Separation technology of waste plastics

2021-11-23 16:23:11 189
本文转载自网络,如有侵权,请联络删除:  废旧塑料分选技术bookmark0环保与平安本栏目由中国化工防治污染技术协会协办王晖顾帼华邱冠周(中南大学化学化工学院,长沙410083)要有效的塑料分选办法。评述了光选、电选、风力分选、密度分选、浮选等废旧塑料分选技术,指出浮选在废旧塑料分选方面具备共同劣势。

Work or regeneration. At present, for the processing or regeneration of waste plastics, processes such as incineration, pyrolysis and conversion, recovery of chemical products and simple regeneration have been developed. In 1998, the amount of waste plastics in Japan reached 9.84 million tons, of which 32% were recovered by incineration; Pyrolysis conversion technology is mainly aimed at waste polyolefin plastics, which are converted into low molecular substances through catalytic cracking. The fuel oil consumed is basically the same as that consumed with crude oil in terms of product quality, and does not contain harmful substances such as lead and ammonia.

In the process of recycling waste plastics, the following prominent problems are encountered: ① secondary pollution and corrosion to facilities in the process of incineration and heat extraction. Hydrogen chloride and cyanide will be produced in the process of PVC incineration. In the consumption of plastics, thermoplastics are the main body, accounting for 82.6%, thermosetting plastics for 16.9%, and other plastics for 0.5%. In thermoplastics, the consumption is concentrated in polyethylene (PE) , polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), polybutylene terephthalate (PET) and acrylonitrile / butadiene / styrene copolymer (ABS) (accounting for 93%), of which low-density polyethylene (LDPE) accounts for 22%, high-density polyethylene (HDPE) and PVC account for 18%, PP accounts for 15%, PS accounts for 13%, wading and, Accounting for 4%, 83% and 3% respectively. In addition, polymethylmethacrylate (MMA), polycarbonate (PC), nylon (nylon) and rubber account for 1% respectively. Other waste plastics such as phenolic resin (PF) and polyurethane (PU) are recycled. The recycling of waste plastics includes three stages: collection, sorting Date of receipt: ⑴ 2-04-27 Fund Project: special fund sponsored by national excellent doctoral dissertation author (00145) Wang Hui et al: waste plastic separation technology (kg / m3), mixture of acetone and tetrabromoethane (mixing in different proportions can show common disadvantages! K hydrogen chloride, NOx and other harmful gases will form significant corrosion to the facilities at the same time; a large number of harmful gases and black smoke will be generated during PS incineration; ② catalyst failure in catalytic cracking process, poor thermal conductivity of waste plastics, and coking on the surface of catalyst will be formed by some non pyrolytic substances mixed in fuel oil during cracking consumption At the same time, the hydrogen chloride produced during PVC pyrolysis will form catalyst poisoning; ③ the separation of waste plastics before recycling chemical products or simple regeneration.

2 separation of waste plastics the separation technology of waste plastics mixture can be divided into dry method and wet method. It is generally believed that wet method is easier to obtain higher separation accuracy than dry method. Optical separation, electric separation, wind separation, density separation and flotation have been applied to different degrees in the separation of waste plastics, among which flotation 2.1 dry separation of different plastics has different infrared spectra For example, the infrared spectral characteristics of PVC are different from those of pet and PP; X-ray can detect the chlorine in PVC. PMMA, PE, PVC and nylon are adopted by electro separation technology respectively, and the purity of the product reaches more than 95% and the recovery rate reaches 98%. Because the difference in charging of plastics is not very clear, especially with regard to the actual plastic treasure, its charging property is different from that of pure plastics, and electro separation is attached Because of the great influence of moisture and humidity, there are many limitations in the separation of waste plastics by electric separation technology.

Wind separation is the separation of plastic particles in the air flow due to the difference of particle size, shape and density, which is suitable for the separation of materials with large density difference. Its facilities can be divided into wind separation cylinder and wind shaking table. In addition to wind factors, it also makes use of the difference of particle friction coefficient. Generally speaking, wind separation is more suitable for the separation of metal and plastic, The efficiency of sorting between waste plastics is not high, and the wind shaking table still has the defect of low solving ability.

2.2 wet separation if you can select a medium with appropriate density to make one of the two plastics sink and the other sink, you can realize the difference between the two. Because waste plastics are often solved with flame retardants and stiffeners, the density of plastics with the same name is often different. It shows the density range of various plastics measured by different researchers, including POM It is polymethylamine, PA is polyamide, and the real point represents the measured results of different material selection + PE quality). Zhang Zhongyan and others have successfully separated metals from plastics, light plastics (ABS, PS, PVC) from glass reinforced resin and aluminum from heavy metals by adopting the separation technology of heavy media (NaCl + water, Ca + water, acetone + tetrabromoethane and tetrabromoethane).

