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Calijirnia, USA based New Logic International Inc has developed a membrane system that is said to overcome the problem offoulina that has long plagued conventional 1 IS membrane technologies. lthough membrane-based systems for the separation of liquids from solids have technology has an inherent flaw, namely membrane fouling. The long-term loss in grown in popularity over throughput capacity is due primarily to the formation of a boundary layer that builds the last 20 years, the up naturally on the membrane’s surface during filtration. In addition to cutting down on the flux performance of the membrane, this boundary or gel layer acts as a secondary membrane reducing the selectivity of the original one. This inability to handle the build-up of solids has tended to limit the use of membranes to feed streams with low concentrations of solids. To help minimise this boundary layer build- up membrane designers use a method known as tangential flow or crossflow filtration that relies on high velocity fluid flow being pumped across the membrane surface to reduce boundary formation. However, it is not economical to create shear forces greater than 10 OOO- 15 OOO/second, which limits the use of these systems to low-viscosity fluids. In addition, increased crossflow velocities result in a significant pressure drop near the filter outlet, which leads to premature fouling that eventually spreads towards the Now according to New Logic International, it has developed an alternative method for producing intense front of the filter, causing the permeate shear waves at the face of a membrane that not only prevents the boundary layer rates to drop to unacceptably low levels. build-up, but allows membranes to process liquids that have a much higher solids content. VSEP lbchmdogy The new technology is called vibratory shear enhanced processing (VSEP), and the shear cleaning action is created by the vigorous vibration of leaf elements in a direction tangent to the faces of the membranes (Figure l).The shear waves produced by the membrane’s vibration cause solids and foulants to be lifted off the membrane surface and remixed with the bulk material flowing through the membrane stack. This high shear processing exposes the membrane pores to a maximum throughput that is said to be between three and ten times that of a conventional crossflow system. VOSEP 20 Januarylfeburary ZOOI TheVSEP membrane filter pack (Figure 2) consists of leaf elements arrayed as parallel discs, separated by gaskets, with a membrane on each side. The disk stack is oscillated above a torsion spring (Figure 3) that moves thestackbackandforth(1.9-3.0cmpeakto peak) at an oscillation frequency of approximately 53 Hz. The oscillation produces a shear intensity at the membrane surface of around 150 OOO/second (equivalent to a g force of over 200), which is approximately ten times the shear rate of the best conventional crossflow systems. More importantly, the shear is focused at the membrane surface, where it is most effective in preventing fouling. At the same time the bulk fluid between the membrane disks remains relatively undisturbed as it flows slowly between the parallel membrane leaf elements. A further benefit of the system is that because it does not depend on feed flow-induced shearing forces, the slurry can be extremely viscous and still be successfully dewatered. The concentrate is extruded between the vibrating disc elements and exits the machine once it reaches a desired concentration level. Thus, the VSEP system can treat liquids and slurries in a single pass, eliminating the need for costly working tanks, ancillary equipment and associated valving. The disc pack hold-up volume of a system with a membrane area of 130 m* is less than 190 lines. As a result, product recovery in batch processes can be relatively high, and the volume of the produce waste after draining the stack is normally less than 11 litres. Upon start-up the system is fed with the slurry, the permeate is produced and the FIttraWn+Separation

Is membrane fouling a thing of the past?

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Calijirnia, USA based New Logic International Inc has

developed a membrane system that is said to overcome the

problem offoulina that has long plagued conventional 1

IS

membrane technologies.

lthough membrane-based

systems for the separation

of liquids from solids have

technology has an inherent flaw, namely

membrane fouling. The long-term loss in

grown in popularity over

throughput capacity is due primarily to the

formation of a boundary layer that builds

the last 20 years, the

up naturally on the membrane’s surface

during filtration. In addition to cutting

down on the flux performance of the

membrane, this boundary or gel layer acts

as a secondary membrane reducing the

selectivity of the original one. This

inability to handle the build-up of solids

has tended to limit the use of membranes

to feed streams with low concentrations of

solids.

To help minimise this boundary layer

build- up membrane designers use a

method known as tangential flow or

crossflow filtration that relies on high

velocity fluid flow being pumped across

the membrane surface to reduce boundary

formation. However, it is not economical

to create shear forces greater than 10 OOO-

15 OOO/second, which limits the use of

these systems to low-viscosity fluids. In

addition, increased crossflow velocities

result in a significant pressure drop near

the filter outlet, which leads to premature

fouling that eventually spreads towards the

Now according to New Logic

International, it has developed an

alternative method for producing intense

front of the filter, causing the permeate

shear waves at the face of a membrane that

not only prevents the boundary layer

rates to drop to unacceptably low levels.

build-up, but allows membranes to process

liquids that have a much higher solids

content.

VSEP lbchmdogy The new technology is called vibratory shear

enhanced processing (VSEP), and the shear

cleaning action is created by the vigorous

vibration of leaf elements in a direction

tangent to the faces of the membranes

(Figure l).The shear waves produced by

the membrane’s vibration cause solids and

foulants to be lifted off the membrane

surface and remixed with the bulk material

flowing through the membrane stack. This

high shear processing exposes the

membrane pores to a maximum

throughput that is said to be between three

and ten times that of a conventional

crossflow system.

