Garbage disposal methods (using garbage (biomass) to produce charcoal, tar and gas) Widely used domestic and foreign municipal waste disposal methods mainly include sanitary landfill, high-temperature composting and incineration, etc. The proportions of the three main waste disposal methods vary according to the geographic environment; garbage composition, the level of economic development, etc., and Table 2-1 shows a comparison of the three kinds of Table 2-1 shows the comparison of the three treatment methods.
Because of the complexity of the composition of municipal waste, and by the level of economic development, energy structure, natural conditions and traditional habits and other factors, so the treatment of municipal waste in foreign countries is generally different with the national conditions, and often a country in the regions also use different treatment methods, it is difficult to have a unified model (Table 2-1). But ultimately, they all take harmlessness, resourcefulness and reduction as the treatment goal. From the point of view of application technology, foreign countries are mainly in the landfill, incineration, composting, comprehensive utilization and other ways, the degree of mechanization is high, and the formation of systems and complete sets of equipment. From the situation of a variety of foreign treatment, there are the following trends: (1) industrially developed countries due to energy, land resources are increasingly tense, the proportion of incineration is gradually increasing; (2) landfill method as the final means of disposal of waste has been a large proportion; (3) most of the developing countries of the agricultural type of composting; (4) a number of other new technologies, such as pyrolysis, reclamation, heap mountain landscaping and other technologies, is making progress.
Incineration is the world's widely used municipal waste treatment technology, large-scale equipped with thermal energy recovery and utilization of waste incineration treatment system, due to comply with the requirements of the recovery of energy, is gradually rising to the mainstream of incineration treatment. Foreign industrialized countries, especially Japan and Western Europe, generally committed to promoting the application of waste incineration technology. The wide application of foreign incineration technology, in addition to economically developed, strong investment, high calorific value of waste, mainly in the incineration process and equipment is mature and advanced. Many famous companies in the world to invest in the development of incineration technology and equipment, and the main equipment and ancillary equipment stereotypes supporting. Foreign industrialized countries are mainly committed to improving the original incineration device and the development of new incinerators, so that it is efficient, energy-saving, low cost, low pollution direction, the degree of automation is getting higher and higher.
China's urban waste disposal started late, as of the end of 1992, the national garbage, feces removal has reached 112.64 million t, while the garbage, feces harmless treatment plant only 371, the total capacity of 71,501 t/d. In recent years, according to the actual situation, from the countermeasures and planning to start, the city of garbage disposal technology has been a useful exploration. Hangzhou, Changzhou, Tianjin, Mianyang, Beijing, Wuhan and other cities in the study of foreign municipal waste treatment technology experience, based on their own design of the garbage with Chinese characteristics of the mechanized composting treatment production line; Shenzhen, Leshan and other cities in the construction of garbage incineration plant success, but also for the application of incineration technology in cities to provide the experience; Shenyang, Anshan and other cities in the implementation of unified management of the hospital garbage, centralized incineration, and out of the special garbage treatment new road. A new way of special garbage treatment. The technical countermeasures of China's urban garbage treatment are: sanitary landfill and high-temperature composting technology, and advocate the development of incineration technology in cities with conditions, especially in economically developed coastal areas. In recent years, cities began to carry out basic and applied research on garbage incineration treatment, developed including NF series of reverse combustion, RF series of pyrolysis, HL series of rotary small garbage combustion furnace and a number of hospital garbage special incinerator, and built a number of small and medium-sized city simple incineration plant (station). 1985, Shenzhen, the introduction of Japan's Mitsubishi incineration of a complete set of technology and equipment, completed the first large-scale (300t / d), the first large-scale incineration of the city garbage treatment plant in China. The first large-scale (300t / d) modern waste incineration and power generation integrated treatment plant for China to carry out the localization of municipal waste incineration equipment to lay the foundation.
On the treatment of municipal waste
Objective analysis of the composition of China's municipal waste changes in recent years, it can be said that, with the development of China's economy and people's living standards, the municipal waste in the combustible and flammable content has increased significantly, and the calorific value of significantly increased, generally after classification, sorting and other pre-treatment of garbage calorific value of the waste has been close to that of the developed countries of municipal waste. Therefore, some cities in China, especially in economically developed coastal areas, etc. have the basis for the development of incineration technology.
The relevant state departments and some experts and scholars have drawn up the implementation of waste incineration in China's urban centers program. A stone stirred up a thousand waves, set off a treatment of urban garbage "incineration" and "anti-incineration" of the controversy, in the people caused a great stir. The government's proposal to build municipal waste incineration plants in major cities has met with fierce opposition from the general public, who say that the establishment of waste incineration zones in urban centers and the edges of cities will do more harm than good. With regard to municipal waste, most countries use incineration and landfill disposal methods. However, the problem is not so simple, the world's green environmental protection organizations are most concerned about the human waste disposal problem is a very tricky thing. The best way to dispose of human waste is no longer the simple incineration and landfill methods we used in the past. Today, human beings are forced to rethink how the waste they produce should be disposed of, and neither burial nor incineration is the best solution.
