U.S. patent application number 14/293844 was filed with the patent office on 2014-09-25 for integrated multi-step solid/liquid separation system for fischer-tropsch processes.
The applicant listed for this patent is Rentech, Inc.. Invention is credited to Sergio MOHEDAS, Harold A. Wright.
Application Number | 20140286834 14/293844 |
Document ID | / |
Family ID | 42107168 |
Filed Date | 2014-09-25 |
United States Patent
Application |
20140286834 |
Kind Code |
A1 |
MOHEDAS; Sergio ; et
al. |
September 25, 2014 |
INTEGRATED MULTI-STEP SOLID/LIQUID SEPARATION SYSTEM FOR
FISCHER-TROPSCH PROCESSES
Abstract
A system for separating liquids from solids comprising an
immobilization unit comprising an immobilization vessel containing
a bed of magnetizable material and a magnet configured to produce a
magnetic field within the immobilization vessel, wherein the
immobilization vessel further comprises an immobilization vessel
outlet and an immobilization vessel inlet for a fluid comprising
liquid and metal-containing particles. A method for separating
solid particles from liquid by introducing a fluid comprising
liquid and a first concentration of solid particles into an
immobilization unit comprising an immobilization vessel and at
least one magnet configured to produce high density magnetic flux
lines within the immobilization vessel and/or a high field gradient
at or near the surface of the magnetizable material when powered,
wherein the immobilization vessel contains therein a bed of
magnetizable material; and removing from the immobilization unit a
product having a second particle concentration less than the first
particle concentration.
Inventors: |
MOHEDAS; Sergio; (Houston,
TX) ; Wright; Harold A.; (Longmont, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rentech, Inc. |
Los Angeles |
CA |
US |
|
|
Family ID: |
42107168 |
Appl. No.: |
14/293844 |
Filed: |
June 2, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12577488 |
Oct 12, 2009 |
8778178 |
|
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14293844 |
|
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61104816 |
Oct 13, 2008 |
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Current U.S.
Class: |
422/187 ;
210/222 |
Current CPC
Class: |
B03C 1/032 20130101;
B03C 1/02 20130101; B03C 1/286 20130101; B03C 2201/20 20130101;
B03C 1/30 20130101; B03C 2201/18 20130101; B01J 8/228 20130101 |
Class at
Publication: |
422/187 ;
210/222 |
International
Class: |
B03C 1/02 20060101
B03C001/02 |
Claims
1. A system for the separation of liquids from solids, the system
comprising: an immobilization unit comprising an immobilization
vessel containing a bed of magnetizable material and a magnet
configured to produce a magnetic field within the immobilization
vessel, wherein the immobilization vessel further comprises an
immobilization vessel inlet for a fluid comprising liquid and
metal-containing particles, and an immobilization vessel outlet for
a reduced-solids liquid.
2. The system of claim 1 wherein the magnet is capable of producing
high density magnetic flux lines within the immobilization
vessel.
3. The system of claim 1 wherein the bed of magnetizable material
comprises a plurality of interwoven fibers.
4. The system of claim 1 wherein the magnetizable material is
configured as magnetizable steel wool.
5. The system of claim 1 further comprising a Fischer-Tropsch
reactor, the Fischer-Tropsch reactor positioned upstream of the
immobilization vessel, the Fischer-Tropsch reactor containing
within it a metal-based Fischer-Tropsch catalyst, the
Fischer-Tropsch reactor comprising an outlet for Fischer-Tropsch
product comprising Fischer-Tropsch product wax and catalyst
particles, the outlet in direct or indirect fluid communication
with the immobilization unit.
6. The system of claim 5 wherein the catalyst is cobalt-based
Fischer-Tropsch catalyst, iron-based Fischer-Tropsch catalyst, or a
combination thereof.
7. The system of claim 6 wherein the catalyst comprises iron
carbide.
8. The system of claim 5 further comprising a primary separator
positioned upstream of the immobilization vessel, an inlet of the
primary separator in fluid communication with the Fischer-Tropsch
outlet and an outlet of the primary separator in fluid
communication with the immobilization vessel inlet.
9. The system of claim 8 further comprising a surge drum between
the primary separator and the immobilization vessel.
10. The system of claim 8 wherein the primary separator is a
dynamic settler.
11. The system of claim 10 wherein the primary dynamic settler
separator comprises a magnetic separation section.
12. The system of claim 8 wherein the primary separator comprises a
cross-flow filtration unit.
13. The system of claim 8 further comprising upgrading apparatus
downstream of the immobilization unit, wherein the upgrading
apparatus is selected from hydrotreating apparatus, hydrocracking
apparatus, isomerization apparatus, and combinations thereof.
14. The system of claim 13 wherein the upgrading apparatus is
operable to provide a fuel selected from the group consisting of
jet, diesel, naphtha, and combinations thereof.
15. The system of claim 8 wherein the reduced-solids liquid is
suitable for direct use as a fuel.
16. The system of claim 8 further comprising at least one
separation apparatus downstream of the immobilization unit, the at
least one separation apparatus operable to provide a chemical
product from the reduced-solids liquid.
17. The system of claim 16 wherein the chemical product is selected
from the group consisting of olefins, alcohols, other
oxygen-containing components, and combinations thereof.
18. The system of claim 1 comprising at least two immobilization
units aligned in series.
19. The system of claim 1 comprising at least two immobilization
units aligned in parallel.
20. The system of claim 1 comprising at least three immobilization
units, with at least two of the immobilization units aligned in
series.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application which claims
the benefit under 35 U.S.C. .sctn.121 of U.S. patent application
Ser. No. 12/577,488, filed Oct. 12, 2009, which claims the benefit
under 35 U.S.C. .sctn. 119(e) of U.S. Provisional Patent
Application No. 61/104,816, filed Oct. 13, 2008, the disclosures of
each of which are hereby incorporated herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] 1. Technical Field
[0004] The present invention relates generally to separating
liquids from solid particles having magnetic properties.
Specifically, the system and method may be used to separate liquid
from solid catalyst particles and may be applied in multi-phase
catalytic reactors where the catalyst comprises solids with
magnetic properties. Such multiphase catalytic reactors may be
Fischer-Tropsch (FT) reactors of a Fischer-Tropsch synthesis
process.
