U.S. patent application number 13/864970 was filed with the patent office on 2013-09-05 for hydrogen generation process using partial oxidation/steam reforming.
The applicant listed for this patent is HYDRADIX, INC.. Invention is credited to Brandon S. CARPENTER, Kishore J. DOSHI, Bradley P. RUSSELL.
Application Number | 20130228722 13/864970 |
Document ID | / |
Family ID | 35462763 |
Filed Date | 2013-09-05 |
United States Patent
Application |
20130228722 |
Kind Code |
A1 |
DOSHI; Kishore J. ; et
al. |
September 5, 2013 |
HYDROGEN GENERATION PROCESS USING PARTIAL OXIDATION/STEAM
REFORMING
Abstract
Partial oxidation/steam reformers (222) which use heat
integrated steam cycles and steam to carbon ratios of at least
about 4:1 to enable efficient operation at high pressures suitable
for hydrogen purification unit operations such as membrane
separation (234) and pressure swing adsorption.
Inventors: |
DOSHI; Kishore J.;
(Fernandina Beach, FL) ; RUSSELL; Bradley P.;
(Wheaton, IL) ; CARPENTER; Brandon S.; (Chicago,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HYDRADIX, INC. |
Des Plaines |
IL |
US |
|
|
Family ID: |
35462763 |
Appl. No.: |
13/864970 |
Filed: |
April 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11597578 |
Oct 9, 2009 |
|
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PCT/US2005/018287 |
May 25, 2005 |
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13864970 |
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Current U.S.
Class: |
252/373 ;
252/374 |
Current CPC
Class: |
B01J 8/0278 20130101;
C01B 3/382 20130101; C01B 3/36 20130101; C01B 2203/043 20130101;
B01J 2208/00504 20130101; C01B 2203/0244 20130101; C01B 2203/0485
20130101; C01B 3/505 20130101; C01B 3/503 20130101; B01J 8/0453
20130101; C01B 2203/84 20130101; B01J 2219/00038 20130101; C01B
3/56 20130101; C01B 3/386 20130101; B01J 2208/00176 20130101; C01B
2203/0405 20130101; C01B 2203/0455 20130101; C01B 2203/127
20130101; C01B 2203/1258 20130101; C01B 2203/1294 20130101; B01J
2208/00628 20130101 |
Class at
Publication: |
252/373 ;
252/374 |
International
Class: |
C01B 3/38 20060101
C01B003/38 |
Claims
1.-27. (canceled)
28. A process for generating hydrogen comprising contacting at
reforming temperature a mixture of hydrocarbon-containing feedstock
which also contains sulfur compound, air and steam with an
effective amount of at least one catalyst for partially combusting
feedstock to generate heat and for reforming said feedstock to
generate hydrogen whereby a reforming effluent stream comprising
hydrogen, carbon monoxide, carbon dioxide, nitrogen and hydrogen
sulfide is provided, wherein: a. said contacting is at a pressure
greater than about 400 kPa absolute, and b. steam is provided in a
mole ratio to carbon in the feedstock in an amount of at least
about 4:1; and cooling the reforming effluent stream to a
temperature suitable for hydrogen sulfide sorption said cooling
comprising indirect heat exchange with water to generate at least a
portion of the steam for the feed to the reformer, and contacting
the cooled reforming effluent stream with a hydrogen sulfide
sorbent to provide a stream having a reduced hydrogen sulfide
concentration.
29. The process of claim 28 wherein the cooled reforming effluent
stream is subjected to pressure swing adsorption to provide a
hydrogen stream having reduced carbon monoxide and carbon dioxide
concentrations and a purge stream containing hydrogen, carbon
dioxide and carbon monoxide.
30. The process of claim 29 wherein the cooled reformer effluent
stream contacts the hydrogen sulfide sorbent prior to being
subjected to pressure swing adsorption.
31. The process of claim 30 wherein the cooled reformer effluent
stream is subjected to pressure swing adsorption and hydrogen
sulfide is sorbed and contained in the purge stream, and the purge
stream is contacted with the hydrogen sulfide sorbent.
32. The process of claim 31 wherein the hydrocarbon-containing
feedstock contains organosulfides and at least one of carbonyl
sulfide and hydrogen sulfide and is contacted with a sorbent for
organosulfides prior to reforming to provide a
hydrocarbon-containing feedstock comprising at least one of
hydrogen sulfide and carbonyl sulfide.
33. The process of claim 28 wherein the hydrocarbon-containing
feedstock contains organosulfides and at least one of carbonyl
sulfide and hydrogen sulfide and is contacted with a sorbent for
organosulfides prior to reforming to provide a
hydrocarbon-containing feedstock comprising at least one of
hydrogen sulfide and carbonyl sulfide.
34.-37. (canceled)
Description
FIELD OF THE INVENTION
[0001] This invention relates to processes for generating hydrogen
involving the partial oxidation and reforming of fuel, especially
to autothermal reforming processes. The hydrogen generators using
the processes of this invention may find beneficial use in
smaller-scale hydrogen plants.
BACKGROUND TO THE INVENTION
[0002] Hydrogen is used as a feedstock for many chemical processes
and has been proposed as an alternative fuel especially for use in
fuel cells in stationary and mobile facilities. Steam reforming of
hydrocarbon-containing feedstock is a conventional source of
hydrogen. Steam reforming of hydrocarbons is practiced in
large-scale processes, often at a facility having refinery or
chemical operations. Thus, for instance, the large-scale hydrogen
plant will likely be able to draw upon the skills within the entire
facility to operate sophisticated unit operations to enhance
hydrogen production efficiency. An additional benefit of having a
large scale hydrogen plant within a facility having refinery or
chemical operations is that the steam generated in the hydrogen
plant from cooling the steam reforming effluent and by heat
exchange with the combustion of waste gases has value to such other
refinery or chemical operations. The benefits of practicing steam
reforming in large-scale plants are also apparent from the nature
of the equipment and process. For instance, steam reforming
generally uses very high temperatures, often in excess of
800.degree. C., which in turn requires expensive materials of
construction. Furthermore, large-scale hydrogen plants typically
provide hydrogen product purity in excess of 99 volume percent with
less than 10 parts per million by volume (ppmv) of carbon
monoxide.
[0003] While the economics of large-scale steam reforming make
attractive the shipping of hydrogen from such a large-scale
reformer to the point of use, hydrogen, nevertheless, is difficult
to store and distribute and has a low volumetric energy density
compared to fuels such as gasoline. Thus an interest exists in
developing economically and practically viable smaller-scale
hydrogen generators to provide hydrogen from a
hydrocarbon-containing feedstock for use or distribution at a point
proximate to the consumer.
[0004] There are a number of practical hurdles for such a
smaller-scale hydrogen generator to overcome before it is
commercially viable beyond overcoming the loss of economy of scale.
For instance, the smaller scale may not support sophisticated
operating and technical staff and thus the hydrogen generator must
be able to operate reliably with minimal operator support while
still providing an economically acceptable hydrogen product meeting
purity specifications. Often smaller-scale hydrogen generators face
problems that do not occur with large-scale hydrogen plants. An
example is that the hydrocarbon-containing feedstocks most often
available to smaller-scale hydrogen generators are natural gas and
LPG, both of which contain odorants (sulfur compounds) for safety
reasons. As sulfur compounds can poison catalysts and may be
unacceptable in the product hydrogen, smaller-scale hydrogen
generators must incur the expense to remove them. Additionally,
smaller-scale hydrogen generators may be stand alone units with no
chemical or refinery operation to which steam can be exported.
[0005] Consideration has been given to the use of less efficient,
but less capital intensive, alternative reforming technology such
as partial oxidation/steam reforming, including autothermal
reforming. But as a portion of the feed is oxidized in the
reformer, efficiency penalties are taken that are not incurred by
steam reforming. Accordingly, for partial oxidation/steam reforming
to be competitive capital costs for the hydrogen generator must be
low, the hydrogen product must meet purity requirements, and the
amount of hydrogen produced per unit of hydrocarbon-containing feed
must be adequately high.
[0006] Partial oxidation/steam reforming, including autothermal
reforming, has been extensively studied. In general, studies have
shown that the reforming reaction is an equilibrium reaction
influenced by temperature and pressure. All other things being
equal, lower pressures and higher temperatures favor the production
of hydrogen, but higher temperatures necessitate more consumption
of fuel, thus are disadvantageous. Similarly, higher ratios of
steam to hydrocarbon-containing feedstock favor the production of
hydrogen, but the vaporization of water requires heat. Hence, most
often partial oxidation reformers use no more than about 3 moles of
steam per carbon in the hydrocarbon-containing feedstock.
[0007] The reformate from partial oxidation/steam reforming will
contain carbon monoxide, carbon dioxide, hydrogen, unreacted
hydrocarbon-containing compounds and nitrogen and argon (with air
being used as the source of the oxygen-containing gas for the
partial oxidation) as well as water. To enhance the efficiency of
partial oxidation/steam reforming, the use of water gas shift to
convert carbon monoxide and water to carbon dioxide and hydrogen is
often used. Processes that have been proposed to remove the
remaining carbon monoxide include selective oxidation and
methanation.
[0008] Membrane and pressure swing adsorption separations can be
effective for purifying the hydrogen product since they can remove
nitrogen, argon, carbon dioxide, carbon monoxide and unreacted
hydrocarbon-containing compounds. However, membrane and pressure
swing adsorption systems typically require the gases fed to them to
be at elevated pressure. Large-scale steam reformers can tolerate
the use of reforming temperatures that are suitable to provide a
reformate at pressures suitable for such separations. However such
is not the case with smaller-scale partial oxidation/steam
reforming units where it is desirable to operate at lower
temperatures in order to avoid expensive metallurgy and reduce
capital costs. And it is not the case for stand alone hydrogen
generators where opportunities to export steam do not exist.
