2023-09-20
Source: Internet
The production and application of activated carbon in domestic and overseas were developed relatively late. Europe and the United States began to develop activated carbon production in the early 20th century. China's activated carbon industry was really established in the 1950s and achieved great development in the 1970s. In China, before the 1970s, the application of activated carbon was mainly concentrated in the sugar, medicinal and MSG industries. After the 1980s, it expanded to industries such as water treatment and environmental protection. In the 1990s, in addition to the above fields, activated carbon The field has been further expanded to include solvent recovery, food and beverage purification, air purification, desulfurization, carriers, medicine, gold extraction, semiconductor applications and other fields. In addition, in the national defense and civil industries, various gas-proof surfaces filled with activated carbon are used to protect against poisonous and harmful gases; in the operation of nuclear reactors, activated carbon is used to adsorb chlorine and nitrogen, as well as radioactive xenon and nitrogen, etc. mixed into the protective gas.
During nuclear reactions, nuclear reactors will release harmful substances such as radioactive iodine, krypton, and xenon. Activated carbon impregnated with iodine can absorb radioactive iodine and eliminate nuclear pollution from radioactively contaminated gases. Under artificial control, people have successfully obtained the nuclear fission energy of U and Pu and used atomic energy for power, power generation, etc. For the atomic energy industry, preventing gas pollution caused by nuclear fission is an important technology. Serious nuclear accidents that have occurred in recent years, such as Three Mile Island (U.S., 1979, Level 5), Chernobyl (Soviet Union, 1986, Level 7), St. Petersburg (Russia, 1992, Level 3), etc., have aggravated the People are afraid of nuclear pollution, so the control of nuclear pollution should be stricter. Compared with the concentration of harmful gases produced in ordinary chemical industry production, the radioactive gases produced in atomic energy facilities are much less, but the efficiency requirements for the capture or removal of radioactive gases are very high.
At present, the method of using activated carbon adsorption to adsorb nuclear fission gas waste is beginning to attract attention. Compared with relatively mature technologies for treating liquid waste from nuclear fission such as filtration, ion exchange and evaporation concentration, the treatment of gaseous waste (i.e. fission gas) is still more difficult, especially the radioactive iodine and xenon formed during nuclear fission, krypton, etc., their harmfulness must be fully noted. Therefore, people are paying more attention to adsorption technology, a suitable and safe method for handling fission gases in recent years. In addition to using adsorption to separate and remove fission gas, this method also acts as a retention bed, which can give fission gas a certain residence time and attenuate radioactive energy through decay, thereby effectively removing radioactive pollution and controlling radioactive pollution.
Radioactive iodine contained in the exhaust gas from atomic energy facilities can be removed by using an activated carbon filter placed in front of the exhaust pipe. The activated carbon used is granular activated carbon with added potassium iodide or iodine. The activated carbon adsorption method can also be used to capture organic iodides such as methyl iodide (CH3I) and iodic acid (HIO3, HIO4, etc.). The adsorption performance of activated carbon is better than lead oxide, silica gel, etc., so activated carbon is superior to other adsorbents.
The activated carbon used in filters for removing radioactive iodine is the one which impregnated with potassium iodide or iodine. Its filling density is 0.45~0.60. Radioactive iodine contained in the exhaust gas can be removed by using an activated carbon filter installed in front of the exhaust pipe. The processing capacity of this design is: when the pressure drop does not exceed 28mm Hg, it can process 28㎡ of air per minute. Currently, rare gas retention devices made of activated carbon are being intensively studied as a method of reducing radioactive energy in gases discharged from boiling water type atomic furnaces (BWR) and have practical application prospects. The effect is expected to be better than what has been used so far. The noble gas attenuation tank method is much better. This device mainly utilizes the characteristic of rare gases being adsorbed by activated carbon, and uses the activated carbon layer as a retention bed. When xenon-containing air passes through the activated carbon layer, the moving speed of xenon in the activated carbon layer is significantly slower than in the air. Rare gases with short half-lives such as 133Xe (half-life of 5.27d) remain in the activated carbon layer and are adsorbed during the movement, and then disappear.
In addition to the adsorption method, other methods can be used for waste gases containing radioactive rare gases (including 85Kr with a capture half-life of 10.27a), such as solvent absorption method, liquefaction method, membrane permeation method, etc. The most realistic methods to separate and recover the radioactive element krypton (85Kr, half-life 10.27a) with a long half-life include activated carbon adsorption, deep freezing separation and permeable membrane methods. However, at this stage, none of the above methods have yet reached the point of practical use. . The reason is not only that activated carbon requires a long time for cooling and heating, resulting in poor thermal efficiency, but also that impurities are mixed in the gas being processed, which can easily cause explosive accidents. In order to improve the above shortcomings of the activated carbon adsorption method, research is currently being conducted on the pressure exchange method of adsorption under pressure and desorption under reduced pressure, and the adsorption at low temperature that combines the thermal cycle method and the pressure shift method, method of desorption under reduced pressure.
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