Fischer-Tropsch Technology (eBook)

Mark Dry, Andre Steynberg (Herausgeber)

eBook Download: PDF | EPUB

2004 | 1. Auflage
722 Seiten
Elsevier Science (Verlag)
978-0-08-047279-9 (ISBN)

Infos

Fischer-Tropsch Technology is a unique book for its state-of-the-art approach to Fischer Tropsch (FT) technology. This book provides an explanation of the basic principles and terminology that are required to understand the application of FT technology. It also contains comprehensive references to patents and previous publications. As the first publication to focus on theory and application, it is a contemporary reference source for students studying chemistry and chemical engineering. Researchers and engineers active in the development of FT technology will also find this book an invaluable source of information.

* Is the first publication to cover the theory and application for modern Fischer Tropsch technology
* Contains comprehensive knowledge on all aspects relevant to the application of Fischer Tropsch technology
* No other publication looks at past, present and future applications

Inhalt

Cover 1
Foreword 5
Preface 7
Contents 11
Introduction to Fischer-Tropsch Technology 23
Orientation 23
Interest and Challenges 26
The Three Basic Process Steps 29
Synthesis Gas Preparation Depends on the Feedstock 30
FT Synthesis Depends on the Feedstock and the Desired Products 31
Product Upgrading Involves Mainly Separation and Hydroprocessing 32
Patents 39
Catalysts 41
Fused Iron Catalysts 41
Precipitated Iron Catalysts 42
Supported Cobalt Catalysts 43
Fischer-Tropsch Reactors 45
Historical Background 48
German Roots for LTFT 48
American Roots for HTFT 51
Modern Commercial Applications 52
Brief Sasol™ History 54
Slurry Phase Synthesis 68
Modern Reactor Development Achievements 71
Pioneer Technology Development 78
Basic Studies 81
References 84
Credits 85
Fischer-Tropsch Reactors 86
Types of Reaction in Commercial Use 86
Fixed Bed Reactors 88
Slurry Phase Reactors 91
Two Phase Fluidized Bed Reactors (HTFT) 94
Circulating Fluidized Bed Reactor (CFB Reactor) 96
Turbulent Fluidized Bed Reactor (SAS Reactor) 97
Historical Development 99
Early Developments 99
Work in Germany 99
Kaiser-Wilhelm-Instituts Fur Kohlenforschung (KWI) 100
I. G. Farbenindustrie A. G. (Farben) 101
Duftschmid Process 103
Ruhrchemie 104
Summary of Early German Reactors 105
Summary of Later German Developments 106
RheinpreuBetaen (Rheinpreussen) 107
The Netherlands 112
United Kingdom 112
United States 113
U.S. Bureau of Mines 113
Standard Oil (Jersey) (Now ExxonMobil) 115
Texaco (Now ChevronTexaco) 116
Gulf 118
Recently Patented Features 118
Design Approach for Modern Slurry Phase Reactors 121
Text Book Teaching 121
Subsequent Contributions 129
Gas Hold-up Prediction 132
Maximum Stable Bubble Size 135
Effect of Column Dimensions 136
Flow Regimes 137
Scale-up for Slurry Phase Reactors 140
Introduction 141
Experimental Set-up and Results 142
Development of Eulerian Simulation Model 148
Simulation Results for Scale Influence 154
Conclusions from the CFD Investigations 163
Influence of Operation at Elevated Pressures 163
Interphase Mass Transfer 166
Conclusions for Scale-up Strategies 167
Modelling Approaches for Slurry Phase Reactors 167
Recommended Design Approach 172
Fluidization Fundamentals and the Sasol Advanced Synthol (SAS) Reactors 177
Powder Classification Based on Fluidization Properties 177
Fluidization Regimes 179
Potential Changes in Powder Classification during Fluidized Bed Operation 183
Potential Changes in Fluidization Regimes due to Changes in Powder Classification 184
