Energy concept for future oil refineries with
an emphasis on separation processes
Antonio Brandão
Department of Chemical Engineering
Federal University of Campina Grande
Campina Grande, Paraiba
December 2011
1
About this presentation
• Motivation:
– Focus on environmental aspects in oil refining is not enough ([Szklo 2007],
[DOE 2000]).
– Energy-efficient processes in oil refining are paramount.
– Need for research in this field is a must.
– Important literature:
• U.S. DOE, Energy Bandwidth for Petroleum Refining Processes, Office of Energy
Efficiency and Renewable Energy, Office of Industrial Technologies, 2006.
• Szklo, A., Schaeffer, R., Fuel specification, energy consumption and CO2 emission
in oil refineries, Energy 32, 1075–1092, 2007.
• Focus:
– What’s up on the future of energy consumption in oil refineries.
– Opportunities: Attempt to give directions, not specific solutions for particular
problems (e.g., impact of sulfur reduction in diesel and/or gasoline).
– Looking at the big picture: Not restricted to separation processes.
• Goal:
2
– Attempting to show what one can expect in terms of more energy-efficient
refineries in the long run.
About this presentation
• Let’s tear things down:
Energy concept = Energy efficiency.
Keep it simple!
Energy concept for
future refineries.
Splitter
Directions will
be given but
problems won’t
be solved here!
Future = Next 20 years???
Nothing futuristic! No revolution!
• Directions will be given… Well, it cannot be different since there are
lots of alternatives to consider. But details won’t be discussed here!
−
3
You may try, e.g., Oil Refining Industry - Process Flow - Data Sheets.pdf, for
specifics.
Outline
1.
2.
3.
4.
A vision for the future
A simple guide to oil refining
Energetic issues in an oil refinery
Thermodynamic analysis and measures to improve energy consumption.
•
•
•
•
•
•
Crude oil distillation (atmospheric and vacuum)
Fluid catalytic cracking
Catalytic hydrotreating
Catalytic reforming
Alkylation
Hydrogen generation
5. Separation processes
6. Recap and future directions
7. References
4
A vision for the future
•
5
According to the API’s Technology Vision 2020: A Technology Vision for
the U.S. Petroleum Refining Industry [API 2000] report,
–
“The petroleum industry of the future will be environmentally sound, energyefficient, safe and simpler to operate. It will be completely automated,
operate with minimal inventory, and use processes that are fundamentally
well-understood. Over the long term, it will be sustainable, viable, and
profitable, with complete synergy between refineries and product
consumers”.
–
“To improve energy and process efficiency, the industry will strive to use
cost-effective technology with lower energy-intensity. Refineries will
integrate state-of-the-art technology (e.g., separations, catalysts, sensors and
controls, biotechnology) to leapfrog current refinery practice and bring
efficiency to new levels”.
Outline
1.
2.
3.
4.
A vision for the future
A simple guide to oil refining
Energetic issues in an oil refinery
Thermodynamic analysis and measures to improve energy consumption.
•
•
•
•
•
•
Crude oil distillation (atmospheric and vacuum)
Fluid catalytic cracking
Catalytic hydrotreating
Catalytic reforming
Alkylation
Hydrogen generation
5. Separation processes
6. Recap and future directions
7. References
6
A simple guide to oil refining
•
According to the North American Industry Classification System
(NAICS) [DOE 2006], petroleum refineries are defined as:
Establishments primarily engaged in refining crude petroleum into
refined petroleum.
Picture of the oil
refinery of the
future, if the oil
consumption
maintains its
forever growing
pace…
Actually, this is a
1876 oil refinery
in California.
7
A simple guide to oil refining [Exxon 2005]
8
A simple guide to oil refining
•
In short:
–
–
–
–
–
–
9
Everything is upgraded to valuable products: More fuel!
Over 43% of production is gasoline.
C.a. 80% is converted to fuel.
It is a huge, extremely complex process facility!!!
Lots of reactions and separations to add value to the products.
Many opportunities for energy savings.
Outline
1.
2.
3.
4.
A vision for the future
A simple guide to oil refining
Energetic issues in an oil refinery
Thermodynamic analysis and measures to improve energy consumption.
