U.S. patent application number 13/978348 was filed with the patent office on 2013-11-07 for method for utilizing thermal energy of product gases in a btl plant.
This patent application is currently assigned to VAPO OY. The applicant listed for this patent is Jorma Kautto, Mika Timonen, Olli-Pekka Viljakainen. Invention is credited to Jorma Kautto, Mika Timonen, Olli-Pekka Viljakainen.
Application Number | 20130291808 13/978348 |
Document ID | / |
Family ID | 43528527 |
Filed Date | 2013-11-07 |
United States Patent
Application |
20130291808 |
Kind Code |
A1 |
Kautto; Jorma ; et
al. |
November 7, 2013 |
METHOD FOR UTILIZING THERMAL ENERGY OF PRODUCT GASES IN A BTL
PLANT
Abstract
The invention for utilizing thermal energy of gases generated in
a BtL plant. A feature of the invention is that the thermal energy
of discharge gas streams generated in the BtL plant is used for
driving various compressor machineries and/or electricity
generation, whereby the plant can operate as a stand-alone
facility.
Inventors: |
Kautto; Jorma; (Vantaa,
FI) ; Viljakainen; Olli-Pekka; (Vantaa, FI) ;
Timonen; Mika; (Jyvaskyla, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kautto; Jorma
Viljakainen; Olli-Pekka
Timonen; Mika |
Vantaa
Vantaa
Jyvaskyla |
|
FI
FI
FI |
|
|
Assignee: |
VAPO OY
Jyvaskyla
FI
|
Family ID: |
43528527 |
Appl. No.: |
13/978348 |
Filed: |
December 23, 2011 |
PCT Filed: |
December 23, 2011 |
PCT NO: |
PCT/FI2011/051154 |
371 Date: |
July 3, 2013 |
Current U.S.
Class: |
122/7R |
Current CPC
Class: |
C10J 3/726 20130101;
Y02E 20/14 20130101; C01B 2203/0465 20130101; F01K 13/00 20130101;
C10J 2300/1659 20130101; C10J 2300/0916 20130101; F01K 17/06
20130101; F22B 1/1846 20130101; C01B 2203/0283 20130101; C10J
2300/1687 20130101; C10K 3/00 20130101; C10K 1/024 20130101; C01B
2203/0233 20130101; C10K 3/04 20130101; Y02P 20/129 20151101; C10J
2300/0959 20130101; C01B 2203/062 20130101; Y02E 50/30 20130101;
Y02E 50/10 20130101; C01B 2203/043 20130101; C10J 2300/1846
20130101; C01B 2203/0811 20130101; C10J 2300/0909 20130101; C10J
2300/1621 20130101; Y02E 50/14 20130101 |
Class at
Publication: |
122/7.R |
International
Class: |
F22B 1/18 20060101
F22B001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 14, 2011 |
FI |
20115038 |
Claims
1. A method for utilizing thermal energy of gases generated in a
BtL plant, wherein the thermal energy of gases generated in the
production process of the BtL plant is utilized in superheating
steam for driving the turbine machineries of the BtL plant.
2. The method of claim 1, wherein the method the compressors and/or
electric generators of the plant process stages are driven by steam
turbines using the steam streams generated in the BtL plant
processes that are superheated by the flue gases of a steam
reformer, that is, an SMR reactor integrated with the BtL plant
equipment and, additionally, to maximize the yield of end products
of the BtL plant, hydrogen is recovered with the help of a PSA
unit.
3. The method of claim 1, wherein the method superheating the
saturated steam streams generated in the BtL processes
substantially increases the self-supported electrical balance of
the BtL and facilitates self-contained operation of the BtL plant
as a stand-alone facility independent from another industrial plant
or power utility, while simultaneously the yield of end product is
maximized.
