U.S. patent application number 14/008355 was filed with the patent office on 2014-01-23 for method of removing heavy hydrocarbons.
This patent application is currently assigned to JAPAN OIL, GAS AND METALS NATIONAL CORPORATION. The applicant listed for this patent is Kenichi Kawazuishi, Tomoyuki Mikuriya, Shuhei Wakamatsu, Fuyuki Yagi. Invention is credited to Kenichi Kawazuishi, Tomoyuki Mikuriya, Shuhei Wakamatsu, Fuyuki Yagi.
Application Number | 20140021094 14/008355 |
Document ID | / |
Family ID | 46930120 |
Filed Date | 2014-01-23 |
United States Patent
Application |
20140021094 |
Kind Code |
A1 |
Kawazuishi; Kenichi ; et
al. |
January 23, 2014 |
METHOD OF REMOVING HEAVY HYDROCARBONS
Abstract
Heavy hydrocarbons contained in FT off gas of a GTL process are
removed by bringing the FT off gas into contact with absorption
oil, by introducing the FT off gas into a distillation tower, by
cooling the FT off gas or by driving the FT off gas into an
adsorbent. A burner tip for heating a reformer tube, using FT off
gas as fuel, is prevented from being plugged by the deposition of
heavy hydrocarbons contained in the FT off gas.
Inventors: |
Kawazuishi; Kenichi;
(Yokohama-shi, JP) ; Yagi; Fuyuki; (Yokohama-shi,
JP) ; Wakamatsu; Shuhei; (Yokohama-shi, JP) ;
Mikuriya; Tomoyuki; (Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kawazuishi; Kenichi
Yagi; Fuyuki
Wakamatsu; Shuhei
Mikuriya; Tomoyuki |
Yokohama-shi
Yokohama-shi
Yokohama-shi
Yokohama-shi |
|
JP
JP
JP
JP |
|
|
Assignee: |
JAPAN OIL, GAS AND METALS NATIONAL
CORPORATION
Tokyo
JP
INPEX CORPORATION
Tokyo
JP
JX NIPPON OIL & ENERGY CORPORATION
Tokyo
JP
CHIYODA CORPORATION
Yokohama-shi, Kanagawa
JP
COSMO OIL CO., LTD.
Tokyo
JP
NIPPON STEEL & SUMIKIN ENGINEERING CO., LTD.
Tokyo
JP
JAPAN PETROLEUM EXPLORATION CO., LTD.
Tokyo
JP
|
Family ID: |
46930120 |
Appl. No.: |
14/008355 |
Filed: |
March 31, 2011 |
PCT Filed: |
March 31, 2011 |
PCT NO: |
PCT/JP2012/001965 |
371 Date: |
September 27, 2013 |
Current U.S.
Class: |
208/91 ; 208/264;
208/85; 208/88; 208/92 |
Current CPC
Class: |
C10G 29/205 20130101;
B01D 2256/24 20130101; B01D 53/02 20130101; B01D 2257/702 20130101;
C10G 21/14 20130101; C01B 3/384 20130101; C10G 2300/1022 20130101;
C01B 2203/0827 20130101; C10G 2/32 20130101; C01B 2203/062
20130101; C01B 2203/0238 20130101; C10G 25/003 20130101; Y02P
20/141 20151101; B01D 53/1487 20130101; C10G 5/04 20130101; B01D
53/002 20130101; C01B 2203/0233 20130101; C10G 7/02 20130101; Y02P
20/142 20151101 |
Class at
Publication: |
208/91 ; 208/88;
208/92; 208/85; 208/264 |
International
Class: |
C10G 7/02 20060101
C10G007/02; C10G 25/00 20060101 C10G025/00; C10G 29/20 20060101
C10G029/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2011 |
JP |
2011-078804 |
Claims
1. A method of producing various hydrocarbon oils from natural gas
comprising: a synthesis gas production step of producing synthesis
gas containing hydrogen and carbon monoxide as main components by
causing natural gas containing methane as main component to react
with steam and/or carbon dioxide in a heated reformer tube filled
with a reforming catalyst; a Fischer-Tropsch synthesis step of
producing Fischer-Tropsch oil by subjecting the synthesis gas
produced in the synthesis gas production step to a Fischer-Tropsch
synthesis reaction and subsequently separating FT off gas
containing gaseous products and unreacted synthesis gas; and an
upgrading step of producing various hydrocarbon oils by subjecting
the Fischer-Tropsch oil to a hydrotreating, hydroisomerization and
hydrocracking process, wherein the FT off gas is recycled as a fuel
for heating the reformer tube after heavy hydrocarbons contained in
the FT off gas is removed.
