Complete guide to waste rubber tire recycling

Introduction of waste rubber tire recycling

Most people see recycling as a way to “protect the environment,” but there is so much more to it than that. Recycling is important because it benefits our economy, protects our health and preserves our resources. In the past few years, there has been a dramatic increase in the recycling of waste plastic and paper as more and more people are becoming aware of the positive economic and environmental effects recycling can bring.

In addition to paper and plastic, other products can be recycled that people are not as aware of, such as rubber. Recycled rubber products can be used in many ways to manufacture new rubber products or to produce fuel by tire pyrolysis.

Waste rubber comes from three principal sources; the largest source consisting of used tires that contain vulcanized rubber. Other sources are waste produced during manufacturing processes and discarded rubber containing products such as examining gloves, rubber sleeves, rubber band etc. Tires are among most problematic sources of waste rubber. These tires are a challenging source of waste, due to the large volume produced, the durability of the tires, and the components in the tire that are ecologically problematic.

Because tires are highly durable and non-biodegradable, they can consume valued space in landfills. In 1990, it was estimated that over 1 billion scrap tires were in stockpiles in the United States. As of 2015, only 67 million tires remain in stockpiles. ?According to an estimate, over 1 billion tires are produced annually in over 400 tire factories. Thus, the potential for recycling millions of used tires is clearly very important. The main source of used tires is the automotive industry, which means cars that use tires as tread. It is estimated that less than 7% of the 300 million used tires take the form of new products and about 11% are converted into electricity. Over 77% are buried, stored or abandoned.

Waste rubber tires are recycled using two processes namely mechanical process, cryogenic process & pyrolysis process. In this section, we will cover all these three process in details.

?Mechanical process for waste rubber tire recycling

Waste rubber tire recycling involves the conversion of waste tires into materials that we can use to create new products. Waste rubber tire recycling refers to the process of recycling used vehicle tires that can no longer be used on the vehicles due to wear and tear or irreparable damage. Used waste rubber tires are among the most problematic and challenging sources of solid waste. Waste rubber tire recycling is performed in following steps:

?Step 1 :- Collection of waste rubber tires

The first step is the collection of waste rubber tire that you want to recycle. In some cases, these materials come from landfills. In some other cases, people deposit it and send it to the recycling center.

Step 2 :- Shredding of waste rubber tires

The next step is to cut them into small pieces. The reason behind shredding is to reduce the size of tire into a material that can be handled easily. Also, tire processing can take two forms i.e., mechanical systems or cryogenic systems.

Mechanical shredding of waste rubber tire: The mechanical system involves shredding scrap tires into smaller chips at ambient temperature. Depending on the proposed use of the recycled rubber, the waste may be cut into smaller and smaller pieces as the fiber is removed. The end product is called 'crumb rubber' which comes in various sizes, depending on the diameter of the crumbs. The higher the mesh size, the smaller the crumb. Because more grinding is required to make the higher mesh crumbs.

Click here to watch waste rubber tire mechanical recycling machine video

Cryogenic shredding of waste rubber tire: The process is called ‘cryogenic’ because the temperature here can go as low as -80 degree Celsius to -120 degree Celsius. Shredded or the whole tire is cooled to -120 degree Celsius and it becomes glass hard and brittle. It is crushed or grounded to a fine size of 50-250 mm in special mills. This process requires less energy and less machinery than the regular process. It is also easier to liberate steel and fiber from the rubber using this process giving us a cleaner product.

Click here to watch waste rubber tires cryogenic recycling machine video

Step 3 :- Sorting

It involves removing textile fibers and steel from the shredded rubber. Typically, this occurs after the shredding process. And it is done using magnets. These magnets draw out the steel fibers from the whole bunch. On the other hand, there is a complex system that removes polyester fibers. This includes shaking screens, low vacuum suction, and wind sifters. Note that this process is very important as they constitute 30 percent of the whole bunch.

Step 4 :- Screening

The stage after separating wires from rubber is screening. The goal of screening is to observe the rubber carefully and ensure no steel is left in the rubber. You will essentially screen large volumes and sizes of rubbers with no wires and sort them according to their sizes. It also involves the elimination of any unwanted substances and reducing the sizes of large rubbers.

?Step 5 :- Cleaning

This involves a thorough cleaning of the screened rubber. Here, we use water and various cleaning agents to get the final product

Step 6 :- Packaging & Transportation

The clean rubber derived from the cleaning stage is packed and delivered to factories that need them as raw materials for their plants. Few examples of these factories include manufacturers of rubber shoes and playground turfs. ?

