Waste Tire Oil Refining

Waste Tire Oil Refining: Exploration of the Balance Between Resource Recycling and Environmental Protection

With the rapid development of the automotive industry, the output of waste tires is increasing year by year. Waste tires, known as "black pollution", have become one of the major environmental problems facing the world. Waste tires are characterized by difficulty in degradation, large volume and high recycling difficulty. Random stacking not only occupies a lot of land, but may also cause fires due to high temperature, open flames, etc., producing toxic and harmful gases. Against this background, waste tire oil refining, as a "turning waste into treasure" resource recycling technology, has gradually attracted industry attention. Through specific processes, it converts waste tires into valuable products such as fuel oil, carbon black and steel wire, realizing the secondary utilization of waste resources, but at the same time facing strict constraints of environmental protection standards. The following will elaborate on the relevant content of waste tire oil refining from the aspects of technical principles, main processes, product value, environmental protection requirements, and industry status and prospects.

I. Technical Principles of Waste Tire Oil Refining

The main components of waste tires include rubber (natural rubber, synthetic rubber), carbon black, steel wire, additives (softeners, antioxidants, etc.). Among them, rubber is a high molecular organic compound mainly composed of carbon and hydrogen elements. The core principle of waste tire oil refining is to use pyrolysis technology to heat and decompose rubber macromolecules into small molecular organic compounds in a closed environment without oxygen or with insufficient oxygen, and then obtain liquid fuel oil, gaseous fuel, as well as solid carbon black and steel wire through condensation, separation and other processes. Simply put, it breaks the polymer chains of rubber through high-temperature decomposition, converting them into valuable small molecular substances to realize resource recycling.

II. Main Processes of Waste Tire Oil Refining

At present, the mainstream waste tire oil refining process is pyrolysis process, which can be divided into batch pyrolysis and continuous pyrolysis according to different heating methods and reaction conditions. The overall process mainly includes pre-treatment, pyrolysis, condensation separation, tail gas treatment, product recovery and other links.

1. Pre-treatment Link

Pre-treatment is the basic step of waste tire oil refining, aiming to remove impurities, reduce the volume of tires and improve the subsequent pyrolysis efficiency. First, the recycled waste tires are sorted to remove stones, metal debris (non-steel wire parts) and other impurities in the tires; then the whole tires are cut into small pieces (usually 5-10 cm particles) by tire cutting machines to facilitate feeding into the pyrolysis furnace; for tires containing steel wire, some processes will separate part of the steel wire in advance by magnetic separation and other methods in the pre-treatment stage, reducing the difficulty of subsequent product separation. The quality of the pre-treatment link directly affects the stability of the pyrolysis process and the purity of the products, and is a key prerequisite for ensuring the oil refining efficiency.

2. Pyrolysis Link

Pyrolysis is the core link of waste tire oil refining. The pre-treated tire particles are fed into a closed pyrolysis furnace and heated up in an oxygen-free or oxygen-deficient environment, with the temperature usually controlled at 400-600℃. Under the action of high temperature, the rubber macromolecules gradually break, generating pyrolysis gas (main components include methane, ethane, propane, alkenes, etc.), pyrolysis oil vapor, as well as solid carbon black and steel wire. The key of this link lies in controlling the heating rate, reaction temperature and reaction time. Different process parameters will directly affect the output and quality of the products. For example, too fast heating rate may lead to insufficient decomposition of rubber and reduce fuel oil output; too high temperature may lead to further pyrolysis of small molecular substances and increase the proportion of gaseous products.

3. Condensation Separation Link

The pyrolysis gas and pyrolysis oil vapor discharged from the pyrolysis furnace enter the condensation system, and the high-temperature vapor is cooled to normal temperature through the condenser. Among them, the liquid pyrolysis oil will be condensed and collected, while the uncondensed gaseous products (non-condensable gas) are stored as fuel gas for heating the pyrolysis furnace or other energy supply. At the same time, the solid products (carbon black and steel wire) after pyrolysis will be discharged from the bottom of the pyrolysis furnace, and the steel wire and carbon black will be separated by screening, magnetic separation and other methods. The steel wire can be directly recycled and reused, while the carbon black needs further processing.

