Article %2d Foster Wheeler Energy%2epdf
-
Upload
smab2162094 -
Category
Documents
-
view
234 -
download
0
Transcript of Article %2d Foster Wheeler Energy%2epdf
8/14/2019 Article %2d Foster Wheeler Energy%2epdf
http://slidepdf.com/reader/full/article-2d-foster-wheeler-energy2epdf 1/6
S I M O N C C L A R K E & B A H R A M G H A E M M A G H A M I
Gas-to-Liquids (GTL) has been the subject of many press conferences and journal articles in the
last four to five years. Attention has been focused on catalyst developments or improvements, the
undoubted outstanding quality of the product fuels, and the challenges facing us as engineers.
Most people are aware of the basic economics behind GTL and the fact they are not clear-cut for
most regions of the world, even though, on paper, typical reported gas prices correspond to
feedstock prices of around US$ 4-6/bbl. However, we must now realise that the time for these type
of debates is over. GTL projects have come of age and the engineering challenges that have been
debated at length over recent years have been resolved. Arguably, the economic arguments have
also been overcome for certain regions of the world, and we are seeing projects in these regionson the verge of construction. This paper will, therefore, concentrate not on debate and challenge,
but on real engineering solutions that have been developed for a range of GTL projects. We will
also attempt to draw some conclusions for the next-generation facilities now being planned for later
in the decade, which will build upon the experiences of these first plants.
Engineering A Gas-to-Liquids Project
TAKING GTL FORWARD
E N G I N E E R I N G S O L U T I O N
Picture Courtesy: ConocoPhillips Compa
O F F S H O R E W O R L D O C T - D E C 2 0 0 3 n 5 5
8/14/2019 Article %2d Foster Wheeler Energy%2epdf
http://slidepdf.com/reader/full/article-2d-foster-wheeler-energy2epdf 2/6
E N G I N E E R I N G S O L U T I O N S
O F F S H O R E W O R L D O C T - D E C 2 0 0 3 n 5 6
The three main process technologies in a
Gas-to-Liquids (GTL) process are
well known:
l Syngas preparation
l Fischer-Tropsch (FT) synthesis
l Hydrocarbon upgrading (mild
hydrocracking/hydrotreating).
Much has been written about theadvantages and disadvantages of a variety of
proprietary technologies for each of these
steps. Debates have raged over partial
oxidation, catalytic partial oxidation,
autothermal reforming, slurry beds, fixed
beds and so on. However, all of these debates
still do tackle the area, which accounts for
40 to 50 per cent of the cost the utility and
offsite support systems.
Virtually all the technologies in a GTL
plant have a common utility thread:
l The need for large quantities of high
grade energy to drive the air separation
processes
l Preheat needs for the syngas generation
step
l Waste heat recovery from syngas and its
effective utilisation
l Supported by "power station"-size
steam and electrical systems,
wastewater treatment facility, an
associated infrastructure.
Process Engineering
Opportunities
The challenges listed above are in faunique opportunities within a GTL facili
that can be exploited as a benefit. GT
projects are unlike any other, with th
particular combination of facilities within
single project entity totally different fro
any other refinery, chemical or powe
based project. Rather than being
hindrance to commercialisation, it shou
be looked at as a differentiator.
l Tankage and product-loading facilities,
which, when compared to a refinery,
may require similar volumes, but whose
utilisation can be low (when considering
projects of around 34,000 barrels per
day (bpd))
l Systems that require virtually 100 per
cent sulphur quarantine to protect sulphur sensitive FT catalyst (tankage,
flare and vent systems)
l Large-scale, reliable electrical systems,
often internally generated derived from
waste heat
l Usual support infrastructure
of administration buildings,
workshops, warehouses, canteens and
medical facilities
l Medium/low grade heat generation by
the FT process
l Hydrogen provision for the
hydrocracker
l Optimum product recovery to maximiseyield
l How to economically reject ~40 per
cent of the feed natural gas heat (GTL
projects are around 60 per cent thermal
efficiency, resulting, therefore, in
around 40 per cent heat rejection to
the surroundings).