4. The method of claim 1, wherein a BtL plant has integrated
thereto a method for utilizing the thermal energy of the flue gases
and/or reformed gas of a steam reformer for superheating the steam
that is used in the BtL plant for driving a syngas turbocompressor
and/or producing electricity as well as improving the hydrogen
yield, whereby a WGS process is included having a steam reformer
connected to a PSA unit.
5. The method of claim 1, wherein a BtL plant generates in its FT
process different FT tail gases, that is, process reject gases,
which are passed to a steam reformer, wherein the FT tail gases are
reformed in such a way that the hydrocarbons of gases are reformed
into hydrogen and substantially into carbon monoxide and therefrom
further to carbon dioxide, from which gas stream after cooling in a
PSA unit hydrogen is recovered, whereupon the remaining gases are
recirculated to a steam reformer for heating the steam reformer to
a correct temperature of about 800-1100.degree. C.
6. The method of claim 1, wherein gases reformed in steam reformer
and flue gases exiting the steam reformer are passed for cooling to
a heat exchanger, whereby the thermal energy of the gas streams is
used for superheating the saturated high-pressure steam exiting the
gasifier.
7. The method of claim 1, wherein heat exchanger comprises
superheaters and, wherein saturated high-pressure steam is
superheated for compressor/turbine and that boilers and a
superheater are employed for producing steam required in steam
reforming.
8. The method of claim 1, wherein to the compressor/turbine
combination and operating as a turbocompressor is connected a steam
condensation turbine, whereto are passed the low-pressure and
middle-high-pressure steam streams generated in the BtL plant and a
generator is provided for electricity generation.
9. Use of thermal energy of gases generated in a BtL plant for
superheating steam streams driving the turbine machineries of the
BtL plant and postprocessing gas streams for hydrogen recovery
therefrom.
10. The use according to claim 9 for utilizing saturated steam
streams generated in a BtL plant, wherein superheating increases
the self-supported electrical balance of the BtL and facilitates
self-contained operation of the BtL plant as a stand-alone facility
independent from another industrial plant or power utility, while
simultaneously the yield of end product is maximized.
11. The use according to claim 9 of a steam reformer such as an SMR
reactor integrated with the BtL plant equipment for superheating
the discharge gas streams generated in the BtL plant to drive the
plant's compressors and/or electricity generation units and,
additionally, to maximize the yield of end products of the BtL
plant, whereby hydrogen is recovered with the help of a PSA
unit.
12. The use according to claim 9 for utilizing the thermal energy
of the flue gases and/or reformed gas for superheating the steam
that is used in the BtL plant for driving the syngas
turbocompressor and/or producing electricity.
13. The use according to claim 9 for improving the yield of the BtL
plant, whereby a WGS process is used having a steam reformer and a
PSA unit integrated with the BtL plant equipment.
14. The method of claim 2, wherein the method superheating the
saturated steam streams generated in the BtL processes
substantially increases the self-supported electrical balance of
the BtL and facilitates self-contained operation of the BtL plant
as a stand-alone facility independent from another industrial plant
or power utility, while simultaneously the yield of end product is
maximized.
15. The method of claim 2, wherein a BtL plant has integrated
thereto a method for utilizing the thermal energy of the flue gases
and/or reformed gas of a steam reformer for superheating the steam
that is used in the BtL plant for driving a syngas turbocompressor
and/or producing electricity as well as improving the hydrogen
yield, whereby a WGS process is included having a steam reformer
connected to a PSA unit.
16. The method of claim 3, wherein a BtL plant has integrated
thereto a method for utilizing the thermal energy of the flue gases
and/or reformed gas of a steam reformer for superheating the steam
that is used in the BtL plant for driving a syngas turbocompressor
and/or producing electricity as well as improving the hydrogen
yield, whereby a WGS process is included having a steam reformer
connected to a PSA unit.
