China is the world's largest producer of tires and consumption, and a major producer of waste tires. According to statistics, in 2017, the number of car ownership in China was 174 million, the total output of automobile tires was about 610 million, a year-on-year increase of 7.9%, the amount of waste tires generated was about 340 million, and the weight reached 12.5 million tons, a year-on-year increase of 5%. . It is estimated that by 2020, China's waste tire production will exceed 20 million tons.
Waste tires have strong heat resistance, biodegradation and mechanical damage resistance. They will not disappear naturally for decades or even longer. Previously, due to the lack of effective centralized management methods, they have become a worldwide problem in environmental pollution control. Recycling of waste tire crushing equipment is the mainstream method for treating waste tire pollution in various countries around the world. According to statistics, in 2017, China recycled 50.48 million tons of waste tires with a recovery rate of only 40%. There is huge room for growth in the future.
Commonly used treatment methods for waste tires include: tire retreading, crushing and removing magnetic powder, making reclaimed rubber, and a new pyrolysis process. The pyrolysis process has been included in the Catalogue of Major Environmental Protection Technology and Equipment Encouraged by the State, and it is also one of the more recommended treatment methods in the comprehensive utilization guidance for waste tires. After the waste tire is treated by pyrolysis, it can be decomposed into fuel oil, carbon black, steel wire and cracked gas.
Production process
The main raw materials of the pyrolysis project are purchased clean waste tires (each of which has been cut into 4~5 pieces; or the sidewalls are cut off, the tread sets are good), no need for cleaning, crushing, wire drawing and other pretreatment processes, directly through the belt conveyor Enter the cracking furnace, the feeding section is about 2 hours, and each equipment feeds about 10t. The cracking furnace is a continuous heating environment. The inside of the furnace is heated to 200~300 °C within 4 hours. At this time, the cracking gas begins to be in a stable state, and the temperature rises slowly in the next 5~8 hours. When the temperature reaches 450. At °C, it can be considered that the tire cracking has been basically completed. A large amount of flue gas is generated during the cracking process, and its components mainly include heavy oil (liquid), light oil (gaseous), cracked gas and a small amount of water vapor, etc., and the flue gas flows into the steam drum through the pipeline. In the steam drum, heavy oil (about 2% of the quality of the waste tire) sinks to the residual oil tank, which is stored in the oil storage tank by the oil pump; the gaseous components enter the circulating water cooling system through the pipeline. The flue gas cooled in the pipeline is divided into a liquid and a gas, wherein the gas is a cracking gas, and the liquid is a mixture of light oil and water. The liquid flows into the oil-water separator, and the separated light oil is stored in the oil tank through the oil pump. A small amount of oily wastewater is atomized and injected into the cracking furnace combustion chamber for use as fuel; the cracked gas is sent to the cracking furnace combustion chamber as a fuel.
After 8 hours of cracking, in addition to fuel oil and cracking gas, carbon black and steel wire are formed in the cracking furnace. After the furnace body stops heating, the project adopts air cooling method, and the heat of the outer wall of the furnace is continuously taken away by the fan exhausting, and the cooling section lasts for about 2 hours. When the furnace body is cooled to about 200 °C, the operator opens the first- and second-stage high-temperature slag discharge machine to slag. After the furnace body is cooled to about 45 ° C, the wire exit (1.1 m × 1.7 m) on the feed door is opened, and the entangled steel wires are dragged out as a whole. Since the tire of the project is fed as a whole tire, there is no cutting and crushing section, and the furnace body keeps rotating during the cracking process. Therefore, the steel wire is twisted together when discharging, and a small amount of carbon black adhered on the steel wire is tapped or shaken. Can be dropped, the steel wire is directly bundled and shipped out. The carbon black steel wire discharge time per device was 2 hours. The total time for the entire tire cracking process is 24 hours.
Waste tire pyrolysis process flow diagram
The products that are decomposed from waste tires are generally used in the following directions:
1) Fuel oil (40-45%)
The fuel oil produced by waste tires is mainly used in the following industries and fields:
A. Power Plant B. Glass Factory C. Cement Factory D. Ceramic Factory E. Aluminum Factory
F. Boiler Plant G. Center Heating Plant H. Pigment Factory I. Ship
2) Carbon black (30 -35 %)
A. Cable jacket B. Conveyor belt C. Hose and door mat D. Black nylon bag
E. Rubber additive F. Automatic parts G. Insulation material H. Colorant in rubber material
I. Plastic tube J. Industrial rubber products K. Fire-fighting materials L. Carbon rods for fuel
3) Steel wire (10-15%)
The steel wire produced from waste tires is mainly sold to steel plants.
4) Cracking gas (10-12%)
The cracked gas is mainly used for recovery to the combustion chamber to heat the main furnace. If the equipment is large in scale and the amount of cracked gas generated is large, it can also be temporarily stored and generated by the generator set.