U.S. patent application number 11/489298 was filed with the patent office on 2008-02-07 for controlling the synthesis gas composition of a steam methane reformer.
Invention is credited to Joseph M. Norbeck, Chan Seung Park.
Application Number | 20080031809 11/489298 |
Document ID | / |
Family ID | 38957307 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080031809 |
Kind Code |
A1 |
Norbeck; Joseph M. ; et
al. |
February 7, 2008 |
Controlling the synthesis gas composition of a steam methane
reformer
Abstract
A method for controlling the synthesis gas composition obtained
from a steam methane reformer (SMR) that obtains its feedstock as
product gas directly from a steam hydro-gasification reactor SHR).
The method allows control of the H.sub.2/CO syngas ratio by
adjusting the hydrogen feed and the water content of feedstock into
a steam hydro-gasification reactor that supplies the SMR. The steam
and methane rich product gas of the SHR is generated by means of
hydro-gasification of a slurry of carbonaceous material and water.
The mass percentages of the product stream at each stage of the
process are calculated using a modeling program, such as the ASPEN
PLUS.TM. equilibrium process. By varying the parameters of solid to
water ratio and hydrogen to carbon ratio, a sensitivity analysis
can be performed that enables one determine the optimum composition
of the slurry feedstock to the SHR to obtain a desired syngas ratio
output of the SMR. Thus one can adjust the hydrogen feed and the
water content of feedstock into the SHR that supplies the SMR to
determine the syngas ratio output of the SMR.
Inventors: |
Norbeck; Joseph M.;
(Riverside, CA) ; Park; Chan Seung; (Yorba Linda,
CA) |
Correspondence
Address: |
BERLINER & ASSOCIATES
555 WEST FIFTH STREET, 31ST STREET
LOS ANGELES
CA
90013
US
|
Family ID: |
38957307 |
Appl. No.: |
11/489298 |
Filed: |
July 18, 2006 |
Current U.S.
Class: |
423/650 |
Current CPC
Class: |
C01B 2203/84 20130101;
C10J 2300/0916 20130101; C01B 2203/0805 20130101; C01B 2203/0233
20130101; C10K 1/165 20130101; C10J 2300/0946 20130101; Y02E 50/32
20130101; C10G 2300/807 20130101; C10J 2300/1659 20130101; Y02P
20/145 20151101; C01B 2203/127 20130101; C10J 2300/0973 20130101;
C10J 2300/0966 20130101; C10K 1/024 20130101; C10K 1/143 20130101;
C10G 2300/42 20130101; C10J 3/00 20130101; C10K 1/16 20130101; C10G
2300/1011 20130101; C01B 2203/148 20130101; C10G 2/30 20130101;
Y02E 50/30 20130101; C01B 2203/062 20130101; C10G 2300/1003
20130101; C01B 2203/1258 20130101; C01B 3/38 20130101; C01B
2203/1241 20130101; Y02E 20/18 20130101; Y02P 30/20 20151101; C01B
2203/04 20130101; C10J 2300/1807 20130101 |
Class at
Publication: |
423/650 |
International
Class: |
C01B 3/24 20060101
C01B003/24 |
Claims
1. A process for converting carbonaceous material in a water
containing slurry to synthesis gas having a desired ratio of
hydrogen to carbon monoxide in the synthesis gas, comprising:
providing a predetermined ratio of hydrogen to slurry water to a
steam hydro-gasification reactor; simultaneously heating the
carbonaceous material in the presence of both said hydrogen and
steam, at a temperature and pressure sufficient to generate a
stream of methane and carbon monoxide rich gas product; removing
impurities from the producer gas stream; and subjecting the
resultant producer gas to steam methane reforming under conditions
whereby synthesis gas comprising said desired ratio of hydrogen and
carbon monoxide is generated.
2. The process of claim 1 wherein at least part of said slurry
water is provided in the form of steam.
3. The process of claim 1 wherein the ratio of hydrogen to slurry
water is determined by analysis of the effect on the synthesis gas
ratio of (a) the ratio of solid content of the carbonaceous
material to the slurry water and (b) the ratio of the hydrogen to
carbon content of the carbonaceous material.
