Gas purification techniques

Thermal post- combustion

As an alternative on a traditional thermal post-combustion the degasses can oxidize in an existing kettle. This is only possibly if the flow of the degas flows is sufficiently low and if no corrosive gases are present or corrosive combustion products are formed. At injection in the existing kettle it has the preference to inject the gases with the combustion air in the kettle and not sidelong in the combustion chamber. In the last case one has a large chance on short circuit flows as a result of which strongly reduces the output can be and insufficient. To reach faster auto therm several methods be used:

• Use of regenerative adsorption. Advantages are smaller gas flows and a higher hydrocarbon quality 

• Use of heat recuperation by means of exchanger: ` recuperative thermal oxidation '

• Use of regenerative beds to heat the air for: ` regenerative thermal oxidation '

The advantages at thermal post-combustion are:

• Proved technology for hydrocarbons

• High efficiencies feasible to an output of 99.9999%

• Well at high VOC concentrations: > 20% LEL (Lowest Explosion Limit)

The disadvantages are:

• High variable cost for fuel at low VOC concentrations

• Not well arranged for strong variable flows

• Shaping of corrosive acid gases at combustion of halogen and
  sulphur containing components

• Not cost effective at low concentrations and high flows.

• Regenerative and recuperative post-combustion have been arranged
  generally better because of the reduced fuel charges by
  energy recuperation

Thermal post-combustion without energy recuperation has been especially arranged in comparison with other post-combustion techniques at:

• Small degas flow (< 860 m³/h)

• High taxes where spontaneous combustion can appear at recuperative
  post-combustion

• High degas temperatures so that few re-stoke is required

• Strongly degasses polluted with substance which at catalytic
  post-combustion the catalyst can do the installation for
  heat recuperation hide or at recuperative post-combustion.

Post-combustion with energy recuperation prefers however the preference
if above problems with heat recovery do not appear. An application for injection in an existing kettle is at the indirect drying of industrial silt. After condensation and acid scrubbing of the dry mists still a small flow does not remain heavy fragrance charged non condensable gases. These gases are injected in the kettle with combustion air. The energetic quality of the degasses is recuperated for the silt drying.

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