Purdue News

October 13, 2003

New scheduling method raises efficiency of electronics recycling

WEST LAFAYETTE, Ind. – An industrial engineer at Purdue University has created a method to increase the efficiency, profitability and capacity of recycling operations for electronic products such as computers and television sets.

The work also promises to open up a new area of research in a field known as scheduling.

More than 1.5 billion pounds of electronic equipment is processed every year in the United States, and the quantity of discarded personal computers is expected to rise substantially over the coming decade.

While these products contain valuable materials, including copper, aluminum and steel, they also harbor hazardous substances such as lead.

Although certain recycling centers specialize in electronic products, there is no software designed for the efficient scheduling of jobs within electronics recycling plants. Such scheduling methods are commonly used to improve production in manufacturing plants, but the goals are different for recycling applications, said Julie Ann Stuart, an assistant professor of industrial engineering at Purdue.

She has developed a method for improving the efficiency of electronics recycling by better managing the flow of incoming products from storage to disassembly.

"In recycling you have a different objective when you schedule jobs than you do in manufacturing, and you need different key measurements to achieve that objective," Stuart said. "We created the key measurements, and we identified the new objective, which may open up an area of research for a whole new class of scheduling problems."

Findings about the new approach are detailed in a paper appearing this month in the IEEE Transactions on Electronics Packaging Manufacturing, published by the Institute of Electrical and Electronics Engineers.

Scheduling is a field in which researchers develop methods to improve efficiency by carefully timing the sequence of tasks in an operation, such as a manufacturing process, in which a critical objective is to complete a product on time. Manufacturers are expected to meet "due dates," or deadlines for the delivery of products.

The priorities, however, are different in recycling; there is no due date, and it often doesn't matter how fast the final "products," raw materials such as copper and steel, are extracted from obsolete machines, Stuart said.

Far more important to the electronics recycler is keeping plenty of space continually available in an area of the plant where products are received and briefly stored immediately before they are recycled.

Electronics recyclers earn a portion of their income just for receiving shipments. Because the arrival of shipments is unpredictable, it is important to always have enough storage space available. If the receiving area – or staging space – is full, incoming shipments have to be turned away or stored in trailers, causing a loss of income or incurring trailer rental fees, Stuart said.

"The recycler wants to empty the staging space as fast as possible to receive more materials," she said. "That's important because they may receive three truckloads this week, one the following week, two the next week and so on."

Recyclers currently try to keep their staging areas as open as possible by first moving the products that can most quickly be taken apart. But that is not the best approach, according to the research findings.

In the new method, the largest products that can be quickly disassembled are the first to be moved out of the staging space. Stuart compared the size-based method with two other strategies, one in which the most valuable products are moved first out of the staging area and another in which the products that can be most quickly disassembled are moved first.

She found that only the size-based method improved the system significantly.

"Moving the larger objects with quick disassembly times first enables you to operate with a smaller staging area," said Stuart, who tested her method with models that simulate recycling operations. "We showed that using our scheduling policy could lower the required maximum staging volume by as much as half. If you are able to reduce the staging space from 30,000 square feet to 15,000 square feet, that represents a considerable savings in overhead."

With increased efficiency also would come greater capacity because the recycler would be able to process a greater number of products within the same space.

Stuart grouped products into families – such as computer monitors and central processing units, television sets, office and kitchen electronics – and she used the turnover rate of products in the staging space as a key measurement, or metric. To determine which objects to move first, she created a technique in which the average size of a product family is divided by the time it takes to begin processing that product.

"If you have large products that don't take very long to start disassembling and you start with those first, you are going to free up that space faster," she said. "This is very easy to implement because you determine an average size for such a group and an average time, and then you update those averages perhaps once a year. You can then use the size-based estimates for a year to schedule products at the recycling center."

Improving plant efficiency could become an issue in the future, as state and federal policy-makers consider how to control waste from electronic products. Certain electronic components contain hazardous materials, including mercury, lead and cadmium, making it important to recycle discarded computers so they are not dumped in landfills. The number of personal computers, televisions and other consumer electronics expected to become obsolete this decade may approach 3 billion units, according to the International Association of Electronic Recyclers.

The more than 1.5 billion pounds of electronic junk processed annually includes about 40 million discarded computer components like printers, monitors and CPUs, according to a report issued earlier this year by the association.

The association report estimates that about 1 billion units of obsolete computer equipment will become potential scrap between now and 2010, and about 3 billion units of consumer electronics will be junked during that time, including 200 million television sets. The increasing flow of e-trash is expected to drive a fourfold growth of the U.S. electronics recycling industry, currently made up of about 400 companies with more than 7,000 employees.

Currently, recycling computers and television sets is not required in most places. But if new requirements are instituted in the future, recyclers will face a significant challenge trying to manage the surging flow of high-tech junk.

"If it ever becomes law to recycle electronics, it would be a good idea to use this scheduling approach so that less costly, smaller recycling centers may achieve the same objective as larger ones," Stuart said.

The research was funded by the National Science Foundation.

Stuart began the work with her student Vivi Christina while she was a faculty member at Ohio State University and completed the research at Purdue. The paper will appear in the April 2003 issue of the monthly publication, IEEE Transactions on Electronics Packaging Manufacturing, which will be available in this month.

Writer: Emil Venere, (765) 494-4709, venere@purdue.edu

Source: Julie Ann Stuart, (765) 494-6256, stuart@purdue.edu

Purdue News Service: (765) 494-2096; purduenews@purdue.edu

Related Web site:
International Association of Electronics Recyclers

Note to Journalists: A copy of the research paper is available from Emil Venere, (765) 494-4709, venere@purdue.edu.

In recent years, growing quantities of end-of-life electronics have increased the amount of attention devoted to product recovery. Research on end-of-life electronics returns has primarily focused on manual disassembly operations. In this paper, we focus on the scheduling problem for a facility with staging, manual disassembly operations and bulk recycling. In bulk recycling, shredding or grinding reduces the size of the material fragments while magnetic, eddy current or other density separation techniques separate the material fragments. Unlike production, there are often no due dates in materials recovery processing. Recyclers can sell the recovered materials to material commodity buyers at any time. However, recyclers wait to accumulate a shipment of material to reduce transportation costs and meet minimum sales quantities. Another important difference between production and recycling is that manufacturers purchase raw materials while recyclers may be paid to receive products. When due dates do not apply to scheduling products for materials recycling and product receipts generate revenue for recycling services, we propose two new metrics: the staging space turnover and the shipment fill time. We use our metrics to analyze new scheduling rules for disassembly and bulk recycling and to evaluate their performance. Using discrete-event simulation models, we test our scheduling rules on seven product families, where product families are defined based on material composition and separation operations. Of the rules we test, the disassembly scheduling rule which ranks product families based on the ratio of product size to disassembly time (SDT) most quickly empties the staging space. Shipment fill time is less sensitive to our scheduling rules. Our results illustrate how a recycler can reduce incoming product inventory with a new scheduling rule.

To the Purdue News and Photos Page