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         Process Description

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Solvent Separation Process Unit - Process Description

The solvent ladened process stream is collected from the production plant and is first passed through the absorption column. The absorption process is performed under almost ambient conditions (1 bar abs. pressure, approx. 20 degrees C) (401.4 inch water, 68F). A special absorption liquid (also known as the re-circulating liquid) is used for the absorption of solvent from the process gas stream.

At the outlet of the absorption column, the solvent free gas stream is directed to other production process lines or discharged. The re-circulating liquid containing high amounts of solvent is also discharged from the absorption column and is directed to the next heat recovery step.

The heat recovery step is aided by the use of heat exchangers. The purpose of this step is to transfer the heat from the re-circulating liquid that has been discharged from the desorption column to the recirculating liquid that has been discharged from the absorption column. This has a dual purpose:

i) The first is to cool and prepare the recirculating liquid from the desorption column for a new absorption cycle.
ii) The second is to heat the solvent ladened recirculating liquid coming out of the absorption column. This step prepares the liquid for treatment in the desorber column. This heat exchange process takes place in the Primary Heat Recovery Unit.

Downstream from the Primary Heat Recovery Unit are two other heat exchangers. One is called the Heating Load Heat Exchanger which further heats the solvent ladened re-circulation liquid to the required 248F. The other is a Cooling Load Heat Exchanger which cools the returning re-circulating liquid.

The solvent ladened re-circulating liquid from the absorption column, now at 248F, is passed through a flash unit. The pressure is reduced and part of the solvent evaporates inside the flasher. The liquid and solvent vapours are separated in the flasher and directed to the desorption column separately. Inside the desorption column the liquid and vapour phases are treated separately. The desorption process is performed under vaccuum conditions and at an elevated temperature (approx. 100 mbar abs., 120 degrees C) (40.1 inch water, 248F).

In the lower desorption column the solvents in the recirculating liquid are desorped (stripped) by aid of steam. In the upper portion of the desorption column the vapour phase undergoes a re-flux process to recondensate the absorption liquid. This step ensures that the absorption liquid does not evaporate together with the solvent vapour. Downstream from the desorption column, a twin condenser for the solvent vapour is located before and after the vacuum pump.

The vacuum pump creates sufficeint suction pressure for the solvent ladened gas stream to pass through the solvent separation unit.

Inside the condensers, the solvent is transformed back to a liquid phase and is then direceted to the solvent separator. Located down stream from the condenser units is the solvent separator, and as the term indicates, it separates the solvent fom the condensed steam. Solvent from this separator is collected and either re-used in the production process or sold as a product.

At the end of the process, small amounts of air and residual non-condensed solvent are redirected back into the inlet gas stream.

  Examples of Application

         Separation of solvent in gas refinary facilities.
         Separation of solvent in the pharmaceutical industry.
         Recovery of solvent at bulk filling terminals.

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