Gas purification techniques

Catalytic post-combustion
A catalytic post-combustion works in a similar manner as a thermal post-combustion with this difference that the gas, after it has passed by the flame, once more goes through a catalyst. This catalyst ensures an accelerated oxidation at lower temperatures. Post-combustions can continue because of this at lower temperatures. The gas is warmed up for the catalyst to approximately 300 - 500 °C. The maximum gas temperature after the catalyst are typical 500 - 700 °C. New low temperature catalysts can work already at 200 - 250 °C. Due the lower temperature the required fuel to reach autothermicity is lower than at thermal post-combustion. Used the catalysts are typically inert metals (platinum, palladium, rhodium) on a ceramic or metallic carrier, base-metal on a ceramic carrier or metal - oxides on a mechanically strong carrier.
For chlorinated connections catalysts as chromium/alumina, cobalt oxide and copper oxide/manganese oxide are use. Platinum based catalysts is suitable for sulphur containing components but becomes fast deactivated in the presence of chlorine. The presence of catalyst poisons such as chemical substances and substance particles can strongly reduce the life span of a catalyst. Examples of catalyst poisons are fast working poisons (vb. Phosphorus, bismuth, arsenic, antimony, lead and mercury), slow working poisons (iron, tin, silicon), reversible inhibitors (sulphur, halogen, zinc), surface maskers (organic fixed substances) and eroding -,masking components (inert particles). It is important to know the composition of the gases well so that the correct catalyst can be selected and unexpected deactivation can be avoided. There are two different systems of catalytic post-combustion, as it happens, fixed bed and fluorescent bed systems. Fixed bed installations can be carried out with a structured catalyst or a caught bed. The structured catalyst exists from monolithic material with the necessary air canals in the direction of the gas flow. Caught bed catalysts exists from catalyst grains which in a tube, plate or barge has been brought as a result of which passes the gases. In fluorescent bed air is upward sent by the catalyst bed. By the high flow speeds the grains in the catalyst bed will move so that entirely expands and as a fluid will behave itself. Catalytic post-combustion can be combined with energy recuperation. These energy recuperation can be both recuperative and regenerative. The advantages of catalytic post-combustion are: More compactly than thermal oxidation Lower oxidation temperature so that less support fuel is necessary Low NO_x production; approximately 20 - 30% of the NO_x at thermal post-combustion CO are destroyed with the other components High constant and reliable performances possible By the low temperature less heat insulation has been required than at thermal post-combustion More lower fire risk with respect to thermal oxidation The disadvantages are: More lower output for fox disposal than thermal oxidation System are sensitive for changes in energy-input of the gas Risk of dioxin shaping connections chlorinated at presence of All catalysts are liable to catalyst far grants and polluting substances. Substance must be removed for post-combustion Deactivated catalyst cannot be regenerated and must be removed. Catalytic oxidation is especially applied at disposal of VOC of solvent evaporation. Examples apply: Fuel bulkloadstations Production of organic chemicals Production of rubber and polymers Resin production Attaching and drying solvent containing coatings. Destruction of ethylene oxide of sterilization at 140 - 235 °C and ongoing concentration of 3000 ppm Click here for more information over scrubber technology, exposure limits and explosive limits For more books and reading information see our website: Air treatment books overview

Gas purification techniques

Catalytic post-combustion