Production of High Quality Petroleum Products from Crude Oil Using Aspen HYSYS

Transcription

1 PETROLEUM CHEMISTRY DEPARTMENT Production of High Quality Petroleum Products from Crude Oil Using Aspen HYSYS Chimdinma Nwagbo Tabot Esther Eyang Faustin Hategekimana A A A Spring, 2015 Supervisor: Dr. Obioma U. Uche, PhD i

2 Production of High Quality Petroleum Products from Crude Oil Using Aspen HYSYS Chimdinma Nwagbo Tabot Esther Eyang Faustin Hategekimana A A A Approved by: Obioma U. Uche, PhD Dr. Linus Okoro (Program Coordinator) Date: ii

3 Certification Statement This paper represents our own work in accordance with University regulations. I authorize American University of Nigeria to lend this thesis to other institutions or individuals for the purpose of scholarly research. Chimdinma Nwagbo Esther Tabot Eyang Faustin Hategekimana I further authorize the American University of Nigeria to reproduce this thesis by photocopying or by other means, in total or in part, at the request of other institutions or individuals for the purpose of scholarly research. Chimdinma Nwagbo Esther Tabot Eyang Faustin Hategekimana Obioma U. Uche, PhD. Dr. Linus Okoro (Program Coordinator) External Examiner iii

4 Abstract The aim of this project is to obtain high yields of consumer petroleum products, such as high cetane number gasoline and light gas oil (diesel), by cracking AGO obtained from crude oil distillation. This project is also aimed at finding a way to increase petrol production rates to meet the increasing demand of fuel in Nigeria. Crude oil assay data from Kaduna refinery was used to represent the feed to the process unit. After distillation, we were able to obtain six crude oil fractions based on their boiling point range. Those products were naphtha, kerosene, diesel oil, AGO, and residue. One of those fractions, AGO, was used as the feed to the catalytic cracking unit. Using a petroleum shift reactor for the cracking process, we were able to get high yield petroleum fractions, cracked naphtha (gasoline) and light gas oil (diesel). iv

5 Acknowledgements First and foremost we would like to thank God because without him none of this would have ever been possible. We would also love to thank our wonderful parents, friends and benefactors who have wished nothing but the best for us. We would also like to give special thanks to our supervisor, Dr Obioma U. Uche who was constantly patient with us as we were doing the project. v

6 List of Figures Figure 1: Schematic of a typical fluid catalytic cracking unit Figure 2: Process flow diagram of the proposed design Figure 3: Detailed view of atmospheric tower T-100 of the proposed design Figure 4: Purchased costs for the individual pieces of equipment of the proposed design vi

7 List of Tables Table 1: Operating conditions for atmospheric tower T Table 2: Properties of inlet feed streams of atmospheric tower T Table 3: Properties of outlet feed streams of atmospheric tower T Table 4: Properties of the inlet and outlet streams of heat exchanger E Table 5: Properties of the inlet and outlet streams of petroleum shift reactor R Table 6: Thermodynamic properties of light gas oil and cracked naphtha products from petroleum shift reactor R Table 7: Comparison of the produced Cracked Naphtha to ASTM standards Table 8: Comparison of the produced Light Gas Oil to ASTM standards Table 9: Size attributes for heat exchangers E-100 and E Table 10: Size attributes for atmospheric tower T Table 11: Size attributes for the kerosene, diesel, and AGO side strippers as well as the flash tank V-100 and petroleum shift reactor R Table 12: Operating conditions and material of construction of equipment Table 13: Hazard and operability analysis of a tower T Table 14: Hazard and operability analysis of petroleum shift reactor R Table 15: Hazard and operability analysis of the heat exchangers Table 16: Hazard and operability analysis of flash tank separator V Table 17: Costs evaluation summary vii

8 Table of Contents Abstract... iv Acknowledgements... v List of Figures... vi List of Tables... vii 1. Introduction Problem Statement Motivation/Objective of the Study Scope and Limitations Literature Review Methodology Detailed Process Description Pre-treating the Crude Oil Feed The Atmospheric Tower Heat Exchanger E Petroleum Shift Reactor R Equipment Specification and Design Heat Exchangers Atmospheric Tower viii

9 6. Plant Safety Analysis Economic Analysis Conclusions and Recommendations References Appendix A: Crude Oil Assay Appendix B: Aspen HYSYS Software Appendix C: Material and Energy Balances ix

