U.S. patent application number 14/469289 was filed with the patent office on 2015-05-21 for process for hydrotreating a coal tar stream.
The applicant listed for this patent is UOP LLC. Invention is credited to Paul T. Barger, Maureen L. Bricker, Joseph A. Kocal, Matthew Lippmann, Kurt M. Vanden Bussche.
Application Number | 20150136652 14/469289 |
Document ID | / |
Family ID | 53172210 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150136652 |
Kind Code |
A1 |
Bricker; Maureen L. ; et
al. |
May 21, 2015 |
PROCESS FOR HYDROTREATING A COAL TAR STREAM
Abstract
A process for hydrotreating a coal tar stream is described. A
coal tar stream is provided, and the coal tar stream is expanded
with an inert gas stream to provide an expanded liquid coal tar
stream. The expanded liquid coal tar stream is hydrotreated. The
coal tar stream can be reacted with a hydrocarbon solvent before it
is expanded.
Inventors: |
Bricker; Maureen L.;
(Buffalo Grove, IL) ; Barger; Paul T.; (Arlington
Heights, IL) ; Kocal; Joseph A.; (Buffalo Grove,
IL) ; Lippmann; Matthew; (Chicago, IL) ;
Vanden Bussche; Kurt M.; (Lake in the Hills, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UOP LLC |
Des Plaines |
IL |
US |
|
|
Family ID: |
53172210 |
Appl. No.: |
14/469289 |
Filed: |
August 26, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61905980 |
Nov 19, 2013 |
|
|
|
Current U.S.
Class: |
208/400 ;
208/211; 208/254R; 208/49; 208/87; 208/89 |
Current CPC
Class: |
C10G 69/04 20130101;
C10G 65/08 20130101; C10G 67/02 20130101; C10G 45/08 20130101; C10G
1/002 20130101; C10G 65/12 20130101; C10G 69/02 20130101; C10G
45/02 20130101; C10G 67/12 20130101 |
Class at
Publication: |
208/400 ;
208/211; 208/254.R; 208/89; 208/49; 208/87 |
International
Class: |
C10G 45/08 20060101
C10G045/08; C10G 65/12 20060101 C10G065/12; C10G 67/04 20060101
C10G067/04; C10G 69/04 20060101 C10G069/04; C10G 69/02 20060101
C10G069/02; C10G 1/00 20060101 C10G001/00; C10G 65/08 20060101
C10G065/08 |
Claims
1. A process comprising: providing a coal tar stream; expanding the
coal tar stream with an inert gas stream to provide an expanded
liquid coal tar stream; and hydrotreating the expanded liquid coal
tar stream.
2. The process of claim 1 wherein hydrotreating the expanded liquid
coal tar stream comprises subjecting the expanded liquid coal tar
stream to hydrodesulfurization, or hydrodenitrogenation, or
both.
3. The process of claim 1 further comprising: processing the
hydrotreated stream by one or more of hydrocracking, fluid
catalytic cracking, alkylation, transalkylation, oxidation, and
hydrogenation to provide at least one product.
4. The process of claim 1 wherein the inert gas is selected from
the group consisting of carbon dioxide, nitrogen, and light
hydrocarbons.
5. The process of claim 1, wherein the hydrotreating takes place at
a temperature range of about 260.degree. C. (about 500.degree. F.)
to about 370.degree. C. (about 700.degree. F.).
6. The process of claim 1, wherein the hydrotreating takes place at
a pressure range of about 4.8 MPa (about 700 psi) to about 8.3 MPa
(about 1200 psi).
7. The process of claim 1, wherein the hydrotreating takes place in
the presence of a catalyst.
8. The process of claim 1 further comprising: feeding the coal tar
stream and a hydrocarbon solvent into a reaction zone; reacting the
coal tar stream and the hydrocarbon solvent in the reaction zone to
provide a liquid coal tar stream; and wherein expanding the coal
tar stream comprises expanding the liquid coal tar stream.
9. The process of claim 8 wherein the hydrocarbon solvent comprises
an aromatic hydrocarbon.
10. The process of claim 8 wherein the coal tar stream and the
hydrocarbon solvent are reacted at a pressure ranging from about
4.8 MPa (about 700 psig) to about 8.3 MPa (about 1200 psig).
11. The process of claim 1 wherein providing the coal tar stream
comprises pyrolyzing a coal feed into at least the coal tar stream
and a coke stream.
