How tire pyrolysis works

Tires are primarily composed of rubber (such as natural rubber and styrene-butadiene rubber), which is composed of long, complex hydrocarbon molecular chains (polymers). When heated to a high temperature in an oxygen-free environment, the chemical bonds within these polymer chains break, breaking them down into smaller molecular weight gases, liquids (oils), and solid residues.

Tire pyrolysis primarily proceeds through the following stages:

1. Pretreatment Stage

Tire Crushing: First, the entire scrap tire is cut into small pieces (typically 2-5 cm square) using a crusher to increase the heating surface area, ensuring more uniform and efficient pyrolysis.

Wire Separation: Most of the steel cord is separated by a magnetic separator and recycled as a by-product.

2. Feeding and Sealing: The processed tire pieces are fed into the main reactor (pyrolysis furnace) through a sealed feeding system.

3. Pyrolysis Reaction Stage (Core Process)

Low-Temperature Stage (below 200°C): This primarily involves the evaporation of moisture from the tire. Volatile Release Stage (200°C - 450°C): Volatile components such as plasticizers and additives in the rubber begin to precipitate.

Main Pyrolysis Stage (450°C - 650°C):

In this temperature range, the long molecular chains of the rubber begin to break on a large scale.

Oil and Gas Generation: The breakage produces a mixed vapor of smaller molecular weight hydrocarbons (i.e., pyrolysis oil and gas).

Carbon Black Generation: At the same time, some fixed carbon, along with carbon black fillers and inorganic materials from the tire, remains, forming solid carbon black.

Steel Wire Melting: The remaining steel wire is melted and collected at the bottom of the furnace.

4. Product Collection and Separation

The high-temperature mixed oil and gas exiting the reactor enters a multi-stage condensation and separation system:

Condensation: The oil and gas first enter a condenser (usually multi-stage) where they are rapidly cooled by cooling water.

Liquidation: The liquefiable portion condenses into a dark brown or black, viscous pyrolysis oil (tire oil), which flows into a storage tank. Non-condensable gases: Light gases that cannot be condensed (primarily composed of methane, ethane, hydrogen, and carbon monoxide) are collected as non-condensable combustible gases.

Gas recycling: These non-condensable combustible gases are typically returned to the reactor's combustion chamber and used as heating fuel, making the entire system energy-self-sufficient and significantly reducing external fuel consumption.

Solid discharge: After the reaction is complete and the system cools, the generated carbon black and melted steel wire are removed separately. The carbon black can be further processed (grinding, pelletizing) and sold.