!
h5. Figure 3: Dissolved gas removal for various filter media. Bed Expansion: 50%
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To determine how much gas is removed per liter of water sent through the filter column, that volume rate of change is then divided by the flow rate of water in L/min.
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$$
\frac{mL\:gas\:removed}{L\:water\:treated} = \frac{\frac{\Delta Volume}{\Delta Time}}{Q_{water}}
$$
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This was done for each sand, and the results are plotted in #Figure 2.
In addition to sand grain size, filter bed depth was altered for the size 40 sand. Data was recorded for the filter depths of 42.5 cm and 60 cm, both expanded by 50% at a flow rate of 345 mL/min. The results are shown in #Figure 4. The deeper bed depth had a steeper slope, and therefore removed more dissolved gases per liter of water than the shallower depth, as summarized by #Figure 5
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!Water Level vs. Time. 40, 2depths.png|height=500px,align=center!
h5. Figure 4: Water level in bubble collector vs. time, using Sand 40 as filter media. Flow rate: 345 mL/min, Bed Expansion: 50%|{anchor:Figure 4}
!Gas removal mL-L,40, 2depths.png|height=500px,align=center!
h5. Figure 5: Dissolved gas removal for Sand 40 at different depths. Bed Expansion: 50%|
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Click here to download the results from this experiment (Excel workbook).
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{latex} {anchor:Figure 2} {float:right|border=2px solid black|width=250px} !Gas removal, mL-L. GB, 40, 30.png|width=250px! h5. Figure 2: Dissolved gas removal for various filter media. Bed Expansion: 50% {float} This was done for each sand, and the results are plotted in [#Figure 2]. In addition to sand grain size, filter bed depth was altered for the size 40 sand. Data was recorded for the filter depths of 42.5 cm and 60 cm, both expanded by 50% at a flow rate of 345 mL/min. The results are shown in [#Figure 3]. The deeper bed depth had a steeper slope, and therefore removed more dissolved gases per liter of water than the shallower depth, as summarized by [#Figure 4] {float:right|border=2px solid black|width=300px} |{anchor:Figure 3} !Water Level vs. Time. 40, 2depths!Bubble Formation Potential.png|height=400px,align=centerwidth=300px! h5. Figure 36: Water[Theoretical levelbubble information bubblepotential|Fluidized collectorBed vs.after time,Super usingSaturator^Dissolved Sand 40atmospheric gases.xmcd] as a filterfunction media.of Flowthe rate:air 345 mL/min, Bed Expansion: 50%|{anchor:Figure 4} !Gas removal mL-L,40, 2depths.png|height=400px,align=center! h5. Figure 4: Dissolved gas removal for Sand 40 at different depths. Bed Expansion: 50%| {float} \\ \\ h2. Conclusions It is clear that the glass beads removed more air per liter of water than the two sands, and that the smaller sand size was more effective than the larger. During the experiments, we noticed that the glass beads tend to float to the top of the column with the bubbles that formed inside it. Though the beads could not leave the column because of a screen at the top, in an actual grit chamber, they would float out into the rest of the plant. So, we decided that, though the beads' size was the most effective at gas removal, it was just too small to be realistic. pressure that the water equilibrated with prior to returning to atmospheric pressure. {float} |
The results from the laboratory tests can be compared with a model of the bubble formation potential (Figure 6). The model predicts that if the water had been previously exposed to air at two atmospheres of absolute pressure, that the bubble formation potential would have been 18 mL/L.
Conclusions
It is evident from the data collected that the glass beads removed more air per liter of water than the two sands, and that the smaller sand size was more effective than the larger. This makes sense since smaller grain sizes have a larger surface area to volume ratio, and thus per volume, provide more surface area on which bubbles can form. However during the experiments, we noticed that the glass beads tended to float to the top of the column with the bubbles that formed around them. Though the beads could not leave the column because of a screen at the top, in an actual grit chamber, they would float out into the rest of the plant, resulting in significant sand loss over time. So although the beads' size was the most effective at gas removal, we concluded that they were just too small to be realistically implemented at the treatment plants. The smaller sand grains, however, were not as easily lifted away by the bubbles and thus provide a more feasible solution.
In addition to sand grain sizes, we also experimented with the effects of sand bed depth on gas removal and found that greater bed depths resulted in better gas removal. Again, this is likely due to the larger amount surface area provided. However, we would like to minimize the amount of sand required to obtain an acceptable gas removal rate in order to minimize the cost of implementation. Thus, further experimentation with this parameter is required to determine the optimal sand bed depth for the sand grain sizes tested.
The team's future research plans are to further explore the effects of sand bed depth, flow rate, and bed expansion on gas removal. After more data has been collected, the team will focus on mathematically modeling the process on MathCAD and implementing a sand filter at the Pilot Plant.