Because of the adverse effect of pressure on the efficiency of
hydrogen production in these partial oxidation/steam reforming
processes, reforming would typically occur at lower pressures, and
then the reformate would be compressed to the required pressures.
However, additional operating and capital costs are entailed in
employing such a compressor. Moreover, membrane and pressure swing
adsorption systems can be particularly disadvantages for a
smaller-scale hydrogen generator due to loss of hydrogen. The
retentate, in the case of membranes, and the purge gas, in the case
of pressure swing adsorption, contain unrecovered hydrogen and thus
reduce the net hydrogen efficiency (NHE) (heating value of purified
hydrogen recovered per unit heating value of hydrocarbon-containing
feedstock to the generator). This reduction in net hydrogen
efficiency can be deleterious to achieving an
economically-competitive smaller-scale hydrogen generator.
[0009] Accordingly, processes are sought that yield a hydrogen
product of suitable quality, including a very low carbon monoxide
concentration; provide favorable economics as compared to shipping
and storage of hydrogen produced by a large-scale hydrogen plant;
are easily operated with minimal needs for technical sophistication
and maintenance.
SUMMARY OF THE INVENTION
[0010] In accordance with the processes of this invention,
attractive economics of hydrogen production can be achieved in
smaller-scale hydrogen generators using partial oxidation/steam
reforming while still enabling the use of membrane or pressure
swing adsorption unit operations to achieve acceptable hydrogen
product purity. The processes of this invention effect the partial
oxidation/steam reforming at high pressures, e.g., at least about
400, preferably at least about 500, kPa absolute, but without the
expected undue reduction in net hydrogen efficiency. The processes
of this invention have conversion efficiencies (Net Hydrogen
Efficiencies or NHE) of at least about 50 percent, preferably at
least about 55 percent, without a water gas shift. With a water gas
shift, net hydrogen efficiencies of at least about 55, and often in
excess of 60, percent may be achieved. The Net Hydrogen Efficiency
is the ratio of lower heating values of the recovered hydrogen
product stream to the lower heating value of the hydrocarbon feed
stream:
N H E = P .times. L H V P F .times. L H V F .times. 100
##EQU00001##
[0011] where [0012] P=molar flow of net hydrogen product (mol/hr)
[0013] LHV.sub.P=lower heating value of product hydrogen (kJ/mol)
[0014] F=molar flow of hydrocarbon feedstock (mol/hr) [0015]
LHV.sub.F=lower heating value of hydrocarbon feedstock
(kJ/mol).
[0016] The term "partial oxidation/steam reforming" as used herein
intended to encompass a catalytic reforming processes in which a
portion of the hydrocarbon-containing feedstock supplied to the
reformer is oxidized in-situ to produce heat for the endothermic
reforming process and a portion of the hydrocarbon-containing
feedstock is reacted, or reformed, with steam to provide a
reforming effluent, or reformate.
[0017] In accordance with the processes of this invention, an undue
adverse effect from high pressure reforming is avoided by the use
of a heat integrated steam cycle employing a ratio of steam to
carbon in the hydrocarbon-containing feedstock above about 4:1.
While these higher steam to carbon ratios are expected to favor the
production of hydrogen in the partial oxidation/steam reforming,
the adverse effect of pressure and of energy consumption required
to vaporize the higher amounts of steam are reduced by using a heat
integrated steam cycle. The heat integrated steam cycle takes
advantage of the increased mass of effluent from the partial
oxidation reformer to generate at least about 40, and preferably at
least about 50, percent of the steam for supply to the reformer at
a high temperature, e.g., at least about 300.degree. C. or
350.degree. C., preferably at least about 400.degree. C., say
450.degree. to 600.degree. C.
[0018] In preferred aspects of the invention, the heat integrated
steam cycle takes advantage of waste gas from hydrogen purification
operations such as membrane separations and pressure swing
adsorptions. The waste gas is combusted to generate, in combination
with the steam generated by cooling the effluent from the reformer,
at least about 90 percent of the steam supplied to the reformer.
The heat from the combustion is also used to heat at least a
portion of the feed to the partial oxidation reformer. In these
preferred aspects, steam and heat are obtained from the unrecovered
hydrogen instead of consuming additional hydrocarbon-containing
feedstock.
[0019] In one preferred embodiment, hydrogen is generated by an
autothermal reforming process at a pressure of at least about 400
kPa absolute which comprises supplying as feed to a partial
oxidation/steam reforming zone hydrocarbon-containing feedstock,
air and steam, wherein free oxygen is provided in a mole ratio to
carbon in the feedstock of between about 0.4:1 to 0.6:1 and steam
is provided in a mole ratio to carbon in the feedstock in an amount
of at least about 4:1; maintaining said zone under partial
oxidation/steam reforming conditions including said pressure to
partially oxidize a portion of the feedstock to generate heat and
to reform a portion of said feedstock to generate hydrogen whereby
a reforming effluent stream comprising hydrogen, carbon monoxide
and carbon dioxide is provided; and cooling the reforming effluent
stream by indirect heat exchange with a stream containing liquid
water to provide a steam-containing stream at a temperature of at
least about 300.degree. C. which is cycled to the partial
oxidation/steam reforming zone wherein at least about 40 percent of
the steam in the feed mixture is produced by said indirect heat
exchange and separating a sufficient portion of the reformate and
combusting said portion to provide a hot combustion gas to (i) heat
at least a portion of the feed by indirect heat exchange with the
hot combustion gas to provide an average temperature of the feed to
the partial oxidation/steam reforming zone of at least about
450.degree. C. and to provide a cooler combustion gas and (ii)
generate the remaining steam to provide said steam to carbon ratio
by indirect heat exchange with the cooler combustion gas.
[0020] In preferred embodiments, the reforming pressure is
sufficient that, especially at reforming temperatures of between
about 640.degree. and 730.degree. C., the reforming effluent
contains less than about 5, preferably less than about 4, mole
percent carbon monoxide (dry basis). Preferably the mole ratio of
carbon monoxide to molecular hydrogen in the reforming effluent is
less than about 0.085:1, often between about 0.03:1 to 0.085:1.
[0021] In further detail, in the broad aspect of this invention
hydrogen is generated at a pressure of at least about 400,
preferably at least about 500 up to about 1500, kPa absolute using
an heat integrated steam cycle. The process comprises: [0022]
supplying as feed to a partial oxidation/steam reforming zone
hydrocarbon-containing feedstock, air and steam, wherein free
oxygen is provided in a mole ratio to carbon in the feedstock of
between about 0.4:1 to 0.6:1 and steam is provided in a mole ratio
to carbon in the feedstock in an amount of at least about 4:1,
preferably about 4.5:1 to 8:1, and most preferably about 4.5:1 to
6.5:1; [0023] maintaining said zone under partial oxidation/steam
reforming conditions including said pressure to partially oxidize a
portion of the feedstock to generate heat and to reform a portion
of said feedstock to generate hydrogen whereby a reforming effluent
stream comprising hydrogen, carbon monoxide and carbon dioxide is
provided; and [0024] cooling the reforming effluent stream by
indirect heat exchange with a stream containing liquid water to
provide a steam-containing stream at a temperature of at least
about 300.degree. C. or 350.degree. C., preferably at least about
400.degree. C., say 450.degree. to 600.degree. C., which is cycled
to the partial oxidation/steam reforming zone wherein at least
about 40, preferably at least about 50, percent of the steam in the
feed mixture is produced by said indirect heat exchange.
Preferably, the reforming effluent is subjected to at least one
subsequent unit operation to separate nitrogen and carbon oxides
from the hydrogen and provide a purified hydrogen product. Such
subsequent unit operations include, but are not limited to,
membrane separation or pressure swing adsorption.
[0025] In another preferred embodiment of the invention, the
reforming effluent is cooled in at least two indirect heat
exchanger stages, each with a feed containing liquid water. By
having the vaporization occur in each indirect heat exchanger
section, several advantages are obtained. For instance, the heat
exchanger surface area can be more effectively used to recover
large amounts of steam. The reforming effluent can be rapidly
cooled, and the amount of steam being produced can be easily and
quickly varied to accommodate changes in production rate. Where a
water gas shift is used, heat exchanger stages may straddle the
shift reactor and heat generated by the exothermic shift reaction
would thus also be recovered as steam for cycling to the
reformer.