10 1. Introduction Automotive Gas Oil (also known as Atmospheric Gas Oil, AGO) is popularly known as diesel with improved quality because most of their properties are almost the same. AGO is a complex mixture of hydrocarbons produced by mixing fractions obtained from the distillation of crude oil with brand-specific additives to improve performance. Under normal conditions it is a liquid with a characteristic odor. Diesel is produced by blending straight-run middle distillates (minimum 40% of middle distillates) with varying proportions of straight-run gas oil, light vacuum distillates, light thermally-cracked distillates and light catalytically-cracked distillates, and is found to have between carbon atoms. It is a distillate generated at the temperature between F in the distillation column. AGO is a petroleum-based fuel, used in powering large vehicles and boats due to its high quality performance. Qualitative AGO is very suitable for running heavy road vehicles, like buses, trucks, tractors and overland shipping for many reasons. Primarily, this is because it is more economical and less volatile than other fuels. In addition, AGO has high fuel efficiency and yields lower emissions and particulate matter Problem Statement The increasing demand for diesel fuels has resulted in the use of higher amount of cracked distillates having poor ignition properties. The ignition properties of diesel fuels can be rated in terms of their cetane number. Diesel fuels having low cetane number may have poor ignition properties such as diesel knock, difficulties to start engines in the cold weather and so on. Such diesel fuels need further treatment in order to improve their cetane number. (Hashimoto, 2000) 1

11 Nigeria has witnessed perennial acute scarcity of highway transportation fuel (gasoline and diesel) over the past three decades. The scarcity has been attributed to the inability of supply to meet the demand for highway transportation fuel which has witnessed an unprecedented growth over the past decades. As much as 4.06 million (in 2003), 5.37 million (in 2004), 6.64 million (in 2005), 3.42 million (in 2006), 5.99 million (in 2007) and 9.24 million (in 2008) metric tons of highway transportation fuel were supplied from both local and imported fuel sources. (Nwachukwu and Umunna, 2008) This shows an average annual growth rate of 27.4%, yet the amount of transportation fuel fell short of demand. Nigeria s domestic diesel consumption has been increasing even as major marketers are asking questions over the government s allocation of the diesel produced at Warri and Port Harcourt refineries. In recent decades, Kaduna and Warri refineries have produced 1,602 metrics tons and 2,670 metrics tons of diesel per day, respectively (West Central Africa Department, 1996). This quantity is allocated to marketers in a manner which major marketers say lacks transparency. Zeon Oil, for instance, received only 20,000 metric tons of the products since the beginning of this year, according to a senior official of the company. In Nigeria, however the diesel consumption rate is 11.8 metrics tons per day. Household, offices, eateries, banks, hospitals and government parastatals are spending millions and would still spend millions on AGO consumption as the electricity supply situation is not likely to change significantly before Hence, the dependence on generators and mini-power plants which are known to use diesel will surge in the future. 2

12 1.2 Motivation/Objective of the Study The aim of this project is to obtain higher yields of petroleum products by processing crude oil feed with similar properties as that used in the Kaduna refinery. These products can be obtained from the atmospheric distillation of crude oil which is a naturally occurring brown to black, flammable liquid. Crude oil consists of a complex mixture of hydrocarbons of various molecular weights, some solid particles and other liquid organic compounds, that are found in geologic formations beneath the Earth s surface. The main function of the distillation tower is to separate the crude oil feed into its various fractions. The separation process takes place at a constant pressure of 1atm, so therefore the separation occurs due to differences in the normal boiling temperatures of the crude components. The AGO obtained from the distillation tower is further reduced to lighter petroleum products by cracking. Cracking is a physical process in which heavy hydrocarbons with higher boiling point are broken down into lighter and more useful hydrocarbon products with lower boiling points. In general, Nigerian crude grades are sweet indicating a low composition of sulfur compounds (< 0.5 wt. %). Such sweet crudes are more environmentally friendly as compared to sour crudes, and therefore more economically viable. 1.3 Scope and Limitations The scope of this project will be limited to the attainment of petroleum products. This will begin from a pre-treatment of crude oil, distillation to obtain multiple fractions and finally cracking of the heavier fractions to obtain high quality petroleum productions. In this project, a petroleum shift reactor was used in the place of a fluidized catalytic cracking unit (FCC unit) in order to reduce the complexity of the proposed design. Unfortunately, the petroleum shift reactor 3

13 unit operation in Aspen HYSIS is not very flexible as it is not possible to alter its working conditions. Furthermore, the petroleum shift reactor does not provide enough information about the cracking reactions which are taking place. This proved to be a major constraint in the manipulation of the composition of the final products. The method employed throughout this project is completely software based. The software used is Aspen HYSYS with Peng Robinson as the preferred fluid package. There are two main processes covered in this project; crude oil distillation and AGO cracking using a catalytic cracking unit. Aspen Process Economic Analyzer (Aspen-PEA) was used to analyze the economic viabilities of the project in general. The results obtained for the process were comparative to those on the industrial level. In the coming chapters of this thesis, the methodology, a description of our proposed process flow diagram (PFD), specification of equipment attributes, as well as plant safety and economic analysis will be discussed. 4

