Spray chamber

 Synonyms, abbreviations and/or process names

—  Dust scrubber

Removed components

—  Dust, particles: fine, sticky, hygroscopic
—  Gaseous components

Diagram

Process description

In spray chambers or spray towers water is sprayed or dispersed in fine droplets, normally via sprayers or “nozzles” at the top of the scrubber, while gas is fed tangentially from underneath – thus forming counter-current flow. Due to the centrifugal effect, there will already be a pre-separation of larger particles in the column. It is also possible to place spray-towers in co-current or cross-current set-up.

High L/G ratios are required to remove fine particles.

Efficiency

Removal efficiency varies between 70 and 99%, depending on particle distribution.

Boundary conditions

—  Flow rate:     2 500 -170 000 Nm3/h
—  Temperature:        4 - 370 °C
—  In-coming concentrations:    100 -10 000 g/Nm3

Auxiliary materials

Water

Environmental aspects

Waste water must be treated or discharged into the sewer network.

Residues which must be dewatered and disposed of.

Energy use

Energy use varies between 0.4 to 2 kWh per 1 000 m3 [5]

Cost aspects

  • Investment
    — 
    For a very basic spray scrubber, investment costs for a to-be-treated gas stream of 10  000 Nm³/h amount to
          ca. 50 000 EUR or 5 000 EUR per 1 000 Nm3/h. For other capacities, one should consider a scale-up factor to
          the power of 0.3 [1, 2].
  • Operating costs
    —  Personnel costs:    ca. 0.25 mh/day
    —  Operational costs:   0.4 – 0.5 EUR per 1 000 Nm³ [5]
    —  Auxiliary and residual materials: The separated dust must be dewatered and disposed of. The water must be
          treated prior to being discharged. Transport costs for the separated dust are determined by the type of residue.

                             Inert: ca. 75 EUR/ton
                             Chemical: 150 – 250 EUR/ton

Advantages and disadvantages

  • Advantages
    —  Simple implementation
    —  No risk of fouling or blockage in the washing section
    —  In addition to dust, gaseous particles are also separated
    —  Available in various construction materials
    —  Able to deal with fluctuating gas flows
    —  Low pressure drops
    —  Little space required
  • Disadvantages
    — Installation type with spray-heads with small openings requires clean washing liquid
    — Blockages in sprayers could lead to a large yield loss
    — Not efficient for the removal of fine dust particles
    — Mass transfer is not very efficient

Applications

Is also used as a cooler to “quench” flue gases.

Spray scrubbers are used in a variety of settings, including:

—  The chemical industry, to separate dust and aerosols;
—  The metal industry for various types of waste gases;
—  Waste incineration installations;
—  Gasification processes;
—  Potato-processing industry for the removal of starch;
—  Glass industry;
—  Melting processes in metallurgy;
—  Foundries;
—  Sintering processes;
—  Drying processes
—  Fertiliser production;
—  Pharmaceutical industry;
—  Plastics industry.

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
  3. Elslander H., De Fré R., Geuzens P., Wevers M. (1993). Comparative evaluation of possible gas purification systems for the combustion of household waste. In: Energie & Milieu, 9
  4. Work-book on environmental measures: “Metal and electro-technical industry” (1998 ). VNG publishers
  5. Supplier information
  6. VDI 3679, Nassabscheider für Partikelförmige Stoffen