Mention thermal waste treatment and most people picture an incinerator. Pyrolysis works on a different principle: the waste is heated in a sealed reactor with no oxygen, so it cannot burn. Instead of flue gas and ash, it yields oil, gas and solid carbon, all of which can be put to further use.
What happens inside the reactor
Plastics and rubber are polymers: long chains built mostly from carbon and hydrogen atoms. Heat them to 400–600 °C with no air present and those chains start to break into shorter hydrocarbons. Chemists call this cracking, and it is the same principle refineries use to process crude oil.
At that temperature the shorter molecules vaporise and pass to a condenser, where most of them become a liquid: pyrolysis oil. The part that stays gaseous after cooling is pyrolysis gas. Left in the reactor is a carbon-rich solid, plus steel cord when the input is tyres.
Four steps in an industrial line
A continuous industrial line is built from modular containers and processes 700–1,000 kg of waste an hour. The process runs in four connected steps.
- Shredding. The waste is cut into small pieces that heat evenly and feed continuously; tyres go down to about 55 × 55 mm. Metals, glass and stone do not decompose, so they are removed first, and wet material lowers efficiency.
- Reactor. The shredded material passes through a heated, oxygen-free reactor, where the polymers crack into vapour and a solid carbon residue.
- Condensation. The vapours are cooled and condense into oil. The gas that does not condense is piped to the CHP unit.
- Combined heat and power. The CHP unit burns the pyrolysis gas to generate electricity and heat for the plant. This covers the line's own demand of about 380 kW, so no permanent grid connection is needed.
For smaller volumes there are compact batch modules that handle 1–3 t a day. Their reactors are heated by electric panels rather than burners, and the control system runs a dedicated programme for each material.
What comes out
The split of outputs depends on what goes in. For plastics, the mass balance is 63% oil, 34% gas and 3% carbon. Tyres yield less oil and more carbon, because they contain carbon black and steel.
- Oil is either a feedstock for petrochemical plants, which crack it back into monomers for new plastics, or a fuel for boilers and CHP units. Our article on chemical recycling of plastics follows the first route in detail.
- Gas runs the plant's CHP unit; surplus power and heat can go to the site or the grid.
- Carbon is used as a sorbent in filters, a concrete additive, an industrial raw material or a soil improver.
- Steel cord from tyres goes to steelworks.
Products registered under REACH can be sold as products rather than waste. The operator then trades a raw material instead of managing another waste stream.
How it differs from incineration and landfill
Burning is a chemical reaction between a fuel and oxygen. An incinerator burns waste in air, recovers the energy as heat or electricity, and leaves behind flue gas, ash and slag. The material itself is gone.
In a pyrolysis reactor there is no oxygen, so nothing can burn. The molecules simply get shorter, and the carbon and hydrogen stay bound in oil, gas and solid carbon, which can be processed, sold or, in the case of the gas, used on site for energy.
Landfill only stores waste. In the Czech Republic, each tonne of recoverable waste landfilled carries a statutory fee on top of the operator's price, rising from 1,600 Kč in 2026 to 1,850 Kč in 2029. From 2030, Act No. 541/2020 Sb. bans landfilling recyclable and recoverable waste, as we explain in our article on the Czech landfill ban.
| Route | What happens to the waste | What is left |
|---|---|---|
| Landfill | stored, material not used | waste in the landfill body |
| Incineration | burned in air, energy recovered | flue gas, ash and slag |
| Pyrolysis | broken down by heat without oxygen | oil, gas, carbon, plus steel from tyres |
Where emissions arise
The reactor is a closed system and releases no flue gas. The only emission point on the line is the CHP unit burning the plant's own pyrolysis gas, and it is subject to the same limits as any gas engine.
That source is assessed in the air-protection permit under Czech Act No. 201/2012 Sb., including a dispersion study. According to the technology manufacturer, pyrolysis oil also has up to 40% lower carbon footprint than the same feedstock made from crude oil.
The details always depend on the waste, its volume and the site. That is why our projects start with an analysis of the input material.
If you are weighing up what pyrolysis could do with your waste, see how we design, build and operate pyrolysis plants.