Question

Common Data:
Consider a steam power plant using a reheat cycle as shown. Steam leaves the boiler and enters the turbine at $4MPa,{350}^{o}C(h_3=3095kJ/kg)$. After expansion in the turbine to $400kPa(h_4=2609kJ/kg)$, the steam is reheated to ${350}^{o}C(h_5=3170kJ/kG)$, and then expanded in a low pressure turbine to $10kPa$$h_6=2165kJ.kg)$ the specific volume of liquid handle by the pump can be assumed to be



The thermal efficiency of the plant neglecting pump work is

• A. $15.8$%
• B. $41.1$%
• C. (48.5)%
• D. $58.6$%

Answer 1

The correct option is B $41.1$%

Given data:

$h_3=3095kJ/kg;h_4=2604kJ/kg$
$h_5=3170kJ/kg;h_4=2165kJ/kg$
$h_1=29.3kJ/kg$



Net work output per $kg$,
$w_{net}=(h_3-h_4)+(h_5-h_6)$
$(3095-2609)+(3170-2165)$
$1491kJ/kg$
net heat supplied,
$q_s=(h_3-h_2)+(h_5-h_6)$
$=h_3-h_1+h_5-h_4\because h_2-h_1$
$=3095-29.3+3170-2609$
$=3626.7kJ/kg$
Thermal efficiency,
$\eta =\frac{w_{net}}{q_s}=\frac{1491}{3626.7}$
$=0.4111=41.11$%