City Garbage Disposal Technology and Direction

Urban living garbage, also known as urban solid waste, it refers to the urban residents in daily life or to provide services for urban daily life activity of solid waste, its main ingredients include: kitchen tailings, waste paper, waste plastics, waste cloth, pieces of scrap metal, waste glass, ceramics, tiles, waste, waste residue and waste household, old appliances, garden waste, etc.

At present, the passage of urban living garbage disposal technology mainly include incineration and landfill, composting, and R DF technology, anaerobic biological bogs and other processing technology also appear in a foreign country and applied to the city life garbage processing.In fact R D F technology, anaerobic biological bogs and other processing technology mostly incineration and landfill is the extension of the development of compost technology.

Landfill is actually one of the oldest garbage disposal method , but also is the ultimate application of garbage disposal.No matter what ways, process, processing waste, and ultimately to adopt the landfill as a means of processing, such as burning will ultimately produce ash, compost can handle only given biodegradable organics, are unable to process waste, with a landfill in order to solve the ultimate way out.Even in waste incineration for the highest percentage of Japan, there are still 10% of household garbage directly into the landfill, and 15% of the total garbage burned garbage incineration residue and 29% of the total processing in addition to the burning of other processing residue into landfills.So, landfill is essential to garbage disposal process and one final step.As a result, the landfill also referred to as the final disposal or landfill disposal.

The land of waste disposal has been implemented for centuries.In the past, it is generally accepted that junk and leachate can get down through the clay and groundwater (or purification), without pollution of groundwater. Therefore, before the 1950 s, garbage dumps field is usually use gravel ditches, pits, dry pond and mountainous area.But in our country, this kind of situation has continued into the 70 s.Some institutions from the 50 s, western countries continue to study, the landfill pollution of groundwater.However, because of urban living garbage produced by the main pollutants in the leachate can be in the clay is obtained by the effect of biological and chemical purification, two design of landfill concepts appeared in the early 70 s : natural attenuation type landfill and closed landfill. the main difference of them is that a type of natural attenuation landfill landfill site without impervious lining and leachate collection pipe system, the main design index is the minimum thickness of clay is not saturated zone, away from the depth of bedrock and the minimum distance of driving Wells, because this kind of landfill leachate were allowed into the clay, purified by clay;While closed landfill site requirements laid anti-seepage lining to prevent leachate into the clay, and leachate collection pipe system for processing.So you can see, in the 50 s, before the landfill landfill mainly attenuation type.In our country, at present the most landfill is still belongs to the landfill.

The type of natural attenuation landfill always change groundwater quality and make it worse. Now the deterioration of groundwater have reached the point where they cannot tolerate in most cities.. Therefore, many countries of the world are basically not allowed to use this method of landfill disposal of municipal waste (of course, can’t used for disposal of hazardous waste and hazardous industrial waste), and can only be used for some relatively stable industrial waste disposal.In our country, the national standard of landfill also make clear a regulation and must be set anti-seepage lining and leachate collection treatment facilities.In law sense, the new landfill site were not allowed to use natural attenuation landfill method.

Closed landfill is currently accepted type of landfill. This design concept strictly requires limits on leachate seeping into underground water, the landfill to minimize pollution of groundwater, and this requires is more and more popular .To meet the design requirements, in the landfill site , a layer or two layers of anti-seepage lining layer are should be laid , installation of leachate collecting system, rain water and groundwater drainage system, even in sealing field with impermeable material closed the landfill, the landfill is currently the mainstream of the landfill site.

At present, our country widely adopts anaerobic landfill landfill (improved anaerobic sanitary landfill). The main difference of design discharge system differenc is the Landfill structure and quasi aerobic landfill leachate collection .The former requires close seal, does not allow air to enter and leachate collection and drainage system outlet water seal, and is not considered the air flow space between drains; While the latter is just the opposite, outlet can’t be sealed, to ensure the air into it , and assure enough space upon tube road department to ensure that the air flow space. Quasi aerobic sanitary landfill can ensure that there were some good oxygen inside the landfill area, especially in the leachate is aerobic area around drain pipe and the exhaust pipe, so that the leachate can be processed and to speed up the decomposition of stability of the internal waste landfill site.

At present, the construction of landfill enter into a peak in our country . But the problems is obvious, the first is the lack of a complete technical system.So far, our country has not established a complete technical system composed of standard, specification and guide, the relevant units design build landfills tend to copy or imitate, American and British technical requirements, slavish, built according to own understanding design even take it for granted. The second is the lack of in-depth study of landfill technology, makes the construction of landfill lack the necessary technical support.Due to various reasons, the unit is very little, garbage disposal technology and research its little, it is difficult to support the requirements of the construction of the landfill in our country at present.Therefore, China often uses foreign landfill site design technology parameter, and sometimes this is difficult to adapt to present situation of China’s economic development and characteristics. Leachate treatment is outstanding example . Due to lack of necessary basic research and technology development, at present our country mostly use leachate treatment from general sewage treatment technology, without fully considering the landfill and the characteristics of leachate, so that is difficult to meet the requirements, the vast majority can not meet the emission requirements.The third is the relatively backward about the construction of landfills run industry in China, notably anti-seepage lining H D few manufacturer of PE, and product quality cann`t meet the requirements, products is less competitive, and almost no development of new products, which leds to that currently most of them use imported material. Like other compaction machine, pipe material, biogas utilization equipment, etc. There are also the same problem. Leakage detection, repair technology and no application, this aspect of the equipment, material is also in a blank state.