12. A process comprising: providing a coal tar stream; feeding the
coal tar stream and a hydrocarbon solvent into a reaction zone;
reacting the coal tar stream and the hydrocarbon solvent in the
reaction zone to provide a liquid coal tar stream; and expanding
the reacted coal tar stream with an inert gas stream to provide an
expanded liquid coal tar stream; and hydrotreating the expanded
liquid coal tar stream.
13. The process of claim 12, wherein the hydrotreating takes place
at a temperature range of about 260.degree. C. (about 500.degree.
F.) to about 370.degree. C. (about 700.degree. F.) and a pressure
range of about 4.8 MPa (about 700 psi) to about 8.3 MPa (about 1200
psi).
14. The process of claim 12 wherein the inert gas is selected from
the group consisting of carbon dioxide, nitrogen, and light
hydrocarbons.
15. The process of claim 12 wherein hydrotreating the expanded
liquid coal tar stream comprises subjecting the expanded liquid
coal tar stream to hydrodesulfurization, or hydrodenitrogenation,
or both.
16. The process of claim 12 further comprising: processing the
hydrotreated stream by one or more of hydrocracking, fluid
catalytic cracking, alkylation, transalkylation, oxidation, and
hydrogenation to provide at least one product.
17. The process of claim 12, wherein the hydrotreating takes place
in the presence of a catalyst.
18. The process of claim 12 wherein the hydrocarbon solvent
comprises an aromatic hydrocarbon.
19. The process of claim 12 wherein the coal tar stream and the
hydrocarbon solvent are reacted at a pressure ranging from about
4.8 MPa (about 700 psig) to about 8.3 MPa (about 1200 psig).
20. The process of claim 12 wherein providing the coal tar stream
comprises pyrolyzing a coal feed into at least the coal tar stream
and a coke stream.
Description
[0001] This application claims the benefit of Provisional
Application Ser. No. 61/905,980 filed Nov. 19, 2013, entitled
Process for Hydrotreating a Coal Tar Stream.
BACKGROUND OF THE INVENTION
[0002] Many different types of chemicals are produced from the
processing of petroleum. However, petroleum is becoming more
expensive because of increased demand in recent decades.
[0003] Therefore, attempts have been made to provide alternative
sources for the starting materials for manufacturing chemicals.
Attention is now being focused on producing liquid hydrocarbons
from solid carbonaceous materials, such as coal, which is available
in large quantities in countries such as the United States and
China.
[0004] Pyrolysis of coal produces coke and coal tar. The
coke-making or "coking" process consists of heating the material in
closed vessels in the absence of oxygen to very high temperatures.
Coke is a porous but hard residue that is mostly carbon and
inorganic ash, which is used in making steel.
[0005] Coal tar is the volatile material that is driven off during
heating, and it comprises a mixture of a number of hydrocarbon
compounds. It can be separated to yield a variety of organic
compounds, such as benzene, toluene, xylene, naphthalene,
anthracene, and phenanthrene. These organic compounds can be used
to make numerous products, for example, dyes, drugs, explosives,
flavorings, perfumes, preservatives, synthetic resins, and paints
and stains. The residual pitch left from the separation is used for
paving, roofing, waterproofing, and insulation.
[0006] Coal tar includes many contaminants. For many processes, it
is desirable to treat a coal stream to remove such contaminants.
However, some treatment processes for coal tar insufficiently
remove contaminants or produce undesirable results, such as
saturated aromatic rings. There is a need to improve treatment of
coal tar streams.
SUMMARY OF THE INVENTION
[0007] One aspect of the invention involves a process for
hydrotreating a coal tar stream. A coal tar stream is provided, and
the coal tar stream is expanded with an inert gas stream to provide
an expanded liquid coal tar stream. The expanded liquid coal tar
stream is hydrotreated.
BRIEF DESCRIPTION OF THE DRAWING
[0008] The FIGURE is an illustration of one embodiment of the
process of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The FIGURE shows one embodiment of a basic coal conversion
process 5. A coal feed 10 is sent to a pyrolysis zone 15.