[0026] In other preferred processes of this invention, hydrogen is
generated from a hydrocarbon-containing feedstock in the essential
absence of a shift reaction zone by: [0027] a. passing to a partial
oxidation reformer at a pressure of between about 400 and 1500 kPa
absolute feed comprising hydrocarbon-containing feedstock, air, and
steam wherein the molar ratio of steam to carbon in the
hydrocarbon-containing feedstock is at least about 4:1, said
reformer being at partial oxidation/steam reforming conditions to
provide a reforming effluent stream comprising at least about 40
volume percent (dry basis) hydrogen, nitrogen, steam, carbon
monoxide and carbon dioxide; [0028] b. cooling the reforming
effluent stream by indirect heat exchange with a stream containing
liquid water to provide a steam-containing stream at a temperature
of at least about 300.degree. C. which is cycled to the partial
oxidation/steam reforming zone wherein at least about 40 percent of
the steam in the feed mixture is produced by said indirect heat
exchange; [0029] c. further cooling the cooled reforming effluent
stream to pressure swing adsorption conditions, said cooling being
sufficient to condense water, [0030] d. during or after the further
cooling, separating the condensed water; [0031] e. subjecting the
further cooled reforming effluent stream to pressure swing
adsorption such that a purified hydrogen stream is produced which
(i) is at least about 98, preferably at least about 99, mole
percent hydrogen, and (ii) contains less than about 10, preferably
less than about 5, ppmv carbon monoxide, and a sorption purge gas
is produced at a pressure between about 5 and 100 kPa gauge which
comprises less than about 30, and sometimes less than about 25,
volume percent hydrogen (dry basis) and nitrogen, carbon dioxide
and carbon monoxide; [0032] f. withdrawing at least a portion of
the purified hydrogen stream as hydrogen product; [0033] g.
combusting in the substantial absence of added fuel, the sorption
purge gas with an oxygen-containing gas in the presence of an
oxidation catalyst to provide a combustion gas having a temperature
of less than about 800.degree. C., preferably less than about
750.degree. C.; [0034] h. subjecting the combustion gas to at least
one indirect heat exchange with a water-containing stream to
generate steam which is cycled to the reformer, and [0035] i.
exhausting the cooled combustion gas, [0036] wherein the Net
Hydrogen Efficiency is at least about 50 percent. Preferably, the
pressure swing absorption comprises four absorbent beds and two
pressure equalizations. Often the purified hydrogen product
comprises at least about 99.9 volume percent hydrogen.
[0037] Another alternative aspect of the processes of this
invention pertains to accommodating hydrocarbon-containing
feedstocks that also contain sulfur compounds. While available
catalysts used for partial oxidation/steam reforming have ample
sulfur tolerance, water gas shift catalysts tend to be highly
sensitive to sulfur components. The processes of this invention
where no water gas shift is used since the reforming effluent has a
lower carbon monoxide content gives the designer of the hydrogen
generator the ability to remove sulfur compounds at virtually any
stage of the process. Removal of sulfur components subsequent to
reforming does have advantages. For instance, the reforming
converts essentially all species of sulfur components typically
encountered such as organosulfides, mercaptans and carbonyl sulfide
to hydrogen sulfide. Thus, the sulfur removal process need only
address hydrogen sulfide removal to reduce the sulfur components to
acceptable concentrations. Chemisorbents such as zinc oxide are
effective for hydrogen sulfide removal, but typically in the
presence of steam temperatures below about 250.degree. C., often
between about 40.degree. and 200.degree. C., are desired for the
chemisorption. In one aspect of the invention no water gas shift
catalyst is employed. Without a sulfur sensitive water gas shift
catalyst, the reformate may be cooled to temperatures suitable for
hydrogen sulfide sorption with the hydrogen sulfide being removed
prior to or after hydrogen purification by separation.
[0038] In these processes hydrocarbon-containing feedstock, which
also contains sulfur compound, air and steam are subjected to
reforming conditions whereby a reforming effluent comprising
hydrogen, carbon monoxide, carbon dioxide and hydrogen sulfide is
provided, wherein the reforming conditions comprise: [0039] a. a
pressure greater than about 400 kPa absolute, and [0040] b. a mole
ratio of steam to carbon in the feedstock of at least about 4:1;
and cooling the reforming effluent stream to a temperature suitable
for hydrogen sulfide sorption said cooling comprising indirect heat
exchange with water to generate at least a portion of the steam for
the feed to the reformer, and contacting the cooled reforming
effluent stream with a hydrogen sulfide sorbent to provide a stream
having a reduced hydrogen sulfide concentration. In more preferred
embodiments of this aspect of the invention, the
hydrocarbon-containing feedstock contains organosulfides and at
least one of carbonyl sulfide and hydrogen sulfide and is contacted
with a sorbent for organosulfides prior to reforming to provide a
hydrocarbon-containing feedstock comprising at least one of
hydrogen sulfide and carbonyl sulfide.
[0041] This invention also pertains to apparatus adapted to use the
heat integrated steam cycle. The hydrogen generator comprises:
[0042] a) a partial oxidation reformer containing partial oxidation
and reforming catalysts and adapted to provide a
hydrogen-containing reformate, said reformer having an inlet
section and an outlet section, [0043] b) a hydrocarbon-containing
feed supply line in fluid communication with the inlet section of
the partial oxidation reformer, [0044] c) an oxygen-containing feed
supply line in fluid communication with the inlet section of the
partial oxidation reformer, [0045] d) an indirect heat exchanger in
fluid communication with the outlet section of the partial
oxidation reformer said heat exchanger having a hot side through
which the hydrogen-containing reformate passes and a cool side in
fluid communication with at least a liquid water supply, said heat
exchanger adapted to provide a steam-containing stream, [0046] e) a
steam line adapted to direct the steam-containing stream from the
heat exchanger to the inlet section of the partial oxidation
reformer, [0047] f) a cooler adapted to receive cooled reformate
from the hot side of the heat exchanger and provide a further
cooled reformate and condensed water, [0048] g) means to remove
condensed water from the further cooled reformate, [0049] h) a
pressure swing adsorber adapted to receive the further cooled
reformate from the cooler, which reformate has had condensed water
removed, and provide a hydrogen product stream and a purge stream
containing hydrogen, [0050] i) a combustor containing oxidation
catalyst adapted to receive said purge stream and an
oxygen-containing gas and provide a combustion gas, and [0051] j)
at least one indirect heat exchanger having a hot side adapted to
receive said combustion gas and a cold side in fluid communication
with a liquid water line adapted to provide steam, said heat
exchanger being in fluid communication with the partial oxidation
reformer. Preferably the oxidation catalyst in the combustor is
adapted to serve as a flame holder. Advantageously, the apparatus
comprises at least one indirect heat exchanger having a hot side
adapted to receive the combustion gas from the combustor and a cold
side in fluid communication with at least one of the
hydrocarbon-containing feedstock supply line, the oxygen-containing
feed supply line and the steam line. Most advantageously the
pressure swing adsorber has four adsorbent beds.
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] FIG. 1 is schematic flow diagram of a process in accordance
with this invention in which the partial oxidation reformer
effluent is subjected to water gas shift conditions and is purified
through pressure swing adsorption.
[0053] FIG. 2 is a schematic flow diagram of a process in
accordance with this invention in which the partial oxidation
reformer effluent is cooled in two heat exchanger stages and is
purified through a selective permeation membrane without the use of
a separate water gas shift reactor.
[0054] FIG. 3 is a schematic flow diagram of a process in
accordance with the invention in which the reformer effluent is
cooled without having been subjected to water gas shift, subjected
to sorption to remove hydrogen sulfide and then purified through
pressure swing adsorption.
[0055] FIG. 4 is a schematic flow diagram of a pressure swing
adsorption system useful in the processes of this invention.
[0056] FIG. 5 is a schematic flow diagram of a process in
accordance with the invention in which the reformer effluent is
cooled in a steam boiler and then purified through pressure swing
adsorption.
[0057] FIG. 6 is a schematic diagram of a hybrid flame and
catalytic oxidation combustor useful in the processes of this
invention.
[0058] FIG. 7 is a cycle diagram for a four bed pressure swing
adsorber useful in this invention.
[0059] FIG. 8A is a schematic diagram of an adsorption bed useful
for pressure swing adsorption in the process of this invention.
[0060] FIG. 8B is a graphic depiction of regeneration of the
adsorption bed shown in FIG. 8A.
[0061] FIGS. 9A, 9B and 9C are depictions of computer simulations
of the effect of pressure on carbon monoxide production in a
partial oxidation/steam reforming process at reforming temperatures
of 650.degree., 700.degree. and 750.degree. C. for
hydrocarbon-containing feedstocks having steam to carbon ratios of
4:1, 6:1 and 8:1, respectively. The figures graphically depict the
percentage that the carbon monoxide mole concentration (dry basis)
is reduced by increasing pressure above 414 kPa gauge.
[0062] FIG. 10 depicts in graphic form the results of a computer
simulation showing the enhancement in net hydrogen efficiency of
generators operating at pressures of 300, 600 and 1200 kPa absolute
that can be achieved through the use of steam to carbon ratios
greater than 4:1.
DETAILED DESCRIPTION
[0063] Feed Components
[0064] The hydrocarbon-containing feeds used in accordance with the
invention are typically gaseous under the conditions of reforming.
Lower hydrocarbon gases such as methane, ethane, propane, butane
and the like may be used. Because of availability, natural gas and
liquid petroleum gas (LPG) are most often used as feeds. Oxygenated
hydrocarbon-containing feeds such as methanol and ethanol are
included as hydrocarbon-containing feeds for all purposes
herein.
[0065] Natural gas and liquid petroleum gas typically contain
odorants such that leaks can be detected. Odorants conventionally
used are one or more organosulfur compounds such as organosulfides,
e.g., dimethyl sulfide, diethyl sulfide, and methyl ethyl sulfide;
mercaptans, e.g., methyl mercaptan, ethyl mercaptan, and t-butyl
mercaptan; thiophenes of which tetrahydrothiophene is the most
common; and the like. The amount used can vary widely. For natural
gas, the organosulfur component is often in the range of about 1 to
20 parts per million by volume (ppmv); and for LPG a greater amount
of sulfur compounds are typically used, e.g., from about 10 to 200
ppmv. It is not unusual for commercially obtained hydrocarbon feeds
to contain also other sulfur compounds that may be natural
impurities such as hydrogen sulfide and carbonyl sulfide. Carbonyl
sulfide concentrations in natural gas and LPG of 0.1 to 5 ppmv are
not unusual.
