Gas purification techniques

Cryogenic condensation

• A sufficiently long stay time and a turbulent flow to be able cool
  down all gas entirely

• The condenser temperature must be low enough and must be foreseen with a sufficient large cool capacity 

• Ventilate the quantity at the organic fraction must be minimized. This air ensures a larger energy usage and a higher quality solvents which cannot be separated away from (lower output). To limit the volume of the air adsorption can be applied where the more concentrated desorption flow are treated in the condenser. This ensures strongly reduced cooling capacity and a raised dissidence
  efficiency in the condenser

• The temperature of the condenser is best chosen under the freezing point
  of the solvent, so that the vapour pressure of the solvent are minimum

• Periodically must be removed the solvents then of the condenser
  suggesting area

Attention must be paid to the material choice for corrosion of the heat exchangers. The typical cooling elements of copper and aluminum have been made. Moreover are the cooling elements that may have been made of stainless steel . Stainless steel gives generally few problems with corrosion. For cryogenic condensation stainless steel has been generally designated because this has generally no potential cracking (corrosion) problems and no problems with compatibilities with organic substances. At use of carbon steel extra attention must be paid for corrosion, response with organic components and friability if the temperature under the transition temperature of that metal sits. Specifically for brine coolers must be paid attention for corrosion since NaCl, CaCl₂ and KCl in the solution sit. Here one must be chosen for adapted material.
If the rest concentration of solvents is after the condenser too high for discharging to the atmosphere the degasses must be treated further. This is possible by means of techniques as adsorption, biological techniques, cold oxidation.

The functioning degree depends on the component and the condenser
temperature.                                                                                                                             The advantages which prevent condensation at these type are:

• Compact technology

• Recovery organic solvents if the solvents purely be to break away
  from

• Desired end concentration can be chosen by correct choice of
  condenser temperature

• High efficiency at high FOX concentrations

The disadvantages are:

• Usage of liquid nitrogen which must be produced or bought

• At wet gas flows one must take into consideration to minimize the shaping of ice in the condenser by preceding demoisterising

Cryogenic condensers are applied on:

• Process gases engines

• Gases originating from rise tanks (especially when filling tanks)

• Small gas flows with high VOC concentrations

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