4. The process of claim 3 wherein said analysis is a sensitivity
analysis using a modeling computer program that relates the
synthesis gas ratio of hydrogen to carbon monoxide to conversion
ratios of the carbon content of the carbonaceous material.
5. The process of claim 4 wherein the computer program is a
modeling program.
6. The process of claim 5 wherein the computer program uses the
ASPEN PLUS.TM. equilibrium process.
7. The process of claim 1 wherein the steam methane reforming is
conducted under conditions whereby the composition of synthesis gas
produced has a H.sub.2: CO mole ratio range of 1.1 to 6.1.
8. The process of claim 1 wherein steam methane reforming is
conducted under conditions whereby the composition of synthesis gas
produced has a H.sub.2: CO mole ratio of 3:1.
9. The process of claim 1 wherein the carbonaceous material
comprises municipal waste, biomass, wood, coal, or a natural or
synthetic polymer.
10. The process of claim 1 in which synthesis gas generated by the
steam methane reforming is fed into a Fischer-Tropsch reactor under
conditions whereby a liquid fuel is produced.
11. A process for converting municipal waste, biomass, wood, coal,
or a natural or synthetic polymer, in a water containing slurry to
synthesis gas, comprising: providing a predetermined ratio of
hydrogen to slurry water to a steam hydro-gasification reactor, the
ratio of hydrogen to slurry water being determined by analysis of
the effect on the synthesis gas ratio of (a) the ratio of solid
content of the carbonaceous material to the slurry water and (b)
the ratio of the hydrogen to carbon content of the carbonaceous
material that would produce synthesis gas comprising hydrogen and
carbon monoxide at a H.sub.2:CO mole ratio range of 1:1 to 6:1;
simultaneously heating carbonaceous material in the presence of
both said hydrogen and steam, at a temperature of about 790.degree.
C. to about 850.degree. C. and pressure about 132 psi to 560 psi
whereby to generate a stream of methane and carbon monoxide rich
gas product; removing impurities from the producer gas stream
substantially at said temperature and pressure; subjecting the
resultant producer gas to steam methane reforming under conditions
whereby to generate synthesis gas comprising hydrogen and carbon
monoxide at a H.sub.2:CO mole ratio range of 1:1 to 6:1; and
feeding synthesis gas generated by the steam methane reforming into
a Fischer-Tropsch reactor under conditions whereby a liquid fuel is
produced.
12. The process of claim 11 comprising transferring exothermic heat
from the Fischer-Tropsch reaction to the hydro-gasification
reaction and/or steam methane reforming reaction.
Description
FIELD OF THE INVENTION
[0001] The field of the invention is the production of synthesis
gas.
BACKGROUND OF THE INVENTION
[0002] There is a need to identify new sources of chemical energy
and methods for its conversion into alternative transportation
fuels, driven by many concerns including environmental, health,
safety issues, and the inevitable future scarcity of
petroleum-based fuel supplies. The number of internal combustion
engine fueled vehicles worldwide continues to grow, particularly in
the midrange of developing countries. The worldwide vehicle
population outside the U.S., which mainly uses diesel fuel, is
growing faster than inside the U.S. This situation may change as
more fuel-efficient vehicles, using hybrid and/or diesel engine
technologies, are introduced to reduce both fuel consumption and
overall emissions. Since the resources for the production of
petroleum-based fuels are being depleted, dependency on petroleum
will become a major problem unless non-petroleum alternative fuels,
in particular clean-burning synthetic diesel fuels, are developed.
Moreover, normal combustion of petroleum-based fuels in
conventional engines can cause serious environmental pollution
unless strict methods of exhaust emission control are used. A clean
burning synthetic diesel fuel can help reduce the emissions from
diesel engines.
[0003] The production of clean-burning transportation fuels
requires either the reformulation of existing petroleum-based fuels
or the discovery of new methods for power production or fuel
synthesis from unused materials. There are many sources available,
derived from either renewable organic or waste carbonaceous
materials. Utilizing carbonaceous waste to produce synthetic fuels
is an economically viable method since the input feed stock is
already considered of little value, discarded as waste, and
disposal is often polluting. Alternatively, one can use coal as a
feedstock to upgrade low grade dirty solid fuel to a value added
convenient clean liquid fuel, such as high quality, environment
friendly synthetic diesel or other hydrocarbon fuels.
