© Obafemi Awolowo University, Ile-Ife, Nigeria For more information contact ir-help@oauife.edu.ng EXERGY ANALYSIS AND OPTIMIZATION OF CRUDE OIL DISTILLATION UNIT (CDU) OF A REFINERY BY DAVID, Oyeyemi Solomon B.Sc. (Hons) Chemical Engineering A THESIS SUBMITTED IN PARTIAL FUFILMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF SCIENCE (M.Sc.) DEGREE IN CHEMICAL ENGINEERING, FACULTY OF TECHNOLOGY, OBAFEMI AWOLOWO UNIVERSITY, ILE – IFE, NIGERIA. 2016 © Obafemi Awolowo University, Ile-Ife, Nigeria For more information contact ir-help@oauife.edu.ng Page 2 OBAFEMIAWOLOWOUNIVERSITY, ILE-IFE, HEZEKIAH OLUWASANMI LIBRARY POSTGRADUATE THESIS AUTHORIZATION TO COPY Author: David Oyeyemi Solomon Title: Exergy Analysis and Optimization of Crude Oil Distillation Unit (CDU) of a Refinery Degree: M.Sc. (CHEMICALENGINEERING) Year: 2016 I, David Oyeyemi Solomon hereby authorize the Hezekiah Oluwasanmi library to copy my thesis in parts or in whole in response to request from individuals and/or organizations for the purpose of private study or research. Signature: Date: © Obafemi Awolowo University, Ile-Ife, Nigeria For more information contact ir-help@oauife.edu.ng Page i CERTIFICATION We certify that this project was carried out by David Oyeyemi Solomon (TP13/14/H/2469) of the Department of Chemical Engineering in partial fulfilment of the requirements for the award of the M.Sc. Degree in Chemical Engineering of the Obafemi Awolowo University, Ile-Ife. Dr. (Mrs.) E. F. Aransiola Dr. O.J. ODEJOBI ….…………………… .….……………………. Head of Department (Supervisor) (Chief Examiner) © Obafemi Awolowo University, Ile-Ife, Nigeria For more information contact ir-help@oauife.edu.ng Page ii DEDICATION This research work is dedicated to Almighty God, the Giver of Life, Jehovah TurakaJah-The Alpha and Omega. Also, to my Father, Pastor M.I. David, who loved to see us succeed in life and to my Sister, David Oluwakemi Esther, you will forever remain in my heart. This work is also dedicated to my wife and children for their understanding and perseverance. © Obafemi Awolowo University, Ile-Ife, Nigeria For more information contact ir-help@oauife.edu.ng Page iii ACKNOWLEDGEMENTS I am highly grateful to Almighty God, for making it possible for me to be alive, to the Holy Trinity who loves me with an everlasting love, I say Thank you. I owe much gratitude to my supervisor, Dr. O.J. Odejobi, for his support. I equally want to acknowledge the support of my wife, Mrs. Olusola David, my wonderful kids and God’s given Jewels, OluwaDamipe and OluwaDamife for their love, understanding and perseverance. I can never forget my brothers and sisters, Pastor&Mrs Olukayode, Pastor&Mrs Samuel David, Elder&Mrs Oluwagbemi David, Pastor&Mrs Onekpe, Mr.&Mrs Ogunniyi and Mrs Damilola David Oworu (The Queen) who through their prayers, advice and financial commitments encouraged me even when I thought quitting. I also express my sincere gratitude to my parent, Lady Evang. S.L. David, for her moral, spiritual, and financial support. I will not forget Mazi Nwaobi for his encouragement for a higher degree. Also, Dr. Ruth Awesu , my academic mentor. You are indeed a mother. Mrs Ikhanne and Mrs Olowu, your unflinching supports and cooperation will not be forgotten. Not forgetting my colleagues Mr Olubori, Mrs Adedeji, Mrs Kolawole, Mr Osinloye, Mr Adenola, Mrs Adenusi, Mr Faseyinu, Mr Bello. God bless you all. I will not also forget these following people for their impacts and contributions to my success in this programme: Mr Eric Akinkoye, Mr Yinka Olabiyi, Mr Niyi Bamimore, Mr Niyi Ishola, Mr Oluwole Ekundayo, Pastor&Mrs Kunle Taiwo, Bro. Femi Kayode, Abayomi Meghoma, Mr&Mrs Idowu, Mr Korede Salmon and others too numerous to mention. You are highly appreciated. © Obafemi Awolowo University, Ile-Ife, Nigeria For more information contact ir-help@oauife.edu.ng Page iv Finally, i express my sincere appreciation to the Head of Department, Dr. (Mrs.) E. F. Aransiola, and to all academic staff of the Department of Chemical Engineering, most especially, Dr. E. A. Taiwo and other administrative staff members in the Department. God bless you all, Amen. © Obafemi Awolowo University, Ile-Ife, Nigeria For more information contact ir-help@oauife.edu.ng Page 1 ABSTRACT This study carried out steady state simulation of the Crude distillation unit of a refinery. The exergy analysis of each process vessel in the crude distillation unit (CDU) of the refinery was performed. The parametric study and optimization of the crude distillation column was done by combining operating parameters that have significant effects on Irreversibility and exergy efficiency of the crude distillation column. This was with a view to identifying the operating conditions for the optimum performance for the column. The simulation of the process was done by using Hyprotech System Simulator (HYSYS) version 8.4 developed by Aspen Technology with Peng Robinson Equation of State (EOS). In addition, a three level Box-Behnken experimental design and quadratic response surface model were used to optimize the exergy efficiency of the unit using Minitab 16. The quadratic model was examined in terms of the goodness of fit and the analysis of variance (ANOVA) at 95% confidence interval was