Battery Recycling and OR
Paper Summary: Closed-Loop Supply Chains for Spent Batteries by F. Schultmann, B. Engels, and O. Renz, Interfaces, November-December 2003
Germany has a “battery decree” that puts the responsibility on manufacturers and importers of collecting, sorting, and, if possible, reprocessing spent batteries. This paper focuses on portable batteries, as opposed to car batteries, industrial batteries, etc. The paper consists of two parts:
1. a flow-sheeting process model to study the impact of using spent batteries in the production of steel
2. a two-stage facility-location problem to optimize the reverse logistics for the spent batteries
The authors state that after sorting batteries, many companies are storing them in “special waste deposits”, not recycling them. This motivates the first part of the paper. Flow-sheeting allows for the simulation of chemical engineering processes including metallurgical ones. So this modeling tool is more from the engineering side than the OR side. Using it, the authors study the impact of increasing the amount of spent batteries fed into a type of steel production (EAF) on technical workings, emissions, and economics. They conclude that such recycling is feasible and will lead to higher steel production costs. They state that the increased costs are comparable to the disposal costs for the batteries, making recycling an appealing option. This claim seems to be a key finding of the paper, but the authors do not provide any supporting information. Details of the simulation are not included though some results are plotted.
The reverse logistics part of the paper contains a nice use of the facility-location problem, wherein spent batteries flow from collection points to sorting facilities to recycling facilities. The paper contains the details of the model in the Appendix (two-stage, mixed-integer linear program) along with maps of Germany indicating the locations of the solutions. Two scenarios are considered, the second of which lays out strategic solutions anticipating future needs.
Some other points:
The authors characterize this as “high-quality” recycling as opposed to “down-cycling”, since the batteries are being recycled into steel. But if the quality of the steel is reduced by incorporating batteries, and if the batteries contain rare metals that are then lost to future isolated use, I’m not sure if this is technically correct. See the book Cradle to Cradle (summarized on this site here) for more on these ideas.
In Germany in 2000, the number of batteries taken back was equal to 31% of the number of batteries sold. (Some batteries taken back that year may have been sold in previous years.) This has got to be at least ten times the level in the US.
The paper does not deal with the forward supply network at all.
Batteries can be sorted automatically to some extent, using various battery attributes, using a UV pigment found on many mercury-free batteries, with x-rays, etc.
To sum up, the operations research content of this paper is concentrated mainly in the formulation of a recycling collection process as a facility-location problem. This is a logical way to formulate the problem. Nothing specific to the recycling plays a role here; no application-driven methodology is introduced. It was interesting to learn about the flow-sheeting process model and concerns therein, though they may have been outside the normal domain of OR. In sum, I found it to be quite an interesting paper and would be interested to learn about what has happened since the paper was published in 2003.
Some quick scanning reveals that 1) the portable battery recycling rate in Germany increased to 39% in 2002, and 2) the EU is following suit with its own version of the legislation, effective 2008.