VOC-collection and removal

VOC emissions (mainly solvents, BTEX, and to a lesser extent phenol, formaldehyde, ete.) result from ehemieally-bonded sand preparation and also, further along the process, from pouring, cooling and shake-out (see Table 3.35 and Table 3.45). These compoimds are noxious and generate odour emissions. 

The abatement of VOCs is hindered by the fact that large voliunes of ambient air are entrained by the collection systems (e.g. canopy hoods) used. 

The following techniques are applicable for the removal of VOCs adsorption to activated carbon post combustion biofilter. 

For adsorption to activated carbon, the exhaust gas flows tiirough a carbon bed. Upon saturation, the carbon is thermally regenerated. Activated carbon has a very high adsorption (and abatement) efficiency. For benzene, the efficiency is 99 %. Nevertheless, it has the following disadvantages  

To successfully exploit post combustion to eliminate VOCs from off-gases, specific minimum concentrations are necessary. These limit values are compound specific and depend on the chosen technique. Post combustion is possible for the exhaust gas from shell moulding. Generally, the exhaust gas from the casting shop does not have high enough VOC levels to operate post combustion. One alternative to post combustion is to use exhaust air from the core blowers as combustion air for the cupola. 

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