[0005] 2. BACKGROUND OF THE INVENTION
[0006] Several methods for separating liquids and solids in a
Fischer-Tropsch process/reactor system have been proposed. These
methods include settling, filtration, and combinations thereof
Magnetic separation alone has also been proposed. Typically,
primary separation and secondary separation are utilized, with
primary separation removing the larger solids and secondary
separation removing smaller solids. Both the primary separators and
the secondary separators may be settlers. Primary settlers may be
dynamic settlers. In certain applications, primary separators are
cross-flow filtration units. Secondary separators are
conventionally cross-flow filtration devices, or settlers.
[0007] Settling is a method utilized to separate solids and
liquids, and may be applied in Fischer-Tropsch processes/reactor
systems. Settlers may be of the vertical type or may be inclined
settlers. See, for example, U.S. Pat. Nos. 6,068,760; 6,712,982;
and 7,078,439. Inclined settlers, also known as lamella type
settlers, may permit higher liquid removal rates than the same size
vertical settler. The design of such settlers is based on particle
settling velocity which is highly dependent on particle diameter.
Thus, once a settler is designed, settling of particles of a
particular diameter or larger is obtained. If attrition, etc.,
reduces the size of the particles, these particles may exit the
settler with the liquid, thus contaminating the liquid. In a
Fischer-Tropsch process, when catalyst particles exit the reactor,
the particles not only contaminate the liquid product but also
decrease the catalyst inventory in the reactor. Both of these
events are detrimental to the process economics.
[0008] Fischer-Tropsch catalysts, which are typically either
iron-based or cobalt-based, are prone to attrition. Typical
particles of fresh catalyst have a size in the range of 20-100
microns. Attrition may result in the formation of particles having
a size of less than 20 microns; in certain applications, particle
size may even reach sub-micron levels. These smaller particles tend
to plug filter media and/or alter the characteristics of the cake
on the filter media, thus compacting the filter, which may become
substantially impermeable. Filtration across compact cakes mandates
a higher pressure drop across the filtration media to obtain the
same amount of liquid filtrate. This creates a vicious cycle of
higher pressure drop leading to more compact cakes and/or media
plugging which may ultimately render the system ineffective.
[0009] Cross flow filtration is one of the most widely used methods
of separation. Cross flow filtration is described, for example, in
U.S. Pat. Nos. 6,929,754 and 6,833,078. In some applications, a
"mild" cross flow filtration method is utilized. By this method, a
`cake` of catalyst particles is formed on the surface of the filter
media, and this cake acts as the primary barrier for the prevention
of solids passing through the filter media and contaminating the
liquid. Some disadvantages of this method, however, are that the
filter medium is usually prone to plugging by small particles which
may be present due to physical and/or chemical attrition during the
use of the media. Filter media are design for a certain micron
rating. For example, with a micron rating of 20 microns, particles
larger than 20 microns will theoretically be retained on the
surface of the media. Particles smaller than 20 microns may travel
through the media and exit or may get stuck within the pores of the
filter medium due to agglomeration, shape and/or other factors.
Even though a backwash method may be used to attempt to unplug the
medium, the medium may become ineffective with time on stream.
Eventually, the filter elements must be removed from the system and
replaced.
[0010] Smaller particles, say less than 20 microns, and mainly
those less than 10 microns and perhaps less than 1 micron tend to
render a "mild" cross flow filtration process ineffective for
separation of liquids and solids in Fischer-Tropsch processes.
These smaller particles also cause separation of the particles from
the liquid by sedimentation alone very difficult. The settling
equipment tends to become large and thus economically
impractical.
[0011] Magnetic separation alone has previously been proposed to
separate solids and liquids in Fischer-Tropsch processes/reactors
systems. For example, see "Magnetic Separation of Iron Catalysts
from Fischer-Tropsch Wax," R. R. Oder, Proceedings of the Petroleum
Chemistry Division, ACS Annual Meeting, CA (Mar. 28-Apr. 1, 2004);
and "Separation of Iron Catalysts from Fischer-Tropsch Wax," R. R.
Oder et al., Twentieth Annual Pittsburgh Coal Conference: Coal,
Energy and the Environment, Pittsburgh, Pa. (Sep. 15-19, 2003).
This form of separation comprises passing a slurry containing the
liquid and solids through a vessel the walls of which have been
magnetized. If the solid particles have magnetic properties, the
particles tend to accumulate on the walls of the vessel and fall to
the bottom of the vessel, continuing to travel in the direction of
the slurry. Thus, particle-reduced liquid may be withdrawn from the
top of the vessel. However, this method tends to be more effective
for smaller particles, for example, sub-micron-sized particles. In
order for the method to be effective for a broad range of particle
sizes, for example, for particles having sizes from sub-micron to
100 microns, the equipment may have to be rather large and the
power needed for the magnetization much higher than the power
required for the separation of particles within a smaller size
range.
[0012] In a Fischer-Tropsch process, wax product streams from which
particles have been removed by primary and optionally secondary
separation, are sent for product upgrading, PU. Catalyst-containing
streams separated in primary and/or secondary separation may be
recycled to the Fischer-Tropsch reactor or disposed according to
regulations. Product upgrading processes at the back end of
Fischer-Tropsch plants typically comprise hydrogenation,
hydrocracking and/or isomerization processes, whereby the
Fischer-Tropsch liquids produced in the Fischer-Tropsch reactors
are refined to obtain desirable products. These product upgrading
processes are often stringent in the amount of solids that can be
tolerated in the liquid feed to be treated, usually limiting the
solids content of the liquid feed to less than 10 ppm by weight.
Particle reduction to the desired specification in the
Fischer-Tropsch liquid product may be challenging.
[0013] Accordingly, there is a need in industry for reliable and
efficient systems and methods for separating catalyst particles
having magnetic properties from liquids.
SUMMARY
[0014] Herein disclosed is a system for the separation of liquids
from solids, the system comprising an immobilization unit
comprising an immobilization vessel containing a bed of
magnetizable material and a magnet configured to produce a magnetic
field within the immobilization vessel, wherein the immobilization
vessel further comprises an immobilization vessel outlet and an
immobilization vessel inlet for a fluid comprising liquid and
metal-containing particles. The magnet may be capable of producing
high density magnetic flux lines within the immobilization vessel.
The bed of magnetizable material may comprise a plurality of
interwoven fibers. The magnetizable material may be configured as
magnetizable steel wool.
