Shredder switch: a number of shredder operators are switching from diesel engines to electric motors.

Natural gas and diesel engines are utilized on many small to medium shredders, typically on 60-inch to 80-inch size mills. There are also some installed with 98-inch mills.

Companies chose gas engines because they were cost effective, based on energy costs at the time of purchase, and/or because electrical power was unavailable.

A typical configuration would utilize two 1,750-hp, 1,100-RPM engines, mechanically mounted in parallel. This configuration requires sheaves, belts and jackshafts to lower the speed to 600 to 700 RPM, which is ideal for a 60-inch or 80-inch mill.

THE GOOD AND THE BAD

Many companies are looking for alternatives to existing gas engine shredder drives for several reasons:

* High fuel costs;

* Volatility in fuel prices;

* Substandard productivity; and

* High maintenance cost.

Among the alternatives that such companies are turning to are electric motors, which in today's business climate can offer a number of advantages:

* Energy cost savings--Although fuel costs and electricity costs vary in different areas, you are likely to see dramatic energy savings;

* Energy price stability--Electricity prices are generally much more stable;

* Better productivity--Electric motors have an overload capability that allows them to work through loads, while gas engines will sag;

* Lower maintenance costs; and

* Lower environmental impact.

There are two types of electric motors commonly used on shredders: alternating current (AC) and direct current (DC). Both can offer advantages and disadvantages.

AN AC OVERVIEW

Some advantages of the AC motor include:

* Only practical choice for 120-inch super shredders;

* Good overload capabilities;

* Very commonly used in the shredder industry; and

* New motors available in any HP/ speed.

Some operators have also discovered disadvantages to AC motors:

* High inrush with load causing lights to flicker in the neighborhood from high demand charges;

* Long lead times

* Motor brush maintenance; and

* Liquid rheostat maintenance and cooling water requirements.

DC DATA

Vendors and users of DC motors cite some of the following advantages:

* Lowest initial cost, 4000 HP and below;

* Short lead times;

* Preferred by power company because of the limit power spikes on load; and

* Better control--run at any speed, jog forward and reverse to clear jams.

DC motors also have their limitations and disadvantages. For instance, DC motors require motor brush maintenance and they are not available to power super-sized shredders.

RETRO POWER

As providers of DC motors, Quad Plus Inc., Joliet, Ill., has found a market serving recyclers and shredder manufacturers who believe DC motors are a good fit in shredder retrofit projects when gas engines are being replaced.

The advantages of DC systems in these cases line up with the goals of people who want to replace their gas engines.

DC motors are only available in a 4,000-hp and below configuration. But since almost all the gas engines in use are coupled with 80-inch and smaller mills, this horsepower is perfect. With the overload capabilities of an electric motor, yards can expect to see significant performance gains.

When doing a retrofit, it is all about return on investment (ROI). With a low initial cost, this type of retrofit can pay for itself very quickly in energy cost savings alone.

When ordering a new shredder, the shredder itself can take 40 or more weeks to deliver, so a long lead time on the AC motor doesn't delay the project. But with a retrofit, having a 12-to-16-week lead time on a DC system can help keep the timeline in place.

Many sites put in gas engines originally because the power company would not allow the yard to put in an AC motor at the time. Because of the lower power spikes under load, DC systems can be installed in many places the AC motors cannot. Note that the DC system usually does not require line upgrades from the power company or expensive power correction equipment.

CASE HISTORIES

Several auto shredding plants have recently been retrofitted to accept DC motors in place of diesel or natural gas engines that formerly powered them.

* In 2004, Darlington Shredding in Darlington, S.C., had an 80-inch mill that was powered by two 2,200-hp diesel engines. The company was looking for more horsepower and converted to two 2,500-hp DC motors. The motors are direct-coupled in series to the mill. The company's operations personnel say they have experienced a dramatic increase in productivity and a decrease in energy costs.

* In 2005, Atlantic Scrap decided to replace two 1,750-hp natural gas engines at its Smithfield, N.C., shredder yard. The engines had been powering a 94-inch mill. Now, two 2,300-hp DC motors power the shredder. The company kept its belt and sheaves so it could run the mill faster and produce more horsepower. Low cost and short delivery were key components to its decision to go with DC. Company managers report a dramatic increase in productivity and a decrease in energy costs.

* At Nichols Aluminum in Davenport, Iowa, the company decided to replace two 1,750-hp natural gas engines on its 80-inch mill in 2006. Nichols selected a system with two 2,500-hp DC motors. The motors are direct-coupled in series to the mill. When Nichols made the decision, its plant had lost one engine. The company had a spare and was running on this. However, when the company factored in the cost of overhauling the engine and energy savings, the payback for the DC system was calculated to take slightly more than one year. This does not count the increased productivity they expect.

The author is the recycling industry manager for Quad Plus Inc., a supplier of DC shredder drives. He can be contacted at [e-mail].