Hazardous waste treatment and disposal and pollution prevention system includes the whole process of hazardous waste generation, collection, transportation, classification, detection, packaging, comprehensive utilization, storage, treatment and disposal.

 

In the production process of petroleum, chemical industry, chemical fertilizer, metallurgy, electric power, pharmaceutical, pesticide, food, chlor-alkali, environmental protection and other industries, there are various chemical media on equipment, pipelines and accessories caused by corrosion. According to relevant information, the annual loss caused by corrosion accounts for about 3% to 4% of the total output value of the national economy; every year, the waste generated by corrosion, the leakage of chemical substances and the accidents caused by it will cause damage to the surrounding atmosphere, water source, soil and other ecology, and at the same time, it will affect people's health or threaten life safety. The selection and application of anti-corrosion materials to extend the service life of process pipelines and equipment can be an important part of the hazardous waste treatment process.

 

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Hazardous waste treatment equipment

 

The treatment and disposal process of hazardous waste generally includes the collection and transportation of hazardous waste, classified temporary storage and exchange, comprehensive utilization, physical and chemical treatment, stabilization and solidification, incineration and safe landfill. The comprehensive utilization and physical and chemical treatment equipment of waste include: waste transport tank, waste storage tank, waste transfer pump, reaction tank, electrolyzer, demulsification and air flotation device, solid-liquid separator (settling tank, filter press, etc.), evaporation and concentration equipment, etc.

 

The corrosion characteristics of hazardous waste determines that the treatment device of hazardous waste cannot use a single steel equipment and steel pipes. It is necessary to use non-steel structure materials or the strength of steel structure supplemented by lining materials with corrosion resistance characteristics of non-metal structure to overcome the corresponding process requirements of temperature resistance, pressure resistance and corrosion resistance in the process.

 

In order to solve the corrosion problem of steel equipment, pipes, pipe fittings, etc., the equipment, pipes, etc. in the treatment device are used in different processes with epoxy glass fiber reinforced plastic (FRP), polyethylene (PE), high density polyethylene (HDPE), ABS, polypropylene (PP), reinforced polypropylene (RPP), polybutylene (PB), unplasticized polyvinyl chloride (PVC-U), perchlorinated polyvinyl chloride (PVC-C), graphite equipment and pipes, titanium equipment and pipelines and other anti-corrosion materials for protection. The production process of epoxy glass fiber reinforced plastic can only be used below 80 ℃, making it unsuitable for use in small flow process pipelines, pipe fittings and pumps. Fluoroplastics can be considered as a solution to the problem of corrosion protection in equipment and piping systems with operating temperatures above 60°C.

 

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Application of Fluoroplastics in Hazardous Waste Treatment Industry

 

The industrial application of fluoroplastics in hazardous waste treatment is widely used in petrochemical, refining, oilfield, dyeing, smelting, pharmaceutical, military, environmental protection and other industries in China, Southeast Asia, Europe and the United States.

 

The main varieties of commonly used fluorine plastics are:

 

(1) Non-plastic processing: polytetrafluoroethylene (PTFE)

 

(2) Thermoplastic processing:

 

● Ethylene propylene fluoride (FEP)

 

● Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA)

 

● Polyvinylidene fluoride (PVDF)

 

● Polyvinyl fluoride (PVF)

 

● Tetrafluoroethylene-ethylene copolymer (ETFE)

 

● Ethylene-chlorotrifluoroethylene copolymer (ECTFE)

 

● Polychlorotrifluoroethylene (PCTFE)

 

Fluoroplastics due to the introduction of negative fluorine atoms in the molecular structure, with a high degree of chemical stability and high and low temperature resistance, in addition to molten alkali metal (or its ammonia solution), chlorine trifluoride and elemental fluorine, it can resist any kind, any concentration of acid, alkali, salt, oxidant, organic solvent and all other strong corrosive medium corrosion. The temperature range is -195~250 ℃. And it also has good lubricity, excellent electrical insulation, outstanding non-stick, unique resistance to atmospheric aging, excellent non-combustibility and small water absorption and other properties.

 

Due to the limitation of its physical and mechanical properties, fluoroplastics should not be used as structural materials, and can only be used as an isolation layer for protection. Generally, carbon steel and other metal materials are used as the structural base material, and the fluorine plastic isolation medium is used to prevent corrosion. Fluoroplastics in the family of polytetrafluoroethylene, polyethylene glycol propylene is the most common application. Polytetrafluoroethylene is mainly used in the manufacture of lined pipes, large equipment, centrifugal pumps and stirring paddles, etc. Polyfluoroethylene propylene is mainly used in the manufacture of lined valves and centrifugal pumps and other products.

 

Fluoroplastics are mainly used in the following aspects in hazardous waste treatment process:

 

(1) As a sealing material for liquid delivery pumps and valves. This part of the application is mainly PTFE, because of its good heat resistance, chemical resistance and self-lubricating properties.

 

(2) Equipment and equipment lining. Mainly PTFE,FEP,PVDF) made of heat exchanger and PTFE dispersion impregnated graphite heat exchanger. For example, graphite evaporator equipment for organic waste liquid treatment, lined PTFE reactor and stirred slurry.

 

(3) Pipes and fittings used to transport corrosive gases and liquids. In the evaporation process of ammonia nitrogen wastewater treatment and organic waste liquid treatment, metal pipes lined with PTFE, FEP,PVDF) and other pipes and fittings and PTFE bellows are used.

 

(4) fluorine plastic pump, valve. The delivery pumps in each waste liquid treatment process adopt steel-lined fluoroplastic pump shells and all-plastic impellers. The use effect of fluoroplastic-lined pistons and piston cylinders in metering pumps with relatively high pressure (the operating pressure in the process is 0.6-1.0MPa) is also very good. The applications of valves mainly include all-plastic ball valves, diaphragm valves, plug valves, steel-lined F46 ball valves, regulating valves, etc.

 

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Application effect

 

Years of application experience, except for the wear and failure of individual lining PTFE pumps due to improper operation or large particle impurities in waste liquid, fluoroplastic products have a wider application range and application effect than commonly used anti-corrosion materials such as FRP, ABS, RPP, PE, etc. in terms of service temperature, wear resistance and corrosion resistance, and pipes and valves in hazardous waste treatment processes, the transfer pump and heat exchange evaporation equipment can be selected, especially in the treatment of wastewater containing CL evaporation and concentration process can completely replace the titanium material equipment, pipes, valves.

 

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Disadvantages of fluoroplastics in process applications

 

(1) with the increase of temperature in processing, it can not change from "high elastic state" to "viscous flow state", so it is difficult to process and weld, and it is difficult to bond due to low surface energy and large surface tension, which limits the wide application of PTFE in the field of corrosion protection.

 

(2) The fluorine plastic product itself has a low degree of rigidity and cannot directly make the overall equipment, but can only be used as an isolation layer for protection. As for the strength and rigidity of the equipment, metal materials are needed to ensure.

 

(3) process forming generally requires high temperature curing, curing time is long, large area construction is not convenient, and the substrate adhesion is poor, the wettability of pigments and fillers is poor, the solubility in organic solvents is not good, the price is more expensive.

 

(4) The application effect of steel-lined pipes in vacuum is not ideal.

 

(5) Due to the inability to process at the project site, the pipeline needs to be made in the manufacturer, and the on-site installation is inaccurate, which limits the pipeline of this process from being widely used.