Entrainment 184
Cyclone and Dipleg Operation 185
The Sasol Advanced Synthol Reactors 186
Design and Scale-up of Fluidized Bed FT Reactors 187
Determination of Voidage 190
Gas and Catalyst Mixing 192
Mass Transfer 192
Conversion Prediction 193
Practical Considerations for the Gas Distributor Design 194
The Influence of Internals 194
The Design of Solids Separation Equipment 194
Gas Velocity Limits 195
Design and Scale-up for Multi-Tubular Fixed Bed FT Reactors 196
Text Book Teaching 196
Reactor Modelling 197
Diffusion Limitations 200
Effect of Recycle 202
Design Equations 203
Heat Transfer 203
Pressure Drop 204
Recommended Design Approach 205
Nomenclature 206
Greek 207
Subscripts 207
References 207
Chemical Concepts used for Engineering Purposes 218
Stoichiometry 218
Conversion 221
Selectivity 222
Synthesis Gas Composition and the FT Reactions 222
Conversion and Selectivity Evaluation 224
Primary and Secondary FT Reactions 226
FT Product Distributions 233
Selectivity at Typical Commercial Conditions 245
FT Selectivity Control 249
The Influence of Operating Temperature 250
Catalyst Metal Type and Promoters (Chemical and Structural) 251
Promotion of Cobalt Catalysts 251
Promotion of Iron Catalysts 253
Gas Composition, Partial and Total Pressures 259
Iron Based Catalysts 265
Cobalt Catalysts 275
Production of Oxygenated Products 276
References 277
Synthesis Gas Production for FT Synthesis 280
Introduction 280
Synthesis Gas Preparation Via Reforming 281
Introduction 281
Feedstock Purification 283
Feed Gas Characteristics and Purification Requirements 283
Principles of Gas Desulphurisation 284
Reactions in the Hydrogenator 286
Hydrogenation Catalysts 288
Reactions in the Sulphur Absorber 289
S Absorption Materials 293
Steam Reforming 294
The Reactions 295
Adiabatic Prereforming 296
Reactor Characteristics and Operating Conditions 297
Adiabatic Prereformers in GTL Applications 300
Modelling of Adiabatic Prereformers 302
Design of Steam Reformers 304
Mechanical Design 305
Tube and Burner Arrangement 305
Inlet and Outlet Systems 308
Gas Inlet 308
Gas Outlet 308
Tube Design 310
Burner Characteristics 311
Modelling of the Reformer 311
Simulation of Furnace Chamber 311
Tube Side 312
Reaction Kinetics 314
Physical Properties 314
Heat Flux and Activity 315
Modelling by CFD 316
Design of Heat Exchange Reformers 318
Types of Heat Exchange Reformers 318
Flue Gas Heated Heat Exchange Reformers 319
Heat Exchange Reformers Heated by Process Gas 320
GHR or 'Two-in, Two-out' 320
GHHER or 'Two-in, One-out' 321
Process Concepts 322
Series Arrangements 322
Parallel Arrangements 324
Metal Dusting 326
Steam Reforming Catalysts 327
The Steam Reforming Catalysts 327
Deactivation by Sintering and Poisoning 328
Carbon Formation 330
Fundamental Aspects of the Steam Reforming Reaction 333
Adiabatic Oxidative Reforming 336
Process Concepts 338
Processes Based on Homogeneous Reactions, Gasification or Partial Oxidation (POX) 341
Processes Based on Heterogeneous Reactions. Catalytic Partial Oxidation (CPO) 342
Processes Based on Combined Homogeneous and Heterogeneous Reactions. Autothermal Reforming (ATR) and Secondary Reforming 342
ATR 342
Secondary Reforming 346
Autothermal Reforming 348
Chemical Reactions 348
Combustion Chemistry 350
Ignition 351
N-Chemistry 353
ATR Process and Reactor Design 354
The ATR Burner and Combustion Chamber 355
Vessel and Refractory 357
Catalyst Bed 358
Catalyst Deactivation in ATR Operation 359
Modelling 360
Computational Fluid Dynamics 360
Chemical Kinetic Modelling 362