[0015] In embodiments, the system further comprises a
Fischer-Tropsch reactor, the Fischer-Tropsch reactor positioned
upstream of the immobilization vessel, the Fischer-Tropsch reactor
containing within it a metal-based Fischer-Tropsch catalyst, the
Fischer-Tropsch reactor comprising an outlet for Fischer-Tropsch
product comprising Fischer-Tropsch product wax and catalyst
particles, the outlet in direct or indirect fluid communication
with the magnetic field vessel. The catalyst may be cobalt-based
Fischer-Tropsch catalyst, iron-based Fischer-Tropsch catalyst, or a
combination thereof. In applications, the catalyst comprises iron
carbide. The system may further comprise a primary separator
positioned upstream of the immobilization vessel, an inlet of the
primary separator in fluid communication with the Fischer-Tropsch
outlet and an outlet of the primary separator in fluid
communication with the immobilization vessel inlet. A surge drum
may be positioned between the primary separator and the
immobilization vessel. The primary separator may be a dynamic
settler. The primary dynamic settler separator may comprise a
magnetic separation section. In embodiments, the primary separator
comprises a cross-flow filtration unit.
[0016] The system may further comprise upgrading apparatus
downstream of the immobilization unit, wherein the upgrading
apparatus is selected from hydrotreating apparatus, hydrocracking
apparatus, isomerization apparatus, and combinations thereof. In
embodiments, the upgrading apparatus is operable to provide a fuel
selected from the group consisting of jet, diesel, naphtha, and
combinations thereof. In embodiments, the reduced-solids liquid is
suitable for direct use as a fuel.
[0017] The system may further comprise at least one separation
apparatus downstream of the immobilization unit, the at least one
separation apparatus operable to provide a chemical product from
the reduced-solids liquid. In embodiments, the chemical product is
selected from the group consisting of olefins, alcohols, other
oxygen-containing components, and combinations thereof.
[0018] In embodiments of the system, the system comprises at least
two immobilization units aligned in series. The system may comprise
at least two immobilization units aligned in parallel. The system
may comprise at least three immobilization units, with at least two
of the immobilization units aligned in series.
[0019] Also disclosed herein is a method for separating solid
particles from liquid by: introducing a fluid comprising liquid and
a first concentration of solid particles into an immobilization
unit comprising an immobilization vessel and at least one magnet
configured to produce high density magnetic flux lines within the
immobilization vessel and/or a high field gradient at or near the
surface of the magnetizable material when powered by a power
source, wherein the immobilization vessel contains therein a bed of
magnetizable material; and removing from the immobilization unit an
immobilization unit product having a second particle concentration,
wherein the second particle concentration is less than the first
particle concentration. The magnetic material may be a high
permeability magnetic matrix. In applications, the magnetizable
material is in the shape of steel wool. The magnetizable material
may comprise a plurality of interwoven fibers. In embodiments, the
second particle concentration is less than 100 ppm-wt, preferably
less than 10 ppm-wt and more preferably less than 1 ppm-wt. The
method may comprise introducing the fluid comprising liquid and a
first concentration of solid particles into a plurality of
immobilization units configured in series, in parallel, or a
combination thereof. The method may be operable continuously, and
the product may comprise a solids content of less than 10
ppm-wt.
[0020] The bed of magnetizable material within the immobilization
vessel may be backwashed to remove solids from the bed. Backwashing
may comprise shutting off the power source to the at least one
magnet and introducing a backwash fluid to the bed. The backwash
fluid may be introduced to the immobilization bed in the same
direction or in the reverse direction to the direction from that in
which the fluid comprising liquid and a first concentration of
solid particles was introduced into the immobilization vessel. The
backwash fluid may be any liquid appropriate for the temperature
and pressure operating conditions of the immobilization vessel. In
applications, the solid particles are catalytic. Such catalytic
particles may be cobalt-based Fischer-Tropsch catalyst, iron-based
Fischer-Tropsch catalyst, or a combination thereof. In specific
embodiments, the catalytic particles comprise iron carbide.
[0021] The disclosed method may further comprising introducing a
synthesis gas-containing stream into a Fischer-Tropsch reactor,
wherein the Fischer-Tropsch reactor comprises solid particles of
Fischer-Tropsch catalyst and is operable for the production of
Fischer-Tropsch liquid hydrocarbon product, and removing from the
Fischer-Tropsch reactor a Fischer-Tropsch product slurry comprising
Fischer-Tropsch liquids and a concentration of catalyst particles.
The Fischer-Tropsch product slurry may be introduced into a primary
separator positioned upstream of the immobilization unit, a primary
separator product having a reduced solids content relative to the
that of the Fischer-Tropsch product slurry may be removed from the
primary separator, and the primary separator product may be
introduced into the immobilization unit. The primary separator may
be a dynamic separator. The immobilization unit product may be
upgraded via at least one selected from hydrotreating processes,
hydrocracking processes, and isomerization processes. Upgrading may
produce a clean fuel selected from jet fuel, diesel, naphtha or a
combination thereof. The immobilization unit product may be
suitable as fuel. The immobilization unit product may be introduced
into at least one separation process whereby a chemical product is
obtained. Such a chemical product may be selected from the group
consisting of olefins, alcohols, other oxygen containing
components, and combinations thereof.
[0022] These and other embodiments and potential advantages of the
disclosed system and method will become apparent upon reading the
detailed description and viewing the accompanying drawings. While
specific examples may be presented in the following description,
other embodiments are also envisioned. The embodiments described
herein are exemplary only, and are not intended to be limiting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] For a more detailed description of the preferred embodiment
of the present invention, reference will now be made to the
accompanying drawings, wherein:
[0024] FIG. 1 is a schematic of a system provided in the prior art
for removing catalyst from wax produced via Fischer-Tropsch
conversion of synthesis gas.
[0025] FIG. 2 is a schematic of a system for removing catalyst from
wax subsequent Fischer-Tropsch conversion of synthesis gas into
hydrocarbons according to an embodiment of the invention.
[0026] FIG. 3a is a schematic of a first configuration of
immobilization units for secondary separation according to an
embodiment of the invention.
[0027] FIG. 3b is a schematic of a second configuration of
immobilization units for secondary separation according to another
embodiment of the invention.
