Supervision and control to improve the productivity of batch reactor equipped with a mono-fluid heating / cooling system

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1 Available online at Enegy Poedia 6 (2011) MEDGREEN 2011-LB Supevision and ontol to impove the podutivity of bath eato equipped with a mono-fluid heating / ooling system Ghania HENINI a*, Fatiha SOUAHI b, Ykhlef LAIDANI a a Hassiba Ben Bouali Univesity, B. P. 151, Hay Essalem 02000, Chlef, Algeia b Eole Nationale Polytehnique, B. P. 182, El Haah, Algéie, Algeia Abstat In this doument, we pesent the themal behaviou of a bath eato to jaket equipped with a mono-fluid heating / ooling system. Heating and ooling ae povided espetively by an eletial esistane and two plate heat exhanges (P.H.E). The ontol of the tempeatue of the eation mixtue is based on the supevision system. This stategy of management of the themal devies is based on the usage of the themal flux as manipulated vaiable. The modulation of the tempeatue of mono-fluid by ation eithe on the heating powe o on the ate of opening of the thee ways valve whih divets the mono-fluid to wads the heat exhange. Obtained esults, to ondut themal fom the eato pilot equipped with a mono-fluid heating / ooling system in simulation following types of tempeatue pofiles (heating - Maintenane - ooling - Maintenane) will be pesented fo the appliation of this new method Published by Elsevie Ltd. Open aess unde CC BY-NC-ND liense. Seletion and/o pee-eview unde esponsibility of [name oganize] Keywods: Bath hemial eato; themal ondut; themal flux; mono-fluid; supevision system; tempeatue ontol. Nomenlatue T ons T do T Set-point tempeatue (K) Doking set-point tempeatue (K) eation mixtue tempeatue (K) * Coesponding autho. Tel.: ; Fax: addess: g. henini@gmail.om Published by Elsevie Ltd. Open aess unde CC BY-NC-ND liense. doi: /j.egypo

2 450 Ghania Henini et al. / Enegy Poedia 6 (2011) Intodution A lage numbe of industial poesses suh as the podution of polymes, fine hemials and phamaeutials fo whih ontinuous podution is not feasible o eonomially attative, ae opeated in bath eato. In many ases this mode of opeation is used to manufatue a vaiety of poduts that involve signifiantly diffeent haateistis suh as the onvesion time, heat of the eation, et. Contol of suh type of eatos is quite often diffiult to ahieve [1] due to thei flexible and multipupose utilization. To guaantee bath to bath epoduibility and impove yield and seletivity, automation of bath eatos must be widely ineased. Due to the omplexity of the eations mixtue and the diffiulties to pefom on-line omposition a measuement, ontol of bath and fed-bath eatos is essentially a poblem of tempeatue ontol [2]. To ay out hemial eations in this type of eatos, fequently an opeating mode onsisting of diffeent phases is used: - A heating phase of the eation mixtue until the desied eation tempeatue; - A eation phase duing whih the tempeatue is maintained onstant; - A ooling phase to avoid by-poduts fomation 3, 4, 5, 6. The ontol pefomanes ae then mainly dependent on the heating-ooling system assoiated with the eato 7, 8. Two main types of heating / ooling systems ae ommonly used in industy: altenative system o multifluid system and the mono-fluid system. This pape deals with a new methodology of supevision and ontol the themal behaviou of eato equipped with a mono-fluid heating/ooling system. Afte a desiption of the eato (pilot plant). In the thid pat, the methodology fo monitoing and ontol of bath eatos is desibed. Then a bief desiption of the poedue of egulation (PFC). Stategy of supevision is given in the fouth pat. The last pat is devoted to the validation of the system of supevision based on the stategy of management of themal devies by analysis of heat flux. 2. Poess Desiption A shemati diagam of the pilot plant is depited in figue 1. The expeimental devie onsists of a 1l jaketed glass eato, fitted with a mono-fluid heating/ooling system. The mono-fluid used in this wok is a mixtue of ethylene glyol and wate, in a atio of 50% in weight, with a flow ate of 1000 l h -1 and at a tempeatue whih vaies between -35 and 110 C. The mono-fluid flow-ate is measued by means of two flow-metes. The heating/ooling system uses a 2000 W eletial esistane and two plate heat-exhanges (PHE). One PHE uses old wate as an utility fluid at a tempeatue aound 15 C and a maximum flow ate of 1500 lh -1, while the othe one uses a mixtue of ethylene glyol and wate, in a atio of 50% in weight, at a tempeatue aound -10 C and a maximum flow ate of 1500 lh -1. The supevision and ontol algoithms pogams ae witten in Fotan 4 and ae implemented on a PC in ode to aomplish the diffeent tempeatue ontol tasks. Fig. 1. Shemati of the pilot-plant

