A combined heat and power (CHP) plant fueled by a fuel oil with heating value of 40 MJ/kg generates 90 kW electricity and 180 kJ/s of useful heat. The overall efficiency (called energy utilization factor, EUF) of the CHP plant is 0.9. The two separate plants produce power with an efficiency ηel of

Question

A combined heat and power (CHP) plant fueled by a fuel oil with heating value of 40 MJ/kg generates 90 kW electricity and 180 kJ/s of useful heat. The overall efficiency (called energy utilization factor, EUF) of the CHP plant is 0.9.
The two separate plants produce power with an efficiency [latex]\eta_{el}[/latex] of 0.4 and useful heat with an efficiency [latex]\eta_{h}[/latex] of 0.85.
Calculate the fuel consumption rate of the CHP plant and the fuel savings compared to the separate power and heat production.

Accepted Answer

1. Fuel consumption rate of CHP plant ([latex]P_{el}[/latex] = 90 kW, [latex]Q_{u}[/latex] = 180 kJ/s)

[latex]m_{\mathrm{CHP}}=(P_{\mathrm{el}}+Q_{\mathrm{u}})/(\mathrm{EUF~{*}~H V})=(90+180)/(0.9\ {*}\ 42,000)=7.14\ {*}\ 10^{-3} \mathrm{~kg/s}[/latex]

2. Fuel consumption rate of two separate plants ([latex]\eta_{el}[/latex] = 0.4 and [latex]\eta_{h}[/latex] = 0.85)

[latex]m_{\mathrm{sep}}=(P_{\mathrm{el}}/\mathrm{h}_{\mathrm{el}}+Q_{\mathrm{u}}/\mathrm{h}_{\mathrm{h}})/\mathrm{HV}=(90/0.4+180/0.85)/42,000)=10.4\ {*}\ \,10^{-3}\,\mathrm{kg/s}[/latex]

3. Fuel savings of CHP plant

[latex]\Delta m_{\mathrm{sav}}=m_{\mathrm{sep}}-\,m_{\mathrm{CHP}}=(10.4-7.14)\ {*}\ 10^{-3}=3.26\ {\mathrm{*}}\ 10^{-3}\ {\mathrm{kg/s}}[/latex]

CHP requires 31.4% less fuel.

Question 14.5: A combined heat and power (CHP) plant fueled by a fuel oil w......

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