In addition to this, the offsite systems are
also significant, especially when dealing with
greenfield remote locations:
l Water treatment to reliably support the
large steam systemsl Effluent treatment of oxygenated
hydrocarbon contaminated water (and
utility system blowdowns)
l Flare systems, dealing with high heat
flows from the hydrocarbon processing
units and high hydraulic flows from the
gas processing units
l Firefighting systems, dealing potentially
with large volumes of hydrocarbons at
their boiling points and hydrogen
containing streams
l Large-scale temporary construction
facilities; a significant issue for
remote locations.
So, whilst the process technology has
generated the most interest, and rightly so
when considering the need for optimum
catalyst and reactor design, we must not
forget that there are equal challenges in thesupport systems when considering
engineering, construction and cost.
The way to look at a GTL facility can be
summarised as:
l A world-scale gas processing and syngas
generation facility at the front, together
with at least two of the largest single-train
air-separation plants ever built
l Large-scale chemical conversion process
in the middle
l A refinery on the "back end"
The Steam Systems
A GTL facility of around 34,000 bp
has a steam system of considerable siz
which, depending on the technolog
selected for each of the processes, will hav
to handle a total steam rate of around 1,50
tonnes per hour. This level of steam handlin
will, no doubt, surprise the refiners, but walso surprise those used to dealing wi
syngas complexes, as this is approximate
double what you would expect from th
syngas capacity.
For GTL, this steam will normally be
two discrete pressure levels one associate
with the syngas generation and on
associated with the Fischer-Tropsc
synthesis. The steam generated by the syng
processes is available at a variety o
conditions, and is largely limited by wh
Figure 1: Basic GTL flow scheme.
8/14/2019 Article %2d Foster Wheeler Energy%2epdf
http://slidepdf.com/reader/full/article-2d-foster-wheeler-energy2epdf 3/6
E N G I N E E R I N G S O L U T I O N
O F F S H O R E W O R L D O C T - D E C 2 0 0 3 n 5 7
you feel able to generate with the syngas
waste-heat boiler (levels are normally limited
by metal-dusting concerns). However, the
steam generated by the FT process is limited
by the FT reaction conditions and is
normally limited to less than 200 0C for
liquid-phase processes.
This steam should be viewed as anopportunity, as it gives unprecedented
flexibility in configuring the utility systems:
l High-pressure (HP) steam pressure and
degree of superheat can be optimised
for a particular cycle and steam
turbine set.
l Medium-pressure (MP) steam can be
superheated, and due to the pressure
level, this could be done easily using
waste heat from another fired heater.
l Use the HP steam for compressor drives,
preheat or power generation. Used
within the air separation unit (ASU), it is
possible to have the main and booster
air compressors on the same shaft w ith
a single large turbine.
l Use the MP steam for preheats or for
power generation. Consider this for
smaller compressor drives, if
economically viable.
l To reduce equipment, simply view the
MP steam as an FT cooling medium and
condense it.
The MP steam has been a problem area
with FT plants in the past, but considerablylarger turbines are now available for using
this valuable utility cost-effectively, again
shifting the basis for what a GTL plant can
achieve. This, coupled with more recent
advances in mechanical design of gearboxes
and complex shaft arrangements, gives the
engineer even more flexibility in using this
grade heat.
The Fuel System
FT plants unfortunately do not convert
the synthesis gas into 100 per cent C5+hydrocarbons. The combined FT reactor
effluent is a cocktail of hydrogen, nitrogen,
CO, CO2, water, water-soluble oxygenated
hydrocarbons, methane and C2+ olefinic
and paraffinic hydrocarbons. This stream
exits the FT reactor in the vapour phase and
is usually condensed, at which point a
hydrocarbon-rich and a water rich phase
are removed. This leaves a vapour stream
for which the engineer has several options:
l Burn as fuel
l Recycle into the process
l Remove "useful" molecules such as
hydrogen
l A combination of the above.
