What is pyrolysis of wastes?
Pyrolysis is the thermal decomposition of materials containing carbon between 300 and 900°C in an oxygen-deprived environment. It can transform any biomass, such as used tyres and plastics, into renewable products. Pyrolysis technology can be as small as a cubic meter (costing a few hundred dollars) or as big as a large industrial energy plant (costing $100M). Some come in containers and are mobile. All the products generated by the technologies meet de needs of various markets, often in the green economy or in circular economy, but also in more traditional markets, such as the energy sector.
Biomass can be converted into solid (biochar), liquid (pyrolytic oil, wood vinegar, phenols or biodiesel, etc.), and gases. If you don’t want liquid, then you don’t condensate the gases and obtain more gases in place of liquid.
Plastic can be converted into liquid (oil, fuel oil or diesel), gases and a bit of solid (coke).
Tyres are converted into solid (black carbon and steel), liquid (oil), and gases.
Environmental benefits of pyrolysis
Climate change is not a myth, let’s act now using pyrolysis!
Greenhouse gases included CO2, CH4 and N2O. Methane (CH4) emissions are of primary concern with regards to climate change because it has a global warming potential of 25 when compared to CO2. CH4 emission sources include biomass burning and landfills representing up to 19% of overall sources along with livestock. In addition, for waste decomposing on land or in landfill, large amounts of greenhouse gases (mainly CO2 and CH4) are emited and cannot be recycled. Pyrolysis of wastes that would otherwise go to landfill or let on land to decay can offsets 2 to 4 tons of CO2 equivalent. It is thus very efficient to transform residues through pyrolysis. In addition, biochar can be used to sequester carbon in soil, in concrete and materials, other ways to mitigate climate change.
What is char or biochar?
Char and biochar are carbon rich (more than 60% C) black materials. Biochar usually refers specifically to char made from virgin fibers while char could be made from used and/or contaminated fibers such as sludge. They look like charcoal. These materials are light and are highly porous. They can sorb contaminants, nutrients, water, gases, and odors. Each char and biochar is unique. Their properties depend on feedstock, processing technology, temperature and residence time during transformation.
Environmental benefits of char and biochar
In the pyrolytic world, black is the new green!
Manufacturing char and biochar helps avoid contamination of air, water and soil by wastes. These products can also be used to filter air and treat water. In addition, biochar is used for CH4 emission reduction from cows if added in their feed, in the litter, in the manure storage tank and then incorporated into the soil, all actions that reduce greenhouse gas emissions. In other industries, it is usually considered that, for every ton of consumed coal, there are 3 tons of CO2 equivalent emissions. Replacement of coal by biochar not only offsets the direct emission during burning, but it also does so during mining and transportation when biochar is produced locally. Pyrolytic products, such as acetic acid, replacing petroleum-based products, also decreases GHG emissions. Similar greenhouse gas emission reduction for alternate applications can likewise be considered when using biochar.
What is wood vinegar?
Wood vinegar, also called pyroligneous acid, is the aqueous phase of the oil derived from the pyrolysis of biomasses. Once the gases are condensed into liquid during pyrolysis, this liquid, often called “the oil”, contains between 15 to 60% water and water soluble products. The water content of pyrolytic oil depends on the feedstock used and its initial water content. Wood vinegar can be extracted from it by one, or a combination of, the following processes: distillation, separation, centrifugation and decantation. Wood vinegar contains more than a hundred chemicals, a large proportion of which being water, followed by acetic acid (0.1 to 10%) and several types of phenols. Wood vinegar meets the needs of various markets such as acetic acid, antifungal, chemical industry, cosmetics, food flavour, food preservative, health products, liquid smoke, organic solvents, pesticide, pH control, plant growth agent, xylitol.
Waste Management and Transformation
Waste-to-energy and waste-to-renewable products can be profitable!
Landfilling wastes takes up lands, pollutes water even when very well designed, emits odours and greenhouse gases, and consume fossil fuels for landfilling and transportation to and from the landfill. Of course, wastes dumped into the wild are even worst in terms of pollution and cause important problems related to wildlife environment such as observed with single use plastics. Used tyres, plastics, contaminated biomasses, all types of materials that contain carbon that would otherwise be sent to landfills could instead be transformed into energy to replace fossil fuels, whether in the form of solid, liquid or gas. Once again, it all depends on the feedstock, the technology and the desired product. These products all have their markets.
Pyrolysis transformation into clean products
In addition, all biomasses that are contaminated with organics (ex: rail road ties) could be cleaned with pyrolysis or gasification technologies. The organic molecules are broken into smaller molecules such as CO, CO2, oil and more. The solid material (char) can then be used for most of the applications listed above. The liquids can be used as renewable fuels or for chemical extracts. The carbon fiber can be freed from resin and become as new when pyrolyzed. Thus, a whole new series of renewable products, in addition to the renewable energy, can be produced from wastes and “non-recyclable wastes”. Therefore, all these new products eliminate the environmental impacts of fossil fuel extraction, mining and long distance transportation in addition to having value on various markets!
Wastes to energy
Transforming wastes into energy saves land, time, transportation costs, creates jobs, and limits the damages caused by fossil fuel extraction, and other polluting activities. Knowing how expensive depollution is, the positive socio-economical impacts of pyrolysis become obvious.