Density range of waste plastics Japan plastics solution Promotion Association has obtained Chengfang 51 through a special hydrocyclone according to the density difference, which can effectively separate plastics with density less than water and plastics with density greater than water, especially plastics with thickness greater than 0.3mm and density difference of about 500kg / m3. The one-time separation rate can reach more than 99.9%. If multistage hydrocyclone or the same hydrocyclone is adopted After repeated separation, plastics with more similar density can be separated.

Flotation is the most effective way to obtain high-quality concentrate in the mineral processing process. Its action mechanism is based on the selective fixation of particles to be separated to bubbles. In the natural state, most plastics are hydrophobic and can float, but the components of plastics to be separated can be realized by controlling the liquid-gas interfacial tension and the adsorption of surfactant 113 141617 '2024 ~ 29 Selective wetting.

Flotation can be competent for the separation of waste plastics with similar density and charging properties, and can achieve high separation accuracy. After years of research, people have been in the laboratory through plasma surface modification and the flotation of mixed plastics in ABS / PS / PA and other systems. The specific conditions are listed in Table 2 and table 3. Moreover, semi industrial tests have been completed in Germany Dry separation of waste plastics. Mineral processing of foreign metal ores, 2 (1) (6) 25 Zhou Bingyan. Solution and treatment technology of waste plastics. Environmental protection, 20 (1) (3) 2022 Qi Yazhu. Pause in recycling and utilization of waste plastics. Urban environment and urban ecology, 2 (1) 1 Zhou Weiping, long Zhengyu. Plastic pollution and its treatment countermeasures. Modern chemical industry, 2 (1) 020 (6) : 1 ~ 4 Li Qingshan, Wang Huimin, Cai Chuanying. A new pause in plastic recycling and utilization. Chemtong Li Wanhai, Zhang songbin, Wang Hong. Preparation of coatings from waste polystyrene foam plastics. Environmental Yang Zhen. Research on styrene monomer consumption by thermal decomposition of waste polystyrene plastics. Environmental Zou Shengou. Plastic depolymerization technology. Plastic technology, 1998, 126 (4) : 5457 Li Hui, Ma Zhengxian. Crushing of waste plastics. China plastics, 2 (1), 15 (4): 8690, Zhang Zhongyan, Zhao genmei, Liang Huqi. Study on the methods of recycling polyester (PET) waste plastics respectively. Environmental science, 199415 (3) : 2629 4.3 communication module communication module is the key to ensure the reliability and real-time communication of high-level and low-level computers. We adopt the master-slave communication structure mode, use the self-developed communication conversion board and RS-485 to define the network communication protocol applicable to the system, and closely cooperate the protocol program with the relevant programs of high-level and low-level computers to ensure one-to-one communication between high-level and low-level computers (no communication is designed between the lower computers of the system).

5 operation results the system has been in normal operation for more than one year, safe and reliable, without any problems and obvious benefits. According to the data provided by the manufacturer, the coal consumption per ton of ammonia has decreased by 4.25%, the steam consumption per ton of ammonia has decreased by 23.7%, the hydrogen nitrogen ratio is controlled at about 2.7, and the error is limited within ± 0.2. The qualified rate of manual hydrogen nitrogen ratio control was only 70%, but now it is stable at more than 93%. It has made great progress In addition, because the computer replaces the old instrument panel, not only the detection is accurate and the control is reliable, but also the 94 working condition parameters of the system are displayed on the screen, which facilitates the operation and reduces the labor intensity.

The author believes that the quality of chemical consumption lies in the reasonable consumption process. The reasonable consumption process is inseparable from advanced detection and control techniques. The old facilities can also consume high-quality products by adopting computer detection and control. For this intermittent consumption process control, conventional PID algorithm and the so-called advanced algorithm, such as optimal control and Kalman filter, state response control, etc We can't get satisfactory results, but adopt fuzzy control. 1. Humanoid intelligent control can get obvious results. Analyzing its causes, the key is that this intermittent consumption process is too complex, and the commonly used second-order model is far from this system. Therefore, it is difficult for general algorithms or advanced algorithms to work. We adopt humanoid intelligent algorithms, which have strong anti-interference ability and stable operation.

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