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Question 14.3: A natural gas-fired condensing boiler has a heating capacity......

A natural gas-fired condensing boiler has a heating capacity of 76 kW. The fuel heating values are LHV = 48 MJ/kg and HHV = 54 MJ/kg. The boiler efficiency based on HHV is 0.858.

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1. Rate of fuel consumption in the boiler (Q_{b} = 48 kW and \eta_{b,HHV} = 0.88)

m_{\mathrm{f}}=Q_{\mathrm{b}}/({\mathbf{h}_{b,HH W}}{HH V})=76\mathrm{~kJ/s}/(0.88*54000\mathrm{~kJ/kg})=1.6\ast10^{-3}\mathrm{~kg/s}=5.758\mathrm{~kg/h}

2. Boiler efficiency based on LHV

\mathbf{h}_{\mathrm{{b,LHV}}}=\mathbf{h}_{\mathrm{{b,HHV}}}\mathrm{HH}\mathrm{V}/ \mathrm{LHV} =0.88*54/48=0.99=99\%.

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