[0028] FIG. 3c is a schematic of a third configuration of
immobilization units for secondary separation according to another
embodiment of the invention.
[0029] FIG. 4 is a schematic of the bench scale separation system
used in the experiments of Example 1.
NOTATION AND NOMENCLATURE
[0030] As used herein, the phrase "immobilization unit" is used to
refer to a separation unit comprising a bed of magnetizable
material which may be magnetized by magnets in contact with a
vessel containing the bed.
[0031] The phrase "immobilization bed" is used to refer to a bed of
magnetizable material within an immobilization unit.
[0032] As used herein, the term "syngas" and the phrase "synthesis
gas" are used to refer to a gaseous stream comprising hydrogen and
carbon monoxide. The "syngas" or "synthesis gas" stream may further
comprise other components, for example, without limitation, the
"syngas" or "synthesis gas" stream may comprise carbon dioxide,
methane, etc.
DETAILED DESCRIPTION
Overview
[0033] The disclosed invention provides a system and method for
separating liquids from solids having magnetic properties. The
system and method feature a unique combination of dynamic settling
in a first step and a bed immobilization method that includes a
magnetic filtration system in a second step. The system and method
may provide a liquid or filtrate substantially free of solid
particles. Although this description is presented with reference to
the separation of Fischer-Tropsch catalyst from liquid
hydrocarbons, it is to be understood that the invention will prove
valuable for numerous separation processes, in particular for
instances where a magnetizable catalyst is present in a liquid
slurry. Description of the Fischer-Tropsch system and process is
not meant to limit the invention to Fischer-Tropsch processes and
systems, and one of skill in the art will realize the broad
applicability of the disclosed invention.
Comparative System
[0034] FIG. 1 is a schematic of a prior art system 100 for removing
catalyst from wax following Fischer-Tropsch (FT) reaction. Prior
art system 100 comprises Fischer-Tropsch reactor 20, primary
separators 40A and 40B and secondary separators 70A and 70B. In
FIG. 1, feed stream 5 comprising synthesis gas is fed into
Fischer-Tropsch reactor 20 comprising Fischer-Tropsch catalyst.
Tailgas 25 exits reactor 20 and liquid wax product streams 30A and
30B are removed from FT reactor 20. It is noted that 2 separation
loops are shown in FIG. 1, but any number of separation loops is
used, including a single separation loop. Liquid product streams
30A and 30B, containing catalyst slurry are treated to separate the
wax product from the catalyst. Primary separators 40A and 40B are
used as a primary separation method, producing catalyst-rich
streams 50A and 50B and liquid-rich (e.g., hydrocarbon or wax-rich)
streams 60A and 60B. Conventionally, primary separators 40A and 40B
comprise some sort of filtration such as "cake" filtration or are
settlers (e.g., dynamic settlers). In applications, primary
separators are cross-flow filtration units as described
hereinabove.
[0035] At least a portion of the separated catalyst in lines 50A
and 50B may be recycled to FT reactor 20 with or without
intervening treatment. In some applications, at least a portion of
slurry in lines 50A and 50B is not recycled. The separated wax in
lines 60A and 60B may be further treated by introduction into
secondary separators 70A and 70B. Secondary separators systems 70A
and 70B are conventionally cross-flow, e.g., "mild" cross-flow
filtration, or "cake" filtration devices or settlers.
[0036] Following primary and optionally secondary separation, wax
product streams 80A and 80B are typically sent to product
upgrading, PU, while catalyst-containing streams 90A and 90B are
typically disposed according to regulations. Backend processes in
FT (Fischer-Tropsch) product upgrading often comprise
hydrogenation, hydrocracking and/or isomerization processes that
refine the liquids produced in the Fischer-Tropsch reactors to
final usable products. These processes may be stringent in the
amount of solids that can be tolerated in the liquid feed to be
treated. Typically, the particle content of the liquid feed to the
product upgrading systems is limited to less than 10 ppm by weight.
This limitation makes achievement of the desired specification in
the Fischer-Tropsch liquid product challenging. Typically,
therefore, multiple separation steps and/or large separation units
are required.
System for Integrated Multi-Step Solid/Liquid Separation
[0037] Description of the invention will now be made with reference
to FIG. 2, which is a schematic of an inventive system for removing
catalyst from hydrocarbon wax product produced via Fischer-Tropsch
conversion of synthesis gas. It is again noted that 2 separation
loops are shown in FIG. 2, as in the prior art system 100 of FIG.
1, however, any number of separation loops is envisioned, including
a single separation loop.
[0038] Integrated System 200 comprises FT reactor 120, primary
separators 140A and 140B, and secondary separators 175A and 175B,
with power sources 174A and 174B, respectively. Each of these
components will be described in more detail hereinbelow. Other
units may be positioned between reactor 120 and the primary
separators 140A and 140B, between primary separators 140A and 140B
and secondary separators (or immobilization units) 175A and 175B as
desired. For example, in instances, one or more surge drums (and/or
pumps) may be positioned between primary separator 140A and
secondary separator 175A, between primary separator 140B and
secondary separator 175B, or both.
Fischer-Tropsch Reactors
[0039] System 200 comprises a Fischer-Tropsch reactor. The
Fischer-Tropsch reactor may be any suitable reactor known in the
art to be suitable for the conversion of synthesis gas into higher
(C.sup.2+) hydrocarbons. In embodiments, the Fischer-Tropsch
reactors are slurry reactors. As the Fischer-Tropsch reaction is
highly exothermic, the Fischer-Tropsch reactor(s) may comprise
internal or external heat exchangers to control the temperature of
the reactor contents.
Fischer-Tropsch Catalyst
[0040] FT reactor 120 comprises Fischer-Tropsch catalyst effective
for catalyzing the conversion of carbon monoxide and hydrogen into
C.sup.2+ hydrocarbons. The disclosed system and method are suitable
when a catalyst has magnetic properties. In embodiments, the
Fischer-Tropsch catalyst is a metal-based catalyst. In preferred
embodiments, the Fischer-Tropsch catalyst comprises a cobalt or
iron-based catalyst. Most preferably, the Fischer-Tropsch catalyst
is an iron carbide catalyst. In specific applications, the catalyst
comprises cobalt. In other applications, the catalyst comprises
iron.
