Patent claim: A stripper according to any of the previous claims said stripper being of fallingfilm type.

Related passage: A frequently used process for the preparation of urea according to a stripping process is the carbon dioxide stripping process as for example described in Ullmanns Encyclopedia of Industrial Chemistry Vol.A27 1996 pp 333350.In this process the synthesis section followed by one or more recovery sections.The synthesis section comprises a reactor a stripper a condenser and but not necessarily a scrubber in which the operating pressure is in between 12 and 18 MPa and preferably in between 13 and 16 MPa.In the synthesis section the urea solution leaving the urea reactor is fed to a stripper in which a large amount of nonconverted ammonia and carbon dioxide is separated from the aqueous urea solution.Such a stripper can be a shell and tube heat exchanger in which the urea solution is fed to the top part at the tube side and a carbon dioxide feed to the synthesis is added to the bottom part of the stripper.At the shell side steam is added to heat the solution.The urea solution leaves the heat exchanger at the bottom part while the vapor phase leaves the stripper at the top part.The vapor leaving said stripper contains ammonia carbon dioxide inert gases and a small amount of water.Said vapor is condensed in a falling film type heat exchanger or a submerged type of condenser that can be a horizontal type or a vertical type.A horizontal type submerged heat exchanger is described in Ullmanns Encyclopedia of Industrial Chemistry Vol.A27 1996 pp 333350.The heat released by the exothermic carbamate condensation reaction in said condenser is usually used to produce steam that is used in a downstream urea processing section for heating and concentrating the urea solution.Since a certain liquid residence time is created in a submerged type condenser a part of the urea reaction takes already place in said condenser.The formed solution containing condensed ammonia carbon dioxide water and urea together with the noncondensed ammonia carbon dioxide and inert vapor is sent to the reactor.In the reactor the above mentioned reaction from carbamate to urea approachesthe equilibrium.The ammonia to carbon dioxide molar ratio in the urea solution leaving the reactor is generally in between 2.5 and 4 molmol.It is also possible that the condenser and the reactor are combined in one piece of equipment.An example of this piece of equipment as described in Ullmanns Encyclopedia of Industrial Chemistry Vol.A27 1996 pp 333350.The formed urea solution leaving the urea reactor is supplied to the stripper and the inert vapor comprising noncondensed ammonia and carbon dioxide is sent to a scrubbing section operating at a similar pressure as the reactor.In that scrubbing section the ammonia and carbon dioxide is scrubbed from the inert vapor.The formed carbamate solution from the down stream recovery system is used as absorbent in that scrubbing section.The urea solution leaving the stripper in this synthesis section requires a urea concentration of at least 45by weight and preferably at least 50by weight to be treated in one single recovery system downstream the stripper.The recovery section comprises a heater a liquidgas separator and a condenser.The pressure in this recovery section is between 0.2 to 0.5 MPa.In the heater of the recovery section the bulk of ammonia and carbon dioxide is separated from the urea and water phase by heating the urea solution.Usually steam is used as heating agent.The urea and water phase contains a small amount of dissolved ammonia and carbon dioxide that leaves the recovery section and is sent to a downstream urea processing section where the urea solution is concentrated by evaporating the water from said solution.The vapor released in the heater of the recovery system comprises ammonia carbon dioxide and water.Said vapor is condensed in a condenser.The heat of condensation is dissipated in cooling water.The formed carbamate is used as absorbent in said scrubber in the synthesis section.Some noncondensed vapor comprising ammonia carbon dioxide and inert leaving that scrubber is sent to a condenser or absorber in order to purify the inert before releasing it into the atmosphere.The pressure in said condenser andor absorber is typically lower than the pressure in the synthesis section.