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How to heat oil out of plastics, tyres and oil shale: What is pyrolysis?
Chemical industry


Eesti Energia is establishing a carbon-neutral and waste-free chemical industry in Ida-Virumaa, which will be processing difficult-to-handle waste such as tyres and plastics together with oil shale into a new useful raw material.

We will replace the production of liquid fuels with the production of chemicals that are needed for making everyday products. This will help solve environmental problems by creating the ability to process all waste plastics and waste tyres generated in the Baltic States, together with oil shale, into chemicals.

We asked the Oil Shale Competence Centre of Tallinn University of Technology to show in the smallest and most tangible way how oil is produced from plastics, tyres and oil shale, later processed into chemicals. The same laboratory located in Kohtla-Järve with Taltech researchers proved that such a thing is even possible. Eesti Energia will start pyrolysis of waste tyres already in 2023; industrial tests with plastics will begin in 2022, meaning that the laboratory will be replaced with the plant.

1. Which wastes are suitable for Enefit's pyrolysis plants?

Waste tyres from which metal and textiles are removed and recycled. Tyres are crushed into small pieces for pyrolysis.

Waste plastics that cannot be recycled in any other way. The big advantage of Enefit’s plants over mechanical sorting and recycling is the possibility to reprocess a mixture of different plastics together with other waste.

By the way, the suitability of the blades of electric wind turbines for the pyrolysis process has also been proven, but future studies will show whether these will actually ever reach Enefit's plants. Recycling blades would help to mitigate the environmental impact of green electricity, as blades are mostly disposed of at the end of their life. There are no problems with recycling the rubber and plastic covering of artificial grass pitches either.

2. What happens to the collected waste before pyrolysis?

Plastic and tyre waste with oil shale are crushed before entering the pyrolysis unit (retort). The crusher is the size of a man in the laboratory, while as a small apartment in the plant. Waste tyres and waste plastics are shredded before reaching the plant.

An important stage is the drying of the raw materials, helping to ensure the flawless functioning of the process and the quality of the final product. While a drying oven is needed for this in the laboratory, the Enefit plant uses hot gas generated during pyrolysis to dry the raw materials, so the raw materials are “blow-dried” with large equipment.

3. How do we know how much plastic and tyre waste can be pyrolysed in a plant at once?

The laboratory of the Oil Shale Competence Centre first proved that tyres and various types of plastics can be pyrolysed separately, as well as in mixtures. The knowledge gained is tested on the next larger devices up to the plant in order to find the best “recipe”. In the first stage, the share of waste in the plant could reach 15 percent, but in the future, it is not excluded that the share of oil shale as a raw material in the chemical that becomes the final product will be less than half. But to get beyond the laboratory, the mixtures must be precisely measured.

4. How does pyrolysis work?

The precisely measured raw materials are carefully mixed in the laboratory and lifted into the most important device of the whole process – the retort. While in the laboratory it is no bigger than a coffee mug, the retort of the pyrolysis plant is 18 meters long and over 6 meters in diameter. In other words, it is a device about the size of a semi-detached house. Unlike in the laboratory, the retort in the plant rotates and mixes the raw materials itself.

Pyrolysis is a natural chemical process where the material is heated in a closed space with no access to air to a temperature where the material begins to break down into various new substances under the influence of added heat. In nature, this is how oil and gas are formed from the remains of living organisms in the earth through oil shale over millions of years. Humanity has known the process since at least the Stone Age when it learned to make tar and pitch from wood by heating it with no access to air.

5. How high does the temperature have to be to heat oil out of plastics, tyres and oil shale?

Very high! The temperature can rise above 500 degrees in the laboratory retort, but in the plant it is constantly up to 485 °C.

6. What is formed during pyrolysis?

The decomposition of organic material takes place along a specific path. The weakest bonds break first. Especially if some small volatile molecules are formed as a result of decomposition, such as methane, water, hydrogen sulphide, carbon dioxide. These form pyrolysis gas. Larger molecules are formed during further decomposition and separated from the pyrolysis mixture, but these are liquid under normal conditions, forming pyrolysis oil.