Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS FOR CO-PRODUCING COMMERCIALLY VALUABLE PRODUCTS
FROM BYPRODUCTS OF FISCHER-TROPSCH PROCESS FOR HYDROCARBON
FUEL FORMULATION IN A GTL ENVIRONMENT
TECHNICAL FIELD
[001] The present invention relates to the modification of the Fischer-Tropsch
sequence of
operations including the Fischer-Tropsch process for the production of
hydrocarbon fuels in an
efficient manner, along with the production of commercially valuable co-
products from
by-products of the hydrocarbon production process.
BACKGROUND OF THE INVENTION
[002] In the prior art, the Fischer-Tropsch process has been used for decades
to assist in the
formulation of hydrocarbons. In the last several years, this has become a
concern given the
escalating environmental concerns regarding poor fuel quality and pollution,
together with the
increasing costs of hydrocarbon exploration and refining. The major producers
in this area have
expanded the art significantly in this technological area with a number of
patented advances and
pending applications in the form of publications.
[003] In the art, advances made in terms of the raw materials that have been
progenitor
materials for the Fischer-Tropsch process, have included, for example, coal-to-
liquid (CTL),
bio-to-liquid (BTL) and gas-to-liquid (GTL). One of the more particularly
advantageous features
of the gas-to-liquid (GTL) technology is the fact that it presents a
possibility to formulate a
higher value environmentally beneficial synthetic diesel product or syndiesel
from stranded
natural gas reserves, which would otherwise have not been commercially
feasible to bring to
market. As is generally known, the Fischer-Tropsch (FT) process converts
hydrogen and carbon
monoxide (commonly known as syngas) into liquid hydrocarbon fuels, examples of
which
include synthetic diesel, naphtha, kerosene, aviation or jet fuel and
paraffinic wax. As a
precursory step, the natural gas is thermally converted using heat and
pressure in the presence of
catalyst to produce a hydrogen rich syngas containing hydrogen and carbon
monoxide. As a
result of the Fischer-Tropsch technique, the synthetic fuels are very
appealing from an
environmental point of view, since they are paraffinic in nature and
substantially devoid of
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contamination. This is particularly true in the case of the diesel fuel
synthesis where the
synthetic product has ideal properties for diesel engines, including extremely
high cetane
rating>70, negligible aromatics and sulphur content, in addition to enabling
optimum
combustion and virtually emission free operation. Synthetic diesel or
syndiesel fuels
significantly reduce nitrous oxide and particulate matter when compared with
petroleum based
diesel fuel.
[004] U.S. Pat. No. 6,958,363 (Espinoza, et al.) teaches -a process for
synthesizing
hydrocarbons where initially, a synthesis gas stream is formulated in a syngas
generator. The
synthesis gas stream comprises primarily hydrogen and carbon monoxide. The
process involves
catalytically converting the synthesis gas stream in a synthesis reaction to
produce hydrocarbons
and water followed by the generation of hydrogen-rich stream in the hydrogen
generator. The
process indicates that the hydrogen generator is separate from the syngas
generator (supra) and
that the hydrogen generator comprises either a process for converting
hydrocarbons to olefins, a
process for catalytically dehydrogenating hydrocarbons, or a process for
refining petroleum, and
a process for converting hydrocarbons to carbon filaments. The final step in
the process in its
broadest sense, involves consumption of hydrogen from the hydrogen-rich stream
produced in
one or more processes that result and increase value of the hydrocarbons or
the productivity of
the conversion of the hydrocarbons from the earlier second mentioned step.
[005] Although a useful process, it is evident from the disclosure of Espinoza
et al. that there is
a clear intent to create olefins such as ethylene and propylene for
petrochemical use, and
aromatics for gasoline production. Additionally, there is a reforming step
indicated to include
the reformation of naphtha feedstock to generate a net surplus hydrogen by-
product which is
then recombined into the process. The naphtha is subsequently converted to
aromatics for high
octane gasoline blend stock.
[006] U.S. Pat. No. 7,214,720 (Bayle et al.) discloses the production of
liquid fuels by a
concatenation of processes for treatment of a hydrocarbon feedstock. It is
indicated in the
disclosure that the liquid fuels begin with the organic material, typically
biomass as a solid
feedstock. The process involves a stage for the gasification of the solid
feedstock, a stage for
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purification of synthesis gas and subsequently a stage for transformation of
the synthesis gas
into a liquid fuel.
[007] This reference indicates in column 2 the essence of the technology:
"A process was found for the production of liquid fuels starting from a solid
feedstock that
contains the organic material in which:
a) The solid feedstock is subjected to a gasification stage so as to convert
said feedstock
into synthesis gas comprising carbon monoxide and hydrogen,
b) the synthesis gas that is obtained in stage a) is subjected to a
purification treatment
that comprises an adjustment for increasing the molar ratio of hydrogen to
carbon
monoxide, H2/CO, up to a predetermined value, preferably between 1.8 and 2.2,
c) the purified synthesis gas that is obtained in stage b) is subjected to a
conversion stage
that comprises the implementation of a Fischer-Tropsch-type synthesis so as to
convert
said synthesis gas into a liquid effluent and a gaseous effluent,
d) the liquid effluent that is obtained in stage c) is fractionated so as to
obtain at least two
fractions that are selected from the group that consists of: a gaseous
fraction, a naphtha
fraction, a kerosene fraction, and a gas oil fraction, and
e) at least a portion of the naphtha fraction is recycled in gasification
stage."
[008] The naphtha recycle stream that is generated in this process is
introduced into the
gasification stage. To introduce the naphtha to the gasification stage as
taught in Bayle et al., is
to modify the H2/C0 ratio in the gasification stage using an oxidizing agent
such as water
vapour and gaseous hydrocarbon feedstocks such as natural gas with the
recycled naphtha, while
maximizing the mass rate of carbon monoxide and maintain sufficient
temperature above
1000 C to 1500 C in the gasification stage to maximize the conversion of tars
and light
hydrocarbons.
[009] U.S. Patent No. 6,696,501 (Schanke et al.) entitled Optimum Integration
Process for
Fischer-Tropsch Synthesis and Syngas Production discloses a process for the
conversion of
natural gas or other fossil fuels to higher hydrocarbons. In the process
disclosed therein the
natural gas or the fossil fuels is reacted with steam and oxygenic gas in a
reforming zone to
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produce synthesis gas which primarily contains hydrogen, carbon monoxide and
carbon dioxide.