•
•
•
•
•
•
Crude oil distillation (atmospheric and vacuum)
Fluid catalytic cracking
Catalytic hydrotreating
Catalytic reforming
Alkylation
Hydrogen generation
5. Separation processes
6. Recap and future directions
7. References
10
Energetic issues in an oil refinery ([DOE 2000],
[Pellegrino 2005])
Energy by source in an oil refinery
Other
7%
Electricity
5%
Natural gas
25%
Refinery
gas
46%
Petroleum
coke
17%
•
•
•
11
•
Refinery gas + petroleum coke + other oil-based by-products accounts for
65% of the energy sources in an oil refinery.
38% of the energy sources in an oil refinery are used to produce non-fuel
products like lubricant oils, wax, asphalt, and petrochemical feedstocks.
Oil refineries generate large amounts of electricity on-site. In the U.S.,
over 40% (1994) of electricity in refineries are on-site generated.
The cost of energy for heat and power accounts for c.a. 40% of the
operating costs in a refinery!!!
Energetic issues in an oil refinery [DOE 2007]
12
Energetic issues in an oil refinery [DOE 1998]
•
•
•
•
•
•
•
13
According to the NAICS (The North American Industry Classification
System), petroleum refineries consumed 3.1 quadrillion Btu (fuel use
alone) in 2002, almost 20% of the fuel energy consumed by the U.S..
From the Table, c.a. 31% is consumed in two distillation processes.
As expected, hydrotreating is also very high, 15% alone.
Hydrogen generation is yet another high energy consumption process.
Large amounts of energy are consumed as fuel, while the rest is
basically steam.
The bullets represent units prone to be “optimized” energetically as they
represent approx. 86% of the energy consumed by the refining process.
We will focus on these units.
Energetic issues in an oil refinery [Worrell 2005]
14
Energetic issues in an oil refinery
15
Energetic issues in an oil refinery [DOE 2000]
•
Future characteristics of oil refineries in terms of energy use:
–
Energy use is optimized throughout the refinery complex (“plantwide energy
optimization”).
– Energy efficiency and process control are integrated (“plantwide process
control”).
– Fouling of heat exchangers is essentially eliminated.
– Innovative heat exchangers are in place (all helical, vertical, no baffles)
– Use of cogeneration in refineries is optimized, and refineries are power
producers.
– Use of very energy-intensive processes (e.g., distillation, furnaces) is
mitigated.
– Source of heat loss (e.g., in pipes) are easily identified through monitoring.
•
How?
–
–
16
Identify entirely new technologies.
Upgrade existing inefficient technologies.
Energetic issues in an oil refinery [DOE 2000]
17
• Replacing the
conventional
energy-intensive
separation processes
has a tremendous
impact on energy
consumption.
• Waste recovery in
the short term.
• Fouling mitigation
and new refining
processes in the mid
and long terms.
• Membrane is the
first step.
• Catalytic distillation
is in the mid run.
• Long run:
distillation beyond
membrane.
• [Pelegrino 1999]
say the target is
15-20% energy
reduction for U.S.
refineries.
0-3 years
3-10 years
10-20 years
Distillation
roadmap
Outline
1.
2.
3.
4.
A vision for the future
A simple guide to oil refining
Energetic issues in an oil refinery
Thermodynamic analysis and measures to improve energy consumption.
•
•
•
•
•
•
Crude oil distillation (atmospheric and vacuum)
Fluid catalytic cracking
Catalytic hydrotreating
Catalytic reforming
Alkylation
Hydrogen generation
5. Separation processes
6. Recap and future directions
7. References
18
Thermodynamic analysis… [DOE 2006]
•
•
•
Remember the 6 processes with the largest energy consumption?
A thermodynamic analysis of these 6 processes is performed here.
Three measures are defined:
–
–
–
•
TW = Theoretical Work: The least amount of energy that a process would
require under ideal conditions. E.g., for separation processes it is basically the
sensible and latent heat of each component in the mixture considered as an
ideal solution, and for reaction systems the heat of reaction under 100%
selectivity at equilibrium conditions.
CW = Current Work: Energy consumed under actual plant conditions where
energy losses from inefficient or outdated equipment and process design, poor
heat integration, and poor conversion and selectivities, among other factors are
considered. Source: USA DOE.
PW = Practical Work: Minimum energy required to run the process in realworld, non-standard conditions by applying cutting edge technologies still on
the drawing board. The savings are then deducted from the CW requirement.
