According to the report of the United Nations Environment Program, the amount of mercury released into the atmosphere by various human activities is 1900-2200 tons per year. Among them, coal- fired thermal power generation and incineration waste emit 1,500 tons of mercury per year into the atmosphere, accounting for humanity. Atmospheric emissions of 70% of mercury, while Asia's emissions of 860 tons, the highest in the world.
Environmental pollution of mercury has serious consequences. In Japan, 2953 people were diagnosed with mink disease, and there were more than 10,000 people with paresthesia, causing serious social problems. The Japanese government has been treating mink disease for 40 years. In the 1970s and 1980s, a small number of cases of chronic poisoning of methylmercury were found among fishermen along the second Songhua River in China, and the outbreak of mink disease was avoided due to timely treatment measures.
In recent years, new breakthroughs have been made in the study of methylmercury toxicity, and studies have revealed that methylmercury is much more harmful to humans than originally thought. According to the latest research results, in 2001, the US Environmental Protection Agency (EPA) issued environmental quality standards for methylmercury in water. According to the new standard, in 2000, nearly 5 million women in the United States had higher levels of mercury than safety standards. Up to 300,000 newborns per year may be affected by mercury and their intelligence and nervous system are affected. UNEP speculates that the world is This data can be as high as millions.
China's largest mercury use in the world China is currently the world's largest use of mercury. In 2000, the world's mercury production was about 2,000 tons, while China's annual mercury use was more than 900 tons, and imports accounted for about 70%. The use of mercury involving many industries and sectors, mainly in the chemical, battery, yellow gold dressing and smelting, electric light and the medical device industry. Taking the electric light source industry as an example, in 2002, more than 2 billion standard cubic meters of mercury-containing waste gas were discharged, more than 1 million tons of mercury-containing wastewater, and nearly 10,000 tons of mercury-containing waste. The annual mercury consumption is 48.8 tons, of which 24.4 tons of mercury is emitted from the process, and the same amount of mercury is present in the electric light source products, and eventually enters the environment. China is a large coal-fired country. In 2003, the total coal consumption was about 1.5 billion tons. In 1995, according to the coal consumption of 1.38 billion tons in the year, 213.8 tons of mercury and 89.07 tons of mercury were emitted into the atmosphere and ash, respectively. The share is relatively large. There are no accurate statistics on mercury emissions from nonferrous metallurgy, gold smelting and other industries.
Mercury pollution is serious China is one of the regions with the most serious atmospheric mercury pollution in the world. The annual average sedimentation of mercury in the atmosphere is greater than 70μg/m 2 . Mercury pollution in Liaohe and Yellow Rivers in China is serious, and the order of pollutants in mercury is in the top three in 5 years. Mercury pollution in China's seas has been increasing from 1995 to 2000. At some coastal water monitoring sites, mercury has become the largest indicator. The environmental pollution of mercury in mercury mines, gold mines, chlor-alkali plants and non-ferrous metal smelters in China is very serious, including environmental factors such as atmosphere, water and soil. In the soil-purifying areas of Guizhou Province, the mercury concentration in the air exceeds the atmospheric mercury concentration standard of residential areas by 17.5 to 2646.3 times, the drinking water exceeds the sanitary standard by one to three times, and the edible part of the crops exceeds the standard by tens to hundreds of times. The mercury pollution of the atmosphere and soil in urban areas of China is also serious, and the proportion of exceeding the standard has increased year by year. The highest mercury content in the air of Guiyang City reached 565.8 ng/m 3 , and the mercury content in the precipitation in most areas was close to or exceeded 0.10 μg/L, and the mercury content in the dustfall was 0.6-5.0 mg/Kg. The average concentration of mercury in the air during the heating period in Beijing was 216.9 ng/m 3 , and the individual locations reached 427.08 ng/m 3 . China's mercury-containing pesticides and chemical fertilizers pose a hazard to agro-ecosystems. Some fertilizers contain up to 5 mg/kg of mercury, and vegetables and some agricultural products are contaminated with mercury.
The situation of mercury pollution prevention and control is grim Currently, China's mercury pollution research has seriously lag behind the situation. Although the Chinese Academy of Sciences and the State Environmental Protection Administration have conducted investigations on the import and export of mercury and the use of mercury in the industry, so far, the production, import, processing, utilization and discharge of mercury are still in an unclear state, and the basic statistics are scarce. , mutual support is poor. In the process of coal burning, metal smelting, sulfuric acid manufacturing, etc., mercury has been released into the atmosphere with exhaust gases. These industries and sectors have become the main source of atmospheric mercury pollution, but lack of in-depth research. In recent years, China has achieved certain results in the management of mercury-containing batteries and the management of small gold industries. However, there are still many mercury and mercury-extracting industries that have not been treated.
Related links Mercury is a chemical with severe physiological toxicity. It can enter the human body through the respiratory tract, esophagus and skin. The absorption of excess mercury in the human body can cause mercury poisoning. Any form of mercury in the environment can be converted into highly toxic methylmercury under certain conditions. After entering the human body, methylmercury mainly invades the human nervous system, especially the central nervous system. Recent pathological studies have shown that methylmercury can cross the placental barrier to invade the fetus, causing congenital diseases in newborns. In addition to damage to the nervous system, the development of the child's immune system and circulatory system is also violated.
Methylmercury in the environment can be transported along the aquatic food chain for high bioaccumulation. In the ocean, sharks, swordfish, tuna, squid and other large fish and seals have the highest mercury content; in lakes and rivers, meatfish at the highest level of the food chain have the highest methyl mercury content. The way humans are affected by methylmercury is mainly the consumption of fish and shellfish and marine mammals contaminated with mercury.
The dryer is a kind of mechanical equipment that uses heat energy to reduce the moisture content of materials. It is used to stop the drying operation of objects and vaporize the moisture (usually moisture or other volatile liquid components) in the materials after heating to obtain solid materials with regular moisture content. The purpose of drying is to meet the requirements of material application or further processing.
The future development of dryers will develop and improve dryers under the conditions of deepening the study of drying mechanism and material drying characteristics, and controlling the operation conditions of different materials; In addition, large-scale, high strength, high economy, and improved compliance with raw materials and quality are the fundamental trends of dryer development. Now let's introduce the function, working principle, classification, operating procedures, selection instructions and cleaning methods of the dryer.
The dryer acts as a refrigeration compressor to suck the low pressure (low temperature) refrigerant in the evaporator into the compressor cylinder. The refrigerant steam is compressed, and the pressure and temperature rise at the same time; The refrigerant steam with high pressure and high temperature is pressed to the condenser. In the condenser, the refrigerant steam with higher temperature and cooling water or air with lower temperature stop heat exchange.
The heat of the refrigerant is taken away by water or air and condensed, and the refrigerant vapor becomes liquid. This local liquid is then sent to the contraction valve, which is throttled into a low temperature and low pressure liquid and enters the evaporator; The low temperature and low pressure refrigerant liquid in the evaporator absorbs the heat of the compressed air and vaporizes (commonly known as "evaporation"), while the compressed air condenses a large amount of liquid water after cooling; The refrigerant steam in the evaporator is sucked away by the compressor.
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