Question

In a steam generator, the feed water supply rate is 205 kg/h, and the rate of coal-fired is 23 kg/h. The net enthalpy rise of water for conversion to steam is 145 kJ/kg. If the calorific value of coal is 2050 kJ/kg, the steam generator efficiency will approximately be:
1. 42%
2. 72%
3. 52%
4. 62%

Answer 1

Correct Answer - Option 4 : 62%

Concept:

Steam generator efficiency:

\({\eta _{steam\;gen}} = \frac{{{m_w}{h_w}}}{{{m_f} \times {C_v}}} \times 100\)

m_w, m_f = mass of water and fuel

Δh_w = change in enthalpy of water

Calculation:

Given:

ṁ_w = 205 kg/hr, ṁ_f = 23 kg/hr, h_w = 145 kJ/kg, C_v = 2050 kJ/kg.

\({\eta _{steam\;gen}} = \frac{{{m_w}{h_w}}}{{{m_f} \times {C_v}}} \times 100\)

\({\eta _{steam\;gen}} = \frac{{{205}\;\times\;{145}}}{{{23} \;\times \;{2050}}} \times 100\%=63.04\%\)