Therefore, the maximum potential for energy savings can be quantified by
PI (Potential Improvement) = CW (Current Work) – PW (Practical Work)
19
Crude oil distillation (atmospheric and vacuum)
•
Atmospheric distillation:
–
–
–
•
Vacuum distillation:
–
–
–
–
20
It is the heart of the refinery.
It produces a range of products, from LPG to heavy crude residue.
High temperature (bottom 600oC), low pressure (near atmospheric) process.
It has heavy crude (high boiling point) as feedstock.
It must then be conducted at vacuum conditions.
It produces light and heavy gas oil and asphalt (or resid).
These products are upgraded.
Crude oil distillation (atmospheric and vacuum)
21
Crude oil distillation (atmospheric and vacuum)
•
Atmospheric distillation energetic assessment [DOE 2006]:
–
–
–
–
22
Theoretical work
Current work
Practical work
Potential improvement
= 22 x 103 Btu/bbl feed
= 114 x 103 Btu/bbl feed
= 50 x 103 Btu/bbl feed
= 64 x 103 Btu/bbl feed
Note: Electricity losses incurs during the
generation, transmission, and distribution
of electricity.
Crude oil distillation (atmospheric and vacuum)
•
Atmospheric distillation energetic assessment [DOE 2006]:
–
–
–
–
•
23
Theoretical work
Current work
Practical work
Potential improvement
= 22 x 103 Btu/bbl feed
= 114 x 103 Btu/bbl feed
= 50 x 103 Btu/bbl feed
= 64 x 103 Btu/bbl feed
The potential improvement can be achieved by ([Gadalla 2003a], [Gadalla
2003b], [ANL 1999], [TDGI 2001], [Liporace 2005], [Seo 2000], [Rivero
2004], [Yeap 2005], [Hovd 1997], [Sharma 1999])
– Control of fouling in the crude preheat train and fired heater.
– Improved heat integration between the atmospheric and vacuum towers.
– Improved tray design and heat integration between trays, and optimization of
the number of trays and operating conditions for improved vapor-liquid contact
and higher throughput.
– Enhanced cooling to lower overhead condenser cooling water from 75 to 50°F.
– Implementation of advanced control or revamp of the control structure
with simple plantwide control.
Crude oil distillation (atmospheric and vacuum)
•
Vacuum distillation energetic assessment [DOE 2006]:
–
–
–
–
24
Theoretical work
Current work
Practical work
Potential improvement
= 46 x 103 Btu/bbl feed
= 92 x 103 Btu/bbl feed
= 54 x 103 Btu/bbl feed
= 38 x 103 Btu/bbl feed
Crude oil distillation (atmospheric and vacuum)
•
Vacuum distillation energetic assessment [DOE 2006]:
–
–
–
–
•
= 46 x 103 Btu/bbl feed
= 92 x 103 Btu/bbl feed
= 54 x 103 Btu/bbl feed
= 38 x 103 Btu/bbl feed
The potential improvement can be achieved by ([Gadalla 2003a], [Gadalla
2003b], [ANL 1999], [TDGI 2001], [Sharma 1999], [Liporace 2005], [Seo
2000], [Rivero 2004], [Yeap 2005])
–
–
–
–
–
25
Theoretical work
Current work
Practical work
Potential improvement
Control of fouling in the fired heater.
Improved heat integration between the atmospheric and vacuum towers.
Improved tray design and heat integration between trays, and optimization of the
number of trays and operating conditions for improved vapor-liquid contact and
higher throughput.
Enhanced cooling to lower overhead condenser cooling water from 75°F to 50°F.
Implementation of advanced control or revamp of the control structure with
simple plantwide control.
Fluid catalytic cracking
•
•
Objective: Convert heavy oils into more valuable gasoline and lighter
products.
Feedstocks are light and heavy gas oil from atmospheric or vacuum
distillation, coking, and deasphalting operations.