Alternatively or additionally, in some processes, a portion of the
coal feed 10 is sent to a gasification zone (not shown), where the
coal feed is mixed with oxygen and steam and reacted under heat and
pressure in the gasification zone to form syngas, which is a
mixture of carbon monoxide and hydrogen. The syngas can be further
processed using the Fischer-Tropsch reaction to produce gasoline or
using the water-gas shift reaction to produce more hydrogen.
[0010] In the pyrolysis zone 15, the coal is heated at high
temperature, e.g., up to about 2,000.degree. C. (3600.degree. F.),
in the absence of oxygen to drive off the volatile components.
Coking produces a coke stream 25 and a coal tar stream 20. The coke
stream 25 can be used in other processes, such as the manufacture
of steel. The coal tar stream 20 from the pyrolysis zone, or coal
tar streams from other sources, is subjected to a treatment process
to provide a treated stream that can be used in various downstream
processes.
[0011] To reduce the aromaticity of the coal tar stream 20, the
coal tar stream 20 can be sent to a reaction zone 35, where the
coal tar stream 20 is reacted with added hydrogen in the presence
of a hydrocarbon solvent 30. The reaction zone 35 can be, for
instance, a continuous stirred-tank reactor (CSTR), a slurry
hydrocracking reactor, or a fixed bed reactor. The hydrocarbon
solvent 30 can include, for instance, a petroleum cut or other
aromatic-type hydrocarbon. Example reaction conditions include a
pressure ranging from about 4.8 MPa (about 700 psig) to about 8.3
MPa (about 1200 psig) and a temperature ranging from about
232.degree. C. (450.degree. F.) to about 371.degree. C.
(700.degree. F.). A catalyst such as a Ni/Mo hydrotreating catalyst
for heavy feeds, or if S level is low enough a Pt/Al.sub.20.sub.3
catalyst, can be used in the reaction zone 35, but is not required
in all embodiments. The reaction zone 35 produces a liquid coal tar
stream 40 that is reduced in aromaticity with respect to the coal
tar stream 20.
[0012] The liquid coal tar stream 40 is fed to an expansion zone
50. The coal tar stream 40 is expanded with an inert gas stream 45
that is fed into the expansion zone 50. The expansion preferably
takes place at high pressure, such as between about 10.3 MPa (about
1500 psi) and about 17.2 MPa (about 2500 psi), with an example
range of about 2000 psi (13.8 MPa). Suitable inert gases include,
but are not limited to, carbon dioxide, nitrogen, and light
hydrocarbons such as CH.sub.4, C.sub.2H.sub.4, C.sub.3H.sub.8, and
C.sub.4H.sub.10. The inert gas stream 45 provides a vapor phase
solvent in the expansion zone 50, and improves solubility of
hydrogen in later hydrotreating, making the liquid phase more
reactive. The expanded liquid coal tar stream 55 includes the
hydrocarbon solvent 30 from the reaction zone 35.
[0013] In other processes, the reaction zone 35 can be omitted, and
the coal tar stream 20 can be fed into the expansion zone 50. In
this arrangement, the expanded liquid coal tar stream would not
include the hydrocarbon solvent 30.
[0014] The expanded liquid coal tar stream 55 is then hydrotreated
in the hydrotreating zone 60. Hydrotreating is a process in which
hydrogen gas is contacted with a hydrocarbon stream in the presence
of suitable catalysts which are primarily active for the removal of
heteroatoms, such as sulfur, nitrogen, and metals from the
hydrocarbon feedstock. In hydrotreating, hydrocarbons with double
and triple bonds may be saturated. Aromatics may also be saturated.
The hydrotreating in the hydrotreating zone 60 preferably takes
place at about 4.8 MPa (about 700 psi) to about 8.3 MPa (about 1200
psi), and at a temperature range of about 260 C (about 500 F) to
about 370 C (about 700 F), a liquid hourly space velocity of about
0.5 hr.sup.-1 to about 4 hr.sup.-1, and a hydrogen rate of about
168 to about 1,011 Nm.sup.3/m.sup.3 oil (1,000-6,000 scf/bbl).
Conditions can vary depending on the solvent.