The synthesis gas is then passed into a Fischer-Tropsch reactor to produce a
crude synthesis
containing lower hydrocarbons, water and non-converted synthesis gas.
Subsequently, the crude
synthesis stream is separated in a recovery zone into a crude product stream
containing heavier
hydrocarbons, a water stream and a tail gas stream containing the remaining
constituents. It is
also taught that the tail gas stream is reformed in a separate steam reformer
with steam and
natural gas and then the sole reformed tail gas is introduced into the gas
stream before being fed
into the Fischer-Tropsch reactor.
[0010] In this reference, a high carbon dioxide stream is recycled back to an
ATR in order to
maximize the efficiency of the carbon in the process. It is further taught
that the primary purpose
of reforming and recycling the tail gas is to steam reform the lower
hydrocarbons to carbon
monoxide and hydrogen and as there is little in the way of light hydrocarbons,
adding natural
gas will therefore increase the carbon efficiency. In the Schanke et al.
reference, the patentees
primarily focused on the production of the high carbon content syngas in a GTL
environment
using an ATR as crude synthesis stream and reforming the synthesis tail gas in
an SMR with
natural gas addition to create optimum conditions that feed to the Fischer-
Tropsch reactor.
[0011] In respect of other progress that has been made in this field of
technology, the art is
replete with significant advances in, not only gasification of solid carbon
feeds, but also
methodology for the preparation of syngas, management of hydrogen and carbon
monoxide in a
GTL plant, the Fischer-Tropsch reactors management of hydrogen, and the
conversion of
biomass feedstock into hydrocarbon liquid transportation fuels, inter alia.
The following is a
representative list of other such references. This includes: U.S. Pat. Nos.
7,776,114; 6,765,025;
6,512,018; 6,147,126; 6,133,328; 7,855,235; 7,846,979; 6,147,126; 7,004,985;
6,048,449;
7,208,530; 6,730,285; 6,872,753, as well as United States Patent Application
Publication Nos.
US2010/0113624; US2004/0181313; US2010/0036181; U52010/0216898;
US2008/0021122;
US 2008/0115415; and US 2010/0000153.
[0012] U.S. Patent No. 7,168,265 discloses an integrated process for producing
LNG and GTL
products, wherein a CO2-containing natural gas feed to an LNG production zone
is first
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pre-treated to separate at least a portion of the CO2 therefrom, and the
resulting CO2 stream
obtained thereby is then directed to a GTL production zone and utilized to
make GTL products
that include methanol and/or methanol derivatives.
[0013] Applicant's Canadian Patent No. 2,751,615 provides a process for
synthesizing
hydrocarbons, comprising: a) formulating a hydrogen rich stream with a syngas
generator; b)
catalytically converting said stream to produce hydrocarbons, containing at
least naphtha; c)
recycling at least a portion of said naphtha to said syngas generator to form
an enhanced
hydrogen rich stream; and d) re-circulating said enhanced hydrogen rich stream
from step (c) for
conversion in step (b) to enhance the synthesis of hydrocarbons.
[0014] Although the processes disclosed in the Canadian Patent No.
2,751,615 allow for the
conversion of greater than 65% of all carbon in the feed streams to
hydrocarbon products, and
the process disclosed in U.S. Patent No. 7,168,265 allow for co-production of
methanol, there
remains a need for technology that provides for an optimized conversion of the
unconverted
process CO2 and other by-products of the hydrocarbon production process to
commercially
valuable co-products such that 100% of all the carbon in captured CO, by-
product streams can be
converted to valuable commercial co-products.
[0015] As part of the further advancements set forth herein, there are
provided processes for the
optimized production of commercially useful co-products from the by-products
of the
hydrocarbon synthesis process. These processes can be integrated within
hydrocarbon synthesis
systems as described, for example, in the Canadian Patent No. 2,751,615.
SUMMARY OF THE INVENTION
[0016] One object of the present invention is to provide an improved
Fischer-Tropsch based
synthesis process for synthesizing hydrocarbons with a substantially increased
yield.
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[0017] A further object of one embodiment of the present invention is to
provide a process for
co-producing commercially valuable products from by-products of a process for
synthesizing hydrocarbons, comprising the steps of:
(a) formulating a first hydrogen rich syngas stream with a syngas
generator;
(b) subjecting a portion of said first hydrogen rich syngas stream to a
hydrogen
separator unit to provide a purified hydrogen by-product stream and a second
hydrogen rich syngas stream;
(c) subjecting at least a portion of said first hydrogen rich syngas
stream, at least a
portion of said second hydrogen rich syngas stream, or a combination thereof,
to
a carbon dioxide removal operation to obtain purified hydrogen rich syngas
stream and a carbon dioxide by-product stream;
(d) catalytically converting said purified hydrogen rich syngas stream to
synthesize
said hydrocarbons; and
(e) converting said purified hydrogen by-product stream and/or said carbon
dioxide
by-product stream into said commercially valuable co-products.
[0018] The present invention amalgamates a series of known unit operations
into a much
improved synthesis route for production of synthetic hydrocarbon fuels and co-
production of
commercially valuable co-products from by-products of this synthetic route.
[0019] In accordance with an embodiment of the instant methodology, the
process may
include an autothermal reforming unit (ATR) operation as a syngas generator.
As is well known
to those skilled in the art, autothermal reforming employs oxygen and carbon
dioxide and or
steam, in a reaction with light hydrocarbon gases like natural gas to form
syngas. This is an
exothermic reaction in view of the oxidation procedure. When the autothermal
reformer employs
carbon dioxide, the hydrogen to carbon monoxide ratio produced is 1:1 and when
the
autothermal reformer uses steam, the ratio produced is approximately 2.5:1.
One of the more
significant benefits of using the ATR is realized in the variability of the
hydrogen to carbon
monoxide ratio.
[0020] The reactions that are incorporated in the autothermal reformer are
as follows:
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2CH4 +02+ CO2 ->3H2+ 3C0 + H20 + HEAT.
When steam is employed, the reaction equation is as follows:
4CH4 + 02 + 2H20 + HEAT 10H2 + 4C0.
