Difference between revisions of "Thermophysical Modeling: Why was UREA modified for the MSE model?"
(Created page with " == The Background == Circa 2009 OLI Systems was asked by one of its customers to model the decomposition of Urea in aqueous solutions. OLI undertook this modeling and crea...") |
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::NH<sub>4</sub>OCN = HOCN + NH<sub>3</sub> | ::NH<sub>4</sub>OCN = HOCN + NH<sub>3</sub> | ||
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+ | == The Problem == | ||
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+ | Almost immediately after the urea decomposition work had been completed there were complaints from the user community. In normal Ammonia and/or CO2 scrubbing or stripping unit operations, OLI was now predicting urea formation. This is not normally reported in the field. In fact if a model had NH<sub>3</sub> or CO<sub>2</sub> then urea would be formed. In addition, all the side products would also be formed. This concerned the OLI user community so much that a temporary fix was created. | ||
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+ | OLI created the species UREAINERT for both the vapor and aqueous phase. It was thought that if the user wanted to use Urea as a species then the inert species would solve the problem. Of course it did not in that if carbon dioxide and ammonia were present then "Active" urea would appear along with the side products. OLI then changed the view and the UREAINERT species was the default and had the same material codes as carbon dioxide and ammonia. This prevented the side reactions from appearing. |
Revision as of 12:40, 11 December 2014
The Background
Circa 2009 OLI Systems was asked by one of its customers to model the decomposition of Urea in aqueous solutions. OLI undertook this modeling and created a model. The basic chemistry of urea decomposition is as follows:
Urea: (NH2)2CO
Water: H2O
Ammonium Carbamate: NH2COONH2
Ammonia: NH3
Carbon Dioxide: CO2
- (NH2)2CO + H2O = NH2COONH2
- NH2COONH2 = NH3 + CO2
There are several side reactions which OLI attempted to model as well. Two molecules of urea can combine to form a species called biuret with a loss of an ammonia molecule.
Biuret: (CONH2)2
The reaction is:
- 2(NH2)2CO = (CONH2)2 + NH3
In addtion, another side reaction is the formation of ammonium cyanate from urea.
Ammonium Cyanate: NH4OCN
- (NH2)2CO = NH4OCN
Finally Ammonia Cyanate decomposes to isocyanic acid and ammonia
Isocyanic Acid: HOCN
- NH4OCN = HOCN + NH3
The Problem
Almost immediately after the urea decomposition work had been completed there were complaints from the user community. In normal Ammonia and/or CO2 scrubbing or stripping unit operations, OLI was now predicting urea formation. This is not normally reported in the field. In fact if a model had NH3 or CO2 then urea would be formed. In addition, all the side products would also be formed. This concerned the OLI user community so much that a temporary fix was created.
OLI created the species UREAINERT for both the vapor and aqueous phase. It was thought that if the user wanted to use Urea as a species then the inert species would solve the problem. Of course it did not in that if carbon dioxide and ammonia were present then "Active" urea would appear along with the side products. OLI then changed the view and the UREAINERT species was the default and had the same material codes as carbon dioxide and ammonia. This prevented the side reactions from appearing.