The key is extracting stored energy out of the waste products ("feedstocks") in a usable form, rather than just dumping the stuff in a river or landfill to decompose and release its energy over long periods of time.
Numbers from the Missouri plant: the total inputs into the system per hour are feedstocks (122.9 million BTU) and outside electricity (3.6 million BTU). Outputs include natural gas (1.4 million BTU), light crude oil (99.5 million BTU), and carbon (6.4 million BTU). There's also additional natural gas produced that feeds back into the system.
The total energy input into the system is 126.5 million BTU/hr, while the total energy output is 107.3 million BTU, which is 84.8% efficient. (They have additional plans to use water vapor to help heating that could increase efficiency to 90%.) However, when subtracting the energy input from the feedstock, I calculate 2980% efficiency (nearly 30x) as compared to the amount of outside energy added to the system.
If you treat the carbon as a mineral output, instead of an energy output, the total efficiency is 82%, and the efficiency with regard to outside energy is about 2800%.
I read this as a net energy loss. Looks the same to me as the ethanol story. If the primary purpose of the plant is really to get rid of waste then this isn't such a bad thing - I guess, Still you have to get rid of the residue from the process. This plant isn't waste free. I just translate "thermal depolymerization" as "baking garbage"
I just can't help thinking that it's sucking down 19 milBTU/hour to burn garbage. I just wonder how cost effective it is compared to dumping the stuff in a land fill? The only way this is going to continue is if they can get people to pay them to get rid of their garbage.