[0021] In accordance with a further embodiment of the instant methodology,
the process may
include a steam methane reformer (SMR) operation as a syngas generator. As is
well known to
those skilled in the art, steam methane reforming employs steam in a reaction
with light
hydrocarbon gases like natural gas and pre-reformed ethane, propane, butane
and or naphtha to
form syngas in an indirect fired heater configuration. This is an endothermic
reaction where
external heat energy is required to support the reaction.
[0022] The primary reaction that is incorporated in the steam methane
reformer is as follows:
Natural Gas+Steam+Heat¨* CO + nH2 + CO2
[0023] With the steam methane reformer, the hydrogen to carbon monoxide
ratio produced
ranges from 3:1 to 6:1. One of the more significant benefits of using the SMR
is realized in the
capability of generating relatively high hydrogen to carbon monoxide ratios,
particularly
attractive where excess hydrogen is needed for other operations, such as for
the synthetic
hydrocarbon upgrading or other co-product as described by the current
invention.
[0024] A further discovery materialized from making use of, for example,
light hydrocarbon
gas as by-product from the Fischer-Tropsch reaction and hydrocarbon upgrader
processing,
commonly known as FT Tailgas and Upgrader offgases, or combined to form a
refinery fuel gas,
as a recycled feedstock to the ATR, SMR or combination thereof together with
the naphtha
recycle feedstock, resulted in a significant increase in the volume of
syndiesel fuel produced. By
way of example, by employing the combination of SMR and ATR with naphtha
recycle, and the
recycled refinery fuel gases, the process is capable of converting at least
50% or greater of all
the carbon introduced to the process to syndiesel with an increase in
production of syndiesel and
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synthetic jet fuel, as compared to conventional Fischer-Tropsch operation and
without the
production of any hydrocarbon by-products. This obviously has significant
economic benefits.
[0025] The present invention amalgamates previously unrecognized
combinations in a
hydrocarbon synthesis process, in particular Fischer-Tropsch based process for
synthesizing
hydrocarbons, which expands the usefulness of these processes, by providing a
number of
integrated strategies which are not available in stand-alone synthesis plants.
In the process of the
present application, in addition to the production of synthetic diesel and
synthetic jet streams, it
is possible to optimally convert excess or by-product CO2, nitrogen (N2) and
hydrogen (H2) to
commercially valuable co-products.
[0026] Referring now to the drawings as they generally describe the
invention, reference will
now be made to the accompanying drawings illustrating preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The dashed lines used in the Figures denote optional operations.
[0028] FIG. 1 is a process flow diagram of methodology known in the prior
art using
autothermal reformer technology;
[0029] FIG. 2 is a process flow diagram of methodology known in the prior
art using steam
methane reformer technology;
[0030] FIG. 3 is a process flow illustrating another methodology of
hydrocarbon synthesis
process in a GTL environment;
[0031] FIG. 4 is a process flow diagram illustrating a further variation of
the methodology of
hydrocarbon synthesis process in a GTL environment illustrated in Figure 3;
[0032] FIG. 5 is a process flow diagram of a still further variation of the
methodology of
Figures 3 and 4 showing the combination of autothermal and steam methane
reforming
technologies;
[0033] FIG. 6 is a process flow diagram illustrating a still further
variation of the process of
Figures 3 and 4, showing the integration of the autothermal and steam methane
technologies;
[0034] FIG. 7 is a process flow diagram illustrating integration of a
methanol production unit
with the hydrocarbon synthesis process in accordance with the present
invention;
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[0035] FIG. 8 is a chart illustrating the optimum feed composition for
methanol production
with the hydrocarbon synthesis process in accordance with the present
invention;
[0036] FIG. 9 is a chart illustrating the optimum stoichiometric H2:CO feed
ratio for
methanol production with the hydrocarbon synthesis process in accordance with
the present
invention;
[0037] Figure 10 is a process flow diagram illustrating integration of
ammonia production
with the hydrocarbon synthesis process in accordance with the present
invention;
[0038] FIG. 11 is a process flow diagram illustrating integration of
methanol and ammonia
production with the hydrocarbon synthesis process in accordance with the
present invention.
[0039] Similar numerals employed in the figures denote similar elements.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Referring now to FIG. 1, to illustrate prior art, shown is a process
flow diagram of a
circuit for converting gas-to-liquids with the result being the production of
naphtha and
syndiesel. The process is generally denoted by numeral 10 and begins with a
natural gas supply
12, which feedstock can be in the form of raw field gas or pipeline quality
treated gas, usually
with bulk sulfur and hydrocarbon liquids removed. The natural gas is then pre-
treated in a
pre-treatment unit 20 to which steam 14, hydrogen 18 and optionally carbon
dioxide 19 may be
added as required. The pre-treatment unit may include, as is well known to
those skilled in the
art, such unit operations as a feed gas hydrotreater, sulfur removal and guard
operation and a
pre-reformer to produce a clean vapour feed stream 22 for the syngas
generator, denoted in FIG.
1 as an autothermal reformer (ATR) unit 24. The ATR 24 may be any suitable
catalytic partial
oxidization unit, however, as an example; an ATR that is useful in this
process is that of
HaldorTopsoe A/S, Uhde GmbH and CB8d Lummus Company. The ATR process and
apparatus have been found to be effective in the methodology of the present
invention and will
be discussed hereinafter.
[0041] Generally, as is known from the ATR process, the same effectively
involves a thermal
catalytic stage which uses an partial oxygen supply 16 to convert the
preconditioned natural gas
feed to a syngas 26 containing primarily hydrogen and carbon monoxide.
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[0042] The so formed syngas is then subjected to cooling and cleaning
operations 28 with
subsequent production of steam 32 and removal of produced water at 34. Common
practice in
the prior art is to employ the use of a water gas shift reaction (WGS) on the
clean syngas 30 to
condition the hydrogen to carbon dioxide ratio to near 2.0:1 for optimum
conditions for the
Fischer-Tropsch unit 40. It is not preferred in this process to include a WGS
reaction as all the
carbon, primarily as CO is used to maximize production of synthesis liquids
product. The
process may optionally use the supplemental addition of hydrogen 42 to
maximize the
conversion to syndiesel. The raw syngas may be further treated, as is well
known to those skilled
in the art, in various steps of scrubbing units and guard units to remove
ammonia and sulfur
compounds to create a relatively pure clean syngas 30 suitable for use in a
Fischer-Tropsch unit.
