Question

A steam power plant operates on a theoretical reheat cycle. Steam at boiler at 150 bar, 550°C expands through the high pressure turbine. It is reheated at a constant pressure of 40 bar to 550°C and expands through the low pressure turbine to a condenser at 0.1 bar. Draw T-s and h-s diagrams. Find : 

(i) Quality of steam at turbine exhaust ; 

(ii) Cycle efficiency ; 

(iii) Steam rate in kg/kWh.

Answer 1

From Mollier diagram (h-s diagram) : 

h₁ = 3450 kJ/kg ; 

h₂ = 3050 kJ/kg ; 

h₃ = 3560 kJ/kg ; 

h₄ = 2300 kJ/kg 

h_f4 (from steam tables, at 0.1 bar) = 191.8 kJ/kg

(i) Quality of steam at turbine exhaust, x₄ : 

x₄ = 0.88 (From Mollier diagram) 

(ii) Cycle efficiency, η_cycle :

(iii) Steam rate in kg/kWh :

Steam rate