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Desorption / Strip units:
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Stripping units / Compact strip units / Vacuum strip units
Stripping is a physical process for the removal of undesired contaminants in water. Stripping out of the liquid phase works when the pollutant concentration in the gas phases is lower than the equilibrium concentration in the liquid phase system. The equilibrium is described using so-called Henry Constants. The Henry Constant is dependent on the pollutants in the system, the pressure and the temperature.
There are basically two types of stripper:  Flow sheet
- Packed Column Strippers
- Sieve plate strippers (compact strippers)
Packed Column Strippers:
With strippers of this type of construction, the water is spread evenly over a column packing and falls to the bottom of the column. Air is blown counter-current through the column. The column packing greatly increases the surface area available for the desorption of the pollutant - and in this way influences the required height and amount of packing needed to reach the treatment targets.
This type of stripper is most often used with substances that are easily strippable such as CHC (tetrachloroethene, tricholroethenene) and AHC (benzene, toluene, xylene). They have also been successfully used with less strippable substances such as MTBE and THF at atmospheric pressures - although generally at low concentrations (if no air treatment is required) or when no other more cost effective or efficient processes are available.
Sieve plate strippers (compact strippers):
This type of column consists of several sieve plates on top of each other. The water is entered at the head of the unit, whilst air is blown through the column in the opposite direction. The air flows upwards through the holes in the plates, so that the water doesn't run down through them, but into the next stage via an overflow (downcomer). The transfer occurs in the bubble layers directly on the individual plates. These sieve tray systems are also constructed by Villiger to operate in a batched mode and are available under the trading name of "Boundary Layer Evaporator" (Type GVD).
Other parameters that influence the design of the strip units are the temperature and pressure at which the units are run.
Temperature:
By increasing the process temperature it is possible to increase the efficiency of a stripping unit. In practice however, this variation plays a minor role as it is energy intensive and secondly, if air treatment is to be by activated carbon then drying of the relative humidity of the air is no longer possible by simple means. (An exception: stripping of NH3).
Pressure:
By stripping under a vacuum, the amount of strip air can be reduced. Vacuum stripping units generally operate in a pressure range of -0.5 to -0.9 bar. The amount of air coming off the unit to be treated can be greatly reduced.
Pollutants:
Following substances can be efficiently stripped with Villiger desorption stripping units:
- Chlorinated hydrocarbons, e.g. Per, Tri, Vinylchloride, Chlorobenzenes etc.
- Aromatic hydrocarbons, e.g. Benzene, Toluene, Xylene, etc.
- Aliphatic hydrocarbons, e.g. Motor fuels
- Polycyclic hydrocarbons, e.g. Naphthalene
- Further solvents such as Tetrahydrofurane etc.
- Ammoniac
- Hydrogen sulphide
Villiger strip / desorption units are manufactured from PE (polyethylene), stainless steel or plastic-coated steel as either single or multi-stage units in a range of standard sizes. The units can be easily adapted to specific applications due to their modular design.
We are happy to recommend the best unit for your application, please ask for our project specification sheet.
We also rent out previously used units at very attractive rates.
We look forward to your enquiry. |
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