Each washing stage has its own liquid system. The first stage is operated with neutral washing liquid (pH 7) enabling the transfer of dust and water soluble compounds into the liquid phase. The waste air being now saturated with water is then treated in a second stage with acidic pH value. Acidic compounds are treated in a third stage with alkaline washing liquid.

The chemicals (oxidants, acid or caustic) are added by dosing stations with specially dimensioned dosing pumps. This way, the washing liquid’s specific pH value and redox potential is kept constantly. This leads to an optimal dosing of chemicals without waste. There is also the possibility to add oxidant such as H₂O₂ to the washing water of only one stage reducing its consumption considerably (See also oxidation from sulphide to sulphate).

Another way to further reduce the operating costs, is to replace a chemical washing stage with a biological one (See also bio scrubber).

Our cross flow scrubbers can be retrofitted easily. This allows to expand the system later on for example by combination with a biological air treatment plant. In this special case, not only pH relevant compounds are removed: The advantages of biofiltration (humidification, cooling/tempering and dust removal) are integrated as well.

Through its multi-stage construction, our cross-flow scrubber additionally ensures the redundancy of the humidification. Furthermore, its low housing height does not only save material but also space.

As shown above, the advantages of a multi-stage scrubbing are diverse. The realization of a cross-flow scrubber, however, is usually much more complex compared to that of a simple air scrubbing system.

As the name clearly implies, the horizontally streaming waste gas crosses the washing liquid which streams from top downwards. The advantages resulting from this typically horizontal construction are as follows:

• Low housing height due to the horizontal construction having positive effects on statics and accessibility.
• Savings in internal ducting due to combination of several washing stages in one plant.
• The washing liquid is distributed by several spraying nozzles arranged in series. Thus, a partial failure of nozzles can be compensated.
• The subsequent division into different washing stages is possible without major constructional modifications, simply by retrofitting with a chemical dosing station.
• Cross-flow scrubbers are generally operated with underpressure. The exhaust fan can thus be installed on the clean gas site without getting in contact with the corrosive and abrasive waste air contaminants.

Since our scrubbers are mainly used for sewage and waste treatment operations (problem of H₂S and NH₃ polluted waste air) a particular choice of materials is required. Our scrubbers are therefore manufactured from corrosion-free glass fibre reinforced plastic. This corrosion resistance is especially necessary when using non-ph-neutral washing solutions and/or oxidants as well as for applications with corrosive waste air contaminants.

• Easy transportability
• Low weight
• Few preliminary works by the customer on site
• Weather resistance
• High temperature resistance

Using a multi-stage cross-flow scrubber especially makes sense…

• in case of complex and variable waste air compositions
• as pre-treatment stage in front of a biofilter/activated carbon filter
• for separation of dust particles and gaseous compounds at the same time
• if redundancy is required (the failure of one washing stage can partly be compensated by the following stages)
• if biological scrubbing is an environmentally friendly and cost-effective alternative