U.S. patent application number 13/809104 was filed with the patent office on 2013-05-09 for fischer-tropsch synthesis process and system.
This patent application is currently assigned to SHENHUA GROUP CORPORATION LIMITED. The applicant listed for this patent is Yifeng Bu, Lei Gong, Quan Lin, Yijun Lv, Yulin Shi, Hongxue Wang, Xiuzhang Wu. Invention is credited to Yifeng Bu, Lei Gong, Quan Lin, Yijun Lv, Yulin Shi, Hongxue Wang, Xiuzhang Wu.
Application Number | 20130116348 13/809104 |
Document ID | / |
Family ID | 43101414 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130116348 |
Kind Code |
A1 |
Shi; Yulin ; et al. |
May 9, 2013 |
FISCHER-TROPSCH SYNTHESIS PROCESS AND SYSTEM
Abstract
The present invention relates to a Fischer-Tropsch synthesis
process and system. The process comprises: a) introducing a
feedstock gas containing CO and H.sub.2 into a first stage
Fischer-Tropsch synthesis reactor to carry out a Fischer-Tropsch
synthesis reaction; b) separating products of the first stage
Fischer-Tropsch synthesis reaction, to separate water from the
unconverted tail gas and to obtain hydrocarbon products and the
unconverted tail gas; c) introducing the unconverted tail gas
obtained in Step b) into a second stage Fischer-Tropsch synthesis
reactor to carry out a Fischer-Tropsch synthesis reaction; d)
separating products of the second stage Fischer-Tropsch synthesis
reaction, to separate water from the unconverted tail gas, with a
portion of the unconverted tail gas of the second stage
Fischer-Tropsch synthesis reaction being returned to the second
stage Fischer-Tropsch synthesis reactor for recycle reactions. The
process and system are suitable for large-scale industrialized
production.
Inventors: |
Shi; Yulin; (Beijing,
CN) ; Wu; Xiuzhang; (Beijing, CN) ; Gong;
Lei; (Beijing, CN) ; Lin; Quan; (Beijing,
CN) ; Lv; Yijun; (Beijing, CN) ; Bu;
Yifeng; (Beijing, CN) ; Wang; Hongxue;
(Beijing, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Shi; Yulin
Wu; Xiuzhang
Gong; Lei
Lin; Quan
Lv; Yijun
Bu; Yifeng
Wang; Hongxue |
Beijing
Beijing
Beijing
Beijing
Beijing
Beijing
Beijing |
|
CN
CN
CN
CN
CN
CN
CN |
|
|
Assignee: |
SHENHUA GROUP CORPORATION
LIMITED
Beijing
CN
|
Family ID: |
43101414 |
Appl. No.: |
13/809104 |
Filed: |
July 8, 2011 |
PCT Filed: |
July 8, 2011 |
PCT NO: |
PCT/CN11/77008 |
371 Date: |
January 8, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/CN2011/077008 |
Jul 8, 2011 |
|
|
|
13809104 |
|
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Current U.S.
Class: |
518/705 ;
422/187 |
Current CPC
Class: |
C10G 2300/4012 20130101;
C10G 2/32 20130101; C10K 1/005 20130101; C10G 2/34 20130101; C10G
2/332 20130101; C10G 2/342 20130101; C10G 2300/4006 20130101 |
Class at
Publication: |
518/705 ;
422/187 |
International
Class: |
C10G 2/00 20060101
C10G002/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 2010 |
CN |
201010228831.6 |
Oct 20, 2010 |
CN |
201010514370.9 |
Claims
1. A two-stage Fischer-Tropsch synthesis process, comprising the
following steps: a) a first stage Fischer-Tropsch synthesis
reaction introducing a feedstock gas containing CO and H.sub.2 into
a first stage Fischer-Tropsch synthesis reactor to carry out a
Fischer-Tropsch synthesis reaction under the action of catalysts,
to obtain products of the first stage Fischer-Tropsch synthesis
reaction; wherein the CO conversion rate in the first stage
Fischer-Tropsch synthesis reactor is controlled at 30%-70%; b)
separation of the products of the first stage Fischer-Tropsch
synthesis reaction separating the products of the first stage
Fischer-Tropsch synthesis reaction, so as to separate water from
the unconverted tail gas and to obtain hydrocarbon products and an
unconverted tail gas of the first stage Fischer-Tropsch synthesis
reaction; c) a second stage Fischer-Tropsch synthesis reaction
introducing the unconverted tail gas obtained from Step b) into a
second stage Fischer-Tropsch synthesis reactor to carry out a
Fischer-Tropsch synthesis reaction under the action of catalysts,
to obtain products of the second stage Fischer-Tropsch synthesis
reaction; d) separation of the products of the second stage
Fischer-Tropsch synthesis reaction separating the products of the
second stage Fischer-Tropsch synthesis reaction, so as to separate
water from the unconverted tail gas and to obtain hydrocarbon
products and an unconverted tail gas of the second stage
Fischer-Tropsch synthesis reaction, with a portion of the
unconverted tail gas of the second stage Fischer-Tropsch synthesis
reaction being returned to the second stage Fischer-Tropsch
synthesis reactor for recycle reactions, wherein the unconverted
tail gas of the first stage Fischer-Tropsch synthesis reaction is
not returned to the first stage Fischer-Tropsch synthesis reactor
for recycle reactions; in Step a), the fresh synthetic gas as the
feedstock gas passes through the first stage Fischer-Tropsch
synthesis reactor in one way, and wherein the separations in Steps
b) and d) comprise oil-water-gas separations of top products of the
Fischer-Tropsch synthesis reactions.
2. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein the volume ratio of CO to H.sub.2 in the feedstock
gas is 0.67-2.2.
3. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein the oil-water-gas separation of the top product of
the first stage Fischer-Tropsch synthesis reaction in Step b)
and/or the oil-water-gas separation of the top product of the
second stage Fischer-Tropsch synthesis reaction in Step d) comprise
the following steps: firstly, carrying out a flash separation with
thermal high pressure separators to obtain thermal high pressure
separator liquids and thermal high pressure separator gases; then,
carrying out a flash separation for the thermal high pressure
separator gases using cold high pressure separators to obtain two
phases: the cold high pressure separator liquids being blended
liquid phase products of light distillate oil and water, and the
cold high pressure separator gases being the unconverted tail
gases.
4. The two-stage Fischer-Tropsch synthesis process according to
claim 3, further comprising: e) introducing the thermal high
pressure separator liquids of the first stage and second stage
Fischer-Tropsch synthesis reactions to a thermal low pressure
separator, carrying out a flash separation to obtain heavy
distillate oil products as a thermal low pressure separator liquid
and a thermal low pressure separator gas; and f) introducing the
cold high pressure separator liquids of the first stage and second
stage Fischer-Tropsch synthesis reactions and the optional thermal
low pressure separator gas to a cold low pressure separator,
carrying out a flash separation to obtain a cold low pressure
separator gas, a light distillate oil product, and a water.
5. The two-stage Fischer-Tropsch synthesis process according to
claim 3, wherein: The thermal high pressure separators is operated
at 120-220.degree. C.; The cold high-pressure separators is
operated at 5-60.degree. C.
6. The two-stage Fischer-Tropsch synthesis process according to
claim 4, wherein: The thermal low-pressure separator is operated at
60-200.degree. C.; The cold low-pressure separator is operated at
5-60.degree. C.
7. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein the CO conversion rate in the first stage
Fischer-Tropsch synthesis reactor is controlled at 40%-65%.
8. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein the first stage Fischer-Tropsch synthesis reaction
in Step a) and/or the second stage Fischer-Tropsch synthesis
reaction in Step c) are carried out under the following reaction
conditions: The reaction temperature is 200-320.degree. C.; The
reaction pressure is 15-50 bar; The superficial gas velocity of
reactor inlet gas is 10-40 cm/s; The ratio (i.e. gas catalyst
ratio) of volumetric flow of reactor inlet gas to the mass of
catalyst is 2000-50000 Nml/g-cat./h.
9. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein the first stage Fischer-Tropsch synthesis reactor
and the second stage Fischer-Tropsch synthesis reactor is one
slurry bed reactor or a plurality of slurry bed reactors in
parallel.
10. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein the volume ratio of CO to H.sub.2 in the feedstock
gas is 1.4-2.
11. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein, the catalysts used in Steps a) and c) are
iron-based or cobalt-based catalysts.
12. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein, the unconverted tail gas of the second stage
Fischer-Tropsch synthesis reaction is blended with all unconverted
tail gases of the first stage Fischer-Tropsch synthesis reaction,
then is introduced into the second stage Fischer-Tropsch synthesis
reactor.
13. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein, the feedstock gas in Step a) is a synthetic gas
underwent purification and water gas shift.
14. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein, the water content in the unconverted tail gas
entering the second stage Fischer-Tropsch synthesis reactor is less
than 0.05% by volume.
15. A two-stage Fischer-Tropsch synthesis system, comprising: A) a
first stage Fischer-Tropsch synthesis reactor, containing
Fischer-Tropsch synthesis catalysts, the first stage
Fischer-Tropsch synthesis reactor at least comprising: a first
stage reactor inlet, located at the bottom of the first stage
Fischer-Tropsch synthesis reactor; a first stage reactor top
outlet, located at the top of the first stage Fischer-Tropsch
synthesis reactor; a first stage Fischer-Tropsch synthesis wax or
slurry outlet, located at a slurry bed zone of the first stage
Fischer-Tropsch synthesis reactor; B) a first stage separation
system, for separating a top product from the first stage reactor
top outlet, thereby separating water from the unconverted tail gas
to obtain hydrocarbon products and unconverted tail gas of the
first stage Fischer-Tropsch synthesis reaction; the first stage
separation system comprising: a first stage separation system
inlet, connected with the first stage reactor top outlet; a
plurality of first stage separation system outlets, comprising: a
first stage hydrocarbon product outlet, and a first stage
unconverted tail gas outlet; C) a second stage Fischer-Tropsch
synthesis reactor, containing Fischer-Tropsch synthesis catalysts,
the second stage Fischer-Tropsch synthesis reactor at least
comprising: a second stage reactor inlet, located at the bottom of
the second stage Fischer-Tropsch synthesis reactor, and connected
with the first stage unconverted tail gas outlet; a second stage
reactor top outlet, located at the top of the second stage
Fischer-Tropsch synthesis reactor; a second stage Fischer-Tropsch
synthesis wax or slurry outlet, located at a slurry bed zone of the
second stage Fischer-Tropsch synthesis reactor; D) a second stage
separation system, for separating a top product from the second
stage reactor top outlet, thereby separating water from the
unconverted tail gas to obtain hydrocarbon products and unconverted
tail gas of the second stage Fischer-Tropsch synthesis reaction,
the second stage separation system comprising: a second stage
separation system inlet, connected with the second stage reactor
top outlet; a plurality of second stage separation system outlets,
comprising: a second stage hydrocarbon product outlet, and a second
stage unconverted tail gas outlet; wherein the first stage
unconverted tail gas outlet is not connect with the first stage
reactor inlet, such that the fresh synthetic gas as the feedstock
gas passes through the first stage Fischer-Tropsch synthesis
reactor in one way; wherein B) the first stage separation system
and/or D) the second stage separation system comprise an
oil-water-gas separation device.
