Reaction kinetic data and calculation of effectiveness factor are showed in [12].

A Dynamic Model For Decoking Process Of Acetylene Hydrogenation Reactor With Two Configuration

O. Dehghani, A. Bolhasani*, S. KaramiyanResearch and Development Department, JAM Petrochemical Complex, Assaloyeh, Iran

AbstractSelective hydrogenation is used to reduce acetyleneconcentration less than 1 ppm due to poisons the catalystsin polymerization plants. the catalysts have to regeneratedue to green oil formation during hydrogenation. closemonitoring of the two regeneration cycles in An olefineplant in JAM petrochemical complex, have revealedcomplications that caused a dramatic reduction in catalystlifetime and also disrupted the temperature profile in thereactor overtime. instead of conventional configurationafter validation of the dynamic model a new configuration

A mixture of air and steam was injected stepwise duringdecoking. First of all, a small amount of air was injected andso the reactor temperature increased rapidly owing to thecoke combustion. After that, the air injection stopped untilthe bed temperature fell off to its original value and againoxygen injection started.After the regeneration cycles it was observed the SORtemperature had to be higher than the vendor’s suggestionand the life cycle of catalysts decreases noticeably. In otherwords the distance between SOR and EOR temperatures

Results and discussion

Introduction

was proposed, simulated and constracted. As a result, theregeneration period decreases significantly by 28 h.

words, the distance between SOR and EOR temperaturesdecreased and the catalysts deactivated sooner thanexpected. this means that they did not regenerate properly.Interestingly, coke deposition on platinum and palladiummight lead to loss of ethylene selectivity and increasedethane production. If only 0.2 mol% ethylene of 10th olefinein JAM complex converts to ethane in 1 day, we may lose$28,800 per day which is approximately $10 million per year.A novel configuration was proposed to regenerate each bedindividually. In fig. 3 and fig. 4 the reactor temperature andmodel outputs for both beds during air injection stage afterpipeline reconfiguration are compared. In this stage, air wasinjected continuously to avoid sudden upsurges in the bed

In order to solve these equations, the following boundaryconditions have been applied:

The required physical specifications in the model are takenfrom a typical catalyst used in 10th olefine plant of JAMpetrochemical complex [12].

Series reactors are used due to high flexibility in control ofreactor temperature and product conversion. After catalystdeactivation, it is essential to regenerate the coked catalystscompletely [1]. Yajun et al. proposed the general formula forgreen oil as: CnH(1.8–1.9)n (14 < n < 17) [2]. Van Deemterpresented a model for coke burning process [4]. Gonzalez etal. examined the effects of temperature changes on reactionkinetics and chemical diffusion [5]. In 1988, Westerterp et Model validation injected continuously to avoid sudden upsurges in the bed

temperature which could be harmful for catalysts. As shownin these figures, not only the coke burning process for theguard bed lasted less than the lead bed, but also the leadbed maximum temperature was significantly higher than theguard bed one. These events are owing to the coke loadaccumulated in the reactors [12].

[ ] pal. introduced a model to investigate heat and mass transferimpacts simultaneously considering internal mass and heattransfer and using Chilton‐Colburn equation as well as Lewisnumber [6]. In 2010, catalyst regeneration and coke burningprocesses in a fixed bed reactor were simulated by Zhang fora Cr2O3/Al2O3 catalyst in a propane dehydrogenationprocess [9]. the catalyst surfaces is only consists of carbon[7]. For this reason, complete reaction of pure carbon withoxygen was only considered in these studies. However, in1967 Massoth showed that hydrogen exists in the cokestructure [3]. Santamaria‐Ramiro et al. showed that cokeformation method (parallel or series) and coke distribution

ConclusionsA study on two two‐year‐old regeneration cycles in thisdomestic Petrochemical Company, uncovered severalproblems associated with the configuration of reactors andpipelines which could lead to diminished catalysts lifetimes

Model validation Experimental data are collected from 10th olefine plant inJAM petrochemical complex during regenaration. Thetemperature profiles which are plant data and model'soutput for both guard and lead bed are compared to gatherin fig. 1 and fig. 2. Some peaks could not be simulated withthe model because they are heat front points. In thesepoints, no combustion reaction occurs and they onlydetected heat fronts of previous combustion zones [12].

