Stripper falling film

The Stainicaibon process is described in Figures 3—7. The synthesis section of the plant consists of the reactor, stripper, high pressure carbamate condenser, and a high pressure reactor off-gas scmbber. In order to obtain a maximum urea yield pet pass through the reactor, a pressure of 14 MPa (140 bar) and a 2.95/1 NH —CO2 molar ratio is maintained. The reactor effluent is distributed over the stripper tubes (falling-film type shell and tube exchanger) and contacted by the CO2, countercurrendy. This causes the partial NH pressure to decrease and the carbamate to decompose. 

Toyo Engineering-AGES Process. The synthesis section of the ACES process (Fig. 8) consists of a reactor, a stripper, two carbamate condensers, a scmbber and operates at 17.5 MPa (175 bars). The reactor is operated at 190°C with a NH /CO2 ratio of 4.0 (mol/mol). Liquid NH is fed directly into the reactor by a centrifugal ammonia pump. Gaseous CO2 is sent from the centrifugal CO2 compressor to the bottom section of the falling-film type stripper. 

The reactor effluent, which contains unconverted NH3 and C02, is stripped in a falling-film type shell and tube exchanger at reactor pressure. The stripping agent, CO2, flows upward, which is countercurrent to the effluent stream. The stripper tubes are make of 25-22-2 stainless steel, which has lasted almost 30 years in some plants. The stripped-off NH3 and CO2 are then partially condensed and recycled to the reactor. The heat from this condensation is used to make 4.5 bar steam. Some of this steam can be used in downstream sections of the plant while some is sent to the turbine on the CO2 compressor108,110. 

To remove chlorate and other salts, the 50 percent diaphragm cell caustic may be extracted with liquid ammonia in a pressurized system. The ammonia fraction then is processed through a stripper to remove and recycle the ammonia. The alkaline stripper bottoms are useful in neutralizing acidic waste streams. The purified caustic is evaporated further, and then fed to an anhydrous concentrator, typically an Inconel falling film evaporator, heated with molten salt. The anhydrous caustic, containing at least 97.5 percent NaOH, is marketed as one solid mass in drums, as flake caustic, or more desirably as beads or prills. The last are marketed in bulk or bags. 

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