MSD "Capacity"


MSD capacity is defined in terms of the amount of gas that can be treated prior to breakthrough of water at 1 ppm. For convenience, the definition includes the number of hours (required by the customer) to breakthrough, gas feed rate and gas moisture content.

      e.g. 100 hrs @ 100 SCFH @ 0.1% water in feed = 1000 SCFH-%-hrs

             100 hrs @ 10 SCFH @ 1% water in feed = 1000 SCFH-%-hrs

MSD dryers can treat gas flows at rates equal to or smaller than the "capacity" indicated by the model number. An MSD-100, for instance, can treat up to 100 SCFH of gas. If the flow rate is larger than 100 SCFH, a larger dryer should be specified, even though the MSD-100 might have adequate capacity on the basis of breakthrough time.


(A)    The flow rate of the feed gas is 100 SCFH. The dew point of the feed gas is -20F when tested at 1 atm. The minimum allowable running time between regenerations is 100 hours. Find the smallest appropriate dryer.

      Draw a vertical line to the curve from and a horizontal line to the right axis from the curve. Read approximately 0.04% H2O by volume.

0.04% x 100 SCFH x 100 hrs = 400 SCFH-%-hrs

     The smallest unit with sufficient capacity is the MSD-500.

(B)    A feed gas is at 5 atm. The dew point of the product gas from an MSD is -100F at 5 atm. Find the dew point of the dried product gas when expanded to 1 atm.

     Draw a vertical line from -100F and a horizontal line to the left axis from the curve.  Read approximately 0.001 mmHg.  Divide 0.001 by 5.  The reduced vapor pressure is approximately 0.0002 mmHg.  Draw a horizontal line from 0.0002 mmHg to the curve and a vertical line to the temperature scale.  Read a dew point of -120F for the expanded product stream.


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