РЕФЕРАТ. Разработка математической модели реактора каталитического крекинга
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1.2. The experience modeling of catalytic cracking process. Approaches to formalizing schema transformations of hydrocarbons Except target reactions of catalytic cracking, a number of secondary acid- catalyzed reactions such as isomerization, alkylation, hydrogen transfer, and conden- sation also occur under FCC conditions. Considered together, the presence of thou- sands of reacting species (both in the feed and in the products), the need for extensive analytical resources available in production facilities, and the computational effort required both in parameter estimation and in model simulation make difficult the de- velopment of detailed and accurate kinetic rate expressions for commercial FCC reac- tions. To overcome these limitations, a typical approach groups different molecules (lumps) according to their boiling point and/or their molecular characteristics (paraf- fins, olefins, naphthenes, and aromatics). One of the first and most widely used catalytic cracking kinetic models was the three-lump model proposed by Weekman, which mainly focused on feedstock conversion and gasoline selectivity. The lumps considered were the feedstock, the gasoline (C 5 -221°C), and the remaining gases plus coke [11]. There is one more the four-lump kinetic model of Pitault et al. (1995). The number of components chosen to represent the complex gas mixture in FCC is admit- tedly low. Other kinetic models, even more detailed kinetic models, are not likely to have a greater range of molar masses, unless extremely heavy feeds are modeled. 118 The molar mass range determines the strength of the feedback of the reactions on the flow. The present kinetic model, though simple, is therefore well suited to study the effect of the feedback of the reactions on the flow, and the performance of the proposed method. Furthermore, the model is easy to implement [12]. The dependence of the rate coefficients and activation energies on the feed is a known limitation of the four-lump model, and should be kept in mind when inter- preting the results. A schematic representation of the model of Pitault et al. (1995), showing the different reactions between the lumps, is given in Fig. А.2 [13]. Figure А.2 – Schematic representation of the four-lump kinetic model for Fluid Catalytic Cracking of Pitault et al. (1995) In FCC riser reactor, the catalytic cracking reactions produce a large number of light molecules from a heavy feedstock. The changes in the number of moles result in a significant variation of the volumetric flow rate along the height of the riser. Therefore, the inclusion of cracking kinetics to model the change of volume along the riser is important in order to adequately predict the hydrodynamics. In this study a six lump kinetic model was implemented, which considers the reactions of gas oil (vacu- um gas oil), gasoline, light gases, including (C 3 H 6 and C 2 H 4 ) and two types of coke The kinetic model has been proposed as demonstrated in Fig. А.3 [15]. The rate of consumption of reactant j can be expressed as [14]: (1) 119 Figure А.3 – Six lump reaction scheme The value of n is supposed to be 2 for gas oil cracking and 1 for gasoline cracking to C 2 H 4 and coke 2. Eq. (1) can be used to formulate the rates of production of individual lumps in the ‘ith’ cell of computational domain. The temperature de- pendence of kinetic parameters appearing in Eq. (1) was described by the Arrhenius expressions: (2) The parameter, η appearing in Eq. (1) represents the catalyst particle activity factor. The catalyst particle deactivation due to the coke production as a result of the cracking reactions and its deposition on the catalyst particles can be related to solid phase residence time and riser reactor temperature [15]: (3) (4) Catalyst particle residence time distribution in the riser reacting zone is a ma- jor issue in the FCC process. Indeed, the smaller the residence time distribution of the solid phase is, the higher the selectivity of the cracking catalytic