17. The method of claim 2, wherein a BtL plant generates in its FT
process different FT tail gases, that is, process reject gases,
which are passed to a steam reformer, wherein the FT tail gases are
reformed in such a way that the hydrocarbons of gases are reformed
into hydrogen and substantially into carbon monoxide and therefrom
further to carbon dioxide, from which gas stream after cooling in a
PSA unit hydrogen is recovered, whereupon the remaining gases are
recirculated to a steam reformer for heating the steam reformer to
a correct temperature of about 800-1100.degree. C.
18. The method of claim 3, wherein a BtL plant generates in its FT
process different FT tail gases, that is, process reject gases,
which are passed to a steam reformer, wherein the FT tail gases are
reformed in such a way that the hydrocarbons of gases are reformed
into hydrogen and substantially into carbon monoxide and therefrom
further to carbon dioxide, from which gas stream after cooling in a
PSA unit hydrogen is recovered, whereupon the remaining gases are
recirculated to a steam reformer for heating the steam reformer to
a correct temperature of about 800-1100.degree. C.
19. The method of claim 4, wherein a BtL plant generates in its FT
process different FT tail gases, that is, process reject gases,
which are passed to a steam reformer, wherein the FT tail gases are
reformed in such a way that the hydrocarbons of gases are reformed
into hydrogen and substantially into carbon monoxide and therefrom
further to carbon dioxide, from which gas stream after cooling in a
PSA unit hydrogen is recovered, whereupon the remaining gases are
recirculated to a steam reformer for heating the steam reformer to
a correct temperature of about 800-1100.degree. C.
20. The method of claim 2, wherein gases reformed in steam reformer
and flue gases exiting the steam reformer are passed for cooling to
a heat exchanger, whereby the thermal energy of the gas streams is
used for superheating the saturated high-pressure steam exiting the
gasifier.
Description
[0001] The invention relates to a method in accordance with the
preamble of claim 1 for utilizing thermal energy of gases generated
in a BtL plant. The invention also relates to a use in accordance
with claim 9.
[0002] In a BtL plant using state-of-the-art technology, solid
biomass is gasified in a high-temperature or a low-temperature
gasifier. The function of a BtL factory is to convert biomass into
liquid fuels (Biomass to Liquid) from syngas generally through
Fischer-Tropsch synthesis. In high-temperature gasification the
gasifier operates at a temperature higher than the ash melt
temperature, more specifically at about 1200-1400.degree. C.
Depending on the technology used, gasification takes place at a
pressure of 1-40 bar. Recently a technology has been developed
particularly suited for high-temperature gasification of biomass at
a gasifier pressure of about 5 bar.
[0003] The gas generated in gasification and further subjected to
purification is generally called syngas, since it is subsequently
used in preparation of other products such as ammonia or long-chain
aromatic hydrocarbons.
[0004] In the manufacture of synthetic biofuels, the raw syngas
generated in gasification must be cooled and purified free from
dust, whereupon other components except hydrogen and carbon
monoxide need be separated from the gas stream. The resulting pure
syngas, i.e., hydrogen and carbon monoxide is passed to a
Fischer-Tropsch reactor (FT reactor), wherein paraffinic
hydro-carbons are generated in the presence of a catalyst. The FT
process is typically carried out at a pressure of 20-40 bar and at
a temperature of about 200.degree. C. The wax-like product thus
obtained is known as biowax.
[0005] The biowax taken out from the FT process requires further
refining to produce therefrom fuels suited for engine use by way
of, e.g., hydrogenation, cracking and distillation. Also these
processes are carried out under elevated pressure (30-80 bar).
Hydrogenation refers to processing in a hydrogen atmosphere,
wherein double bonds between carbons are saturated. Cracking in
turn refers to breaking excessively long hydrocarbon chains in a
reactor. Distillation finally separates the fuel fractions from
each other thus resulting in diesel fuel, naphtha, kerosene,
liquefied petroleum gas, etc.