16. The two-stage Fischer-Tropsch synthesis system according claim
15, wherein the first stage Fischer-Tropsch synthesis reactor and
the second stage Fischer-Tropsch synthesis reactor is one slurry
bed reactor or a plurality of slurry bed reactors in parallel.
17. The two-stage Fischer-Tropsch synthesis system according claim
15, wherein the number of the first stage Fischer-Tropsch synthesis
reactors is greater than or equal to the number of second stage
Fischer-Tropsch synthesis reactors.
18. The two-stage Fischer-Tropsch synthesis system according claim
17, wherein oil-water-gas separation systems of B) the first stage
separation system and/or D) the second stage separation system
comprise: thermal high pressure separator(s), comprising: a thermal
high pressure separator inlet, connected with the first stage
separation system inlet or the second stage separation system
inlet, a thermal high pressure separator liquid outlet, and a
thermal high pressure separator gas outlet; cold high pressure
separator(s), comprising: a cold high pressure separator inlet,
connected with the thermal high pressure separator gas outlet, a
cold high pressure separator liquid outlet, and a cold high
pressure separator gas outlet.
19. The two-stage Fischer-Tropsch synthesis system according claim
18, further comprising: a thermal low pressure separator,
comprising: a thermal low pressure separator inlet, connected with
the thermal high pressure separator liquid outlet(s) of the first
stage separation system and/or the second stage separation system,
a thermal low pressure separator gas outlet, a thermal low pressure
separator liquid outlet; optionally, a cold low pressure separator,
comprising: a cold low pressure separator inlet, connected with the
thermal low pressure separator liquid outlet and/or the cold high
pressure separator liquid outlet, a cold low pressure separator gas
outlet, a light distillate oil outlet, a Fischer-Tropsch synthesis
water outlet.
20. The two-stage Fischer-Tropsch synthesis system according claim
18, further comprising a CO.sub.2-removing system, the
CO.sub.2-removing system comprising: a CO.sub.2-removing solvent
inlet, a CO.sub.2-removing solvent outlet, a CO.sub.2-removing
system gas inlet, connected with the cold high pressure separator
gas outlet, a CO.sub.2-removing system gas outlet, connected with
the second stage reactor inlet.
21. The two-stage Fischer-Tropsch synthesis system according to
claim 15, wherein the first stage Fischer-Tropsch synthesis reactor
is one slurry bed reactor or a plurality of slurry bed reactors in
parallel, and the second stage Fischer-Tropsch synthesis reactor is
one slurry bed reactor.
22. The two-stage Fischer-Tropsch synthesis system according to
claim 15, further comprising: a wax filter, arranged inside or
outside the first stage Fischer-Tropsch synthesis reactor and the
second stage Fischer-Tropsch synthesis reactor.
23. The two-stage Fischer-Tropsch synthesis process according to
claim 1, wherein, when iron-based catalysts are adopted, the volume
ratio of H.sub.2 to CO in the feedstock gas is 1.4-1.8; when
cobalt-based catalysts are adopted, the volume ratio of H.sub.2 to
CO in the feedstock gas is 1.8-2.2.
24. The two-stage Fischer-Tropsch synthesis process according to
claim 12, wherein the blend volume ratio of the unconverted tail
gas of the second stage Fischer-Tropsch synthesis reaction to the
unconverted tail gas of the first stage Fischer-Tropsch synthesis
reaction is 0.5-5.
25. The two-stage Fischer-Tropsch synthesis process according to
claim 12, wherein CO.sub.2 in the unconverted tail gas of the
second stage Fischer-Tropsch synthesis reaction is removed before
the blending.
Description
TECHNICAL FIELD
[0001] The present invention relates to a Fischer-Tropsch synthesis
process and system, particularly to a two-stage Fischer-Tropsch
synthesis process and system.
BACKGROUND ART
[0002] As the price of oil rises increasingly in recent years,
people place a higher emphasis on the technology for developing and
producing alternative oil products. They produce synthetic gases
using coal, natural gas or other substances, process synthetic
gases underwent water gas transformation and synthetic gas
purification technology according to the requirements of
Fischer-Tropsch synthesis catalysts for synthetic gases, take the
processed synthetic gases as feedstocks to produce hydrocarbons and
the byproducts oxygen-containing compounds through Fischer-Tropsch
synthesis, and then process them using mature petroleum processing
techniques to produce high-quality environment-friendly oil
products. The core of the process is Fischer-Tropsch synthesis
techniques. Thus, it can be seen that to develop new
Fischer-Tropsch synthesis techniques is of great significance for
developing production techniques of alternative oil products.
[0003] Coal Liquefication Technology (authors: Gao Jinsheng, Zhang
Dexiang, Chemical Industry Press, March 2005, Edition 1) describes
Sasol's mature Fischer-Tropsch synthesis process. The process is
fundamentally a single-stage process. According to reactor types,
the process is divided into the Arge process using fixed beds, the
Kellogg process using fluidized beds, and the Sasol slurry bed
Fischer-Tropsch synthesis process using slurry beds. In Sasol Plant
I, tail gas of the Arge process is selected as feedstock of the
Kellogg process, and there is no two-stage technical process using
the same reactor.
[0004] Slurry bed reactor is a triphase bubbling column, operated
in medium temperatures, wherein the feedstock gas (gas phase)
bubbles in molten Fischer-Tropsch synthetic wax (liquid phase) and
granules of catalysts (solid phase). Feedstocks of preheated
synthetic gas enter the reactor from the bottom of the reactor, and
diffuse into the slurry composed by the generated liquid wax and
granules of catalysts. During the process of the bubbles rising
upward, the synthetic gas constantly goes through Fischer-Tropsch
synthesis reactions to generate more Fischer-Tropsch synthesis
waxes. The heat generated from the reaction is taken out by the
steam produced by the built-in cooling coil. The wax products are
separated in the built-in filter of the reactor slurry bed reaction
zone to get out of the reactor, or the wax products are obtained in
the method of separating Fischer-Tropsch synthesis waxes from solid
particulates of catalysts with a solid-liquid separation device
laid outside after the slurry is extracted out. After the tail gas
coming out from the top of the reactor is cooled, light components
and water can be recovered. The obtained hydrocarbon products are
sent to a downstream product-refining device, and the water is sent
to a recovery device for disposal.
[0005] The slurry bed reactor possesses a good heat transfer carry
outance, enables the reactants in it mix well, is favorable for
controlling reaction temperature and moving reaction heat out, and
enables isothermal operation, thereby obtaining a higher reaction
rate at a higher average operating temperature; the reactor
features simple control and low operation costs; by replacing
catalysts regularly, the average lifespan of catalysts is easy to
control; the selectivity of the process is even easier to control,
thereby improving the quality of intermediate products. Therefore,
when synthetic wax and diesel oil are mainly produced, the slurry
bed Fischer-Tropsch synthesis has obvious advantages, and becomes a
development trend of the Fischer-Tropsch synthesis technology.
[0006] The slurry bed reactor is designed uniquely. In order to
keep the characteristics of a slurry bed, firstly, the catalysts
shall be produced into fine granules for suspending in a liquid
phase zone; secondly, the operation shall be carried out in a
specific reaction temperature range, so that the Fischer-Tropsch
synthesis waxes generated from the reaction exist in a liquid phase
to provide slurry conditions. In addition, the operation shall be
carried out at a certain gas flow rate (superficial gas velocity),
thus preventing granules of catalysts from sedimentation due to a
too low gas flow rate, and preventing the gas from carrying
granules of catalysts out of the reactor due to a too high gas flow
rate. Therefore, when there is a need to improve the productivity
of the Fischer-Tropsch synthesis device, i.e. to increase the gas
flow volume of feedstocks of the Fischer-Tropsch synthesis, the
diameter of the reactor shall be increased to maintain the gas
speed required for an empty column.
[0007] However, when there is a need to improve the capability of
the device for producing Fischer-Tropsch synthetic oil to more than
500,000 tons/year, limited by reactor manufacturing technologies,
transport conditions, etc., the maximum diameter of a reactor at
present can only reach around 10 meters. Therefore, at least two
slurry bed reactors are required for the processing. Currently the
megaton Fischer-Tropsch synthetic device that has been put into
industrialized production is designed as two sets of complete
conventional single-set slurry bed reactors with Fischer-Tropsch
synthesis process and parallel operations. Oil-water-gas separation
systems are provided for products at the top of each reactor, most
of the tail gas is recycled back to each reactor to obtain the
required total carbon conversion rate, and a small portion of the
tail gas is vented out.