Burial of municipal waste can lead to serious geologic soil and water contamination. Because human life waste includes a lot of toxic and harmful substances and germs, viruses and all kinds of heavy metal elements, it is very easy to jeopardize the normal survival and reproduction of human beings and organisms.
Radiation treatment of municipal solid waste with gamma rays and electron beam irradiation, in order to achieve sterilization, disinfection effect of a harmless treatment method.
Sewage treatment plant sludge and other wastes containing a large number of bacteria, viruses, parasitic eggs and other pathogens, the vitality is very strong, the use of ordinary heating or lime and other sterilization methods are difficult to completely kill. These solid wastes are applied to farmland as fertilizer, and some pathogens can survive in the soil for months, causing soil and water pollution and threatening the health of humans and livestock.
In the early 1970s, the agricultural field in the application of radioactive technology based on the formation of "waste radiation treatment" new technology. European Society for Nuclear Techniques in Agriculture (ESNA) has set up a "waste radiation treatment group". 1977 in Sweden held the second international "waste radiation" conference.
Waste radiation treatment method than the chemical, biological and fermentation treatment method has many advantages, it is simple equipment, easy to operate, with a pump or other transmission tools to send the waste into the radiation treatment equipment, radiation irradiation can be achieved after sterilization purposes, and radiation penetration is strong, sterilization is more thorough. Sludge after irradiation, the particles will also be small to large, so that the sludge has good dehydration and sedimentation properties.
The United States and Germany have built this treatment plant. The United States is located in Boston Deer Island sludge radiation treatment plant, the daily capacity of 375m? Its equipment is shown in the figure. Sludge transfer drum material is stainless steel, length 132 cm, diameter 45 cm. The minimum radiation dose used is 400,000 rad (rad), and the electron beam energy is 850 kilo-electron volts.
Germany in Wandel's sludge radiation treatment plant, the hourly capacity of 6m?, the plant covers an area of 400 square meters, 9 meters high, the use of the minimum radiation dose is also 400,000 rad.
Practical experience has proved that the sludge radiation treatment equipment, the higher the energy of the electron beam, through the electron beam radiation area of the sludge layer thickness can be greater. In general, the sludge layer thickness of 1.5 ~ 5 mm, the energy of the electron beam corresponding to 750 kiloelectronvolts to 1.5 megaelectronvolts; the width of the sludge layer to 1.2 meters, the flow rate of 2 m / s is appropriate.
The radiation method of sludge treatment is not expensive. German Federal **** and the country of a plant area of 150 ㎡ treatment plant, can handle 200,000 to 1 million people of urban sewage treatment plants discharged sludge, the cost of its treatment for each ton of sludge 2.70 West German marks.
Because of the different types and quantities of pathogens contained in the waste, the effective radiation dose is not the same, the general safety dose of less than 1 million rads. Commonly used radiation sources include 60 cobalt, 137 cesium, 90 strontium, 85 krypton and so on. Utilizing waste radioisotopes is an economically feasible method.
When radiation treatment is carried out, as long as the radiation source is sealed, such as placed in a concrete or other receptacle with a wall thickness of 1.5 meters, as well as the radiation dose does not exceed the above safety value, there will be no radioactive contamination, and there is no problem of eliminating the radioactive absorbed amount of reprocessing.
Additionally about the rural garbage disposal is also an urgent, to solve the problem. The general method of waste disposal can be summarized as material utilization, energy utilization and landfill disposal of three methods.
Material utilization, also known as material recycling, refers to the reuse, recycling and regeneration of the material properties of garbage through physical conversion, chemical conversion (including chemical modification and thermal conversion such as pyrolysis and gasification) and biological conversion (including microbial conversion, insect conversion, and animal conversion, etc.), including the traditional recycling of material resources and the conversion of perishable organic garbage into high-quality material resources.
Energy utilization, also known as energy recycling, refers to the conversion of the internal energy of garbage into heat and electricity, including incineration for power generation, heat supply and cogeneration.
Landfill disposal, refers to landfill disposal of unwanted waste that cannot be resourcefully processed (including material utilization and energy utilization).
If we look at the whole life cycle of garbage, garbage treatment should also include source reduction and emission control. Strictly speaking, reduction refers to source reduction, which is to reduce the waste of resources and the output of waste in the process of production and life by changing the habits of product design, raw material purchasing, consumer purchasing and consuming, and changing the business model. Generally speaking,
Waste treatment should adhere to the concept of first source reduction and emission control, then material utilization, then energy utilization and finally landfill disposal of hierarchical treatment and utilization, balanced development of all aspects of waste treatment, and give full play to the role of various ways of waste treatment, in particular, to strengthen the material use of classified waste, reduce the amount of waste generated and reduce the amount of waste emissions after each level of treatment.