[0006] If gasification is carried out at a pressure lower than that
of the FT and refining processes, the syngas pressure must be
elevated. Conventionally this step takes place after the syngas is
cooled and filtered free from solid impurities. Pressure elevation
is accomplished by gas compressors that are available in plural
different types. Typically they can be categorized as axial,
radial, piston and screw compressors. Most generally, syngas
compression has been performed using axial and radial compressors.
A suitable compressor type is selected based on the required
pressure elevation, gas composition and volume.
[0007] A common feature of compressors is that they are rotary
equipment. The mechanical energy required for compression is
typically derived from an electric motor or, alternatively, from a
steam or gas turbine. E.g., syngas compression in a BtL plant
having a gasification fuel power of 300-500 MW at a pressure of
about 5 to 35 bar, requires an input power of about 10-17 MW.
[0008] Instead of air, gasification is carried out using oxygen
that must be pressurized for the gasification process. Oxygen can
be prepared from air by first cooling it into liquid form and then
distilling the air gases apart from each other. The compressor
power of an air gas plant is 10-15 MW for a syngas plant of 300-500
MW gasification fuel power. At an oxygen plant, compressors are
needed in the cooling process and oxygen pressure elevation to the
gasification process pressure.
[0009] In the BtL process, the pressure decreases after the
pressurization step downstream toward the process exit end. This is
due to the pressure losses occurring in the different process
stages in a cumulative manner. If gas streams are desired to be fed
backward in the process, the pressure levels of such streams must
be elevated by compression. These compressors, however, are
relatively low-powered with regard to the compression power
required to move the main gas stream, typically in the order of
200-700 kW per compressor.
[0010] Moreover, if the process includes liquefaction of carbon
dioxide for its capture, the pressure of gaseous carbon dioxide
must be elevated prior to its cooling to about 20 bar followed by
cooling to -50.degree. C. with the help of heat exchangers and an
expansion valve. The input power requirements of carbon dioxide
compression and compressors of the cooling equipment in a BtL plant
of 300-500 MW gasification fuel power is in the order of 10-15 MW,
whereby the liquefied amount of carbon dioxide is about 50-75
t/h.
[0011] As is obvious from the above discussion, the number of
various compressors consume a major portion of the electrical
energy required by a BtL plant. Hence, notwithstanding the possible
in-plant electric energy generation of the BtL plant based on its
process steam resources, the plant is dependent on external
electricity.
[0012] The invention is primarily directed to syngas compression,
but more generally the invention may be applied to other use, for
example to the process steps mentioned above that require
compression.
[0013] Herein it must be noted that a BtL process generates
saturated steams at different pressure levels, especially at a high
pressure, from the cooling of raw syngas and the gasifier itself.
More particularly, controlled cooling of the FT synthesis releases
a large volume of saturated steam at a middle-high pressure.
Besides the relatively small own-use requirements of the BtL
process itself, the dominatingly largest consumer of backpressure
steam in the plant is biomass drying. Nevertheless, the BtL plant
has plentiful inherent supply of low-pressure steam.
[0014] Typically, due to the above-mentioned reasons, the goal is
to integrate a BtL plant with another industrial plant capable of
using its excess steam. Advantageously steam is used, e.g., in
drying paper, pulp and cardboard as well as in district heating and
electricity generation. Steam available from a BtL plant reduces
the fuel consumption of the factory to be integrated therewith.
[0015] A problem herein, however, arises therefrom that finding a
suitable factory for integration poses a major limitation to the
viable number of potential locations for erecting a BtL plant. As
the BtL plant must be located on the remaining area of the
factory's real estate having no earlier reservations, the layout of
the BtL plant often becomes less optimal. Neither will a
logistically optimally integrated plant location necessarily be the
most advantageous site for the BtL plant.
[0016] Further noteworthy is that the BtL plant and the factory
integrated therewith must be constructed to cope with such
constraints that either one of the plants/factories is not running
continuously, which means that both of them need be equipped with
stand-alone facilities. Hence, integration does not necessarily
result in a cost reduction of overall investment, but on the
contrary, requires erection of integration facilities and processes
for stand-alone operation.
