Unie Van Kunstmestfabrieken B.v.

Stamicarbon B.v.

Henk C Burks

Andreas J Biermans

Kees Jonckers

Karel G Raemaekers

An improved process and apparatus for the concentration of an aqueous urea solution by evaporation of water in a single pass shell and tube heat exchanger having a substantially vertical tube bundle within the shell. The aqueous urea solution is introduced into the top of the vertical tube bundle and caused to fall as a film down the inside of said tubes whereby it is heated and water evaporated therefrom to form a concentrated urea solution. The heat for this evaporation is provided by condensing at least a part of a gas mixture containing NH.sub.3, CO.sub.2 and H.sub.2 O in the shell side of the heat exchanger. This gas mixture is introduced into a lower portion of the shell wherein it is caused to flow upwardly in shell in contact with said tube bundle, counter-current to the flow of the aqueous urea solution within the tubes whereby heat from said condensation is transferred to said aqueous urea solution flowing down the inside of the tubes. The shell side is provided with baffle means adapted to permit the gas mixture and condensate to flow upwardly in the shell side in contact with the tubes, while substantially preventing the back flow of either the gas mixture or the condensate within the shell side.

Process for concentrating an urea solution by evaporation

A method and apparatus for determining the saturation temperature of a solution containing a dissolved substance, the crystals of which are optically anisotropic. The solution is placed in an optical measurement vessel under conditions wherein crystals of said substance are present, and the temperature of said crystal containing solution is gradually increased to at least the temperature at which all of the crystals dissolve. The temperature of the solution is continuously measured. Simultaneously with the temperature increase, a beam of linearly polarized light is directed into the optical measurement vessel in a manner such that it is transmitted through said solution; the transmitted beam of light, after having passed through the solution, is directed through a light polarizing analyzer having a direction of polarization normal to that of said beam of light; and at least a portion of any light transmitted through said analyzer is directed to a light measuring photodetector. Any light passing through crystals while present in the solution is optically rotated such that it is transmitted through the analyzer to the measuring photodetector, and the intensity of the transmitted light reaching said photodetector decreases to a lower, substantially constant level when all of the crystals have dissolved. The saturation temperature is the temperature of the solution at the time the light measured by the photodetector reaches this lower, substantially constant level.

Method and apparatus for determining the saturation temperature of a

A process for determining the composition of an aqueous solution of ammonia and carbon dioxide from which ammonium carbamate or ammonium carbonate crystallizes out upon cooling to below the saturation temperature. The density and the saturation temperature of the solution are measured, and the ammonia, carbon dioxide, and water composition is determined by reference to densities and saturation temperatures of aqueous solutions of ammonia and carbon dioxide of known composition. The composition thus determined can be used to effect control over the composition of such aqueous solutions.

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Oirsbeek, Netherlands

Henk C Burks