VOSEP

20 Januarylfeburary ZOOI

TheVSEP membrane filter pack (Figure 2)

consists of leaf elements arrayed as parallel

discs, separated by gaskets, with a membrane

on each side. The disk stack is oscillated

above a torsion spring (Figure 3) that moves

thestackbackandforth(1.9-3.0cmpeakto

peak) at an oscillation frequency of

approximately 53 Hz. The oscillation

produces a shear intensity at the membrane

surface of around 150 OOO/second

(equivalent to a g force of over 200), which

is approximately ten times the shear rate of

the best conventional crossflow systems.

More importantly, the shear is focused at the

membrane surface, where it is most effective

in preventing fouling. At the same time the

bulk fluid between the membrane disks

remains relatively undisturbed as it flows

slowly between the parallel membrane leaf

elements. A further benefit of the system is

that because it does not depend on feed

flow-induced shearing forces, the slurry can

be extremely viscous and still be successfully

dewatered.

The concentrate is extruded between

the vibrating disc elements and exits the

machine once it reaches a desired

concentration level. Thus, the VSEP system

can treat liquids and slurries in a single

pass, eliminating the need for costly

working tanks, ancillary equipment and

associated valving.

The disc pack hold-up volume of a

system with a membrane area of

130 m* is less than 190 lines. As a result,

product recovery in batch processes can be

relatively high, and the volume of the

produce waste after draining the stack is

normally less than 11 litres.

Upon start-up the system is fed with the

slurry, the permeate is produced and the

FIttraWn+Separation

suspended solids in the feed are collected

inside the filter pack. After a programmed

time interval, a valve is opened to release

the accumulated concentrated solids, and

then closed to allow the concentration of

additional feed material. This cycle can be

repeated indefinitely.

Filter Pack Cross Section Clear Permeate Feed

Membrane selection is one of the most

important parameters influencing the

quality of the separation. According to the

company, its VSEP filter packs can

incorporate almost every type of membrane

currently available on the market including

acrylic, nylon, polypropylene,

polysulphone, etc. Other important

parameters that affect system performance

are pressure, temperature, vibration

amplitude and residence time. All of these

elements are optimised during testing and

entered into the programmable logic

controller (PLC) of the system.

I Concentrate

\ l--_- Membrane Permeate Channel

The operating pressure is created by

the feed pump, and aVSEP machine can

routinely operate at pressures as high as

67 bar. Although higher pressures can

produce increased permeate flow rates,

they also use more energy. Therefore, an

operating pressure is set that optimises the

balance between flow rates and energy

consumption. In the majority of cases the

filtration rate can also be improved by

increasing the operating temperature. The

temperature limit on a standard VSEP

system is 92 ‘C, but higher temperature

constructions are also available.

Using nanofiltration membrane

modules in the VSEP systems

enabled approximately 85% of the

feed pressate to be recovered as

clean water and the remaining

recycled as a concentrated

stream.

VOSEP Resonating Drive System

’ Filter Pack Drive

Torsion Spring -

case study

At a facility of a leading manufacturer of

medium density fibre (MDF) board

three VSEP systems incorporating

nanofiltration membrane modules were

installed to help the slurry generated by

the dewatering of the pulp meet

environmental legislation.

The VSEP produced a

concentrated stream at a flow

rate of 38-57 l/mitt, which was

recycled either to the chip belt

dryer or to the pulp refiner,

while the clean water permeate

stream (300-320 l/min) was

discharged to the plant holding

ponds and then recycled as

process water.

The traditional methods for treating

this type of slurry are dissolved air

floatation (DAF) followed by a multimedia

filter, bag filters or traditional reverse

osmosis. However, following an evaluation

of the operating costs the decision was

taken to install theVSEP systems.

Substantial savings in operating costs were

expected primarily because of the

elimination of the need for the addition of

either chemicals or polymers to the slurry.

The feed to the VSEP units

contained between 2000-

8000 mg/l of total suspended

solids (TSS), had a chemical

oxygen demand (COD) of

20 000-70 000 mg/l and 2000-

5000 mg/l of oil and grease. The

permeate concentration was

reduced to approximately 1 mg/l ofTSS,

500 mg/l of COD, and 10 mg/i of oil and

grease, which were all below the necessary

requirements.

electronics industry, and treatment of

effluent produced from paint and pigment

concentration and washing.

The manufacturing facility operated

24 hours a day, 350 days per year. The

maximum pressate flow rate to be treated

in the process was over 350 litres per

minute (l/min).

The VSEP technology has been

successfully used in a number of other

applications including: treatment of

whitewater and bleach plant effluent in

the pulp and paper industry, raw water

treatment for the chemical manufacturing

industry, recovery of heavy metals in the

Forfurther information contact: New Logic

International Inc, 1295 67th Street, Emeryville,

CA 94608, USA.

Tel: +I 510 655 7305;

Fox: +1 655 7307;

E-mail: [email protected];

Website: www, vxep. corn

FHtmtlon+~paratlon January/Feburay 2001 21