[0004] Liquid transportation fuels have inherent advantages over
gaseous fuels, having higher energy densities than gaseous fuels at
the same pressure and temperature. Liquid fuels can be stored at
atmospheric or low pressures whereas to achieve liquid fuel energy
densities, a gaseous fuel would have to be stored in a tank on a
vehicle at high pressures that can be a safety concern in the case
of leaks or sudden rupture. The distribution of liquid fuels is
much easier than gaseous fuels, using simple pumps and pipelines.
The liquid fueling infrastructure of the existing transportation
sector ensures easy integration into the existing market of any
production of clean-burning synthetic liquid transportation
fuels.
[0005] The availability of clean-burning liquid transportation
fuels is a national priority. Producing synthesis gas (a mixture of
hydrogen and carbon monoxide, also referred to as "syngas") cleanly
and efficiently from carbonaceous sources, that can be subjected to
a Fischer-Tropsch process to produce clean and valuable synthetic
gasoline and diesel fuels, will benefit both the transportation
sector and the health of society. Such a process allows for the
application of current state-of-art engine exhaust after-treatment
methods for NO.sub.x reduction, removal of toxic particulates
present in diesel engine exhaust, and the reduction of normal
combustion product pollutants, currently accomplished by catalysts
that are poisoned quickly by any sulfur present, as is the case in
ordinary stocks of petroleum derived diesel fuel, reducing the
catalyst efficiency. Typically, Fischer-Tropsch liquid fuels,
produced from synthesis gas, are sulfur-free, aromatic free, and in
the case of synthetic diesel fuel have an ultrahigh cetane
value.
[0006] Biomass material is the most commonly processed carbonaceous
waste feed stock used to produce renewable fuels. Waste plastic,
rubber, manure, crop residues, forestry, tree and grass cuttings
and biosolids from waste water (sewage) treatment are also
candidate feed stocks for conversion processes. Biomass feed stocks
can be converted to produce electricity, heat, valuable chemicals
or fuels. California tops the nation in the use and development of
several biomass utilization technologies. Each year in California,
more than 45 million tons of municipal solid waste is discarded for
treatment by waste management facilities. Approximately half this
waste ends up in landfills. For example, in just the Riverside
County, California area, it is estimated that about 4000 tons of
waste wood are disposed of per day. According to other estimates,
over 100,000 tons of biomass per day are dumped into landfills in
the Riverside County collection area. This municipal waste
comprises about 30% waste paper or cardboard, 40% organic (green
and food) waste, and 30% combinations of wood, paper, plastic and
metal waste. The carbonaceous components of this waste material
have chemical energy that could be used to reduce the need for
other energy sources if it can be converted into a clean-burning
fuel. These waste sources of carbonaceous material are not the only
sources available. While many existing carbonaceous waste
materials, such as paper, can be sorted, reused and recycled, for
other materials, the waste producer would not need to pay a tipping
fee, if the waste were to be delivered directly to a conversion
facility. A tipping fee, presently at $30-$35 per ton, is usually
charged by the waste management agency to offset disposal costs.
Consequently not only can disposal costs be reduced by transporting
the waste to a waste-to-synthetic fuels processing plant, but
additional waste would be made available because of the lowered
cost of disposal.
[0007] The burning of wood in a wood stove is a simple example of
using biomass to produce heat energy. Unfortunately, open burning
of biomass waste to obtain energy and heat is not a clean and
efficient method to utilize the calorific value. Today, many new
ways of utilizing carbonaceous waste are being discovered. For
example, one way is to produce synthetic liquid transportation
fuels, and another way is to produce energetic gas for conversion
into electricity.
[0008] Using fuels from renewable biomass sources can actually
decrease the net accumulation of greenhouse gases, such as carbon
dioxide, while providing clean, efficient energy for
transportation. One of the principal benefits of co-production of
synthetic liquid fuels from biomass sources is that it can provide
a storable transportation fuel while reducing the effects of
greenhouse gases contributing to global warming. In the future,
these co-production processes could provide clean-burning fuels for
a renewable fuel economy that could be sustained continuously.
