Development of a model-based control algorithm for an ammonia synthesis column

Abstract

This paper presents an approach to the development of a model-based control system for a multi-shelf synthesis column used in ammonia production. The proposed approach is based on the application of a combined mathematical model that integrates deterministic and experimental–statistical modeling methods. Such a combination makes it possible to achieve a high level of model adequacy, ensure adaptability to varying operating conditions, and expand the applicability of the model for the analysis and control of complex chemical engineering processes.

Using the proposed approach, a mathematical model of a three-shelf ammonia synthesis column equipped with an internal heat exchanger was developed. Based on this model, an information and logical scheme of the control object was refined, which made it possible to identify the key internal interactions between process variables and to assess their influence on the output parameters of the synthesis column. On this basis, an operating algorithm for a model-based control system was developed.

The obtained mathematical description enabled the formulation of an optimality criterion for column operation and the solution of an optimization problem aimed at determining the optimal flow rates of “cold” bypass streams. This makes it possible to maintain the operating conditions of the column in a region close to the optimal regime and to ensure a rapid transition of the system to this region during operation. The optimal value of ammonia concentration at the outlet of the synthesis column was determined using the Hooke–Jeeves optimization method.

A functional automation scheme was developed, and the set of technical means required for implementing the proposed control system in industrial automatic process control systems was analyzed. The implementation of the developed model-based control system will reduce deviations of technological parameters from their optimal values and improve the operational efficiency of the ammonia synthesis column.