[0066] Regardless of the form, sulfur compounds are generally
undesirable in the product hydrogen and can be deleterious to
catalysts used in hydrogen generators such as water gas shift
catalysts. The processes of this invention provide flexibilities in
where sulfur is removed. If desired, the hydrocarbon-containing
feed can be desulfurized. Any convenient desulfurization technique
may be used including sorption and hydrodesulftrization. In an
aspect of this invention, the desulfurization occurs subsequent to
reforming. In the reforming process, substantially all the sulfur
components are converted to hydrogen sulfide. Hydrogen sulfide can
then be removed from the reformate by sorption. If desired a guard
bed can be used upstream of the reformer containing transition
metal exchanged molecular sieve such as zinc or copper exchanged
zeolite X or zeolite Y to assist in the removal of sulfur
compounds, especially thiophenes such as tetrahydrothiophene.
[0067] The hydrocarbon-containing feeds can contain other
impurities such as carbon dioxide, nitrogen and water. In the
processes of this invention, it is preferred that the concentration
of carbon dioxide be less than about 5, preferably less than about
2, volume percent (dry basis).
[0068] Water in addition to that contained in the other feed
components to the process is used to achieve the high steam to
carbon ratios of the feed to the partial oxidation reformer. Due to
the large quantities of water contained in the feed to and the
reformate from the reformer, recycling of water is usually
effected. The water is preferably deionized water.
[0069] Air is typically used as the source of the oxygen for the
partial oxidation/steam reforming. The term "air" as used herein is
intended to include air or oxygen-enriched air, i.e., up to about
30 volume percent oxygen.
[0070] The feed components to the reformer are admixed prior to
contact with the catalyst in the partial oxidation reformer. Due to
combustion risks, the hydrocarbon-containing fuel and air are
typically not admixed until immediately prior to contacting the
catalyst. Steam may be in admixture with one or both of the
hydrocarbon-containing feedstock and the oxygen-containing feed
prior to entry into the reformer. In preferred aspects of the
invention liquid water is admixed with another feed, preferably the
hydrocarbon-containing feed, and is vaporized. Thus, the load on
compressors to bring the feeds to the reforming conditions is
reduced.
[0071] The hydrocarbon-containing feedstock and the air may be
heated prior to being introduced into the partial oxidation
reformer. The water is preferably introduced into the reformer as
superheated steam. Generally, the temperature of the steam, which
may be in admixture with the hydrocarbon-containing feedstock or
the air, is at least about 300.degree. C., and often between about
400.degree. C. and 700.degree. C., preferably between about
450.degree. C. and 650.degree. C. In the preferred aspects of the
invention, air is heated prior to being introduced into the partial
oxidation reformer. When the hydrocarbon-containing feedstock is
heated, especially to temperatures above about 400.degree. C., it
is heated in the presence of steam or liquid water, which is
vaporized to provide steam. Often the ratio of steam to carbon for
this heating is at least about 1:1.
[0072] The mole ratio of total water (i.e., the water contained in
all of the hydrocarbon-containing feed mixture with steam, the
water in mixture with air and that separately introduced) to carbon
in the hydrocarbon-containing feed (steam to carbon ratio) is at
least about 4:1, preferably between about 4.5:1 to 8:1. The mole
ratio of free oxygen to carbon in the hydrocarbon-containing feed
is generally within the range of about 0.4:1 to 0.6:1.
[0073] Process Conditions
[0074] The partial oxidation/steam reforming is catalytic. The
overall partial oxidation and steam reforming reactions for methane
are expressed by the formulae:
CH.sub.4+0.5O.sub.2.fwdarw.CO+2H.sub.2
CH.sub.4+H.sub.2OCO+3H.sub.2
The reformer may comprise two or more discrete sections, e.g., a
first contact layer of oxidation catalyst followed by a second
layer of steam reforming catalyst, or may be bifunctional, i.e.,
oxidation catalyst and steam reforming catalyst are intermixed in a
single catalyst bed or are placed on a common support. The partial
oxidation reformate comprises hydrogen, nitrogen, argon, carbon
oxides (carbon monoxide and carbon dioxide), steam and some
unconverted hydrocarbons.
[0075] Partial oxidation/steam reforming conditions typically
comprise a temperature (measured at the catalyst outlet) of at
least about 600.degree. C. up to about 800.degree. C., and is
preferably between about 640.degree. and 730.degree. C. In the
broad aspects, partial oxidation/steam reforming includes reforming
processes where supplemental external combustion of a fuel, e.g.,
hydrocarbon-containing feedstock or hydrogen-containing stream such
as an anode waste gas from a fuel cell, is used to provide heat for
reforming by indirect heat exchange. As between the in situ partial
oxidation and the supplemental external combustion for indirect
heat exchange, the partial oxidation preferably generates at least
70 percent, and preferably substantially all, of the heat
(excluding the heat carried with the feed to the reformer from heat
exchange with the reformate or from the combustion of unrecovered
hydrogen such as contained in the purge gas from a pressure swing
adsorber, the retentate from a membrane separation and anode waste
gas if the hydrogen product is used as a feed to a fuel cell),
i.e., an autothermal reforming process.
[0076] The pressure in the reforming conditions of the processes of
this invention is at least about 400 kPa, say from about 500 kPa to
1500 or 2500 kPa, preferably from about 500 kPa to about 1200 kPa,
absolute. When the reformer effluent is subjected to a hydrogen
purification operation that depends upon a differential in pressure
such as pressure swing adsorption and membrane separation,
advantageously the partial oxidation/steam reforming conditions
comprise a pressure suitable for the operation without an
intervening compression.
[0077] FIGS. 9A, 9B and 9C illustrate from a computer simulation
the effect important role that temperature plays in enabling
pressure to influence the carbon monoxide concentration. As can be
seen from the graphic depictions, if the temperature is too high,
e.g., 750.degree. C., pressure has a significantly attenuated
effect in reducing carbon monoxide concentration. At partial
oxidation/steam reforming temperatures within the scope of this
invention, i.e., below about 730.degree. C., pressure has a more
pronounced ability to reduce carbon monoxide concentration in the
reformate.
[0078] On a dry basis, the components of the effluent from the
reformer fall within the ranges set forth below:
Reformer Effluent Components, Dry Basis
TABLE-US-00001 [0079] Mole Percent, Dry Basis, Partial oxidation/
Component steam reforming Hydrogen 35 to 55, frequently 40 to 50
Nitrogen 25 to 45, frequently 30 to 40 Carbon monoxide 1 to 5,
frequently 2 to 4 Carbon dioxide 10 to 20, frequently 12 to 15
[0080] A purified hydrogen product is obtained from the reformate
through one or more unit operations.
[0081] A water gas shift is the most commonly used catalytic
process for converting carbon monoxide into carbon dioxide and more
hydrogen. Generally, the shift reactor contains at least one water
gas shift reaction zone. In the shift reactor carbon monoxide is
exothermically reacted in the presence of a shift catalyst in the
presence of an excess amount of steam to produce additional amounts
of carbon dioxide and hydrogen.
[0082] The shift reaction is an equilibrium reaction, and lower
carbon monoxide concentrations are favored at lower temperatures.
Thus conventionally a plurality of shift stages are used from high
temperature, e.g., in excess of 350.degree. or 400.degree. C., to
lower temperature, e.g., below about 250.degree. C. The heat
integrated steam cycle of this invention can eliminate the
necessity of having a water gas shift in order to achieve
acceptable net hydrogen efficiencies, thus saving in capital costs
and operating complexities. If a water gas shift is desired to
obtain even higher net hydrogen efficiencies, the heat integrated
steam cycle enables most of the benefit to be obtained using only a
water gas shift at moderate, or medium, temperature shift
conditions, e.g., between about 250.degree. C. and about
400.degree. C. If a water gas shift is used, the Net Hydrogen
Efficiency is often at least about 55, and sometimes above 60,
percent.
[0083] Other catalytic processes for reducing carbon monoxide in
the reformate include selective oxidation. While in the broad
aspects selective oxidation can be used, it is generally less
preferred not only because of the addition of equipment and
operating complexities, but also, the selective oxidation can
consume some of the hydrogen.
[0084] For many applications, the hydrogen product from the
reforming has to have a high hydrogen concentration, e.g., 98
volume percent hydrogen or better. Thus, not only must carbon
monoxide be removed, but also other components contained in the
reformate such as carbon dioxide, nitrogen and water. The high
pressure reformate of this invention makes feasible hydrogen
purification by membrane or pressure swing adsorption.
[0085] Any suitable membrane and membrane configuration may be used
for separation of hydrogen as a permeate. Typical membranes include
polymeric membranes operable with feed temperatures of between
about ambient and 150.degree. C. and metallic membranes, e.g.,
platinum or palladium, at feed temperatures of up to 500.degree. C.
The pressure on the permeate side of the membrane is often less
than about 200 kPa absolute.
[0086] Pressure swing adsorption is a preferred unit operation for
purifying the reformate. Desirably the pressure swing adsorption
provides a hydrogen product stream of at least about 98, preferably
at least 99, or 99.5, volume percent hydrogen and contains less
than about 10 or 20, preferably less than about 5, ppmv of carbon
monoxide. Usually the pressure swing adsorption recovers at least
about 60, preferably at least about 70, percent of the hydrogen
contained in the stream fed to the pressure swing adsorption.