[0009] A number of processes exist to convert biomass and other
carbonaceous materials to clean-burning transportation fuels, but
they tend to be too expensive to compete on the market with
petroleum-based fuels, or they produce volatile fuels, such as
methanol and ethanol that have vapor pressure values too high for
use in high pollution areas, such as the Southern California
air-basin, without legislative exemption from clean air
regulations. An example of the latter process is the Hynol Methanol
Process, which uses hydro-gasification and steam reformer reactors
to synthesize methanol using a co-feed of solid carbonaceous
materials and natural gas, and which has a demonstrated carbon
conversion efficiency of >85% in bench-scale demonstrations.
[0010] Synthesis gas can be produced through one of two major
chemical processes, steam reforming and partial oxidation. Steam
reforming is used when the feed consists of light hydrocarbons such
as natural gas, and when hydrogen is the main product. Partial
oxidation is used with heavier feeds, or when a relatively high
yield of carbon monoxide is desired. Table 1 summarizes various
commercial processes under operation for the production of
synthesis gas [1].
TABLE-US-00001 TABLE 1 Syngas Ratio Chemical Process Feedstock
(H.sub.2/Co, mole) Steam Reforming Natural gas, steam 4.76 Steam
Reforming Methane, steam 3 Steam Reforming Naptha, steam 2 Steam
Reforming Natural gas, CO.sub.2, steam 2 Partial Oxidation Coal,
steam, O.sub.2 0.68 Partial Oxidation Coal, steam, O.sub.2 0.46
Partial Oxidation Coal, steam, O.sub.2 2.07
[0011] The ratio of hydrogen to carbon monoxide in the synthesis
gas is called the syngas ratio and is strongly dependent on the
process used and the nature of the feedstock.
[0012] Syngas is used as a feedstock in the manufacture of various
chemicals and also in the gas-to-liquid processes, which use the
Fischer-Tropsch synthesis (FTS) to produce liquid fuels.
Alternatively, syngas can be used in the so called integrated
gasification combined cycle, where it is directly burned with air
to produce the heat necessary to operate steam turbines used in
electricity generation. Depending on the desired usage, the
H.sub.2/Co ratio of syngas needs to be adjusted. Table 2 summarizes
the optimum syngas ratios required for different processes [2].
TABLE-US-00002 TABLE 2 Syngas Ratio Required Desired Product
Chemical Process (H.sub.2/Co, mole) Synthetic fuels FTS - Co
catalyst 2.05 2.15 Synthetic fuels FTS - Fe catalyst 1.65 Methanol
2 Ethylene glycol 1.5 Acetic acid 1 Benzene-toluene-xylene 1.5
[0013] In general, the syngas ratio can be lowered by using the
pressure swing adsorption process or by using hydrogen membrane
systems. Alternatively, adding a downstream water-gas shift reactor
can increase the syngas ratio.
[0014] A process was developed in our laboratories to produce
synthesis gas in which a slurry of particles of carbonaceous
material in water, and hydrogen from an internal source, are fed
into a hydro-gasification reactor under conditions to generate rich
producer gas. This is fed along with steam into a steam pyrolytic
reformer under conditions to generate synthesis gas. This process
is described in detail in Norbeck et al. U.S. patent application
Ser. No. 10/503,435 (published as US 2005/0256212), entitled:
"Production Of Synthetic Transportation Fuels From Carbonaceous
Material Using Self-Sustained Hydro-Gasification." In a further
version of the process, using a steam hydro-gasification reactor
(SHR) the carbonaceous material is heated simultaneously in the
presence of both hydrogen and steam to undergo steam pyrolysis and
hydro-gasification in a single step. This process is described in
detail in Norbeck et al. U.S. patent application Ser. No.
10/911,348 (published as US 2005/0032920), entitled: "Steam
Pyrolysis As A Process to Enhance The Hydro-Gasification of
Carbonaceous Material." The disclosures of U.S. patent application
Ser. Nos. 10/503,435 and 10/911,348 are incorporated herein by
reference.
[0015] Producing synthesis gas via gasification and producing a
liquid fuel from synthesis gas are totally different processes. Of
particular interest to the present invention is the production of
synthesis gas using a steam methane reformer (SMR), a reactor that
is widely used to produce synthesis gas for the production of
liquid fuels and other chemicals. The reactions taking place in the
SMR can be written as follows.
