Heat in openLCA negative CO2 emission

Question

Hi! I am trying to model the heterotrophic fermentation of microalgae to produce biogas. In my project, biogas is used for heat production through combustion. I've used it as a source of thermal energy for other processes. The database I used is ecoinvent_3.91 (cut-off), and the Life Cycle Impact Assessment (LCIA) method I employed was openLCA - CML-IA baseline. When I ran my system, I was very surprised to see that I had negative emissions, primarily due to the avoided heat production. The negative emissions from the heat were much larger (on an absolute scale) than the positive emissions from the glucose being fed to the microalgae. As a result, the total CO2 emissions are negative. Just wanted a sanity check to see if this is correct. Does avoiding heat typically result in such a significant credit?

Answer 1

Hi, the credits for the avoided heat (via system expansion) depend of course on what you set as provider, i.e. from which production heat would otherwise come if not from your process. Often, heat from gas is used, which can have a large effect. To get a more detailed answer, you could post a screenshot of your process or processes that you modeled.

Thank you, Andreas