| 摘要 |
<p>1,129,787. Production of urea. NORSK HYDRO ELEKTRISK KVAELSTOFAKTIESELSKAB. 23 Feb., 1967 [10 March, 1966], No. 8774/67. Heading C2C. Urea is produced from ammonia and carbon dioxide which react at elevated temperature and pressure to form ammonium carbamate and urea under indirect cooling with water, whereby steam is simultaneously produced, whereafter unreacted ammonium carbamate is decomposed into NH 3 and CO 2 by expanding the reaction mixture in one or more pressure steps before the final expansion to approximately atmospheric pressure, and heat is supplied in at least one of said pressure steps, and at least in the last pressure step the reaction mixture is treated with CO 2 gas in countercurrent flow, whereafter the off-gas streams from each pressure step are recirculated to the urea synthesis stage, characterized in that the major amount of the fresh C0 2 -gas necessary for the urea production is supplied at the carbamate decomposition step as hot gas, and that the expanded CO 2 -rich gas and off-gas streams from the other pressure steps are compressed to the synthesis pressure and returned as a hot gas stream to said urea synthesis stage. The total quantity of fresh CO 2 required for the urea synthesis is preferably supplied in the form of hot gas to the carbamate decomposition step and is suitably supplied to the last pressure step. Suitable forms of apparatus for carrying out the process are described.</p> |