4. Tail Gas Treatment Link

A small amount of tail gas will be generated during the waste tire oil refining process, which may contain toxic and harmful pollutants such as hydrogen sulfide, sulfur dioxide and particulate matter. Direct emission will cause serious pollution to the environment. Therefore, tail gas treatment is a key link to meet environmental protection standards. Usually, a combined process of "desulfurization + dust removal + purification" is adopted. First, desulfurization equipment is used to remove sulfides in the tail gas (to avoid acid rain after combustion), then dust remover is used to remove particulate matter, and finally activated carbon adsorption and other purification processes are used to ensure that the tail gas is discharged after meeting the national emission standards. Some advanced processes will also recycle the treated tail gas to further improve energy utilization efficiency.

III. Products and Value of Waste Tire Oil Refining

Through the oil refining process, waste tires can obtain four main products: pyrolysis fuel oil, carbon black, steel wire and non-condensable gas. Each product has clear application scenarios and economic value, realizing the full-component utilization of waste tires.

1. Pyrolysis Fuel Oil

Pyrolysis fuel oil is one of the core products of waste tire oil refining, accounting for about 40%-50% of the weight of waste tires. According to the different subsequent processing precision, it can be divided into crude fuel oil and refined fuel oil. Crude fuel oil has a high calorific value (usually 42-45MJ/kg) and can be directly used as fuel oil for industrial boilers and kilns in heating, power generation and other fields; after refined purification (removing sulfur, nitrogen, heavy metals and other impurities), it can be further converted into blending raw materials for finished oils such as diesel and gasoline, or used in the production of lubricating oil, asphalt and other products. Pyrolysis fuel oil has a large market demand, especially in the industrial energy field, providing core economic benefit support for waste tire oil refining projects.

2. Carbon Black

Carbon black is one of the solid products after waste tire pyrolysis, accounting for about 30%-35% of the weight of waste tires. The original pyrolysis carbon black has low purity and contains a small amount of impurities. After grinding, screening, modification and other processing, it can be used as a reinforcing agent for rubber products (replacing part of new carbon black), a filler for plastic products, as well as in ink, coating, electrode materials and other fields. In addition, carbon black can also be used as fuel for combustion power generation in industrial boilers or power stations. The recycling of carbon black not only reduces the dependence on primary carbon black, but also reduces resource waste, with significant economic and environmental benefits.

3. Steel Wire

The steel wire in waste tires will not undergo chemical reactions during the pyrolysis process and will be discharged from the bottom of the pyrolysis furnace in solid form, accounting for about 10%-15% of the weight of waste tires. The recycled steel wire can be directly recycled and smelted after simple derusting and processing, used in the production of steel, iron wire and other products, realizing the recycling of metal resources. The recycling of steel wire is less difficult and its value is relatively stable, which is one of the auxiliary economic benefit sources of waste tire oil refining projects.

4. Non-condensable Gas

Non-condensable gas is the uncondensed gaseous product in the condensation separation link, mainly composed of hydrocarbon gases such as methane, ethane and propane, accounting for about 5%-10% of the weight of waste tires. Non-condensable gas has a high calorific value and can be directly used as fuel for heating the pyrolysis furnace, replacing external energy sources such as coal and natural gas, realizing energy self-sufficiency and reducing the operating cost of the project. Some remaining non-condensable gas can also be stored by compression for other energy demand scenarios, further improving resource utilization efficiency.

IV. Environmental Protection Requirements and Specifications for Waste Tire Oil Refining

Due to the potential environmental risks of toxic and harmful gases, particulate matter, heavy metals and other pollutants generated during the waste tire oil refining process, countries around the world have formulated strict environmental protection standards and supervision requirements for this industry. China has also included waste tire oil refining in the supervision scope of hazardous waste treatment and disposal, requiring enterprises to have corresponding environmental protection qualifications to ensure that the production process complies with environmental protection specifications.

1. Pollutant Emission Control

For waste gas emission, enterprises are required to be equipped with complete purification facilities such as desulfurization, dust removal, denitration and activated carbon adsorption to ensure that the concentrations of pollutants such as sulfur dioxide, nitrogen oxides, particulate matter and VOCs (volatile organic compounds) in the tail gas meet the requirements of the "Integrated Emission Standard of Air Pollutants" (GB 16297) and local relevant standards; for waste water emission, a small amount of washing waste water, cooling waste water and other waste water generated during the production process need to be treated to meet the "Integrated Waste Water Discharge Standard" (GB 8978) before being discharged or recycled; for solid waste (such as waste activated carbon, pyrolysis residue, etc.), it needs to be disposed of by qualified units in accordance with the relevant regulations on hazardous waste management, and random stacking is strictly prohibited.

