No description available.

No description available.

No description available.

In this thesis, an alternative control method based on Fuzzy Inference System (FIS) is proposed to keep the product composition of a distillation column constant. This study compares a proposed FIS to traditional PID (proportional, integral, derivative) control technique and analyzes the results. The FIS is applied to the control of the tray temperature of the distillation column by using indirect feed split control structure to modulate the steam flow with management of the tray temperature. In turn, this modulation maintains the composition of product at specified levels. Rockwell fuzzy designer is used to develop the fuzzy logic controller. Both a fuzzy logic controller and a PID controller are downloaded in the Rockwell ControlLogix L62 process controller. Chemstations Chemcad simulation software is used to run the distillation column simulations. Simulation results are programmed into L62 process controller to behave as a dynamic distillation column. Results show that the proposed fuzzy logic controller is more tolerant to disturbances in the feed flow and feed composition of the distillation column than the PID controller.

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Distillation is one of the most widely used processes for the separation of fluids with different volatilities. Due to the popularity of this process it is often assumed that the hydrodynamic behaviour inside distillation columns is well-defined. However, this is not always the case and this study therefore endeavoured to provide additional insight into the topic through a systematic investigation into the hydrodynamics and the capacity limitations of a sieve tray distillation column. The objective of the study was to measure and evaluate the effects of the following variables on entrainment and weeping: - Fluid flow rate (gas and liquid). - Plate geometry (i.e. hole diameter and fractional hole area). - Liquid properties (i.e. surface tension, viscosity and density). - Gas properties (i.e. viscosity and density). The hydrodynamic effects were evaluated at zero mass transfer in a pilot-scale tray column, by passing pure liquids and gases in counter current configuration. The pilot column was rectangular in shape with internal dimensions of 175 mm by 635 mm. A chimney tray was used to capture the weeping liquid, while a de-entrainment tray was used in combination with a mist eliminator pad to capture the entrained liquid. The fractional hole areas for the sieve trays under investigation were 7%, 11% and 15% and the hole diameters were 3.2 mm (⅛ in.), 6.4 mm (¼ in.) and 12.7 mm (½ in.). The experimental liquids were ethylene glycol, butanol, water and silicone oil, while the gases were air and carbon dioxide (CO2). These experimental measurements produced over 10 000 data points for entrainment and over 7 000 data points of weeping. The results were repeatable and the entrainment values compared reasonably well with previous data produced by Nutter (1971) and Uys (2012). The differences between entrainment for the different liquids were more significant in the spray regime than in the froth regime, and butanol was entrained more readily than silicone oil, ethylene glycol and water. Fluids that caused a larger spray layer in the dispersion zone produced more entrainment. Entrainment increased with decreasing liquid density, decreasing liquid surface tension and decreasing liquid viscosity. The more unstable the dispersion layer, the