A single-effect evaporator is used to concentrate 60000 kg h-1 of a 40 wt % NaOH  solution which is fed to the evaporator at 40°C.  The concentrated liquid is a 55 wt % NaOH  solution. Saturated steam at 3 atm is available for heating.  The vapour space in the evaporator  is at a pressure of 10 kPa.  The overall heat transfer coefficient is 2000 W m^-2 K^-1 Determine:

a)  the amount of vapour produced.  

b)  the area required for the evaporator.   Include clearly values of relevant properties.              
 
c)  the economy.