650 million tons per year, and the comprehensive utilization rate is only about 29%. The accumulated stock is 6.64 billion tons, and people
5.5 tons, covering an area of about 55,000 hectares. 1989, the national discharge of chemical waste residue16.97 million tons.
900,000 tons of radioactive waste residue, most of which has not been treated harmlessly and scientifically, is becoming more and more toxic.
Hazardous waste has become a potential danger. According to statistics, China has 6% ~ 7% municipal solid waste every year.
The growth rate of 1996 is 60 million tons, but the average harmless treatment rate of garbage is less than 5%, and a large number of them are not.
The treated industrial waste residue and urban garbage dump are stored in suburbs and other places, forming a siege situation and becoming a serious second child.
Secondary pollution source. By the year 2000, the total industrial solid waste in China will increase to about 700 million tons.
At present, sanitary landfill, high-temperature composting and incineration are widely used methods of municipal solid waste treatment at home and abroad. The proportion of these three main garbage disposal methods depends on the geographical environment; The composition of garbage and the level of economic development are different. Table 2- 1 shows the comparison of the three treatment methods.
Table 2- 1 Comparison of Three Garbage Disposal Methods
Tongzuo
Pretreatment process can recover some raw materials, but it depends on the proportion of available substances in garbage.
There are no examples of field separation and recovery, but it is possible.
Resource recovery
appropriate
High-ranking, higher-ranking, more important
reduce
construction investment
It is difficult to establish a stable composting market.
Can generate heat or electric energy.
Recoverable biogas can generate electricity.
Product markets
Non-compost should be buried, accounting for 20~25% of the initial amount.
Only the residue needs landfill treatment, accounting for 10% of the initial amount.
not have
Final disposal
From the point of view of harmlessness, the biodegradable organic matter in garbage is ≥ 10%, and from the point of view of fertilizer efficiency, it should be >: 40%.
The low calorific value of garbage is more than 3300kJ/kg without adding auxiliary fuel.
Inorganic matter > 60%
Water content 0.5t/d
Applicable conditions
Easy, only need to avoid densely populated areas, the influence radius of odor is less than 200m, and the transportation distance is moderate.
It's easy, it can be close to urban buildings, and the traffic distance is close.
Considering the terrain and geological conditions, it is difficult to prevent surface water and groundwater pollution. Generally, it is far from the urban area and the transportation distance is also far.
Selected location
medium
small
big
Cover an area
Reliable and rich in domestic experience.
reliable
reliable
engineering reliability
okay
okay
Ok, pay attention to fire prevention.
operational safety
compost
Be lit
Sanitary garbage dump
content
The influence of three ways
Continued table 2- 1
It is necessary to control the content of heavy metals in compost products.
not have
Only in landfills.
soil contamination
There is a slight smell, and the pollution index is unlikely.
It can be controlled, but measures should be taken to control trace toxic substances, such as carbendazim.
Yes, but it can be controlled by covering compaction and other measures.
atmospheric pollution
Heavy metals may pollute groundwater through compost products.
There are no organic pollutants in the ash, so measures such as solidification can be taken to prevent pollution.
It is possible that although seepage control measures can be taken, leakage will still occur.
underground water pollution
It is similar to sanitary landfill in non-composting landfill.
There is nothing in the treatment plant, so there is less possibility of surface water pollution when the ashes are buried.
It is possible, but measures can be taken to reduce the possibility.
surface water pollution
compost
Be lit
Sanitary garbage dump
content
Technical countermeasures
At present, the technical countermeasures of municipal solid waste treatment in China are: sanitary landfill and high-temperature composting, and encouraging qualified cities, especially coastal economically developed areas, to develop incineration technology. In recent years, cities began to carry out basic research and application research on waste incineration, and developed NF series reverse combustion, RF series pyrolysis, HL series rotary small waste burners and a number of special incinerators for hospital waste. And a number of simple incineration plants (stations) have been built in small and medium-sized cities. 1985, Shenzhen imported complete sets of incineration technology and equipment from Mitsubishi, and built the first large-scale (300t/d) modern waste incineration power generation comprehensive treatment plant in China, which laid the foundation for the localization of municipal waste incineration devices in China.
Shanghai Pudong garbage incineration plant
1000t bag filter
The largest building under construction in China.
Waste incineration plant
Garbage collection process
Future prospects
China has made a new breakthrough in municipal solid waste treatment technology.
The Professional Committee of Solid Waste Treatment and Utilization of China Environmental Protection Industry Association recently held a meeting with Longde Environmental Protection Technology Co., Ltd..
The developed pyrolysis of medical waste and domestic waste and related equipment were reviewed. They are from the Tsinghua University and China branches.
Experts from universities and other units unanimously defined this technical achievement as "the first in China".
