How do I use LCA to calculate CO2 from 1t of coke combustion, not just CO2 from producing coke

Question

I want to use openLCA to calculate the carbon emission of 1t pig iron, but I think the calculation result is wrong. 495kg of coke only produces 0.107kg of coke, which is not correct. 0.101kg of CO2 should be the CO2 produced in the process of producing coke. The carbon emission factor of coke should be 3tCO2/t coke, can someone tell me how to calculate the CO2 produced by coke combustion? I want to use openLCA to calculate the carbon emission of 1t pig iron, but I think the calculation result is wrong, 495kg coke only produces 0.107kg coke, which is not correct, right? 0.101kg of CO2 should be the CO2 produced in the process of coke production, and the carbon emission factor of COKE should be 3tCO2/t coke. Can someone tell me how to calculate the CO2 produced by Coke combustion?

Answer 1

Hello Honortao,

You need a process for comubstion of coke. What you have is the process for producing coke. A process in ecoinvent that shows combustion of coke is:

heat production, at coal coke industrial furnace 1-10MW | heat, district or industrial, other than natural gas | Cutoff, S

Be aware that this process uses energy as a reference unit. If you investigate backwards in the processes, it appears that 0,04 kg of hard coal produces 1 MJ of coke energy. Then scale this up to 495 kg, you get 12.395 MJ of coke. I dont know if this is realistic, but this would be the method to do it.

Furthermore, it seems like you are evaluating the resource consumption of producing coke, not the global warming potential. Resource consumption in many LCIA methods are measured in Sb-eq. You have to choose GWP in the dropdown menu over your results.

Comments

thanks a lot
this is really helpful
I want to calculate the amount of CO2 produced by burning Coke in a blast furnace rather than other industrial furnaces.
Can I use the carbon emission factor of coke multiplied by the amount of coke used to calculate the carbon emission from its combustion, and define it as CO2-fossil  in my output items
Looking forward to your reply

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Hello Honortao, i think the answer to your question has a technical nature.
Combustion of a fuel will always yield the same CO2, if the combustion is complete, and you ignore the surrounding system. So if you know that the blast furnace has a 100% complete combustion rate, then yes, you can use the carbon emission factor.
When you take the surrounding system into consideration, in a life cycle perspective, you can not just use the carbon emission factor. The machinery, ingnition energy, auxilliary materials, etc. also need to be considered and they can vary a lot based on technology.

Short answer: You can use the carbon emission factor if this process is of low importance to the whole system, or if it is impossible to find better quality data. If it is important, and it is possible to find secondary data, i would use this data. Normally i would recommend using the given process as a proxy, but if you specifically are assessing one technology against another, then of course it doesnt make sense.

I hope this helps.

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thanks a lot
i can not search the given process-coke combustion in the blast furnace as a proxy

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Okay. Then i hope it is possible for you to find secondary literature to support your analysis. If this is not possible you will either have to gather primary data, usually in cooperation with a company, or use proxy data with a lower data quality.
The most important thing is that you reflect on the quality of the data points, and the sensitivity of the results, in the interpretation of the analysis.
Good luck