THE CONTROL OF A FLUID CATALYTIC CRACKING UNIT

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Abstract

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

Abstract

CHAPTER ONE

INTRODUCTION

1.1 Background to the Study

1.2 Problem Statement

1.3 Justification

1.4 Aim and Objectives

1.5 Scope

CHAPTER TWO

LITERATURE REVIEW

2.1 Historical Background of Petroleum Refining

2.2 Crude Oil and its Constituents

2.2.1 Hydrocarbon classification

2.2.2 Hydrocarbon compounds

2.2.3 Related works

2.3 FCC Feed Characterization

2.3.1 Feedstock physical properties

2.3.2 Density

2.3.2.1 API Gravity

2.3.3 Watson factor KW

2.3.4 True boiling point (TBP) method for crude characterization

2.3.5 Pour point

2.3.6 Cloud point

2.3.7 Octane number

2.3.8 Sulfur content:

2.3.9 Refractive index

2.3.10 Bromine number and bromine index

2.3.11 Viscosity

2.3.12 Conradson, ramsbottom, micro carbon, and heptane insolubles

2.3.14 Process variables

2.3.15.1 Dependent and independent variables

2.4.1 Catalyst component

2.4.2 Zeolite chemistry

2.4.3 Zeolite types

2.4.4 Role of zeolite in FCCU

2.5 FCCU Pilot Plant

2.5.1 FCC Pilot plant description

2.6 Cracking

2.6.1 Fluid catalytic cracking

2.6.2 Fluid catalytic cracking unit

2.6.3 FCC converter

2.6.4 Feed preheat

2.6.5 Riser—reactor—stripper

2.6.6 Riser catalyst separation

2.6.7 Disengager

2.6.8 Stripping Section

2.6.9 Steam ring applications

2.7 Catalyst Regeneration

2.7.1 Advantages of complete combustion

2.7.2 Disadvantages of complete combustion

2.7.3 Regenerator–heat/catalyst recovery

2.7.4 Regenerator bed temperature

2.7.5 Standpipe/slide valve

2.7.6 Regenerator catalyst separation

2.7.7 Flue gas heat recovery schemes

2.8 Fractionator

2.8.1 Products and equipment involved in fractionation

2.8.1.1 Bottom product

2.8.1.2 Light cycle oil

2.8.1.3 Gas – light naphtha – heavy naphtha

2.8.1.4 The absorber

2.8.1.5 Ethane stripper

2.8.1.6 Debutanizer

2.8.2 Vapor recovery section

2.9 Nigerian Fluid Catalytic Cracking Units

2.10 Reactor design

2.10.1 Fluidized bed reactor

2.10.2 Behavior of fluidized bed

2.10.2.1 Minimum fluidization velocity

2.10.2.2 Pressure drop

2.10.2.3 Bed expansion ratio (R)

2.10.2.4 Bed fluctuation ratio (r)

2.10.2.5 Fluidization quality (FQ)

2.10.3 Mass of solid in the bed

2.10.4 Terminal velocity, Ut

2.10.5 Reactor design

2.11 Process Selection

2.11.1 Types of FCC designs

2.11.1.1 Side-by-side configuration:

2.11.1.2 Stacked configuration:

CHAPTER THREE

METHODOLOGY

3.1 Preamble

3.2 Design Basis

3.3 Process Selection and PFD Development

3.4 Process Description

3.5 Manual Design Procedure

3.5 .1 Material and energy balances

3.5.3 FCC Unit Surge Drum D-01

3.5.4 FCC Unit Feed Surge Pump P-01

3.5.5 FCC Unit Heat Exchanger E-01

3.5.6 FCC Unit Heat Exchanger E-02

3.5.7 FCC unit heat exchanger E-03

3.5.8 FCC unit feed preheater F-01

3.5.9 FCC unit reactor R-01

3.5.10 FCC unit main fractionator C-01

3.5.11 FCC unit air fin cooler A-01

3.5.12 FCC unit overhead separator D-02

3.6 Computer (Hysys) Simulation

3.6.1 Process simulation procedure

3.6.2 Process 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

CHAPTER FOUR

RESULTS AND DISCUSSION

4.1 Material and Energy Balance

4.3 Detailed Equipment Specification

4.4 Working Drawing of Individual Equipment

4.5 Fabrication

4.5.2 Heat exchangers

4.5.3 Overhead condenser

4.5.4 FCC Fired heater

4.5.5 FCC converter parts

4.5.6 Main fractionator

4.6 Process Control

4.7 Safety Consideration

4.7.1 Feed preheating circuit

4.7.2 Converter

4.7.3 Main fractionator

4.8 Start up Procedure

4.9 Shut Down Procedure

4.10 Contribution to Knowledge/ Novelty of the Work

CHAPTER FIVE

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

5.2 Recommendations

References

Appendix

Computer Simulation Details showing screen shots of Hysys simulation results.