14 2. Literature Review Automotive gas oil (also called atmospheric gas oil, AGO) is one of the fractions obtained through the crude oil refining process. The carbon number of AGO ranges from carbon atoms, and is produced by atmospheric distillation process at a temperature between 200 and 350 C. The principal measure of diesel fuel quality is its cetane number which is a measure of the delay of ignition of a diesel fuel. A higher cetane number indicates that the fuel ignites more readily when sprayed into hot compressed air. Fuels with higher cetane numbers, normally "premium" diesel fuels with additional cleaning agents and some synthetic content, are available in some markets (Majewski, 2013). AGO is a petroleum-based fuel that is used to power many types of vehicles and boats. It is made of a blend of crude oil components called hydrocarbons. The components for making this fuel are refined out of crude oil, usually by fractional distillation. Though it is often used for similar purposes to those of gasoline, it burns differently, and so needs a different type of engine to work. Although diesel is heavier and less volatile than gasoline, it is often more efficient, especially with heavy loads. The crude oil refining was performed in this project to obtain the product for the cracking process. The crude is first pre-heated before distillation. The crude oil fractions obtained through distillation process are mainly off gas, naphtha, kerosene diesel, AGO and bottom distillates. Typical operating conditions in the column are liquid/vapor phase hydrocarbons at 752 F and 6-16 psi from top to bottom. The normal atmospheric tower pressure drop is 0.1 psi/tray for design and the target for operation. Other side units within the tower are pumparounds, side strippers, reboiler and a condenser. These sub-units aid in the effective operation of the tower. 5

15 Generally, there are several crude oil pretreatment processes that are done before distillation processes. The most commonly performed pretreatment process in the petroleum industry is crude oil desalting, which is done to reduce corrosion, plugging, and fouling of equipment and to prevent poisoning the catalysts in processing units. Others pre-treatments methods are pre-heating, pre-flashing, etc. The choice of any of those pre-treatments is dependent on the characteristics of crude oil feed. Before the distillation process was started, crude oil feed pre-treatment was done. Those pre-treatment processes are pre-flashing and heating. The pre-flashing unit was designed to separate liquid phase and vapor crude oil phases, while the heating unit was designed to heat the crude feed to a certain temperature required for atmospheric tower separation. Catalytic cracking is one of the most important refinery processes in petroleum industries. It involves the use of various units such as fluidized catalytic cracking, hydro cracking etc. According to studies in the United States fluidized catalytic cracking process (FCC) provides about 35 to 45% of the blending stocks in the refinery of gasoline (Arvind, 2012).In early years, cracking was achieved by the thermal cracking process but recently it has been replaced by the catalytic process due to its high efficiency and selectivity i.e. gasoline is being produced with higher octane value and less heavy fuel oils and less light gases. The light gases produced in the process contain more olefin hydrocarbons than those obtained from the thermal cracking process. Fluid catalytic cracking (FCC) units perform the most vital role in the modern refinery process because they are used for producing more economic refinery products. In general, the feed to the FCC unit is the residual product from the distillation column. The fluid catalytic 6

16 cracking (FCC) units convert a portion of the heavy material into lighter products, mainly gasoline and atmospheric gas oil. The FCC process employs a catalyst in the form of very fine particles (size of the catalyst is about 70 microns), which behave as a fluid when aerated with vapor. Thus, the catalyst acts as an agent for both mass transfer and heat transfer operations. The catalyst moves from regenerator to reactor and vice versa as fresh or spent catalyst and provides heat to the reactor. A modern FCC catalyst has four major components: crystalline zeolite, matrix, binder, and filler. The catalysts used in this process are zeolites. Zeolite is the primary active component and can range from about 15 to 50 weight percent of the catalyst. The zeolite used in FCC catalysts is referred to as faujasite and is composed of silica and alumina tetrahedra with each tetrahedron having either aluminum or a silicon atom at the center and four oxygen atoms at the corners. It is a molecular sieve with a distinctive lattice structure that allows only a certain size range of hydrocarbon molecules to enter the lattice,.i.e. it is selective. In general, the zeolite does not allow molecules larger than 8 to 10 nm (Sami and Matar, 2000). Usually two types of FCC units are used on an industrial scale; these are side by side type and ortho-flow or stacked type reactor. In side by side reactor which was initially used in the project for simulation purposes, the reactor and regenerator is a separated vessel placed side by side. In case of stacked type reactor, rector and regenerator are mounted together, the later mounted above before. In this project, we have simulated the fractional distillation of a crude oil blend in order to obtain a high-quality AGO product which has been fed to a cracking unit. The petroleum shift reactor was eventually used instead of a classical FCC unit since it performs similar cracking reactions. The FCC unit has two basic components; the reactor and the regenerator (see figure 1 below). The cracking reaction in the catalytic reactor takes place at 995 F and a pressure of 7

