Thermal Decomposition and Recovery of Dialysis Used Plastics

[China Packaging Network] The decomposition technology of waste plastics shows diversity with the development of the recycling industry.

Technically speaking, the implementation of this technology needs to be carried out at high temperature, the investment in the equipment used is much more expensive than the previous recovery method, the recovery cost is relatively high, and the phenomenon of coking occurs during the reaction, thus limiting the technology The application. However, with the increase of people’s “scientific and technological sense”, the waste plastics industry will surely set off a wave of thermal decomposition and recovery technologies.

working principle

Thermal decomposition is the use of plastic energy in the plastic packaging waste heat under the conditions of the compound bonds broken, from large molecular weight organic matter into a small molecular weight fuel gas, liquid material (oil, grease, etc.) and coke.

Process flow

Technical features

advantage:

(1) The use value of decomposition products is high;

(2) The number of repeated processing of waste plastics is not limited;

(3) Pyrolysis technology can handle mixed recycled products, but it needs to be classified according to chlorine products and non-chlorine products;

Disadvantages:

(1) Large investment and high recovery cost;

(2) Coking in the reaction process

(3) Strict technical operation requirements.

Technical classification

According to the heating mode: external heat type and internal heat type

Divided by operating temperature: high temperature pyrolysis and low walk pyrolysis

According to the product points: gas production technology and oil production technology

According to the type of pyrolysis furnace: rotary furnace, shaft furnace, moving bed and fluidized bed. ,

Process influencing factors

temperature

With different thermal decomposition temperatures, the products and yields obtained after thermal decomposition are also different. Even if the same product has different pyrolysis temperatures, the physical properties are not the same. Decomposition temperature is high, gas production is increased, and oil and carbides are reduced accordingly. In addition, the decomposition temperature is different, the gas component also changes, the higher the temperature, low-molecular-carbon carbides such as CH4 and H2 in the gas increases.

speed

The thermal decomposition rate is different and the gas composition produced is also very different.

Moisture content

The relationship between moisture content in plastic packaging waste and thermal decomposition production is negatively correlated. The amount of refined fuel gas produced by the 1t waste varies according to the amount of water contained. If the amount of fuel produced is changed to 1t of combustible waste, it will have almost no effect on the change in water content. However, the waste water is large and the heat balance of pyrolysis is difficult, requiring a large amount of auxiliary fuel.

In the process of gasification, if water vapor is injected, the water coal gasification reaction occurs due to water, coal and CO2, so that the carbon content in the residue is reduced, and the proportion of H2 and CO in the gas is increased.

Air content

External thermal pyrolysis is carried out under anaerobic conditions, resulting in a high calorific value of gas; internal pyrolysis, due to the introduction of air to the gas product contains a considerable amount of nitrogen and CO2, lower gas calorific value, pure oxygen heat The gas product solution has a higher calorific value than the gas generated by air.

Therefore, from the actual operation point of view, the difference in the actual operation of this technology is still very large, and its reflection effect varies with the equipment and process conditions used. Its main cracking component is generally based on liquid oil or gas, but also oil, gas, solid and other products. If a vertical furnace gasification decomposition device is used, 58% of the fuel gas can be obtained; if a fluidized bed gasification device is used, 84% of the fuel gas can be obtained.