Control Of A Fluid Catalytic Cracking Unit
The performance of the FCC units plays a major role on the overall economics of refinery plants. Any improvement in operation or control of FCC units will result in dramatic economic benefits. Fluid Catalytic Cracking (FCC) Units of Nigerian Refineries produced petroleum products at far below their installed capacities. This work is aimed at examining the control of a fluid catalytic cracking unit. The FCCU was designed to process 0.56bbl/hr of Escravos gas oil and fabrication of same was carried out. Equipment fabricated include Feed Surge Drum (Diameter 0.631m and Height 1.002m), Feed/LCO Heat Exchanger (Shell Diameter 0.260m, Tube Diameter 0.030m and Exchanger Length 1.000m), Feed/DCO Heat Exchanger(Shell Diameter 0.275m, Tube Diameter 0.0245m and Exchanger Length 1.000m), Feed/Slurry Heat Exchanger(Shell Diameter 0.260m, Tube Diameter 0.024m and Exchanger Length 1.000m), Feed Fired Heater (Base Diameter 0.872m, Height 1.745m and Tube Diameter 0.024m), Riser Reactor (Diameter 0.545m and Height 1.817m), Main Fractionator (Column Diameter 0.520m and Column Height 2.925m) and Overhead Condenser (Shell Diameter 0.310m, Tube Diameter 0.0245m and Condenser Length 1.000m). Both manual and Hysys simulation software were used to carry out the design and the results obtained were compared to ascertain most acceptable technique for the design of FCCU. While Hysys simulation gave more detailed and effective results, the manual design technique shows little discrepancy to Hysys simulation result. Therefore, the manual design technique is also valid and can also serve in the absence of the software for FCCU design.
Table Of Contents
- Table of Content
- 1.1 Background to the Study
- 1.2 Problem Statement
- 1.3 Justification
- 1.4 Aim and Objectives
- 1.5 Scope
- 2.1 Historical Background of Petroleum Refining
- 2.2 Crude Oil and its Constituents
- 2.3 FCC Feed Characterization
- 2.4 FCC Catalyst
- 2.5 FCCU Pilot Plant
- 2.6 Cracking
- 2.7 Catalyst Regeneration
- 2.8 Fractionator
- 2.9 Nigerian Fluid Catalytic Cracking Units
- 2.10 Reactor design
- 2.11 Process Selection
- 3.1 Preamble
- 3.2 Design Basis
- 3.3 Process Selection and PFD Development
- 3.4 Process Description
- 3.5 Manual Design Procedure
- 3.6 Computer (Hysys) Simulation
- 3.7 Detailed Equipment Design and Specification
- 3.8 Working Drawings of Individual Equipment
- 3.9 Fabrication
- 3.10 Development of Controls, Safety Considerations, Start-up and Shut Down Procedure
Results And Discussion
- 4.1 Material and Energy Balance
- 4.2 Manual and Simulation Results
- 4.3 Detailed Equipment Specification
- 4.4 Working Drawing of Individual Equipment
- 4.5 Fabrication
- 4.6 Process Control
- 4.7 Safety Consideration
- 4.8 Start up Procedure
- 4.9 Shut Down Procedure
- 4.10 Contribution to Knowledge/ Novelty of the Work
Conclusions And Recommendations
- 5.1 Conclusions
- 5.2 Recommendations
1.1 Background to the Study
The fluid catalytic cracking (FCC) unit present challenging multivariable controls problems, because it is a very sensitive and complex refinery system. The selection of inputs and outputs variables is an important issue, as the pairing of chosen controlled and manipulated variables for decentralized control. Continuous catalyst regeneration makes it possible to manage the yields which are achieved by catalyst cycling between the reaction and regeneration units. This ensures the reactor is continuously supplied with freshly regenerated catalyst, and product yields are maintained at fresh catalyst levels. Reliable and accurate control is important for total process efficiency USEIA, (2015).
Unlike atmospheric distillation and vacuum distillation, which are physical separation processes, FCC is a chemical conversion process used in petroleum refineries. It is used to convert the high-boiling, high-molecular weight hydrocarbon (HC) fractions of petroleum crude oils to more valuable gasoline, olefinic gases, and other products. Catalytic cracking produces more gasoline with a higher octane rating. It also produces by-product gases that are more olefinic and more valuable, than by thermal cracking Gary and Handwerk (2001), and Speight, (2006). The feedstock to an FCC is usually that portion of the crude oil that has an initial boiling point of 340 °C or higher at atmospheric pressure and an average molecular weight ranging from about 200 to 600 or higher. This portion of crude oil is often referred to as heavy gas oil (HGO) and/or vacuum gas oil (HVGO). The FCC process vapourises and breaks the long-chain molecules of the high-boiling hydrocarbon liquids into much shorter molecules by contacting the feedstock, at high temperature and moderate pressure, with a fluidized powdered catalyst Speight (2006).
Petroleum refinery is a complex industry that generates a diverse slate of fuel and chemical products, from gasoline to heating oil (Rader, 1996). The refining process involves separating, cracking, restructuring, treating, and blending hydrocarbon molecules to generate petroleum products. Technological perspective is essential for a basic understanding of the complex refinery processes, a design based perspective is essential to develop a greater insight with respect to the physics of various processes, as design based evaluation procedures enable a successful correlation between fixed and operating costs and associated profits.