3 Ghania Henini et al. / Enegy Poedia 6 (2011) Methodology fo monitoing bath eato Fo the study of the behaviou of the poess, the stutue of egulation in asade using the tehnique of peditive funtional ontol (PFC) is put the yea appliation. Two ontol levels '1 and 0 ae onsideed. Two ontolles ae used in the ontol level '1'. The fist one in hage of supevision, it omputes the equied themal flux to be exhanged between the mono-fluid flowing inside the jaket and the eation mixtue. The seond one is devoted to ompute the set-point tempeatue (Tions) whih will be taked by the inlet jaket tempeatue. In the ontol level '0', thee slave ontolles ae used to ontol the mono-fluid tempeatue. One plaed on the eletial esistane whih omputes the eletial powe value and the two othe on the two plant heat exhanges to ompute the mono-fluid flow ate fation dispathed to one of them. The plan blok fo the asade ontol of this poess is given in the figue 2. Fig. 2. Shemati of the plant blok en asade ontol Themal behaviou of the eato The eato an be desibed by the following themal balanes: - Themal balane on the eation mixtue: dt V U A, p dt - Themal balane on the mono-fluid flowing inside the jaket: T sde T F T T Q dt sde V de U A p T T sde F T ede T sde (2), dt The intenal model is given by the following ontinuous system tansfe funtion equation using the Laplae tansfom: T U 1 A 1 p p U p Q p, p q eh Whee V time onstant of the eato, U q U A p T sde T the themal flux, U A, p exhanged between eation mixtue and the mono-fluid flowing inside the jaket, Qeh F T T Q the distubane aused by feed eatants and the heat eleased by the hemial eation. (1) (3)

4 452 Ghania Henini et al. / Enegy Poedia 6 (2011) Stategy of supevision The potool of the themal ondut is based on the following onept: The egulato alulates the ontol vaiable whih is intepeted as a themal flux. This last one is then ompaed with themal flux limits, alulated on-line fo the vaious devies to hoose the adequate element of the themal loop. One this ealized hoie, the manipulated vaiable is alulated aoding to the hosen devie Limit themal apaities Eletial esistane This element of the themal loop is used to heat the mono-fluid he an eeive a maximum eleti powe P ele (max). This maximum powe will be onsideed as the maximum flux that an exhange the monofluid with the eation mixtue though the jaket. The evolution of the outlet tempeatue of the eletial esistane is given by the following themal: We distinguish two limits maximum themal flux (Q maxh ) and minimum (Q minh ), suh as: Q P (max) max h ele Q min h 0.0 (6) Plate heat exhanges It uses two themal balanes to alulate the themal flux limit oesponding to these two heat exhanges. The fist onens the mono-fluid duing its passage though the jaket and the othe is the intehange between the eation mixtue and mono-fluid pesent in the jaket. These balane sheets ae tanslated by following both equations: Q F 1 T e T s T T T T e s Q 2 U A, p (8) A, p (9) U U, p U p, A p, By pesevation of heat, we an wite: Q 1 = Q 2 (10) (4) (5) (7) Fom the equations (7, 8 and 10), the outlet tempeatue of the jaket is alulated by the following elation: U A, p F 2 T e U A, p T T (11) s U A, p F 2

5 Ghania Henini et al. / Enegy Poedia 6 (2011) Te T 0 (Cold wate): in the ase of the heat exhange using old wate; e T 0 T (Glyol wate): in the ase of the heat exhange using the glyol wate. To alulate these minimal themal flux Qminef and Qmineg, oesponds to the use of heat exhanges with old wate and with glyol wate espetively, we shall use the equations (7) o (8) by taking as extenal tempeatue of T S that alulated by the equation (11). Q max ef 0 (12) Q max eg 0 (13) Supevision algoithm Figue 3 gives an appoximate global epesentation of the evolution of the themal flux apaities of the diffeent fluids as a funtion of the eato tempeatue; the minimum and maximum apaities oespond to the bode of the zones. Thee zones ae distinguished: Zone 1: use of the eletial esistane Zones 2: use of the heat exhange with old wate Zones 3: use of the heat exhange with glyol wate When the themal flux takes a positive value, it oesponds to a demand fo heating and only the eletial esistane is onened (phase = 1). A negative value means a equest of old; in that ase one of both heat exhanges will be used aoding to the value of the themal flux. So, a value in the ange (Qminef, Qmaxef), means a equest of ooling by the old wate, then only the heat exhange in the old wate is onened, (phase = 2), a value in the ange (Qmineg, Qminef), means a equest of ooling by the glyol wate and only the heat exhange fo glyol wate is onened, (phase = 3). A flow hat of the oveall poedue is given in figue 4. Fig. 3. Evolution of the themal flux apaities fo the diffeent fluids