A carbon dioxide removal unit (not shown) may optionally be included in the
clean syngas
stream 30 to reduce the inert load and maximize the carbon monoxide
concentration to the
Fischer-Tropsch unit 40. The syngas is then transferred to a Fischer-Tropsch
reactor 40 to
produce the hydrocarbons 49 and water 48. The so formed hydrocarbons are then
passed on to a
product upgrader, generally denoted as 50, and commonly including a
hydrocarbon cracking
stage 52, a product fractionating stage 60 with naphtha being produced at 66
as a fraction, as
well as diesel 68 as an additional product. The diesel 68 formulated in this
process is commonly
known as syndiesel. As an example, this process results in the formulation of
1000 barrels per
day (bbl/day) based on 10 to 15 million standard cubic feet/day (MMSCFD) of
natural gas. As is
illustrated in the flow diagram, a source of hydrogen 74 is to be supplemented
to the
hydrocarbon cracking unit 52 denoted as streams 54. Further, energy 32 from
the syngas
generator 24, typically in the form of steam, may be used to generate power
and this is equally
true of the Fischer-Tropsch reactor 40 creating energy 46.
[0043] Table 1 establishes a comparison between FT diesel and conventional
petroleum
based diesel.
TABLE 1
Specification of FT-diesel in comparison to Conventional Diesel
Diesel Fuel Specification FT-Diesel Conventional Diesel
Chemical formula Paraffin C12H26
=
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Molecular weight (kg/kmol) 170-200
Cetane number >74 50
Density (kg/1) at 15 C. 0.78 0.84
Lower Heating Value (MJ/kg) at 15 C. 44.0 42.7
Lower Heating Value (MJ/1) at 15 C. 34.3 35.7
Stoichiometric air/fuel ratio (kg air/kg fuel) 14.53
Oxygen content (% wt) ¨0 0-0.6
Kinematic viscosity (mm2/s) at 20 C. 3.57 4
Flash point ( C.) 72 77
Source: KMITL Sci. Tech. J. Vol. 6 No. 1 January-June 2006, P. 43
[0044] As a further benefit, known to those skilled in the art, the process
as described by FIG.
1 and all configurations of the current invention, the addition of a further
side stripper column
(not shown) off the fractionation in stage 60 may be included to produce a new
fraction of about
25% of the volume of the syndiesel fuel (200 to 300 barrels per day
(bbl/day)), referred to as
El -jet fuel. Table 2 describes a typical characteristic of FT jet fuel.
TABLE 2
Typical Specification of FT-Jet Fuel
Typical Product Specification FT Jet Fuel
Acidity mg KOH/g 0.10
Aromatics % vol max <25.0
Sulfur mass % <0.40
Distillation C.
Min 125 C. max 190 C.
50% recovered
270 C.
End Point
Vapor Pressure kPa max 21
Flash Point C.
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Density 15 C., kg/m3 750-801
Freezing Point C. max ¨51
Net Heat Combustion MJ/kg min 42.8
Smoke Point mm, min 20
Naphthalenesvol % max <3.0
Copper Corrosion 2 hr @ 100 C., max
No I
rating
Thermal Stability
Filter Pressure drop mm Hg, max 25
Visual Tube rating, max <3
Static Test 4 hr @ 150 C. mg/ I 00 ml, max
Existent Gum mg/100 ml, max
[0045] Naphtha 66 can be generally defined as a distilled fraction of the
Fischer-Tropsch FT
hydrocarbon liquids, categorized by way of example with a typical boiling
range of 30 C to 200
C, and more preferred 80 C to 120 C. The specific naphtha specification will
be optimized for
each application to maximize syndiesel production, maximize the recovery of
light liquid
hydrocarbon fractions such as propane and butane and partially or fully
eliminate the naphtha
by-product.
[0046] Suitable examples of F1 reactors include fixed bed reactors, such as
tubular reactors,
and multiphase reactors with a stationary catalyst phase and slurry-bubble
reactors. In a fixed
bed reactor, the FI: catalyst is held in a fixed bed contained in tubes or
vessels within the reactor
vessel. The syngas flowing through the reactor vessel contacts the FT catalyst
contained in the
fixed bed. The reaction heat is removed by passing a cooling medium around the
tubes or
vessels that contain the fixed bed. For the slurry-bubble reactor, the FT
catalyst particles are
suspended in a liquid, e.g., molten hydrocarbon wax, by the motion of bubbles
of syngas
sparged into the bottom of the reactor. As gas bubbles rise through the
reactor, the syngas is
absorbed into the liquid and diffuses to the catalyst for conversion to
hydrocarbons. Gaseous
products and unconverted syngas enter the gas bubbles and are collected at the
top of the reactor.
Liquid products are recovered from the suspending liquid using different
techniques such as
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separators, filtration, settling, hydrocyclones, and magnetic techniques.
Cooling coils immersed
in the slurry remove heat generated by the reaction. Other possibilities for
the reactor will be
appreciated by those skilled.
[0047] In the FT process, H2 and CO combine via polymerization to form
hydrocarbon
compounds having varying numbers of carbon atoms. Typically 70% conversion of
syngas to
Fl liquids takes place in a single pass of the FT reactor unit. It is also
common practice to
arrange the multiple FT reactors in series and parallel to achieve conversion
levels of 90+%. A
supplemental supply of hydrogen 42 may be provided to each subsequent FT
reactor stages to
enhance the conversion performance of the subsequent FT stages. After the FT
reactor, products
are sent to the separation stage, to divert the unconverted syngas and light
hydrocarbons
(referred to as FT tailgas), FT water and the FT liquids, which are directed
to the hydrocarbon
upgrader unit denoted as 50. The Fl tailgas becomes the feed Stream for
subsequent FT stages
or is directed to refinery fuel gas 64 in the final FT stage. The upgrader
unit typically contains a
hydrocracking step 52 and a fractionation step 60.
[0048] Hydrocracking denoted as 52 used herein is referencing the splitting
an organic
molecule and adding hydrogen to the resulting molecular fragments to form
multiple smaller
hydrocarbons (e.g., C10H22+H2¨>C4H10 and skeletal isomers+C6H14). Since a
hydrocracking
catalyst may be active in hydroisomerization, skeletal isomerization can occur
during the
hydrocracking step. Accordingly, isomers of the smaller hydrocarbons may be
formed.
