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Integrerad schemaläggning och styrning av en luftsepareringsanläggning vid varierande elpris
KTH, School of Chemical Science and Engineering (CHE).
2015 (Swedish)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Integrated Scheduling and Control of an Air Separation Unit Subject to Time-Varying Electricity Prices (English)
Abstract [sv]

I detta examensarbete presenteras en ny metod för att göra schemaläggningsbeslut inom processindustrin

och samtidigt ta hänsyn till det dynamiska beteendet hos processen. En modell av en luftsepareringsanläggning

som producerar kvävgas och utnyttjar ett rörligt elpris användes för att exemplifiera denna

metod. Modellen omfattade en kryogenisk destillationskolonn med en integrerad återloppskokare /kondensator,

en multiströms värmeväxlare, en kompressor, två turbiner och en kondensator. Den innehöll

5079 ekvationer och 437 differentiella variabler. Dynamisk optimering användes för att approximera

det dynamiska beteendet hos processen vid skiftningar mellan olika driftpunkter. Den registrerade data

utnyttjades sedan för att identifiera en reducerad modell som fångade det transienta beteendet hos relevanta

processvariabler. Den reducerade modellen bestod av 525 ekvationer och 67 differentiella variabler.

Den identifierade modellen visade på god matchning mellan relevanta processvariabler i de simulerade

övergångarna och den reducerade modellen.

Den reducerade modellen användes för att optimera schemaläggningen av luftsepareringsprocessen så

att elkostnaden över en tredagars period minimerades. De optimala resultaten visade på en minskning av

kostnaden på 2.6 % jämfört med en konstant produktionstakt. Schemat implementerades och simulerades

i den fullt dynamiska modellen över de första 24 timmarna för att jämföra relevanta processvariabler med

den reducerade modellen. Resultaten visade på god matchning mellan de båda modellerna.

Detta examensarbete visar att en exakt reducerade modell kan användas för att snabbt hitta ett

optimalt schema över ett större processystem. Detta genom att kraftigt minska systemets storlek utan

att offra noggrannhet av det dynamiska beteendet.

Abstract [en]

A novel framework for making plant scheduling decisions while considering the plant process dynamics

is presented in this thesis. A model of an air separation unit built to supply nitrogen gas and subject

to time-varying electricity prices was used to illustrate this framework. The model includes a cryogenic

distillation column with an integrated reboiler/condenser, a multi-stream heat exchanger, a compressor,

two turbines, and a liquefier. It consisted of 5079 equations and 437 differential variables. The dynamic

behavior of the process during operating point transitions was determined using dynamic optimization.

This data were used to establish a reduced order dynamic model of the system which captures the

transient behavior of relevant process variables. The reduced order model consisted of 525 equations and

67 differential variables. The identified model showed a good fit between the relevant process variables

in the simulated transitions and the reduced order model.

The air separation unit process schedule was optimized using the reduced order model to minimize

electricity cost over a three day time horizon. The optimal result showed a 2.6 % reduction in electricity

cost compared to a flat production rate. The optimal schedule was implemented and simulated in the

full dynamic model for the first 24 hours to compare the relevant process variables to the reduced model

predictions. The result displayed good match between the reduced model and the full dynamic model.

This thesis shows that an accurate reduced order dynamic model can be used for quickly finding

the optimal schedule of large process systems. This by greatly reducing the size and complexity of the

system without sacrificing accuracy of the dynamic behavior. Furthermore, it also shows the economic

benefits of the integrating scheduling and control to count for the dynamic behavior of the system.

Place, publisher, year, edition, pages
2015. , 66 p.
Keyword [en]
Scheduling, control, integrated, time-varying parameters, air separation unit
Keyword [sv]
schemaläggning, styrning, integrerad, tidsberoende parametrar, luftseparationsanläggning
National Category
Other Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-173823OAI: oai:DiVA.org:kth-173823DiVA: diva2:855080
Available from: 2015-09-18 Created: 2015-09-18 Last updated: 2015-09-18Bibliographically approved

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