Denitration of thermal power plant reductant choice is a very important part of the entire denitration system. In the denitration system, the reductant is the largest consumable (catalyst costs more to the SCR for the SNCR). Its cost of consumption has a direct impact on the overall economic assessment of the denitrification system. At present, there are three kinds of most commonly used reductants in the world: denitrification, ammonia and urea. Both urea and ammonia can be used as a reductant for SCR and SNCR, however, urea has more significant advantages in terms of performance and safe operation. Thermal power plant denitrification reducing agent selection influencing factors are: 1) Transport and storage security, including the prevention of terrorist attacks and releases; 2) the possible impact (including economic and other impacts) in the event of an accident; 3) approval of the operation permit 4) area; 5) Investment and operating costs. First, anhydrous ammonia (liquid ammonia), ammonia and urea characteristics The characteristics of anhydrous ammonia: also known as liquid ammonia, GB12268-90 provisions of the dangerous goods, dangerous goods No. 23003. Colorless gas, irritating stink odor. Ammonia liquefied ammonia will expand 850 times, and the formation of ammonia cloud. Ammonia vapor and air mixture explosion limit of 16 ~ 25% (the most susceptible concentration of 17%) and the case of high temperature (93 ° C and above) the risk of explosion, ammonia and air mixture reaches the above concentration range in case of fire will burn and explosion, In the presence of oil or other flammable substances, the risk is higher. Ammonia is a toxic substance that can cause acute and chronic poisoning and can cause death in severe cases: (1) ammonia is a corrosive, colorless, with a strong smell of gas; (2) Although most of the time is safe to use, in the event of an accident, it will form a deadly cloud that will endanger workers working in the field and people living in nearby communities. (3) Direct contact with ammonia irritates the skin, burns the eyes, temporarily or permanently blinds the eyes and causes headache, nausea and vomiting. (4) Serious, can lead to respiratory system water (lung or laryngeal edema), may result in death; (5) Long-term exposure to ammonia, can cause lung injury, resulting in cough or shortness of breath bronchitis. Ammonia characteristics: ammonia and anhydrous ammonia are dangerous chemicals. Ammonia solution: ammonia solution containing> 50% ammonia, Dangerous goods code 23003. 35% <<50% ammonia <Dangerous goods list >> "Dangerous chemicals list (2002 version)" GB12268-90 provisions of the dangerous goods, dangerous goods No. 22025.10% <Ammonia ammonia ≤ 35% Solution, Dangerous goods No. 82503; reducing agent used for denitration usually 20% ~ 25% concentration of ammonia. Colorless transparent liquid, easy decomposition of ammonia, the higher the temperature, the faster the decomposition can form an explosive atmosphere. In case of high fever, the container pressure increases, the risk of cracking and explosion. Reacts violently with strong oxidants and acids. Contact with halogens, mercuric oxide, and silver oxide can form vibration-sensitive compounds. Combustion and explosion are initiated by exposure to the following: trimethylamine, amino compounds, 1-chloro-2,4-dinitrobenzene, o-chloronitrobenzene, platinum, , Boron halides, mercury, iodine, bromine, hypochlorite, chlorine bleach, amino compounds, plastics and rubbers. Corrosion of copper, brass, bronze, aluminum, steel, tin, zinc and its alloys and so on. If overflow, ammonia liquid diffusion range than anhydrous ammonia, the concentration range easier to control. But there is a strong irritating odor, because the liquid does not require pressure vessel storage, relatively anhydrous ammonia is relatively safe. However, exposure limits (spillage of ammonia concentration, as described below) affect the human body regardless of whether it comes from anhydrous ammonia or ammonia: From a transportation point of view, ammonia is more dangerous than ammonia at this human contact frequency because it is only 19% -29% in concentration and 4 times more likely to come into contact with anhydrous ammonia (99 +%) On, better than anhydrous ammonia. Must be carefully considered. Urea characteristics: Urea is white or light yellow crystals, soluble in water, the aqueous solution was neutral reaction. Aqueous solutions of different urea concentrations have different crystallization temperatures, 40% by weight aqueous urea solution has a crystallization temperature of about 2 ° C and 50% by weight urea aqueous solution has a crystallization temperature of about 18 ° C. Solid urea is highly hygroscopic and hygroscopicity drops drastically due to the addition of hydrophobic substances such as paraffins to the production of urea or the formation of Methylene Diurea (MDU) with a moisture-resistant film. Compared with anhydrous ammonia and aqueous ammonia, urea is a non-toxic and harmless chemical which is commonly used in agriculture. It has no possibility of explosion and is completely non-hazardous. Urea in transportation, storage without the need for safety and risk considerations, but do not need any urgent procedures to ensure safety. Second, different reductant safety management standards Due to liquid ammonia, ammonia in the transport process improper measures or equipment damage and other unexpected factors, triggered a number of safety accidents, resulting in some loss and adverse effects. Even in the United States, where technology and management are advanced, safety accidents caused by liquid ammonia and ammonia can not be completely avoided. Due to the relative backwardness of technology management in our country and the weak sense of safety production, liquid ammonia accidents are frequent in recent years. In recent years, the number of accidents in our country has been still high. From an economic development stage, it has entered the period of high-level production safety accidents. The state's control of safety requirements and sources of danger is becoming more and more stringent. Our country's leaders and officials in charge of security have also repeatedly stressed the importance of fully raising awareness of the importance of safe production, carrying out the state's laws and regulations on "safety production laws," putting people first and fully understanding the truth that there is no security without efficiency. Control of major dangerous sources and management of hidden dangers of major accidents, strengthen key supervision and process tracking control so as to ensure that accidents involving mass casualties and accidents that have a significant impact on the society do not occur. According to the relevant provisions of the "List of Hazardous Chemicals" (GB12268-90) and "Identification of Major Hazard Sources" (GB18218-2000), liquid ammonia and ammonia constitute dangerous goods. Liquid ammonia exceeds 40 tons at the place of production and the storage place exceeds 100 Tons constitute a major source of danger. The following safety practices should be followed for liquid ammonia storage and preparation systems: The construction and implementation of liquefied ammonia project should follow the "Measures for the Implementation of Security Permission of Construction Projects with Frequent Dangerous Chemicals" promulgated by the State Administration of Work Safety in 2006; < 1 2 > Metal 3D Printing - Slm / Dmls Metal 3D Printing - Slm / Dmls,3d Printing Service Metal ,Metal 3d Printing Service Stainless Steel,3d Printing Service Metal Aluminum Ningbo Rongna Technology Co.,Ltd , https://www.machiningcustom.com
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The two technologies have many similarities: both use laser scanning and selectively fuse (or melt) metal powder particles, glue them together and build them layer by layer. Similarly, the materials used in both processes are granular metals.
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