17 about 25 psi. This reaction deposits coke (carbon), which remains on the surface of the catalyst, thus decreasing the efficiency of the catalyst as well as its activity. To maintain the activity of the catalyst, it is necessary to burn off the deposited carbon on the catalyst. This was done in a regenerator after which the active catalyst is fed back to the reactor. The regenerator operates at a temperature of about 1319 F and a pressure of about 35 psi, hence the regenerator operated at about 10 psi higher pressure than the reactor The energy required for the endothermic reaction comes from the regenerator in which the coke deposited on the catalyst is burned off in presence of air via an exothermic reaction. Catalytic cracking units which are designed to use the supply of heat from the regenerator for the purpose of cracking are known as heat balance units. 8

18 Figure 1: Schematic of a typical fluid catalytic cracking unit (International Journal of Computer Communication and Information System, 2010). 9

19 3. Methodology We decided to use Aspen HYSYS for the simulation of the AGO cracking process. The Aspen HYSYS software application performs process simulation by carrying out material and energy balances over the process unit. In addition, the Aspen Process Economic Analyzer (Aspen-PEA) tool can be used to obtain an economic analysis of any proposed design. In using Aspen HYSYS, we are able to achieve our project goals within a certain degree of accuracy. Aspen HYSYS is an application that provides models for the analysis of the feasibilities of processes. It is often applied in the study and investigation of several operating parameters on various processes. It is an effective tool, offering a high degree of efficiency in accomplishing process design. The flexibility accompanying the logical and consistent approach to how HYSYS delivers its capabilities makes it an extremely efficient multipurpose simulation process tool. Its effectiveness is attributed to the following design aspects: Multi-flow sheet architecture Modular operations Event driven operations Object oriented design. The preferred fluid package for the process under consideration is Peng-Robinson equation of state (EOS) since it can handle the hypothetical components (pseudo-components). Pseudo-components are coded variables used to simplify design construction and model fitting. The crude oil feed properties are provided as a crude assay which is essentially the chemical evaluation of crude oil feedstock by petroleum testing laboratories. 10

20 Once the crude oil feed has been specified in Aspen HYSYS, it undergoes some pretreatment; after which it is fed into the atmospheric distillation tower. Within the distillation unit, it is distilled into naphtha, diesel kerosene, AGO and heavy distillate (atmospheric residue). The main purpose of the project is cracking of AGO to obtain lighter and more useful products like naphtha and light gas oil. In order to reduce the complexity of the design project, a petroleum shift reactor has been used in place of the typical cracking unit. The AGO is sent for cracking in the petroleum shift reactor to obtain higher yields of lighter petroleum products. 11

21 4. Detailed Process Description 4.1 Pre-treating the Crude Oil Feed Figure 2 shows our proposed process flow diagram (PFD) developed using Aspen HYSYS. A crude oil stream is fed to the preflash unit V-100 at the rate of lb/h, a temperature of 450 Fand a pressure of 50 psia. The preflash unit then splits the feed stream into liquid and vapor phases at the same temperature and pressure as the feed. The exiting liquid and crude vapor streams have flow rates of lb/h and 2441lb/h respectively. The liquid from the bottom of the preflash vessel enters the heat exchanger and comes out as a hot stream at 500 F. The crude vapor and heated liquid crude streams then enters the mixer MIX-100 where the two streams are completely mixed to form the feed for the atmospheric tower T-100. Prior to entering T-100, the mixed feed is heated in heat exchanger E-100 in order to obtain the required feed conditions for the distillation column. In E-100, the tower feed is heated from 498 F to 618 F. Thus, pre-treated crude oil enters the atmospheric tower at a flow rate of lb/h, pressure of 48 psia and temperature of 618 F. The atmospheric tower T-100 is a column having 29 trays in which the feed enters the tower at the 14 th tray. 12

