Problem 12.2: What is the maximum number of cycles allowed

From Chapter 12 Problem Set. Level 3: Optimization.

Question

What is the maximum number of cycles allowed by the alkalinity limit?

Answer

Show answer

Evaporation removes only pure water – dissolved solids cannot evaporate and remain behind in the tower. This is why concentration increases even though no solids are being added beyond what arrives in the makeup. Blowdown removes concentrated water, carrying dissolved solids out of the system and relieving the accumulation. The water treater controls blowdown because evaporation is fixed by the heat load – it cannot be reduced without reducing the cooling demand itself. Blowdown is the only controllable mechanism for managing how concentrated the tower water becomes.