For the feed stage of the column the material and the enthalpy-balance have to be adjusted accordingly. Three additional types of stages need to be considered at the dividing walls which are shown in Figure . A stage separated by a dividing wall is shown in Figure . We will assume that there is no heat transfer through the dividing wall. This means that we can consider a separated stage as two independent stages k and k and formulate the MESH equations given above for each one of them. Analogously a stage divided by more than one wall is modeled by more than two independent stages.