[0015] The hydrogenation can take place in the presence of a
catalyst. Typical hydrotreating catalysts include at least one
Group VIII metal, preferably iron, cobalt and nickel, and at least
one Group VI metal, preferably molybdenum and tungsten, on a high
surface area support material, preferably alumina. Other typical
hydrotreating catalysts include zeolitic catalysts, as well as
noble metal catalysts where the noble metal is selected from
palladium and platinum. Hydrotreating can include
hydrodesulfurization, hydrodenitrogenation, or both.
[0016] The resulting hydrotreated stream 65 provides a pre-treated
stream that can be subject to a processing zone 70 to provide one
or more products 75. This pre-treated stream can be relatively free
of contaminants such as sulfur and nitrogen. Example hydrotreated
streams 65 have a sulfur content of about 50 ppm or less, and a
nitrogen content of about 10 ppm or less. Hydrotreating, reaction,
and/or expansion conditions can be tuned to provide a desirable
decontamination of the coal tar stream 40.
[0017] The processing zone 70 can process the hydrotreated stream
65 by hydrocracking, fluid catalytic cracking, alkylation,
transalkylation, oxidation, hydrogenation, or a combination of such
processes. The hydrotreated stream 65 can also be blended in
fuel.
[0018] The hydrotreated stream 65 may be fractionated.
Alternatively, the coal tar stream 20, 40 may be fractionated
before treatment. Coal tar comprises a complex mixture of
heterocyclic aromatic compounds and their derivatives with a wide
range of boiling points. The number of fractions and the components
in the various fractions can be varied as is well known in the art.
A typical separation process involves separating the coal tar into
four to six streams. For example, there can be a fraction
comprising NH3, CO, and light hydrocarbons, a light oil fraction
with boiling points between 0.degree. C. and 180.degree. C., a
middle oil fraction with boiling points between 180.degree. C. to
230.degree. C., a heavy oil fraction with boiling points between
230 to 270.degree. C., an anthracene oil fraction with boiling
points between 270.degree. C. to 350.degree. C., and pitch.
[0019] The light oil fraction contains compounds such as benzenes,
toluenes, xylenes, naphtha, coumarone-indene, dicyclopentadiene,
pyridine, and picolines. The middle oil fraction contains compounds
such as phenols, cresols and cresylic acids, xylenols, naphthalene,
high boiling tar acids, and high boiling tar bases. The heavy oil
fraction contains benzene absorbing oil and creosotes. The
anthracene oil fraction contains anthracene. Pitch is the residue
of the coal tar distillation containing primarily aromatic
hydrocarbons and heterocyclic compounds.
[0020] Hydrocracking is a process in which hydrocarbons crack in
the presence of hydrogen to lower molecular weight hydrocarbons.
Typical hydrocracking conditions may include a temperature of about
290.degree. C. (550.degree. F.) to about 468.degree. C.
(875.degree. F.), a pressure of about 3.5 MPa (500 psig) to about
20.7 MPa (3000 psig), a liquid hourly space velocity (LHSV) of
about 1.0 to less than about 2.5 hr-1, and a hydrogen rate of about
421 to about 2,527 Nm3/m3 oil (2,500-15,000 scf/bbl). Typical
hydrocracking catalysts include amorphous silica-alumina bases or
low-level zeolite bases combined with one or more Group VIII or
Group VIB metal hydrogenating components, or a crystalline zeolite
cracking base upon which is deposited a Group VIII metal
hydrogenating component. Additional hydrogenating components may be
selected from Group VIB for incorporation with the zeolite
base.
[0021] Fluid catalytic cracking (FCC) is a catalytic hydrocarbon
conversion process accomplished by contacting heavier hydrocarbons
in a fluidized reaction zone with a catalytic particulate material.
