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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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