2. The method according to claim 1, wherein the heavy hydrocarbons
are hydrocarbons having five or more carbon atoms per molecule.
3. The method according to claim 1, wherein the heavy hydrocarbons
are removed by bringing the FT off gas into contact with absorption
oil directly.
4. The method according to claim 3, wherein the absorption oil is
one of kerosene and gas oil.
5. The method according to claim 1, wherein the heavy hydrocarbons
are removed by distilling the FT off gas.
6. The method according to claim 1, wherein the heavy hydrocarbons
are removed by cooling the FT off gas.
7. The method according to claim 1, wherein the heavy hydrocarbons
are removed from the FT off gas by adsorption.
8. The method according to claim 7, wherein an adsorbent used for
the adsorption is active carbon.
Description
TECHNICAL FIELD
[0001] This invention relates to a method of removing heavy
hydrocarbons contained in off gas produced from the Fischer-Tropsch
reaction step of the gas-to-liquid (GTL) process and utilizing the
treated off gas as fuel in the synthesis gas production step of the
GTL process.
BACKGROUND ART
[0002] Natural gas is regarded as a promising fuel that places less
load to the environment as compared with petroleum-based fuels
because, when combusted, natural gas gives off neither sulfur
oxides nor particulate substances that will contaminate the
environment and produces less carbon dioxide per unit amount of
generated heat.
[0003] For this reason, natural gas is increasingly attracting
attention as an alternative fuel that can replace petroleum in the
field of energy supply because solutions to the above environmental
problems are urgently being looked for and diverse resources are
required all over the world.
[0004] The GTL technology is known to provide methods of producing
liquid synthetic hydrocarbons such as naphtha, kerosene, gas oil
and so on by way of chemical reactions using natural gas as a raw
material. Processes based on the GTL technology generally include a
step of producing synthesis gas (i.e. a gaseous mixture of carbon
monoxide and hydrogen) by way of a reforming reaction (synthesis
gas production step), a step of producing synthesis oil containing
straight chain hydrocarbons as main components from the synthesis
gas by way of a Fischer-Tropsch (FT) synthesis reaction (FT
synthesis step) and a step of turning the synthesis oil into
product oil by way of a hydrotreating, Hydroisomerization and
hydrocracking reaction (upgrading step).
[0005] Synthesis gas is produced by way of a reforming reaction of
natural gas. Known techniques for producing synthesis gas,
utilizing a reforming reaction, include the steam reforming method,
the CO.sub.2 reforming method, the autothermal reforming method
(ATR), the catalytic partial oxidation method (CPDX) and the direct
partial oxidation method (PDX).
[0006] From the viewpoint of underlying principles, reforming
reactions are roughly classified into: steam reforming reaction of
producing synthesis gas by adding steam to natural gas, following
the reaction equation (1) shown below; and carbon dioxide reforming
reaction of producing synthesis gas by adding carbon dioxide to
natural gas or by using carbon dioxide contained in natural gas,
following the reaction equation (2) shown below. Note that
reforming reactions of methane contained in natural gas are
represented as examples in the equations shown below.
CH.sub.4+H.sub.2O.fwdarw.CO+3H.sub.2
.DELTA.H.sub.298=+206 kJ/mol equation (1)
CH.sub.4+CO.sub.2.fwdarw.2CO+2H.sub.2
.DELTA.H.sub.298=+248 kJ/mol equation (2)
[0007] As seen from the above equation (1) and (2), both of the
above listed reforming reactions are endothermic reactions, meaning
that the heat necessary for carrying out the reactions needs to be
externally supplied. In this regard, in the case of ATR, CPDX and
PDX, the reforming reaction is driven to proceed by completely
oxidizing a part of the raw material natural gas by means of a
burner and/or a catalyst and using the heat that is generated when
carbon dioxide and water are produced from hydrocarbons such as
methane. Therefore, the overall reaction system is an exothermic
reaction and hence no heat needs to be externally supplied.
