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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



E N G I N E E R I N G S O L U T I O N S


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.





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





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%





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





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

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