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Reactors. Reactors. Reactor: a “container” where a reaction occurs Examples: Clear well at water treatment plant (chlorine contact) Activated sludge tank at wastewater treatment plant Treated wastewater discharge into a stream: stream = reactor

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Reactors1
Reactors

  • Reactor: a “container” where a reaction occurs

  • Examples:

    • Clear well at water treatment plant (chlorine contact)

    • Activated sludge tank at wastewater treatment plant

    • Treated wastewater discharge into a stream: stream = reactor

    • Treated wastewater discharge into Cayuga lake:lake = reactor

    • Gas tank leaking into soil:soil = reactor


Reactor types

Flow with dispersion

C

t

Completely Mixed reactor

t

Pipe flow reactor

t

Reactor types

What are your expectations?

Feed Solution (glucose solution for pipe flow)

Injection port

Peristaltic pump

or

C

C

or

reactors


Advection mean flow

C

x

C

x

Advection: mean flow

What does it look like a short time later?


Dispersion velocity fluctuations

C

x

Dispersion: velocity fluctuations

Fick's first law

Fick's second law

What does it look like a short time later?

C

x


Reaction

C

C

x

x

Reaction

What does it look like a short time later?


Advection dispersion reaction

C

C

x

x

Advection/Dispersion/Reaction

In three dimensions

where


Reactors closed vs open
Reactors: Closed vs. Open

  • Closed: have little dispersion across the inlet and outlet boundaries

    • Well defined reactor volume

    • Examples

      • __________________________________

      • ______

  • Open: have significant dispersion across the inlet and outlet boundaries

    • Backmixing

    • Example

      • _______

tank with a small inlet and a small outlet

lake

river



Reactor characterization
Reactor Characterization

volume

  • Time scales

    • hydraulic residence time

    • average time for tracer to get from inlet to outlet

  • Closed systems

    • “dead volume”

  • Open systems

    • dispersion upstream

    • “dead volume”

=

flow rate

?


Peclet number
Peclet Number

  • Ratio of advection to dispersion

    • how far does advection carry the fluid/width of tracer plume

  • High Peclet means primarily advection (_______________)

  • Low Peclet means lots of mixing

  • Approximation for low dispersion (Pe>10)

plug flow


Completely mixed flow reactor
Completely Mixed Flow Reactor

  • Closed reactor with no dead volume so theoretically t = .

  • What is C0? How might you check this?


Flow with dispersion equation
Flow With Dispersion Equation

  • Solution for pulse mass input with advection and dispersion in only one direction

  • Beware of units!!!! Adopt a consistent set!

  • How can we get the dispersion coefficient?


Estimating the dispersion coefficient
Estimating the Dispersion Coefficient

Approximation for Pe>10

Definition of Pe

Solve for Dd

Substitute approximation


Mass conservation
Mass conservation

  • How much tracer comes out in 10 seconds?

  • What are the potential errors?

  • What level of accuracy do you expect?


Ideal tracer
Ideal Tracer

  • same properties as fluid

    • viscosity

    • temperature

    • density

    • non reactive

  • additional properties

    • low background concentrations

    • easily measured

    • cheap

    • non toxic


Real tracers
Real Tracers

Tracer type

distinguishing

analytical

examples

property

instrument

salt

conductivity

Conductivity

NaCl

meter

Dyes

color

Spectrophoto-

methylene blue

meter

fluorescent

fluorescence

Fluorometer

rhodamine WT

dye

radioactive

radioactive

Liquid

C14

ions

decay

scintillation

counter

Dissolved gas

Gas

Gas

Sulfur

chromatograph

hexafluoride


Reactor lab tracer
Reactor Lab Tracer

  • Sodium chloride measured with conductivity probe

  • Red dye # 40 so we can see it

  • Density problem: 1.012 g/cm3

  • Which reactors would be affected by density difference?

  • How can we solve it?


Density matching
Density Matching

glucose

Sodium chloride


Monitoring
Monitoring

  • Conductivity Probe location

    • pipe flow

    • porous media column

    • completely mixed flow reactor

  • Data acquisition

    • conductivity probe monitored by meter that sends data to computer

    • computer will display a graph of conductivity vs. time

    • output is a tab delimited text file containing

      • sample times

      • conductivity


Porous media reactor
Porous Media Reactor

  • What are x, A, and U for the porous media reactor?

  • How could we get the dispersion coefficient?

  • What part of our laboratory model doesn’t this equation describe?


Data manipulation
Data Manipulation

  • What would happen if you collected data for a week?

  • No clear approach, perhaps eliminate data after 99% of the mass is accounted for?

  • No need to collect data after the effluent concentration is stable.


Conductivity as f nacl
Conductivity as f(NaCl)

  • Use the slope of the four point calibration curve and the baseline conductivity of each of the reactors to convert the conductivity data to NaCl concentration

600





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