[0017] The excess steam generated in a stand-alone situation should
be utilized maximally effectively--which situation, in the lack of
steam consumers, requires electricity generation with the help of a
steam turbine. However, use of saturated steam in turbines is
impossible unless it is superheated by way of burning gaseous fuel,
e.g., in a separate superheater boiler that otherwise is a
redundant unit in the process.
[0018] Now the present invention provides an arrangement capable of
overcoming the above-discussed problems. This object of the
invention relates to a situation, wherein there is a deficit of
electricity and plentiful excess of saturated steam simultaneously
in the BtL process. Electricity is required to energize various
compressors driven by electric motors. Simultaneously, steam is
delivered to a process or power plant of the integrated factory
wherein the steam drives turbines producing electricity. A portion
of this electricity can be returned for use in the BtL process.
[0019] In the embodiment of the invention, the essential aim is to
utilize the excess steam on-site and thereby reduce the quantity of
purchased electricity. These two goals can be combined by driving
the compressors with the steam generated in the BtL plant
processes. Thereby the conversion losses of mechanical energy into
electricity and back into mechanical energy are minimized. For
using steam in turbines, it must first be superheated. Next will be
described a method, wherein superheating the steam is accomplished
with the help of process equipment known as steam reformer.
[0020] Steam reformer is a unit generally used oil refining
industry for producing hydrogen from methane and heavier
hydrocarbon fractions for use in oil refinement. Reforming is
accomplished by feeding steam into the gas being reformed with the
help of a suitable catalyst and under high temperature. The process
is also known by English terms Steam Methane Reformer (SMR) or
Steam Reformer Unit (SRU).
[0021] Next is described a method, wherein superheating of steam is
accomplished using the SMR technique. The raw syngas resulting from
the gasification stage of the BtL process contains an insufficient
amount of hydrogen for the FT process. Therefore, addition of
hydrogen is necessary by means of a process based on a water gas
transfer reaction known as the WGS technique (WGS=Water Gas Shift).
In this process carbon monoxide (CO) is separated from syngas
generated in gasification, into the gas stream is injected steam
and, in a subsequent catalyzed reaction, hydrogen is generated as
follows:
CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2
[0022] The FT process of a BtL plant and different stages of oil
refinement generate various tail gases, wherefrom hydrogen can be
recovered using the SMR technique. Thereby the yield of the BtL
process is improved and the thus produced hydrogen is more
ecological, i.e., derived from a biomass as compared to a
situation, wherein the hydrogen source is a fossil resource such as
methane.
[0023] Tail gases, whose free translation into Finnish is "rear-end
gases" and which are generated in the Fischer-Tropsch process and
subsequent postprocessing stages, stem from the biomass-based raw
material of the plant and contain different kinds of light
hydrocarbons. Conventionally, hydrogen is produced from the methane
of natural gas using the SMR technique:
CH.sub.4+H.sub.2O.fwdarw.CO+3H.sub.2
[0024] Now this technique is applied to the tail gases generated in
the FT process. Thus, gas molecules with a longer chain such as
propane are reformed as follows:
C.sub.3H.sub.8+3H.sub.2O.fwdarw.3CO+7H.sub.2
[0025] wherefrom carbon monoxide can be further utilized in the
process via the WGS reaction:
CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2
[0026] Accordingly, the BtL process can be complemented with WGS
and/or SMR processes for improved yield and adjustment of its
hydrogen-to-carbon monoxide ratio. In regard to methane, for
instance, the overall reaction is:
CH.sub.4+2H.sub.2O.fwdarw.CO.sub.2+4H.sub.2
[0027] For utilizing in the high-pressure turbine the high-pressure
saturated steam resulting from cooling the raw syngas of the
gasifier, the steam must be superheated, since no water condensed
during the expansion of steam may be passed to the turbine.