higher the entrainment. The liquid density strongly influenced weeping, i.e. weeping increased with increasing liquid density. On the other hand, gases with higher densities – and thus with a higher mass flow rates at similar volumetric flow rates through the sieve tray – displayed less weeping and more entrainment than less dense gases, because of an increased upward drag force on the fluids. When considering tray geometry and when operating in the spray regime, the magnitude of entrainment increased with decreasing fractional hole area, while the dependency of entrainment on fractional hole area was more prominent at lower fractional hole areas. When operating in the froth regime – typically above 23 m3/(h.m) – the fractional hole area had a relatively small influence on the magnitude of entrainment, while the cross-flowing liquid rate dominated related effects. In the spray regime, i.e. typically below 23 m3/(h.m), the entrainment increased with increasing sieve tray hole diameter, while hole diameter had a relatively small influence on entrainment at higher liquid flow rates between 23 and 60 m3/(h.m). However, at even higher liquid flow rates in the froth regime, i.e. above 60 m3/(h.m), the effect of hole diameter on the entrainment became more prominent again, with increased entrainment for smaller hole diameters. The effect of hole diameter on weeping differed with changing fluid combinations and the 12.7 mm hole size caused notably less weeping than the 3.2 mm and 6.4 mm trays at higher liquid flow rates. It is believed that weeping occurred preferentially at so-called localised high pressure zones on the sieve tray. At high gas and liquid flow rates, the resultant extended dispersion layer allows minimal intimate contact between the plate and the liquid (minimising such localized high-pressure zones). In effect, the liquid ‘jumps’ over the entire flow path length in the test rig, thus resulting in low weeping rates at high gas and liquid rates. The effects of fractional hole area and hole diameter on entrainment and weeping can be correlated with combinations of well-known hydrodynamic dimensionless numbers, such as the Weber number (We), Froude number (Fr) and Reynolds number (Re). Within the limitations of this study, the flow-Froude number was shown to be the most useful dimensionless number, since it displayed a monotonic relationship with magnitude of entrainment for different combinations of fluid systems and tray configurations. Furthermore, both the construction number and fluid density ratio could be used in a sensible manner to correlate some of the effects of tray geometry on entrainment. / AFRIKAANSE OPSOMMING: Distillasie word wêreldwyd op groot en klein skaal toegepas as ʼn metode om chemiese komponente van mekaar te skei, gebasseer op hul verskil in vlugtigheid. Die hidrodinamiese gedrag van vloeistowwe en hul damp binne ʼn distillasiekolom beïnvloed die effektiwiteit van die skeidingsproses. Hierdie studie beoog dus om bykomende insig te verskaf tot die hidrodinamika en kapasiteitsbeperkings van ʼn plaat-distilleerkolom. Die doelwit van die studie was om die invloed van die volgende veranderlikes op die meesleuring en deurdripping van vloeistowwe te ondersoek: - Gas- en vloeistof vloeitempo. - Plaatgeometrie (i.e. gatdeursnit en fraksionele deurvloei-area). - Vloeistofeienskappe (i.e. oppervlakspanning, viskositeit en digtheid). - Gaseienskappe (i.e. viskositeit en digtheid). Die hidrodinamiese studie is uitgevoer in ʼn reghoekige plaatkolom met interne afmetings van 