reaction is, leading to low coke and undesirable gas production. The residence time distribution of the solid phase, E(ti), is related to the tracer concentration, Ci, in each sample i along the sampling period [16]. In this simulation, a step change in the tracer concentration at the reactor inlet performed abruptly from 0 to C0. The tracer concentration at the out- 120 let is computed and normalized to the concentration C 0 to obtain the non-dimensional curve F(t) in the range of 0–1 as given below: (5) The value of catalyst particle residence time (tc) can be calculated using Eq. (6) [4]: ∫ ∫ ∫ (6). For naphtha steam catalytic cracking over Fe/HZSM-5, the other six-lump ki- netic model was developed. The reaction network is shown in Fig. А.4 can be used to describe the naphtha steam catalytic cracking. Generally, the more lumps a model in- cludes, the more kinetic parameters need to be estimate d and, therefore, the more ex- perimental data are required. Naphtha is composed of non-aromatic carbons (paraf- finic carbons, naphthenic carbons) and aromatic carbons. During steam catalytic cracking processes, non-aromatic carbons can easily crack into paraffinic carbons. Aromatic carbons cannot crack into gaseous products, because ring-opening reactions of aromatic carbons are hard to take place in the operating conditions of heavy oil catalytic cracking [17]. Liquid hydrocarbons are products of polymerization, aromati- zation, and condensation. Because the reaction temperature of catalytic cracking is very high, some gaseous products with high molecular weight can undergo secondary cracking reactions. Besides, olefins can convert into liquid by polymerization and aromatization reactions. Therefore, the feedstock was considered as one lump. Due to the fact that the aimed products of naphtha steam catalytic cracking are light olefins, including ethylene (C 2 H 4 ) and propylene (C 3 H 6 ), they were considered as two sepa- rate lumps. So, the trend of variation of ethylene and propylene can be predicted sep- arately. Besides the light olefins, there are a large amount of gaseous byproducts, such as hydrogen, methane, ethane, propane, butane, etc. These gaseous byproducts can also be considered as one lump. Liquid hydrocarbon is byproduct of steam cata- lytic cracking and is the product of polymerization, aromatization, and condensation. 121 Although ethylene and propylene are primary products, they are also contributed in the formation of the secondary products. By increasing the residence time and de- creasing the steam ratio, more chances can be taken in order to accelerate the second- ary reactions. This is due to assigning more time to the reactions and raising the con- centration of reactants. Consequently, the reaction between ethylene and propylene lumps and liquid hydrocarbon lump was considered. Coke was considered as one lump, despite its low yield, because the prediction of yield of coke is very significant for the cracking system. An advantage of this model is that the proposed model can predict the yields of the aimed products (ethylene and propylene) directly. Only ten rate constants are used to describe the complex steam catalytic cracking process, and this is also an advantage [18]. Figure А.4 – Reaction network of the six-lump model New complex reaction network with the nine lumped kinetics model for the aromatization reaction of FCC gasoline. In the network, the aromatization reaction species were first lumped into n-paraffins, i-paraffins, olefins, aromatics, coke, , , and . Three main type reactions among these lumped components were considered in the aromatization reaction network, such as paraffin dehydrogena- tion and cyclization, paraffin isomerization and cracking to low carbon hydrocarbon. For the purpose of simplification, some reactions seldom take place and reactions of less importance were eliminated from the network. Its nine lumps web model of FCC gasoline studied on its reaction mechanism were shown in Figure А.5 [19]. 