High temperature, catalytic cracking
reactions:
26
Fluid catalytic cracking
27
Fluid catalytic cracking
•
Energetic assessment [DOE 2006]:
–
–
–
–
28
Theoretical work
Current work
Practical work
Potential improvement
= 40 x 103 Btu/bbl feed
= 209 x 103 Btu/bbl feed
= 132 x 103 Btu/bbl feed
= 77 x 103 Btu/bbl feed
Fluid catalytic cracking
•
Energetic assessment [DOE 2006]:
–
–
–
–
•
= 40 x 103 Btu/bbl feed
= 209 x 103 Btu/bbl feed
= 132 x 103 Btu/bbl feed
= 77 x 103 Btu/bbl feed
The potential improvement can be achieved by ([Linhoff 2002], [ANL
1999])
–
–
–
–
–
29
Theoretical work
Current work
Practical work
Potential improvement
Addition of a power recovery turbine.
Conversion of condensing turbine drive to electric motor drive (wet gas
compressor).
Improved heat integration, pinch analysis.
Minimization of other miscellaneous losses.
Extra: Implementation of advanced control or revamp of the control
structure with simple plantwide control.
Catalytic hydrotreating
•
•
•
•
•
30
Objective: Remove sulfur, nitrogen, and metals and upgrade heavy
olefinic feed by saturation with hydrogen to produce paraffins.
It commonly appears in multiple locations in a refinery (5 or more of
these units).
They are usually placed upstream of units where catalyst deactivation
may occur from feed impurities.
Typically we can distinguish: Naphtha hydrotreater, kerosene
hydrotreater, and gas oil hydrotreater.
Main reactions:
Catalytic hydrotreating
31
Catalytic hydrotreating
•
Energetic assessment [DOE 2006]:
–
–
–
–
32
Theoretical work
Current work
Practical work
Potential improvement
= 30 x 103 Btu/bbl feed
= 88 x 103 Btu/bbl feed
= 55 x 103 Btu/bbl feed
= 33 x 103 Btu/bbl feed
Catalytic hydrotreating
•
Energetic assessment [DOE 2006]:
–
–
–
–
•
= 30 x 103 Btu/bbl feed
= 88 x 103 Btu/bbl feed
= 55 x 103 Btu/bbl feed
= 33 x 103 Btu/bbl feed
The potential improvement can be achieved by ([ANL 1999], [Gary
2001], [Linhoff 2002], [Liebmann 1998])
–
–
–
–
–
33
Theoretical work
Current work
Practical work
Potential improvement
Improved pre-heater performance.
Improved catalyst.
Improved heat integration, pinch analysis.
Minimization of other miscellaneous losses.
Extra: Implementation of advanced control or revamp of the control
structure with simple plantwide control.
Catalytic reforming
•
•
•
Objective: Convert naphthas and heavy straight-run gasoline into highoctane gasoline blending components, as well as hydrogen generation.
It essentially restructures hydrocarbon molecules to increase the octane of
motor gasoline.
Main reactions:
–
–
–
–
34
Dehydrogenation of naphthenes to aromatics:
Methylcyclohexane → Toluene + 3H2
Methylcyclopentane → Cyclohexane → Benzene + 3H2
Dehydrocyclization of paraffins to aromatics:
n-Heptane → Toluene + 4H2
Isomerization:
n-Hexane → Isohexane
Methylcyclopentane → Cyclohexane
Hydrocracking:
n-Decane → Isohexane + nButane
Catalytic reforming
35
Catalytic reforming
•
Energetic assessment [DOE 2006]:
–
–
–
–
36
Theoretical work
Current work
Practical work
Potential improvement
= 79 x 103 Btu/bbl feed
= 269 x 103 Btu/bbl feed
= 203 x 103 Btu/bbl feed
= 66 x 103 Btu/bbl feed
Catalytic reforming
•
Energetic assessment [DOE 2006]:
–
–
–
–
•
= 79 x 103 Btu/bbl feed
= 269 x 103 Btu/bbl feed
= 203 x 103 Btu/bbl feed
= 66 x 103 Btu/bbl feed
The potential improvement can be achieved by ([ANL 1999], [Gary
2001], [Packinox 2003])
–
37
Theoretical work
Current work
Practical work
Potential improvement
Improved feed and interstage process heater performance (e.g., improved
convection section heat recovery).
– Replace horizontal feed/effluent heat exchangers with vertical plate and
frame exchanger.
– Improved equipment efficiency (e.g., recycle and net gas compressor, reactor
product air cooler).
– Additional process cooling to improve light ends recovery (vapor
compression vs. ammonia absorption).
– Minimization of other miscellaneous losses.
