Safety technology of the hottest urea production

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Urea production safety technology

urea (h2nconh2), also known as urea or carboamide, is a white crystal with a relative molecular weight of 60.055. Urea is abundant in human and mammalian urine. The imported sensor is American Quanli sensor liquid, a world-famous sensor manufacturer. Urea is soluble in water, ethanol and benzene, and almost insoluble in ether and chloroform

the nitrogen content of urea ranks first among solid nitrogen fertilizers, reaching more than 46%. It is a neutral quick acting fertilizer. When applied to the soil, there is no acid root that deteriorates the soil, and the decomposed carbon dioxide can also be absorbed by plants

urea is also widely used in industry. It can be used as raw material for manufacturing high polymers such as urea formaldehyde resin and polyurethane (as plastic, spray paint and adhesive). It can also be used as an additive for various purposes (as ink material, bonding oil, etc.), and urea can also be used in medicine, forestry, tanning, animal feed, refining of petroleum products, etc

the first industrial plant that uses ammonia and carbon dioxide as raw materials to produce urea was built and put into operation by I. g. Farben in 1922, using hot mixture compression cycle. In 1932, DuPont company of the United States used the direct synthesis method to prepare urea ammonia water, and began to produce solid urea in 1935. The unreacted substances returned to the synthesis tower in the form of ammonium carbamate aqueous solution, which is the embryonic form of the current full circulation method of aqueous solution

the development of China's urea industry began in 1958. First, Nanjing Yongli Ning plant built a semi circulating production method device with a daily output of 10 tons of urea, and its replacement Jingzhen built a semi circulating production method device with an annual output of 15000 tons in Shanghai Wujing chemical plant. In 1975, China's first carbon dioxide stripping unit was also completed and put into operation in Shanghai Wujing chemical plant. Since the 1970s, China has built large-scale fertilizer production plants with an annual output of 300000 tons of synthetic ammonia and 520000 ~ 600000 tons of urea. So far, more than 30 sets of large chemical fertilizer production plants have been built, becoming the main base for urea production in China. These urea plants use petrochemical products or semi-finished products as raw materials, so most of them belong to the petrochemical industry. There are many kinds of strain gauge tension and pressure sensors at home and abroad. Due to the close correlation between the production of synthetic ammonia and urea, the production processes are introduced as follows

1. Synthetic ammonia production

the main process of nitrogen fertilizer production is the production of hydrogen, and the nitrogen required for synthetic ammonia comes directly or indirectly from air. At present, most nitrogen fertilizer plants in the world use petrochemical raw materials or their by-products to produce hydrogen or carbon monoxide, and only a few manufacturers use electrolytic water method to produce hydrogen. Due to the restriction of power cost, this method is difficult to form large-scale industrial production

the process of producing hydrogen and carbon monoxide from petrochemical raw materials is a chemical process. From the perspective of its reaction type, it can be roughly divided into hydrocarbon steam catalytic conversion method and hydrocarbon partial oxidation method. The former uses natural gas, oil field gas, blast furnace gas, refinery gas, naphtha and other light hydrocarbons as raw materials; The latter is dominated by heavy hydrocarbons such as coal and residual oil

domestic synthetic ammonia production uses light hydrocarbons such as natural gas, oilfield gas and naphtha as raw materials, as well as heavy oil and residual oil as raw materials. From the perspective of development trend, in order to make full use of resources, it is more reasonable to use petroleum gas and heavy oil as raw materials

the main process flow diagram of two types of synthetic ammonia is shown in Figure 1

Figure 1 hydrocarbon steam conversion method

the brief production process of hydrocarbon steam conversion method is as follows: natural gas (mainly composed of methane) is mixed with steam after desulfurization, and the advanced primary reformer converts most of methane into hydrogen, carbon monoxide and carbon dioxide under the action of appropriate pressure and temperature and nickel catalyst. Then, air is introduced into the secondary reformer and burned in the furnace to continue the conversion, while providing nitrogen, the main component of ammonia synthesis. The carbon monoxide in the conversion gas reacts with water vapor at different temperatures and under the action of iron and copper catalysts in the high and low shift furnaces to produce hydrogen and carbon dioxide. The dioxygen in the shift gas is purchased in large quantities in plastic bags every day in the supermarket. The carbon monoxide is absorbed by the solution in the decarbonization tower and sent to the urea workshop. Carbon monoxide and carbon dioxide in the decarburized gas react with hydrogen at a suitable temperature and under the action of nickel catalyst to produce methane and water vapor. Finally, the mixed gas of nitrogen and hydrogen is compressed to 24MPa by the compressor and sent to the synthetic tower. Under the action of 540 ℃ and iron catalyst, nitrogen and hydrogen undergo synthetic ammonia reaction, and the tower gas is cooled to condense and separate ammonia, which is the synthetic ammonia product

Figure 2 partial oxidation method

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