Each of the different GTL processes has
different methods of handling this stream,
including some once-through processes that
propose simply combusting the entirestream in a specially designed gas turbine.
However, all of these processes have the
following in common:
l This stream represents the single largest
quantity of high-grade heat within the
process (ignoring, for now, small
vents and light ends productions in
other units).
l The stream is of low heating value, due
to the CO2
and nitrogen it contains
(typically <350 Btu/SCF), which
represents challenges in designing a
stable fuel system and combustors.
GTL facilities, whilst exothermic overall,
do have needs for high-grade heat, as this
can be exploited more cheaply in general
than, say, the FT steam. Users include preheat
requirements for chemical conversion (in
syngas generation and hydrocracking), steam
superheating, large rotating equipment
within the ASU (the fuel could be used for
gas turbines), and power generation. The
challenge is to have a good database of costs
and ensure that you are targeting the highest
value energy at the right user.
Capital Cost vs Process
Efficiency
All engineers are used to the perennial
debate over cost and efficiency. This debate
is totally valid for GTL facilities, but it is worth
remembering that the conventional answers
are no longer true, and you should
investigate what fits the particular economics
of your project.
The reasons for this relate to the unique
process and economic constraints that exist within GTL:
l The process rejects ~40 per cent of the
feed energy as waste heat. Due to the
significant investment in air or water-
cooling facilities, efficiency is a key issue
in capital cost reduction.
l The plants are very equipment-
intensive; so, unfortunately,
opportunities are limited to reduce cost
of a large "thing" (such as a single turbine),
but savings in utility cycles chip away at
all equipment items in the system an
so reduce cost.
l The plants are capital intensive, so a larg
portion (>50 per cent) of the cash flo
is capital repayment. This results in th
usual capital versus operatin
expenditure balance being tippe
towards capital costs.The requirement to check life-cyc
costs is, therefore, more important tha
normal, but it is essential that an
optimisation of this type is done against ha
economic data and decision-makin
indicators (net present value, NPV, rath
than payback), which reflect reality and no
some project quirk.
Engineering Challenges
Engineering of GTL facilities ha
progressed beyond just process engineerin
that typifies most pre-feasibility and feasibili
studies. During these early stages of proje
development, engineering developme
outside of the process development h
focussed on the following main areas:
l Plot plan and piping arrangements
l Construction philosophy stick-bui
modular/barge mounted
l Foundation and civil design/si
preparation
l Heavy lift studies (the plant include
some significant reactor vessels)
l Risk management l Standards and specifications
l Local development
l Environmental impact.
The layout of GTL facilities was identifie
early as being cost-critical due to the proce
intensity of the projects. This manifeste
itself both in terms of savings from laying o
the large quantities of equipment involve
and also in minimising piping runs of ve
large gas and steam systems. This saves no
only basic bulk material costs, but als
minimises pressure drops and ensuredelivery of utilities at intended condition
The other main area of interest in these ear
stages was associated with the large reacto
involved, with detailed assessments mad
into the foundation and civil requirement
and also the construction methodology fo
these large vessels.
Throughout these exercises, a commo
thread has been whilst FT-based GTL plan
contain proven technology throughout th
process, not all these processes have bee
8/14/2019 Article %2d Foster Wheeler Energy%2epdf
http://slidepdf.com/reader/full/article-2d-foster-wheeler-energy2epdf 4/6
E N G I N E E R I N G S O L U T I O N S
O F F S H O R E W O R L D O C T - D E C 2 0 0 3 n 5 8
used together before, let alone actually
constructed together. For example, whilst at
first sight a plant of this scale and complexity
would logically be stick built, it must be
remembered that often remote locations are
being targeted, with minimal local
infrastructure and resources, and also the
technical complexity of the plants requiresa degree of specialist supervision. The
modularised plant also presents some
challenges, through the size of the modules
required versus the number of modules,
through to targeting module yards with the
required capability and transport of very
large modules and the construction
sequence. For this reason, stick-built is the
construction method of choice for
developed sites, and modular designs are
used for remote locations.
