Question

A fuel with the composition of heptane (C7H16) is burned in an electricity-generating plant, with efficiency 36%. If the fuel has a specific energy of 26 MJ/kg, calculate CO2 emissions in units of kg/MJ electricity produced.

Answer 1

the combustion of heptane is given by the equation

C7H16 + 11 02 ----> 7 C02 + 8H20

from the above

reation

theoretical moles of C02 produced = 7 x moles of C7H16

we know that

efficiency = ( actual / theoretical ) x 100

so

36 = ( actual moles of C02 / 7 x moles of C7H16 ) x 100

actual moles of C02 = 2.52 x moles of C7H16

we know that

mass = moles x molar mass

so

mass of C02 produced = moles x molar mass

mass of C02 produced = 2.52 x moles of C7H16 x 44

also

moles of C7H16 = mass of C7H16 / molar mass of C7H16

so

mass of C02 produced = 2.52 x mass of C7H16 x 44 / 100

mass of C02 produced = 1.1088 x mass of C7H16

now cosnider specific energy

specific energy = energy / mass of C7H16

mass of C7H16 = energy produced / specific energy

so

mass of C02 produced = 1.1088 x energy produced / specific energy

mass of C02 produced / energy produced = 1.1088 / specific energy

mass of C02 produced / energy produced = 1.1088 / 26

mass of C02 produced / energy produced = 0.0426

so

mass of C02 emmitted is   0.0426 kg / MJ of electricy produced