Evaluation performance of a radial flow ammonia converter

摘要

Modeling of fixed bed catalytic reactors is of great industrial importance. An industrial Ammonia synthesis reactor is considered as a case study to develop and verify the model that best represents the reactor behavior. Mathematical models are frequently used to evaluate the reactor performance during the catalyst life time. Ammonia converter performance is determined by the reaction rate, which depends on the operating variables. Two differential equations describe mathematically the steady-state behavior of the reactor section of a converter. The first models the concentration - position relationship for transformation of the reactants to products (conversion profile), the second handles the temperature - position behavior of the reacting synthesis gas, the catalyst, and the vessel internals (temperature profile). The one-dimensional pseudo-homogeneous model has been implemented in MATLAB to solve the governing equations and compare the solution with measured conversion and temperature profiles taken from ammonia plant III at the Abu-Qir Fertilizers Company. The derivation of the model on the basis of bed radius (dr) enables to follow-up the temperature distribution inside the bed at any bed radius, especially the temperature transmitters passes inside the catalyst bed, this is more accurate and allows to investigate the effect of varying the reactor operating conditions on the ammonia production rate. The model was verified for both design and operating conditions and the results obtained from the model favorably compared with plant data indicate very good agreement. The developed model is utilized to calculate the catalyst activity coefficient (β) with time and predict the first bed outlet temperature which is considered the highest temperature in the reactor (cannot be practically measured) and also this model has used as a guide to adjust the synthesis loop operating conditions in order to improve the performance of the converter and determine optimum operating conditions such as optimum inlet bed temperature to obtain higher productivity. The effect of variation of operating conditions such as loop pressure, inlet flow rate, inert content and inlet ammonia concentration on ammonia production was studied. Finally, addition of a new catalytic fourth bed (booster converter) in series downstream the existing reactor was also studied to increase the conversion per pass of the ammonia synthesis reaction, optimizing the loop operating conditions, increase ammonia production rate and save Energy.