[0087] Any suitable adsorbent or combination of adsorbents may be
used for the pressure swing adsorption. The particular adsorbents
and combinations of adsorbents used will, in part, depend upon the
components of the feed to the pressure swing adsorber, the sought
compositions in the purified hydrogen product and the geometry and
type of pressure swing adsorber used. Adsorbents include molecular
sieves including zeolites, activated carbon activated alumina and
silica gel. Particularly advantageous sorbents include a
combination of sorbents with the first portion of the bed being
composed of activated carbon which is particularly effective for
water, methane and carbon dioxide removal followed by one or more
molecular sieves such as NaY, 5A, 13X, lithium or barium exchanged
X, silicalite and ZSM-5. The sorbents may be of any suitable
particle size given the constraints of pressure drop and bed
lifting for an up-flow fixed bed.
[0088] The pressure swing adsorber may be of any suitable design
including rotary and multiple bed. The purging of the bed may be by
vacuum, but most conveniently for simplicity, the purge is above
ambient atmospheric pressure. A preferred pressure swing adsorption
system for low maintenance operation uses at least four fixed beds.
By sequencing the beds through adsorption and regeneration steps, a
continuous flow of purified hydrogen stream can be achieved without
undue loss of hydrogen. With at least four beds, one bed at a given
time will be adsorbing, while other beds will be undergoing
regeneration or pressure equalization steps. Preferably, at least
one, and more preferably two or three, pressure equalization steps
are used to increase hydrogen recovery.
[0089] FIG. 7 is a cycle chart for a four bed pressure swing
adsorption system operated with two pressure equalizations. Bed 1
is first in an adsorption step where cooled reformate is fed to the
bed and purified hydrogen product is obtained. In the next cycle
step for Bed 1, the pressure in the bed is decreased, and the
released gas, which is rich in hydrogen, is used to increase the
pressure in Bed 3. This is the first pressure equalization (1E) and
Bed 1 is providing the pressure (1EP) and Bed 3 is receiving (1ER).
Then the pressure in Bed 1 is further decreased with the off gases
being used to purge Bed 2 with the off gases being the sorption
purge gas. A second pressure equalization (2E) then occurs between
Bed 1 (2EP) and Bed 2 (2ER). In the next step, the pressure in Bed
1 is released, usually to slightly above ambient, in a
countercurrent blowdown (BD) operation. The gas from the blowdown
may be combusted in a waste stream combustor. Then Bed 1 is
subjected to a countercurrent purge using provide purge from Bed 4
to produce a sorption purge gas. At the conclusion of the purge,
the pressure in Bed 1 is increased via the second pressure
equalization with Bed 4. In the final sequence, the pressure in Bed
1 is increased by the first pressure equalization from Bed 3 and
lastly by counter current repressurization with purified hydrogen
product. Each of the beds proceeds through the same sequence of
cycle steps.
[0090] FIG. 7 is illustrative of a cycle diagram for a four bed
pressure swing adsorption system. The use of more beds is well
within the skill of the art in pressure swing adsorption design.
The cycle times are selected to provide the hydrogen product of a
desired purity. The cycle times may be adjusted with changes in
throughput to maintain constant purity or may be constant with the
purity changing with changes in throughput. As another
modification, purified hydrogen product may also be introduced
during the 1E step.
[0091] As the reformate contains nitrogen, the ability to provide a
purified hydrogen product having very low carbon monoxide content,
is facilitated. See, for instance, FIG. 8A. Vessel 802 has inlet
808 and outlet 810 and contains activated carbon as the leading
portion of the bed 804. In that section of the bed, the water,
carbon dioxide and unreacted hydrocarbon-containing feedstock,
e.g., methane, are effectively adsorbed. The next section of the
bed 806 comprises lithium X molecular sieve, which is more
selective for the adsorption of carbon monoxide than nitrogen.
Thus, regeneration will be based upon nitrogen breakthrough. As can
be seen from FIG. 8B, the carbon monoxide adsorption front will
still be far from breakthrough when the bed requires regeneration.
Argon is also present in air and can be removed with the nitrogen
via the pressure swing adsorption.
[0092] Heat Integrated Steam Cycle
[0093] The processes of this invention use a heat integrated steam
cycle to enable attractive operation at high reforming pressures.
The integrated steam cycle accommodates and uses to advantage the
high steam to carbon ratios fed to the partial oxidation reformer
and enables attractive Net Hydrogen Efficiencies to be
obtained.
[0094] In a fundamental aspect of the integrated steam cycle, the
hot reformate is used to generate a significant portion of the
steam fed to the reformer and provides some superheating to the
steam. In more preferred aspects, a stream is separated from the
reformate and combusted to provide additional heat for the
reforming. This heat is preferably used to provide by an indirect
heat exchange, an average feed temperature of the feed to the
reformer of at least about 450.degree. C., and more preferably, at
least about 500.degree. C., say, 500.degree. C. to 650.degree. C.
The cooled combustion gas is then used to generate additional
steam, and preferably all the remaining steam, for the feed to the
reformer. The separation may be a side stream of some of the
reformate, or may be the purge gas or retentate form a pressure
swing adsorption or membrane separation unit operation used to
provide a purified hydrogen product.
[0095] As shown in FIG. 10, at higher reforming pressures, the use
of an integrated steam cycle can enhance the Net Hydrogen
Efficiency. FIG. 10 is described in further detail later in this
specification. With reference to FIG. 10, at a steam to carbon
ratio of 3.0:1, the increase in reforming pressure from 300 to 600
kPa absolute results in a decrease in Net Hydrogen Efficiency from
55.4 percent to about 50.3 percent. But at higher steam to carbon
ratios, the gap narrows. At a steam to carbon ratio of 5.0:1, the
gap is only about 1.6 Net Hydrogen Efficiency percentage points, a
decrease of nearly 70 percent. Similarly, an increase in pressure
from 300 to 1200 kPa at a lower steam to carbon ratio, e.g., 3.5:1,
causes a loss of about 10 Net Hydrogen Efficiency percentage
points. If, however, the steam to carbon ratio is increased to
about 5.5:1, not only does the gap narrow to about 4 Net Hydrogen
Efficiency percentage points, but also, the increase in steam to
carbon ration is actually adversely affecting the Net Hydrogen
Efficiency of the lower pressure operation.
[0096] In the processes of this invention, at least about 40, say,
about 50 to 60 or even 75, percent of the steam supplied to the
partial oxidation reformer is generated by cooling the reforming
effluent. The large amount of steam in the feed to the reformer
serves to increase the mass of the reformate to assure that
sufficient thermal energy is available to generate the sought
amount of steam through cooling the reformate. The high temperature
of the reforming effluent is effectively used not only to provide a
substantial portion of the steam requirements but also to super
heat to the steam-containing stream. In general, at higher steam to
carbon ratios, it is preferred to generate a greater proportion of
the steam by heat exchange with the reformate than at the lower
ratios. This is especially true where a purified hydrogen product
is obtained by membrane or pressure swing adsorption treatment and
the purge or retentate gas is combusted to provide heat to feed to
the reformer. Thus, the heat from the reformate is primarily used
for the generation of steam and to a lesser extent for superheating
the steam. Preferably, the amount of the steam generated by cooling
the reformate does not exceed that which results in the
steam-containing stream having a temperature of less than about
300.degree. C., and preferably not less than about 400.degree.
C.
[0097] Aspects of this invention contemplate the use of two or more
stages of heat exchange with the hot reformate. In those aspects,
it is preferred to use a first stage which cools the reformate from
the temperature it exits the reformer to within the range of
250.degree. to 400.degree. C., preferably 280.degree. to
350.degree. C. By first stage it is contemplated that one or more
indirect heat exchangers may be used as a design convenience. In at
least one subsequent stage, the reformate is cooled to a
temperature within about 5.degree. C. to 50.degree. C. above the
boiling point of water at the pressure of the reformate. Liquid
water is introduced into the cold side of each of the stages. Often
the first stage heat exchanger, the stage proximate to the
reformer, receives from about 30 to 80 percent of the total liquid
water introduced into the heat exchangers used to cool the
reformate.
[0098] The reformate from the heat exchange sections will contain
water and will typically be at a temperature of less than about
250.degree. C., and often about 120.degree. to 210.degree. C.,
which is higher than desired for subsequent unit operations.
Accordingly, the reformate is further cooled to a temperature below
about 100.degree. C., preferably to a temperature in the range of
about 20.degree. to 80 C., and most preferably to about 25.degree.
to 50.degree. C., and the condensed water is recycled.
[0099] In the preferred aspects of the invention, the heat
integrated steam cycle employs the unrecovered hydrogen from
hydrogen purification processes such as membrane separations and
pressure swing adsorptions. Additional steam can be provided by
combusting waste gas from these operations. Often these waste gases
contain up to about 30 volume percent hydrogen (dry basis), and
thus the combustion gases have substantial heating values. For
instance, the purge from the pressure swing adsorption system
usually contains about 10 to 30, often 15 to 25, volume percent
hydrogen (dry basis). Between the cooling of the reforming effluent
and indirect heat exchange with the combustion gas, at least about
90, and preferably essentially all, the steam supplied to the
partial oxidation reformer is generated. Advantageously, the
temperature of the combustion gas may be below that which requires
expense materials of construction, e.g., below about 800.degree.
C., and preferably below about 750.degree. C.
