Control assessment for heat integrated systems. An industrial case study for ethanol recovery

Abstract

Highlights•Heat integration is needed for energy reduction but can deteriorate controllability •Soundly designed controllers can handle complex processes •The deterioration of controllability was handled by the controllers •Large energy savings are possible with a good dynamic response Abstract:Heat integration is essential for reducing the energy consumption of process industries. However, it may render the dynamic operation more interactive and difficult to control. This paper assesses the implications of heat integration in controllability and performance in energy reduction. The assessment, both on open loop and closed loop, was carried out based on an industrial case study and compared to a modified case without heat integration. Although the heat integrated system Page 2 of 31 A c c e p t e d M a n u s c r i p t 2 displayed a certain deterioration of controllability, the control system made possible an efficient operation. To this goal, different control systems were tested, from a decentralized control system to a model predictive controller. The type of controller used in the process barely influenced the performance of the process since the aim was exclusively to ensure the regulation of the process to fixed setpoints. The reduction of energy consumption achieved thanks to heat integration was considerably larger than the losses due to poor control of the process, confirming the importance of heat integration in energy intensive processes.

Process control in intensified continuous solids handling

“…Indeed, the theoretical increment in process efficiency gained through any PI application might be compromised if the plant is difficult to control and therefore cannot be operated at its nominal operating point [7]. Traditionally, process control design has been conducted separately after the process design and usually by other experts.…”

“…In addition, PI processes typically involve faster and more complex dynamics (response times) [3], and it is suggested that in intensified processes, the dynamics of sensors and actuators may also play a crucial role in controller design and control performance [11,12]. In general, the higher degree of integration will make the process more challenging to control and will perhaps restrict the implementation of highly intensified processes in industry [7]. Many of the published works on control design for intensified processes deal with reactive distillation (see, e.g., [10,[13][14][15]), but reported work in the area of solids 1 http://ibd-project.eu/…”

Effect of ionic liquids as entrainers on the dynamic behavior of ethanol-water extractive columns

“…The dynamic performance of more complex distillation systems for ethanol recovery has also been studied. Mauricio-Iglesias et al [29] evaluated the influence of heat integration in the ethanol-water distillation process, showing that the energy savings are achieved at the expense of a deterioration in the process controllability. Ramírez-Marquez et al [30] analyzed the dynamic behavior of alternative separation processes for ethanol dehydration by extractive distillation, considering different intensified arrangements based on thermally coupled distillation systems.…”

Control Design Tools for Intensified Solids Handling Process Concepts

“…As process control is an intrinsic part of process engineering, without a process control assessment, the target of DFSS, and new concepts, is unreachable. The theoretical increment in process efficiency gained through PI might be compromised if the plant is difficult to control and therefore cannot be operated at its nominal operating point (Mauricio-Iglesias et al 2013).…”