Fluid Catalytic Cracking Handbook (eBook)

An Expert Guide to the Practical Operation, Design, and Optimization of FCC Units

Reza Sadeghbeigi (Autor)

eBook Download: PDF | EPUB

2000 | 2. Auflage
352 Seiten
Elsevier Science (Verlag)
978-0-08-050659-3 (ISBN)

Infos

This thoroughly updated edition of Fluid Catalytic Cracking Handbook provides practical information on the design, operation, troubleshooting, and optimization of fluid catalytic cracking (FCC) facilities. Based on the author's years of field experience, this expanded, second edition covers the latest technologies to improve the profitability and reliability of the FCC units, and provides several no-to-low-cost practical recommendations. A new chapter supplies valuable recommendations for debottlenecking and optimizing the performance of cat cracker operations.

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This thoroughly updated edition of Fluid Catalytic Cracking Handbook provides practical information on the design, operation, troubleshooting, and optimization of fluid catalytic cracking (FCC) facilities. Based on the author's years of field experience, this expanded, second edition covers the latest technologies to improve the profitability and reliability of the FCC units, and provides several "e;no-to-low-cost"e; practical recommendations. A new chapter supplies valuable recommendations for debottlenecking and optimizing the performance of cat cracker operations.

Inhalt

Front Cover 1
Fluid Catalytic Crackivg Handbook: Design, Operation and Troubleshooting of FCC Facilities 4
Copyright Page 5
Contents 8
Acknowledgments 12
Preface to the Second Edition 13
Chapter 1. Process Description 16
Chapter 2. FCC Feed Characterization 55
Chapter 3. FCC Catalysts 99
Chapter 4. Chemistry of FCC Reactions 140
Chapter 5. Unit Monitoring and Control 154
Chapter 6. Products and Economics 197
Chapter 7. Project Management and Hardware Design 221
Chapter 8. Troubleshooting 249
Chapter 9. Debottlenecking and Optimization 291
Chapter 10. Emerging Trends in Fluidized Catalytic Cracking 322
Appendix 1. Temperature Variation of Liquid Viscosity 353
Appendix 2. Correction to Volumetric Average Boiling Point 354
Appendix 3. TOTAL Correlations 355
Appendix 4. n-d-M Correlations 356
Appendix 5. Estimation of Molecular Weight of Petroleum Oils from Viscosity Measurements 357
Appendix 6. Kinematic Viscosity to Saybolt Universal Viscosity 359
Appendix 7. API Correlations 360
Appendix 8. Definitions of Fluidization Terms 362
Appendix 9. Conversion of ASTM 50% Point to TBP 50% Point Temperature 365
Appendix 10. Determination of TBP Cut Points from ASTM D-86 366
Appendix 11. Nominal Pipe Sizes 368
Conversion Factors 370
Glossary 372
Index 378
About the Author 384

Textauszug

CHAPTER 2 FCC Feed Characterization

Refiners process many different types of crude oil. As market conditions and crude quality fluctuate, so does cat cracking feedstock. Often the only constant in FCC operations is the continual change in feedstock quality.

Feed characterization is the process of determining the physical and chemical properties of the feed. Two feeds with similar boiling point ranges may exhibit dramatic differences in cracking performance and product yields.

FCC feed characterization is one of the most important activities in monitoring cat cracking operation. Understanding feed properties and knowing their impact on unit performance are essential. Troubleshooting, catalyst selection, unit optimization, and subsequent process evaluation all depend on the feedstock.

Feed characterization relates product yields and qualities to feed quality. Knowing the effects of a feedstock on unit yields, a refiner can purchase the feedstock that maximizes profitability. It is not uncommon for refiners to purchase raw crude oils or FCC feedstocks without knowing their impact on unit operations. This lack of knowledge can be expensive.

Sophisticated analytical techniques, such as mass spectrometry, are not practical for determining complete composition of FCC feedstocks on a routine basis. Simpler empirical correlations are more often used. They require only routine tests commonly performed by the refinery laboratory. They are excellent alternatives, but they have their limitations:

• They are usually intended for an olefin-free feed.

• They cannot distinguish among different paraffinic molecules.

• They cannot segregate an aromatic compound that may also contain a paraffinic and naphthenic structure group.

Nevertheless, these correlations are very practical tools for tracking unit performance and for troubleshooting. They are also important in process design and catalyst research.

The two primary factors that affect feed quality are:

• Hydrocarbon Classification

• Impurities

HYDROCARBON CLASSIFICATION

The hydrocarbon types in the FCC feed are broadly classified as paraffins, olefins, naphthenes, and aromatics (PONA).

Paraffins

Paraffins are straight or branched chain hydrocarbons having the chemical formula CnH2n+2. The name of each member ends with –ane; examples are propane, isopentane, and normal heptane (Figure 2-1).

Figure 2-1 Examples of paraffins.

In general, FCC feeds are predominately paraffinic. The paraffinic carbon content is typically between 50 wt% and 65 wt% of the total feed. Paraffinic stocks are easy to crack and normally yield the greatest amount of total liquid products. They make the most gasoline and the least fuel gas, but also the lowest octane number.

