Gas purification techniques

Thermal post- combustion
The degasses with the necessary quantity of combustion air are brought on a high temperature. This temperature varies at thermal post-combustion between 750 and 1200 °C. The gases are kept sufficiently long on this high temperature where pollution (VOC, scent) with oxygen are oxidized up to CO₂, H₂O, N₂, SO_x, HCl. The efficiency of post-combustion is influenced by the temperature, resident time, turbulent (for mixing) and availability of oxygen. At traditional VOC a combustion temperature between 750 and 1000°C is enough. At environmental dangerous and halogenated components a post-combustion between 1000 and 1200 °C has been designated to guarantee a complete destruction of these components. At high temperatures destruction goes more rapidly than at lower temperatures. This can be help at the choice of the size of the combustion chamber. A large combustion chamber with a lower temperature has larger investment costs but lower fuel costs. A smaller combustion chamber on a higher temperature will have the same output at lower investment costs and higher fuel costs.
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. Click here for more overview scrubbers For more books and reading information see our website: Air treatment books overview

Gas purification techniques

Thermal post- combustion