Hydrocracking a hydrocarbon stream derived from Fischer-Tropsch synthesis
preferably takes
place over a hydrocracking catalyst comprising a noble metal or at least one
base metal, such as
platinum, cobalt-molybdenum, cobalt-tungsten, nickel-molybdenum, or nickel-
tungsten, at a
temperature of from about 550 F to about 750 F (from about 288 C to about
400 C) and at a
hydrogen partial pressure of about 500 psia to about 1,500 psia (about 3,400
kPa to about 10,400
kPa).
[0049] The hydrocarbons recovered from the hydrocracker are further
fractionated in the
fractionation unit 60 and refined to contain materials that can be used as
components of mixtures
known in the art such as naphtha, diesel, kerosene, jet fuel, lube oil, and
wax. The combined unit
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consisting of the hydrocracker 52 and hydrocarbon fractionator 60 are commonly
known as the
hydrocarbon upgrader 50. As is known by those skilled in the art, several
hydrocarbon treatment
methods can form part of the upgrader unit depending on the desired refined
products, such as
additional hydrotreating or hydroisomerization steps. The hydrocarbon products
are essentially
free of sulfur. The diesel may be used to produce environmentally friendly,
sulfur-free fuel
and/or blending stock for diesel fuels by using as is or blending with higher
sulfur fuels created
from petroleum sources.
[0050] Unconverted vapour streams, rich in hydrogen and carbon monoxide and
commonly
containing inert compounds such as carbon dioxide, nitrogen and argon are
vented from the
process as FT tail gas 44, hydrocracker (HC) offgas 56 and fractionator (frac)
offgas 62. These
streams can be commonly collected as refinery fuel gas 64 and used as fuel for
furnaces and
boilers to offset the external need for natural gas. These streams may also be
separated and
disposed of separately based on their unique compositions, well known to those
skilled in the
art.
[0051] A supplemental supply of hydrogen 74 may be required for the HC unit
54 and the
natural gas hydrotreater 18. This hydrogen supply can be externally generated
or optionally
provided from the syngas stream 30 using a pressure swing absorption or
membrane unit (not
shown), although this feature will increase the volume of syngas required to
be generated by the
syngas generator 24.
[0052] Further, useable energy commonly generated as steam from the syngas
stage, denoted
by numeral 32, may be used to generate electric power 70. This is equally true
of useable energy
that can be drawn from the Fischer-Tropsch unit, owing to the fact that the
reaction is very
exothermic and this represents a useable source of energy. This is denoted by
numeral 46.
[0053] Referring now to FIG. 2, to further illustrate the prior art, shown
is an alternate
process flow diagram of a circuit for converting gas-to-liquids with the
result being the
production of naphtha and syndiesel. The components of this process are
generally the same as
that described in FIG. 1 with the common elements denoted with the same
numbers. For this
14
CA 02872194 2014-11-18
process, the syngas generator is changed to be a steam methane reformer (SMR)
25. The SMR
25 may be any suitable catalytic conversion unit, however, as an example, an
SMR that is useful
in this process is that of HaldorTopsoe A/S, Uhde GmbH, CB&I Lummus Company,
Lurgi
GmbH/Air LiquideGruppe, TechnipInc, Foster Wheeler and others. The SMR process
and
apparatus have been found to be effective in executing the methodology of the
present invention
to be discussed hereinafter. Generally, as is known from the SMR process, the
same effectively
involves a thermal catalytic stage which uses steam supply and heat energy to
convert the
preconditioned natural gas feed to a syngas 27 containing primarily hydrogen
and carbon
dioxide.
[0054] An advantage of the SMR technology is that the syngas is very rich
in hydrogen with
a ratio of hydrogen to carbon monoxide typically greater than 3.0:1. This
exceeds the typical
syngas ratio of 2.0:1 usually preferred for the Fischer-Tropsch process. As
such, a hydrogen
separation unit 33 may be used to provide the hydrogen requirement 74 for the
GTL process. As
discussed previously, well known to those skilled in the art, the hydrogen
separator may be a
pressure swing adsorption, an absorption unit and or a membrane separation
unit or any
combination. A water gas shift reaction may also be optionally installed ahead
of the hydrogen
separator. Further, although the SMR does not require an oxygen source as with
the ATR
technology, the SMR process requires external heat energy, typically provided
by natural gas 13
or optionally by use of the excess refinery gas 76 and 104 derived from the FT
tail gas 44 or
upgrader offgases 56 & 62.
[0055] The SMR 25 may contain any suitable catalyst and be operated at any
suitable
conditions to promote the conversion of the hydrocarbon to hydrogen (H,) and
carbon
monoxide(C0). The addition of steam and natural gas may be optimized to suit
the desired
production of hydrogen and carbon monoxide. Generally natural gas or any other
suitable fuel
can be used to provide energy to the SMR reaction furnace. The catalyst
employed for the steam
reforming process may include one or more catalytically active components such
as palladium,
platinum, rhodium, iridium, osmium, ruthenium, nickel, chromium, cobalt,
cerium, lanthanum,
or mixtures thereof. The catalytically active component may be supported on a
ceramic pellet or
a refractory metal oxide. Other forms will be readily apparent to those
skilled.
CA 02872194 2014-11-18
[0056] FIG. 3, depicts an embodiment of the technology described in the
Canadian Patent
No. 2,751,615. Many of the preliminary steps of the process described in Fig.
3 are common
with the process depicted in FIG. 1. At least a portion of the less desirable
FT product, naphtha
66 is recycled as ATR 24 feed through the pre-treatment unit 20 and is fully
destroyed and
converted to additional syngas. Based on the full recycle and conversion of
the naphtha, the
diesel production increase of greater than 10% can be realized, with the
elimination of an
undesirable by-product hydrocarbon stream.