Table D1: Product Distribution

Table: D2: Surge Pump Feed Condition

Table: D3 Surge Pump Performance

Table D4: Exchanger Feed Condition

Table D5: Exchanger Performance

Table D6: Exchanger Feed Condition

Table D7: Exchanger Performance

Table D8: Exchanger Feed Condition

Table D9: Exchanger Performance

Table D10: Heater Feed Condition

Table D11: Heater Specs

Table D12: Heater Rating

Table D13: Reactor Feed Condition

Table D14: Reactor Operating Condition

Table D15: Reactor Geometry

Figure D1: Column Stages

Figure D2 Temperature Profile

Table D16: Column Profiles

Table D17: Column Tray Sections

Table D18: Column Pressure Drop

Figure D3 Pressure Profile

Table D20: Condenser Condition

Table D21: Overhead Separator Condition

Table D22: Overhead Separator Sizing

LIST OF TABLES

Table 2.1: Review of related work

Table 2.2: Classification of different types of Crude oil

Table 2.3 Typical KRPC Feed Properties

Table 2.4 Regenerator Temperatures and Operating Modes

Table 2.5 Reactions occurring in the regenerator

Table 2.6 Important Reactions occurring in FCC

Table 2.7: Nigerian Refineries and their respective FCC Capacities

Table 3.1:Mini FCCU Design Basis

Table 3.2 Feed Composition

Table 3.3: Typical KRPC FCC feed charactristics

Table 4.1: Summary of Material Balance across FCC Unit Surge Drum (D01)

Table 4.2: Summary of Material Balance across FCC Unit Surge Pump (P01)

Table 4.3: Summary of Material Balance across FCC Unit Pre-Heater (E01)

Table 4.4: Summary of Material Balance across FCC Unit Pre-Heater (E02)

Table 4.5: Summary of Material Balance across FCC Unit Pre-Heater (E03)

Table 4.6: Summary of Material Balance across FCC Unit Fired heater (F01)

Table 4.7: Summary of Material Balance across FCC Unit Reactor (R01)

Table 4.8: Summary of Material Balance across FCC Unit Main Fractionator (C01)

Table 4.9: Summary of Material Balance across FCC Unit Air Fin Cooler (A01)

Table 4.10: Summary of Material Balance across FCC Unit Overhead Separator (D02)

Table 4.11: Summary of Energy Balance (Heat Loads) Across All Equipment

Table 4.12: Reactor Product Distribution from Aspen Hysys and Manual Design

Table 4.13: Main Fractionator Aspen Hysys and Manual Design

Table 4.14: Aspen Hysys Reactor Product Distribution

Table 4.15: Aspen Hysys Reactor Feed Condition

Table 4.16: Aspen Hysys Reactor Geometry

Table 4.17: Aspen Hysys Simulation Design Parameters for Fractionator

Table 4.18: Summary of Furnace Design Parameters

Table 4.19: Summary of Column Design Parameters

Table 4.20: Summary of Hysys Simulated Condenser/Heat exchanger Design Parameters

Table 4.21: Summary of Surge Pump Design Parameters

Table 4.22: Summary of Surge/Reflux Drums Design Parameters

Table 4.23: Surge Drum (D-01) Design Parameters

Table 4.24: Surge Pump (P-01) Design Parameters

Table 4.25: Pre-Heater (E-01) Design Parameters

Table 4.26: Pre-Heater (E-02) Design Parameters

Table 4.27: Pre-Heater (E-03) Design Parameters

Table 4.28: Heater (H-01) Design Parameters

Table 4.29: Column (C-01) Design Parameters

Table 4.30: Reactor (R-01) Design Parameters

Table 4.31. Riser termination dimentsions

Table 4.32: Cooler (A-01) Design Parameters

Table 4.33: Overhead Separator (D-02) Design Parameters

Table 4.34: Design and actual values used for fabrication

LIST OF FIGURE

Figure 2.1 Zeolite Catalyst sites

Figure 2.2: FCC Pilot Plant Basic Equipment

Figure 2.3 Cracking Reactions

Figure 2.4a: Position of FCC in the Refinery

Figure 2.4b Flow Diagram of Fluid Catalytic Cracking Process

Figure 2.5: FCC Unit Schematic Diagram

Figure 2.6 FCC Unit Scheme Diagram

Figure 2.7a Typical schematic of Exxon flexi-cracker

Figure 2.7b Typical schematic of Kellogg Brown & Root—KBR

Figure 2.8 Universal Oil Products (UOP) Fluid Catalytic Cracking Unit

Figure 2.9 SWEC side by side FCC Unit

Figure 2.10a the Converter Schematic

Figure 2.10b the Converter Internals

Figure 2.11 Typical Feed Preheat System

Figure 2.12 Typical Riser Y

Figure 2.13 Two stage cyclone system.