6 454 Ghania Henini et al. / Enegy Poedia 6 (2011) Fig. 4. Flow hat of the supevisoy and ontol in the ase of the eletial esistane 5. Results and disussion In this pape, we pesent the simulation esults obtained fo the tempeatue ontol of an exothemi aid-base neutalization hemial eation between the hydohloi aid (HCl) and the sodium hydoxide (NaOH). The set-point tempeatue pofile is omposed by: fist stage: heating fom 20 to 40 C duing 1000 s; seond stage: onstant tempeatue at 40 C duing 1500s; thid stage: ooling fom 40 to15 C duing 1200 s and fouth stage: maintain at 15 C duing 500 s. In ode to eliminate disontinuities esulting fom hange of stage, the set-point pofile was filteed by a poedue alled doking poedue 6, 9. The esults ae pesented in Figue (5-7). Figue 5 we an notie that the adjusted set-point tempeatue (Tons) is oetly taked by the eation tempeatue (TR) and (Tdo). The only exeption, onens at the beginning of the phase of maintenane and the phase of ooling a slight diffeene appeas then of the hange of devie. Figue 6 shows the evolution of the manipulated vaiable () whih oesponds o in the fation of the powe of heating powe alulated by the egulato duing the use of the eletial esistane o in the fation of the flowate of the mono-fluid alulated duing the use of the heat exhange with old wate eithe the heat exhange with glyol wate. On the figue, this vaiable oesponds to the fation of the heating powe duing a muh of the pofile. Figue 7 shows a egula evolution of the equied themal flux. This vaiable takes a positive value in time equal has zeo to 2400 s (Uq Qminh) allowing the use of the eletial esistane and when it beomes negative (Qminef Uq Qmaxef) in time equal 2430 s to 2610 s it allows the use of PHE whih use the old wate and in time equals 2790 s to 3810 the use of PHE with glyol wate, then to 3840 s it takes a value positive. We an notie that Uq plays a eal supeviso ole beause it pemits the hange of appaatus only when thee ae an ugent heating o an ugent ooling.

7 Ghania Henini et al. / Enegy Poedia 6 (2011) Fig. 5. Evolution of tempeatue (Tons), the adjusted set-point (Tdo) and eation mixtue (TR) Fig. 6. Evolution of the manipulated vaiable () Fig. 7. Evolution of themal flux and limits themal flux Anothe simulation has been pefomed fo a diffeent set-point pofile, with the solution of hydohloi aid was fed at 1800s. The simulation onsists in a fou steps tempeatue set-point pofile: 1 st phase: heating fom 20 to 30 C duing 1000 s, 2 nd phase: onstant tempeatue set-point of 30 C duing 5000 s, 3 d phase: ooling fom 30 C to 20 C duing 1000 s, 4 th phase: onstant tempeatue set-point at 20 C duing 500s. Results ae given in figues (8-10). Figue 8 shows that at the beginning of the feeding the eation mixtue tempeatue (TR) oveshoots the set-point tempeatue (Tons) and (Tdo). The egulation system eats always by ommuting of the eletial esistane as the figue 9 and also epesents this distubane is tanslated by the osillations of the manipulated vaiable () figue 10. At the end of feeding, we obseve one unde ovetaking of 1 C appoximately, whih ae due to the fat that the tempeatue of the mono-fluid is lose of 30 C and the system late to etun on the landing. Figue 9 we an obseve that the themal flux in time 5940 s is negative in the ange of use of the PHE with old wate and 5970 s until 6000 s the use of the PHE with glyol wate then we obseve aftewad the quality of themal behavio beomes again oet.