Olefins

Olefins are unsaturated compounds with a formula of CnH2n. The name of these compounds ends with –ene, such as ethene (ethylene) and propene (propylene). Figure 2-2 shows typical examples of olefins. Compared to paraffins, olefins are unstable and can react with themselves or with other compounds such as oxygen and bromine solution. Olefins do not occur naturally; they show up in the FCC feed as a result of preprocessing the feeds elsewhere. These processes include thermal cracking and other catalytic cracking operations.

Figure 2-2 Examples of olefins.

Olefins are not the preferred feedstocks to an FCC unit. This is not because olefins are inherently bad, but because olefins in the FCC feed indicate thermally produced oil. They often polymerize to form undesirable products, such as slurry and coke. The typical olefin content of FCC feed is less than 5 wt%, unless unhydrotreated coker gas oils are being charged.

Naphthenes

Naphthenes (CnH2n) have the same formula as olefins, but their characteristics are significantly different. Unlike olefins that are straight-chain compounds, naphthenes are paraffins that have been “bent” into a ring or a cyclic shape. Naphthenes, like paraffins, are saturated compounds. Examples of naphthenes are cyclopentane, cyclohexane, and methylcyclohexane (Figure 2-3).

Figure 2-3 Examples of naphthenes.

Naphthenes are desirable FCC feedstocks because they produce high-octane gasoline. The gasoline derived from the cracking of naphthenes has more aromatics and is heavier than the gasoline produced from the cracking of paraffins.

Aromatics

Aromatics (CnH2n-6) are similar to naphthenes, but they contain a resonance stabilized unsaturated ring core. Aromatics (Figure 2-4) are compounds that contain at least one benzene ring. The benzene ring is very stable and does not crack to smaller components. Aromatics are not a preferred feedstock because few of the molecules will crack. The cracking of aromatics mainly involves breaking off the side chains resulting in excess fuel gas yield. In addition, some of the aromatic compounds contain several rings (polynuclear aromatics) than can “compact” to form what is commonly called “chicken wire.” Figure 2-5 illustrates three examples of a polynuclear aromatic compound. Some of these compacted aromatics will end up on the catalyst as carbon residue (coke), and some will become slurry product. In comparison with cracking paraffins, cracking aromatic stocks results in lower conversion, lower gasoline yield, and less liquid volume gain, but with higher gasoline octane.

Figure 2-4 Examples of aromatics.

Figure 2-5 Examples of a polynuclear aromatic molecules.

FEEDSTOCK PHYSICAL PROPERTIES

Characterizing an FCC feedstock involves determining both its chemical and physical properties. Because sophisticated analytical techniques, such as mass spectrometry, are not practical on a daily basis, physical properties are used. They provide qualitative measurement of the feed’s composition. The refinery laboratory is usually equipped to carry out these physical property tests on a routine basis. The most widely used properties are:

• °API Gravity

• Distillation

• Aniline Point

• Refractive Index (RI)

• Bromine Number (BN) and Bromine Index (BI)

• Viscosity

• Conradson, Ramsbottom, Microcarbon, and Heptane Insoluble

°API Gravity

The °API gravity measures the density of a hydrocarbon liquid. Specific gravity (SG) is another common measurement of density. The liquid SG is the relative weight of a volume of sample to the weight of the same volume of water at 60°F (15.5°C).

Compared with specific gravity, °API gravity magnifies small changes in the feed density. For example, going from 24°API to 26°API changes the specific gravity by 0.011 and the density by 0.72 lb/ft3 (0.0115 gram/cm3). Neither is very significant, but a two-number shift in °API gravity can have significant effects on yields.

The SG relates to °API gravity by the following equations:

Since °API gravity is inversely proportional to specific gravity, the higher the °API gravity, the lighter the liquid sample. In petroleum refining, °API gravity is routinely measured for every feed and product stream. The ASTM D-287 is a hydrometer test typically performed by a lab technician or unit operator. The method involves inserting a glass hydrometer into a cylinder containing the sample and reading the °API gravity and the fluid temperature on the hydrometer scale. Standard tables similar to Table 2-1 convert the °API at any temperature back to 60°F. The °API gravity is always reported at 60°F (15.5°C).

Table 2-1 °API Gravity at Observed Temperature

For a highly paraffinic (waxy) feed, the sample should be heated to about 120°F (49°C) before immersing the hydrometer for testing. Heating ensures that the wax is melted, eliminating erroneous readings.

Daily monitoring of °API gravity provides the operator with a tool to predict changes in unit operation. For the same distillation range, the 26°API feed cracks more easily than the 24°API feed because the 26°API feed has more long-chain paraffinic molecules. In contact with the 1,300°F (704°C) catalyst, these molecules are easier to rupture into valuable products.

Long straight-chain paraffins are important to the economics of an FCC unit. They crack easily to gasoline and LPG, with minimal production of slurry and fuel gas.

The simple °API gravity test provides valuable information about the quality of a feed. But the shift in...

Produkt-Details

• Erscheint lt. Verlag: 8.6.2000
• Sprache: englisch
• Themenwelt: Mathematik / Informatik ► Mathematik
• Themenwelt: Naturwissenschaften ► Chemie ► Analytische Chemie
• Themenwelt: Naturwissenschaften ► Chemie ► Technische Chemie
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Weitere Fachgebiete ► Land- / Forstwirtschaft / Fischerei
• ISBN-10: 0-08-050659-3 / 0080506593
• ISBN-13: 978-0-08-050659-3 / 9780080506593