In a boiler, heat is transferred from the products of combustion to the steam. The temperature of the products of combustion decreases from 1100 C to 550 C while the pressure remains constant at 0.1 MPa. The average constant pressure specific heat of the products of combustion is 1.09 kJ/kg-K. The water enters at 0.8 MPa, 150 C and leaves at 0.8 MPa, 250 C. 

Determine the exergy destroyed for this process per kilogram of water evaporated.