– Extra: Implementation of advanced control or revamp of the control
structure with simple plantwide control.
Alkylation
•
•
•
•
38
Objective: Produce branched paraffins that are used as blending
components in fuels to boost octane levels without increasing the fuel
volatility.
There are two alkylation processes: sulfuric acid-based and hydrofluoric
acid-based.
Both are low-temperature, low-pressure, liquid-phase catalyst reactions.
Main reaction:
Alkylation (H2SO4 process)
39
Alkylation (H2SO4 process)
•
Energetic assessment [DOE 2006]:
–
–
–
–
40
Theoretical work
Current work
Practical work
Potential improvement
= -58 x 103 Btu/bbl feed
= 335 x 103 Btu/bbl feed
= 156 x 103 Btu/bbl feed
= 179 x 103 Btu/bbl feed
Alkylation (H2SO4 process)
•
Energetic assessment [DOE 2006]:
–
–
–
–
•
Theoretical work
Current work
Practical work
Potential improvement
= -58 x 103 Btu/bbl feed
= 335 x 103 Btu/bbl feed
= 156 x 103 Btu/bbl feed
= 179 x 103 Btu/bbl feed
The potential improvement can be achieved by ([Gadalla 2003a], [TDGI
2001], [DOE 2006], [Schultz 2002])
– Improved compressor efficiency, from 25% to 50%.
– Improved heat integration, pinch analysis.
– Use of a dividing wall column design or other advanced separation
technology.
– Upgraded control system: revamp of the control structure with simple
plantwide control.
41
Hydrogen production
•
•
•
•
Objective: Generate (complement) H2 for hydrocracking, hydrotreating,
hydroconversion, and hydrofinishing process throughout the refinery.
Sources for hydrogen in a refinery are basically by-products from
catalytic reforming, recovery from H2 rich off-gases, and the hydrogen
plant production.
The principal process for converting hydrocarbons into hydrogen is
catalytic steam reforming.
The main reactions are
CH4 + H2O  CO + 3H2
CO + H2O  CO2 + H2
CnHm + H2O  nCO + (m+2n)/2H2
•
42
(-Ho298 = -206 kJ/mol)
(-Ho298 = 41 kJ/mol)
(-Ho298 = -1109 kJ/mol for nC7H16)
The main reaction, methane conversion, must be carried out at high
temperature, high steam to carbon ratio, and low pressure to achieve
maximum conversion.
Hydrogen production
43
Hydrogen production
•
Energetic assessment [Rostrup-Nielsen 2005]:
–
–
–
–
•
Theoretical work
Current work
Practical work
Potential improvement
= 67 x 103 Btu/bbl feed
= 111 x 103 Btu/bbl feed
= 71 x 103 Btu/bbl feed
= 30 x 103 Btu/bbl feed
The potential improvement can be achieved by ([Rostrup-Nielsen 2005])
–
Higher (optimized) reforming temperature (> 900 oC) and lower (optimized)
steam to carbon ratio (< 2.0).
– Reformer design that does not export steam.
– Catalysts to reduce carbon formation.
– Membrane reforming technology with CO2 sequestration.
– Extra: Implementation of advanced control or revamp of the control
structure with simple plantwide control.
44
Summary
Process
TW
PW
CW
PI = CW - PW
PI = PI/CW(%)
103 Btu/bbl feed
1. Atmospheric distillation
22
50
114
64
56
-58
156
335
179
53
46
54
92
38
41
-58
152
255
103
40
5. Catalytic hydrotreating
30
55
88
33
38
6. Fluid catalytic cracking
40
132
209
77
36
7. Hydrogen production
67
71
111
30
27
8. Catalytic reforming
79
203
269
66
24
2. Alkylation H2SO4
3. Vacuum distillation
4. Alkylation HF
•
•
•
•
•
45
The overall savings, including capacities, can reach up to 42%.
Atmospheric + vacuum distillations have the largest potential for savings.
Followed by alkylation and catalytic treatments.
Note that separation sections are also included in the conversion processes.
As a general potential improvement in the short term, I particularly
would also include assessment of the control structure design of the
entire refinery.
Summary
•
•
•
•
•
46
Remember this picture?
Now have a look at the figures on the right.
Gasoline requires the largest amount of
energy to be produced. While gasoline
makes up 43% by volume of refinery
product output, its production consumes
62% of the refinery energy requirement.
