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Catalytic Oxidation

 

Content

1. Process description

2. Large scale CatOx systems

3. Small scale compact CatOx systems

4. Applications

5. Advantages of CatOx vs RTO

  

1. Process description 

Thermal oxidation converts VOCs (Volatile Organic Compounds) in CO2 at temperatures as high as 700-900C. Catalytic Oxidation consists in adding catalysts in the combustion chamber, which helps to reduce the oxidation temperature down to 200-400C.

 

Catalytic Oxidation suffers from the reputation to be sensitive to some inhibitors like inorganic acids (HCl, HF,), heavy metals, and consequently Regenerative Thermal Oxidation (RTO), an incinerator with internal heat recovery materials, but still working at 700-900C, is for this reason preferred.

 

Nowadays, highly resistant catalysts exist, even against inorganic acids, and we exclusively work with companies developing their own catalysts and constantly improving this technology that still has the major advantage to work at low temperature, which confers a longer lifetime to the installation

Compared to Regenerative Thermal Oxidation (RTO), it also integrates less regulated components, like valves.

 

The catalyst is composed of a carrier coated with active material. The carriers are either pellets or multi-channel (honeycomb) blocs, or a combination of both, and the active material is a metal oxide or a noble metal.

 

                                 

 

Honeycomb blocs have the advantage to have a lower pressure drop but to have a lower specific catalyst content. Recently, needle crystal catalysts with very high specific surface have been coated on the surface of honeycomb structures, giving a catalyst with high reactivity and low pressure drop. This catalyst allows to build compact systems with low pressure drop:

 

 

2. Large scale CatOx systems (> 1000m3/h) 

 

 

For large scale systems, we propose a unique concept that integrates, prior to the catalytic oxidation chamber:

 

1. a first heat exchanger that increases the T up to a value where all the organic compounds are under volatile form

 

2. a cold plasma chamber that pre-oxidise the VOCs in order to reduce the catalytic oxidation T

 

3. a 2d heat exchanger in order to increase the T as close as possible to the oxidation T

 

 

This CatOx system starts working auto-thermally at concentrations above 500mg/m3

 

If the emission from the oxidation chamber contains HCL, HF or other corrosive inorganic acids, it is treated on special adsorbents prior to entering the heat exchanger

 

3. Small scale compact CatOx systems (<1000m3/h) 

Recently, needle crystal catalysts with very high specific surface have been coated on the surface of honeycomb structures, giving a catalyst with high reactivity and low pressure drop. This catalyst allows to build compact systems with low pressure drop:

 

 

 

Multi-catalyst stage CatOx systems integrate different kinds of cataysts. Cheap pellets of metal oxides are often used as first treatment, since they are less sensitive to poisons, absorb them and can already achieve a high conversion yield. Noble metals, often coated on honeycombs blocs, are used as final treatment. At this stage, the possible poisons are removed.

 

 

 

 

Multi-pretreatment stage systems integrate various processes to better protect the catalyst and reduce the energy supply and the oxidation T:

- a tubular heat exchanger, recovering the heat from the cleaned gas in order to pre-heat the exhaust gas; if the emission contains fluid aerosols, like oil droplets, the heat exchanger will make all these contaminants volatile.

- a mechanical filters or a high speed cyclone in order to remove the particles.

 

 

4. Applications 

VOC emissions at concentrations higher than 0.5g/m3, at high temperatures (up to 400C) and containing fluid aerosols

 

5. Advantages of CatOx vs RTO (Regenerative Thermal Oxidation) 

  •  Lower T => longer installation lifetime, carbon steel still can be used
  •  Less regulated accessories, like valves, etc => lower shut-down risk
  •  Lower by-products formation, like CO and NOx; No risk of dioxine formation in case of presence of chlorinated VOC
  •  Shorter start up time
 

© 2008 Air Quality Concept