[0057] In the embodiment shown in FIG. 3, several other optional features
are desirable in
addition to naphtha recycle, to enhance the production of syndiesel,
including; (i) a hydrogen
separation unit is added to remove excess hydrogen from the enhanced syngas
for supply to the
Fl unit 40 and product upgrades 50; (ii) A portion of hydrogen rich streams
not desired to be
used as fuel, separately or combined all together as refinery fuel 64, can be
recycled back 102 to
the ATR 24 by way of the pre-treatment unit 20; (iii) A optional carbon
dioxide removal stage
21 may be installed on the F.1 syngas feedstream to reduce the inert vapour
load on the FT unit
40, and at least a portion of the carbon dioxide 12 may be reintroduced into
the ATR 24 by way
of the pre-treatment unit 20 for purposes of reverse shifting and recycling
carbon to enhance the
production of syndiesel.
[0058] FIG. 4 sets forth a further variation on the overall process that is
set forth in FIG 3. As
is evinced from FIG. 4, many of the preliminary steps are common with that
which is shown in
FIG. 2. In this variation, and similar to the variation described by FIG. 3,
the process employs
the recycle of at least a portion of the naphtha 100 to enhance the production
of syndiesel using a
SMR syngas generator. Similarly the optional features described for FIG. 3 can
equally apply to
FIG. 4.
[0059] A further variation of the overall process embraced by the
technology discussed in the
Canadian Patent No. 2,751,615 shown in FIG. 5. In essence, the process flow as
shown in FIG. 5
combines the unit operations of the SMR 25 and the ATR 24 syngas generators
with the primary
embodiment of this invention, namely the recycle of at least a portion of the
naphtha, to create
16
CA 02872194 2014-11-18
the maximum conversion of carbon to syndiesel. Further, the optional features
as described in
FIGS. 3 and 4, combined with the naphtha recycle, may create even further
benefits to further
enhancement of syndiesel production without any nonuseful by-products. The
sizing of the ATR
and SMR syngas generators are specific to each feed gas compositions and site
specific
parameters to optimize the production of syndiesel. Further the feedstreams
for the ATR and
SMR may be common or uniquely prepared in the pre-treatment unit to meet
specific syngas
compositions desired at 26 and 27. Similarly, the hydrogen rich syngas stream
or portion
thereof, from the SMR can be optionally preferred as the feed stream to the
hydrogen separation
unit 33. By way of example, the preferred steam to carbon ratios at streams 22
and 23 for the
ATR and SMR may be different, thereby requiring separate pre-treatment steps.
[0060] Turning to FIG. 6, as shown is yet another variation of the overall
process disclosed in
the Canadian Patent No. 2,751,615 combining the benefits of FIGS. 3 and 4. In
this
embodiment, both the SMR and ATR unit operations, combined with the naphtha
recycle are
amalgamated into an integrated unit operation whereby the heat energy created
by the ATR 24
becomes the indirect heat energy required by the SMR reactor tubes 25. This
embodiment
allows the integrated ATR/SMR unit, the XTR to be strategically designed to
maximize the
carbon conversion to syndiesel by creating the optimum Fischer-Tropsch 40 and
hydrogen
separator 33 syngas feed with optimum hydrogen to carbon monoxide ratio and
the minimum
quantity of natural gas, steam and oxygen, while maximizing syndiesel
production without the
production of any non-useful hydrocarbon by-product. All other optional
features remain the
same as FIGS. 3, 4 and 5. As used herein, "integrated" in reference to the
ATR/SMR means a
merged unit where the two distinct operations are merged into one.
[0062] The hydrocarbon synthesis processes described in prior art and in
the Canadian Patent
No. 2,751,615 are very efficient in retaining and managing carbon, and can
produce a very high
yield synthetic hydrocarbon products while converting greater than 60% of the
carbon in the
feed streams, and more preferred greater than about 70% of the carbon in the
feed streams. The
unconverted carbon (about 30%) can be captured and commercially sold for
commercial use or
for enhanced oil recovery, or less preferred, but more typically sequestered
or discharged to
atmosphere as Green House Gases (GHG). The present invention provides a means
for
17
CA 02872194 2016-07-12
converting the by-product CO2 into commercially valuable co-products in an
optimal manner.
One embodiment of the present invention is to integrate a methanol (CH3OH)
synthesis unit to
use all of the excess process and combustion derived CO2 and any externally
available CO2,
through reaction with portions of hydrogen rich syngas and purified hydrogen
(H2), in the
production of these commercially valuable co-products.
[0063] In the hydrocarbon synthesis processes described herein and in the
Canadian Patent
No. 2,751,615, oxygen may be used in the ATR or PDX syngas generator. In one
embodiment,
an oxygen plant (ASU - Air Separation Unit) is used to separate air into near
pure oxygen 02
and near pure nitrogen (N,) streams. This N2 is typically partially or
entirely vented to
atmosphere if there is no commercial or process unit use. A further embodiment
of the present
invention is to integrate an ammonia (NH3) synthesis unit to convert the
excess N2 into ammonia
through reaction with purified hydrogen stream H2. In another embodiment of
the present
invention, a portion of the ammonia is further converted to urea by reaction
with by-product
CO2 in a urea synthesis unit.
[0064] The hydrocarbon synthesis process described herein and in the
Canadian Patent No.
2,751,615 uses a rich hydrogen syngas from a syngas generator to feed an
optimum H2:C0 ratio
of 1.8 to 2.1, more preferred ratio of 2.0 to Fischer Tropsch (FT) Synthesis
Unit.
Simultaneously purified hydrogen (H2) by-product is produced from the Syngas
Generators for
synthetic hydrocarbon upgrading use. Both the rich hydrogen syngas stream and
purified
hydrogen streams can be used coincidental base feed streams for the methanol
and ammonia co-
production discussed above.
[0065] Common hydrocarbon synthesis process units, such as Syngas
Generators, including
Steam Methane Reformers (SMR), Auto-Thermal Reformers (ATR), Partial Oxidation
Units
(PDX) or combinations of above units can be used for the base hydrocarbon
synthesis complex
and integrated for use as co-production syngas generator or hydrogen units for
Ammonia and
Methanol synthesis. The incremental increase in unit capacities provide
economies of scale
co-production that support lowest cost production.
18
CA 02872194 2014-11-18
[0066] In the process of the present invention near 100% of all the by-
product CO2 streams
captured from the hydrocarbon production as unconverted carbon streams, fuel
gas streams and
flue gas streams from combustion systems (i.e. furnaces, boilers, power
generators) can be
converted to valuable commercial co-products.