CH.sub.4+H.sub.2O.fwdarw.CO+3H.sub.2 (1)
or
CH.sub.4+2H.sub.2O.fwdarw.CO.sub.2+4H.sub.2 (2)
Carbon monoxide and hydrogen are produced in the SMR by using steam
and methane as the feed. Heating process water in a steam generator
produces the required steam. The methane is usually supplied in the
form of compressed natural gas, or by means of a light molecular
weight off-gas stream from a chemical or refinery process.
BRIEF SUMMARY OF THE INVENTION
[0016] This invention provides an improved, economical method to
control the synthesis gas composition obtained from a steam methane
reformer that obtains its feedstock as product gas directly from a
steam hydro-gasification reactor. The method allows control of the
H.sub.2/CO ratio by adjusting the hydrogen feed and the water
content of feedstock into the SHR that supplies the SMR.
[0017] As described above, the steam and methane rich product gas
of the SHR is generated by means of hydro-gasification of the
slurry, which is a mixture of carbonaceous material and water. This
product gas, a mixture of methane rich gas and steam, where the
steam is present as a result of the superheating the water in the
feedstock, serves as an ideal feed stream for the SMR. Impurities
are removed from the SHR product stream, such as fine particles of
ash & char, hydrogen sulfide and other inorganic
components.
[0018] The mass percentages of the product stream at each stage of
the process are calculated using a modeling program, such as the
ASPEN PLUS.TM. equilibrium process that can relate the synthesis
gas ratio of hydrogen to carbon monoxide to conversion ratios of
the carbon content of the carbonaceous material. In accordance with
the invention, by varying the parameters of solid to water ratio
and hydrogen to carbon ratio, a sensitivity analysis can be
performed that enables one determine the optimum composition of the
slurry feedstock to the SHR to obtain a desired syngas ratio output
of the SMR. Thus, the ratio of hydrogen to slurry water is
determined by analysis of the effect on the synthesis gas ratio of
(a) the ratio of solid content of the carbonaceous material to the
slurry water and (b) the ratio of the hydrogen to carbon content of
the carbonaceous material. This enables one to adjust the hydrogen
feed and the water content of feedstock into the SHR that supplies
the SMR to provide the desired ratio of hydrogen to carbon monoxide
in the synthesis gas output of the SMR.
[0019] More particularly, a process is provided for converting
carbonaceous material to synthesis gas, comprising simultaneously
heating carbonaceous material in an SHR in the presence of a
predetermined ratio of hydrogen and water in the form of steam, at
a temperature and pressure sufficient to generate a stream of
methane and carbon monoxide rich gas product, which can be called a
producer gas. Impurities are removed from the producer gas stream
substantially at the process temperature and pressure, and the
resultant producer gas is subjected to steam methane reforming in
an SMR under conditions whereby synthesis gas comprising hydrogen
and carbon monoxide is generated having a hydrogen/carbon monoxide
ratio determined by the ratio of hydrogen and water in the SHR.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] For a more complete understanding of the present invention,
reference is now made to the following descriptions taken in
conjunction with the accompanying drawing, in which:
[0021] FIG. 1 is a flow diagram of the process of this
invention;
[0022] FIG. 2 is a flow diagram of the mass balance of the process;
and
[0023] FIG. 3 is a sensitivity analysis using the ASPEN PLUS.TM.
modeling program showing various conversions and the syngas ratio
when parameters of solid to water ratio and hydrogen to carbon
ratio are varied.
DETAILED DESCRIPTION OF THE INVENTION
[0024] This invention enables one to control of the H.sub.2/CO
ratio output of an SMR by adjusting the hydrogen feed and the water
content of feedstock into the SHR that supplies the SMR. The steam
and methane rich product gas of the SHR is generated by means of
hydro-gasification of the slurry, which is a mixture of
carbonaceous material and water. This product gas, a mixture of
methane rich gas and steam, where the steam is present as a result
of the superheating the water in the feedstock, serves as an ideal
feed stream for the SMR.
