Ammonia plants optimization cases

Execution times for the overall ammonia plant model, of which the C02 capture system is a small part, are on the order of 30 s for the parameter estimation case, and less than a minute for an Optimize case. The model consists of over 65,000 variables, 60,000 equations, and over 300,000 nonzero Jacobian elements (partial derivates of the equation residuals with respect to variables). This problem size is moderate for RTO applications since problems over four times as large have been deployed on many occasions. Residuals are solved to quite tight tolerances, with the tolerance for the worst scaled residual set at approximately 1.0 x 10 9 or less. A scaled residual is the residual equation imbalance times its Lagrange multiplier, a measure of its importance. Tight tolerances are required to assure that all equations (residuals) are solved well, even when they involve, for instance, very small but important numbers such as electrolyte molar balances. 

In many cases it is of interest to an ammonia producer to improve the production economics of an existing plant by the addition of new equipment or modification of existing equipment, by optimization of the operation, for example by installation of new and more efficient catalysts, or in some cases by a change of feedstock, etc. An important element in such a modernization of an ammonia plant, which is most often referred to as a revamp of the plant, is in many cases a modernization of the converter system. 

Each revamp project must be tailor-made to enable optimization of production, consumption and capital investment based on the specific case. In the most comprehensive and most extensive revamp projects, the energy efficiency may be increased to a level comparable with that of the new low-energy ammonia plants. The required capital investment will, however, in most cases be too high to justify such extensive revamps. 

Kendrick and Stoufiestijk [171 in 1978 developed uniform, computerized methodology for selectir a plant location and provided examples of optimal locations for Egyptian fer zer industries. The linear model considers all production and logistic costs of raw material supply and product distribution. Similar models have been widely used [18]. It has been proven that fertilizer plant location depends on the product and the location of raw material resources. Low nutrient-containing fertilizers should be produced near the users area (e.g., SSP, ammonium carbonate, ammonium sulfate). HighHiutrient fertilizers, in particular phosphate fertilizers, should be produced as near as possible to the raw material source to minimize transportation costs. In many cases it would be feasible to produce ammonia and concentrated phosphoric acid in a mother plant and process intermedi-... 

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