[0041] A suitable catalyst is described in U.S. patent application
Ser. No. 12/198,459, which is hereby incorporated herein to the
extent that it provides details or explanations supplemental to
those disclosed herein. Depending on the preselected alpha, i.e.,
the polymerization probability desired, a precipitated iron
catalyst may have a weight ratio of potassium (e.g., as carbonate)
to iron in the range of from about 0.005 and about 0.015, more
preferably in the range of from 0.0075 to 0.0125, and most
preferably about 0.010. Larger amounts of alkali metal promoter
(e.g., potassium) may cause the product distribution to shift
toward the longer-chain molecules, while small amounts of alkali
metal may result in a predominantly gaseous hydrocarbon
product.
[0042] The weight ratio of copper to iron in the iron
Fischer-Tropsch catalyst may be in the range of from about 0.005
and 0.050, more preferably in the range of from about 0.0075 and
0.0125, and most preferably about 0.010. Copper may serve as an
induction promoter. In preferred embodiments, the weight ratio of
Cu:Fe is about 1:100.
[0043] The catalyst may be an iron Fischer-Tropsch catalyst
comprising structural promoter. The structural promoter may
significantly reduce the breakdown of the catalyst in a SBCR
(slurry bubble column reactor). The structural promoter may
comprise silica, and may enhance the structural integrity during
activation and operation of the catalyst. In embodiments, the
catalyst comprises a mass ratio of SiO.sub.2:Fe of less than about
1:100 when the structural promoter comprises silica and less than
about 8:100 when the structural promoter comprises silica sol.
[0044] In embodiments, the at least one structural promoter is
selected from oxides of metals and metalloids and combinations
thereof. The structural promoter may be referred to as a binder, a
support material, or a structural support.
[0045] Depending on the level of structural promoter comprising
silicate and the preselected alpha, i.e. the polymerization
probability desired, the weight ratio of K:Fe may be from about
0.5:100 to about 6.5:100. More preferably, the weight ratio of K:Fe
is from about 0.5:100 to about 2:100. In some embodiments, the
weight ratio of K:Fe is about 1:100.
[0046] In some embodiments wherein the structural promoter
comprises silica sol, the weight ratio of iron to potassium is in
the range of from about 100:1 to about 100:5. In some embodiments,
the weight ratio of iron to potassium is in the range of from about
100:2 to about 100:6. In more preferred embodiments, the weight
ratio of iron to potassium is in the range of from about 100:3 to
about 100:5. In some embodiments, the weight ratio of iron to
potassium is in the range of from about 100:4 to about 100:5. In
some preferred embodiments, the weight ratio of iron to potassium
is in the range of from about 100:2 to about 100:4. In some
specific embodiments, the weight ratio of iron to potassium about
100:3. In other certain embodiments, the weight ratio of iron to
potassium is about 100:5.
[0047] In embodiments wherein the structural promoter comprises
silica sol, the weight ratio of iron to copper may be in the range
of from about 100:1 to about 100:7. In some embodiments, the weight
ratio of iron to copper is in the range of from about 100:1 to
about 100:5. More preferably, the weight ratio of iron to copper is
in the range of from about 100:2 to about 100:6. Still more
preferably, the weight ratio of iron to copper is in the range of
from about 100:3 to about 100:5. In some preferred embodiments, the
weight ratio of iron to copper is in the range of from about 100:2
to about 100:4. In other specific embodiments, the weight ratio of
iron to copper is about 100:5. In yet other specific embodiments,
the weight ratio of iron to copper is about 100:3.
[0048] Broadly, in embodiments, wherein the structural promoter is
silica sol, the iron to SiO.sub.2 weight ratio may be in the range
of from about 100:1 to about 100:8; alternatively, in the range of
from 100:1 to 100:7. More preferably, in some embodiments, wherein
the structural promoter is silica, the iron to SiO.sub.2 weight
ratio may be in the range of from about 100:2 to about 100:6. Still
more preferably, the weight ratio of iron to silica is in the range
of from about 100:3 to about 100:5. In some preferred embodiments,
wherein the structural promoter is silica, the iron to SiO.sub.2
weight ratio is about 100:5. In embodiments, wherein the structural
promoter is silica, the iron to SiO.sub.2 weight ratio may be in
the range of from about 100:3 to about 100:7; alternatively, in the
range of from about 100: 4 to about 100:6. In some preferred
embodiments, the Fe:Cu:K:SiO.sub.2 mass ratio is about
100:4:3:5.
[0049] During Fischer-Tropsch conversion, the percent by weight of
the disclosed iron catalyst in the slurry in Fischer-Tropsch
reactor 120 (for example, in a slurry bubble column reactor, or
SBCR) may be in the range of from 5 to 15 percent by weight of iron
in the slurry, in the range of from 7.5 and 12.5 percent by weight,
or about 10 percent by weight of the slurry.
Primary Separators
[0050] System 200 comprises at least one primary separator. In the
embodiment of FIG. 2, system 200 comprises two primary separators,
primary separators 140A and 140B. The primary separators each
comprise an inlet fluidly connected to an outlet of FT reactor 120.
Primary separators 140A and 140B each also comprise an outlet
fluidly connected to a line for a catalyst-rich product (lines 150A
and 150B, respectively), and an outlet fluidly connected to a line
for catalyst-lean product (lines 160A and 160B, respectively).
[0051] In embodiments, primary separators 140A and 140B are
settlers. In preferred embodiments, primary separators 140A and
140B are dynamic settlers. In specific embodiments, primary
settlers 140A and 140B are dynamic settlers which combine magnetic
separation (magnetic/dynamic settlers) as described in U.S.
provisional patent application 60/971,093 to Mohedas. Such a
magnetic dynamic settling vessel comprises at least one magnetic
field within the vessel, at least one fluid inlet 131A/131B for
introduction of the fluid stream having a starting solids content,
at least one exit 133A/133B for a fluid stream comprising a solids
content not greater than the inlet solids content, at least one
exit 134A/134B for a fluid stream comprising a solids content not
less than the inlet solids content, and a vertical feed conduit
132A/132B extending at least 70% of the distance from the at least
one fluid inlet to the at least one exit for a fluid stream
comprising a solids content not less than the inlet solids content.