[0025] The mass percentages of the product stream at each stage of
the process are calculated using a modeling program, such as the
ASPEN PLUS.TM. equilibrium process. By varying the parameters of
solid to water ratio and hydrogen to carbon ratio, a sensitivity
analysis can be performed that enables one determine the optimum
composition of the slurry feedstock to the SHR to obtain a desired
syngas ratio output of the SMR. Thus one can adjust the hydrogen
feed and the water content of feedstock into the SHR that supplies
the SMR to determine the syngas ratio output of the SMR.
[0026] Impurities are removed from the SHR product stream, such as
fine particles of ash & char, hydrogen sulfide and other
inorganic components. These impurities must be removed in order to
prevent poisoning of the catalyst used in the SMR. Conventionally,
a combination of particulate filters, a solvent wash (amines,
Selexol.TM., Rectisol.TM.), and hydro-desulphurization by means of
the Claus process are used for this purpose. In the Claus process,
H.sub.2S is partially oxidized with air in a reaction furnace at
high temperatures (1000-1400.degree. C.). Sulfur is formed, but
some H.sub.2S remains unreacted, and some SO.sub.2 is made
requiring that the remaining H.sub.2S be reacted with the SO.sub.2
at lower temperatures (about 200-350.degree. C.) over a catalyst to
make more sulfur. To maintain the SMR feed stream at high
temperatures, a gas cleanup unit is provided that operates at
process pressures and at a temperature above the steam condensation
point. The unit is located between the SHR and SMR.
[0027] More particularly, a process is provided for converting
carbonaceous material to synthesis gas of a desired H.sub.2/CO
ratio, comprising simultaneously heating carbonaceous material in
an SHR in the presence of a predetermined ratio of hydrogen and
water in the form of steam, at a temperature and pressure
sufficient to generate a stream of methane and carbon monoxide rich
gas product, which can be called a producer gas, the ratio of
hydrogen and water being determined by a modeling program, such as
the ASPEN PLUS.TM. equilibrium process. In accordance with the
invention, by varying the parameters of solid to water ratio and
hydrogen to carbon ratio, a sensitivity analysis is performed that
enables one determine the optimum composition of the slurry
feedstock to the SHR to obtain a desired syngas ratio output of the
SMR. Impurities are removed from the producer gas stream
substantially at the process temperature and pressure, and the
resultant producer gas is subjected to steam methane reforming in
an SMR under conditions whereby synthesis gas comprising hydrogen
and carbon monoxide is generated having a hydrogen/carbon monoxide
ratio determined by the ratio of hydrogen and water in the SHR.
[0028] In a specific process, for converting municipal waste,
biomass, wood, coal, or a natural or synthetic polymer to synthesis
gas, the carbonaceous material is simultaneously heated in the
presence of both hydrogen and steam, at a temperature of about
790.degree. C. to about 850.degree. C. and pressure about 132 psi
to 560 psi whereby to generate a stream of methane and carbon
monoxide rich producer gas. Impurities are removed from the
producer gas stream substantially at the process temperature and
pressure, following which the resultant producer gas is subjected
to steam methane reforming under conditions whereby to generate the
desired synthesis gas ratio of hydrogen and carbon monoxide. For
example, the required H.sub.2:CO mole ratio of a Fischer-Tropsch
reactor with a cobalt based catalyst is 2.1:1. By appropriate
adjustment, as described below, of the H.sub.2/H.sub.2O ratio, a
H.sub.2/CO mole ratio range of about 3 to 1 can be achieved to
provide an excess of hydrogen, which can be separated and fed into
the SHR to make a self-sustainable process, i.e., without requiring
any external hydrogen feed. The synthesis gas generated by the
steam methane reforming can be fed into a Fischer-Tropsch reactor
under conditions whereby a liquid fuel is produced. Exothermic heat
from the Fischer-Tropsch reaction can be transferred to the
hydro-gasification reaction and/or steam methane reforming
reaction.
[0029] FIG. 1 is a flow diagram of a SHR to SMR process in which a
desired H.sub.2/CO ratio output of an SMR is obtained by adjusting
the hydrogen feed and the water content of feedstock into the SHR
that supplies the SMR. An internally generated hydrogen feed 10 is
fed into an SHR 12 along with a carbonaceous feedstock 14 and water
16, which are heated to 750.degree. C. at 400 psi in the SHR 12.
