Soot, electrostatic precipitator

The removal of soot from smoke is another example of the coagulation of a colloid. When smoke is passed through an electrostatic precipitator (Fig. 17.24), the suspended solids are removed. The use of precipitators has produced an immense improvement in the air quality of heavily industrialized cities. 

The pyrolysis products, together with the fluidizing gas (i.e. the noncondensable pyrolysis gases), leave the reactor via a cyclone, where dry carbon soot and filler materials are precipitated. A cooling system and an electrostatic precipitator condense the liquid fraction of the pyrolysis products. The waste heat is used to heat up the fluidizing gas. A stream of pyrolysis products is branched off the main product cycle and refined in the rectification unit described for the smaller test plant. 

Electrostatic precipitators and scrubbers (see Charge them up and drop them out Electrostatic precipitators and Washing water Scrubbers, later in this chapter), combined with filters, have been effective in reducing the release of soot, ash, and sulfur dioxide into the atmosphere and have reduced the occurrence of London smog. 

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