[0008] Chinese Patent Publication No. CN1611565 (application No.:
CN200310108146.X) discloses a process for producing liquid fuels
using a synthetic gas, comprising a Fischer-Tropsch synthesis unit,
a C.sub.3-C.sub.5 recovery unit, and an oil-refining unit. The
Fischer-Tropsch synthesis unit is divided into two stages, and all
products thereof are wax and condensates; the two stages of
Fischer-Tropsch synthesis devices respectively recycle partial tail
gas; the remaining tail gas of a first stage Fischer-Tropsch
synthetic gas is introduced into a second stage Fischer-Tropsch
synthesis device as feedstock gas; the remaining tail gas of the
second stage Fischer-Tropsch synthesis device is introduced into
the C.sub.3-C.sub.5 recovery unit. The C.sub.3-C.sub.5 recovery
unit recovers most of the components above C.sub.3 in the tail gas
in the method of in-depth cooling, and the components enter the
oil-refining unit together with the waxes and condensates produced
by the two stages of Fischer-Tropsch synthesis units to produce
liquid fuels. This process adopts two-stage device Fischer-Tropsch
synthesis, which can lower CH.sub.4 productivity in the method of
reducing the single-stage CO conversion rate. However, in this
process, partial tail gas in the first stage Fischer-Tropsch
synthesis device is recycled, which increases the investment and
operation expenses of the recycle compressor system and lowers the
economical efficiency of the whole process. In addition, the first
stage Fischer-Tropsch synthesis device adopts partial tail gas
recycling, which reduces the load of the reactor for processing
feedstocks of fresh synthetic gas, and lowers the oil yield.
[0009] Chinese Patent Publication No. CN1948438 (application No.:
CN200610140020.4) relates to a Fischer-Tropsch synthesis method,
comprising the following steps: a) introducing feedstocks of a
synthetic gas into a first stage Fischer-Tropsch synthesis reactor
to carry out a Fischer-Tropsch synthesis reaction under the action
of catalysts; b) separating the products of the first stage
Fischer-Tropsch synthesis reaction, with a portion of tail gas
being returned to the first stage Fischer-Tropsch synthesis reactor
for recycle reactions, and C.sub.1-C.sub.4 hydrocarbons contained
in other tail gases being converted to synthetic gases; c) mixing
the converted tail gas from Step b) with the recycled tail gas from
the second stage Fischer-Tropsch synthesis reaction, introducing
the mixed gas into the second stage Fischer-Tropsch synthesis
reactor to carry out a Fischer-Tropsch synthesis reaction under the
action of catalysts; d) separating the products of the second stage
Fischer-Tropsch synthesis reaction, with most of the tail gas being
returned to the second stage Fischer-Tropsch synthesis reactor for
recycle reactions, and the remaining tail gas being vented out. In
this method, a gas recycling process is adopted and a gas recycle
compressor is provided in the first stage, which lowers the
capability of the reactor for processing fresh synthetic gases;
moreover, when the tail gas is introduced into the second stage,
the process for producing natural gas into synthetic gas through
self-heating oxidation is required to convert C.sub.1-C.sub.4 light
hydrocarbons to synthetic gases, which increases the costs of
devices.
[0010] Chinese Patent Publication No. CN100575457C (patent No.:
ZL200610140019.1) relates to a Fischer-Tropsch synthesis method,
comprising the following steps: (1) introducing feedstocks of coals
for producing synthetic gases into a first stage Fischer-Tropsch
synthesis reactor to contact iron-based catalysts, and making them
react under the Fischer-Tropsch synthesis reaction conditions; (2)
separating the products of the first stage reaction, with the tail
gas left after the reaction being removed CO.sub.2 and entering a
C1-C4 hydrocarbon conversion device to produce CO and H.sub.2,
introducing the converted tail gas into a second stage
Fischer-Tropsch synthesis reactor to contact and react with
cobalt-based catalysts under the Fischer-Tropsch synthesis reaction
conditions; (3) separating the products of the second stage
reaction, venting a portion of the tail gas, with other tail gases
being returned to the first stage Fischer-Tropsch synthesis reactor
for recycled use. In this method, a slurry bed is used for the
first stage reactor, and a portion of the feed gas is the recycled
gas of tail gas of the second stage reaction. Cobalt-based
catalysts are used for the second stage reaction, although this
reaction has a higher space time yield, taking heat from reaction
is hard to control, as the reactor is a fixed bed. Moreover, the
fixed bed process is hard to use in a large scale.
SUMMARY OF THE INVENTION
[0011] The object of the present invention is to provide a
Fischer-Tropsch synthesis process and system, particularly a
two-stage Fischer-Tropsch synthesis process and system.
[0012] An aspect of the present invention relates to a
Fischer-Tropsch synthesis process, comprising the following
steps:
[0013] a) a first stage Fischer-Tropsch synthesis reaction
[0014] introducing a feedstock gas containing CO and H.sub.2 into a
first stage Fischer-Tropsch synthesis reactor to carry out a
Fischer-Tropsch synthesis reaction under the action of catalysts,
to obtain the products of the first stage Fischer-Tropsch synthesis
reaction;
[0015] b) separation of the products of the first stage
Fischer-Tropsch synthesis reaction
[0016] separating the products of the first stage Fischer-Tropsch
synthesis reaction, so as to separate water from the unconverted
tail gas and to obtain hydrocarbon products and unconverted tail
gas of the first stage Fischer-Tropsch synthesis reaction;
[0017] c) a second stage Fischer-Tropsch synthesis reaction
[0018] introducing the unconverted tail gas obtained from Step b)
into a second stage Fischer-Tropsch synthesis reactor to carry out
a Fischer-Tropsch synthesis reaction under the action of catalysts,
to obtain products of the second stage Fischer-Tropsch synthesis
reaction;
[0019] d) separation of the products of the second stage
Fischer-Tropsch synthesis reaction
[0020] separating the products of the second stage Fischer-Tropsch
synthesis reaction, so as to separate water from the unconverted
tail gas and to obtain hydrocarbon products and unconverted tail
gas of the second stage Fischer-Tropsch synthesis reaction, with a
portion of the unconverted tail gas of the second stage
Fischer-Tropsch synthesis reaction being returned to the second
stage Fischer-Tropsch synthesis reactor for recycle reactions.
[0021] Another aspect of the present invention relates to a
Fischer-Tropsch synthesis system, comprising:
[0022] A) a first stage Fischer-Tropsch synthesis reactor,
containing Fischer-Tropsch synthesis catalysts, the first stage
Fischer-Tropsch synthesis reactor at least comprising:
[0023] a first stage reactor inlet, located at the bottom of the
first stage Fischer-Tropsch synthesis reactor;
[0024] a first stage reactor top outlet, located at the top of the
first stage Fischer-Tropsch synthesis reactor;
[0025] a first stage Fischer-Tropsch synthesis wax or slurry
outlet, located at a slurry bed zone of the first stage
Fischer-Tropsch synthesis reactor;
[0026] B) a first stage separation system, for separating the top
products of the first stage reactor top outlet, thereby separating
water from the unconverted tail gas to obtain hydrocarbon products
and the unconverted tail gas of the first stage Fischer-Tropsch
synthesis reaction; the first stage separation system
comprising:
[0027] a first stage separation system inlet, connected with a
first stage reactor top outlet;
[0028] a plurality of first stage separation system outlets,
comprising:
[0029] a first stage hydrocarbon product outlet, and
[0030] a first stage unconverted tail gas outlet;
[0031] C) a second stage Fischer-Tropsch synthesis reactor,
containing Fischer-Tropsch synthesis catalysts, the second stage
Fischer-Tropsch synthesis reactor at least comprising:
[0032] a second stage reactor inlet, located at the bottom of the
second stage Fischer-Tropsch synthesis reactor, and connected with
a first stage unconverted tail gas outlet;
[0033] a second stage reactor top outlet, located at the top of the
second stage Fischer-Tropsch synthesis reactor;
[0034] a second stage Fischer-Tropsch synthesis wax or slurry
outlet, located at a slurry bed zone of the second stage
Fischer-Tropsch synthesis reactor;
[0035] D) a second stage separation system, for separating top
products of the second stage reactor top outlet, thereby separating
water from the unconverted tail gas to obtain hydrocarbon products
and the unconverted tail gas of the second stage Fischer-Tropsch
synthesis reaction, the second stage separation system
comprising:
[0036] a second stage separation system inlet, connected with a
second stage reactor top outlet;
[0037] a plurality of second stage separation system outlets,
comprising:
[0038] a second stage hydrocarbon product outlet, and
[0039] a second stage unconverted tail gas outlet.
[0040] The process and system of the present invention overcome the
defects of the conventional Fischer-Tropsch synthesis process for
producing liquid products, such as high device investment and
operation expenses, low space time yield, and low CO utilization
ratio, simplify the technical process, and are suitable for
large-scale industrial production.
BRIEF DESCRIPTION OF THE DRAWINGS
[0041] FIG. 1 is a flow chart for a two-stage large-scale
Fischer-Tropsch synthesis process in the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0042] The present invention is carried out based on the
understanding about the fundamental features of the Fischer-Tropsch
synthesis reaction (particularly Fischer-Tropsch synthesis reaction
of iron-based catalysts).
[0043] The Fischer-Tropsch synthesis reaction of iron-based
catalysts is divided into two types:
CO+H.sub.2.fwdarw.HC (hydrocarbon)+H.sub.2O (1)
CO+H.sub.2OCO.sub.2+H.sub.2 (2)
wherein the second type reaction (2) is a water gas shift reaction
(WGS reaction), and it is a reversible reaction, the CO conversion
thereof accounts for 15-35% of the total carbon conversion.
[0044] Obviously, the method for improving the Fischer-Tropsch
synthesis reaction rate, increasing the capability of the device
for producing Fischer-Tropsch synthetic oil, and improving CO
utilization ratio lies in increasing the flow volume of the
effective synthetic gas (CO+H.sub.2) at the reactor inlet (can be
represented by partial pressure of the effective synthetic gas when
a specific superficial gas velocity is maintained), and reducing
WGS forward reaction velocity. It can be seen from the WGS reaction
characteristics that, there are two effective means for reducing
WGS forward reaction velocity and improving CO utilization ratio:
a. decreasing H.sub.2O partial pressure in the system; b. improving
CO.sub.2 partial pressure in the system.
[0045] On the other hand, as the second type of WGS reactions
exists on iron-based catalysts, reducing water partial pressure in
the system is favorable for decreasing WGS forward reaction
velocity, which relatively increases the concentration of CO
reactants that are converted to hydrocarbons in the first type of
Fischer-Tropsch synthesis reactions, and is favorable for improving
the Fischer-Tropsch synthesis reaction rate.
[0046] The inventor finds that when the reactor is arranged in
stages and gas phase removing is carried out between the stages,
Fischer-Tropsch synthesis reaction rate can be improved, and
productivity of the device can be increased.