Superheating can be accomplished in a separate superheater boiler
or by the hot flue gases of the steam reformer which is more
appropriately adaptable to the BtL process. In the reformer takes
place the reforming the tail gas of the FT process that contains a
mixture of different hydrocarbons. The temperature of the gas being
reformed is typically elevated to about 900-1100.degree. C. by
burning a portion of the gas or some other fuel in the boiler.
[0028] The process temperature is so high that the exhausted flue
gases may still be used for superheating steam, which means that
superheating the steam can be accomplished with a minimal extra
investment to the SMR technique without the need for installing a
boiler. The flue gases are clean as they originate from ash-free
tail gases, that is, from exhaust and surplus gases. Obviously, the
SMR unit may also be heated using externally fed fuels such as
natural gas or other combustible gases resulting from the BtL
process.
[0029] The excess backpressure steam may be converted into
electricity in a steam condensation turbine. The condensing turbine
may be a separate piece of equipment or integral with the syngas
turbocompressor. Also the back-pressure turbine can be separate
from the compressor thus facilitating entirely independent
operation of the compressors and turbines.
[0030] This arrangement allows more efficient utilization of the
entire process chain. The essential features of the invention are
the crucial factors in the method and its use. More specifically,
the invention is characterized by what is stated in the claims.
[0031] In the following, the invention is described in more detail
with the help of a preferred embodiment by making reference to
appended FIGS. 1-3, in which drawings:
[0032] FIGS. 1-3 show process flow schematics of arrangements for
implementing the method according to the invention.
[0033] FIG. 1 shows a flow schematic for producing biofuels from
solid biomass. The biomass 12 being fed into the process is dried
and its particle size is homogenized in raw material preprocessing
step 1 suitable for feeding to the gasifier. The preprocessed
biomass is fed to oxygen gasification 3 having such a high
temperature that makes the tar components of gas to decompose
entirely. Decomposition of tar components is essential to prevent
them from condensing in the process equipment downstream of the
gasification step. The process oxygen is prepared in oxygen plant
2.
[0034] Raw syngas 28 is cooled in step 4 and is filtered free from
dust in process 5. Subsequently, gas pressure can be elevated by
compressor 24 to the level required by FT reactor 8. Prior to the
feed to the FT reactor, the carbon monoxide-hydrogen ratio of the
gas is adjusted in WGS reactor 6 and from the syngas are separated
other gaseous components and catalyst poisons 7 that are derouted
to stream 22. The biowax resulting from the FT process is
postprocessed in a refinery plant 9 into fractions 15 suitable for
different uses such as biodiesel.
[0035] Cooling of raw syngas 28 is carried out with the help of a
heat exchanger in process 4, whereto high-pressure infeed water 20
is passed. In the heat exchanger the water is evaporated into steam
and removed in saturated state. In the beginning of plant start-up,
gasification 3 is functional but not the downstream stages 6-9 of
the process. This means that the saturated steam must be passed via
a pressure reduction valve 25 to backpressure network 38 as shown
in alternative 26a of FIG. 1. This operational state must be
continued so long until pure syngas is received at compressor 24.
Hereinafter, the compressor can be started to output compressed
syngas 27.
[0036] If the compressor and turbines are permanently connected to
each other by a common shaft, that is, are forced to rotate with
each other either at the same speed or, via a gearbox, at different
speeds, a small amount of cooling steam must be passed to the
turbines when the machineries are driven by an electric motor.
[0037] If turbine 23 is designed to be driven by saturated steam,
the steam can be routed to the turbine via the path shown in block
26b of FIG. 1. However, as high-pressure turbines are not generally
designed to receive saturated steam, in this case the steam is
passed to the backpressure network via path 26a so long until steam
reformer 10 becomes operational up to which moment the compressor
has been driven by an electric motor. Subsequently, the saturated
steam stream is directed to the path shown in block 26c of FIG.
