Analysis on several major principles and specific practices of waste plastics

The use of plastics has made a significant contribution to protecting human health and the environment, preserving natural resources and reducing waste. Only 4% of the annual oil production is used to make plastics. Many uses of plastics have a long life cycle, and the used plastics can often be recycled for secondary use. The use of plastic means:

Reduced material use in a given application (eg, packaging has decreased by nearly 80% over the past 20 years; few packages have been lost due to packaging protection);

Use less energy in production than traditional methods (eg plastics are converted at low energy density);

Consume less fuel during transportation and handling (eg plastics in automotive and packaging applications);

Produces less pollution during manufacturing and use;

It produces very little waste plastic after use (for example, in comparison with conventional materials like metal and glass in terms of volume and weight).

1. General principles for the recycling and disposal of waste plastics internationally

Environmentally sound disposal at the Basel Conference (1992) is defined as taking all feasible measures to ensure that toxic or other wastes are managed in a manner that protects people's health and the environment and avoids the adverse effects that may result from such waste. The waste system that is prioritized by international waste management policies is the prevention or reduction of waste through reuse, recycling, regeneration and residue treatment. This strategy includes an integrated approach to waste disposal for raw material recovery. This provides general guidance on the identification, environmentally sound management, recycling and final disposal of waste plastics.

2. Waste plastic technology management principles

21 Stop and reduce waste from the source

In order to make plastics sustainable in the economic process, it is necessary to consider the impact on the environment during material preparation and product design, and to minimize the consumption of raw materials while minimizing the impact of plastics on the environment. For example, before the plastic products enter the market, the plastic classification mark is used to indicate the material properties of the plastic products or their accessory parts, which is convenient for sorting in later recycling. In fact, this is to protect the manufacturer and industry of the product, and to reduce the use of plastic raw materials on the part, which is beneficial to technological progress and cost reduction. In addition, the use of materials is standardized, specialized, and labeled to make materials easy to recycle. Therefore, in order to solve the difficulties in the cycle, the following measures should be considered:

Product standardization, using the same materials to manufacture the same product;

Designed products should be easy to disassemble and separate:

The type of material to be marked;

Minimize the type of materials used;

Use new flame retardant technology, such as no halogen compounds.

Due to the different lifetimes of different plastics in different applications, there is no exact direct connection between the product and the waste. Many plastics are shortened in use, so more waste is actually obtained. However, in the production, processing and use of plastics, waste is generated, which is essential to be properly treated to protect human health and the environment.

22 centralized management principles of authorization

Waste plastics are the highest calorific value in waste, and the re-use value is also very high. If waste plastics can effectively achieve the purpose of recycling and environmental protection, the mandatory recycling and disposal is essential, so the state Laws, regulations or government administrative measures are indispensable factors, and the responsibilities of all parties involved in waste disposal should be clear and unified management should be strengthened.

The centralized recycling and disposal of waste plastics is the primary condition for the comprehensive disposal and disposal of waste plastics by the government-supported and authorized waste recycling and recycling operations. Establishing a comprehensive disposal mechanism for waste plastics is an effective way to solve the environmentally sound disposal of waste plastics.

3. The main ways to recycle used plastics

31 physical mechanical recycling of waste plastic

Due to its plasticity and reusability, plastic recycling can effectively reduce resource waste and promote environmental protection. The practices and experiences of developed countries in the West are worth learning. The successful strategy for solving plastic development and environmental problems is to implement the “three R” strategy, namely, reduction of plastic products, reuse (Reuse) and recycling of plastic waste ( Recycle).

European mechanical recycling of waste plastics: According to data released by the European Plastics Manufacturers Association on April 19, 2002: Recycled and otherwise recycled plastics in all application areas increased significantly in 2000, reducing waste plastics in waste Dispose of. In 2000, demand for plastics in Western Europe increased by 3% to 367.69 million tons, but total recycling through mechanical recycling, recycled raw materials and energy recovery increased by 11%. An analysis of plastic consumption and recycling in Western Europe in 2000 showed that despite the increase in demand for plastics, the total amount of waste plastics used after use was still less than 1% of the total waste of all materials, and the growth of waste plastics recovered by 36%, which has been reduced. One of the most important factors in the disposal of waste plastics is the reduction of the negative impact of plastics on the environment. In 2000, more than 50% of the waste plastics used for packaging were recycled in the Netherlands, Switzerland, Denmark, Norway, Germany, Sweden, Austria and Belgium.

Recycling of discarded plastics in the United States and Japan: It is reported that the American Plastics Industry Association (SPI) has established more than 6,800 collection points in the United States, and nearly 1,000 in Japan. In the new way of recycling waste plastics, the Japanese Ministry of the Environment plans to build 150 waste plastic power stations throughout Japan in the next 8 years. By 2010, the current waste-to-energy generation capacity will be increased by 5 times, and the annual waste-to-energy generation will reach 4 million kilowatts. Above, it is lower than the cost of wind power and ocean power generation. In addition, Taiwan Province of China also attaches great importance to the recycling of waste plastics, with 138 collection points.

