The high use of energy must therefore be as effectively as possible. This has been achieved by making use of the venturi effect in the so called venturi scrubbers. The thus separated particles are finally eliminated to the sewage system with the overflowing washing liquid of the venturi scrubber.

Characteristics of the Tholander process in key words

Our responsibility as plant manufacturer is not only the delivery of the plant but also its customer friendly operation. This is why we attach great importance to easy maintenance and high operational safety of the plant.

According to our product philosophy, the multi-venturi scrubber offers the following general advantages resulting from its construction and the use of FRP:

• High separation results
• Little space demand / compact size
• Corrosion resistance
• Weather resistance
• Temperature insensitivity
• High operational safety
• Wide ranging applications

The wide-ranging applications can be seen from the following examples:

• Animal farming: Separation of partly adhesive dusts and of ammonia allowing substantial odour reduction
• Food industry: Separation of fatty aerosols (e.g. frying industry, smoke houses). Since the main source for odour is in the oil itself, a partly deodorization is achieved as well.
• Composting with humid, dusty waste air. By using a multi-venturi scrubber, a polishing biofilter can be protected against plugging with dust at peak loads
• Hot and humid, dusty waste air (e.g. chipboard production, oil mills, composting). Using a multi-venturi scrubber additionally reduces the exhaust temperature to values appropriate for biofiltration.

Venturi scrubbers are especially suitable for sticky, adhesive aerosols and fine dusts in humid waste air. In filtrating systems these particles would, however, lead to adherence and irreversibly high filter resistance. By using a wet separation process, the aerosols are washed out and cannot stick anymore (They are finally eliminated to the sewage system with the overflowing washing liquid of the venturi scrubber).

The so called venturi effect in the venturi zone is based on the fact that a particularly intense contact area between gas and liquid phase is generated. For this purpose, the streaming surface is narrowed while the washing liquid is sprayed into the so called venturi zone. In this way, the exhaust air and the dust particles contained therein are accelerated to 50 - 150 m/s. The sprayed out washing water droplets and the resulting deceleration of the dust particles during the "collision" allows to "capture" the aerosols in the water droplets.

Following this step, the washing water droplets and the therein suspended dust particles are caught by a droplet separator and led back into the washing liquid circulation afterwards. To obtain such high separation efficiency, the exhaust fan must be upgraded through a higher energy consumption to compensate the pressure lose of the venturi nozzle and the droplet separator.

For the separation of fine and sticky dusts or dusts from humid waste air, we have chosen an extended version of the venturi scrubber being especially efficient and compact: our so called "multi-venturi scrubber". The special feature of this scrubber is its multiple venturi effect with an efficient but compact droplet separation.

In this case, the venturi effect is not achieved by reducing a duct but by using our separation plates. These plates require less space compared to venturi nozzles arranged in series. The washing liquid is sprayed into the scrubbing zone being equipped with these special separation plates. Bigger droplets are separated on these plates and washed out constantly by means of the irrigation system. Sticky particles can thus be eliminated as well. Smaller washing water droplets are, however, separated in the packing bed of the downstream cross-flow scrubber.

The constant irrigation prevents the dust particles from adhering and additionally improves the separation efficiency of the dust loaded water droplets so that they are not transferred to the clean gas site which would otherwise lead to recontamination. Apart from its excellent suitability for dust removal, the multi-venturi scrubber has further reduction effects:

• Our multi-venturi scrubber is also suitable for odour reduction as the odour molecules accumulate on the surface of the dust particles. This way, the molecules are eliminated together with the dust particles. Another advantage of our multi-venturi scrubber is the good washing effect for water soluble odour contaminants which is achieved by the downstream cross-flow scrubber. The pH value of the washing liquid can be adjusted by a dosing station so that alkaline and/or acidic odour compounds can be washed out even more effectively.
• With this pH adjustment it is also possible to achieve specific removal efficiencies for single substances. An example is the removal of ammonia with acidic treatment.
• When hot waste gas streams are present, the multi-venturi scrubber can also be used as quench in combination with a cooling tower for cooling of the air.