Odour removal

Although the natural zeolites are widely used (around 4 million tpa) they are not particularly valuable as commercial catalysts. This is due to a number of factors including natural variations in crystal size and porosity as well as the actual small pore size, which limits their synthetic usefulness. Natural zeolites do, however, find widespread use in applications such as removal of heavy metals from water, odour removal and building materials e.g. cavity grouting and sprayed concrete). 

Ozone is useful since it is a powerful oxidising agent, but the molecule itself is toxic to both animal and plant life and its release into the environment must be avoided. The problem of ozone decomposition is therefore technologically important. For example, ozone needs to be reduced in airplane cabins, submarines and office environments. Discharges from sterilisation, odour removal and waste water treatment units must also have their ozone levels lowered [466,544]. 

Rinsing plastics in special formulated (detergent) solutions (aqueous alkaline solutions with surfactants) can also help in odour removal, in particular in the elimination of vinyl monomers, styrene, acrylates and acrylics, as well as unsaturated hydrocarbons. 

Pilot scale data for amine removal have been provided by Finland. A biofilter unit (diameter 0.8 m, height 1 m) was installed in a core-making off-gas line, after an acid scrubber. The equipment included a fan and a dewing unit, with which the dampness of the biofiltration unit was adjusted to an optimum level. The odour removal was measured using an olfactometer. Results for the odour and total hydrocarbon levels are given in Table 4.50. Variations in the input analysis are due to process variations. The results show that filtration results in a significant odour and hydrocarbon reduction. 

Odour removal gas purification solvent recovery Drying air, gases and liquids... 

An intermediate case between in-process and end-of-pipe use is that of product purification, including colour and odour removal. Some examples of this using H2O2 will also be identified. Such a purification step can itself produce effluent, the nature of which is a factor in choosing the oxidant. 

Adsorption Preferential adsorption of one component on to a solid surface Removal of water vapour by silica gel or molecular sieves. Odour removal... 

Recently, zeolites have been used as molecular sieves for functional powders in odour removal and as plastic additives. 

Rotating packed bed Excellent for mass-transfer limited processes. Uniform dispersion high turbulence thin films good controllability Some development work still proceeding Limited use outside odour removal/clean-up Crystallisation reactive stripping... 

Filter life tends to vary considerably with these units but, generally, if the filter is cleaned of clogging particles regularly, i.e. rinsed free of dust with plain water or vacuum cleaned, then, depending on usage, the filter could last up to six months. Air velocity, humidity and temperature all, obviously, have an influence on the effectiveness of odour-removing filters. 

Odours are not necessarily a problem when the compressor is correctly sized, cited and maintained. However, it does not take much odour in the inlet air or created in the compressor system to produce an offensive situation in a breathing hood. The most effective and common approach to odour removal is the use of activated... 

Because an electrostatic precipitator has no efifect on gaseous impurities, it is usual for such a separator to be fitted with an odour removing activated carbon filter... 

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