Distillate fuel oil is the next most energyintensive product stream, consuming 17% of
refinery energy requirement.
The remaining 21% is distributed fairly
evenly between the other product streams.
TBtu/year
1,305
62.1%
355
16.9%
76
3.6%
113
5.4%
77
3.7%
37
1.8%
51
2.4%
75
3.6%
12
0.6%
Outline
1.
2.
3.
4.
A vision for the future
A simple guide to oil refining
Energetic issues in an oil refinery
Thermodynamic analysis and measures to improve energy consumption.
•
•
•
•
•
•
Crude oil distillation (atmospheric and vacuum)
Fluid catalytic cracking
Catalytic hydrotreating
Catalytic reforming
Alkylation
Hydrogen generation
5. Separation processes
6. Recap and future directions
7. References
47
Separation processes
•
•
The majority of the available literature is related to the issue concerning
distillation, and they are heavily concentrated in the atmospheric and
vacuum columns. I bet you know the reason!
Future solutions for improving energy efficiency in separation processes in
oil refineries are basically related to:
–
–
–
–
–
•
48
Membrane technology.
Fouling mitigation.
Optimization and “advanced” process control.
Heat integration.
Design of efficient separation systems.
What follows are mostly on the drawing board, i.e., no real-world
implementation.
Separation processes
•
Membrane technology (still an on going development):
–
–
–
49
[Wauquier 2000] discusses that membrane technology is still an infant in the
world of grown-up inefficient processes in the oil industry. Its main application
is in hydrodesulfurization processes in catalytic hydrotreating units, replacing
existing separation processes with energy savings up to 20%.
Nevertheless, [Goulda 2001] and [White 2000] claimed a fuel reduction of
36,000 bbl/year (or 20% w.r.t. the conventional process) by adding a
membrane unit in the dewaxing unit to recover part of the solvent stream. The
membrane is selective to the solvent from the solvent/oil/wax mix.
According to [Szklo 2007], further research is needed to develop appropriate
membrane materials that can withstand the harsh conditions in petroleum
refining processes.
Separation processes
•
Fouling mitigation (basically monitoring):
–
[Panchal 2000] presented a performance monitoring via an Excel® spreadsheet
of the preheat train for a crude distillation unit. The authors claim that by using
their technique the energy loss in a period of 2 years can be reduced by almost
60%.
– [Nasr 2006] proposed a model of crude oil fouling in preheat exchangers with
the aim of better controlling fouling formation. In contrast with other models,
the one proposed by the authors consider the mechanisms of formation and
natural removal.
– [Yeap 2005] presented the application of existing fouling models to maximize
heat recovery in the preheat train of the crude oil distillation. The authors’
conclusion was that designing for maximum heat recovery results in a less
efficient system over time due to fouling effects.
– However, [Szklo 2007] states that the very complex mechanisms which lead to
fouling are still not properly understood to the extent they can be safely used
for fouling mitigation techniques (anti-fouling agents and coatings).
50
Separation processes
•
“Advanced” process control and optimization (essentially modeling):
–
–
–
–
51
[Domijan 2005] optimized a crude distillation unit by using a model that, according to
the authors, has some advantages over commercial ones since it is adapted to real plant
conditions, it is open source as well as flexible and fast. Moreover, it can also identify
fouling level and be applied for planning shutdowns and maintenance stops. They
claimed they found an optimal solution that saves up to 3.2% of energy consumption visà-vis actual operating conditions.
[Seo 2000] considered the optimal design of the crude distillation unit (atmospheric,
vacuum, and naphtha stabilizer) by optimizing feed locations, heat duties of
pumparounds and operating conditions of the preheat train. They use a MINLP
framework. They claim the energy recovery in pumparounds and preheat train could save
up to 20 million kcal/h.
[Hovd 1997] proposed the implementation of MPC in a crude oil distillation. They used
the MPC package (D-MPC) of Fantoft Prosess and a linear model of the process obtained
using first-principle model equations and laboratory data. They implemented the MPC
strategy in a refinery in Sweden and reported a reduction in energy consumption
equivalent to USD20,000/year for a project investment of USD250,000.
[Gadalla 2003b] performed a very simple optimization of existing heat-integrated
distillation systems for crude oil units where the column (with fixed configuration) and
the associated heat exchanger network are considered simultaneously. Only one design
(retrofit) variable is assumed: area of the HEN. They claimed savings up to 25% over the
base case.