122 Figure А.5 – Nine lump web models of FCC gasoline The 11-lump kinetic model is shown in Figure А.6. The density, specific heat, viscosity, thermal conductivity, and heat of formation of the reactive species, used in this study were collected from the Nayak et al. (2005). The values for their molecular weight were given by Pitault et al. (1994). Since the 10-lumps model contains one single group to represent both the coke and the light gases (the C-group), its proper- ties were defined as the weighted average of these species present in it. From others works, it is verified that 30 % of coke and 70 % of light gas composes the C-groups. This proportion is considered in the present work, in order to determine molar mass of the C-group. The molecular weight used for a dry gas was given by Peixoto and Medeiros (2001), and the catalyst properties used in this study are the same by Lopes et al. (2011) [20]. Figure А.6 – 11-lump kinetic model 123 A 14-lump reaction kinetics model [21] was used to represent the FCC reac- tions, which is shown in Fig. А.7 (The 14 lumps are listed in Table А.2 [22]). Figure А.7 –14-lump reaction network for the FCC reactions Table А.2 – Lumps of the 14-lump kinetic model Lump symbol Lump Boiling range Ph Heavy paraffinics 500 °C+ Pm Medium paraffinics 350–500 °C Pl Light paraffinics 221–350 °C Nh Heavy naphthenics 500 °C+ Nm Medium naphthenics 350–500 °C Nl Light naphthenics 221–350 °C FAh Heavy aromatics in resin and asphaltene 500 °C+ Ah Heavy aromatics expert Fah 500°C+ Am Medium aromatics 350–500 °C Al Light aromatics 221–350 °C GO Gasoline C5-221 °C LPG Liquid petroleum gas C3+C4 DG Dry gas C1+C2+H2 CK Coke Therefore, at the present time processes of deep conversion processing of oil raw materials, especially catalytic cracking and hydrocracking, are actively imple- mented at Russian refinery. On the bassis of the literature review, we can conclude that the catalytic cracking technology develops rapidly, and is actual in the world, this technique allows producing a valuable light fraction and heavy gas oil feedstock. In this particular construction of industry catalytic cracking units differ significantly and determine unit capacity, quality of the product composition, along with the process mode and type of used cracking catalysts [23-28]. 124 To date, the Russian refineries being catalytic cracking units expected to in- crease the depth of crude oil conversion processing and increase the yield of high- octane gasoline component. Optimization of catalytic cracking process is possible not only for the improvement of equipment design of the process, but also for using the method of mathematical modeling. The literature review about the modeling of catalytic cracking processes shows the relevance of models development based on the catalyst deactivation with the coke compounds [29-36]. For processes of deep conversion of oil, the approaches to formalizing schema of hydrocarbons transformations are mostly based on the pro- cess for aggregating the boiling point of the individual fractions. 125 Приложение Б Схемы некоторых установок каталитического крекинга: (a) каскадная установка UOP ; (b) модель IV; (c) Exxon установка на флюидизированном катализаторе; (d) R2R установка (Монтгомери) Приложение В Календарный план-график проведения НИОКР по теме № работ Вид работ Исполнители i Tк , кал. Дн. Продолжительность выполнения работ янв. февр. март апрель май июнь 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2 1 Составление и утверждение тех- нического задания Руководитель 4 2 Выбор направления исследований Руководитель, магистрант 3 3 Календарное пла- нирование работ по теме Руководитель, ма- гистрант 3 4 Изучение литерату- ры, составление формализованной схемы превращений магистрант, инженер 80 5 Разработка матема- тической модели Магистрант, лаборант руководитель 92 6 Расчет на разрабо- танной математиче- ской модели Магистрант 30 7 Сопоставление ре- зультатов экспери- ментов с теоретиче- скими исследова- ниями Магистрант 21 8 Оценка эффектив- ности полученных результатов Руководитель 9 127 № работ Вид работ Исполнители i Tк , кал. Дн. Продолжительность выполнения работ янв. 3 февр. март апрель май июнь 1 2 3 1 2 3 1 2 3 1 2 3 1 2 9 