In addition, the complex nature of the
plant, and the specialists required from the
technology providers for commissioning and
start-up, makes this a schedule-critical task
in more ways than one. The utility-intensive
nature of the plant also makes provision of
start-up equipment cost-critical, as these will
tend to be shutdown once normal operation
is achieved. For remote locations, early start-
an order of magnitude more important than
"conventional" enterprises, such as
refinery upgrades.
At the FEED stage, a detailed study of all
alternatives must be carried out so that the
FEED package is well defined and all activities
are fully specified. If these projects are being
considered for lump-sum turnkey bidding,the FEED package must be sufficiently
defined to allow for this contracting strategy.
Failure to define requirements adequately
will lead to elongation of the bidding process,
possible bid recycle, delays, and failure of
the engineering, procurement and
construction (EPC) contractors to provide
bids within the narrow range required to
close out the project financing, ultimately
leading to higher bids.
For these reasons, the level of activity,
and the experience and expertise of the
FEED contractor must be considered early
These are covered in more detail below
The sequence of construction work mu
be carefully reviewed to enable eac
different trade to commence wo
sequentially or with a short lead-time, agai
to avoid site congestion.
Numerous heavy lifts are involved for
GTL facility, some of which are absolutecritical to overall construction schedul
The plot must be so planned as to enab
timely sequencing of these lifts, and minimis
the heavy-lift window to reduce cos
However, this must not be over
constrained, so as to allow some flexibili
in the construction sequence. The abov
again demonstrates the need for adequa
definition during FEED for these issues
be properly investigated and resolved, wit
beneficial engineering carried out in ke
targeted areas, to ensure adequat
EPC definition.
Figure 2: Indicative cost breakdown.
up of certain areas of the plant, to act as
service providers to the remaining sections,is also needed.
Engineering & Construction
The above highlights some of the areas
that have been studied at length in the course
of GTL plant evolution. However, we are
now in a situation where all the studies and
feasibilities have been investigated, and now
the designs must be confirmed.
In the GTL arena, two large projects have
recently completed basic (i.e., front-end
engineering design, or FEED) design, withone now undergoing detailed engineering.
For projects of these sizes to be controllable
in cost and schedule terms, all of the issues
studied must now be resolved.
A project of this magnitude requires more
than 20,000 engineering deliverables. To
optimise the considerable efforts involved,
correct sequencing of the engineering effort
is essential. The timely exchange of vendor
information is paramount to avoid recycling
of technical data, which, for GTL projects is
within the commercialisation cycle of the
GTL technology by the technology provider,
or all the hard work performed in the
laboratory and with pilot plants will not
translate into a bankable project entity.
A good example of this is the plot plan. A
well-thought-out and properly developedplot layout is a major contributor to the
success of the engineering work. Whilst
optimisation of the plot area, as highlighted
earlier, is essential for cost, one should also
study the constructability of the plant, to
avoid "boxed in" construction difficulties,
and also allow for construction work to
progress on multiple fronts.
The plot plan also defines the
commissioning requirements, which, for
GTL, are somewhat different than normal.
Commissioning a GTL facility is an a
all its own. Most projects are usually tagge
as "construction-driven", with the emphas
on the activities and sequences required
bring the facility to mechanical completio
However, the unique nature of GT
projects, and the way that they have evolveto reduce cost, means that GT
projects should really be tagged as
commissioning-driven".
No new facility can create the cash flow
that the project financiers are looking fo
until such facilities are commissioned
started up, and producing the product a
specified - plants that are mechanical
complete do not generate products. GT
projects have partly reduced their capit
costs by successfully integrating the usef
Syngas production
FT synthesis
Product work-up
Other process units
Utilities
Offsites
20%30%
15%
10%
10%
15%
8/14/2019 Article %2d Foster Wheeler Energy%2epdf
http://slidepdf.com/reader/full/article-2d-foster-wheeler-energy2epdf 5/6
E N G I N E E R I N G S O L U T I O N
O F F S H O R E W O R L D O C T - D E C 2 0 0 3 n 6 1
energy produced by the plant back into
itself. The downside is that start-upequipment has been cut back to the bare
minimum. This presents some interesting
challenges for the commissioning teams.
