Membrane processes in environmental technology

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Membrane processes in environmental technology

• Introduction to the
• Practical Exercises
• Hans Saveyn Prof. Paul Van der Meeren

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3 Practical exercises

• Reverse Osmosis of saline water
• Ultrafiltration of nanosuspensions
• Membrane performance and cost evaluation with the
  simulation program Memsys

3
General info

• Practical exercises presence obligatory
• Team work (rotating groups of 3-4 people)
• Every week 1 exercise/group
• One report has to be made per group and handed in
  before the start of the next exercise
• Preparation is necessary
• Quotation has important impact on final mark (for
  part of prof. Van der Meeren) !

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1.Reverse osmosis of saline water

• Aim desalinate NaCl solution by RO
• Practical work on a pilot scale RO unit
• Calculate specific parameters for the membrane
  and operation

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2.Ultrafiltration of nanosuspensions

• Aim filter nanosupsenions of silica by crossflow
  ultrafiltration
• Practical work on a labscale filter
• Determine several parameters and investigate the
  effect of concentration polarization

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3.Membrane performance and cost evaluation

• Aim to use a membrane simulation program
  (Memsys) in order to evaluate membrane
  performance and cost of operation
• Investigate the influence of particle size and
  concentration on steady state cake thickness and
  steady state permeate flux
• Calculate the time averaged permeate flux and
  operation time needed for the different scenarios
• Evaluate the total treatment cost of water by UF
  membrane technology

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3.Membrane performance and cost evaluation

• ProgramMemsys (by Sandeep Sethi and Mark R.
  Wiesner)
• Computer Simulation Model for Performance and
  Cost Modeling of Ultrafiltration and
  Microfiltration
• References
• Sethi S. (1994) Performance and Cost Modeling of
  Low-Pressure Membrane Filtration Processes. M.S.
  Thesis, Rice University, Houston, Texas.
• Sethi S and Wiesner MR (1995) Performance and
  Cost Modeling of Ultrafiltration. Journal of
  Environmental Engineering, 121 (12) 874-883
• Program freely downloadable from
  http//www.ruf.rice.edu/wiesner/memsys.htmlDOWNL
  OAD

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Memsys simulation program introduction

• Operates in MS-DOS mode (runs also on Windows
  based PCs)

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Memsys simulation program introduction

• Easy operation with menu structure

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Memsys simulation program introduction

• MEMSYS is a computational tool for evaluating the
  performance and cost of crossflow ultrafiltration
  (UF) and microfiltration (MF) systems.
• The computer program is written in FORTRAN and
  runs on the PC-DOS environment. It includes a
  menu-driven interface for running model
  components, manipulating data, and graphically
  analyzing performance results.
• A performance module estimates the steady-state
  permeate flux and initial removal of particles
  and organic matter. Capital and operating costs
  can be calculated subsequently, using the
  permeate flux estimates provided by the
  performance model. Alternatively, the user may
  run the cost module independently, and input
  permeate flux information directly to evaluate
  costs.
• The variation of permeate flux, cake thickness,
  and other dependent parameters, along the length
  of the membrane, can be plotted and analyzed
  using the graphics module.

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Memsys simulation program introduction

• Synopsis of model The model estimates
  steady-state permeate flux based on particle
  transport by
• shear-induced diffusion
• Brownian diffusion
• permeate drag
• bulk convective transport of the boundary layer
  along the membrane surface
• Initial removal of particles and macromolecular
  natural organic matter (NOM) by the membrane is
  estimated using simple expressions for particle
  capture in an idealized membrane pore. These
  expressions are based on theoretical aspects of
  hindered solute transport in membrane pores.

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Memsys simulation program introduction

• Macromolecular dimensions are calculated from
  molecular weight using a power law expression.
• For the purposes of calculating permeate flux, a
  scheme for weighting particle and macromolecular
  sizes based on their influent concentrations and
  relative diffusivities is used to reduce the
  heterodisperse suspensions input to the program
  to an average particle diameter.

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Memsys Limitations and simplifications

• The model holds in situations where the solute
  accumulation near the membrane is thin relative
  to the radius of the membrane element. The
  assumption of constant bulk suspension
  concentration limits the model to situations
  where the thickness of the cake formed on the
  membrane is small compared to the element radius.
  The solution would thus be an approximate one in
  situations where the channel gets plugged.
• The performance model holds only under laminar
  flow of the suspension through the membrane
  modules.
• Polydisperse suspensions are considered by
  calculating an average parameter or mean particle
  size.

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Memsys Limitations and simplifications

• Transient effects are not considered in
  evaluating the performance of the membrane
  filter. In other words, long term phenomena, such
  as pore fouling, are neglected.
• Gravitational effects are not considered. Hence,
  all solute particles are assumed to be neutrally
  buoyant.
• The model to calculate permeate quality assumes
  membrane pores to be cylindrical and the solute
  particles to be spherical. Solute-Membrane
  interactions and concentration polarization are
  not considered.

