Using pyrolysis to deal with waste tires is arguably the most economical and environmentally friendly solution.
My family recently started a company (Eneform) to find a commercially viable solution to waste tires. Although it’s not a well-known problem, it is a big one. There are about 1 billion tires that go to waste every year. There aren’t many ways to responsibly dispose of tires but the most promising solution seems to be pyrolysis.
To quickly summarise pyrolysis - you put the tires in a vacuumed chamber and heat them to around 500 degrees celsius. The heat causes the tires to break down into 4 useable products: diesel, LPG, steel, and carbon. All of these products are commercial grade; the carbon can actually be used to make new tires. Even the heat is generated from the waste tires. You can sell the outputs directly or you can use them to generate power which can be sold back to the grid.
Pyrolysis has been used successfully in several industries. Eneform has improved it by making it a continuous cycle (like a factory line) rather than a batch process. The outputs are cleaner and more consistent using this method. The system also combines many smaller pyrolysis systems together (rather than using one large one). This means that the cost to start a site is low and then sites can scale up once they become commercially sustainable .
No good solutions
So why is this important? There are currently only a small number of ways to deal with end-of-life tires. Most of the tires are either stockpiled or sent to landfill. Tires in landfills can tear the liners which causes contaminants to leach into surface and ground water. Stockpiles harvest pests and are a huge fire risk. Surprisingly the most common cause of the fires are humans that want to retrieve the relatively valuable steel cable that is in the tires.
Other alternatives include:
This is a broad category and covers a number of different ways that waste tires can be used. These include: reuse as a base for new tires; asphalt and concrete aggregate; and construction of walls, roadways, houses, and artificial reefs. These options are seen as inefficient and are ultimately unsustainable with the increasing supply of waste tires. Also, due to their heavy metal and other pollutant content, tires pose a risk for the leaching of toxins into the groundwater when placed in wet soils.
Tire derived fuel (TDF) is composed of shredded tires, commonly mixed with coal or other fuels such as wood to be burned in concrete kilns, power plants, or paper mills. Tires produce the same energy as petroleum and approximately 25% more energy than coal. Historically, there has not been any volume use for waste tires other than burning that has been able to keep up with the volume of waste generated yearly. However, the use of TDF for heat production is controversial due to the possibility of toxin production.
Vulcanization is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur or other equivalent curatives or accelerators. Devulcanization is the reversal of this process to allow for the reuse of the materials. This technology has not produced material that can supplant unvulcanized materials. The main problem is that the carbon-sulfur linkages are not readily broken without the input of costly reagents and heat.
The value in a tire
There is a surprising amount of value left in a tire. The trouble is extracting that value economically and environmentally. While tire derived fuel goes a long way to accessing this potential, pyrolysis offers a much cleaner and efficient solution.
You can see there is a small quantity of pyrolysate is considered “waste”. While this waste could be used in heavy fuel burners, for financial purposes Eneform consider it a disposal cost. It is expected that this quantity will decrease in production when using a more efficient distillation column, but even so, the total waster for an average car tire has been reduced from 14kg to 420g. All other outputs are valuable.
The waste industry isn’t necessarily the sexiest, but there is more than enough room for innovation and entrepreneurship.