In recent years, China's domestic waste incineration has been rapidly developed. As of the end of 2015, 219 domestic waste incineration plants have been built in the country, with a daily processing capacity of 216,000 tons, accounting for more than 32% of the total amount of MSW decontaminated in China and expected to exceed 50% by 2020 It means that incineration will replace landfill and become the leading technology of municipal solid waste disposal in China.
Domestic waste incineration is a violent high-temperature thermochemical reaction process. Its environmental impact and environmental risks mainly come from the flue gas produced by high-temperature incineration. The most concern of society and the public is also incineration of flue gas, so flue gas purification is the configuration of waste incineration system and The focus and focus of operations management. To some extent, the process of development and improvement of domestic waste incineration technology is the process of continuous improvement of flue gas purification. With the continuous improvement of the level of flue gas purification, the flue gas discharged into the atmosphere is getting cleaner, and the purification system intercepts the capture of fine particles - domestic waste incineration fly ash (hereinafter referred to as fly ash) becomes more and more "dirty dirty". Due to the enrichment of toxic heavy metals and two VA British pollutants, fly ash in all countries in the world belong to the need to focus on the control of hazardous waste.
China's domestic waste incineration has made rapid progress and made great progress, but the treatment of fly ash is far from satisfactory, becoming the weakest link in pollution control and risk management in the entire process of domestic waste incineration. Due to the lack of reliable statistics, the actual harmless treatment rate of fly ash in China has not been known yet, but the estimation is much lower than expected. Recent reports frequently reported in the media fly ash disorderly stacking, non-standard handling and the use of the case also fully illustrates this point. July 1, 2014, China's new "domestic garbage incineration pollution control standards" formally implemented, flue gas purification standards further to the international advanced level, the control of domestic garbage incineration "last mile" pollution should focus on fly ash treatment, Otherwise, a "time bomb" will be planted for the environmental management of solid waste in our country.
The National Catalog of Hazardous Waste, effective from August 1, 2016, integrates incineration fly ash into domestic waste landfill disposal and co-processing into cement kilns into the exemption list. However, the technological route of our country's fly ash treatment is not clear yet. There are still some controversies on the different technologies of the fly ash treatment by government, industry, enterprises and experts.
Based on the comprehensive analysis of the properties of MSW incineration fly ash and the existing treatment technologies in our country, this paper takes the improvement of the environmental quality as the basic goal, takes the control of environmental risks and follows the environmental ethics as the basic principle, The applicable technical route for processing.
First, China's basic characteristics of municipal solid waste incineration fly ash
Accurately and comprehensively understanding the basic properties of domestic MSW fly ash is the basis for handling technical route selection. The basic properties of domestic waste incineration fly ash are:
(1) a huge amount of production. China's municipal solid waste incineration incinerator and a fluidized bed incinerator two mainstream furnace type, the current capacity of the two accounted for about two thirds of the total domestic waste incineration capacity and processing capacity. Mechanical grate incinerator fly ash generation is small, about 3 ~ 5% of the amount of waste into the furnace; fluidized bed incinerator fly ash generated larger, about 10% to 15% of the amount of garbage into the furnace. According to this estimation, in 2014 China's domestic waste incineration fly ash production of about 4 million tons, of which mechanical furnace incinerator fly ash about 1.5 million tons, fluidized bed incinerator fly ash about 2.5 million tons. According to the official statistics released by the Ministry of Environmental Protection, the total amount of hazardous wastes generated in China in 2014 was only 36.34 million tons, showing the importance of fly ash in the management of hazardous wastes in China.
(2) enrichment of heavy metals and two VA British. Most of the heavy metals in domestic waste incineration and two VA Ying were intercepted by the flue gas purification system and enriched in fly ash, so fly ash is an important "heavy metal" and two VA in the environment, which is clearly included in our country Hazardous waste directory "for hazardous waste, apply to mechanical grate incinerator fly ash, the same applies to the fluidized bed incinerator fly ash, without further identification to determine its properties. This property must be clearly adhered to, otherwise it will bring confusion in the environmental regulation of municipal solid waste incineration and market competition.
