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About Filtering Systems
Filtering systems separate contaminants and unwanted
fluid and solid substances from fluid substances. Basic filtering systems
consist of a filter through which the contaminated fluid passes. The
filter media allows passage of the fluid, while preventing the contaminants
to pass. Filtering system products include strainers, liquid cartridges,
housings and filters, cartridge filters, bag filters, membranes and ultrapure
filters. Filtering systems can filter hydraulic and quench oil, diesel
fuel, machine tool coolant and numerous other industrial fluids. Industrial
filtration remains necessary to purify substances like air and water,
especially drinking water. Filtering system manufacturers are commonly
utilized by a number of industries: wastewater/sewage treatment, food
and beverage processing, automotive/trucking, agricultural, pharmaceutical,
chemical, mining and pulp and paper.
Filtering system manufacturers can make several different kinds of systems
for filtering water. Electrodialysis (ED) uses membranes to desalt or
electrically concentrate solutions by allowing passage of either the
positively or negatively charged ions, into which the salt was dissociated,
while excluding passage of ions of the opposite charge. The membranes
and other active surfaces have a tendency to become fouled or scaled.
Electrodialysis reversal (EDR) deals with this problem by reversing the
electrical current and exchanging the fresh product water and the concentrate
wastewater streams within the membrane stack many times per hour, removing
the fouling and scaling constituents from one cycle in the next. Reverse
osmosis (RO) is a cost-effective pretreatment for ion-exchange demineralization
that unloads 95-99% of dissolved salts, TOC and silica from the water
supply. RO is a multi-stage process in which cylindrical pressure vessels
house interconnected cellophane-like membrane elements with hole sizes
of less than .0002 microns, through which incoming dirty water is forced.
The first hydraulic stage yields about 50% recovery of product water,
the second 75% and the third about 85%, depending on concentrate chemistry.
Other filtering system methods include electrodeionization (EDI) and
ultrafiltration (UF) processes.
Other processes are used to treat various fluids. Vacuum filters, which
include drum, disc, horizontal belt, tilting and table filters, are simple,
reliable machines used in the chemical, food and pharmaceutical industries.
Vacuum filtering systems consist of a vacuum filter, one or two vacuum
receivers, one or two filtrate pumps, a vacuum pump and piping and instrumentation.
Pressure filters, not including rotary drum pressure filters, are semi-continuous
type machines that typically operate in batches (though continuous filters
are also available), which are fed from and discharged to a continuous
process, making necessary a surge tank upstream of the filter and a batch
collection of cake downstream. The rate of filtration depends on the
properties of slurry. Filterpresses consist of a head and a follower,
in between which is sandwiched vertical rectangular plates that are interconnected
by a continuous feed port. Filterpresses are used in applications where
the moisture content is necessarily low for thermal cake drying or incineration,
when high filtrate clarity is required for polishing applications, when
good cake release assisted by squeezing is needed, when the cake is disposed
as land fill for spreading and when large filtration areas are required
in a small space. Other filtering systems methods include rotary drum
pre-coat filters and thickeners.
When selecting filtering systems, consider contaminant particle properties,
such as size and shape, the filtration rate of the filtration media and
filter location. Chemical compatibility to associated chemicals is also
important. Other factors include the viscosity and temperature of the
solution and the load capacity of the filter media. Filtering system
manufacturers and suppliers will want a definition of the slurry. Do
the solids to be captured settle at a reasonably high velocity and with
efficiency? Is any part of the slurry toxic, flammable or explosive,
and is emulsified oil present? They will also want to know about the
process, as in if chemicals can be added to enhance the separation and
if solute recovery is important. Finally, they will need to know if the
solids output should be continuous or batch, if it matters at all. Many
filtering systems are designed for general purposes, but filter requirements
may differ.
Featured
Articles
http://www.lenntech.com/absolute-nominal-filters.htm
http://www.tekleen.com/guide/ind_feb_2003.pdf
Types of Filtering Systems
- involves the use of a porous
cartridge filter, commonly made of polypropylene (PP) or ceramic, which
catches particles as liquids pass through it. Cartridge filtration
is an easy filtration method but not suitable for liquids with high
turbidity and fouling remains a common problem leading to filter replacement.
- , also called “centrifugal filters” or “cyclone
separators,” use cyclones in which substances, such as immiscible
liquids, gases and solids, are separated during rapid rotation from
the contaminated fluid. The rotation of the cyclone is caused by the
entrance of the pressurized fluid from which the contaminants must
be removed.
- removes contaminants through the use of a chemical
medium, such as activated carbon, in the filter. Chemical filtration
remains common in the filtration of gases.
- is a filtering process that involves electrically
charged media that use an electric field to filter substances and remove
particles as small as .01 micrometers in size. As the substances pass
through the charged media, certain particles are attracted to the charged
media.
- is the process of passing fluid through a filter to remove contaminants.
- includes filters, strainers, and housings.
- may involve the removal
of particles from a liquid, known as “liquid-solid filtration,” or the separation of
liquids from gases, known as “gas-liquid filtration.”
- involves the use of a membrane as the filter
media to allow the passage of substances such as air and water, while
preventing
the passage of other substance particles. Membrane filters are small
and automated and used for applications that include purifying blood
during dialysis treatments, removing bacteria and odors and desalinating
water.
- is a type of membrane filtration used to remove extremely
small particles. The effectiveness of nanofiltration lies between
that of reverse osmosis and ultrafiltration.
- is necessary to remove particles and contamination
that may hinder the functioning of equipment. Oil filtration
remains common
in the automotive/trucking and agricultural industries, as well
as other industries that utilize equipment requiring the use of
motor, hydraulic and other types of oils.
- ,
excluding rotary drum pressure filters, are semi-continuous machines
whose collection of filtrate is dependent upon the
operating mode of the filter (e.g. constant flow rate, constant pressure
or both, with pressure rising and flow rate reducing). Pressure
filtration is
a batch process that is typically fed from and discharged to
a continuous
process and requires a surge tank located upstream from the
filter
and a batch collection of cake downstream.
- is a type of filtration method in which water is
pushed under pressure through a membrane, while contaminants
are prevented
from passing through the filter. Filtered contaminants include
sodium, phosphorus, aluminum, lead and fluoride.
- involves the purification of water for drinking
purposes. Wastewater is also filtered to remove excess
particles.
- is a biological filtration process involving the
exposure of the filter medium to air to facilitate nitrification.
Wet/dry filters are commonly used in aquariums.
- is a type of membrane filtration that removes particles
ranging from 0.002 to 0.1 micrometers in size. Filtered
substances include bacteria and viruses.
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