Dear Muhammad Tauseef,

The point where the two composite streams touch is called the "mass-exchange pinch point" and, hence, the name "pinch diagram" (Figure attached). On the pinch diagram, the vertical overlap between the two composite streams represents the maximum feasible amount of the VOC that can be transferred from the wastewater streams to the process MSA's. It is referred to as the "integrated mass exchange." The vertical distance of the lean composite stream which lies above the upper end of the waste composite stream is referred to as "excess process MSA's." It corresponds to that capacity of the process MSA's to remove pollutants which cannot be used because of thermodynamic infeasibility. According to the designer's preference or to the specific circumstances of the process such excess can be eliminated from service by lowering the flow rate and/or the outlet composition of one or more of the process MSA's. Finally, the vertical distance of the waste composite stream which lies below the lower end of the lean composite stream corresponds to the mass of pollutant to be removed by external MSA's. External MSA's can then be screened based on the cost of each external MSA per unit mass of VOC removed.

Regards,

Prem Baboo

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