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Industrial pyrolysis process at Contec S.A.

Is pyrolysis better than gasification?

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The United Nations Environment Programme (UNEP) says global solid waste will increase from 2.3 to 3.8 billion tonnes between 2023 and 2050.

Industrial production and consumption patterns create ever-increasing waste, now considered a planetary crisis on par with climate change and biodiversity loss. Fortunately, we can solve multiple waste challenges by treating end-of-life products as resources instead of waste

Recovering materials and inherent energy from end-of-life products limits natural resource extraction, pollution, and climate change — protecting our environmental health.

In this article, you will better understand pyrolysis vs gasification, and how they are similar (and different).

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What is (tire) pyrolysis?

Pyrolysis is a thermochemical process for recycling end-of-life tires (ELTs) and plastic, industrial, and agricultural wastes.

It breaks down carbon compounds in solid materials at high temperatures of 300 to 850°C in an oxygen-free atmosphere. The lack of oxygen prevents combustion but decomposes complex carbonaceous material into simpler products.

According to Shah and others (2023), the pyrolytic products are as follows:

  • Solids account for 20-50 per cent of the products as char, which contains residual solids from the feedstock, and ash. 
  • Liquids (30-50 per cent) like tar and oil as a mixture of aromatic hydrocarbons. The heating value is 5-15 MJ/kg.
  • Syngas (20-50 percent) is a mixture of methane, carbon dioxide, carbon monoxide, hydrogen, and other volatile compounds. The heating value of this low calorific gas is 3-12 MJ/Nm3.

The pyrolysis process is endothermic and requires heat, which, as in Contec’s tire pyrolysis plant, is provided by the pyrolytic gas (which contains the basic components of syngas). When treated through pyrolysis, ELTs yield tire pyrolysis oil (TPO), recovered Carbon Black (rCB), pyrolytic gas, and recovered steel.

Pyrolysis of ELTs achieves a large reduction in waste, with little or no pollutants and emissions. However, pyrolysis isn’t the only thermochemical solution available for recycling.

What is gasification?

Like pyrolysis, gasification is also a thermochemical treatment. Through gasification, carbonaceous materials are partially oxidised into mainly gas products.

The oxidising agents can be oxygen, air, steam, or mixtures of these gases. According to Shah and others (2023), temperature can reach 800 to 1100°C when air is used as the agent. When pure oxygen is the gasification agent, temperatures can get as high as 1500°C.

Gasification can treat solid wastes like agricultural, industrial, municipal, and oily sludges, as well as, ELTs and coal. 

Pyrolysis is a necessary preceding step for gasification, as the complex hydrocarbons produced through pyrolysis, such as char, tar/oil, and gas, act as gasification feedstocks. Gasification heats pyrolytic char and tar to even higher temperatures, further breaking them down into methane, carbon dioxide, carbon monoxide, and hydrogen.

The product profile of gasification, according to Shah and others (2023), is as follows:

  • Solids account for 30-50 per cent of input weight and comprise metals and inorganic elements.
  • Liquids (10-20 per cent) are oil and tar.
  • Syngas (30-60 per cent) has high carbon monoxide and hydrogen fractions and more carbon dioxide than pyrolytic gas. The oxygen, as a gasification agent, produces syngas with a low heating value of 3-12 MJ/Nm3, while steam yields syngas with higher heating values of 10-14 MJ/Nm3.

Gasification is part of the pyrolysis process, but the similarities don’t end here.

Pyrolysis vs gasification: common points

The similarities in pyrolysis and gasification often cause people to confuse the two processes.

  • Both are thermochemical processes that break down complex solid wastes into simpler compounds.
  • Both produce valuable energy-dense products, such as syngas, bio-oil, and char, that can be used as fuels.
  • Gasification and pyrolysis, as recycling processes, reduce solid waste volumes and recover energy and materials with minimal pollution and carbon emissions.

That said, these are two different thermochemical processes, often used to achieve different results.

Let’s look at how they differ.

Pyrolysis vs gasification: differences

Despite the similarities between them, pyrolysis and gasification are different processes. Some of the main differences are:

  • Pyrolysis occurs without oxygen, while gasification is a partial oxidation process that requires oxygen as a gasification agent.
  • Pyrolysis temperatures are far lower than those used in gasification.
  • Gasification is always preceded by pyrolysis, acting only on the pyrolytic products. However, pyrolysis doesn’t need to be followed by gasification.
  • According to Durak, gasification can be combined with carbon capture and storage technologies to handle emissions, making it more environmentally conscious than pyrolysis alone.
  • Pyrolysis is better for treating plastic waste, as tar formation during gasification is an operational challenge that reduces gas yield.
  • Input materials significantly influence the composition and amounts of pyrolysis products, but this matters less in gasification, as it’s limited to differences in tar and char.

Which is better: pyrolysis or gasification?

Pyrolysis and gasification can have a low environmental impact.

  • Due to incineration’s high pollution and emissions, pyrolysis and gasification can be an alternative to waste-to-energy technologies.  
  • Both processes can significantly reduce landfilling and associated pollution problems.
  • Both processes can offer decentralised local solutions compared to landfilling or export.

According to Durak, pyrolysis and gasification each have strengths and weaknesses.

The choice of the recycling method depends on waste/feedstock availability, cost, and composition, as well as energy requirements, equipment availability, target products, and objectives of the waste treatments.

  • Each process produces syngas for electricity generation and char used for soil amendment.
  • The syngas from gasification are made into methane or liquid after further conversion to produce transportable and storable fuels. Pyrolysis oils, after refining, are used as liquid fuel or for electricity generation.
  • The liquid fuel from both processes acts as feedstock: gasification products are used to make fertilisers, while Tire Pyrolysis Oil is used to manufacture virgin Carbon Black.
  • Pyrolysis char is processed into rCB, an alternative to fossil-based tire fillers.

Pyrolysis can produce more energy per unit of waste treated than gasification. Gasification, on the other hand, can produce fuels from coal.

Tire pyrolysis at Contec

Pyrolysis and gasification can be used in sustainable manufacturing to reduce global dependence on fossil fuels for energy, fuels, and feedstocks. Commercialisation of the two technologies is underway.

Contec has one of less than five commercial pyrolysis plants in the European Union. The plant processes ELTs using a proprietary molten salt technology, Molten®, which Contec developed to make the process efficient and reduce safety problems commonly associated with pyrolysis. Contec uses a proprietary pyrolysis process to turn end-of-life tires into new commodities. Learn more about our process.

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