[0100] Preferably the combustion gas is used first to heat via
indirect heat exchange one or more of the feed streams to the
partial oxidation reformer to temperatures of at least about
450.degree. to 750.degree. C., say, 500.degree. C. or 550.degree.
to 650.degree. C. or 700.degree. C. The feed streams heated usually
include at least a portion of a steam-containing stream in
combination with either air or hydrocarbon-containing feedstock.
The combustion gas after heating the one or more feed streams to
the partial oxidation reformer will still contain significant heat
values. Usually the combustion gas, after the heat exchange, will
be at temperatures within the range of 200.degree. to 500.degree.
C. and is used to generate additional steam.
[0101] The waste gas from the purification operation, i.e.,
retentate from a membrane separation or purge from a pressure swing
adsorption, is combusted with an oxygen containing gas, usually air
or, in the case of an integrated fuel cell, oxygen-containing waste
gas from the fuel cell. The waste gas may be combined with
additional fuel such as anode waste gas or hydrocarbon-containing
feedstock. In the preferred embodiments, the gas for combustion is
either the waste gas or the waste gas combined with anode waste gas
from a fuel cell, especially where the hydrogen product from the
hydrogen generator is used as a feed to the fuel cell.
[0102] Preferably the combustion of the waste gas is catalytic,
e.g., using a platinum metal based combustion catalyst, to enhance
stability of the combustion. The temperature of the combustion gas
exiting the combustion zone is generally between about 500.degree.
and 800.degree. or 1000.degree. C., and preferably to avoid the
need of expensive materials of construction, the temperature of
combustion effluent is between about 600.degree. and 750.degree.
C.
[0103] The combustion may be effected in the same vessel as an
indirect heat exchange with a fluid intended to be fed to the
partial oxidation reformer, or the combustion effluent may be
passed to one or more physically separate heat exchangers.
Preferably the combustion gas heats the steam or oxygen-containing
feed or a combination of both. Higher temperatures of the heated
gas are generally preferred to increase the amount of heat being
carried to the reformer. Often the gas heated by the combustion gas
is at a temperature in the range of about 450.degree. to
750.degree. C., say, 500.degree. to 700.degree. C. The combustion
gas will still contain significant heat values. Usually the
combustion gas, after this heat exchange, will be at temperatures
within the range of 200.degree. to 500.degree. C. and can be used
to generate steam to cycle to the partial oxidation reformer.
[0104] In one preferred embodiment, the combustion gas is used to
heat in an indirect heat exchanger the oxygen-containing feed and
at least a portion of the steam to be fed to the reformer. The
cooler combustion gas is then used as the heat source for a boiler
to generate a portion of the steam for the reforming, usually
between about 10 to 60 percent of the steam. This steam may be
combined with the oxygen-containing feed and, if desired, the
remainder of the steam, and passed to the indirect heat exchanger
having the hot combustion gas on the hot side.
[0105] The heat exchangers used to cool the reformate and to
contact the combustion gas may be of any convenient design,
including boilers if the cold side feed is essentially only water,
and may comprise a unitary structure such as can be permitted with
microchannel heat exchanger designs. The heat exchangers may be
cocurrent, crosscurrent or counter current.
[0106] The apparatus may find attractive application in facilities
that generate from about 1 to 1000, especially from about 10 to
200, kilograms of hydrogen per day.
[0107] Preferred aspects of the invention will be further described
in connection with the drawings.
[0108] With reference to FIG. 1, hydrocarbon-containing feed for
the hydrogen generator is supplied via line 102 at a rate
controlled by valve 104. The feed is admixed with liquid water from
line 106 supplied at a rate controlled by valve 108. This admixture
further contains recycled water from line 110. The mixture is
provided to heat exchanger 112, which is in counter current,
indirect heat exchange with the effluent from water gas shift
reactor 126.
[0109] In heat exchanger 112, at least a portion of the liquid
water is vaporized as the effluent from the shift reactor is
cooled. The heated fluid from heat exchanger 112 is passed via line
118 to heat exchanger 116 which is depicted as being in
countercurrent, indirect heat exchange with effluent from
autothermal reformer 122.
[0110] While the conditions of the heated fluid in line 118 may be
such that liquid water remains, it is usually preferred to add
liquid water between heat exchangers 112 and 116. This water is
provided from line 106 and the flow rate of water is controlled by
valve 114. If desired, liquid water may be introduced at one or
more points in heat exchanger 116.
[0111] The fuel and vaporized water admixture from heat exchanger
116 is passed via line 120 to autothermal reformer 122 containing
catalyst for partial oxidation and steam reforming. Into reformer
122 is also introduced a heated air stream via line 166.
[0112] The effluent from reformer 122 is passed via line 124
through heat exchanger 116 to water gas shift reactor 126. The
cooling provided by heat exchanger 116 is sufficient to lower the
temperature of the effluent to water gas shift temperatures,
preferably to a temperature between about 280.degree. and
350.degree. C. where the equilibrium will favor a shift effluent
containing less than 2 mole percent carbon monoxide (on a dry
basis).
[0113] The temperature of the gases subjected to the water gas
shift will increase as the reaction is slightly exothermic. The
effluent from shift reactor 126 is passed through heat exchanger
112 to heat exhanger/condensor 130 where the temperature of the
gases are reduced to those suitable for pressure swing adsorption.
The condensed water can be recycled to heat exchanger 112 via line
110. Cooling water from line 132 is used to cool the shift effluent
gases. Line 128 then directs the shift effluent gases to pressure
swing adsorption system 134. A useful pressure swing adsorption
system is depicted in connection with FIG. 4. As the pressure of
the shift effluent is high, no additional compressor may be
necessary to provide attractive feed pressures for the pressure
swing adsorption.
[0114] Purified hydrogen is withdrawn from pressure swing
adsorption system 134 via line 136. The purge from pressure swing
adsorption system is passed via line 138 to combustor 140 as it
contains hydrogen useful as fuel. Combustor 140 is preferably a
catalytic combustor and is depicted as providing heat to air heater
156. In an advantageous aspect of this invention, the purge gas
provides sufficient fuel value to heat the incoming air to a
suitable temperature for introduction into reformer 122. As shown,
air for combustion is provided via line 142 in an amount controlled
by valve 144. If desired, one or more components may be added to
the purge stream. Additional fuel may be added via line 146 at a
flow rate controlled by valve 148. If the hydrogen is used in a
fuel cell, cathode and/or anode waste gas may be added via line 150
at a rate controlled by valve 152. The combustion effluent exits
via line 154.
[0115] Combustor 140 is in indirect heat exchange with air heater
156. Air is introduced via line 158 at a rate controlled by valve
160 into heater 156. If desired, liquid water from line 162 can be
added to line 158 at a flow rate controlled by valve 164. The water
may be added in an amount to provide air exiting heater 156 at a
desired temperature for use in the reformer. It may also be another
source of water to maintain the desired steam to carbon content in
reformer 122. The heated air exits via line 166 and is directed to
the inlet of reformer 122.
[0116] With reference to FIG. 2, hydrocarbon-containing feed for
the hydrogen generator is supplied via line 202 at a rate
controlled by valve 204. The hydrocarbon-containing feed is admixed
with liquid water from line 206 supplied at a rate controlled by
valve 208. This admixture further contains recycled water from line
210. The mixture is provided to heat exchanger 212 which is in
counter current, indirect heat exchange with the effluent from
autothermal reformer 222.
[0117] In heat exchanger 212, at least a portion of the liquid
water is vaporized as reformate is cooled. The heated fluid from
heat exchanger 212 is passed via line 218 to heat exchanger 216
which is depicted as being in cocurrent, indirect heat exchange
with effluent from autothermal reformer 122.
[0118] While the conditions of the heated fluid in line 218 may be
such that liquid water remains, it is usually preferred to add
liquid water between heat exchangers 212 and 216. This water is
provided from line 206 and the flow rate of water is controlled by
valve 214. If desired, liquid water may be introduced at one or
more points in heat exchanger 216.
[0119] The fuel and vaporized water admixture from heat exchanger
216 is passed via line 220 to autothermal reformer 222 containing
catalyst for partial oxidation and steam reforming. Into reformer
222 is also introduced a heated air stream via line 266.
[0120] The effluent from reformer 222 is passed via line 224
through heat exchanger 216 and then through heat exchanger 212 to
heat exhanger/condensor 230 where the temperature of the gases are
reduced to those suitable for hydrogen purification. The condensed
water can be recycled to heat exchanger 212 via line 210. Cooling
water from line 232 is used to cool the shift effluent gases. Line
228 then directs the shift effluent gases to membrane separator
234. As the pressure of the shift effluent is high, no additional
compressor may be necessary to provide attractive feed pressures
for the membrane separation.
[0121] Purified hydrogen is withdrawn from membrane separator 234
via line 236. The high-pressure retentate from membrane separator
234 is passed via line 238 to combustor 240 as it contains
unrecovered hydrogen useful as fuel. If desired, the high-pressure
retentate can be passed to an expander/turbine (not shown) to
recover power. Combustor 240 is preferably a catalytic combustor
and is depicted as providing heat to air heater 256. In an
advantageous aspect of this invention, the retentate provides
sufficient fuel value to heat the incoming air to a suitable
temperature for introduction into reformer 222. As shown, air for
combustion is provided via line 242 in an amount controlled by
valve 244. However, if desired, one or more components may be added
to the purge stream. Additional fuel may be added via line 246 at a
flow rate controlled by valve 248. If the hydrogen is used in a
fuel cell, cathode and/or anode waste gas may be added via line 250
at a rate controlled by valve 252. The combustion effluent exits
via line 254.
