Domestic waste incineration fly ash disposal technology

Release Time：2022-11-22 Source：Battery Recycling Machine Share：

        With the rapid development of urbanization and the increasing improvement of people's living standards, the amount of urban domestic waste generation has also increased rapidly, with the national urban domestic waste removal volume reaching 228.018 million tons in 2018, and the problem of domestic waste treatment and disposal has attracted much attention. Domestic waste incineration power generation has gradually become the mainstream way of domestic waste disposal in China because of the advantages of obvious reduction, less land resources and energy realization. The "13th Five-Year Plan" issued by the National Development and Reform Commission and the Ministry of Housing and Urban-Rural Development indicates that the national target for urban domestic waste incineration power generation is 54% in 2020, and the daily treatment scale of domestic waste incineration will reach 591,400 tons. Domestic waste incineration fly ash (hereinafter referred to as fly ash) is a powdered material collected from the flue gas purification system of domestic waste incineration, which belongs to hazardous waste (code HW18). In recent years, with the rapid growth of urban household waste generation, the amount of fly ash generated is increasing, and according to the projection of China Cement Association, by the end of the 13th Five-Year Plan, the annual fly ash generation in China will be as high as about 10 million tons.
 

The importance and urgency of fly ash disposal


        Fly ash contains organic pollutants such as benzo(a)pyrene, benzanthracene, dioxin and other heavy metals such as Cr, Cd, Hg, Pb, Cu and Ni, which are highly hazardous solid wastes. Dioxins are chlorinated tricyclic aromatic organic compounds with multiple toxic effects, which are irreversibly teratogenic, carcinogenic and mutagenic; Hg and its compounds are extremely neurotoxic and can cause serious damage to multiple organs of the human body. If fly ash is not disposed of properly, it can cause serious toxic damage to the environment. In 2018, Beijing's household waste disposal volume was 9.751 million tons and fly ash generation was about 120,000 tons, while the safe landfill pit capacity of the only company in Beijing that meets the conditions for landfilling fly ash, GTC Beijing Eco Island Technology Co. The only company in Beijing that can meet the conditions for landfilling fly ash, Beijing Ecological Island Technology Co. Therefore, there is an urgent need to find an effective way to dispose fly ash effectively and save land resources.
 

Difficulties of fly ash disposal technology


        The production and components of domestic waste are significantly different from those of developed countries, which makes them have different characteristics.

        1. High content of chlorine element. The acidic substances such as hydrogen chloride produced by the incineration of chlorinated plastics in domestic waste react with the alkaline substances in the flue gas cleaning system and enter the fly ash, and the salt in food waste is also enriched in the fly ash. The high chlorine content is one of the most obvious characteristics of fly ash in China, for example, the chlorine content of fly ash in Beijing area is over 20%, and the chlorine in fly ash mainly exists in the form of soluble chlorine salts, such as sodium chloride, potassium chloride, calcium chloride, etc.

        2. The composition is complex and fluctuates greatly. In addition to heavy metals and dioxins and other toxic and harmful substances, fly ash also contains calcium, silicon, aluminum, iron oxides, chlorine salts and carbon, sulfur and phosphorus elements. The content of each substance (element) in the fly ash will fluctuate greatly with the changes of domestic waste components, seasons, incineration conditions, flue gas purification level, etc., which will bring great difficulties to the disposal of fly ash treatment.
 

Analysis of the current situation of fly ash disposal technology


        1. The general situation of technology. According to the Technical Specification for Fly Ash Pollution Control of Domestic Waste Incineration (draft for review) being developed by the Ministry of Ecology and Environment, fly ash disposal is divided into two ways: landfill and resource-based. Landfill is the traditional method of disposal of fly ash, while resourceization is a new treatment method developed in recent years. Before the disposal of fly ash in landfill or resource utilization, appropriate pretreatment of fly ash is required. Current pretreatment technologies for fly ash include water washing, solidification/stabilization, high-temperature sintering, high-temperature melting, and low-temperature pyrolysis.

        Among them, the solidification/stabilization-landfill technology refers to the inclusion of toxic and hazardous components in the fly ash to cover them or make them appear chemically inert, and then enter the landfill for landfill. The cement kiln co-disposal technology is to use the fly ash as cement raw material after washing (chlorine salt removal), and then completely decompose the dioxins through high temperature firing in the cement kiln, and solidify and stabilize the heavy metals in the cement clinker, while the wastewater from washing is treated and reused. The high-temperature sintering technology is a mixture of fly ash or raw materials such as industrial solid waste or clay, which is heated to the melting point of the fly ash after adding additives such as fluxes and binders to form a lightweight dense solid that can be used as ceramic pellets. The plasma melting technology is a mixture of fly ash or raw materials such as solid waste, with additives, and then heated to the melting point of the fly ash using a heat source generated by a plasma torch, and then cooled to form a dense glass body. Low-temperature pyrolysis technology involves the removal of dioxins from fly ash at low temperatures and then using it as a substitute raw material for the production of building materials products. In general, solidification/stabilization-landfill technology is now widely used in domestic fly ash disposal; cement kiln co-disposal is a fly ash resource utilization technology successfully developed in recent years; high-temperature sintering and ceramic pellets are currently used in fly ash disposal in Tianjin; plasma melting, as an important way of high-temperature melting of fly ash, has been tested on a medium scale in recent years; low-temperature pyrolysis is an emerging fly ash treatment technology, and relevant units are working on it. Low-temperature pyrolysis is an emerging fly ash disposal technology, and the relevant units are carrying out relevant research.
 