22 Figure 2: Process flow diagram of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. 4.2 The Atmospheric Tower The main distillation column consists of 29 trays, 3 side strippers (SS) (Kerosene SS, Diesel SS and AGO SS), and 3 pump-arounds (kerosene pump-around, diesel pump-around and AGO pump-around). A detailed view of the distillation column is displayed in figure 3. Those trays are the passage ways for crude oil as well as inlet feeds and products. The feed to the column enters at 618 F and 48 psia. The column separates the feed into six fractions namely: Naphtha, Waste Water, Kerosene, Diesel, Atmospheric Gas Oil (AGO) and Residue. Three pump-arounds with coolers were installed; these equipments have the role of drawing feed from specific tray, reducing its temperature and sending it back to the tray above. Those pump-arounds are for the kerosene, diesel and AGO fractions. The side strippers use a reboiler and steam for purification. For our kerosene side stripper design, the distillate is drawn from the 7 th tray of the column and sent to kerosene side stripper. 13

23 The kerosene side stripper heats the products and gives off pure kerosene as the product, while the lighter component (distillate with boiling point lower than kerosene) are sent back to the tray above of the column. The same processes take place for both diesel and AGO fractions, but for diesel, the feed is drawn from the 17 th tray of the column and the lighter compounds were sent back to the 16 th column. For AGO, the feed is drawn from the 22 nd tray of the column, while the lighter components are returned back to the 21 st column. In order to allow the column to converge, tray efficiencies were specified with ranges varying between 45-90%. Tables 1, 2, and 3 display the operating conditions as well as stream properties associated with the distillation column. Figure 3: Detailed view of atmospheric tower T-100 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. 14

24 Number of trays 29 Top stage pressure(psia) 18.7 Reboiler pressure (psia) 36.7 Top stage temperature ( F) Bottom temperature ( F) 1351 Reboiler Duty (Btu/h) Kero Pump-around duty (Btu/h) AGO pump-around duty(btu/h) Diesel Pump-around duty(btu/h) Table 1: Operating conditions for atmospheric tower T-100 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. Stream Name Temperature ( F) Pressure (psia) Flowrate (lb/h) Diesel AGO Main Stream Table 2: Properties of inlet feed streams of atmospheric tower T-100 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. Stream Name Temperature ( F) Pressure (psia) Flowrate (lb/h) Naphtha Waste Water Kerosene Diesel AGO Residue Table 3: Properties of outlet feed streams of atmospheric tower T-100 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. 15

25 4.3 Heat Exchanger E-101 The role of the heat exchanger is to perform heat integration for the purpose of recovering the heat lost. The hot AGO enters a heat exchanger at a temperature of 607 F, and exchanges heat with the liquid crude from flash tank, which enters the heat exchanger at 400 F. The AGO feed is cooled down to a temperature of 529 F, while the liquid crude is heated to a temperature of 500 F. Relevant properties of the streams associated with exchanger E-101 can be seen in table 4. Stream AGO Feed 1 Liquid crude Hot liquid Temperature( F) Pressure (psia) flow rate (lb/h) Duty(Btu/h) Table 4: Properties of the inlet and outlet streams of heat exchanger E-101 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products Petroleum Shift Reactor R-100 A petroleum shift reactor was used instead of a fluid catalytic cracking (FCC) unit to perform cracking reactions for this project. The feed for petroleum shift reactor was AGO obtained as a distillate from the atmospheric tower T-100. Properties of the inlet and outlet process streams to the petroleum shift reactor R-100 are shown in table 5. The feed was cracked into lighter useful elements such as light gas oil and cracked naphtha (called gasoline) with percentage yield of 90% and 10% respectively. In order to make the petroleum shift reactor converge, the product temperatures were specified, as well as their initial and final boiling points. 16

26 Stream Feed 1 Light gas oil Cracked Naphtha Temperature( F) Pressure(KPa) flow rate(lb/h) Table 5: Properties of the inlet and outlet streams of petroleum shift reactor R-100 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. The gasoline and light diesel oil products from the petroleum shift reactor R-100 were obtained through cracking the AGO. Properties Cracked naphtha Light gas oil Vapor phase fraction 0 0 Temperature( O F) Pressure(psia) Mass flow(lb/h) Std ideal liquid volume(barrel/day) Molecular weight Mass density(lb/ft 3 ) Viscosity(cP) Table 6: Thermodynamic properties of light gas oil and cracked naphtha products from petroleum shift reactor R-100. From the results obtained from table 6, 15,650 barrels/day of light gas oil and 1,756 barrels/day of cracked naphtha were obtained from a feed of 20,000 barrels/day of crude oil. We were also able to obtain the measurable properties for the product streams. We then compared the values to the ASTM range for each petroleum product (see tables 7 and 8). Property ASTM Range Cracked Naphtha Cetane number Kinematic Viscosity (mm 2 /S) at 40 C Flash Point ( C) Table 7: Comparison of the produced Cracked Naphtha to ASTM standards Property ASTM Range Light Gas Oil Kinematic Viscosity (mm 2 /S) at 100 C Flash Point ( C) Table 8: Comparison of the produced Light Gas Oil to ASTM standards 17