[0047] When cobalt-based catalysts exist, although WGS reaction
seldom occurs, the presence of water produced from the
Fischer-Tropsch synthesis reaction will also affect the
Fischer-Tropsch synthesis reaction rate.
[0048] The present invention is provided based on the understanding
about the features of the Fischer-Tropsch synthesis reaction, and
the tests for the same.
[0049] In the present invention, the terms "connected with . . . "
and "connected to" mean that two objects connect directly or via
common components or devices (e.g. a valve, a pump, a heat
exchanger).
[0050] If without confliction, all the Examples, embodiments and
features of the present invention can be combined with each
other.
[0051] The present invention relates to a Fischer-Tropsch synthesis
process, comprising the following steps:
[0052] a) a first stage Fischer-Tropsch synthesis reaction
[0053] introducing a feedstock gas containing CO and H.sub.2 into a
first stage Fischer-Tropsch synthesis reactor to carry out a
Fischer-Tropsch synthesis reaction under the action of catalysts,
to obtain products of the first stage Fischer-Tropsch synthesis
reaction;
[0054] b) separation of the products of the first stage
Fischer-Tropsch synthesis reaction
[0055] separating the products of the first stage Fischer-Tropsch
synthesis reaction, so as to separate water from the unconverted
tail gas and to obtain hydrocarbon products and unconverted tail
gas of the first stage Fischer-Tropsch synthesis reaction;
[0056] c) a second stage Fischer-Tropsch synthesis reaction
[0057] introducing the unconverted tail gas obtained from Step b)
into a second stage Fischer-Tropsch synthesis reactor to carry out
a Fischer-Tropsch synthesis reaction under the action of catalysts,
to obtain products of the second stage Fischer-Tropsch synthesis
reaction;
[0058] d) separation of the products of the second stage
Fischer-Tropsch synthesis reaction
[0059] separating the products of the second stage Fischer-Tropsch
synthesis reaction, so as to separate water from the unconverted
tail gas and to obtain hydrocarbon products and unconverted tail
gas of the second stage Fischer-Tropsch synthesis reaction, with a
portion of the unconverted tail gas of the second stage
Fischer-Tropsch synthesis reaction being returned to the second
stage Fischer-Tropsch synthesis reactor for recycle reactions.
[0060] Preferably, unconverted tail gas of the first stage
Fischer-Tropsch synthesis reaction is not returned to the first
stage Fischer-Tropsch synthesis reactor for recycle reactions.
[0061] Preferably, in Step a), the fresh synthetic gas as the
feedstock gas passes through the first stage Fischer-Tropsch
synthesis reactor in one way.
[0062] Preferably, control the CO conversion rate in the first
stage Fischer-Tropsch synthesis reactor at 30%-70%, more preferably
at 40%-65%, and further preferably at 50%-60%.
[0063] Preferably, the water content in the feedstock gas is less
than 0.05%, preferably less than 0.01%, more preferably less than
0.005%, and most preferably less than 0.0001% (volume ratio).
[0064] Preferably, the water content in the unconverted tail gas
entering the second stage Fischer-Tropsch synthesis reactor is less
than 0.05%, preferably less than 0.01%, more preferably less than
0.005%, and most preferably less than 0.0001% (volume ratio).
[0065] Preferably, control the CO conversion rate in the first
stage Fischer-Tropsch synthesis reactor at 30%-70%, more preferably
at 40%-65%, and further preferably at 50%-60%.
[0066] The separations in Steps b) and d) comprise oil-water-gas
separations of top products in Fischer-Tropsch synthesis reactions.
Preferably, oil-water-gas separations of top products in the first
stage Fischer-Tropsch synthesis reaction in Step b) and/or
oil-water-gas separations of top products in the second stage
Fischer-Tropsch synthesis reaction in Step d) comprise the
following steps:
[0067] firstly, carrying out flash separation using a thermal
high-pressure separator ("thermal high separator" for short) to
obtain thermal high-pressure separator liquids and gases;
[0068] then, carrying out flash separation for the thermal high
pressure separator gases using a cold high pressure separator
("cold high separator" for short) to obtain two phases: cold high
pressure separator liquid being a blended liquid phase product of
light distillate oil and water, and cold high pressure separator
gas being unconverted tail gas.
[0069] Preferably, the thermal high-pressure separator is operated
at 120-220.degree. C., preferably at 140-180.degree. C. Preferably,
the cold high-pressure separator is operated at 5-60.degree. C.,
more preferably at 10-50.degree. C.
[0070] Preferably, the process of the present invention further
comprises:
[0071] e) introducing the thermal high pressure separator liquids
of the first stage and second stage Fischer-Tropsch synthesis
reactions to a thermal low pressure separator ("thermal low
separator" for short), and carrying out flash separation again to
obtain heavy distillate oil products and thermal low pressure
separator gases; and optionally
[0072] f) introducing the blended liquid phase products of the cold
high pressure separator ("cold high separator" for short) of the
first stage and second stage Fischer-Tropsch synthesis reactions
and optional thermal low pressure separator gases into a cold low
pressure separator ("cold low separator" for short), and carrying
out flash separation to obtain cold low pressure separator gases,
light distillate oil products and water.
[0073] The thermal low-pressure separator can run at 60-200.degree.
C., preferably at 70-180.degree. C., more preferably at
80-160.degree. C., and most preferably at 90-140.degree. C. The
cold low-pressure separator can run at 5-60.degree. C., preferably
at 20-50.degree. C.
[0074] Preferably, the first stage Fischer-Tropsch synthesis
reaction in Step a) is carried out under the following reaction
conditions.
[0075] Preferably, as to the first stage Fischer-Tropsch synthesis
reaction in Step a), the reaction temperature is 200-320.degree.
C., preferably 235-275.degree. C., and more preferably
245-265.degree. C.
[0076] Preferably, as to the first stage Fischer-Tropsch synthesis
reaction in Step a), the reaction pressure is 15-50 bar, preferably
20-40 bar, and more preferably 25-35 bar.
[0077] Preferably, as to the first stage Fischer-Tropsch synthesis
reaction in Step a), the superficial gas velocity of reactor inlet
gas is 10-40 cm/s, preferably 15-35 cm/s, and more preferably 15-25
cm/s.
[0078] Preferably, as to the first stage Fischer-Tropsch synthesis
reaction in Step a), the ratio (i.e. gas catalyst ratio) of
volumetric flow of the feedstock gas (the reactor inlet gas) to the
mass of catalyst is 2000-50000 Nml/g-cat./h, preferably 5000-30000
Nml/g-cat./h, and more preferably 8000-20000 Nml/g-cat./h.
[0079] Preferably, the second stage Fischer-Tropsch synthesis
reaction in Step c) is carried out under the following reaction
conditions.
[0080] Preferably, as to the second stage Fischer-Tropsch synthesis
reaction in Step a), the reaction temperature is 200-320.degree.
C., preferably 235-275.degree. C., and more preferably
245-265.degree. C.
[0081] Preferably, as to the second stage Fischer-Tropsch synthesis
reaction in Step a), the reaction pressure is 15-50 bar, preferably
18-38 bar, and more preferably 25-35 bar.
[0082] Preferably, as to the second stage Fischer-Tropsch synthesis
reaction in Step a), the superficial gas velocity of the reactor
inlet is 10-40 cm/s, preferably 15-35 cm/s, and more preferably
15-25 cm/s.
[0083] Preferably, as to the second stage Fischer-Tropsch synthesis
reaction in Step a), the volume ratio (i.e. gas catalyst ratio) of
gas flow to catalyst at the reactor inlet is 2000-50000
Nml/g-cat./h, preferably 5000-30000 Nml/g-cat./h, and more
preferably 8000-20000 Nml/g-cat./h.
[0084] Preferably, as to the first stage Fischer-Tropsch synthesis
reaction in Step a), the volume ratio of CO to H.sub.2 in the
feedstock gas is 0.67-2.2, preferably 0.8-2, more preferably 1-2,
and most preferably 1.4-2.
[0085] Preferably, the feedstock gas in Step a) is a synthetic gas,
and is preferably a synthetic gas underwent purification and
water-gas shift. Fresh synthetic gas is preferred as the feedstock
gas.
[0086] Preferably, the catalysts used in Steps a) and c) are
iron-based or cobalt-based catalysts. Preferably, when iron-based
catalysts are adopted, the volume ratio of H.sub.2 to CO in the
feedstock gas is 1.4-1.8, preferably 1.4-1.7, more preferably
1.5-1.7, and most preferably 1.5-1.6. Preferably, when cobalt-based
catalysts are adopted, the volume ratio of H.sub.2 to CO in the
feedstock gas is 1.8-2.2, preferably 1.9-2.1, more preferably
1.95-2.05, and most preferably 2.0.
[0087] Preferably, the number of the first stage Fischer-Tropsch
synthesis reactor is equal to or more than the number of the second
stage Fischer-Tropsch synthesis reactor, more preferably, the
number of the first stage Fischer-Tropsch synthesis reactor is more
than the number of the second stage Fischer-Tropsch synthesis
reactor. When the number of the first stage Fischer-Tropsch
synthesis reactor or the number of the first stage Fischer-Tropsch
synthesis reactor is more than one (i.e. more than two), the
Fischer-Tropsch synthesis reactors of this stage are in
parallel.
[0088] Preferably, the first stage Fischer-Tropsch synthesis
reactor and the second stage Fischer-Tropsch synthesis reactor are
slurry bed reactors. Preferably the first stage Fischer-Tropsch
synthesis reactor is one slurry bed reactor or a plurality of
slurry bed reactors in parallel, and the second stage
Fischer-Tropsch synthesis reactor is one slurry bed reactor. Also,
Fischer-Tropsch synthesis reactors can be fixed beds, fixed
fluidized beds, and fluidized beds.
[0089] Preferably, the unconverted tail gas of the second stage
Fischer-Tropsch synthesis reaction is blended with all the
unconverted tail gas of the first stage Fischer-Tropsch synthesis
reaction, and then is introduced into the second stage
Fischer-Tropsch synthesis reactor. Preferably, the blend volume
ratio of the unconverted tail gas of the second stage
Fischer-Tropsch synthesis reaction to the unconverted tail gas of
the first stage Fischer-Tropsch synthesis reaction is 0.5-5,
preferably 1-3, and more preferably 1.5-2.5. Preferably, CO.sub.2
in the unconverted tail gas of the second stage Fischer-Tropsch
synthesis reaction is removed before the blending. For example,
removing of CO.sub.2 is carried out with hot potassium carbonate
CO.sub.2-removing process or in water washing method.