The resulting producer gas is directed to a gas clean up filter 18,
e.g. a candle filter assembly, at about 350.degree. C. at about 400
psi. From there, after removal of sulfur and ash, the effluent is
directed to an SMR 20 where synthesis gas is generated and fed to a
Fischer-Tropsch reactor 22., from which pure water 24, and diesel
fuel and/or wax 26 is obtained. A portion of hydrogen is diverted
from the SMR 20, at 28 to be fed back to the HGR 12. Heat 30 from
the Fischer-Tropsch reactor 22 is used to supplement the heat at
the SMR.
[0030] Operating the unit above the bubbling temperature of the
water allows the water to be present as steam in the gaseous
product stream from the SHR, thereby enabling the process to retain
most of the sensible heat in the effluent stream. The following
example will illustrate the invention.
EXAMPLE
[0031] A mass balance process flow diagram is shown in FIG. 2. The
mass percentages of the product stream at each stage of the process
are provided in the figure. ASPEN PLUS.TM. equilibrium process
modeling was used to calculate these values. ASPEN PLUS.TM. is a
commercial computer modeling program that allows a process model to
be created by specifying the chemical components and operating
conditions. The program takes all of the specifications and
simulates the model, executing all necessary calculations needed to
solve the outcome of the system, hence predicting its behavior.
When the calculations are complete, ASPEN PLUS.TM. lists the
results, stream by stream and unit by unit, and can present the
data in graphical form with determining ordinate and abscissa
[0032] As shown in FIG. 2, an SHR feedstock of hydrogen and 41%
coal slurry results in the production of synthesis gas with a 3.4:l
mole ratio of hydrogen to carbon monoxide in the SMR. The required
feed hydrogen for the SHR can be supplied through external means or
by internal feedback of a portion of the hydrogen produced in the
SMR. In a particular example, a slurry of 41% coal, 52% water and
7% hydrogen is used, obtained following the procedures of Norbeck
et al. U.S. Ser. No. 10/911,348. This results in an output from the
SHR to the cleanup filter of a gaseous mixture containing 32 wt %
CH.sub.4, 2 wt % H.sub.2, 2 wt % CO, 3 wt % CO.sub.2, 51 wt %
H.sub.2O, 4 wt % ash, 5 wt % char, and 1 wt % other impurities.
[0033] In this example, the filter is operating at 300.degree. C.
and 28 atmospheres of pressure. Any filter capable of operating at
the process temperature can be used at the gas cleanup station. One
such commercially available filter is a candle filter, which is
well known to the art. See, for example U.S. Pat. No. 5,474,586,
the disclosure of which is incorporated herein by reference. An
available gas cleanup unit that can be used in this invention is
what is known as a candle filter in which a series of candle-shaped
filters are carried in a filter vessel. The candle filters are made
of stainless steel metal frit to remove fine particulate matter
(ash, inorganic salts and unreacted char) from the gas stream. The
slurry is fed into the vessel at a bottom inlet and filtrate is
taken out at a top outlet. Particulate matter is taken from another
outlet as cake. Sulfur impurities existing in the SHR product gas,
mostly in the form of hydrogen sulfide, are removed by passing the
product gas through a packed bed of metal oxide sorbents in the gas
cleanup unit, particulate matter being taken from a cake
outlet.
[0034] Active sorbents include, but are not limited to, Zn based
oxides such as zinc oxide, sold by Sud-Chemie, Louisville, Ky.
Porous metal filter elements are available from Bekaert in
Marietta, Ga. in the appropriate forms and sizes, such as
Bekpor.RTM. Porous Media-which is made from stainless steel
sintered fiber matrix with a pore size of 1. These sorbents and
filter elements allow the effects of pressure drop and gas-solid
mass transfer limitations to be minimized. At a pressure of 28
atm., temperatures in the range of 300.degree. C. to 500.degree. C.
and space velocities up to 2000/hr have been used in the
desulphurization of SHR product gas. The hydrogen sulfide content
of the gas is diminished by means of sulfidation of the sorbents to
levels low enough to avoid the deactivation of the SMR catalyst.
The used sorbents in the gas cleanup unit can either be replaced
with fresh sorbents or regenerated in-situ with diluted air in
parallel multiple sorbent beds.
