Predicting the products of crude oil distillation columns

138 Pages·3.785 MB·English

by  Liu Jing.

PREDICTING THE PRODUCTS OF
CRUDE OIL DISTILLATION
COLUMNS
A thesis submitted to the University of Manchester
for the degree of Master of Philosophy
in the Faculty of Engineering and Physical Sciences
2012
By
Jing Liu
School of Chemical Engineering and Analytical Science
Contents
Abstract 15
Declaration 17
Copyright 18
Acknowledgements 19
1 Introduction 20
1.1 Features of crude oil distillation systems . . . . . . . . . . . . . . . . . . 21
1.2 Heat integration in crude oil distillation systems . . . . . . . . . . . . . 23
1.3 Motivation and objectives of this work . . . . . . . . . . . . . . . . . . . 25
1.4 Overview of this thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2 Literature Review 27
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2 Shortcut distillation column model . . . . . . . . . . . . . . . . . . . . . 28
2
2.2.1 Total reflux condition (Fenske method) . . . . . . . . . . . . . . 28
2.2.2 Minimum reflux condition (Underwood method) . . . . . . . . . 31
2.2.3 Finite reflux condition and theoretical stages . . . . . . . . . . . 34
2.2.4 Average relative volatility . . . . . . . . . . . . . . . . . . . . . . 35
2.2.5 Extensions and applications of these shortcut methods . . . . . . 36
2.3 Design of crude oil distillation columns . . . . . . . . . . . . . . . . . . . 37
2.3.1 Existing design and analysis of crude oil distillation systems . . . 38
2.3.2 Shortcut models for crude oil distillation columns . . . . . . . . . 40
2.4 Product characteristics for crude oil distillation columns . . . . . . . . . 43
2.4.1 Industry product specifications for crude oil distillation columns 43
2.4.2 Product specifications for shortcut models . . . . . . . . . . . . . 46
2.4.3 Existingmethodsforcharacterizingcrudeoilproductsinshortcut
models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
2.5 Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
3 Shortcut Modelling of Crude Oil Distillation Columns 54
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
3.2 Furtheranalysisonthelimitationsoftheexistingmethodsforconnecting
industry product specifications to those of shortcut models . . . . . . . 55
3.2.1 Effect of reflux ratio on predicting product compositions in
shortcut models. . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.2.2 Algorithm analysis of the existing methods . . . . . . . . . . . . 59
3
3.2.3 Summary and proposal . . . . . . . . . . . . . . . . . . . . . . . 62
3.3 Applying Fenske method to crude oil distillation columns . . . . . . . . 62
3.3.1 Application of Fenske method in simple crude oil distillation
columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.3.2 Illustrativeexample: ApplyingFenskemethodtoasimplesteam-
stripped crude distillation column . . . . . . . . . . . . . . . . . 66
3.3.3 Application of the Fenske method in steam-stripped complex
columns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.3.4 Illustrative example: Applying the Fenske method to a complex
crude oil distillation column (geometric mean α) . . . . . . . . . 72
3.3.5 Illustrative example: Applying the Fenske method to a decom-
posed crude oil distillation column (feed α) . . . . . . . . . . . . 78
3.3.6 Application of the Fenske method in an atmospheric crude
distillation column . . . . . . . . . . . . . . . . . . . . . . . . . . 81
3.3.7 Illustrative example: Applying the Fenske method to an atmo-
spheric distillation column . . . . . . . . . . . . . . . . . . . . . . 81
3.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4 Systematic selection of Fenske parameters and applications 84
4.1 Methodology Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
4.2 Selecting Fenske parameters for simple distillation columns . . . . . . . 85
4.2.1 TBP curve reconstruction . . . . . . . . . . . . . . . . . . . . . . 85
4.2.2 Systematic approach for selecting Fenske parameters of a simple
column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
4
4.2.3 Illustrative example: Applying proposed approach to a simple
distillation column . . . . . . . . . . . . . . . . . . . . . . . . . . 93
4.3 Selecting Fenske parameters for a sequence of simple columns . . . . . . 95
4.3.1 Systematic approach for selecting Fenske parameters of a se-
quence simple columns . . . . . . . . . . . . . . . . . . . . . . . . 95
4.3.2 Illustrative example: Applying proposed approach to a crude oil
distillation column . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.4 Applying proposed approach to optimize a specific product flow rate in
a crude oil distillation column . . . . . . . . . . . . . . . . . . . . . . . . 102
4.5 Applying the proposed approach to optimize the total product income
for a crude oil distillation column . . . . . . . . . . . . . . . . . . . . . . 107
4.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5 Case Studies 113
5.1 Case study 5.1: Profit improvement by maximizing the flow rate of the
most valuable product of a crude oil distillation column . . . . . . . . . 113
5.1.1 Base case data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
