RNG from sludge

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2 years 8 months ago #177 by HBennett
RNG from sludge was created by HBennett
Hi,

I have been using the RNG from Organic waste pathway in GHGenius in place of there not being a WWTP sludge category. I am a bit confused as to what the organic waste methane emission factor (input tab F47) is being used for in terms of the emissions displaced co-product output in the Upstream Results HHV tab? What is this factor?

Also I wanted to make sure I am using the correct pathway by not using the RNG from manure pathway?

Thanks!

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2 years 8 months ago #178 by doconnor
Replied by doconnor on topic RNG from sludge
F47 calculates the avoided landfill emissions when the organic waste is processed to RNG rather than landfilled.

For sewage sludge, which probably isn't landfilled this cell should be set to zero.

You are using the correct pathway for this feedstock.

Regards
Don O'Connor

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2 years 8 months ago #181 by HBennett
Replied by HBennett on topic RNG from sludge
Hi Don,

Thanks for your response! That makes sense. I am also wondering why the fuel production cell BM11 on the upstream results calls on the equipment emission factor for AD which corresponds to the alt fuel production BT28 instead of BU28. I changed my input feedstock ratio to match my data but because this cell is calling on data from the manure pathway for AD instead of organic waste it gives me higher emissions. I tried changing the manure inputs to match mine which gives me a value that makes more sense but it is still calling on the fuel characteristic value for generic grass instead of organic waste making the values in Alt fuel prod BT28 and BU28 not the same. Should I change BT28 in Alt fuel prod to call on the organic waste fuel characteristic value?

Thanks!

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2 years 8 months ago #182 by doconnor
Replied by doconnor on topic RNG from sludge
The issue you point out is effectively that there is a column on Equip Emis Factors for AD to SG, but not for organic waste to SG. This leads to cell BX22 having some formula references to 'Alt Fuel Prod'!BT28, which is AD to SG, but contributing to BX25 which is used in the organic waste pathway.
Under most circumstances this is a non-issue. The equation in BX22 is multiplied by zero unless sequestration is applied. Over the years this sort of situation is probably the most common fix we have made in the model: a number that is zero is calculated wrong but still comes out to zero.
If sequestration is turned on then this could be an issue. If that's the case then

=('Fuel Char'!F141/'Fuel Char'!$K$141*1000000-BX13*0.75-BX14*0.4286-BX11-BX18*'Misc Fuel'!$A$116-1000*'Fuel Char'!F118*'Fuel Char'!D118/('Alt Fuel Prod'!BT28*'Energy Use'!$K$57))*3.6641*IF(SEQUESTRATION2,-Sequestration!AS19,0)

should be changed to

=('Fuel Char'!F142/'Fuel Char'!$K$142*1000000-BX13*0.75-BX14*0.4286-BX11-BX18*'Misc Fuel'!$A$116-1000*'Fuel Char'!F118*'Fuel Char'!D118/('Alt Fuel Prod'!BX28*'Energy Use'!$K$57))*3.6641*IF(SEQUESTRATION2,-Sequestration!AT19,0)

The changes include references to the fuel characteristics of OW instead of AW (twice), changing the Alt Fuel Prod reference, and directing the fraction sequestered to SG from OW instead of from AD (both default to 85%).

We will look at adding a column to the Equip Emiss Sheet in the next version of the model.

Regards

Don O'Connor

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2 years 8 months ago #183 by HBennett
Replied by HBennett on topic RNG from sludge
Thank you Don that makes sense. I have sequestration off currently. Out of curiosity how do you turn it on?

This is the part of the expression in Upstream Results HHV Cell BM11 that I am talking about:
"'Energy Use'!BT$115*'Equip Emis Factors'!$BX25"

I am still a bit confused as eventually in the Equip Emis Factors sheet the cell BX81 is referenced for the AD pathway which uses the manure inputs and characteristics.
I want to know if I should change cell BX81 expression from:

='Fuel Char'!D118*Input!F46/'Alt Fuel Prod'!BT28*1000

To:

='Fuel Char'!D118*Input!F46/'Alt Fuel Prod'!BU28*1000

So that it references my fuels energy density in the fuel characteristics opposed to the manure one?

Thanks!

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2 years 8 months ago #185 by rdo
Replied by rdo on topic RNG from sludge
You would turn sequestration on by toggling Input!B69 to 1 instead of 0. That would turn it on for all alt-fuels.

You're totally right about BX81. Usually down there are raw text inputs so it slipped my mind to even check when I was drafting the response that Don posted. That would in fact make a difference even with sequestration turned off.

-Ryan O'Connor

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2 years 8 months ago #187 by HBennett
Replied by HBennett on topic RNG from sludge
Ok thanks I will just change it so it is referencing only the organic waste energy density.

For the carbon sequestration is there a way to turn on sequestration of carbon for application of organic fertilizer or sludge (like manure) to fields?

Or is sequestration in GHGenius just for carbon capture?

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2 years 8 months ago #189 by rdo
Replied by rdo on topic RNG from sludge
The sequestration only takes CO2 out of the fuel production step. That might be better modelled as a coproduct displacing some combination of fertilizers.

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