[0035] The output of the SHR-cleanup unit is a methane rich,
producer gas containing 36 wt % CH.sub.4, 2 wt % H.sub.2, 2 wt %
CO, 3 wt % CO.sub.2, and 57 wt % H.sub.2O, having a steam to
methane mole ratio of 1:4. The output of the SHR is fed to the SMR,
which is operating at 800.degree. C. and 28 atmospheres to yield
synthesis gas having a mole ratio of H.sub.2 to CO of 3.4, and
containing 4 wt % CH.sub.4, 14 wt % H.sub.2, 58 wt % CO, 3 wt %
CO.sub.2, and 21 wt % H.sub.2O.
[0036] The syngas ratio obtained from the SMR can be adjusted by
varying the solid to water ratio and hydrogen to carbon ratio in
the SHR feedstock. Sensitivity analysis was performed using the
ASPEN PLUS.TM. equilibrium modeling tool by varying these
parameters. The results are in FIG. 3, showing various conversions
and the syngas ratio when parameters of solid to water ratio and
hydrogen to carbon ratio are varied. The solid lines () represent
the percentage of carbon converted to CH.sub.4 (mole CH.sub.4/mole
C.sub.in). The long dashed lines () represent the percentage of
carbon converted to CO (mole CO/mole C.sub.in). The dotted lines ()
represent the percentage of carbon converted to CO.sub.2 (mole
CO.sub.2/mole C.sub.in). The dash-dot-dot-dash lines () represent
sustainable H.sub.2, and the short dashed lines () represent the
syngas ratio of H.sub.2/CO (mole H.sub.2/mole CO).
[0037] The last parameter is of key interest in this invention.
FIG. 3 clearly demonstrates that the final syngas ratio can be
adjusted by adjusting the water to solid ratio (represented as
H.sub.2O/ Cin mass ratio in FIG. 3) and the hydrogen to carbon
ratio of the feedstock. Thus, an optimum composition of the slurry
to obtain a sustainable hydrogen feedback and the desired syngas
ratio for the Fischer-Tropsch synthesis (2.1:1) was found to be 3.1
when the mole ratio of hydrogen to carbon in the feed was set to
one.
[0038] More generally, the process of this invention can produce
composition of synthesis gas having a H.sub.2:CO mole ratio range
of 1:1 to 6:1. The resulting effluent is a synthesis of gases rich
in hydrogen, carbon monoxide, and steam. Hydrogen produced in the
SMR is recycled back to the HGR. Consequently, no outside source of
hydrogen is needed to maintain steady state operation. The HGR and
SMR processes, therefore, may be considered to be chemically
self-sustaining. The remaining synthesis gas is then available for
the production of fuels and process heat.
[0039] In an embodiment of the invention, the synthesis gas is fed
to a Fischer-Tropsch reactor in a process that can produce a
zero-sulfur, ultrahigh cetane value diesel-like fuel and valuable
paraffin wax products. The absence of sulfur enables low pollutant
and particle emitting diesel fuels to be realized. Useful
by-products can be produced, foe example, purified water, which can
be re-cycled to create the slurry feed into the process. The
Fischer-Tropsch reactions also produce tail gas that contains
hydrogen, CO, CO.sub.2, and some light hydrocarbon gases. Hydrogen
can be stripped out of the tail gas and recycled either to the HGR
or the Fischer-Tropsch reactor. Any small amounts of other gases
such as CO and CO may be flared off.
[0040] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims. Moreover, the scope of the present application is
not intended to be limited to the particular embodiments of the
process and apparatus described in the specification. As one of
ordinary skill in the art will readily appreciate from the
disclosure of the present invention, processes and apparatuses,
presently existing or later to be developed that perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein may be
utilized according to the present invention. Accordingly, the
appended claims are intended to include such processes and use of
such apparatuses within their scope.
REFERENCES
[0041] 1. Van der Laan, G. P., Thesis, University of Groningen,
Netherlands, 1999. [0042] 2. Sheldon, R. A., Chemicals from
Synthesis Gas, 1983 and FT Technology: Studies in surf Science and
Catalysis, ed. Steynberg, A., Dry, M. E., Vol 152, 2004.
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