[0122] Combustor 240 is in indirect heat exchange with air heater
256. Air is introduced via line 258 at a rate controlled by valve
260 into heater 256. If desired, liquid water from line 262 can be
added to line 258 at a flow rate controlled by valve 264. The water
may be added in an amount to provide air exiting heater 256 at a
desired temperature for use in the reformer. It may also be another
source of water to maintain the desired steam to carbon content in
reformer 222. The heated air exits via line 266 and is directed to
the inlet of reformer 222.
[0123] With reference to FIG. 3, hydrocarbon-containing feed for
the hydrogen generator is supplied via line 302 at a rate
controlled by valve 304. In this embodiment, the feed also contains
sulfur components, e.g., such as would be contained as odorants in
natural gas. These sulfur components can include organosulfides,
mercaptans, carbonyl sulfide and the like. The
hydrocarbon-containing feed is admixed with liquid water from line
306 supplied at a rate controlled by valve 308. This admixture
further contains recycled water from line 310. The mixture is
provided to heat exchanger 312 which is in counter current,
indirect heat exchange with the effluent from autothermal reformer
322.
[0124] In heat exchanger 312, at least a portion of the liquid
water is vaporized as reformate is cooled. The heated fluid from
heat exchanger 312 is passed via line 318 to heat exchanger 316
which is depicted as being in countercurrent, indirect heat
exchange with effluent from autothermal reformer 322.
[0125] While the conditions of the heated fluid in line 318 may be
such that liquid water remains, it is usually preferred to add
liquid water between heat exchangers 312 and 316. This water is
provided from line 306 and the flow rate of water is controlled by
valve 314. If desired, liquid water may be introduced at one or
more points in heat exchanger 316.
[0126] The fuel and vaporized water admixture from heat exchanger
316 is passed via line 320 to autothermal reformer 322 containing
catalyst for partial oxidation and steam reforming. Into reformer
322 is also introduced a heated air stream via line 366.
[0127] The effluent from reformer 322 is passed via line 324
through heat exchanger 316 and then through heat exchanger 312 to
heat exhanger/condensor 330 where the temperature of the gases are
reduced to those suitable for hydrogen purification. The condensed
water can be recycled to heat exchanger 312 via line 310. Cooling
water from line 332 is used to cool the reformer effluent gases.
Line 328 then directs the cooled gases to hydrogen sulfide sorber
333 and then to pressure swing adsorption system 334.
[0128] The sulfur components contained in the feed are
substantially converted to hydrogen sulfide in the autothermal
reformer 322. Since in this embodiment of the invention, no water
gas shift stage is used and sulfur-tolerant catalysts for the
autothermal reforming are available, the complexities of removing
sulfur can be avoided. Hydrogen sulfide can readily be removed from
gas streams by sorption, especially chemisorption. Moreover, since
sulfur components in feeds such as natural gas are in very small
quantities, a relatively small bed of sorbent is usually
sufficient.
[0129] Hydrogen sulfide sorber 333 contains a suitable sorbent for
hydrogen sulfide such as zinc oxide. As depicted, the hydrogen
sulfide sorption is downstream of heat exchanger/condenser 330. In
some instances it may be preferred to remove hydrogen sulfide from
the reformate while it is at higher temperatures, e.g., up to about
250.degree. C., which enhances the rate of chemisorption on
sorbents such as zinc oxide. In such case, the hydrogen sulfide
sorber may be upstream of the heat exchanger/condenser.
Alternatively, the hydrogen sulfide adsorber may be placed in line
338.
[0130] As the pressure of the reformer effluent is high, no
additional compressor may be necessary to provide attractive feed
pressures for the pressure swing sorption system. Purified hydrogen
is withdrawn from pressure swing adsorption system 334 via line
336. The purge from pressure swing adsorption system is passed via
line 338 to combustor 340 as it contains hydrogen useful as fuel.
Combustor 340 is preferably a catalytic combustor and is depicted
as providing heat to air heater 356. In an advantageous aspect of
this invention, the purge gas from the pressure swing adsorption
system provides sufficient fuel value to heat the incoming air to a
suitable temperature for introduction into reformer 322. As shown,
air for combustion is provided via line 342 in an amount controlled
by valve 344. However, if desired, one or more components may be
added to the purge stream. Additional fuel may be added via line
346 at a flow rate controlled by valve 348. If the hydrogen is used
in a fuel cell, cathode and/or anode waste gas may be added via
line 350 at a rate controlled by valve 352. The combustion effluent
exits via line 354.
[0131] Combustor 340 is in indirect heat exchange with air heater
356. Air is introduced via line 358 at a rate controlled by valve
360 into heater 356. If desired, liquid water from line 362 can be
added to line 358 at a flow rate controlled by valve 364. The water
may be added in an amount to provide air exiting heater 356 at a
desired temperature for use in the reformer. It may also be another
source of water to maintain the desired steam to carbon ratio in
reformer 322. The heated air exits via line 366 and is directed to
the inlet of reformer 322.
[0132] FIG. 4 depicts a four bed pressure swing adsorber useful for
purifying hydrogen produced by autothermal reforming with air. A
feed containing hydrogen, nitrogen, argon, water, carbon dioxide,
carbon monoxide and any unreacted hydrocarbon-containing feedstock
is passed via line 402 to one of vessels 404, 406, 408 and 410
which is in the adsorption phase of the cycle. Each of the vessels
has a valve, 404A, 406A, 408A and 410A, respectively, to permit
flow of the feed to the vessel at one end. Each of the vessels at
the same end is in fluid communication with a purge header 412
through valves 404B, 406B, 408B and 410B. Each of the vessels is in
fluid communication at the opposing end with purified product
header 414 through valves 404E, 406E, 408E and 410E. Also on said
opposing end, each vessel is in fluid communication with
pressurization header 415 through valves 404F, 406F, 408F, and
410F. Further on said opposing end, each vessel is in fluid
communication with provide equalization/provide purge header 416
through valves 404C, 406C, 408C, and 410C. Finally on said opposing
end, each vessel is in fluid communication with receive
equalization/receive purge header 417 through valves 404D, 406D,
408D, and 410D.
[0133] A proportional control valve 431 is provided on the
purge/equalization header in order to control the rate of pressure
change in the beds during provide purge and provide equalization
steps. An additional proportional control valve 432 is provided on
the pressurization header in order to control the rate of
pressurization. A further control valve 430 is provided on the tail
gas line 412 in order to control the rate of blowdown.
[0134] Each of the vessels is filled with adsorbent, e.g., a
granular activated carbon adsorbent for about 30 volume percent of
the bed closest to the feed inlet and the remainder being a beaded
lithium exchanged X molecular sieve.
[0135] For the bed undergoing adsorption, its valves A and E are
open and purified hydrogen product stream enters header 414. Once a
bed goes off the adsorption step of the cycle valves A and B are
closed and the C valve is opened. The gases, which primarily are
those in the interstitial spaces in the vessel, are passed into
header 416 and are introduced into the vessel undergoing
represurization through the D valve. Once the two vessels are at
substantially the same pressure, the gases are passed to the vessel
being purged. The purging is done at low pressure, e.g., less than
about 50 kPa above ambient atmospheric pressure. After the purge
step is completed, the B valve is closed at the bottom of the bed
undergoing purge and the two beds equalize in pressure (second
equalization). Following the second equalization, the C valve is
closed and the B valve is opened and the pressure within the vessel
is dropped to the low pressure for purging. Once this blow down is
completed, the D valve is opened such that the gas from the vessel
in the provide purge step of the cycle can purge the bed. In the
next step, the B valve is closed and the bed is partially
repressurized by equalizing pressure with another bed through the D
valve. In the final step, the bed is further repressurized through
the D valve by equalizing with another bed undergoing the first
equalization step. Valve D is then closed after the pressure
equalization is completed, and the purified hydrogen product stream
continues to fill the vessel through the F valve until
substantially the pressure for adsorption is reached. Valves A and
E are then opened to restart the adsorption step.
[0136] Advantageously, the pressure swing adsorption unit in FIG. 4
is designed to use only two proportional control valves thereby
simplifying automation, reducing the tuning requirements in the
field, and improving operability.
[0137] With respect to FIG. 5, hydrocarbon-containing feed is
supplied by line 502 to a hydrogen generator. As depicted, the feed
is passed through desulfurizer 504 which is a solid adsorbent bed
desulfurizer to remove organosulfur compounds. Thereafter, the
hydrocarbon-containing feed is passed via line 520 to be combined
with steam and heated in indirect heat exchanger 512B prior to
being passed to autothermal reformer 506. Air for the autothermal
reforming is supplied by line 508 and is combined with steam in
line 550, passed through indirect heat exchanger 544 and then via
line 552 to reformer 506.
[0138] The reformate from autothermal reformer 506 exits via line
510 and is cooled in indirect heat exchanger 512B and boiler 512A.
Heat exchanger 512B and boiler 512A may be in separate or the same
vessel. Liquid water is supplied to boiler 512A by line 514, and is
vaporized with the steam exiting boiler 512A via line 516 being
directed to indirect heat exchanger 512B. The steam in line 516 is
admixed with hydrocarbon-containing feed from line 520. The steam
and hydrocarbon-containing feed mixture, after being heated in
indirect heat exchanger 512B are passed to reformer 506 via line
518.
