Question

A steam power plant receives heat from a furnace at a rate of 300 GJ/h. Heat losses to the surrounding air from the steam as it passes through the pipes and other components are estimated to be about 16 GJ/h. If the waste heat is transferred to the cooling water at a rate of 140 GJ/h, determine (a) net power output and (b) the thermal efficiency of this power plant.

Answer 1

Answer:

Net Power output  144 GJ/h

$\eta = 51.41 %$

Explanation:

Given data:

Heat received = 300 GJ/h

                        $= \frac{300\times 10^9}{3600} J/s$

                        $= 77.78 \times 10^6 W$

Heat lost $Q_2 = 16 GJ/h$

Heat to the water $= Q_3 = 140 GJ/h$

Net Power output $= Q_1 - Q_2 -Q_3$

                  = 300 - 16 - 140

                   = 144 GJ/h

                   $=\frac{144\times 10^9}{3600} = 40\times 10^8 J/s$

thermal efficiency

$\eta = \frac{net\ power}{heat\ supplied}$

$= \frac{40\times 10^6}{ 77.78 \times 10^6}$

       = 0.514 = 51.41 %