Mist filter

Synonyms, abbreviations and/or process names

—  Demister
—  Aerosol filter
—  Deep bed filter

Removed components

—  Dust
—  Droplets
—  Aerosols

Diagram

 

Process description

Mist filters are generally made up of woven elements of metal or synthetic mono-filaments.

It is a deep bed filtration process where the gas stream is led through a particular configuration of filter elements. Separation takes place against the filter material. In deep bed filtration, filter function is spread across the depth of the entire filter until saturation occurs and the filter needs to be cleaned via rinsing. In the case of high efficiency filter elements, rinsing needs to occur on a regular basis considering the likelihood of blockages. The filter is able to self-clean when droplets or aerosols are collected.

Variants

No specific variants.

Efficiency

The removal yield can be as high as 99% for dust and aerosols. Filter elements with smaller mesh sizes for dust collection (1 – 3 µm) are more efficient, though there is a greater risk of blockage.

Boundary conditions

—  Flow rate:                1 000 -150 000 Nm3/h
—  Temperature:         < 170°C
—  In-coming concentrations:         < 1 mg/Nm3
—  Aerosols:                                    A few g/Nm3

Auxiliary materials

—  Filter medium
—  Scrubbing liquid for cleaning

Environmental aspects

Scrubbing liquid laden with collected dust

Energy use

Depends on pressure drop over the filter system

Cost aspects

  • Investment
    —  < 2 300 EUR for 1 000 Nm³/h [1, 2]
  • Operating costs
    —  Personnel costs:    ca. 2 500 EUR per year (2 hours per week) [1, 2]
    —  Auxiliary and residual materials: 250 to 600 EUR per year for 1 000 Nm³/h [1, 2]

Case study: Droplet separation after fluid injection [4]

—  Flow rate: Flow 30 000 m³/h
—  Three-phase droplet separation with differing mesh sizes
—  Investment costs for filter + assembly: 25 700 EUR
—  Filter replacement costs stage 1: 2 500 EUR These can be cleaned (replacement only necessary after excessive
      pollution)
—  Filter replacement costs stage 1: 3 500 EUR: These can be cleaned (replacement only necessary after excessive
      pollution)
—  Filter replacement costs stage 1: 4 300 EUR: These must be replaced every 6-8 months

Advantages and disadvantages

  •  Advantages
    —  Self-cleaning when liquids are collected
    —  Suitable for filtering aerosols
  • Disadvantages
    —  Dirty scrubbing liquid when filter is cleaned
    —  High pressure drops when solid particles are collected
    —  Blockage risk

Applications

After steam boilers and gas scrubbers in:

—  Chemicals industry
—  Textile industry
—  Plastic processing

References

  1. Factsheets on Air-emission reduction techniques, www.infomil.nl, Infomil
  2. Common waste water and waste gas treatment and management systems in the chemical sector, BREF document, European IPPC Bureau, http://eippcb.jrc.es, 2002
  3. Air Pollution Technology Fact Sheets and Technical Bulletins, US EPA, http://www.epa.gov/ttn/catc/products.html, 1999-2002
  4. Supplier information