[0008] In the case of the steam reforming method and the CO.sub.2
reforming method, on the other hand, a reformer tube that is filled
with a catalyst is arranged in a furnace and the heat necessary for
the reforming reaction is externally supplied by using a heating
means such as a burner.
[0009] The steam reforming method and the CO.sub.2 reforming method
require a large amount of heat for the reforming reactions
particularly when synthesis gas needs to be produced on a large
scale. Hence, since a large reforming equipment needs to be
installed, a scale merit is hardly exploited. For this reason, ATR
and PDX are believed to be suitable for large scale production.
[0010] However, both ATR and PDX involve a step for adding oxygen
to natural gas, which requires an oxygen plant that is highly
costly. Additionally, since heat is produced to a large extent when
oxygen is added to natural gas, a risk of explosion exists. This
means that designing and running an oxygen plant are subjected to
various restrictions.
[0011] On the other hand, both the steam reforming method and the
CO.sub.2 reforming method provide an advantage that, since oxygen
is not introduced into natural gas and their reforming reactions
themselves are endothermic, synthesis gas can be produced in safe.
Additionally, when the steam reforming method and the CO.sub.2
reforming method are concurrently employed, the hydrogen/carbon
monoxide ratio in the produced synthesis gas can be brought close
to 2.0, which is advantageous for the subsequent FT synthesis
reaction.
[0012] As for the disadvantage of the steam reforming method and
the CO.sub.2 reforming method of externally supplying heat, the
efficiency of energy use of the overall GTL process can be improved
by reutilizing the FT off gas produced from the subsequent FT
synthesis step as fuel for heating the reformer tube. FT off gas
refers to gas containing the synthesis gas left unreacted and other
gases such as methane that are secondarily produced in the FT
synthesis step.
[0013] In the FT synthesis step, a unit (--CH.sub.2--) of a
hydrocarbon chain is produced from hydrogen and carbon monoxide and
such units are synthetically combined to grow hydrocarbon chain.
This reaction is an exothermic reaction as a whole that is
expressed by the reaction equation (3) shown below.
(2n+1)H.sub.2+nCO.fwdarw.C.sub.nH.sub.2n+2+nH.sub.2O
.DELTA.H.sub.298=-167 kJ/mol-CO equation (3)
[0014] The number of carbon atoms of the hydrocarbons produced from
the FT synthesis reaction is not fixed and hydrocarbons showing
various degrees of polymerization (n numbers) are produced. The
ratio of the number of the units (--CH.sub.2--) that are actually
used for the growth of hydrocarbon chains to the total number of
the produced units is referred to as chain growth probability
.alpha. and the extent to which hydrocarbon chains showing a
certain degree of polymerization are produced is determined by the
chain growth probability .alpha. (Anderson-Schulz-Flory
distribution). In the FT synthesis step, the reaction is conducted
with .alpha.>0.85 that boosts the production of the kerosene and
gas oil fraction, which is the main target of the GTL process, or
.alpha.>0.90 that boosts the production of the heavier wax
fraction, from which kerosene and gas oil can be obtained by
hydrocracking. However, lighter hydrocarbons that cannot be
satisfactorily grown are also produced to a small extent even with
an .alpha. value in the above cited region. Furthermore, not all
the synthesis gas fed to the FT synthesis step is consumed and the
hydrogen and the carbon monoxide that are supplied are partly left
unreacted.