[0090] Preferably, in Step b), top products of the reactor are
introduced into the thermal high-pressure separator (e.g. at
120-220.degree. C., preferably at 140-180.degree. C.), to carry out
flash separation to separate gas phase from heavy oil phase. Gas
phase streams are introduced into the cold high-pressure separator
(e.g. at 5-60.degree. C., preferably at 10-50.degree. C.), to carry
out flash separation again to obtain blended liquid phase products
of gas, light distillate oil and synthetic water.
[0091] Preferably, in Step d), top products of the reactor are
introduced into the thermal high-pressure separator (e.g. at
120-220.degree. C., preferably at 140-180.degree. C.), to carry out
flash separation to obtain gas phase and heavy oil phase. Gas phase
streams are introduced into the cold high-pressure separator (e.g.
at 5-60.degree. C., preferably at 10-50.degree. C.), to carry out
flash separation again to obtain blended liquid phase products of
gas, light distillate oil and synthetic water.
[0092] The discharge amount of tail gas is determined by the
contents of CO and H.sub.2 in the tail gas to ensue that the
contents of CO and H.sub.2 in the tail gas are not less than 40%,
when the contents of CO and H.sub.2 in the tail gas are greater
than 50%, the discharge amount shall be decreased; when the
contents of CO and H.sub.2 in the tail gas are less than 40%, the
discharge amount shall be increased.
[0093] Another aspect of the present invention relates to a
Fischer-Tropsch synthesis system, comprising:
[0094] A) a first stage Fischer-Tropsch synthesis reactor,
containing Fischer-Tropsch synthesis catalysts, the first stage
Fischer-Tropsch synthesis reactor comprising:
[0095] a first stage reactor inlet, located at the bottom of the
first stage Fischer-Tropsch synthesis reactor;
[0096] a first stage reactor top outlet, located at the top of the
first stage Fischer-Tropsch synthesis reactor;
[0097] a first stage Fischer-Tropsch synthesis wax or slurry
outlet, located at a slurry bed zone of the first stage
Fischer-Tropsch synthesis reactor;
[0098] B) a first stage separation system, for separating top
products of the first stage reactor top outlet, thereby separating
water from the unconverted tail gas to obtain hydrocarbon products
and unconverted tail gas of the first stage Fischer-Tropsch
Synthesis reaction, the first stage separation system
comprising:
[0099] a first stage separation system inlet, connected with the
first stage reactor top outlet;
[0100] a plurality of first stage separation system outlets,
comprising:
[0101] a first stage hydrocarbon product outlet, and
[0102] a first stage unconverted tail gas outlet;
[0103] C) a second stage Fischer-Tropsch synthesis reactor,
containing Fischer-Tropsch synthesis catalysts, the second stage
Fischer-Tropsch synthesis reactor comprising:
[0104] a second stage reactor inlet, located at the bottom of the
second stage Fischer-Tropsch synthesis reactor, and connected with
the first stage unconverted tail gas outlet;
[0105] a second stage reactor top outlet, located at the top of the
second stage Fischer-Tropsch synthesis reactor 102;
[0106] a second stage Fischer-Tropsch synthesis wax or slurry
outlet, located at a slurry bed zone of the second stage
Fischer-Tropsch synthesis reactor;
[0107] D) a second stage separation system, for separating top
products of the second stage reactor top outlet, thereby separating
water from the unconverted tail gas to obtain hydrocarbon products
and unconverted tail gas of the second stage Fischer-Tropsch
Synthesis reaction, the second stage separation system
comprising:
[0108] a second stage separation system inlet, connected with a top
outlet of the second stage reactor;
[0109] a plurality of second stage separation system outlets,
comprising:
[0110] a second stage hydrocarbon product outlet, and
[0111] a second stage unconverted tail gas outlet.
[0112] Preferably, the first stage unconverted tail gas outlet is
not connect with the first stage reactor inlet.
[0113] Preferably, the first stage separation system in B) and/or
the second stage separation system in D) comprise an oil-water-gas
separation device.
[0114] Preferably, the oil-water-gas separation system of the first
stage separation system in B) and/or the oil-water-gas separation
system of the second stage separation system in D) comprises:
[0115] a thermal high-pressure separator, comprising:
[0116] a thermal high-pressure separator inlet, connected with the
first stage separation system inlet or the second stage separation
system inlet;
[0117] a thermal high-pressure separator liquid outlet, and
[0118] a thermal high-pressure separator gas outlet;
[0119] a cold high-pressure separator, comprising:
[0120] a cold high-pressure separator inlet, connected with the
thermal high-pressure separator gas outlet;
[0121] a cold high-pressure separator liquid outlet, and
[0122] a cold high-pressure separator gas outlet.
[0123] Preferably, the Fischer-Tropsch synthesis system of the
present invention further comprises:
[0124] a thermal low-pressure separator, comprising:
[0125] a thermal low-pressure separator inlet, connected with the
thermal high-pressure separator liquid outlet of the first stage
separation system and/or the second stage separation system,
[0126] a thermal low-pressure separator gas outlet,
[0127] a thermal low-pressure separator liquid outlet; optionally,
a cold low-pressure separator, comprising:
[0128] a cold low-pressure separator inlet, connected to the
thermal low-pressure separator liquid outlet and/or the cold
high-pressure separator liquid product outlet,
[0129] a cold low-pressure separator gas outlet,
[0130] a light distillate oil outlet,
[0131] a Fischer-Tropsch synthesis water outlet.
[0132] Preferably, the Fischer-Tropsch synthesis system of the
present invention further comprises a CO.sub.2-removing system,
which comprises:
[0133] a CO.sub.2-removing solvent inlet,
[0134] a CO.sub.2-removing solvent outlet,
[0135] a gas inlet of the CO.sub.2-removing system, connected with
a gas outlet of the cold high-pressure separator,
[0136] a gas outlet of the CO.sub.2-removing system, connected with
a second stage reactor inlet.
[0137] Preferably, the first stage Fischer-Tropsch synthesis
reactor and the second stage Fischer-Tropsch synthesis reactor is
one slurry bed reactor or a plurality of slurry bed reactors in
parallel; preferably, the first stage Fischer-Tropsch synthesis
reactor is one slurry bed reactor or a plurality of slurry bed
reactors in parallel, while the second stage Fischer-Tropsch
synthesis reactor is one slurry bed reactor.
[0138] Preferably, the number of the first stage Fischer-Tropsch
synthesis reactor is more than or equal to the number of the second
stage Fischer-Tropsch synthesis reactor, and preferably more than
the number of the second stage Fischer-Tropsch synthesis
reactor.
[0139] Preferably, the Fischer-Tropsch synthesis system of the
present invention further comprises a wax filter, arranged inside
or outside the first stage Fischer-Tropsch synthesis reactor and
the second stage Fischer-Tropsch synthesis reactor.
[0140] Preferably, the Fischer-Tropsch synthesis system of the
present invention further comprises a Fischer-Tropsch synthesis wax
outlet, arranged at the central slurry zone of the first stage
Fischer-Tropsch synthesis reactor and the second stage
Fischer-Tropsch synthesis reactor.
[0141] Preferably the process and system of the present invention
is a two-stage Fischer-Tropsch synthesis process and system.
[0142] The process of the present invention is simply described as
follows: as for megaton large-scale industrialized device, as more
than two reactors are required, the fresh synthetic feedstock gas
passes through a first stage Fischer-Tropsch synthesis reactor in
one way, top products of the first stage Fischer-Tropsch synthesis
reactor undergo oil-water-gas separation, the obtained unconverted
tail gas is introduced into a second stage Fischer-Tropsch
synthesis reactor, top outlet products of which undergo
oil-water-gas separation once again, after that, most of the tail
gas recycles back to the second stage Fischer-Tropsch synthesis
reactor to obtain the required total CO conversion rate. This
technical device is highly integrated, all liquid phase products
obtained from the thermal high-pressure separators in the two
stages of reactions enter a same thermal low-pressure separator for
flash separation once again to obtain heavy distillate oil, while
all liquid products (mixtures of light distillate oil and synthetic
water) of the cold high-pressure separators in the two stages of
reactions flow to a same cold low-pressure separator for
separation, thus obtaining light distillate oil and Fischer-Tropsch
synthesis water products.
[0143] In a preferred embodiment, the two-stage large-scale
Fischer-Tropsch synthesis process provided in the present invention
comprises the following steps:
[0144] a) introducing the feedstock gas of fresh synthetic gas into
a first stage Fischer-Tropsch synthesis reactor to carry out a
Fischer-Tropsch synthesis reaction under the action of
catalysts;
[0145] b) carrying out flash separation for top products of the
first stage Fischer-Tropsch synthesis reactor using a thermal
high-pressure separator and a cold high-pressure separator
consecutively to obtain heavy oil phase, blended liquid phase of
light oil and synthetic water, unconverted tail gas, and likes as
first stage Fischer-Tropsch synthesis reaction products;
[0146] c) blending the cold high-pressure separator gas of the
first stage Fischer-Tropsch synthesis with the recycled tail gas of
the second stage Fischer-Tropsch synthesis reaction, and
introducing the blended gas into the second stage Fischer-Tropsch
synthesis reactor to carry out a Fischer-Tropsch synthesis reaction
under the action of catalysts;
[0147] d) carrying out flash separation for the second stage
Fischer-Tropsch synthesis reaction products using a thermal
high-pressure separator and a cold high-pressure separator
consecutively to obtain heavy oil phase, blended liquid phase of
light oil and synthetic water, tail gas, etc., with most tail gas
being returned to the second stage Fischer-Tropsch synthesis
reactor for recycle reactions, and other tail gases being vented
out;
[0148] e) introducing thermal high-pressure separator liquids of
the first stage and second stage Fischer-Tropsch synthesis
simultaneously to a thermal low-pressure separator, carrying out
flash separation again to obtain heavy distillate oil products;
[0149] f) introducing blended liquid phase products of cold
high-pressure separators of the first stage and second stage
Fischer-Tropsch synthesis simultaneously to a cold low-pressure
separator, carrying out flash separation again to obtain light
distillate oil and synthetic water products.
