Chemical Engineering and Processing 46 (2007) 198–209 Enhancing sugar cane process performance through optimal production scheduling H. Heluane a , M. Colombo a , M.R. Hern´ andez a , M. Graells b , L. Puigjaner b,∗ a Departamento de Ingenier´ ıa Qu´ ımica, Universidad Nacional de Tucum´ an, Av. Independencia 1800, 4000 Tucum´ an, Argentina b Chemical Engineering Department, Universitat Polit` ecnica de Catalunya, ETSEIB, Av. Diagonal 647, 08028 Barcelona, Spain Received 4 January 2006; received in revised form 15 May 2006; accepted 15 May 2006 Available online 9 June 2006 Abstract Process design and operation is concerned with the optimal selection and efficient utilization of resources along time. The operational efficiency of equipment units depends strongly on the maintenance policy employed. This work addresses critical operational issues in the sugar cane industry such as the problem of determining the optimal cyclic cleaning policy in the evaporation section and the corresponding optimum steam consumption pro- file of both evaporation and crystallization sections. A main feature of this problem is the performance decay with time of each evaporation unit which must be restored by appropriate cleaning operations. in this paper, a detailed mixed integer nonlinear programming (MINLP) performance model which includes the effect of fouling on the overall heat-transfer coefficient is considered. The problem formulation can also handle multiple-unit par- allel evaporation lines. Problem solution provides for each production line the optimal cleaning schedule, mass flow to be processed, and vapor bleeds. © 2006 Elsevier B.V. All rights reserved. Keywords: Cyclic production and cleaning scheduling; Evaporation; Continuous process; Sugar manufacturing; Mathematical programming 1. Introduction In the sugar cane industry, a substantial cost reduction can be achieved through efficient inventory management, reduction of the excess manufacturing capacity and rational use of resources. Important cost reductions can also be achieved by coordinating the use of the manufacturing resources and process operations. The key role of effective tools for scheduling and planning activities within the process industries has gained increasing recognition in recent years especially because improved cus- tomer service, reduced inventory, lower manufacturing costs, and global operations are achieved [1]. Heating processes are commonly employed in chemical plants in order to achieve product specific properties. In the spe- cific case of sugar cane production the juice is concentrated in evaporator units by heating until sucrose crystals are obtained. In this process, solid deposits are formed on the heating sur- faces (fouling) with a consequent increase of the heat transfer resistance with time and a dramatic decrease in the overall per- ∗ Corresponding author. Tel.: +34 93 401 6678; fax: +34 93 401 0979. E-mail address: Luis.Puigjaner@upc.edu (L. Puigjaner). formance of the evaporator. Therefore, additional costs are added like the increase of operating costs due to a frequent cleaning of the equipment to restore its original performance. Fouling affects nearly every plant relying on heat exchangers for its operation. The common practice to mitigate fouling is to implement cleaning-in-place (CIP) operations. This is espe- cially applicable to processes affected by rapid fouling, such as that occurring in the production of milk, sugar cane juice, lemon juice, etc. [2]. During evaporator operation, as a consequence of the formation of solid deposits on heating surfaces, evapora- tion rates decrease with time whenever the driving force is kept constant. Consequently, the evaporator must be shutdown to be cleaned and the cycle must be restarted. Several works have proposed methods for the optimization of cleaning schedules for a single heat exchanger [3–5]. However, in process plants, multiple interconnected heat transfer units are used and the operating conditions of each equipment affect the overall heat exchange performance. Therefore, a rational main- tenance policy must be applied to the heat exchangers network in order to accomplish the desired production at a minimum cost. Scheduling of process operations has been addressed by many authors for different scenarios with special emphasis in batch process applications. But less attention has been paid to the 0255-2701/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2006.05.015