P&P scrubbers for a clean environment
A scrubber or absorber is a process engineering apparatus in which a gas stream is brought into contact with a liquid stream in order to absorb components of the gas stream in the liquid.
Absorption is the (selective) absorption of gases or vapors (the so-called absorptives or, in the bound state, the so-called absorpts) in selectively dissolving liquids (solvent, washing liquids, solvent or absorbent) or solids with the formation of a molecularly disperse distribution (absorbate, absorbent) until phase equilibrium is reached.
The transitional components of the gas flow can therefore be solid, liquid or gaseous substances. Due to the simple mechanical structure, pure solvents such as water, but also suspensions such as milk of lime (e.g. for flue gas desulphurization) can be used as scrubbing liquid. This process used in flue gas desulfurization is a reactive extraction.
P&P scrubbers are individually dimensioned and designed for your application by our experienced process engineers. Depending on the requirements of the process, a quench for cooling the process gas can also be installed before the scrubber. This and general temperature control also makes it possible to remove water from the process gas by cooling it below the dew point.
In most designs, the gas scrubber is divided into six sections. From bottom to top they have the following task:
- in the sump of the gas scrubber the scrubbing liquid collects and is drawn off,
- in the gas inlet, the gas is fed in and an even load of the interior is achieved by built-in components,
- in the contact section the washing of the components in the gas flow takes place,
- in the washing liquid feed, the washing liquid is fed and distributed,
- in the demister entrained components of the washing liquid are separated and
- in the head the cleaned gas stream leaves the gas scrubber
Operating principle for gaseous components
The gas scrubber works similar to the rectification column by repeated mixing and separation of the liquid and gaseous phases with formation of phase equilibria. In contrast to the rectification column as well as in the extraction column, there is no reflux in the gas scrubber. Although the physical functions are the same, apparatuses with a simple mechanical construction are referred to as gas scrubbers and more complex apparatuses as scrubbing columns.
The efficiency of gas scrubbers is determined by
- the contact time,
- Surface of the washing liquid,
- the diffusion distance in the gas phase,
- the difference in concentration between gas phase and liquid phase or an added reagent
- the temperature
- the pressure
The efficiency can therefore be increased by:
- a longer retention time,
- maximizing the surface area of the wash solution by using special nozzles, internals and packing,
- a stronger mixing of the phases in the gas scrubber itself
- a reduction of the concentration in the liquid phase by more washing liquid or a chemical reaction
- a lower temperature in the absorber
- higher pressures in the absorber
Scrubbers can be used particularly successful in environmental protection technology:
- Large flue gas streams with high loads of different, even heavy boiling pollutants
- Fluctuating exhaust and pollutant loads
- Dust, aerosol and gaseous pollutants in the exhaust gas to be treated
- High gas flow densities and short residence times in the scrubber
- Desired recovery of the absorptive
- Separation of pollutants up to legal limits
Typical applications are for example:
- HCl scrubbers for the flue gases of waste incineration plants
- This process produces aqueous hydrochloric acid
- Flue gas desulfurization plants
- Either with aqueous Ca(OH)2- or CaCO3 solutions that produce CaSO4
- Or using NaOH solutions that produce NaHSO3
We would be pleased to advise you on your specific scrubber solution.