[0015] Hydrocarbons having a large number of carbon atoms and
showing a high boiling point that are the target of the FT
synthesis reaction are taken out as liquid components, while
H.sub.2O and lighter hydrocarbons such as methane and ethane that
are byproducts of the reaction as well as unreacted hydrogen and
carbon monoxide are taken out as mixed gaseous components. Of
these, hydrogen and carbon monoxide can be reutilized in the FT
synthesis reaction. Therefore, H.sub.2O and other unnecessary
substances are removed from the mixed gaseous components by cooling
and condensing the gaseous components by means of cooling water and
the mixture gas containing hydrogen, carbon monoxide, methane,
ethane and other low boiling point hydrocarbons that are not
condensed are recycled to the FT synthesis reaction. However, since
methane and some other hydrocarbons do not react further even if
led back to the FT synthesis reaction, the ratio of methane
contained in the gaseous components gradually rises. To prevent the
methane and some other hydrocarbons from being accumulated in the
FT synthesis reaction system, part of the mixture gas is drawn out
and removed as off gas (FT off gas). The off gas produced in this
way contains combustible components such as methane to a large
extent and hence it can be used as fuel for heating the reformer
tube.
SUMMARY OF INVENTION
Technical Problem
[0016] However, FT off gas contains a small extent of heavy
hydrocarbons that are the target product of the FT synthesis
reaction. Particularly, heavy hydrocarbons having five or more
carbon atoms per molecule can be thermally decomposed or
polymerized and deposited as liquid or solid substances when
heated. Therefore, when off gas is used as fuel for heating the
reformer tube without being preprocessed, the deposited heavy
hydrocarbons can plug a tip of the burner for heating the reformer
tube to prevent the burner from stably operating for heating and
consequently reduce the efficiency of the GTL process.
Solution to Problem
[0017] As a result of intensive research efforts, the inventors of
the present invention completed this invention as means for solving
the above-identified problem. According to the present invention,
there is provided a method of producing various hydrocarbon oils
from natural gas including:
[0018] a synthesis gas production step of producing synthesis gas
containing hydrogen and carbon monoxide as main components by
causing natural gas containing methane as main component to react
with steam and/or carbon dioxide in a heated reformer tube filled
with a reforming catalyst;
[0019] a Fischer-Tropsch synthesis step of producing
Fischer-Tropsch oil by subjecting the synthesis gas produced in the
synthesis gas production step to a Fischer-Tropsch reaction and
subsequently separating FT off gas containing gaseous products and
unreacted synthesis gas; and
[0020] an upgrading step of producing various hydrocarbon oils by
subjecting the Fischer-Tropsch oil to a hydrotreating,
hydroisomerization and hydrocracking process, wherein
[0021] the FT off gas is recycled as a fuel for heating the
reformer tube after heavy hydrocarbons contained in the FT off gas
is removed.
Advantageous Effects of Invention
[0022] According to the present invention, heavy hydrocarbons
having five or more carbon atoms per molecule that are contained in
the FT off gas are removed before the FT off gas is supplied to the
burner. Thus, the burner tip is prevented from being plugged as a
result of thermal decomposition or polymerization of such heavy
hydrocarbons, and the reformer tube is allowed to stably operate
for a long period. Additionally, since FT off gas can be utilized
effectively as fuel, the efficiency of energy use of the overall
GTL process can be improved.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is a schematic illustration of the method of removing
heavy hydrocarbons in Example 1.
[0024] FIG. 2 is a schematic illustration of the method of removing
heavy hydrocarbons in Example 2.
[0025] FIG. 3 is a schematic illustration of the method of removing
heavy hydrocarbons in Example 3.
[0026] FIG. 4 is a schematic illustration of the method of removing
heavy hydrocarbons in Example 4.
[0027] FIG. 5 is a schematic illustration of the method of removing
heavy hydrocarbons in Example 5.
DESCRIPTION OF EMBODIMENTS
[0028] Embodiments of a method of recycling FT off gas as fuel for
a synthesis gas production step according to the present invention
will be described below.
[0029] The synthesis gas produced by means of a reforming reaction
is driven to flow into a bubble tower reactor installed on the way
of the FT synthesis step from the bottom thereof. The bubble tower
reactor is filled with slurry consisting of liquid hydrocarbons
produced as a result of an FT synthesis reaction and catalyst
particles. When the synthesis gas rises through the slurry
contained in the tower, hydrocarbons are produced as a result of an
FT synthesis reaction between carbon monoxide and hydrogen gas.