[0150] The two-stage Fischer-Tropsch synthesis process of the
present invention will be further elaborated in detail in the
following pages, but the present invention is not therefore subject
to any limitations.
[0151] The fresh synthetic gas in Step a) of the above
Fischer-Tropsch synthesis process can be produced from coal,
natural gas or organic substances, but it must be purified to
remove sulfur and other substances contained therein that are
harmful to Fischer-Tropsch synthesis catalysts. Coal Liquefication
Technology (Chemical Industry Press, authors: Gao Jinsheng and
Zhang Dexiang, published on March 2005) describes in detail the
technologies related with synthetic gas production, purification
and shift. The volume ratio of H.sub.2 to CO in fresh synthetic gas
is 0.67-2.2, preferably 0.8-2, more preferably 1-2, and most
preferably 1.4-2.
[0152] The first stage Fischer-Tropsch synthesis reaction in Step
a) is carried out under the following reaction conditions: the
reaction temperature is 200-320.degree. C., preferably
235-275.degree. C.; the reaction pressure is 15-50 bar, preferably
20-40 bar; superficial gas velocity of reactor inlet gas reaches
10-40 cm/s, preferably 15-35 cm/s; the volume ratio of feedstock of
fresh synthetic gas to catalyst is 2000-50000, preferably
5000-30000. The present invention belongs to low-temperature
Fischer-Tropsch synthesis reactions.
[0153] In Step b), top products of the reactor enter a thermal
high-pressure separator, and carry out flash separation at
120-220.degree. C., preferably 140-180.degree. C., so as to
separate gas phase (thermal high-pressure separator gas) from heavy
oil phase (thermal high-pressure separator liquid). Gas phase
streams enter the cold high-pressure separator, and carry out flash
separation again at 5-60.degree. C., preferably 10-50.degree. C. to
obtain blended liquid phase products (cold high pressure separator
liquids) of gas, light distillate oil and synthetic water.
[0154] In Step c), the recycled tail gas of the second stage
Fischer-Tropsch synthesis reaction is blended with the cold high
pressure separator gas from Step b) after first stage
Fischer-Tropsch synthesis conversion at a volume ratio (recycle
ratio) of 0.5-5, preferably 1-3, and is introduced into the second
stage Fischer-Tropsch synthesis reactor. The second stage
Fischer-Tropsch synthesis reaction is carried out under the
following reaction conditions: the reaction temperature is
200-320.degree. C., preferably 235-275.degree. C.; the reaction
pressure is 15-50 bar, preferably 18-38 bar; superficial gas
velocity of the reactor inlet is 10-40 cm/s, preferably 15-35 cm/s;
the volume ratio of gas flow of the reactor inlet to catalyst is
2000-50000, preferably 5000-30000.
[0155] In Step d), top products of the reactor enter a thermal
high-pressure separator, and carry out flash separation at
120-220.degree. C., preferably 140-180.degree. C. to obtain gas
phase (thermal high-pressure separator gas) and heavy oil phase
(thermal high-pressure separator liquid). Gas phase streams enter
the cold high-pressure separator, and carry out flash separation
again at 5-60.degree. C., preferably 10-50.degree. C. to obtain
cold high-pressure separator gas and cold high-pressure separator
liquids (blended liquid phase products of light distillate oil and
synthetic water). Most of the cold high-pressure separator gas is
recycled back to the reactor, and a portion of it is vented out as
tail gas. The discharge amount of tail gas is determined by the
contents of CO and H.sub.2 in the gas, usually the contents of CO
and H.sub.2 are not less than 40%, and preferably not less than
50%. The gas recycled back to the reactor shall be deprived of
CO.sub.2 before being blended with cold high-pressure separator gas
of the first stage Fischer-Tropsch synthesis. Common
CO.sub.2-removing methods such as hot potassium carbonate method or
water washing method can be used to remove CO.sub.2 in recycled
gases. For the hot potassium carbonate CO.sub.2-removing method,
CO.sub.2 absorption column is a common device, the generated
potassium bicarbonate desorbs CO.sub.2 in a regeneration column,
and the obtained potassium carbonate solution returns to the
absorption column again. As for the water washing method, only a
water-washing tank needs to be provided.
[0156] This process controls the severity of process conditions of
the first stage Fischer-Tropsch synthesis, such that the CO
conversion rate of the first stage Fischer-Tropsch synthesis ranges
at 35%-70%, preferably 40%-65%; the process also ensures space time
yield of catalysts, lowers the severity of process conditions of
the second stage Fischer-Tropsch synthesis, such that CO one-way
conversion rate of the second stage Fischer-Tropsch synthesis is
lower than 50%, thus ensuring low methane yield and high oil
product yield during the whole process. After combination of the
first stage and second stage Fischer-Tropsch synthesis, the total
CO conversion rate reaches more than 90%.
[0157] Fischer-Tropsch synthesis reactors in Steps a) and c) adopt
slurry bed reactors. The first stage Fischer-Tropsch synthesis
reactor can be one or a plurality of slurry bed reactors, while
merely one slurry bed reactor is provided for the second stage.
[0158] The catalysts used in Steps a) and c) can be iron-based or
cobalt-based slurry bed catalysts. In case of iron-based catalysts,
the volume ratio of H.sub.2 to CO in the fresh synthetic gas is
preferably 1.4-1.8. In case of cobalt-based catalysts, the volume
ratio of H.sub.2 to CO in the fresh synthetic gas is preferably
2.0. Cobalt-based catalysts are suitable for processing natural gas
based synthetic gases, and iron-based catalysts are suitable for
processing coal-based synthetic gases.
[0159] Main products (hydrocarbon products) produced by the
Fischer-Tropsch synthesis device in the present invention are
hydrocarbon gases (containing lower olefins), light naphtha and
heavy naphtha, diesel distillate, wax and synthetic water, and
particularly naphtha, diesel distillate, and wax as main
products.
[0160] The wax produced in the Fischer-Tropsch synthesis reactor is
separated from catalysts through a filter arranged in the reactor,
and is then discharged out as products, or it can be obtained by
extracting out the slurry in the reactor and separating it from
granules of catalysts through a solid-liquid separation device
arranged outside. If a filter is arranged outside, the granules of
catalysts obtained from separation shall be recycled back to the
reactor to continue participating in the reaction.
[0161] Compared with the prior art, the two-stage Fischer-Tropsch
synthesis process provided in the present invention can bring the
following beneficial effects:
[0162] A. Compared with the prior art, the two-stage process of the
present invention eliminates the recycle gas compressor system of
the first stage Fischer-Tropsch synthesis, and thereby reduces
equipment investment expenses and relevant operation expenses.
[0163] B. In the first stage:
[0164] (1) The total conversion rate (i.e. one-way conversion rate)
is moderate, the products are reasonably distributed, and the
selectivity of methane is low;
[0165] (2) All gases of reactor inlet are fresh synthetic gases,
being dry and free of moisture, and the total CO conversion rate of
the first stage Fischer-Tropsch synthesis is controlled at 35%-75%.
Therefore, the partial pressure of gas-phase vapor in the reactor
is lower than that when the total CO conversion rate reaches more
than 90% in a state of parallel connection, WGS reaction rate is
lower than that of parallel connection, and CO.sub.2 productivity
and selectivity are both lowered;
[0166] (3) Partial pressure of effective gas of the reactor inlet
reaches 100%, and under the conditions of slurry bed reactor,
maximum fresh synthetic gas is operated at high space velocity,
which is rather beneficial to Fischer-Tropsch synthesis reaction
and obtaining the most space-time yield.
[0167] C. In the second stage:
[0168] (1) The cold high-pressure separator gas of the first stage
Fischer-Tropsch synthesis is used as a fresh synthetic feed gas of
the second stage, which is equivalent to carrying out gas phase
condensation dehydration when the reaction of the single-reactor
process proceeds halfway in the parallel connection method. This
can be understood as the reaction portion of the total CO
conversion rate above 65% when partial pressure of gas phase water
in the second stage Fischer-Tropsch synthesis reactor is lower than
that of a single reactor (can be deemed as the latter half stage of
the reactor in case of a single-reactor process in the parallel
connection method). Therefore, this is helpful for improving the
reaction rate of Fischer-Tropsch synthesis;
[0169] (2) As the accumulative conversion rate reaches over 90%
comprising the first stage Fischer-Tropsch synthesis reactor, the
second stage Fischer-Tropsch synthesis can be carried out with a
lower one-way conversion rate than that of parallel connection, and
the product distribution can also be improved.
[0170] Fresh synthetic gas passes through the first stage
Fischer-Tropsch synthesis reactor in one way at a high space
velocity, and then the gas phase stream, after being condensed and
dehydrated, is introduced into the second stage Fischer-Tropsch
synthesis reactor. By this way, the present invention reasonably
adjusts the severity of the two stages of technical parameters.
This will improve the unit space time yield of catalysts, lower the
productivity of methane, and achieve the objects of shorter entire
process duration, lower investment, less operation energy
consumption, higher catalyst space time yield, and lower methane
productivity under the conditions of saving one recycle gas
compressor and greatly reducing recycle gas compression operation
expenses.
[0171] Now the process in the present invention will be further
explained in combination with drawings. However, the present
invention will not therefore be subject to any limitations. In
order to emphasize the idea of the process in the present
invention, many necessary devices for industrial application such
as heaters, pumps, valves and heat exchangers are omitted in the
drawings.
