Wet Scrubbers

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Exeon provide a range of wet scrubbers, designed where appropriate to reduce concentrations of chemicals / pollutants on discharge airflows, to meet required emission levels.

Wet scrubber: removal mechanism

Wet scrubbers remove contaminants from a gas stream by passing the contaminant air stream through a packed structure, with a ‘scrubbing liquor’ injected to absorb the contaminant. They are essentially “showers” where the contaminant airstream is ‘washed’ by the recirculating liquid in order to absorb the pollutants.

At the bottom of the scrubber there is a tank with the solution used for this process that is characterized by a specific pH that determine its acidity or basicity. The acqueous solution used inside scrubbers will have a pH suitable to abate the pollutants. The basic VIC are reduced thanks to an acid reagent, while the acid VIC are reduced through the use of a basic reagent.

To guarantee the abatement efficiency, the solution contained into the tank under the scrubber is linked to reagent tank. In this way, a special pump transfers the reagent directly inside the tank in order to compensate the pH values.

As you can see, the polluted air due to the production process is extracted through the duct, it then flows inside the fan and then is treated inside the two scrubbers.

The process in the picture is a two-stage abatement system where the air enters inside the first scrubber, where take place the reduction of basic compound like ammonia, to than flows in the second tower designed to remove the acid compound like hydrogen sulfide. Both scrubbers are equipped by tanks connected to reagent tanks where are stored the acid or basic reagents use to stabilize the pH. The plant can be equipped also with oxidant reagent in order to reduce the bacterial load before the emission.

The design of the scrubber tower is designed to maximise contact area to encourage mass transfer, achieved by the use of a random packed bed.

They can be designed for very high efficiencies with relatively low capital and running costs.

Types of scrubber

Packed Tower Scrubber

Wetted packed towers are the simplest and most commonly used approaches to gas scrubbing.

  • Large contact area to remove contaminants from gas flow
  • Uses loose-filled random packing
  • Low running costs and capital investment

Venturi Scrubber

Venturi scrubbing is a most effective technique for the removal of particulates from a gas stream, even down to sub-micron size.

  • Brings together scrubbing liquor and gas stream within venturi throat
  • Cost effective and efficient scrubbing technique
  • Can be used in combination with a chemical scrubber

Wet scrubber: parameters

The main parameters that regulate the particulate capture process are:

  • Particles size: the more particle is large, the easier is his capture;
  • Droplets size:capture efficiency increases with the decreasing of droplets size;

Relative velocity between the particles and the droplets: the increase of the speed increase the removal efficiency.

Types of wet scrubbers

A possible classification of the types of wet scrubbers is carried out on the basis of the phase to which energy is supplied. Particularly, energy may be supplied to:

  • the gaseous phase: this is the case of Venturi scrubbers or of plate columns
    the liquid phase: this is the case of spray towers
  • both liquid and gaseous phases: is the case of packed or floating bed scrubbers
  • The most important systems are packed columns. They consist of cylindrical chambers, that are internally filled with a packed bed structure. Equipments like this may be used also with countercurrent spray systems.
  • The optimal definition of the scrubber (typology, sizing, final efficiency estimation) for the specific application is realized in an analytical way alongside our experience and the experimental tests carried out.