Separation processes
•
Heat integration:
–
–
–
52
[Gadalla 2006] optimized an existing crude distillation column where a gas
turbine/generator is integrated with the preheat furnace. They claim energy
reductions of up to 21%. The idea was then to maximize the energy generated
in the gas turbine by adjusting the temperature of the feed, reflux ratio, steam
flow rates, temperature difference of each pumparound, and the flow rate of the
liquid through each pumparound.
[Gadalla 2005] studied the design of an internally heat-integrated distillation
column for separating an equimolar propylene-propane mixture where the 57
stages of the stripping column are heated by the first 57 stages of the
rectification column. They claim that by increasing the heat transfer rate per
stage, energy savings can reach up to 100% of reboiler duties. For this, the
compressor power would increase only 15% w.r.t. the base HIDiC case.
By applying pinch analysis, [Plesu 2003] propose to thermally couple crude
distillation units and delayed coking units through the utility system. They
basically proposed to send the vacuum bottoms to the delayed coking unit at a
higher thermal load and use this artifice to generate part of the steam needed in
the crude distillation unit. They do not report energy saving figures.
Separation processes
•
Heat integration:
–
[Liebmann 1998] proposed a systematic algorithm based on pinch analysis that
lends to automation of the design procedure of crude oil distillation units where
the column, the heat exchanger network, and their simultaneous interactions
are considered together. Modifications that further increase the efficiency of
the process are: installation of reboilers rather than stripping stream and the
thermal coupling of column sections. They claimed that units conceived by this
method can save up to 20% energy w.r.t. the base case.
– [Szklo 2007] states that heat integration and waste heat recovery appears as one
of the main options for saving fuel in the short to mid terms.
53
Separation processes
•
Design of efficient separation systems:
–
[Szklo 2007] discussed the use of catalytic distillation (CD) as an indeed very
promise alternative to hydrotreating units, namely to FCC gasoline. The idea is
to fractionate the gasoline by distillation, which yields several gasoline
fractions, and then treat each fraction for sulfur according to their prevailing
sulfur compound reactivities, all in the same unit. Lighter fraction are treated
more severely while the heavier ones undergo desulfurization at higher
temperatures at the bottom of the CD column. The authors claimed that up to
62% of energy can be saved w.r.t. conventional HDS processes.
– [Szklo 2007] also discussed the application of biodesulfurization in
replacement of conventional HDS with energy savings of up to 80%. However,
the technology is still at its dawn, and the main barriers are the understanding
of biological mechanisms of biocatalysts and the development of efficient twophase biodesulfurization systems.
– [Schultz 2002] defended the thesis that dividing-wall columns (DWC) can save
up to 30% in energy costs. In this technology, remixing of components towards
the bottom or top of a direct sequenced train which causes thermal inefficiency
is mitigated by cutting the product at their maximum compositions. However,
[Szklo 2007] emphasized the need for further development of DWC for major
distillation processes in the oil refining industry.
54
Separation processes
•
Design of efficient separation systems:
–
According to [Pellegrino 1999] a potentially attractive refining process
modification is to input the crude directly into controlled thermal cracking
units, thereby bypassing CDU. The idea is to crack large hydrocarbon
molecules (e.g., large asphaltene-type molecules) into smaller ones. They
reported a reduction in energy consumption of 23% in addition to the fact that
up to 80% of the energy generated in the unit can be recovered as reusable
energy.
– [EIPCCB 2001] discussed the use of a radical revamp that encompasses
atmospheric and vacuum distillation, gasoline fractionation, naphtha stabilizer
and gas plant in one unit: progressive distillation. It consists of a fairly
complex set of separation steps and extensively uses pinch technology to
minimize heat supplied by external means. The savings can reach up to 30% on
total energy consumption for these units.
55
Outline
1.
2.
3.
4.
A vision for the future
A simple guide to oil refining
Energetic issues in an oil refinery
Thermodynamic analysis and measures to improve energy consumption.
