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Filter groups and filter types

In the pharmaceutical and chemical industries, dedusters or filter systems are used to bind the dust generated during production. The particles in the air are separated by the installed filter cells, so that ultimately, the air is cleaned and the danger from the dust is eliminated.

The type of dust or the composition of the air mixture as well as the requirements from the process result in the selection criteria for the filter cells.

Filter cells are available in various types, designs and materials. The following article provides a brief overview of the designs and classifications of the filters.

To compare the differently-designed individual filter cells with each other or match them with process requirements, a classification system can be used that is defined on the basis of standards.

Classification of the filter cells

To correctly assign the various filter classes or filter groups, the following overview of the examined air filters will show when which classification applies.

Overview of air filters

Air filters are classified according to their ability to separate particles of different sizes.

"Dust filters" are available for use with high dust loading and coarse particles in the air. These are further classified into "coarse dust filters" and "fine dust filters" - depending on particle size. For these filters, the classification is based on the EN ISO 16890 standard.

When very fine or finest particles are to be filtered, "suspended-particle filters" are used. A further classification is made here into "standard suspended-particle filters" and "high-performance suspended-particle filters". Again, the classification is made with reference to the actual particle size. The classification is based on the EN 1822-1 standard.

Classification according to EN ISO 16890

The basis of the classification is formed by the separation degree of the filter cell. This indicates how many particles are retained by the filter material and how many particles are still present in the exhaust air after passing through the filter. The value of importance here is the separation capacity of particles with sizes from 0.3 µm to 10 µm.

Using this value, the corresponding filter group can be assigned in accordance with the EN ISO 16890 standard.

The standard provides 3 levels, according to which the filter cells are classified:

  • PM1: Separation capacity for particles from 1 µm (0.3-1 µm)

  • PM2.5: Separation capacity for particles from 2.5 µm (0.3-2.5 µm)

  • PM10: Separation capacity for particles from 10 µm (0.3-10 µm)

When at least 50% of the specified particles are separated, the filter cell has reached the corresponding level. In this case, the "minimum efficiency" determined on a new filter cell is referred to. Parallel to this, the "mean efficiency" is also measured over the entire filter cell.

In the procedure for determining the filter group, the first step is to determine the mean efficiency together with the minimum efficiency for the 3 particle sizes. At the level where at least 50% of the separation is achieved, the mean efficiency is taken and rounded off to the nearest interval of five. The classification can then be specified with these values.

Example: ISO ePM2.5 80%

On occurrence that a filter cell meets the conditions for several levels, it is up to the manufacturer of the filter cells to decide which indication the product is itemized with.

Classification according to EN 1822-1

The DIN EN 1822-1 standard refers to the classification of high-performance particle filters and high-performance suspended-particle filters, as used in clean-room technology or the pharmaceutical industry. Apart from the classification of the filter cells, the production and the testing are also specified in the standard. It must be observed here that part 1 of the DIN EN 1822 standard applies for the classification of the filters. The provisions for production and testing, however, are specified in parts 2-5 of ISO 29463.

The DIN EN 1822-1 standard distinguishes between filter groups and filter classes:

 

Filter Group Filter Class Integral
Value of
Separation
Degree in
MPPS		 Integral
Value of
Permeability
Degree in
MPPS		 Local Value
of
Separation
Degree in
MPPS		 Local Value
of
Permeability
Degree in
MPPS
EPA =
High-performance
particle filter		 E10
E11
E12		 ≥ 85 %
≥ 95 %
≥ 99,5 %		 ≤ 15 %
≤5%
≤ 0,5 %		 -
-
-		 -
-
-
HEPA =
Suspended-particle
filter		 H13
H14		 ≥ 99,95 %
≥ 99,995 %		 ≤ 0,05 %
≤ 0,005 %		 ≥ 99,75 %
≥ 99,975 %		 ≤ 0,25 %
≤ 0,025 %
ULPA =
High-performance
suspended-particle filter		 U15
U16
U17		 ≥ 99,999 5 %
≥ 99,999 95 %
≥ 99,999 995 %		 ≤ 0,000 5 %
≤ 0,000 05 %
≤ 0,000 005 %		 ≥ 99,9975 %
≥ 99,99975 %
≥ 99,99999 %		 ≤ 0,0025 %
≤ 0,00025 %
≤ 0,0001 %

 

Basis of the classification here is the minimum separation degree of the filter cell for particles sized 0.1 - 0.3 µm, the "MPPS", as explained in the article Principle of Filter Influence Factors.