References[1] A Behroozi M S Hatamipour A Rahimi Mathematical modeling and

along the reactor did not affect the temperature profileconsiderably [8].In the present research, a model for coke burning processwas developed. Moreover, the model results were validatedwith industrial data from domestic plant for typical fixed bedseries reactors. Subsequently, a novel configuration issuggested based on the model predictions and so thepipelines were changed in order to implement the proposedmethod to the reactors. It is interesting that a modelpredictions and plant data from reconfiguration beds are ingood agreements.

pipelines which could lead to diminished catalysts lifetimes.Therefore, a new configuration was suggested to overcomethese complications in regenerative process and improvecatalysts efficiency. In this situation, each bed is regeneratedindividually which should be consistent with themanufacturer’s time frame. By doing this, the amounts ofnitrogen and steam consumptions are reduced noticeablyrelative to the actual amounts observed in the plant andsudden temperature increases before decoking areprevented. in fig. 5 old and new pipe line are illustrated.

Kinetics of reaction [1] A. Behroozi, M.S. Hatamipour, A. Rahimi, Mathematical modeling and parametric study of coke-burning process in a hydrocracker reactor, Comput. Chem. Eng. 38 (2012) 44–51. [2] L. Yajun, Z. Jing, M. Xueru, Study on the formation of polymers during the hydrogenation of acetylene in ethylene–ethane fractions, Chem. Ind. Eng. Soc. China Am. Inst Chem. Eng. 82 (1982) 688–695. [3] F. Massoth, Oxidation of coked silica-alumina catalyst, Ind. Eng. Chem. Res. Process Des. Dev. 6 (1967) 200–207.[4] J.J.V. Deemter, Heat and mass transport in a fixed catalyst bed during regeneration, Ind. Eng. Chem. 46 (1954) 2300–2302.[5] L. Gonzalez, E. Spencer, Studies on the numerical solution of a model simulating fixed bed regeneration, Chem. Eng. Sci. 18 (1963) 753–766.[6] K.R. Westerterp, H.J. Fontein, F.P.H. van Beckum, Decoking of fixed-bed catalytic reactors, Chem. Eng. Technol. 11 (1988) 367–375.[7] P.B. Weisz, R.B. Goodwin, Combustion of carbonaceous deposits within porous catalyst particles: II Intrinsic burning rate J Catal 6 (1966)

Kinetics of reactionThe coke can be formulated as CHn, with n varying between0.4 and 1.3 [3]. The typical TPO tests of deactivated catalystsin 10th olefine plant of JAM petrochemical complex showedthat the best quantity for n is 0.5. In the presence of catalystsand above 400 _C the coke reacts completely with oxygen[10]. So:

within porous catalyst particles: II. Intrinsic burning rate, J. Catal. 6 (1966) 227–236.[8] A. Byrne, R. Hughes, J. Santamaria-Ramiro, The influence of initial coke profile and hydrogen content of coke on the regeneration of fixed beds of catalyst, Chem. Eng. Sci. 40 (1985) 1507–1515.[9] X. Zhang, Z. Sui, X. Zhou, W. Yuan, Modeling and simulation of coke combustion regeneration for coked Cr2O3/Al2O3 propane dehydrogenation catalyst, Chin. J. Chem. Eng. 18 (2010) 618–625. [10] C. Kern, A. Jess, Regeneration of coked catalysts—modelling and verification of coke burn-off in single particles and fixed bed reactors, Chem. Eng. Sci. 60 (2005) 4249–4264.[11] M.R. Rahimpour, O. Dehghani, M.R. Gholipour, M.S. Shokrollahi Yancheshmeh, S. Seifzadeh Haghighi, A. Shariati, A novel configuration for Pd/Ag/a-Al2O3 catalyst regeneration in the acetylene hydrogenation reactor of a multi feed cracker, Chem. Eng. J. 198–199 (2012) 491–502.[12] O Dehghani M R Rahimpour A new configuration for decoking

The rate of reaction is first order kinetic according to both oxygen and coke [13]. So: 

Reaction kinetic data and calculation of effectiveness factorare showed in [12].

Mathematical modelling

Fig. 2. lead bed's temperature profile(old pipe line) Fig. 1. Guard bed's temperature profile(old pipe line)

Fig. 2. lead bed (old pipe line)Fig. 1. guard bed (old pipe line)

[12] O. Dehghani, M.R. Rahimpour, A new configuration for decoking process in series reactors, Chem. Eng. J. 215–216 (2013) 418–431.A plug flow was assumed in the reactor. Regeneration is an

adiabatic process. Because of high thermal conductivity, thereis no temperature gradiant with in the catalyst. Radialconcentration and temperature distribution, effect of externalmass transfer and axial dispersion of mass and heat arenegligible. Coke distribution is uniform. Due to the highsuperficial velocity, heat conduction through the bed isnegligible in comparison with heat convection. the pressuredrop across the bed is very low. So mass and energy balanceare:

Fig. 1. lead bed's temperature profile(new pipe line) Fig. 2. lead bed's temperature profile(new pipe line)

Fig. 4. lead bed (newpipe line)Fig. 3. guard bed (newpipe line)