In embodiments, the at least one magnetic field is provided by at
least one magnetic component. The at least one magnetized component
may be selected from the group consisting of at least a portion of
the external walls of the magnetic dynamic settling vessel, at
least a portion of the internal walls of the settling vessel,
magnetic baffles, magnetic fins, magnetic rods, magnetic plates,
another magnetized internal component, and combinations thereof. In
some embodiments, the at least one magnetized component comprises
at least a portion of the walls of the magnetic dynamic settling
vessel. In embodiments, the at least one magnetized component is an
internal component.
[0052] In some embodiments, a magnetic dynamic settling vessel of
the primary separation comprises an upper portion comprising
vertical external walls and a narrower lower portion comprising
inclined external walls. In embodiments, at least a portion of the
vertical walls, at least a portion of the inclined walls, or at
least a portion of both is magnetized. The at least a portion of
the vertical walls, at least a portion of the inclined walls, or at
least a portion of both may be magnetized by at least one
externally positioned magnet.
[0053] In embodiments the at least one magnetic field is created
within the vessel in the slurry body (slurry volume) without
necessarily having a magnetized component within the magnetic
dynamic settling vessel. The at least one magnetic field may be
throughout the vessel. In preferred embodiments, the at least one
magnetic field is within the bottom section of the magnetic dynamic
settling vessel.
[0054] In embodiments, primary separation further comprises a
second dynamic settler, the second dynamic settler comprising at
least one secondary dynamic settler inlet in fluid connection with
the at least one exit for a fluid stream comprising a solids
content not less than the inlet solids content; at least one
secondary dynamic settler concentrated solids exit; and at least
one secondary dynamic settler liquid product exit.
[0055] The magnetic dynamic settling vessel of the primary
separation may be capable of producing an exit fluid stream
comprising a solids content not greater than 5000 ppm by weight. In
some embodiments, the magnetic dynamic settling vessel is capable
of producing an exit fluid stream comprising a solids content not
greater than 2500 ppm by weight. In some embodiments of the system,
the magnetic dynamic settling vessel is capable of producing an
exit fluid stream comprising a solids content not greater than 1000
ppm by weight. The magnetic dynamic settling vessel may be operable
at a liquid linear upward velocity greater than least 15 cm/h. In
embodiments, the magnetic dynamic settling vessel is operable at a
liquid linear upward velocity greater than 45 cm/h. Alternatively,
the magnetic dynamic settling vessel may be operable at a liquid
linear upward velocity greater than 90 cm/h.
Secondary Separators
[0056] System 200 comprises at least one secondary separator. In
the embodiment of FIG. 2, system 200 comprises two secondary
separators 175A and 175B. Secondary separators 175A and 175B each
comprise inlets fluidly connected with the lines for catalyst-lean
product from the primary separators (lines 160A and 160B,
respectively), and outlets fluidly connected to lines for
substantially catalyst-free hydrocarbon product (lines 185A and
185B, respectively).
[0057] In some embodiments of system 200, a plurality of secondary
separators is configured in series and/or in parallel. For example,
as shown in FIG. 3a, which is a schematic of a first configuration
210 of `immobilization units` (i.e. secondary separators utilizing
magnetic field) for secondary separation, two or more secondary
separators may be aligned in parallel. In the embodiment of FIG.
3a, three secondary separators, 240, 241, and 242 are aligned in
parallel. Catalyst/wax slurry) is introduced via line 201 and lines
221, 222, and 223 into secondary separators 240, 241, and 242,
respectively. Catalyst-lean liquid exits secondary separators 240,
241, and 242 via lines 231, 232, and 233, respectively.
[0058] As another example, as shown in FIG. 3b, which is a
schematic of a second configuration 220 of immobilization units for
secondary separation, two or more secondary separators may be
aligned in series. For example, in the embodiment of FIG. 3b,
secondary separators 243, 244, and 245 are aligned in series.
Catalyst slurry is introduced via line 202 into the first secondary
separator, 243, of a series of secondary units. Within first
secondary separator 243, catalyst material is separated from
catalyst-lean material, which is subsequently introduced into the
second secondary separator, 244 via line 224, and so on. For
example, from second secondary separator 244, catalyst-reduced
material in line 225 may be introduced into the third secondary
separator, 245, of the series. Substantially catalyst-free liquid
may exit the train of separators, for example, via line 234 of
configuration 220 of FIG. 3b.
[0059] As yet another example, as shown in FIG. 3c, which is a
schematic of a third configuration 230 of immobilization units for
secondary separation, three or more secondary separators may be
aligned in a combination of serial and parallel flow. For example,
in the embodiment of FIG. 3c, slurry in line 203 is introduced via
lines 226 and 227 into parallel trains of secondary separators in
series. The first train comprises secondary separators 246 and 247
aligned in series connected via line 228, with material introduced
into separator 246 via line 226 and exiting as a catalyst-reduced
liquid via line 228. Catalyst-reduced material in line 228 is
introduced into the next secondary separator in the first train,
secondary separator 247, and material exits therefrom via line 235.
In a parallel manner, slurry in line 227 is introduced to the first
secondary separator of the second train of serially aligned
separators, secondary separator 248. Catalyst-reduced material
exiting secondary separator 248 via line 229 is introduced into the
second secondary separator of the second train, secondary separator
249. Catalyst reduced material exits the second train of
configuration 230 via line 236.
[0060] In this manner any number and alignment of secondary
separators may be utilized. Secondary separators 175A and 175B may
be reactors similar to those described in U.S. Patent Publication
20070280864 to Kenneth Cross which was filed Dec. 7, 2007. In this
publication, a High-Efficiency Nano-Catalyst Immobilization reactor
or HENCI is discussed. The HENCI reactor comprises immobilized
catalyst which may be used for the catalytic breakdown of
halogenated hydrocarbons. By this disclosure, vessels containing a
similar high permeability material and magnetized as disclosed in
U.S. Patent Publication 20070280864 are used to extract magnetic
catalyst from a slurry comprising the catalyst, rather than being
loaded with catalyst prior to reaction and reacting the reactants
within the immobilization vessel. By this disclosure, therefore,
magnetic field immobilization units are adapted for separation of
solids and liquids, rather than for promoting reaction thereof.
[0061] As depicted most clearly in FIG. 4, secondary separator 325
may comprise magnets 350 surrounding at least a portion of the
outer walls of immobilization vessel 330. Lines 355 and 370 are
exit lines for secondary separator 325. Magnets (not shown in FIG.
