is 650 million tons per year, with a comprehensive utilization rate of only about 29%. The cumulative accumulation of 6.64 billion tons, people
5.5 tons per capita, occupying an area of about 55,000 hectares. In 1989, the country discharged 16.97 million tons of chemical waste residue, radioactive
900,000 tons of radioactive waste residue, most of them have not been harmlessly treated and scientifically disposed of, and the growing amount of toxic
hazardous wastes have become a potential danger. According to statistics, the country's urban living garbage at an annual rate of 6% to 7%
growth rate of 60 million tons in 1996, but the rate of harmless garbage treatment on average less than 5%, a large number of untreated industrial slag and municipal garbage piled up in the outskirts of the city and other places to form a siege of the city situation, becoming a serious source of secondary
secondary pollution. 2000 China's total industrial solid waste will grow to 900,000 tons of radioactive waste, most of which are not harmless treatment and scientific disposal, the growing toxic
harmful waste has become a potential danger. In 2000, China's total industrial solid waste will grow to about 700 million tons.
Currently widely used at home and abroad in the treatment of municipal waste disposal methods are sanitary landfills, high-temperature composting and incineration, etc., the proportion of the three main waste disposal methods, due to geographic environment; waste composition, level of economic development and other factors are different, Table 2-1 for the comparison of the three treatment methods.
Table 2-1 Comparison of the three types of waste treatment
The same as the left
The pre-treatment process can recover some of the raw materials, but it depends on the proportion of the waste that can be utilized.
No examples of on-site sorting for recycling, but potential.
Resource recovery
Moderate
Higher
Lower
Construction investment
Difficult to establish a stable market for compost.
Can produce heat or electricity.
Biogas can be recovered to generate electricity.
Product Markets
Non-compostable material needs to be disposed of in a landfill, 20-25% of the initial volume.
Only the residue needs to be disposed of in a landfill, which is 10% of the initial volume.
No
Final disposal
From the point of view of harmlessness, biodegradable organic matter in the waste ≥ 10%, from the point of view of fertilizer efficiency should be >40%.
Waste low calorific value >3300kJ/kg without adding auxiliary fuel.
Inorganic matter>60%
Moisture content 0.5t/d
Applicable conditions
Easy to use, only need to avoid residential areas, the radius of influence of the odor is less than 200m, and the transportation distance is moderate.
Easy, can be built close to the city, the transportation distance is relatively close
Difficult to consider the topography, geological conditions, to prevent surface water, groundwater pollution, generally far from the city, the transportation distance is farther.
Site selection
Medium
Small
Large
Coverage
Reliable, there is considerable experience in China
Reliable
Reliable
Technical Reliability
Good
Well
Good, pay attention to the fire
Operation Safety
Composting
Incineration
Sanitary landfill
Contents
Effects of three methods
Continued from Table 2-1
There is a need to control the heavy metal content of composted products.
None
Limited to landfill areas .
Soil contamination
Slight odor, unlikely contamination indicator.
Controllable, but traces of highly toxic substances such as dioxins (Doxlin) need to be controlled.
Yes, but it can be controlled by covering and compaction measures
Air pollution
Heavy metals and other heavy metals may pollute the groundwater with the composted products
There are no pollutants in the ash, such as organic matter, and it only needs to be cured and other measures taken to prevent pollution in the landfill.
It is possible that leakage may occur even though seepage control measures can be taken.
Groundwater contamination
In non-compostable landfills it is similar to sanitary landfills.
Without the treatment plant, surface water contamination is less likely to occur when the ash is landfilled than when it is landfilled.
It is possible, but measures can be taken to reduce the likelihood.
Surface water pollution
Composting
Incineration
Sanitary landfill
Contents
Technical measures
Currently, China's municipal waste treatment technology is: sanitary landfill and high-temperature composting technology is the main one, and advocate that the cities with the conditions, especially in economically developed coastal areas, the development of incineration technology. In recent years, the city began to carry out basic and applied research on waste incineration, the development of a series of reverse combustion, including the NF series, RF series of pyrolysis, HL series of rotary small garbage combustion furnace and a number of hospitals special garbage incinerator, and the construction of 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 (300 t). 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.
Shanghai Pudong waste incineration plant
1000TD bag filter
China's largest
waste incineration plant is being built
Rubbish recycling process
Future Prospects
China's municipal waste treatment technology to obtain new breakthroughs
Chinese Environmental Protection Industry Association solid waste treatment and utilization committee, recently held in Baodong, China. The Solid Waste Treatment and Utilization Committee of China Environmental Protection Industry Association (CEPIA) has recently conducted a technical review of the pyrolysis of medical waste and domestic waste and related equipment developed by Longde Environmental Technology Co. Experts from Tsinghua University and the China Academy of Science and Technology (CAST) unanimously recognized this technology as the "first of its kind in China".
