Carbon Footprint Calculation 1

[sheiko]

Hello people,

The following sentences are taken from a recent article from Hydrocarbon Processing Magazine that i have found interesting enough to be read:

"In quantifying relative CO2 emissions, it is surprising how much the carbon footprint can vary between processes (...)

Quantitative comparison requires defining an equivalent unit of CO2 emission for any form of energy expended. This is asiest done via fuel gas, where oxidation of 1 mole of methane (CH4) emits 1 mole of CO2. For other energy forms, equivalents must be calculated by more complex methods, as summarized in Table 1 (...)" <-- SEE ATTACHED

"All of these values are calculated rather conservatively. For example, generating electric power in a lignite-fired power plant requires more CO2 than in a gas-power plant and that too does not have more than approximately 40% efficiency. Actually, per kWh electric power, one can assume between 439 g CO2 /kWh and 1,306 g CO2 /kWh, which corresponds to 0.22 m³ CO2/kWh to 0.65 m³ CO2/kWh. For our calculation, we assumed 0.26 m³ O2 /kWh, i.e., a low value."

Could somebody explain the calculations in the table? I believe there are shortcut or maybe mistakes in the conversions...



"We don't believe things because they are true, things are true because we believe them."

 

[quark]

I am not sure about the unit consumption of various processes mentioned, as calculating them requires further details. Otherwise, the calculations are straight forward, with some calculation errors, though.

35200 kJ/Hr is 35200/3600 kW which is 9.78 kW (kW-Hr/Hr is a round about term and is equal to kW)

If 9.78kW energy emits 1 cu.mtr of CO2 then 40% efficiency plant emits 1 cu.mtr of CO2 per 3.912 kW. So, each kW emits 1/3.912 = 0.255 or 0.26 cu.mtr of CO2.

If 1 cu.mtr production of N2 consumes 0.2 kW then the CO2 emission is 0.2/3.912 = 0.05 cu.mtr (This is like if 3.912 kW emits 1 cu.mtr of CO2 then how much emission there will be from 0.2 kW)

1 cu.mtr of compressed air consumes 0.15 kW so CO2 emission will be 0.15/3.912 = 0.038 cu.mtr of CO2

Cooling water = 0.75/3.912 = 0.191 cu.mtr of CO2
Demin. Water (20% might be for blowdown, evaporation and drift losses which seems to be huge) = 0.75*1.2/3.912 = 0.23 cu.mr of CO2

For HP steam, it is latent heat + sensible heat of water. Latent heat is correct but sensible heat is a bit low (4.2*151 = 634 kJ/kg at lower temperature and 4.93*151 = 744 kJ at higher temperature). 1 kg/hr of steam emits (1678+744)/35200 = 0.0688 cu.mtr of CO2.

For LP steam, it is latent heat (difference of vapor and liquid enthalpies)

 

[moltenmetal]

Though the calc itself is relatively straightforward, the biggest problem with this sort of calc is how easy it is to either add ridiculous things to the calc or leave obvious things out. Whether you do one or the other tends to depend on your political objective in doing the calc...

Rather, I favour simply taxing the fossil fuels in the first place. Then no calcs are necessary: the most economical process is the one which wastes the least of these fuels, regardless whether the waste occurs in making starting materials, plant equipment etc., or in processing steps along the way. Of course that only works if everyone charges the tax, and hence is improbable.

 

[dcasto]

Molten, the carbon cap and tax rules has nothing to do with efficiency of the process. In the US our President says he will dismantle every coal plant before he is out of office. SO, coal makes more CO2 per BTU released than other fuels, we have to have the complex equations.

 

[sheiko]

Quark,

In "...each kW emits 1/3.912 = 0.255 or 0.26 cu.mtr of CO2."

Do you mean m3 or m3/h?


"We don't believe things because they are true, things are true because we believe them."

 

[sheiko]

Or...do you mean kW or kWh?

"We don't believe things because they are true, things are true because we believe them."