1.
[0038] In FIG. 2 is shown the layout of a steam flow network of a
process related to the present invention. Therein the saturated
steam stream 26c of FIG. 1 is passed via superheater 33, whereby a
superheated steam stream 39 is generated suitable for feeding to
turbine 23.
[0039] While a saturated-steam condensation turbine 24b is
connected on the same shaft with a high-pressure turbine 24a and
compressor 23, it can also operate as a separate machinery.
Operating the machineries separate from each other allows better
runnability of the plant in special situations and start-up
occasions. The efficacy and investment cost of a system of a fixed
configuration will be more advantageous in a process running
extended periods of stable operation.
[0040] A BtL process is substantially self-sufficient as regards to
backpressure steam 38. The excess steam may be utilized, e.g., in
condensation-steam generation of electricity or use in
heat-intensive processes such as those of a paper mill or chemical
plant. When the steam condensation turbine 24b is mounted on the
same shaft with the high-pressure turbine 24a, the synchronous
motor 34 mounted on the same shaft can also perform as a generator
when the combined power of turbines 24a and 24b exceeds the power
demand of compressor 23.
[0041] The excess amount of backpressure steam 38 varies from
winter to summer inasmuch as biomass drying 37 consumes in the
winter even three times more steam than in the summer due to the
higher moisture content of the biomass in the winter and lower
temperature of drying air taken from outdoors. The output of
saturated high-pressure steam 26 from the gasifier and other steam
generation from the BtL process 35 remain unchanged irrespective of
the season. When necessary, to the backpressure steam network of
the BtL plant can be fed also other excess steam streams, e.g.,
from the backpressure steam network 36 of a pulp mill, for
instance.
[0042] In an equilibrium state, all high-pressure steam 26
available is passed via a high-pressure turbine 24a to the
backpressure steam network 38. The excess steam is passed to a
steam condensation turbine 24b and subsequently condensed in a
condenser 30. If the cooling capacity provided by the steam
condensation turbine is insufficient, the excess steam can be
cooled, e.g., in an auxiliary cooler 31 connected to a waterway.
The condensates 29 are returned to the process as infeed water
20.
[0043] In FIG. 2 is also shown an intermediate cooling unit 32 for
cooling the syngas 28 being compressed. Depending on the technology
used, the number of intermediate cooling stages can be plural,
e.g., 4-6. The warm exit water of the intermediate cooler can be
utilized, e.g., for drying the biomass raw material of the BtL
plant provided that the water temperature is sufficiently high,
advantageously about +50.degree. C. or higher.
[0044] In FIG. 3 is shown a flow schematic for an SMR process
according to the invention. Together with steam 40b, combustible
gases 16a not utilized in the process are fed to the SMR reactor
10, which is heated by burning a portion of the reject gases 16b
and purge gases 44b of the PSA unit with the help of combustion air
13. The process generates reformed gas 17, wherefrom hydrogen is
separated after cooling in PSA unit 42.
[0045] The PSA exit or purge gases 44 also contain combustible
gases that are routed to serve as fueling the SMR unit. The PSA,
that is, the Pressure Swing Absorption reactor is a unit capable of
separating gases of different molecular weight from each other,
e.g., generally hydrogen 43 from a gas mixture of carbon dioxide
and hydrogen.
[0046] The process may also be implemented without a PSA unit by
way of feeding the reformed gas stream with the help of a
recirculation compressor 11 to the compressed syngas stream 27 as
shown in FIG. 1.
[0047] From SMR 10 the exiting flue gas 18 and reformed gas 17 are
hot and thus contain enough energy at a high temperature sufficient
for superheating in superheaters 33a and 33b the saturated steam
26c exiting the gasifier. For instance, saturated steam at a
pressure of 90 bar has a temperature of about 305.degree. C. For
feeding to the turbine, the temperature must be further elevated to
about 500.degree. C. When necessary, the temperature of superheated
steam may be adjusted by spraying 41 feed water 20 into the steam
stream.
