2.66 First, solve using only two of the constraints (1. salt concentration in washed pigment and 2. optimum washwater feed rate).

P2.66 Titanium dioxide (TiO2) is a major pigment in white paint. You are in product? charge of designing a washer for processing raw pigment. should be designed to handle 10,000lb/h raw pigment (40 wt%TiO2, 20wt% salt, and 40wt% water). In the washer, the raw pigment is mixed with washwater. Pilot plant studies show that the optimum washwater feed rate is 6lb washwater per lb raw pigment feed. 100% of the TiO2 in the raw pigment is recovered in the washed pigment. The washed pigment product leaving the washer contains 50wt%TiO2, and the salt content in the washed pigment must be no more than 100 parts salt per 1 million parts TiO2. The plant manager would like to dump the wastewater into a nearby river. The local water quality control regulatory agency will allow at most a discharge of 30,000lb/h at a maximum salt content of 0.5%. Draw a flow diagram. Complete a DOF analysis and state whether this process is completely specified. If the problem is incorrectly specified, explain how you might change the design to fix the situation. Clearly explain your reasoning. (Adapted from G. V. Reklaitis, Introduction to Material and Energy Balances