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Memsys Main Menu
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Memsys Main Menu

• Global options
• Set options on how to calculate certain
  parameters
• Data Manager
• Enter data concerning operation, feed composition
  and costs
• Performance Analyzer (PA)
• Evaluate operation (permeate flux and quality)
  based on entered data from the Data Manager
• Cost Estimator (CE)
• Evaluate process cost based on permeate flux
  data, operating time (to be calculated manually)
  and entered data from the Data Manager
• Results Display
• Shows earlier calculated PA or CE data
• Graph View
• Allows plotting of certain parameters
• Print
• Dos shell

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Behind the program

• The physics

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Memsys Model development

• Cake build up on membrane depends on total
  diffusivity
• Total diffusivity is composed of Brownian
  diffusivity Dbrn and shear-induced hydrodynamic
  diffusion Dsh
• Brownian diffusivity
• Shear induced diffusion (particle motion under
  shear flow)

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Memsys Performance analysis

• Small particles (lt0.01 µm) exhibit high Brownian
  diffusivity (random walk)
• Larger particles (gt1 µm) exhibit high
  shear-induced diffusivity (are easily dragged
  away)
• Combination of both diffusivities allows to
  predict the steady state cake thickness and
  steady state permeate flux by an iterative method
  for a given membrane system and feed stream
  composition
• This is done in the software by running the
  Performance Analyzer, after having entered the
  membrane and feed data in the Data Manager

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Memsys Operating time and time averaged permeate
flux calculation

• After calculation of the steady state permeate
  flux, and other cake parameters, the operating
  time can be calculated from the recovery
  requirements, the permeate flux evolution and the
  steady state permeate flux
• The time averaged flux can be calculated from the
  permeate flux evolution and the steady state
  permeate flux
• Both parameters are needed for the cost
  estimation

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Memsys Operating time and time averaged permeate
flux calculation

• Working principle of membrane set-upWasting of
  the bulk liquid is only supposed to happen during
  backflushing (continuous recirculation of bulk
  liquid during filtration)

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Memsys Operating time and time averaged permeate
flux calculation

• Recovery expressions
• Reorganisation to get operating time t0
• Time averaged permeate flux Vw average needed !!!

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Memsys Operating time and time averaged permeate
flux calculation

• To calculate the time averaged permeate flux, the
  permeate flux evolution as a function of time has
  to be considered
• The permeate flux will decline in time until the
  steady state permeate flux (as given by the
  Memsys program) is reached at time tss (steady
  state time)
• From tss onwards, the flux will remain constant

Permeate flux
time
tss
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Memsys Operating time and time averaged permeate
flux calculation

• Two possible scenarios
• Operating time t0 lt tss
• Operating time t0 ? tss

Permeate flux
time
t0
tss
Permeate flux
time
t0
tss
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Memsys Operating time and time averaged permeate
flux calculation

• Permeate flux evolution as a function of time
  before steady state is reached

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Memsys Operating time and time averaged permeate
flux calculation

• Calculation of steady state time tss t for
  which Vw(t)Vw steady state

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Memsys Operating time and time averaged permeate
flux calculation

• Final calculation of t0

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Memsys Operating time and time averaged permeate
flux calculation

• Final calculation of t0 working algorithm
• First calculate tss
• Then calculate t0 with the first expression
• If calculated t0 lt tss, then keep this t0 value,
  otherwise calculate t0 again by the second
  expression

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Memsys Operating time and time averaged permeate
flux calculation

• Final calculation of Vw average

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Memsys Operating time and time averaged permeate
flux calculation

• Parameters necessary for calculation of the time
  averaged permeate flux Vw average and the
  operating time t0 are partly input parameters
  entered in the Data Manager (Rm, Rrec, Vbf, tbf)
  or can be retrieved from the simulation program
  after running the Performance Analyzer (?b,Vw
  clean water,Rst, Vw steady state)
• After calculation of the time averaged permeate
  flux and the operating time , these values have
  to be entered in the program
• Time averaged permeate fluxGlobal options?
  Permeate Flux?User defined flux
• Operating timeData Manager?Cost data? Item 5
  Operating Period

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Memsys Cost Estimation

• When having entered the correct time averaged
  permeate flux and operating time, the Cost
  Estimator can be run to produce a cost estimation
  of the process

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Exercise

• Evaluate the steady state permeate flux and
  steady state cake thickness for the default data
  series
• Calculate the values of ?c, tss, the operating
  time t0 and the time averaged permeate flux Vw
  average
• Evaluate the total treatment cost (/m³) of the
  process by entering the calculated time averaged
  permeate flux and the operating time in the
  program and then running the Cost Estimator
• Be careful when converting non SI - units !!!