The reaction in catalytic cracking is carried out in the absence of
substantial added hydrogen or the consumption of hydrogen. The
process typically employs a powdered catalyst having the particles
suspended in a rising flow of feed hydrocarbons to form a fluidized
bed. In representative processes, cracking takes place in a riser,
which is a vertical or upward sloped pipe. Typically, a pre-heated
feed is sprayed into the base of the riser via feed nozzles where
it contacts hot fluidized catalyst and is vaporized on contact with
the catalyst, and the cracking occurs converting the high molecular
weight oil into lighter components including liquefied petroleum
gas (LPG), gasoline, and a distillate. The catalyst-feed mixture
flows upward through the riser for a short period (a few seconds),
and then the mixture is separated in cyclones. The hydrocarbons are
directed to a fractionator for separation into LPG, gasoline,
diesel, kerosene, jet fuel, and other possible fractions. While
going through the riser, the cracking catalyst is deactivated
because the process is accompanied by formation of coke which
deposits on the catalyst particles. Contaminated catalyst is
separated from the cracked hydrocarbon vapors and is further
treated with steam to remove hydrocarbon remaining in the pores of
the catalyst. The catalyst is then directed into a regenerator
where the coke is burned off the surface of the catalyst particles,
thus restoring the catalyst's activity and providing the necessary
heat for the next reaction cycle. The process of cracking is
endothermic. The regenerated catalyst is then used in the new
cycle. Typical FCC conditions include a temperature of about
400.degree. C. to about 800.degree. C., a pressure of about 0 to
about 688 kPa g (about 0 to 100 psig), and contact times of about
0.1 seconds to about 1 hour. The conditions are determined based on
the hydrocarbon feedstock being cracked, and the cracked products
desired. Zeolite-based catalysts are commonly used in FCC reactors,
as are composite catalysts which contain zeolites, silica-aluminas,
alumina, and other binders.
[0022] Alkylation is typically used to combine light olefins, for
example mixtures of alkenes such as propylene and butylene, with
isobutane to produce a relatively high-octane branched-chain
paraffinic hydrocarbon fuel, including isoheptane and isooctane.
Similarly, an alkylation reaction can be performed using an
aromatic compound such as benzene in place of the isobutane. When
using benzene, the product resulting from the alkylation reaction
is an alkylbenzene (e.g. toluene, xylenes, ethylbenzene, etc.). For
isobutane alkylation, typically, the reactants are mixed in the
presence of a strong acid catalyst, such as sulfuric acid or
hydrofluoric acid. The alkylation reaction is carried out at mild
temperatures, and is typically a two-phase reaction. Because the
reaction is exothermic, cooling is needed. Depending on the
catalyst used, normal refinery cooling water provides sufficient
cooling. Alternatively, a chilled cooling medium can be provided to
cool the reaction. The catalyst protonates the alkenes to produce
reactive carbocations which alkylate the isobutane reactant, thus
forming branched chain paraffins from isobutane. Aromatic
alkylation is generally now conducted with solid acid catalysts
including zeolites or amorphous silica-aluminas
[0023] The alkylation reaction zone is maintained at a pressure
sufficient to maintain the reactants in liquid phase. For a
hydrofluoric acid catalyst, a general range of operating pressures
is from about 200 to about 7100 kPa absolute. The temperature range
covered by this set of conditions is from about -20.degree. C. to
about 200.degree. C. For at least alkylation of aromatic compounds,
the temperature range is about from 100-200 C at the pressure range
of about 200 to about 7100 kPa.
[0024] Transalkylation is a chemical reaction resulting in transfer
of an alkyl group from one organic compound to another. Catalysts,
particularly zeolite catalysts, are often used to effect the
reaction. If desired, the transalkylation catalyst may be metal
stabilized using a noble metal or base metal, and may contain
suitable binder or matrix material such as inorganic oxides and
other suitable materials. In a transalkylation process, a
polyalkylaromatic hydrocarbon feed and an aromatic hydrocarbon feed
are provided to a transalkylation reaction zone. The feed is
usually heated to reaction temperature and then passed through a
reaction zone, which may comprise one or more individual reactors.
Passage of the combined feed through the reaction zone produces an
effluent stream comprising unconverted feed and product
monoalkylated hydrocarbons. This effluent is normally cooled and
passed to a stripping column in which substantially all C5 and
lighter hydrocarbons present in the effluent are concentrated into
an overhead stream and removed from the process. An aromatics-rich
stream is recovered as net stripper bottoms, which is referred to
as the transalkylation effluent.