27 5. Equipment Specification and Design The importance of sizing the process equipment is to perform a better economic analysis as the default equipment size attributes provided by Aspen HYSYS will often yield inaccurate cost estimates. Depending on their specific function, process equipment was sized using volume, length, diameter, or surface area. The following sub-sections present the size attributes for the different pieces of equipment in our proposed design. 5.1 Heat Exchangers For the heat exchangers, the log mean temperature was calculated using shell and tube inlet and outlet temperatures. Using the heat duty, estimates of the overall heat transfer coefficient U, and correlation charts for the efficiency of heat transfer, the surface area were calculated. Table 9 displays the results of sizing for heat exchangers E-100 and E-101. Note that the material of construction for both exchangers was carbon steel due to the low operating pressure (< 10 bars). Equipment E-100 E-101 Diameter(ft) Area(ft 2 ) Table 9: Size attributes for heat exchangers E-100 and E-101 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. 5.2 Atmospheric Tower The complete design of a distillation column requires the determination of many parameters such as the feed location, number of trays or column diameter, tray design or packing type, and separation between trays. Atmospheric towers may use packed stages or trays. Packing is usually preferred for loads that are temperature sensitive or corrosive, as the range in packing 18

28 materials is wider than that commonly available for trays. Packing pressure drop is also much lower than trays. Kister states that packing pressure drop is typically three to five times lower than that of trays (Ludwig, 1997). For this reason, packing columns are favored wherever pressure drop is important or where it is economical to minimize it. In addition, packing columns are normally used for lower loads because of the mass transfer characteristics of packing. If the liquid rate is high the boundary layer will increase, reducing the mass transfer (Ibrahim, 2014). Packing columns are also used for smaller towers, with diameters less than 3 ft, as it is difficult to access such towers from the inside in order to install and maintain the trays. Although an oversized diameter may be used to overcome this difficulty, packing is normally cheaper and more desirable than other designs. Tray columns, on the other hand, are used for larger columns with high liquid loads. With lower liquid loads, trays can have high residence times leading to undesired affects such as fouling and sedimentation. In addition, trays will have difficulty maintaining a good weir loading and distribution across the tray, resulting in lower than expected tray efficiencies. For these reasons, it is often more economical to handle high liquid loads in tray columns. Whereas packings are prone to severe misdistribution problems in large-diameter columns, these problems are far less severe in tray columns. Tray columns are also to be preferred where fouling or solid accumulation and deposition is anticipated because of the long history of success trays have had in fouling service applications. Trays can handle solids a lot easier than packed columns, as solids tend to accumulate in packing voids, but the higher gas and liquid velocities on trays provide a sweeping action that keeps tray openings clear (Ibrahim, 2014). 19

29 strippers. Tables 10 and 11 show the size attributes of the atmospheric tower and associated side Packed section Main column Internal type Packed Diameter(ft) 10 Height(ft) 40 Packed space(ft) 3 Packed volume(ft 3 ) Hold up(ft 3 ) Table 10: Size attributes for atmospheric tower T-100 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. Vessel Kero SS Diesel SS AGO SS V-100 R-100 Diameter (ft) Length(ft) Volume(ft 3 ) Orientation Horizontal Horizontal Horizontal Vertical Vertical Table 11: Size attributes for the kerosene, diesel, and AGO side strippers as well as the flash tank V-100 and petroleum shift reactor R-100 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. 20

30 6. Plant Safety Analysis In today s modern highly complex, oil refineries proper material selection has become one of the most important factors in the design and repair of refinery processing equipment. In this project, proper material selection was considered to ensure that the expectations of the designers for safety, reliability and economy are actually realized. On the other hand, improper materials selection can result in unexpected equipment failures which can lead to significant losses. A hazard and operability study (HAZOP) is an organized and efficient examination of an existing process or operation in order to recognize and evaluate problems that may represent risks to personnel or equipment. In the industry, the analysis is carried out by a suitably experienced multi-disciplinary team (HAZOP team) during a set of meetings. Basically, what is being examined during this analysis is the equipment, its material of construction and operating conditions. This evaluation is to determine the deviation, causes, consequences and actions to be taken should incase there is any incident. In this project we are using carbon steel for the material of construction with forging temperature of 2410 F and burning temperature of 2680 F. 21

