MATHEMATICAL SIMULATION OF AMMONIA ABSORPTION FROM A GAS-VAPOR MIXTURE

DOI: 10.6060/tcct.20165911.5355
Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2016. V. 59. N 11. P. 112-116

Frequently, low concentration ammonia solutions are formed in a number of indus-tries. Obtaining of marketable ammonia water with concentration of 25% from the ammonia solutions is possible by a consecutive carrying out desorption and absorption processes. A desorption of ammonia takes place by an interaction between the ammonia solution flowing on a plates and a steam flow and we obtain steam-gas mixture with concentration higher than in a source solution. And a condensation of water vapor and absorption of ammonia with forming marketable ammonia water takes place into a tubular absorber. The process of ammonia desorption from the steam-gas mixture is took up in this article. A mathematical model of process allowing predicting process parameters for providing ammonia water with required concentration was proposed. At the simulation, the following physical model was used. The steam-gas mixture consisting of water and ammonia vapors enters into a tube bank. Coolant (water) circulates outside of tubes. The water vapors are condensed by a con-tact with an inner surface and then the ammonia absorption occurs by a film of condensate. As the result the ammonia water is accumulated into a cell formed by a tube plate and an ab-sorber bottom and it is exported from apparatus by a condensate extractor. At the simulation we supposed that the flows of water and of gas into the tubes and freezing flow into the out-side of tubes move counter under perfect replacement mode. A heat exchange with environ-ment doesn’t take place. A mode of apparatus is stationary. The mathematical model consists of equations of material and of heat balance for a surface element, equations of equilibrium pressures of mixture components, equations for calculation of mole fractions of solution components and of partial pressures of steam-gas vapor components. The solution of system of equations was realized in the mathematical application Mathcad by finite-difference meth-od. An ammonia concentration into the solution and the vapor, flow rate of liquid phase and flow rate of ammonia into it, the temperatures of the steam-gas mixture, of the coolant and of the film of solution along the apparatus height was calculated. The dependence of solution temperature at the apparatus output and ammonia concentration into it on flow rate of cool-ant was determined. The experiments showed the increase in coolant flow rate at the constant initial temperature leads to the decrease in the temperature of the solution and a little in-crease in ammonia concentration into it at the apparatus output.

Key words: absorption, ammonia, vapor water, mathematic simulation, tubular absorber

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2016, Т. 59, № 11, Стр. 112-116

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