System-level co-products

Question

It appears it's not possible to see the resulting quantities of disconnected co-products when calculating a product system. So for example, if you have a process for gasoline combustion that you connect to an upstream refinery, you'll get the emissions from the refinery but not the amount of diesel that's co-produced with the gasoline. A result that's perhaps useful if you're just looking at system expansion. Or perhaps you might want to know the quantities to allocate at the system level rather than at the process.

Another use case would be a waste-to-product process, where a waste treatment process has a waste input flow and a product flow output.

As of now, it seems the only way you could get those co-product quantities is to convert them all into waste flows, so that they show up in the Outputs of an inventory result.

A colleague swears that this wasn't always the case - that the quantities for disconnected co-products in the system were shown in inventory results. Was there a change to this at some point?

Answer 1

Hi,

Interesting question. I hope that I understood you correctly.
In general, you will see the amount of product flow without a provider in the inventory of your product system. But this works for product flows on the input side. However, if it is in the output table, you will have a multi-out process that needs to be solved somehow. So, yes, there you will not see it because openLCA works with one reference flow and not two per process (product system). Also, "Another use case would be a waste-to-product process, where a waste treatment process has a waste input flow and a product flow output." -> delivers two functions (waste treatment and production of product XY) and hence requires allocation.

So in general, the disconnected flows are there. What you describe is an allocation issue as it is not possible to hold two reference flows as quantitative reference. All the LCA databases I am aware of solved the multi-output issues for you already and you only have one product flow as a reference.

Hope this helps

Comments

Well, I'm not exactly asking to have two reference flows. I want the one reference flow (say 1 kg of combusted gasoline) and then know how much of another co-product was produced in an upstream process (0.6 kg of diesel, at refinery). If that diesel was a "waste flow" then it would be shown, but since it's a disconnected product flow, the output quantity is never given.

I recognize the product flow from waste treatment process might be an oddity, and I suspect the matrix approach to solving these problems probably doesn't allow that.

For what it's worth, we used to get these co-product flows from the software formerly known as GaBi all the time. Most of it was unintentional and not necessarily helpful, but they were there. At the time, I think they used another calculation approach to solve the systems.