5.1.2 Optimization approach and results . . . . . . . . . . . . . . . . . 116
5.2 Casestudy5.2: Maximizingthetotalproductincomeforanatmospheric
distillation column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
5.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
6 Conclusions and future work 124
6.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
5
6.2 Future work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
References 128
A Data for illustrative example 3.3.5 133
B HYSYS-Matlab interface for vapour-liquid equilibrium calculation 135
6
List of Tables
2.1 Method for defining light and heavy components (Gadalla et al., 2003b) 47
3.1 Interpolation method for determining product compositions in the work
of Suphanit (1999) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.2 True boiling point curve data of a crude oil (Watkins, 1979, p.129) . . . 66
3.3 Crude oil compositions in the form of pseudo-component (corresponding
to Table 3.2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.4 Crude oil feed conditions and product specifications . . . . . . . . . . . 67
3.5 Steam conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.6 Selections of key components and recoveries for the simple column in
Figure 3.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
3.7 Simulation specifications for a decomposed crude oil distillation column
(Figure 3.11b) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
3.8 Initial selection of key components for the decomposed columns . . . . . 75
3.9 New selection of key components and recoveries for the decomposed
columns shown in Figure 3.11b (trial and error results) . . . . . . . . . . 75
3.10 Pumparound specifications for the atmospheric distillation column . . . 82
7
3.11 Product property specifications for the atmospheric distillation column . 82
3.12 Selection of key components and recoveries for the atmospheric distilla-
tion column shown in Figure 3.29a (trial and error results) . . . . . . . . 82
3.13 Product property calculations for the atmospheric distillation column
(Fenske results obtained from the specifications in Table 3.12) . . . . . . 82
4.1 Crude oil TBP data (Watkins, 1979) . . . . . . . . . . . . . . . . . . . . 87
4.2 Product specifications for applying the proposed approach to a simple
distillation column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.3 Optimized Fenske parameters for the simple distillation column . . . . 94
4.4 Product specifications for applying the proposed approach to an atmo-
spheric column . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.5 Optimization results with comparison to product specifications . . . . . 99
4.6 Optimized Fenske parameters corresponding to the results in Table 4.5 . 99
4.7 Optimization results and specifications of Chen (2008, Chap. 3) . . . . . 101
4.8 Optimized key components and recoveries of Chen (2008, Chap. 3)
(corresponding to results in Table 4.7) . . . . . . . . . . . . . . . . . . . 101
4.9 Crude oil cost and prices of the product streams obtained from an
atmospheric distillation column (Chen, 2008, p. 145) . . . . . . . . . . . 103
5.1 Case Study: Crude oil TBP data (Watkins, 1979, p. 129) . . . . . . . . 115
5.2 Case Study: Product properties of the base case . . . . . . . . . . . . . 115
5.3 Case Study: Unit prices of all the streams (Chen, 2008, p. 145) . . . . . 115
5.4 Product property results for maximizing the flow rate of heavy gas oil . 116
8
5.5 Optimizedkeycomponentsandrecoveriescorrespondingtoresultsshown
in Table 5.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
5.6 Profit increase of a case study in the work of Chen (2008, p.184) . . . . 118
5.7 Case study: Product constraints for the product income optimization. . 119
5.8 Optimal product results of the product income maximization . . . . . . 121
5.9 Key components and recoveries for the results shown in Table 5.8 . . . . 121
9
List of Figures
1.1 Schematic diagram of crude oil distillation systems . . . . . . . . . . . . 21
1.2 Optimization framework for design of heat-integrated crude oil distilla-
tion systems (Chen, 2008, p. 150) . . . . . . . . . . . . . . . . . . . . . . 24
2.1 Pinch zone locations for binary and multi-component mixtures (adapted
from Smith (2005, p. 167)) . . . . . . . . . . . . . . . . . . . . . . . . . 32
2.2 Decomposition of the atmospheric distillation column (Liebmann, 1996) 39
2.3 ModificationoftheFUGmethodtoovercometheassumptionofconstant
vapour flow rates (adapted from Suphanit (1999)) . . . . . . . . . . . . 41
2.4 True boiling point curve of a crude oil . . . . . . . . . . . . . . . . . . . 44
2.5 Temperaturerelationshipsaroundthecutpointbetweenadjacentfrations
(Watkins, 1979, p. 22) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
2.6 TBPcurvesofacrudeoilanditsfractionsforanatmosphericdistillation
column (Parkash, 2003, p. 4) . . . . . . . . . . . . . . . . . . . . . . . . 46
2.7 Componentdistributionratiosforafractionationcolumn(Alattasetal.,
2011) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2.8 CDU representation for the product planning model using FI method
(Alattas et al., 2011) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
10