How to model avoided emissions

Question

Hi, 

I'm new on openLca and I'm trying to model a biogas upgrading system. It produces biomethane and it captures CO2 from the biogas. How can I model the avoided emission of CO2 and the avoided exctraction of natural gas that will produce the same amount of energy of the produced biomethane? I try adding them as negative output flows, but I'm not sure it is correct.

Many thanks in advance for your help

Best,

Melissa

Answer 1

Hi Melissa, interesting question, so input is biogas which consists of CO2 and Ch4 (and maybe other components) and output is biogas with a higher share of CH4 and less CO2? What do you do to reduce the CO2 content, do you have an absorber e.g.? Is the CO2 released elsewhere or bound, somehow? You do not model the creation of biogas probably?

How can I model the avoided emission of CO2 and the avoided exctraction of natural gas that will produce the same amount of energy

There are several possibilities, one would be to model three systems, natural gas, biogas "raw" and biogas CH4-enriched, for producing the same amount of heat, and compare them, you will then see fewer CO2 emissions from the CH4-enriched gas (assuming CO2 is truely bound). You should also consider leakages though.

I hope this helps! Best wishes, Andreas

Comments

Hi Andreas,
thank you for your answer.
From the experimental data, I know the composition of the biogas (input) and of the biomethane (output), also at trace compound level;  the quantity of CO2 that is captured and the energetic content of the produced biomethane.
The upgrading system uses wood ashes and the CO2 is trapped in solid form through chemical reactions. Then the ashes are disposed in a landfill (as it would have happened anyway).
I model the LCA with 1 kWh of biomethane as functional unit.
I'll try to do as you say.
Can I do only one LCA?

thank you for your time and help,
best wishes

Melissa