It can be seen that the physical and mechanical recovery of waste plastics is an internationally accepted practice and the best choice for resource recycling. It is in line with China's national conditions and related policies, and it has been consistently adhered to by China for many years. The basic recycling process is: waste plastic → pretreatment → identification → classification → cleaning cleaning → crushing → granulation → recycling,

32 mechanical recycling classification

After use, the plastic must be separated from the non-plastic material. It is more desirable and more reasonable to divide the plastic into a single variety before reprocessing and for secondary use. Unless the plastic composition is clearly marked with its type, it is necessary to consider the identification of expertise. A small amount of plastic is not worth separating and recycling, but it can be used for energy recovery. The following techniques are suitable for plastic separation.

33 chemical recycling recycling of waste plastics

The recycling of some plastics is not economical because of its physical defects. It is more valuable and scientific to require chemical recycling. For example, polyurethane plastics, which are used to synthesize other polymers by alcoholysis, hydrolysis, alkali hydrolysis, aminolysis, pyrolysis, acid hydrolysis, hydrocracking and other methods to recover polyols and other substances.

Almost all plastics can be cracked with small molecular substances under high temperature and high pressure conditions. This method is the process of raw material recovery and belongs to chemical recovery. However, the chemical recovery process consumes more energy than the physical recovery. The process control is much more complicated, and the generated gas, liquid, and solid residues need to be handled well, so as not to pollute the environment.

34 waste plastic energy recovery

While some recycled plastic recycling is good for the environment, there are many small pieces of waste plastic dispersed in other wastes. If economic costs are not considered, the separation and cleaning of such waste may have a higher environmental burden than the benefits of recycling. There are still residues that cannot be recovered during the recycling process. If recycling cannot be justified, then energy regeneration may be an environmentally friendly and cost-effective way to regain the value of the resources inherent in waste plastics. In general, plastics contain high energy values ​​that help wet or plant waste incineration when mixed with other wastes.

Through research and practice over the past 10 years, it has been concluded that waste plastics can be safely and efficiently incinerated at high temperatures. The maximum amount of energy recovered from the fuel is always obtained, and the toxic organic compounds are completely decomposed. When waste combustion produces a high-pressure steam stream to the generator, more than 85% of the energy is efficiently recovered, the low-pressure steam stream is used in industry, and the hot water is used for home heating. Most waste regenerative plants do not always take care of all three.

The Basel meeting has prepared a draft technical guide on ground burning. They pointed out that there are four key factors in the environmental impact of incineration and recovery of energy:

1. The natural state of waste incineration

2. Incineration condition control

3. Purification of exhaust gases

4, residue treatment

There are four different types of waste plastic waste used for energy recovery, each with its own recycling value.

fuel

Net heat value (MJ/kg)

gasoline

40

coal

25

PF (disused plastic)

42 (reference)

PDF (paper and plastic pellets)

20

RDF (derived garbage fuel)

15-17

MSW (Urban Solid Waste)

10

wood

8

In general, the total energy recovery from waste is one of the more scientific and economical methods of plastic recycling, but it may also pollute the environment and affect human health (the average heat of combustion of plastics is calculated as 42?03kj/kq). The secondary pollution of energy recovery is manifested in the following aspects:

Greenhouse effect

Acid gases, metals and particles

Toxic organic matter

Although plastic can be recycled, it cannot be regenerated again and again, or forever. But this does not mean that they have lost their use value. Currently, countries generally use energy recovery equipment for incineration to obtain energy.

4. Final disposal of waste plastics

If the waste plastics completely loses the value of reuse, they are treated according to the general principles of waste disposal. Landfill and incineration are their last choices. Plastic waste is allowed to be landfill where the recycling methods listed above are not possible. Incineration without energy recovery is often used to reduce the volume of waste residues in landfills, but incinerators are mandated to be essential and meet the same environmental standards as energy recovery incinerators.

41 incineration without energy recovery

The main difference between an energy recovery and non-energy recovery incinerator or plant is a potential source of energy that can be converted into electrical energy by thermal steam. Both types of devices meet emission standards.

The form of incineration waste, incineration control conditions, purification of waste gas and disposal of waste residue are important factors.

42 landfill

Landfill is still one of the most common waste disposal methods in most countries, and the Basel meeting has developed a draft technical guidance for the establishment of special engineering landfills for wastes with one or more toxic characteristics. These guidelines also take into account existing landfill sites and require strict controls and frequent remedial measures. Only those landfills that meet the requirements of the Basel meeting are used.

It has been noted that the landfilled organic matter is biodegraded to produce flammable methane. Polymers used in ordinary plastics are inert and they cannot be attacked by microorganisms. Because plastic does not rot, it is considered a stabilizer in landfills.

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