Improving Performances of a Cement Rotary Kiln: A Model Predictive Control Solution Silvia Maria Zanoli, Crescenzo Pepe, and Matteo Rocchi Università Politecnica delle Marche, Ancona, Italy Email: {s.zanoli, c.pepe}@univpm.it Abstract—In this work an advanced control system design aimed to the improvement of economic benefits and control performances of a cement rotary kiln located in an Italian cement plant is discussed. A Model Predictive Controller, together with other functional blocks designed to manage normal and critical situations, constitutes the core of the proposed strategy. Accurate identification procedures, aimed at obtaining accurate dynamical process models, have been performed. A suited cooperation of system modules and an ad hoc design of each of them allowed the meeting of control specifications, the increase of system reliability and the reduction of the standard deviation of critic process variables. In this way, the system can more safely operate closer to its operative bounds. The implementation of the proposed control system on a real plant has proven its soundness, leading to improvements in terms of energy efficiency, product quality and environmental impact, compared to the previous control system. Index Terms—cement rotary kiln, advanced process control, model predictive control, economic optimization, environmental emissions, process control I. INTRODUCTION In today’s world, cement is the substratum for civil engineering and its applications. The world cement production has grown in a constant manner since the early ‘50s. In particular, in recent decades, there was an increasing need for innovations in the production chain, as well as an increased need for a high level of automation, also due to the complex chemical and physical processes involved [1]. In this context may be placed the process control optimization, which, by using advanced control strategies, has the task of finding a compromise between the economic goals and the productive ones. This idea has an enormous benefit: payback time is in the order of the weeks, or months, in opposition to the years required by a relevant replace of an old hardware unit [2]. This challenge has motivated the present work, which consists in the study, development and implementation of an advanced control system for the optimization of a rotary kiln process located in an Italian cement plant. For the formulation of the proposed system, Model Predictive Control (MPC) techniques have been adopted [3]. Manuscript received July 2, 2015; revised October 6, 2015. Model Predictive Control is an optimization-based closed loop control strategy, able to handle multi-input multi-output (MIMO) processes with constraints on the manipulated and controlled variables. Through the minimization of a cost function, it can also guarantee set- point tracking, while monitoring control efforts [4], [5]. The control system has been developed using a custom-made software: This choice was originally motivated by the need of not relaying on industrial and commercial products, in order to limit the economic burdens as well as to the need to customize the controller to specific needs of the system at issue. In addition to the development of the Model Predictive Controller core module, the proposed control system has been equipped with other modules, at the scope to manage normal and critical situations. The system policy is based on the cooperation of these modules, which, together with an ad hoc module design, allowed the fulfillment of the required plant specifications. The paper is organized as follows: in the Section II, after a brief introduction on the cement rotary kiln process, control specifications issues are defined. Section III describes the proposed advanced process control design. In Section IV, the control system results are discussed, through a comparison with the previous control structure performances. Finally, conclusions and future developments are reported in Section V. II. CEMENT ROTARY KILN CONTROL PROBLEM A. A Briefly Description of the Process The cement is a hydraulic binder in the form of fine dust, inorganic and non-metallic. The fundamental component of the cement is the product of the baking of natural minerals, called clinker, which, combined with other components, gives rise to various types of cement. The clinker is made from lime, silica, alumina, iron and magnesium oxides, and other minor parts. This work is focused on the clinker production phase of a dry process cement industry, a highly energy consuming process. The clinker process is the most important subpart of the cement production, in terms of potentially polluting emissions, quality and cost of the product. In Fig. 1, the clinker production process is schematically represented. The raw meal, before the introduction in the rotary kiln, is preheated through a suspension pre-heater, while it is up in the air with exhaust gas of the combustion from the Journal of Automation and Control Engineering Vol. 4, No. 4, August 2016 ©2016 Journal of Automation and Control Engineering doi: 10.18178/joace.4.4.262-267 262