Определение целе- сообразности про- ведения ОКР Руководитель 2 10 Составление пояс- нительной записки Магистрант, Руководитель 30 11 Сдача работы на рецензию Магистрант 8 12 Подготовка к защи- те дипломной рабо- ты Магистрант 8 13 Защита дипломной работы Магистрант, руко- водитель 1 Магистрант Руководитель Инженер Лаборант 128 Приложение Г Характеристика токсических, пожаро- и взрывоопасных свойств сырья, полупродуктов, готовой продукции и от- ходов производства Наименование сырья, полупродуктов, гото- вой продукции- (вещества, % масс), от- ходов производства Агрегатное состояние при нор- мальных условиях Класс опаснос- ти по ГОСТ 12.1.007 ПДК в воздухе рабо- чей зоны производ- ственных помеще- ний, мг/м 3 Характеристика токсичности (воздействия на организм человека) Норматив- ные доку- менты 1 2 3 4 4 6 1) Сырье смесевое (вакуумный дистиллят, гач, петролатум, экс- тракт, деасфальтизат) Горючая жидкость 4 900/300; масляный туман 5 Раздражает слизистую оболочку и кожу челове- ка ТУ 38.101 1304- 90 2) Газ сухой углеводо- родный газ 4 Предельные углево- дороды С2-С10 900/300, сероводо- род 10 (в смеси с уг- леводородами С1-С5 - 3), метан 7000, пропилен 100 Сухой газ оказывает вредное действие на цен- тральную нервную систему. При вдыхании сме- си воздуха с газом выше ПДК – человек получа- ет острые отравления. Признаками отравления является головокружение, озноб, тошнота и по- теря сознания. ТУ 38.301- 19-134-2001, СТО 7.401102- 2001 3) Рефлюксы - головка стабилизации горючая легковос- пламеняю- щаяся жид- кость 4 300/100 Рефлюкс при попадании на кожу вызывает ее сухость и может привести к обморожению ко- нечностей, дерматитам и экземам. Попадая в ор- ганизм через дыхательные пути пары рефлюкса действуют на центральную нервную систему, вызывают острые и хронические отравления СТО 401103- 2000 129 1 2 3 4 4 6 4) Фракции бензино- вые - компоненты то- варных бензинов бесцветная прозрачная жидкость 4 300/100 Контакт с фракциями бензиновыми вторичных процессов не ведет к поражению центральной нервной системы, сердечно-сосудистой системы, кроветворных органов, нарушению обменных процессов, не вызывает усиленного роста тка- ней. Не обладают способностью к кумуляции, про- никновению через неповрежденные кожные по- кровы, не вызывает повышенной чувствитель- ности организма. Обладают наркотическим дей- ствием, раздражают слизистую оболочку глаз, верхние дыхательные пути и кожные покровы. При длительном воздействии на кожу человека могут вызывать острые воспаления и хрониче- ские экземы. ГОСТ Р 51866-2002, СТО 7.401402- 2007 5) Газойль легкий про- цессов каталитическо- го крекинга и коксова- ния горючая жидкость 4 900/300 Легкий газойль раздражает слизистую оболочку и кожу человека. При попадании на кожу вызы- вает ее сухость ТУ 38.301- 19-31-91, СТО 7.401204 -20 10 6) Газойль тяжелый горючая жидкость 4 900/300 Тяжелый газойль раздражает слизистую оболоч- ку глаз и кожу человека ТУ 38.301- 19-87-97, СТО 7.401214-98 130 1 2 3 4 4 6 7) Катализатор КО-10 (для окисления СО до СО2 в газах регенера- ции) порошкооб- разный мик- росфериче- ский 4 2 Контакт с катализатором КО-10 не ведет к по- ражению центральной нервной системы, сердеч- но-сосудистой системы, кроветворных органов, нарушению обменных процессов. Не обладает способностью к кумуляции, не вызывает усиле- ния роста тканей, обладает слабым раздражаю- щим действием на кожу и слабым повреждаю- щим действием на слизистые оболочки глаза, относится к слабым аллергенам. ТУ 38.401920-05 8) Катализатор микро- сферический цеолитсо- держащий порошкооб- разный мик- росфериче- ский 5 6/2 Катализаторная пыль в концентрациях, превы- шающих допустимую, раздражающе действует на слизистую оболочку дыхательных путей. Ка- тализатор в воздушной среде и сточных водах в присутствии других веществ и факторов токсич- ных соединений не образует ТУ 38.301- 19-151-2005 (с изм 1 5) 9) Инертный газ Газ без цве- та и запаха 4 не предусмотрена Человек, находящийся в атмосфере с небольшим содержанием инертного газа в воздухе, испыты- вает кислородное голодание, а при значитель- ных концентрациях может погибнуть от удушья ГОСТ 9293- 74, СТО 7.401205- 2010 |