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The DuoCondex-process

The DuoCondex®- Process, for which several patents have been filed by Messer, is a condensation process for the recovery of volatile substances (for example, solvents, fuel vapours, CFCs etc.) from process gas streams. The process utilises liquid nitrogen at a temperature of -196°C. At this extremely low temperature not only vapours but also gaseous substances can be nearly completely condensed or frozen out; for this reason the DuoCondex®-Process is highly suitable for the cleaning of high load waste gas streams from industrial plants.

Depending on requirements, DuoCondex® plants can be designed with one or two stages. The basic one stage version is normally sufficient for the condensation of vapours from solvents which are liquid under ambient conditions. The two stage option described below is used when the process gases to be cleaned also contain gaseous pollutants such as MeCl (methyl chloride) or CCl2F2 (R 12).

In the first stage (condenser) of a DuoCondex® plant, the gas flow to be treated is cooled to a temperature of approx. -100°C. This liquefies and separates a majority (usually more than 95%) of the condensable substances in the process gas. During the second stage (purifier), further cooling, partially down to -170°C, takes place. This leads to almost total freezing out of the remaining process gas load.

The purifier is cooled by cryogenic liquid nitrogen which evaporates and therefore provides maximum cooling potential. The gaseous nitrogen exiting the apparatus subsequently serves as coolant for the main condenser (step 1). The condenser is also cooled by the purified process gas leaving the purifier. This provides the cooling capacity necessary for the first stage whilst maintaining low nitrogen consumption. The process gas is thereby heated close to ambient temperatures and can be released into the atmosphere without further treatment.

The first stage of the DuoCondex® plant is cooled using only gaseous medium (gaseous nitrogen/clean gas) as a result of which there is very little ice formation in the equipment. In addition, hardly any aerosols which could affect the clean gas load are created.

The most favourable operating conditions for the condenser exist when the equipment is cooled as evenly as possible. Cold nitrogen and clean gas therefore flow through a thermo-controller, a special energy exchanger which aligns the temperature of the cold gas streams, before they enter the condenser. An intelligent control system evaluates various process parameters and adjusts the thermo-controller during each operating phase so that the DuoCondex® plant functions optimally. As a result, ice formation is kept to a minimum during the cleaning phase, rapid and even cooling is possible and the thermo controller also serves as a heat source during defrosting.