Pyrolysis process for waste rubber tire recycling

Pyrolysis of waste scrap rubber tires offers an environmentally and economically attractive method for the transformation of waste tires into useful products, heat and electrical energy. Pyrolysis refers to the thermal decomposition of scrap tires either in the absence or lack of oxygen. The input raw materials for pyrolysis are pre-treated car, bus or truck tire chips. Scrap tires are an excellent fuel because of their high calorific value which is comparable to that of coal and crude oil.

Pyrolysis is the most recommended alternative for the thermochemical treatment of waste rubber tires and extensively used for conversion of carbonaceous materials in Europe and the Asia-Pacific. Pyrolysis is a two-phase treatment which uses thermal decomposition to heat the rubber in the absence of oxygen to break the tire into its constituent parts.

Click here to watch pyrolysis plant video for waste rubber tire recycling

The pyrolysis method for scrap tires recycling involves heating of whole or halved or shredded tires in a reactor containing an oxygen free atmosphere and a heat source. In the reactor, the rubber is softened after which the rubber polymers disintegrate into smaller molecules which eventually vaporize and exit from the reactor. These vapors can be burned directly to produce power or condensed into an oily type liquid, called pyrolysis oil or bio-oil.

Some molecules are too small to condense and remain as a gas which can be burned as fuel. The minerals that were part of the tire, about 40% by weight, are removed as a solid. When performed well a tire pyrolysis process is a very clean operation and has nearly no emissions or waste.

?The nature of the feedstock and process conditions defines the properties of the gas, liquid and solid products. For example, whole tires contain fibers and steel while shredded tires have most of the steel and sometimes most of the fiber removed.

Processes can be either batch or continuous. The energy required for thermal decomposition of the scrap tires can be in the form of directly-fired fuel, electrical induction and or by microwaves (like a microwave oven). A catalyst may also be required to accelerate the pyrolysis process.

Application of products derived from pyrolysis process

The main advantage of the technology is to obtain high quality products which can be used at various places in following manners: -

1. Pyrolysis oil is an alternative source of energy, which can be used as liquid fuels for industrial furnaces, foundries and boilers in power plants due to their higher calorific value.
2. Carbon black can be used in mixtures for various purposes like metallurgy, production of paints and building materials, in the manufacturing of fuel briquettes etc.
3. The gas generated during the process can be used for the system operation, as well as to electricity generation
4. Metal cord / steel can be used in the metallurgical industry

Applications of waste rubber tires recycling

Recycling waste rubber is beneficial from both ways i.e., economically and environmentally. Other than these benefits, rubber recycling has some other benefits as well. Some of them are listed below:

Medical Industry

In manufacturing of hospital floors and surgical gloves to provide comfort for medical professionals and patients.

Metal Industry

Steel mills can use tires as a carbon source, replacing coal or coke in steel manufacturing

Sports Industry

Infill for synthetic turf , indoor and outdoor running tracks, and fitness mats – broadening sports and fitness opportunities across the country

Construction Industry

Rubberized asphalt on roadways providing surface durability while reducing traffic noise.

Fashion Industry

Recycled rubber can be used in the making of sandals

?Other general applications

Other than these benefits, there are some more benefits of ground rubber commonly referred to as size-reduced rubber. For example, it can be used in paving projects or be molded into products. Common examples of rubber molded products include carpet padding, rubber flooring materials, patio decks, livestock mats, movable speed bumps, sidewalks, dock bumpers, railroad crossing blocks just to mention but a few.

Conclusions

Disposal of waste rubber is a significant issue from an environmental point of view since the natural degradation of rubber takes several years. Vulcanized rubbers are extensively used in a wide range of applications (mainly the tire industries) because of their mechanical strength, excellent durability, abrasion resistance, and low cost. The recycling of discarded tires as the main fraction of waste rubbers has attracted increasing attention due to the large amounts of waste tires as an environmental issue.

Waste tires are dangerous and beneficial both, if recycled properly. Because they are non-biodegradable and energy-efficient, they fill up landfill space, release harmful gases, causing serious environmental havoc.

At the same time, when we recycle tires, we create new products, provide employment and revenues for the government, prevent diseases and environmental pollution, and eliminate other dangers. Recycling saves impressive amounts of energy, which ultimately reduces greenhouse gas emissions.

Labh Group provides complete plant & turnkey solutions for waste rubber tire recycling. For more information contact us at [email protected]

About Labh Group :

Labh Group is a leading engineering, technology, consulting and manufacturing conglomerate, working closely with diversified industries spanning across food processing, agriculture, plastics, chemicals, healthcare, packaging and other industries and business sectors offering complete turn-key solutions including advanced engineering, Industry 4.0 solutions, expert technical and management consultancy and Digital Transformation. From the most demanding to the most distant customers across the globe, we empower them for rewriting their future with our depths of knowledge, unique ideas, technical expertise, creative solutions and enduring results, all at the most optimal costs, right at their doorsteps!

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