175 mm x 635 mm. Die vloeistof en gasfases is in kontak gebring op ʼn teenstroom basis, met geen massa-oordrag wat plaasvind nie. ʼn Skoorsteenplaat het die vloeistof opgevang wat deurdrip terwyl ʼn ekstra plaat aan die bokant van die kolom die meegesleurde vloeistof opgevang het. Hierdie ekstra plaat is gebruik tesame met ʼn mis-elimineerder om al die meegesleurde vloeistof op te vang. Plate met verskillende deurvloei-areas (7%, 11% en 15%) en gat deursnitte (3.2 mm, 6.4 mm en 12.7 mm) is gebruik in die ondersoek. Die vloeistowwe wat gebruik is, sluit in etileen glikol, butanol, water en silikon olie. Lug en koolstofdioksied is as gasse gebruik. Die eksperimentele data het goeie herhaalbaarheid getoon en is vergelykbaar met die gepubliseerde data van Nutter (1971) en Uys (2012). Meer as 10 000 data punte is gemeet vir vloeistofmeesleuring en meer as 7 000 vir deurdripping. Die verskil in hoeveelheid meesleuring tussen die vloeistowwe, soos ondersoek in hierdie studie, was mees beduidend in die spoei-regime. Butanol is die meeste meegesleur, gevolg deur silikon olie en dan etileen glikol. Water is die minste meegesleur is. Vloeistowwe wat ʼn groter sproeivolume in die dispersielaag bo die plaat gevorm het, is die meeste meegesleur. Meesleuring het toegeneem met ʼn afname in digtheid, oppervlakspanning en viskositeit van die vloeistof. ʼn Onstabiele dispersielaag bo die plaat het meer meesleuring tot gevolg gehad. Vloeistofdeurdripping is sterk beïnvloed deur vloeistofdigtheid, i.e. deurdripping het sterk toegeneem met digtheid. Gasse met ʼn hoër digtheid veroorsaak weer ʼn afname in deurdripping a.g.v. die hoër opwaartse sleurkragte wat ʼn gas met hoë digtheid op die vloeistof uitoefen. In die sproei-regime (tipies by vloeistofvloeitempos laer as 23 m3/(h.m) is gevind dat meesleuring toeneem met ʼn afname in fraksionele deurvloei-area. Meesleuring se afhanklikheid van fraksionele deurvloei-area was meer beduidend by laer fraksionele deurvloei-areas. In die skuim-regime (tipies by vloeistofvloeitempos hoër as 23 m3/(h.m)) was die afhanklikheid van meesleuring op fraksionele deurvloei-area relatief klein. In die sproei-regime is gevind dat meesleuring toeneem met ʼn toename in gat deursnit, terwyl dieselfde veranderlike ʼn minder beduidende invloed op meesleuring getoon het by hoër vloeistofvloeitempos (tussen 23 en 60 m3/(h.m)). By vloeitempos hoër as 60 m3/(h.m) het meesleuring weer begin toeneem met ʼn afname in gat deursnit. By hoë vloeistofvloeitempos het die plaat met 12.7 mm gat deursnit aansienlik minder deurdripping getoon as plate met 3.2 mm en 6.4 mm deursnitte. Daar word vermoed dat deurdripping hoofsaaklik plaasvind by lokale hoëdruk gebiede op die plaat. By hoër vloeistof- en gasvloeitempos beslaan die dispersielaag ʼn groter volume en is daar dus minder gebiede van digte vloeistofkontak met die plaat, wat ʼn afname in die lokale drukgebiede veroorsaak. Dit lei tot ʼn afname in deurdripping by hoër gas- en vloeistofvloeitempos. Die invloed van fraksionele deurvloei-area en gatdeursnit op meesleuring en deurdripping korreleer goed met kombinasies van welbekende hidrodinamiese dimensielose getalle, i.e. die Webergetal (We), die Froudegetal (Fr) en die Reynoldsgetal (Re). Die vloei-Froudegetal is mees bruikbaar om die invloed van vloeistof-en-gas kombinasies en kolomuitleg op meesleuring te korreleer. Die konstruksiegetal asook die digtheidsverhoudings tussen vloeistof en gas kan op ʼn sinvolle manier aangewend word om van die invloede van plaatgeometrie op meesleuring te beskryf.

