In many industrial and chemical operations, sub-micron emissions occur at various points in the process. A small amount of sub-micron particles can stabilize a steam plume. The heavy opacity related with such plumes is often out of proportion to the concentration of particulates in the exhaust. These fume coalescers employ both impingement and Brownian diffusion as collection mechanisms. The larger mist particles impinge directly on the fibers and coalesce, while the finer particles, which are in theory small enough to escape through the pores of the filter, do not do so in practice, because of their random or Brownian motion. The motion causes them to deviate from the main direction of travel, eventually colliding with the fiber. For both these collection mechanisms, the finer the fiber in the fiber bed, the smaller the particle it can arrest. For a known particle size distribution, it is thus possible to design a fume coalescer for specific collection efficiency. This coalescer can also remove sub-micron soluble solid particles. For these applications, the candles are continuously irrigated.
The coalescers are used in a variety of applications. In the chemical industry, acid mist generated in contact sulfuric acid plants, oleum storage tank vents, nitric acid plants, phosphoric acid plants, etc. can be very efficiently controlled using them. The operation of the fume coalescer requires little maintenance. The pressure drop through the candle is less than 15 in. W-G. The coalescer is also used to control metal pickling fumes, fumes of sodium chloride, brine mists and acid mists in chlorine plants. It is used for hydrocarbon emission control. Asphalt loading and storage areas, exhaust from textile tenter frames, plasticizer fumes from various heat curing operations and other condensable hydrocarbon emissions from various industrial processes use them for efficient control of visible emissions.
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