[0030] Of the synthesized hydrocarbons, liquid ones are led into a
separator as slurry along with catalyst particles. The solid
components such as catalyst particles and the liquid components
including liquid hydrocarbons are separated from each other in the
separator. The separated solid components are then returned to the
bubble tower reactor. The liquid components, on the other hand, are
supplied to a distillation tower and heated for fractional
distillation of producing a naphtha fraction (boiling point: about
150.degree. C. or lower), a kerosene/gas oil fraction (boiling
point: about 150.degree. C. to 350.degree. C.) and a wax fraction
(boiling point: about 350.degree. C. or higher). Subsequently, each
fraction is fed to the upgrading step.
[0031] On the other hand, the gaseous components including
unreacted synthesis gas and synthesized gaseous hydrocarbons are
discharged from the top of the bubble tower reactor and supplied to
a hydrocarbon collector. Any type of hydrocarbon collector can be
used. A hydrocarbon collector to be used herein typically cools the
gaseous components by means of a heat exchanger using cooling water
and separates the liquid components including condensed water and
liquid hydrocarbons from the gaseous components that are left
uncondensed. Among the separated liquid components, water is
removed and liquid hydrocarbons are led into the distillation
tower. The gaseous components left in the hydrocarbon collector
after the separation mainly include unreacted synthesis gas and
light hydrocarbons such as methane and ethane, but they also
include heavy hydrocarbons, which are also left there by a small
amount. The gaseous components are reintroduced into a bottom
section of the bubble tower reactor and reutilized for the FT
synthesis reaction. At this time, a part of the reintroduced
gaseous components is drawn out and discharged as off gas (FT off
gas) in order to prevent accumulation of methane, ethane and the
like which does not react further in the bubble tower reactor, and
the FT off gas is utilized as fuel gas for heating the reformer
tube for the reforming reaction in the synthesis gas production
step.
[0032] However, thus discharged FT off gas that is to be recycled
and utilized as fuel gas for the reforming reaction also contains
heavy hydrocarbons by a small amount. When off gas containing such
heavy hydrocarbons is utilized as fuel gas, the contained heavy
hydrocarbons are deposited by way of thermal decomposition and
polymerization and plug the burner tip to become an obstacle for
the operation of stably heating the reformer tube for a long
period. According to the present invention, this problem is
dissolved by removing the heavy hydrocarbons contained in FT off
gas before the FT off gas is utilized as fuel for heating a
reformer tube.
[0033] Now, the present invention will be described in more detail
by way of preferred embodiments of the method of removing heavy
hydrocarbons according to the present invention. Note, however,
that the present invention is by no means limited to the following
embodiments.
[0034] The first embodiment of the present invention is a method of
bringing FT off gas into contact with absorption oil directly in
order to absorb the heavy hydrocarbons contained in FT off gas by
the absorption oil.
[0035] While any oil can be used as the absorption oil so long as
it can absorb hydrocarbons having five or more carbon atoms per
molecule contained in FT off gas, relatively light kerosene or gas
oil may preferably be used. The kerosene fraction or the gas oil
fraction that is a final product of a GTL process, for example, can
be used. Alternatively, if appropriate intermediate oil is
available in a GTL process, such oil may be used. The kerosene or
gas oil fraction obtained as a result of fractional distillation by
a distillation tower or a product obtained by hydrotreating such a
fraction may be used as the intermediate oil.
[0036] Similarly, the conditions of absorption are not subjected to
any particular limitations and it can be appropriately selected
depending on the absorption oil to be used and other
considerations. However, the temperature is preferably between
10.degree. C. and 50.degree. C. and close to the room temperature
and the pressure is preferably between 2.4 MPaG and 3.2 MPaG from
the viewpoint of preventing absorption oil from evaporating.
[0037] The second embodiment of the present invention is a method
of introducing FT off gas into a distillation tower and distilling
and separating the heavy hydrocarbons contained in the FT off
gas.