Combined Modelling of Flow and Chemistry 363
Fixed Bed Simulation of the Catalytic Bed 365
Autothermal Reforming (ATR) in GTL Applications 366
Industrial Operation at Low H2O/C Ratio 367
Development and Demonstration at PDU-Scale 367
ATR Process Performance Tests Related to GTL Applications 369
Other Technologies 370
Catalytic Partial Oxidation 371
Oxygen Membrane Reforming 374
Synthesis Gas Preparation Via Gasification 375
Introduction 375
Possible Applications for Gasification Processes 376
Integrated Gasification Combined Cycle (IGCC) 377
Characteristics of Coal Important for Gasification 381
Gasification Chemistry 382
Classification of Gasifiers 385
Fixed Bed Gasifiers 390
Sasol-Lurgi Fixed Bed Dry Bottom Gasifier 393
British Gas Lurgi (BGL) Slagging Gasifier 397
Fluidized Bed Gasifiers 398
KRW Fluidized Bed Gasifier 400
The High Temperature Winkler (HTW) Gasifier 402
The Transport Gasifier 404
Entrained Flow Gasifiers 405
Texaco Gasifier 408
Shell Gasifier 411
Lurgi Multi-Purpose Gasifier (MPG) 413
E-Gas Two-Stage Gasifier 415
Combinations of Sasol-Lurgi and Entrained Flow Gasifiers 417
Particulate Removal 419
References 419
Commercial FT Process Applications 428
Feedstock and Technology Combinations 428
Alternative Routes for the Production of Fuels and Chemicals 430
Commercial FT Plants 435
Sasol (Sasolburg and Secunda, South Africa) 435
PetroSA/Mossgas (Mossel Bay, South Africa) 439
Shell SMDS (Bintulu, Malaysia) 440
Introduction to the Gas Loop 442
Gas Loop for HTFT Synthesis with a Sasol-Lurgi Fixed Bed Coal Gasifier 442
Advanced Gas Loop Design Considerations 444
Gas Loop for HTFT Synthesis with High Temperature Gasification of Carbon Rich Feedstocks 446
Gas Loop for LTFT Synthesis Using Iron Catalysts 448
Gas Loop for HTFT with Natural Gas Feed 449
Gas Loop for LTFT Cobalt Catalyst with Natural Gas Feed 452
Synthesis Gas at the Consumption Ratio 453
Synthesis Gas below the Usage Ratio 455
Technology Targets for Gas to Liquids (GTL) Applications 458
Carbon Losses 459
Ways to Avoid Carbon Losses 460
Avoiding Reformer CO2 Production 460
Potential to Decrease Capital Costs 463
Technology Targets 464
Expected Future Plant Configurations for Natural Gas Conversion 465
Overall Capital Cost 465
Equipment and Process Reliability 469
Desired Products 470
Options for the Production of High Value Hydrocarbons 470
Lower Olefins from Naphtha 471
Detergent Alkylates and Paraffin Processing 472
Lubricant Base Oils 472
Light Olefins 473
Combined LTFT and HTFT 473
The Simplified HTFT Chemical Hub Concept 474
Conclusions for the Production of High Value Hydrocarbons 474
Coal Conversion Using FT Technology 476
Combined Production of Hydrocarbon Liquid and Electrical Power 478
Cases Studied 480
Discussion of the Results 482
Coal Conversion Using Sasol-Lurgi Gasifiers 487
Comparison with the Use of Remote Natural Gas 491
Conclusions for Coal Conversion Using FT Technology 492
Environmental Aspects 492
Fischer-Tropsch Reaction Water Treatment 498
Environmental Issues for Coal based Plants 499
References 501
Processing of Primary Fischer-Tropsch Products 504
Introduction 504
Historical Perspective 505
Upgrading of High Temperature Fischer-Tropsch(HTFT) Products 508
Influence of Feed Properties on Refining Approach 508
Hetero-Atom Constraints 509
Petrol Component Properties 509
HTFT Diesel Properties 510
Carbon Number Distribution 511
HTFT Fuels Refining 511
C3 Hydrocarbons 512
C4 Hydrocarbons 513
C5 Hydrocarbons 514
C6 Hydrocarbons 515
C7 Hydrocarbons 516
C8 Hydrocarbons 517
C9-C10 Hydrocarbons 518
C11-C22 Hydrocarbons 518
