Problem 132

The calculation of stoichiometric relations is surely a very simple example for the first part of material flow management. The next part is the study of the main mass balances, i.e. the foundation for process optimization.

For this problem, the flow rates and inlet concentrations for three effluent streams are given in Table 13.4 (Wang and Smith 1994). The total flow rate is 90 m3 h-1.

The limit effluent concentration must be ce = 20 mg L-1 DOC. Only a part of this wastewater is to be treated to a removal degree of a = 0.99 and as low a flow rate as possible should be treated. The composite curve with the three wastewater streams is shown in Fig. 13.14.

The total mass flow rate in the influent is Qcin = 17.8 kg h-1 DOC. The limiting wastewater stream line goes through the pinch (0.1/5.8) and forms two similar triangles with the ordinate and abscissa of Fig. 13.14.

Calculate the limit flow rate of the treated water and design a network for the water system.

Table 13.4 Wastewater streams for Problem 13.2 (Wang and Smith 1994).

Stream No. Flow rate Concentration j Qj C

0 0

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