VENTURI SCRUBBERS

Description

Venturi scrubbers are among the most effective means of removing submicron particulate material from gas streams. Reactive trace gases can also be removed.

Venturi scrubbers operate by passing either the gas or a scrubbing liquor through a constriction (the venturi) at high velocity. This creates a high relative velocity between the gas and the liquid, which causes intimate mixing and increases the chances of particles impinging on the scrubbing liquor. The liquid-gas mixture is then passed through a built-in cyclone or baffle plates, where the slurry droplets are collected. The slurry is returned to a sump for recycling or treatment and disposal. Venturi scrubbers are self-cleaning and have no moving internal components.

There are three types of venturi scrubber. In the conventional venturi scrubber, the gas stream is passed through the venturi and the liquor is entrained, whereas in the similar water jet eductor, the scrubbing liquor is passed through the venturi nozzle and the contaminated gas is entrained into the stream of liquor. The self-induced spray scrubber achieves intimate mixing by passing the contaminated gas through a constriction partly submerged in scrubbing liquor. This creates a spray in which particulate material is scrubbed.

Application

Venturi scrubbers remove particles and liquid droplets larger than 01 µm. They are ideal for gas flows containing high particulate levels and are particularly suitable for the collection of inflammable vapours. They are used in the fertiliser, chemical, paper, metalworking and mining industries.

Water jet eductors will remove sticky or gummy particulate material from a gas stream. Self-induced spray scrubbers have a lower operating pressure drop and can be slightly less efficient at particle separation; they are generally not used for trace gas removal.

Sizing

Venturi scrubbers with high efficiencies of submicron particle removal have relatively high power consumptions and operating costs. A typical venturi scrubber may have a gas flow of about 8000 m3/hour. It would require a 3 kW fan to drive the gas, and a 1 kW pump to recirculate the scrubbing liquor. Self-induced spray scrubbers have slightly lower operating costs.

In some venturis the cross sectional area of the throat can be varied to keep the operating pressure drop constant. In this way, a constant efficiency can be maintained in spite of variations in throughput.