31 Operating Conditions Design Conditions Equipment Temperature Pressure Temperature Pressure Material of ( o F) (psi) ( o F ) (psi) Construction V CS E CS E CS T CS Table 12: Operating conditions and material of construction of equipment in the proposed design for the cracking of AGO distillate to obtain lighter petroleum products 22

32 Parameter Deviation Cause Consequences Action Flow High flow Flow controller fault Column level, temperature, and pressure Increase. Overpressurization of Column. Column controls Will attempt to correct. Flow indicator with high flow and temperature alarms, emergency feed shutdown Low or No flow Feed pump failure; Jammed feed valve. Reduced column temperature and rate of reaction Flow indicator with low flow alarm Temperature High temperature Low temperature Temperature controller fault, reboiler malfunction Temperature controller fault, reboiler malfunction Column level, temperature, and pressure increase. Over pressurization. Reduced column temperature and rate of separation Temperature indicator with high temperature alarm and emergency shutdown procedures Temperature indicator with low temperature alarm. Pressure High Pressure Flow controller fault, Temperature controller fault Column level, temperature, and pressure increase. Over pressurization. Pressure indicator reporting to feed control valve and to Pressure Safety Valve (open-to-air) Low pressure Feed pump failure; jammed feed valve Reduced column temperature and rate of separation Flow indicator with low flow alarm Table 13: Hazard and operability analysis of a tower T-100 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. 23

33 Parameter Deviation Cause Consequence Action Flow High flow Damage to control valves, instruments. Uncontrolled production Additional valves and compressors are needed Long time Temperature Low flow Low yield Industrial failure Allow the valve to send enough fluids Addition reactions Cracking and reverse reactions High temperature Relative high pressures Over cracking reaction Low treated kerosene yield More light has and H 2 S Structural material damage, Unwanted products(light components) Decrease reaction resident time Low temperature to prevent creaking Cool down the streams of kerosene Low temperature No cracking reaction take place Pressure High Pressure Relative high temperature Low productivity Shift reactor damage( out of order) Energy supply is needed in place Decrease temperature Low pressure Not meeting cracking conditions Low production of lighter products Compressors are needed to achieve desired pressure Table 14: Hazard and operability analysis of petroleum shift reactor R-100 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. 24

34 Parameter Deviation Cause Consequence Action Flow High flow Outlet cool stream Not achieving desired stream temperature Additional heater is needed in series Low flow Overheated outlet stream Energy waste Reduce energy supply( utility stream) Temperature High temperature Destruction of heater Accidents of nearby engineers Decrease temperature Low temperature Outlet cool stream Stream not reaching desired temperature Pressure High Pressure Relative high temperature Accidents Energy supply is needed in place Increase pressure Decrease temperature Fracturing of equipment Low pressure Much spending Compressors are needed Use of high temperature to achieve desired pressure Table 15: Hazard and operability analysis of the heat exchangers of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. 25

35 Parameter Deviation Cause Consequences Action Flow High flow Damages to control valves, gauges. Leads to structural damage of next unit Reduce flow decreasing pressure Low or No flow Less or no mass flow Low yield of product Material damage Open valves, increase relatively pressure Temperature High temperature Uncontrolled heat supply and high pressures Structural material damage Change material of construction(stainless steel, adjust heat supply Low temperature Temperature of feed being too low Poor productivity in pre-flashing Increase inlet stream temperature Pressure High Pressure Relative high temperature Control valve damage Structural and material fracturing Material of construction with thick wall is recommended, Decrease pressure Low pressure Pipe leaks Lowers production rate Compressors in place Table 16: Hazard and operability analysis of flash tank separator V-100 of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. 26

36 7. Economic Analysis After sizing the process equipment, the Aspen-PEA was used to perform the economic analysis of the proposed design. In particular, total capital costs, operating costs, as well as utility cost, were obtained. Table 12 show the summary of how much is the project cost based on the cost of each equipment unit as well as utility cost. As shown in the table below, the total capital cost is $11,715,300. The total utilities cost for our design is $8,548,290, on an annual basis which indicates that it will be very expensive to operate a process unit based on the proposed design. Total Capital Cost $11,715,300 Total Utilities Cost $8,548,290 Equipment Cost $2,800,600 Total Installed Cost $5,481,100 Table 17: Costs evaluation summary of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. The total equipment cost is $2,800,600 with the detailed cost of individual equipment indicated in figure 4. The most expensive piece of equipment is the atmospheric tower T-100 which costs $ 1,798,700. Generally, the equipment costs will be dependent on the material of construction as well as the dimensions. It should be noted that most of the equipments in our proposed design are of carbon steel (CS). 27

