Question

A steam power plant operates on the Rankine cycle modified to include superheat. The steam leaves the superheater at a pressure of 40 bar and a temperature of 500oC. After expansion in the turbine, which has an isentropic efficiency of 82%, the steam exhausts into the condenser at a pressure of 0.2 bar. Neglecting feed pump work calculate :-

1. The Thermal Efficiency of the plant.

2. The specific steam consumption.

3. The required mass flow rate of steam if the power output is 10 MW.

4. Calculate the power required to drive the feed water pump

Answer 1

Given data is, pressure p_1 = 40 bar temperature T = 500 degree C eta = 82% p_2 = 0.2 from stream tables at 40 bar, t_2 = 500 degree C h_2 = 3443.72 kj/kg S_2 = 7.0881 kj/kg k at 0.2 bar form table 0.2 times 10^9 = 20 kpa T_3 = 60.09 degree C h_f = 25.13 kj/kg h_g = 2809.96 kj/kg S_f = 0.8313 kj/kg k S_g = 7.9090 kj/kg k S_2 = (S_f)_0.2 + (S_F_g) x x = 7.0881 - 0.8313/7.9090 - 0.8313 = 6.2568/7.077 therefore x = 0.584 Now, h_s = (251.3) + (0.884) (2609.96 - 251.3) therefore h_3 = 2336.35 kj/kg W_turbine actual = eta_icent (h_2 - h_3) = 0.82 (3443.72 - 2536.35) W_turbine = 908.04 kj/kg Thermal efficiency is eta_thermal = w_turbine - w_pump/h_2 - h_1 from steam tables S_4 = 0.8313 kj/kg k S_1 = 0.8313 kj/kg k w_pump = integral r dp

Answer 2

11.7. The heat-rejection system for a condenser of a steam power plant (Fig. 11-5) is to be designed for minimum first plus pumping cost. The heat- rejection rate from the condenser is 14 MW. The following costs in dollars must be included: First cost of cooling tower, 800A0.6, where A = area, m? Lifetime pumping cost, 0.0005w³, where w = flow rate of water, kg/s Lifetime penalty in power production due to elevation of temperature of cooling water, 270t, where t = temperature of water entering the con- denser, °C The rate of heat transfer frơm the cooling tower can be represented adequately by the expression q, W 3.7(w2)tA. GEOMETRIC PROGRAMMING 259 93°F Partly sunny A O O 4x a u 14:29 9/10/2564 404 ans prt sc delete