8 456 Ghania Henini et al. / Enegy Poedia 6 (2011) Fig. 8. Evolution of tempeatue (Tons), the adjusted set-point (Tdo) and eation mixtue (TR) Fig. 9. Evolution of themal flux and limits themal flux Fig. 10. Evolution of the manipulated vaiable () To demonstate, again, the pefomane of the supevisoy stategy, anothe simulation has been pefomed fo a diffeent set-point pofile of an exothemi eation of mononitation. 1 st phase: heating fom 20 to 30 C duing 1000 s; 2 nd phase: onstant tempeatue set-point between 1000 s and s with feeding; 3 d phase: ooling fom 30 C to 20 C duing 1000 s; 4 th phase: onstant tempeatue setpoint at 20 C duing 500s. Results ae given in figues (11-13). Figues (11-13) show at the time of the intodution of feeding, whih is then aompanied by a themal bad behaviou haateized by osillations of the themal flux, the manipulated vaiable (), and the tempeatue of the eation mixtue, and it thoughout the peiod of feeding until the end of the feeding. These osillations ae due to the fat that we did not take into aount the elease of heat in the model of supevision what geneated aftewad poblems of behaviou whih ae not easy to maste.

9 Ghania Henini et al. / Enegy Poedia 6 (2011) Fig. 11. Evolution of themal flux and limits themal flux Fig.12. Evolution of the manipulated vaiable () Fig. 13. Evolution of tempeatue (Tons), the adjusted set-point (Tdo) and eation mixtue (TR) 6. Conlusion A new methodology fo ontol and supevision has been developed. The appliation of suh a methodology to pilot-plant bath eato has been epesented. It tuned out that at least good basi modelling of the poess in neessay. Thus the hoie of intenal model is uial impotane fo (PFC), sine the apaity of pedition onstitutes the base of all the speifiations of pefomane. Howeve, it is neessay to know the paametes elated to the eation with a etain degee of auay. Even if the bath eato must emain polyvalent, the eations wee geneally subjeted to a etain numbe of studies. Othewise, simulation studies have shown when the heat eleased by the hemial eation was onsideed, the ontol system pemits a bette taking of the set-point tempeatue pofile. This stategy is not limited to a mono-fluid heating/ooling system pesented in this pape, but may be extended to any system whateve the numbe of fluids is. Theefoe the supevision tehnique an be onsideate as an appopiate solution fo the tempeatue ontol of bath eatos, and the developed ontol stategy an be implemented to ontol industials bath eatos. Refeenes [1] Juba MR., Hamme JW. Pogess and hallenges in bath poess ontol, Po CPC III CACHE (Elsevie, Amstedam), [2] Fiedi M, Pene R. Design and ontol of bath eatos: An industial viewpoint, Compt. Chem. Eng. (19)1995; S357-S368. [3], & Anne-Ahad G. Supevisoy tempeatue ontol of bath eatos: Appliation to industial plant, Vol.1. In ADCHEM 2000 pp (Pepints). [4] Bouhenhi H, Cabassud M, Le Lann MV, & Casamatta G. A heating/ooling management to impove ontollability of bath eato equipped with a mono-fluid heating/ooling system. In Euopean Symposium on Compute Aided Poess Engineeing 10 (Floene Italy). Sauo pieui 2000; pp

10 458 Ghania Henini et al. / Enegy Poedia 6 (2011) [5] Xaumie F, Le Lann MV, Cabassud M, Le Lann MV, & Casamatta G. Expeimental appliation of nonlinea model peditive ontol: tempeatue of an industial semi-bath pilot plant-eato. Jounal of poess Contol 2002; 12, [6] Bouhenhi H, Cabassud M, Le Lann MV. Peditive funtional ontol fo the tempeatue ontol of a hemial bath eato. Computes and Chemial Engineeing 2006; 30, [7] Bebe R. Contol of bath eatos: A eview, Methods of Model Based Poess Contol, R. Bebe (Ed) (Kluwe Aademi Publishes, Dodeht, The Nethelands), 1995; pp [8] Louleh Z, Cabassud M and Le Lann MV. A new stategy fo tempeatue ontol of bath eatos: Expeimental appliation, Chem Eng J. 1999; 75: [9] Bouhenhi H, Cabassud M, Le Lann MV. A geneal simulation model and a heating/ooling stategy to impove ontollability of bath eatos, Tans. IChemE. 2001; Vol. 79, Pat A.