In order to solve the problem of municipal waste, Tianjin University has conducted in-depth research on waste pyrolysis technology, and achieved many domestic and foreign achievements.
Patents. On this basis, Longde Environmental Protection Technology Company further developed the technology and equipment.
This technology is successfully combined with gasification technology, carbon dioxide reduction and related catalytic combustion technology.
Pollution is more effectively controlled, and organic waste is fully converted into available resources. In 2002, Baotou environmental sanitation industry
The company introduced technology and related equipment, established a systematic garbage disposal site, and recycled garbage.
Satisfactory results have been achieved in utilization and so on. Experts participating in the review believe that this pyrolysis method is used in medical care.
Domestic garbage conforms to the development direction of solid waste treatment of "reduction, harmlessness and resource utilization", and the energy recovery rate is high.
It has the advantages of less secondary pollution and good comprehensive economic benefits, and has broad development prospects. At the same time, related packages
The equipment is reasonable in design, high in automation level and occupies less land, which meets the requirements of engineering application and market transformation.
French municipal solid waste treatment technology
France is developing new municipal waste treatment technology to replace burning and filling domestic waste.
Bury. Treating organic waste by methanation and sorting packaging materials by mechanization, and
From the point of view of environment and economy, this is a promising method. The characteristic of methanation treatment is to make organic matter
The quality is isolated from the air, and the degradation is accelerated in an oxygen-free environment. Garbage should be treated before methanation.
After sorting and methanation, composting is completed. It was opened by Valorga international engineering company.
The characteristic of patented technology is that the reactor is organic during operation.
Fermentation. There are 300 openings at the bottom of the reactor, from which pressurized biogas is injected.
(8 atmospheres). Biogas is produced by garbage fermentation. The reactor stirs and mixes the garbage.
During the day, garbage is continuously transported to the bottom of the reactor and bypassed by biogas.
The inner wall of the reactor is made of cement before reaching the outlet. This process keeps the garbage in the reactor.
The residence time is 3 weeks until it is completely degraded. Organisms produced during bacterial fermentation.
Biogas is collected and stored at the outlet and can be reused by generating heat and electricity.
Smoke pollution in China
China is a country whose energy structure is mainly coal burning, and air pollution belongs to soot pollution.
Dust, sulfur dioxide (SO2) and nitrogen oxides (nitrogen oxides) are the main air pollutants in China.
In the early stage of industrialization in 1950s, the national coal consumption was 2000-1100,000 tons.
Sulfur oxide emissions of 500-200 million tons; In the second stage of industrialization in 1960s and 1970s, coal consumption.
The amount is 10000-4500000 tons, and the sulfur dioxide emission is 300000-7000000 tons; Starting from 1980.
In the third stage of industrialization, the annual coal consumption reached 800 million tons, and the sulfur dioxide emission was 900- 1500.
Ten thousand tons; At the same time, a considerable amount of nitrogen oxides are produced in the process of coal burning, such as coal-fired power plants in China in 2000.
The emissions of nitrogen oxides reached 2.9 million tons. Therefore, the characteristics of China's energy structure lead to more serious corrosion.
Corrosion, leading to acid rain and other pollution, especially in coal-fired power plants, sulfur dioxide or nitrogen
The prevention and control of oxides is imperative.
Traditional desulfurization technology
At present, the application ratio of various flue gas desulfurization technologies in China is as high as 85%
The limestone/gypsum wet process technology and equipment imported from abroad are introduced. Lime-gypsum method is a wet scrubbing method. Limestone or lime slurry is used to absorb SO2 in flue gas. The by-product of this method is gypsum (CaSO4 2H2O).
SO2 absorption and oxidation are completed in the main absorption tower, and in the absorption tower and the tower kettle respectively.
(1) absorption (2) oxidation
Cao +H2O→ Calcium hydroxide
2 caso 3 1/2H2O+O2+3H2O→2 caso 4 2H2O
Ca(OH)2+SO2→caso 3 1/2H2O+ 1/2H2O Ca(HSO 3)2+ 1/2o 2+H2O→caso 4 2H2O+SO2↑
CaCO3+SO2+ 1/2H2O→caso 3 1/2H2O+CO2↑
caso 3 1/2H2O+SO2+ 1/2H2O→Ca(HSO 3)2
Organic additives are added to the absorption liquid to prevent equipment from scaling. The final product of this method is gypsum. The simple limestone/gypsum method does not recycle the final product, but directly discards it. The finished gypsum separated by post-treatment can also be recycled.