 
        The new version of the National Hazardous Waste Inventory, which came into effect on August 1, 2016, includes the process of fly ash disposal in domestic landfills and cement kiln co-processing in the exemption list management, indicating that solidification/stabilization-landfill technology and cement kiln co-processing are the mainstream technologies for fly ash disposal recognized by the Chinese government.

        (1) Solidification / stabilization - landfill. According to the Hazardous Waste Landfill Pollution Control Standard (GB18598-2001), fly ash can be landfilled in hazardous waste landfills after meeting the stabilization control limit, and the Sanitary Landfill Pollution Control Standard for Domestic Waste (GB18598-2008), which was revised and promulgated in 2008, stipulates that fly ash can be landfilled in separate units of landfills after pre-treatment to meet the admission requirements. Landfill.

        Curing/stabilization is the pretreatment technology for fly ash disposal in landfills, and its main function is to control and reduce the leaching of heavy metals in fly ash. Curing/stabilization technology mainly includes cement curing method and chemical stabilization method, of which chemical stabilization method has been more frequently reported in recent years due to its small volume increase and better curing effect, and the commonly used chemicals can be divided into inorganic and organic categories, inorganic chemicals mainly include gypsum, phosphate, sulfide (sodium thiosulfate, sodium sulfide), ferrate, silicate, silica gel, lime, etc., and organic chemicals Organic agents mainly include mercaptoamine salts, EDTA-linked polymers, citrate, polyphosphates, chitosan derivatives, etc.

        Curing / stabilization - landfill is currently a common way of domestic fly ash disposal, but in the pre-treatment process before landfill is still lacking a unified technical specification, the Ministry of Housing and Urban-Rural Development is organizing the relevant units to step up the development of "domestic waste incineration fly ash curing / stabilization treatment technology standards.

        (2) Cement kiln co-disposal. In the application of cement kiln co-disposal technology, two fly ash disposal production industrial lines with a total annual capacity of 70,000 tons have been built in China, both of which have reached production standards and stable operation.

        After the adoption of cement kiln co-disposal of fly ash, the leaching toxicity of heavy metals in cement clinker meets the standard requirements of Technical Specification for Cement Kiln Co-Disposal of Solid Waste (GB30760-2014), the concentration of pollutants in the flue gas emission is lower than the limit value in the Cement Kiln Co-Disposal of Solid Waste Pollution Control Standard (GB30485-2013), and the quality of cement meets the standard of General Silicate Cement (GB175-2008). GB175-2008) standard.

        With the advantages of complete disposal, no secondary pollution and resource utilization, the cement kiln co-disposal of fly ash technology has been recognized by government departments and selected in the National List of Advanced Pollution Prevention Technologies in the field of solid waste management issued by the former Ministry of Environmental Protection in 2017 and the Ministry of Industry and Information Technology's Catalogue of Technologies and Products Encouraged to be Promoted and Applied in the Building Materials Industry (2018-2019 version), which is a national Encourage the promotion and application of environmental protection technologies.

        3. Comparison of mainstream technologies. Curing/stabilization-landfill and cement kiln co-disposal technologies have their own strengths, and the results of a comprehensive comparison in terms of environmental hazards and reliability, economics, etc. are shown in the table.

        As shown in the table below, cement kiln co-disposal technology has obvious advantages over solidification/stabilization-landfill technology because of its high resourceization, low environmental risk and no land occupation.
 

        Analysis of the development trend of fly ash disposal technology


        1. Mainstream technology. Curing/stabilization-landfill disposal technology is the main disposal method of fly ash in China, but this technology occupies valuable land resources, highly toxic dioxins and heavy metals still exist, and there are potential environmental risks. In the future, with the improvement of relevant standards and technologies, it can be applied to small and medium-sized cities with low fly ash generation and relatively abundant land resources.

        The cement kiln co-disposal technology uses cement kilns to dispose of fly ash, realizing the harmless disposal and resource utilization of fly ash, and solving the problem of "garbage surrounding the city" and "the last kilometer road" while promoting the green transformation development of the cement industry, with significant social and environmental benefits. Social and environmental benefits. With mature technology and perfect standard system, cement kiln co-disposal of fly ash is the technology of choice for large and medium-sized cities with cement plants and has good development prospects.

        At present, GTC Group's Beijing GTC Lushui Environmental Protection Technology Co., Ltd. has formed a complete cement kiln co-disposal fly ash technology after years of research and development with the technical support of Beijing General Research Institute of Building Materials Science Co.

        2. Other related technologies. High-temperature sintering technology is characterized by a high dioxin degradation rate of more than 95% in fly ash, and the sintered product is a light and dense solid, which can be used as ceramic pellets, but the process route of this technology is more complicated, the tail gas treatment is more difficult, more secondary fly ash is produced, and there are many technical problems to overcome.

        The use of plasma melting can completely decompose dioxins and other organic pollutants in the fly ash, and ultimately produce non-toxic and harmless glass body slag can be directly used for building materials, but the technology due to the high cost of disposal, technical difficulties, and the problem of secondary fly ash, is currently only in the small-scale disposal stage, the technology has a long way to go to promote the application.

        Low-temperature detoxification technology is currently relatively few units of research, technical maturity is not high, the low-temperature degradation of dioxins and volatile heavy metal pollution control is the bottleneck of its technology.

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