According to the U.S. Environmental Protection Agency (EPA), about 100 million pounds of tire components discarded during the manufacturing process are dumped in landfills nationally each year because the body ply – the tire’s largest component – can’t be effectively recycled. That is, until tire pyrolysis gains more of a foothold throughout the industry.

Pyrolysis of scrap tires offers an environmentally and economically attractive method for transforming waste tires into useful products, heat, and electrical energy.

As Salmon Zafar, chief executive officer of waste management consulting firm, BioEnergy Consult explained, tire pyrolysis is one of the most popular methods for disposal of scrap tires in many parts of the world. Tire-derived fuel (TDF) or pyrolysis oil is one of the largest applications of scrap tires in U.S., however, it is currently being challenged by crumb rubber due to the steep fall in oil prices in recent years. Cement plants are the biggest consumers of TDF in the country.

The EPA described TDF as a high Btu-value fuel with lower emissions, including lower greenhouse gas emissions than comparable traditional fuels, in a 2009 Advanced Notice of Proposed Rulemaking. In earlier studies, the EPA concluded, “With proper emission controls, burning tires for their fuel energy can be an environmentally sound method of disposing of a difficult waste.”

Klean Industries in Vancouver, BC, has been building and operating tire carbonization facilities at a scale north of 100 metric tons per day since the 1980s.

According to Marc Smith, business development and sales at Klean Industries, the recovery of valuable resources, such as tires, done in the right format delivers the highest possible returns both financially and environmentally, without the need for subsidies.

“Sadly, however, little money has been invested over the decades into new tire recycling methods and infrastructure, as the current market is largely supported by recycling subsidies that support a broken industrial model whereby the consumers have been paying for the downcycling of tires into lower value materials and or into a tire-derived fuel to only see tires be incinerated or landfilled,” Smith said.

Currently, Klean Industries is seeing a glut of low-value products on the market and a saturation of raw materials from tires that have a very low economic value.

“This saturation is also driving change in the marketplace as industry is now looking for more valuable products that have a wide range of applications in order to monetize the value position further while offsetting costs and delivering better returns,” Smith said. “The benefits of a circular economy are slowly coming to light and are now starting to be understood and acted upon.”

At Its Core

In the past, the main approach to tire disposal was to get paid for the disposal of tires with a secondary interest in the oil.

But as the environmental concerns surrounding tire disposal and recycling continue to emerge, tire pyrolysis is gaining momentum throughout the industry.

The pyrolysis method for scrap tire recycling involves heating whole, halved or shredded tires in a reactor containing an oxygen-free atmosphere and a heat source. In the reactor, the rubber is softened after which the rubber polymers disintegrate into smaller molecules, which eventually vaporize and exit from the reactor.

“These vapors can be burned directly to produce power or condensed into an oily type liquid, called pyrolysis oil or bio-oil,” Zafar said. “Some molecules are too small to condense and remain as a gas, which can be burned as fuel. The minerals that were part of the tire, about 40 percent by weight, are removed as a solid in the form of carbon black.”

According to Metso Corporation, a leading provider of tire pyrolysis, from a single tire, approximately one-third of the weight is steel, one-third becomes pyro black (carbon black plus additives) and the final third, pyrolysis system, are carbon black char, oil, steel, and non-condensable gases.

Metso’s tire pyrolysis process involves a pyrolysis reaction in which the chips go through three stages inside the kiln. First, the rubber becomes brittle and separates from the steel, resulting in rubber char. In the second stage, the oil and gas are forced from the rubber char and swept from the kiln. In the last tire pyrolysis stage, the char is fully processed into a carbon black-like substance and separated from the steel wires.

The char is sent through a processor to cool it and then sent to a grinding, pelletizing, and bagging system where it is packaged for transport. The steel is cooled and the steel wires are compacted and made available for transport to a steel recycler or steel-processing furnace. The Metso two-stage condenser system is where the off-gas is pulled through and the oil is extracted.

Metso Corporation developed its tire pyrolysis system to produce a high-quality carbon product that could be used in rubber manufacturing. As a result, the company’s plant design and recycling process follows the same principles as that of a chemical processing plant.

When performed well, the tire pyrolysis process is a very clean operation and has nearly no emissions or waste.

Diran Apelian, Alcoa-Howmet Professor of Mechanical Engineering at Worcester Polytechnic Institute, said tires are a great example of what can be done economically as long as there is a collection system in place.

“Rubber tires, when exposed to liquid nitrogen, undergoes a transformation and becomes brittle like a glass, and rubber tires can be pulverized, which are further reused as additives in highway surfaces, parks, stadiums, and many other surfaces,” Apelian said. “It’s a great way to recover and reuse the product at end of life.”

On the Horizon

The tire recycling industry in the U.S. is among the strongest and most diverse worldwide. In fact, according to Zafar most of states have their own laws regarding the disposal of waste tires along with environmental stewardship programs and highly developed end-products.

“The carbon black market has historically displayed a steady growth profile and there is increasing demand for carbon black from the tire industry and other end users,” Zafar said.

Smith said the industry is on the precipice of change on a global basis with respect to energy and raw material costs, specifically with the massive boom in population growth that is taking place around the planet. “We are going to see consumption habits and the volume of consumption significantly change over the coming decades. This then combined with the pressure on the environment is also going to create change,” Smith said. “We see nothing but significant growth in our future, and that’s not just in tire pyrolysis, but also in plastic recycling and creating energy from waste as a whole.”

Rubber Recycling Innovations

Recognizing the detrimental effect that discarded tires have on the environment, RVS Rubber Solutions, a student startup based at Case Western Reserve University, has developed a viable solution to this environmental hazard: A new technology that extracts the rubber and steel from within the components in a cost-effective and environmentally friendly way.

The brainchild of Pavel Galchenko, a Case Western Reserve sophomore studying biochemistry and applied data science, and Yohann Samarasinghe, a sophomore studying nanoengineering and business at the University of California, San Diego, RVS Rubber has developed a process to repurpose the rubber within the material, reducing and potentially eliminating waste, while providing rubber products manufacturers with high-quality material to make them less dependent on environmentally harmful virgin rubber for a range of applications.

Here’s how it works: RVS Tech induces vibrations within the plies to break the rubber off the steel to create an almost perfect separation of the base components. This is also done without degrading the quality of the rubber, resulting in various reusable applications in the consumer marketplace.

RVS Rubber Solutions expects its technology to revolutionize the rubber recycling process.

“We recycle the component materials from tires rejected during their manufacturing in a very cost-efficient process,” Samarasinghe said. “We are a ‘negative-waste company,’ meaning we are actually reducing the amount of waste material entering landfills from other producers by reintroducing the rejected tire component into the consumer market after our RVS Tech has processed it.”

By Maura Keller