Burning garbage incineration is the use of high temperature to garbage thoroughly oxidative decomposition of organic matter, then it can minimize waste reduction at last . Garbage of bacteria, viruses are completely destroyed, the stench gas is broken down by high temperature, which can achieve harmless at fastest speed.

Modern urban refuse incineration first was started in 1874, Britain’s Nott ham built the first garbage martin furnace in the England , then the United States, Germany, France and other countries also built waste incineration plants. But due to the low waste calorific value and less developed incineration technology at the beginning ,burning gas is amazing, so incineration did not become the mainstream. From the 60s, garbage incineration was in rapid development. the garbage incineration has become the main treatment means in developed countries, such as Japan, Switzerland, Denmark, the garbage incineration has reached more than 70%. In our country, shenzhen incinerators were built and put into operation since 1990, also started to build incinerators from then. The development of waste incineration technology in our country are in two directions: one is to draw lessons from foreign technology and market experience, introduced or generic type furnace and equipment abroad. Another is based on general coal-fired or industrial furnaces for reference, draw lessons from the domestic matured coal-fired power plant boiler combustion technology , transplanted the coal technique and technology on garbage incineration, and use domestic self-madesimple incinerator.

Waste incineration is a very complicated and intense oxidation combustion reaction. In general, the waste incineration will undergo dewatering, degassing, burning, burning, shut down several steps. Theoretically, CO 2 C l, H, N, SO 2 and H 2 O 2, will be produced in the reaction process , but in the actual combustion process due to instability in the nature of garbage, and the waste mixed with oxygen mass transfer problems and many other uncertain factors, there are thousands of kinds of organic waste in the process of combustion reaction, the final reaction products are not necessarily the above several things ,If combustion control is improper , may produce toxic compound products, such as dioxins, polycyclic hydrocarbons, aldehydes, furan, etc.Therefore, to achieve the best effect of burning and the lowest secondary pollution, it requires the control of burning process in a good plan, known as the “3 t + E” control principle, which is good in furnace temperature control, full of furnace flue gas turbulence degree, reaction time and the appropriate air supply. Generally speaking, low combustion temperature and the flue gas residence in too short time will produce the incomplete combustion, but high temperature also has many bad effects, such as easy to burn out grate, furnace wall, make the garbage melting agglomerate blocking the flue, and can produce nitrogen oxides.Therefore, the general requirements within the garbage incinerator combustion chamber outlet temperature between 800 ~ 950 ℃, and the flue gas residence time is ok between 1 ~ 2 seconds. According to the standard of our country, the garbage incinerator combustion chamber outlet temperature is not less than 850 ℃, and the flue gas residence time under this temperature shall not be less than 2 seconds;If outlet temperature in furnace reach 1000 ℃, the flue gas residence time can be up to 1 second.To the requirement of air supply, the rules of oxygen content in flue gas is between 6% ~ 12%.and loi value is 5% measuring the degree of garbage harmless garbage ash thermal .

Waste incineration process will produce many harmful gases, such as dust, acid gas H C l, SO2, H, N O F) X, CO, hydrocarbons, heavy metals, dioxins, so flue gas emissions should be dealt with appropriately before incinerator. Our country promulgated”garbage incineration pollution control standard (GW K B3-2000) of xity life “which puts forward more stricts on the pollutant emissions standards. Dioxins in waste incineration flue gas is most striking. Dioxins are composed of 210 kinds of isomers, containing chlorobenzene compounds toxicity equivalent to 1000 times of potassium cyanide. Dioxin is easy to dissolve in fat accumulation in the body, can cause acne skin, headaches, hearing loss, depression, insomnia and other symptoms.Even in the case of a trace, long-term intake, can also cause cancer, malformation, etc., known as the world’s most poisonous substances. In general control dioxin from the several aspects.First of all, reduce and avoid the chlorine substance into the garbage incinerator.Secondly, through the “3 t” to suppress the generation of dioxin.Third, in the process of flue gas treatment as far as possible to shorten the retention period of 250 ~ 400 ℃ temperature field.Fourth, through the spray and powder activated carbon, setting activated carbon absorption tower and a device to set the catalytic decomposition method from flue gas to remove the dioxin. In addition, the need to control dioxin concentrations in fly ash, the general method has advantage of reducing atmosphere decomposition process of fly ash, fly ash melting decomposition and supercritical water decomposition, etc.

As landfill, our country has not established a waste incineration technology system, garbage incineration technology is still in infancy. Urban house refuse in our country has not yet been classified collection, and therefore have relatively low calorific value of the waste, it is also the main reason to hinder the waste incineration technology application.Construction of the waste incineration equipment is relatively backward, andeven the very poor furnace type are still adopted in some areas ;And the design of the key parts of the furnace processing technology does not pass, unreasonable control equipment, flue gas purification equipment and so on, all affect the processing technology in the application of our country.The lack of professional research, design strength, lack of necessary basic research and applied research, also seriously restricts the development of this technology. Technology market is in confusion, there are some obsolete or abroad don’t also mature technology and equipment in the domestic market.Therefore, issued by the ministry of construction, ministry of science and technology, environmental protection bureau garbage disposal technology policy requirements, measured using burning as the main way of garbage disposal, but in the economically developed coastal cities and large cities, due to the lack of land and huge waste with the pair of contradiction is hard to coordinate, and with the economy and the enhancement, burning will be forced to resort in processing technology.

Now there is a new type of garbage disposal technology, which is carbonized, reach the purpose of garbage disposal by carbonization, not only can carbonation life garbage, industrial waste, but also can be all kinds of carbide material, and in the process of carbide, no flue gas discharge, no sewage, completely achieve zero emissions, is currently the world’s most advanced garbage disposal technology.