[0067] Figure 7 describes one configuration of the present invention
whereby a Methanol
Synthesis Unit receives base syngas feed from the Syngas Generators as
generally described in
Figures 1 to 6, and is combined with the feed of excess CO2 and H2 to create
the optimum
methanol syngas feed stream, wherein optimum methanol synthesis stoichiometric
ratio is
defined as;
(H2-0O2)/(CO+CO2) = 2.03
With further processing the methanol can be used to produce numerous products
such as DME
gasoline/diesel, formaldehyde, MTBE, acetic acid, etc.
[0068] In further details, in the embodiment shown in Figure 7, natural gas
12 and/or steam
14 and/or oxygen 204 are used as a feedstock to a syngas generator(s) 24 to
generate a first
hydrogen rich syngas stream 27a, where the ratio of hydrogen to carbon
monoxide is in the
range of about 2:1 to about 6:1. The hydrogen rich syngas generator 24 is
typically composed of
a steam methane reformer (SMR) or an auto thermal reformer (ATR) or parallel
or series
combinations thereof. Alternatively, the syngas generator 24 can be as a
hybrid combination of
an ATR/SMR referred to as a XTR.
[0069] A portion of the first hydrogen rich syngas stream 27a can be
subjected to hydrogen
separation unit 33 to generate a purified hydrogen by-product stream 74 and a
second hydrogen
rich syngas stream 27b. The second hydrogen rich syngas stream 27b has a
hydrogen to carbon
monoxide ratio less than that of the first hydrogen rich syngas stream 27a.
[0070] Any portion of the first hydrogen rich syngas stream 27a and the
second hydrogen
rich syngas stream 27b, or a combination thereof, can be subjected to carbon
dioxide removal
19
CA 02872194 2014-11-18
unit 21 to generate purified hydrogen rich syngas stream 27c and a carbon
dioxide byproduct
stream 21a.
[0071] In one embodiment a combination of the first hydrogen rich syngas
stream 27a and
the second hydrogen rich syngas stream 27b is fed to the carbon dioxide
removal unit 21.
[0072] In one embodiment, after removal of carbon dioxide, the first
hydrogen rich syngas
stream 27a and the second hydrogen rich syngas stream 27b can be combined to
obtain purified
hydrogen rich syngas stream 27c and the carbon dioxide by-product stream 21a.
[0073] The first hydrogen rich syngas stream 27a and the second hydrogen
rich syngas
stream 27b are combined before or after CO2 removal in unit 21 to create an
optimum
Fischer-Tropsch syngas stream where the preferred ratio of the hydrogen to
carbon monoxide is
2:1. The purified hydrogen rich stream 27c is then fed to the Fischer-Tropsch
upgrader unit 40
to formulate synthesized hydrocarbons.
[0074] Any portion of the first hydrogen rich syngas stream 27a, the second
hydrogen rich
syngas stream 27b, the purified hydrogen rich syngas stream 27c, or a
combination thereof, can
be reacted with carbon dioxide by-product stream 21a, or at least a portion of
the purified
hydrogen by-product stream 74, or a combination thereof to generate an optimum
methanol feed
stream to co-produce methanol 202 in methanol synthesis unit 200, in addition
to the
synthesized hydrocarbons as discussed above. The optimum feed stream for the
methanol
production involve the following reactions:
CO + 2H2 = CH3OH (primary reaction)
CO2 + 3H2 = CH3OH (secondary reaction)
wherein the optimum stoichiometric ratio is defined as (H2-0O2/C0+ CO2) = 2.03
[0075] The purification of the first hydrogen rich stream 27a at hydrogen
unit 33 can be
achieved via pressure swing adsorption (PSA), membrane or liquid absorption
technology or
CA 02872194 2014-11-18
combination of above, or by treating the first hydrogen rich syngas stream to
a water gas shift
(VVGS) reaction prior to pressure swing adsorption (PSA), membrane or liquid
absorption with
optional CO2 removal unit for separate removal of an additional CO2 by-product
stream 21b.
The CO2 by-product stream 21b can optionally be removed from feed stream to
PSA or after
PSA from the tail gas. The CO2 by-product stream 21b is removed directly as a
by-product from
the membrane and liquid absorption steps. The CO2 by-product stream 21b can be
used in the
production of methanol 202, alone or in combination with the carbon dioxide
stream 21a
discussed above.
[0076] In a further embodiment, the unconverted FT Vapours 44 can be
further treated in a
CO, Removal unit 22 to create additional CO2 by-product stream 21c.
Additionally, a further
optional embodiment is to provide separate or dedicated CO2 Removal and
Capture unit(s) 23 to
recover additional CO-, stream 21d from plant combustion flue gas sources from
SMR furnaces,
utility and power boilers and process furnaces using plant fuel gas made up of
natural gas, plant
off-gas streams, and or combinations of above. At least a portion of the
additional CO2
by-product streams 21c and 21d can be combined with the CO2 by-product streams
21a and/or
21b to enhance the production of the methanol co-product.
[0077] Figure 8 describes the optimum composition for syngas feeding the
methanol
synthesis unit based on the main active components CO, H2 and CO2, relative to
the amount of
CO2 in the syngas.
[0078] Figure 9 further describes the optimum syngas H2:CO ratios relative
to the amount of
CO2 in the syngas. It is noted that for all methanol syngas feed streams,
where the CO2 content
is greater than zero (typical and preferred), the H2:CO ratio is always
greater than 2.0, which is
the optimum for Fischer-Tropsch synthesis.
[0079] The high purity oxygen 204, typically greater than 95% purity, more
preferred greater
than 98% purity, for use in the syngas generator 24, when the syngas generator
comprises an
ATR or PDX, can be generated by subjecting air to an air separation unit (ASU)
206, along with
the generation of a nitrogen by-product stream 208.
21
CA 02872194 2014-11-18
[0080] Figure 10 describes one configuration of the present invention
whereby an Ammonia
Synthesis Unit receives excess hydrogen feed 74 from the Hydrogen Separation
Unit 33, and
combined with the feed of nitrogen by-product (N2) 208, creates the optimum
feed to produce
anhydrous ammonia (NH3) co-product.
N2 3H2 = NH3
With further processing and with the addition of by-product CO2 from the
hydrocarbon
production, urea can be co-produced as follows;
2NH3+ CO2= NH2CONH2 + H20.
