PLATE SCRUBBERS

Description

Plate scrubbers are used to remove dust, noxious gases and odours from gaseous emissions. The gas stream to be cleaned is initially washed with a scrubbing liquor spray and then passed through the perforated plates within the scrubbers, which are flooded with a separate scrubbing liquor supply. Scrubbing is accomplished by the intimate contact between the gas and the scrubbing liquid as it passes through the perforations in the plate. In most cases the gas is demisted with a mist eliminator before venting to the atmosphere. There are three main types of plate scrubbers.

Sieve plate scrubbers have horizontal perforated plates and can remove dust and noxious gases from gaseous emissions. Impingement scrubbers have an additional baffle plate located above the plate perforations upon which particles impinge and are separated more efficiently. Screen plate scrubbers consist of vertical plates made from an irrigated double layer of wedge wire and are used for odour control.

Application

Plate scrubbers can simultaneously remove particles and absorb gases into the scrubbing liquor. They are used to remove acid and alkali gases from plating, anodising and pickling processes. They can remove hydrocarbon and other chemical fumes from incineration, and are used in the textile, ceramic, engineering and metal industries.

Impingement scrubbers are relatively simple systems that offer a high capture efficiency with coarse dusts. They will typically capture 99% of particles of 10 µm diameter, 92% at 2 µm and 80-85 % at 1 µm. Capture efficiencies are low with sub-micron particles. Sieve plate scrubbers are able to remove particles down to 3 µm.Screen plate scrubbers are used to remove odours, from sewage treatment plants for example, and are suitable for throughputs of 1500-12,000 m3/hour. Screen plate scrubbers are not suitable for the removal of particulate material.

Sizing

The operating costs of an impingement scrubber arise from the fan that drives the gas, and the pumps that recirculate the liquid. Electrical consumption is dependent upon the volume of gas to be treated, the geometry of the ductwork, and the required efficiency of the cleaning process.

Gas flows of 2,000-170,000 m3/hour can be treated in impingement scrubbers. Static pressure losses range from 40-200 mm water gauge, higher pressure losses being associated with higher capture efficiencies. A gas flow of 50,000 m3/hour would require a fan with a power consumption of the order of 100 kW, and a scrubbing liquid recirculation pump of about 5 kW.

A typical sieve plate scrubber with four plates treating a gas stream of 2500 m3/hour would require a 15 kW recirculation pump and a 3 kW fan.