EnglishFrenchDutch
because          
"air is our first         
nutriment & medicine"         
(Hippocrate, 400BC)         
Print E-mail

Photo-Oxidation

 

Odour & VOC oxidation with the power of UV light !

 

 

Content

1. Oxidation Process Description

2. Process Description

3. Applications

4. Advantages

5. Dimensioning

6. References

 

1. Photo-Oxidation: Oxidation Process Description  

Photo-Oxidation consists in degrading VOC and some inorganic contaminants, like NH4 and H2S, with short UV waves (UV-C) at room temperature. UV-C waves (100 to 280nm) have 2 degradation actions:

  • direct photolysis of contaminants strongly absorbing in the UV-C region (VOCs, NH3, H2S, mercaptans, amines,):

                                    C2H6 + hv ->  CH3 + HC + 2H

                                    H2S + hv   ->   H + HS

  • oxidation of the photolysed molecules thanks to the productioin of highly reactive oxygen radicals (O*, OH-, H2O2), which gives CO2, SO2, N2, as end product:

                                    3 O2 + hn (185nm)   2O3

                                    O3  +  hn  (254nm)   O2 + O*

 

 

The combination of these 2 degradation processes gives harmless end-products like:

 

                                    C2H6 + hv  + O* ->   CO2 + H2O

                                    H2S + hv + O*   ->  SO2 + H2O

                                    NH4 + hv + O*  ->   N2 + H2O

 

2. Photo-Oxidation: Process Description 

 

Photo-oxidation is a 2 steps system:

 

1.  oxidation module: the emission comes first into contact with the UV-C lamps. The contaminants are photolysed and already partially oxidized in CO2 with the oxygen radicals.

 

2. catalyst module: the uncompletely oxidized molecules adsorb on the catalyst where their oxidation is completed; the catalyst can also neutralize the unreacted oxygen radicals

 

 

In order to efficiently treat peaks of concentration or short polar VOC, an intermediate catalyst module ca be installed between 2 oxidation modules.

 
The number of UV-C lamps increases with:
  •  the VOC concentration
  •  the requested abatement yield.

Above 500mg/m3 VOC and 95%  abatement yields , the working costs for the UV-C lamps become too high and technologies like CatOx become attractive.

 

Photo-Oxidation is a single or multi-duct system:

 

 

 

 

One duct can treat max 8.000m3/h emission

 

 

 

 

For higher flow rates, the number of ducts = flow divided by 8.000.

 

The picture shows a system with

3 x 2 ducts for treating a solvent emission of 32.000m3/h

 

Process conditions:

  • the catalyst requests a T < 40C and a relative humidity %RH < 85%
  • the VOC concentration must be < 500mg/m3

If the T is lower than 40C but the relative humidity higher than 85%, a heating element before the lamps has to be added in order to reduce the humidity.

 

Maintenance:

  • the UV-C lamps must be replaced after 8.000 working hours
  • the catalyst must be replaced after 2.000 working hours

3. Applications 

  • degradation of VOCs (< 500mg/m3) and H2S, NH3, mercaptan, amine, (< 50ppm);
  • emission at T < 40C and %RH < 85%

4. Advantages 

  • Degradation at room temperature
  • low investment (carbon steel), energy (lamp, fan) and maintenance costs
  • long equipment life time
  • Compact, modular and silent system; indoor and outdoor location possible
  • No start-up time; no fluid supply and waste production

5. Dimensioning 

  • Each duct has a section of 1m x 1m and a maximum flow capacity of 8000 m3/h
  • For higher flows, the number of ducts = flow divided by 8.000
  • For flows smaller than 3000m3/h, a section of 700 x 700mm is preferred.

6. References 

on request

 

 

© 2008 Air Quality Concept