Heavier than C22 Hydrocarbons 519
Refinery Integration 520
Tar Integration 521
Natural Gas Integration 521
LTFT and HTFT Integration 522
Oil Integration 522
Other Integration Schemes 523
The Future of HTFT Refining 523
Upgrading of Low Temperature Fischer-Tropsch Products 525
Characterisation of the Primary LTFT Products 525
LTFT Primary Product Refining 526
Hydrocracking of Heavy Paraffins 528
Hydrotreating of FT Paraffins 529
Catalytic Dewaxing / Hydroisomerisation 530
Hydroprocesssing Catalysts for LTFT Primary Products 531
Basic Concepts 531
Catalyst Carriers 532
Metal Components 533
Hydroprocessing Flow Sheet Options to Produce Diesel 533
Alternative Process Options 536
Characteristics of the LTFT Distillate Products 536
LTFT Diesel 536
LTFT Diesel as a Blending Component 540
LTFT Diesel Fuel Performance 540
LTFT Diesel Environmental Characteristics 542
LTFT Diesel Product Applications 542
LTFT Naphtha 542
LTFT Naphtha as Petrochemical Feedstock 543
LTFT Naphtha Fuel Performance 547
LTFT Naphtha as a Blending Component 547
Other Applications for LTFT Products 549
Large Scale Production of High Value LTFT Products 549
References 550
FT Catalysts 555
Introduction 555
Catalyst Preparation and Characterisation 555
Iron Based Catalysts 555
Low Temperature Catalysts for Wax Production (LTFT) 555
Preparation and Characterisation 555
Reduction and Conditioning of Precipitated Iron LTFT Catalysts 560
Iron Based Catalysts for High Temperature Synthesis (HTFT) 562
Catalyst Preparation and Characterisation for the HTFT Process 562
Reduction and Conditioning of Fused Iron Catalysts 568
Carbon Deposition on HTFT Iron Catalysts 571
Alternative Iron Based Catalysts 576
Phase Changes of Iron Catalysts during FT Synthesis 577
Cobalt Based Catalysts for LTFT Operation 580
Preparation of Cobalt Catalysts 580
Metal Catalysts other than Cobalt or Iron 588
Catalyst Deactivation during FT Synthesis 588
Poisoning by Sulphur and other Compounds 589
Deactivation of Iron FT Catalysts 590
Low Temperature FT (LTFT) Operation 590
Handling of Spent LTFT Iron Catalyst 594
High Temperature FT (HTFT) Operation 595
Deactivation of Cobalt Catalysts 597
Recent Co Catalyst Patents 600
FT Kinetics 605
Iron Catalysts 606
Cobalt Kinetics 614
Comparison of the FT Activity of Iron and Cobalt Catalysts 615
References 618
Basic Studies 623
Surface Species, Reaction Intermediates and Reaction Pathways in the Fischer-Tropsch Synthesis 623
Surface Species and Reaction Intermediates 623
Reaction Pathways in the Fischer-Tropsch Synthesis 627
'Alkyl' Mechanism 627
'Alkenyl' Mechanism 631
'Enol' Mechanism 632
'CO-insertion' Mechanism 634
Rate of Co-consumption in the FT Synthesis 635
Rate of CO Consumption for the Formation of Organic Products 636
CO2 Formation 644
Product Distributions 645
Products of Fischer-Tropsch Synthesis 645
Basic Model: Ideal Chain Growth with One Sort of Products 646
Ideal Chain Growth: Desorption as Olefin and Paraffin 650
Deviations from Ideal Distributions: Secondary Reactions of Olefins 652
Diffusion Enhanced Olefin Readsorption Model 655
Effect of Solubility on Olefin Readsorption 661
Background 661
Extended Model 665
Analogue Models 675
Effects of Process Parameters on Olefin Reactions 676
Formation and Readsorption of Oxygenates 679
Formation of Branched Products 681
Non Ideal Distributions Due to Several Growth Sites or Mechanisms 686
Controlling Selectivity in the FT Synthesis 688
Branched Compounds 693
Formation of Specific Product Classes 696
References 698
Index 703
Studies in Surface Science and Catalysis 713