[0048] After exiting the high-pressure superheaters 33a and 33b,
the temperature of flue gases 18 is still quite high allowing the
flue gas to be utilized for producing steam 40 at a lower pressure
on a boiler 46a and a superheater 46b, heating waters for drying
biomass or, alternatively, preheating 47 the combustion air of the
SMR unit in a heat exchanger 45. The cooled flue gases can be
discharged to chimney 19.
[0049] In the above-described fashion, the present invention is
directed to a novel method and use capable of utilizing the thermal
energy of gases formed in a BtL plant for in-plant use. The method
offers significant benefits, more specifically by utilizing the
thermal energy of gas streams generated in a BtL plant for
superheating steam for driving the turbine machineries of the BtL
plant and postprocessing the tail gases in order to maximize the
yield of the plant's end product.
[0050] This goal is achieved by driving the compressors and/or
electric generators of the BtL plant process stages by steam
turbines using the steam streams generated in the BtL plant
processes that are principally superheated by the flue gases of a
steam reformer, that is, an SMR reactor 10, integrated with the BtL
plant equipment. Additionally, the plant yield is maximized by
recovering hydrogen 43 at a PSA unit 42.
[0051] In this fashion, supercharging the saturated steam streams
exiting BtL processes significantly improves the self-supported
electrical balance of the BtL and facilitates self-contained
operation of the BtL plant as a stand-alone facility independent
from another industrial plant or power utility.
[0052] According to the invention, a BtL plant has integrated
thereto a method for utilizing the thermal energy of the flue gases
18 and/or reformed gas 17 of a steam reformer 10 for superheating
39 the steam that is used in the BtL plant for driving the syngas
turbocompressor 23, 24 and/or producing electricity as well as
improving hydrogen yield 43, whereby a WGS process is included
having a steam reformer 10 connected to a PSA unit 42.
[0053] A BtL plant generates in its FT process 8 different FT tail
gases, that is, process reject gases 16, that are passed to a steam
reformer 10, wherein the FT tail gases are reformed 17 in such a
way that the hydrocarbons of gases 17 are reformed into hydrogen 43
and substantially into carbon monoxide and therefrom further to
carbon dioxide 44, from which gas stream after cooling 33, 46 in a
PSA unit 42 is recovered hydrogen 43, whereupon the remaining gases
44 are recirculated to a steam reformer 10 for heating the steam
reformer 10 to a correct temperature of about 800-1100.degree. C.
Gases 17 reformed in steam reformer 10 and flue gases 18 exiting
the steam reformer 10 are passed for cooling to a heat exchanger
33, whereby the thermal energy of the gas streams is used for
superheating the saturated high-pressure steam 26c exiting the
gasifier. In this fashion the thermal energy of gases generated in
a BtL plant is utilized for superheating gases used for driving the
turbine machineries of the BtL plant.
[0054] As described above, a process generates a large volume of
saturated steam streams, e.g., those exiting from the cooling of
the gasifier vessel envelope or the syngas stream. In accordance
with the present invention, superheating these gases can be
accomplished with the help of the hot gases generated in the
process such as the flue gas of the steam reformer. Superheating is
absolutely necessary to make steam usable in turbines and further
for driving compressors. Resultingly, the present invention makes
it possible avoid the need for acquisition of a separate
superheater boiler.
[0055] Another significant benefit is that the plant can be erected
without having an another plant located nearby such as a paper
mill, for instance, that is capable of using saturated steam. Now
the method according to the invention permits integration of a
power plant with the process. Moreover, the saturated steam can be
used in other processes such as drying paper and pulp or in the
production of district heating energy.
[0056] To a person skilled in the art it is obvious that the
invention is not limited by the above-described exemplary
embodiments, but rather may be varied within the inventive spirit
and scope of the appended claims.
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