Turning waste into resources: The pyrolysis vs. incineration debate
Incineration is the most widely-used waste-to-energy process, however, innovative technologies like pyrolysis are gaining increased attention for being better for the environment. Tire pyrolysis is a technology that produces synthesis gas (syngas) and tire pyrolysis oil with various applications.
In this article, you can compare pyrolysis vs incineration to determine if pyrolysis is a better circular solution for your means, especially for reducing waste streams like end-of-life tires.
What is (tire) pyrolysis?
Pyrolysis is a form of thermal decomposition of carbon-containing substances, such as end-of-life tires (ELTs), wood, biomass, and plastics, when heated to high temperatures between 400 to 1000°C without oxygen. Lack of oxygen prevents combustion and allows complex carbonaceous material to decompose thermally into simpler products: low- to medium-calorific-value gases; liquids, oils, or tars; and solid char.
ELTs thermally decomposed through pyrolysis break down into syngas, pyrolysis oil, and char. This waste-to-energy technology can transform low-energy density materials into high-energy-density biofuels and high-value chemicals. The proportion of gas, liquids, and solids produced can be varied by changing the heating rate or temperature.
Pyrolysis reduces up to 100 per cent of waste in terms of weight and volume and can produce transportable and storable fuels. Moreover, the emissions and other pollutants released by pyrolysis are little or negligible.
What is (tire) incineration?
Incineration is the combustion of solid organic materials, like tires, in the presence of oxygen at very high temperatures, 850 to 1000°C. The process produces heat, flue gas, and ash.
Incinerators are generally large-scale and connected to steam boilers heated by combustion to produce hot steam that turns turbines to generate electricity. The partially cooled steam after rotating the turbines serves as a heat source for buildings or industrial uses. The process is inefficient; not all of the heat produces steam. Some heat is lost through flue gas and ash.
The ash is residual or bottom ash from combusted materials and fly ash from incombustible materials. The ash is a waste and has to be landfilled.
The flue gas from incineration contains carbon dioxide, water vapour, and nitrogen produced by burning carbon compounds. Depending on the material combusted, flue gas can also contain toxic pollutants like particulate matter, sulphur dioxide, nitrogen oxides, hydrogen chloride, dioxins, furans, and heavy metals like mercury and cadmium, which are hazardous to health.
Incineration decreases waste volumes by 80 – 90 per cent and helps reduce methane and other pollutants produced at landfills. By preventing methane production, every ton of waste incinerated prevents the release of one ton of carbon dioxide equivalent into the atmosphere.
Figure 1: An Incineration Plant (Image Credits: Use of Incineration MSW Ash: A Review)
Early incinerators were relatively basic and often burned waste without significant sorting or separating hazardous, bulky, or recyclable materials. Modern incinerators have improved furnace design and processes to ensure complete combustion, presorting of waste, and flue gas cleaning equipment that has reduced incinerator pollution.
Pyrolysis and incineration: what are the common points between them?
To compare these two waste-to-energy technologies, it’s necessary to consider the similarities and differences between incineration and pyrolysis. The common aspects of the two processes are listed below:
- Decomposition of Organic Matter: Both incineration and pyrolysis are methods for breaking down carbonaceous waste into different chemical compounds.
- Thermal processes: Both incineration and pyrolysis are thermal processes where heat is used to treat waste and initiate chemical reactions.
- Production of Gaseous Compounds: Both processes generate gaseous compounds as end products due to organic matter decomposition.Pyrolysis produces syngas, which is collected and used as fuel. Flue gas from incineration is not used and must be cleaned to remove gaseous pollutants and particulate matter before being released into the environment.
- Waste reduction: One of the most vital achievements of both incineration and pyrolysis is significant reduction in landfill waste.
Pyrolysis vs incineration: what are the differences?
While these common points exist, it’s important to note some key differences between incineration and pyrolysis:
- Oxygen requirement: Though both are thermal processes, incineration requires oxygen. Pyrolysis occurs without oxygen in an inert atmosphere, such as nitrogen.