[0025] The transalkylation reaction can be effected in contact with
a catalytic composite in any conventional or otherwise convenient
manner and may comprise a batch or continuous type of operation,
with a continuous operation being preferred. The transalkylation
catalyst is usefully disposed as a fixed bed in a reaction zone of
a vertical tubular reactor, with the alkylaromatic feed stock
charged through the bed in an upflow or downflow manner. The
transalkylation zone normally operates at conditions including a
temperature in the range of about 130.degree. C. to about
540.degree. C. The transalkylation zone is typically operated at
moderately elevated pressures broadly ranging from about 100 kPa to
about 10 MPa absolute. The transalkylation reaction can be effected
over a wide range of space velocities. That is, volume of charge
per volume of catalyst per hour; weight hourly space velocity
(WHSV) generally is in the range of from about 0.1 to about 30
hr-1. The catalyst is typically selected to have relatively high
stability at a high activity level.
[0026] Oxidation involves the oxidation of hydrocarbons to
oxygen-containing compounds, such as aldehydes. The hydrocarbons
include alkanes, alkenes, typically with carbon numbers from 2 to
15, and alkyl aromatics, Linear, branched, and cyclic alkanes and
alkenes can be used. Oxygenates that are not fully oxidized to
ketones or carboxylic acids can also be subjected to oxidation
processes, as well as sulfur compounds that contain --S--H
moieties, thiophene rings, and sulfone groups. The process is
carried out by placing an oxidation catalyst in a reaction zone and
contacting the feed stream which contains the desired hydrocarbons
with the catalyst in the presence of oxygen. The type of reactor
which can be used is any type well known in the art such as
fixed-bed, moving-bed, multi-tube, CSTR, fluidized bed, etc. The
feed stream can be flowed over the catalyst bed either up-flow or
down-flow in the liquid, vapor, or mixed phase. In the case of a
fluidized-bed, the feed stream can be flowed co-current or
counter-current. In a CSTR the feed stream can be continuously
added or added batch-wise. The feed stream contains the desired
oxidizable species along with oxygen. Oxygen can be introduced
either as pure oxygen or as air, or as liquid phase oxididents
including hydrogen peroxide, organic peroxides, or peroxy-acids.
The molar ratio of oxygen (O2) to alkane can range from about 5:1
to about 1:10. In addition to oxygen and alkane or alkene, the feed
stream can also contain a diluent gas selected form nitrogen, neon,
argon, helium, carbon dioxide, steam or mixtures thereof. As
stated, the oxygen can be added as air which could also provide a
diluent. The molar ratio of diluent gas to oxygen ranges from
greater than zero to about 10:1. The catalyst and feed stream are
reacted at oxidation conditions which include a temperature of
about 300.degree. C. to about 600.degree. C., a pressure of about
101 kPa to about 5,066 kPa and a space velocity of about 100 to
about 100,000 hr-1.
[0027] Hydrogenation involves the addition of hydrogen to
hydrogenatable hydrocarbon compounds. Alternatively, hydrogen can
be provided in a hydrogen-containing compound with ready available
hydrogen, such as tetralin, alcohols, hydrogenated naphthalenes,
and others via a transfer hydrogenation process with or without a
catalyst. The hydrogenatable hydrocarbon compounds are introduced
into a hydrogenation zone and contacted with a hydrogen-rich
gaseous phase and a hydrogenation catalyst in order to hydrogenate
at least a portion of the hydrogenatable hydrocarbon compounds. The
catalytic hydrogenation zone may contain a fixed, ebulated or
fluidized catalyst bed. This reaction zone is typically at a
pressure from about 689 k Pa gauge (100 psig) to about 13790 k Pa
gauge (2000 psig) with a maximum catalyst bed temperature in the
range of about 177.degree. C. (350.degree. F.) to about 454.degree.
C. (850.degree. F.). The liquid hourly space velocity is typically
in the range from about 0.2 hr-1 to about 10 hr-1 and hydrogen
circulation rates from about 200 standard cubic feet per barrel
(SCFB) (35.6 m3/m3) to about 10,000 SCFB (1778 m3/m3).
[0028] While at least one exemplary embodiment has been presented
in the foregoing detailed description of the invention, it should
be appreciated that a vast number of variations exist. It should
also be appreciated that the exemplary embodiment or exemplary
embodiments are only examples, and are not intended to limit the
scope, applicability, or configuration of the invention in any way.
Rather, the foregoing detailed description will provide those
skilled in the art with a convenient road map for implementing an
exemplary embodiment of the invention. It being understood that
various changes may be made in the function and arrangement of
elements described in an exemplary embodiment without departing
from the scope of the invention as set forth in the appended
claims.
* * * * *