Textauszug

Studies in Surface Science and Catalysis, Vol. 152, Suppl. (C), 2004

ISSN: 0167-2991

doi: 10.1016/S0167-2991(04)80459-2

Chapter 2 Fischer-Tropsch Reactors

A.P. Steynberga

a Sasol Technology R&D, P.O. Box 1, Sasolburg, 1947, South Africa

M.E. Dry, B.H. Davis, B.B. Breman

1 TYPES OF REACTOR IN COMMERCIAL USE

There are four types of Fischer-Tropsch (FT) reactor in commercial use at present. Three broad categories of catalyst are used in these reactors. The four types of reactor are:

• Circulating fluidized bed reactor

• Fluidized bed reactor

• Tubular fixed bed reactor

• Slurry phase reactor

The fluidized bed reactors operate in the temperature range 320 °C to 350 °C. This temperature range is 100 °C higher than the typical operating temperature range used with the reactors shown on the right hand side of Fig. 1 of around 220 to 250 °C. Hence the term high temperature Fischer-Tropsch (HTFT) used to describe the reactors on the left hand side and the term low temperature Fischer-Tropsch used to describe the reactors on the right hand side of Fig. 1.

Figure 1 Types of FT reactor in commercial use

The key distinguishing feature between the HTFT and LTFT reactors is the fact that there is no liquid phase present outside the catalyst particles in the HTFT reactors. Formation of a liquid phase in the HTFT fluidized bed reactors will lead to serious problems due to particle agglomeration and loss of fluidization, [1, 2]. It was postulated by Caldwell [3] that reactors will be prone to waxing if the Anderson-Schulz-Flory (ASF) plot intersects the vapour pressure plot. These concepts are explained in more detail in Chapter 3. The slope (α) of the ASF plot is a measure of the chain-growth probability for the production of hydrocarbon products. The catalyst and operating conditions may be selected to obtain the desired chain-growth probability (α) or, in other words, the desired product spectrum.

The four reactor types are illustrated in Fig. 1.:

Table 1 shows the minimum temperature at which the reactor can operate to maximize a given hydrocarbon cut. For a given target α value, this determines the lower end of the feasible temperature range. This means that fluidized bed reactors cannot be used for maximized production of products heavier than the gasoline/naphtha cut [4]. At the upper end of the feasible temperature range, the typical catalysts used for fluidized bed reactors cannot operate much above 350°C without excessive carbon formation.

Table 1 Chain-growth probabilities (α) to maximize various product cuts and the minimum reactor temperature required to avoid a liquid phase [4]

Cut maximized (by mass fraction)	α	Minimum temperature to avoid liquid condensation (°C)

C2 − C5

0.5081

109

C5 − C511

0.7637

329

C5 − C18

0.8164

392

C12 − C18

0.8728

468

The LTFT reactors are shown on the right hand side of Fig. 1. Heavy hydrocarbons in the form of liquid wax are present in these reactors.

Either precipitated iron catalysts or supported cobalt catalysts may be used in LTFT reactors. The choice of catalyst will be discussed in more detail later. At this point, note that commercial scale reactors exist or are under construction using both types of catalyst in both types of LTFT reactor.

Fluidized bed reactors are subdivided into two-phase (solid and gas), HTFT and three phase (solid, liquid and gas), LTFT systems. When the main objective is the production of long chain waxes the LTFT process is used and either multi-tubular fixed bed or three phase fluidized bed slurry reactors can be considered. For the HTFT process where alkenes and/or straight run fuels are the main products then only two phase fluidized systems are used.

Both types of HTFT reactor, shown on the left and side of Fig. 1, are also currently in commercial operation. The circulating fluidized bed (CFB) reactors are in use at the world’s largest GTL plant in Mossel Bay, South Africa. The Sasol Advanced Synthol (SAS) reactors are used at the world’s largest synthetic hydrocarbon plant which is based on coal derived synthesis gas in Secunda, South Africa. This is the reactor of choice for future HTFT applications.

