2.5 kg s-1 of a solution at 288 K containing 10 m % of dissolved solids...

  

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2.5 kg s-1 of a solution at 288 K containing 10 m % of dissolved solids is fed to a backward - feed double effect evaporator operating at a pressure of 20 kN m-2 in the second effect. If the product is to consist of a liquid containing 68 m % of dissolved solids and dry saturated steam is fed to the steam coils in first effect. The surface of each effect is 50 m2 and the overall heat transfer coefficients are 1.7 and 2.8-kW m-2 K-1 in the first and second effect respectively. Assume that the concentrated solution exhibits a boiling-rise of 5 K, that the latent heat has a constant value of 2260 kJ kg-1 and that the specific heat capacity of the liquid stream is 2.05(1+) kJ kg-1K-1. (a) what should be the pressure of the inlet steam to the first effect? (b) If this process is operated in forward feed the steam efficiency 1.50kgvapor/kginletsteam. Does the steam efficiency have improved in backward feed mode? Give reason. 2.5 kg s-1 of a solution at 288 K containing 10 m % of dissolved solids is fed to a backward - feed double effect evaporator operating at a pressure of 20 kN m-2 in the second effect. If the product is to consist of a liquid containing 68 m % of dissolved solids and dry saturated steam is fed to the steam coils in first effect. The surface of each effect is 50 m2 and the overall heat transfer coefficients are 1.7 and 2.8-kW m-2 K-1 in the first and second effect respectively. Assume that the concentrated solution exhibits a boiling-rise of 5 K, that the latent heat has a constant value of 2260 kJ kg-1 and that the specific heat capacity of the liquid stream is 2.05(1+) kJ kg-1K-1. (a) what should be the pressure of the inlet steam to the first effect? (b) If this process is operated in forward feed the steam efficiency 1.50kgvapor/kginletsteam. Does the steam efficiency have improved in backward feed mode? Give reason.

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