The classification proceeds in three steps: Firstly, the particle size at the separation minimum is determined on the unfolded filter material (MPPS). In the second step, the absence of leaks (= local separation degree) is tested. Finally, the integral separation degree of the filter element is determined using a test aerosol for the particle size in the separation minimum.

Based on the values acquired, the filter element can be assigned to the corresponding filter class using the overview in the standard.

The following diagram shows the areas in which the various filter classes or filter groups can be used.

 

dust_sizes

Filter cell designs

Depending on the manufacturer, application and requirement, various designs are available for filter elements.

Different factors play a role in the selection: Various points must be considered, from process requirements to the installation situation, resulting from the design of the filter system, to the question of costs.

This article reflects on the designs of the "cartridge filter", "lamella filter" and "cassette filter" - i.e. the filters that are used in the filter systems supplied by HET Filter GmbH.

The three filter designs feature different characteristics, as described below:

Cartridge filter

  • Design:
    In cartridge filters, the folded filter
    material (filter fleece) is located
    within a cylindrical carrier basket.
    This design allows for cost-effective
    production.
  • Application:
    For air with high dust loading
  • Classification:
    Coarse and fine filters according to
    EN ISO 16890
  • Besonderheiten:
    Due to the design, the filter cannot
    be changed under safe-change
    conditions, meaning that only low
    containment requirements can be
    met with this filter type. The
    requirements are described in the
    blog articles on "Containment".
 cartridge_filter

Lamella Filter

  • Design:
    Lamella filters consist of a folded
    fleece that can be installed either
    horizontally or vertically. The
    respective filter stage of a deduster
    consists of several of these lamella
    filters. Due to the design, the
    individual lamella filters can be
    dedusted by means of pulsed
    compressed air. The compressed
    air causes the elements to vibrate,
    so that the particles loosen and fall
    into the dust discharge. Due to the
    simple design, this type of filter is
    relatively inexpensive.
  • Application:
    For air with high dust loading;
    for complicated dusts
  • Classification:
    Coarse and fine filters according to EN ISO 16890
  • Special features:
    Due to the design, the filter cannot
    be changed under safe-change
    conditions, meaning that only low
    containment requirements can be
    met with this filter type. The
    requirements are described in the
    blog articles on "Containment".
 lamella_filter_without_dimensions

Cassette filter

  • Design:
    In cassette filters, the filter material
    is contained in a robust, conductive
    housing made of galvanized steel
    or stainless steel. When used in
    non-hazardous areas, the frame
    can also be made of wood (MDF).
    The filter fleece is folded in layers
    or in a V-shape and cast with the
    housing by means of casting
    compound. Spacers are positioned
    between the individual layers to
    ensure that the layers remain open
    during air intake and that the air
    can flow unhindered through the
    filter. Also, they are dischargeable,
    in order to prevent electrostatic
    charges.
  • Application:
    For finest dusts, as occurring in the
    pharmaceutical industry.
    Dust loading to 2,000 mg/m3
    Flow rates to 2,000 m3/h
    Usable in various filter systems due
    to standardized dimensions.
  • Classification:
    HEPA filters according to EN 1822;
    dust filter according to EN ISO 16890
  • Special features:
    Filter changing is possible under
    safe-change conditions, i.e.,
    containment requirements up to
    OEB6, among others, can be met
    with this type of filter.
    The filter cells are dedustable,
    which increases the service life.
 cassette_filter

Summary

Filter cells are available with a wide range of features and design options. The selection depends on the properties of the dust as well as the requirements of the process. Therefore, exact knowledge of the dust, required by the filter-system manufacturer, is indispensable for the design of the filter systems. This is the only way to select the correct filter elements, so that in the end their task is fulfilled - providing clean air, without risk to people and the environment.

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