Η παρούσα διπλωματική εργασία έχει ως θέμα την μελέτη μιας κολόνας διύλισης και πιο συγκεκριμένα την εκτίμηση των συγκεντρώσεων του υγρού σε κάθε δίσκο της με χρήση του βέλτιστου γραμμικού φίλτρου Kalman, καθώς και τον έλεγχό της. / -

Distillation systems consist of one or more distillation columns, in which a mixture is separated into higher-value products, and a heat exchanger network (HEN) that recovers and reuses heat within the system. For example, crude oil distillation systems comprise crude oil distillation units (CDU), in which crude oil is distilled into products for downstream processing, a HEN and a furnace. Heat-integrated distillation systems present complex interactions between the distillation columns and HEN. These interactions, together with the many degrees of freedom and process constraints, make it challenging to retrofit or modify the operating conditions of existing distillation processes to accommodate changes in process operating conditions. Retrofit designs aim to re-use existing equipment when process objectives change, for example to increase throughput, improve product quality, or reduce energy consumption or environmental impact. To achieve these retrofit objectives, operational, structural and/or flowsheet modifications to the overall system (distillation columns and HEN) may be considered, subject to specifications and system constraints. This work proposes an optimisation-based approach to retrofit design for the capacity expansion of heat-integrated distillation systems, with a particular focus on crude oil distillation systems. Existing retrofit approaches found in the open research literature consider operational optimisation, replacing column internals, adding preflash or prefractionation units and HEN retrofit to increase the capacity of existing systems. Constraints considered usually relate to the distillation column hydraulic limits, product quality specifications and heat exchanger performance (e.g. minimum temperature approach and, pressure drop). However, no existing methodologies consider these possible modifications simultaneously; thus, beneficial interactions between flowsheet modifications, operational changes, heat integration and equipment modifications may be missed. In this work, retrofit design solutions for crude oil distillation are developed using a stochastic optimisation framework implemented in MATLAB to optimise the system operating parameters and to propose flowsheet, column and HEN modifications. Within the framework, the optimiser can propose addition of a preflash unit, modifications to the CDU internals and changes to its operating conditions; the separation system is then simulated using Aspen HYSYS (via the MATLAB interface) and the hydraulic performance of the column is analysed using published hydraulic correlations. The optimiser also proposes modifications to the HEN (i.e. installed heat transfer area, HEN structure and operating conditions), which is then simulated to evaluate heating and cooling utility demand. Either simulated annealing and global search optimisation algorithms are applied to identify the optimal design and operating conditions that meet the production requirements and product specifications. Industrially relevant case studies demonstrate the effectiveness and benefits of using the proposed retrofit approach. The case studies illustrate that combined structural and operational modifications can be effectively and systematically identified to debottleneck an existing crude oil distillation system with a relatively short payback time, while simultaneously reducing energy consumption per barrel of crude oil processed.

The increasing trend of world-wide energy consumption emphasizes the importance of ongoing optimization of new and existing technologies. In this dissertation, two energy–intensive systems are simulated and optimized. Advanced estimation, optimization, and control techniques such as a moving horizon estimator and a model predictive controller are developed to enhance the profitability, product quality, and reliability of the systems. An enabling development is presented for the solution of complex dynamic optimization problems. The strategy involves an initialization approach to large–scale system models that both enhance the computational performance as well as the ability of the solver to converge to an optimal solution. One particular application of this approach is the modeling and optimization of a batch distillation column. For estimation of unknown parameters, an L1-norm method is utilized that is less sensitive to outliers than a squared error objective. The results obtained from the simple model match the experimental data and model prediction for a more rigorous model. A nonlinear statistical analysis and a sensitivity analysis are also implemented to verify the reliability of the estimated parameters. The reduced–order model developed for the batch distillation column is computationally fast and reasonably accurate and is applicable for real time control and online optimization purposes. Similar to estimation, an L1-norm objective function is applied for optimization of the column operation. Application of an L1-norm permits explicit prioritization of the multi–objective problems and adds only linear terms to the problem. Dynamic optimization of the column results in a 14% increase in the methanol product obtained from the column with 99% purity. In a second application of the methodology, the results obtained from optimization of the hybrid system of a cryogenic carbon capture (CCC) and power generation units are presented. Cryogenic carbon capture is a novel technology for CO2 removal from power generation units and has superior features such as low energy consumption, large–scale energy storage, and fast response to fluctuations in electricity demand. Grid–level energy storage of the CCC process enables 100% utilization of renewable power sources while 99% of the CO2 produced from fossil–fueled power plants is captured. In addition, energy demand of the CCC process is effectively managed by deploying the energy storage capability of this process. By exploiting time–of–day pricing, the profit obtained from dynamic optimization of this hybrid energy system offsets a significant fraction of the cost of construction of the cryogenic carbon capture plant.

This master‘s thesis deals with the design of a control system for a distillation column. It deals with the issue of distillate production and acquaints the reader with the necessary knowledge that is necessary to understand the purpose of the work. The practical part of the work presents a specific distillation column, the means for its control and the method of implementation of the control system, then the visualization of the control system and the method of control. Part of the work is the evaluation of the results and benefits of the work.

The aim of this master’s thesis was to create a control system for laboratory distillation column model. There are two different models considered. Real and software model. For the real model suitable components were selected and the model was built. Software model allows safe testing of control algorithm functionality without the need of real model. The simple visualization that works with both models was developed. Both distillation column models - real and software - were tested as a last phase of work.