Basic difference between Micro filtration, Ultra filtration & R.O

0.0001µm           0.001µm                                  0.2µm                                 10µm*

1A0 <———–> 10A0           <———–>    200A0     < —————–>  100,000A0

Reverse                                          Ultra
Osmosis                                         Filtration

Microfiltration

  •  µm – Micron
  • Smallest pencil dot, which we can see by necked eye, is about 40mm.
  • Relative comparison

There are various filtration & seperation procedures follows by industry for removal of un-wanted particles (contamination) like :

  • Centrifuge
  • Continous vacuum filter
  • Disc type knife filter
  • Filter press
  • Contridge filter (Micro filtration)
  • Dialysis
  • Electro dialysis
  • Reverse osmosis
  • Ultra filtration / Neno filtration system

MICRO FILATRATION (CARTRIDGE FILTER)

Filtration for the removal of suspended particles from the range of 0.2 mm to 100 or 150 mm is generally known as micro filtration or cartridge filter. This is pressure filter in line as shown in the picture.

Pressurized fluid comes in to the housing and due to pressure, passing from the cartridge, where actual filtration takes place and contamination retain on/over the cartidges and clear fluid comes out from the center of the cartridge. This is out to in system.

One needs to monitor the filter by pressure difference (delta P – the difference inlet pressure and outlet pressure). Initially, when cartridge is clean, clean pressure drop will be minimum and as it got contaminated, pressure drop will increase gradually. At 2.5 or 3 Kg/cm2 g pressure drop, one needs to change the cartridge in case of re-usable cartridge.

If the flow rate is more, we need to give number of cartridges in one housing as shown here.

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Type Of Cartridges

Depending on filter media we can classify the filter cartridges as depth or surface filter. Also they are available in various materials like, Polypropylene, Cotton, Cellulose, Glass-fibre, Nylon, PTFE, PES, Ceramic, S.S. Screen, Sintered S.S. or Bronze etc.

Surface Filter

Filter media where the pores are within the same ‘Plane’ i.e. Screen or Surface filter as shown in the picture here.

Depth Filter

Filter media where the pores are distributed throughout the thickness of the medium. Particles are stopped both on the upstream surface and within the medium.

Standard Cartridges

Generally cartridges are avaliable as per international standard in 10″, 20″, 30″ and 40″ length cylinders. O.D. of the cartridge is approx 70mm and I.D. is 25 mm.

Pleated Cartridge

In pleated cartridges , actual filter media is in pleated from to cover more surface area. It is pleated on perforated core. It is supported with any other media, which is coarser to give minimum pressure drop and good strength to the cartridge. Outer cage is provided to give mechanical strength to the cartridge.

Most precise filter elements for guaranteed removal efficiency is pleated polymer cartridges.

Paper, S.S. wire-mesh, polypropylene, Nylon – N66, Polyethersulfone, Fluropolymer, Glassfibre or PTFE material pleated filter cartridges are widely available.

Depth Catridges

Polypropylene, Cotton, Nylone, Cellulose, Ceramic,Sintered S.S. & Sintered Bronze media are available in depth type cartridges. Many manufacturers make graded pore structure depth media, which gives efficient filtration because of proper pore distribution. (Cross section of Depth cartridge)

As shown here, Cross section of graded pore structure cartridges, bigger particles retain on the outer surface of the cartridge and most upper layer of the cartridges. While smaller particles retain at inner and very small particles retains at the inner layer of the cartridge. Thus entire depth of the cartridge utilizes and hence filtration is very economical.

Thus graded pore structure depth filter cartridge are good pre-filer, because it traps bigger particles then its rating.

Filter Selection & Sizing

Following parameters are to be considered for selection of the filter :

  • Fluid to be filtered
  • Flow rate
  • Filtration rating (Micron – Cut off)
  • Operating Pressure
  • Operating temperature
  • Viscosity of the fluid at operating temperature
  • Filter material (Chemical compatibility)
  • Load of suspended particles
  • Continuous or batch process – Batch size etc..
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