- Temperature: Incineration requires very high temperatures above 850 to 1000°C. In pyrolysis, the process occurs at lower temperatures from 400 to 1000°C.
- Residues: Incineration produces significant amounts of ash as a residue, which is waste and has to be landfilled. The ash is contaminated by toxic pollutants that will pollute the soil. In contrast, the solids produced through pyrolysis are high-value products like char.
- Energy Recovery: Incineration produces energy in the form of electricity or heat generation. Pyrolysis produces transportable and storable biofuels like syngas and tire pyrolysis oil, which can be used as fuel for combustion for industrial purposes and as a partial substitute for diesel.
Why incineration is not a good solution
Incineration has several disadvantages due to its environmental and health impact:
- Incineration reduces recycling: Incineration can compete with recycling for materials, as burning waste may be more cost-effective and convenient than recycling. It discourages recycling efforts and decreases the recovery of recyclable materials.
- Emission of carbon dioxide: Incineration releases carbon dioxide, contributing to climate change. Total greenhouse gas reduction by incineration compared to even landfilling is uncertain. Carbon emissions from incinerating materials like plastics can be higher than landfilling if the incinerator is inefficient.
- Emission of hazardous end products: Incineration produces dangerous byproducts, including toxic flue gases and ash. Recent research in the EU has indicated a high level of harmful pollutants and particulate matter in the environment around incinerators.
- Health risks: Incineration can pose health risks to those living close to incinerators due to exposure to air pollutants and hazardous emissions. Prolonged exposure to these pollutants can lead to respiratory, cardiovascular, and other health concerns.
- Pollutants enter the food chain: Pollutants from incineration can find their way into the food chain, which is a significant concern for public health. For example, dioxin has been found in chicken eggs and vegetables grown in areas surrounding incinerators, making them unsafe for consumption.
Due to the negative environmental and health impacts, public perception and concerns about incineration make it difficult to install new incinerators.
Pyrolysis is better than incineration: here’s how
Pyrolysis is preferable as a waste-to-energy process compared to incineration for many reasons (Ławińska, 2022).
- Efficiency: Pyrolysis is more efficient than incineration as 100 per cent of materials are recovered.
- Versatile system: Pyrolysis can treat various waste streams, including biomass, plastics, and ELTs.
- Emissions Reduction: Pyrolysis creates significantly less carbon emissions than incineration, whose main product is carbon dioxide.
- Health benefits: Pyrolysis doesn’t create toxic pollutants or particulate matter in the products. Therefore, it has no adverse effects on human health. Moreover, no expensive clean-up or dust removal systems are required.
- Low-temperature use: The lower temperatures in used pyrolysis cause less equipment corrosion, lowering maintenance costs. Also, lower temperatures allow for the recovery of ferrous and non-ferrous metals in the solid component.
- Pyrolysis control: It’s easier to control pyrolysis as it’s an endothermic process compared to incineration, which is exothermic.
- Circular and Storeable products: Pyrolysis products can be stored, processed, and marketed later. The creation of recovered pyrolytic products such as gas, pyrolysis tire oil, Carbon Black, and steel makes it more sustainable and suitable for a circular economy.
Pyrolysis is still a relatively new technology compared to incineration, and fewer pyrolysis plants are in operation worldwide than incinerators. The infrastructural gap of pyrolysis plants will be reduced when its cost-effectiveness is worked out.
Tire pyrolysis at Contec
Contec operates one of the EU’s few tire pyrolysis pilot plants in Poland.
The company has developed and integrated a proprietary molten salt technology, Molten®, to make the production process more efficient and minimise the safety risks associated with pyrolysis.
Incineration and pyrolysis share some common aspects, such as the thermal decomposition of organic matter and the production of gaseous compounds. Still, they’re distinct processes, and pyrolysis’ advantages of efficiency, controllable operating conditions, high-value end products, and low environmental impact make it a more sustainable and better choice for the circular economy. Find out more about Contec’s sustainable TPO.
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