In addition, the ASU, which can be
considered as being at the heart of the utility
network for these facilities, requires early start-
up to enable commissioning of the other part
of the facility as it is a key utility provider. For
early ASU start-up, certain elements of the
steam system will, therefore, require early
completion, commissioning and start-up.
This dictates the construction schedule as wellas the original plot layout. The steam systems
are also key to commissioning activities that
are being undertaken elsewhere within
the facility.
For the more remote sites with no outside
battery limit services, the GTL facility must
also provide its own power from the start,
creating another commissioning challenge.
The implications of having some of the key
utility systems "live" whilst construction is
being completed in other areas of the facility
is significant. Approximately, one-quarter of
the GTL work involves the ASU and its
associated facilities. Therefore, the ASU design
and construction work must be carefully
integrated with the remainder of the plant.
The core technology of slurry-bed-based
FT GTL technology is the reactor and its
associated equipment. These very complex
pieces require very well defined
specifications, drawings and layouts at the
FEED stage. The EPC contractor cannot be
expected to be fully familiar with these details
of GTL technology, as no large-scale
commercial-scale slurry bed-based GTLfacility has yet been constructed.
It is likely that the third or fourth GTL
project will ease the burden on the EPC
contractor, but until then, it is up to the
technology provider and FEED contractor
to ensure that the years of experience are
well-presented and developed sufficiently
for the EPC contractor. This element is also
again essential to ensure that sufficiently
high-quality bids are obtained from the EPC
contractors to enable closure of the
project financing.The parameters one has to consider to
ensure cost-effectiveness during construction
are selection of the plot layout, availability of
lay-down area, resource (skill/trade)
availability, camp facilities and other logistical
issues. All of these must be considered at the
outset if cost and schedule implications are
to be avoided. This is always good advice for
any project and not specific to GTL, but again
the technological complexity of GTL facilities
requires a special kind of diligence to ensure
that inappropriate "industry normal practice"
is not blindly applied.
Interfaces are also key to the success of
a GTL project - both internally for the
various technologies that are being
integrated, and externally with the site and
environment in general. In addition to these
considerations, a GTL facility is usually
sandwiched between an upstream project
of some type (perhaps wellhead facilities,
pipeline and a gas plant) and a downstream
development (export facilities and
perhaps some form of infrastructure an
utilities development).Synchronising these interfaces represen
considerable challenges to the proje
planner, as different contractors and eve
different owner teams will be involved.
the GTL facility is integrated into thes
enterprises in the form of process technolog
and utilities, the challenges faced a
even greater.
As a final thought on engineering,
is worth considering some of the quantitie
involved for a generic 34,000 bp
grassroots facility:l Equipment count -
~400 (excluding vendor packages)
l Average pipe diameter - ~8 inches
As evidenced in Figure 3, the quantitie
involved are significant, making a grassroo
~34,000 bpd GTL facility rough
equivalent to a grassroots ~100,000 bp
refinery in engineering an
construction terms.
Schedule
The optimum schedule for building
34,000 bpd GTL facility is around 30-3
months from start of detailed engineering
mechanical completion. A further fiv
months is required to carry the plant throug
pre-commissioning, commissioning, star
up and performance tests up t
commercial completion.
This schedule can be shortened b
carrying out some beneficial engineerin
prior to the effective date of the EP
contract, thus ensuring that selection
Sasol gas conversion
process.
Fischer-TropschConversion
Hydrocarbon product
Wax product
Naphtha
KeroseneDiesel
Productupgrading
OxygenNatural gas
Naturalgas
reforming
Synthesis gas
8/14/2019 Article %2d Foster Wheeler Energy%2epdf
http://slidepdf.com/reader/full/article-2d-foster-wheeler-energy2epdf 6/6
E N G I N E E R I N G S O L U T I O N S
O F F S H O R E W O R L D O C T - D E C 2 0 0 3 n 6 2
long-lead items is made prior to the
contract award. A small premium may be
attached to this method of execution, but
an overall analysis of the cash flows shows
that this is money well spent on an NPV
(net present value) basis when considering
overall schedule implications.