Compared to many industrial operations the FT reaction is highly exothermic. The average heat released per ‘CH2’ formed is about 145 kJ [5]. This is an order of magnitude higher than typical catalytic reactions in the oil refining industry. Any increase in the operating temperature of the FT synthesis will result in an undesirable increase in the production of methane and may result in catalyst damage. For HTFT in particular, high temperatures result in excessive carbon deposition. It is therefore very important that the rate of heat transfer from the catalyst particles to the heat exchanger surfaces in the reactor is high in order to maintain near-isothermal conditions inside the catalyst beds.

1.1 Fixed bed reactors

Vertical spaced packed bed and radial flow reactors with cooling between the beds are not satisfactory because of the negative effects of temperature rises within each individual adiabatic bed. The preferred fixed bed reactor type is multi-tubular with the catalyst placed inside the tubes and cooling medium (water) on the shell sides. Having a short distance between the catalyst particles and the tube walls (by using narrow tube diameters) and operating at high gas linear velocities, to ensure turbulent flow, greatly improves the transfer of the heat of reaction from the catalyst particles to the cooling medium. In order to achieve high percent conversions of the fresh feed gas it is common practice to recycle a portion of the reactor tail gas. This practise also of course increases the linear velocity through the reactor and hence further increases the rate of heat transfer. Recycle of liquid hydrocarbon product is also known to improve the temperature profile in the fixed catalyst bed.

The smaller the catalyst pellets or extrudates used the higher are the conversions achieved (Chapter 7). The combination of narrow tubes, high gas velocities and small particles, however, will result in unacceptably high differential pressures over the reactor. This will increase gas compression costs and also could cause disintegration of weak catalyst pellets. Catalyst loading and unloading may also become troublesome with narrow tubes. For all the above reasons compromises have to be made between the opposing operating and design factors. The activity of the catalyst employed also has to be taken into account. For iron based catalysts 5 cm ID tubes are satisfactory but with the more active cobalt catalysts it is more difficult to control the bed temperatures. Thus the more active the catalyst the narrower the tubes should be.

Because of the abovementioned compromises that need to be made there will inevitably be radial as well as axial temperature gradients in the reactor tubes. In the case of iron based catalysts the axial gradient will be much more marked than in the case of cobalt based catalysts because for iron catalysts the rate of the FT reaction decreases much faster with bed length. As a result of this only a portion of the catalyst bed will operate at the optimum temperature, the other sections being either at lower or higher temperatures. Multi-tubular reactors are usually not suitable for high temperature FT operations. For iron based catalysts for instance, carbon deposition occurs at higher temperatures [6] and this will result in catalyst swelling and blockage of the reactor tubes. Large multi-tubular reactors can consist of thousands of tubes. This results in high construction costs. Such reactors are very heavy and this limits the size to which they can be scaled up as transportation can become the limiting factor. The design of the tube-sheets (the plates at either end through which the tubes pass) becomes very challenging for large scale reactors.

Despite the above disadvantages these reactors do have some advantages. They are easy to operate. There is no equipment required to separate the heavy wax products from the catalyst since the liquid wax simply trickles down the bed and is collected in a downstream knock-out pot. For slurry bed reactors additional equipment is required to achieve the complete separation of the finely divided catalyst from the liquid wax. The most important advantage, for the fixed bed multi-tubular reactor, is that the performance of a large scale commercial reactor can be predicted with relative certainty based on the performance of a pilot unit consisting of a single reactor tube.

For coal derived syngas, temporary slippage of catalyst poisons such as H2S through the gas purification section is likely to occur. In the case of multi-tubular reactors this will result in only the upper sections of catalyst being deactivated leaving the balance of the catalyst bed relatively...

Produkt-Details

• Erscheint lt. Verlag: 30.10.2004
• Sprache: englisch
• Themenwelt: Sachbuch/Ratgeber
• Themenwelt: Naturwissenschaften ► Chemie ► Technische Chemie
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Umwelttechnik / Biotechnologie
• ISBN-10: 0-08-047279-6 / 0080472796
• ISBN-13: 978-0-08-047279-9 / 9780080472799