[0081] The process depicted in Figure 10 is a variation of the process flow
diagram depicted
in Figure 7, wherein at least a portion of the purified hydrogen by-product
stream 74 is reacted
with at least a portion of the nitrogen by-product stream 208 generated from
the air separation
unit 206, to produce ammonia 212 through an ammonia synthesis unit 210. The
ammonia may
then be optionally reacted with the carbon dioxide by-product streams 21a,
21b, 21c, 21d or any
combination thereof to produce urea 216 through a urea synthesis unit 214.
[0082] Figure 11 describes another configuration of the present invention
whereby Ammonia
and Methanol Synthesis Units 210 and 200 as described in Figures 10 and 7,
respectively, are
integrated with the hydrocarbon production plant as described in Figures 1
through 6, and the
combined processes produce synthetic diesel/jet, synthetic wax, ammonia and
methanol, with
optional further processing to obtain DME gasoline/diesel and urea fertilizer.
[0083] The following examples are based on a 104 MMSCFD dry pipeline
natural gas (MW
=17 and 2% CO?) feed capacity 12, and can also be configured for the processes
such as
described in the Canadian Patent No. 2,751,615. This GTL technology
configuration is very
efficient in retaining and converting carbon into about 10,000 BPD of
synthetic hydrocarbon
products from FT Synthesis unit 40 at an overall carbon conversion rate of
greater than 65%.
22
CA 02872194 2014-11-18
There is a by-product CO2 stream 21a of about 1900 TPD available from the CO2
Removal Unit
21 after the production of optimum rich hydrogen syngas stream 27c with H2:CO
ratio = 2.0 for
Fischer Tropsch synthesis (assuming minimal CO2 in stream 27c). If The
following Examples
describe how valuable commercial co-products are produced according to one
embodiment of
the present invention.
[0084] Example 1
This example describes the design basis of a co-production Methanol Plant 200,
whereby an
additional portion of about 356 MMSCFD of syngas stream 27c is removed from
the
Fischer-Tropsch synthesis feed and directed as the base feed to unit 200. The
natural gas 12
required by syngas generator 24 will be increased to about 50% to 204 MMSCFD
and the
by-product CO2 stream 21a would increase to 3800 TPD. Combining a portion of
about 656
TPD CO2 from by-product stream 21a with about 40.6 MMSCFD H2 from stream 74,
the result
would be the optimum feed for co-production of 5,000 TPD or 1,800,000 TPY of
Methanol
by-product. This is the current world scale commercial methanol plant.
a) Partial Stream 27c 356 MMSCFD or 39,035 moles/hr syngas with H2:CO = 2.0
b) Partial Stream 21a 656 TPD CO2 or 1370 moles/hr CO2
c) Partial Stream 74 40.6 MMSCH.) H2 or 4452 moles /hr H2
d) The total syngas to Unit 200 44,856 moles/hr, or 67.94% H2, 29.06% CO, 3.0%
CO,
e) Therefore, optimum syngas to Unit 200 = (67.94-3.0)/29.06+3.0) = 2.03
f) Total stream of 13,011 moles/hr CO + 1,370 moles/hr CO2+ 30,475 moles/hr H2
results in 14,381 moles/hr CH3OH or about 460,000 lb/hr = 5,000 TPD or
1,800,000 TPY methanol
[0085] Example 2
This example describes a design basis of a co-production Ammonia Plant 210,
whereby the Air
Separation Unit produces 3,900 TPD of high purity oxygen 206 for the ATR use.
The
subsequent by-product of nitrogen results in 15,300 TPD N2 as stream 210. A
portion of about
306 MMSCFD H2 from stream 74 is combined with a portion of about 4,194 TPD N2,
the result
23
CA 02872194 2014-11-18
would be the optimum feed for the co-production of 5,000 TPD or 1,800,000 TPY
of Ammonia
by-product. This is the current world scale commercial ammonia plant.
a) Partial Stream 208 consisting of 4,194 TPD N2 or 11,333 moles/hr
b) Partial Stream 74 consisting of 306 MMSCFD H2 or 33,553 moles/hr H2
c) The total feed stream to Unit 210 of 44,886 moles/hr, or 25.2% N2 and 74.8%
H2
d) 11,333 moles/hr N2 33,553 moles/hr H2results in 22,666 moles/hr NH3 or
about
453,320 lb/hr = 5,000 TPD or 1,800,000 TPY ammonia
[0086] Example 3
This example describes a design basis for a co-production Urea Plant 214,
whereby a portion of
the ammonia production 212 and additional by-product CO2 from the GTL plant
(21a, b, c or d)
is combined to produce urea fertilizer.
a) Partial Stream 212 consisting of 4,202 TPD NH3 or 19,048 moles/hr
b) A further portion of Stream 21a consisting of 3,144 TPD CO2 and Partial
Stream
21 b, c or d consisting of 1,417 TPD CO2 for total of 4,561 TPD CO2 or 9,524
moles/hr CO2
c) The total feed stream to Unit 214 of 28,572 moles/hr, or 66.7% NH3 and
33.3%
CO2
d) 19,048 moles/hr NH3 + 9,524 moles/hr CO2 results in 9,524 moles/hr
NH2CONH2
or about 628,584 lb/hr = 6,800 TPD or 2,400,000 TPY urea
[0087] The examples described above illustrate how the integration of the
co-product units
can recover a significant portion of the GTL plant GHG CO2 emissions and co-
produce 5,000
TPD Methanol and 5,000 TPD Ammonia or 6,800 TPD of Urea, and result in a "Near
Zero
GHG Emissions World Class GTL plant".
[0088] These embodiments of the present invention can be used with all
existing and new
grassroots hydrocarbon production plants of any scale to enhance performance
and economics.
[0089] The net effect of the present invention is that the hydrocarbon
synthesis complex
becomes:
24
CA 02872194 2014-11-18
= The lowest cost producer of synthesized hydrocarbon products and co-
products such as
ammonia and methanol.
= 100% of all the carbon in captured CO2 by-product streams can be
converted to valuable
commercial co-products.
= The GTL Complex is "Near-Zero GHG Emission Green production plant"-best
in class.
[0090]
Although embodiments of the invention have been described above, it is not
limited
thereto and it will be apparent to those skilled in the art that numerous
modifications form part
of the present invention insofar as they do not depart from the spirit, nature
and scope of the
claimed and described invention.
