Optimization For Grade Transitions In Polyethylene Solution Polymerization

Transcription

1 Opmzaon For Grade Transons In Polyehylene Soluon Polymerzaon Jun Sh Lorenz T. Begler Inan Hamdan Sara Munjal John Wassck Sco Bury Shawn Fes Ale Kalos Cener of Advanced Process Decson-makng Deparmen of Chemcal Engneerng Carnege Mellon Unversy The Dow Chemcal Company Mar 4

2 Background LLDPE Soluon Polymerzaon Produc Oule Separaor Recycle Lnear low-densy polyehylene LLDPE Made by copolymerzaon of ehylene wh longer-chan olefns ocene buene heene propylene Long loop wh hea echangers Connuous operaon Mulple feed posons for: Ehylene Comonomer Caalys Solven Hydrogen Hea Echanger Flow loop Pellezer Caalys nle Monomer nle Hea Echanger. Che I Kao e al. Non-adabac olefn soluon polymerzaon November 999. US Paen J.J. Zacca and W.H. Ray. Modellng of he lqud phase polymerzaon of olefns n loop reacors. Chemcal Engneerng Scence 48: Pump

3 Projec Overvew Movaon and Objecves Curren Pracce Dfferen grades produced n a sngle producon lne Grade ranson akes a long me PID conroller for flowrae and emperaure conrol Hard o mplemen comple ransons; Room for mprovemen Objecves Develop a model based conrol and opmzaon framework o Mnmze ranson me Mnmze offgrade producs Poenal Value Reducon of ranson me Guded comple ransons Increased flebly n producon wheel

4 Projec Progress Model Developmen and Offlne Opmzaon Vapor Recycle Ehylene hydrogen Lqud Recycle solven comonomer Vapor Purge Spler Lqud Fresh nle Loop Reacor Separaor Model Developmen CSTR wh surrogae VLE model Mehod of momen for produc propery predcon Recycle me delay model Process consrans Offlne Dynamc Opmzaon Sngle sage opmzaon Mulsage opmzaon f mn QQ + u u RR Pellezer d Produc measuremens 4

5 Dealng wh Specfcaon Bands Mulsage Opmzaon ρρ.9 ±.5gg/cccc nsead of ρρ.9 gg/cccc TRANSITION A o B OUTPUT INPUT Inpu change Grade A n-spec Offgrade producon Grade B n-spec STAGE STAGE STAGE TIME Movaon: In-spec produc s qualfed for sale. Specfcaon band should be aken no accoun when calculang off-grade.. Nysrom e al Compuers & Chemcal Engneerng

6 sages: n-spec of A ou-of-spec and n-spec of B. Mnmze a combnaon of he off-spec produc beween and and he ranson me -. A regularzng erm ha promoes a smooh unque soluon. Applcaon of -pon collocaon on 8 fne elemens over 4.5 hours An NLP problem wh over 6 equaons and over 6 varables Smulaneous dynamc opmzaon wh movng fne elemen 6 Dealng wh Specfcaon Bands Mulsage Opmzaon Bs As B A R Bs Q Bs g g p u f s d u u Mn ] [ ] [... ] [.. β α Offspec Trans. Tme Regularzng Term Dynamc model Grade A n-spec n Sage Grade B n-spec n Sage Connuy beween sages Inal and Fnal Condons

7 Case Sudes Grade Transons beween Two Grades Operaon condons for wo dfferen grades 4 Properes Manpulaed Varables MI Converson Densy Tj F F8 FH Fc Fs Mel nde Ehylene converson rae Produc densy Inle coolng waer emp Ehylene nle flow Comonomer nle flow Hydrogen nle flow Feed caalys Solven nle flow Meanng Uns Grade A Grade B g/mn g/cm o C L/s L/s L/s L/s L/s * -4.9* * -4.65* -.58 For each ranson sep change smulaon s performed as a baselne Typcal way o perform grade ransons; May go o nfeasble regon Specfcaon bands: ±.5gg/cccc for densy ±5% for mel nde. 4. J.J. Zacca and W.H. Ray. Modellng of he lqud phase polymerzaon of olefns n loop reacors. Chemcal Engneerng Scence 48:

8 To Lower Densy and Hgher MI Comparson of Oupu Profles The mulsage soluon A faser ranson o reach he boundary of he second band More oscllaons whn he specfcaon band Beer performance Calculae he ranson me and he amoun of off-grade produc Transon me S+S Off-grade produc S densy g/cc MI g/mn.9 4 X:.6.9 Y:.955 X:.65 X:.5 Y:.4 Y: n mn Trans. Tme Duraon of S Sep change Sngle-sage Mulsage.. X:.7888 Y:.8669 X:.4 Y:.46 X:.65 X:.6 Y:.8665 Y: me hr sep change sngle-sage mul-sage 8

9 Novely Bul and negraed a surrogae VLE model Accurae predcons wh reduced model compley Sngle-sage formulaon A common approach n dynamc opmzaon of grade ransons Bu no mnmzng ranson me or off-grade produc drecly. Also sngle value arge s no praccal. Mulsage formulaon Specfcaon bands are consdered n some sudes where negraed schedulng and dynamc opmzaon problem s solved. Takes specfcaon bands no accoun Capable of mnmzng ranson me and off-grade produc drecly Has beer performance grealy reduces he ranson me and he off-grade produc 9

10 Poenal Value and Fuure Work Poenal Value Reducon of ranson me and off-grade produc Guded comple ransons Increased flebly n producon wheel Fuure Work Wh accurae model and consrans we obaned he resulng opmal ranson profles can be used as opmal rajecores. The performance can be furher mproved by unng parameers and refnng he model. Idenfyng all he consrans and evaluang he soluons are necessary Onlne opmzaon and conrol ssues wll be consdered n ne sep. Compuaonal me should be lowered f repeaed opmzaon runs are performed durng he process Unceranes/dsurbances need o be aken no accoun