[0172] As shown in FIG. 1, after purification and adjustment, a
fresh synthetic gas feedstock 1 of CO and H.sub.2 (e.g. volume
ratio is 0.67-2.2) exchanges heat with Fischer-Tropsch synthesis
products through heat exchangers 105 and 103, and then is
introduced into a first stage Fischer-Tropsch synthesis reactor 102
to carry out a Fischer-Tropsch synthesis reaction under the action
of Fischer-Tropsch synthesis catalysts. As the Fischer-Tropsch
synthesis reaction is a strong exothermic reaction, the reaction
heat is taken out using a steam coil, the temperature of the whole
reactor is controlled by the pressure of a steam pocket 101, a
byproduct steam 26 is produced, the wax generated is separated from
the catalyst through a built-in filter in the reactor to obtain a
product wax 13, a mixture (i.e. top product) 2 of the feedstock gas
after reaction and partial light distillate of Fischer-Tropsch
synthesis products comes out from the top of a reactor 102,
exchanges heat with the feedstock gas in a heat exchanger 103, and
then carries out gas-liquid separation in a thermal high pressure
separator 104 to separate a thermal high pressure separator liquid
(thermal high pressure separator liquid phase product) 11 and a
thermal high pressure separator gas 3; the thermal high pressure
separator gas 3 exchanges heat with the feedstock gas, then lowers
its temperature to around 50.degree. C., and then carries out gas
liquid separation in a cold high pressure separator 106 to separate
out a cold high pressure separator gas (unconverted tail gas) 4 and
a cold high pressure separator liquid (blended liquid phase
products of light distillate oil and water) 6. The cold high
pressure separator gas 4 discharged from the top of the cold high
pressure separator 106 is blended with a second stage recycled tail
gas 35, a blended gas 40 steps up its pressure through a recycle
gas compressor, exchanges heat with a top product 33 of the second
stage Fischer-Tropsch synthesis reactor through a second stage heat
exchanger 115 and a heat exchanger 113, and then is introduced into
a second stage Fischer-Tropsch synthesis reactor 112 for
Fischer-Tropsch synthesis conversion. Like the first stage
Fischer-Tropsch synthesis reactor 102, the reaction temperature of
the second stage Fischer-Tropsch synthesis reactor 112 is
controlled by a steam pocket 111, and a byproduct steam 25 is
produced, the wax generated from the second stage Fischer-Tropsch
synthesis is separated from the catalyst through a built-in filter
in the reactor to obtain a Fischer-Tropsch synthesis wax 43, which
is blended with a first stage Fischer-Tropsch synthesis wax 13 to
obtain a wax 88 as the product out of the device. The top product
33 of the second stage Fischer-Tropsch synthesis reactor exchanges
heat with the feedstock gas through a heat exchanger 113, and then
carries out gas liquid separation in a thermal high pressure
separator 114 to separate out a thermal high pressure separator
liquid 37 and a thermal high pressure separator gas 34, the thermal
high pressure separator gas 34 exchanges heat with the feedstock
gas through a heat exchanger 115, then lowers its temperature to
around 50.degree. C., and then carries out gas liquid separation in
a cold high pressure separator 116 to separate out a cold high
pressure separator liquid 36 and a cold high pressure separator gas
10. A portion of the cold high pressure separator gas 10 is
discharged as a tail gas 38, the discharge amount is determined by
the contents of CO and H.sub.2 in the tail gas to ensue that the
contents of CO and H.sub.2 in the tail gas are not less than 40%,
when the contents of CO and H.sub.2 in the tail gas are greater
than 50%, the discharge amount is decreased; when the contents of
CO and H.sub.2 in the tail gas are less than 40%, the discharge
amount is increased. Most of the remaining cold high pressure
separator gas 27 is introduced into a decarburization system (i.e.
a CO.sub.2-removing system) 109, therein the gas contacts a
decarburization solvent 5, most CO.sub.2 in the gas enters a
decarburization solvent to form a alkali sludge 50 and be
discharged out of the decarburization system 109, the
CO.sub.2-removed gas as a recycle gas 35 is blended with the cold
high pressure separator gas 4 from the first stage Fischer-Tropsch
synthesis, and then is introduced into a recycle gas compressor 110
for increasing pressure, the increased blended gas 40 returns to
the second stage Fischer-Tropsch synthesis reactor inlet after heat
exchange. First stage and second stage cold high pressure separator
liquids 6 and 36, after being blended, blend with a thermal low
pressure separator gas 39, and then enter a cold low pressure
separator 118 to be separated as a Fischer-Tropsch synthetic water
68 comprising oxygen-containing compounds, a Fischer-Tropsch
synthesis cold low pressure separator product (light distillate
oil) 58, and a cold low pressure separator gas 48 out of the
device. The first stage and second stage thermal high pressure
separator liquids 37 and 11, after being blended, enter a thermal
low pressure separator 117 to be separated as a thermal low
pressure separator liquid (heavy distillate oil) 78 and a thermal
low pressure separator gas 39, wherein the heavy distillate oil 78
is discharged out of the device as a product, the thermal low
pressure separator gas 39, after being cooled (e.g. cooled to
5-50.degree. C.), is blended with cold high pressure separator
liquids 6 and 36, and is introduced into the cold low pressure
separator 118 for separation.
[0173] The Fischer-Tropsch synthesis reaction is a strong
exothermic reaction. In order to keep the slurry bed zone of the
Fischer-Tropsch synthesis reactor being operated at a constant
temperature, a steam coil is arranged in the reactor slurry zone to
enable the slurry to exchange heat with the hot water flowing
through the steam coil, and a portion of hot water, after absorbing
heat, discharges out the reaction heat by the way of isothermal
vaporization. The reaction heat of the first stage Fischer-Tropsch
synthesis reactor 102 is moved out of the reactor by means of
producing the byproduct steam 26 after exchanging with hot water.
After exchanging heat with the slurry in the first stage
Fischer-Tropsch synthesis reactor, the hot water 23 from the steam
pocket 101 forms a mixture of partial hot water isothermal vaporous
steam and hot water and returns to the steam pocket 101, wherein
the steam 26 is vented after a pressure control by the steam pocket
101, and the liquid level of the steam pocket is maintained by
replenishing a hot water 21. Likewise, the reaction heat of the
second stage Fischer-Tropsch synthesis reactor 112 is moved out of
the reactor by means of producing the byproduct steam 25 after
exchanging with hot water. After exchanging heat with the slurry in
the second stage Fischer-Tropsch synthesis reactor, the hot water
24 from the steam pocket 111 forms a mixture of partial hot water
isothermal vaporous steam and hot water and returns to the steam
pocket 111, wherein the steam 25 is vented after a pressure control
by the steam pocket 111, and the liquid level of the steam pocket
is maintained by replenishing a hot water 22. A replenishing hot
water 20 required by the two steam pockets is provided outside the
device, and the steam discharged out through pressure control
accumulates to become a byproduct steam 28 of the device, and is
discharged out of the Fischer-Tropsch synthesis device, or it is
used as a heat source.
[0174] According to the understanding of the person skilled in the
art, the first stage Fischer-Tropsch synthesis reactor 102 shown in
FIG. 1 can be one reactor or a plurality of (more than two, e.g.
two, three, or four) reactors in parallel; likewise, the second
stage Fischer-Tropsch synthesis reactor 112 can be one reactor or a
plurality of (more than two, e.g. two, three, or four) reactors in
parallel.
[0175] The process of the present invention overcomes the defects
of high equipment investment and operation expenses, low space time
yield, and low CO utilization that exist when synthetic gas is used
as a feedstock to produce liquid products using a conventional
Fischer-Tropsch synthesis process. In addition, the process of the
present invention integrates techniques, simplifies technical
process, and is suitable for large-scale industrialized
production.
Experiments
I. Partial Pressure Experiment of Inlet Effective Gas
[0176] The inventor tests the Fischer-Tropsch synthesis reaction
performances under partial pressures of inlet effective gases of
different reactors using stirred tank slurry bed reaction devices
and iron-based catalysts, and the results are shown in Table 1.
TABLE-US-00001 TABLE 1 Experiment Results of Partial Pressures of
Inlet Effective Gases of Different Reactors Condition No. Condition
1 Condition 2 Technical condition: Gas catalyst ratio of fresh gas,
Nml/g/h 8400 7140 H.sub.2/CO ratio of fresh gas, v/v 1.7 1.7
Nitrogen content in fresh gas, mol % 8 8 Tail gas recycle ratio,
v/v 2.33 2.75 Superficial gas velocity of reactor inlet, cm/s
Benchmark Benchmark Reaction temperature .degree. C. Benchmark
Benchmark Reaction pressure, MPa Benchmark Benchmark Experiment
result: Total CO conversion rate, % 75 81 CO.sub.2 selectivity, mol
% 13.3 14.7 CH.sub.4 selectivity, mol % 3.6 4.4 CO one-way
conversion rate, % 30 32 C.sub.5.sup.+ space time yield, g/g-cat/h
1.0 0.9 Nitrogen content in recycled gas, mol % 18 21
[0177] The data in Table 1 shows that, if the superficial gas
velocity of reactor inlet, the reaction temperature and the
reaction pressure remain the same, when the gas catalyst ratio of
fresh synthetic gas decreases from 8400 Nml/g-cat./h in Condition 1
to 7140 Nml/g-cat./h in Condition 2, although the total CO
conversion rate can be improved, the space time yield and device
productivity are both decreased due to the decrease of effective
gas partial pressure of the reactor inlet. The experiment results
show that making efforts to improve effective gas partial pressure
of reactor inlet is helpful for improving oil productivity of the
device, under same superficial gas velocity.
II. Reaction Rate Experiment Under Different Water Partial
Pressures
[0178] Carry out an experiment based on the following feed gas
conditions: CO.sub.2 mole fraction is 0.3, CO mole fraction is 0.2,
H.sub.2 mole fraction is 0.4, and total reaction pressure P is 2
MPa. The obtained data on Fischer-Tropsch synthesis reaction rate
under different water partial pressures are shown in Table 2:
TABLE-US-00002 TABLE 2 Comparison of Fischer-Tropsch Synthesis
Reaction Rates under Different Water Partial Pressures Water Water
content content in feed in feed gas Reaction gas Reaction phase,
rate phase, rate Reaction rate Catalysts Y.sub.H2O, % r.sub.FT
Y.sub.H2O, % r.sub.FT improvement, % Fe/Cu/K 0.05 0.043319 0.005
0.048891 11.4% Sediment Fe 0.05 0.006769 0.005 0.012941 91.2%
100Fe/0.3Cu/0.2K 0.05 0.028508 0.005 0.054936 92.7% (sediment)
Ruhrchemie LP 0.05 0.014306 0.005 0.027326 91.0% 33/8
[0179] As seen from the experiment results in Table 2, although
different catalysts have different sensitivities to water partial
pressure, decreasing water contents in feed gas can remarkably
improve all Fischer-Tropsch synthesis reaction rates. If the feed
gas is dehydrated and the water content therein is decreased by 90%
from 0.05%, to 0.005% (50 ppm) (volume ratio), the Fischer-Tropsch
synthesis reaction rate can increase by 11%-93%. Thus, it can be
seen that the effect is very remarkable.