A refinery is a chemical plant that processes crude oil and produces several valuable products; it contains different types of units that perform a variety of different operations. The main goal is to take the undesirable components of the crude oil and upgrade them into more valuable products. Gasoline, diesel, and jet fuel are among the most valuable products. Refineries perform three basic operations which are Separation (fractional distillation), Conversion (cracking and rearranging the molecules), and Treatment.
Fluid Catalytic Cracking process is an important and widely used way to convert heavy feedstock into lighter, more valuable products. There are approximately 400 FCC units operating worldwide, with total processing capacity of over twelve million barrels per day (12 MMbbl/day) (Hug, 1998). Various feedstocks can be used, such as gas oils, vacuum gas oils or residual materials. Typical products are gasoline, light fuel oils and olefin-rich gases. The principal purpose of a cracking unit is to break high molecular weight hydrocarbons into smaller pieces of lower boiling point fractions, especially gasoline (Dwyer and Rawlence, 1993). Originally, thermal operations were used to crack heavy oil, but the discovery of a catalyst that gives a higher yield of gasoline with a higher octane number quickly brought on the use of catalytic cracking units. Today, the most commonly used catalytic cracking unit is the Fluid Catalytic Cracker or FCC (Wilczura-Wachnik, 1973). The fluid cracker consists of a catalyst section and a fractionating section that operate together as an integrated processing unit. The catalyst section contains the reactor and regenerator, which, with the standpipe and riser, forms the catalyst circulation unit (Ibsen, 2006).
This research work is intended at the design and fabrication of a fluid catalytic cracking unit of a Mini-Refinery for the ultimate purpose of improving present yield of gasoline in Nigerian refineries through pilot testing in the mini refinery FCCU of improved catalyst and different feed composition.
1.2 Problem Statement
Nigeria is one of the top oil-producing nations in the world but processing this oil into finished products has been a major challenge for the country. The Nigerian FCCU produced petroleum products at far below their installed capacity and this is as a result of neglect by stake holders in areas of research and developments in the fields of enhancing catalyst development and new FCC feedstock. Also this due to unavailability of operational data that can be used to improve the production capacity. There is therefore the need to provide testing base for research in both fields and also in providing operational data to boost oil processing capacity and be self-reliant when it comes to petroleum and petroleum processing.
- Pilot plants can serve as small scale of larger commercial units.
- Fabricated Pilot FCCU can serve as study aid for students of chemical engineering and related fields.
- Research and development data will be provided for specific FCC feed stock.
- Research into catalyst development & testing will be enhanced.
- Job creation
1.4 Aim and Objectives
The aim of this work is to carry out a control of a fluid catalytic cracking unit.
The specific objectives of this work include:
- Identify suitable process selection for the Pilot plant
- Carry out material and energy balances
- Development of a Preliminary design of equipment
- Detailed design of Major equipment
- Plant layout
- Instrumentation and control
- Fabrication of the Pilot Plant.
The scope of this work is limited to the control of a fluid catalytic cracking unit through the design and fabrication of a Fluid Catalytic Cracking Unit of a Mini – Refinery to process 5 barrels per batch in Nigeria as well as the safety consideration of such a plant.
Conclusions And Recommendations
A mini Fluid Catalytic Cracking Unit with a capacity of processing 5bbl/batch was designed and fabricated. Detailed equipment design using manual and Hysys software was carried out. Process control and safety considerations of the entire unit was also carried out. Although Hysys simulation shows more detailed and effective results, manual design technique gave result close to Hysys simulation. Hence, the manual design technique can be used for FCCU design in the absence of the software.
Equipment fabricated include
- Feed Surge Drum (Diameter 0.631m and Height 1.002m),
- Feed/LCO Heat Exchanger (Shell Diameter 0.260m, Tube Diameter 0.030m and Exchanger Length 1.000m),
- Feed/DCO Heat Exchanger(Shell Diameter 0.275m, Tube Diameter 0.0245m and Exchanger Length 1.000m),
- Feed/Slurry Heat Exchanger(Shell Diameter 0.260m, Tube Diameter 0.024m and Exchanger Length 1.000m),
- Feed Fired Heater (Base Diameter 0.872m, Height 1.745m and Tube Diameter 0.024m),
- Riser Reactor (Diameter 0.545m and Height 1.817m),
- Main Fractionator (Column Diameter 0.520m and Column Height 2.925m) and
- Overhead Condenser (Shell Diameter 0.310m, Tube Diameter 0.0245m and Condenser Length 1.000m).
The Fabrication was carried out by a certified professional fabrication company using locally sourced materials within the confines of the work.
The following recommendations should be considered:
- Installation, piping, instrumentation and test running of the fabricated equipment should be carried out.
- The pilot plant when installed should be used for research and development that address salient design problems
- Fluid Catalytic Cracking and catalyst enhancement processes.
- Other Units such as the Gas Treatment Unit (GTU) and Gas Concentration Unit (GCU) for proper handling of the overhead gas and flue gases should be looked into.
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