In order to solve the problem of municipal garbage, Tianjin University has conducted in-depth research on garbage pyrolysis technology and obtained a number of national
patents. On this basis, Longde Environmental Protection Technology Company carried out further research and development on this technology and equipment,
successfully integrating this technology with gasification technology, carbon dioxide reduction and related catalytic combustion technology,
more effectively controlling pollution and fully transforming organic wastes into utilizable resources.
In 2002, Baotou Sanitation Industry Co. >In 2002, the Baotou Sanitation Industry Company introduced this technology and related equipment, built a systematic garbage disposal site, and achieved promising results in the recycling of garbage
utilization of resources. The experts who participated in the evaluation considered that the use of this pyrolysis method to treat medical and
lifestyle wastes is in line with the development direction of solid waste treatment of "reduction, harmlessness, and resourcefulness", and has the advantages of high energy recovery rate,
small secondary pollution, and good comprehensive economic benefits, and has a broad prospect for development. At the same time, the related complete sets of
equipment design is reasonable, high level of automation, occupies a small area, to meet the conditions of engineering applications and market transformation.
French municipal waste treatment technology
France is developing new municipal waste treatment technology to replace incineration and landfill of domestic waste
. Methanation of organic waste and mechanized sorting of packaging materials are environmentally and economically promising. The characteristic of methanization is that it isolates the organic matter from the air and accelerates its degradation in an anaerobic environment. The technology developed and patented by Valorga International Engineering is characterized by a reactor that ferments organic matter during operation. The base of the reactor has 300 openings through which pressurized biogas
(8 atmospheres) is injected. The biogas is produced by fermenting the waste. The reactor stirs and mixes the waste.
During the day, the waste is continuously transported to the bottom of the reactor, where it is pushed by the biogas to go around the
cemented inner wall of the reactor before reaching the outlet. This process keeps the waste in the reactor for three weeks until it is completely degraded. The biogas produced during the bacterial fermentation process is collected and stored at the outlet, where it can be reused in the form of heat and electricity.
China's soot pollution
China is a country whose energy structure is dominated by coal burning, and its air pollution is of the soot-type, with dust,sulfur dioxide (SO2) and nitrogen oxides (NOx) being the main pollutants in the atmosphere. In the initial development stage of industrialization in the 1950s, the national coal consumption of 20-10 million tons, sulfur dioxide (SO2) emissions of 50-2 million tons; in the second stage of industrialization in the 1960s and 1970s, the coal consumption of 10-45 million tons, sulfur dioxide emissions of 3-7 million tons; since the 1980s, coal consumption of 10-45 million tons, sulfur dioxide (SO2) emissions of 3-7 million tons; since the 1980s, coal consumption of 10-45 million tons, sulfur dioxide (SO2) emissions of 3-7 million tons; since the 1980s, coal consumption of 10-10 million tons, sulfur dioxide (SO2) emissions of 3-7 million tons. 7 million tons; since the 1980s in the third stage of industrialization
industrialization, the annual consumption of coal amounted to 80,000 million tons, sulfur dioxide emissions of 9-15
tons; at the same time in the coal combustion process produces a considerable amount of nitrogen oxides, such as China's coal-fired power plants
in 2000, the NOx emissions reached 2.9 million tons. Therefore, the characteristics of China's energy structure has led to more heavy corrosion
corrosion, the formation of acid rain and other pollution, especially in coal-fired power plants, for sulfur dioxide or nitrogen
oxides prevention and treatment is imperative.
Traditional desulfurization technology
Currently domestic flue gas desulfurization technology, the application of the proportion of up to 85%
of the introduction of wet limestone/gypsum method from abroad process and equipment. Lime - gypsum method is the use of limestone or lime slurry to absorb SO2 in the flue gas, belongs to the wet scrubbing method, the by-product of this method is gypsum (CaSO4-2H2O).
The two steps of SO2 absorption and oxidation are completed in the main absorption tower, respectively in the absorption tower and the tower kettle.
(1) Absorption (2) Oxidation
CaO+H2O→Ca(OH)2
2 CaSO3-1/2H2O+O2+3H2O→2 CaSO4-2H2O
Ca(OH)2+SO2→CaSO3-1/2H2O+1/2H2O Ca(HSO3)2+1/ 2O2+H2O→CaSO4-2H2O
Ca(OH)2+SO2→CaSO3-1/2H2O+1/2H2O Ca(HSO3)2+1/ 2O2+H2O→CaSO4-2H2O+SO2↑
CaCO3+SO2+1/2H2O→CaSO3-1/2H2O+CO2↑
CaSO3-1/2H2O+SO2+1/2H2O→Ca(HSO3)2
Organic additives are added in the absorbing liquid to prevent the scaling of the equipment. The end product of this method is gypsum. The end product of this method is gypsum. Simple limestone/gypsum method does not recycle the end product, directly discarded; can also be used to separate the finished gypsum post-treatment recycling.
