J

!When a significant portion of the column product is vapor, the |achievable energy recovery from the product is diminished, because j the dew point of vapor leaving the reflux drum in the two-stage ]

j system is lower than the dew point of vapor leaving the column j overhead in the conventional scheme. As a result, the savings from I condensing reflux at a higher temperature are offset by having to j condense the product at a lower temperature. Further, the reflux |drum temperature drops as condensation progresses, and this may limit | reflux condensation. For these reasons, the two-stage condensation I scheme is mainly suitable when the product is mostly liquid. !

Since the cost of the additional condenser is relatively high, the |

two-stage condensation method is most suitable to larger-scale units, j

In large-scale units, such as refinery crude columns, payouts of the i order of 6 months were reported (27,28).

HEAT RECOVER/

REflux/pRODuCT DRUM

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