EXAMPLES
Example 1
[0180] In Example 1, the process shown in FIG. 1 is used. The fresh
feedstock gas is a synthetic gas obtained from gasified coal
through purification and water gas shift, wherein the volume ratio
of H.sub.2 to CO is 1.54, the H.sub.2 content is 60.7%, and the CO
content is 39.3% (volume ratio).
[0181] Iron-based catalysts are used for both the first stage and
the second stage of the present Example, and the catalyst is
SFT418-7 developed by Beijing Research Institute of China Shenhua
Coal to Liquid and Chemical Co., Ltd and produced by Zhejiang Taide
New Material Co., Ltd. Before carrying out in the Fischer-Tropsch
synthesis reaction, the catalyst is deoxidized in the reactor.
[0182] The Fischer-Tropsch synthesis reaction is carried out under
the process conditions listed in Table 3.
Comparison Example 1
Parallel Connection Method
[0183] To better demonstrate the benefits of the present invention,
the parallel connection method for two sets of single-reactor
Fischer-Tropsch synthesis devices that are industrially implemented
in a large scale at present is selected for comparison. The process
conditions for parallel connection are shown in the last column of
Table 3.
TABLE-US-00003 TABLE 3 Process conditions of Fischer-Tropsch
Synthesis Reaction for Example 1 and Comparison Example 1 Technical
method Example 1 (The present Comparison invention) Example 1 First
Second (Prior art) Technical condition stage stage Each reactor*
Reaction temperature .degree. C. 255 255 255 Reaction pressure, MPa
2.8 2.8 2.8 Gas catalyst ratio of fresh synthetic 4000 0 2000 gas
feedstock, Nml/g-cat./h Gas catalyst ratio of reactor inlet, 4000
4000 4000 Nml/g-cat./h Recycle ratio, v/v 0 0.73 1:1 Superficial
gas velocity of reactor 15 15 15 inlet, cm/s Temperature of thermal
160 160 160 high-pressure separator, .degree. C. Temperature of
cold high-pressure 45 45 45 separator, .degree. C. Temperature of
thermal 120 120 120 low-pressure separator, .degree. C. Temperature
of cold low-pressure 40 40 40 separator, .degree. C. Water content
in unconverted tail -- 0.005 0.005 gas recycled to second stage
Fischer-Tropsch synthesis reactor (%) *Notes: 1) The process
conditions of the two reactors in Comparison Example 1 are the
same; 2) Gas catalyst ratio is a ratio of volumetric flow of feed
gas to mass of catalysts in reactor within a unit time period.
[0184] The specific data for substantive effect of the process in
the present invention are shown in Table 4.
TABLE-US-00004 TABLE 4 Experiment Results Process Example 1
Comparison (The present invention) Example 1 First and (Prior art)
First Second second 2 reactors in Results stage stage stages
parallel CO one-way conversion 54.7 64.8 59.7 rate, % Total CO
conversion 54.7 81.4 91.7 83.6 rate, % CO.sub.2 selectivity (mole
24.7 27.8 25.3 23.5 fraction to converted CO), % CH.sub.4
selectivity (mole 5.1 9.1 6.7 6.6 fraction to total hydrocarbon
products), % Hydrocarbon space time 0.445 0.290 0.735 0.705 yield,
g/g-cat./h Ratio of totally recycled 0 0.42 0.42 1 gas to fresh
synthetic gas, v/v
[0185] In Example 1, fresh synthetic gas feedstocks at the time of
first stage Fischer-Tropsch synthesis pass through all at once, and
CO conversion rate is 54.6%. After the first stage Fischer-Tropsch
synthesis reaction, the gas shrinks. To meet the superficial gas
velocity of the second stage Fischer-Tropsch synthesis reactor
inlet, the recycled gas for the second stage Fischer-Tropsch
synthesis shall be replenished, and the recycle ratio is 0.76 v/v.
CO one-way conversion rate of the second stage Fischer-Tropsch
synthesis is 61.8%, and the total conversion rate reaches 81.4%.
The total reaction results after integration of the first and
second stages are as follows: total CO conversion rate reaches
91.7%, CO.sub.2 selectivity (mole fraction to converted CO) is
25.3%, CH.sub.4 selectivity (mole fraction to total hydrocarbon
generated) is 6.7%, and hydrocarbon space time yield reaches 0.735
g/g-cat./h.
[0186] Under the conditions of the same catalyst, the same
superficial gas velocity of reactor inlet, and the same reaction
temperature and pressure, the integration results of the two sets
of single-reactor devices in the parallel connection method are as
follows: CO one-way conversion rate is 59.7%, the total conversion
rate is merely 83.6%, CO.sub.2 selectivity (mole fraction to
converted CO) is 23.5%, CH.sub.4 selectivity (mole fraction to
total hydrocarbon generated) is 6.6%, and hydrocarbon space time
yield is 0.705 g/g-cat./h. As to the Comparison Example, the
recycle ratio of every reactor is 1.0 v/v, viz. two recycle gas
compressors are required, and the total amount of recycle gas
reaches the amount of fresh synthetic gas. To improve CO
utilization rate, it usually requires increasing the total CO
conversion rate to over 90%. At this time, it needs decreasing the
amount of fresh synthetic gas and increasing the recycle ratio to
over 1.5.
[0187] According to the results of Examples, CO.sub.2 selectivity
and CH.sub.4 selectivity in the process of the present invention
are approximately equivalent to those in the conventional prior art
when the same amount of fresh synthetic gas is processed; the total
CO conversion rate in the present invention is 8% higher than that
in the prior art; hydrocarbon productivity of the device (space
time yield) is 4% higher than that in the prior art; one recycle
gas compressor is decreased; the required amount of recycle gas
decreases 58%, and the operation expenses of the gas recycle
compression system can be largely reduced.
Example 2
[0188] In Example 2, the process shown in FIG. 1 is used. The fresh
feedstock gas is a synthetic gas obtained from gasified coal
underwent purification and water gas shift, wherein the volume
ratio of H.sub.2 to CO is 1.8.
[0189] Iron-based catalysts are used for both the first stage and
second stage of the present example, and the catalyst is the same
as that in Example 1. The process conditions are listed in Table
5.
Example 3
[0190] In Example 3, the process shown in FIG. 1 is used. The fresh
feedstock gas is a synthetic gas obtained from natural gas, wherein
the volume ratio of H.sub.2 to CO is 2.
[0191] Cobalt-based catalysts are used for both the first stage and
second stage of the present example, and the compositions of the
catalysts are 15Co:5Zr:100Al.sub.2C.sub.3. The preparation process
is as follows: pouring the alumina baked at 500.degree. C. in
atmosphere into water solution of zirconium nitrate in advance in
the method of preliminary wetting, carrying out evaporating
dehydration and drying with drumming, adding
Co(NC.sub.3).sub.26H.sub.2O water solution again in the preliminary
wetting method, drying, and dipping into cobalt nitrate water
solution. Repeating the above process for three times, until the
cobalt content in the catalyst predecessor conforms to the
requirement, then adding some binder, extruding, pelletizing,
drying, baking, and reducing to obtain qualified cobalt-based
catalysts. The process conditions are listed in Table 5.
TABLE-US-00005 TABLE 5 Process conditions of Examples 2 and 3
Process Example 2 Example 3 (the present (the present invention)
invention) First Second First Second Process condition stage stage
stage stage Reaction temperature .degree. C. 240 270 260 210
Reaction pressure, MPa 2.3 2.3 2.3 2.3 Gas catalyst ratio of fresh
7200 0 50000 0 synthetic gas feedstock, Nml/g-cat./h Gas catalyst
ratio of reactor 7200 4000 50000 7667 inlet, Nml/g-cat./h Recycle
ratio, v/v 0 0.91 0 1.50 Superficial gas velocity of 10 10 40 40
reactor inlet, cm/s Temperature of thermal 140 140 220 220
high-pressure separator, .degree. C. Temperature of cold 5 5 60 50
high-pressure separator, .degree. C. Temperature of thermal 60 60
80 80 low-pressure separator, .degree. C. Temperature of cold 5 5
40 30 low-pressure separator, .degree. C. Water content in
unconverted -- 0.003 -- 0.01 tail gas recycled to second stage
Fischer-Tropsch synthesis reactor (%)
TABLE-US-00006 TABLE 6 Experiment Results of Examples 2 and 3
Process Example 2 (the present Example 3 (the present invention)
invention) First First and and First Second second First Second
second Results stage stage stages stage stage stages CO one-way
64.9 43.8 60.0 37.7 conversion rate, % Total CO 64.9 75.0 91.2 60.0
70.1 88.0 conversion rate, % CO.sub.2 selectivity 33.3 38.6 34.8 0
0 0 (mole fraction to converted CO), % CH.sub.4 selectivity 3.57
4.12 3.7 7.2 8.4 7.58 (mole fraction to total hydrocarbon
products), % Hydrocarbon 0.752 0.165 0.917 0.620 0.405 1.025 space
time yield, g/g- cat./h Ratio of 0 0.45 0.45 0 0.66 0.66 totally
recycled gas to fresh synthetic gas, v/v
[0192] If the conventional process wants to reach the total CO
conversion rate of the present invention, the amount of the
processed fresh synthetic gas shall be reduced, and the recycle
ratio shall be increased. Productivity of the device is further
decreased, and the compression energy consumption of recycle gas is
further increased.
[0193] Slurry bed reactors are used as examples in the above
examples to describe the present invention. The person skilled in
the art knows that the above process and system are also suitable
for fixed beds, fixed fluidized beds and fluidized beds after
proper adjustment.
[0194] Of course, the present invention can also have other
specific embodiments. The above is merely preferred embodiments of
the present invention but not to limit the present invention.
Within the spirit of the present invention, the person skilled in
the art may have various alterations and changes based on contents
of the present invention. Any alterations and changes thereof
should be covered in the protection scope of the present
invention.
* * * * *