Calculating coal CO2 emission intensity (kg CO2 emitted/kWh delivered)

[darkPassenger]

Hi all,

Would really appreciate some help on this problem I can't seem to figure out.

Brown coal has an energy content of 15MJ/kg, carbon content 65% by weight, burning in a 30% efficient steam power plant. Calculate the CO2 emission intensity (kg CO2 emitted/kWh delivered).Assume complete combustion where all the available carbon in the fuel is converted to carbon dioxide gas.

Thanks in advance :)

 

[phyzguy]

You need to at least make an attempt before anyone will help you. What do you know and what have you tried?

 

[darkPassenger]

I'm getting confused about how the carbon content effects the efficiency i.e. the amount of energy obtained when the coal is burnt. Here's what I've come up with so far:

Brown coal: 15MJ/kg

Efficiency = power output/power input. --> 0.3 = x/15
x = 4.5 MJ. So after burning the coal we get 4.5MJ worth of useful energy/kg. Thus, 10.5MJ/kg is not useful. Would it be right to assume that this useless energy comes from the 650g of carbon in 1kg of coal? Don't know how to proceed after this.

Any help would be great, thanks :)

 

[Andre]

How much CO2 is produced from burning 0.65 kg Carbon?

What's the nuclear mass of carbon and oxygen?

 

[darkPassenger]

Ok so C + O2 --> CO2
After a quick mole calculation, with C:CO2 in a 1:1 ratio I get 2.38 kg of CO2 produced from burning .65kg of Carbon. Would the kWh (energy) delivered by burning this coal just be 4.5MJ or is it something else?

 

[phyzguy]

Ok so C + O2 --> CO2
After a quick mole calculation, with C:CO2 in a 1:1 ratio I get 2.38 kg of CO2 produced from burning .65kg of Carbon. Would the kWh (energy) delivered by burning this coal just be 4.5MJ or is it something else?

Yes, I think you're on the right track now. I think you're correct that burning 1 kg of coal produces 2.38kg of CO2 and 4.5 MJ of electrical energy. But you still need to convert 4.5MJ to kWh in order to get the final answer.