Optimisation of the level control for an ammonia evaporator

Model-Based-Design Control

In some factories, manufacturing processes are closely monitored. In the event of irregularities, it is tempting to change the settings. However, a mistake can be made and cause a lot of damage. In such cases, it is better to simulate first.

Acsystème worked with Yara to provide expertise on level controls at the Montoir-de-Bretagne production unit. This manufacturer in the agriculture sector closely monitors the ammonium nitrate manufacturing process. The end product is irritating and toxic to humans, and explosive above a certain temperature. Irregularities have been observed in the manufacturing process for some time, without any possible correction. The only available possibility was to wait for the annual maintenance operation, to test a new setting and then wait until the following year to make further changes. Not very efficient.×430.jpg

To solve this issue, Acsystème applied a modelling and simulation approach: Model Based Design. This method consists of modelling the manufacturing process on a computer, and testing various settings, even the explosive ones, in simulation. without any interruption of manufacturing. We therefore modelled all the chemical process components (neutraliser, storage tanks) unitarily with their related regulation systems in Matlab and Simulink. Then, the overall equipment was modelled by interconnecting the various components. The resulting model was then validated in simulation, by comparing simulation results with on-site measurements.

Based on this model, a regulation system was designed to solve the issues encountered by the ammonium nitrate production unit. Different strategies could be tested and calibrated on the model. Management is satisfied with the results and now plans to implement the proposed regulation system at the next plant shutdown. The chemical process is now better controlled as a result of this simulation step. The customer also ensures the safety of its equipment.

Sébastien Saliou, October 2013

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