Petrol Rafinerisi Katalitik Dönüşüm Ünitesinde İşlenen Naftanın Kinetik Modellemesi

Abstract

Petrol rafinerilerinde atmosferik distilasyon sonucu elde edilen ve benzinin hammaddesini oluşturan naftanın yapısında parafin ve naften gibi düşük oktanlı hidrokarbonlar bulunmaktadır. Hidrojen ile muamele görmüş nafta şarjı, aralarında fırınların bulunduğu dört adet dönüştürücü reaktöründen oluşan sürekli katalizör rejenerasyon (CCR) ünitesinin reaktör kısmına gönderilmekte ve burada dönüştürücü katalizörü üzerinde yüksek sıcaklık ve çok düşük basınçta, yüksek oktanlı izoparafin ve ağırlıklı olarak aromatik moleküllere dönüştürülmektedir. CCR ünitesi reaktör kısmında katalitik dönüştürücü reaksiyonları hareketli katalizör yataklar içerisinde meydana gelmekte ve dehidrojenasyon, izomerizasyon, dehidrosiklizasyon, dehidroalkilasyon, hidrojenle kırılma reaksiyonları sonucu üretilen ve reformat adını alan yüksek oktanlı benzinin yanı sıra hidrojence zengin gaz ve az miktarda sıvılaştırılmış petrol gazı (LPG) elde edilmektedir. Benzin oktan sayısının (RON) arttırıldığı CCR ünitesinin üretim kapasitesi, benzin talebine göre değişiklik göstermektedir. Günlük operasyon koşullarında bu parametrelerin devamlı değişmesi RON değerinin de değişmesine neden olmaktadır. Bu değişiklik, son ürün olan benzinin RON değerini etkilemekte, kontrol edilemeyen zararlar meydana gelmektedir. Bu çalışma ile CCR ünitesi reaktör kısmındaki kinetik modelleme ile dördüncü dönüştürücü reaktöründen çıkan ürün bileşiminin öngörülmesi ve pratik bir şekilde oktan sayısının belirlenmesi için bir yöntem geliştirilmiştir. Ayrıca oktan arttırıcı katkı maddesi olan metil tersiyer bütil eterin (MTBE) karışım içerisindeki oranlarının azaltılması, böylece hem üretim maliyetlerinin düşürülmesi, hem de kimyasal madde kullanımının azaltılması ile çevreye verilen zararın en aza indirgenmesi amaçlanmıştır. Tez çalışması ile geliştirilen yöntem, CCR ünitesi reaktör kısmına giren nafta şarjı bileşiminin kümeleme yöntemi ile tanımlanması, reaksiyon hız sabitlerinin hesaplanması, reaksiyonların ısı kapasitelerinin hesaplanması, reaksiyon ısılarının hesaplanması, reaksiyon ısıları kullanılarak nafta dönüştürücü reaksiyonlarına ait denge sabitlerinin hesaplanması, hız sabitlerinin ve denge sabitlerinin kullanılması ile nafta dönüştürücü reaksiyonlarına ait reaksiyon hızlarının belirlenmesi, reaksiyon hızları kullanılarak boru tipi reaktör (BR) modeline göre kütle ve enerji eşitliklerinin Matlab ile çözülmesiyle CCR ünitesi reaktör kısmındaki dördüncü dönüştürücü reaktöründen çıkan ağırlıkça ürün kompozisyonunun belirlenmesi, saha verilerini modelde kullanırken ‘En Küçük Kareler Yöntemi’ (EKK) ile uygulanması, model parametreleri tahmini yapılması, dördüncü dönüştürücü reaktöründen çıkan ürün kompozisyonunun hacminin hesaplanması, hesaplanan ürün kompozisyonunun hacmi, tanımlanan parafin, izoparafin, naften ve aromatik (PONA) kümelerinin saf bileşen oktan sayıları ve bu kümelerin nafta şarjındaki oktan sayısına etki katsayıları kullanılarak CCR ünitesi reaktör kısmındaki dördüncü dönüştürücü reaktöründen çıkan benzin oktan sayısının belirlenmesi adımlarını içermektedir.

