ABSTRACT
The purpose of this work is to model and simulate the Fluid Catalytic Cracking Unit (FCCU) riser of a refinery having Kaduna Refining and Petrochemical Company (KRPC) Kaduna as a study. The unit’s operation is cracking of heavy gasoil (VGO) to light weight oils in the presence of catalyst (zeolite).  The method employed involves the collection of operating  conditions,  feed  stock  stream  analysis  data  from  the  refinery which  was processed in order to obtain mass fractions of the representative specie involved in the cracking reactions. A model equation was obtained and simulated using Comsol Multiphysics software. Furthermore mass and energy balance were carried out. The results of the simulation of the model showed a good agreement with the experimental results. In addition to gases and oils, gasoline obtained was 54% by weight fraction. The result obtained from the simulation was close to the data obtained from KRPC as well as results from other researchers. Thus the model obtained can be used for the simulation of crudes other than the Nigerian crude and the computational software used is recommended for the optimization of process
CHAPTER ONE
1.0 INTRODUCTION
The merits of the fluid catalytic cracking unit are, firstly, that as a result of the overall speeding up of the process, the cracking temperature can be lowered somehow and the process can be conducted at a low pressure and secondly, which is most important, the selective action of the catalyst accelerates reactions that lead to the accumulation in the cracking, gasoline of arenes, iso-alkanes and iso-alkenes possessing high octane numbers (Erikh et al., 1988).
The features of the catalytic cracking mechanism in comparison with thermal cracking sharply affect the composition and properties of the gas and gasoline. The gas contains less low-molecular components, but much more isobutene. The gasolines are enriched in isoalkanes and arenes (Erikh., et al 1988).
The need for products derived from crude oil is essential in all facets of life whether in the developed, developing or underdeveloped countries. This has led to the search for more oil reservoirs by the geologists and geophysicists and subsequent refining of this crude oil by chemical engineers and engineers from other related fields of engineering. The fluid catalytic cracking unit (FCCU) in the refinery is where feed oil (heavy hydrocarbon chain oil) from the crude distillation unit (CDU) and atmospheric distillation unit (ADU) are cracked into lighter molecules of hydrocarbons. The feed oil is contacted with catalyst in the presence of very hot air in the riser reactor which is now sent to the fractionators to give gasoline of high octane number, light gas oil, heavy gas oil, feed for petrochemical unit and coke. The coke is sent to the regenerator to be burnt off and the catalyst recycled for another operation.
Among the products of the FCCU, gasoline is the most important, in that it is used to run most motor vehicles, generators to give power and used as solvent in some industries and road side mechanics.
The reactor used in the FCCU is the most important equipment of the unit as it is the central processing unit where physical fluids or solids are converted to desired products taking into consideration the residence time in which the reaction is expected to take place in an economically viable way. In view of this, modelling of the riser reactor is important in order to achieve maximum yield of gasoline and other FCCU products.
1.1 Aim and Objectives of the Work
The aim of this work is to model and simulate the cracking reactions that occur in the riser reactor and this will be achieved using the following objectives.
1 To develop a mathematical model that describes the reactions of interest that takes place in the reactor system.
2 To investigate the influence of the riser to give light end products with high octane number.
3 To simulate the developed model using a computer programme and compare the simulated results with the experimental results.
1.2 Scope and Limitation of the Study
This work is limited to the riser of the FCCU of Kaduna refining and petrochemical company (KRPC). The study focuses its attention on the riser reactor and all the cracking reactions responsible for the heavy gasoil conversion into lighter petroleum fractions.
The simulation would be done with the use of COMSOL Multi physics software to run the energy and mass balances with the data collected from Kaduna Refining and Petrochemical Company (KRPC). These data are operating conditions, reactor dimensions, catalyst properties and feedstock composition.
1.3 Justification for the work
The justification of this work is based on the fact that petroleum refining operations is presently responsible for about 70-85% of world energy and the FCCU is an important unit in the refinery, knowing that the chief product is gasoline. Model equation developed will help to predict the behaviour and performance of riser reducing volume of laboratory experimentation and tedious calculations. The problem sometimes envisaged with industrial plant is in the changing of some variables in order to obtain better yield of product but this work intends to discover through modelling and simulation of riser on how to enhance better yield of light products. The use of COMSOL Multiphysics software version 3.4 is reasonable because it has in the Comsol Engineering Lab an environment where mass and energy balances and also chemical reactions can be simulated.
This material content is developed to serve as a GUIDE for students to conduct academic research
MODELLING AND SIMULATION OF A REFINERY FLUID CATALYTIC CRACKING UNIT RISER
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