[0038] Any distillation tower can be used so long as it can
separate hydrocarbons having five or more carbon molecule per
molecule from the FT off gas introduced in it by distillation. A
distillation tower may be additionally installed for a GTL process
that embodies the present invention. However, if a distillation
tower that can separate hydrocarbons having five or more carbons
per molecule from the FT off gas introduced therein exists in a GTL
process, the FT off gas may be introduced in it. For example, a
distillation tower is normally operated to separate the product
(hydrogenated naphtha), obtained by hydroprocessing the naphtha
fraction drawn from the top of a distillation tower, into liquid
naphtha and gas containing light hydrocarbons as main components.
Then, FT off gas may be introduced into such a distillation tower
and the gas obtained as a result of such separation may be used as
fuel for heating a reformer tube.
[0039] While the conditions of distillation are not subjected to
any particular limitations, preferably the operation of
distillation is conducted with a temperature between -50.degree. C.
and 40.degree. C. and a pressure level between 2.4 MPaG and 3.2
MPaG at the tower top.
[0040] The third embodiment of the present invention is a method of
cooling FT off gas and condensing and separating the heavy
hydrocarbons contained in it.
[0041] While the cooling conditions are not subjected to any
particular limitations so long as the hydrocarbons having five or
more carbon atoms per molecule contained in FT off gas are
separated under the selected conditions, preferably the temperature
is between 5.degree. C. and 20.degree. C. and the pressure is
between 2.4 MPaG and 3.2 MPaG for example. Similarly, any cooling
method can be used. For example, cooling water or a heat exchanger
using water discharged from the GTL process may be used.
[0042] The fourth embodiment of the present invention is a method
of removing the heavy hydrocarbons contained in FT off gas by
adsorption.
[0043] While any adsorbent can be used so long as it can separate
the hydrocarbons having five or more carbon atoms per molecule
contained in FT off gas, active carbon can be employed to adsorb
the hydrocarbons for instance. When active carbon is employed, the
operating condition of an adsorption is preferably such that the
temperature is between 20.degree. C. and 40.degree. C. and the
pressure level is between 0 MPaG and 3.2 MPaG. Additionally, the
active carbon is preferably regenerated by way of a steaming
treatment that is conducted at a temperature between 100.degree. C.
and 150.degree. C. and a pressure level between 0 MPaG and 0.35
MPaG. With this method, two adsorption towers may preferably be
installed in a GTL process and operated alternately for adsorption
and regeneration. Then, the adsorption towers can be operated
continuously.
[0044] Any of the above-described first through fourth embodiments
may not necessarily be adopted alone. In other words, the
advantages of the present invention can be boosted when, for
example, FT off gas is brought into contact with absorption oil
(the first embodiment) or an adsorbent is applied thereto (the
fourth embodiment) while the FT off gas is being cooled (the second
embodiment).
[0045] Now, the present invention will be described by way of
examples for the purpose of better understanding of the present
invention. However, the present invention is by no means limited by
the examples.
Example 1
[0046] Gas produced from an FT synthesis step in a plant using GTL
technology, that includes unreacted synthesis gas and gaseous
hydrocarbons, was cooled and the gas phase and the liquid phase
were separated from each other to obtain FT off gas having a
composition shown in Table 1. Note that, in Table 1, Cn denotes
hydrocarbons having n carbon atoms per molecule and C5+ denotes
hydrocarbons having five or more carbon atoms per molecule. The
temperature and the pressure of the obtained FT off gas was
respectively 45.degree. C. and 2.75 MPaG and the flow rate of the
FT off gas was 1,000 kmol/h (=15,284 kg/h). The content of the
heavy hydrocarbons having five or more carbon atoms per molecule
was 4.32 wt %.
TABLE-US-00001 TABLE 1 Components Composition ratio of FT off gas
(mol %) H.sub.2 27.29 N.sub.2 0.16 CO 15.56 CO.sub.2 0.58 H.sub.2O
0.45 C1 53.40 C2 0.39 C3 0.81 C4 0.48 C5+ 0.79 Total 100.00
[0047] The obtained FT off gas was cooled to 10.degree. C. under a
pressure level of 2.7 MPaG and the condensed liquid components were
separated from the uncondensed fuel gas. Then, the heavy
hydrocarbons contained in the liquid components were collected
(FIG. 1). Subsequently, the content of the heavy hydrocarbons
having five or more than five carbon atoms per molecule contained
in the fuel gas were measured.
