Thermal backwash

Figure 16 Process flowsheet of a GAC system with regeneration. In this complete GAC adsorption and regeneration system, four GAC columns can be operated in parallel or in series. Spent carbon is transferred to a multiple-hearth furnace for thermal regeneration. Regenerated carbon is mixed with virgin makeup and pumped back to the GAC columns. The GAC columns are backwashed periodically. (From Ref. 27.)...

The filters are backwashed occasionally to remove any suspended solids that may have accumulated on the surface of the bed. Backwashing does not remove material adsorbed in the pores of the carbon. Although a few installations regenerate their carbon using thermal, steam, solvent extraction, or other techniques, most applications see replacement of carbon when exhausted. Typical "life" of carbon used for TOC removal is 6 -12 months. For chlorine removal, the typical "life" is 12 - 18 months. 

One disadvantage of this soldering method is that the thermal energy is not well localized. Most machines typically emit a hot-gas jet too large to be isolated to reflow only the device of interest. The gas jet, once impinged upon the board and component leads, is deflected and its backwash can be problematic. It may cause unwanted reflow of previously formed joints, especially on closely spaced adjacent components. This problem is typically overcome by the use of baffles that are either applied to adjacent components or by a singular baffle that confines the gas jet to the component to be soldered. 

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