Disadvantages
Although it plays a certain role in reducing sulfur dioxide pollution in industrial flue gas, but at the same time, it produces gypsum sulfide as a by-product. Wet limestone / gypsum method of desulfurization equipment to deal with 1 ton of sulfur dioxide produced desulfurization gypsum 2.7 tons, with the installed capacity of China's coal-fired power plants year by year, is expected to 2010, the stockpile of desulfurization gypsum and other by-products of gypsum will be more than 100 million tons. Although the introduction of equipment manufacturers are keen to publicize the reuse of desulfurization gypsum, can replace the natural mining of mineral gypsum. In fact, the utilization of desulfurization gypsum is only a theoretical statement. China's mineral gypsum resources are quite rich, this kind of ore is easy to mine, cheap and beautiful. The compressive strength and tensile strength of desulfurization gypsum can not compete with mineral gypsum, no one is willing to use it, and most of them are discarded. Abandoned desulfurization gypsum is like a pile of "snow mountain", after being exposed to the sun volatile "acidic substances" and aggravate the threat of "acid rain". Moreover, the desulfurization gypsum washed away by rainwater will pollute surface water and groundwater. Thus, the old sulfur dioxide pollution in the flue gas is treated, and the new desulfurization gypsum secondary pollution is generated. Secondly, the survey shows that if all the wet limestone / gypsum method to deal with the sulfur dioxide produced, China will be a new annual increase of several tens of millions of tons of carbon dioxide. At present, the total annual emission of carbon dioxide in the world has far exceeded the capacity of nature through plant photosynthesis and seawater absorption and dissolution. The excessive deposition of carbon dioxide in the atmosphere will lead to a continuous rise in the earth's surface temperature. Studies have shown that carbon dioxide, once emitted into the atmosphere, can survive for up to 200 years. Long-term excessive carbon dioxide accumulation in the low altitude will increase the concentration of the atmosphere, hindering the Earth's heat loss, resulting in reduced rainfall, dry rivers, climate warming, environmental degradation, disrupting the balance of the whole nature, triggering droughts and floods and other disasters. China's annual carbon dioxide emissions already account for 13.2% of the world's total emissions. As early as 1997, China signed the Kyoto Protocol, which commits that by 2010, the amount of carbon dioxide and other six greenhouse gases emitted by China will not only not increase, but also be reduced by 5.2% compared with 1990. This time frame has become quite urgent. After the old sulfur dioxide pollution in the flue gas is treated, new carbon dioxide emissions in the atmosphere are added, resulting in new pollution.
Lye/waste lye flue gas desulfurization process
Lye method is one of the more commonly used desulfurization method, which uses an alkaline solution to absorb SO2 in the flue gas, generating HSO32-, SO32- and SO42-, the reaction equation is as follows:
SO2 + OH-→ HSO3-
HSO3- + OH-→ SO32-+H2O
SO2+OH-→ SO32-+H2O. -+H2O
Oxidation part:
HSO3-+1/2O2→SO42-+H+
SO3-+1/2O2→SO42-
Alkaline solution can be used sodium alkali (mainly sodium carbonate, sodium hydroxide, etc.; sodium alkali solubility, absorption rate is higher, do not scale, is not easy to plug.), or a variety of existing plants in the plant. Or factory existing waste lye can be utilized in a variety of insufficient part of the supplement (generally sodium alkali), can make full use of the plant's original resources, to achieve the purpose of waste to waste.
Ammonia process
Ammonia method is to use ammonia to wash the waste gas containing SO2, the formation of (NH4)2SO3-NH4HSO3-H2O absorption liquid system. The solution of (NH4)2SO3 has a very good absorption capacity of SO2, is the main absorber in the ammonia method. Ammonia is a mature method of flue gas desulphurization, which has been applied to industrial projects earlier. The cost of desulphurization is low and the ammonia can be left in the product to be used as nitrogen fertilizer, which makes the product of high value, but the source of ammonia is limited by the region and the production industry. Nonetheless, ammonia is still a promising method for treating low concentrations of SO2.
Wet flue gas desulphurization and dust removal integrated process
Wet flue gas desulphurization and dust removal integrated process is a kind of high-efficiency and economic FGD process designed for the unique excellent performance of cyclone plate tower, combined with the actual situation of domestic enterprises. Dust removal efficiency ≥ 98%, desulfurization rate of 75% to 90%, to meet the current domestic governance requirements; special design of combined mist removal device to prevent the fan with water.
The method generally uses lime as absorbent, or with calcium carbide slag and other alkaline slag. The reaction principle is as follows:
CaO+H2O→Ca(OH)2
Ca(OH)2+SO2→CaSO3-1/2H2O+1/2H2O
CaCO3+SO2+1/2H2O→CaSO3-1/2H2O+CO2↑
CaSO3-1/2H2O+ SO2+1/2H2O
CaSO3-1/2H2O+ SO2+1/2H2O
This method generally uses lime as absorbent, or uses calcium carbide slag and other alkaline waste. SO2+1/2H2O→Ca(HSO3)2
The desulphurization liquid will be recycled after sinking ash and replenishing alkali in the comprehensive recycling pool.
The by-products of this method can be recycled or discarded. Limestone is widely available, easy to obtain, inexpensive and effective, and has been successfully implemented in many domestic enterprises.
Comparison of various processes