•
•
•
•
•
•
Crude oil distillation (atmospheric and vacuum)
Fluid catalytic cracking
Catalytic hydrotreating
Catalytic reforming
Alkylation
Hydrogen generation
5. Separation processes
6. Recap and future directions
7. References
56
Recap and future directions
•
It seems there is no radical revolution going on in the oil refining industry
so to handle energy efficiency. Instead, the 2020 Vision report [API 2000]
lists:
–
–
–
–
Reduction of fouling in heat exchangers is a definite priority.
Improved convection in furnaces is necessary.
Cogeneration needs to be optimized.
Use of conventional distillation should be minimized. Try membrane and
catalytic distillation.
– Let’s not forget research in catalysis.
– Comprehensive mathematical process models in oil refinery are a must for
short term results [DOE 2000].
– Process optimization is definitely in the oil refinery agenda [Domijan 2005].
•
•
57
•
Investments in R&D represent one way to help drive the industry toward
a higher level of energy efficiency. However, implementation is still at its
very infancy as there are still technological/psicological barriers.
Accordingly, separation processes need to be updated. However, one
should look at the big picture.
Needless to say, energy reduction  CO2 emission reduction!
Recap and future directions
•
Wanna a hint to decide your PhD project? Energy efficiency program
for future oil refineries. Ease, 5 (huge) PhD projects:
–
–
–
–
–
58
Fouling: modeling and elucidation of its mechanism in the crude distillation
unit (atmospheric and vacuum columns and respective HEN) as well as
development of anti-fouling chemicals that little affects refining products’
quality.
Membrane: there’s still a technological barrier with the current membranes.
More research is needed to extend the application to other separation units
throughout the refinery.
Advanced process control and optimization: investigation of plantwide
control and optimization (I only found information about these issues applied
to individual units).
– Check also Hydrocarbon Processing Advanced Process Control and
Information Systems 2005.pdf.
Heat integration: investigation of more plantwide heat integration
opportunities by pinch or exergy analysis.
Distillation design: more on reactive (catalytic) distillation and dividing-wall
technology applied to energy-intensive units (FCC, alkylation, hydrotreating,
reforming, and crude distillation units). Especially, biodesulfurization.
Outline
1.
2.
3.
4.
A vision for the future
A simple guide to oil refining
Energetic issues in an oil refinery
Thermodynamic analysis and measures to improve energy consumption.
•
•
•
•
•
•
Crude oil distillation (atmospheric and vacuum)
Fluid catalytic cracking
Catalytic hydrotreating
Catalytic reforming
Alkylation
Hydrogen generation
5. Separation processes
6. Recap and future directions
7. References
59
References
•
•
•
•
•
•
•
•
60
•
[Gadalla 2003a] – Gadalla, M., Jobson, M., and Smith, R., Increase Capacity and Decrease
Energy for Existing Refinery Distillation Columns, Chemical Engineering Progress, April 2003,
p. 44.
[ANL 1999] - Petrick, M. and Pellegrino, J., The Potential for Reducing Energy Utilization in
the Refining Industry, Argonne National Laboratory, ANL/ESD/TM-158, August 1999.
[Linhoff 2002] - Linhoff March, a division of KBC Process Technology Ltd., The Methodology
and Benefits of Total Site Pinch Analysis, 2002,
http://www.linnhoffmarch.com/resources/technical.html.
[Gary 2001] - Gary, J.H., and Handwerk, G.E., Petroleum Refining: Technology and
Economics, 4th Edition, Marcel Dekker, Inc., New York, NY., 2001.
[Packinox 2003] - Reverdy, F., Packinox, Inc., High-Efficiency Plate and Frame Heat
Exchangers, presented at the 2003 Texas Technology Showcase, Houston, Texas, March 2003.
[Schultz 2002] - Schultz, M.A., Stewart, D.G., Harris, J.M., Rosenblum, S.P., Shakur, M.S., and
O’Brien, D.E., Reduce Costs with Dividing-Wall Columns, Chemical Engineering Progress, p.
64, May 2002.
[TDGI 2001] - The Distillation Group, Inc., Distillation: Energy Savings Improvements with
Capital Investments (Section 4), 2001,
http://www.distillationgroup.com/distillation/H003/H003_04.htm.
[Liporace 2005] – Liporace, F. S. and Oliveira, S. G., Real-time fouling diagnosis and heat
exchanger performance, Petrobrás, Internal communication, 2005.
[Exxon 2005] – ExxonMobil, A simple guide to oil refining, 2005,
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