(3) high content of volatile elements. The properties of domestic waste incineration fly ash with the composition of the garbage, the season, incineration conditions, flue gas purification levels and other changes have a greater volatility, but the main chemical components of fly ash for calcium, silicon and aluminum, close to ordinary silicate Cement, there is a certain material basis for resource utilization of building materials. However, the content of volatile elements such as chlorine, sulfur, potassium and sodium in fly ash is relatively high, which has a great influence on its disposal and utilization. In particular, due to the chlorinated plastic and salt content of kitchen waste into the furnace burned, resulting in China's chlorine content of fly ash was significantly higher than the developed countries, greatly increased the difficulty of handling and utilization of fly ash.
Second, China's domestic waste incineration fly ash treatment technology route analysis
Hazardous waste management is essentially risk management, with the goal of keeping the environmental risks of pollutants within acceptable limits. There are mainly two ways to control environmental risks: one is to destroy sources of pollutants by source destruction, that is, to reduce sources of pollution; secondly, to reduce the migration of pollutants, that is, to cut off the routes of exposure. The risk of fly ash mainly comes from the heavy metals and VAIs enriched in it. Two VA British although highly toxic, but little content in the fly ash, and very low water solubility, control of its migration is relatively easy. Heavy metals in the fly ash content is high, and easy to dissolve water release, is the most important environmental risk control.
Based on the basic properties of fly ash and risk control of the main ways, the world's fly ash treatment are mainly land (including geological) disposal and building materials using two technology routes. Landfill technology is mature, the process is short, can effectively cut off the exposure of pollutants in order to achieve the goal of minimizing environmental risks, which has been the mainstream of fly ash processing technology line has been widely recognized and applied. The mechanism of building materials utilization is not yet clear, the technology is not yet mature, the process is more complex, and pollutant exposure increases. As a whole, it is not conducive to achieving the goal of minimizing environmental risk. Only sporadic applications in the world are available. Domestic waste incineration fly ash which way to deal with, depending on the natural and socio-economic conditions of countries and regulatory standards. Specifically, land disposal includes post-cure stabilization and landfill disposal, and deep mine storage. Building materials utilization includes cement kiln co-processing, sintering and melting.
Solidification and stabilization into hazardous waste safety Landfill disposal is the most secure disposal. However, due to the huge amount of fly ash generated, even if all the storage capacity of the hazardous waste safety landfill built in our country is used to dispose of new fly ash, it will be completely filled in less than a year. At the same time, the safety investment cost of landfill is high, with the admission fee of 1,500 yuan per tonne of fly ash, which is equivalent to the treatment cost per ton of solid waste. The increase of mechanical grate incinerator is about 60 yuan and the fluidized bed incinerator is increased About 180 yuan. Considering the indispensable solidification stabilization before landfill, the cost of safe landfill disposal is even higher. At present, China's domestic waste incineration normal (not cheap!) The winning bid price is generally 60-80 yuan per ton of waste, just to pay the cost of disposal of fly ash landfill are not enough. It can be seen from this that it is not feasible or economically feasible to enter the disposal of hazardous waste landfill sites after the stabilization of fly ash has stabilized.
Taking into account the above situation, China's "Amendment to the Standards for the Control of Sanitary Landfill Pollution" issued by China in 2008 requires that fly ash, after being pretreated to meet certain admission requirements, can enter the landfill of a sanitary landfill for disposal. Compared with the requirement for admission of fly ash into a safe landfill, the entry requirements for entering the sanitary landfill increase the moisture content and the content limit of 2 VA, and the requirements for heavy metals are also more stringent. For example, lead, cadmium , Nickel, arsenic leaching concentration limits decreased several times to several times. Several years of practice show that some heavy metals (such as lead) are difficult to stably reach the admission criteria, and heavy metals mainly rely on organic or inorganic chelating agents, long-term fixed effect there is some uncertainty. In addition, under real conditions, two VA content in fly ash can not be sampled and tested frequently, which brings great difficulties to standard implementation and environmental regulation. However, this provision still provides a more viable option for the standardized handling of fly ash. As long as it is properly managed, it can fully control the environmental risks of fly ash.
Deep mine storage is to place the fly ash in a container for long-term storage in the deep mine space isolated from the biosphere after mining, requiring long-term stability in the geology, absence of groundwater, multi-layer impermeable barrier with depth at the surface 400 M below the preferred mine as rock salt mine, is considered to be the most secure high-toxic refractory solid hazardous waste disposal methods. The technology is mainly popular in environmental protection requirements of Germany, Germany government in 2002 specifically promulgated the "underground waste filling Ordinance" to regulate and promote the development and application of the technology. The fly ash in Germany is mainly used for deep mine storage. There is no systematic research and practical experience in this area in our country.
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