used to evaluate the adequacy of the fitted quadratic model. The results of the base case irreversibility and exergy efficiency of the investigated crude distillation column were 134.6 MW and 74.6% respectively. The exergy efficiency and irreversibility of the control volume were found to be 427.0 MW and 48.07%. The mixer, phase separator and the distillation unit are the largest contributors to the overall irreversibility. The statistical model predicted an optimum exergy efficiency of 95.6% for the combinations of Heated crude pressure of 513.6 kPa, heated crude temperature of 182 oC , and hot crude temperature of 353 oC; and Heated crude pressure of 513.6 kPa, heated crude temperature of 182 oC, and condenser pressure of 121 kPa for the crude distillation column. The exergy efficiencies of the process vessels were calculated to be 71.3%, 71.6%, 22.8%, 75.6%, 88.8%, 38.5% and 46.3% for the mixer, phase separator, Heater 1, pre-flash drum, pump, Heater 2 and, furnace respectively. © Obafemi Awolowo University, Ile-Ife, Nigeria For more information contact ir-help@oauife.edu.ng Page 2 The study concluded that optimization of the crude distillation column was necessary for better performance, improved and increased yield. It was also established that variations in the process parameters of other process vessels like the preflash drum, and the furnace directly affects the performance of the crude distillation column. © Obafemi Awolowo University, Ile-Ife, Nigeria For more information contact ir-help@oauife.edu.ng Page 3 CHAPTER ONE INTRODUCTION 1.1 Background of Study The refinery is one of the most highly energy intensive industries with the cost of energy for heat and power accounting for 40% of the operating cost (Al-Muslim and Dincer, 2005). Crude oil in its original state is of no value until it is separated into its constituents and distillation processes are used extensively in achieving this separation (Al-Muslim and Dincer, 2005). Petroleum refining processes and operations take place in different units like crude distillation unit (CDU), vacuum distillation unit (VDU), delayed coking process unit, fluid coking process unit, fluid catalytic cracking (FCC) unit, alkylation unit, hydrotreating unit, hydrocracking unit, catalytic reforming unit and isomerization process unit. However, the objective of the crude oil distillation is to separate the mixture into several fractions like naphtha, kerosene, diesel and gas oil. Processing of crude oil into its constituent properties takes place in crude distillation column, once the oil has been through the desalination and cleaning processes. The main fractions or “cuts” obtained have specific boiling-point ranges and can be classified in order of decreasing volatility into gases, light distillates, middle distillates, gas oils and residual. The light fractions separation is achieved using a crude oil distillation unit (CDU) and a vacuum distillation unit is used for separating heavier fractions (Perry and Green, 1997). The complexity is due to multiple products, side- strippers, heat exchangers and pump arounds, which turn the task of improving the energy efficiency of such a column into a complex one © Obafemi Awolowo University, Ile-Ife, Nigeria For more information contact ir-help@oauife.edu.ng Page 4 (Santana and Zemp, 2001). The crude oil distillation plant has many components of interest like crude oil furnace, the distillation towers and the network of heat exchangers which may be analyzed thermodynamically. 1.1.1 Concept of exergy Exergy is defined as the maximum amount of work which can be obtained as a process is changed reversibly from the given state to a state of equilibrium with the environment, or the maximum work that can be obtained from any quantity of energy (Kotas, 1995). Energy is a key element of the interactions between nature and society; and it is also considered a key input for economic development. The main aim of conventional energy analysis of a crude oil distillation plant is to maximize the yield of the desired products. However, for economic and environmental reasons and the limited resources of energy, utilization of those energy resources needs to be maximized (Al-Muslim and Dincer, 2005). Energy (first law) and exergy (combination of first and second laws) analyses are the two basic tools to do so and their applications in industry during design and optimization has grown enormously. Exergy analysis has become more popular because it identifies areas where high losses of potentially useful work occur. Similarly, significant attention has recently been directed towards the use of exergy analysis in the assessment of chemical processes and their environmental impacts by several workers (Al- Muslim and Dincer, 2005). Thermodynamics is a concept derived from the Greek words “therme”, meaning heat and “dynamis”, meaning power (Donald, 2008). Thermodynamics can be defined as the science of energy and exergy including a number of concepts of temperature, pressure, enthalpy, heat, work, energy, as well as entropy. First law of thermodynamics generally fails to identify losses of work and potential improvements or the effective ABSTRACT INTRODUCTION 1.1 Background of Study 1.1.1 Concept of exergy