Example 13.1 Water minimization for acrylonitrile (AN) production

Water minimization case study of the AN process (El-Halwegi, 1997) in Examples 2.1, 3.1, and 4.1 is revisited here. The limiting water data for the problem are given in Table 13.1 (reproduced from Table 4.2). Assuming that pure freshwater is used, determine the following RCN targets using the ATM:

1. Minimum freshwater and wastewater ¤owrates 2. The pinch concentration and the pinch-causing source


The four-step procedure is followed to formulate the ATM for the AN case study:

1. Construct the cascade diagram, with all quality levels (qk) of process sinks and sources arranged in descending order. When the quality levels for fresh resources do not coincide with any of the process sinks and sources that are present, additional levels are added. An arbitrary value is also added at the ‡nal level qn (lowest among all quality levels) to allow the calculation of the residual impurity/ property load.