The raw material gas in forming the structure of naphtha has low-octane hydrocarbons such as paraffin, naphthene and is obtained by atmospheric distillation in the oil refinery. Naphtha feed is flowing with in the excess hydrogen to transforming to high-octane hydrocarbons such as isoparaffins, aromatics in reactor section of continuous catalyst regeneration unit (CCR). A petroleum refinery includes many unit operations and unit processes. The latest and most modern type of catalytic reformers are called continuous catalyst regeneration (CCR) reformers. Such units are characterized by continuous in-situ regeneration of part of the catalyst in a special regenerator, and by continuous addition of the regenerated catalyst to the operating reactors.. Many of the earliest catalytic reforming units were non-regenerative in that they did not perform in situ catalyst regeneration. Instead, when needed, the aged catalyst was replaced by fresh catalyst and the aged catalyst was shipped to catalyst manufacturers to be either regenerated or to recover the platinum content of the aged catalyst. Very few, if any, catalytic reformers currently in operation are non-regenerative The first unit operation in a refinery is the continuous distillation of the petroleum crude oil being refined. The overhead liquid distillate is called naphtha and will become a major component of the refinery's gasoline (petrol) product after it is further processed through a catalytic hydrodesulfurizer to remove sulfur-containing hydrocarbons and a catalytic reformer to reform its hydrocarbon molecules into more complex molecules with a higher octane rating value. The naphtha is a mixture of very many different hydrocarbon compounds. It has an initial boiling point of about 35 °C and a final boiling point of about 200 °C, and it contains paraffin, naphthene (cyclic paraffins) and aromatic hydrocarbons ranging from those containing 4 carbon atoms to those containing about 10 or 11 carbon atoms. The naphtha from the crude oil distillation is often further distilled to produce a "light" naphtha containing most but not all of the hydrocarbons with 6 or fewer carbon atoms and a "heavy" naphtha containing most, but not all, of the hydrocarbons with more than 6 carbon atoms. The heavy naphtha has an initial boiling point of about 140 to 150 °C and a final boiling point of about 190 to 205 °C. The naphthas derived from the distillation of crude oils are referred to as "straight-run" naphthas. It is the straight-run heavy naphtha that is usually processed in a catalytic reformer because the light naphtha has molecules with 6 or fewer carbon atoms which, when reformed, tend to crack into butane and lower molecular weight hydrocarbons which are not useful as high-octane gasoline blending components. Also, the molecules with 6 carbon atoms tend to form aromatics which is undesirable because governmental environmental regulations in a number of countries limit the amount of aromatics , most particularly benzene, that gasoline may contain. Catalytic reforming reactions occur on moving-bed reactors with low pressure and high temperature in CCR unit. Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil (typically having low octane ratings) into high-octane liquid products called reformates, which are premium blending stocks for high-octane gasoline. The process converts low-octane linear hydrocarbons (paraffins) into branched alkanes (isoparaffins) and cyclic naphthenes, which are then partially dehydrogenated to produce high-octane aromatic hydrocarbons. These reforming reactions are dehydrogenation, isomerization, dehydroxylation, dehydroalkylation and hydrocracking. There are many chemical reactions that occur in the catalytic reforming process, all of which occur in the presence of a catalyst and a high partial pressure of hydrogen. Depending upon the type or version of catalytic reforming used as well as the desired reaction severity, the reaction conditions range from temperatures of about 495 to 525 °C and from pressures of about 5 to 45 atm. The dehydrogenation also produces significant amounts of by product hydrogen gas, which is fed into other refinery processes such as hydrocracking. The dehydrogenation of naphthenes to convert them into aromatics as exemplified in the conversion methylcyclohexane (a naphthene) to toluene (an aromatic). A side reaction is hydrogenolysis, which produces light hydrocarbons of lower value, such as methane, ethane, propane and butanes. In addition to a gasoline blending stock, reformate is the main source of aromatic bulk chemicals such as benzene, toluene, xylene and ethylbenzene which have diverse uses, most importantly as raw materials for conversion into plastics. The dehydrogenation and aromatization of paraffins to aromatics (commonly called dehydrocyclization) as exemplified in the conversion of normal heptane to tolüene. However, the benzene content of reformate makes it carcinogenic, which has led to governmental regulations effectively requiring further processing to reduce its benzene content. The isomerization of normal paraffins to isoparaffins as exemplified in the conversion of normal octane to 2,5-Dimethylhexane (an isoparaffin). The hydrocracking of paraffins into smaller molecules as exemplified by the cracking of normal heptane into isopentane and ethane. The hydrocracking of paraffins is the only one of the above four major reforming reactions that consumes hydrogen. The isomerization of normal paraffins does not consume or produce hydrogen. However, both the dehydrogenation of naphthenes and the dehydrocyclization of paraffins produce hydrogen. The overall net production of hydrogen in the catalytic reforming of petroleum naphthas of hydrogen gas (at 0 °C and 1 atm) so excess meter of liquid naphtha feedstock. The hydrogen is also necessary in order to hydrogenolyze any polymers that form on the catalyst. Furthermore, increased gasoline octane number (RON) has been produced in CCR so that CCR unit production capacity is affected by gasoline demand varies. Daily changeable operating conditions affect on RON, means occuring undesirable give-away. The success of this project is to obtain the composition of the 4th reactor exit and is able to predict the RON. Furthermore, it is possible to prevent RON give-away. In this work, lump model is used to define naphtha reforming reactions and also, plug flow reactor (PFR) model is used for mass and energy balances. Moreover, at least square method is used for tuning. Finally, it is able to predict the model parameters and 4th reactor exit composition. Also, gasolin octane number (RON) can be determined. All conclusions are suitable for real process variable so the simulation is very successful.