AD - Ratio Total Energy to Fuel Output Energy

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2 months 1 week ago #277 by rockb
Could someone please explain why for anaerobic digestion, the ratio of total energy to fuel output energy is multiplied by the emissions for fuel production on the "Upstream Results" HHV tab?

My understanding is that the ratio of total energy to fuel output energy considers the organic waste input in kg and multiplies it by the energy density of this waste. Why would adding a more energy-dense organic input cause more emissions?

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2 months 1 week ago #278 by rdo
The general answer to why adding a more energy-dense organic increases emissions is because we assume that all inputs cause an output. If coproducts or fuel are not increasing with increased inputs, then emissions must be.

What I suspect you're looking at is just confusing based on the way the model deals with the intermediate calculations. In many cases this calculation may look confusing because between Alt Fuel Prod and Upstream Results we would have broken the total out into NG/Diesel/Electricity/Biomass percents on Energy Use, so multiplying by the total energy later is just bringing things back to non-percent values.

However I'm not sure about your specific question. Could you point out the cell that is causing confusion, because I'm not entirely sure where you're looking based on the description. Thanks.

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2 months 1 week ago #279 by rockb
The particular cell is the Fuel production value for CRNG from Organic Waste on the "Upstream Results HHV" tab. (Cell BO11)

What sparked the question is that this particular facility is using effluent from pulping operations to feed into the AD. As a result, I believe the energy density of the organic waste put into the reactor is much lower than that cited on the Fuel Char tab. This results in the emissions being much higher than they should be. I believe the correct approach is to edit the energy density on the Fuel Char tab.

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2 months 6 days ago #280 by rdo
Yes, changing that on Fuel Char is likely the correct approach.

And I'll reiterate that you need not be too worried about that total energy value showing up. The basic format of most fuels on row 11 is as follows:

[(% of energy as NG) * (NG emis) + (% of energy as diesel) * (diesel emis) + ...] * (total energy)

Where each of the percent terms being of the form

(NG energy) / (total energy)

So overall the total energy just cancels itself out. There's obviously a bit more to the equations, but that's the bulk of it.

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