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Membrane technology 5 5
Concentrate In1
I Hydraulic Stage 1
Electrical
Membrane Stage 1
(+)Anode J
Figure2.22 Exampleofstaginginelectrodialysis
2.4.2 Specific energy demand
Pressure-driven processes
The energy consumption of any pressure-driven process operating
continuously is given by product of the pressure and flow, thus the total energy
consumption per unit mass of permeate product, ignoring pumping efficiency, is
given by:
1
E=-~AP+- We 1 (2.23)
P@ M
where p is the permeate density, Wel the supplementary plant electrical energy
consumption (e.g. for instrumentation and aeration or other turbulence
promotion methods) and M the mass flow of permeate. CAP represents the sum
of the individual pressure changes, which can include the pressure drop across
the membrane APm, as given by Equation (2.5), the concentrate-permeate
osmotic pressure difference All*. from Equation (2.9), the hydraulic losses
APlosses associated with forcing the retentate through the membrane channels
and the pressure derived from the various contributions to membrane fouling. In
the case of reverse osmosis, the total pressure for an individual membrane
module is given by:
