Technically pyrolysis is defined as the thermal degradation of material at a high temperature in the absence of oxygen gas. The resulting byproducts of this degradation are condensate (water/tar) and non-condensable gasses. If the feedstock is biomass, then the byproducts can also include biochar. The proportions for each of these byproducts mainly depend on the feedstock and operating conditions.
Some pyrolyzers are called ‘slow pyrolyzers’ because they break down the feedstock slowly, resulting in carbon, syngas, oxides, and biochar as significant byproducts.
The other type of system is referred to as a fast pyrolyzer, and the resulting outputs can include solids, liquids, and gasses. In biomass applications, the focus is often on bio-oils and biochars as an effective carbon sequestration output.
The primary goal of most pyrolysis technologies is to convert existing feedstocks into higher-value intermediate liquids, which can then be refined and added to a range of products, including hydrocarbon fuels, petrochemicals, and oxygenated fuel additives.
It is worth noting that the biggest hurdle in the way of small on-site pyrolysis systems is that it often requires temperatures over 1,000 °C. There needs to be enough heat for the deconstruction process to occur. Since no oxygen is involved in the process, the feedstock does not combust. Instead, the molecules decompose into carbons, liquids, and a subset of combustible gasses.
The combustible gasses can be condensed into flammable liquids, sometimes referred to as pyrolysis oils. These distributed pyrolysis plants can also emit permanent gasses such as CO2, H2, and CO, in addition to light hydrocarbons which can then be combusted to provide the needed heat for the process.
If all things are equal, output yields can often be optimized. Depending on process conditions, feedstocks and energy inputs can vary significantly.
The good thing about effective pyrolysis processes is that they can be self-sustaining. The combustion of syngas and other products can be used as fuel to drive the process. Pyrolysis is an energy-intensive process, so heat management is extremely important.
Today, there are various types of on-site pyrolysis units and a growing number of mobile units. The units are mainly optimized for specific inputs and outputs. Many pyrolysis technologies have started running on renewable energy, biomass, solar, and hydrogen. All of these could contribute to our net-zero goal over time. But as we’ll examine below, all pyrolysis gas yields and bio-oil are not equal.
At present, there are many types of on-site pyrolysis systems. Furthermore, more efficient pyrolysis technologies are being developed as we speak. Many technologies exist, which are not discussed below.
Many cities use pyrolysis as part of their waste management efforts. These municipalities use pyrolysis to process trash, including plastic waste. The advantage here is to reduce the volume of waste while at the same time regenerating monomers and polymers, which are then treated. However, the practice isn’t entirely clean, and many technology companies and university research programs are working on new innovations to improve process efficiencies.
At present on-site tire, pyrolysis is a highly developed technology. Products from car tire pyrolysis include carbon black, bitumen and steel. Oil is also produced during tire pyrolysis, but the oil has a high sulfur content with significant polluting potential that must be managed.
Many cities use on-site pyrolysis to process and manage sewage sludge, usually at 500 degrees. This process helps enhance hydrogen production with built-in carbon capture. Some technologies also use sodium hydroxide to produce hydrogen gas. This hydrogen can then be used in fuel cell vehicles.
On-site pyrolysis is also highly beneficial for thermal cleaning or cleansing. This process is used to remove organic substances like coatings, polymers, and plastics from parts like spinnerets, extruder screws, and static mixers. The process is carried out at between 310 and 540 degrees Celsius. The organic material is converted into hydrocarbons, carbonized gas, and volatile organic compounds, keeping the inorganic elements intact.
One of the most promising applications for pyrolysis is in on-site methane pyrolysis for producing turquoise hydrogen. This carbon-neutral process removes solid carbon from methane gas. The single-step process produces high-value hydrogen and effectively sequestered carbon at a low cost. This unique process also eliminates the need for expensive transportation and storage of hydrogen because all of the feedstock is held in existing natural gas infrastructure.
When hydrogen is used as fuel, the only byproduct is water. That’s why hydrogen is often described as the fuel of the future. Hydrogen fuel applications include everything from transportation to fueling electric turbines and producing ammonia fertilizer. Many other applications are oriented around industrial and commercial process heating.
Methane pyrolysis takes place at over a thousand degrees centigrade, which allows for the separation of carbon from natural gas. The solid carbon output is of industrial quality and is then sold and can be used for the manufacture of asphalts, tars, tires, and pigments. Plus, this approach prevents carbon from entering the atmosphere.
One of the first new technology plays in methane pyrolysis was piloted by Monolith Materials in 2015. The study was meant to observe the scaling of methane pyrolysis using renewable power. The success of that project then led to one being established in Hallam, which now produces 14 metric tons of hydrogen daily.
The large-scale and centralized nature of Monolith’s pyrolysis model is the opposite approach to the small-scale and decentralized nature of the “Modern Hydrogen” model advocated by Washington-based technology company Modern Electron. Experts agree that many different hydrogen technology solutions will be needed to successfully decarbonize our economy.
On-site pyrolysis is an exciting and rapidly evolving technology space. Recent federal legislation, including the “Inflation Reduction Act,” includes major economic incentives to technology companies, project developers, and customers in the growing hydrogen marketplace.