37 Cost($) Figure 4: Purchased costs for the individual pieces of equipment of the proposed design for the cracking of AGO distillate to obtain lighter petroleum products. 28

38 8. Conclusions and Recommendations From our proposed design, we have been able to convert a feed of 20,000 barrels/day of a crude blend that is similar to the one that is sent to the Kaduna Refinery, and were able to get 15,650 barrels/day of light gas oil and 1,756 barrels/day of cracked naphtha. This would help meet with the growing demand of diesel fuels in Nigeria. We have been able to increase the amount of crude oil that Nigeria refines by about 4%, all for a total capital cost of $11.7 million. We would like to recommend that FCC unit be used for the cracking process instead of the petroleum shift reactor since it performs a better job than petroleum shift reactor. We would also like to propose that a vacuum distillation column be used to fully separate and produce different grades of gas oils. 29

39 References Nelson, W.L. Petroleum refinery engineering, 4th ed. pp , New York, McGraw Hill Book Co (1958). Chevron. Diesel Fuel Technical Review (FTR-2). Chevron Products Company, USA. (1998). Craig Freud Enrich, Ph.D. How Oil Refining Works, science how stuffs work. David S.J. Jones and Peter P. Pujado. Handbook of Petroleum Processing (First Ed.). The Netherlands, Springer (2006). Eledu I. Precious, Adeyemo J. Oluwatosin and Kierian T. Ekere. Crude Oil Characterization Using Aspen Hysys for Modelling and Simulation of Distillation Units. School of Arts and Science, American University of Nigeria, Yola, Nigeria. (2013). West central Africa department, Federal Public expenditure Review Kuprys, Algirdas. Possibility of Using Liquefied oil Gas in Transport, Transport ( ) 24.1 (2009): Sneesby, Martin G. Simulation and Control of Reactive Distillation, Curtin University of Technology, School of Engineering, March Nwachukwu, Maxwell and Umunna, Harold Chike. Determinants of the dynamics of demand for highway transportation fuel in Nigeria. OPEP Energy review, Nigeria. Perry, D. G. Perry s Chemical Engineers' Handbook, Eighth Edition (2007). Utama, T. T. Distillation Column and Sizing. Malaysia: KLM Technology Group. (June 2013). Aspen Tech. Oil characterization (2003).EAI, 2-5. Ludwig, E. E. Applied Process Design for Chemical and Petrochemical Plants, Volume 2. Gulf Professional Publishing (1997). Meyer, R.A. Encyclopaedia of Physical Science and Technology, 2 nd edition. Academic Press Inc., Vol. 9, London, pp , (1992). Brian Moriyama. HAZOP Study of a distillation column. CENG 124B, April 24,

40 Appendix A: Crude Oil Assay Assay Basis True Boiling point Liquid Vol % Distilled Temperature ( o F) Molecular Weight Light End Liquid Volume Light Ends Liquid Volume Percent Light Ends Composition NBP [C] Methane Ethane Propane i-butane n-butane i-pentane n-pentane H 2 O

41 Appendix B: Aspen HYSYS Software 1. Additional of components 2. Fluid Package Selection 3. Light end composition input 32

42 4. Installing crude oil feed 5. Installing the pre-flash, mixer and heater units 33

43 34

44 6. Installing the tower 35

45 36

46 7. Installing Side strippers and pumparounds 37

47 8. Running the simulation 38

48 Appendix C: Material and Energy Balances Material Balance Composition of ho.t crude, with flowrate 620.7lbm/h = composition of naphtha, with flowrate 66.84lbm/h. For i-butane; (0.0086*620.7) = (0.0803*66.84) For n-butane; (0.0052*620.7) = (0.0482*66.84) For i-pentane (0.0150*620.7) = ( ) For n-pentane; (0.0189*620.7) = (0.1755*66.84) = Energy Balances E-100 (Heat flow from mixed crude) + (heat flow from Q-100) = (heat flow from hot crude) ( ^8) + ( ^7) = ( ^8) ^8 = ( ^8) 39

49 T-100 Heat inflow = heat outflow Heat inflow = ( ^5) + ( ^6) + ( ^8) + ( ^6) = ^8 outflow = ( ^6)+( ^6)+( ^7)+( ^6)+(-23.25)+( ^7) = ^8 Therefore, heat inflow heat outflow ^ ^8 E-101 Heat inflow = heat outflow ( ^7)+( ^8) = ( ^8)+( ^8) ^ ^8 PS-100 Heat inflow = heat outflow ( ^8) = ( ^8) + ( ^7) ^ ^8 40