Single-effect Evaporators: Example Problems
Try to solve these problems before watching the solutions in the screencasts.
Example Problem 1
A 5.0 wt% sugar solution at 110ºC and 2.0 bar is feed to a single-effect evaporator that operates at 1.0-bar pressure. The evaporator is heated by saturated steam at 140ºC. The overall heat transfer coefficient is 2 kJ/(m2 s K) and the heat transfer area is 56 m2. What feed flow rate of sugar solution can be processed in order to concentrate the sugar to 8.0 wt%. What steam flow rate is needed if it all condenses to saturated liquid? What is the steam economy (kg water evaporated per kg of steam condensed)?
Example Problem 2
A 1.5 wt% aqueous salt solution is concentrated to 4 wt% in a single-effect evaporator. The feed rate to the evaporator is 7500 kg/h and the feed is at 85ºC. The evaporator operates at 1.0 bar. Saturated steam at 170 kPa heats the evaporating solution. What heat transfer area is required if the heat transfer coefficient is 2500 W/(m2 K). List all assumptions.