Figure 2.14a Example of a two stage stripper

Figure 2.14b Catalyst Stripper

Figure 2.15 Typical Rings with a Shaw-Designed Residue Catalytic Cracker

Figure 2.16: A typical Regenerator using Lift air to transfer Catalyst

Figure 2.17 FCCU Schematic Slide Valve Installed

Figure 2.18 FCC typical Fractionator Circuit

Figure 2.19: Fluidization regime in FCC

Figure 2.20: Pressure drop across a fluidized bed

Figure 2.21: Conceptual Fluidized Reactor

Figure 2.22: Typical Side-by-Side FCC Reactor

Figure 2.23: ExxonMobil Flexi-cracker side-by-side design

Figure 2.24: FCC side-by-side Reactor Design (a) RFCC Unit by SWEC (b) R2R Unit by Axens

Figure 2.25: UOP Side-by-Side Design

Figure 2.26: Kellogg Orthoflow Stacked Design (a) FCC Converter (b) Resid FCC Converter

Figure 2.27: Other Stacked designs by Kellogg (a) OrthoflowTM (b) Resid FCC (c) MaxifinTM

Figure 3.1: Methodology block diagram

Figure 3.1 Simplified Stack FCC reactor

Figure 3.2: Process Flow Diagram of Fluid Catalytic Cracking

Figure 3.3: Manual Design PFD of Pilot FCC Unit

Figure 3.4 Flow Streams of Surge Drum (D-01)

Figure 3.5: Flow Streams of Surge Pump (P-01)

Figure 3.6: Flow Streams of FCC Unit Heat Exchanger (E-01)

Figure 3.7: Flow Streams of FCC Unit Heat Exchanger (E-02)

Figure 3.8: Flow Streams of FCC Unit Heat Exchanger (E-03)

Figure 3.9: Flow Streams of FCC Unit Preheater (F-01)

Figure 3.10: Flow Streams of FCC Unit Reactor (R-01)

Figure 3.11: Flow Streams of FCC Unit Main Fractionator (C-01)

Figure 3.12: Flow Streams of FCC Unit Air Fin Cooler (A-01)

Figure 3.13: Flow Streams of FCC Unit overhead Separator (D-02)

Figure 3.14 Hysys Modeled Pilot FCCU

Figure 4.4.1 Mini FCC surge drum

Figure 4.4.1: Mini FCC Surge Drum

Figure 4.4.2 Mini FCC heat exchanger

Figure 4.4.2: Mini FCC Heat Exchanger

Figure 4.4.3 Mini FCC fired heater

Figure 4.4.4 Mini FCC reactor

Figure 4.4.4: Mini FCC Reactor

Figure 4.4.5 Mini FCC main fractionator

Figure 4.4.6 Mini FCC surge drum

Figure 4.4.7 Mini FCC plant layout

Figure 4.5.1 Feed Surge drum

Figure 4.8: FCC Process Flow Control

Figure 4.9: Proposed Feed Pump Instrumentation

Figure 4.10: Proposed Feed Preheater Instrumentation

Figure 4.11: Converter Steam Injection Points

Figure 4.12: Propsed Converter Pressure Tapping Points

Figure 4.13: Proposed Main Fractionator Pressure Control

LIST OF PLATES

Plate I: Pictorial View of Fluid Catalytic Cracking Converter

Plate II: Air Grid in Fabrication Shop

Plate III: Pictorial View of CO Boiler Unit

Plate IV a: Dissected View of FCCU Pilot Plant 3D Diagram

Plate IV b: Dissected View of FCCU Pilot Plant 3D Diagram

Plate IV c: Complete View of FCCU Pilot Plant 3D Diagram

Plate V: Fabricated Surge Drum

Plate VI: Fabricated Heat Exchangers with Red Oxide and Aluminium Spray

PlateVII: Shell and Tube of Overhead Condenser, before and after Red Oxide Spray

Plate VIII: Fabricated Fired Heater, before and after installation on furnance platform

Plate IX: Fabricated Reactor Parts before coupling (a) Stripper (b) 2-Stage Cyclone (c) Riser

Plate X: Fabricated Reactor Parts before coupling (a) Air grid (b) Regenerator (c) Disengager with circmesh

Plate XI: Fabricated Main Fractionator (a) Sieve tray arrangement (b) Sieve tray (c) Column sprayed with Aluminium Coat (d) Column Sprayed with Red Oxide

CHAPTER ONE

INTRODUCTION

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.

1.3 Justification

i. 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:

i. Identify suitable process selection for the Pilot plant

ii. Carry out material and energy balances

iii. Development of a Preliminary design of equipment

iv. Detailed design of Major equipment

v. Plant layout

vi. Instrumentation and control

vii. Fabrication of the Pilot Plant.

1.5 Scope

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.

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