Example 2
[0048] The FT off gas obtained in Example 1 was introduced into a
distillation tower and the fuel gas drawn from the tower top and
the liquid components drawn from the tower bottom were separated
from each other (FIG. 2). The pressure of the FT off gas at the
tower top was 2.65 MPaG and the temperature at the tower bottom was
198.degree. C. while the temperature at the tower top was
-37.degree. C. Thereafter, the content of the heavy hydrocarbons
having five or more carbon atoms per molecule contained in the fuel
gas that was obtained at the tower top was measured.
Example 3
[0049] The FT off gas obtained in Example 1 was brought into
contact with absorption oil that was equivalent to gas oil in a
single stage under conditions of a pressure level of 2.7 MPaG and a
temperature of 48.degree. C. of the FT off gas and the heavy
hydrocarbons absorbed in the absorption oil were collected (FIG.
3). Table 2 shows the distillation property of the employed
absorption oil. The flow rate of the absorption oil was 10,000
kg/h. Thereafter, the content of the hydrocarbons having five or
more carbon atoms per molecule that were contained in the fuel gas
and not absorbed by the absorption oil was measured.
TABLE-US-00002 TABLE 2 Distillation (%) (.degree. C.) 5 250 10 264
20 271 50 296 80 335 90 361 95 382
Example 4
[0050] The temperature at which the FT off gas was brought into
contact with absorption oil in Example 3 was lowered to 10.degree.
C. and the heavy hydrocarbons were collected (FIG. 4). The flow
rate of the absorption oil was 10,000 kg/h. Thereafter, the content
of the heavy hydrocarbons having five or more carbon atoms per
molecule that were contained in the fuel gas and not absorbed by
the absorption oil was measured.
Example 5
[0051] The FT off gas same as that of Example 3 was brought into
contact with absorption oil by means of an 8-stage absorption tower
to collect the heavy hydrocarbons (FIG. 5). The pressure of the FT
off gas at the tower top was 2.65 MPaG and the temperature at the
tower bottom was 49.degree. C. while the temperature at the tower
top was 50.degree. C. The flow rate of the absorption oil was
10,000 kg/h. Thereafter, the content of the heavy hydrocarbons
having five or more carbon atoms per molecule that were contained
in the fuel gas and not absorbed by the absorption oil was
measured.
Examples 6 Through 8
[0052] In Examples 6 through 8, experiments respectively same as
those of Examples 3 through 5 were conducted except that the flow
rate of absorption oil was doubled to 20,000 kg/h.
[0053] Table 3 shows the content of the heavy hydrocarbons having
five or more carbon atoms per molecule contained in the fuel gas
that was obtained after removing heavy hydrocarbons, the flow rate
of the collection liquid or the absorption oil and the ratio by
which the heavy hydrocarbons contained in the FT off gas were
distributed to the collection oil or the absorption oil of each of
Examples 1 through 8. In each of the examples, the effect of
removing heavy hydrocarbons from fuel gas was proved.
TABLE-US-00003 TABLE 3 flow rate of distribution of heavy fuel gas
collection hydrocarbons content of liquid/ to to collection flow
heavy absorption fuel liquid/absorption rate hydrocarbon oil gas
oil (kg/h) (wt %) (kg/h) (wt %) (wt %) Ex. 1 14940 2.34 344 52.9
47.1 Ex. 2 14627 0.06 657 1.4 98.6 Ex. 3 14716 1.52 10568 33.9 66.1
Ex. 4 14411 0.53 10873 11.5 88.5 Ex. 5 14550 0.53 10734 11.7 88.3
Ex. 6 14544 1.02 20740 22.6 77.4 Ex. 7 14237 0.32 21047 6.8 93.2
Ex. 8 14362 0.09 20922 2.0 98.0
This application claims the benefit of Japanese Patent Application
No. 2011-078804, filed Mar. 31, 2011, which is hereby incorporated
by reference herein in its entirety.
* * * * *