2) may surround at least a portion of the outer body of secondary
separators 175A and 175B. The secondary separator comprises a bed
of packed material, 340, which is magnetizable. In the embodiment
of FIG. 2, secondary separators 175A and 175B are packed with a
magnetizable material, 176A and 176B, respectively. The
magnetizable material may be in the form of steel wool, thin
metallic filaments or other configuration suitable for packing. The
immobilization bed within the immobilization vessel of the
secondary separator may comprise a high permeability magnetic
matrix. The matrix may comprise interwoven metallic fibers.
[0062] Secondary separator 325 (and secondary separators 175A and
175B of FIG. 2) may be connected to a source of power, (not shown
in FIG. 4; similar to 174A and 174B, respectively in FIG. 2) for
providing the desired magnetic field(s) within. Powering the magnet
or magnets may result in the formation of high density magnetic
flux lines within the immobilization vessel and/or a high field
gradient at or near the surface of the packing material. The cost
of this power may be comparable to the cost of power needed to pump
very high flow rates through a cross flow filtration unit typical
of the prior art, that operates in high recirculation mode,
potentially making the herein disclosed system and method desirable
from an economic standpoint.
[0063] The secondary separators in the catalyst/wax separation
system utilize a unique method to immobilize small magnetic
particles, with sizes ranging from nanometer-size to hundreds of
microns in size. The small magnetic particles are immobilized on a
bed filled with material upon which a magnetic field has been
applied (e.g., steel wool or the like). The beds may comprise high
permeability magnetic matrix material in the form of steel wool or
woven type filling material for reactor beds having various
geometries of packing structure. The packing structure may resemble
packing structures used in packed distillation towers.
[0064] In embodiments, the secondary separator is capable of
reducing the solids content of an inlet fluid comprising liquid and
solid particles to a concentration of less than about 100 ppm-wt,
more preferably less than 10 ppm-wt, and most preferably to less
than 1 ppm-wt.
Product Upgrading Units
[0065] System 200 may further comprise one or more product
upgrading units, PU units (not shown in FIG. 2). Product upgrading
units may be any suitable units known in the art for upgrading the
Fischer-Tropsch hydrocarbons produced in the Fischer-Tropsch
reactors. In embodiments, a PU unit is selected from hydrotreating
units, hydrocracking units, fractionators, separators, and
combinations thereof.
Surge Drums
[0066] In applications, one or more surge drums may be positioned
between primary separator 140A and secondary separator 175A,
between primary separator 140B and secondary separator 175B, or
both. The surge drums may serve to hold material exiting the
primary separators prior to introduction thereof into secondary
separators. For example, this may be used when a secondary
separator is taken offline for service, replacement, or repair.
Such surge drums may also be positioned between reactor 120 and
primary separators 140A and/or 140B, if desired. One or more pumps
may be positioned between surge drums and immobilization units 175A
and 175B.
Process for Separation of Catalyst from Liquids
[0067] Description of a process for separating solid particles from
liquids will now be made with reference to FIG. 2. In this process,
synthesis gas in line 105 is introduced into Fischer-Tropsch
reactor 120. Reactor 120 comprises Fischer-Tropsch catalyst as
described hereinabove. Reactor tailgas exits Fischer-Tropsch
reactor 120 as tailgas stream 125. This tailgas may comprise
unconverted carbon monoxide and hydrogen (i.e. synthesis gas), and
other product gases or gases introduced with the synthesis gas. A
portion of the synthesis gas in tailgas 125 may be recycled to FT
reactor 120 for further conversion to hydrocarbons.
[0068] Product comprising catalyst slurry exits reactor 120 via
lines 130A and 130B and is introduced into primary separators 140A
and 140B, respectively. Primary separators 140A and 140B serve to
remove the larger particles from the reactor effluent in lines 130A
and 130B. In embodiments, (during normal operation, for example)
the separated fluid exiting the primary separator in lines 160A and
160B comprises a solids content of less than 0.5% by weight (5,000
ppm); less than 0.25% by weight (2,500 ppm), less than 0.1% by
weight (1,000 ppm), less than 0.05% by weight (500 ppm), or less
than 0.01% by weight (100 ppm). In embodiments, the separated fluid
exiting the primary separators via lines 160A and 160B (during
start-up/activation, for example, which conditions are rough on the
catalyst) comprises less than 5% by weight (50,000 ppm), less than
3% by weight (30,000 ppm), less than 2% by weight (20,000 ppm),
less than 1% by weight (10,000 ppm) or less than about 0.5% by
weight (5,000 ppm).
[0069] Catalyst separated from the liquid product by primary
separators 140A and 140B and exiting the primary separators via
lines 150A and 150B may, in certain applications, be recycled to FT
reactor 120. Separated catalyst in lines 150A and 150B may or may
not undergo intervening treatment prior to recycle to FT reactor
120.
[0070] Separated wax streams in lines 160A and 160B, which contain
less catalyst than the product stream exiting reactor 120 via lines
130A and 130B, are introduced into secondary separators 175A and
175B. In embodiments, the fluid introduced into the secondary
separators 175A and 175B comprises less than about 2% solids by
weight, less than 1% solids by weight, or less than about 0.5%
solids by weight. When separated wax streams in lines 160A and 160B
comprising wax and solid particles are passed through the magnetic
fields within immobilization beds 176A and 176B of secondary
separators 175A and 175B, respectively, the solid particles with
magnetic properties are attracted to the magnetized packing
material (e.g., wires of wool) and deposit throughout the bed,
becoming immobilized. In embodiments, the magnetic particles are
distributed substantially uniformly through the bed of magnetized
material.
[0071] With proper residence time, the wax streams exiting
secondary separators 175A and 175B via lines 185A and 185B may be
substantially particle-free. In embodiments, the solids content of
an inlet fluid comprising liquid and solid particles is reduced to
a concentration of less than about 100 ppm-wt, more preferably less
than 10 ppm-wt, and most preferably to less than 1 ppm-wt via
secondary separation.
[0072] In this manner, Fischer-Tropsch catalysts based on cobalt
and/or iron and other catalysts having strong enough magnetic
properties to be attracted by the magnetic fields and/or the
magnetic field gradients created within the beds of secondary
separators 175A and 175B, may be separated from liquid product
produced in reactor 120 (e.g., an FT reactor).
