By: Javier Vélez Arocho
The automotive industry in Puerto Rico generates approximately 4,700,000 tires per year, according to the 2018 annual report from the Department of Natural and Environmental Resources’ Solid Waste Management Division.
The state government sent used tires to states like Alabama to be used as raw material to produce cement. However, changes in the industry and the global pandemic reduced the demand significantly for used tires, leaving hundreds of thousands of tires stored by businesses on the Island without proper infrastructure.
PRDNER’s regulations prohibit discarding used tires at local landfills, forcing the government to search for new alternatives to address this growing environmental problem. The disposal of scrap tires may result in accidental or malicious fires with pollution emissions. Such fires are difficult to contain because of the tires’ high flammability because of the pockets of air present in the piles.
For the past 20 years, several significant fires have occurred on tire-storing facilities, causing millions in damages and unknown health issues. Besides harming the environment, this represents a tremendous waste of resources. For instance, a typical tire contains as many British thermal units (Btu) of energy as two and one-half gallons of gasoline.
Many countries, including the USA, Korea, and Germany, currently use scrap tires as an alternative fuel through the liquefaction process. Depending on the market, tire oil serves as raw material for heating fuel, base lube oil stocks, and asphalt. Industries currently refine tire oil like crude; however, metals in tire oil, is a concern as it may damage refinery infrastructure.
What are the essential components of a tire?
The essential components of a new tire are natural rubber (NR), Styrene-Butadiene Rubber (SBR), and Butadiene Rubber (BR). During the manufacturing process, Sulfur is used for vulcanizing, while steel and carbon black as reinforcing agents. Also, an aromatic extender oil softens and enhances the rubber’s workability. These components are essential to building a tough and durable product, but they are also 100% recyclable.
Energy Recovery from scrap tires
The Puerto Rico Department of Natural and Environmental Resources has jurisdiction over constructing a facility to process scrap tires. Now, any tire-processing equipment’s success depends on both environmental performance (emission) and process economics. The two most important factors affecting process economics are the tipping fees charged for tire disposal and products’ selling prices.
Some researchers advise adding other solid waste, like plastic and paper, to tires pyrolysis to improve the economic revenue. However, we believe the technology is already available to focus on refining the one material with a great demand; pyrolytic oil.
What is pyrolysis?
In the pyrolysis process, the tires’ organic volatile matter gets decomposed to low molecular weight products, liquid, or gases. The inorganic components and the non-volatile carbon black remain a solid residue that is relatively unaltered and useful for recycling. Similarly, pyrolytic oil contains monoterpene such as limonene, a high-value light hydrocarbon.
The limonene has fast-growing wide industrial applications, including the formulation of industrial solvents, resins, and adhesives, dispersing agent for pigments, fragrance in cleaning products, and environmentally friendly solvents.
Tire Pyrolysis Process
Several pyrolysis types are available in the market to convert used or scrap tires into fuel oil, like catalytic pyrolysis, vacuum pyrolysis, and plasma pyrolysis. (Pote, R.N., Patil, R.K. Combustion and emission characteristics analysis of waste tyre pyrolysis oil. SN Appl. Sci. 1, 294 (2019). https://doi.org/10.1007/s42452-019-0308-8)
How to choose the right technology to gasify scrap tires?
An essential element to consider while choosing the right technology or equipment to gasify scrap tires is to select a unit with a long history of performance. It will be beneficial to purchase the system from a manufacturer with vast experience in this field. The reason for this approach is the effects technology can have on the pyrolytic product’s yield and composition (char, liquid, and gas); in other words, the more stable, the better.
Rubber tires start to decompose at 375°C. As the heat increase, the solid start to decrease, and both gas and liquid begin to increase until 475°C. Then, above 475°C, the yields of both liquid and gas decrease and increase, respectively, due to the decomposing of some oil vapor into permanent gases. A temperature of 500°C is the optimum for pyrolytic oil products.
The increasing temperature over 500°C increases the gas yield to the detriment of liquid, but hardly varies the products’ characteristics. Also, no decrease in the stable output means a completed pyrolysis process. The correct equipment processes the appropriate feedstock size to maintain balanced reaction times while maintaining optimum operational levels. Lower residence times involve lower reactor volumes to process a specific load of tires and lower the system’s cost.
What is the best reactor technology?
There are many pyrolysis reactors out there, including fixed-bed, rotary kiln, and conical spouted bed reactors. Depending on the desired final product, the client will need a specific reactor. For example, fixed-bed reactors are preferred for oil production, while a two-staged reactor is preferred if Hydrogen gas will be the final product.
How safe is pyrolysis to human health and the environment?
Thermal decomposition is the used tire treatment technology based on thermal destruction of feedstock under the high temperatures and lack of oxygen into the products with the smaller molecular weight: liquid pyrolysis oil, carbon black, and metal. Pyrolisis technology addresses the challenge of non-polluting waste management.
Decomposition of tires takes an average of 150 years in the natural environment and is accompanied by the leaching of toxic organic compounds into the soil. Most of the old tires are stored in landfills, reducing their lives and negatively impacting the environment. However, with pyrolysis, no residues that require disposal are left after treatment. The process outputs do not contain highly toxic substances, and the combustion products are not released.
The process efficiently maintains the emissions of harmful substances below the specified requirements.
Also, high-quality products obtained during the process are the main advantage of the technology. Low-temperature pyrolysis decomposes the tires into commercial-grade products, which serve other purposes.
Pyrolysis became the alternative technology for energy recovery that has minimum impact on the environment and can generate heat and electricity. Pyrolysis of tires is the most environmentally friendly and cost-effective waste treatment technology, capable of process recyclables, obtain valuable materials and produce electricity.
What is the permit process for a gasifying unit?
Depending on the number of critical pollutants produced yearly (tons/year), the proposed project may require a Title V (Major Emission Permit) or a regular Emission Source Permit (PFE-Permiso de Fuente de Emission in Spanish) from the Puerto Rico Department of Natural and Environmental Resources/PR Environmental Quality Board.
Our company recommends smaller units to avoid lengthy permitting processes. A regular PFE permit takes weeks to obtain, while a Title V permit may take 3-4 years to complete due to the technical and analysis requirements.
What are the environmental benefits of the pyrolysis process?
The environmental benefits of the pyrolysis process of scrap tires include avoiding their disposal directly into landfills preventing the pollution of the soil, rivers, coastal areas, and air due to the emission of chemical pollutants formed during their decomposition. Also, there is no need to extract raw materials to produce steel, oil, and carbon black produced in the pyrolysis facility. The steel produced in the scrap tire pyrolysis plant is cleaner than the steel produced in the current modes.
The carbon black made in scrap tires’ pyrolysis process is cleaner than the currently marketed carbon black. The proposed method produces cleaner fuels than petroleum byproducts, and, as the pyrolysis process generates oil, the fuel has a low cost. The use of gas and fuel oil from the tire pyrolysis process can supply part of the Island’s population’s need for these fuels. The recycling of scrap tires into fuel production may reduce the search for new oil fields.
This article gives you an idea of the possibilities of developing a facility to treat scrap tires to obtain valuable byproducts like oil for energy production. Our recommendation is always to select available technologies with data, years of performance, and technical support. Diatom Environmental Services, LLC personnel can assist you with expert knowledge in the permitting process.