| 摘要 |
The method for cleaning of gas waste and liquid waste from a melamine plant, consisting in that streams of gas waste and liquid waste are subject to the following operations in a continuous and closed cycle: decomposition of urea, expelling ammonia from the liquid waste, absorption of this ammonia together with ammonia from the gas waste and return to the melamine production process, characterised in that the ammonia expelling process is run in a stripping column under a pressure of approx. 0.5 MPa and at a temperature of approx. 100 degrees C using steam fed as counter-current to the lower part of the column under a pressure of 0.3 to 0.6 MPa, while in the central part of the column the solution of liquid waste is received which has no ammonia and contains urea and melamine and is then compressed to the pressure of 4 MPa and through a heat exchanger system directed to a hydrolyser where it is heated up to a temperature of approx. 210 to 230 degrees C and where the liquid is kept for approx. 40 to 60 minutes and then the solution thus obtained and containing products of urea decomposition is expanded and directed to the central part of the stripping column and from the top of this column vapours containing ammonia are received and then mixed with fresh gas waste from the melamine plant and the stream of hydrated ammonia from the NH3 liquefaction system are directed to the absorbing column where these gases are sprinkled with water and/or hydrated with ammonia at liquid to gas stream ratio between 5:1 and 10:1 by volume and then sprinkled with a cold steam condensate, or with a cold liquid from the stripping column with a liquid to gas stream ratio between 1:1 and 5:1 by volume upon which the liquid leaving the absorption column and containing ammonia is carried away to the process of melamine production, and the gases collected at the top of this column and pollutant-free are carried away to atmosphere.
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