March 2004

Turning Up the Heat on Scrap Tires
Energis LLC Creates Benefits Through Co-Processing; Commitment to Alternative Fuels/Raw Materials

Nearly 80% of the scrap tires generated in the United States each year are recycled. That means roughly 230,000,000 tires. If you’ve ever wondered where some of those scrap tires wind up, simply visit one of the ten U.S. cement manufacturing facilities of Holcim (US) Inc. currently permitted to co-process “tire-derived fuel” (TDF). Holcim (US) Inc. is a wholly owned subsidiary of Holcim Ltd. of Switzerland, one of the world’s leading suppliers of cement, aggregates, concrete and construction-related services.

At Holcim plants in Dundee, Michigan and Ada, Oklahoma, the giant kilns of the cement-making operation are fueled in part by the combustion of whole scrap tires. Tire-derived fuel offers an extremely efficient energy alternative to traditional fossil fuels such as coal. TDF is also an ideal, high-volume opportunity for disposing of one of the more difficult to deal with forms of waste today.

The blending of TDF with traditional fuels is part of a practice known as co-processing. Essentially, co-processing is a method of meeting the energy and raw materials needs of an existing industrial process with excess or waste by-products from different industrial processes.

Mario Romero is president of Energis LLC, a wholly owned subsidiary of Holcim (US) Inc. The unit provides co-processing services to Holcim and to businesses in a variety of other industries. “Holcim (then known as Holnam Inc.) took delivery of its first load of TDF in the early 1990s. This move came as part of Holcim’s involvement with research and consumption of alternative fuels and raw materials, or AFR, during the previous decade,” said Mr. Romero. “Today, nine of ten Holcim (US) cement plants permitted to co-process scrap tires as TDF are currently doing so. Two of the nine consume whole scrap tires. The other seven burn TDF in various chip or shred forms,” he added.

The perfect fuel
Making cement is an energy and fuel intensive process. As an alternative fuel, TDF is blended with fossil fuels to fire the kilns that melt limestone and other raw materials for cement. The molten slurry recombines into small stones called cement “clinker.” When it cools, clinker is ground to a powder and mixed with about 5% gypsum to become Portland cement.

“Co-processing scrap tires is an ideal source of energy for making cement,” said Mr. Romero. “The temperatures required for melting limestone demand a lot of fuel. Tire-derived fuel yields as much heat energy per pound as the best quality coal.”

While there are dozens of chemical elements, scrap tires are made up of essentially three components – carbon black, oil and steel. To make cement, the raw material temperature inside a cement-making kiln must reach close to 2,800 degrees F. Near the tip of the flames, temperature is closer to 3,500 degrees F. At that level of heat, scrap tires burn completely, leaving no trace of unburned material. The hydrocarbons that make up the rubber in TDF are no more complex or difficult to destroy than those of coal. In fact, many of the components of scrap tires actually become part of the finished cement product during combustion. Iron from the molten steel wire and belts for example, is a necessary ingredient of cement. “Our goal is to help Holcim produce the highest quality cement products in the world,” continues Romero. “Using scrap tires as fuel through co-processing helps us to achieve exactly that,” he said.

“At the same time, there are additional benefits of fuel cost savings, and a reduced dependence on virgin, fossil fuels. For every ton of scrap tires consumed, fewer raw materials are mined, and CO2 emissions are reduced. Of course, we can’t forget that use of tire-derived fuel keeps millions of scrap tires out of landfills, and from accumulating in places that may promote disease or environmental blight. This is where co-processing really makes sense. At present, TDF is, by far, the number one application for recycled scrap tires,” he said.

Feeding the beast
On average, tire-derived fuel can replace 5 – 25% of the heat energy requirements at Holcim’s U.S. based cement plants that use this fuel. In Europe, some Holcim installations burn as much as 80% TDF.

Tire-derived fuel is delivered to Holcim cement-making operations around the country in chip, shred or whole tire form. Some facilities burn higher grade, wire-free chip while others have different needs. At the Dundee, Michigan plant, a tipping platform off-loads bulk whole tires into a feed hopper. From the hopper, gravity delivers whole tires to a singulator, which deposits tires one at a time onto a feed conveyor. The conveyor moves a long line of whole tires several stories up to a covered platform on top of the kiln.

As the kiln rotates, a metering device weighs the inbound scrap tires and deposits a uniform quantity of TDF through a special hatch in the kiln. Every 70 seconds, as many as four whole tires are consumed. That’s an appetite of nearly 5,000 scrap tires every 24 hours.

There are 11 Holcim cement-making facilities in total across the United States. Nine Holcim plants currently using TDF or whole scrap tires receive the material from a network of regional suppliers. Through co-processing, Holcim converts nearly 15,000,000 scrap tires to heat energy each year.

Commitment to AFR
Holcim has been involved with alternative fuels and raw materials for more than 20 years. In addition to burning scrap tires, the company has adjusted its processes to accommodate 8 different alternative fuel types and 16 alternative raw materials. That’s where Energis comes in.

According to Mario Romero, “Energis coordinates the alternative fuels and raw materials programs at Holcim’s plants in the U.S., which use about 1.5 million tons of AFR. Three of those plants use hazardous waste-derived fuels such as used oils, solvents and paints. Others burn plastics, wood chips, fluids and even diaper trimmings.”

Alternative raw materials for cement-making include such things as foundry sand, mill scale and spent lime from wastewater treatment operations. “Our chemists ensure the AFR is suitable for our needs, and is consistent with the quality outcomes Holcim has established,” said Romero.

Without co-processing, these materials would have to be landfilled or otherwise treated before they were disposed of. Both options are much less desirable alternatives for the environment.

A key feature of the AFR policy at Holcim is the firm’s commitment to preserve natural resources and reduce the global impact of their activities. That means strict compliance with all regulations, the promotion of best practices and close monitoring and control of all processes and emissions. To that end, the company uses no radioactive wastes, bio-hazardous wastes or any material that may present a health or safety issue. Energis, and its predecessor facilities have gone nearly 25 years without a violation of any kind or a lost-time accident. Considering the scope and enormity of the operation – that’s impressive.

Mario Romero sums it up. “We are guided by a clear vision and dedication to ‘sustainable development’ – meeting the needs of the present without compromising the ability of future generations to meet their needs. Our involvement in co-processing and AFR is an important part of that long-term vision,” he said.