disadvantaged
Although it has played a certain role in reducing sulfur dioxide pollution in industrial flue gas, it also produced by-products such as gypsum sulfide. Limestone/gypsum wet desulfurization equipment produces 2.7 tons of desulfurization gypsum for each treatment of 1 ton of sulfur dioxide. With the increasing installed capacity of thermal power plants in China, it is estimated that by 20 10, the storage capacity of desulfurization gypsum and other by-products gypsum will exceed 654.38+billion tons. Although the related manufacturers of imported equipment are keen to promote the reuse of desulfurized gypsum, it can replace natural mineral gypsum. In fact, the utilization of desulfurization gypsum is only a theoretical statement. China is rich in mineral gypsum resources, and this kind of ore is easy to mine and cheap. However, the compressive strength and tensile strength of desulfurization gypsum can't compete with mineral gypsum, and no one wants to use it. Most of them were abandoned. Waste desulfurization gypsum is like piles of "snow mountains", and the "acidic substances" volatilized after sun exposure aggravate the threat of "acid rain". Moreover, the desulfurization gypsum washed by rain will pollute surface water and groundwater. So as to control the sulfur dioxide pollution in the old flue gas and the secondary pollution of the new desulfurization gypsum. Secondly, the survey shows that if all wet limestone/gypsum is used, China will increase tens of millions of tons of carbon dioxide every year. At present, the total annual emission of carbon dioxide in the world has far exceeded the ability of nature to dissolve through plant photosynthesis and seawater absorption. Excessive deposition of carbon dioxide in the atmosphere will lead to a continuous increase in the surface temperature of the earth. Studies have shown that once carbon dioxide is discharged into the atmosphere, it can last for as long as 200 years. Long-term excessive accumulation of carbon dioxide at low altitude will increase atmospheric concentration. It hinders the loss of the earth's heat, leads to the decrease of rainfall, the drying up of rivers, the warming of the climate and the deterioration of the environment, destroys the balance pattern of the whole nature, and causes disasters such as droughts and floods. China's total annual carbon dioxide emissions have accounted for 13.2% of the world's total emissions. As early as 1997, China signed the Kyoto Protocol. It is promised that by 20 10, the emission of six greenhouse gases, such as carbon dioxide, in China will not increase, but it will be 5.2% lower than that in 1990. This time limit is quite urgent. Sulfur dioxide pollution in old flue gas has been controlled, and carbon dioxide emissions in the atmosphere have increased, resulting in new pollution.
Alkaline solution/waste alkali solution flue gas desulfurization process
Alkaline solution method is one of the commonly used desulfurization methods. In this method, SO2 in flue gas is absorbed by alkaline solution to generate HSO32-, SO32- and SO42-. The reaction equation is as follows:
SO2+OH-→HSO3-
HSO3-+OH-→SO32-+H2O
Oxidation part:
HSO3-+ 1/2O2→SO42-+H+
SO3-+ 1/2O2→SO42-
The alkaline solution can be sodium alkali (mainly sodium carbonate, sodium hydroxide, etc.). ); Sodium and alkali have high solubility, high absorption rate, no scaling and no blockage. ), or can supplement all kinds of available waste alkali liquor (generally sodium alkali) in the factory, so as to make full use of the original resources of the factory and achieve the purpose of treating waste with waste.
Ammonia treatment
The ammonia process is to wash the waste gas containing SO2 with ammonia water to form an absorption liquid system of (NH4)2SO3-NH4SO4 O3-H2O. (NH4) 2SO3 in this solution has a good absorption capacity for SO2 and is the main absorbent in ammonia process. Ammonia method is a mature flue gas desulfurization method, which was applied in industrial engineering earlier. This method has low desulfurization cost, and ammonia can be left in the product in the form of nitrogen fertilizer, thus producing the product.
Integrated process of wet flue gas desulfurization and dust removal
Wet flue gas desulfurization and dust removal integrated process is an efficient and economical flue gas desulfurization process based on the unique excellent performance of swirl plate tower and the actual situation of domestic enterprises. The dust removal efficiency is more than or equal to 98%, and the desulfurization rate is 75% ~ 90%, which meets the current domestic treatment requirements. Specially designed combined demisting device to prevent the fan from carrying water.
This method generally uses lime as absorbent or alkaline waste residue such as carbide slag. The reaction principle is as follows:
Cao +H2O→ Calcium hydroxide
ca(OH)2+SO2→caso 3 1/2H2O+ 1/2H2O
CaCO3+SO2+ 1/2H2O→caso 3 1/2H2O+CO2↑
caso 3 1/2H2O+SO2+ 1/2H2O→Ca(HSO 3)2
Desulfurization solution is precipitated in a comprehensive circulating pool and recycled after alkali supplementation.
By-products obtained by this method can be recycled or discarded. Limestone is widely available, the raw materials are easily available, the price is low, and the treatment effect is good, which has been successfully implemented in many domestic enterprises.
Comparison of various processes