Quality regulation and energy saving through control and monitoring techniques for industrial multicomponent distillation columns

摘要

This Thesis deals with the problem of the quality control and monitoringudand the related energy consuming aspects in industrial multicomponentuddistillation columns. These have important relevance especially in case ofudunits subjected to important changes in operating conditions whichudmanifests in fluctuation of the product concentration.udDue to the low reliability of the seldom available and delayed analyticudcomposition measurements, they cannot be employed for an efficientudonline monitoring of the separation. Instead, this Thesis proposes the useudof composition observers with passive innovation mechanism and drivenudby temperature measurements. The passive structure allows to limit theudnumber of ODEs to be online integrated, which is a central issue to obtainuda product suitable for the industrial implementation. The design of thisudpassive structure involves the choice of number and location of theudtemperature sensors, the choice of the innovated component and the set ofudmodeled components in the (possibly simplified) estimation model. Thisudissue is addressed with a simple and systematic methodology that employsudsteady state information about the per-component temperature gradient ofudthe column and detectability measures and conditions. Differently fromudthe majority of the works in literature, the proposed methodology allowsudalso to assess the feasibility of obtaining good estimation performanceudusing the available temperature sensors in real columns.udEven the analytic composition measurements cannot be employed forudquality control in feedback control loops mainly due to delay problems.udInstead, temperature feedback controllers are usually used. But even if theudtemperature sensor is well located (and in this Thesis a criterion for sensorudlocation is suggested based on an extension of the slope criterion to theudmulticomponent case), when the operating conditions undergo changes,udthe indirect regulation of the product quality cannot be achieved, withudalternating periods of under and over-purification that also adverselyudaffect the energy requirement for the column functioning. Thus, in this Thesis an application oriented solution is proposed consisting in adding audfeedforward temperature setpoint compensation that guarantee a closeudquality regulation, including a more efficient management of the energy,udunder the changing operating modes of the column.udThe methodologies and techniques proposed and described in this Thesisudare tested with an industrial multicomponent IC4-NC4 splitter located atudthe Sarlux Refinery (Sarroch, Italy), which, motivated by the good results,udhas already implemented the composition estimator and is going toudimplement the feedforward setpoint compensator.