[0139] The cooled reformate exits boiler 512A and is directed to
air cooler 522 and to knock out pot 524. Condensed water is
withdrawn via line 526 and is preferably recycled as water feed to
the reformer. The gas phase from knock out pot 524 passes via line
528 to pressure swing adsorption system 530. A hydrogen product
stream is withdrawn from the pressure swing adsorption system via
line 532 and a purge stream from the system is withdrawn via line
534. Line 534 first directs the purge through a hydrogen sulfide
sorption bed 536 and then to combustor 540. Air is supplied to
combustor 540 via line 538.
[0140] In combustor 540, the hydrogen, carbon monoxide and
unreacted hydrocarbon-containing feed in the purge are combusted to
provide a combustion gas. Typically, this combustion is catalytic
or employs a flame holder to enhance stability of the combustion.
It is readily apparent that combustor 540 and heat exchanger 544
could be a single unit.
[0141] The combustion gas is then passed via line 542 to the hot
side of heat exchanger 544. The cooled combustion gas still has
substantial heat content and is passed from heat exchanger 544 to
boiler 546. Liquid water is passed via line 548 to boiler 546 and
the generated steam is withdrawn via line 550 and combined with air
from line 508 for passage to the cool side of heat exchanger 544.
The cooled combustion gas is exhausted from boiler 546 via line
554.
[0142] FIG. 6 is a schematic representation of a hybrid combustor
which can be used in the process depicted in FIG. 5. Combustor 600
is provided with sorption purge inlet conduit 602. Primary air
supply conduit 604 supplies air for the combustion. The primary air
enters combustor between outer shell 606 and inner shell 608, which
surrounds the combustion zone. Thus, the air is preheated before
being mixed with the sorption purge gas. The mixing occurs by air
passing through perforations in the sorption purge inlet
conduit.
[0143] This mixture is passed from conduit 602 into plenum 616.
Distributor 614 is provided at the end of conduit 602 to facilitate
uniform mixing of the sorption purge gas and primary air.
Distributor 614 may be a baffle. Plenum 616 has a gas-permeable,
cylindrical side wall 618 composed of oxidation catalyst. For
purposes of illustration only, the wall is a wire mesh having
openings in the range of about 0.01 to 2, preferably, 0.05 to 1,
millimeter in major dimension. Preferably, the pressure drop
through the catalyst is less than about 20, preferably less than
about 5, and most preferably less than about 2, kPa. Usually, the
first 0.1 to 1 centimeter of the top of the cylindrical side wall
is gas impermeable. The oxidation catalyst supports sufficient
catalytic combustion that stable flame combustion can occur. From
time to time, the fuel and air mixture inside the plenum may not be
at conditions sufficient to support flame combustion. Hence, the
combustion occurs proximate to the oxidation catalyst. The portion
of the combustion that is catalytic will vary with the
throughput.
[0144] Plenum 616 also has gas impermeable frustoconical top in a
sealing relationship with conduit 602 and the cylindrical side
wall. The bottom of plenum 616 is also sealed with a gas
impermeable base, which abuts the bottom of the cylindrical side
wall. The hot combustion gas and flame exit radially from the
cylindrical side wall into a combustion zone defined by a
concentric baffle 620. Concentric baffle 620 is in a fluid sealed
relationship with plenum 616 above the portion of the cylindrical
side wall that is active for the combustion. The lower portion of
baffle 620 is open to combustion gas flow from the combustion
zone.
[0145] Secondary air is provided via secondary air conduit 610
which enters the zone between plenum 616 and inner shell 608.
Baffle 612 is provided proximate to the inlet from conduit 610 to
assist in distributing the secondary air around plenum 616. As
shown, the secondary air passes on the outside of concentric baffle
620 and is heated while cooling the combustion gas. Then, the
secondary air is combined with the gas passing from the combustion
zone defined by the cylindrical side wall and concentric baffle
620. The combined gas, the combustion gas, is withdrawn via line
622.
[0146] In operation, where the sorption purge gas has little
heating value and a relatively low flame temperature, little, if
any, secondary air will be required to achieve the sought
temperature for the combustion gas. In some instances, it may be
desired to heat the primary air such that desirable flame
temperatures are obtained. With little or no secondary air
introduction, the temperature outside concentric baffle 620 will
approximate that of the combustion zone and indirect heat transfer
will occur with the primary air. However, with higher secondary air
flow rates, the heat from the combustion zone will primarily be
absorbed by the secondary air with a lesser increase in temperature
of the primary air.
[0147] Table 1 sets forth computer simulation data including those
used in the preparation of FIGS. 9A, 9B and 9C, respectively.
TABLE-US-00002 TABLE 1 ATR Temp Pressure S/C ATR CO ATR H2 O2/C
H2/Feed Feed Hydrogen deg C. psig ratio mole frac mole frac ratio
ratio Nm3/hr Nm3/hr 650 60 4 0.0477 0.4855 0.40 1.79 54.0 96.6 650
100 4 0.0422 0.4611 0.40 1.62 54.0 87.4 650 140 4 0.0381 0.4410
0.40 1.49 54.0 80.5 650 60 6 0.0379 0.5155 0.40 1.99 54.0 107.8 650
100 6 0.0349 0.4992 0.40 1.87 54.0 100.8 650 140 6 0.0324 0.4839
0.40 1.75 54.0 94.7 650 60 8 0.0309 0.5299 0.40 2.10 54.0 113.3 650
100 8 0.0294 0.5197 0.40 2.01 54.0 108.7 650 140 8 0.0278 0.5090
0.40 1.93 54.0 104.0 700 60 4 0.0634 0.5082 0.40 1.99 54.0 107.6
700 100 4 0.0593 0.4941 0.40 1.88 54.0 101.6 700 140 4 0.0556
0.4804 0.40 1.78 54.0 96.1 700 60 6 0.0482 0.5261 0.40 2.11 54.0
114.0 700 100 6 0.0466 0.5190 0.40 2.05 54.0 110.8 700 140 6 0.0449
0.5109 0.40 1.98 54.0 107.2 700 60 8 0.0385 0.5343 0.40 2.16 54.0
116.6 700 100 8 0.0378 0.5306 0.40 2.13 54.0 114.9 700 140 8 0.0370
0.5260 0.40 2.09 54.0 112.8 750 60 4 0.0753 0.5151 0.40 2.08 54.0
112.2 750 100 4 0.0734 0.5092 0.40 2.03 54.0 109.6 750 140 4 0.0711
0.5022 0.40 1.97 54.0 106.5 750 60 6 0.0568 0.5272 0.40 2.15 54.0
116.0 750 100 6 0.0562 0.5246 0.40 2.13 54.0 114.9 750 140 6 0.0554
0.5214 0.40 2.10 54.0 113.4 750 60 8 0.0455 0.5334 0.40 2.18 54.0
117.6 750 100 8 0.0452 0.5322 0.40 2.17 54.0 117.0 750 140 8 0.0449
0.5306 0.40 2.15 54.0 116.2
[0148] Table 2 sets forth data from computer simulations on a
hydrogen generator of the type set forth in FIG. 5 (except that the
hydrocarbon-containing feed in line 502 is introduced directly to
autothermal reformer 506 without preheating) which data were used
in the preparation of FIG. 10.
TABLE-US-00003 TABLE 2 P (kPa) Total S:C % S:C To ATR Boiler NHE
300 3.0 50 55.4 300 4.0 50 58.1 300 4.5 50 59.0 300 5.0 50 58.9 300
6.0 67 55.7 600 3.0 50 50.4 600 4.0 50 54.6 600 5.0 50 57.3 600 5.5
55 56.3 600 6.0 67 54.0 1200 3.5 43 45.7 1200 4.5 50 50.2 1200 5.5
50 53.4 1200 6.0 50 51.3 1200 6.5 60 48.8
[0149] Table 3 provides the conditions for the operation of the
hydrogen generator used in this simulation. This simulation is
based on natural gas feed, and produces a reformate (at the maximum
NHE point) containing approximately: 43 mol % hydrogen, 38 mol %
nitrogen, 13 mol % carbon dioxide, 3.5 mol % carbon monoxide, and
1.5 mol % methane. The reformer effluent temperature is 675.degree.
C. In all cases, 75 percent of the hydrogen is recovered as
purified hydrogen product and contains less than 5 parts per
million by volume carbon monoxide. The steam to carbon ratio is the
sum of the S/C for each of heat exchangers 544 and 546 (combustion
gas heat exchange) and 512 (reformate heat exchange) in Table 3.
The Net Hydrogen Efficiency will be higher if a water gas shift is
used.
TABLE-US-00004 TABLE 3 Heat Exchanger 544 & 546 Heat Exchanger
512 Heated Cooled Heated Pressure Feed Combustion Feed Cooled kPa,
Temp., Gas Temp, Temp., Reformate absolute S/C .degree. C. .degree.
C. S/C .degree. C. Temp., .degree. C. 300 1.5 600 361 1.5 600 317
300 2.0 600 255 2.0 600 253 300 2.25 600 197 2.25 600 230 300 2.5
540 154 2.5 600 212 300 2.0 540 154 4.0 270 154 600 1.5 600 406 1.5
600 305 600 2.0 600 299 2.0 600 249 600 2.5 600 184 2.5 600 203 600
2.5 480 177 3.0 530 175 600 2.0 520 171 4.0 230 174 1200 2.0 600
383 1.5 600 325 1200 2.25 600 311 2.25 600 217 1200 2.75 600 195
2.75 550 198 1200 2.7 470 198 3.0 510 196 1200 3.0 275 197 3.0 600
196 1200 2.6 235 199 3.9 320 198
* * * * *