Other methods that can be used toshorten the schedule are:
l Pre-assembly of units, either offsite and
then delivered, or onsite prior to
installation in the required area
l Modularisation
l Vendor alliances for unusual or
specialist equipment items - in some
area, GTL facilities require equipment
items that are outside the normal range
of items that vendors supply, or require
dramatic increases in size to beyond 20,000
bpd, with developments in:
l Slurry reactor design, fabrication
and erectionl ASU sizes, "springboarding" off increased
air compressor sizes
l Greater confidence in terms of reliability
with single-train utility systems, with
potentially very large de-aerator and
condensate-handling facilities
l Large steam turbines, able to deal with
FT-derived steam
l Gas turbine developments, both in size
and design, for low British thermal unit
(Btu) gases.
Figure 3: Bulk material quantities.
Mr Simon Clarke is Manager (Gas-
to-Market Technology) for Foster
Wheeler Energy Limited, based in
Reading, UK. Since 1997, his main
activities have been in the GTL
arena, playing a leading role in
Foster Wheeler's team supporting Sasol in their
GTL developments and the recent front-end
engineering activities for the Qatar and Nigeria GT
projects. Contact details: Foster Wheeler Energy
Limited, Shinfield Park, Reading, Berkshire,
RG2 9FW, UK;
E-mail: [email protected]
Mr Bahram Ghaemmaghami is a
Project Director with Foster Wheele
Energy Limited, also based in
Reading, UK. He is responsible for
Foster Wheeler's current GTL
projects, including Qatar (Ras Laffa
and Nigeria (Escravos). His contact address is
same as that of Mr Clarke.
E-mail: [email protected]
these amazing projects, will ensure that GT
is indeed the launch pad to a ne
hydrocarbon future. The EPC contract f
Qatar Petroleum and Sasol's Oryx GT
project at Ras Laffan, in Qatar, has now bee
awarded, making this technology the mo
significant advance in gas processing of th
new millennium.
600,000
500,000
400,000
300,000
200,000
100,000
0
Concrete (m3)
Paving & gravel (m2)
Insulation (m2)
Piping (m)
Welding (dia ins)
Cabling (m)
specialist engineering efforts, due to
unusual application (low-pressure
saturated steam or lower heating value
fuel are two common examples).
The Future For GTL
If we take the current crop of GTL
projects as having been successful in their
engineering and economic development,
and these are considered to be robust
enough to attract project financing, we can
state that no current barriers exist to current
GTL project implementation.
These achievements must be
applauded, but we must consider how the
projects will develop in technology and
engineering terms. The GTL projects to be
executed towards the end of this decade
are likely to have some startling differences
to the current ones as technology advances
are made, and as we build upon the project
execution and operational experiences that
will result.Next-generation GTL facilities will
probably differ in two distinct areas, over
and above the general "creeping"
improvements in machinery and catalysts.
The first, and most likely area, which we
have already seen to some extent, is in
economies of scale. The current crop of
GTL facilities are considering multiple trains,
with the slurry bed technologies in the
~15,000 bpd train size. We are likely to see
The second and exciting area o
development is in the syngas generation ste
Developments in novel approaches, suc
as ceramic membranes, would be a step
change in technology terms, allowin
syngas generation without an air-separatio
unit. In the nearer term, however, we a
likely to see projects using gas-heatinreforming. Several types of this technolog
are available, with several others
development, but all sharing the commo
characteristic allowing the heat in th
synthesis gas to be "recycled" back into th
pre-heat or conversion steps. This remove
or reduces the need for large-scale high
grade energy use in preheating, an
simplifies waste heat recovery from th
syngas in generating steam.
These technology and equipme
developments, together with continue
advances and experience in engineerin