Hazardous waste refers to the waste with one or more hazardous characteristics such as toxicity, corrosivity, flammability, reactivity or infectivity listed in the national hazardous waste list or identified according to the national hazardous waste identification standards and methods, including solid, semi-solid and liquid waste. At present, 479 kinds of hazardous wastes in 46 categories are listed in the national catalogue of hazardous wastes (2021 Edition).

Affected by the adjustment of the list of hazardous wastes, "waste removal action" and environmental protection supervision, China's hazardous waste disposal market has grown rapidly. Especially in 2020, affected by the outbreak of covid-19 during the Spring Festival, it is expected that the national output of medical waste will increase by more than 20%. Driven by the growth of medical waste output, the output of hazardous waste in China may exceed 100 million tons in 2020. Domestic hazardous waste treatment methods can be divided into resource utilization and harmless disposal. Resource utilization mainly includes hydrometallurgy, pyrometallurgy to extract precious metals, waste mineral oil / organic solvent recovery, etc. after years of development, supply and demand have basically reached a balance. The main technologies of harmless disposal include safe landfill, rotary kiln incineration, cement kiln co incineration and emerging disposal technologies represented by plasma gasification and melting. According to the calculation that the average disposal price of hazardous wastes is 3500 yuan /t, the market space for harmless disposal of hazardous wastes will reach 100billion yuan in 2020. Based on the investment scale of 60 ~ 80 million yuan per 10000 tons, the new market scale of hazardous waste harmless disposal project construction will reach 80billion yuan by 2020. Due to the limitations of weak technology research and development capacity, long qualification approval time, and the mismatch between qualification and demand, the contradiction between supply and demand is prominent and the capacity gap is huge in the hazardous waste treatment market. In order to deal with a wide variety of hazardous wastes, people should improve the applicability of technology. Among many hazardous waste treatment technologies, plasma gasification and melting technology has strong adaptability to raw materials and good environmental protection. It is a technology with great development prospects to realize the harmless and resource-based disposal of hazardous waste. The research and promotion of this technology is at the right time.

Plasma gasification and melting disposal technology uses the plasma torch to ionize the inert gas and form a 4726.85 ℃ plasma arc. Under the action of ultra-high temperature, anoxic environment and reactive active particles, the organic matter in hazardous waste is decomposed into syngas containing hydrogen, carbon monoxide, water and other gases, which can be used as fuel or chemical raw materials; Inorganic substances are melted to form vitreous slag (mainly composed of silicate and metal), which can be used to recover metals and make building materials. Plasma gasification and melting disposal technology has the function of solid hazardous waste reduction.

It has the advantages of good effect (high slag density), low secondary discharge (complete decomposition of dioxin precursors), high thermal efficiency, and no secondary landfill of treated residues. It can be used alone to dispose of most hazardous wastes (37 categories) such as hw01 ~ hw13, hw15 ~ hw25, hw27, hw29, hw34 ~ hw37, HW39, hw40, hw46 ~ hw50, which are especially suitable for the disposal of low calorific valueHighly toxic hazardous wastes, such as medical waste, asbestos waste, rotary kiln incineration fly ash and slag, etc.

Hazardous wastes have a wide variety, complex characteristics, wide regional distribution, and the output of a single waste production enterprise is small. The transfer of hazardous wastes is strictly controlled at the national level. For example, many western provinces prohibit the transfer of hazardous wastes outside the province; Jiangsu Province requires that hazardous wastes be safely disposed of on the spot without leaving the city. There are strict qualification requirements for the disposal of hazardous wastes. The qualification application threshold is high, difficult and long cycle. With the tightening of environmental supervision and the continuous promotion of the "entry" of industrial enterprises, hazardous waste disposal facilities will be used as public facilities supporting the industrial park to help the park achieve zero emission of pollutants. Based on the above situation, combined with the full cycle management policy and normative analysis of hazardous waste treatment and disposal, the future disposal terminal construction forms of hazardous waste disposal projects include: hazardous waste disposal center within the regional planning system; The park and waste production units are equipped with hazardous waste disposal plants / workshops; Transformation of resource utilization and harmless disposal process in waste production enterprises; On site disposal services in small mobile complete plant waste production enterprises. Although the operation cost of plasma gasification and melting disposal technology is high, it is increasingly favored by the industry because of its strong adaptability and excellent environmental protection. It is in the stage of technology demonstration in China, and has not been applied on a large scale, so it has a good market prospect.

In combination with the development trend of the industry, the following introduces an off grid power coupled plasma treatment system for hazardous wastes suitable for industrial parks, as shown in Figure 1.

The photovoltaic panels arranged in the park absorb the incoming sunlight and convert it into electric energy, which is absorbed by the battery pack, and then adjusted and integrated by the dc/dc converter to output a stable voltage for the use of the plasma hazardous waste treatment system. When the system is running, the plasma torch directly converts electric energy into ionized high-temperature gas with a central temperature of about 5000 ℃. After pretreatment such as crushing, the hazardous waste is pushed into the plasma gasification furnace by the feeder. Under the action of the high-temperature jet generated by the plasma torch, the organic matter in the hazardous waste is pyrolyzed and gasifiedinto combustible gases such as CO and h, which are discharged from the syngas outlet on the top of the furnace and enter the secondary combustion chamber. Inorganic matter forms high-temperature molten matter at the bottom of the furnace, and forms vitreous slag after water chilling, which is discharged from the slag discharge port at the bottom of the furnace and stored as general solid waste. At the same time, the waste liquid enters the waste liquid burner through the waste liquid pump, and is mixed in the secondary combustion chamber to form high-temperature flue gas. The high-temperature flue gas enters the air mixing chamber and is cooled to 175 ℃. After the acid gas is removed by the semi dry deacidification device, it enters the dust collector for dust removal. The flue gas after dust removal is sent to the chimney by the induced draft fan for discharge. The fly ash and waste liquid collected in the secondary combustion chamber, air mixing chamber, semi dry deacidification device and dust collector are returned to the feed hopper, mixed with hazardous waste, and then enter the plasma gasification furnace for melting treatment again. Syngas can be purified as general industrial raw materials according to the needs of the park, and the air mixing room can also be changed into a waste heat recovery device to provide heat for the park. During the operation of plasma gasifier, in addition to requiring a certain amount of clean compressed air to generate plasma, the plasma torch shell needs deionized water cooling. At the same time, a certain auxiliary wind is needed to homogenize the plasma heat energy with very concentrated energy. In the reaction process, an appropriate amount of auxiliary materials, such as coke, limestone, glass slag, etc., should be added. The function of coke is to form a furnace bed with voids in the reaction furnace. Molten inorganic substances fall into the slurry pool at the bottom of the reaction furnace through the gap. At the same time, coke also provides part of the heat energy for melting inorganic substances. The function of limestone is to increase the fluidity of molten slurry and play a certain role in acid-base neutralization. When there is less silicon in the material, some glass slag should be added to obtain vitrified slag with better quality. The off grid power coupled plasma hazardous waste treatment system is a combination of several mature subsystem technologies: photovoltaic power generation, plasma torch, syngas purification and syngas for power generation or chemical production are mature processes mastered by domestic enterprises. Each module equipment has strong versatility, simple device structure and small floor area, A system with a daily processing capacity of 5t covers an area of only 100m²(excluding photovoltaic), therefore, from the perspective of technical feasibility, the project construction only needs to do a good job in the combination of subsystems and improve the process, which has the possibility of popularization.