2. Production Process Supervision

Enterprises are required to establish a sound environmental management system, conduct real-time monitoring of parameters such as temperature, pressure and pollutant emission during the production process, ensure the stable operation of the production process, and avoid excessive pollutant emission caused by process fluctuations. At the same time, the production site is required to have good anti-seepage and anti-leakage facilities to prevent oil pollution, waste water and other from seeping into the ground and polluting soil and groundwater. In addition, enterprises are also required to be equipped with emergency treatment facilities to deal with sudden environmental risk events (such as pyrolysis furnace leakage, fire, etc.).

3. Qualification and Approval Requirements

In China, enterprises engaged in waste tire oil refining projects need to obtain relevant qualifications such as the "Hazardous Waste Operation Permit" and "Pollution Discharge Permit". Before project construction, they need to complete approval procedures such as environmental impact assessment and safety evaluation to ensure that the project complies with national industrial policies and environmental protection requirements. In recent years, China has continuously tightened the supervision of the waste tire oil refining industry, eliminated a number of small workshop-style enterprises with backward processes and substandard environmental protection, and promoted the industry to develop in a standardized and large-scale direction.

V. Industry Status and Development Prospects of Waste Tire Oil Refining

1. Industry Status

Globally, the waste tire oil refining industry has formed a certain industrial scale, especially in countries and regions with scarce resources and high environmental protection requirements, this technology has been widely used. As a major automobile country, China has the largest output of waste tires in the world, producing more than 300 million waste tires every year, which provides a sufficient raw material base for the waste tire oil refining industry. At present, China's waste tire oil refining enterprises are mainly distributed in industrially developed regions such as Shandong, Henan and Hebei. The industry includes both large-scale enterprises with advanced processes and complete environmental protection facilities, and some small enterprises with backward processes and substandard environmental protection. In recent years, with the continuous tightening of national environmental protection policies, the industry reshuffle has accelerated, small and backward enterprises have been gradually eliminated, and the market share of large-scale and standardized enterprises has continued to increase.

2. Development Prospects

From the perspective of resource recycling and environmental protection, waste tire oil refining technology has significant positive significance and broad development prospects in the future, but it also faces challenges such as technological upgrading and environmental protection constraints. On the one hand, with the increasingly prominent global energy shortage problem, the market demand for energy products such as fuel oil and gas generated by waste tire oil refining will continue to exist, providing motivation for the development of the industry; on the other hand, with the continuous improvement of environmental protection standards, the industry will further develop in a green and efficient direction, and the requirements for process technology will continue to improve. Enterprises with advanced pyrolysis technology, efficient environmental protection facilities and full industrial chain recycling capacity will gain more development space. At the same time, with the continuous breakthrough of technology, the added value of waste tire oil refining products will be further improved in the future. For example, converting pyrolysis fuel oil into high-purity finished oil through refined processing, and modifying carbon black into high-performance rubber reinforcing agent, which will further improve the economic benefits and competitiveness of the industry.

3. Facing Challenges

At present, the waste tire oil refining industry still faces many challenges: first, there are "scattered, messy and polluting" enterprises in some regions, and the environmental pollution problems caused by illegal production affect the overall image of the industry; second, there is still a gap between the core technology and the international advanced level, the localization rate of continuous pyrolysis process is low, and the equipment stability and product recovery rate need to be improved; third, the refined processing capacity of products is insufficient, most enterprises still mainly produce crude fuel oil and ordinary carbon black, with low product added value; fourth, the industry standards and supervision system still need to be further improved, and there are cases of inadequate supervision in some regions, which affect the healthy development of the industry.

VI. Summary

As an effective waste resource recycling technology, waste tire oil refining has realized "turning waste into treasure" and is of great significance in solving "black pollution" and alleviating energy shortage. Through pyrolysis process, this technology converts waste tires into valuable products such as fuel oil, carbon black and steel wire, with significant economic and environmental benefits. But at the same time, the waste tire oil refining industry must also strictly abide by environmental protection standards and realize green development through technological upgrading and standardized management. In the future, with the continuous tightening of environmental protection policies and the continuous progress of technology, the waste tire oil refining industry will gradually get rid of the label of "scattered, messy and polluting" and develop in a large-scale, refined and green direction, making greater contributions to the global resource recycling and environmental protection cause.