Secondary Separator Magnetic Material Regeneration
[0073] The secondary separators may be cleaned via cessation of the
magnetic field and backwash with an appropriate fluid. This
regeneration of the magnetized material in the secondary separators
may permit reduced operating costs. When it is desirable to clean a
secondary separator, that separator may be taken offline, and the
balance of the separators left online This feature can be used in
an industrial setting to continually process material by having
several secondary separators in parallel (and/or in series), as
depicted in FIGS. 3a-3c, for example, with some units in separation
mode and some in backwash mode. The backwash fluid may be a portion
of the fluid being separated. Desirably, however, the backwash
fluid may be another available fluid in the plant with a lower
value since the backwashed liquid/catalyst mixture will either be
sold for a relatively low price, sent to a tertiary separation
system, or disposed.
Features/Advantages
[0074] With the unique two step separation system and method of use
presented herein, a system to separate liquids from solids, in
particular, the wax from an Fe and/or Co-based Fischer-Tropsch
catalyst in FT processes, may become more effective and/or reliable
than traditional systems and may permit the use of smaller
equipment to achieve solids content specifications on the liquids.
For example, the system and method may be used to reduce the solids
content in Fischer-Tropsch reactor product comprising liquid
hydrocarbons (wax), yielding solids-reduced (and perhaps
substantially solids-free) product in line 185A and 185B which may
subsequently be introduced into a product upgrading system.
[0075] The disclosed system and method may permit reduced-size
secondary separation units with a concomitant reduction in capital
costs. The potential for reduced operating costs also exists due to
the fact that the packing material of the separation units (steel
wool, etc.) may be reused following cleaning by removing the
magnetic field(s) and backwashing with appropriate liquid.
EXAMPLE
[0076] Bench scale tests were performed using cold flow and
simulating Fischer-Tropsch streams 160 exiting a primary separation
unit downstream of a Fischer-Tropsch reactor. Several bench scale
tests were conducted using a secondary separation unit as described
herein (i.e., a particle immobilization unit) to separate a liquid
from nano/micro catalyst particles containing iron. FIG. 4 is a
schematic of the bench scale separation system 300 used in this
experiment.
[0077] A proxy liquid operating at room temperature was used to
mimic the physical properties (density, viscosity, etc.) of
Fisher-Tropsch wax at typical conditions at the exit of a
Fischer-Tropsch reactor and downstream of a primary separation
unit. The proxy liquid consisted of a mixture of a saturated
poly-alpha olefin oil (branded as DURASYN.RTM. 164) and n-decane.
The catalyst particles comprised Fe and had a mean particle size of
12 microns and a particle size distribution encompassing particles
having sizes in the range of from sub-micron to 100+ microns.
Catalyst particles and proxy liquid were mixed in slurry reservoir
305. Mixing was promoted via agitator 315. Slurry 320 in slurry
reservoir 305 was pumped via slurry pump 310 and line 324 into
secondary separator 325.
[0078] Secondary separator (or particle immobilization unit) 325
comprised an immobilization vessel 330. Immobilization vessel 330
was a cylindrical vessel having a diameter, D, of 4 inches and a
length, L, of about 6 inches. Vessel 330 was filled with a metallic
matrix (separation media) 340 comprising stainless steel 400 series
wool made of wires with a diameter of around 45 microns. The amount
of metallic wool used in this test was a piece of approximately 4
inch diameter by 6 ft long before compacting it inside the
immobilization vessel 330. A magnet unit 350 surrounding the
immobilization vessel 330 provided an open core magnetic field
inside vessel 330 of about 500 gauss (without the metallic matrix).
This translates to a relatively high field gradient near the
surface of the wool. The liquid-solid mixture (slurry) contained
0.5% by weight of solid. Slurry was fed to the secondary separator
325 at approximately 0.25 to 0.5 gpm. After a few minutes
re-circulating the mixture with the magnetic field applied to the
vessel 330, samples of the fluid stream at the outlet of the
immobilization vessel were taken via valve 385 and line 380.
Analysis of these samples showed that the solid content of the
fluid was reduced from the original 0.5% wt to less than 1
ppm-wt.
[0079] When the fluid at the outlet became essentially clear, the
power 335 to the magnet 350 of the secondary separator 325 was
discontinued (stopping the magnetic field), pumping was stopped,
and valve 390 closed. Valve 390 is connected to slurry reservoir
305 via line 395. A reverse flow was applied via valve 385 and line
380 to backwash the solid content from the metallic matrix 340.
Backwash liquid comprising dislodged particles may be removed from
system 300 via valve 375 and line 376. Backwashing proved to be
very effective, and, after backwash, the metallic wool was
substantially solids-free.
[0080] It was discovered that, with the appropriate flow rate and
retention times within secondary separator 325, the particle
concentration of the liquid in line 360 could be reduced to less
than about 10 ppm, which may be required in subsequent product
upgrading steps. The proper retention time can, in applications, be
achieved by recirculation of the wax-catalyst mixture rather than
by a once-through operation.
[0081] While preferred embodiments of the invention have been shown
and described, modifications thereof can be made by one skilled in
the art without departing from the spirit and teachings of the
invention. The embodiments described herein are exemplary only, and
are not intended to be limiting. Many variations and modifications
of the invention disclosed herein are possible and are within the
scope of the invention. Where numerical ranges or limitations are
expressly stated, such express ranges or limitations should be
understood to include iterative ranges or limitations of like
magnitude falling within the expressly stated ranges or limitations
(e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater
than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use of the term
"optionally" with respect to any element of a claim is intended to
mean that the subject element is required, or alternatively, is not
required. Both alternatives are intended to be within the scope of
the claim. Use of broader terms such as comprises, includes,
having, etc. should be understood to provide support for narrower
terms such as consisting of, consisting essentially of, comprised
substantially of, and the like.
[0082] Accordingly, the scope of protection is not limited by the
description set out above but is only limited by the claims which
follow, that scope including all equivalents of the subject matter
of the claims. Each and every claim is incorporated into the
specification as an embodiment of the present invention. Thus, the
claims are a further description and are an addition to the
preferred embodiments of the present invention. The disclosures of
all patents, patent applications, and publications cited herein are
hereby incorporated by reference, to the extent they provide
exemplary, procedural or other details supplementary to those set
forth herein.
* * * * *